Interface Of Dissimilar Materials Research Articles

Microstructure and strength of Al-sapphire interface by means of the surface activated bonding method

Sapphire (α–Al2O3) and Al were joined by means of the surface activated bonding (SAB) method in an ultrahigh vacuum at room temperature. Tensile tests have shown that failure occurred not along the interface but inside the Al bulk near the interface. High resolution transmission electron microscopy has revealed the formation of a direct interface between Al and sapphire, indicating the possibility to artificially fabricate an atomically direct interface of dissimilar materials at room temperature. However, an intermediate layer was partially observed, which might be attributed to the effect of fast atom beam irradiation of the sapphire surface.

Evaluation of Singular Stress Field at the End of the Interface of Dissimilar Materials Using Akin's Singular Element.

A three-noded triangular element proposed by Akin, which has a stress singularity of O (γ-λ), was investigated. A singular element was incorporated into a general-purpose finite element program MARC, in order to analyze the two-dimensional stress field of joints made up of dissimilar materlals. A typical eight-noded isoparametric element was also used to analyze the same problem. Finally, by comparing the accuracy and efficiency of the two example problems, we have shown that Akin's singular element is very useful for the analysis of the stress field at the interface of dissimilar materials.

Thermal Stresses and Their Singularities due to Temperature Discontinuity on the Interface of Dissimilar Materials (3D Analysis).

Thermal Stresses and Their Singularities due to Temperature Discontinuity on the Interface of Dissimilar Materials (3D Analysis).

A model of debonding instability for solid propellant rocket motor: Part I — Uniform longitudinal and transverse stress rate

The interface between a soft and a hard material is vulnerable to debonding because of the prevailing high stress gradient that could be further aggravated under dynamic transient conditions. Such a situation is common in a solid-fuel rocket motor where unstable debonding could be triggered from the initiation of a macrocrack near the interface. The transition from a survival state to a failure state requires knowledge of how the nonlinear, dissipative and nonhomogeneous effects of the dissimilar material interface would interact with load. The solid-fuel rocket motor problem is modeled by a three-layered composite system made of steel, adhesive and rubber under plane extension. Assessed are the time dependent nonhomogeneous deformation and possible failure modes. Only initial properties of the materials were used to determine the evolution of nonequilibrium response. This is made possible by application of the isoenergy density theory that accounts for internal heat generation and energy dissipation effects. Results are presented in two parts. In Part 1, the applied stress rates are assumed to be 0.75 ksi/s in both the longitudinal and transverse direction while Part II assumes different stress rates in these two directions. At approximately one second after loading, a slanted but straight macrocrack of about 5 × 10 −3 in. is predicted to occur in the rubber next to the interface. This initial crack was found to become unstable at eight seconds and was estimated to be close to the adhesive/rubber interface over a length of 1.88 in. The onset of fracture depended directly on the load transient behavior.

Thermal Stresses and Their Singularities due to Temperature Discontinuity on the Interface of Dissimilar Materials.

A thermal stress problem of a coated half-space due to a temperature discontinuity on the interface is solved exactly using the two-dimensional thermoelastic theory. Stress singularities at the point of discontinuity of temperature are obtained in closed form. The results show that the normal stresses have jumps of the inverse tangent type and the shear stress has singularity of the logarithmic type. From the comparison with the singularities of the corresponding problem of a point heat source at the interface, the important result is obtained that the types of singularities for the two problems are different but the intensities are the same. In other words, the types of singularities depend on the type of loading but their intensities depend only on the combinations of materials and do not depend on the type of thermal loading.

Thermal Residual Stresses in Bonded Dissimilar Materials and Their Singularity.

Thermal residual stress distributions on the interface and in the vicinity of the intersections of the surfaces and the interface of dissimilar materials are calculated by the boundary element method. Thermoelastic constant terms are calculated using Airy's stress function. The thermal residual stresses, when the thermoelastic constant terms are subtracted, show free-edge stress singularity. The value of the order of thermal residual stress singularity and the stress distributions agree well with the theoretical ones calculated using Airy's stress function. The thermal stress singularity disappears for certain ranges of wedge angles of the pair of materials, as predicted.

Preparation and properties of optically transparent, pressure‐cured poly(methacrylate) composites

AbstractThe objective of this work was to develop optically transparent glass fiber reinforced poly(methyl methacrylate) (PMMA) composites by matching the refractive index of the glass fiber reinforcement to that of the PMM, A matrix, thereby minimizing the quantity of light which is normally scattered and reflected at the interface of dissimilar materials. A pressure curing process is described for preparing composites 10 by 15 by 0.6 cm thick and containing up to ∼ 35% glass fiber. By curing at 65°C under 6.9 MPa N2 for 18 H, composites have been produced with optical quality surfaces and flexural strengths more than seven times that of commercial PMMA of the same thickness. A transparent composite containing 10.4 vol% of 13 μm diameter fiber had an 84% optical transmission (92% maximum for PMMA) at 600 nm and 25°C.

Stress based criterion for an interface crack kinking out of the interface in dissimilar materials

Fracture criteria of an interface crack out of the interface between two dissimilar isotropic elastic solids are proposed and discussed. The present criterion is based on the maximum stress (σ θmax) which can be characterized by the stress intensity factors for an interface crack before kinking. The predicted kinking angles are compared with those obtained by He and Hutchinson's energy release rate criterion and also with some experimental results.

異種接合材における自由縁特異応力場の支配領域とその消失

Free edge stress singularities on and near the interface of dissimilar materials were investigated using a characteristic equation deduced in terms of Airy's stress function and the boundary element method. The values of the order of stress singularities determined by boundary element analyses under uniform tension agreed well with the values calculated by using the characteristic equation. The stress singularities disappear for certain combinations of wedge angles of the pair of materials. The stress distribution calculated by the boundary element method in the vicinity of the intersection of the surfaces and the interface agreed well with that obtained by using the stress function.

