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Mechanics of Solids 2011 Part 9

Tham khảo tài liệu 'mechanics of solids 2011 part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 1-112 Section 1 FIGURE 1.6.12 Practical fracture mechanics with NDE nearly instantaneous measurement of crack size and the actual stress intensity factor via advanced thermoelastic stress analysis. The member s loading including boundary conditions need not be known to obtain reliable data using this method. Creep and Stress Relaxation Creep and stress relaxation are related time- and temperature-dependent phenomena with creep occurring under load control and stress relaxation under deformation control. In both cases the material s temperature is a governing factor regarding what happens. Specifically for most metals the creep and relaxation regimes are defined as high homologous relative dimensionless temperatures normally those above half the melting point in absolute temperature for each metal. Thus solder at room temperature creeps significantly under load while steel and aluminum do not. However some creep and relaxation may occur even at low homologous temperatures and they are not always negligible. For polymers the creep regime is above the glass transition temperature. This is typically not far from room temperature. Figures 1.6.13 and 1.6.14 show trends of creep and stress relaxation in the large-scale phenomenon region. FIGURE 1.6.13 Creep under constant load. da dt A a n. A and n are material parameters. FIGURE 1.6.14 Stress relaxation under constant deformation. ơ ơ0e Et h. E and T are material parameters. Stress vs. rupture life curves for creep may be nearly linear when plotted on log-log coordinates Figure 1.6.15