Creep And Weatherablity Characteristics Of PTFE Coated Fabrics

Membrane structure is a new type of tensile structure form developed since the middle of the 20th century. Fabric membrane material is the main load -bearing component in membrane structure, which directly influences the safety and durability of membrane structure. To meet the needs of the general engineering design, researches focusing on the strength indexes of coated fabrics have been carried out, for its short developing history in China.As the extensive application of membrane structures and the construction of some large scale and complicated membrane structures, durability of membrane structures and membrane materials is gradually concerned. However, researches on durability need high cost and a longer time, hence related works are not carried out fully. Therefore, this paper carries out comparatively systematic experimental researches on the creep and weather-ability characteristics of PTFE coated fabric, establishes the creep constitutive model of PTFE coated fabric, meanwhile curves describing the strength decrease with time of PTFE coated fabric considering environmental effects are given, offering valuable datas for futher researches on durability of membrane structures.The main researches of this paper are summarized in three parts:(1) Creep constitutive model research of PTFE coated fabric. Based on the viscoelasticity theory of composites, creep characteristics and mechanism of PTFE membrane material is discused, pointing out that creep is composed of general elastic deformation, high elastic deformation and viscous flow deformation. Meanwhile, one-dimensional and multi-dimensional stress creep model, creep experience model, and viscoelasticity creep model are also studied. At last, the creep constitutive model of PTFE coated fabric—modified time hardening model is proposed, providing theoretical guidance for researches on the creep property of PTFE coated fabric.(2) Experimental research on the creep property of PTFE coated fabric. Creep experiment of PTFE coated fabric under three different stress levels lasting for 24 hours is designed and accomplished, creep strain-time curves of of PTFE coated fabric warp and weft specimens are obtained. Modified time hardening model are used as creep constitutive model of PTFE coated fabric, and parameters of modified time hardening model are determined through creep strain-time curves of of PTFE coated fabric warp and weft specimens. The research results indicates that modified time hardening model can well describe the property of PTFE coated fabric, PTFE coated fabric is of good creep resistance, and warp specimens are better than weft specimens.(3) Weatherability of PTFE coated fabric in cold region. Long term outdoor exposure experiment on PTFE coated fabric is carried out, specimens after 1 year's, 2 years'and 4 years'outdoor exposure have been obtained and of which the tensile and tear strength have been tested, curves describing the strength variation with time of PTFE coated fabric warp and weft specimens are fitted then. Based on these curves, the mechanical properties of PTFE coated fabric after a number of years are predicted, providing the basis for durability design of membrane structure.