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Michel J.C.,Laboratory of Mechanics and Acoustics | Lopez-Pamies O.,State University of New York at Stony Brook | Ponte Castaeda P.,University of Pennsylvania | Triantafyllidis N.,Ecole Polytechnique - Palaiseau | Triantafyllidis N.,University of Michigan
Journal of the Mechanics and Physics of Solids | Year: 2010

The present work is a detailed study of the connections between microstructural instabilities and their macroscopic manifestations as captured through the effective properties in finitely strained fiber-reinforced elastomers, subjected to finite, plane-strain deformations normal to the fiber direction. The work, which is a complement to a previous and analogous investigation by the same authors on porous elastomers, (Michel et al., 2007), uses the linear comparison, second-order homogenization (S.O.H.) technique, initially developed for random media, to study the onset of failure in periodic fiber-reinforced elastomers and to compare the results to more accurate finite element method (F.E.M.) calculations. The influence of different fiber distributions (random and periodic), initial fiber volume fraction, matrix constitutive law and fiber cross-section on the microscopic buckling (for periodic microgeometries) and macroscopic loss of ellipticity (for all microgeometries) is investigated in detail. In addition, constraints to the principal solution due to fiber/matrix interface decohesion, matrix cavitation and fiber contact are also addressed. It is found that both microscopic and macroscopic instabilities can occur for periodic microstructures, due to a symmetry breaking in the periodic arrangement of the fibers. On the other hand, no instabilities are found for the case of random microstructures with circular section fibers, while only macroscopic instabilities are found for the case of elliptical section fibers, due to a symmetry breaking in their orientation. © 2010 Elsevier Ltd. All rights reserved.


Martini D.,Laboratory of Mechanics and Acoustics | Martini D.,Aix - Marseille University | Hochard C.,Laboratory of Mechanics and Acoustics | Hochard C.,Aix - Marseille University | And 2 more authors.
International Journal for Numerical Methods in Engineering | Year: 2012

The full-field reconstruction method presented here is suitable for real-time structural monitoring purposes, such as improving the performances of structures. The aim is to characterize mechanical fields and boundary conditions while the structure is in service, using just a few on-line measurements. This characterization is an ill-posed inverse problem, the solution of which requires making some prior assumptions. The structures studied are assumed to be in steady-state configurations and to show linear mechanical behavior, and the loading zones are assumed not to be overstressed; the mechanical fields are monitored only inside the structures. The full-field identification is regularized using the boundary conditions, which are identified from strain measurements, and the mechanical fields are then reconstructed from these identified boundary conditions. On the basis of Saint-Venant's principle, the boundary conditions are approximated with a few parameters, the basis functions of which are obtained from the projections of Trefftz-like solutions onto the boundaries of the structures. These approximate boundary conditions are linked to the global mechanical responses of the structures. Lastly, this full-field reconstruction method is applied to plate-like structures with holes subjected to in-plane loads. The results show that the load identification procedure efficiently regularizes the full-field reconstruction method, and that this method is suitable for structural monitoring purposes. The sensitivity of this method to errors is similar to that of the load identification procedure, and the maximum errors in the solutions are located at the boundaries. © 2012 John Wiley & Sons, Ltd.


Hochard C.,Laboratory of Mechanics and Acoustics
ECCM 2012 - Composites at Venice, Proceedings of the 15th European Conference on Composite Materials | Year: 2012

A model defined on the ply scale to describe the rupture in the fibre direction for statics and fatigue loadings was proposed. This model is based on a reduction of strength in the fibre direction for high levels of transverse damage. This phenomenon of reduction of strength in the fibre direction for high levels of transverse damage can also be observed on 0° tubular specimen solicited in fatigue in torsion up to a level of high damage followed by a tensile test in the fibre direction. In addition, an original approach based on a Fracture Characteristic Volume has been developed to predict the fibre failure of laminated structures with stress concentrations for static loadings. The FCV is a cylinder defined at the ply scale on which an average stress is calculated. The parameters of the FCV are identified starting from a homogeneous test and a test which presents a stress concentration.


Hochard C.,Laboratory of Mechanics and Acoustics
16th European Conference on Composite Materials, ECCM 2014 | Year: 2014

A model defined on the ply scale to describe the rupture in the fibre direction for statics and fatigue loadings was proposed. This model is based on a reduction of strength in the fibre direction for high levels of transverse damage. This phenomenon of reduction of strength in the fibre direction for high levels of transverse damage can be observed on 0° tubular specimen solicited in fatigue in torsion up to a level of high damage followed by a tensile test in the fibre direction. New tests on damaged tubular specimen loaded in compression show that the reduction of strength appears earlier for compression load in the fibre direction. Other tests to study the evolution of damage for high constant load and for different load speed are under investigation.

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