AMR.896.574_2
Content
Advanced Materials Research Vol. 896 (2014) pp 574-577 © (2014) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMR.896.574
Application of Carbon Fiber-Based Composite for Electric Vehicle Miftahul Anwara, Sukmaji Indro Cb, Wijang Wisnu Rc, and Kuncoro Diharjod
Department of Mechanical Engineering, Faculty of Engineering, Sebelas Maret University Jl. Ir. Sutami 36A Surakarta, 57126 Central Java, Indonesia
a
[email protected] (corresponding author), [email protected], [email protected], d [email protected]
Abstract. In the present work, we study how to improve mechanical properties of carbon fiber reinforced plastics (CFRP) in order to increase crashworthiness probability. Experimentally, hybrid carbon /glass fiber composite was made in order to get higher mechanical properties. As a result, with increasing carbon fiber volume fraction (% vol.), tensile strength and flexural strength of the composite are increased. Simulation of impact testing is also performed using data properties taken from the experiment with variation of impact forces on front bumper structure. By varying external load to the bumper, the result shows that higher thickness of hybrid carbon/glass fiber composite has always smaller stress values than thinner one. On the other hand, the displacement of hybrid carbon/glass car bumper increases linearly with increasing external load. Introduction Achieving vehicle safety in crash conditions involves a continuous iterative process that starts with the definition of a structural material and design, and ends when all criteria are satisfied in order to reduce potential injury to occupant which is also called as crashworthiness.[1,2] In automotive industry, primary issues for producing the crashworthy vehicles are light weight but strong material structure, and overall cost production. This issue leads toward nontraditional materials, i.e., composite,[3-5] in which capable of participating in the energy absorption process associated with accident. Recently, fiber reinforced plastics (in particular CFRP) are already an important material in automotive industry due to its lightweight, strong mechanical properties and high energy absorption structure.[6,7] However, massive use of CFRP in entire vehicle structures, e.g., bumper, trunk, hood etc., resulting in high fabrication cost.[8,9] One technique to higher the mechanical properties without exsessive cost increase is to incorporate carbon fiber with other material, known as hybrid composite.[10] Therefore, as a next step, it is essential to construct and manipulate new carbon-based composite material with higher mechanical properties and to analyze crashworthiness probability for the application in the prototype of Indonesia electric vehicle. For that purposes, in this work, we present the experiment on hybrid carbon/glass fiber composite as well as the simulation of impact testing on car front bumper, as the first step, toward future crashworthy vehicles. Experiment on Hybrid Carbon/Glass Fiber Composite Experiment on tensile strength and flexural strength of hybrid carbon/glass fiber composite was performed in order to provide higher the mechanical properties and to lower the fabrication cost. To make specimens (Fig. 1 (a)) of hybrid carbon-glass fiber/polyester composite (with 60/40 % vol. ratio), carbon fiber and glass fiber are used as reinforcement of composite, while polyester is used as matrix and methyl ethyl ketone peroxide (MEKPO) as a catalyst. Woven roving sheets of carbon fiber (200 gr/m2) and glass fiber (300 gr/m2) was arranged in order as shown in Fig. 1(b). Woven carbon fiber sheets placed always at the top and bottom site. The middle site is varied according to the expected volume fraction ratio of carbon/glass fiber. These materials then are mixed by hand lay-up technique. Next, the composite was pressed using vacuum bagging technique with pressure 〜5 Psi to remove the air void inside the composite, as the porous can be formed by the trapped of many air void. To obtain optimum result, we varied carbon/glass fiber volume fraction (20/80, 30/70 and 50/50 % vol.), while the matrix is kept constant.
All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 114.79.29.114-09/02/14,07:38:25)
Advanced Materials Research Vol. 896
575
Tensile and flexural strength measurement (according to ASTM D638 [11] and ASTM D790 [12]) was performed using tensile and flexural strength test machine provided in Material Laboratory, Sebelas Maret University.
