Thesis defense by Julien Cadieu (DuMAS)

Summary 

This thesis presents the effects of thermokinetic loading on the mechanical behavior of a thermoplastic acrylic resin laminated composite material reinforced with continuous glass fibers. Low-speed indentation/impact tests at different loading speeds and temperatures are used to study the mechanical response of the composite structure. These loads are representative of the loads that the laminated composite may encounter during service (impact during transport, falling tools during maintenance, gravel impact, etc.). The structural responses of the laminated composite studied (maximum force reached, stiffness, energy absorbed, energy dissipated) are estimated. The damage mechanisms induced by these stresses are studied from the microscopic to the macroscopic scale using a scanning electron microscope (SEM) and an optical microscope. The effects of thermokinetic loads on the damage mechanisms observed are discussed. Indentation and impact stresses are known to induce a particular damage mechanism: interlaminar cracking, known as delamination. Considered one of the most critical types of damage, delamination is driven by a material parameter called the energy restitution index G. The estimation of G remains a subject of debate today. This energy restitution index is generally studied using Double Cantilever Beam (DCB) tests. A series of DCB tests at different loading speeds and temperatures allows the effects of thermokinetic loading on the fracture behavior of the laminated composite under study to be investigated. The relevance of DCB tests at high loading speeds is then questioned in this thesis. Results from the literature highlight a dependence of the "material" parameter studied on the geometry of the test specimen. A phenomenon of multi-delamination in the laminated composite is highlighted and complicates the estimation of the fracture surface created. This further complicates the estimation of the critical energy restitution rate.

COMPOSITION OF THE JURY

• Ms. Catherine FROUSTEY, University of Bordeaux, Thesis Supervisor

• Mr. Laurent GUILLAUMAT, Arts et Métiers Rapporteur

• Mr.Jean-François FERRERO, Paul Sabatier University, Examiner

• Ms. Nadia BAHLOULI, University of Strasbourg, Rapporteur

• Mr. Jean-Benoit KOPP, Arts et Métiers, Examiner

• Mr. Julien JUMEL, ENSTA Bretagne, Examiner

• Mr. Pierre GERARD, ARKEMA, Guest

PRACTICAL INFORMATION

• Monday, December 9 at 2 p.m.
• Arts et Métiers Campus Arts et Métiers  Bordeaux-Talence
• LRL Lecture Hall
• Public defense