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Laminated composite structures, while offering weight savings compared with their metal counterparts, are susceptible to ply separation, (i.e., delamination mode of failure) due to the lack of through-thickness fiber reinforcements. In this paper, numerical simulations are used to gain an enhanced understanding of angled composite beam delamination when subjected to four-point bending consistent with the ASTM D-6415 test standard, with an expectation that the learning gained from this work is extensible to laminated composite components in general. While illustrating mesh sensitivity, manufacturing and frictional effects, four items of interest are examined: (1) the undamaged state/pre-peak load response, (2) the through-thickness peak tensile capability, (3) the post-peak load drop, and (4) the subsequent post-peak damaged response. A Finite Element Analysis (FEA) model is developed that incorporates the Smeared Crack Approach (SCA) to capture progressive failure modes within the element formulations directly, effectively eliminating the need for a priori specification of discrete delamination zones. The ability to incorporate failure directly within the element structure is particularly notable where laminates may not realistically permit a high number of interface layers or where geometry may be complex. Leveraging experimental data of curved composite laminates subject to four-point bending, the proposed approach successfully predicts the correct behavior throughout the damage progression. Additionally, this study offers an insight into effects of manufacturing-induced imperfections and frictions between the specimen and fixture on the prediction of inter-laminar strength of a curved composite part. [ABSTRACT FROM AUTHOR]

An exact analytical model based on a higher-order beam theory (HBT) is developed for an accurate prediction of the flexural response of two layered composite beams with partial shear interactions. This is achieved by taking a third order variation of the longitudinal displacement over the beam depth for the two layers separately. The deformable shear connectors joining the two different material layers are modelled as distributed shear springs along the beam length at their interface. The principle of virtual work is used to derive the governing equations which are solved analytically using a Navier type solution technique. To assess the performance of the proposed model, numerical examples of composite beams are solved using the model. The results predicted by the model are compared with published results and the numerical results produced by a one dimensional finite element model based on HBT as well as a detailed two-dimensional finite element modelling of composite beams. [ABSTRACT FROM AUTHOR]

The objective of this work is the characterization and the assessment of the damage in CFRP composite laminates with different stacking sequences subjected to low velocity impact and flexural loading. Charpy impact test and three-point bending test were used in order to obtained the impact response and flexural behavior of different laminates. An experimental test series was carried out to determine impact energy absorption, flexural strength and stiffness and failure mechanisms of composite laminates made from M 21 E / IMA , an unidirectional prepreg used in Airbus A350 XWB primary structures. It is important to note that both elastic moduli and strength in the principal material directions are different under tension and compression. The flexural modulus is expected to have an intermediate value between the tensile and compression moduli. We analyze the effect of this type of multimodulus materials [1–3] in order to evaluate the influence of the geometry of the specimen on the failure modes (shear or flexural failure modes) observed in the three-point bending test and compare the results with tensile and compression behavior. Two main lay-up configurations have been analyzed: Unidirectional laminates [ 0 ] 12 , [ 90 ] 12 , [ 45 ] 12 and multidirectional laminates (cross-ply [ 0 / 90 ] 3 s , angle-ply [ ± 45 ] 3 s and quasi-isotropic laminates [ 0 / 90 / ( ± 45 ) 2 ] s ). Unidirectional laminates are rarely used in structural components but help to assess the different types of damage (splitting, matrix cracking, delamination) and response of the specimens under low-velocity impact and flexural loading. They are usually combined with plies of varying orientation in multidirectional laminates. These laminates exhibit a more complex behavior due to coupling effects and the combination of different failure modes. In this study, both impact and flexural response for the different laminates have been compared. Special attention is paid in the response of multidirectional laminates under flexural (and impact) loading. Shear effects are very important in this type of laminates. Only a limited number of experimental studies have been developed in this context [4–7]. Additionally, the failure modes observed under impact and flexural loading were correlated with fracture energy absorption and load–deflection behavior respectively for the unidirectional and multidirectional laminates. The results have shown that the effect of the stacking sequences on the impact and flexural response depicted similar trends than in the case of tensile response studied in previous works [8–11]. Furthermore, the present work has shown a distinctive behavior of [ ± 45 ] 3 s angle-ply laminate.under impact loading due to its pseudo-ductile behavior. This laminate exhibited the best impact performance in terms of averaged absorbed energy but the flexural strength and stiffness drastically decreased compared to [ 0 ] 12 laminate. Finally, SEM and optical micrographs of fracture surfaces were used to gain an insight into the assessment of different type of damage of the previous laminates. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a flexural analysis of I-shaped laminated composite beams. A general analytical model applicable to thin-walled I-section composite beams subjected to vertical load is developed. This model is based on the shear-deformable beam theory, and accounts for the flexural response of the thin-walled composites for arbitrary laminate stacking sequence configuration, i.e. unsymmetric as well as symmetric. Governing equations are derived from the principle of the stationary value of total potential energy. Numerical results are obtained for thin-walled composites under vertical loading, addressing the effects of fiber angle and span-to-height ratio of the composite beam. [Copyright &y& Elsevier]