Toshimichi Fukuoka

Proposition of Helical Thread Modeling With Accurate Geometry and Finite Element Analysis

Distinctive mechanical behavior of bolted joints is caused by the helical shape of thread geometry. Recently, a number of papers have been published to elucidate the strength or loosening phenomena of bolted joints using three-dimensional finite element analysis. In most cases, mesh generations of the bolted joints are implemented with the help of commercial software. The mesh patterns so obtained are, therefore, not necessarily adequate for analyzing the stress concentration and contact pressure distributions, which are the primary concerns when designing bolted joints. In this paper, an effective mesh generation scheme is proposed, which can provide helical thread models with accurate geometry to analyze specific characteristics of stress concentrations and contact pressure distributions caused by the helical thread geometry. Using the finite element (FE) models with accurate thread geometry, it is shown how the thread root stress and contact pressure vary along the helix and at the nut loaded surface in the circumferential direction and why the second peak appears in the distribution of Mises stress at thread root. The maximum stress occurs at the bolt thread root located half a pitch from nut loaded surface, and the axial load along engaged threads shows a different distribution pattern from those obtained by axisymmetric FE analysis and elastic theory. It is found that the second peak of Mises stress around the top face of nut is due to the distinctive distribution pattern of σ z .

Finite element simulation of bolt-up process of pipe flange connections with spiral wound gasket

It is well known that a large amount of scatter in bolt preloads is observed when boltingup a pipe flange connection, especially in the case of using a spiral wound gasket. In thisstudy, a numerical approach is proposed, which can simulate the bolt-up process of a pipeflange connection with a spiral wound gasket inserted. The numerical approach is de-signed so as to predict the scatter in bolt preloads and achieve uniform bolt preloads atthe completion of pipe flange assembly. To attain the foregoing purposes, the stress-strainrelationship of a spiral wound gasket, which shows highly nonlinear behavior, is identifiedwith a sixth-degree polynomial during loading and with an exponential equation duringunloading and reloading. Numerical analyses are conducted by three-dimensional FEM,in which a gasket is modeled as groups of nonlinear one-dimensional elements.@DOI: 10.1115/1.1613304#

Elastic Plastic Finite Element Analysis of Bolted Joint During Tightening Process

Mechanical behavior of bolted joints during the tightening process with torque control is analyzed by FEM as elastic plastic contact problems. Three-dimensional analysis was conducted employing two-dimensional model with each node having three degrees of freedom that attains high computation efficiency. Such important factors as development of plastic zones, variations of load distributions along engaged threads, the relationships between axial bolt stress and nut rotation angle were analyzed in order to provide an effective guideline when tightening critical structures with high bolt preloads. It was also shown that the proposed numerical method can be applied to evaluate the tightening process by plastic region tightening used extensively in recent years. The validity of the numerical method is demonstrated by comparing the calculated bolt elongation with that obtained from experiment.

Finite element simulation of bolt-up process of pipe flange connections

Achieving uniform bolt preload is difficult when tightening a pipe flange with a number of bolts. Several bolt-tightening strategies have been proposed so far for achieving uniform bolt preloads. It seems, however, that effective guidelines for tightening pipe flange connections have not been established. In this study, a numerical approach is presented for estimating the scatter in bolt preloads and achieving the uniform bolt preloads when tightening each bolt one by one in an arbitrary order. Numerical analyses are conducted using three-dimensional FEM as an elastic contact problem. The analytical objects are pipe flanges specified in JIS B 2238 with an aluminum gasket inserted. The validity of the numerical procedures proposed here is ascertained by experiment.

Evaluations of the Tightening Process of Bolted Joint With Elastic Angle Control Method

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

Systematical FE Analysis of Bolt Assembly Process of Pipe Flange Connections

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

Finite Element Analysis of the Thermal and Mechanical Behaviors of a Bolted Joint

Mechanical and thermal behaviors of the bolted joint subjected to thermal load are analyzed using axisymmetric FEM, where the effects of thermal contact resistance at the interface and heat flow through small gap are taken into account in order to accurately evaluate the variations of bolt preloads. It is expected that the numerical procedure proposed here provides an effective means for estimating the strength of such critical structures as pressure vessels, internal combustion engines, steam and gas turbines, etc. Air experimental equation that can compute the thermal contact coefficient at the interface composed of common engineering materials has been proposed in the previous paper. In this study, a simple equation for evaluating the amount of heat flow through small gap is shown by defining apparent thermal contact coefficient. Accordingly, a numerical approach has been established, which can accurately analyze the thermal and mechanical behaviors of a bolted joint, by incorporating the two kinds of thermal contact coefficients into FE formulation. By use of the FE code thus developed, it is shown that only a slight difference in coefficients of linear expansion among the joint members significantly affects the variations of bolt preloads. The validity of the numerical approach is demonstrated by experimentation.

Effects of Flange Rotation on the Sealing Performance of Pipe Flange Connections

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

Effective Bolting Up Procedure Using Finite Element Analysis and Elastic Interaction Coefficient Method

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

Finite Element Simulation of the Tightening Process of Bolted Joint With a Bolt Heater

The tightening operation with a bolt heater has advantages surpassing those of other tightening methods. Currently, a bolt heater is mainly applied to tighten huge bolts that cannot be clamped by other means, and the tightening operation is usually supported by the expertise of skilled workers. In this paper, a numerical approach is presented to aim at a broader use of bolt heater technique by elucidating the tightening mechanism. The effects of thermal contact resistance existing around a bolted joint are taken into account for a better accuracy in the numerical analyses. Based on the numerical results obtained, a series guideline to help the tightening operation when performed by less skilled workers is proposed.