DC potential drop calibration in matrix-cladded Ti MMC specimens with a corner notch

The direct current potential drop (PD) technique has been employed to continually monitor the growth of a corner crack in continuous silicon carbide (SiC) fibre reinforced titanium matrix composite specimens with matrix cladding layers. The propagation of the crack can be divided into two stages: (i) in the monolithic matrix cladding layer; and (ii) in both the cladding layer and the composite region. The relationship between the PD value and the crack length has been calibrated by using a combination of heat tinting and beach marking techniques. Separate equations have been used to calculate the crack length in the two stages of crack propagation, and the influence of the volume of non-conducting SiC fibres in the composite region on the calculation of crack length in the second stage of crack propagation has been considered. The crack length deduced from the PD technique is within 5% of the actual lengths measured from specimen fracture surfaces.