Strain Life
Empirical equation modeling low cycle fatigue behavior relates plastic strain amplitude to the number of loading cycles required to induce mechanical failure. The Coffin-Manson relation quantifies plastic deformation strain range in solder joints subjected to thermal cycling. The mathematical relationship governs fatigue life estimation for metallic interconnects under cyclic mechanical loading.
The relationship ceases to apply when elastic strain dominates plastic strain or when thermal dwell times introduce significant creep deformation that requires modified constitutive models.
Fatigue Calculation
Cyclic temperature swings induce thermomechanical strain due to coefficient of thermal expansion mismatches between joined materials. The relation converts calculated plastic strain range into predicted cycles to failure using an empirical exponent and ductility coefficient. Higher strain amplitudes dramatically shorten fatigue life because the relationship relies on a power law dependence.
Parameter Fitting
Isothermal mechanical fatigue testing yields raw strain and cycle data required to extract model constants. Precision extensometers and load cells record force and displacement hysteresis loops during mechanical cycling. Parameter verification requires fitting strain range against cycles to failure across multiple strain levels.
Standardized test procedures dictate specimen geometry and loading rates to prevent experimental artifacts from biasing the exponent.
Thermal Boundary
High ambient temperatures accelerate creep mechanisms that invalidate pure plastic strain assumptions. Temperature fluctuations alter material ductility constants during long term operational exposure. Stress relaxation during extended dwell periods shifts failure modes from pure plastic fatigue to creep strain accumulation.
The Coffin-Manson relation understates damage when thermal creep dominates structural response.
