Amilcar Quispitupa

Design Analysis of the Mixed Mode Bending Sandwich Specimen

A design analysis of the mixed mode bending (MMB) sandwich specimen for face—core interface fracture characterization is presented. An analysis of the competing failure modes in the foam cored sandwich specimens is performed in order to achieve face—core debond fracture prior to other failure modes. The analysis facilitates selection of the appropriate geometry for the MMB sandwich specimen to promote debond failure. An experimental study is performed using MMB sandwich specimens with a H100 PVC foam core and E-glass—polyester faces. The results reveal that debond propagation is successfully achieved for the chosen geometries and mixed mode loading conditions.

Face/core mixed mode debond fracture toughness characterization using the modified TSD test method

The modified tilted sandwich debond (TSD) test method is used to examine face/core debond fracture toughness of sandwich specimens with glass/polyester face sheets and PVC H45 and H100 foam cores over a large range of mode-mixities. The modification was achieved by reinforcing the loaded face sheet with a steel bar, and fracture testing of the test specimens was conducted over a range of tilt angles. The fracture toughness exhibited mode-mixity phase angle dependence, especially for mode II dominated loadings; although, the fracture toughness remained quite constant for mode I dominated crack loadings. The fracture process was inspected visually during and after testing. For specimens with H45 core the crack propagated in the core. For specimens with an H100 core, the crack propagated between the resin-rich layer and the face sheet.

Failure of uniformly compression loaded debond damaged sandwich panels — An experimental and numerical study

This paper deals with the failure of compression-loaded sandwich panels with an implanted circular face/core debond. Uniform compression tests were conducted on intact sandwich panels with three different types of core material (H130, H250 and PMI) and on similar panels with circular face/core debonds having three different diameters. The strains and out-of-plane displacements of the panel surface were monitored using the digital image correlation technique. Mixed mode bending tests were conducted to determine the fracture toughness of the face/core interface of the panels. Finite element analysis and linear elastic fracture mechanics were employed to determine the critical buckling load and compression strength of the panels. Modeling approaches and failure criteria are discussed. Numerically determined crack propagation loads in most of the cases show a fair agreement with experimental results, but in a few cases up to 45% deviation is seen between numerical and experimental results. This can be ascribed to several factors such as the large scatter in the measured interface fracture toughness, differing crack tip details and crack growth mechanisms between the panels and the mixed mode bending specimens. Tentative strength reduction curves are presented, but uncertainty concerning the intact strengths of the materials used needs to be removed before these can be utilized with confidence.