BS 8571 Test Method for Determining Fracture Toughness in Metallic Materials Using Single Edge Notched Tension (SENT) Samples

EUROLAB laboratory provides testing and compliance service within the scope of BS 8571 standard. This British standard gives methods for determining fracture toughness in metallic materials in terms of δ (crack tip opening displacement, CTOD) and J (experimental equivalent of J-integral) using single-sided notched stress (SENT) samples.

This British standard also provides a method for determining fracture toughness as resistance to ductile crack elongation (R-curve), or a single point determination of fracture toughness at the initiation of unstable crack elongation or pop-in. The method uses specimens notched and fatigue pre-cracked in the base metal, weld metal or heat affected zone (HAZ). The samples are loaded with tension and the force and crack opening displacement are recorded.

A test sample is cut from the source material. The sample is machined and notched to provide a test sample with the tip of the notch in the base metal, weld metal or HAZ.

During bending, a controlled alternating force is applied to the specimen, extending a fatigue crack from the notch tip to the target area. The sample is then tested in tension by clamping or pin loading the sample into the handles of a tensile testing machine.

Force and clip gauge displacement are recorded continuously during testing. To generate a resistance curve, a set of identical samples is tested against different displacements and then unloaded. These data, together with measurements of specimen and crack sizes, are used to determine fracture toughness and crack extension for the resistance curve. Alternatively, it is possible to test a single sample to obtain a fracture toughness value.

If specified by the customer, post-test metallography is performed to confirm that the crack tip is present in the target weld property or microstructure and to determine the microstructure in which crack elongation occurs.

The test sample temperature will be determined by the customer and will be controlled and recorded with an accuracy of ±2°C. For this purpose, a thermocouple or platinum resistance thermometer should be placed in contact with the surface of the sample no further than 5 mm from the crack tip.

EUROLAB assists manufacturers with BS 8571 test compliance. Our test experts, with their professional working mission and principles, provide you, our manufacturers and suppliers, the best service and controlled testing process in our laboratories. Thanks to these services, businesses receive more effective, high-performance and quality testing services and provide safe, fast and uninterrupted service to their customers.