Dynamic fracture detection using the force-displacement reciprocity: Application to the compact compression specimen

Dynamic fracture toughness is determined by impacting fracture specimens and determining the onset of crack propagation. In such experiments characteristic impedance (actuator-specimen) matching problems can affect the accuracy of the measured forces. In addition, fracture time is mostly determined by means of surface rather than bulk devices (e.g. gages). In this paper we address these issues in linear-elastic materials. Based on the H-integral we show that either the measured forces or the displacements (whichever is more accurate) can be used to calculate the evolutions of the stress intensity factors. These evolutions must be identical by virtue of the reciprocity between forces and displacements, at least until some bulk fracture process develops. Examples are presented to illustrate how these observations can be applied to 'fine-tune' dynamic fracture experiments and complement fracture gage readings.