Modelling of fracto-mechanoluminescence damage sensor for structures

Accepted Manuscript Title: Modelling of fracto-mechanoluminescence damage sensor for structures Author: B.P. Chandra V.K. Chandra Piyush Jha PII: DOI: Reference:

S0924-4247(15)00182-X http://dx.doi.org/doi:10.1016/j.sna.2015.04.005 SNA 9148

To appear in:

Sensors and Actuators A

Received date: Revised date: Accepted date:

20-12-2014 4-4-2015 8-4-2015

Please cite this article as: B.P. Chandra, V.K. Chandra, P. Jha, Modelling of fractomechanoluminescence damage sensor for structures, Sensors and Actuators: A Physical (2015), http://dx.doi.org/10.1016/j.sna.2015.04.005 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Modelling of fracto-mechanoluminescence damage sensor for structures B.P. Chandra1*†, V.K. Chandra2, Piyush Jha3 School of Studies in Physics and Astrophysics, Pt. Ravishankar Shukla University, Raipur

ip t

1

492010, (C.G.) India 2

Department of Electrical and Electronics Engineering, Chhatrapati Shivaji Institute of

3

cr

Technology, Shivaji Nagar, Kolihapuri, Durg 491001 (C.G.), India

Department of Applied Physics, Raipur Institute of Technology, Chhatauna, Mandir Hasuad,

Abstract

us

Raipur 492101 (C.G.), India

an

The present paper reports the modelling of fracto-mechanoluminescence damage sensor which is useful for real-time and remotely monitoring of both the magnitude and location of damage of

M

the structure without the use of electrodes. In this technique, the intense fracto– mechanoluminescent material of several micron size is mixed in liquid resin and then coated on the surface of structure whereby the occurrence and strength of the damage is given by the

d

intensity of the resulting mechanoluminescence (ML) light. Monitoring of the position of

te

damage is achieved by identifying the colour of ML light emitted as the ML particles coated in different locations emit ML light of different colours. The modelling of fracto-

Ac ce p

mechanoluminescence damage sensor is based on the fact that the total ML intensity depends on the total area of the newly created surfaces (damage). For a projectile having large contact area such as a cylinder, below the characteristic impact velocity vc, at which the sample is compressed to 1/e of its thickness, both the peak ML intensity Im and the total ML intensity IT increase linearly with the impact velocity; however, above vc, both Im and IT tend to attain saturation value. In the case of impact of a projectile having small contact area such as a ball, below vc, both Im and IT increase quadratically with the impact velocity; however, above vc, both Im and IT tend to attain saturation value. In the case of a projectile having large contact area the total volume of the sample is compressed and only the rate of creation of new surfaces increases with the impact velocity; however, in the case of a projectile having small contact area, in addition to the increase of strain rate with impact velocity, the effective volume compressed by the impact also increases linearly with the impact velocity, and therefore, the rate of creation of new 1 Page 1 of 41

surfaces increases quadratically with the impact velocity. A good agreement is found between the experimental and theoretical results.

ip t

Keywords: Mechanoluminescence; Triboluminescence; Sensor; Phosphors; Damage.

cr

*Corresponding author: [email protected], Phone No.: +91-771-2263650 †

us

Emeritus Professor

Ac ce p

te

d

M

an

Phone No.: +91-771-2263650

2 Page 2 of 41

1. Introduction In the recent past, the fracto-mechanoluminescence phenomenon has attracted the attention of a large number of researchers all over the world because of its potential application for damage sensor of structures [1-6]. In fact, mechanoluminescence (ML) is the phenomenon of

ip t

cold light emission from a solid as a response to a mechanical stimulus given to it. The cold light emissions induced by elastic deformation, plastic deformation, and fracture of solids are known

cr

as elastico mechanoluminescence (EML), plastico mechanoluminescence (PML), and fracto mechanoluminescence (FML), respectively [7,8]. Whereas nearly 50% of all inorganic salts and

us

organic molecular solids exhibit ML during their fracture, only a limited number of solids show ML during their elastic deformation and plastic deformation. The elastico ML of SrAl2O4: Eu, CaZnOS: Mn2+, BaTiO3- CaTiO3:Pr3+, etc. and fracto ML of europium dibenzoylmethide

an

triethylammonium(EuD4TEA), ditriphenylphosphine oxide manganese bromide, freshly grown impure saccharin, etc. is so intense that it can be seen in day light with naked eye.

M

Currently the techniques being used for damage detection and monitoring of civil, aerospace, and military structures are: acoustic based methods (acoustic emission and ultrasonic

d

testing) [9–12]; electro-imaging methods such as thermography, ultrasonic pulse velocity (UPV), and ground penetrating radar (GPR) [13–24]; radiography such as X-ray, gamma-ray, and

te

neutron ray [25]; and fiber optics methods [25–27]. These techniques have major drawbacks that they do not provide in-situ (excluding fiber optic methods) and distributed sensing [10,26,27].

Ac ce p

Because of these drawbacks real-time monitoring of the structural states is not possible. Moreover, the associated cost resulting from the downtime required for periodic nondestructive inspections can be very high for civil structures like bridges and aerospace structures like aircrafts. There is also the prohibitive cost arising due to fatal accidents when such structures fail without warning. Fracto-mechanoluminescence sensor systems are able to overcome the above mentioned challenges because they have the potential for wireless, in-situ, and distributed sensing that can enable real-time continuous monitoring. A fracto-ML damage sensor system comprising highly efficient fracto-mechanoluminescent materials could allow simple, real-time monitoring of both the magnitude and location of damage with minimal parasitic influence to the host structure [1-6]. The mechanoluminescent materials which emit intense light when they are fractured have been developed by Bourhill and his co–workers as real–time optical damage sensors [1-4]. In 3 Page 3 of 41

this technique, the intense fracto–mechanoluminescent material of several micron size is mixed in liquid resin and then coated on the surface of structure by curing at a suitable temperature whereby the occurrence and severity of the damage is given by the intensity of the resulting mechanoluminescent light. Monitoring of the position of damage is achieved either by designing

ip t

an array of sensors, with each sensor in the array comprising a different mechanoluminescent material and, thus, mechanoluminescencing over a discrete wavelength range or by designing an

cr

array of mechanoluminescent sensors with each and every sensor having the same type of mechanoluminescent material whereby a wavelength–shifting is produced using a range of

us

conventional fluorescent dyes in which the ML from the doped resin pumps the dye, which then emits at a different wavelength. Such an arrangement allows location monitoring simply by detecting the wavelength of the emitted light. Each sensor in the array can be fibre–optically

an

connected to a central detector capable of measuring in real–time both the intensity (for damage occurring severity) and wavelength (for damage location) of the emitted light. Furthermore, the

M

use of only one detection unit reduces complexity and helps to reduce parasitic weight. In such sensors, no light is emitted until the crystalline mechanoluminescent material has actually

d

fractured, therefore, no false alarms are generated. Scientists have succeeded in doping composite structures for aircraft with fine mechanoluminescent crystals. When an impact cracks

te

the doped resin, it sends a tiny flash of light analogous to a pain signal along the fibres to a detector. Thus, the intensity of light directly gives the magnitude of the damage and the

Ac ce p

wavelength of the light emitted indicates the location of damage. Although fracto-mechanoluminescence damage sensor for structures is very important and useful, the systematic correlation between the signal and source, i.e., between the damage (ML intensity) and impact stress or impact velocity is not known till now. In the present paper the modelling of fracto-mechanoluminescence damage sensor for structures is performed and the systematic correlation between the damage (ML intensity) and impact velocity is explored, in which a good agreement is found between the theoretical and experimental results. The present study may be helpful in the development and refinement of fracto-mechanoluminescence damage sensor. In the past, using the fracture mechanics an attempt has been made to correlate the ML intensity and impact velocity, where the derivation is lengthy, involves many assumptions, and correlates the ML intensity indirectly with the impact velocity [28]. In this paper, using a new theory based on successive fragmentation of crystallites, a correlation is 4 Page 4 of 41

developed between the damage and the impact velocity, which is comparatively short and directly correlates the ML intensity with the impact velocity. Furthermore, the present paper explains the basic principle involved in damage sensor. 2.

