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Approche expérimentale et numérique de l'usure du carbure de tungstène sous impact-glissement

Abstract : Tungsten carbide cutting tools are very frequently used for tunnel boring machines, as inserts on the drag bits at the front face. With their high toughness, hardness and their wear resistance, they are highly suitable for this kind of application. During excavation, those tools are subjected to important mechanical stresses mostly represented as repetitive impacts combined with the sliding motion induced by the rotation of the cutting wheel. In this regard, their lifetime should be optimized in order to reduce the maintenance operations cost. This thesis highlights the wear mechanisms associated to the impact-sliding motion of tungsten carbide cutting tools. An experimental approach is presented with an impact-sliding test rig allowing to represent the contact dynamics closed to the one observed during the excavation. The test rig is developed with a ball/flat configuration. The ball undergoes a vertical sinusoidal motion derived by an electromagnetic shaker and impacts the inclined tungsten carbide sample. There are two vertical foils underneath the tungsten carbide, which slide backward during the impact: this induces the sliding motion. Three types of tungsten carbides with different chemical compositions, production processes and mechanical properties have been tested. AISI 52100 and SiC balls are considered in this study. Abrasion and adhesion are mainly observed on wear scars, with cracks initiation for the more brittle tungsten carbide. Wear volume depends on many factors : the impact energy, the number of impacts, the impact angle, the ball material, the hardness of materials and the environment under which they are tested. The reference material wears out the most with larger wear scars. The sliding motion contributes greatly on the wear and SiC ball tends to create a sacrificial layer in some conditions. Tests run under argon showed that adhesion is less likely to occur at the contact. Besides, a 3D finite element dynamic model has been developed with the use of ABAQUS/Explicit. Experimental data are taken into account in order to obtain simulation conditions analogous to those in the experimental study. This numerical approach gives an insight on wear phenomena involved in this impact-sliding contact. In addition to this, parameters that were unreachable experimentally could be calculated (sliding distance, friction dissipated energy, plastic deformation energy). Energetic wear coefficient, calculated experimentally, can be correlated with the dissipated energy and the plastic deformation energy. Cracking features are linked to the contact stress distribution. Numerical results provide an input on experimental data and help in understanding complex wear processes entailed in this impact-sliding conditions.
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Marième Fall. Approche expérimentale et numérique de l'usure du carbure de tungstène sous impact-glissement. Autre. Université de Lyon, 2018. Français. ⟨NNT : 2018LYSEC009⟩. ⟨tel-02537342⟩

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