EVALUATION OF DATA REDUCTION METHODS FOR THE MIXED-MODE BENDING TEST

Results are presented from a combined numerical and experimental study to assess the accuracy of six different methods of data reduction for the mixed-mode bending test, These include two methods in the literat ure that use only the load data from the test, a modification to one o f these methods to improve accuracy, two variations of compliance cali bration, and a newly proposed ''load-deflection method.'' First, the a ccuracy of the various methods were evaluated by comparison to finite element predictions for a typical laminate, Second, the various method s were applied to double cantilever beam and end-notched flexure test data that had previously been reduced by well-established techniques, Finally, five laminates were tested in the mixed-mode bending fixture at each of five mode ratios: G(II)/G = 0.2, 0.4, 0.6, 0.8, and 1.0. Th e data from these tests were reduced by the various data reduction met hods. The mean value of the critical energy release rate G(c) at G(II) /G = 0.4 was compared to the mean G(c) obtained by compliance calibrat ion of a separate set of five single leg bending test specimens, and G (c) at G(II)/G = 1.0 was compared to the mean G(c) obtained by complia nce calibration of a separate set of five end-notched flexure test spe cimens, By these comparisons, by physical considerations of the test r esults, and by examinations of the standard deviations of the various data pools, it was concluded that a method that uses only load data fr om the test is the most accurate, For improved accuracy, a modificatio n to this method is suggested that involves only the experimental dete rmination of the bending rigidities of the cracked and uncracked regio ns and the use of these results in the reduction of data.