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The presented literature review of cruciform shapes used for biaxial characterization of materials indicates that the majority of shapes can be divided into two large groups when the following selection criteria are taken into consideration: (i) the shape of the outer boundaries and (ii) the load capacity needed to achieve failure in the biaxial region. Manipulation of the outer shape boundaries appears to be essential to bundle the applied loads to the central zone where failure is intended to be built up. For each group, one particular cruciform design is reported whereby the outer boundaries are based on a single curved shape. Although the use of discontinuous double radii edges should be avoided according to earlier reports [1,2], it is shown here through the construction of an optimization algorithm, that the use of a single curve for the outer boundaries leads to strains in the arms that are strongly dependent on these single curved edges. Numerical simulations based on the finite element method as well as experiments performed on polymeric test pieces in combination with DIC measurements, show good agreement on this matter and demonstrate this sensitivity very clearly. [ABSTRACT FROM AUTHOR]

Abstract: Low-velocity impact tests on cast acrylic (PMMA) plates were conducted using an instrumented drop-weight impact machine under various temperatures. Radial cracks were induced and the impact force histories were recorded. Results indicated that there was a glass transition temperature of cast acrylic between 185 and 200°F. Ultrasonic assessments on the impacted acrylic plates were then performed using different transducers. Focused transducers provided more accurate results than flat ones. In addition, the higher the ultrasound frequency, the better the resolution. Finally, the drop-weight impact responses were simulated using LS-DYNA. Two node-splitting techniques, sudden releasing and stepwise releasing, based on maximum tensile stress failure criterion, were implemented for this study. The maximum tensile stress failure criterion was adopted to capture the onset of crack initiation and crack propagation. The node release methods enabled us to calculate the strain energy release rates of cast acrylic. Numerical simulations were compared with experimental results and good agreements were achieved. [Copyright &y& Elsevier]