Evaluation and Influencing Factors Discussion of Combined Standard Uncertainty of Fracture Toughness

According to the test method of plane strain fracture toughness for metal material, the compact tension specimens were adopted to evaluate the combined standard uncertainty, and the uncertainty equations and the calculated values were given. Through the analysis, it was considered that the standard uncertainty was most affected by the condition load PQ, and the specimen geometry factor f(α) had a minor effect on the standard uncertainty. The accuracy and precision of the measurement of average crack length were the main influencing factor of the stress intensity factor. Finally, the influence on the crack flatness and measuring precision was analyzed and discussed from the aspects of specimen machining, clamp design, crack prefabrication and crack measurement.