Figure 1. (a) Specimen sample for tensile measurement with variation of carbon/glass fiber volume fraction [(1) 20/80, (2) 30/70 and (3) 50/50 % vol.]. (b) Optical microscope image showing cross-sectional view of arrangement of carbon and glass fiber of hybrid composite. (c) and (d) are tensile strength and flexural strength vs carbon fiber fraction of hybrid carbon/glass fiber reinforced composite. The matrix (polyester) is kept constant at 60 % vol. Dashed line is the eye guide for increasing trend of the hybrid composite. Figures 1.(c) and 1.(d) show tensile strength and flexural strength of hybrid carbon/glass composite with variation of carbon fiber weight fraction i.e., 20, 30 and 50 % vol. For hybrid carbon/glass composite, the increase of fiber fraction results in the increase of tensile strength of the composite from 246 to 307 MPa, respectively. On the other hand, flexural strength of hybrid carbon/glass composite is also increased linearly from 100 MPa to 190 MPa at fiber volume fraction of 20 and 50 % vol., respectively. The increasing trends of tensile and flexural strength are most probably due to the increasing of fiber-fiber interaction and fiber-matrix interaction [13] between carbon fiber, glass fiber and polyester matrix. Moreover, more uniform layers arrangement of carbon fiber as shown in Fig. 1.(b) results in the strength in the tensile and flexural properties of hybrid composite. Woven shape of carbon and glass fiber could also absorb external stress in x-y direction, while arranged sheet of fibers strengthen the composite in z direction. Simulation of impact testing Simulation of impact testing with finite element method (FEM) was used to simulate the real condition of car accident on the front bumper since the highest crash probability usually occurs at the front of the car. The simple scenario of collision between two cars was simulated using Solidwork simulator. One car moves and hit the second fixed car with variation of load i.e., 1, 3, 5, 8 and 10 kN, which is associated to different mass and velocity of the first car. We measured stress distribution and displacement of car front bumper after collision. For stress distribution and displacement measurement, hybrid carbon/glass fiber composite was used and carbon fiber/epoxy as a comparison. Highest tensile strength value (307 MPa) from the experiment was used in the material properties input in the simulation. In order to find the optimum stress and displacement value of front bumper, we varied the thickness of the composite i.e., 3 mm, 4 mm and 5 mm. During collision, crush load is uniformly distributed to entire car front bumper. Figure 2 shows stress distribution images of car front bumper for hybrid carbon/glass fiber composite [Fig. 2 (a) – (c)] and CFRP (Fig. 2.(d)) composite for comparison with thickness variation. Even though the crush load is uniformly distributed, Fig. 2 suggests that maximum stress on the
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Advanced Materials Science and Technology
bumper is observed at the center of lower band of the bumper. Lower band of bumper is not backed up with crushing element compared with higher band of bumper, thus it is much weaker than other part of the bumper. Figure 2. Simulation of stress distribution of front bumper for carbon fiber [(a) – (c)] and glass fiber (d) as a comparison measured with commercial Solidwork simulator. Thickness of the composites is used as a parameter, from 3 mm to 5 mm. Stress distribution value is described in color variation from blue (minimum value) to red (maximum value) in unit of MPa. The displacement value is taken using dashed line as an initial condition of the front bumper before and after collision.
The displacement is also observed in the car bumper as shown in Fig. 2. Displacement values are calculated by subtracting crushed portion after and before (initial condition marked by dashed line in Fig. 2) collision. Despite the accurate values of displacement are shown in transitional displacement figure of car bumper (not shown), in Fig. 2 the displacements regions are observable at the place where the maximum stress occur. In general, the displacement of car bumper decreases with increasing composite thickness as shown Fig. 2(a) to (c). In order to extract general information, the results of maximum stress and displacement have been quantitatively plotted in the graph shown in Fig. 3 obtained for varied composite thickness 3, 4, and 5 mm respectively. The results are also obtained for different composite, i.e., CFRP (black lines) composite with tensile strength 600 MPa for comparison. For both result values (maximum stress and displacement), the increase in composite thickness results in the decrease in values of maximum stress and displacement. On the other hand, increasing external load increases maximum stress linearly for 4 and 5 mm thickness. However, for 3 mm thickness maximum stress (up to 700 MPa) and displacement (up to 120 mm)are also increased at almost exponentially, which can be most likely due to less carbon fiber content in the composite leads to the decrease of material strength.
