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Indentation experiments on novel sandwich composite tubes
Author’s Accepted Manuscript Indentation experiments on novel sandwich composite tubes Abbas Niknejad, Alireza Moradi, Niloofar Beheshti
www.elsevier.com
PII: DOI: Reference:
S0167-577X(16)30782-0 http://dx.doi.org/10.1016/j.matlet.2016.05.041 MLBLUE20852
To appear in: Materials Letters Received date: 29 February 2016 Revised date: 22 April 2016 Accepted date: 7 May 2016 Cite this article as: Abbas Niknejad, Alireza Moradi and Niloofar Beheshti, Indentation experiments on novel sandwich composite tubes, Materials Letters, http://dx.doi.org/10.1016/j.matlet.2016.05.041 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 galley proof before it is published in its final citable 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.
Indentation experiments on novel sandwich composite tubes Abbas Niknejad1,*, Alireza Moradi1, Niloofar Beheshti2 1
Mechanical Engineering Department, Yasouj University, P.O. Box: 75914-353, Yasouj, Iran 2
Civil Engineering Department, Yasouj University, P.O. Box: 75914-353, Yasouj, Iran
Abstract This article introduces a novel energy absorber of sandwich tube with the agglomerated cork core and the composite tube during the indentation process under the applied quasi-static lateral loading by a solid cylindrical rigid indenter. Also, the corresponding cork specimens and the empty composite tubes are tested, too. The solid cylindrical cores made of agglomerated cork are prepared by punching a cork sheet with 200 kg/m3 density and positioned into the composite tubes to manufacture the cork-filled tubes. The results show that the cork-filled composite tubes have an energy absorption capacity up to 5.65 times of the corresponding cork sample and up to 6.06 times of the corresponding empty tube. Also, it is found that total absorbed energy by a cork-filled composite tube is 174 % higher than summation of absorbed energy by the corresponding empty tube and the cork sample. Also, specific absorbed energy by all the specimens is discussed. Keywords: Agglomerated cork; Composite materials; Indentation process; Energy absorption; Sandwich tubes; Porous materials.
1. Introduction Energy absorption is an interesting concern for many researchers and it relates to safety of some engineering structures. Porous materials are one of suitable selections as energy absorber, so, some previous papers investigated mechanical behavior of different porous materials such as scaffolds [1], metal foams [2] and agglomerated cork [3]. Sanchez-Saez et al. [4] studied multi-impact behavior of agglomerated cork, experimentally. Gameiro and Cirne [5] studied dynamic crushing of agglomerated cork-filled tubes. Some articles discussed effects of porous polyurethane foam as the filler into composite [6 and 7] and metal tubes [8]. Also, Morris et al. [9] and Hafeez and Almaskari [10] studied indentation process on circular metal and composite tubes, respectively. This article introduces a novel composite sandwich tube as the new energy absorber during the indention process, using rigid solid cylindrical rods with different diameters. On the other hand, some solid cylinders made of *Corresponding
author at: Mechanical Engineering Department, Yasouj University, P.O. Box: 75914–353, Yasouj, Iran. Tel.: +98 74 33229889; Fax: +98 74 33221711. E–mail address: [email protected] (A. Niknejad).
agglomerated cork are laterally compressed and also, similar cork specimens are positioned into cylindrical composite tubes as the filler and the achieved sandwich tubes are laterally tested and their energy absorption behavior under the applied quasi-static lateral loading is discussed.
