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.
Out-of-Phase Strain
Meaning
Mechanical deformation condition where the peak load and the peak displacement of a battery component do not coincide in time. In the context of battery packs, out-of-phase strain is often observed in the interconnects and busbars during combined thermal and vibration loading. This misalignment between stress and reaction can lead to accelerated fatigue failure in the welded joints of the electrical system.
Fatigue Mechanism
Mechanism of the damage is driven by the lag between the rapid vibration of the vehicle chassis and the slower thermal expansion of the cells. When out-of-phase strain occurs, the material experiences higher energy dissipation per cycle than in a synchronized load state.
Testing Protocol
Protocol for evaluating this effect involves specialized thermo-mechanical fatigue testing in a laboratory. Engineers apply out-of-phase strain to busbar samples by heating the material while simultaneously applying compressive force to simulate the constraints of a rigid pack housing. The test reveals how the grain structure of the copper or aluminum degrades under the contradictory forces of expansion and external pressure.
It is a critical metric for predicting the life of heavy-duty truck batteries that endure constant road vibration while cycling at high temperatures. Data from these tests allow manufacturers to select alloys with higher ductility for critical electrical pathways.
Design Countermeasure
Countermeasure for this failure mode includes the use of flexible braided connectors or expansion loops in the wiring harness. Designing for out-of-phase strain ensures that the battery remains electrically stable even when the physical housing is subjected to complex multi-axis loads.