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Mechanical characterisation of fusion materials by indentation test
Fusion Engineering and Design 58 – 59 (2001) 755– 759 www.elsevier.com/locate/fusengdes
Mechanical characterisation of fusion materials by indentation test B. Riccardi a,*, R. Montanari b, L.F. Moreschi c, A. Sili d, S. Storai c a
Associazione EURATOM-ENEA sulla Fusione, Centro Ricerche Frascati, CP 65, 00044 Frascati, Rome, Italy Dipartimento di Ingegneria Meccanica, Uni6ersita` di Roma-Tor Vergata, Via di Tor Vergata 110, 00133 Rome, Italy c Associazione EURATOM-ENEA, ENEA CR Brasimone, PB 1, 40032 Camugnano (BO) Italy d Dipartimento Chimica Industriale e Ingegneria dei Materiali, Uni6ersita` di Messina, Salita Sperone 31, Messina, Italy b
Abstract FIMEC is an indentation test, which permits the evaluation of yield and ultimate tensile stress and to draw indication about the ductile to brittle transition temperature. The apparatus has been recently implemented with a feedback system to maintain strictly constant the penetration speed of cylindrical punch during the test. So, experiments performed on several materials, as those for first wall and blanket, show that the scattering between data from FIMEC and from standard tensile test is reduced within the range 9 0.06, i.e. it is comparable with the scattering obtained in different tensile tests on the same material. A numerical simulation has been carried out to understand the basic mechanism of the process. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Fusion materials; Indentation test; Numerical simulation; Non destructive testing
1. Introduction FIMEC is a penetration test which employs a flat WC punch of small size (diameter= 1 mm, height=1.5 mm). From load – penetration depth (L–P) curves it is possible to estimate the yield (|Y) and ultimate tensile stress (|U). In certain conditions, i.e. penetration rate=0.1 mm min − 1 and deformation rate in tensile test= 10 − 3 s − 1, |Y $ qY/3 where qY is the specific load (the load divided by the punch contact area) at the end of the first work hardening stage. For very ductile * Corresponding author. Tel.: + 39-06-9400-5159; fax: + 39-06-9400-5147. E-mail address: [email protected] (B. Riccardi).
materials (e.g. pure copper and aluminium), |U $ qS/3 where qS is the saturation specific load [1]. Moreover, from tests at different temperatures it is possible to draw indication about the ductile to brittle transition temperature (DBTT) as obtained by Charpy standard tests. Details about the application of the method for investigating DBTT are reported in previous papers [1–4]. Due to the small quantity of material involved in the test, FIMEC is very useful to check local properties of mechanical structures, e.g. weld joints, or materials subjected to different thermal treatment and it appears interesting for characterising materials irradiated in IFMIF or in other neutron sources with small irradiation volumes. Furthermore, FIMEC is a not a destructive test
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B. Riccardi et al. / Fusion Engineering and Design 58–59 (2001) 755–759
and thus it is suitable, in principle, for monitoring ‘in situ’ the state of materials under load or the evolution of radiation damage in the same sample. Recently, the apparatus has been implemented with a feedback system. The motor control unit is connected to an LVDT and the feedback system provides constant advancement speed of punch with applied load changes up to 10 kN. In this paper, results obtained with the new configuration on several metals and alloys, most of them of fusion interest, are presented. Moreover, WC indenters of smaller diameters (0.8 and 0.7 mm) were realised and tested to verify the general validity of the FIMEC method and to further decrease the volume of material involved in the test. In order to understand the basic mechanism of the process and how the L–P curve is related to the standard stress– strain curve, the indentation process was studied by finite element (FE) analysis. In addition, a metallographic study was carried out to achieve direct evidence about metal plastic flow around the punch during FIMEC tests. Some imprints have been cut along the cylinder axis, the section surfaces have been mechanically polished, etched and finally observed by optical and scanning electron microscopy. Results of these observations have been compared with strain maps from FE simulations.
