【作者】 徐旺；

【导师】 武岳；

【作者基本信息】 哈尔滨工业大学 ， 结构工程， 2011， 硕士

【摘要】 膜结构是20世纪中叶发展起来的一种新型张力结构形式。膜材作为膜结构的主要承力构件,直接影响到膜结构的安全性和耐久性。由于我国的膜结构发展历史较短,以往人们对膜材的研究大多集中在其强度指标上,目的是满足一般工程设计的需求。随着膜结构建筑的广泛应用,以及一些大型复杂膜结构的建造,膜材以及膜结构的耐久性研究逐渐受到人们的关注。但是由于膜材的耐久性研究费用高、周期长,因此相关工作开展的尚不够充分。本文以建筑用PTFE膜材为例,开展了较为系统的蠕变试验和自然暴露试验研究,建立了膜材的蠕变本构模型,给出了考虑环境因素的膜材强度随时间衰减曲线,为进一步研究膜结构的耐久性提供了宝贵的数据资料。论文工作主要包括以下三方面:(1)PTFE膜材的蠕变本构模型研究。基于复合材料的粘弹性理论,探讨了PTFE膜材的蠕变特性和蠕变机理,指出蠕变是普弹变形、高弹变形以及粘流变形三部分叠加的结果。通过对一维应力及多维应力蠕变理论模型、常用的蠕变经验模型和材料的粘弹性力学模型进行探讨,提出了PTFE膜材的蠕变本构模型——改进的时间硬化模型,为后续的PTFE膜材蠕变特性研究提供了理论指导。(2)PTFE膜材的蠕变特性试验研究。设计并完成了3种不同应力水平下PTFE膜材的蠕变试验,蠕变试验时间为24小时,获得了PTFE膜材经向和纬向试件的蠕变应变—时间曲线。采用改进的时间硬化模型作为PTFE膜材的蠕变本构模型,根据膜材经向和纬向试件在不同应力水平下的蠕变试验曲线确定了本构模型中的参数。研究结果表明,改进时间硬化模型能够较好的描述PTFE膜材的蠕变特性;PTFE膜材的抗蠕变性能较好,且经向抗蠕变性能优于纬向。(3)PTFE膜材在寒冷地区的耐候性能研究。开展了PTFE膜材在哈尔滨地区的长期自然暴露试验研究,获得了暴露1年、2年和4年的膜材试样,通过测试试样的拉伸强度和撕裂强度,拟合出PTFE膜材的经向和纬向强度随时间变化曲线。基于拟合曲线可以对PTFE膜材在使用若干年后的力学性能进行预测,为膜结构的耐久性设计提供了依据。更多还原

【Abstract】 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.更多还原