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Content archived on 2024-05-21

Functional life prediction of elastomeric components


To maintain the competitiveness of supplier and end-user industries of components made from rubber, greater knowledge of processing, design and service environment factors on functional life is needed. To solve this problem the objectives are:
(a) identify and quantify key factors in processing, design and service environment that control the functional life of rubber components, and
(b) develop computer simulation models that can be used to rapidly predict the performance of improved processes or designs.
The objectives will be achieved by:
(1) investigation of mixing and moulding factors on functional life,
(2) modelling components behaviour in service,
(3) development of materials tests and performances models,
(4) validation of computer simulation models with component test and end-user trials.
The expected results are:
(i) validated predictive models that simulate component performance in automotive break systems,
(ii) know-how and predictive models to optimise processing and design, assess alternative materials, define accelerated test conditions, reduce prototype testing, reduce development time, and improve reliability.
Laboratory test methods and procedures:
For materials evaluation, test methods and procedures were developed for hyperelastic, viscoelastic and fatigue properties for elastomers accounting for thermal and other service related effects. Rheological test procedures were developed for uncured material. A test to quantify the strength of weak rubber-rubber interfaces and assess factors affecting weak interfaces was developed. A gas decompression test was developed to diagnose the presence of weak interfaces in manufactured components. For component evaluation an accelerated durability test was developed for brake booster diaphragms.

Material models:
Material models and associated parameters were derived for the rheological, hyperelatic, viscoelastic and fatigue properties of the elastomers of interest.Processing factors and functional lifeThe influence of processing on functional life was assess in terms of weak interfaces, orientation and state of mix. Key factors and the influence of these were identified. For weak interfaces, flow, pressure and tack were identified. A method for quantifying orientation was developed which can be used with mould filling software to predict orientation and in addition mould shrinkage. Under some circumstances orientation may be exploited to enhance strength and fatigue resistance. Fatigue life was found not to be very sensitive to the state of mix, but significant benefits might be gained from high states of mix.

Service factors and functional life:
Thermal effects in particular were considered and the relative importance of various temperature extremes determined.

Simulation of moulding processes:
Model components were simulated using commercial software and were used to develop and validate procedures developed for simulation of the moulding processes. Key material and equipment parameters were identified from sensitivity studies and procedures developed to overcome limitations of current commercial software to account for rubber behaviour. The effects of component and mould design changes on process conditions and material requirements were assessed using the procedures developed.

Simulation of functional response:
A simulation of the functional response of brake booster diaphragms was developed using commercial software. The model was validated against measurements made in the durability test.Critical regions and conditions were identified. The simulation enabled the effects of design changes on functional performance were assessed.

Life Prediction:
From material models and simulations, failure conditions in brake booster diaphragm components were predicted. Both energetics and strain were identified -life approaches were used and thermal effects were accounted for. The critical conditions for the diaphragm.

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