Free-edge Stress Singularities Research Articles

Free-edge Stress Singularities and Edge Modifications for Fiber Pushout Experiments

A comprehensive investigation of the fiber pushout test reveals that the existence of free-edge stress singularities hinder the accurate measurement of interfacial shear strengths. An integrated analytical, numerical, and experimental investigation is conducted to remove the free-edge stress singularities by modifying the edge design in a model fiber pushout test. The proposed interfacial joint angles are applicable to most composite material systems. The microdroplet test is recommended over the fiber pushout test since the convex shape of the microdroplet matrix makes it a natural choice.

Dissimilar material joints with and without free-edge stress singularities: Part I. A biologically inspired design

An integrated experimental and numerical investigation was conducted for removing the free-adge stress singularities in dissimilar material joints. A convex inter-face/joint design, inspired by the shape and mechanics of trees, will result in reduced stress singularities at bimaterial corners for most engineering material combinations.In situ photoelasticity experiments on convex polycarbonate-aluminum joints showed that the free-edge stress singularity was successfully removed. As a result, the new design not only improves the static load transfer capacity of dissimilar meterial joints, but also yields more reasonable interfacial tensile strength evaluation. For convex polycarbonate-aluminum and poly(methyl methacrylate)-aluminum joint specimens, the ultimate tensile load increased up to 81% while the total material volume was reduced by at least 15% over that of traditional butt-joint specimens with severe free-edge stress singularities.

Dissimilar Material Joints With and Without Free-edge Stress Singularities: Part II. An Integrated Numerical Analysis

Dissimilar Material Joints With and Without Free-edge Stress Singularities: Part II. An Integrated Numerical Analysis

Dissimilar Material Joints With and Without Free-edge Stress Singularities: Part I. A Biologically Inspired Design

Dissimilar Material Joints With and Without Free-edge Stress Singularities: Part I. A Biologically Inspired Design

Dissimilar material joints with and without free-edge stress singularities: Part II. An integrated numerical analysis

Numerical investigations were conducted on plane and axisymmetric convex joints of polycarbonate—aluminum and poly(methyl methacrylate)—aluminum interfaces to gain a better understanding of the stress state along the interface and also to aid an experimental study conducted on the same issue. Two-dimensional plane—stress investigations of convex joints revealed the successful elimination of the free-edge stress singulatities along the specimen width although stress singularities, along the thickness direction, persisted. A convex axisymmetric design, with the same material combination and joining angles, proves to be a better design in order to achieve an overall elimination of free-edge stress singularities of dissimilar materials and structures.

Design for Scarf Joint by Paying Attention to Stress Singularity for Free-Edge of Dissimilar-Metal Interface.

The scarf joint of dissimilar-metal is useful to increase the bonded area. However, the optimization of scarf angle is required for maintaining the joint strength, because brittle intermetallic compounds are necessarily formed at the interface of dissimilar-metal. The design techniques on joint strength characteristics have not fully been clarified. In this study, stress singularities at the intersection of free surfaces and the interface of various dissimilar-metal were investigated using singular analysis. As a result, it was made clear that the no free-edge stress singularities existed in the range of scarf angles, that were determined by the combination of dissimilar-metal. Especially, it was informed that the no free-edge stress singularities existed at the scarf angle of 57° and 123°singularities in case of the copper and aluminum scarf joint. It was also confirmed using finite element analysis that the reduction of stress concentration could be observed by paying attention to the condition of no free-edge stress.

Stress Singularity for Free-Edge of Interface of Copper/Aluminium Friction Welded Joint with Intermetallic Compounds.

The friction welding for copper and aluminium is useful to minimize the diffusion thickness at the interface between copper and aluminium. The minimization of diffusion thickness is required for maintaining the joint strength. However, it is well known the growth of brittle intermetallic compounds, such as CuAl2, CuAl and Cu9Al4, during the use at high-temperature. The effect of intermetallic compound layers on joint strength characteristics has not fully been clarified. In this study, elastic properties of intermetallic compound layers were investigated using depth-sensing micro-indentation technique. And stress singularities at the intersection of free surfaces and the interface between copper and aluminium were investigated using singular analysis. It was informed that the no free-edge stress singularities existed at the nelghborhood of apex angles of 55°and 125°. It was also confirmed using finite element analysis that the reduction of stress concentration could be observed by paying attention to the condition of no free-edge stress singularities in case of the copper and aluminium friction welded joint with brittle intermetallic compound layers.

接合界面形状適正化による摩擦圧接継手の衝撃強度の向上

The friction welding for copper and aluminium is useful to minimize the diffusion thickness at the interface between copper and aluminium. However, it is generally difficult to maintain the joint strength. Because brittle intermetallic compounds are necessarily formed at the friction weld interface between copper and aluminium. In this study, stress singularities at free-edge and intersection of copper/aluminium interface were investigated using finite element analysis.It was informed that the no free-edge stress singularities existed below an apex angle of 59°and between angles of 98°and 129°Also, intersection stress singularities exist over all apex angles except an apex angle of 90°.However, in case of apex angles between 98°and 129°, compressive stress concentration existed near the intersection of copper/aluminium interface. In this experiment, copper and aluminium friction welded joints were fabricated as to minimize (>1μm) the welding condition of the diffusion thickness at the interface between copper and aluminium. It was confirmed that the good tensile strength could be observed in all specimens tested. However, the Charpy impact energy became comparatively low in case of an apex angle of 90°and 135°, and showed a remarkable high impact energy can be obtained in case of no free-edge stress singularities.

