Stress Singularity Parameters Research Articles

Evaluation of Adhesion Strengths based on Stress Singularity Parameters at Dissimilar Interfaces

Evaluation of Adhesion Strengths based on Stress Singularity Parameters at Dissimilar Interfaces

Interfacial Strength of Plasma-sprayed Hydroxyapatite Coatings

Both tensile and shear adhesion strength tests were performed to evaluate interfacial strength between hydroxyapatite coatings on titanium alloy substrates subjected to anodization and heat treatment prior to deposition as well as post-deposition heat treatment. Results of the tensile adhesion strength tests were influenced by the size of the blasting media and the processing of pre- and post-heat treatments but not influenced by anodization. The finite element method (FEM) analysis of stress distribution during the shear adhesion strength test was also performed to evaluate the degree of stress singularity. The results show that the stress singularity parameters were dominant factors of stress distribution in the stress singularity fields, and they were also expected to influence the “essential” interfacial strength. In addition, the size of the blasting media had the same influence on the shear and tensile adhesion strength tests. This suggests the possibility of estimating tensile adhesion strength using the results of shear adhesion strength.

F603 インバータ基板のはんだ接合部の熱疲労寿命の評価 : 応力特異性パラメータを用いた評価(F6.企業におけるCAE活用,フォーラム)

It is well known that thermal fatigue easily occurs in the solder joints of inverter circuit board. In this study, we tried to evaluate thermal fatigue life of solder joints with the stress singularity parameters near the solder joint edges. Firstly, we made constitutive equations of the solder materials and confirmed its precision. Next, using FEM analyses, we calculated stress singularity parameters near the solder joint edges for power modules under the conditions of thermal cycle experiments and power cycle experiments. Finally, we made evaluation equations of thermal fatigue life for solder joints by connecting stress singularity parameters and experiment results with fatigue laws.

107 異材接合体角部近傍の応力特異性解析(OS1-2 オーガナイズドセッション《計算力学と数値シミュレーション》)

Recently, bonded structure is used for many machine parts and electronic components. But, it may cause stress concentration near the corners. This leads to a decrease in strength, and reliability is lost. Therefore, it is necessary to evaluate the stress characteristics at a vicinity of vertex in bonded structures. There is stress singularity parameter to evaluate the stress characteristics. The stress state of a junction interface can be known by analyzing this singularity parameter. In this paper, stress characteristics in the junction interface of anisotropic bonded structures are analyzed by finite element method. As a result, the influence that the joint angle gave to the stress characteristic is clarified.

A Fracture-Based Criterion for Debonding Strength of Adhesive-Bonded Double-Strap Steel Joints

This paper addresses the debonding strength of adhesive-bonded double-strap steel joints. A fracture-based criterion was formulated in terms of a stress singularity parameter, i.e., the stress intensity factor, which governs the magnitude of a singular stress field near the joint ends. No existing crack was assumed. A total of 24 steel joint specimens were tested under constant amplitude fatigue loadings at stress ratio of 0.2 and frequency of 2 Hz. The joint stiffness ratio was slightly less than one to control the maximum adhesive stresses at the joint ends. To detect the debonding, a simple and practical technique was developed. The test results showed that the interfacial failure near the steel/adhesive corner was a dominant failure mode. The failure was brittle and the debonding life was governed by the crack initiation stage. The finite element analysis was employed to calculate the stress intensity factors and investigate the effects of the adhesive layer thickness, lap length and joint stiffness ratio on the debonding strength.

A Diagram for Evaluating Delamination of GFRP/Stainless-steel Adhesive Joints by Using Stress Singularity Parameters

Static tests on double-lap and T-type adhesive joints were performed. We developed a device that applies contact pressure to glass-fiber reinforced plastics/stainless-steel double-lap adhesive joints. The device contains a bolt with which a strain gauge is bonded for controlling contact pressure. Using this device, we investigated the effect of contact pressure on the delamination strength of double-lap adhesive joints. We applied tensile shear loading to double-lap adhesive joints under contact pressure to their adhesive interfaces. We found that the delamination strength of the double-lap adhesive joints increased with increasing contact pressure. On the contrary, when we applied compressive shear stress to them, the delamination strength stayed constant. Therefore the delamination strength of double-lap adhesive joints is dominated by normal stress when contact pressure under tensile shear loading is applied. On the other hand, it was dominated by shear stress when contact pressure under compressive shear loading was applied. Then stress singularity parameters for double-lap and T-type adhesive joints were performed by the FEM. Stress distributions near the bonding edge could be expressed by the stress singularity parameters. Finally, a delamination evaluation diagram using stress singularity parameters was developed. This diagram enables us to evaluate the delamination strength of adhesive joints.

