Tensile stress-yield strength ratio

The data in Tables I and II show that a decrease in the ratio of the tensile stress to tensile yield strength for PC caused an increase in the number of cycles to initiate wear. For PVC a decrease in normal load was accompanied by an increase in the coefficient of friction. Hence, the stress-to-strength ratio did not change and there was no significant change in the number of cycles to initiate wear. Both these relationships are consistent with Equation 1. 

Safety Factor The ratio of design burst pressure over the maximum allowable working pressure (MAWP) or design pressure it can also be expressed as the ratio of tensile or yield strength over the maximum allowable stress of the material. 

II shows that the number of cycles to Initiate the wear track Is Inversely related to the ratio of the tensile stress to yield strength. 

The ratio of the calculated maximum tensile stress to the tensile yield strength was negatively correlated with the cycles to initiate wear which is in agreement with Equation 1. For three very different polymers, PC, PVC, and UHMWPE it was found that the ratio of stress to strength also was negatively correlated with the cycles to initiate wear. However, the limited number of experiments would preclude any generalization of this finding. 

An indication of the inherent ability of a material to plastically deform locally in the presence of a severe stress-raiser is provided by the notch-yield ratio (NYR)—the ratio of the notch-tensile strength to the tensile yield strength. 

V = Poisson s ratio (Tf = flow stress (Tty = tensile yield strength (Tfu = tensile ultimate strength... 

Based on the stress-strain diagram the values tensile stress at yield cXy and tensile strength at maximum (7m as well as the associated normative yield strain and nominal strain 8tM or normative strain 8m at tensile strength as well as strain at break 8b can be calculated (Eqs. 4.6. 11). For completely recorded diagrams the nominal strain at break 8tB can be determined additionally (Eq. 4.12). Because of the dependence on software and test equipment, especially sampling rate, the tensile stress at break (Tb should not be used (Eq. 4.13). Due to the viscoelastic behaviour of the plastics modulus of elasticity in tension is determined as secant modulus between the strain limits of 0.05 % and 0.25 % (Eq. 4.14). If the transverse strain is recorded simultaneously using strain gauges Poisson ratio jl can be calculated (Eq. 4.15). 

For reinforcement, an appropriate minimum ratio of the ultimate tensile stress to the yield tensile strength should be defined, to ensure a minimum ductility. 

In case the validity of the ratio fjf = 2 between the ultimate compressive strength /, and yield strength (0.2% proof stress) could be considered, Rondal Rasmussen (2004), then the characteristic value of yield strength is 300 MPa and the design value may be estimated as 190 MPa. It is known that the tensile strength may be considered about one third of the compressive strength (about 60 MPa). 

A1 in Mg alloys increases strength and fluidity in casting. Mg-Al alloys are susceptible to SCC [63,100,101,103-109] in air, distilled water and chloride-containing solutions. SCC-induced fractures may occur at stresses as low as 50% of the yield strength. Figure 8.4(a) shows that SCC susceptibility increased as the Al content increased from 1% to 8% [106]. If the failure stress at 100000s is compared with values of tensile yield stress [110,111], the (ratio of failure stress)/(tensile yield stress) decreases to values somewhat lower than those in Table 8.1. The tensile stress values are for comparable material but may not be exactly the same as those in [106]. Nevertheless, Fig. 8.4 does indicate the high SCC susceptibility of some alloys. 

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