Stress Relaxation of Tufted Carpets and Carpet Components

Abstract

Dimensional stability of tufted carpets has been a continuing problem in the industry for years. When a tufted carpet is installed by the stretch method, it experiences stress relaxation over time which can cause the carpet to buckle, wrinkle and become loose with the only option being a costly re-stretching of the carpet. Since woven carpets seldom require re-stretching, the carpet buckling problem seems to be linked primarily to the tufted construction. This research seeks to analyze the various components of the tufted carpet composite structure and identify the role each component plays in the phenomenon of stress relaxation. Since a carpet is always stretched in both dimensions simultaneously during installation, understanding its biaxial stress decay is important. To this end, a biaxial loading system has been used to test various samples of the primary backing alone (before tufting), primary backing after tufting (with tufts), the secondary backing alone, and the finished carpet after attaching the backings with various binder weights per area. The four variables under consideration include: primary and secondary backing constructions, tufting density, and latex weight, with the secondary backing and latex weight expected to have the greatest effects on stress decay. In order to collect the most information, the biaxial test system was connected to a computer-based data acquisition system to continuously monitor stress levels and generate stress relaxation curves over a 20-hour testing period. A viscoelastic model that included representations of each component in the carpet structure was used to analyze and understand the influence of the components on the stress relaxation of carpets.