Viscoelastoplastic modeling of compressional behaviors of kapok fibrous assembly

• Published in: Textile research journal 2014-10, Vol.84 (16), p.1761-1775
• Main Authors: Yan, Jinjiang, Wang, Fumei, Xu, Bugao
• Format: Article
• Language: English
• Subjects: Assembly; Cellulose fibers; Compressing; Compression testers; Constitutive relationships; Fibers; Mathematical models; Studies; Textiles; Viscoelasticity
• ISSN: 0040-5175; 1746-7748
• DOI: 10.1177/0040517514528564

Kapok fiber is a kind of cellulosic fiber harvested from the kapok fruit and has many unique properties and potential applications owing to its high degree of hollowness. It is important to understand the mechanical properties of the kapok fiber under transverse compression because its hollow structure can be squashed easily. In this research, kapok fibers were carded slightly to form a kapok fibrous assembly (KFA) in which the fibers were straightened and parallel. A KFA was considered as an approximately isotropic matrix material in the transverse direction. The fiber arrangement in a KFA was geometrically modeled with a pipe-piling structure. The viscoelastoplastic model and its constitutive equations were established to characterize the mechanical response of the KFA under transverse compression. Three compressional stages (A – the viscoelastic stage, from the initial point 0 to the yielding point 1; B – the viscoelastoplastic stage, from the yielding point 1 to the point 2; and C – the senior viscoelastic stage, from the yielding point 2 to the point at the maximum compressional load) were observed from the stress–strain curve, and four parameters were determined to describe the elastic, viscoelastic, and viscoplastic behaviors under each compression cycle performed on the Instron compression tester. The results indicate that the variable elasticity of the KFAs exists throughout the total compression, viscoelasticity appeared only in stage C, and the viscoplastic property was evident in stage B. The KFAs did not exhibit viscoelastic behavior in stages A and B because the viscoelastic element of the Kelvin model failed to work in these two stages. The influence of conditioning humidity on the parameters was also investigated.