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Applied Composite Materials: An International Journal for the Science and Application of Composite Materials (v.9, #1)
Identification of the Non-linear Behaviour a 4D Carbon–Carbon Material Designed for Aeronautic Application by L. Dagli; Y. Remond (pp. 1-15).
The global mechanical behaviour of a 4D carbon–carbon (C– C 4D) composite material is described. Designed for aeronautic applications and particularly for the brake discs of heavy air craft, this material is a layered composite reinforced in three directions in the plane (−60°, 0°, 60°) to which the fourth direction of reinforcement is perpendicular. Having ascertained the compliance matrices in the plane to which the braking surface is parallel, we have determined the engineering constants of an elementary ply from the basic assumptions of the classical laminations theory (CLT). Finally, to construct both linear-elastic and elastoplastic constitutive equations of the C– C 4D, we propose a thermodynamic model that accurately characterises the behaviour of this material. This simple model can be identified from simple mechanical tests.
Keywords: breaking; carbon– carbon; compression test; damage; laminates; mechanical testing; multi-directions; tensile test
Fracture Behavior of Particle Reinforced Metal Matrix Composites by X. Xia; H. J. McQueen; H. Zhu (pp. 17-31).
The contributions of the reinforcement volume fraction and annealing temperatures to crack opening force and propagation energy are systematically studied by three point bending tests and by SEM investigations. The bending test data show that for the same reinforcement volume fraction, 2618 and 7075 Al composites require much higher force to open the cracks than 6061 matrix. This relates to the much higher levels of solute elements which causes matrix hardening. Studies reveal that the energy absorption level of the materials during crack propagation depends on both matrix strength and ductility which relates to the reinforcement volume fraction, composition and heat treatment conditions. Large deformation zones are found in front of the crack tip before crack propagation which indicate a ductile failure mode for the composites. Studies also reveal that cracks initiate generally at the particle/matrix interfaces for the low volume fraction reinforced composites. However, for the high volume fraction reinforced composites, crack initiation has been found from both reinforcement/matrix interfaces and broken particles. This indicates that increasing reinforcement volume fraction and matrix strengthening tend to change the fracture mode from interface debonding to particle cleavage cracking.
Keywords: fracture; metal matrix
Delamination Controlled Ballistic Resistance of Polyethylene/Polyethylene Composite Materials by H. Harel; G. Marom; S. Kenig (pp. 33-42).
We have investigated ballistic response of polyethylene/polyethylene (PE/PE) composites to impact by Uzi bullets. For comparison, limited work was carried out on PE/aramid fiber hybrids and PE fiber/Polycarbonate plate laminates. The plates exhibited an average ballistic resistance, V 50, of approximately 90 m/s per 1 kg/m2 area density. In term of the protection level per thickness, the ballistic resistance was 76 m/s per 1 mm. Visual and microscopic examinations identified indentation and delamination as the prevailing failure mechanisms. The delamination, energy calculated on the basis of a simple delamination model considering the fracture surface energy of the matrix, was shown to fully balance the dissipated kinetic energy of the bullet, while the contribution of the fiber fracture process was negligible. This is taken as strong circumstantial evidence for the significant role of this failure process in the ballistic resistance of these composites.
Keywords: polyethylene/polyethylene composites; ballistic performance; delamination
Review of Finite Element Simulation Methods Applied to Manufacturing and Failure Prediction in Composites Structures by A. K. Pickett (pp. 43-58).
Computer simulation is today a mature and essential part of many design practices that has led to improved designs and reduced development times and costs. So far most applications have concerned metal parts and processes with only a limited number of works investigating composite materials. This situation, particularly for industries now dependant on a simulation based design, will have to change if composites are to be seriously considered as a substitute for metals. This paper presents an overview of simulation applied to specific composites problems including sheet forming, 3D-braiding and impact. This work represents nearly a decade of research and development in various national and European projects. It is shown that significant progress has been made and that these complex problems can now be tackled by using state-of-the-art commercial software.
Keywords: computational modelling; forming; braiding; impact behaviour