Fatigue Strength Evaluation Methods Using Stress Distributions

The stress and displacement fields near the bonding edge, sharp notch, and contact edge show singularity behaviours, so methods of evaluating the strength of these points using maximum stresses calculated by a numerical stress analysis, such as the finite element method, are generally not valid. We have previously presented a new method of evaluating the strength of these singular points using two stress singularity parameters H and λ. In this paper we have developed a method of formularizing critical stress-singularity parameter Hth for each order of stress singularity λ by utilizing critical distance stress theories (point method and line method), which can be derived from two typical strength parameters, namely, fatigue limit σw0 and threshold stress-intensity factor range ΔKth. These estimated critical Hth (λ) value agreed well with the experimentally measured value. Using these simple critical distance stress approach we estimated the fretting-fatigue-crack initiation criteria for any contact edge angle and optimized the contact-edge geometry. Moreover, we apply this new strength criteria to general stress concentration structures.

Standardization of strength evaluation methods using critical distance stress

The stress and displacement fields near the bonding edge, sharp notch, and contact edge show singularity behaviors, so methods of evaluating the strength of these points using maximum stresses calculated by a numerical stress analysis, such as the finite element method, are generally not valid. We have previously presented a new method of evaluating the strength of these singular points using two stress singularity parameters H and λ. The difficulty with this method was in obtaining the critical value of the intensity of the stress singularity parameter H c for each order of stress singularity λ. Then we have developed a method of formularizing critical value of stress singularity parameter H c for each order of stress singularity λ by utilizing critical distance stress theory. Firstly we apply this method to the delamination strength evaluation. The estimated delamination criteria H c( λ) agrees well with the experimental results. Then we apply this method to general sharp notch corner and contact edge fatigue problems. In these cases the fatigue-crack initiation criteria can be derived from two typical strength parameters, namely, fatigue limit σ w0 and threshold stress intensity factor range Δ K th. These estimated critical H th( λ) value agrees well with the experimentally measured value. Using this simple critical distance stress approach we estimated the fretting fatigue-crack initiation criteria for any contact edge angle and optimized the contact edge geometry. Moreover, we can apply this new strength criterion to stress singularity fields for general stress-concentration structures.

GFRP/ステンレス鋼接着継手のはく離評価線図

Static tests on double-lap and T-type adhesive joints were performed. We developed a device that applies contact pressure to glass-fiber reinforced plastics/stainless-steel double-lap adhesive joints. The device contains a bolt with which a strain gauge is bonded for controlling contact pressure. Using this device, we investigated the effect of contact pressure on the delamination strength of double-lap adhesive joints. We applied tensile shear loading to double-lap adhesive joints under contact pressure to their adhesive interfaces. We found that the delamination strength of the double-lap adhesive joints increased with increasing contact pressure. On the contrary, when we applied compressive shear stress to them, the delamination strength stayed constant. Therefore the delamination strength of double-lap adhesive joints is dominated by normal stress when contact pressure under tensile shear loading is applied. On the other hand, it was dominated by shear stress when contact pressure under compressive shear loading was applied. Then stress singularity parameters for double-lap and T-type adhesive joints were performed by the FEM. Stress distributions near the bonding edge could be expressed by the stress singularity parameters. Finally, a delamination evaluation diagram using stress singularity parameters was developed. This diagram enables us to evaluate the delamination strength of adhesive joints.

