ISSN: 0884-6804
Page Count: 8

Redesign of the Mixed-Mode Bending Delamination Test to Reduce Nonlinear Effects
Crews, JH
Research engineer and senior scientist, NASA Langley Research Center, VA

Reeder, JR
Research engineer and senior scientist, NASA Langley Research Center, VA

Abstract

The mixed-mode bending (MMB) test uses a lever to apply simultaneously Mode I and Mode II loading to a split-beam specimen. An iterative analysis that accounts for the geometric non-linearity of the MMB test was developed. The analysis accurately predicted the measured load-displacement response and the strain energy release rate, G, of an MMB test specimen made of APC2² (AS4/PEEK). The errors in G when calculated using linear theory were found to be as large as 30% in some cases. Because it would be inconvenient to use a nonlinear analysis to analyze MMB data, the MMB apparatus was redesigned to minimize the nonlinearity. The nonlinear analysis was used as a guide in redesigning the MMB apparatus. With the improved apparatus, loads are applied just above the midplane of the test specimen through a roller attached to the lever. This apparatus was demonstrated by measuring the mixed-mode delamination fracture toughness of APC2. The nonlinearity errors associated with testing this tough composite material were less than ±3%. The data from the improved MMB apparatus analyzed with a linear analysis were similar to those found with the original apparatus and the nonlinear analysis.

Keywords:
composites, delamination, mixed-mode, nonlinear analysis, test apparatus, toughness, PEEK

Paper ID: CTR10078J
DOI: 10.1520/CTR10078J
ASTM International is a member of CrossRef.