PSI - Issue 28

6

Rhys Jones et al. / Procedia Structural Integrity 28 (2020) 26–38 Author name / Structural Integrity Procedia 00 (2019) 000–000

31

1.0E‐04

1.0E‐05

1.0E‐06

da/dN (m/cycle)

1.0E‐07

1.0E‐08

1.0E‐09

Fig. 1. Values of logarithmic da/dN versus logarithmic ∆√ re-plotted from Yao et al. (2108a). The three test programs are termed: ‘Yao Test 1’, ‘Yao Test 2’ and ‘Yao Test 3’. For the duplicate tests, ‘Yao Test 1’ and ‘Yao Test 2’, the two multidirectional DCB Mode I test specimens were made using 32 plies (i.e. giving a nominal thickness of 5.0 mm) and for ‘Yao Test 3’ the multidirectional DCB Mode I test specimen was made using 48 plies (i.e. giving a nominal thickness of 7.5 mm). Values are given in the legend for the pre-crack extension length, a p - a o , prior to the start of measurements from a DCB fatigue test. In Fig. 2 the results discussed above for the latest multidirectional work are shown together with the previously measured data using DCB tests which possess many different values of specimen thickness, type of lay-up, etc. The data are again plotted in the form of the log da/dN versus log ∆√ for various values of the pre-crack extension length, a p - a o , prior to the start of measurements being taken for a given fatigue test. As for Fig. 1, in general, as the initial pre-crack extension length, a p - a o , used for the measured set of data from a fatigue test is increased, then the plot of the log da / dN versus log ∆√ moves to the right. However, again, there is some scatter in the plots in this respect due to some inherent scatter in the experimental results.  √ G (√(J/m 2 )) Yao Test 1 9.9 mm Yao Test 1 20.9 mm Yao Test 1 29.3 mm Yao Test 1 38.0 mm Yao Test 1 51.3 mm Yao Test 1 62.9 mm Yao Test 2 11.4 mm Yao Test 2 20.5 mm Tao Test 2 28.4 mm Yao Test 2 37.4 mm Yao Test 2 70.6 mm Yao Test 3 12.8 mm Yao Test 3 20.6 mm Yao Test 3 33.7 mm Yao Test 3 46.7 mm Yao Test 3 58.8 mm Yao Test 3 88.4 mm 18 3