2. Experiments This article studied energy absorption by some agglomerated cork specimen, hollow composite tubes, and agglomerated cork-filled composite tubes during the indentation process. For this purpose, three solid cylindrical rods with different diameters of 10.0, 20.0 and 30.0 mm were machined from hardened steel to consider them as rigid material, comparing with the experimental specimens; and they were used as indenter. Length of the indenters was selected equal to 50.0 mm; while lengths of all the specimens were 40.0 mm. In each test, the specimen was positioned between a rigid platen and a rigid indenter in a DMG machine, model 7166. The indenter was positioned parallel to specimen axis. Three different groups consist of solid cylindrical agglomerated cork specimens, hollow composite tubes, and agglomerated cork-filled composite tubes were prepared and tested according to Figure 1. In each group, there were three similar specimens with the same corresponding characteristics and they were laterally compressed by three different indenters of 10.0, 20.0 and 30.0 mm diameters. All the agglomerated cork specimens and fillers were in solid cylindrical form with 41.6 mm diameter; and they were produced by punching a sheet of agglomerated cork with 10.0 mm thickness and density of 200 kg/m3. Four pieces of the punched cork were affixed by the thin layer of Pattex glue to produce the cork cylinder with 40.0 mm length. The tubes were made of woven Eglass fiber and epoxy resin with the same inner diameter of 41.6 mm and wall thickness of 3.0 mm. The fiber fabric was weaved at a +15/-15 configuration respect to the tube cross-section. Code of each specimen consists of two parts: a number, and one or two letters. The number indicates diameter of the indenter; and the C, T and CT show cork specimen, empty composite tube and agglomerated cork-filled composite tube, respectively (Figure 1).
2
Figure 1. Three different specimens consist of a solid cylindrical agglomerated cork specimen (C), a hollow composite tube (T) and a cork-filled composite tube (CT). 3. Results and discussion Figure 2a and b compares total absorbed energy (TAE) and specific absorbed energy (SAE) by all the specimens during the indentation process, respectively. Figure 2a and b illustrates that when indenter diameter increases, TAE and SAE (total absorbed energy per specimen mass) by the agglomerated cork specimens, empty composite tubes, and cork-filled composite tubes increase, too. The figure shows that by enhancing the indenter diameter from 10.0 mm to 30.0 mm, TAE and SAE by the agglomerated cork specimens increases, intensively. It is due to applying the external load on a limit zone of the cork specimens. On the other hand, during the indentation process on the solid cylindrical cork specimens, due to the almost zero value of the cork Poisson ratio, the external load is applied on the cork particles that are positioned under the indenter along the loading direction. Therefore, in the indentation progress on the cork samples, just some cork particles associate in the deformation and energy absorption process. Thus, by increasing the indenter diameter, volume of the cork that contributes in the deformation progress increases; consequently, TAE and SAE of the cork samples enhances, intensively. The cork specimens were tested up to the fracture. The same trend is not considered in the cork-filled tubes. In other words, although, by enhancing the
3
indenter diameter, TAE and SAE of the cork-filled tubes increases, these increments in the specimen 30-CT is very small, comparing with the specimen 20-CT and it is due to presence of the composite tube around the cork core. On the other hand, when the solid cork cylinder is used as the filler into the composite tubes, the tube transforms the concentrated force into the distributed load on the cork core (Figure 3). During the indentation process on the corkfilled tubes, a solid rod as the indenter applies the concentrated external load on the outer surface of the tube; and due to continuity of the composite tube, inner surface of the tube applies the distributed load on the cork core, consequently, more volume of the cork associates in the deformation and energy absorption process. The same approximated values of TAE of the specimens 20-CT and 30-CT show that when diameter of the indenter is considerable in comparison with the tube diameter, increment of indenter diameter cannot change TAE and SAE of the cork-filled tubes.
