09 Décembre – Thesis defense - Lucien Cadieu
14 h Amphi LRL - Esplanade des arts et métiers (Talence)
Thermo-kinetic loading effects on the mechanical behaviour of a thermoplastic composite laminate.
This thesis presents the effects of thermo-mechanical loadings on the mechanical response of a new thermoplastic based composite laminate material. Indentation/low velocity impact tests lead at different velocities and temperatures allow to study the mechanical response of the composite structure. These loadings are representative of the different loadings a composite laminate structure might encounter during its service life (impacts during transport or maintenance like a dropped tool). The mechanical answer of the composite structure is studied (maximum load, stiffness, absorbed energy, dissipated energy...). The induced damage mechanisms are studied from the microscale to the macroscale with the help of a scanning electron microscope and an more regular optical microscope. The effects of thermo-mechanical loadings on the damage mechanisms in the laminate are observed and discussed.
Indentation and impact loading conditions are known to induce a particular damage mechanism : inter-laminar fracture also known as delamination. Considered to be one of the most critical damage mechanism for composite laminates, delamination is governed by a material parameter called the energy release rate. The estimation of this parameter is still subject to debate nowadays. This energy release rate is generally studied with double cantilever beam (DCB) tests. An experimental DCB campaign was lead with tests done at different opening speeds and temperatures to study the thermo-mechanical loading effects on the rupture behavior of the laminate. The relevance of the DCB tests at higher opening rates is questioned in this thesis. Results from the literature show that the studied «material » parameter is dependent to the sample geometry for DCB tests. A multi-delamination phenomenon in the laminate rendering is highlighted and complexifies the estimation of created fracture surface. This makes the estimation of the energy release rate very difficult.