Bolt Preloads Research Articles

Thermo-mechanical behavior of retro-reflector and resulting parallelism error of laser beams for Wendelstein 7-X interferometer

A 10 channels interferometer will be used in the Wendelstein 7-X (W7-X) for plasma density control and density profile tracking with laser beams passing through the plasma. Due to complex shape of non-planar modular coils and divertor structure, there are no large poloidally opposite ports on the plasma vessel (PV). Therefore 10 in-vessel Corner Cube Retro-reflectors (CCRs) will be used. The CCRs are integrated in the water cooled heat shield and exposed directly to thermal loads from plasma radiation. Thermo-mechanical issues are very important for the design of the CCR because deformation and flatness as well as mutual angles of the three reflecting surfaces would affect the parallelism of the laser beams and the functionality of the interferometer. Intensive work has been done to explore a suitable design for the CCR concerning thermo-mechanical behavior. Previous studies Ye et al. (2008, 2009) and Köppen et al. (2011) focused on structural optimization to decrease thermal stress in the reflecting plates under the thermal loads, and on computation and check of curvature radii of the deformed reflecting surfaces with the design criterion that the curvature radius must be bigger than 200m. The paper presents detailed thermo-mechanical analysis of the current improved CCR under thermal loads and bolt preloads. The results of the thermo-mechanical analysis were used for the study of the resulting parallelism error of the laser beams with newly developed and more reasonable design criterion.

651 許容漏えい量を考慮した内圧を受ける金属平型ガスケット付き管フランジ締結体のボルト初期締付け力決定法

651 許容漏えい量を考慮した内圧を受ける金属平型ガスケット付き管フランジ締結体のボルト初期締付け力決定法

원자력발전소 고강도 앵커 볼트의 파괴역학적 건전성평가

증기발생기 수직 지지대를 고정하고 있는 고강도 앵커 볼트의 응력부식균열에 대한 건전성 평가는 원자력발전소 기기 건전성 유지와 관련하여 중요한 현안 가운데 하나이다. 이에 따라 미국E PRI에서는 고강도 앵커 볼트의 건전성 평가를 위한 기준균열계수 개념 기반의 평가 절차를 제시한 바 있으며, 본 연구에서는 EPRI에서 제시한 절차에 입각하여 증기발생기 수직 지지대 고정용 앵커 볼트의 응력부식균열 및 취성 파괴에 대한 건전성 평가를 수행하였다. 이를 위해 볼트 예비하중과 운전하중을 고려한 3차원 유한요소 응력해석을 수행하여 볼트 단면에 작용하는 공칭응력을 결정하였으며, 결정된 볼트 응력과 EPRI 절차를 이용하여 앵커 볼트의 균열 건전성을 평가하였다. 또한 3차원 탄성 유한요소 파괴역학 해석을 수행하여 EPRI에서 제시한 기준균열계수의 정확성을 검증하였다.

Experimental Investigation of the Effects of Bolt Preload on the Dynamic Response of a Bolted Interface

Often in the study of bodies that undergo shock loading, it is desirable to measure the response of such structures with an instrumentation package. This instrumentation can be separated from the external housing by several preloaded interfaces. To better understand the effects of preload on the nonlinear dynamics introduced into the measurement, a simple preloaded interface test fixture was fabricated. Both low amplitude modal impact tests and high amplitude shock loading tests were used to analyze the effects of varying preload between the bodies on the linear and nonlinear dynamics observed in the response of the coupled bodies. The results of these measurements indicated that increases in preload reduced nonlinearity, but could amplify force transmission. Based on these results, a three degree of freedom system model was created to represent the dominant linear modes of response and the qualitative nonlinear characteristics that were observed in the high amplitude shock loading experiments.

Analysis of Thermal and Mechanical Behavior of Pipe Flange Connections by Taking Account of Gasket Compression Characteristics at Elevated Temperature

Sealing of contained fluids is the primary performance required for pipe flange connections. It is well known that the leakage is likely to occur when contained fluids at high temperature are concerned. Due to the differential thermal expansion of each part, bolt preloads that tighten a pair of pipe flanges tend to decrease. Therefore, it is significantly important for the joint safety to estimate the amount of bolt preload reduction at the design stage. In this paper, a finite element approach is proposed to analyze thermal and mechanical behavior of pipe flange connections at elevated temperature, by incorporating the stress–strain curves of sheet gaskets measured in the temperature range which covers its usual service condition. Then, the reduction rate of bolt preloads at elevated temperature is systematically evaluated. The analytical objects are pipe flange connections tightened with aramid sheet gaskets. When a pipe flange connection is subjected to thermal load, the gasket stress usually decreases along unloading curves. The temperature dependency of gasket stiffness is considered by defining Young’s modulus in unloading E*, which can be introduced into FE formulation using ordinary solid elements. Numerical results show that bolt preloads are decreased by as much as 30% of the initial value when using aramid sheet gaskets of 3 mm thickness. The effectiveness of the proposed numerical method has been confirmed by comparing the numerical results of bolt preload reduction to experimental ones.

