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The certification of aeronautical composite structures is based on a pragmatic approach, which is intended to be safe and essentially experimental but with a strong test/calculation dialogue called the “Test Pyramid”. However, this has proved to be extremely expensive and it appears necessary to reduce its cost either by developing Virtual testing, or by developing richer tests on an intermediate scale between coupon specimens and structural parts. It was in the aim of meeting this objective that the VERTEX program (French acronym for “Experimental modeling and Validation of compositE strucTures under complEX loading”) was launched in 2012. After positioning the VERTEX program in relation to the literature, this review will explain the methodology and present the measurement methods specifically developed for this scale. Then, three scientific themes that have been studied will be detailed (large notches, impact and wrinkling case studies). Finally, a proposal for validating the structures using envelope curves will be put forward, an assessment made, and perspectives presented.

Airworthiness certification requires proof of structure strength, which is performed generally through a building block approach. To achieve this, representative intermediate-scale experiments generated by test benches are, in general, needed, in addition to material characterization on a coupons scale and structure testing on a large scale. The VERTEX test bench can generate the combined loading of tension/compression-shear-pressure on structural elements and was modelled with Finite Elements to perform virtual testing, representative of its intermediate-scale specificity. The numerous bolted joints of the bench were modelled and their behavior was identified in previous tests, so the model could quantitatively estimate the transfer function of the bench, which is the relationship between the displacements imposed by the jacks and the resulting loads on a given sample. The VERTEX model was identified to represent load shapes and amplitudes based on a training set and was later confronted by a validation set of tests of tension and shear. A model with ideal boundary conditions was also developed for a comparison, but it failed to predict some load shape specificities and did not give any indication of the loading amplitude. Application cases of the developed model are shown to assess a range of virtual testing possibilities.

Aeronautical composite primary structures must evidence sufficient residual strength in the presence of damage for compliance with damage tolerance requirements. The study of stiffener debonding on panels subjected to compression after impact is performed in that scope. Compression leads to the buckling of the skin between the stiffeners, and thus a complex loading of the bonding between the skin and the stiffener. This paper describes the development of a stiffened specimen for the VERTEX multiaxial test rig as a first step towards the study of the damage tolerance evaluation of stiffened structures, under combined loadings and at the intermediate scale of the test pyramid. By using virtual testing, the specimen was designed to produce the phenomenology of interest as the first damage, i.e., the debonding of the stiffener from the centre. Three samples were manufactured and subjected to low velocity impacts at various locations and energies. Then the three samples were subjected to compression after impact, up to the stiffener debonding, under a post-buckling regime of the skin. Test loading evolution is described with force fluxes and global strains, obtained from in situ stereo-correlation. The different impacts were found to give different types of damage but similar residual strength to compression after impact.

With the growing demand for composite parts, more and more designs or re-designs are required to use such materials. This paper presents a new methodology for designing composite structures by considering three essential variables: the geometry, the architecture and the manufacturing process. The methodology proves to be useful during the pre-design phase of the project, when important decisions have to be taken regarding the choice of the manufacturing route and the investments needed. The methodology starts from the design (the geometry of which relies on the designer's creativity) and then gives clear insight into the possibilities offered by the concepts from a composite point of view. These include the types of architecture and technologies that are compatible as well as the manufacturing processes. The GAP methodology (Geometry, Architecture, Process) is intended to provide an efficient way to start a composite project by giving a broad overview of the possibilities and by reducing the risks of poor decisions at the very beginning of the project. In this article, innovative composite structure design issues will be presented before the methodology itself is explained. Two generic case studies are then presented to illustrate how the GAP methodology works. Keywords: Design methodology, Composite materials, Manufacturing processes, Conceptual design

This paper focuses on the study of the effect of rectification by grinding on the mechanical behavior in quasi-static tests (compression and inter-laminar shear) of two long fiber composite materials machined by two cutting processes: tool machining (edge cutting) and abrasive diamond cutting (ADS). Two sets of specimens of different surface roughness are generated by varying the cutting conditions for each material. One set is rectified. First, the results of compression and inter laminar shear tests show that the mechanical behavior is highly affected by the surface roughness. Secondly it is shown that the operation of rectification improves the mechanical behavior. However this improvement is highly affected by the surface roughness of the specimen before rectification and is dependent on the long fiber composite material.

PhotoVoltaic (PV) systems are often subjected to operational faults which negatively affect their performance. Corresponding to different types and natures, such faults prevent the PV systems from achieving their nominal power output and attaining the required level of energy production. Regarding the operational optimization of PV systems, this paper aims primarily at surveying and categorizing different types of PV faults, classified as electrical, internal, and external, where each is thoroughly investigated: internal faults occur at the PV cellular level, and can either be short circuit, open circuit, bridging, or bypass diode faults. External faults on the other side are mainly classified as temporary (i.e., clouds shading, snowstorms, etc.) or permanent (e.g., glass breakage, frame defects, etc.) mismatch faults. Lastly, electrical faults involve common circuitry problems, such as short circuits (e.g., line to ground, line to line, etc.), power processing units’ faults (e.g., inverter faults), and arc faults. As for the detection methods, six major fault detection methods are investigated for the AC side of the PV system with twenty-nine total AC based fault detection methods. On the other hand, eleven major fault detection methods are surveyed for the DC side of PV systems with seventy-three total DC based fault detection methods. The investigated methods are critically analyzed, and compared relevantly to each other, within the mutual sub-sets. The resulting tabulated comparative data assessments for PV faults (i.e., cause-effect relationships, impact on the PV system performance), as well as for faults detection methods (i.e., priority for application, etc.) compose a rich background for related PV systems’ performance security fields, where a nexus future work is also suggested.

The objective of this paper is to propose tools for the lifecycle management of infrastructure by showing the slow degradation processes for which inspection data are accessible, especially the data obtained from non-destructive testing (NDT) and structural health monitoring (SHM). One major characteristic of these degradation processes is their multiphasic nature; consequently, they can be discretised into different phases with specific physical kinematics where specific maintenance actions and measurement techniques can be performed. Within this framework, we propose implementing a degradation meta-modelling approach fed with measurements (NDT, SHM). This approach is based on state-dependent stochastic processes for modelling the degradation and maintenance of reinforced concrete structures that are subjected to chloride-induced deterioration. The benefit of using multiphasic degradation meta-models in the lifecycle management of infrastructure is illustrated through numerical examples that include single and multi-action management policies.

This paper presents a review of the issues concerning sandwich structures for aeronautical applications. The main questions raised by designers are first recalled and the complexity of sandwich structure design for aeronautics is highlighted. Then a review of applications is presented, starting with early examples from the 1930s and the Second World War. The growth in the use of sandwich materials in civil and military applications is then developed. Recent research and innovations conclude the paper.