The homogenisation of shear-torsion behaviours for orthotropic sandwich plates such as corrugated cardboards is a difficult task, even numerically. We decompose the plate torsion into two beam torsions in order to analytically calculate its torsion rigidity. A simple but fairly accurate model based on Bredt theory is proposed for the torsion rigidity of double corrugated core plates. The in-plane shear rigidity is also analytically determined using beam theory. For non-symmetric plate sections, an analytical formulation is developed for the shear-torsion coupling problem. Very good agreement is obtained between the three-dimensional shell simulations and our fast H-model for a non-linear buckling problem coupling the membrane-shear-bending-torsion effects.

Boriding is a thermochemical surface treatment used to improve corrosion and wear resistance of hardened steels. In this work, we study the effect of boriding treatment in solid medium on the cyclic fatigue resistance of C20 carbon steel. Specimens of untreated and borided C20 steel in a solid medium consisting of 5% B4C, 5% NaBF4 and 90% SiC were subjected to rotating-bend fatigue device. The results showed that the improvement in fatigue resistance carried by the boriding treatment on C20 steel is low. This was explained by the presence of FeB boride in addition to Fe2B boride, which leads to surface cracking.

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