13th International Conference on Fracture June 16–21, 2013, Beijing, China -6- 0 100 200 300 400 500 600 700 800 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 Load (N) Displacement (mm) Crack Growth from a initial length a0 A A0 B0 B 0 200 400 600 800 1000 0 200 400 600 800 0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 Energy (mJ) Load (N) Displacement (mm) Load External force Energy Stored elastic energy Fracture energy (a) (b) 0 20 40 60 80 100 120 140 160 180 200 0 100 200 300 400 500 600 700 800 0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 Crack length (mm) Load (N) Displacement (mm) Load Visual crack length 0 200 400 600 800 1000 0 20 40 60 80 100 120 140 160 0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 Energy (mJ) Visual crack length (mm) Displacement (mm) Crack length (mm) Fracture energy (c) (d) Figure 4. a) load-displacement curve for a specimen with a crack that grows with Δa length from initial length a0: A0ABB0 (External force energy); ABB0 (Stored Elastic Energy) and B0A0A (Fracture energy). b) Energy balance according to the displacement loading. c) Plot of load-displacement curve and crack front propagation measured by image analysis. d) Plot of fracture energy curve and crack front propagation. 3.3. Acoustic Emission Analysis The recorded AE data are presented with respect to both AE-event (located material change giving rise to acoustic emission) and AE-hit (detected and measured signal for each cannel). To perform comparison with the mechanical results (energy balance) we consider one of the most important characteristic parameter of the AE in the amplitude-time domain, namely AE energy. With conventional AE energy analysis, the AE waveforms are squared and integrated over time. Although that analysis produces an energy measure, the resulting units do not lend themselves to direct comparisons with other energy analyses.
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