Papers by Author: H. Ghasemnejad

Abstract: In this paper the failure behaviour of natural stitched composite materials in the skin-stiffener of wind turbine blade structures are investigated. For this study, the laminated composite beams were stitched using Flax yarns before curing process. Two stiffener structures of T-beam and Box-beam are studied in this paper. These specimens were tested under quasi-static loading condition to compare the failure resistance of adhesive and stitched bonding methods. Furthermore, the cohesive zone modelling (CZM) which is known as a variation in the cohesive stresses with the interfacial opening displacement along the localised fracture process zone is used to predict bonding failure in the skin-stiffener of wind turbine blade structures.

Abstract: Advanced finite element analysis (FEA) is carried out to simulate the off-axis crushing process of glass/epoxy twill/weave composite box structures. The FE results were compared to relevant experimental result and it was shown that the applied model is capable to predict the damage behaviour and energy absorption of composite box aero-structures under off-axis loading condition.

Abstract: The mixed-Mode interlaminar fracture toughness, GI/IIC, of z-pinned hybrid laminated composites is studied to investigate the effect of 3D-composites on the crack propagation resistance of delaminated composite structures. In this regard, the mixed-Mode interlaminar fracture toughness, GI/IIC, was measured using asymmetric double cantilever beam (ADCB) test method. The hybrid ADCB and z-pinned hybrid composite beams were laid-up from [G0/C0]4, [G0/C90]4, [G90/C0]4 and [G90/C90]4 to study the effect of z-pinning on the interlaminar fracture toughness. From the obtained results from test it was found that the resistance of z-pin fibres against the crack propagation in z-pinned hybrid composites can significantly increase the mixed-mode interlaminar fracture toughness.

Abstract: In this paper the effect of delamination position on the critical buckling load and buckling mode of hybrid composite beams is investigated. Experimental and numerical studies are carried out to determine the buckling load of delaminated composite beams. The laminated composite beams with various laminate designs of [G90]6, [C90]8, [C0/G0]4 and [C90/G90]4 were manufactured and tested to find the critical buckling load. Three different defect positions were placed through the thickness to find three main buckling modes. It was found that delamination position and lay-up can affect the buckling mode and also the critical buckling load. By approaching the delamination position to the outer surface of the specimen the buckling load decreases. The buckling process of hybrid and non-hybrid composite beams was also simulated by finite element software ANSYS and the critical buckling loads were verified with the relevant experimental results.

Abstract: 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.

Abstract: In this paper the energy absorption of thin-walled aluminium tubes used as crash boxes in the body structure of a vehicle has been optimized. In order to achieve this, various cross-sections of extruded aluminium were chosen and their behaviour under dynamic impact loading was investigated. The crash boxes were made from aluminium alloy 6060 temper T4. Finite element software LS-DYNA in ANSYS was used for modelling. For each cross-section, the results of dynamic crushing load versus crushing distance was obtained from the FE simulation and the results were compared with the experimental and numerical work on a square crash box in the literature. Parameters such as the crush force efficiency and the specific energy of various crash boxes were compared with the relevant ones for the square crash box and the most efficient crash box was recommended.