The quality of innovating PDC bits materials needs to be determined with accuracy by measuring cutting efficiency and wear rate, both related to the overall mechanical properties. Therefore, a lathe-type test device was used to abrade specific samples. Post-experiment analyzes are based on models establishing coupled relations between cutting and friction stresses related to the drag bits excavation mechanism. These models are implemented in order to evaluate cutting efficiency and to estimate wear of the diamond insert. From here, an original approach is developed to encompass cutting efficiency and wear contribution to the overall sample quality toward abrasion. Four main properties of PDC material were used to define quality factor: cobalt content in samples that characterizes hardness/fracture toughness compromise, other undesired phase as tungsten carbide weakening diamond structure, diamond grains sizes and residual stresses distribution affecting abrasion resistance.

No abstract

International audienceThis paper presents ananalysis of the excavation forces involved in the cutting action and in the frictionof a cutter/rock contact.A vertical lathe-type device provided data on the forces applied on a single cutterunder dry excavation conditions.A cutting device was used to perform cutting experiments with unwornand worn cutters.A tribometer wa sused to perform friction tests on the cutters wear flat previouslyrealized with the vertical lathe.The experiments display results conform to theliterature as the non-dependence of the cutting coefficient to the rock properties.Then, this study focuses on the cuttingforces and explains that these forces include a component of rocks hearing and impact friction.Theimpact friction is induced by the interaction between ejected rock particles and the cutting active area.The evidence of this impact friction is then brought by the formation of an eroded zone on the cuttingactive are

No abstract

International audienceThe tribological behavior of commercial roller cone bit inserts was studied by using a rotary tribometer and abrasive alumina counterfaces. Three cemented carbide WC–Co inserts were selected with different cobalt content and WC grain size distribution. During tests, a nominal load was set at 264 N, the velocity at 0.5 m ⋅ s− 1 and the test time at 1 h. The experimental measurements were performed using load, torque, displacement sensors, an acoustic emission sensor and four thermocouples. These measurements showed that the friction coefficient and the mean contact temperature decrease with the cemented carbide's cobalt content. The acoustic emission energy displayed a clear dependence with the mean WC grain size and the WC–Co fracture toughness. It was also found that the insert's wear is proportional to the load but not to the time (or distance). Eventually, a third body approach clearly showed that the inserts and the counterfaces contribute to form an interfacial abrasive paste. The stability, the composition and the cohesion of this paste govern the tribological behavior of the WC–Co/alumina contact