Characterization of shocked beryllium

While numerous studies have investigated the low-strain-rate constitutive response of beryllium, the combined influence of high strain rate and temperature on the mechanical behavior and microstructure of beryllium has received limited attention over the last 40 years. In the current work, high strain rate tests were conducted using both explosive drive and a gas gun to accelerate the material. Prior studies have focused on tensile loading behavior, or limited conditions of dynamic strain rate and/or temperature. Two constitutive strength (plasticity) models, the Preston-Tonks-Wallace (PTW) and Mechanical Threshold Stress (MTS) models, were calibrated using common quasi-static and Hopkinson bar data. However, simulations with the two models give noticeably different results when compared with the measured experimental wave profiles. The experimental results indicate that, even if fractured by the initial shock loading, the Be remains sufficiently intact to support a shear stress following partial release and subsequent shock re-loading. Additional “arrested” drive shots were designed and tested to minimize the reflected tensile pulse in the sample. These tests were done to both validate the model and to put large shock induced compressive loads into the beryllium sample

A synchrotron x-ray diffraction study of the local residual strains around a single inclusion in an Al/W metal-matrix composite

An X-ray technique for local measurements of the internal residual stress near inclusions in metalmatrix composites (MMCs) is presented. The technique utilizes medium- to high-energy monochromatic X-rays from a synchrotron source and a combination of slits on the entry and exit sides of the sample in order to determine the strains from small volumes deep within the composite sample. The strains of the individual matrix grains are sampled and averaged, allowing for a much improved spatial resolution. An analyzer is used in order to avoid well-known systematic errors related to geometry and stability of the beam. First results are obtained on a model system consisting of a 500 µm continuous W fiber imbedded in an A1 matrix. Two specimens were investigated with typical Al grain sizes of 1 mm and 30 µm. With a gage volume of 10×10×170 µm3, we obtained count rates on the order of 5000 cps and an accuracy in the strain measurements of Δε≤5×10−5. For both specimens, we found no variations of the radial and transverse strain components with the distance to the fiber, indicating either a complete debonding of the system, a very weak interface, or interface deterioration due to chemical reaction. Intragranular strain fluctuations on the order of ε=±10−4 were found to build up close to the grain boundaries. For the specimen with the smaller Al grain size, sampling data from approximately 15 grains at the same distance to the fiber was sufficient for averaging out the intergranular fluctuations. Finally, we observe effects from the conventional metallurgic sample preparation up to 400 µm from the surface, emphasizing the relevance of bulk techniques