Significance of Present Study

ip t

In our previous paper, we have studied the real-time sensing of the amplitude and duration of impact stress using elastico- mechanoluminescence (EML) of the films of ZnS:Mn

cr

and SrAl2O4:Eu [29], in which the impact of a small ball from a low height onto the ML film was used for the EML excitation. The impact stress was in the elastic region, in which the

us

fracture of ML particles did not take place. It was shown that the impact stress can be sensed by measuring the EML intensity, and the pulse duration of the impact stress can be monitored by measuring the value of time corresponding to the peak of the EML intensity versus time curve.

an

The present study is related to the fracto ML, i.e., the ML induced by fracture of solids, in which applied pressure is high and the damage or newly created surface area is related to the total ML

M

intensity. Therefore, the ML measurement in this case can be used for the monitoring of damage. Thus the present study is completely different from the previous one. Using the theory based on

d

successive fragmentation of crystallites, a correlation is developed between the damage and the impact velocity for the first time. The modelling of fracto-mechanoluminescence damage sensor

te

for structures is performed. Furthermore, new concepts are provided with regard to large and small contact area between the impacted load (or ball) and the ML particles and comparison

Ac ce p

between the related ML response is made.

3. Mechanisms of fracto ML of crystals The fracto ML can be understood on the basis of the Langevin model for the creation of charged surfaces during the movement of a crack in a piezoelectric crystal [30]. When a crack moves in a piezoelectric crystal, one of the newly created surfaces gets positively charged and the other surface gets negatively charged in which a strong electric field is generated between the two walls of a crack. The piezoelectric constant is generally of the order of 10-12 -10-11 Coulomb per Newton (CN-1) and the stress needed to separate the surfaces of crystals is of the order of Y/100 (where Y is the Young’s modulus of elasticity of the crystal), which comes out to be order of 108 Nm-2. Thus, the charge density ρ of the newly created surfaces is of the order of 10-4-10-3 Coulomb m-2. The electric field F between the oppositely charged surfaces will be, F = ρ / εo , where εo is the permittivity of free space, equal to 8.85×10-12 C2N-1m-2. Thus, an 5 Page 5 of 41

electric field of the order of 107-108 Vm-1 may be generated between the newly created oppositely charged surfaces. This field may cause the dielectric breakdown of the surrounding gases and in turn may give rise to the gaseous discharge ML. The field may also cause the dielectric breakdown of the crystals, and the recombination of free charge carriers may give rise

ip t

to recombination luminescence. Furthermore, the accelerated electrons moving from negatively charged surfaces towards the positively charged surface may excite cathodoluminescence (CL).

cr

It has been found that, in addition to the piezoelectric crystals, a large number of nonpiezoelectric crystals also exhibit ML [31]. Thus, it seems that the charging of newly created

us

surfaces also takes place due to the movement of charged dislocations, baro-diffusion of defects in crystals, local piezoelectric field caused by impurities and defects, creation of noncentrosymmetric structure by the stress required for fracture, local piezoelectric field caused by

an

the large strain at fracture, fracturing of centrosymmetric ionic crystals in a direction which actually generates charged surfaces, the presence other phases in solvated materials, presence of

M

non-centrosymmetric phase due to disorder in materials, charging of the sites (like oxygen, halogen, etc) of different electro-negativity in neutral polar molecules, etc.

d

In the above processes, if there is total transfer of energy from the excited gas molecules to the luminescence centres or the light produced due to gas discharge is absorbed completely by

te

the crystals, then only the solid state FML will be produced. Moreover, if the electric field will not be sufficient to cause the gas discharge, then also the gas discharge FML will not be

Ac ce p

observed. Furthermore, if the surface charges relax before the penetration of gases between the walls of the cracks, then also the gas discharge ML will not be observed. On the other hand, if there is partial transfer of energy from the excited gas molecules to the luminescence centres or partial absorption of the light produced due to the gas discharge by the crystals, then the combination of both the solid state FML and gas discharge FML will be observed. Furthermore, if the crystals do not possess luminescence centres, then there will be no transfer of energy from the excited gas molecules to the luminescence centres or absorption of gas discharge by the luminescence centres, and in this case only the gas discharge FML will be observed. Thus, depending on the prevailing conditions either gas discharge or FML resembling other types of luminescence or combination of these two may be obtained.

4. Modelling of fracto-luminescence Damage Sensor for structures 6 Page 6 of 41

Here, we would like to derive a correlation between the total ML intensity and the impact velocity on the basis of a new approach, called the successive fragmentation of the crystallites. 4.1 Correlation between the newly created surfaces and compression of crystals If dN is the number of crystallites formed due to the deformation of a crystal from strain ε

ip t

to (ε +dε) , then we can write the following equation

dN  Md

…(1)

cr

where M is the multiplication factor which when multiplied with the strain gives the number of crystallites formed.

us

Considering that: (i) the multiplication factor M depends on volume V of the sample as more volume will contain more cleavage planes or microcracks, and (ii) the multiplication factor

an

M also depends the number N of the previously existing crystallites at the strain ε, Eq. (1) can be written as

or,

dN N    NV f  dt 

M

dN  NV f d

…(2)

f



, is the probability for crack-formation during deformation of the

te

time, and p=1/τ =  V

d

where M = α VfN, in which α is a constant, f is an exponent, τ =1/ (V f  ) , is the characteristic

crystal.

Ac ce p

Integration of Eq. (2) gives

log N  V f t  C1

…(3)

where C1 is the constant of integration. For just below the fracture time tf, at which ε =εf (fracture strain at which the fracture starts), N =1, and therefore, Eq.(3) gives, C1=-α Vf  tf . Thus, from Eq. (3), we get

N  exp[V f  ( t  t f )]  exp[V f (   f )

…(4)

For N number of crystallites, the number of cracks Nc created in the crystal is given by





N c  N  1  exp V f    f   1

…(5)

As the movement of each crack produces one ML pulse, the number of ML pulses Np is given by





N p  N c  exp  V f    f   1

…(6)

7 Page 7 of 41

It is evident from Eq.(6) that, after the fracture strain f , the number of ML pulses should increase exponentially with   f  . Now, two conditions arise: (i) V f (   f ) <<1, and (ii) V f (   f ) >>1.

ip t

Condition I: V f (   f ) <<1 In this case, Eq. (6) can be expressed as N p   V f (   f )

cr

….(7)

It is evident from Eq.(7) that, after the fracture strain f , the number of ML pulses

us

should increase linearly with   f  .

an

Condition II: V f (   f ) >>1

In this case, after neglecting 1, Eq. (6) can be expressed as

N p  N c  [exp[V f (   f )]

…. (8)

M

It is evident from Eq.(8) that, in this case, the number of ML pulses should increase exponentially with   f  .

d

Both, the number of crystallites N and the area of newly created surfaces S

te

increase with the deformation of crystals. With the increasing deformation of crystals, the number of crystallites increases and the size of crystallites becomes smaller and smaller.

Ac ce p

Therefore, with the increase of crystallites, the area of newly-created surfaces increases. If S0 is the characteristic surface area, that is, the area of newly-created surfaces at which the number of crystallites becomes equal to e times the initial number, then we can write the following equation dN N  dS S 0

or,

dN dS  N S0

…(9)

Integrating Eq. (9), we get log N 

S  C2 S0

…(10)

where C2 is the constant of integration. As S=0, for N=1, we get C2=0, and therefore, Eq. (10) can be written as

8 Page 8 of 41

log N 

S S0

or, S= S0 log N

…(11)

If sa is the average size of the crystallites after the deformation, then S=sa N , and

ip t

Eq. (11) can be expressed as S=sa N=S0 (log N) S 0 (log N ) N

cr

or, s a 

….(12)

should decrease with increasing number of the crystallites.

us

Equation (12) indicates that the average size of crystallites after the deformation The newly created surface area S will increase at higher rate for larger size of the

an

crystals, and therefore S0 should depend on the volume of crystals. Considering the fact, we can write S0  b V f  , where b’ is a constant and f’ is an exponent. Thus, Eq. (12) can be written as

M

S  bV f  (logN)

…(13)

