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International audience; The cohesive zone modelling (CZM) is extensively used for the simulation of delamination propagation of composite laminated materials. The Finite Element (FE) method is able to support the CZM. Nevertheless, a refined mesh in the cohesive zone is required to describe accurately the energy dissipation. A 1D-beam simplified analysis based on the macro-element (ME) technique has been developed for the stress analysis of bonded joints, supporting damage evolution adhesive material law. The objective of this paper is to provide a validation of the ability of this macro-element technique for the simulation of delamination propagation in pure mode I of composite laminates. This validation is led through a comparative study between experimental test results, 3D FE model predictions and 1D-beam ME predictions. The experimental test campaign allows in particular for the assessment of the interlaminar strength and critical energy release rate in pure mode I. The thermoset unidirectional (UD) prepreg composite material IMA/M21E is used for this paper.

In this paper, the influence of the internal pressure on the damage resistance of composite overwrapped pressure vessels due to contact loading is studied experimentally. Pressure vessels with different internal pressures are loaded quasi-statically using an indenter. The damage is evaluated by use of computed tomography scans. Subsequently, the residual burst pressure is determined. The damage resistance is shown to increase for an increasing internal pressure during impact. In order to assist future experimental programs, a numerical model that can predict both the mechanical response and the initiated damage for pressurized vessels is exploited.

International audience; The interest in functionally graded adhesive (FGA) joints has been increasing in recent years. For example, FGAs offer the opportunity to optimize the strength of multi-material bonded joints by locally tailoring the adhesive properties and without modifying the design of the adherends to be joined. The development of dedicated stress analyses to predict the stress distribution is then of the highest interest to control the strength of such joints. The Finite Element (FE) method is able to address the stress analysis of FGA joints but is computationally costly. Simplified stress analyses have then been developed. The objective of this paper is to assess the prediction of simplified stress analyses, solved through the macro-element (ME) technique, with respect to those of FE models. It is shown that the predictions of ME models are in a sufficient agreement with the FE models to be employed at a pre-sizing stage. The influence of the overlap length is then investigated by the means of the simplified stress analyses. A noticeable result is the existence of an overlap length for which the adhesive peak shear stress is minimal, in the 1D-bar kinematics framework.

Functionally graded adhesive (FGA) joints involve a continuous variation of the adhesive properties along the overlap allowing for the homogenization of the stress distribution and load transfer, in order to increase the joint strength. The use of FGA joints made of dissimilar adherends under combined mechanical and thermal loads could then be an attractive solution. This paper aims at presenting a 1D-bar and a 1D-beam simplified stress analyses of such multimaterial joints, in order to predict the adhesive stress distribution along the overlap, as a function of the adhesive graduation. The graduation of the adhesive properties leads to differential equations which coefficients can vary the overlap length. For the 1D-bar analyses, two different resolution schemes are employed. The first one makes use of Taylor expansion power series (TEPS) as already published under pure mechanical load. The second one is based on the macro-element (ME) technique. For the 1D-beam analysis, the solution is only based on the ME technique. A comparative study against balanced and unbalanced joint configurations under pure mechanical and/or thermal loads involving constant or graduated adhesive properties are provided to assess the presented stress analyses. The mathematical description of the analyses is provided.

International audience; This paper presents an experimental study of CAI (compression after impact) of tapered composite laminate. Two types of layup with thickness changing from 4 mm to 6 mm are considered. A new CAI testing rig, suitable for the specimens and a brief description of impact damage are presented first. Then, the behavior of impacted specimens under compressive loading is discussed along with the effects of ply drop-off parameters (taper angle, ply drop-off disposition and configuration) and impact point location on the failure mechanism. Finally, the residual strength in CAI of tapered laminates is compared with equivalent flat laminates. The results show that compressive behavior of the specimens is mostly governed by a coupling between compression and bending, generated by the discontinuity of the neutral axis in the tapered region. Despite this difference of behavior with flat laminates, the presence of ply drop-off has little effect on the residual strength in CAI.

The present paper studies an optimum design method for proposing new types of fiber reinforced composite plates with locally anisotropic structure. A finite element program is developed to analyze vibration of such locally anisotropic plates, and the fundamental frequency is taken as an object function to be maximized. First, for demonstrating the effectiveness of local anisotropy, the optimum distributions of short fibers are calculated without directional constraints using a simple genetic algorithm (GA), and the layerwise optimization (LO) concept is used to reduce the computation time in the finite element calculation. Secondly, optimum arrangements of continuous curvilinear fibers are obtained under the continuity constraints where fiber directions are considered as projections of contour lines of a cubic polynomial surface. Numerical results show that the local anisotropy successfully improves frequency property and the optimum directions of short fibers indicate physically reasonable orientations. Also, the plates with optimally shaped continuous fibers yield higher fundamental frequencies than the conventional plates with parallel fibers.

This paper presents results of the feasibility of carbon/epoxy composites (CFRP) as a future helicopter flexbeam material. Torsional behaviors of unidirectional CFRP and glass/epoxy composites (GFRP) with the same resin matrix were investigated. The initial torsional rigidity of CFRP was almost identical to that of GFRP. The torsional rigidities calculated using finite element analyses (FEA) agreed with the experimental results: the torsional rigidities are governed mainly by the material’s shear stiffness. Torsion fatigue tests were also conducted by controlling the angle of twist of the sinusoidal wave under a constant tensile axial load. No catastrophic failure occurred with either GFRP or CFRP, although decreased amplitudes of torque and torsional rigidities were observed according to the number of cycles. Results of X-ray CT inspections and numerical calculation by FEA revealed that degradation of a torsional rigidity is caused mainly by splitting crack propagation along the fiber direction. The torsion fatigue life of CFRP was superior to that of GFRP. Consequently, results confirmed that CFRP exhibits excellent properties as a torsional element of a helicopter flexbeam in terms of torsional rigidity and tension–torsion fatigue behaviors.