Meaning
Material deformation parameters quantify the reduction in volume that occurs when monomers bond into polymer chains. Tracking chemical shrinkage strain is necessary for predicting the final shape of a composite part. This contraction happens independently of thermal cooling.
Covalent Contraction
Molecular bonds occupy less space than the free-moving molecules of a liquid resin. As the curing process proceeds the chemical shrinkage strain builds up within the mold. This force can pull the resin away from the tool surface and create surface finish issues.
Geometric Deviation
Manufacturing precision suffers when the internal forces of the material cause the part to warp. Calculating the chemical shrinkage strain allows a tool designer to build a mold that is slightly larger than the final part. This adjustment compensates for the predictable loss of volume during the reaction.
Cure Progression
The timing of the contraction dictates whether the stress remains in the part or is relieved by flow. If the chemical shrinkage strain occurs while the resin is still liquid the material simply moves to fill the gap. Once the gel point is reached the contraction translates directly into internal stress that can lead to micro-cracking.
Monitoring the rate of this change provides the data needed to adjust the cure cycle for maximum part quality.