Study on the Strength of GFRP/Stainless Steel Adhesive Joints Reinforced with Glass Mat

The adhesive strengths of glass fiber reinforced plastics/metal adhesive joints reinforced with glass mat under tensile shear loads and tensile loads were investigated analytically and experimentally. First, the stress singularity parameters of the bonding edges were analyzed by FEM for various types of adhesive joints reinforced with glass mat. The shear stress and normal stress distributions near the bonding edge can be expressed by two stress singularity parameters. Second, tensile shear tests were performed on taper lap joint and taper lap joint reinforced with glass mat and tensile tests were performed on T-type adhesive joint and T-type adhesive joint reinforced with glass mat. The relationships between the loads and the crosshead displacements were measured. We concluded that reinforcing adhesive joints has a greater effect on strength under tensile load than under tensile shear load. The adhesive joints strength reinforced with glass mat can be evaluated by using stress singularity parameters.

2210 GFRP/ステンレス鋼二重重ね合せ接着継手強度に及ぼす面圧の影響(J10-1 接着界面強度評価,J10 締結・接合部の力学とプロセス)

We developed a device that applied contact stress to glass fiber reinforced plastics/stainless steel double lap adhesive joints. Using this device, we investigated the effect of contact stress on the strength of adhesive joints. The device was composed of a bolt adhered to a strain gauge to control the applying load. Tensile shear stress was applied to double lap adhesive joints in condition to apply contact stress to adhesive interfaces. We found that the strength of the adhesive joints increased according to increasing contact stress. We conclude that adhesive strength applied contact stress can be evaluated with stress singularity parameters for normal stress.

Evaluation Method for Fatigue Strength of FRP/Metal Adhesive Joints Considering Mean Stress

The fatigue strength of two types of FRP/metal adhesive joints at low temperature, a double lap joint and an embedded joint, was evaluated analytically and experimentally. First, the stress singularity parameters of the delamination edges under mechanical and thermal loadings were analyzed by FEM for various delamination lengths. The delamination propagation rate of the double lap joint under mechanical cyclic loadings at room temperature was measured. Using the relationship between the measured propagation rates and the analyzed ranges of stress singularity intensity, we estimated the fatigue strength of the embedded joint, which coincided well with the measured one. Second, we developed an evaluation method that separates the effects of temperature on fatigue strength into two effects: thermal residual stress and low temperature. Third, the fatigue strengths of the double lap joints were measured for various mean stresses. Fatigue limit of adhesive joints was experimentally measured and compared with analytical intensity of stress singularity. A method for evaluating the fatigue strength of adhesive joints by taking mean stress into account was developed.

Simulation of fretting-fatigue life by using stress-singularity parameters and fracture mechanics

Fretting-fatigue cracks start very early in a fretting-fatigue life. The fretting-fatigue life is dominated by the propagation of small cracks. Therefore, predicting the start of fretting-fatigue cracking and the propagation of the cracks is a very important part of estimating fretting-fatigue strength and fretting-fatigue life. The start of a fretting-fatigue crack was estimated by using the stress-singularity parameters at the contact edges. The way in which the crack propagates was then estimated by using fracture-mechanics analysis, in which the wear on the contact surfaces and the direction of crack propagation were taken into account.

Fatigue strength CAE system for three-dimensional welded structures

ABSTRACT Fatigue strength assessment methods are applied to practical arc-welded structural features that have complex three-dimensional geometry. Two methods are investigated in the present research. The criterion of the first method is cyclic plastic zone size, which is calculated from stress singularity parameters. The criterion of the second method is hot spot stress. These fatigue strength criteria are proved to be applicable to the fatigue strength assessment of practical arc-welded structural features. These criteria enable a critical point at which fatigue cracks are most likely to initiate to be specified for each type of welded joint and load. Consequently, the critical point simplifies the classification of various welded joints. Furthermore, a fatigue strength computer-aided engineering system, which includes functional engines for the evaluation of the fatigue strength of a designed shape, is proposed.