2. The FIMEC apparatus In the FIMEC apparatus load cell, LVDT displacement measuring system and linear actuator, which drives the indenter advancement, are mounted on a metallic frame dimensioned to have an elastic deformation of about 1 mm in the maximum load condition (10 kN). The linear actuator is an electro-mechanical drive equipped with a stepping motor. The motor rotation is transmitted to a ball screw via a precision reduction gear; the ball screw converts the rotary motion at the gear output to translation, which is guided by means of a pre-loaded ballspline. Indenters are flat punches (b = 1, 0.8 and 0.7 mm, h=1.5 mm) made of WC to guarantee good
rigidity and non-deformability. They are mounted at the end of the translator rod, whose advancement speed is adjustable in the range from 0.0001 to 0.02 mm s − 1. The motor control unit is connected to an LVDT and a feedback system provides constant speed with applied load changes up to 10 kN. The LVDT system measures the distance between specimen holder and indenter with a resolution of 1 mm. The load cell resolution is 1 N. The operations of FIMEC apparatus and the on-line data acquisition are controlled by a specific software. All the punches (b= l, 0.8 and 0.7 mm) have been manufactured by sintering of WC powders with fine granulometry.
3. Experimental data Table 1 compares the values of yield stress |Y from tensile tests and of qY/3 from FIMEC with and without feedback system. The parameter Z= (|y − qy/3)/|y indicates how far the values obtained from FIMEC tests are from the corresponding data measured in tensile tests. Yield stress values determined from FIMEC are satisfactory, in particular those obtained by means of the experimental apparatus employing the feedback system. The feedback system guarantees that the penetration rate remains constant during the test and does not depend on the metal work-hardening. This is important because the penetration rate affects the shape of L–P curves and thus, the qY values determined from them [1]. The scattering between data from FIMEC and from standard tensile tests is strongly reduced in the tests with a strict control of punch advancement speed. For the tested materials Z* is always lower than Z and comparable with data scattering (7%) usually observed in standard tensile tests performed on different probes of the same material [5]. Fig. 1 shows the L–P curves obtained by testing the same material (F82H mod.) with indenters of different diameters (1.0, 0.8 and 0.7 mm). A substantially perfect overlapping of the three curves is observed (see framed figure) after a suitable normalisation. L–P curves obtained using indenters with b=0.8 and 0.7 mm have been
B. Riccardi et al. / Fusion Engineering and Design 58–59 (2001) 755–759
corrected by multiplying load values by S1/S0.8 and S1/S0.7 respectively, where S1, S0.8 and S0.7 are the material– punch contact areas.
4. Numerical simulation The mathematical solution of the problem of the indentation of an elastic continuum half-space by a rigid solid of revolution punch was given by Bussinesq [6]. If the punch is a cylinder, the distribution of pressure q on the contact area is given by the following equation: q=
P
(1)
2pa a 2 −r 2
where P is the total load of the punch, a is the radius of the punch and r is the distance from the centre of the contact circle. This distribution of pressure is not uniform, the smallest value being at the centre and equal to half of the average pressure on the contact area P/(2pa 2). At the boundary of the contact area the pressure became infinite leading to a very localised yielding, which practically does not affect the pressure distribution itself. The penetration load P versus punch displacement l is given by the equation:
P=
757
2Eal 1− w 2
(2)
where w is Poisson’s ratio and E is Young’s modulus. Relation (2) implies that the L–P curve is linear in its elastic part and the slope is the indentation contact stiffness S=
dP dl
(3)
