Scaling effects on the strain rate sensitivity of unidirectional and [+45/-45]$_{s}$ laminates under tensile loading

Abstract

The effects of geometric scaling on the strain rate sensitivity of unidirectional and [+45/-45]$_{s}$ laminates under uniaxial tensile loading has been investigated experimentally. Two material systems, Toray T800/3900-2B carbon/epoxy unitape and Newport NB321/7781 fiberglass/epoxy fabric, were used in the study. The nominal strain rates investigated ranged from quasi-static (0.0002 s$^{-1}$) to moderate strain rates of 50 s$^{-1}$ across the scaled specimen geometries. The geometric scaling effects at different strain rates were quantified in terms of the Weibull modulus. At each strain rate, the average failure stress of [0]$_{4}$ carbon, [0]$_{4}$ fiberglass, and [±45]$_{s}$ fiberglass showed a declining trend with increasing specimen size. However, the percentage of the strength reduction was less significant at higher strain rates compared to the quasi-static strain rate. In contrast to the other stacking sequences, [+45/-45]$_{s}$ carbon specimens showed a maximum percentage in strength reduction at a high strain rate compared to the quasi-static strain rate, indicating increased scaling effect with strain rate. The magnitude of Weibull modulus ($m$) for the specimens increased with strain rate indicating diminishing scaling effects, while [+45/-45]$_{s}$ carbon specimens exhibited an opposite trend.