Michael Welch - Academia.edu (original) (raw)

Papers by Michael Welch

Journal of Mechanical Engineering – Strojnicky časopis, 2024

Classical analysis methods have shown that flexural, in-plane, deflections due to shear strain in... more Classical analysis methods have shown that flexural, in-plane, deflections due to shear strain in the flange pack of preloaded bolted joints produce bending moments and tensile loads on bolts within the joint. These bending moments and tensile loads are most noticeable in joints that are required to support large in-plane loads and torsional moments. The shear loads on the bolt associated with the flexural deflections can result in the bolt head, or nut, slipping relative to the flanges. This slippage will in turn result in mechanical loosening of the joint. The bending moments associated shear loads and tensile loads produced by the combination of both out-of-plane and in-plane external loads and torsional moments are in addition to the bolt preload. These additional loads, combined with a high initial bolt preload, can cause yielding of the bolt, which can also result in relaxation of the initial preload. This article reviews earlier work in determining the tensile bolt stresses induced in preloaded bolts by the external loads and presents methods of calculating the amount of preload relaxation that could occur from each mechanism discussed.

This supplementary material to the main paper "An Empirical Approach to a Comprehensive Damage-Eq... more This supplementary material to the main paper "An Empirical Approach to a Comprehensive Damage-Equivalent Stress Function for Fatigue" presents plots of all the results data from the research work, including results not presented in the paper.

FME Transactions, Dec 2022

This article presents Wöhler plots, or S-N curves, for use in the analysis of bolt fatigue of pre... more This article presents Wöhler plots, or S-N curves, for use in the analysis of bolt fatigue of preloaded bolted joints. Preloaded bolts under cyclic loading have a high mean stress with a small alternating stress. This is combined with a large stress concentration at the thread root. The method of fatigue analysis presented uses S-N curves with a zero mean stress. The high mean stress experienced by the bolts is accounted for using a function to calculate a damage-equivalent stress. Notch sensitivity was considered to modify S-N curves for materials with chemical compositions encompassed within the material specifications for high strength bolts. This produced S-N curves for stress concentrations relevant to bolt threads. Curve fitting techniques were used to express these curves as a function of the equivalent stress and stress ratio. An estimate of residual stresses in bolts produced by thread rolling was made.The work provides a practical method of calculating fatigue life.

FME Transactions, 2022

This paper develops an empirical damage-equivalent stress function for fatigue. Classical analysi... more This paper develops an empirical damage-equivalent stress function for fatigue. Classical analysis methods are used to 'fit' an equation to a number of S-N curves for various grades of carbon steel. The resulting equivalent-damage stress function is applicable to steels subjected to a wide range of heat treatments, from normalised up to hardened and tempered to 1900MPa. It is also applicable to a wide range of stress concentrations, unnotched up to Kt = 5.0 and typical of screw threads. A range of stress ratios and mean stresses are also considered. The function overcomes some of the limitations of existing methods of 'correcting' for mean stress. Existing methods are limited in that, while they may give good results over a range of conditions, there are some circumstances where the results are highly inaccurate. The damage-equivalent stress function is suitable for use in automated calculation procedures such as spreadsheets, MathCAD ©, and SMathStudio ©.

International Journal of Modern Research in Engineering and Technology, 2022

The purpose of this technical note is to develop an understanding of the influence of asymmetrica... more The purpose of this technical note is to develop an understanding of the influence of asymmetrical geometry within preloaded bolted joints. Classical analysis methods are applied to the analysis of preloaded bolted joints that use asymmetrical bolt group patterns. Both a detailed analysis of asymmetrical joints, using classical beam theory, and a less detailed design analysis are considered. The detailed analysis method is extended, using Rotscher's pressure cone, and is suitable to produce calculated bolt loads that can be used in a fatigue analysis. The design analysis provides a quick method of establishing the structural integrity of the asymmetrical joint. The detailed analysis method can be applied to the structure being connected by the bolted joint and the welds connecting the structure to the joint flanges. The design method is also appropriate for application to sprung suspension systems. The methods presented are suitable for use in automated procedures of calculation, such as spread sheets, MathCAD ©, SMathSutdio ©, etc.

Journal of Mechanical Engineering – Strojnicky časopis, 2021

The purpose of this paper is to develop an understanding of how bolt preloads are distributed wit... more The purpose of this paper is to develop an understanding of how bolt preloads are distributed within a joint as each bolt is tightened in turn by the use of a calibrated torque wrench. It discusses how the order that the joints nuts/bolts are tightened can affect the final bolt preload. It also investigates the effect on incrementally increasing the bolt preload through a series of applications of the controlled torque tightening sequence.
Classical analysis methods are used to develop a method of analysis that can be applied to most preloaded bolted joints. It is assumed that the static friction coefficient is approximately 15% less than the dynamic friction.
It is found that the bolt preload distribution across the joint can range from slightly above the target preload to significantly less than the target preload. The bolts with a preload greater than the target preload are found to be those tightened towards the end of the tightening sequence, usually located close to the outer edges of the joint’s bolt array. The bolts with a preload less than the target preload are those tightened early in the tightening sequence, located centrally within the joints bolt array.
The methods presented can be used to optimise bolted joint design and assembly procedures. Optimising the design of preloaded bolted joints leads to more efficient use of the joints.

Journal of Mechanical Engineering – Strojnicky časopis, 2020

The purpose of this technical note is to present a method of analysis of a joint made using a sin... more The purpose of this technical note is to present a method of analysis of a joint made using a single row of bolts, typical of a bolts around the edge of a closure plat or a simple bracket. Classical analysis methods are applied to the joint subjected to combinations of both in-plane and out-of-plane loads and moments. An analysis of loads and stresses in a single bolt is developed. The note brings together a number of concepts and links them into a practical design analysis process that is applicable for many cases of joints made with a single bolt or a single line of bolts and are adequate to demonstrate the structural integrity of the joint. In some cases finite element methods may be more appropriate, and the methods discussed can be used in the validation process.

Journal of Mechanical Engineering – Strojnicky časopis, 2019

The purpose of this paper is to present a paradigm, or guide, to the analysis of preloaded bolted... more The purpose of this paper is to present a paradigm, or guide, to the analysis of preloaded bolted joints made using multiple bolts. Classical analysis methods are applied to the interaction of the joint elements subjected to combinations of both in-plane and out-of-plane loads and moments. The distribution of the external loads and moments within the preloaded joint is determined in relationship to individual bolts. An analysis of loads and stresses in individual bolts and dowels along with flange bending and thread shear in tapped or threaded holes is developed. The article brings together a number of concepts and links them into a practical design analysis process that is applicable for many cases of preloaded bolted joints and are adequate to demonstrate the structural integrity of each element of the joint. Interpretation of results, within the context of design standards, is provided. In some cases finite element methods may be more appropriate, and the methods discussed can be used in the validation process.

Journal of Mechanical Engineering – Strojnicky časopis, 2018

Classical analysis methods are applied to show how flexural deflections due to shear strain in th... more Classical analysis methods are applied to show how flexural deflections due to shear strain in the flange pack produce bending moments and tensile loads on bolts within preloaded bolted joints. It was found that in joints made with long bolts these loads can be significant. The loads can cause yielding of the bolt, reducing bolt preload. The methods presented are adequate to demonstrate the structural integrity of joints made with long bolts or with a small footprint.