Meaning
Natural or logarithmic measure of deformation used to describe large extensions in polymer melts. Hencky strain tracks the cumulative stretching of a material element, which is vital for predicting wall thickness in thermoformed parts. It differs from engineering strain by accounting for the changing reference length as the material expands.
Logarithmic Metric
Calculations for high-extension flows become more accurate when using this logarithmic approach. When a sheet is stretched to several times its original size, the linear measure fails to capture the true molecular orientation. Curves flatten.
Engineers use this metric to define the limits of a material’s stretchability before it undergoes necking or failure.
Stretching Process
Thermoforming machines pull the heated plastic into complex shapes that require the resin to withstand high levels of Hencky strain. If the material cannot reach the required strain level at the processing temperature, the part will tear. Heat distributes.
This measurement is especially useful for designing moulds with deep draws where the material must stretch significantly into the corners. Melt strength and the rate of extension influence the maximum strain the polymer can sustain during the vacuum phase of the cycle.
Calculating Values
Calculating these values accurately avoids the creation of weak points in the container.
