Recent research on methods of determining the dynamic fracture resistance for rapidly propagating cracks has progressed to the point where standardized testing procedures are being proposed. Because direct measurements of dynamic fracture resistances cannot be made, the resistances must be inferred from other measurements. In the present paper, an analysis which is fundamental to a method whereby the dynamic fracture toughness as a function of crack speed can be inferred from measurements of the specimen's end displacement at initiation of crack growth and of the total crack extension is described. All of the reference curves required for making the inference are developed for a standardized CT specimen. The procedure for using these curves to establish the dynamic fracture toughness-crack speed relationship and the minimum fracture toughness is given.
Nomenclature
a crack length B specimen thickness E Young's modulus F fracture energy Gtm minimum fast fracture energy K stress intensity factor K1D fast fracture toughness KIm Minimum fast fracture toughness v Poisson's ratio P load on specimen compliance r extend of plastic zone near crack tip cry yield strength T kinetic energy U strain energy V speed of propagating crack W width of specimen 8pi. pin displacement Y~.d displacement at cracked end of specimen