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When a fiber break occurs in longitudinal tension of a unidirectional composite, dynamic stress concentrations arise, which can be different from the ones found considering only static loading. The current paper analyzes the dynamic stress concentration factors (SCF) around a fiber break in unidirectional carbon fiber/epoxy composites. 3D finite element models with random and hexagonal fiber distributions were analyzed to investigate the evolution of stress concentrations as a function of time and position. The results indicate that dynamic effects result in much higher SCFs with a larger effective area around the broken fiber. The increase of SCFs in the closest fibers was determined to be larger for lower fiber volume fractions due to the presence of dynamic effects. Similar to the static case, a lower volume fraction causes higher maximum dynamic SCF in random packings. Results also support the high prevalence of coplanar cluster breaks observed in the experiments. [ABSTRACT FROM AUTHOR]

The vibration and stability of axially loaded sandwich cylindrical shells with the functionally graded (FG) core with and without shear stresses and rotary inertia resting Pasternak foundation are investigated. The dynamic stability is derived based on the first order shear deformation theory (FSDT) including shear stresses. The axial load and dimensionless fundamental frequency for FG sandwich shell with shear stresses and rotary inertia and resting on the Pasternak foundation. Finally, the influences of variations of FG core, elastic foundations, shear stresses and rotary inertia on the fundamental frequencies and critical axial loads are investigated. [ABSTRACT FROM PUBLISHER]

Step lap joints are kinds of lap structures, where butted laminations of each layer are consecutively offset in succeeding layers in the same direction. They are mainly designed this way to reduce the peel stresses at the edges of the overlap area observed in single lap joints. In their service, lap joints are often subjected to bending loads. However, the performance of a step lap joint under flexural loading has not been studied in the literature yet. For this purpose, 3D advanced finite-element (FE) models of the step lap joints were developed via ABAQUS-Standard. DP 460 and A2024-T3 aluminum alloy were used for the adhesive layer and adherends, respectively. The polymeric adhesive layer was modelled using cohesive zone elements with quadratic nominal stress criteria and power law interaction of the energies to characterize the damage initiation and damage evolution, respectively. A surface-to-surface contact method with a penalty algorithm and a hard contact model was used to characterize the contact between the adherends and the punch. Experimental data were used to validate the numerical model. The effects of the configuration of the step lap joint on its performance in terms of the maximum bending load and the amount of energy absorbed were analyzed in detail. A step lap joint with three steps (three-stepped lap joint) was found to show the best flexural performance, and when the overlap length at the upper and lower steps was increased, the amount of energy absorbed by the joint increased markedly.