Substituting the value of N from Eq. (8) in Eq. (13), we get

te

or, S  b V ( f  f ) (   f )

d

S=sa N= bV f  [log exp{  V f (    f )}] …(14)

As the number of cleavage planes increases with increasing perimeter of the crystals, we

Ac ce p

can take, f=1/3, because the perimeter is proportional to V1/3. As the area of newly created surface for the first crack increases linearly with the product of width W and height H of the crystal, we can take, f '= 2/3, as WH is proportional to V2/3. Thus, (f+f’) = 1, and Eq. (14) can be expressed as

S  b V (   f )

…(15)

As the total ML intensity of ML increases linearly with the area of newly created surfaces [32], Eq. (15) indicates that the total ML intensity should increase linearly with the strain and volume of the crystals. 4.2 Impact velocity dependence of the ML intensity 4.2.1 For low impact velocity In fact, in the ML experiments, following two types of measurements have been made: (i) The surface area of projectile pressing the sample is larger as compared to the contact area of the 9 Page 9 of 41

sample, and (ii) the surface area of projectile pressing the sample is smaller as compared to the contact of the sample. 4.2.1.1 Projectile with larger contact area such as cylinder If v0 is the initial impact velocity of the piston used to deform the sample, and τr is

ip t

the time-constant for the decrease of impact velocity with time, then the rate of change of dx t  v 0 exp(  )  v 0 exp( t ) dt r

us

where ξ=1/τr , and x is the compression of the crystal at any time t.

cr

compression of the crystal can be expressed as

…(16)

If H is the thickness of the crystal, then the strain rate is given by

v0 exp(t ) H

an

 

…(17)

Using Eqs. (15) and (17), the rate of creation of new surfaces can be expressed as

M

dS b Vv0  exp( t ) dt H

…(18)

If ρ is the surface charge density due to the piezoelectrification, then the rate of dS  b  Vv 0  exp(   t ) dt H

te

Gq  

d

generation of surface charges of the newly created surfaces can be written as …(19)

Ac ce p

If τq is the time constant for the relaxation of surface charges, then the rate of change of surface charges is given by

dQ bVv0  exp(t )   Q dt H

…(20)

where β=1/τ , and Q is the surface charges at any time t. q

Integrating Eq. (20) and taking Q=0, at t=0, we get Q

b  Vv 0 [exp( t )  exp(   t )] H (   )

…(21)

If η is the ML efficiency relating the ML intensity and rate of relaxation of surface charges, then the ML intensity I can be expressed as I   Q 

 0 b Vv 0 [exp( t )  exp(  t )] H (  )

…(22)

10 Page 10 of 41

Equation (22) indicates that I will be zero at t=0, and t= ∞ ; thus I will be maximum for a particular value of time t=tm. Differentiating Eq. (22) and equating it to zero, the time tm corresponding to the peak of ML intensity is given by 1  ln( ) (   ) 

…(23)

ip t

tm 

cr

Substituting t=tm, from Eq. (23), in Eq. (22), the ML intensity Im corresponding to the peak of the ML intensity can be expressed as

bVv0 H

us

Im 

…(24)

Integrating Eq. (22) the total ML intensity can be expressed as 



an

b Vv 0 b Vv 0 [exp( t )  exp(  t )]dt  H (  ) H 0

I T   Idt   0

…(25)

M

From Eq. (22), for α>>ξ, the decay of ML intensity can be expressed as

I  I m exp[ (t  t m )]

…(26)

te

slope will be equal to ξ (=1/τr).

d

Equation (26) indicates that the ML intensity should decay exponentially, in which the If the sample will be deformed at very high impact velocity, then ξ will be much greater

Ac ce p

than β. In this case, Eq. (24) can be written as I

 0 b Vv 0 [exp(   t )  exp( t )] H (   )

…(27)

Using Eq. (27), the decay of ML intensity can be expressed as I  I m exp[  (t  t m )

…(28)

Equation (28) indicates that, for ξ>>β, the decay time of ML intensity will be equal to the relaxation time (1/β) of surface charges. 4.2.1.2 Projectile with smaller contact area such as a ball When a ball is dropped on to the sample, then the maximum contact area increases with the impact velocity v0, and therefore, the effective volume responsible for the ML emission increases with v0. The contact area is given by [29] A c  rx m

…(29)

11 Page 11 of 41

where r is the radius of the ball dropped on to the sample and xm the maximum compression of the sample at the impact velocity v0. Integration of Eq. (18) gives v0 exp( t )  C 3 

…(30)

ip t

x

where C3 is the constant of integration.

v0 [1  exp(t )] 

us

x

cr

Taking x = 0, at t = 0, we get, C 3  v 0 /  . Thus, Eq. (30) can be expressed as

…(31)

From Eq. (31), the maximum compression xm at the impact velocity v0 is given by v0 

an

xm 

From Eqs. (29) and (32), we get rv 0 

M

Ac 

….(32)

…(33)

d

As only the surface area below the contact area will be compressed the effective volume

Ve 

rv 0 H 

te

Ve of the sample responsible for the ML emission will be given by … (34)

Ac ce p

where H is the thickness of the sample

Thus, substituting V=Ve, from Eq. (34) in Eqs. (24) and (25), we get

Im 

and, I T 

rbv 02 

… (35)

rbv 02 2

… (36)

Thus, for the ML excitation by impact of a ball, both Im and IT should increase linearly with v 02 , or with the impact energy of the impacting ball.

4.2.2 For high impact velocity Due to the work hardening the rate of increase of maximum compression xm with the impact velocity v0 decreases with increasing impact velocity of the load used to deform the sample. Therefore, we can write the following expression 12 Page 12 of 41

dxm x  g 0  m  g 0  x m dv0 vc

…(37)

where δ=1/vc , and vc is the characteristic impact velocity at which the sample is compressed to 1/e (here, e is the base of natural logarithm).

xm 

ip t

Integrating Eq. (37), and taking xm=0, at vo=0, we get

g 0 [1  exp(v 0 )] 

…(38)

cr

If H is the initial thickness of the sample, then for high impact velocity, it is compressed to ψH, where ψ is a fraction slightly less than 1, and it shows that the maximum compression will

us

be slightly less than H, and thus, we have, g0/δ=ψH, and therefore Eq. (38) can be written as x m  H [1  exp(v0 )]

…(39)

an

For the fracture time τr, using Eq. (39), the effective impact velocity ve associated with xm is, ve=xm/τr, and thus, ve can be expressed as

H[1  exp(v 0 )] r

M

ve 

…(40)

Thus, because of the changing hardness of crystallites with compression, the total

d

compression is controlled by the effective compression rate ve. Therefore, writing ve in place of

bVva bV [1  exp(v0 )]  r H

…(41)

Ac ce p

Im 

te

v0, and taking ξ=1/τr, Eqs. (24), and (25) can be expressed as

IT 

bVva  bV [1  exp(v0 )] H

…(42)

Equations (41) and (42) indicate that, for the high impact of a projectile with

larger contact area on to the sample, initially both Im and IT should increase linearly with the impact velocity and later on they should attain a saturation value for higher values of the impact velocity.

For high impact velocities, Eqs. (35) and (36) related to the impact of a ball can be expressed as

Im 

rb[1  exp(v 0 )]2 

…(43)

13 Page 13 of 41

rb [1  exp(v 0 )] 2 IT  2

…(44)

Equations (43) and (44) show that, for the high impact velocity of a small ball on the sample, initially both Im and IT should increase quadratically with the impact velocity and later on

ip t

they should attain a saturation value for higher values of the impact velocity.

For low impact velocity δv0<<1, and by expanding the exponential term in Eqs. (41) to

bVv 0 r

us

Im 

cr

(44), we get

I T  b Vv0

bC eH 2 v 02  r2

an

Im 

M

b C e H 2 v 02 IT  r

…(45) …(46) …(47) …(48)

Equations (45) and (46) indicate that for low impact velocity, both Im and IT should increase linearly

d

with impact velocity of the projectile having larger contact area used to deform the sample.

Equations (47)

te

and (48) show that, for high impact velocity, both Im and IT should increase quardratically with the impact velocity of the ball used to deform the sample.