Figure 3. Maximum stress (a) and displacement (b) vs external load of front bumper for hybrid carbon-glass composite with thickness variation simulated with commercial Solidwork simulator. The inset of (a) and (b) show more detail differences for high external load of each thickness. Moreover, comparing with CFRP (black), maximum stress and displacement values of hybrid composite for 4 (blue) and 5 mm (green) thickness are significantly comparable as shown in Fig. 3 and Figs. 2 (b–d). At higher external load (8 kN and 10 kN), however, maximum stress and displacement value of CFRP increase higher than that of hybrid composite by 20 MPa and 5 mm different, respectively as shown in the inset of Fig. 3. It is reasonable to assume that for hybrid composite, even though tensile strength value is smaller than that of CFRP, combination between properties of carbon fiber and glass fiber will increase internal properties of hybrid composite.
Advanced Materials Research Vol. 896
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Therefore, hybrid composite absorbs more kinetic energy than CFRP which is very important for future crashworthy vehicles. Additionally, factor of safety of bumper structure for hybrid composite was also analyzed during simulation. Factor of safety of car bumper is 2.24 at 8 kN external load which is still acceptable and safe for the occupant.[14] Conclusions The results shown in this paper indicate that hybrid carbon/glass fiber composite has higher mechanical properties even compared with other materials i.e., CFRP. On the other hand, hybrid carbon/glass fiber composite, with an appropriate mixed fiber/matrix fraction, can be one possible choice to provide higher mechanical properties. Using the simulation of impact testing of font car bumper, we also showed that crashworthiness probability can be increased by increasing thickness of the bumper. Using hybrid carbon/glass composite for front bumper in the simulation of impact testing provided smaller stress and displacement in car structure than that of CFRP at high external load. These findings can be useful for the design of future vehicle structures in order to provide light, strong and low cost Indonesia electric vehicles. Acknowledgement We thank Cornellius H. R., Heri S. and Yunanto A. P. for their contributions during simulation and experiments. This work was partially supported by Grants-in-Aid for National Electric Car (023.04.2.1.189882/2013) from the Ministry of Education and Culture of Republic Indonesia. References
[1] G. Steieglitz, Parallels between aviation and automotive safety research, in: Passenger car design and highway safety, Association for the Aid of Crippled Children and Consumer Union of U.S. Inc, New York, 1962, p. 194. S. Newstead, L. Watson, M. Cameron, Vehicle safety ratings estimated from police reported crash data: 2008 update. Australian and New Zealand crashes during 1987-2006, Monash University Accident Research Center Report, Report No. 280, 2008. V. P. McConnell, Automotive composite: A design and manufacturing guide, Ray Publishing, Wheat Ridge, 1997, pp. 6-7. R. Piellisch, Beyond gasoline: Autos remains elusive for carbon composite structures, but alternative cars still hold a great market potential, Soc. for the Advancement of Material and Process Engineering. Journal 32 (1997) 1165-1186. G. Belingardi, M. P. Cavatora, D. S. Paolino, Repeated impact response of hand lay-up and vacuum infusion thick glass reinforced laminates, Int. J. Impact Eng. 35 (2008) 609-619. H. Wallentowitz, I. Leyer, and T. Pharr, Material for future automotive body structure, Business Briefing: Global Automotive & Manufacturing, Reference Section, 2003, pp. 1-4. G. Lu, T. X. Yu, Energy Absorption of structure and material, Woodhead Publishing, Cambridge, 2003, p. 317. J. L. James, Carbon Fibers, in: Chemical Insight & Forecasting: IHS Chemical, Process Economics Program Report, Report No. 165, 1983. J. L. James, Carbon Fibers, in: Process Economics Program Report, Chemical Insight & Forecasting: IHS Chemical, Report No. 165A, 1992. A. K. Kaw, Mechanics of Composite Materials, second ed., CRC Press, Taylor & Francis Group, Tampa, 2005. ASTM Standard D638-02, Standard Test Method for Tensile Properties of Plastics, Annual Book of Standards, ASTM International, West Conshohocken, PA, 2003, pp.46-58. ASTM Standard D 790-02, Standard Test Method for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical insulating materials, Annual Book of Standards, ASTM International, West Conshohocken, PA, 2002, pp.146-154. S. Y. Fa, X. Hu, C. Y. Yue, Effect of fiber length and orientation distributions on the mechanical properties of short-fiber-reinforced-polymers: A Review, Mater. Sci. Res. Int. 5 (1999) 74-83. K. S. Bernstein, R. Kujala, V. Fogt, P. Romine, Structural design requirements and factors of safety for spaceflight hardware: For human spaceflight, JSC 65828 Rev. A, NASA JSC, Houston, TX, 2011.
