Coated woven materials are developing for a wide range of applications, but their mechanical behavior is still poorly describing and their shear properties poorly understood. This paper deals with the experimental study of the shear behavior of coated woven materials under cyclic biaxial loading. The aim is to implement the biaxial test in the bias direction, in order to study the shear properties of coated woven materials. We used cruciform specimens with three incisions in each arm. Strain homogeneity in the central part of this specimen had validated by measurements of the strain field, using Stereo Digital Image Correlation (SDIC). Moreover, we carried out a local strain measurements in the useful part of the specimen, using a CCD camera. This enabled us to characterize the variation in the angle between warp and weft, as well as to measure deformation along the warp and weft. These results show a coupling between cyclic shear effects and deformation in both warp and weft directions. Indeed, they reveal an original phenomenon of cyclic ratcheting strain in both warp and weft directions. This phenomenon, which to our knowledge, has not been observed before in woven materials, manifests itself in a systematic increase in strain values in both warp and weft directions with each shear cycle.
The main objective of this project is to design a laboratory-scale experimental setup to study the influence of electrolytic microbubble generation on the hydrodynamic forces and vibrations of marine structures subjected to flow. The project aims to reduce the overall drag of submerged structures as well as the amplitude of flow-induced vibrations by exploiting the electrical conductivity of seawater. The structure under study will be made of composite material, ensuring resistance to harsh conditions in a marine environment, as well as energy performance for applications in the fields of marine engineering (marine renewable energies, naval, floating structures). It will be subjected to a subcritical turbulent flow at different Reynolds numbers. This composite material structure must provide a sufficient amount of gas to reduce drag and flow-induced vibrations. At the end of this project, the goal is to determine the optimal electrolysis conditions for the wall in terms of bubble size and quantity to reduce drag and minimize structural vibrations. In this paper, we focus on the state of the art regarding the electrolysis of saltwater, drag reduction on a wall in flow, the evaluation of fluctuating lift and drag coefficients, and the influence of bubble addition in the wake of a cylinder. The drag formulas existing in the literature help in choosing the material and shape of the structure, as well as the design of the sensors that will measure the variation in drag for the case of a single-phase flow and a two-phase flow with the presence of electrolytic bubbles.
The occurrence of crack closure significantly impacts the fatigue life of materials and structural components. Whether it is induced by the nature of the loading, the fabrication process or the geometry of the structure, its magnitude and effect should be considered to further improve predictive models of fatigue crack propagation. However, the definition of reliable experimental methods for the observation and assessment of fatigue crack closure, and in particular suited to structure testing, remains a challenge. The present study aims to provide a novel approach for the assessment of fatigue crack closure via the continuous wavelet transform of infrared thermography data. The processing of the temperature signal close to the crack in a coherent time-frequency space allows for the identification of crack closing and opening instants associated with high-frequency components. The method is meant to be suited to any testing configuration (conventional compact tension specimen or full-scale structures) with minimum operator-dependent parameters.
Cracking in composite laminates containing 9-plies adjacent to 90 degrees plies is studied experimentally and numerically using the coupled criterion and finite element calculations. Different damage mechanisms are considered, namely transverse cracking in 90 degrees, cracking in 9-plies, or debonding between adjacent misoriented plies. The influence of the stacking sequence on the damage mechanism sequence is investigated. Experimental observations of the composite edge under tensile loading evidence 9-ply cracking (i) at an imposed strain level much larger than first transverse cracking in 90 degrees ply for a sufficiently large orientation mismatch between adjacent plies or (ii) at a similar imposed strain level if the mismatch angle between two adjacent plies is small. The latter phenomenon may be mitigated by the presence of a 0 degrees ply between the 90 degrees and the 9-plies. These conclusions are supported by numerical simulation of the experimentally observed damage mechanisms, evidencing a change in the damage mechanism sequence depending on the 9-ply misorientation. The numerical simulations also highlight that debonding between adjacent plies may occur as it becomes more favorable that adjacent ply crack re-initiation for sufficiently large adjacent ply mismatch angle.