Ac ce p

5. Discussion

5.1 Correlation Between the Theoretical and Experimental Results For the ML measurements, commercial crystals of sugar were used and Nacetylanthranilic acid crystals were grown from their solution in acetic acid and water. The ZnS:Mn phosphor having 1,000 ppm of Mn2+ were prepared by firing the constituent materials at 1100 0C for 1 hour in nitrogen atmosphere. The crystals of triphenylphosphineoxide manganese bromide were synthesized following the procedure described in our previous paper [33], and then, using a mortar and pestle and a mortar the crystals grown were ground to microcrystalline size. The time dependence of ML intensity and impact velocity dependence of ML intensity were measured following the procedure described in our previous paper [31]. In this technique, the crystals were fractured by dropping a load of 400 gm from different heights, in which the impact velocity was determined from the formula, vo  2 gh , where g is acceleration due to gravity and h is the height through which the load is dropped on to the crystals. The ML intensity was 14 Page 14 of 41

measured using a photomultiplier tube whose output was connected to a storage oscilloscope. In another method, the ML was excited by dropping a steel ball of 130 gm from different heights on to the sample powder of 100 mg placed on to the Lucite plate in which the sample was covered with an aluminum foil and fixed using an adhesive tape. After each test, the ball was

ip t

cleaned and the other sample powders were used. In this case, also the ML intensity was measured using a photomultiplier tube whose output was connected to a storage oscilloscope.

cr

The photomultiplier tube was kept below the Lucite plate.

Fig 1(a) shows that, when a fluorescent N-acetylanthranilic acid (NAAA) crystal is

us

fractured by the impact of a moving cylinder of mass 400 gm, then initially the ML intensity increases linearly with time, attains a peak value Im at a particular time and later on it decreases with time. This result is in accordance with Eq. (22). Fig 1(b) illustrates the time dependence of

an

the ML intensity for non-photoluminescent sugar crystals fractured by the impact of a moving cylinder. The time dependence of the ML intensity of sugar crystals is also similar to that of

M

NAAA crystal shown in Fig. 1(a). It is seen from Fig 1(a) and Fig, 1(b) that, for both NAAA and sugar crystals, the peak of the ML intensity Im increases with increasing impact velocities.

d

Fig. 2(a) and Fig. 2(b) show the semilog plot of I versus (t-tm) for NAAA and sugar crystals, respectively. It is seen that the plots are straight lines with negative slopes and the value

te

of slope does not change significantly with increasing value of the impact velocity of the cylinder used to deform the crystal. Such results are evident from Eq. (23). The value of ξ is

Ac ce p

determined from the slope of this plot for different values of the impact velocity v0, and it is found to be 555 μs and 526 μs, respectively for NAAA and sugar crystals, respectively. Figs. 3 shows that the peak ML intensity Im of NAAA and sugar crystals increases linearly with increasing impact velocity of the piston used to deform the crystals. This finding is in accord with Eq. (45). Figs. 4 illustrates that the total ML intensity IT of NAAA and sugar crystals increases with increasing impact velocity of the piston used to deform the crystals. This result follows Eq. (46).

Fig.5 (a,b) shows the dependence of ML intensity on the impact energy (or

1 Mv02 , where 2

M is the mass of the ball used to deform the sample) for Mn complexes of two different crystallite sizes mixed in a resin [1]. It is seen that, after a particular threshold impact energy the

15 Page 15 of 41

the total ML intensity increases with the impact energy of the ball. Such relation is evident from Eqs. (48). Fig. 6 shows the dependence of ML intensity of triphynylphosphineoxide manganese bromide powders and ZnS:Mn phosphor on v02, where the ML was excited by drooping a steel is

to

ip t

ball. It is seen that the ML intensity increases linearly with v02. This is in accord with Eq. (48). It be noted that triphynylphosphineoxide manganese bromide is very intense

cr

mechanoluminescent material whose ML emission can be seen in day light with naked eye.

Fig. 7 shows the dependence of the peak radiance at 700 nm of Z-cut lithium niobate

us

disks of about 3.6 mm thick and 36 mm diameter on the impact velocity [34]. It is seen that, initially the radiance increases linearly with the applied stress and impact velocity and then it tends to attain a saturation value for higher values of the impact velocity. Such result follows Eq.

an

(42). Fig. 8 shows that the semilog plot of (1-I/I0) versus v0 for Z-cut lithium niobate disks is a straight line with a negative slope, where I is the radiance for any impact velocity v0 and I0 is the

M

saturation value of the radiance. This finding is in accord with Eq. (42). The value of slope δ calculated from the slope of Fig. 8 is found to be δ= 3.427 s/km, which gives that the

d

characteristic impact velocity vc=1/δ=0.291 km/s. The value of vc is high because the sample has large size. In this experiment, lithium niobate disks of about 3.6 mm thick and 36 mm diameter

te

were impacted with either 6061-T1-T6 aluminium or tungsten carbide impactors. All dimensions of the impactor and target were chosen in order to maintain uniaxial states of strain in the

Ac ce p

specimen for times of interest. The light emitted from the target was monitored over the 12.5 mm centre diameter of the sample except when the image was magnified to determine the spatial extent of the luminescent pattern. The luminescence from lithium niobate was studied in the stress range from 1.6 to 21.0 GPa.

The modelling of fracto-mechanoluminescence damage sensor is based on the fact that the total ML intensity depends linearly on the total area of the newly created surfaces (damage). It is found that, for the projectile having large contact area, below the characteristic impact velocity vc, at which the sample is compressed to 1/e of its thickness, both the peak ML intensity Im and the total ML intensity IT increase linearly with the impact velocity; however, above vc, both Im and IT tend to attain a saturation value. In the case of impact of a ball, i.e., for the projectile having small contact, below vc, both Im and IT increase quadratically with the impact velocity; however, above vc, both Im and IT tend to attain a saturation value. 16 Page 16 of 41

The expressions (45) to (48) indicate that the fracto ML intensity of the materials to be used for the fracto-mechanoluminescence damage sensor can be enhanced by using the materials having high fracto-mechanoluminescence efficiency η, high surface charge density ρ at fracture, i.e., high piezoelectric constant dρ and high Young’s modulus of elasticity Y (as ρ=d0xY/100),

ip t

and appreciable thickness of coating ( as the ML intensity increases with volume of the sample), high value of the compression factor ψ, and high value of the rate constant for compression ξ

cr

(=1/τr). Using these concepts suitable fracto-mechanoluminescent materials for damage sensor can be tailored. The value of δ should be of moderate value as high value of ψ will give low value sensor unsuitable for high range of the impact velocity.

us

of the characteristic impact velocity (δ=1/vc) to make the fracto-mechanoluminescence damage

an

Thus there is a good agreement between the theoretical and experimental results. 5.2 Materials Tested by Mechanoluminescence Structural Health Monitoring Technique

M

In the recent past, the structural health monitoring using ML technique has been performed on concrete structures, vinyl ester matrix, composite laminates, reinforced concrete, cementbased materials, .and carbon fiber–reinforced polymer (CFRP) [6, 35-42]. Using ML technique,

d

no study on the structural health monitoring of metals has been made till now. Olawale et al. [35]

te

have studied the development of a ML based sensor system for concrete structures, in which the cementitious optical sensor was prepared by physically mixing fly ash, water, cement, and

Ac ce p

ZnS:Mn phosphors. The thoroughly blended mixture was cured by adding water, and the resulting paste was poured into a mold. The samples were then allowed to cure for predetermined number of days. The prepared molds had two plastic optical fibers already attached within, to allow for their embedment in the cured cementitious patch. The fibers pick up the ML signals emitted as the material is loaded, thereby indicating levels of internal damage. While the cement acts as the binder, the fly ash helps in improving the patch’s properties by enhancing strength development, reducing voids and negating the effect of shrinkage. The samples used had dimension of 50 x 50 x6.25 mm. The samples were loaded in a custom-built impact rig where they were impacted with a pneumatically-controlled piston at specific pressure values. The rig was fed by a compressed air line, and controlled with an adjustable pressure and release valve. Just after the impact, the ML intensity increases rapidly with time, attains a peak value nearly at 0.20 ms, and then it decays with a decay time of 0.18 ms. The results show that a ZnS:Mn concentration level of 10% gives the best ML response without adversely affecting the 17 Page 17 of 41

compressive strength of the patch, while also minimizing the use of the expensive ZnS:Mn crystals. The ML response increased as the concentration of ZnS:Mn in the system is increased. The highest response was obtained at a concentration level of 25% but resulted in significant reduction in the system’s compressive strength. The study proved that the ML can be used for

ip t

structural health monitoring.