[2]
[3] [4]
[5] [6] [7] [8] [9] [10] [11] [12]
[13] [14]
Application of Carbon Fiber-Based Composite for Electric Vehicle Miftahul Anwara, Sukmaji Indro Cb, Wijang Wisnu Rc, and Kuncoro Diharjod
Department of Mechanical Engineering, Faculty of Engineering, Sebelas Maret University Jl. Ir. Sutami 36A Surakarta, 57126 Central Java, Indonesia
a
[email protected] (corresponding author), [email protected], [email protected], d [email protected]
Abstract. In the present work, we study how to improve mechanical properties of carbon fiber reinforced plastics (CFRP) in order to increase crashworthiness probability. Experimentally, hybrid carbon /glass fiber composite was made in order to get higher mechanical properties. As a result, with increasing carbon fiber volume fraction (% vol.), tensile strength and flexural strength of the composite are increased. Simulation of impact testing is also performed using data properties taken from the experiment with variation of impact forces on front bumper structure. By varying external load to the bumper, the result shows that higher thickness of hybrid carbon/glass fiber composite has always smaller stress values than thinner one. On the other hand, the displacement of hybrid carbon/glass car bumper increases linearly with increasing external load. Introduction Achieving vehicle safety in crash conditions involves a continuous iterative process that starts with the definition of a structural material and design, and ends when all criteria are satisfied in order to reduce potential injury to occupant which is also called as crashworthiness.[1,2] In automotive industry, primary issues for producing the crashworthy vehicles are light weight but strong material structure, and overall cost production. This issue leads toward nontraditional materials, i.e., composite,[3-5] in which capable of participating in the energy absorption process associated with accident. Recently, fiber reinforced plastics (in particular CFRP) are already an important material in automotive industry due to its lightweight, strong mechanical properties and high energy absorption structure.[6,7] However, massive use of CFRP in entire vehicle structures, e.g., bumper, trunk, hood etc., resulting in high fabrication cost.[8,9] One technique to higher the mechanical properties without exsessive cost increase is to incorporate carbon fiber with other material, known as hybrid composite.[10] Therefore, as a next step, it is essential to construct and manipulate new carbon-based composite material with higher mechanical properties and to analyze crashworthiness probability for the application in the prototype of Indonesia electric vehicle. For that purposes, in this work, we present the experiment on hybrid carbon/glass fiber composite as well as the simulation of impact testing on car front bumper, as the first step, toward future crashworthy vehicles. Experiment on Hybrid Carbon/Glass Fiber Composite Experiment on tensile strength and flexural strength of hybrid carbon/glass fiber composite was performed in order to provide higher the mechanical properties and to lower the fabrication cost. To make specimens (Fig. 1 (a)) of hybrid carbon-glass fiber/polyester composite (with 60/40 % vol. ratio), carbon fiber and glass fiber are used as reinforcement of composite, while polyester is used as matrix and methyl ethyl ketone peroxide (MEKPO) as a catalyst. Woven roving sheets of carbon fiber (200 gr/m2) and glass fiber (300 gr/m2) was arranged in order as shown in Fig. 1(b). Woven carbon fiber sheets placed always at the top and bottom site. The middle site is varied according to the expected volume fraction ratio of carbon/glass fiber. These materials then are mixed by hand lay-up technique. Next, the composite was pressed using vacuum bagging technique with pressure 〜5 Psi to remove the air void inside the composite, as the porous can be formed by the trapped of many air void. To obtain optimum result, we varied carbon/glass fiber volume fraction (20/80, 30/70 and 50/50 % vol.), while the matrix is kept constant.
All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 114.79.29.114-09/02/14,07:38:25)
Advanced Materials Research Vol. 896
575
Tensile and flexural strength measurement (according to ASTM D638 [11] and ASTM D790 [12]) was performed using tensile and flexural strength test machine provided in Material Laboratory, Sebelas Maret University.
