Showing papers by "Jack R. Vinson published in 1997"

Ballistic Impact of Thin-Walled Composite Structures

Abstract: Methods of analysis have been developed that provide the means to determine whether a ballistic impactor of known shape, mass, and striking velocity will penetrate a given thin-walled composite material structure and if it does, what the residual velocity of the impactor will be. The methods developed require performing penetration experiments at two striking velocities (with suitable replicates for statistical purposes) for any given composite structural target. From this minimum number of tests, one can predict the penetration, nonpenetration, and residual velocity of an impact at other striking velocities. This provides a dramatic reduction in the amount of expensive testing required to study penetration due to ballistic impact. It also provides a less expensive and less time-consuming means to select the best material system and structural configuration to resist ballistic impact. Finally, it shows that the physics of ballistic impact and the penetration phenomena is modeled satisfactorily. These methods also accurately predict the ballistic limit.

Effects of high strain rate compression on the mechanical properties of a uniweave as4/3501-6 composite laminate with through-thickness stitching

Abstract: Polymer matrix composites offer excellent mechanical properties such as high specific strength and stiffness, making them attractive for applications in several naval, aerospace, automotive, and recreational-sports structural components. Although many composite materials are selected for applications where high strain rate loading is probable, little is known of their response to shock loading. Material properties can vary significantly with strain rate. Therefore, the use of static properties in the analysis and design of structures which undergo dynamic loading may unfortunately lead to very conservative, overweight designs or lead to designs which fail prematurely and unexpectedly. The use of dynamic material properties ensures that designs are optimized for structural integrity and weight efficiency when subjected to dynamic loading. In this study, a Split Hopkinson Pressure Bar is used to obtain high-strain-rate, compressive mechanical properties of a uniweave AS4/3501-6 composite laminate with and without reinforcement stitching in the through-thickness. Due to geometry restrictions on the test specimens, stitched specimens contain only a single, through-thickness stitch. Therefore, while this study may not give insight to the macroscopic benefits of reinforcement stitching, it does give insight to stitching effects local to the stitched area. For both in-plane and out-of-plane directions, the compressive mechanical properties of yield stress, yield strain, ultimate strength, ultimate strain, and modulus of elasticity are determined for strain rates varying from 234 sec"1 to 1216 sec"1.

High Strain Rate Properties of Cycom 5920/1583

Abstract: Polymer matrix composites offer excellent properties such as high speci® c strength and stiffness, which make them attractive for many naval, aerospace, and automotive applications. Although they are candidate materials for many applicationswhere high strain rate loading is probable, little is known of the material responses to shock loading for most composite materials. Because mechanical properties vary signi® cantly with strain rate, the use of static properties in the analysis and design of structures that undergo dynamic loadings can, on one hand, lead to a very conservative overweight design or, on the other hand, can lead to designs that fail prematurely and unexpectedly. The use of dynamic material properties will ensure the design of composite structures, which are weight ef® cient and structurally sound when they are subjected to dynamic loads. A split Hopkinson pressure bar is used to obtain compressive mechanical properties of Cycom 5920/1583, an uniaxial cloth, E-glass/rubber toughened epoxy composite being used presently by the Electric Boat Division of General Dynamics for undersea structures. Yield stress, yield strain, ultimate stress, ultimate strain, andmodulus of elasticity values are presented and analyzed wherein the strain rates vary from 60 to 1150 s i 1 .

