Research On The Creep Performance Of Flax Fiber Reinforced Composites Under Hygroscopic Conditions

Due to the environment degradation,and more interests of people aroused on the environmental protection,eco-friendly composite materials are developing accordingly.As a kind of natural materials,natural fibers have abundant reserves,lower price,high specific strength,high specific modulus.Additionally,natural fibers have many particular advantages such as degradability and eco-friendly properties.Therefore,the application of natural fiber as the reinforcement of composite material is a development of advanced composite materials.Mechanical properties of natural fibers are degraded because if moisture absorbed in when they expose in moist air or in water.Natural fiber has an obvious creep performance.At present,the creep of natural fiber reinforced composites has not widely researched,and in the limited work attentions focused on the experimental study and the macroscopic fitting model based on phenomenological observations.In this work,micro-scale modelling of viscoelasticity of flax fiber reinforced composite is approached.Firstly,the advantages and disadvantages of various creep models were investigated.Three-parameter solid model was used to simulate the viscoelastic behaviors of both resin matrix and flax fiber.Six-element models to predict viscoelasticity of flax fiber reinforced unidirectional composites were proposed through arranging the three-parameter solid models of resin matrix and flax fiber in series and parallel patterns,respectively.Secondly,bulk resin,flax fiber and flax fiber reinforced unidirectional composites specimens were prepared,and the moisture absorption experiments of bulk resin and flax fiber reinforced unidirectional composite were conducted.The moisture weight gain curves results of the two materials show that moisture absorption processes agreed Fick's law.The creep tests of all these three specimens were carried out and their creep curves under different humidity were measured.The accuracies of the six-element models were verified by experimental studies.Finally,a humidity distribution dependent equivalent bending modulus model for bulk resin material was derived,in which the creep parameters relate to moisture content in exponent form.By averaging,an engineering formula was obtained through it.The comparation with experiment proves this simplified model can well characterize creep behavior of bulk resin material which with various moisture concentrations.