Refinements to the Mixed-Mode Bending Test for Delamination Toughness

Abstract

The mixed-mode bending (MMB) test for delamination toughness was first introduced in 1988. This simple test is a combination of the standard Mode I (opening) test and a Model II (sliding) test. This MMB test has become widely used in the United States and around the world for mixed-mode toughness measurements. Because of the widespread use of this test method, it has been standardized by ASTM Committee D30 as ASTM Standard Test Method D6671. During the standardization process a round robin test activity was conducted that led to several modifications to the test protocol. These modifications included a new method for calculating toughness from the measured test quantities, a more accurate way of setting the mixed-mode ratio to be tested, and the inclusion of a new alignment criterion for improved consistency in measured values. The rational for these modifications, which were included in the test protocol before standardization, are discussed in this paper.