INVESTIGATION OF PENCIL-LEAD BREAKS AS ACOUSTIC EMISSION SOURCES

Abstract

Pencil-lead breaks are widely used as a reproducible source for test signals in acoustic emission (AE) applications.Experimental and numerical studies are presented that focus on the differences in surface displacements obtained from pencil-lead breaks under different angles and free lead lengths.Experimentally, a setup for measurement of rupture forces during pencil-lead breaks was designed.The experiments were carried out with different lead diameters, different free lead lengths and under various angles with respect to an aluminum block.The measured forces were used as parameters for validation of finite element modeling of pencil-lead breakage.The model for the pencil-lead break source was developed using multi-scale modeling and dynamic boundary conditions.Various experimental conditions were simulated, and the resulting surface displacement and forces at the contact between lead and aluminum block were evaluated to obtain numerical source functions for pencil-lead breaks.A comparison is made between source functions of finite element simulation and analytical source functions as proposed in literature.The obtained source functions elucidate the difference in signal magnitudes for the various angles and lead lengths and yield insight in the microscopic processes during lead fracture.