Figure 1. (a) Specimen sample for tensile measurement with variation of carbon/glass fiber volume fraction [(1) 20/80, (2) 30/70 and (3) 50/50 % vol.]. (b) Optical microscope image showing cross-sectional view of arrangement of carbon and glass fiber of hybrid composite. (c) and (d) are tensile strength and flexural strength vs carbon fiber fraction of hybrid carbon/glass fiber reinforced composite. The matrix (polyester) is kept constant at 60 % vol. Dashed line is the eye guide for increasing trend of the hybrid composite. Figures 1.(c) and 1.(d) show tensile strength and flexural strength of hybrid carbon/glass composite with variation of carbon fiber weight fraction i.e., 20, 30 and 50 % vol. For hybrid carbon/glass composite, the increase of fiber fraction results in the increase of tensile strength of the composite from 246 to 307 MPa, respectively. On the other hand, flexural strength of hybrid carbon/glass composite is also increased linearly from 100 MPa to 190 MPa at fiber volume fraction of 20 and 50 % vol., respectively. The increasing trends of tensile and flexural strength are most probably due to the increasing of fiber-fiber interaction and fiber-matrix interaction [13] between carbon fiber, glass fiber and polyester matrix. Moreover, more uniform layers arrangement of carbon fiber as shown in Fig. 1.(b) results in the strength in the tensile and flexural properties of hybrid composite. Woven shape of carbon and glass fiber could also absorb external stress in x-y direction, while arranged sheet of fibers strengthen the composite in z direction. Simulation of impact testing Simulation of impact testing with finite element method (FEM) was used to simulate the real condition of car accident on the front bumper since the highest crash probability usually occurs at the front of the car. The simple scenario of collision between two cars was simulated using Solidwork simulator. One car moves and hit the second fixed car with variation of load i.e., 1, 3, 5, 8 and 10 kN, which is associated to different mass and velocity of the first car. We measured stress distribution and displacement of car front bumper after collision. For stress distribution and displacement measurement, hybrid carbon/glass fiber composite was used and carbon fiber/epoxy as a comparison. Highest tensile strength value (307 MPa) from the experiment was used in the material properties input in the simulation. In order to find the optimum stress and displacement value of front bumper, we varied the thickness of the composite i.e., 3 mm, 4 mm and 5 mm. During collision, crush load is uniformly distributed to entire car front bumper. Figure 2 shows stress distribution images of car front bumper for hybrid carbon/glass fiber composite [Fig. 2 (a) – (c)] and CFRP (Fig. 2.(d)) composite for comparison with thickness variation. Even though the crush load is uniformly distributed, Fig. 2 suggests that maximum stress on the
576
Advanced Materials Science and Technology
bumper is observed at the center of lower band of the bumper. Lower band of bumper is not backed up with crushing element compared with higher band of bumper, thus it is much weaker than other part of the bumper. Figure 2. Simulation of stress distribution of front bumper for carbon fiber [(a) – (c)] and glass fiber (d) as a comparison measured with commercial Solidwork simulator. Thickness of the composites is used as a parameter, from 3 mm to 5 mm. Stress distribution value is described in color variation from blue (minimum value) to red (maximum value) in unit of MPa. The displacement value is taken using dashed line as an initial condition of the front bumper before and after collision.
The displacement is also observed in the car bumper as shown in Fig. 2. Displacement values are calculated by subtracting crushed portion after and before (initial condition marked by dashed line in Fig. 2) collision. Despite the accurate values of displacement are shown in transitional displacement figure of car bumper (not shown), in Fig. 2 the displacements regions are observable at the place where the maximum stress occur. In general, the displacement of car bumper decreases with increasing composite thickness as shown Fig. 2(a) to (c). In order to extract general information, the results of maximum stress and displacement have been quantitatively plotted in the graph shown in Fig. 3 obtained for varied composite thickness 3, 4, and 5 mm respectively. The results are also obtained for different composite, i.e., CFRP (black lines) composite with tensile strength 600 MPa for comparison. For both result values (maximum stress and displacement), the increase in composite thickness results in the decrease in values of maximum stress and displacement. On the other hand, increasing external load increases maximum stress linearly for 4 and 5 mm thickness. However, for 3 mm thickness maximum stress (up to 700 MPa) and displacement (up to 120 mm)are also increased at almost exponentially, which can be most likely due to less carbon fiber content in the composite leads to the decrease of material strength.
Figure 3. Maximum stress (a) and displacement (b) vs external load of front bumper for hybrid carbon-glass composite with thickness variation simulated with commercial Solidwork simulator. The inset of (a) and (b) show more detail differences for high external load of each thickness. Moreover, comparing with CFRP (black), maximum stress and displacement values of hybrid composite for 4 (blue) and 5 mm (green) thickness are significantly comparable as shown in Fig. 3 and Figs. 2 (b–d). At higher external load (8 kN and 10 kN), however, maximum stress and displacement value of CFRP increase higher than that of hybrid composite by 20 MPa and 5 mm different, respectively as shown in the inset of Fig. 3. It is reasonable to assume that for hybrid composite, even though tensile strength value is smaller than that of CFRP, combination between properties of carbon fiber and glass fiber will increase internal properties of hybrid composite.
