The mechanical properties of polymers, particularly as a function of temperature and strain rate, are key for implementation of these materials in design. In this paper, the compressive response of low density polyethylene (LDPE) was investigated across a range of strain rates and temperatures. The mechanical response was found to be temperature and strain rate dependent, showing an increase in stress with increasing strain rate or decreasing temperature. A single linear dependence was observed for flow stress on temperature and log strain rate over the full range of conditions investigated. The temperature and strain rate data were mapped using the method developed by Siviour et al. based on time-temperature superposition using a single mapping parameter indicating that there are no phase transitions over the rates and temperatures investigated. Taylor impact experiments were conducted showing a double deformation zone and yield strength measurements in agreement with compression experiments.

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The ballistic perforation response of knits formed from continuous filament aramid is reported and compared to conventional armor textiles and commodity fabrics. The ballistic experiments consist of 6.0-mm-diameter glass spheres impacted into gelatin-backed targets with areal densities from 200-1000 g/m 2. These ballistic experiments are complemented with quasistatic reverse-perforation experiments to gain insights into deformation and failure for these materials. In-plane stretch experiments are also performed to quantify modulus and strain-tofailure. The results show that, while the ballistic performance of traditional woven textiles is generally superior to knitted aramids, knits formed from continuous filament aramid are significantly better than knits formed from staple yarn. Knitted structures are limited by two main factors: failure of a single yarn tends to lead to catastrophic deconstruction and perforation, and the low in-plane modulus of knits leads to poor lateral stress transfer and energy distribution during higher speed impact. Importantly, however, knits provide significantly more reversible

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A Kolsky bar method is described that is suitable for measuring the flexural strength of ceramics under valid testing conditions in a high-rate three-point bending configuration. A three-bar arrangement is used-one input bar and two output bars-to provide measurements of force and displacement at each loading point. Small diameter bars are used to improve the force measurement made by the incident bar which in many cases would be inaccurate. An analytical model is formulated to predict the desired incident pulse based on the conditions of the experiment and the desire for a particular prescribed strain-rate. A finite element analysis is also conducted to determine suitable specimen geometries that will yield valid data at the desired rate. It is shown that stiff beam geometries improve specimen equilibrium and can reduce inertial effects. However, the use of small diameter bars necessitates unusually precise pulse-shaping. To achieve additional flexibility in pulse-shaping, a tapered striker is used in conjunction with a ductile wave-shaper to generate the desired incident pulse. A down-side of this approach is that a suitable taper geometry must be determined. It is shown that this geometry can be designed quickly and accurately using a simple one-dimensional finite element approach. The methods are demonstrated by measuring the dynamic flexural strength of a-SiC.