When the extension of the plastic area becomes significant the L–P pattern is no longer linear but becomes a curve with decreasing slope. A discontinuity in the curve slope can be detected when material protrusion begins. In order to reproduce the full load penetration history looking at the possibility of a detection of the characteristic loads qL (load corresponding to the end of linear stage) and qY, a finite element analysis of the flat top indentation process was carried out by means of the ABAQUS general purpose code [7]. The simulation, performed by means of an axisymmetric model using a high refinement mesh, was carried out by using a static elastic–plastic analysis and by an adaptive mesh dynamic analysis based on a hybrid Lagrangian– Eulerian material description with the possibility to maintain automatically a high quality mesh when very large deformations occur. The indenter, initially assumed in contact with the sample,
Table 1 Comparison between yield stress |Y obtained in standard tensile tests and qY/3 obtained in FIMEC tests. Z =(|Y−qY/3)/|Y (asterisk (*) indicates data obtained using the experimental apparatus with the feedback system) Material
Cu Zn Mo Cu–5%Zn–7%Sn GlidCopa Cu–0.65Cr–0.08%Zr Fe–40%Al+1%Y2O3 MANET II BATMAN-1951 F 82 H Mod. AISI 316 L a
Tensile test
FIMEC test
|Y (MPa)
qY/3 (MPa)
q */3 (MPa) Y
190 55 540 145 483 306 922 640 510 520 310
185 55 560 127 420 285 980 575 440 490 355
195 55 560 149 460 310 900 640 500 500 330
Glidcop (Cu–0.48Al2O3) deformed 20%.
Z
Z*
0.03 0 −0.04 0.12 0.13 0.07 −0.06 0.10 0.14 0.06 0.14
−0.03 0 −0.04 −0.03 0.05 −0.01 0.02 0 0.02 0.04 0.06
758
B. Riccardi et al. / Fusion Engineering and Design 58–59 (2001) 755–759
The micrograph in Fig. 3 shows the plastic flow around the FIMEC imprint in F82H mod. that was satisfactory reproduced by the FEM simulation (Fig. 2). The calculated load penetration curve (Fig. 4) showed the same trend as the experimental one: the detection of the qL limit depends on the elastic–plastic behaviour of material. In fact, plastic deformation of the contact region starts for a load higher than qL. The original slope of the numerical curve was found to be in good agreement with relationship (3) but both of them are steeper than the experimental one: surface imperfections mainly on the indenter tip but also on the sample may account for the discrepancy, while the effect of the indenter elasticity was found to be modest. Specific analyses are underway to assess the matter. At qY load level, all the material under the contact region is in the plastic range and starts to protrude. The detection of this point can be easily Fig. 1. L – P curves of F82H mod. steel obtained using punches of different diameters. In the frame, a perfect overlapping of the three curves is observed after normalisation.
was simulated by means of a rigid surface whilst a sliding boundary region was used to define the contact surface on the sample. The indentation simulation was carried out by imposing the indenter penetration and monitoring the counter reaction force. The full penetration dynamic analysis, even if performed with a dynamic code, is representative of the penetration process because the used parameters permit to get a quasi-static response. The analysis has been focussed only on the indentation of the F82H mod. martensitic steel at room temperature; the plastic part of the stress– strain curve was modelled by means of Hollowan’s relationship |= km n where k =813.63 MPa and the average work hardening coefficient n =0.07168 [8]. In the plastic range, the material was assumed to follow the von Mises plasticity criterion. The deformed plot obtained, with von Mises equivalent plastic strain contour, is shown in Fig. 2; the deformed shape and protrusion around the indentation fits quite well the experimental one.
Fig. 2. FEM deformed plot with the contour of the von Mises equivalent plastic strain (defined as mMISES = (2/3)mpl·mpl where mpl is the plastic strain tensor).
B. Riccardi et al. / Fusion Engineering and Design 58–59 (2001) 755–759
759
Fig. 4. Numerically calculated load – penetration curve.
Fig. 3. Indentation imprint micrograph.
performed by determining a discontinuity in the L– P curve slope. The calculated L– P curve reproduced the experimental one at high penetration values. In particular the maximum load (at 1 mm penetration) differs from the experimental value by less than 7% and thus within the experimental error of a tensile test.
