Meaning
Creep compliance represents a time-dependent ratio of strain to stress in viscoelastic materials subjected to a constant load over a fixed duration. Designers evaluate creep compliance to predict how plastic components deform when exposed to long-term static pressure at varying temperatures. Data points gathered from short-term laboratory testing extrapolate the material behavior into the future service life of the finished part.
The measure ceases to provide accurate predictions once the temperature approaches the glass transition point or if the load exceeds the linear viscoelastic region of the polymer.
Performance Parameter
Engineers select resins by comparing the inverse of the modulus across multiple time increments to account for the gradual loss of stiffness. This creep compliance characterizes the susceptibility of a specific geometry to dimensional drift under mechanical stress. Regrind percentages within a feedstock mixture lower the molecular weight of the matrix and increase the numerical value of this property relative to virgin resin.
Moulding cycles must account for these variations because high internal stress levels increase the rate of deformation in the final assembly.
Material Specification
Datasheets report these values based on standard tensile or flexural tests performed under laboratory conditions. A professional laboratory controls environmental variables precisely to isolate the temporal response of the polymer chain. These published numbers offer a baseline for material selection rather than a guarantee of performance in actual field conditions.
Part geometry influences the actual strain rate in ways that generic material test bars cannot fully capture.
Economic Consequence
Inaccurate forecasting of long-term deformation results in high warranty claims or total assembly failure. Manufacturers avoid this liability by specifying materials with lower values for this property even when the initial unit cost remains higher. High creep compliance demands thicker wall sections or additional ribbing to maintain structural integrity throughout the intended lifespan of the product.
Proper selection of raw materials prevents the premature replacement of parts that sag or bind under continuous load.
