WINTEREV 04

winterev 04The EPMA European Hard Materials Group held the first meeting of its themed "WINTEREV" series at Teddington, UK on Friday 27th February 2004. The meeting was hosted by the UK National Physical Laboratory and was attended by 16 persons from industry, academia and RTOs. The meeting brought together centres of expertise and interested industrial organisations to discuss the various issues of toughness testing of hardmetals. The performance of hardmetals, in many applications, is toughness constrained. Industry uses toughness measurements in dialogue with customers and it is necessary to understand the dependence of this property on structure. Fracture toughness tests are viewed as essential by some industrial companies, both for internal and external material comparisons and for conducting trade with customers. However, other companies tend to use these test methods for research and quality control rather than in customer specifications. Fracture toughness tests are thought to be relevant in making assessments of fitness for purpose, but are not often used as a design tool – because function is usually determined by a suite of properties, and the engineer uses a combination of experience and data to assign hardmetals that fit a specific need.

There is a range of different tests for hard materials for measuring fracture toughness, KIc; the parameter that controls the propagation of cracks in brittle materials. Some of these test methods have been accepted by international standards bodies. However, in several cases the standards bodies offer more than one test, without guidelines as to which test method should be used on which material, and under which conditions. The main problem with all these tests is introducing the stress-free crack required for pre-cracking, usually from a machined notch; for this reason certain tests give more variable results than others, and there are differences in values measured, dependent on test methods. Other important variations are often introduced by heat treatment and surface polishing. The meeting concluded that there was a need for test methods to be rationalised and accompanied by clear guidelines for use.

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