Volume 3, Issue 9 (October 2006)
Geometry and Data Reduction Recommendations for a Standardized End Notched Flexure Test for Unidirectional Composites
Recommendations are made for choosing a test geometry and data reduction method for a standardized end-notched flexure test for unidirectional fibrous laminated polymeric composites with glass or graphite reinforcements. To this end, the accuracies of a variety of commonly used data reduction methods are evaluated over a range of geometries. This is done using a combination of numerical and experimental approaches. It is determined that the compliance calibration method of data reduction, with an associated expression for compliance, C, of the form C=A+ma3, provides the best combination of accuracy and usability of all those data reduction methods considered. Here, A and m are curve fitting parameters and a is the crack length, and the expression for compliance is obtained prior to the fracture test by a series of compliance tests at different crack lengths to a load approximately equal to 50 % of that required for fracture. When this approach is used along with the associated recommendations for slenderness ratio of the specimen and roller diameters of the fixture, it is shown that the toughness that is extracted from the test will be within 3 % of its true value for materials with coefficients of friction, μ, along the interface containing a preimplanted insert of 0.0≤μ≤0.5. All materials for which experimental data are available show μ to be within this range. As such, this compliance calibration method is recommended as the sole data reduction method for the standardized test.