In their other study, Olawale et al. [36] have reported that ZnS:Mn crystals embedded in

cr

vinyl ester matrix experience a degradation in their ML responses by the 15th cycle of impact for all the impact levels studied. However, repeatable signals at high impact levels indicating danger

us

can be obtained after 8 cycles of impact. Such result shows the viability of ML-based sensor systems for detecting and preventing damage.

an

Dickens et al. [37] have investigated the ML of composites comprised of a thin polymer (vinyl ester resin,VER). doped with ZnS:Mn, in which the samples were created by direct mixing

M

of micron sized ZnS:Mn phosphor in vinyl ester resin, and processed in a picture frame mold. The mold cavity was made from stainless steel with a range of 0.102-0.580 mm thickness,

d

comprising a 100 × 100 mm inner frame. The compression plates were preheated to 65.56 °C to aid curing of the amalgamated matrix. After attaining the accepted temperature profile and time,

te

an initial application of hydraulic force was made at 44482.2 N. This occurred for approximately 10 min. The casted samples were then allowed to cool under room temperature. The mold was

Ac ce p

then removed from the press and the sample was extracted from the mold. Square specimens were then cut out by a laser system in 20 × 20 mm coupons. Initially it was thought that excitation would appear during processing by hydraulic pressing; however, particle size is extremely small, and the viscous blend prohibited any pre-emissive ML. It is found that the ML intensity increases with the kinetic energy of dropped load. It is observed that the ML emission takes place for less than 0.1 J.

Dickens et al. [38] have investigated the feasibility of using zinc sulphide manganese concentrated vinyl ester resin as a photon emitter for damage monitoring of polymer composites under flexural loading. Unreinforced vinyl ester resins doped with optical emitting materials (ZnS:Mn phosphors) in ratios of 5 – 50 % by weight were cast, and subjected to flexural loading using standard 3-point bend tests. The intent of this work was to observe the transient response of ML throughout the failure cycle. They found that the ML crystals emit light at various 18 Page 18 of 41

intensities corresponding to crystal concentration and imminent matrix fracture. It was observed that the concentrated samples showed nearly 50% reductions of mechanical moduli. Scanning electron microscopy (SEM) revealed particulate inclusions with shearing bands and semblance of particle to resin adhesion. Despite significant parasitic affect to mechanical properties, the

ip t

mechanoluminescent properties occur at yielding and point of matrix fracture.

Dickens et al. [39] have manufactured the composite laminates doped with various

cr

concentrations (0 to 10 %wt.) of a mechanoluminescent material (ZnS:Mn). Laminates were manufactured using a vacuum infusion process. Dispersing the ZnS:Mn particulates was

us

cumbersome because their density was higher than the resin that caused settling during resin infusion. The dispersion of ZnS:Mn is critical to their use in the health monitoring of the host

an

structure. Considering these facts, a method for mechanical agitation using a rotational vacuum infusion apparatus was developed employing centrifugal motion. They determined the degree of

M

dispersion in the resulting laminates using scanning electron microscopy and the energy dispersive scanning feature of the electron microscope for elemental mapping. Studies of the effect of ZnS:Mn concentration on the tensile strength of laminates showed that increasing the

d

ZnS:Mn concentration reduced the tensile strength.

te

Jang et al. [40] have reported the detection of reinforced concrete crack using mechanoluminescence paint. A 1000 mm-long specimen with 50 MPa concrete mix design strength and

Ac ce p

2.0 shear-span ratio was designed for the experiment. For the preparation of ML paint 100 gm of epoxy, 30 gm of hardener, 2 gm of additive and 19.5 gm of powder ML particles were used. At first, the ML paint was coated on one face of the specimen, and then a concrete strain gauge and an LVDT were installed in order to confirm the strain rate and the displacement that differs according to cracks. After accumulating energy in the ML paint to the specimen by using an ultraviolet lamp, it becomes able to record the crack propagation of the concrete by using a ultralow-light-level superhigh-speed camera.

Using the 3-point bending test, a quantitative

evaluation on the mechanical properties of cracks such as the cracking aspect and length of reinforced concrete was conducted. Through the results of this experiment, it was possible to confirm the crack propagation speed and the mechanical correlation such as between loads and cracks and between deflection and cracks. Such study is found to be quite successful in analyzing the characteristics of cracks. 19 Page 19 of 41

Aich et al. [6] have studied the ML for distributed damage assessment in cement-based materials. Their study demonstrates a simple, but novel, image processing protocol to detect and quantify luminescence from crack formation in cement-based matrices. Mortar cubes of 5.1 cm x 5.1 cm were loaded in compression with an external coating of manganese-doped zinc

ip t

sulfide mechanoluminescent material. The concentration of mechanoluminescent material and rate of loading were varied to evaluate luminescence response. A digital single lens reflex

cr

camera was employed to capture luminescence from the resulting cracks, which formed and propagated during failure. The images were then analyzed with an image processor, and total

us

luminescence/pixel along the cracks was quantified. Results show that overall luminescence increases with the increase in mechanoluminescent concentration as well as with the rate of loading. Thus, a novel method was reported that can be applied to monitor crack formation in

an

cement-based materials, providing reliable accuracy in luminescence quantification.

distribution

for

M

Recently, Aich et al. [41] have reported the detection of crack formation and stress carbon

fiber–reinforced

polymer

(CFRP)

specimens

through

mechanoluminescence-based imaging. The study demonstrates the ability of surface-coated

d

mechanoluminescent materials to detect damage in CFRP specimens. An experimental protocol

te

was developed to test the efficiency of the mechanoluminescent-based diagnostic method using carbon fiber–reinforced polymer coupons under combined bending– compression conditions.

Ac ce p

Luminescence, emitted from the mechanoluminescent coatings under quasi-static loading was detected by capturing digital images. An image processing software was used to quantify change in luminescence as a function of mechanoluminescent phosphor concentration. It was observed that 10%, 20%, and 30% mechanoluminescent coating resulted in 25.3, 27.9, and 40.4 (arbitrary units)

total

luminescence,

respectively,

which

shows

a

positive

correlation

of

mechanoluminescent concentration with luminescence. In the study, finite element simulation was also performed to understand the stress and strain distribution and to aid in understanding and correlating light emission regions on the carbon fiber–reinforced polymer coupons under bending deformation. The study demonstrates a valuable step toward the development of a robust technology that employs mechanoluminescent materials for early damage detection, consistent with theoretical predictions of damage occurrence.

20 Page 20 of 41

Terasaki et al. [42] have investigated visualization of active crack on bridge in use by mechanoluminescence sensor. When certain mechanoluminescent particles dispersedly coated on a structure, each particle acts as a sensitive mechanical sensor, while the two-dimentional emission pattern of the whole assembly reflects well the dynamical stress distribution inside the

ip t

structure and mechanical information around crack and defect. Thus, the remarkable strong points of ML sensing technique have been applied to a bridge in use. For the ML monitoring test

cr

at bridge, a relatively old bridge (established in 1954, 3-span continuous T-type RC bridge, length 24.4 m, width: 7.89 m) was selected. The ML sheet type sensors were put around the

us

central area (700×400 mm) of the main girder, and ML images originated from dynamic load application via general traffic vehicles were recorded by using lab-made CCD camera under roughly dark condition. Intense. In this experiment ML patterns were successfully detected not

an

only along visible crack but also at round soundless part on the girder at a glance with crack and invisible progressing microcrack.

