Stress Distribution In Composites Research Articles

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.

Local stress distribution in composites for pulled-out fibers with axially varying bonding

We present a study on the local stress distribution in a composite for a single-fiber pulled-out model. We consider an interphase between a fiber of finite length and the matrix, and we take into account varying bonding conditions in the axial direction between the fiber and the interphase and between the interphase and the matrix. Bonding is modeled by a modification of the classical spring-layer model, in which the quality of bonding between two constituents is quantified by a proportionality constant that describes the ratio of the displacements to the acting shear stresses in an interface. The problem is studied for linear elastic and for viscoelastic problems by the means of the elastic–viscoelastic correspondence principle. In numerical examples, we illustrate the development of the normal stresses in the constituents and of the interfacial shear stresses for different bonding conditions as well as for viscoelastic creep in the matrix.

Micromechanical analysis of the stress transfer in single-fiber composite: The influence of the uniform and graded interphase with finite-thickness

• A new theoretical model is developed to analyze the stress transfer between fiber and matrix. • The interphase is assumed to be homogeneous or power-graded variation with radial location. • The present model is verified through a finite element model. • Stress distribution in composites are obtained under different conditions. A theoretical model is developed to analyze the stress transfer between fiber and matrix through the interphase with finite thickness. The Young's modulus of interphase is assumed to be homogeneous uniform or power-graded along radial direction while other material parameters are constants. The bonds between fiber and interphase as well as between interphase and matrix are perfect. The geometrical equations are strictly satisfied except that the radial displacement gradient with respect to the axial direction is neglected, as its magnitude is much smaller than that of the axial displacement gradient with respect to the radial direction. The equilibrium equations along radial direction are strictly satisfied, while the equilibrium equations along axial direction are satisfied in the integral forms. In addition, both the interfacial displacement and stress continuity conditions as well as stress boundary conditions are enforced exactly. Two coupled 2nd-order ordinary differential equations can be obtained in terms of average axial stresses in fiber and matrix. Finite element analysis (FEA) with refined mesh for single-fiber composite containing uniform interphase with finite thickness is developed to validate the present model. Series of parameter studies are performed to investigate the influence of interphase properties and thickness as well as the fiber volume content and model length on the stress distribution in composites.

Multiscale analysis of non-periodic stress state in composites with periodic microstructure

The size of a fine scale domain to be employed for accurate evaluation of a strongly non-periodic stress distribution in composites with periodic microstructure can be relatively large. Consequently, direct numerical simulation approach may become impractical.A method suggested to overcome this difficulty hinges on the Discrete Fourier Transform. It allows to determine a non-periodic stress field in the fine scale domain that includes many periodic cells by analysis of a single representative (repetitive) cell with Bloch type boundary conditions. The analysis is carried out with respect to the complex-valued displacements and stress transforms, and actual values of the stress strain field components at any point of the fine scale domain are given by the inverse transformation. The method is illustrated by the analysis of crack problems for the two-dimensional periodically voided material.

Elastic–plastic thermomechanical response of composite co-axial cylinders

A new method is developed in this paper to deal with the thermomechanical response of continuous fiber-reinforced composites. Treating the matrix as an elastic-perfectly plastic solid, the analytical formulae of the deformations and stresses of the matrix are obtained from the plasticity theory, axisymmetric equilibrium equation, and stress–strain and strain–displacement relations. The fiber is taken to be an anisotropic, elastic material, and the formulae calculating its deformations and stresses are also presented. The boundary conditions and the consistence of deformations and stresses between the fiber and matrix, and between elastic and plastic regions of the matrix are employed to determine the unknown constants in the analytical formulae. With the developed method, the thermomechanical stress distributions in composites reinforced with circumferentially orthotropic, radially orthotropic and transversely isotropic fibers are investigated, and how the elastic-perfectly plastic property and different materials of the matrix affect the thermomechanical response of the composites is discussed. For the thermomechanical loads and composite systems given in this paper, the elastic-perfectly plastic property of the matrix can reduce the compressive stresses in the fiber, and the tensile circumferential and axial stresses in the matrix. A strong matrix can raise the compressive stresses in the fiber, and the tensile circumferential and axial stresses in the matrix.

A Raman Study Into the effect of Transcrystallisation on Thermal Stresses in Embedded single Fibres

Thermal stresses have been measured in single carbon fibre polypropylene matrix composites using micro Raman spectroscopy. The study focuses on the influence of a transcrystalline interlayer on the thermal residual stress distribution in composites. A series of three experiments were made in order to systematically study the influence of thermal history, transcrystalline interlayer thickness and matrix supermolecular structure. From the experiments it was shown that the transcrystalline interlayer results in higher thermal residual shear stress. This was explained by anisotropy in the transcrystalline interlayer resulting in higher radial thermal expansion and thus higher radial stress.

Effects of material properties of interfacial layer on stresses in fibrous composites subjected to thermal loading

In the present work, the effects of material properties of the interfacial layer (or coating) on the stress distributions in unidirectional fibrous composites subjected to a thermal loading are elastic–plastically analysed based on a a four-phase model consisting of fibre, coating, matrix and surrounding body. A linear strain-hardening stress-plastic strain relation with temperature independence is proposed to describe the plastic behaviour of the coating. The governing equation for the coating is established and its closed form solution is obtained based upon the Tresca's yield criterion and the associated flow rule. Some numerical examples are provided to illustrate the effect of the material properties of the coating on the stress distributions in the composites. The results indicate that the use of a plastically deformable coating with a combination of material properties that is able to smooth out the property mismatches between fibre and matrix can reduce the stresses in the coating and the associated risk of interfacial failure under thermal loading.

Raman spectroscopic study of the stress distribution in continuous fibre-reinforced ceramic matrix composites

Raman spectroscopy was applied to silicon carbide/carbon continuous fibre-reinforced ceramic matrix composites to study the microstructure and composition changes in the fibres in the matrices after the consolidation of the composite at high temperatures by hot pressing, and also the stress distributions in the composites using the reinforced fibres as sensors. © 1997 John Wiley & Sons, Ltd.

Spectroscopic-mechanical analysis of stress distribution in composites

A Raman spectroscopic-mechanical technique has been used directly to assess the effects of temperature and thermal history on the stress distribution of model composites. The experimental data describing the stress distribution are consistent with previous theoretical studies. However, a quantitative interpretation is still unavailable due to the lack of information regarding the structure and properties of the reinforcement fibres used in the composites.