13th International Conference on Fracture June 16–21, 2013, Beijing, China 3 necessary to be defined at each nodal point along the front [18]. A half of element and element surface is related to the node in calculation of the energy release rate. In linear elastic fracture mechanics (LEFM), the energy release rate G is connected to the stress intensity factor K as: K= G⋅ E' , with E' = E for plane stress E 1− ν2 for plane strain ⎧ ⎨ ⎪⎪ ⎩ ⎪ ⎪ (3) In above equation, E denotes the Young’s modulus and µ Poisson’s ratio. 3. Experimental procedure Standard compact tension (CT) specimens (50mm wide × 12.5mm thick) confirming to ASTM E647 and rod specimens (10mm in diameter and 138mm long) are tested. The chemical components of the tested material AISI 304 stainless steel are given in Table. 1. The heat treatment of the raw material is undertaken in vacuum with 1100 °C for one hour and followed by quick cooling in air. The straight-front initial notch was generated in the rod by wire-electrode cutting. The initial flaw depth is taken 1.5mm for all load ratios. Table 1. Chemical composition of AISI304 Element C Si Mn P S Cr Ni (wt %) 0.040 0.41 1.05 0.035 0.003 17.1 8.1 All tests were performed on MTS 810 servo-hydraulic tension-torsion test machine at room temperature. The CT specimens were tested at the load ratios R=0.1, 0.3 and 0.5 with a loading frequency of 15 Hz. The rod specimens were tested at the load ratios R=0, 0.1 and 0.4 with a loading frequency of 10 Hz. To reduce the experimental error, two specimens were tested at a given loading condition and the test results show a good repeatability. All specimens were tested under a loading with sinusoidal waveform and in force control. Figure 4. Typical beach marked crack surfaces of CT (left) and rod (right) specimen. Instantaneous crack fronts were recorded by creating beach marks using a waveform that the mean load
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