Meaning
Molecular level failure process involves the repeated breaking of polymer chain segments that have been stretched into fine strands across microscopic cracks inside a material. Fibril fatigue scission is the primary mechanism that causes micro-crazes in battery housings to transform into larger, visible cracks after thousands of small vibrations or thermal expansion cycles.
Mechanical Breakdown
Energy from cyclic stress slowly cuts through the physical bonds of the fibrils as each vibration pull on the tiny bridges between the separation voids. Any fibril fatigue scission eventually weakens the entire crazed zone until the bridge can no longer hold the opposing surfaces together against the internal pack pressures. This gradual cutting is difficult to detect early because it occurs deep within the microstructure of the polymer before any outward sign of weakening appears.
Scientists observe this under electron microscopes to determine how different additives in the plastic can slow down the breaking process and extend the total material life.
Environmental Factors
Chemical interactions with moisture or leaked electrolyte can accelerate the rate of this breaking by lowering the energy needed to sever the covalent bonds between carbons. Rapid fibril fatigue scission reduces the toughness of the plastic part which makes the battery container more likely to crack open during a collision or drop event. Observations show that cold environments make the fibrils more brittle and increase the scission rate because the segments cannot stretch and flex as easily to absorb the energy.
Heat also poses a risk because thermal vibrations add extra energy that facilitates the breakdown of long chain molecules into smaller fragments with less load bearing capacity.
Failure Boundary
Limit of the safe operating period is reached when enough strands have snapped to allow the micro-voids to merge into a single path for a deep fracture. Monitoring the frequency of fibril fatigue scission helps engineers define the replacement interval for structural components that are regularly exposed to harsh operating conditions. Materials that exhibit high resistance to this specific molecular decay are favored for load bearing tabs and mounting points where a structural break would lead to catastrophic module failure.
Final quality tests verify that the selection of polymers for high voltage barriers includes a margin of safety for this fatigue mechanism over the twenty year design target.
