1-112 Section 1 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 temper- ature 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. Stress vs. rupture life curves for creep may be nearly linear when plotted on log-log coordinates (Figure 1.6.15). FIGURE 1.6.12Practical 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. FIGURE 1.6.13Creep under constant load. dε/dt = A(σ) n . A and n are material parameters. FIGURE 1.6.14Stress relaxation under constant deformation. σ = σ 0 e –Et/η . E and η are material parameters. . log-log coordinates (Figure 1.6.15). FIGURE 1.6.12Practical fracture mechanics with NDE: nearly instantaneous measurement of crack size and the actual stress intensity factor via advanced thermoelastic. 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. Stress vs. rupture life curves