Proposal of New MOTE Methods for Brittle Fracture Toughness Determination

Abstract

If more than one fracture toughness test is performed for the same material, the representative fracture toughness value is obtained from the minimum of three equivalent (MOTE) in accordance with the related standards. MOTE is evaluated by referring to the lowest value of the test results when the number of results is 3 to 5, the second lowest when 6 to 10, and the third lowest when 11 to 15. With the conventional process, it is clear, however, that the value depends on the number of test results. When comparing the MOTE evaluation values with 3 and 5 test results, the MOTE based on 5 results is statistically lower than that with 3 results because both MOTEs refer to the lowest value, while increasing the number of test results from 5 to 6 will increase MOTE because the reference of MOTE changes from the lowest value to the second lowest. However, we are of the view that the number of test results should not affect the evaluation value.

Based on the above, we considered two new evaluation methods which are independent of the number of test results, and investigated the effectiveness of those methods by analytical and experimental approaches. As a result, the proposed methods continued to give a constant evaluation value regardless of the number of tests, and the variance was less than that of the conventional method in many cases. Therefore, we concluded that the proposed methods are superior to the conventional method.