High Strain Rate Properties of Cycom 5920/1583 Cloth Glass/Epoxy Composites

Abstract: Polymer matrix composites offer excellent properties such as high speci® c strength and stiffness, which make them attractive for many naval, aerospace, and automotive applications. Although they are candidate materials for many applications where high strain rate loading is probable, little is known of the material responses to shock loading for most composite materials. Because mechanical properties vary signi® cantly with strain rate, the use of static properties in the analysis and design of structures that undergo dynamic loadings can, on one hand, lead to a very conservative overweight design or, on the other hand, can lead to designs that fail prematurely and unexpectedly. The use of dynamic material properties will ensure the design of composite structures, which are weight ef® cient and structurally sound when they are subjected to dynamic loads. A split Hopkinson pressure bar is used to obtain compressive mechanical properties of Cycom 5920/1583, an uniaxial cloth, E-glass/rubber toughened epoxy composite being used presently by the Electric Boat Division of General Dynamics for undersea structures. Yield stress, yield strain, ultimate stress, ultimate strain, and modulus of elasticity values are presented and analyzed wherein the strain rates vary from 60 to 1150 s i 1 .

High strain rate tensile properties of a woven glass fabric composite

Abstract: A high rate Instron machine was used to study the dynamic tensile properties of a DOW DERAKANE 510A vinyl ester resin reinforced with 24 oz. woven roving glass fabric (510A/WR) composite. The composite was fabricated using two different methods: i) contact molding; and ii) the Seemann Composites Resin Infusion Molding Process (SCRIMP). The composites were tested in both the fill and warp directions at strain rates varying from 0.3 5/s. Overall, 36 tests were performed, generating ultimate stress, ultimate strain, and tensile modulus data. The results indicate that there is no significant difference in mechanical properties of either material over the 0.3 5/s interval, suggesting that the materials are strain rate insensitive. However, it is observed that at all three strain rates tested, the average ultimate stress and strain exceeded the static material properties for each material in both the fill and warp directions. For both materials, an increase in average ultimate stress with, increasing strain rate trend is identified. The tensile modulus remained unchanged with increasing strain rate 1 Graduate Research Assistant, Department of Mechanical Engineering, University of Delaware. 2 H. Fletcher Brown Professor of Mechanical & Aerospace Engineering, University of Delaware; Fellow, AIAA; Fellow, ASME; Author to whom correspondence should be addressed. Copyright © 1997 by the American Institute of Aeronautics and Astonautics, Inc. All rights reserved. for both materials in each direction. In terms of strength and stiffness, the SCRIMP material outperformed the contact molded material in both directions at all three strain rates tested. INTRODUCTION Woven fabric composites offer more balanced properties in the fabric plane than unidirectional laminae due to their bi-directional reinforcementfl]. This type of reinforcement aids in enhancing impact resistance. That, coupled with low fabrication costs and ease of handling, have made fabrics attractive for many structural applications. Although they are candidate materials for many applications where high strain rate loading is probable, little is known of their response to shock loading. Because mechanical properties vary significantly with strain rate, the use of static properties in the analysis and design of structures which undergo dynamic loadings can lead to a very conservative overweight design, or on the other hand can lead to designs which fail prematurely and unexpectedly. The use of dynamic material properties will ensure the design of composite structures which are weight efficient and structurally sound when they are subjected to dynamic loads. At present, a program is underway at the University of Delaware under the sponsorship of the Office of Naval Research (Dr. Y.D.S Rajapaske) that involves three tasks, namely: i) high strain rate testing in compression and tension, using the Split Hopkinson Pressure Bar (SHPB) facility, and the high rate Instron testing machine, and correlation and analysis of the dynamic material properties obtained; ii) examination of specimens tested using optical and electron microscopy to characterize the deformation and fracture processes; and iii) evaluation of the suitability of current models to describe the deformation and failure of these materials at high strain rates and their modifications or, whenever necessary, the development of new models. The present study, concentrates on task 1. Specifically, the high rate Instron testing machine is used to obtain tensile data. The high rate Instron machine is capable of achieving strain rates on the interval of 0.1 to 5/s. This intermediate range will fill the gap that has existed between typical static tests (0.001/s) and the work being performed on the SHPB, which yields accurate results in the strain rate 1362 American Institute of Aeronautics and Astronautics Copyright© 1998, American Institute of Aeronautics and Astronautics, Inc.