Stress Singularity for Free-Edge of Dissimilar-Metal Interface and Design for Friction Welded Joint.

The friction welding for dissimilar-metal is useful to minimize the diffusion thickness at the welded interface. The minimization of diffusion thickness is required for maintaining the joint strength. However, it is generally difficult to maintain the joint strength. Because brittle intermetallic compounds are necessarily formed at the friction welded interface of dissimilar-metal. The design techniques on joint strength characteristics have not fully been clarified. In this study, stress singularities at the intersection of free surfaces and the interface of various dissimilar-metal were investigated using singular analysis and finite element analysis. As a result, it was made clear that the no free-edge stress singularities existed in the range of apex angles, that were determined by the combination of dissimilar-metal. Especially, it was confirmed that the compressive stress could be observed in the no singular range below an apex angle of 60°by filite element analysis. Finally, the design technique of dissimilar-metal friction welded joint was investigated by paying attention to the geometry of welded interface. "

Improvement of Impact Energy for Copper/Aluminium Friction Welded Joint due to the Shape of Interface Edge.

The friction welding for copper and aluminium is useful to minimize the diffusion thickness at the interface between copper and aluminium. The minimization of diffusion thickness is required for maintaining the joint strength, because brittle intermetallic compounds are formed at the friction weld interface between copper and aluminium. However, the improvement techniques on joint strength characteristics have not fully been clarified. In this study, stress singularities at the intersection of free surfaces and the interface between copper and aluminium are investigated using finite element analysis. It was confirmed that the no free-edge stress singularities existed in case of convex angle. In this experiment, copper and aluminium friction welded joints with convex apex angle were fabricated as to minimize the diffusion thickness, such ad > 1 μm at the interface between copper and aluminium. It was confirmed that the good tensile strength could be observed in any cases. The Charpy impact energy became comparatively low values in case of 90 degree of apex angle, and revealed a remarkable good impact energy can be obtained in case of the convex angle that showed no free-edge stress singularities.

Effect of Edge Shape of Coating Interface on Adherent Strength.

A thermal spraying process is useful to coat on substrates without any thermal damages. Therefore, it is possible to coat the high melting-point material, such as steels on the low melting point material, such as aluminum. However. it is generally difficult to improve the adherent strength between dissimilar materials. Because the stress concentration due to the material heterogeneity arises at the edge of coating interface. In this study, stress singularities at the intersection of free surfaces and the interface between steels and aluminum were investigated. It made clear that the no free-edge stress singularities existed below an apex angle of θ=20∼30°and between angles of about θ=90°and 150°. In the four-point bending test for the thermal sprayed aluminum with carbon steel and 13% chromium stainless steel, it was confirmed that the good adherent strength could be observed in order of θ=90°< 120°< 150°in case of no free-edge stress singulalities. This tendency of adherent strength was good agreement with the stress states around the edge of coating interface that were obtained by finite element analysis.

Improvement of Impact Strength for Copper/Aluminium Friction Welded Joint.

The friction welding for copper and aluminum is useful to minimize the diffusion thickness at the interface between copper and aluminium. The minimization of diffusion thickness is required for maintaining the joint strength. However, it is generally difficult to maintain the joint strength. Because brittle intermetallic compounds are necessarily formed at the friction weld interface between copper and aluminium. The improvement techniques on joint strength characteristics have not fully been clarified. In this study, stress singularities at the intersection of free surfaces and the interface between copper and aluminium were investigated using finite element analysis. It was informed that the no free-edge stress singularities existed below an apex angle of 59° and between angles of 98° and 126°. In this experiment, copper and aluminium friction welded joints were fabricated as to minimize (>1μm) the welding condition of the diffusion thickness at the interface between copper and aluminium. It was confirmed that the good tensile strength could be observed in all cases tested. However, the Charpy impact energy became comparatively low in case of an apex angle of 90°, and showed a remarkable high impact energy can be obtained in case of no free edge stress singulalities.

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.

Geometrical conditions of no free-edge stress singularities in edge-bonded elastic dissimilar wedges.

Geometrical conditions of no free-edge stress singularities in edge-bonded elastic dissimilar wedges.

A fracture mechanical treatment of free edge stress singularities applied to a brazed ceramic/metal compound

The theoretical fracture mechanical treatment of craek problems in regular stress fields is extended to account for singular stresses as occur in bi-material systems whenever a discontinuity in material properties and geometry exists. The singular stress fields are derived for arbitrary material combination and geometry and the global stress state as occurs in a real compound is obtained by Finite Element (FE) calculations. Then especially the mode I stress intensity factors are calculated for semi-elliptical surface cracks in the ceramic component of a brazed ceramic/metal joint. Critical crack sizes are determined for failure analysis of the compound.