Figure 2. Total absorbed energy (a) and specific absorbed energy (b), by all the specimens during the indentation process. Based on the other viewpoint, Figure 2 demonstrates effects of different configurations of the specimens on their TAE and SAE. The figure shows that in most of the cases, TAE and SAE of the empty composite tubes is less than the corresponding cork specimens with the same indenter conditions. Also, in most of the cases, TAE and SAE of the cork samples is less than the corresponding cork-filled tubes. In the recent comparison, there is an exception in the TAE and also, an exception in the SAE. On the other hand, unlike the mentioned trend, TAE of the cork sample 10-C is less than the empty tube 10-T and it may be justified as the following. Experimental observations show that in the indentation process on the empty tubes, three plastic hinge lines are created in the tube wall, independent of indenter diameter. One of them is formed in the contact zone of the tube and the indenter and two other plastic hinges are created at left and right side points of the circular tube cross-section; and changing the indenter diameter
4
does not change these energy absorption mechanisms. Also, the performed experiments on the empty tubes show that there is an unbending and a bending process at a limit zone of the tube wall that is in contact with the indenter and around this zone; and when indenter diameter reduces the mentioned zone of the unbending and bending processes reduces, too; while the other energy absorption mechanisms (three plastic hinge lines) remain constant, without the considerable changes. Therefore, in the indentation process on the empty composite tubes, share of unbending and bending processes into TAE is limited, so, by reducing the indenter diameter, TAE of the empty tubes decreases, gradually. But, in the cork specimens, when indenter diameter reduces, volume of the cork that associates in the deformation process reduces with the same fraction, approximately; and so, TAE of the cork sample decrease, intensively. It justifies the mentioned exception in the TAE. The other exception occurred in the SAE. Figure 2b shows that SAE by the cork specimen 30-C is higher than the cork-filled tube 30-CT and it is unlike the other corresponding sample trend and it may be justified as the following. In a cork-filled tube compared to a cork sample, the tube transforms the concentrated load on the cork core into the distributed load and it increases energy absorption capacity. But, in the filled specimen 30-C, due to the large diameter of the indenter, the lateral load is distributed on the cork cylinder. Also, the distributed load is applied on the cork core of the filled-tube 30CT; but, due to the tube mass, total mass of the sample 30-CT is 3.19 times of the sample 30-C, while both of them deform under the distributed load. Therefore, absorbed energy/mass ratio of the specimen 30-CT is less than the sample 30-C.
Figure 3. The cork-filled specimen 30-CT during the indentation process. Figure 2a indicates that when occupied volume by an energy absorber under the applied lateral load by a solid rod and its TAE are the main parameters of the design, the present article suggests agglomerated cork-filled tubes; and they are preferred to the cork specimens and empty tubes. TAEs by three similar specimens 20-C are 38.65, 39.53, and 40.35 J that shows repeatability of the experiments. Figure 4 illustrates load-displacement curves of the specimens 20-C, 20-T and 20-CT; and the curve 3 shows summation of lateral load of the specimen 20-C and 20-T.
5
The figure shows a sudden downfall at 32.6 mm displacement of the corresponding curve of the cork sample 20-C due to the cork fracture; and consequently, in the summation curve 3. But, the figure shows that in the cork-filled tube 20-CT, this fracture phenomenon is delayed up to 39.3 mm displacement and it is due to transforming the concentrated load into the distributed load. Also, Figure 4 illustrates that the summation curve 3 is always under the corresponding curve of the filled tube 20-CT; and their load differences demonstrate interaction effects between the cork core and the tube wall.
Figure 4. Lateral load-displacement curves of the specimen 20-C, 20-T and 20-CT and summation of lateral load of the samples 20-C and 20-T. Furthermore, Figure 2b indicates that when SAE and mass of an energy absorber under the indentation process are the main parameters of the design, the present research work recommends two options. If diameter of the probable indenter is very smaller than (for example, one-fourth of) the specimen diameter, the cork-filled tubes are preferred to the cork samples and empty tubes; and if diameter of the probable indenter is in the same order of (for example, three-fourth of or equal to) the specimen diameter, the agglomerated cork samples are preferred to both of the other configurations.
6
4. Conclusion This research introduced a novel sandwich tubes with the agglomerated cork core and the composite tube as a new energy absorber during the indentation process. The performed experiments indicate that TAEs by the cork-filled tubes are 2.11-5.65 times of the corresponding cork samples and also, are 5.29-6.06 times of the corresponding empty tubes. Also, the results show that TAEs by the cork-filled tubes are 1.48-2.74 times of summations of TAEs by the corresponding cork samples and the empty tubes. Therefore, the above results suggest solid agglomerated cork cylinders and cork-filled tubes as suitable energy absorber parts against applied loads by external indenters.
Acknowledgements The authors gratefully acknowledge Mr. Sina Rastegarzade for his help with the photography.
