Showing papers by "Jack R. Vinson published in 1998"
20 Apr 1998
TL;DR: In this article, the results of quasi-static and dynamic tests of the composite were compared to those of the material at quasi static tests, showing significant increase in compressive yield strength and decrease in yield strain at high strain rates.
Abstract: Experimental results are presented for the mechanical properties of Kevlar 29 / Polyethylene thermoplastic matrix composite in compression at high strain rates. Results of quasi static tests are also presented. Fiber volume fraction (Vf) in the composite is 85%. The composite is quasi - isotropic. All the tests were conducted at room temperature. High strain rate tests were conducted using a Split Hopkinson Pressure Bar (SHPB) and the quasi static tests were conducted in an Instron machine. The yield stress and yield strain are presented for strain rates varying from 400/s to 1535/s in one of the in-plane (i.e. 1 and 2 directions) directions and from 1010/s to 2165/s in the 3 direction. The data from the 29 dynamic tests and 6 quasi static tests were statistically analyzed and discussed in some detail. The dynamic test results are represented by equations wherever possible and compared to the static test results. Significant increase in compressive yield strength and decrease in yield strain are observed at high strain rates compared to those of the material at quasi static tests.
4 citations
20 Apr 1998
TL;DR: In this paper, the split-Hopkinson bar is used to examine the dynamic properties of unidirectional, cross-ply, and angle-ply laminates of IM7/977-3 graphite/epoxy composites under compressive loading.
Abstract: Excellent mechanical properties such as high-strength , low-weight, fatigue life, and impact resistance, as well as advanced manufacturing methods and tailor ability of the lay-up make polymer matrix composites attractive candidates for use in several performance-oriented structures. However, not much is known of these composites' response to impact loading, which usually occurs at much higher strain rates than the strain rates used to measure the quasi-static mechanical properties of materials. Because mechanical properties vary with strain rates, it is necessary to know the properties of composites at the strain rates necessary for various applications to ensure that designs are optimized for structural integrity and weight efficiency including a dynamic loading of the structure. In this study, the split-Hopkinson bar is used to examine the dynamic properties of unidirectiona l, cross-ply, and angle-ply laminates of IM7/977-3 graphite/epoxy composites under compressive loading. The specimens were approximately 3/8" cubes, and were prepared using a water-cooled diamond grit blade. Dynamic tests were conducted in all the primary directions. Quasi-static tests were also done for comparison purposes. The high strain rate values vary from 200 - 1000 /s. The dynamic data of IM7/977-3 graphite/epoxy composites were obtained from 36 tests for the unidirectional composites and 24 tests for both the cross-ply and angle-ply composites. The data were statistically analyzed and discussed in some detail. There were significant increases in the dynamic ultimate strength values from the quasi-static values for all types of stacking sequences and directions; however, the strength values did not show any significant variation in the high strain rate region. The strain values did not show any trend in these tests.
1 citations
01 Feb 1998
TL;DR: In this paper, a cantilever beam with piezoelectric upper and lower surface strips is chosen as a vehicle for such sensitivity analyses, and it is shown that either stabilizing or destabilizing effects can be achieved depending on the phase relations of the three viscoelastic responses.
Abstract: In a previous paper, the authors formulated and evaluated the general nonlinear 3-D large deformation theory of anisotropic nonhomogeneous piezo-electrothermo-viscoelasticity including thermal expansion, curing and aging effects. For linear materials and small deformations, a piezoelastic/piezo-viscoelastic analogy was established in terms of integral Fourier and Laplace transforms. These developments are used in the present paper to evaluate the dynamic interactions between viscoelastic material damping and piezoelectric effects on voltage generation and structural control. A cantilever beam with piezoelectric upper and lower surface strips is chosen as a vehicle for such sensitivity analyses. The model has three distinct viscoelastic properties, namely the beam itself, the strip rigidity and a viscoelastic-emf constitutive relation. It is shown that either stabilizing or destabilizing effects can be achieved depending on the phase relations of the three viscoelastic responses.