Engineering aspects of natural rubber: Finite element analysis and fracture mechanisms
Dr. A. Stevenson, Managing Director of the Materials Engineering Research Laboratory (MERL) UK
Natural rubber has proven to be a versatile and durable material for a wide range of engineering applications. Its main advantage over synthetic elastomers is its high tear strength and fatigue resistance for application that do not require prolonged service at elevated temperatures. Low cost is also a considerable advantage for high volume applications, although of less concern for many critical engineering components where the engineering costs outweigh the cost of materials.
Natural rubber components continue to hold an important place in non-tyre automotive components as well as the material usage in tyres. Natural rubber has also found an important niche in demanding offshore engineering components and in one recent case laminated natural rubber flexelements were installed as primary load bearing components in a deep-water offshore platform for the Norwegian sector of the North Sea, after fatigue testing up to 5000 tonnes.
The first part of this lecture will review the basic properties of natural rubber that are important for engineering applications. This will be illustrated by a number of engineering applications from the past 150 years.
In the second part of the lecture some new advances will be presented from research at MERL on finite element and fatigue life analyses and multiaxial testing.
New computer software has been developed that integrates fracture mechanics and fatigue life calculations to enable the number of service cycles to a certain depth of crack to be calculated. Current research is also underway to integrate this approach with the long term effects of chemical ageing. For many modern engineering components it is important to characterise the combined effects of loading in different directions simultaneously (eg. combined shear with compression).
Natural Rubber - Quality and processing aspects
N. Levin FPRI, Consultant Trelleborg Lanka (PVT) Ltd., Sweden
Natural rubber (NR) was for over 50 years the sole polymer available for manufacturing of rubber products. When synthetic rubber was introduced, mainly after the second world war, most rubber converters complained about the difficulties to process the new rubber types.
The reasons for complaints were obvious. Machinery and techniques used were develo-ped to handle natural rubber and the rubber technicians had learned how to handle it.
Over the next three decades the use of synthetic rubber increased, finally ending up in the situation of today when 60% of all polymers used are synthetic. The remaining NR rubber is used in products where it is gives superior properties, as in heavy tyres and engineering products. During the last 15 years the demands on product performance as well as processing behaviour have increased tremendously. The converters have demanded improved processing properties and better consistency of the raw materials. The synthetic polymer manufacturers have responded quicker to the demands and fruitful discussions have developed between suppliers and users.
The document will discuss a product manufacturer's view on NR specifications and show how developments in compounding, mixing and processing techniques can improve the production results.
The future development of rubber production and quality in Indonesia
Dr. A.F.S. Budiman, Executive Director of Gapkindo (Rubber Association of Indonesia)
Natural rubber has been and will stay an important export product for Indonesia. The country is currently the second largest producer of natural rubber in the world after Thailand.
The present proportions of rubber by type are 90% Technically Specified Rubber (TSR), 6% Ribbed Smoked S-heet (RSS), 3% Latex Concentrate and 1% others. Smallholder rubber covers 83% of the total Indonesian rubber area (3.29 million hectares) and contributes 74% of the total rubber production in Indonesia which was 1.45 million tons in 1995.
The majority of smallholders raw materials are meant to produce Standard Indonesian Rubber (SIR) and could be generalized as field coagula derived from either acid or natural coagulation of latex that have undergone maturation to various extents at different moisture contents. These coagula are purchased by SIR factories in the form of slabs, unsmoked sheets or lumps.
The paper will discuss the position of natural rubber. It will describe efforts made on the improvement of Indonesian smallholders raw material quality and productivity to achieve three C's: Cleanliness, Consistency and Cost-effectiveness.