References [1] L. Bertolla, I. Dlouhy, A. Philippart, A.R. Boccaccini, Mechanical reinforcement of Bioglasss-based scaffolds by novel polyvinyl-alcohol/microfibrillated cellulose composite coating, Materials Letters 118 (2014) 204–207. [2] Lubomir Orovcik, Martin Nosko, Peter Svec Sr., Stefan Nagy, Miroslav Cavojsky, Frantisek Simancik, Jaroslav Jerz, Effect of the TiH2 pre-treatment on the energy absorption ability of 6061 aluminium alloy foam, Materials Letters 148 (2015) 82–85. [3] S. Sanchez-Saez, E. Barbero, J. Cirne, Experimental study of agglomerated-cork-cored structures subjected to ballistic impacts, Materials Letters 65 (2011) 2152–2154. [4] S. Sanchez-Saez, E. Barbero, S.K. Garcia-Castillo, I. Ivanez, J. Cirne, Experimental response of agglomerated cork under multi-impact loads, Materials Letters 160 (2015) 327–330. [5] C.P. Gameiro, J. Cirne, Dynamic axial crushing of short to long circular aluminium tubes with agglomerate cork filler, International Journal of Mechanical Science 49 (2007) 1029–1037. [6] Abbas Niknejad, Hassan Assaee, Seyed Ali Elahi, Ali Golriz, Flattening process of empty and polyurethane foam-filled E-glass/vinylester composite tubes – An experimental study, Composite Structures 100 (2013) 479–492. [7] B. Rezaei, A. Niknejad, H. Assaee, G.H. Liaghat, Axial splitting of empty and foam-filled circular composite tubes-an experimental study, Archives of Civil and Mechanical Engineering 15 (2015) 650–662.
7
[8] A. Niknejad, M.M. Abedi, G.H. Liaghat, M. Zamani Nejad, Absorbed energy by foam-filled quadrangle tubes during the crushing process by considering the interaction effects, Archives of Civil and Mechanical Engineering 15 (2015) 376–391. [9] Edmund Morris, A.G. Olabi, M.S.J. Hashmi, Analysis of nested tube type energy absorbers with different indenters and exterior constraints Thin-Walled Structures 44 (2006) 872–885. [10] F. Hafeez, F. Almaskari, Experimental investigation of the scaling laws in laterally indented filament wound tubes supported with V shaped cradles, Composite Structures 126 (2015) 265–284.
Highlights This article introduces a novel energy absorber of sandwich tubes. The composite tubes are filled by solid agglomerated cork cylinder. The sandwich tubes are laterally compressed during the indentation process. The corresponding cork specimens and the empty composite tubes are tested, too. Energy absorption behaviors of three types of the specimens are discussed.
8
www.elsevier.com
PII: DOI: Reference:
S0167-577X(16)30782-0 http://dx.doi.org/10.1016/j.matlet.2016.05.041 MLBLUE20852
To appear in: Materials Letters Received date: 29 February 2016 Revised date: 22 April 2016 Accepted date: 7 May 2016 Cite this article as: Abbas Niknejad, Alireza Moradi and Niloofar Beheshti, Indentation experiments on novel sandwich composite tubes, Materials Letters, http://dx.doi.org/10.1016/j.matlet.2016.05.041 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 galley proof before it is published in its final citable 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.
Indentation experiments on novel sandwich composite tubes Abbas Niknejad1,*, Alireza Moradi1, Niloofar Beheshti2 1
Mechanical Engineering Department, Yasouj University, P.O. Box: 75914-353, Yasouj, Iran 2
Civil Engineering Department, Yasouj University, P.O. Box: 75914-353, Yasouj, Iran
Abstract This article introduces a novel energy absorber of sandwich tube with the agglomerated cork core and the composite tube during the indentation process under the applied quasi-static lateral loading by a solid cylindrical rigid indenter. Also, the corresponding cork specimens and the empty composite tubes are tested, too. The solid cylindrical cores made of agglomerated cork are prepared by punching a cork sheet with 200 kg/m3 density and positioned into the composite tubes to manufacture the cork-filled tubes. The results show that the cork-filled composite tubes have an energy absorption capacity up to 5.65 times of the corresponding cork sample and up to 6.06 times of the corresponding empty tube. Also, it is found that total absorbed energy by a cork-filled composite tube is 174 % higher than summation of absorbed energy by the corresponding empty tube and the cork sample. Also, specific absorbed energy by all the specimens is discussed. Keywords: Agglomerated cork; Composite materials; Indentation process; Energy absorption; Sandwich tubes; Porous materials.