M

responding ML intensity reflecting the crack mouth opening displacement (CMOD) of visible

5.3 Stochastic Nature of the Damage of Materials Tested by Mechanoluminescence

d

Structural Health Monitoring Technique

te

Practically, quasibrittle materials such as concrete, rocks, tough ceramics, sea ice, dry snow slabs, wood, some biomaterials, etc. fail at some different nominal strengths with respect to

Ac ce p

their structural size. In fact, smaller structures fail in a ductile manner which usually involves distributed cracking with strain-softening. The stress redistribution caused by fracture and distributed cracking engenders an energetic size effect, in which the nominal strength of structures decreases with increasing structure size. In fact, a structure having size far larger than the fracture process zone fails in an almost perfectly brittle manner and, if the failure occurs right at the crack initiation, then the failure load is governed by the statistically weakest point in the structure, and such result gives a basis to the statistical size effect. Stochastic fracture modelling is a general approach in which locations, size, orientation and other properties of fractures are treated as random variables with inferred probability distributions. In the simplest case, once the parameters of the distributions are inferred, the fracture model is constructed by Monte Carlo simulation [43]. The fundamental difference between a physical and a stochastic model, is that,

while the physical model seeks to understand and predict the process fully, the stochastic model 21 Page 21 of 41

accepts that some aspects of the physical process are out of range, at least for practical purposes, and must be replaced in the model by some unknowable and hence random process. The main reason for making the uncertainties explicit, for building them into the model, is that it is only in this way that one will be able to quantify the variability in the predicted outcomes. The resulting

ip t

stochastic model should reproduce those aspects of the physical phenomenon which are relevant and accessible to measurement.

cr

In recent years, the stochastic model of damage and fracture has become interesting and it has attracted the attention of a large number of workers [43-48]. So far the ML-based structural

us

health monitoring is concerned, limited studies have been made on the correlation between ML and damage of the tested materials such as reinforced concrete, cement-based materials, carbon

an

fiber–reinforced polymer (CFRP), ZnS:Mn phosphor embedded concrete structures, ZnS:Mn phosphor embedded vinyl ester polymer, and ZnS:Mn mixed laminates [6, 35-42]]. In a brittle crystal the cleavage planes are weaker planes. As the number of planes in a crystal is

M

proportional to the perimeter, the disorder in the crystal will be proportional to perimeter or Vf= V1/3, where f=1/3. Equation (2) in section 4 shows that the rate of creation of new cracks during

d

the deformation of a brittle crystal can be expressed by using a crack formation probability

te

p=  V f  , where V is the volume of the crystal, f is an exponent,  is the strain rate, and α is a constant. Subsequently, it has been shown by Eqs. (14) and (15) that the damage or the total area

Ac ce p

of newly created surface can be expressed as, S  bV ( f  f ) (   f ) or , S  bV(   f ) , where b' is a constant, ε the strain, f' is an exponent, f the fracture strain at which the fracture starts, and f+f'=1. As the total ML intensity IT increases linearly with the area of newly created surfaces [32], it can be expressed as

I T  T S  T bV(   f )  T bV

…(49)

where T is the ML intensity from produced by the creation of unit surface area. It is to be noted that for v0/ξ=v0τr=ε, Eq. (25) becomes similar to (49). It is evident that Eq. (49) correlates the damage S ,i.e., the newly created surface area with the volume V of crystal. In brittle crystalline materials fracture can occur by cleavage as the result of tensile stress acting normal to crystallographic planes with low bonding (cleavage 22 Page 22 of 41

planes). In amorphous or non-crystalline brittle solids, by contrast, the lack of a crystalline structure results in conchoridal fracture with cracks proceeding normal to the applied tension. In non-crystalline brittle solids Eq. (49) may also be applicable if, in such solids the weaker sites (microcracks, voids, notches, surface scratches and corners, etc.) inside the solids, which

ip t

amplifies the applied stress depends on the perimeter and volume of solids in a similar way to that for brittle crystals.

cr

It is evident from Eq. (49) that, for low value of strain the damage S in a solid of a given volume should increase linearly with strain; however, for higher value of strain the nonlinearty

us

should occur between S and strain because of the strain hardening in the solids; and for very large value of strain the solids will become so hard that it will be difficult to compress them. It is

an

to be noted that, generally the material to be tested by ML sensor possess large sizes, and therefore, uncompressible condition does not arise, and response of damage by the ML sensors

M

can be realized.

5.4 Certain salient features of ML-based structural health monitoring

d

Some of the salient features of ML-based structural health monitoring system are as

te

follows: (i) The wire connection is more practical as fibre-optical. In fact, the ML technique for structural health monitoring needs only one fibre waveguide from all sensors to connect it with

Ac ce p

detector unit. This is advantage of ML based sensors, and (ii) it has been reported that, at high impact energy (at hypervelocity impact), the ML sensor can be used [49,50]. However, one can also use acoustic or pressure sensor at high impact energy. The proposed ML sensor can also be used for high vibration applications to the systems like panzer, jet, etc., and (iii) the use of optical fibres is not very suitable for ML-based projectile damage sensors because the optical fibres can be broken at high impact energies. Some innovative approach is needed in this direction.

6. Conclusions In fracto-mechanoluminescent damage sensor for structure, the intense fracto– mechanoluminescent material of several micron size is mixed in liquid resin and then coated on to the surface of structure by curing at suitable temperature. In this technique, the occurrence and strength of the damage is given by the intensity of resulting mechanoluminescent light. 23 Page 23 of 41

Monitoring of the position of damage is achieved by identifying the colour of ML light emitted as the ML materials coated in different locations emit ML light of different colours. The important conclusions drawn from present investigation are as given below: (i)

Considering the successive fragmentation of the crystallites an expression is derived for

ip t

the impact velocity dependence of the rate of creation of the new surface area of the crystallites, and thereby for the impact velocity dependence of the ML intensity. It is

cr

found that, both the rate of creation of the new surface area of the crystallites and the transient ML intensity increase with the impact velocity of the projectile used to

us

fracture the sample.

(ii) Considering the fact that the total ML intensity depends linearly on the total area of the newly created surfaces (damage), modelling of fracto-mechanoluminescence damage

an

sensor is performed. It is found that, for the projectile having large contact, below the characteristic impact velocity vc, at which the sample is compressed to 1/e of its

M

thickness, both the peak ML intensity Im and the total ML intensity IT should increase linearly with the impact velocity; however, above vc, both Im and IT should tend to

d

attain a saturation value. In the case of impact of a projectile having small contact area such as ball, below vc, both Im and IT should increase quadratically with the value.

te

impact velocity; however, above vc, both Im and IT should tend to attain a saturation

Ac ce p

(iii)In the case of a projectile having large contact area the total volume of the sample is compressed and only the rate of creation of new surfaces increases with the impact velocity; however, in the case of a projectile having small contact area, in addition to the increase of strain rate with the impact velocity, the effective volume compressed by the impact also increases linearly with the impact velocity, and therefore, the rate of creation of new surfaces increases quadratically with the impact velocity.

(iv)The materials to be used for the fracto-mechanoluminescence damage sensor should not exhibit significant elastico ML and plastico ML so that no false alarms are generated. (v) The characteristic impact velocity vc (=1/δ) of the fracto-mechanoluminescent materials to be used should be high; otherwise, it will not be possible to analyze the srtrength of damages caused by high impact velocity. As vc depends on the particle size of

24 Page 24 of 41

phosphors, the particle size should be given due consideration while coating the phosphors on the surface of structures. (vi)The expressions derived for fracto ML intensity of the materials to be used for the fractomechanoluminescence damage sensor indicates that the ML intensity can be

ip t

enhanced by using the materials having high fracto-mechanoluminescence efficiency η, high surface charge density ρ at fracture, i.e., high piezoelectric constant dρ and

cr

high Young’s modulus of elasticity Y (as ρ=d0xY/100), and appreciable thickness of coating ( as the ML intensity increases with volume of the sample), high value of the

us

compression factor ψ, and high value of the rate constant for compression ξ (=1/τr). Using this concept suitable fracto-mechanoluminescent materials for damage sensor can be tailored. The value of δ should be of the moderate value as high value of ψ

an

will give low value of the characteristic impact velocity (δ=1/vc) to make the fractomechanoluminescence damage sensor unsuitable for high range of the impact A good agreement is found between the experimental and theoretical results.

Acknowledgement

d

(vii)

M

velocity.

te

One of the authors (BPC) is thankful to the University Grants Commission, New Delhi,

Ac ce p

India for the award of Emeritus Fellowship.

