Time-Dependent Relaxation
Decay of internal tension in a textile material held at a constant stretched state occurs over a period of time. This phenomenon, termed viscoelastic stress relaxation, is common in polymer fibers and affects the shape retention of garments. It happens because the molecular chains in the fiber slowly reorganize to relieve the applied stress.
Viscoelastic Behavior
Synthetic fibers exhibit both elastic and viscous properties when subjected to mechanical forces. During viscoelastic stress relaxation, the initial high force required to stretch the material decreases, even though the elongation remains constant.
Testing Protocol
Laboratory tests record the change in force over time under controlled temperature and humidity conditions. High temperature accelerates viscoelastic stress relaxation, which is a factor during industrial processes like heat setting. Technicians use these curves to determine the stability of different yarn types.
The test run is completed over several hours to capture both the rapid initial decay and the slower long-term relaxation. This data is critical for predicting yarn behavior during knitting or weaving.
Product Performance
Elastomeric yarns in stretch garments must maintain their recovery force to keep the clothing tight against the body. Excessive viscoelastic stress relaxation can cause the garment to bag and lose its fit over time. Manufacturers test these yarns to ensure that they maintain adequate tension.
Proper testing ensures that the final garments meet the expectations of consumers.