5. Conclusions Experimental data from several materials confirmed the general validity of FIMEC test, which can be usefully employed for testing irradiated or ‘in service’ materials and for characterising local mechanical properties in metal welds. Tests performed using indenters of smaller diameter (0.7 and 0.8 mm) gave results in agreement with those obtained with the usual punch (1 mm). This is important because the volume of material involved in the test is smaller. In addition, the result appears promising in the perspective to design and manufacture portable FIMEC devices.
The numerical simulation allowed a preliminary understanding of the mechanical phenomena which produce the L–P curve.
References [1] P. Gondi, R. Montanari, A. Sili, Small scale non-destructive stress-strain and creep tests feasible during irradiation, J. Nucl. Mater. 212 – 215 (1994) 1688. [2] P. Gondi, A. Donato, R. Montanari, A. Sili, A miniaturized test method for mechanical characterization of structural materials for fusion reactors, J. Nucl. Mater. 233 – 237 (1996) 1557. [3] P. Gondi, R. Montanari, A. Sili, S. Foglietta, A. Donato, G. Filacchioni, Applicability of the FIMEC indentation test to characterise materials irradiated in the future IFMIF high intensity neutron irradiation source, Fusion Technol. (1996) 1607. [4] A. Donato, P. Gondi, R. Montanari, F. Moreschi, A. Sili, S. Storai, A remotely operated FIMEC apparatus for the mechanical characterization of neutron irradiated materials, J. Nucl. Mater. 258 – 263 (1998) 446 – 451. [5] B.W. Christ, Effect of specimen preparation, setup and test procedures on test result, Metals Handbook 9th ed., vol. 8 (1985), p. 32. [6] J. Bussinesq, (1885) Application des Potentiels a l’Etude de l’Equilibre e du Movement del Solides Elastiques, (dummy edn), Paris: Gautier-Villar. [7] ABAQUS Explicit 5.8, User’s Manual, Hibbit Karlsson and Sorensen Inc., Pawtucket, RI, 1998. [8] G. Filacchioni, private communication, 1999.
Mechanical characterisation of fusion materials by indentation test B. Riccardi a,*, R. Montanari b, L.F. Moreschi c, A. Sili d, S. Storai c a
Associazione EURATOM-ENEA sulla Fusione, Centro Ricerche Frascati, CP 65, 00044 Frascati, Rome, Italy Dipartimento di Ingegneria Meccanica, Uni6ersita` di Roma-Tor Vergata, Via di Tor Vergata 110, 00133 Rome, Italy c Associazione EURATOM-ENEA, ENEA CR Brasimone, PB 1, 40032 Camugnano (BO) Italy d Dipartimento Chimica Industriale e Ingegneria dei Materiali, Uni6ersita` di Messina, Salita Sperone 31, Messina, Italy b
Abstract FIMEC is an indentation test, which permits the evaluation of yield and ultimate tensile stress and to draw indication about the ductile to brittle transition temperature. The apparatus has been recently implemented with a feedback system to maintain strictly constant the penetration speed of cylindrical punch during the test. So, experiments performed on several materials, as those for first wall and blanket, show that the scattering between data from FIMEC and from standard tensile test is reduced within the range 9 0.06, i.e. it is comparable with the scattering obtained in different tensile tests on the same material. A numerical simulation has been carried out to understand the basic mechanism of the process. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Fusion materials; Indentation test; Numerical simulation; Non destructive testing
1. Introduction FIMEC is a penetration test which employs a flat WC punch of small size (diameter= 1 mm, height=1.5 mm). From load – penetration depth (L–P) curves it is possible to estimate the yield (|Y) and ultimate tensile stress (|U). In certain conditions, i.e. penetration rate=0.1 mm min − 1 and deformation rate in tensile test= 10 − 3 s − 1, |Y $ qY/3 where qY is the specific load (the load divided by the punch contact area) at the end of the first work hardening stage. For very ductile * Corresponding author. Tel.: + 39-06-9400-5159; fax: + 39-06-9400-5147. E-mail address: [email protected] (B. Riccardi).
