Meaning
Time-dependent mechanical degradation processes in which polymers undergo concurrent inelastic deformation and microstructure deterioration under sustained or cyclic loads are driven by the rearrangement of molecular chains and the growth of microvoids. Structural simulation engineers analyze viscoplastic damage accumulation to predict the life expectancy of polymer components operating at elevated temperatures. This process differs from pure plastic damage because it depends on the rate of loading and the temperature of the material.
The limit of this accumulation marks the onset of macroscopically visible cracks.
Rate Sensitivity
High loading rates restrict the movement of polymer chains, reducing the rate of creep and damage progression under sudden impacts. Under slow or sustained loads, the material undergoes viscoplastic damage accumulation more readily as chains have time to untangle and slip. Temperature increases this molecular mobility, accelerating the damage rate even at low applied stresses.
Microstructural Softening
Voids and crazes grow in the amorphous zones between crystalline regions, reducing the load-bearing cross-section. This softening increases the stress on the remaining intact material, speeding up the failure process.
Processing Parameters
Moulding conditions that yield high crystallinity and fewer internal voids improve resistance to this long-term degradation. Using regrind material can reduce the molecular weight and increase the rate of damage accumulation, leading to early part failure. Controlling the cooling rate in the mold ensures a uniform crystalline structure that extends the service life.
