In this paper, fatigue life estimation for delamination growth of laminated fibre reinforced polymer (FRP) composite structures in mode I and mode II based on fracture mechanics is presented. The proposed method was applied to delamination of glass/epoxy laminated composite. Both the threshold energy release rate ( ) and the delamination propagation based on Paris' law were studied. The double cantilever beam (DCB) specimen for mode I and 3 points End-Notched Flexure (3ENF) specimen for mode II were used for monotonic fracture tests and the resistance and as a function of delamination length were determined. For DCB tests, the fatigue onset life test was conducted and the threshold energy release rate, , was found for the subcritical region. Constant amplitude, displacement controlled cyclic fatigue test for both modes was conducted and the delamination crack growth rate ( ) as a function of maximum cyclic energy release rate and for DCB and 3ENF specimens were determined, respectively. From curve fitting to the experimental data, the Paris' law material constants C and m for mode I and mode II were obtained. Finally, the SEM fractography studies of delaminated surfaces of 3ENF static and fatigued specimens have been done and the different features observed on these surfaces were discussed.

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The present paper investigates specific sustained crushing stress (SSCS) of various composite laminate designs and stiffened boxes under axial crushing test. In this regard, an optimum composite crash box design is sought by studying the effect of laminate design and stiffeners on SSCS. Crash boxes were fabricated from carbon/epoxy twill-weave fabrics of [0]4, [45]4 and [0,45]2. The progressive failure with three distinct crushing modes of transverse shearing, lamina bending and brittle fracture was observed for three laminate designs. Two new assembled composite boxes were made from channels and V-shape stiffener and tested in quasi-static condition. Adhesive bonding was used in joining the channelled and stiffened boxes. Measured amount of SSCS for all models were compared to find an optimum crash box. It was found SSCS increases with increasing proportion of 0° plies in the laminate.