FRACTURE MECHANICS PROPERTIES AT INTERMEDIATE STRAIN RATES,TRANSFERABLE TO COMPONENTS

摘要

The evaluation of fracture mechanics properties at intermediate strain rates can be carried out on the basis of different standards.The starting point of the lecture is a comparative evaluation of the relevant standards and test procedures.The aim offracture mechanics tests at intermediate strain rates are not only general material characterizations but often the applicabilityof the determined parameters to bigger sizes in the evaluation of real components.In this situation the definition of componenttransferable material parameters is an important problem.In this context the crack initiation point is of dominant importance.Incase of multiple specimens testing typically the definition of the crack initiation point based on the results of stretch-zonemeasurements.With the scope of a bigger research program for the evaluation of the behaviour of bulk containers made of spheroidal graphitecast iron (ductile cast iron DCI) grad GJS-400 one task is the determination of component transferable fracture mechanic valuesat intermediate strain rates at different temperatures.This group of materials shows damage behaviour at intermediatestrain rates without typical stretching, located at the crack tip.Therefore the crack initiation value can not by determined bystretch-zone measurements.By static loading crack growth was detected as a process of dissociation of the graphite particlesand crack growth between the particles ('graphite-particle-blunting').Based on this scanning electron fractography of the DCIa characteristic microstructure parameter – the mean distance between the graphite particles – is used as the definition of thecrack initiation point.