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Sato C.,Precision and Intelligence Laboratory
International Journal of Adhesion and Adhesives | Year: 2011

The residual stresses in an adhesive layer between adherends with different curvatures were investigated analytically assuming the adherends as linear elastic beams and the adhesive layer as linear viscoelastic springs. A governing equation giving the time variation of adhesive thickness caused by the viscoelastic deformation is presented. The equation is an ordinary differential equation of the 4th order including a convolution equation of the creep compliance or the relaxation function equivalent to the linear viscoelastic characteristics of the adhesive. The equation gives also the distribution of a normal stress perpendicular to the interface between the adhesive and the adherends. The governing equation can be transformed into a complex number domain s by the Laplace transform, but it is difficult to solve generally the transformed equation in the s domain. However, when the adherends are long enough, the transformed equation at the end of the joint can be expressed in a simple form that can be treated analytically. In this case, the autoconvolution of the stress variation with time at the joint end is in proportion with the time integrals of the relaxation function of the adhesive. Therefore, the residual stress in the adhesive layer can be calculated by a numerical integration and a numerical auto-deconvolution, which is easier than other numerical calculations. This method has also another advantage in which the relaxation function or the creep compliance of the adhesive can be applied directly to the calculation without any mechanical analogy expressed with springs or dashpots of the adhesives characteristics. The applicable region of the method, however, is limited by the necessary condition of long adherends. © 2011 Elsevier Ltd. All rights reserved. Source


Kawasaki S.,Tokyo Institute of Technology | Nakajima G.,Denka Company Ltd | Haraga K.,HARAGA Adhesion Technology Consulting Co. | Sato C.,Precision and Intelligence Laboratory
Journal of Adhesion | Year: 2016

A novel method to manufacture functionally graded adhesive joints that is easier to implement than previous methods is proposed and investigated in this study. For this method, a mixture of two adhesives, one that is rigid and brittle and one that is flexible, was applied to adherends with various mixing ratios. Second generation acrylic adhesives (SGAs) were used in this study because they can be cured at a wide range of mixing ratios. To evaluate the mechanical properties of the resulting adhesive mixtures, bulk specimens with different mixing ratios were prepared and tested. Each of the adhesives had two components (e.g., agents A and B), with similar chemical compositions, but agent A includes an oxidizer, and agent B includes a reducer. Thus, mixing of both agents A does not produce any chemical reaction and similarly for agents B; this property enabled us to perform honeymoon adhesion. A mixture of agents A was applied to the surface of an adherend, and a mixture of agents B was applied to that of the other adherend at various mixing ratios. Then, one of the adherends was placed onto the other to make a joint. After the joint cured, the hardness of the adhesive layer was evaluated at certain points on the surface using nano-indentation to verify the applicability of the proposed method. Based on bulk tensile tests, it was concluded that the mechanical properties of SGAs could be controlled by changing the mixing ratio of the SGAs. In addition, the results of the hardness test of the adhesive layer, which corresponds to the Youngs modulus of the material, depended strongly on the mixing ratio of adhesive. © Copyright 2016 Taylor & Francis Group, LLC. Source


Wadood A.,Japan National Institute of Materials Science | Takahashi M.,IHI Corporation | Takahashi S.,IHI Corporation | Hosoda H.,Precision and Intelligence Laboratory | Yamabe-Mitarai Y.,Japan National Institute of Materials Science
TMS Annual Meeting | Year: 2013

Near-equiatomic Ti-Pt intermetallic alloys exhibit very high (e.g. above 1200K) transformation temperatures. However, binary Ti-Pt intermetallic alloys exhibit negligible shape recovery and low strength due to low critical stress for slip deformation. Then, in this study, effects of 5atomic percent addition of group IV transition elements on room temperature to high temperature strength, shape recovery and transformation temperatures of Ti-50at%Pt were compared. Strength was decreased and ductility was increased by increasing testing temperature. Ti-50Pt-5Hf exhibited higher strength at room temperature compared to Ti-50Pt-5Zr and Ti-50Pt. However, strength of Ti-50Pt-5Zr was found much higher than Ti-50Pt-5Hf and Ti-50Pt when tested at 50K below Mf. Transformation temperatures were decreased and shape memory effect was improved by addition of group IV elements. Source


Shinada E.,Precision and Intelligence Laboratory | Nagoshi T.,Precision and Intelligence Laboratory | Chang T.-F.M.,Precision and Intelligence Laboratory | Sone M.,Precision and Intelligence Laboratory
Materials Science in Semiconductor Processing | Year: 2013

Self-annealing in electroplated Cu films is the dramatic evolution of the microstructure in electroplated Cu near room temperature, and it occurs during a transient period of hours following the electroplating process. This study discusses the change of grain size and orientation in self-annealing of Cu films electroplated by an additive-free sulfate bath using X-ray diffraction and electron backscatter diffraction techniques. We found that the self-annealing started at the interface between the substrate and the electroplated Cu film. Immediately after the electroplating process, orientation of the Cu grains in the region near the interface was similar to that of the substrate. This indicates that the grain growth was affected by the substrate. Then, grain growth and change in orientation of the electroplated Cu film at room temperature became independent from the orientation of the substrate. The electroplated Cu film had many high-angle-grain boundaries (HAGBs) before incubation, and the fraction of HAGBs reduced as incubation time increased. Self-annealed Cu grains in the electroplated Cu film had many multiple twins, which came from low stacking-fault energy of Cu. © 2012 Elsevier Ltd. All rights reserved. Source

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