Core drilling in reinforced concrete using polycrystalline diamond (PCD) cutters: Wear and fracture mechanisms

The wear and fracture mechanisms of PCD cutters active during the core drilling of reinforced concrete have been documented. All have analogies with well known mechanisms from rotary and rotary-percussive rock drilling and also metal cutting (machining). At rotational velocities up to 5 m/s and normal and cutting forces around 2000 N per 5 mm cutter (equating to principal stresses of around 500 N/mm2 at the cutting edge), gross fracturing of relatively un-worn cutters early in drilling is the predominant failure mechanism. Chipping at various size scales is observed with approximately the same rate of occurrence as cutter wear, which is mainly caused by attrition abrasion in concrete and to a lesser extent by chemical (diffusive) wear in the reinforcement steel. Chipping occurs by brittle fracture (unstable crack growth) at the small- to mid-scale and by fatigue crack growth at the large scale.