1. Introduction Energy absorption is an interesting concern for many researchers and it relates to safety of some engineering structures. Porous materials are one of suitable selections as energy absorber, so, some previous papers investigated mechanical behavior of different porous materials such as scaffolds [1], metal foams [2] and agglomerated cork [3]. Sanchez-Saez et al. [4] studied multi-impact behavior of agglomerated cork, experimentally. Gameiro and Cirne [5] studied dynamic crushing of agglomerated cork-filled tubes. Some articles discussed effects of porous polyurethane foam as the filler into composite [6 and 7] and metal tubes [8]. Also, Morris et al. [9] and Hafeez and Almaskari [10] studied indentation process on circular metal and composite tubes, respectively. This article introduces a novel composite sandwich tube as the new energy absorber during the indention process, using rigid solid cylindrical rods with different diameters. On the other hand, some solid cylinders made of *Corresponding
author at: Mechanical Engineering Department, Yasouj University, P.O. Box: 75914–353, Yasouj, Iran. Tel.: +98 74 33229889; Fax: +98 74 33221711. E–mail address: [email protected] (A. Niknejad).
agglomerated cork are laterally compressed and also, similar cork specimens are positioned into cylindrical composite tubes as the filler and the achieved sandwich tubes are laterally tested and their energy absorption behavior under the applied quasi-static lateral loading is discussed.
2. Experiments This article studied energy absorption by some agglomerated cork specimen, hollow composite tubes, and agglomerated cork-filled composite tubes during the indentation process. For this purpose, three solid cylindrical rods with different diameters of 10.0, 20.0 and 30.0 mm were machined from hardened steel to consider them as rigid material, comparing with the experimental specimens; and they were used as indenter. Length of the indenters was selected equal to 50.0 mm; while lengths of all the specimens were 40.0 mm. In each test, the specimen was positioned between a rigid platen and a rigid indenter in a DMG machine, model 7166. The indenter was positioned parallel to specimen axis. Three different groups consist of solid cylindrical agglomerated cork specimens, hollow composite tubes, and agglomerated cork-filled composite tubes were prepared and tested according to Figure 1. In each group, there were three similar specimens with the same corresponding characteristics and they were laterally compressed by three different indenters of 10.0, 20.0 and 30.0 mm diameters. All the agglomerated cork specimens and fillers were in solid cylindrical form with 41.6 mm diameter; and they were produced by punching a sheet of agglomerated cork with 10.0 mm thickness and density of 200 kg/m3. Four pieces of the punched cork were affixed by the thin layer of Pattex glue to produce the cork cylinder with 40.0 mm length. The tubes were made of woven Eglass fiber and epoxy resin with the same inner diameter of 41.6 mm and wall thickness of 3.0 mm. The fiber fabric was weaved at a +15/-15 configuration respect to the tube cross-section. Code of each specimen consists of two parts: a number, and one or two letters. The number indicates diameter of the indenter; and the C, T and CT show cork specimen, empty composite tube and agglomerated cork-filled composite tube, respectively (Figure 1).
2
Figure 1. Three different specimens consist of a solid cylindrical agglomerated cork specimen (C), a hollow composite tube (T) and a cork-filled composite tube (CT). 3. Results and discussion Figure 2a and b compares total absorbed energy (TAE) and specific absorbed energy (SAE) by all the specimens during the indentation process, respectively. Figure 2a and b illustrates that when indenter diameter increases, TAE and SAE (total absorbed energy per specimen mass) by the agglomerated cork specimens, empty composite tubes, and cork-filled composite tubes increase, too. The figure shows that by enhancing the indenter diameter from 10.0 mm to 30.0 mm, TAE and SAE by the agglomerated cork specimens increases, intensively. It is due to applying the external load on a limit zone of the cork specimens. On the other hand, during the indentation process on the solid cylindrical cork specimens, due to the almost zero value of the cork Poisson ratio, the external load is applied on the cork particles that are positioned under the indenter along the loading direction. Therefore, in the indentation progress on the cork samples, just some cork particles associate in the deformation and energy absorption process. Thus, by increasing the indenter diameter, volume of the cork that contributes in the deformation progress increases; consequently, TAE and SAE of the cork samples enhances, intensively. The cork specimens were tested up to the fracture. The same trend is not considered in the cork-filled tubes. In other words, although, by enhancing the
3
indenter diameter, TAE and SAE of the cork-filled tubes increases, these increments in the specimen 30-CT is very small, comparing with the specimen 20-CT and it is due to presence of the composite tube around the cork core. On the other hand, when the solid cork cylinder is used as the filler into the composite tubes, the tube transforms the concentrated force into the distributed load on the cork core (Figure 3). During the indentation process on the corkfilled tubes, a solid rod as the indenter applies the concentrated external load on the outer surface of the tube; and due to continuity of the composite tube, inner surface of the tube applies the distributed load on the cork core, consequently, more volume of the cork associates in the deformation and energy absorption process. The same approximated values of TAE of the specimens 20-CT and 30-CT show that when diameter of the indenter is considerable in comparison with the tube diameter, increment of indenter diameter cannot change TAE and SAE of the cork-filled tubes.
