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Second world war


During the Second World War V-Section bands clamps were developed for use in the air craft industry. Often the name Marmon clamp is associated with the clamps as the Marmon Corporation initially produced them. Due to the fact the clamps had a single fastener and simplicity they provided quick serviceability; a key feature on warplanes. Today V-Section clamps are used on turbochargers as a connection method between the turbine housing and the compressor housing.

The clamps are assembled onto the flanges of these housings and torque is applied to the nut on the T-bolt. This in turn gives inward radial force on the v-section of the clamp. It also provides the wedging action that is required in order to clamp together the flanges of the housings.

For most bolted joints, subsequent to the application of tightening torque there will be some torque loss. This is a result of relieved torsion stresses in the bolt once the tightening process has stopped.

In a majority of the bolted joints, after the application of tightening torque there will be some torque loss. This is due to the fact that once tightening has stopped, some of the torsion stresses in the bolt are relieved; this reduction may be from as little as 0% to 50% (this is for very extreme case! Will not be seen very often in today's industrial applications), depending on friction and other joint conditions. The error in torque measurement could be as high as 28% (Junker & Wallace, 1984)

In V-Band connections there is the possibility of capacity loss. This can be attributed to the combination of torque relaxation, circularity of the V-Band and the temperature of the surrounding environment. The T-Bolt needs to provide the required clamping load for V-section band clamp, and should be designed to withstand the stresses induced in them. Hence it is important to know the relationship between the applied torque and the stress distribution in the bolt.

There has been a number of instances since V-Band were first used on Turbocharger where the torque that has been applied to the nut of the V-band has fallen away to the point where the V-Band has become loose. This is obviously not expectable under any circumstances and there needs to be investigations to try and find a root course for the problem.

It is worth noting that error in torque measurement can be as much as 28%. (Junker & Wallace, 1984)

V section band clamps have many advantages over the more traditional bolts to join to item together. These are as follows. There is only one nut to tighten on a V-Band therefore the amount of time spent tightening this v section band join is greatly reduced They are many time lighter than using a number of bolts to secure two times together. This is especially useful in automotive and airspace application, due to the global drive to make the world CO2 emissions as small as possible, reducing weight reduces Co2 emissions

Great time saving can be made when a V-Band is used to assemble two item this is due to them only having one nut to tighten and also there only be one set up to produce of them to be used in industry.

They are also cost effective when maintenance is required this is due to them being easy to remove and refit should this be required.

For these reason it is easy to see exactly why they are used throughout industry and have been so for many years not. Not only car they easy to maintain but in the long run they can save money and even speed up the assembly process of components


To investigate the amount of relaxation in the tightening torque of the nut on the T-bolt at ambient temperature.

The relationship between the applied torque to the nut on the T-bolt and corresponding stress distribution in the bolt.


The scope of this project is to research into methods and reasons why the v section band clamp relaxes and to try to find a relationship between that relaxation and any point along the v section band clamp's construction.

There will be some experimental testing of the V-Band itself especially looking at the bolt and the way in which it behaves under loading of the nut.

Further testing will look into the amount of torque relaxation that the V-Band experiences over periods of time and for different sized V-Bands. There will also be an area of testing to try and find the creep data for the materials that are used within the V-Band. There will also be a long term test developed in order to see exactly what is happening during the tightening of V-Bands.

There will also be a finite element analysis model developed in order to predict where the stresses and forces are generated when the V-Band is tightened. This will be verified using experimental results previous research and tests and will provide a solid basis for development of the model for outside the scope of this project.

Mathematical and theoretical models will also be created in order to verify and aid with torque relaxation predictions and calculations.


Currently costing is hard to predict as there scale of the research is still unknown. However there will be strain gauges required for practical testing. Specialised equipment and a powerful computer for analysis of FEA models. As well as fees to publish in journals articles. Currently it is felt that the research will cost no more than five thousand GBP (£5000) per year



While V-Bands are very good at the job for which they are intended they are not without fault. One of these fault areas is what this dissertation will look into. This area is the torque relaxation of the V-Band over time. It is currently not possible to predict the torque loses that a V-Band will experience due to there being very little knowledge as to why it occurs. It is hoped that this report will investigate these losses and hypotheses on the reason behind them. For the majority of this report it will be assumed that he V-Band are used on Turbocharger alone, but the principle outlined can be adapted to suit any use of V-Bands

Warranty clams

One of the major reasons for investigating the relaxation of the V-Band is to prevent future warranty claims on turbochargers. It is known by the major manufacturers and users of V-Bands that they do relax over time. This relaxation can cause failure of the entire turbocharger as explained below.

Turbochargers are produced with very tight tolerencing and work at very high speeds typically between 20,000 and 100,000 RPM but some smaller turbocharger can reach speeds of many hundreds of RPM. For this reason if any component in the assembly of the turbocharger were to move by any small amount it would cause catastrophic failure of the entire turbocharger, or the entire engine of the vehicle it is being used upon.

