A Novel Approach for Determining, Evaluating, and Applying Stress-Concentration Factors for Rotary-Shouldered Connections

This paper presents a new stress concentration factor (SCF) analysis methodology for rotary shouldered connections (RSCs). The proposed method uses finite element analysis (FEA) as a primary tool to explore the maximum peak stress trends in RSCs and calculates SCF to represent the connection performance. The paper provides a thorough discussion on the SCF analysis methodology and its application in evaluating drill string connection designs. The paper also compares peak stress trends and SCF values among various RSC designs to assist in evaluation and selection of connections for drilling, completion and intervention riser applications.

API rotary-shouldered drill stem connections have a seal surface that is required to carry internal pressure. We assume that this seal will hold the pressure from routine drilling operations, but drill stem tests, stuck pipe, or other special situations can apply much higher differential pressures to the drill string. Currently, there is no analytical solution for predicting the pressure that can be safely contained by one of these industry-standard connections. This leads to extra cost and logistical difficulties in those instances where significant pressures are expected. Some proprietary connections are designed for this high-pressure service, but these may be unnecessary if the API connection can safely tolerate those pressure loads. Without an accurate predictive equation, however, relying upon the pressure capacity of an API connection injects uncertainty and risk into the drilling process. This paper addresses that problem by developing a predictive pressure-capacity equation for rotary-shouldered connections. To cover a broad spectrum of rotary-shouldered connections with the predictive equation, Finite Element Analysis (FEA) was used to model six different connection types with varying dimensions and tensile loads applied. Over 70 distinct models were created to fully describe the effects of internal pressure on a rotary-shouldered connection. Patterns in those results were associated with physical stress and strain effects to create an analytical equation that accurately describes the stress state at the seal surface under various pressure loads. It is this equation that predicts the pressure capacity of an API rotary-shouldered connection. In order to put this equation into use, laboratory testing is recommended to both confirm the FEA results and define an actual failure criterion (that is, at what seal stress the connection begins to leak). Possible paths forward are discussed, along with important considerations for obtaining meaningful test data.

The concentration of stress and strain in finite thickness elastic plate containing a circular hole

The presence of opening in construction is unavoidable for the purpose of reducing stress. A small opening at the construction serves as access to continue the installed construction that runs through the web or girder. However, the presence of the hole also creates an unavoidable problem, the concentration of stress in the area around the hole that will gradually reduce the strength of the ship's construction. Stress concentration occurs due to changes in geometry, causing the flow of stress initially uniformly driven and following the existing geometry. This analysis aims to determine the value of stress concentration factors on the wrang plate due to variations in the shape of scallops. The research method is performed numerically using finite element analysis to find variations in the model with the lowest stress concentration factor. This variation consists of 3 different scallops models with 2 load, drag and press conditions. The values of stress concentration factors are grouped into 3 modes according to mechanical fractures in press loading conditions. Based on the analysis of panel models with compressed loads, it can be seen that model III has the smallest stress concentration factor value in case modes I and III but for mode II the value of the smallest stress concentration factor in model II.

Determination of operating load limits for rotary shouldered connections with three-dimensional finite element analysis

The aim of this systematic review is to provide an overview of finite element analyses comparing standard and short dental implants concerning biomechanical properties and to detect the most relevant parameters affecting periimplant stress concentrations. After screening the literature and assessment of studies, 36 studies were included in this review. Eighty-three percent of the studies state that short dental implants have to bear higher stress concentrations compared with standard length implants. At the same time, 44% of articles note that implant diameter can be considered a more effective design parameter than implant length to reduce stress concentrations and to avoid an overload of periimplant bone. Regardless of implant dimension, in all studies, the highest stress concentrations are found in the cortical section around the upper part of the implant. Unaffected of bone quality, implant diameter is found to play a key role to minimize periimplant stress concentrations. Concerning stress reduction implant length gains increasing relevance with decreasing bone density. Furthermore, splinting of short implants constitute an appropriate tool to avoid crestal overloading.

In this paper, the rectangular hole problem is investigated for a long high-temperature superconducting slab under electromagnetic forces. The effects of rectangular hole on the magnetic flux density distribution in the slab are considered in either the Bean model or the Kim critical state model in the case of the descending field both for the zero-field cooling (ZFC) and the field cooling (FC) magnetization processes. Based on the finite element method, both the corresponding stress concentration factors near the corners and the distributions of nonzero principle stress along the hole edge are numerically calculated and discussed. Numerical results obtained show that the ZFC activation process has more significant influence on the stress concentration factors than the FC activation process. For every activation process, the peak values of stress concentration factors in the Bean model are larger than the corresponding ones in the Kim model. In addition, in the Kim model, the peak values of stress concentration factors generally decrease with the increasing of the introduced dimensionless parameter <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$p$</tex></formula> . Additionally, the stress concentration factors usually increase with the increasing of the ratio of length and width of the hole. The present study should be helpful to the design and application of high-temperature superconductors.

