Meaning
Empirical relationship equations correlate plastic strain amplitude with the number of load cycles to failure in metals subjected to low-cycle fatigue. Fatigue calculations using the manson coffin law model material behavior where cyclic plastic deformation dominates over elastic strain. The equation expresses plastic strain range as an inverse power-law function of reversal cycles, featuring material constants derived from uniaxial strain-controlled testing.
Engineers apply this power law to predict thermal-mechanical fatigue lives in battery busbars and power electronics interconnects undergoing severe temperature cycling.
Strain Relation
Total strain amplitude splits into elastic and plastic components, with the plastic term governed by the fatigue ductility exponent and coefficient. Under conditions governed by the manson coffin law, plotting plastic strain amplitude against cycles to failure yields a straight line on logarithmic axes. The slope of this line reflects the material’s inherent resistance to cyclic plastic damage.
Parameter Calibration
Experimental determination of model constants requires fully reversed strain-controlled fatigue tests performed on standard cylindrical specimens. Data fitting establishes the fatigue ductility coefficient from the strain intercept at one half-cycle and the ductility exponent from the log-log slope. The parameters for the manson coffin law remain constant across moderate temperature ranges but shift under extreme thermal exposure.
Life Prediction
Structural software integrates the plastic strain formulation to estimate component life in high-strain pack locations. Modern battery enclosure designs use the resulting cycle counts to establish maintenance intervals.
