Evaluation of Data Reduction Methods

Abstract

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 literature that use only the load data from the test, a modi® cation to one of these methods to improve accuracy, two variations of compliance calibration, anda newly proposed a load-de ection method.o First, the accuracy of the variousmethods were evaluated by comparison to ® nite element predictions for a typical laminate. Second, the various methods were applied to double cantilever beam and end-notched exure test data that had previously been reduced by well-established techniques. Finally, ® ve laminates were tested in the mixed-mode bending ® xture at each of ® ve mode ratios:GII/G = 0.2, 0.4, 0.6, 0.8, and 1.0. The data from these tests were reduced by the variousdata reduction methods. The mean value of the critical energy release rate Gc at GII/G = 0.4 was compared to the mean Gc obtained by compliance calibration of a separate set of ® ve single leg bending test specimens, and Gc at GII/G = 1.0 was compared to the meanGc obtained by compliance calibration of a separate set of ® ve end-notched exure test specimens. By these comparisons, by physical considerations of the test results, and by examinations of the standard deviations of the various data pools, it was concluded that a method that uses only load data from the test is the most accurate. For improved accuracy, a modi® cation to this method is suggested that involves only the experimental determination of the bending rigidities of the cracked and uncracked regions and the use of these results in the reduction of data.