Experimental investigation of interfacial crack arrest in sandwich beams subjected to fatigue loading using a novel crack arresting device

A recently proposed face-sheet–core interface crack arresting device is implemented in sandwich beams and tested using the Sandwich Tear Test configuration. Fatigue loading conditions are applied to propagate the crack and determine the effect of the crack stopper on the fatigue growth rate and arrest of the crack. Digital image correlation is used through the duration of the fatigue experiment to track the strain evolution as the crack tip advances. The measured strains are related to crack tip propagation, arrest, and re-initiation of the crack. A finite element model is used to calculate the energy release rate, mode mixity and to simulate crack propagation and arrest of the crack. Finally, the effectiveness of the crack arresting device is demonstrated on composite sandwich beams subjected to fatigue loading conditions

Thermomechanical interaction effects in composite sandwich structures – initial experimental analysis and derivation of mechanical properties

An experimental study of the effect of increasing temperature on the tensile modulus of PVC foam is presented. The focus is on obtaining reliable measurements of specimen deformation using optical techniques based on digital image correlation (DIC). A FE model that accounts for the 3D strain distribution in the specimen was used to inform the test specimen design. A new testing methodology and test rig design is devised and described in the paper. Firstly, tests are conducted at room temperature using DIC to obtain the strain on two opposite surfaces of the specimen simultaneously, to assess the effect of any specimen misalignment and devise a correction approach referred to as a ‘misalignment ratio’. In the elevated temperature test only one face was optically accessible through an optical window in a thermal chamber. Therefore the experiments are performed over a temperature range of 30°C to 90°C using only a single camera and the misalignment ratio applied. It is shown that the proposed methodology provides precise measurements and the thermal degradation of the tensile modulus can be obtained

The effect of temperature on the failure modes of polymer foam cored sandwich structures

The influence of elevated temperature on the stability of sandwich structures is investigated. A new analytical solution is proposed that enables the calculation of the critical wrinkling stress in sandwich beams subjected to load and elevated temperatures. The effect of a through thickness temperature gradient is accounted for by imposing different stiffnesses of the core for the different temperatures. The sandwich beam studied in the paper is loaded in a simply supported four-point bending configuration, where one of the face sheets is heated. The experimental approach utilises high-speed imaging where the strains are calculated from measured displacements obtained from digital image correlation (DIC). A shift of the failure mode from face sheet yielding to face sheet wrinkling is observed with increasing temperatures. The results from the new analytical method agree well with corresponding experimental results. Finite element analysis is also conducted, which shows excellent correspondence with the theory and the experimental data. The work clearly demonstrates that under certain conditions the load response of the sandwich beam can become nonlinear and unstable, and hence will fail well below face sheet yielding load because of the loss of stiffness of the core material

An efficient beam element for the analysis of laminated composite beams of thin-walled open and closed cross sections

A condensed fully coupled beam element for thin-walled laminated composite beams having open or closed cross sections is presented. An analytical technique is used to derive the cross-sectional stiffness of the beam in a systematic manner considering all the deformation effects and their mutual couplings. An efficient finite element approximation is adopted for the transverse shear deformation, which has helped to conveniently implement the C1 continuous formulation required by the torsional deformation due to incorporation of warping deformation. The performance of the element is tested through the solution of numerical examples involving open section I and channel (C) beams and closed section box beams under different loading conditions, and the obtained results are compared with model as well as experimental results available in literature.<br/