In operation, drill bit tips are subjected to cyclic loads and amplitude vibrations. These fluctuating load profiles induce cyclic stresses that can often result in catastrophic fatigue failure. To ensure drill bit tips are fit for purpose and to predict their expected service life, components must be tested under worst-case combined compression and torsional loads.

A specialist loadstring fixture, supplied by the drill bit manufacturer, was mounted onto an 8874 table top servohydraulic testing system. The standard system is capable of generating combined axial and torsional loads up to 25 kN and 100 Nm. The lower adapter was mounted directly to the lower T-slot table and features a chuck to hold the shank of the drill bit. The upper part of the fixture features a clamp to the carbide tip, which interfaces directly with the Biaxial Dynacell™ load cell.