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A bolt heater is frequently used when tightening large bolts that cannot be tightened with other methods. Although the tightening process inherently needs a fair amount of working hours, a bolt heater is less expensive than the other tightening tools and it can be applied to the tightening operation in a narrow space. In this paper, an elementary method is proposed to evaluate the tightening process with a bolt heater, aiming at its broader use for middle-sized bolts. One-dimensional finite difference method is employed to analyze the heating process with taking the effects of heat transfer through small gaps into consideration, by which the corresponding bolt elongation is calculated for the specified heating period. The equation relating the bolt elongation and axial bolt force is also proposed, in which the effects of interface stiffness due to surface roughness are incorporated for better estimation of the axial bolt force. The effectiveness of the elementary method proposed here is demonstrated by experiments.Copyright © 2005 by ASME

It is well known that the scatter of bolt loads occurs when bolting up a pipe flange connection with a number of bolts. In general practice, two factors presumably have dominant effects on the non-uniform loads. One is due to the scatter of bolt clamping force when adopting a torque control method. The second is elastic interaction due to the flange deformation occurring in the process of successive bolt tightening. In this study, bolt-up finite element simulations of the pipe flange connection are conducted by considering the scatter of bolt clamping force when using the torque control method. The interrelationship of the effects of the scatter of clamping forces and the elastic interaction on the preload scatter occurring in the bolt-up process is investigated.Copyright © 2004 by ASME

In the pipe flange connection with a raised face, the non-uniform gasket contact stresses in the radial direction are occurred due to the flange rotation. The gasket contact stress distributions have dominant effects on the sealing performance of the pipe flange connection. However, the leak testing of a gasket is usually performed under the uniform gasket contact stress using the rigid platen. It is very important to establish a method which predicts the leak rate from the actual pipe flange connection using the results of the leak test conducted under the ideal condition. To do so, there is a need to know the sealing performance of the actual pipe flange connection. In this study, the leakage tests and the finite element simulations are conducted for some pipe flange connections with different gasket width and different flange thickness, which might cause different flange rotation angle. The effects of the flange rotations on the sealing performance and the mechanical behavior of the pipe flange connection are examined.Copyright © 2004 by ASME

Various clamping methods are used to tighten bolted joints and the selection is made according to its configuration, bolt size, etc. Angle control method is commonly used among them and it is usually applied when tightening bolts to the plastic region. However, elastic angle control method is sometimes used to tighten important structures, e.g., for the case where the clamping bolts are to be disassembled in a periodical inspection. In this paper, the tightening process of elastic angle control method is studied and the expression relating axial bolt force and nut rotation angle is proposed, in which the effects of surface roughness of contact surfaces and the inclined angle existing around nut loaded surface are incorporated. The validity of the proposed equation is demonstrated by experiment. It is shown that the elastic angle control method is preferably applied to the case of a bolted joint with large grip length being tightened with high bolt stress.Copyright © 2004 by ASME

Achieving uniform bolt preloads is an important and difficult issue, when bolting up a pipe flange connection with a number of bolts. Repeated bolt-up operations are, therefore, commonly conducted to get uniform bolt loads. In this study, an effective one-pass bolting up procedure to get uniform bolt loads is proposed by using finite element analysis with elastic interaction coefficient method being incorporated. Furthermore, multi-pass bolting up procedure is also examined to avoid high initial bolt clamping forces that might be generated in the one-pass tightening. These procedures are applied to class 300 lb 20 inch flanges with solid-metal flat gasket and compressed asbestos sheet gasket. The validity of the procedures is substantiated by conducting bolting up experiment using calculated initial clamping forces.Copyright © 2004 by ASME

The purpose of this study is the proposal of guidelines for bolt-up operation of pipe flange connections with joint sheet gasket or spiral wound gasket. Numerical calculations are systematically executed for pipe flanges with wide variety of nominal size by using finite element analysis, which can simulate the bolt-up process of a pipe flange connection, because the tightening performance of the pipe flange connection largely depends on the bolt-up process. Gaskets also have dominant effects on the tightening performance. It is, however, impossible to determine the number of tightening passes to get uniform bolt preloads for all kinds of gaskets. A simplified modeling method of nonlinear stress-strain relationship of gasket is, therefore, evaluated and a representative material property of gasket is selected to develop the bolt assembly guideline. The bolt-up procedure, in which four bolts located 90 degrees from each other are tightened with the same magnitude of preload at the installation process, is investigated.Copyright © 2003 by ASME

