The damage tolerance of various lay ups of thin carbon/epoxy laminates (1.6 2.2 mm thick) is examined by compression after impact (CAI) tests, using a new testing device which adapts to the thicknesses of the specimens and does not require tabs nor any modification of the specimen geometry. The compression stress state was not modified by the presence of the device, as was verified by numerical simulation. With this device, CAI tests were done of different carbon/epoxy laminate lay ups (quasi isotropic, cross ply and woven) and the values of the residual strength and the normalized residual strength of the laminates were obtained as a function of the impact energy. The woven laminate was found to offer the highest residual strength under all the impact energies, and the quasi isotropic laminate the least loss of normalized strength as the impact energy was raised.
A finite element numerical model for carbon/epoxy woven laminates has been used to predict residual velocity and damaged area when subjected to high impact velocities. Experiments using a gas gun were conducted to investigate the impact process and to validate the model, measuring the two variables previously indicated. A morphology analysis was also made to investigate the different breakage mechanisms that appear during the penetration process. The influence of the impact velocity and obliquity has been studied using the numerical tool, in a wide range of impact velocities and considering two impact angles, 0°and 45°.
In this paper, flexural vibrations of cracked micro-and nanobeams are studied. The model is based on the theory of nonlocal elasticity applied to Euler-Bernouilli beams. The cracked-beam model is established using a proper modification of the classical cracked-beam theory consisting of dividing the cracked element into two segments connected by a rotational spring located at the cracked section. This model promotes a discontinuity in bending slope, which is proportional to the second derivative of the displacements. Frequency equations of cracked nanobeams with some typical boundary conditions are derived and the natural frequencies for different crack positions, crack lengths, and nonlocal length parameters are calculated. The results are compared with those corresponding to the classical local model, emphasizing the differences occurring when the nonlocal effects are significant.
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