Optimizing the precision of the four-point bend test for the measurement of thin film adhesion

The four-point bend test (4PB) has emerged as the test method of choice for adhesion studies of thin films. The precision of the 4PB test is examined here by studying the effect of notch depth, pressing speed, specimen width, edge polishing, and pin spacing. It is shown that proper control of these variables is critical for obtaining high precision, statistically significant, and reproducible 4PB test data. Finite element analyses are presented in order to further understand and interpret the experimental results.