Stress concentration effects of undercut defect and reinforcement metal in butt welded joint

Experimental investigation on stress concentration factors of cold-formed high strength steel tubular X-joints

The elastic stress and strain fields in a plate of finite thickness containing an elliptical hole are systematically investigated using the 3D finite element method. It is found that the stress and strain concentrations are different in the plate of finite thickness even if the plate is in an elastic state. The relation between the stress and the strain concentration factors depends on Poisson’s ratio, the hole’s geometric configuration and the plate thickness. The stress concentration factor is equal to the strain concentration factor only at the notch root of the plate surface. The stress (or strain) concentration factor at the notch root of the plate surface decreases rapidly with increasing thickness and becomes lower than the stress and strain concentration factors corresponding to the plane stress state or at the notch root of the mid plane. It is too low to reflect the overall stress concentration as the thickness increases or as the b/a ratio decreases. The maximum stress concentration factor occurs on the mid plane only when the plate is thinner than the transition thickness of the stress concentration factor. When the plate is thicker than the transition thickness of the stress concentration factor, the distance between the location of the maximum stress concentration factor and plate surface tends to be constant with increasing thickness for the plate with a given b/a ratio. The differences between the maximum value and the surface value of the stress and strain concentration factors increase rapidly and tend to their respective constant values with increasing plate thickness. The smaller the b/a ratio, the larger these differences. The difference of the stress concentration factor is larger than that of the strain concentration factor in the same plate.

The S-N approach with hot-spot stress range concept is a widely used method for the fatigue design of tubular connections in fixed offshore structures. In order to use this method, realistic values of stress concentration factors (SCFs) in the tubular connections are required. A number of alternative parametric equations are available for the calculations of SCFs. However, there is still a paucity of test data on realistically constructed and sized specimens for some basic joint types to validate these equations and to select the most suitable equations for use in design. This paper presents results of a total of 45 elastic tests carried out on 15 realistically constructed and sized tubular joint specimens of either T, Y, X or K configuration. The tests concentrate on joints with high ? (brace to chord diameter) ratios. The SCFs of these specimens under either axial, in-plane bending and out-of-plane bending loads were estimated using strain gauges readings. Three different extrapolation techniques have been used to interpret the measured results. An assessment on the reliability of SCF parametric equations for fatigue design has been carried out in the light of the new test data. INTRODUCTION A jacket type offshore structure consists mainly of tubular connections with brace and chord members. Most of these members are made of steel tubulars with circular hollow section which are joined together by full-penetration welds. One important aspect in design and analysis of the jacket structures is to check for the fatigue damage of these tubular joints under environmental loads. The S-N approach with 'hot-spot' stress range concept is a widely used method for the fatigue assessment. To use this approach, realistic values of stress concentration factors (SCFs) for the joints are required. A number of alternative parametric equations are available for the calculations of SCFs. However, there is still a paucity of data on realistically constructed and sized specimens for some basic joint types to validate these equations especially for joints with high ? (brace to chord diameter) ratios. As part of a joint industry research project, 45 elastic tests were carried out on 15 large scale steel specimens to measure the SCFs for joints with high ? ratio. The SCFs results are presented here and compared with the predictions of the available parametric equations. Adopting the approach of the previous papers(1,2), this paper addresses the reliability of the existing parametric equations in predicting SCFs in the light of the new test data. Implications of the use of SCF equations in design are also commented. Details of the tests described in this paper can be found in a HMSO report(3). TEST PROGRAMME Test specimens The test programme comprises elastic tests on nine T/Y-joint, three X-joint and three K-joint specimens with chord members of 508mm (20in) diameter. For all T/Y and X joints, except for one specimen, the ? ratios are ranging between 0.8 and 1.0. A K joint where ? = 1 is also included in the programme. Details of the specimens and their dimensional parameters are given in Table 1. Three loading modes, namely, axial, in-plane bending and out-of-plane bending, were considered.

