13th International Conference on Fracture June 16–21, 2013, Beijing, China -3- Table 1. Chemical composition of Zr-4 tube Sn Fe Cr O Si Al C Hf N Pb 1.30 0.22 0.11 0.13 0.0096 0.0051 0.0130 0.0053 0.0040 <0.0025 Figure 3. Geometry of assembled specimen 2.2. Experiment Results Fig. 4 shows the fretting scars and cracks of two specimens for cases of maximum strain εmax=0.6%. Ellipse fretting scars are made after 104 cycles. And the crack does not occur at the middle of the contact area where the wear depth reached the maximum, but at the edge of the initial contact area. Fig. 5 shows the comparison between fatigue S-N curve of the standard specimens and fretting fatigue S-N curve of the tube specimens. σmax is the maximum engineering stress calculated by the measured force and the area of the section, σmin is the minimum one, and Δσ=σmax- σmin is the amplitude of the stress. Nf is the number of cycles when the specimen cracks. It is illustrated that the influence of fretting on the fatigue resistance occurs above 104 cycles and becomes stronger in higher cycle fatigue situation. The fretting decreases fatigue strength of material above 50% after 105 cycles. For cases of ε max=0.4~0.8% (specimen no.6~15), the results are listed in Table 2. l1 and l2 is the length of the fretting scars on two sides of the specimen, and d1 and d2 are the corresponding distances from the crack to the middle of the fretting wear scar. The mean value of d equals 0.52834mm, and variance of d equals 0.0416mm2.
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