Wave propagation and group velocity

Recent advances in modelling of metal machining processes

A model for the axisymmetric growth and coalescence of small internal voids in elastoplastic solids is proposed and assessed using void cell computations. Two contributions existing in the literature have been integrated into the enhanced model. The first is the model of Gologanu-Leblond-Devaux, extending the Gurson model to void shape effects. The second is the approach of Thomason for the onset of void coalescence. Each of these has been extended heuristically to account for strain hardening. In addition, a micromechanically-based simple constitutive model for the void coalescence stage is proposed to supplement the criterion for the onset of coalescence. The fully enhanced Gurson model depends on the flow properties of the material and the dimensional ratios of the void-cell representative volume element. Phenomenological parameters such as critical porosities are not employed in the enhanced model. It incorporates the effect of void shape, relative void spacing, strain hardening, and porosity. The effect of the relative void spacing on void coalescence, which has not yet been carefully addressed in the literature. has received special attention. Using cell model computations, accurate predictions through final fracture have been obtained for a wide range of porosity, void spacing, initial void shape, strain hardening, and stress triaxiality. These predictions have been used to assess the enhanced model. (C) 2000 Elsevier Science Ltd. All rights reserved.

An extended model for void growth and coalescence - application to anisotropic ductile fracture

The problem of impact damage in laminated composite structures, and the consequent reduction in residual strength, has been a topic of continual research for over two decades. The number of journal papers on the subject now runs into four figures and most have been conscientiously reviewed by Abrate(1991, 1994, 1998). This review is not intended to be in the academic tradition, with emphasis on acknowledging the authorship of all the various research initiatives. Instead we present our opinions so that the reader can appreciate our current understanding of the problem, our capability of predicting by analysis, and the scope of the design tools for avoiding structural damage, or at least designing damage tolerant aerospace structures.

Impact on composite structures

Constitutive boundary conditions and paradoxes in nonlocal elastic nanobeams

Bending of Euler–Bernoulli beams using Eringen’s integral formulation: A paradox resolved

Compression after impact of thin composite laminates

This work examines the response of carbon fibre-reinforced epoxy matrix (CFRP) laminates at low impact velocity and in low temperature conditions. Square specimens of carbon fibre/epoxy laminates with different stacking sequences (unidirectional, cross-ply, quasi-isotropic and woven laminates) were tested using a Drop Weight Tower device. The test temperature ranged from 20 down to −150 °C. After the impact tests, the damage extension was measured by C-Scan ultrasonic inspection and the damage mechanisms were studied by optical and scanning electron microscopy. Results showed the influence of temperature, of ply reinforcement architecture and of stacking sequence on the mechanical behaviour of the CFRP laminates subjected to low velocity impulsive loads.

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Damage in CFRPs due to low velocity impact at low temperature

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°.

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Ramón Zaera

Papers

Bending of Euler–Bernoulli beams using Eringen’s integral formulation: A paradox resolved

Compression after impact of thin composite laminates

Damage in CFRPs due to low velocity impact at low temperature

Experimental and numerical analysis of normal and oblique ballistic impacts on thin carbon/epoxy woven laminates

Vibrations of Bernoulli-Euler beams using the two-phase nonlocal elasticity theory