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a b s t r a c tThe analyses of cracked laminates based on a variational principle and related approaches are appraised in this paper. The limitations of the existing methodology on the analyses of more general laminate configurations have been identified. It has been revealed that the limiting factor is the lack of boundary conditions for uncracked laminae. Natural boundary conditions have then been derived from the variational principle to meet the need. Such boundary conditions are mathematically sound but cannot be simply interpreted from the physical construction of the problem intuitively. A well posed boundary value problem has thus been formulated for laminates containing however many cracked and uncracked laminae. Appropriate mathematical tools can then be employed to solve the boundary value problem. The capability of analysing cracked laminates has been enhanced significantly, as a result.

Herein, we report the fabrication and characterization of high-strength Kevlar epoxy composite sheets for structural application. This process includes optimization of the curing conditions of composite preparation, such as curing time and temperature, and the incorporation of nanofillers, such as aluminum oxide (Al2O3), silicon carbide (SiC), and multi-walled carbon nanotubes (MWCNT) in different weight percentages. Differential scanning calorimetry (DSC) was utilized to investigate the thermal stability and curing behavior of the epoxy, finding that a minimum of 5 min is required for complete curing under an optimized temperature of 170 °C. Moreover, mechanical characterization, including flexural and drop-weight tests, were performed and found to be in good agreement with the DSC results. Our results show that nanofiller incorporation improves the mechanical properties of Kevlar epoxy composites. Among the tested samples, 0.5% MWCNT incorporation obtained the highest mechanical strength.

Thermal loading of fiber reinforced composites during traditional machining is inevitable. This is due to the fact that most of the mechanical energy utilized in material removal is converted into heat, which is subsequently dissipated into the workpiece and the cutter, and is carried away by the chips. Heat conduction into the workpiece during machining might cause thermal damage due to matrix softening and decomposition if the generated temperatures exceeded the glass transition temperature of the epoxy resin. In this work, the amount of heat flux applied to the machined edge and the temperature distribution in multidirectional CFRP and GFRP composite laminates was determined using an iterative inverse heat conduction method. The transient heat conduction problems in the laminate and cutter were simulated independently using the finite element method and the amount of heat flux applied to each was determined. It was also found that the heat flux conducted to the workpiece represented only a small fraction of the total heat and is more influenced by the feed speed than the spindle speed. The temperature of the machined surface was estimated and correlations with the resulting machined surface texture were made.

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