A principal cause of wear of in-bed heat exchanger tubes in bubbling fluidized bed combustors (BFBCs) arises from the collapse of bubble wakes and “teardrop” voids against the tubes. This collapse results in a hammering effect wherein very dense aggregates of bed particles are periodically driven upward, slamming against tube undersides with great force. This effect is simulated in a specially designed wear rig by quickly driving a specimen rod downward within a bed of fluidized particles. Through the use of this rig, many aspects of BFBC metal wastage have been reproduced, including wear rates, circumferential wear distributions and wear microstructure. In this study, acrylic and aluminum specimens coated with a thin gold layer were exposed in the wear rig for very short times in order to obtain information on the nature and distribution of impacts. Variations in impact size, shape, density, and type were observed around the circumference of the rod. There were similarities in appearance between these impacts and those found in impingement erosion and in two-body abrasion although the scale of damage was much less than that typically seen. Only one-quarter of the particle contacts with the surface were truly damaging. The mean time between damaging impacts at a specific location in the region of maximum wear was approximately 4 min. The principal mechanism of metal removal was probably low cycle fatigue resulting from three-body abrasion.