講座 やさしい材料解析技術 高分解能電顕法による複合材料の異相界面解析

講座 やさしい材料解析技術 高分解能電顕法による複合材料の異相界面解析

Computation of stress intensity factors for interfacial cracks

Characteristic complex stress intensity factors for plane and penny-shaped cracks located at the interface of dissimilar materials are computed using the boundary element method. To improve the accuracy of the solutions, special elements that properly model the near tip displacement and stress fields are used at the crack-tip. The results show that the boundary element method procedure provides a highly accurate and efficient tool for the numerical solution of bi-material fracture mechanics problems. The numerical results also confirm the dependence of the stress intensity factors on material properties for interfacial cracks. Further, the results show that the -variation of stress intensity factors with crack length for the bi-material case is essentially identical to the corresponding variation in homogeneous material solutions.

Reminiscing on silane coupling agents

—When K. L. Mittal asked me to provide a historical account of the applications of silane coupling agents in adhesion, I decided to write in the form of a personal account of my last 45 years in this line of study. No attempt is made to make the history comprehensive, or to recognize the host of other researchers who have contributed to our understanding of adhesion across an interface of dissimilar materials. It has been an immensely interesting area of study with many practical applications in composites and bonded structures.

Impact Stress of a Bar Imperfectly Fixed Subjected to the Impingiment of Finite Mass.

When a striker of finite mass impinges on the end of bar which is imperfectly fixed at its distal end, the impact stress of striker and bar is analysed by accounting for reflection coefficient of stress wave at the striker-bar interface and terminal end of bar. The reflection coefficients of stress wave in this case are determined in the same way with the evaluation of reflection and transmission of wave passing through shafts having discontinuous cross-sectional area or interface of dissimilar materials. The results of analysis are compared with impact stress of bar perfectly fixed and experiment. The impact stress of bar imperfectly fixed is about 60%-80% of perfectly. The period of impact stress acting in imperfect fixing bar is shorter than in perfect fixing bar. Although the magnitude of impact stress predicted by the analysis is in agreement with the experiment, the shape of wave is a little difference. It is shown that the impact stress of striker-bar interface can be indirectly determined by evaluating the stress caused in striker.

Fracture criteria on kinking of a crack out of the interface in dissimilar materials.

The authors deal with fracture criteria on kinking of an interface crack out of the interface in dissimilar materials based on the maximum stress (σθmax) concept similar to the mixed-mode fracture criterion for a crack in a homogeneous material. If the bimaterial constant e of dissimilar materials is zero or small, the kinking angles can easily be determined independent of the distance r from a crack tip. However, if e becomes large, the kinking angles cannot be determined and the angles strongly depend on the distance r due to the oscillation singularity. This criterion is compared with the energy release rate criterion of He and Hutchinson.

General formulation and analysis of hyperbolic heat conduction in composite media

Some recent experimental results show the existence of reflections of thermal waves at the interface of dissimilar materials in superfluid helium. In light of these results, a theoretical investigation of thermal waves in composite is provided to give a theoretical foundation to the observed phenomenon. A general one-dimensional temperature and heat flux formulation for hyperbolic heat conduction in a composite medium is presented. Also, the general solution, based on the flux formulation, is developed for the standard three orthogonal coordinate systems. Unlike classical parabolic heat conduction, heat conduction based on the modified Fourier's law produces non-separable field equations for both the temperature and flux and therefore standard analytical techniques cannot be applied in these situations. In order to alleviate this difficulty, a generalized finite integral transform technique is proposed in the flux domain and a general solution is developed for the standard three orthogonal coordinate systems. The general solution is applied to the case of a two-region slab with a pulsed volumetric source and insulated exterior surfaces which displays the unusual and controversial nature associated with heat conduction based on the modified Fourier's law in composite regions.

Considerations on branching phenomenon of fatigue crack along the interface of epoxy plates with different Young's moduli.

Fatigue cracks growing perpendicularly to the interface of dissimilar materials often arrested or branched at the interface, This branching crack phenomenon seems to be important to improve the fatigue life of composite material or to evaluate the fatigue life. In this paper, the branching crack phenomenon is investigated in detail using epoxy dissimilar plate specimens with various Young's modulus ratios (E2/E1) and different bonded strengthes. It is found that the branching crack along the interface can occur in only limited conditions. That is, Young's modulus ratio E2/E1 is higher than 1.14 and an applied displacement range ΔV (or load range) is higer than a critical value, which becomes large with increase of E2/E1 and becomes lower in the case of iow bonded strength. A new model to explain these branching crack phenomenon is proposed and discussed based on linear fracture mechnics.

Heat transfer at the interface of dissimilar materials: Evidence of thermal-comparator experiments

A recent publication has drawn attention to a marked directional dependence of the heat flow at the interface of certain contacting metals, and considers the effect to be associated with the mechanism of conduction at the points of metallic contact. The effect is now investigated in terms of the reading of a thermal comparator having initial temperatures both above and below that of the test sample. No such directional difference is found in this way for the metal combinations for which the effect had previously been reported, namely steel and aluminium, and steel and aluminium alloy, nor is any difference found for the combinations of a metal (steel) with either a semiconductor (germanium) or an electrical insulator (a ceramic material based on soapstone), for which it is to be expected that differences in the heat conduction mechanism would be more pronounced. It is concluded that the use of the thermal comparator for thermal conductivity determinations is not complicated by any such directional effect.