332 B. P. Wingate and M. W. Czabaj flexure specimen [0 2, 902, (+45, -45)2]s 0° 90° 0° 90° [03, 90, 75, 60, 45, 30]s X Y Z b a c Fig. 44.1 (a) Vertical flexure fixture and specimen designed for in situ imaging of damage evolution (b, c) Detailed specimen geometry and stacking sequences for each tested laminate a b 0 500 1000 1500 2000 2500 3000 3500 4000 Displacement (µm) 0 2 4 6 8 10 12 14 16 18 Load (N) 5 9.5 10 11.5 13 15 15.5 16.5 Specimen Response Scan Locations Displacement (µm) 0 500 1000 1500 2000 2500 3000 3500 4000 0 2 4 6 8 10 12 14 16 18 20 Load (N) 8.5 10.5 13 16 17 17 19 Specimen Response Scan Locations Fig. 44.2 Experimental response and scan locations for (a) 15◦ angle change specimen (b) 45◦ and 90◦ angle change specimen between adjacent plies. This stacking sequence was designed to promote interaction and simultaneous growth of transverse cracks and delaminations. Both stacking sequences included a stack of 0◦ plies on the top and bottom surfaces to increase the overall flexural rigidity of the specimens. Prior to testing, a semi-circular notch was machined into each specimen to ensure initiation of fracture in the gauge region. The exact stacking sequences and machined notch geometry are presented in Fig. 44.1b, c. X-rayCTin situflexure testing was done in displacement control at a rate of approximately 0.5 mm/min. At each notable damage event, identified from live X-ray projections or by a drop in load, the test was paused and the specimen was scanned. This process was repeated several times until sufficient damage accumulated in the gage region. The force-displacement response for each laminate is shown in Fig. 44.2. In this figure, the red dots correspond to load levels at which the test was
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