Meaning
Small internal cavities develop within a polymer matrix as localized stress concentrations grow and join together during tensile deformation. Micro-void coalescence occurs when the matrix undergoes plastic flow or ductile failure, separating the resin from secondary particles or rubbery phases. These gaps act as initiation points for fracture propagation within high-density polyethylene or polypropylene moldings.
Structural Failure
Ductile tearing proceeds through the connection of these internal gaps as the material reaches its limit of elongation. Mechanical energy consumption increases when the density of these cavities remains low, as the ligament between each void must undergo significant drawing before rupture occurs. Excessive filler content reduces the distance between sites, facilitating premature separation.
Processing Dynamics
Injection speed and holding pressure dictate the thermal distribution that governs how these internal structures form inside a tool. Rapid cooling traps residual stresses that lower the energy threshold for cavity formation during service life. Moulders mitigate the appearance of these internal defects by adjusting melt temperatures to ensure consistent morphology across the cross section of a part.
Economic Consequence
Increased scrap rates arise when these internal separations occur under standard operating loads, leading to brittle performance that falls outside expected material specifications. Regrind material often contains contaminants that trigger premature void formation, forcing a reduction in secondary processing cycles. Parts exhibiting heavy internal cavity structures fail to retain load-bearing capacity over extended duty periods.
