13th International Conference on Fracture June 16–21, 2013, Beijing, China -4- Fig.3 Shear stress-strain relationship of sintered nano-silver joint Fig.4 Shear strength of sintered nano-silver joint 3.2 Fatigue tests of fully reversed at elevated temperature 3.2.1 Fatigue behavior Figure 5 shows shear stress-strain hysteresis loop under different loading amplitudes. From Fig. 5 we can find that the shear strain amplitude increases with the loading amplitude increasing under fully reversed loading situation. The increasing of hysteresis loops with loading amplitudes demonstrates the larger energy dissipating per unit volume during a cycle, which results in fewer cycles. The plot of shear strain range versus number of cycles as shown in Fig.6 illustrates that the initial shear strain range increases as the increasing of the loading amplitudes. The evolution of shear strain range can be divided into three stages. The first stage has the longest duration of about 60-80 percent of the fatigue life and takes almost constant shear strain amplitude. When the fatigue test steps into the second stage of 80-90 percent of fatigue life, the shear strain slowly increases, which can be considered as the crack initiation. The final 10 percent of fatigue life is involving the third stage, during which the fatigue damage accumulation accelerates and results in ultimate failure. The true strain-stress hysteresis loops of the nano-silver joint at load amplitude of 6MPa and 8MPa are displayed at Fig. 7. The enclosed area of the hysteresis loop represents the cyclic plastic energy consumed in each cycle. At certain loading amplitude, with the increasing of the cycles, the enclosing area increases gradually. The enclosed area of hysteresis loop experiences a rapid increase before the nano-silver joint comes to the final failure.
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