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Optical methods have been developed to measure large strains. Two alternatives are presented: the first one uses a cross grating, obtained by an innovative manufacturing process and the second one uses a mark‐tracking technique. The production of the grating is based on the deposit of a thin film through a master grid under vacuum. This creates small studs independent of each other, on the specimen surface. For the grid interrogation two techniques are discussed, one using the analysis of the optical diffraction figure and the other one the Fast Fourier Transform algorithm. Markers are simply deposited on the studied surface with a pen and strain determination is then obtained by mark‐tracking. The experimental validation consists of several simple tensile tests. Experimental results for polymers and latex materials confirm the quality of measurement. Strains are measured for values up to 1,200% without loss of information, with a strain accuracy close to 5times10‐4 at minimum gauge lengths of 0.125 mm.

The aim of this work was to show the influence of spruce fibres on polypropylene, by way of an experimental thermo-mechanical approach. These studies were performed by the simultaneous measurement of the strain field and the thermal field. A digital image correlation method was used for the strain measurements. The thermal field was obtained with the help of an infrared camera. The heat equation established in the context of classical thermodynamics of irreversible processes allowed us to evaluate the heat sources. The main difference between the plain resin and the composite material was that the heat sources dissipated by the composite were locally lower. In tensile tests the plain material allowed the creation of a neck zone with very high strain values. In fracture tests, it also generated very high strains localised at the crack tip. For the composite, the results of tensile tests showed that the presence of wood fibres led to a quasi-brittle failure of the specimen. In fracture tests, a better overstress accommodation was observed near the crack tip by distributing the strains in a wider zone.

In this paper, an inverse approach based on gradient conjugate method for thermal conductivity tensor and heat capacity per unit volume measurement is summarized. A suitable analysis is done for the mesh in finite element method and for the time steps for the time integration. For a composite material, it is shown the importance to identify the thermal conductivity tensor components in the principal axes.

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