Stress-Plastic Strain Power Law Relation

If the amplitude of plastic strain Asp/2 is plotted in a log-log scale as function of the stress amplitude AaJ2, usually a line is obtained. This is shown in Fig. 6.2 obtained using experimental data relative to hot rolled Man-Ten steel of 330 MPa yield and type RQC-100 steel quenched and tempered to 840 MPa yield strength from [1] and to ductile cast iron tested by Milella. The linear relationship that holds for almost all metals and alloys has induced Masing [2] to introduce a ffa— p dependence of the type 

6 Strain-Based Fatigue Analysis Low Cycle Fatigue 

Metal or alloy Heat treatment (7y/gy (MPa) n/n Cyclic behavior 

First number refers to monotonic condition, second to cyclic one 

Therefore, the unloading portion CD of the cycle can be described by the equation 

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