German Reyes

Mechanical Behavior of Thermoplastic FML-reinforced Sandwich Panels Using an Aluminum Foam Core: Experiments and Modeling

Sandwich panels manufactured using thermoplastic fiber-metal laminates (FML) skins and an aluminum foam core were tested under quasi-static and low-velocity impact loading conditions. The quasi-static properties of the sandwich beams were evaluated using the three-point bend test geometry. Energy absorbing mechanisms such as buckling and interfacial delamination in the FML skin, as well as indentation, crushing, and densification in the aluminum foam have been observed to contribute to the excellent energy absorbing characteristics offered by these systems. The low-velocity impact behavior of the sandwich panels was evaluated using an instrumented dropping weight impact tower and modeled using an energy balance approach. A breakdown of the energy absorption revealed that these sandwich structures absorb much of the impact energy due to contact and bending effects. Finally, four-point bend testing after low-velocity impact revealed that these systems offer excellent residual flexural strength with relative values remaining close to 80% of the original strength after a 32 J impact.

A Multiresolution Transformation Rule of Material Defects

The ability to quantify the material damage at different length scales is critical in the multiscale analysis of material behavior from nanoscale to macroscale. In this article, on the basis of the equivalence of complementary elastic energy we propose a multiresolution rule that transforms different levels of material defects to the equivalent degradation of material properties. It facilitates a sequential memory-efficient processing of massive material defects in a multiresolution framework, and also supports a functionality of partial damage conversion to serve different needs in subsequent numerical analyses. Numerical simulation was conducted with different settings of material defects. The analysis results indicate the efficacy of the proposed method, offering a potential (i) to interface between multiscale material defects and (ii) as an effective method of homogenization for the determination of the damage variable in continuum damage mechanics.

Static and Low Velocity Impact Behavior of Composite Sandwich Panels with an Aluminum Foam Core

The static and low velocity impact response of aluminum foam based sandwich structures manufactured using thermoplastic composite skins has been studied. The three-point bend (3PB) test geometry was used to evaluate the static properties of the sandwich structures. An examination of the quasi-statically tested specimens revealed failure modes such as indentation, core yielding, and face wrinkling. The low velocity impact behavior of the sandwich systems was investigated using an instrumented dropping weight impact tower and modeled using an energy balance approach. Experimental results revealed that these systems exhibited excellent energy absorbing characteristics under dynamic loading conditions. Furthermore, it has been shown that a simple energy balance model based on the dissipation of energy during the impact event can be used to successfully model the low velocity impact response of the composite reinforced sandwich structures. A breakdown of the energy dissipation revealed that thermoplastic composite reinforced aluminum foam sandwich structures absorb much of the impact energy due to the bending and contact effects.