Figure 2. Total absorbed energy (a) and specific absorbed energy (b), by all the specimens during the indentation process. Based on the other viewpoint, Figure 2 demonstrates effects of different configurations of the specimens on their TAE and SAE. The figure shows that in most of the cases, TAE and SAE of the empty composite tubes is less than the corresponding cork specimens with the same indenter conditions. Also, in most of the cases, TAE and SAE of the cork samples is less than the corresponding cork-filled tubes. In the recent comparison, there is an exception in the TAE and also, an exception in the SAE. On the other hand, unlike the mentioned trend, TAE of the cork sample 10-C is less than the empty tube 10-T and it may be justified as the following. Experimental observations show that in the indentation process on the empty tubes, three plastic hinge lines are created in the tube wall, independent of indenter diameter. One of them is formed in the contact zone of the tube and the indenter and two other plastic hinges are created at left and right side points of the circular tube cross-section; and changing the indenter diameter
4
does not change these energy absorption mechanisms. Also, the performed experiments on the empty tubes show that there is an unbending and a bending process at a limit zone of the tube wall that is in contact with the indenter and around this zone; and when indenter diameter reduces the mentioned zone of the unbending and bending processes reduces, too; while the other energy absorption mechanisms (three plastic hinge lines) remain constant, without the considerable changes. Therefore, in the indentation process on the empty composite tubes, share of unbending and bending processes into TAE is limited, so, by reducing the indenter diameter, TAE of the empty tubes decreases, gradually. But, in the cork specimens, when indenter diameter reduces, volume of the cork that associates in the deformation process reduces with the same fraction, approximately; and so, TAE of the cork sample decrease, intensively. It justifies the mentioned exception in the TAE. The other exception occurred in the SAE. Figure 2b shows that SAE by the cork specimen 30-C is higher than the cork-filled tube 30-CT and it is unlike the other corresponding sample trend and it may be justified as the following. In a cork-filled tube compared to a cork sample, the tube transforms the concentrated load on the cork core into the distributed load and it increases energy absorption capacity. But, in the filled specimen 30-C, due to the large diameter of the indenter, the lateral load is distributed on the cork cylinder. Also, the distributed load is applied on the cork core of the filled-tube 30CT; but, due to the tube mass, total mass of the sample 30-CT is 3.19 times of the sample 30-C, while both of them deform under the distributed load. Therefore, absorbed energy/mass ratio of the specimen 30-CT is less than the sample 30-C.
Figure 3. The cork-filled specimen 30-CT during the indentation process. Figure 2a indicates that when occupied volume by an energy absorber under the applied lateral load by a solid rod and its TAE are the main parameters of the design, the present article suggests agglomerated cork-filled tubes; and they are preferred to the cork specimens and empty tubes. TAEs by three similar specimens 20-C are 38.65, 39.53, and 40.35 J that shows repeatability of the experiments. Figure 4 illustrates load-displacement curves of the specimens 20-C, 20-T and 20-CT; and the curve 3 shows summation of lateral load of the specimen 20-C and 20-T.
5
The figure shows a sudden downfall at 32.6 mm displacement of the corresponding curve of the cork sample 20-C due to the cork fracture; and consequently, in the summation curve 3. But, the figure shows that in the cork-filled tube 20-CT, this fracture phenomenon is delayed up to 39.3 mm displacement and it is due to transforming the concentrated load into the distributed load. Also, Figure 4 illustrates that the summation curve 3 is always under the corresponding curve of the filled tube 20-CT; and their load differences demonstrate interaction effects between the cork core and the tube wall.
