Since the 1960's, fracture toughness parameters such as KIC, Crack Tip Opening Displacement (CTOD), and latterly JIC and R curves have been used by engineering designers to quantify the defect tolerance of components and structures subjected to both static and cyclic loads.

Exova Group has, for the past twenty years, been involved in the development of techniques for both standard and non-standard fracture toughness tests. For static fracture toughness testing a wide range of machines are available to handle all types of standard specimen configurations, e.g. bend, compact tension, centre cracked tension, etc. in a range of sizes up to loads of 2MN.

Exova Materials Singapore has accreditation for conducting standard fracture toughness tests and is equipped to provide materials data for the most sophisticated assessment techniques.

For many of the fracture toughness determinations a comprehensive suite of computer programs has been developed which enables rapid and cost-effective testing and analysis. For example, determination of JIC or J0.2 from a single specimen by the unloading compliance method.

CRACK GROWTH

As the techniques of engineering design and materials assessment become increasingly sophisticated, particularly

with the advent of low-cost, high-power micro-computers, engineers are utilising a much broader range of materials properties in their designs calculations.

One area in which there is a large amount of interest is Crack Growth. This may be Crack Growth under conditions of cyclic loading, sustained loading or stress corrosion cracking. Frequently Crack Growth rate is related to the applied loading via fracture mechanics parameters.

Exova Group has many years' experience in Crack Growth testing to national and international standards, as well as particular customer requirements. These tests can be carried out at cryogenic or elevated temperatures or under controlled environmental conditions and include:

Fatigue Crack growth rate testing: da/dN vs Delta K using an automatic system for control, data acquisition and analysis. Fatigue Crack Growth threshold determinations also using an automated control, data capture and analysis system. Sustained load cracking tests, including Stress Corrosion Cracking.
Fatigue Crack Growth under elastic-plastic conditions.

Exova Group has extensive experience in a range of potential drop techniques. These include applied current AC potential drop and pulse DC potential drop. The company also has experience in other methods of monitoring crack extension including compliance based techniques and bonded gauge methods.