inspected visually. The bi-material specimens were tested at all three temperatures in two orientations, with the load roller pressing on the CFRP and with the load roller pressing on the GFRP. 16.4 Results 16.4.1 DCB Results The bulk material GFRP-GFRP and CFRP-CFRP specimens showed no temperature dependence on the energy release rate as shown in Fig. 16.7. The CFRP-CFRP specimens do display a slight rising resistance curve at the ambient and elevated temperatures. This may appear to be evidence of fiber bridging, like in unidirectional composites, but this phenomenon was not observed during the testing. The GFRP has a critical energy release rate of approximately 280 J/m2 while the CFRP varied from 280–320 J/m2. The similarity is not surprising as they both contain the same matrix. The GFRP may be slightly less tough as the fracture surface appeared to fail at the fiber-resin interface as there was dry fiber on one of the fractured Table 16.1 Energy release rates for various test geometries Span (2L) Crack length GAvg (J/m2) COV (%) 102mm 0.3 L 2636 16.1 0.5 L 1434 5.0 0.69 L 1308 18.6 127mm 0.3 L 2532 15.1 0.5 L 1575 8.8 0.69 L 1319 25.2 152mm 0.3 L 3082 5.4 0.5 L 1282 1.6 0.69 L 1273 3.7 Fig. 16.6 Calculated energy release rates from varying initial crack lengths and spans 162 B.T. Werner et al.
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