Advanced Materials Research Vol. 896
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Therefore, hybrid composite absorbs more kinetic energy than CFRP which is very important for future crashworthy vehicles. Additionally, factor of safety of bumper structure for hybrid composite was also analyzed during simulation. Factor of safety of car bumper is 2.24 at 8 kN external load which is still acceptable and safe for the occupant.[14] Conclusions The results shown in this paper indicate that hybrid carbon/glass fiber composite has higher mechanical properties even compared with other materials i.e., CFRP. On the other hand, hybrid carbon/glass fiber composite, with an appropriate mixed fiber/matrix fraction, can be one possible choice to provide higher mechanical properties. Using the simulation of impact testing of font car bumper, we also showed that crashworthiness probability can be increased by increasing thickness of the bumper. Using hybrid carbon/glass composite for front bumper in the simulation of impact testing provided smaller stress and displacement in car structure than that of CFRP at high external load. These findings can be useful for the design of future vehicle structures in order to provide light, strong and low cost Indonesia electric vehicles. Acknowledgement We thank Cornellius H. R., Heri S. and Yunanto A. P. for their contributions during simulation and experiments. This work was partially supported by Grants-in-Aid for National Electric Car (023.04.2.1.189882/2013) from the Ministry of Education and Culture of Republic Indonesia. References
[1] G. Steieglitz, Parallels between aviation and automotive safety research, in: Passenger car design and highway safety, Association for the Aid of Crippled Children and Consumer Union of U.S. Inc, New York, 1962, p. 194. S. Newstead, L. Watson, M. Cameron, Vehicle safety ratings estimated from police reported crash data: 2008 update. Australian and New Zealand crashes during 1987-2006, Monash University Accident Research Center Report, Report No. 280, 2008. V. P. McConnell, Automotive composite: A design and manufacturing guide, Ray Publishing, Wheat Ridge, 1997, pp. 6-7. R. Piellisch, Beyond gasoline: Autos remains elusive for carbon composite structures, but alternative cars still hold a great market potential, Soc. for the Advancement of Material and Process Engineering. Journal 32 (1997) 1165-1186. G. Belingardi, M. P. Cavatora, D. S. Paolino, Repeated impact response of hand lay-up and vacuum infusion thick glass reinforced laminates, Int. J. Impact Eng. 35 (2008) 609-619. H. Wallentowitz, I. Leyer, and T. Pharr, Material for future automotive body structure, Business Briefing: Global Automotive & Manufacturing, Reference Section, 2003, pp. 1-4. G. Lu, T. X. Yu, Energy Absorption of structure and material, Woodhead Publishing, Cambridge, 2003, p. 317. J. L. James, Carbon Fibers, in: Chemical Insight & Forecasting: IHS Chemical, Process Economics Program Report, Report No. 165, 1983. J. L. James, Carbon Fibers, in: Process Economics Program Report, Chemical Insight & Forecasting: IHS Chemical, Report No. 165A, 1992. A. K. Kaw, Mechanics of Composite Materials, second ed., CRC Press, Taylor & Francis Group, Tampa, 2005. ASTM Standard D638-02, Standard Test Method for Tensile Properties of Plastics, Annual Book of Standards, ASTM International, West Conshohocken, PA, 2003, pp.46-58. ASTM Standard D 790-02, Standard Test Method for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical insulating materials, Annual Book of Standards, ASTM International, West Conshohocken, PA, 2002, pp.146-154. S. Y. Fa, X. Hu, C. Y. Yue, Effect of fiber length and orientation distributions on the mechanical properties of short-fiber-reinforced-polymers: A Review, Mater. Sci. Res. Int. 5 (1999) 74-83. K. S. Bernstein, R. Kujala, V. Fogt, P. Romine, Structural design requirements and factors of safety for spaceflight hardware: For human spaceflight, JSC 65828 Rev. A, NASA JSC, Houston, TX, 2011.
[2]
[3] [4]
[5] [6] [7] [8] [9] [10] [11] [12]
[13] [14]
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