13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- Fig. 1. Scheme of the specimens, thickness 4 mm: a) specimen with central hole; b) specimen with edge crack. Specimens were stretched under static loads at electro-mechanical testing machine Instron 5582. Strain gauging data was registered using integrated transducer of the testing machine. Registration of acoustic emission (АE) signals was performed by PC-based hard-software measuring technique [7]. For analysis of acoustic emission data, the derivative on AE events accumulation over loading time (acoustic emission count rate) was calculated as the basic informative attribute of АE data. Surface imaging was carried out by Canon EOS 550D DSLR camera. The camera has been equipped by telephoto lens Canon EF-S 100-400 mm 1/4-5.6 IS. A certain region of the image was determined for calculation of the average value of shear strain intensity. For example, specimen with central holes the area of the image with the size of 3300×4950 pixels (the physical sizes ~32×52,5 mm) was taken. The sizes of the regions for strain estimation were chosen in order to ensure observation of formation and development of macro scale shear–bands for various types of specimens. Use of simultaneous registration has allowed us to register and compare parameters under analysis during entire time of the experiments 3. Experimental results 3.1. Macroscale level. Analysis of strain gauging data Loading diagrams of specimens with central holes and edge cracks are resulted in fig. 2. With increase of the notch dimension for both types of specimens the elongation and ultimate strength at fracture are decreased. The derivative dσ/dt was calculated and is shown on fig. 3. Further, for comparison of the deformation behavior of specimens with central holes and edge cracks, the results obtained by 3 methods for the composite specimen with ∅7 mm hole and 14,5 mm edge crack are described. Fig. 2. «σ-ε» graphs: a) specimens with open holes: 1) ∅7mm, 2) ∅10mm, 3) ∅13mm); b) specimens with edge cracks: 1) 14,5mm, 2) 18 mm, 3) 21,5 mm
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