Issue 40

Z. Zhang et alii, Frattura ed Integrità Strutturale, 40 (2017) 149-161; DOI: 10.3221/IGF-ESIS.40.13 157 (opening ratio of 10%). As shown in Fig. 8, the dissipation energy of SPA would increase as the opening ratio decreases, which also shows that the energy dissipation performance is much better than SPB. a.SPA b.SPB Figure 8 : Dissipation capacity comparison of different opening types of dampers with different opening ratios. Relationship between skeleton hysteresis curve and temperature rise A big percentage of energy absorbed from outside is dissipated as thermal energy during the irreversible process of fatigue, the amount of heat dissipation during the process is influenced by many factors, such as the load type, stress level, sample size, surface treatment status and surrounding temperatures. Thus the heat dissipation could reflect the energy dissipation during the process of fatigue, in other words, studying the heat dissipation could help study the law of energy dissipation of fatigue. The thermal energy produced during the deformation of materials is the product accompanied with the evolution of crystal microstructure, and it is not related with the damage revolution process. But the change of temperature field due to heat dissipation could reflect and monitor the evolution process of microstructure flaws and the plastic deformation of crack tip. The amount of heat dissipation could reflect the difference during different damage processes and also reflect the irreversibility of material fatigue damage. The relationship between the mechanical performance and average temperature rise for dampers with four different opening ratios is shown in Fig. 9. As shown in the figure, the temperature field for the sample was taken by the Infrared camera at the peak load displacement of 1mm and 6mm, the inflection point of temperature rise almost corresponds to the yield point of skeleton hysteresis curve, which indicates that the heat energy during the elastic period is much less while the temperature rise increases suddenly after the yield point and would keep increasing during the stiffness degeneration period. Also the local temperature rise is much higher with higher opening ratio for the same displacement load. For the specific dampers, the highest local temperature rise locates near the holding position of the sample for SPA10 and SPA15, while SPA20 and SPA25 happens near the openings, which indicates that the local plastic yield is the key to induce the average temperature rise of the whole plate. Also, the temperature rise of SP10 is less than the three other dampers, and the yield point is not very obvious, which is caused by the warping effect that results in the out-of-plane of the center in the damper during the experiment. This is because there is elastic deformation along the direction perpendicular to the neutral layer, the temperature rise near the sample holding position is much higher than the opening location of the plate, so the local temperature rise was not obvious and the steel damper did not yield yet. The total work due to load provided such energy that caused the out-of- plane and could increase the total hysteresis dissipation energy. The out-of-plane deformation, instead of damage, caused the stiffness degeneration along the loading direction. In contrast, the out-of-plane phenomenon is not very obvious due to large opening ratio, so damage is the main reason that causes stiffness degeneration so as that the temperature rise is higher. The change of thermal energy for the four dampers is shown in Fig. 9, in which Fig. 9a and b shows the thermal dissipation energy and thermal convective energy during the experiment. In Fig.9, the blue line is the temperature signal; the green line is the energy dissipation; the orange line is the bearing capacity; and the pink line is the strength degradation of the different dampers. 0 2 4 6 8 10 0.0 5.0E3 1.0E4 1.5E4 2.0E4 2.5E4 3.0E4 SPA10 SPA15 SPA20 SPA25 Energy dissipation of sum-loop E(J) Displacement(mm) 0 2 4 6 8 10 0.0 5.0E3 1.0E4 1.5E4 2.0E4 2.5E4 3.0E4 Energy dissipation of sum-loop E(J) Displacement(mm) SPB10 SPB15 SPB20 SPB25