Experimental Crack Front Investigation of Unpoled Soft Lead Zirconate Titanate (PZT) Using the Single Edge V-Notched Beam (SEVNB) Method

The Single Edge V-Notched Beam (SEVNB) method is a well-known method to determine the R-curve of a material. Knowing the applied force and the corresponding crack length, the fracture toughness can be calculated easily under the assumption of a straight crack front. However, the crack front usually exhibits a curved shape when growing in a stable manner. Thus, for a measurement in which the crack length is determined optically, the discrepancy between measured and effective crack length needs to be considered. In this work, the crack front in PZT bending bars is investigated experimentally. The measurements have shown that the crack front takes its characteristic shape immediately after crack initiation and then propagates without changing its shape remarkably. The investigated bending bars exhibit a discrepancy of (275 +/- 8) mu m between optically measured and the maximum crack length in the middle of the crack front.