The aim of this paper is to investigate the effects of non-dimensional geometric parameters on stress concentration factors (SCFs) of circular hollow section CHS brace-to-H-shaped section T-connections under axial compression. This type of welded joints is used increasingly in steel construction. However, its fatigue design is not covered by codes, and its fatigue strength has not been given the deserved attention by researchers. This research, however, bridges the gab on SCFs in this type of welded connections when being loaded in axial compression. here, parametric study based on the numerical analysis was performed to evaluate the effect of CHS brace diameter to H-shaped chord flange width ratio (β), H-shaped chord flange width to thickness ratio (2γ) and CHS brace thickness to H-shaped chord flange thickness ratio (τ) on SCFs in the brace and the chord of the connection. Based on practical considerations, the validity range of these parameters was 0.3 ≤ β ≤ 0.7, 16 ≤ 2γ ≤ 30 and 0.2 ≤ τ ≤ 0.1. Three-dimensional finite element (FE) study using commercial software ABAQUS was performed to study the hot spot stress distribution and hence SCFs in this type of welded joints. To begin with, the results of FEM were verified against available experimental data and good agreement was achieved. Afterwards, 48 joints were modeled in Abaqus to study the effect of geometrical parameter on SCFs in brace and chord. Based on the results of this extensive study, the effect of geometrical parameters was revealed. The paper, thus, shows that whilst β increases, SCFs in the brace and chord increases. Moreover, increasing the parameter 2γ results in an increase in SCFs in the two members. However, the change in τ has no significant effect on the SCFs in the brace or the chord. Values of SCFs are found to be between 2 and 7.

Fatigue test results on the large size roller chains for power transmission (Tsubakimoto RS 0206) was reported in this paper. The test results were discussed on the fatigue strength of large size roller chains and compared with those obtained on the small size roller chains reported in the provious issue.For fatigue testing two kinds of Losenhausen oil pressure type fatigue testing machines were used, that is, UHS type (capacity, static load 35ton, dynamic load 20ton) and UHP type (capacity, static load 20ton, dynamic load 10ton). The former was used for repeated load over 10ton, and the latter for under 9ton. Also fatigue tests on steel plates for chain links were carried out by Haighs fatigue testing machine (capacity 1.5ton) for comparison's sake. The driving speed of the testing machines was 800cycle/min at Losenhausen machine and 1800cycle/min at Haigh machine.The results obtained are as follows:1. The critical part of the chains applied to tests was the cross section of roller links perpendicular to longitudinal direction, where bushes were press-fitted.2. The endurance ratio of the large size roller chains is about 1/4. This value is larger than that for small size roller chains which was about 1/7, as previously reported. The reason is considered to be due to the fact that the endurance ratio of roller link plate materials for large size roller chains was larger than that for smaller ones.3. The effective stress concentration factor for the large size roller chain was 3.4 at 107, and 2.2 at 105.4. Eliminating the effect of fitting pressure, the value of the effective stress concentration factor was calculated to be 4.8 at 107, which is nearly equal to the value of the stress concentration factor for the eye end plate loaded by a pin with clearance.

Problems. When designing bolted joints (BJ), it is necessary, in particular, to carry out their verification calculations for strength. At the same time, it is desirable to use express analysis: calculations by simple formulas of sufficient accuracy. For BJ of plates made of layered polymer composite materials (PCM), the problem has not yet been solved. The aim of the study. The task is to test the accuracy of three known formulas for quick calculation of the value of the stress concentration factor (SCF) in zone of contact of bolt-hole with a rigid cylinder (bolt). The study was carried out on contrasting examples of materials and schemes of reinforcement of plates made of PСM, taking into account possible clearance between bolt and hole in the real range: from zero to 1% of diameter. Methodology of implementation. Numerical calculations were made using the finite element method (contact problem) for the BJ of plates made of layered PCM. 3D orthotropy of each monolayer was provided. Three simple formulas of express analysis were tested. The results are summarized in the tables and many illustrations are given. Research results. Numerical estimates of depending of the SCF in zone of the surface of the bolt-hole from considered factors are obtained. The factors are the material characteristics, the schemes of reinforcement of plates made of layered PСM and the values of the clearance between bolt and hole in the plates, as well as the accuracy of the considered formulas. Conclusions. Changing the material and the scheme of reinforcement of plate made of layered PСM leads to a significant change in the values ​​of maximum stresses and SCF in zone of the bolt-loaded hole in the weakened by hole cross section of a plate. Considered formulas of the express analysis have insufficient accuracy for consideration of contrast properties of materials and schemes of reinforcement of a plate. Changing size of clearance between bolt and hole in the range from zero to 1% of the diameter leads to relatively small changes in SCF: up to 10% maximum. Additional research is needed.

EXPERIMENTAL STRESS CONCENTRATION FACTOR IN CONCRETE-FILLED STEEL TUBULAR T-JOINTS