materials (e.g. pure copper and aluminium), |U $ qS/3 where qS is the saturation specific load [1]. Moreover, from tests at different temperatures it is possible to draw indication about the ductile to brittle transition temperature (DBTT) as obtained by Charpy standard tests. Details about the application of the method for investigating DBTT are reported in previous papers [1–4]. Due to the small quantity of material involved in the test, FIMEC is very useful to check local properties of mechanical structures, e.g. weld joints, or materials subjected to different thermal treatment and it appears interesting for characterising materials irradiated in IFMIF or in other neutron sources with small irradiation volumes. Furthermore, FIMEC is a not a destructive test
0920-3796/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 0 - 3 7 9 6 ( 0 1 ) 0 0 5 6 1 - 0
756
B. Riccardi et al. / Fusion Engineering and Design 58–59 (2001) 755–759
and thus it is suitable, in principle, for monitoring ‘in situ’ the state of materials under load or the evolution of radiation damage in the same sample. Recently, the apparatus has been implemented with a feedback system. The motor control unit is connected to an LVDT and the feedback system provides constant advancement speed of punch with applied load changes up to 10 kN. In this paper, results obtained with the new configuration on several metals and alloys, most of them of fusion interest, are presented. Moreover, WC indenters of smaller diameters (0.8 and 0.7 mm) were realised and tested to verify the general validity of the FIMEC method and to further decrease the volume of material involved in the test. In order to understand the basic mechanism of the process and how the L–P curve is related to the standard stress– strain curve, the indentation process was studied by finite element (FE) analysis. In addition, a metallographic study was carried out to achieve direct evidence about metal plastic flow around the punch during FIMEC tests. Some imprints have been cut along the cylinder axis, the section surfaces have been mechanically polished, etched and finally observed by optical and scanning electron microscopy. Results of these observations have been compared with strain maps from FE simulations.
2. The FIMEC apparatus In the FIMEC apparatus load cell, LVDT displacement measuring system and linear actuator, which drives the indenter advancement, are mounted on a metallic frame dimensioned to have an elastic deformation of about 1 mm in the maximum load condition (10 kN). The linear actuator is an electro-mechanical drive equipped with a stepping motor. The motor rotation is transmitted to a ball screw via a precision reduction gear; the ball screw converts the rotary motion at the gear output to translation, which is guided by means of a pre-loaded ballspline. Indenters are flat punches (b = 1, 0.8 and 0.7 mm, h=1.5 mm) made of WC to guarantee good
rigidity and non-deformability. They are mounted at the end of the translator rod, whose advancement speed is adjustable in the range from 0.0001 to 0.02 mm s − 1. The motor control unit is connected to an LVDT and a feedback system provides constant speed with applied load changes up to 10 kN. The LVDT system measures the distance between specimen holder and indenter with a resolution of 1 mm. The load cell resolution is 1 N. The operations of FIMEC apparatus and the on-line data acquisition are controlled by a specific software. All the punches (b= l, 0.8 and 0.7 mm) have been manufactured by sintering of WC powders with fine granulometry.
3. Experimental data Table 1 compares the values of yield stress |Y from tensile tests and of qY/3 from FIMEC with and without feedback system. The parameter Z= (|y − qy/3)/|y indicates how far the values obtained from FIMEC tests are from the corresponding data measured in tensile tests. Yield stress values determined from FIMEC are satisfactory, in particular those obtained by means of the experimental apparatus employing the feedback system. The feedback system guarantees that the penetration rate remains constant during the test and does not depend on the metal work-hardening. This is important because the penetration rate affects the shape of L–P curves and thus, the qY values determined from them [1]. The scattering between data from FIMEC and from standard tensile tests is strongly reduced in the tests with a strict control of punch advancement speed. For the tested materials Z* is always lower than Z and comparable with data scattering (7%) usually observed in standard tensile tests performed on different probes of the same material [5]. Fig. 1 shows the L–P curves obtained by testing the same material (F82H mod.) with indenters of different diameters (1.0, 0.8 and 0.7 mm). A substantially perfect overlapping of the three curves is observed (see framed figure) after a suitable normalisation. L–P curves obtained using indenters with b=0.8 and 0.7 mm have been
B. Riccardi et al. / Fusion Engineering and Design 58–59 (2001) 755–759
corrected by multiplying load values by S1/S0.8 and S1/S0.7 respectively, where S1, S0.8 and S0.7 are the material– punch contact areas.
