Dynamic Drop Tower Impact Qualification Parameters for Consolidated Battery Tubs
Dynamic drop tower qualification of consolidated battery tubs requires controlling impactor kinetic energy, strain-rate sensitivity, and elastic intrusion limits.
Cowper-Symonds Strain Hardening
Meaning
Computational material models use mathematical equations to represent how metals behave under high-speed loading conditions. The empirical model known as cowper-symonds strain hardening calculates the dynamic yield strength of a material as a function of the plastic strain rate. It governs the structural analysis of aluminum and steel battery enclosures, where high-speed impact forces cause the protective frame to deform rapidly.
The boundary of this model lies in its empirical nature, meaning it requires extensive experimental calibration and is less accurate outside the calibrated strain rate range.
Strain Rate
Material behavior changes during high-velocity impact events like those experienced in vehicle crashes. By applying cowper-symonds strain hardening, the simulation accounts for the increase in yield stress that occurs as the rate of deformation rises. Steel alloys often exhibit a notable strength increase at high strain rates.
Sourcing engineers use these dynamic properties to select lightweight alloys that offer higher energy absorption during impact.
Numerical Simulation
Explicit finite element analyses of battery housings depend on accurate strain rate inputs to predict intrusion distances. Incorporating cowper-symonds strain hardening prevents simulations from overestimating the deformation of protective shielding. The software adjusts the material flow stress in each element based on the local strain rate.
This yields a more realistic representation of the energy dissipation in the crush zone.
Experimental Verification
Laboratory testing of material specimens at different strain rates provides the necessary parameters for the model. Tensile tests conducted on high-speed servo-hydraulic machines yield stress-strain curves across multiple orders of magnitude. Sourcing contracts often require steel and aluminum suppliers to provide these high-rate test datasets.
Without this testing, the simulation model remains unverified.