Effect of temperature on the damage of hybrid thick composites subject to drop-weight and ballistic impacts
Item
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Title
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Effect of temperature on the damage of hybrid thick composites subject to drop-weight and ballistic impacts
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Identifier
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d_2009_2013:9d15164266b5:10785
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identifier
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10965
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Creator
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Budhoo, Yougashwar,
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Contributor
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Feridun Delale | Benjamin Liaw
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Date
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2011
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Language
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English
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Publisher
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City University of New York.
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Subject
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Mechanical engineering
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Abstract
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The aim of this study is to investigate the low velocity and ballistic impact responses of thick-section hybrid fiber composites at various temperatures. Plain-woven S2-Glass and IM7 Graphite fabrics are chosen as fiber materials reinforcing the SC-79 epoxy. Four different types of composites consisting of alternating layers of glass and graphite woven fabric sheets are considered. The tensile tests were conducted following ASTM Standards D3039 (Standard Test Method for Tensile Properties of Polymer Matrix Composite Materials) and D3518 (Standard Test Method for In-Plane Shear Response of Polymer Matrix Composite Materials by Tensile Test of a +/-45° Laminate) on hybrid and non-hybrid plain weave composite materials. Strips (6.35mmx25mmx250mm) of non-hybrid IM-7 Graphite/SC-79 epoxy denoted as GR for brevity, non-hybrid S-2 Glass/SC-79 epoxy called GL for short, hybrid GR/GL/GR and hybrid GL/GR/GL specimens were tensile tested. The tests were conducted at -60°C, -20°C, room temperature, 75°C and 125°C. Then the rule of mixtures was used to predict the Young's moduli of GL/GR/GL and GR/GL/GR using the experimental values obtained from the stress-strain curves of the GL and GR specimens. The predicted Young's moduli of GL/GR/GL and GR/GL/GR were then compared to those obtained experimentally. It was found that the calculated Young's and shear moduli match closely (within 6%) to those obtained experimentally. The Poisson's ratio was measured using strain gages. Classical lamination theory was used to calculate the thermal stresses developed in the hybrid woven composite, which were then compared to the maximum stress values obtained experimentally from the unidirectional tensile tests, to determine whether they were significant. It was determined that the calculated thermal stresses are negligible (in the order of 2.5%) compared to the failure stress of the composite, and thus will be neglected in impact modeling and computations.;Next, low-velocity impact tests were conducted using an Instron-Dynatup 8250 impact test machine equipped with an environmental chamber operable from -52 °C to 316 °C. Test temperatures were achieved in the same manner as in tensile testing. The impact tests were performed at an energy level of 30 Joules. Both destructive cross-sectional micrographs and nondestructive ultrasonic techniques used to evaluate the damage created by impact. Ultrasound C-scans were performed using a Physical Acoustics Corporation UltraPAC immersion ultrasonic imaging system.;The Finite Element code LS-DYNA was chosen to perform numerical simulations of low velocity and later ballistic impact on thick-section hybrid composites. The experimentally obtained force-time histories, strain-time histories and damage patterns of impacted composites are compared with Finite element results. Good agreement between experimental and FE results has been achieved when comparing dynamic force, contact stiffness, deflection, energy, strain histories and damage patterns from experimental measurements and FE simulations. It was shown that the variation of results obtained from our low velocity impact experiments for the hybrid composite was very small (in the order of 8%) when compared to those of the non- hybrid composite material. Also, when looking at the hybrid or non-hybrid composites, the effect of temperature at -60°C, -20°C was not significant, whereas at 75°C and 125°C was very significant.;The final portion of this research deals with ballistic impact experiments on the above mentioned composites and numerical modeling. Ballistic impact tests were performed using helium pressured high-speed gas-gun. In this case also, high and low temperatures were achieved in the same manner as those in the tensile testing. From experiments, it is concluded that GL has a better ballistic impact resistance compared to the other three composites layups. The ballistic limit of GL increases with an increase in test temperature, while GR is decreased. The ballistics limits for the hybrids were in between of those for GL and GR.
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Type
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dissertation
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Source
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2009_2013.csv
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degree
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Ph.D.
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Program
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Engineering