OS1408 リングジョイントガスケット付き管フランジ締結体のFEM応力解析及び密封性能評価 : ボルト初期締付け力のばらつきの影響

OS1408 リングジョイントガスケット付き管フランジ締結体のFEM応力解析及び密封性能評価 : ボルト初期締付け力のばらつきの影響

Experimental Strain Investigation of Bolt Torque Effect in Mechanically Fastened Joints

In this study, a different issue of mechanical engineering interests is determined for threaded fastened joints. A series of photoelastic experiments were performed to determine the maximum strains for the holes in a tensile flat plate subjected to bolt-nut loads. Pertinent strain distributions were examined to determine the roll of the torques on the bolts in mini mizing the strain; hence stress concentration. The experimental determination of maximum strains is needed as a way to validate future theoretical and numerical results, and provide a valuable aid to their application. The emphasis of this paper is on deformation. The results indicate that strains can decrease significantly with the increase of the bolt's pre-load.

Effects of the Nominal Diameter and Scattered Bolt Preloads on Sealing Performance of Pipe Flange Connection with Non-asbestos gaskets under Internal Pressure

Effects of the Nominal Diameter and Scattered Bolt Preloads on Sealing Performance of Pipe Flange Connection with Non-asbestos gaskets under Internal Pressure

Scatter of bolt preloads in pipe flange connection tightened by air impact wrench and the effect on the sealing performance

Scatter of bolt preloads in pipe flange connection tightened by air impact wrench and the effect on the sealing performance

Bolt Preload Reduction of Pipe Flange Connections after Plant Shutdown

Bolt Preload Reduction of Pipe Flange Connections after Plant Shutdown

The Study of High Strength Bolt Preload with Hydraulic Tensioner Installation

Preloading the high strength bolt using hydraulic extension method is a fast and efficient method for bolt installation. Hydraulic bolt tension device can guarantee the initial tension of bolt well. However, if the relation of initial tension and the final remaining preload of bolt cannot be determined, the preload on the bolts still cannot be guaranteed. This paper uses theoretical analysis method to research the relation between the eventual preload and the initial tension of high strength bolts on Heavy-duty Gantry beams. Then we proposes a set of calculation method of bolt installation preload and the initial tension and provides theoretical basis for the installation of heavy-duty segmented beam.

Effect of Cylinder Head Bolt Preload on Piston Ring Conformability and Engine Blow

Effect of Cylinder Head Bolt Preload on Piston Ring Conformability and Engine Blow

654 軸方向外力が作用する円筒ボルト締結体の座面弾塑性変形解析と初期ボルト軸力の設定方法いついて(フランジガスケット締結体の力学と密封性能評価III)

654 軸方向外力が作用する円筒ボルト締結体の座面弾塑性変形解析と初期ボルト軸力の設定方法いついて(フランジガスケット締結体の力学と密封性能評価III)

808 内圧を受ける大口径管フランジ締結のFEM応力解析と密封性能評価 : ボルト初期締付け力のばらつきの影響(OS8-2 フランジガスケット締結体の力学と密封性能評価)

808 内圧を受ける大口径管フランジ締結のFEM応力解析と密封性能評価 : ボルト初期締付け力のばらつきの影響(OS8-2 フランジガスケット締結体の力学と密封性能評価)

811 内圧及び温度変動下での管フランジ締結体の応力解析と密封性能評価(OS8-3 フランジガスケット締結体の力学と密封性能評価)

The authors have been evaluating the effects of the material properties of spiral wound gaskets(SWG) and the sealing performance of the pipe flange connections at thermal changes with numerical and experimental analysis. In this experiment we used 3" pipe flange connections and tightened by torque wrench. And then, we heated and measured leak volume. On the other hand we evaluated with the experimental leakage test and 3-D FE analysis in this study. Considering the circumstances mentioned above, we inspected stress analysis under scatter on bolt preloads and thermal changes.

