Role of friction and loading parameters in four-point bend adhesion measurements

Abstract

The effects of salient testing parameters on four-point adhesion measurements of thin-film structures on silicon substrates were systematically studied. These included specimen geometry, applied displacement rate, and load point separation. Measured fracture energy values,Gc, were observed to increase as the ratio of applied moment arm to specimen thickness was decreased beyond a value of ∼4, particularly for specimens withGc> 5 J/m2. Testing parameters that affect the steady-state crack velocity were also found to affect reportedGcvalues. The resulting trends inGcvalues are shown to be related to loading-point friction and environmentally assisted cracking effects. Good practice testing guidelines are suggested to improve the accuracy and precision of four-point bend measurements.