Figure 4. Lateral load-displacement curves of the specimen 20-C, 20-T and 20-CT and summation of lateral load of the samples 20-C and 20-T. Furthermore, Figure 2b indicates that when SAE and mass of an energy absorber under the indentation process are the main parameters of the design, the present research work recommends two options. If diameter of the probable indenter is very smaller than (for example, one-fourth of) the specimen diameter, the cork-filled tubes are preferred to the cork samples and empty tubes; and if diameter of the probable indenter is in the same order of (for example, three-fourth of or equal to) the specimen diameter, the agglomerated cork samples are preferred to both of the other configurations.
6
4. Conclusion This research introduced a novel sandwich tubes with the agglomerated cork core and the composite tube as a new energy absorber during the indentation process. The performed experiments indicate that TAEs by the cork-filled tubes are 2.11-5.65 times of the corresponding cork samples and also, are 5.29-6.06 times of the corresponding empty tubes. Also, the results show that TAEs by the cork-filled tubes are 1.48-2.74 times of summations of TAEs by the corresponding cork samples and the empty tubes. Therefore, the above results suggest solid agglomerated cork cylinders and cork-filled tubes as suitable energy absorber parts against applied loads by external indenters.
Acknowledgements The authors gratefully acknowledge Mr. Sina Rastegarzade for his help with the photography.
References [1] L. Bertolla, I. Dlouhy, A. Philippart, A.R. Boccaccini, Mechanical reinforcement of Bioglasss-based scaffolds by novel polyvinyl-alcohol/microfibrillated cellulose composite coating, Materials Letters 118 (2014) 204–207. [2] Lubomir Orovcik, Martin Nosko, Peter Svec Sr., Stefan Nagy, Miroslav Cavojsky, Frantisek Simancik, Jaroslav Jerz, Effect of the TiH2 pre-treatment on the energy absorption ability of 6061 aluminium alloy foam, Materials Letters 148 (2015) 82–85. [3] S. Sanchez-Saez, E. Barbero, J. Cirne, Experimental study of agglomerated-cork-cored structures subjected to ballistic impacts, Materials Letters 65 (2011) 2152–2154. [4] S. Sanchez-Saez, E. Barbero, S.K. Garcia-Castillo, I. Ivanez, J. Cirne, Experimental response of agglomerated cork under multi-impact loads, Materials Letters 160 (2015) 327–330. [5] C.P. Gameiro, J. Cirne, Dynamic axial crushing of short to long circular aluminium tubes with agglomerate cork filler, International Journal of Mechanical Science 49 (2007) 1029–1037. [6] Abbas Niknejad, Hassan Assaee, Seyed Ali Elahi, Ali Golriz, Flattening process of empty and polyurethane foam-filled E-glass/vinylester composite tubes – An experimental study, Composite Structures 100 (2013) 479–492. [7] B. Rezaei, A. Niknejad, H. Assaee, G.H. Liaghat, Axial splitting of empty and foam-filled circular composite tubes-an experimental study, Archives of Civil and Mechanical Engineering 15 (2015) 650–662.
7
[8] A. Niknejad, M.M. Abedi, G.H. Liaghat, M. Zamani Nejad, Absorbed energy by foam-filled quadrangle tubes during the crushing process by considering the interaction effects, Archives of Civil and Mechanical Engineering 15 (2015) 376–391. [9] Edmund Morris, A.G. Olabi, M.S.J. Hashmi, Analysis of nested tube type energy absorbers with different indenters and exterior constraints Thin-Walled Structures 44 (2006) 872–885. [10] F. Hafeez, F. Almaskari, Experimental investigation of the scaling laws in laterally indented filament wound tubes supported with V shaped cradles, Composite Structures 126 (2015) 265–284.
Highlights This article introduces a novel energy absorber of sandwich tubes. The composite tubes are filled by solid agglomerated cork cylinder. The sandwich tubes are laterally compressed during the indentation process. The corresponding cork specimens and the empty composite tubes are tested, too. Energy absorption behaviors of three types of the specimens are discussed.
8