No abstract

Fiber reinforced polymer composite structures have very comparable mass densities to that of water. As a result, the effect of the Fluid-Structure-Interaction (FSI) is much greater for those composite structures than for conventional metallic structures. As a result, this study investigates the effects of FSI on composite structures. A series of underwater impact testing has been conducted to understand the dynamic responses of composite structures coupled with the FSI effects. Both air-backed and water-backed underwater impacts are considered and their behaviors are compared to the dry impact test results in order to determine the FSI effects. Furthermore, multiphysics-based computational analyses have been undertaken so as to better understand and interpret the experimental results. The results of this study will provide knowledge necessary to apply composite materials to underwater structural applications.

This paper investigates the mechanical behavior of a copper–solder interface when subjected to varying strain rate loading between 0.05 s−1 and 10.0 s−1. The copper is alloy 101, and the solder is lead-free type with a composition of 96% tin and 4% silver. Both uniform and nonuniform two-level strain rate loadings were applied. For the two-level strain rate loading, the strain rate was changed from one level to another during the loading process as a step change. The strain rate tests were performed at room temperature as well as at an elevated temperature of 65 °C. The test results showed significant effects of uniform and nonuniform strain rates as well as temperature on fracture surface, peak stress, fracture strain, modulus, and stored energy density until fracture. Generally, a higher strain rate increased the peak stress and fracture strain, but decreased the modulus. The heated specimens showed significantly reduced strength and fracture strain at high strain rates when compared to the specimens tested at room temperature. For the two-level strain rates, the sequence of the loading rates affected the material behavior significantly. The peak stress under the two-level strain rates might be located outside the range that was determined by the two individual uniform strain rates occurring in the two-level rates. On the other hand, the fracture strain under two-level strain rate loading always fell inside that range. An expression was proposed to predict the interface fracture strains for the case of a two-level strain rate loading based on the data of each respective single-level strain test. The prediction was reasonable when compared to the experimental data with an average absolute error of 10%.