Literature Review


There literature for the topic of torque relaxation within V-section band clamps is very limited as this are of research has never really been explored until now. However there and many book, paper and journals that will still be of help and my literature study has uncovered some that it is felt will be of help to the research.

Literature Study


Handbook of Bolts and Bolted Joints contains vast amounts of information all to do with bolted joint and fasteners. It talks about how all bolted joints suffer from torque relaxation. There is information about the interaction between nuts and bolt including many reference table, which will aid the research and add to its depth of work.

BICKFORD, J. H., NASSAR, S., (1998) Handbook of Bolts and Bolted Joints. New York: Marcel Dekker, INC. P.169

(Bickford, 1998)

This book will aid with the hypothesis that torque relaxation is due to material science. Research in to dislocations and crystallisation of the materials is covered with in this texted. There and numerous examples of each. It cover this area in death and will be key to this research area.

Introduction to Materials Science for Engineers. New Jersey: Pearson Education LTD, (Nask, 1999)


This paper has great detail in the ways in which bolted joints interact. It summarises the area that affect the torque application to a nut and bolt, and evaluates the effectiveness of measuring and ailing torque to a bolted joint.

Junker .H, Wallace PW . The bolted joint: economy of design through improved analysis and assembly methods. ImechE1984 vol 198B.

(Junker & Wallace, 1984)

It would appear for this papers critical analysis of the methods used to apply a torque to a bolted joint that this is an area worth including to the research. Is cover, tightening of the nut and bolt with and without lubrication. Analysing the results of such a method including outcomes.

Monagan. J.M, The Influence of libication on the design of yield tightened joints, University of Dublin, FIMechE, 1996 (Monagan, 1996)

PHD Thesis

The PHD Thesis my Kiumars Shoghi investigates the stress and strain relations of a V-section band clamp. It contains information around that topic that will be useful towards this proposed area of research. It does not instigate torque relaxation.

Stress and strain analysis of flat and v section band clamps. PHD Thesis Oct 2003. Kiumars Shoghi (Shoghi, 2003)


There are many website that offer information based around the topics of fastener relaxation but again there is no materials based around torque relaxation within v section band clamps. Some useful website have been discovered however and there details are below.

Tightening bolt and relaxation is a website that has been designed to help with the problem if torques relaxation. Is details about the methods and types of torque loss that a fastener can experience. It criticizes the use of manual torque equipment. This website also has a large download resource

(Thompson, 2010).

Current Affairs

There have been numerous repost with in the turbocharger industry that the torque relaxation effect has caused a turbo charger to fail, however there is little to no publication of these facts due to company integrity polices.


There are two main experts that will provide key information to aid this research, DR Simon Barrans, University of Huddersfield. Dr Kiumars Shoghi, Analyst as a large worldwide turbocharger manufacture. with the hope of the university and the outside company with research will be closely monitored to ensure it says on track.

There are many more items within the literature review for this research but in order to keep this proposal sort some items have been omitted. A full literature review can be obtained on request.



Gantt Chart

This Gantt Chart has been produced to show the basic time scale of the research and also to provide a list of item that are planned to be covered by the research.

Work Breakdown Structure

Below is a work breakdown structure for this project. It outlines the main tasks that are required in order to complete this project fully and comprehensively. It has been broken down into four levels, each dependent on each other and necessary for project completion.

Flow diagram

The below flow diagram show the flow of work in order to complete the research and to meet it objectives


Analysis And Summary Of Literature Review

With the aid of the literature


Appendix A Reference list

BICKFORD, J. H., NASSAR, S., (1998) Handbook of Bolts and Bolted Joints. New York: Marcel Dekker, INC. P.169


Dr S. M. Barrans (2008) NMM 3500 Module handbook, Avanaced Mechanical Analysis. School of Computing and Engineering, The University of Huddersfield

Stress and strain analysis of flat and v section band clamps. PHD Thesis Oct 2003. Kiumars Shoghi

Junker .H, Wallace PW . The bolted joint: economy of design through improved analysis and assembly methods. ImechE1984 vol 198B.

James F. Shackelford. (2009) Mechanism of dislocation climb. [Diagram] In:Shackelford, J.F. (2009) Introduction to Materials Science for Engineers. New Jersey: Pearson Education LTD,


Bickford, J.H., (1998.) Handbook of bolts and bolted joints. New york: Marcel Dekker INC.

Junker, H. & Wallace, P.W., (1984.), 'Economy of design though improved analysis and assembly', The Bolted Joint, vol 198B, no. 1, pp. 2-3.

Monagan, J.M., (1996.) The influence of libication on the design of yield tightened joints. Paper. Dublin: University of Dublin University of Dublin.

Nask, S., (1999.) Introduction to Materials Science for Engineers. New Jersey.

Shoghi, K., (2003.) Sress and strain analysis of flat and v section band clamps. PhD Thesis. Huddersfield: The University of Huddersfield The University of Huddersfield.

Thompson, K.D., (2010.) Tightening Bolt and Relaxation. [Online] (1) Available at: [Accessed 06 January 2010].

Simon Ashton U0556849Page 12

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