Time Dependent Behaviour of Rubber

A discussion meeting organised by the Rubber in Engineering Committee
of the Institute of Materials, Minerals & Mining

Event: Afternoon Technical Discussion Meeting
Date: Friday 22rd June 2007
Start time: 2pm
Venue: IOM3, 1 Carlton House Terrace, LONDON.
Location: map and directions

Programme

Start 2:00pm

1) Some practical aspects of creep and stress relaxation – D Derham (MERL)

Probably in most engineering applications of rubber, the closely related phenomena of creep and stress relaxation  are only of minor - if any - importance.  Provided 'good quality' rubber compounds are used, creep and/or stress relaxation do not become an issue.  However, there are a few applications where relaxation behaviour becomes the dominant performance parameter - and these are largely applications involving seals and sealing.

We will start by describing creep and stress relaxation in practical terms, and how they may be measured.  Here we are talking mainly about physical relaxation - but we must be aware that chemical relaxation will also occur.  We will then go on to discuss why seals can fail - not because of simple stress relaxation considerations, but because of the more complex variants on relaxation which occur in service.  Service conditions may involve changes in temperature, changes in pressure of a contained fluid, physical movement of pipe joints - and so on.  All of these influence the rates of relaxation.

We will then examine how the viscoelastic and thermodynamic components of the stress are affected by these changes in conditions, and the near impossibility of determining losses in sealing force at all accurately in the real world - except in the simplest applications - other than by simulated service testing.

2) Separating Relaxation  Processes: An Approach To The Estimation Of Long-Term Stress Relaxation
In Elastomers – S Ronan (DIK)

Stress relaxation experiments have become increasingly importance for the determination of elastomeric properties. There is an increasing need for these tests in recent years with the introduction of stress relaxation standards such as those applied to sealing rings for underground pipes. The automotive industry has also begun to specify stress relaxation experiments for critical sealing components in its vehicles. Due to increased performance demands, service temperatures are higher and auto fluids and oils are becoming more aggressive. The paper introduces a possible concept to predict or estimate the stress relaxation of elastomers over long periods resulting from tests conducted in short testing time-frames.

3) Cyclic Stress softening in elastomer compounds in different deformation modes – S Asare (QMUL)
Cyclic stress softening often known as the Mullins effect is a well known phenomenon in elastomer materials. In recent times different damage mechanics approaches have been proposed to predict the change in stiffness of elastomers under cyclic loading. This paper will explore these approaches and show using experimental evidence how the cyclic stress softening is dependent not only upon the extent of the maximum strain in the sample but also the detailed form of the deformation mode.

4) Life Prediction of Rubbers Based on the Precision Measurement of Compression Stress Relaxation - Claude Hepburn (Consultant)

These talks are all followed by discussion and tea will be served at 4pm.

All times are approximate. Programme is subject to change.

Attendance at the meeting is free of charge for members of the IOM3, however a small nominal charge (less than £20) may be made on the day to none members. To attend you must first reserve your place by contacting Roly Whear (see below) giving your contact details (company, telephone number, address and email).

Roly Whear                                                                 
Jaguar Cars Limited                                                   
53G2/4
Banbury Road
Gaydon
Warks
CV33 0RR

Tel: +44 (0)1926 645543
Email: rwhear1@jaguar.com