In bolt assembly process of pipe flange connections, repeated bolt-up operations are conducted to achieve uniform preloads. Nobody, however, knows how many times of bolt-up operation is required to achieve uniform preloads. It is important for practicing workers to know the number of bolt-up operations. The number of bolt-up operation required to get uniform bolt preloads depends on the nominal diameter of pipe flange, the number of bolts, the types of gasket, etc. In this study, systematical finite element analyses of bolt-up operation are conducted for JPI class 150in and 300in flanges with a compressed asbestos sheet gasket. The number of bolt-up operations required to achieve uniform preloads is estimated for each pipe flange connection.Copyright © 2002 by ASME

The most important factor for the leakage problem of pipe flange connections is considered to be contact pressure distribution at the gasket bearing surface in service. In this study, the mechanical behaviors of the pipe flange connection are evaluated using FEM as a three-dimensional contact problem, in which a gasket is modeled as a nonlinear one-dimensional gasket element. Here, the contact pressure distributions at the gasket bearing surface and the variations of the bolt stress are estimated under uniform bolt preloads or nonuniform ones due to the elastic interaction during bolting up. The numerical procedure proposed here can successively deal with the processes of bolt-up, applying inner pressure and applying bending moment. The analytical objects are pipe flanges specified in JIS B 2238 with compressed asbestos sheet gaskets being inserted. The validity of the numerical method is ascertained by experiment.

It is vitally important to ensure the safety of brittle materials. Therefore, it is essential to deeply understand the interaction of the material's microstructure and crack propagation. In this study, we constructed a multi-phase-field crack model which can express crack propagation in polycrystal. To evaluate the basic characteristics of the developed model, we performed two-dimensional crack propagation simulations in a bicrystal where a crack enters an inclined grain boundary by changing the ratio of the grain boundary energy to the crack surface energy. As a result, it is confirmed that the model can reasonably determine the crack path, depending on those conditions. Furthermore, by performing crack propagation simulations in a polycrystal, it is concluded that the model can properly express transgranular and intergranular cracks.

5 を満たす領域としてバリアント2を示している. この結果より, 母相中に配置した結晶欠陥から形成したマルテンサイト相は,時間とともに成長している. また, 最初にマルテンサイト相が形成した結晶粒以外においても, 変態によって生じた内部応力場に誘起されて次々とマルテンサイト相が形成している. さらに, 図2(d)(e) の矢印で示すように, マルテンサイト相は自身が形成することで生じる弾性ひずみエネルギーが最小となるように, プレート状もしくは板状の形態を呈していることがわかる. 図3 には, 3 つのバリアントおよび母相を含むマルテンサイト組織の形態を示す. この図より, 変態ひずみによって生じる弾性ひずみエネルギーを最小化するように, 結晶粒ごとに異なる2つのバリアントが層状組織を形成していることがわかる. なお, 本稿では変態中に塑性変形が生じない系での解析結果を示したが, 講演会当日は塑性変形を伴うマルテンサイト変態のシミュレーション結果について報告する.5 参考文献

A bolted joint is subjected to high stress concentration at the thread root because of its complicated geometry involved. Plastic regions are produced around the bottom of thread root, even under relatively low bolt axial force. It is predicted that the plastic deformation thus produced might affect such important mechanical behaviors of bolted joint as load distributions along threads, the relationships between bolt axial force and angle of nut rotation, etc. In many practical applications, bolts are tightened with considerably high clamping force, especially when tightening critical structures. Thus, it is considered that numerical studies taking the effects of plastic deformation into account are extremely important. However, many previous studies have only dealt with a bolted joint under pure tension. When tightening bolted joints with torque control shear stresses are generated in addition to the tensile stress due to bolt clamping force. In this study, mechanical behaviors of bolted joint during tightening with torque control are analyzed by FEM as an elasto-plastic contact problem, where three-dimensional analysis is conducted employing two dimensional model with each node having three degrees of freedom.