Investigation On The Mesoscopic Deformation Mechanism And Constitutive Relation Of Pre-Impregnated Fabric

The space inflatable structure is a novel structure applied in space engineering. Because of the light mass, small folded volume and high deployment reliability and so on, it becomes a valid path for building large space structure in future space engineering. Pre-impregnated fabric is the key material used in the space inflatable structure. However, because the resin of the pre-impregnated fabric is uncured, its deformation character and mechanism differ from the pure fabric material and the cured fabric composite. Consequently, the constitutive equations of pure fabric and the cured fabric composite can not be applicable to pre-impregnated fabric. Therefore, a constitutive equation is needed to be established according to the constitutive principle. The pre-impregnated fabric is made of fabric and uncured resin. As a result, the strengthened solid and fluid should be concerned in the research. This is a new mechanical problem. It extends composite material mechanics. Investigations on the constitutive equation of pre-impregnated fabric will provide the theories for designing and the statics, dynamics and thermal analysis research of the space inflatable structure.Shear finite deformation is the sole concern of this paper. Picture frame experiment is adopted to test the shear properties of fabric materials. Because pre-impregnated fabric is the viscoelastic material, of which deformation is associated with time, the present paper carries on the different displacement rate experiments. Obviously, nonlinearity and phases when pre-impregnated fabric is deformed can be further verified through experiment curve, which provides the basis for the establishment of the mesoscopic analytical model and the constitutive equation of the pre-impregnated fabric.Through analysis of every constituent mutual interacting and deformation mechanism of the pre-impregnated fabric, the shear deformation is divided by shear and compaction phases and some analytical models are built according to different phases. These models are the resin damping function and the crossover friction of the warp and weft tows in the shearing phase. Along with shearing, resin will be driven from the inter-tow region and the tows are interacted. In the compaction phase, a lateral compaction shear resistance moment is occurred. A balanced equation is built through these analytical models and a theoretical curve is obtained. The picture frame experiment curve is used to verify the theoretical curve and the two curves are well coincided.According to the properties of pre-impregnated fabric, Helmholtz free energy function is indicated by 5 variables from the second law of thermodynamics. On the principle of invariables, several invariants have been deduced which can describe the viscoelastic properties of pre-impregnated fabric. In response to basic theory of constitutive equation, a constitutive equation is obtained. This constitutive equation can objectively describe the viscoelastic properties of pre-impregnated fabric. At last, different displacement rates of picture frame experiments are used to verify the constitutive equation and the two curves are well coincided.