Val-ExpNum

Experimental part

Part of Jérémy WOUTS' post-doctoral work concerned the characterization in longitudinal and radial compression of 3 wood species: balsa, oak and red cedar. The aim of this experimental campaign was to evaluate the effect of speed, lateral restrictions and orientation on the characteristic response of each species and, above all, on their energy absorption capacity. Investigations covered 4 loading speeds, 3 types of lateral restriction and 2 material directions. A total of 600 samples were tested during the first 6 months of the project. The experimental campaign was carried out following the methodology and protocols developed during Jérémy WOUTS' CIFRE thesis.

Additional tests were carried out on scrap machined in the longitudinal direction. The aim was to explore different solutions to suppress the initial peak observed in dynamics. Indeed, this type of peak is detrimental to energy absorption.

Additional tests were carried out on scraps machined in the longitudinal direction.

A post-processing procedure was also developed and tested during the thesis. The latter made it possible to establish analytical laws describing the evolution of critical parameters as a function of velocity. Comparison of the responses for different confinements enabled us to invalidate or confirm the validity of the reference test (static compression in rigid confinement) but also to interpolate the influence of lateral restrictions on the response of the 3 species.

Numerical part

The material model developed during the thesis was adapted to the 3 species. The material parameters required for the numerical simulation were therefore identified from the experimental tests.

The numerical model developed:

• Takes into account the velocity effect
• Restores fiber decohesion during longitudinal compression without lateral restriction
• Restores the dynamic peak observed for the longitudinal direction.

The material model developed has made it possible to validate drop configurations for absorbing hoods the following drop cases:

• Axial drop,
• The oblique fall with an alignment of the point of impact and the center of gravity,
• The wide-angle oblique fall (40-60°),
• The horizontal drop for which the wood is stressed transversely.