Effect of Hole Arrangement on Failure Mechanism of Multiple-Hole Fiber Metal Laminate under On-Axis and Off-Axis Loading

Mechanical joints are commonly required in structures made of fiber metal laminate (FML), which pose a threat due to multi-site stress concentrations at rivet or bolt holes. Thus, for a reasonably designed FML joint, it is essential to characterize the failure mechanism of multiple-hole FML; however, little information about this has been found in open literature. In the present work, influences of hole arrangement and loading strategy (on-axis or off-axis) on the failure mechanism of multiple-hole FML were investigated, by performing finite element analyses and energy dissipation analyses with elastoplastic progressive damage models that took curing stress into account. Six types of specimens with holes arranged in parallel and staggered forms were designed, whose geometrical parameters were in strict accordance with those specified for composites joints. It indicated that the stress distribution, gross/net notched strength, critical fracture path, and damage evaluation process were only slightly influenced by the hole number and hole arrangement. On the other hand, they were strongly influenced by the loading strategy, due to the transition of failure domination. Results presented here can provide evidence for introducing design regulations of composite joints into the more hybrid FML, and for reasonably determining its multiple-hole strength merely based on the sing-hole specimen.

Effects of curing stress on the stiffness of a cement-mixed sand

Research into naturally cemented soils (e.g. sandstones) has increased considerably, mostly be-cause of growing interest in offshore oil wells at depths that can, at times, exceed 1000 m. Performing tests directly with on-site soil samples is ideal. However, it's acquisition, transportation and preservation are in-credibly difficult. In order to perform the tests required for this study, the samples were made to simulate the bonding found in naturally cemented soils. Artificially cemented sands were cured under stresses of either 500, 2000 and 4000 kPa, or simply under atmospheric pressure. These specimens were then subjected to drained triaxial compression tests. The results have shown that the curing type has influence over the artifi-cially cemented sand's yield surface and stiffness. The stiffness was vastly superior in specimens cured under higher levels of stress