Multiaxial Critical Plane Strain Life Analysis for Conformal Cooled Tooling
Multiaxial critical plane strain-life analysis models out-of-phase thermal and pressure fatigue on internal conformal cooling walls to prevent die failure.
Fatemi-Socie
Meaning
Shear-based fatigue damage formulations incorporating maximum normal stress predict crack initiation in materials subjected to complex multiaxial strain cycles. The fatigue model known as Fatemi-Socie calculates micro-crack damage by combining cyclic shear strain range with peak normal stress normalized by material yield strength. Within battery structural design, Fatemi-Socie governs durability evaluation of aluminum structural frames, battery enclosure attachment brackets, and busbar connections exposed to combined torsion and bending loads.
The formulation governs shear strain range, peak normal stress, material sensitivity constants, and yield strength values. The criterion stops applying to brittle materials dominated by mode I tensile failure or situations operating under pure hydrostatic pressure where shear strains remain zero.
Parameter Formulation
The damage parameter multiplies maximum shear strain range by a term containing maximum normal stress divided by yield strength. A material-dependent coefficient adjusts how strongly normal stress accelerates shear-driven fatigue damage on the critical plane. Normal stress acts to open micro-cracks, reducing friction across crack faces during cyclic shear displacement.
Normalizing by yield strength maintains non-dimensional consistency across different alloy systems used in vehicle structures.
Critical Plane Search
Execution requires evaluating candidate planes across all spatial angles to locate the plane experiencing maximum damage. The orientation of maximum shear strain range defines candidate planes, and peak normal stress occurring during the shear cycle gets evaluated on those specific planes. Out-of-phase multiaxial loading causes the critical plane orientation to shift compared to in-phase loading profiles.
Numerical solvers calculate cumulative damage across complex load histories using rainflow cycle counting applied to shear strain histories.
Durability Testing
Engineering verification compares predicted fatigue lives against physical multiaxial test results obtained from hollow tubular specimens under combined axial and torsional loading. Battery enclosure structures undergo multi-axis shake table testing to validate predicted failure locations and cycle counts. Test engineers compare physical crack initiation sites against high-damage nodes identified by the Fatemi-Socie algorithm.
Errors in life prediction typically arise from inaccurate mean stress tracking or uncaptured surface roughness effects from manufacturing processes.
Strain-Life Multiaxial Fatigue Analysis for Conformal Cooled High Conductivity Aluminum Molds
Multiaxial strain-life fatigue analysis using critical plane models prevents early cracking in conformal cooled high-conductivity aluminum molds under thermal cycles.