25 Page 25 of 41

References [1] I. Sage, R. Badcock, L. Humerstone, N. Gedders, M. Kemp, G. Bourhill, Triboluminescent damage sensors, Smart Mat. Srtuct. 8 (1999) 504-510.

ip t

[2] I. Sage, R.A. Badcock, L. Humberstone, N. Geddes, M. Kemp, S. Bishop, G. Bourhill, Squeezing light out of crystals: triboluminescent sensors, in: Smart Structures and Materials

cr

1999: Smart Materials Technologies, SPIE, first ed., Newport Beach, CA, USA, 1999, pp.

us

169–179.

[3] I. Sage, L. Humberstone, N. Geddes, M. Kemp, S. Bishop, G. Bourhill, Getting light through black composites:embedded triboluminescent structural

an

damage sensors, Smart Mater. Struct. 10 (2001) 332-337.

[4] I. Sage, G. Bourhill, Triboluminescent materials for structural damage

M

Monitoring, J. Mater, Chem. 11 (2001) 231-245.

[5] D. O. Olawale, T. Dickens, W.G. Sullivan, O. Okoli, J. O. Sobanjo, B. Wang, Progress in

te

1418.

d

triboluminescence-based smart optical sensor system, J. Lum. 131 (2011) 1407[6] N. Aich, A. Appalla, N. B. Saleh, P. Ziehl, Triboluminescence for distributed damage

Ac ce p

assessment in cement-based materials, Journal of Intelligent Material Systems and Structures, 24 (2013) 1714-1721.

[7] B.P. Chandra, in Luminescence of Solids, edited by D. R. Vij (Ed.), (Plenum Press, New York, 1998), Chap. 10, 361. [8] B.P. Chandra, “Mechanoluminescent smart materials and their applications, in Electronic and Catalytic Properties of Advanced Materials, edited by A. Stashans, S. Gonzalez, H. P. Pinto, (Transworld Research Network, Trivandrum, Kerala, India, 2011), p.1-37. [9] D.M. McCann, M.C. Forde, Review of NDT methods in the assessment of concrete and masonry structures, NDT & E Int. 34 (2001) 71-84. [10] K.P. Chong, N. J. Carino, G. Washer, Health monitoring of civil infrastructures, Smart Mater. Struct. 12 (2003) 483-493. 26 Page 26 of 41

[11] M. Ohtsu, M. Shigeishi, Y. Sakata, Non-destructive Evaluation of Defect in Concrete by Quantitative Acoustic Emission and Ultrasonics, Ultrasonics 36 (1998) 187-195. [12] Y. Berthaud, Damage measurements in concrete via an ultrasonic technique: Part I.

ip t

Experiment, Cement Concr. Res. 21 (1991) 73-82. [13] S. Nabulsi, S. Yehia, O. Abudayyeh, I. Abdelqader, D. Randolph, Imaging of waves

for

bridge

deck

evaluation,

in:

Proceedings

of

the

cr

electromagnetic

Electro/Information Technology Conference, EIT 2004, IEEE, 2004, pp. 59–61.

us

[14] J.T. Kuntz, J.W. Eales, Evaluation of bridge deck conditions by the use of infrared and ground penetrating radar, in: Proceedings of the Conference on Bridge Official, Pittsburgh,

an

Pennsylvania, 1985, pp. 121–127.

[15] U.B. Halabe, K.R. Maser, E.A. Kausel, Condition assessment of reinforced concrete

M

structures using electromagnetic waves, ACI Mater. J. 92 (1995) 511-523. [16] J. Hugenschmidt, Nondestructive evaluation of bridge decks using GPR, Benefits and limits,

d

Nondestructive Evaluation and Management, Zurich, Switzerland, 1997, pp. 362–367.

te

[17] K.R. Maser, Condition assessment of transportation infrastructure using ground penetrating

Ac ce p

radar, J. Infrastruct. Syst. 2 (1996) 94-101. [18] G. Pla-Rucki, M. Eberhard, Imaging of reinforced concrete: State-of the- Art review, J. Infrastruct. Syst. 1 (1996) 134-141. [19] H. Chen, S. Halabi, Impulse radar reflection waveform of simulated reinforced concrete bridge decks, Mater. Eval. 52 (1994) 1382-1388. [20] A. Loulizi, Development of Ground Penetrating Radar Signal Modeling and Implementation for Transportation Infrastructure Assessment, Virginia Polytechnic Institute and State University, 2001, pp. 1-263. [21] J.H. Bungey, Sub-surface radar testing of concrete: A review, Constr. Build. Mater. 18 (2004) 1-8.

27 Page 27 of 41

[22] O. Buyukozturk, H.C. Rhim, Radar Imaging of concrete specimens for nondestructive testing, Constr. Build. Mater. 11 (1997) 195-198. [23] M.I. Skolnik, Radar Handbook, McGraw-Hill Co., New York, 1970.

ip t

[24] R. Pugliesi, M.L.G. Andrade, Study of cracking in concrete by neutron radiography, Appl. Radiat. Isot. 48 (1997) 339-344.

cr

[25] R.M. Measures, Structural Monitoring with Fiber Optic Technology, Academic Press,

us

California, 2001.

[26] C.I. Merzbacher, A.D. Kersey, E.J. Friebele, Fibre-optic sensors in concrete: A review,

an

Smart. Mater. Struct. 5 (1996) 196-208.

[27] P. Childs, A.C.L. Wong, W. Terry, G.D. Peng, An In-Line In-Fibre Ring Cavity Sensor for

M

Localized Multi-Parameter Sensing, Meas. Sci. Technol. 19 (2008) 065302 (8 pp.). [28] B.P. Chandra, V.K. Chandra, P. Jha, Rashmi Patel, S.K. Shende, S. Thaker, R.N. Baghel, Fracto-mechanoluminescence and mechanics of fracture of solids, J. Lumin. 132 (2012)

te

d

2012-2022.

[29] B.P. Chandra, V.K. Chandra, S.K. Mahobia, P. Jha, R. Tiwari, B. Haldar, Real-time

Ac ce p

mechanoluminescence sensing of the amplitude and duration of impact, Sensors and Actuators A 173 (2012) 9-16.

[30] B.P. Chandra, V.K. Chandra, P. Jha, Models for intrinsic and extrinsic fractomechanoluminescence of solids, J. Lumin. 135 (2013) 139-153. [31] B. P. Chandra, S.Tiwari, M. Ramrakhiamni., M.H. Ansari, Mechanoluminescence in centrosymmetric crystals, Crystal Res. Tech. 26 (1991) 767-781. [32] B.P. Chandra, M. S. Khan, M. H. Ansari, Cleavage mechanoluminescence in crystals, Crystal Res. and Tech. 33, 289-300.

[33] B.P. Chandra, M. S. K. Khokhar, R. S. Gupta, B. Majumdar, Tetrahedral manganese (II) complexes: intense and unique type of mechanoluminophors, Pramana: J. Phys. 29 (1987) 399-407. 28 Page 28 of 41

[34] P.J. Brannon, R.W. Morris, J.R. Asay, Shocked- induced luminescence from Z-cut lithium niobate, J. Appl. Phys. 57 (1985) 1676-1679. [35] David O Olawale, Garrett Sullivan, Tarik Dickens, Steven Tsalickis, Okenwa I Okoli1,

ip t

John O Sobanjo, Ben Wang, Development of a triboluminescence based sensor system for concrete structures, Structural Health Monitoring 11 (2012) 139-147.

cr

[36] David O. Olawale, Tarik Dickens, Alvin Lim, Steve Tsalickis, Okenwa Okoli, Ben Wang, John O. Sobanjo, Characterization of the Triboluminescence Performance of ZnS:Mn Under American

us

Repeated Mechanical Loading for Smart Optical Damage Sensor System,

Society of Nondestructive Testing (ASNT) conference on NDE/NDT for highways and

an

bridges: Structural materials technology, August 16-20, 2010, New York pp.706-712. [37] T.J. Dickens, D. Olawale, Sullivan G, G. Sullivan, J. Breaux, O. O. I. Okoli, B. Wang (2011) Toward triboluminescent sensor realization for SHM: statistical modeling of

M

triboluminescent composites. In: TomizukaM (ed) SPIE 7981: Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2011. San Diego, CA: SPIE,

d

79810J-79810J-79813.

