A new approach to evaluate fracture toughness of structural materials

A new method, designated as Spiral Notch Torsion Test (SNTT), is developed recently to measure the intrinsic fracture toughness (K-IC) of structural materials. The SNTT overcomes many of the limitations inherent in traditional techniques and makes it possible to standardize fracture toughness testing. It is uniquely suitable for testing a wide variety of materials used extensively in pressure vessel and piping structural components and weldments, including others such as ceramics, their composites, and concrete. The SNTT system operates by applying pure torsion to uniform cylindrical specimens with a notch line that spirals around the specimen at a 45 deg pitch. The K-IC values are obtained with the aid of a three-dimensional finite-element computer code. TOR3D-KIC, developed at Oak Ridge National Laboratory (ORNL). The fundamental mechanism of SNTT approach is also described in the paper.