Quantitative modelling of viscoelasticity of isotropic fibrous composites with viscoelastic matrices

Despite the wide usage of isotropic fibrous composites with a viscoelastic polymer matrix,no analytic model for their mechanical behaviour is known.This paper develops such a model for time-dependent Young’s modulus,showing that for typical constituents the time constants of composites are up to about 6% greater than the matrix shear time constant.Viscoelasticity is strongly suppressed for stiff fibres even at modest fibre volume fractions.Comparison with known results for particle and oriented fibre composites confirms isotropic fibrous composites as between the two in terms of viscoelastic behaviour,but more similar to the latter.

Stress Distribution in Composites with Co-Phase Periodically Curved Two Neighboring Hollow Fibers

In this paper,stress distribution is examined in the case where infinite length co-phase periodically curved two neighboring hollow fibers are contained by an infinite elastic body.The midline of the fibers is assumed to be in the same plane.Using the three-dimensional geometric linear exact equations of the elasticity theory,research is carried out by use of the piecewise homogeneous body model.Moreover,the body is assumed to be loaded at infinity by uniformly distributed normal forces along the hollow fibers.On the inter-medium between the hollow fibers and matrix surfaces,complete cohesion conditions are satisfied.The boundary form perturbation method is used to solve the boundary value problem.In this investigation,numerical results are obtained by considering the zeroth and first approximations to calculate the self-equilibrium shear stresses and normal stress at the contact surfaces between the hollow fibers and matrix.Numerous numerical results have been obtained and interpreted about the effects of the interactions between the hollow fibers on this distribution.

Micromechanics of Thermal Conductive Composites:Review,Developments and Applications

Micromechanics investigations of composites with fiber-shaped reinforcement are extensively applied in the engineering design and theoretical analysis of thermal composites in the aerospace engineering and high-tech industry.In this paper,a critical review of various classical micromechanics approaches is provided based on the classification framework and the development of micromechanics tools.Several numerical micromechanics tools have been developed to overcome limitations through exactly/approximately solving the internal governing equations of microstructures.The connections and limitations of those models are also investigated and discussed,based on which three recently developed numerical or semi-analytical models are explained,including finite-element micromechanics,finite-volume direct averaging micromechanics,and locally exact homogenization theory,as well as machine learning tools.Since it is almost inevitable to mention the interfacial effects on thermal behavior of fibrous composites,we review the new mathematical relations that interrupt the original continuity conditions due to the existence of interphase/interface within unit cells.Generally speaking,the interphase/interface is demonstrated to play a significant role in influencing the effective coefficients and localized thermal fields.The present work also briefly reviews the application of micromechanics tools in emerging engineered woven composites,natural fibrous composites,and ablative thermal protection composites.It is demonstrated that sophisticated micromechanics tools are always demanded for investigating the effective and localized responses of thermal fibrous composites.

Biomimetics of Campaniform Sensilla:Measuring Strain from the Deformation of Holes

We present a bio-inspired strategy for designing embedded strain sensors in space structures. In insects, the campaniform sensillum is a hole extending through the cuticle arranged such that its shape changes in response to loads. The shape change is rotated through 90° by the suspension of a bell-shaped cap whose deflection is detected by a cell beneath the cuticle. It can be sensitive to displacements of the order of 1 nm. The essential morphology, a hole formed in a plate of fibrous composite mate- rial, was modelled by Skordos et al. who showed that global deformation of the plate （which can be flat, curved or a tube） induces higher local deformation of the hole due to its locally higher compliance. Further developments reported here show that this approach can be applied to groups of holes relative to their orientation. , The morphology of the sensillum in insects suggests that greater sensitivity can be achieved by arranging several holes in a regular pattern; that if the hole is oval it can be ＂aimed＂ to sense specific strain directions; and that either by controlling the shape of the hole or its relationship with other holes it can have a tuned response to dynamic strains. We investigate space applications in which novel bio-inspired strain sensors could successfully be used.

Optimization of Micro Structures to Elastoplastic Properties in Fiber Reinforced Composite Materials

The computational method (finite element method, FEM) in conjunction with micro mechanics is employed to design and analyze better micro structures of fibrous composites. In this way, the effective mechanical properties can be related quantitatively to the micro structures of the composites. For the optimal design , the geometric parameters are considered as design variables, and the effective elastic and plastic properties as optimal target functions. The effects of fiber shape and distribution on the effective elastic and plastic properties are examined. The numerical results indicate that the overall transverse properties are rather sensitive to fiber geometric parameters.