Evaluation of the mechanical behavior of W7-X central support connections by means of semi-automated FE analysis

The stellarator Wendelstein 7-X is under construction at the Max-Planck-Institut für Plasmaphysik in Greifswald. Its superconducting coil system is fixed by a massive structure. During machine operation the coils exert high forces and moments against each other and the central support structure (CSS). Therefore, the detailed analysis of the coil to CSS connections, the so-called central support elements (CSE), is a critical item. The major details of the design have been frozen; nevertheless, there is still need for detailed analysis of the CSEs due to assembly issues, and later on for exploring operational limits of the machine. These analyses have to be performed quickly, reliably, and shall provide results in a standardized form to enable timely responses to the assembly team. Special numerical tools – finite element (FE) parametric models of CSEs – have been developed for the purpose of such analyses. In the models, the geometry, material properties, contact conditions, loads as well as results presentation are defined in a parametric way. The use of the developed models for the definition of the final weld parameters, bolt preloads, assessment of acceptable tolerances, and optimal positions of the CSE-wedges before welding is also discussed.

Micromechanical modelling and gasket stress evaluation in flange joints under bolt load and internal pressure

Stresses in Teflon-filled spiral wound gaskets in flange joints are analysed by an axisymmetric finite-element method using micromechanical models constructed based on layer geometry. The constituents of the gasket are represented by hyperelastic and elasto-plastic material models. The inplane and bending stiffness and the non-linearity of the gasket are considered through micromechanical modelling. The micromechanical model is validated with experimental data available in the literature. An improved gasket stress distribution across the width of the gasket is obtained under different bolt preloads and internal pressures. At lower bolt preloads, only half of the gasket is effective for sealing. The results are compared with the average gasket stress model results with bolt axial force.

Phenomenological Modeling and Numerical Simulation of Relaxation in Bolted Composite Joints

The effects of various bolt preloads, viscoelasticity, and external applied static and dynamic loads on bolt load relaxation in a carbon/epoxy composite bolted joint have been studied. Both phenomenological modeling and finite element analysis (FEA) of bolt-connected three-point bending specimens were employed in the studies. Relaxation of 1.25—4.25% over a period of 30 h was observed depending on the initial preload and applied external loads. Both static and dynamic applied loads were considered. It was observed that for any magnitude of external load the bolt load relaxation decreases with increasing initial preload. These findings emphasize the importance of the magnitude of the preload. Comparing the bolt load relaxation in steel and composite joints for the duration of 30 h, it was concluded that only about 1/3 of the relaxation in composite specimens is due to viscoelastic behavior of the polymer matrix in the composite, and the remaining 2/3 of the relaxation is due to other mechanisms such as bolt thread slip, plasticity and/ or external excitation.

Bolt preload scatter and relaxation behaviour during tightening a 4 in-900# flange joint with spiral wound gasket

Gasketed bolted flange pipe joints are found prone to leakage during operating conditions. Therefore, performance of a gasketed flange joint is highly dependent on the proper joint assembly with proper gasket, proper gasket seating stress, and proper preloading in the bolts of a joint. For a gasketed flange joint, the two main concerns are the joint strength and the sealing capability. To investigate these, a detailed three-dimensional non-linear finite-element analysis (FEA) of a gasketed joint is carried out using a spiral wound gasket. FEA results are compared with the experimental results and are found to be in good agreement, hence validating the FE model developed. Bolt scatter, bolt bending, and bolt relaxation are considered to be the main factors affecting the joint performance. In addition, the importance of proper bolt tightening sequence and number of passes and the influence of elastic and elasto-plastic material modelling on joint performance are also presented. Stress variation in the flange due to flange rotation highlighted joint strength, and gasket contact/seating stress variation highlighted the sealing performance during bolt up. Modelling the non-linearity of the spiral wound gasket using non-linear elements highlights reduced joint strength and sealing performance. Summarizing, a dynamic mode in a gasketed joint is concluded, which is the main reason for its failure.

557 温度変動及び内圧下におけるノンアスジョイントシートガスケット付き管フランジ締結体のFEM応力解析と密封性能評価 : ボルト初期締付け力のばらつきの影響(フランジガスケット締結体の力学と密封性能評価IV,オーガナイズドセッション)

557 温度変動及び内圧下におけるノンアスジョイントシートガスケット付き管フランジ締結体のFEM応力解析と密封性能評価 : ボルト初期締付け力のばらつきの影響(フランジガスケット締結体の力学と密封性能評価IV,オーガナイズドセッション)