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Dynamic Testing and Properties of Rubber O-rings and Their Application in Soft Drop Weight Tests of Low Strength Materials /


Mechanical behavior of low strength materials and elements at high strain rates was studied using a drop tower at UCSD. A commercial drop tower was modified to conduct high strain-rate impact compression tests. Instrumentations including strain gauges, accelerometers and a high speed camera were used to establish equilibrium conditions and stress strain relation of samples with high accuracy. Dynamic response of strongly nonlinear, viscoelastic toroidal rubber elements (o-rings) is studied. Nonlinear dynamic model using strain-rate dependence initially proposed for contact of spherical particles by Brilliantov et. all, and Morgado et. all is modified for strongly nonlinear viscoelastic behavior of o-ring. The model successfully describes the dramatic difference between static and dynamic behavior of o-ring being consistent with measurements in high strain rate experiments. Weaker than linear strain-rate dependence is observed when impact velocity increased. A modified model with power-law strain -rate dependence is proposed based on experimental results. It satisfactory describes the results in a whole range of strain and strain-rates corresponding to different velocities of impact. The testing results of pre -compressed o-rings demonstrated a smaller force at similar strains in comparison with o-rings without pre- compression. At the same time, the slope of force-strain curve demonstrated a higher rigidity for precompressed o- rings. It also was observed that deformation of o-rings exhibited strong memory effect in precompressed state. This behavior of pre-compressed o-rings was explained using a model considering memory effect as a function of initial pre-compression. The model explained the observation from experiment that pre-compression of o- rings contribute to dynamic stiffness which exhibits a stiffer behavior in the initial stage of deformation. The investigated properties of o-rings were used to develop soft drop weight tests eliminating high amplitude noise generic for experimental setup. The results of soft drop weight tests were verified by testing Al samples, whose the mechanical properties are well known. High strain-rate stress versus strain relations of Al 6061-T6 and Al 6061-0 were measured using soft drop weight tests and the results are in agreement with data reported in previous literatures using Hopkinson Split Pressure Bar under similar strain rates. The soft drop weight test was also used to obtain parameters for material model of Adiprene L -100 used in UCSD blast simulator. The loading and unloading curves of Adiprene L-100 under different strain- rates were measured and successfully used to generate tabulated date for elastomer material model used to optimize dynamic load of UCSD blast simulator. Stress strain relations of Al-W composites were measured using soft drop weight tests. It was found that deformation mechanisms and mechanical properties of the composites were significantly different for samples with different mesostructure corresponding to different processing routes

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