Fracture Toughness Testing Now Performed at Laboratory Testing Inc.

Online, August 2, 2012 (Newswire.com) - Laboratory Testing Inc. (LTI) has added Fracture Toughness Testing to the list of materials testing services performed by the laboratory to ensure the safety, reliability and integrity of materials. The fracture toughness test is performed on a specimen with a pre-existing crack to determine resistance to further crack extension. Fracture toughness testing measures the conditions under which an existing crack in a material will lengthen when under prescribed loading conditions. LTI performs Fracture toughness tests to ASTM standards E399 and E1820. Fracture toughness is an important material property in design applications since flaws such as cracks, voids, inclusions, weld defects and discontinuities cannot be completely avoided. The fracture toughness test is also valuable in determining whether there is a danger of failure when a flaw is discovered in an existing structure.

The computerized fracture toughness test equipment at Laboratory Testing Inc. can generate 55,000 lbs. of tensile or compressive force. An environmental chamber controls the test temperature between -150° F and +350° F. LTI has fixturing to test various specimens in a range of sizes, including SE(B) (single edge bend) and C(T) (compact tension) specimens. The fracture toughness test requires a precisely
machined specimen prepared to specification. The Machine Shop at LTI prepares all required specimens including those with an EDM notch.

Fracture toughness testing according to ASTM E399 applies a continuously increasing load to the specimen and determines KIC. ASTM E1820 uses a rising load with periodic partial unloading to measure the instantaneous crack length and provides both KIC and JIC. The stress-intensity factor, "K", is used to characterize the fracture toughness of linear elastic materials, which are typically high strength materials that fail in a brittle manner. "J" describes elastic-plastic fracture toughness in more ductile materials which are better able to deform and resist crack growth under load. The Roman numeral subscript "I" indicates the test process in which a tensile load is applied normal to the direction of the crack plane.