928 応力特異場パラメータを用いたダブテールのフレッティング疲労評価法

928 応力特異場パラメータを用いたダブテールのフレッティング疲労評価法

応力特異場パラメータを用いた接着・接触部の強度評価と他への展開

The stress and displacement fields near the bonding edge, sharp notch, and contact edge show singularity behaviors, so methods of evaluating the strength of these points using maximum stresses calculated by a numerical stress analysis, such as the finite element method, are generally not valid. We have previously presented a new method of evaluating the strength of these singular points using two stress singularity parameters H and λ. The difficulty with this method was in obtaining the critical value of the intensity of the stress singularity parameter Hc for each order of stress singularity λ. We therefore present in this paper methods of formularizing Hc by λ based on typical strength parameters such as the fatigue limit σ_<w0> and the threshold stress intensity factor range ΔK_<th>. These critical value Hc (λ) agreed well with the experimental results. Using these easily obtained formularized critical value Hc (λ), we can estimate the fretting fatigue crack initiation criteria for each contact edge angle, and thus optimize the contact edge geometry. Finally, we discuss the development of these strength criteria in terms of stress singularity fields for general stress concentration fields.

特異場理論を応用した半導体デバイス無転位設計手法の検討

During fabrication of semiconductor devices, the stresses on a silicon substrate sometimes cause dislocations and worsen the electric characteristics of the device. Therefore, a dislocation-free fabrication process needs to be developed to improve reliability. In this paper, a process design method using stress singularity parameters (K and λ) is proposed. In order to prevent the dislocation generation, the process parameters, such as the device structure, materials and process temperatures, are set to keep the stress singularity parameters (K and λ) under the critical values of dislocation generation Kdc. These parameters are predicted using FEM method considering the internal stress of thin films. The process design was applied to a bipolar transistor and a MOS transistor and the experimental results agreed very well with the prediction. It was confirmed that this new process design method is effective in improving device reliabirity.

Standardizing of Strength Evaluation Methods Using Stress Singularity Parameters.

The stress and displacement fields near the bonding edge, sharp notch, and contact edge show singularity behaviors, so methods of evaluating the strength of these points using maximum stresses calculated by a numerical stress analysis, such as the finite element method, are generally not valid. We have previously presented a new method of evaluating the strengh of these singular points using two stress singularity parameters H and λ. The difficulty with this method was in obtaining the critical value of the intensity of the stress singularity parameter Hc for each order of stress singularity λ. We therefore present in this paper methods of formularizing Hc by λ based on typical strength parameters such as the fatigue limit σw0 and the threshold stress Intensity factor range ΔKth. These critical value Hc(λ) agreed well with the experimental results. Using these easily obtained formularized critical value Hc(λ), we can estimate the fretting fatigue crack initiation criteria for each contact edge angle, and thus optimize the contact edge geometry. Finally, we discuss the development of these strength criteria in terms of stress singularity fields for general stress concentration fields.

衝撃 ＰＭＭＡ／Ａ１板突合せ接着継手の衝撃引張強度特性

The dynamic strengths of adhesively bonded dissimilar butt joints were investigated numerically and experimentally. Stress distributions and the variation of stress with time in the joint were analyzed by the finite element method. A stress singularity parameters approach was applied for evaluating the dynamic tensile strength of adhesively bonded dissimilar butt joints, composed of PMMA and Al alloy plates. The dynamic strength of the joint under impact loading was calculated by a new simple method proposed in this study. The statistical analysis of the dynamic tensile strength of the joints by using the Weibull distribution was presented. It was found that the dynamic tensile strength of the joints increased significantly with increasing loading rate.

半導体デバイスにおけるシリコン基板転位発生予測手法の提案 転位発生限界値のデバイス構造依存性

During fabrication of semiconductor devices, the stresses in a silicon substrate sometimes generate dislocations at high temperatures. As most of the dislocations are generated at the stress singularity fields in the silicon substrate, dislocation generation should be discussed with stress singularity problems. In this paper, prediction method for dislocation generation was proposed, and the strength of dislocation generation was measured and described using stress singularity parameters, K and λ. In the experiment, the specimens were silicon substrates with stressed SiN thin-film bands, at whose edges the stress singularity fields were formed. Parameter K was varied by changing the bandwidth, and λ was controlled by changing the shape of the band's edge. The strength was determined by the critical sizes of the bands for the generation. Dislocation-free process of ULSI can be designed to apply the prediction method.