te

[38] T.J. Dickens, J. Breaux, D.O. Olawale, W.G. Sullivan, O.I. Okoli, Effects of ZnS:Mn concentrated vinyl ester matrices under flexural loading on the triboluminescent yield,

Ac ce p

Journal of Luminescence; 132 (2012) 1714-1719; [39] T. J. Dickens, O. I. Okoli, Enabling damage detection: manufacturing composite laminates doped with dispersed triboluminescent materials, Journal of Reinforced Plastics and Composites 30 (2011) 1869–1876. [40] I. Y. Jang, S. K. Kim, J. S. Kim, K. Y. Ann, C. G. Cho, Detection of Reinforced Concrete Crack Using Mechano-Luminescence Paint, Applied Mechanics and Materials,

316-317

(2013)1049-1054. [41] N. Aich, E. Kim, M. E. Batanouny, J. P. Tuttle, J. Yang, P. Ziehl, N. B Saleh, Detection of crack formation and stress distribution for carbon fiber–reinforced polymer specimens through triboluminescent-based imaging Journal of Intelligent Material Systems and Structures (2014) doi: 10.1177/1045389X14535017. 29 Page 29 of 41

[42] N. Terasaki, C.N. Xu, C. Li , L. Zhang, C. Li, D. Ono, M. Tsubai, Y. Adachi, Y. Imai, N. Ueno,

T.

Shinokawa,

Visualization

of

active

crack

on

bridge

in

use

by

mechanoluminescent sensor, Proc. SPIE 8348, Health Monitoring of Structural and Biological Systems 2012, 83482D (April 26, 2012); doi:10.1117/12.921036.

ip t

[43] C. Xu, P A. Dowd, A new computer code for discrete fracture network modelling, Comps & Geosc., 36: 292-301, 2010.

cr

[44] A. Duan , Y. Tian, J. G. Dai, W.L. Jin, A stochastic damage model for evaluating the internal deterioration of concrete due to freeze–thaw actionMaterials and Structures, 47,

us

1025-1039 (2014).

[45] C. Park, W. J. Padgett, New Cumulative Damage Models for Failure Using Stochastic

an

Processes as Initial Damage, IEEE Transactions on Reliability, 54 (2005) 530-540. [46]) N. Roy, R.N. Ghosh, S.C. Bose, 5th International Conference on Creep, Fatigue and Creep-

M

Fatigue Interaction September 24-26, 2008, Kalpakkam, India

d

[47] M.W. Belayneh, S. K. Matthäi, M. J. Blunt, S. F. Rogers, Comparison of deterministic

93 (2009) 1633–1648

te

with stochastic fracture models in water-flooding numerical simulations AAPG Bulletin, .

Ac ce p

[48] M. Noroozi, R. Kakaie, S.E. Jalali, Comparison of deterministic with stochastic fracture models in water-flooding numerical simulationsJournal of Geology and Mining Research, 7(2015) 1-10.

[49] N.P. Bergeron, W.A. Hollerman, S.M. Goedeke, M. Hovater, W. Hubbs, A.Finchum, R.J. Moore, S.W. Allison, D.L. Edwards, Experimental evidence of triboluminescence induced by hypervelocity impact, Int. J. Impact Eng. 33 (2006) 91–99. [50] N.P. Bergeron, W.A. Hollerman, S.M. Goedeke, R.J. Moore, Triboluminescent properties of zinc sulfide phosphors due to hypervelocity impact, Int. J. Impact Eng. 35 (2008) 1587– 1592.

30 Page 30 of 41

Figure Captions

ip t

Fig.1 (a) Time dependence of the ML intensity of 2 x 2 x 2 mm3 fluorescent N-acetylanthranilic acid crystals (Curves I, II and III correspond to the impact velocity 99, 198 and 313 cm/s

cr

respectively), and (b) time dependence of the ML intensity of 2 x 2 x 2 mm3 nonphotoluminescent sugar crystals (Curve I, II and III corresponds to the impact velocity 99, 198

us

and 313 cm/s respectively).

Fig.2 (a) Semilog plot of ML intensity versus time for 2 x 2 x 2 mm3 fluorescent N-

an

acetylanthranilic acid crystals (Curves I, II and III correspond to the impact velocity 99, 198 and 313 cm/s respectively), and (b) semilog plot of ML intensity versus time for 2 x 2 x 2 mm3 non-

M

photoluminescent sugar acid crystals (Curves I, II and III correspond to the impact velocity 99, 198 and 313 cm/s respectively).

d

Fig.3 Dependence of peak ML intensity Im on impact velocity vo (a- fluorescent N-

te

acetylanthranilic acid crystals, and b-. non-photoluminescent sugar crystals). Fig.4 Dependence of total ML intensity IT on impact velocity vo (a- fluorescent N-

Ac ce p

acetylanthranilic acid crystals, and b-. non-photoluminescent sugar crystals). Fig. 5 Plot of the ML intensity versus impact energy of a ball for two Mn complexes of different crystallite sizes mixed in a resin (after Sage et al., ref. [1]). Fig. 6 Plot of the ML intensity versus impact energy of a ball for: (a) ZnS:Mn phosphor, and (b) triphenylphosphineoxide manganese bromide. Fig. 7 Dependence of the peak radiance at 700 nm of Z-cut lithium niobate disks of about 3.6 mm thick and 36 mm diameter on the impact velocity (the data taken from Fig. 5, and stress is converted into velocity from the data given in Table 1, from Brannon et al., ref. [34]). Fig. 8 Semilog plot of (1-I/I0) versus v0 for Z-cut lithium niobate disks of about 3.6 mm thick and 36 mm diameter. 31 Page 31 of 41

ip t Ac ce p

te

d

M

an

us

cr

Fig.1

32 Page 32 of 41

ip t Ac ce p

te

d

M

an

us

cr

Fig.2

33 Page 33 of 41

ip t cr

Ac ce p

te

d

M

an

us

Fig.3

34 Page 34 of 41

ip t cr

Ac ce p

te

d

M

an

us

Fig.4

F ig. 5

35 Page 35 of 41

ip t cr us an M d te Ac ce p Fig. 6

36 Page 36 of 41

ip t cr us an M d te Ac ce p Fig. 7

37 Page 37 of 41

ip t cr us an M d te Ac ce p Fig. 8

38 Page 38 of 41

39

Page 39 of 41

d

te

Ac ce p us

an

M

cr

ip t

Short Biographies of Authors

B.P. Chandra obtained his Ph.D. in Physics from Pt. Ravishankar University, Raipur, CG, India

ip t

in the year 1974 and also D.Sc. in Physics from Rani Durgavati University, Jabalpur, MP, India in the year 1992. He is an UGC Emeritus Professor, at School of Studies in Physics and

cr

Astrophysics, Pt Ravishankar Shukla University, Raipur, CG, India. His current fields of interest

us

include optoelectronic materials, optoelectronic devices, electronic instrumentations.

an

V.K. Chandra obtained his Ph.D. in Electronics & Telecommunication Engineering from Pt. Ravishankar University, Raipur, CG, India in the year 2006. He is an Associate Professor of Electrical and Electronics Engineering at Chhatrapati Shivaji Institute of Technology, Durg

M

491001, CG, India. His current fields of interest include optoelectronic materials, optoelectronic

te

d

devices, electronic instrumentations.

Piyush Jha obtained his M.Phil. in Physics from Rani Durgavati University, Jabalpur, MP, India

Ac ce p

in the year 2008 and also Ph.D.in Physics, from Rani Durgavati University, Jabalpur, MP, India in the year 2013. He is an Assistant Professor of Applied Physics, at Raipur Institute of Technology, Raipur, CG, India. His current field of interest is optoelectronic materials.

40 Page 40 of 41

Highlights Using mechanoluminescence damage sensor both the magnitude and location of damage can be determined.

ip t

The modelling is based on dependence of the total ML intensity on the total area of the newly created surfaces (damage).

cr

The ML response is different for the projectile having large contact area and the projectile having small contact area.

Ac ce p

te

d

M

an

us

The present study identifies the parameters of mechanoluminescent materials used in damage sensor for structures.

41 Page 41 of 41