Dynamic shear bands: an investigation using high speed optical and infrared diagnostics

This paper presents an experimental investigation of the initiation and pro pagation characteristics of dynamic shear bands in C300 maraging steel. Pre -fatigued single edge notched specimens were impacted on the edge under the notch to produce shear dominated mixed mode stress fields. The optical tec hnique of coherent gradient sensing (CGS) was employed to study the evoluti on of the mixed mode stress intensity factors. Simultaneously, a newly deve loped two-dimensional high speed infrared (IR) camera was employed to obser ve the temperature field evolution during the initiation and propagation of the shear bands. Possible criteria for failure mode selection are discusse d. The IR images, for the first time, revealed the transition of crack tip plastic zone into a shear band and also captured the structure of the tip o f a propagating shear band. These thermographs support the notion of a diff use shear band tip and reveal "hot spots" distributed along the length of a well-developed shear band. (C) 2001 Elsevier Science Ltd. All rights reser ved.