4. Numerical simulation The mathematical solution of the problem of the indentation of an elastic continuum half-space by a rigid solid of revolution punch was given by Bussinesq [6]. If the punch is a cylinder, the distribution of pressure q on the contact area is given by the following equation: q=
P
(1)
2pa a 2 −r 2
where P is the total load of the punch, a is the radius of the punch and r is the distance from the centre of the contact circle. This distribution of pressure is not uniform, the smallest value being at the centre and equal to half of the average pressure on the contact area P/(2pa 2). At the boundary of the contact area the pressure became infinite leading to a very localised yielding, which practically does not affect the pressure distribution itself. The penetration load P versus punch displacement l is given by the equation:
P=
757
2Eal 1− w 2
(2)
where w is Poisson’s ratio and E is Young’s modulus. Relation (2) implies that the L–P curve is linear in its elastic part and the slope is the indentation contact stiffness S=
dP dl
(3)
When the extension of the plastic area becomes significant the L–P pattern is no longer linear but becomes a curve with decreasing slope. A discontinuity in the curve slope can be detected when material protrusion begins. In order to reproduce the full load penetration history looking at the possibility of a detection of the characteristic loads qL (load corresponding to the end of linear stage) and qY, a finite element analysis of the flat top indentation process was carried out by means of the ABAQUS general purpose code [7]. The simulation, performed by means of an axisymmetric model using a high refinement mesh, was carried out by using a static elastic–plastic analysis and by an adaptive mesh dynamic analysis based on a hybrid Lagrangian– Eulerian material description with the possibility to maintain automatically a high quality mesh when very large deformations occur. The indenter, initially assumed in contact with the sample,
Table 1 Comparison between yield stress |Y obtained in standard tensile tests and qY/3 obtained in FIMEC tests. Z =(|Y−qY/3)/|Y (asterisk (*) indicates data obtained using the experimental apparatus with the feedback system) Material
Cu Zn Mo Cu–5%Zn–7%Sn GlidCopa Cu–0.65Cr–0.08%Zr Fe–40%Al+1%Y2O3 MANET II BATMAN-1951 F 82 H Mod. AISI 316 L a
Tensile test
FIMEC test
|Y (MPa)
qY/3 (MPa)
q */3 (MPa) Y
190 55 540 145 483 306 922 640 510 520 310
185 55 560 127 420 285 980 575 440 490 355
195 55 560 149 460 310 900 640 500 500 330
Glidcop (Cu–0.48Al2O3) deformed 20%.
Z
Z*
0.03 0 −0.04 0.12 0.13 0.07 −0.06 0.10 0.14 0.06 0.14
−0.03 0 −0.04 −0.03 0.05 −0.01 0.02 0 0.02 0.04 0.06
758
B. Riccardi et al. / Fusion Engineering and Design 58–59 (2001) 755–759
The micrograph in Fig. 3 shows the plastic flow around the FIMEC imprint in F82H mod. that was satisfactory reproduced by the FEM simulation (Fig. 2). The calculated load penetration curve (Fig. 4) showed the same trend as the experimental one: the detection of the qL limit depends on the elastic–plastic behaviour of material. In fact, plastic deformation of the contact region starts for a load higher than qL. The original slope of the numerical curve was found to be in good agreement with relationship (3) but both of them are steeper than the experimental one: surface imperfections mainly on the indenter tip but also on the sample may account for the discrepancy, while the effect of the indenter elasticity was found to be modest. Specific analyses are underway to assess the matter. At qY load level, all the material under the contact region is in the plastic range and starts to protrude. The detection of this point can be easily Fig. 1. L – P curves of F82H mod. steel obtained using punches of different diameters. In the frame, a perfect overlapping of the three curves is observed after normalisation.
