A Criterion to Control Nonlinear Error in the Mixed-Mode Bending Test

Abstract

Abstract:The mixed-mode bending test ha_'.been widely used to measure delamination toughness and was recently standardized by \STM as Standard Test Method D6671-01. This simple test is a combination of the stal_dard Mode I (opening) test and a Mode II (sliding) test. This test uses a unidirectionai composite test specimen with an artificial delamination subjected to bending loads to characterize when a delamination will extend.When the displacements become large, the linear theory used to analyze the results of the test yields errors in the calculated toughness values. The current standard places no limit on the specimen loading and therefore test data can be created using the standard that are significantly in error. A method of limiting the error that can be incurred in the calculated toughness values L,.needed. In this paper, nonlinear models of the MMB test are refined. One of the nonlir, ear models is then used to develop a simple criterion for prescribing conditions where tht: nonlinear error will remain below 5%.