Laurent Guillaumat

Influence of some test parameters on specimen loading determination methods in instrumented Charpy impact tests

Abstract This paper is devoted to the analysis of the influence of some test parameters on impact load and specimen displacement measurements in instrumented Charpy impact tests. As impact material behaviour is a multi-parameter problem, design of experiment method is used in order to organise test campaign and to assess the most influence variables. On one side, it is shown that procedures based on tup load measurement are strongly affected by test parameter setting. On the other side, methods based on specimen displacement estimation appear to be a simplest way due to limited dynamic effects on the sample.

Quasi-static and fatigue properties of a balsa cored sandwich structure with thermoplastic skins reinforced by flax fibres

This paper presents the results of several experimental analyses performed on a bio-based sandwich structure. The material studied is made up of thermoplastic skins reinforced by flax fibres and applied to a balsa core. It is produced by a single-step liquid resin infusion process. First, the skin–core interfacial properties were measured and compared with those of the existing materials. Then, several quasi-static and dynamic analyses were performed to study the flexural behaviour of sandwich beams. The elastic and ultimate properties of the skins and core were deduced from these flexural tests. In addition, a failure mode map was developed based on the existing theories to explain the failure modes observed under different boundary conditions. The influence of the statistical spread of the core’s mechanical properties on the failure of sandwich beams was considered. Moreover, fatigue analyses were conducted to determine the fatigue resistance of this bio-based structure. Its behaviour was compared with that of the previously tested non-bio-based sandwich beams. Finally, the fatigue loss factor evolution of this structure under several loading ratios was measured and discussed. This study aims to determine some of the main mechanical properties of this material to see whether or not it might be suitable for industrial applications currently using glass fibre reinforced polymer/foam cored sandwich structures.

Analytical and numerical study based on experimental investigation of different curved sandwich composites manufactured by filament winding process

Sandwich structures, due to their high stiffness versus lightness ratio, are used progressively in high performance products. In order to design these structures with the most appropriate dimensions and material combinations, relevant mechanical properties must be well understood. This work aims to estimate the elastic properties of composite sandwiches from a curved structure taking into account the manufacturing process. In the case of filament winding process, specimens are necessarily cylindrical or barrel extracted. In our case, these types of structures are tested in 3- and 4-point bending to analyze their behavior experimentally using predictive models and design rules. Different configurations are adopted for bending tests to analyze and discuss global mechanical behavior. Furthermore, the acoustic emission technique is used to detect the initial appearance of damage mechanisms and to examine their evolution in terms of amplitude peaks and localization. Finally, a correlation between these acoustic emission signals and the damage initiation mechanisms is proposed, considering their effects on the mechanical behavior of each tested material.