was simulated by means of a rigid surface whilst a sliding boundary region was used to define the contact surface on the sample. The indentation simulation was carried out by imposing the indenter penetration and monitoring the counter reaction force. The full penetration dynamic analysis, even if performed with a dynamic code, is representative of the penetration process because the used parameters permit to get a quasi-static response. The analysis has been focussed only on the indentation of the F82H mod. martensitic steel at room temperature; the plastic part of the stress– strain curve was modelled by means of Hollowan’s relationship |= km n where k =813.63 MPa and the average work hardening coefficient n =0.07168 [8]. In the plastic range, the material was assumed to follow the von Mises plasticity criterion. The deformed plot obtained, with von Mises equivalent plastic strain contour, is shown in Fig. 2; the deformed shape and protrusion around the indentation fits quite well the experimental one.
Fig. 2. FEM deformed plot with the contour of the von Mises equivalent plastic strain (defined as mMISES = (2/3)mpl·mpl where mpl is the plastic strain tensor).
B. Riccardi et al. / Fusion Engineering and Design 58–59 (2001) 755–759
759
Fig. 4. Numerically calculated load – penetration curve.
Fig. 3. Indentation imprint micrograph.
performed by determining a discontinuity in the L– P curve slope. The calculated L– P curve reproduced the experimental one at high penetration values. In particular the maximum load (at 1 mm penetration) differs from the experimental value by less than 7% and thus within the experimental error of a tensile test.
5. Conclusions Experimental data from several materials confirmed the general validity of FIMEC test, which can be usefully employed for testing irradiated or ‘in service’ materials and for characterising local mechanical properties in metal welds. Tests performed using indenters of smaller diameter (0.7 and 0.8 mm) gave results in agreement with those obtained with the usual punch (1 mm). This is important because the volume of material involved in the test is smaller. In addition, the result appears promising in the perspective to design and manufacture portable FIMEC devices.
The numerical simulation allowed a preliminary understanding of the mechanical phenomena which produce the L–P curve.
References [1] P. Gondi, R. Montanari, A. Sili, Small scale non-destructive stress-strain and creep tests feasible during irradiation, J. Nucl. Mater. 212 – 215 (1994) 1688. [2] P. Gondi, A. Donato, R. Montanari, A. Sili, A miniaturized test method for mechanical characterization of structural materials for fusion reactors, J. Nucl. Mater. 233 – 237 (1996) 1557. [3] P. Gondi, R. Montanari, A. Sili, S. Foglietta, A. Donato, G. Filacchioni, Applicability of the FIMEC indentation test to characterise materials irradiated in the future IFMIF high intensity neutron irradiation source, Fusion Technol. (1996) 1607. [4] A. Donato, P. Gondi, R. Montanari, F. Moreschi, A. Sili, S. Storai, A remotely operated FIMEC apparatus for the mechanical characterization of neutron irradiated materials, J. Nucl. Mater. 258 – 263 (1998) 446 – 451. [5] B.W. Christ, Effect of specimen preparation, setup and test procedures on test result, Metals Handbook 9th ed., vol. 8 (1985), p. 32. [6] J. Bussinesq, (1885) Application des Potentiels a l’Etude de l’Equilibre e du Movement del Solides Elastiques, (dummy edn), Paris: Gautier-Villar. [7] ABAQUS Explicit 5.8, User’s Manual, Hibbit Karlsson and Sorensen Inc., Pawtucket, RI, 1998. [8] G. Filacchioni, private communication, 1999.