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Applied Composite Materials: An International Journal for the Science and Application of Composite Materials (v.6, #2)
Creep/Creep-Recovery Response of Fibredux 920C-TS-5-42 Composite under Flexural Loading by Rui Miranda Guedes; António Torres Marques; Albert Cardon (pp. 71-86).
The flexural behavior of unidirectional composites at 90° to the axis was investigated. The experimental data and finite element method results indicate that beam specimens undergo large deformations. An analytical model was developed to calculate the correct maximum stress level obtained during the flexural tests. Models have been developed to describe the time-dependent viscoelastic-viscoplastic stress-strain relationship of unidirectional fibre reinforced thermoset matrix composites. A procedure that extends the classical lamination theory to include time related response of composite materials for membrane and flexural loading resulted in a FORTRAN program, LAMFLU. For Fibredux 920C-TS-5-42 graphite-epoxy composite the constants in the stress-strain relationships were determined from data obtained in four-point bending tests. The model characteristics for tensile loading have been determined by Qin [1] and were adapted to the LAMFLU procedure. The maximum strain history calculated with both models was compared with experimental results from two different flexural loading programs.
Keywords: viscoelasticity; viscoplasticity; cyclic mechanical loading; flexural loading; tensile loading
Optimum Design of Laminated Composite Plates Undergoing Large Amplitude Oscillations by K. Sivakumar; N. G. R. Iyengar; Deb Kalyanmoy (pp. 87-98).
The optimum design of composite laminated plates under going large amplitude free vibration is discussed. Von Karman's nonlinear strain displacement relations are considered to account for large amplitude. A higher order shear deformation theory with parabolic variation of transverse shear stresses through thickness is used in the finite element formulation. A nine-noded isoparametric element with 7 dof per node is adopted. Ritz formulation for nonlinear finite element analysis is implemented and the direct iteration method is used to solve the governing nonlinear equation. Optimization is carried out using genetic algorithm (GA) with tournament selection scheme.
Keywords: laminated plates; large oscillations; genetic algorithm; optimum design; finite element analysis
A Macromechanical Damage Model of Fibrous Laminated Composites by G. A. Abu-Farsakh; S. A. Barakat; F. H. Abed (pp. 99-119).
A new model for the damage factor in terms of strain energy densities is derived and proposed. The damage factor values can be predicted directly from the stress–strain data using the aforementioned model. Moreover, an expression of crack density ratios in terms of total strain energy densities is inferred. Their validity has been shown by comparing their results with the limited experimental data. The proposed model compares well with the model and the experimental data of Voyiadjis performed on metal-matrix laminates. A new technique, used to predict reasonably the values of crack density ratios at any fiber orientation angle using measured data in the principal material directions, is also developed. Due to difficulties encountered in the evaluation of amount of damage in composite materials up to failure, especially, when using experimental techniques, it was shown that the proposed method for finding the damage factor and crack-density ratios is sufficient and gives reasonable predictions.
Keywords: damage; modeling; fiber composites; crack-density; strain energy
Effect of Heat Treatment on the Drilling Performance of Aluminium/SiC MMC by S. Barnes; I. R. Pashby; A. B. Hashim (pp. 121-138).
The extremely abrasive reinforcing phases present in metal matrix composites (MMCs) are known to dominate their machining behaviour. Consequently, the properties of the matrix material are often ignored. The work reported here investigated the influence of matrix microstructure on the drilling performance of a 2618 aluminium alloy reinforced with 18% silicon carbide particles. The drills used were 8 mm diameter, titanium nitride coated K10 carbide with through-tool cooling. The workpiece material was drilled in four heat treatment conditions: as-extruded, solution treated and solution treated and aged for 12 and 20 hours. Drilling performance was assessed by measuring the wear on the drills, cutting forces, surface finish and the condition of the worn cutting edges. The results indicated that softer as-extruded and solution treated materials produced less wear and lower cutting forces than the harder aged materials. However, the height of the burrs produced during drilling were found to be greater with the softer materials and the quality of the drilled surface was also inferior. Examination of the worn cutting edges indicated that the wear mechanism was primarily one of abrasion although some attrition and edge chipping was also observed. It was concluded that when drilling these materials, the heat treatment condition of the matrix exerts a significant influence on machinability.
Keywords: drilling; metal matrix composites; cemented carbide drills; heat treatment; solution treated; aged; wear; forces; sub-surface damage