Parting Line Steel Preload Calculation for Multi Cavity Injection Moulds
Calculate multi cavity parting line preload by balancing machine clamp force against internal hydraulic separation force to maintain positive shut-off land sealing stress.
Compressive Fatigue
Meaning
Material failure resulting from repeated cyclic loading under pressure represents a primary concern for structural polymer components. Compressive fatigue occurs when a part is subjected to fluctuating loads that never transition into tension. This phenomenon leads to internal micro-cracking and eventual loss of part geometry.
Stress Cycle
Load amplitude and frequency determine the rate at which damage accumulates within the polymer matrix. Compressive fatigue is particularly aggressive in semi-crystalline resins where the crystalline lamellae can slide or deform under pressure. High-frequency cycles accelerate the onset of failure by preventing the material from recovering its original shape.
Hysteresis Heating
Energy dissipation during each loading cycle causes an internal temperature rise that softens the plastic. Compressive fatigue performance drops as this heat builds up, because the lowered modulus allows for greater deformation. A part might fail through thermal softening long before the mechanical limit of the resin is reached.
Service Life
Cumulative damage models allow engineers to predict when a component will no longer support its intended load. Compressive fatigue limits the use of certain soft-touch elastomers in high-repetition industrial seals or bumpers. When the internal structure of the polymer finally collapses, the part may show visible whitening or a permanent set that prevents it from functioning.
Engineers must account for the environment because moisture or chemical exposure can accelerate the rate of crack propagation under these specific load conditions. The test terminates when the part reaches a predefined level of deformation or a total loss of load-bearing capacity.