Fatigue resistance

The strength of bitumen, and of many other materials, is reduced by repeated loading. A study contacted by Heukelom on the tensile strength of bitumen proved that the bitumen s resistance to fatigue is solely dependent on its stiffness. From the nomograph developed, the fatigue strength of the bitumen may be determined by each stiffness value (Heukelom 1966 Shell Bitumen 2003). 

During their life cycle many rubber components are subjected to forces that produce relatively high deflections or strains within the rubber. The component designer will attempt to minimise these strains but for the best life expectancy the rubber compound must also be optimised for the application. This will be discussed in Chapter 3. 

ISO/TS 16949, Quality Management Systems - Particular Requirements for the Application of ISO 9001 2008 for Automotive Production and Relevant Service Part Organizations, 2009. 

The basic requirement for the rubber compound is that it will meet the customer s requirements in terms of physical properties and service life. In reality it is necessary to look beyond these bounds. The manufacturer must consider a number of aspects before committing to produce any item. 

The producer of rubber injection moulded components will either have access to in-plant rubber compounding facilities or will purchase compound from a trade supplier. In both cases the control of the process is vital. If the process is in-house, control is then a matter of company policy. If a trade compounder is used, there needs to be a close liaison between the supplier and the injection moulding company to establish quality principles. 

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Fatigue improvement Fatigue resistance Fatigue strength... 

The solder and ahoy market, including low melting or fusible ahoys, is a principal user of indium (see SoLDERS AND BRAZING ALLOYS). The addition of indium results in unique properties of solders such as improved corrosion and fatigue resistance, increased hardness, and compatibhity with gold substrates. To fachitate use in various appHcations, indium and its ahoys can be easily fabricated into wine, ribbon, foil, spheres, preforms, solder paste, and powder. 

In the category of industrial appHcations, nylon is the predominant fiber used in the carcass of bias tmck, racing car, and airplane tires because of its exceUent strength, adhesion to mbber, and fatigue resistance. Nylon is used less in the carcass of radial tires for automobiles and in replacement bias and bias-belted tires because of the development of temporary flat spots. For this reason, nylon has lost most of this market to polyester. 

Other Metals. Tellurium has been added to copper-base, lead-base, and tin-base bearing aUoys. In babbit-type aUoys, teUurium controls the stmcture and improves uniformity and fatigue resistance by restraining the tendency to segregation (see Bearing Materials). 

Nylon, an aUphatic polyamide, was introduced as a commercial tire cord in 1947 and grew in usage to - 5.4 billion kg/yr (- 2 billion Ib/yr) in the 1990s (10,11). Nylon-reinforced tires use nylon-6 poljmier (polycaprolactam) fibers as well as nylon-6,6 (poly(hexamethylenediainine adipamide)) fibers. Nylon tire cords are characterized by extremely good fatigue resistance in compression and good adhesion to most mbber compounds with simple RFL adhesives. 

Name Strength, cN /Tex Modulus, cN /Tex Thermal shrinkage Density T, °C Mp, °C Compression fatigue resistance... 

Greater amounts of copper increase the proportion of needles or stars of Cu Sn in the microstmcture. Increase in antimony above 7.5% results in antimony—tin cubes. Hardness and tensile strength increase with copper and antimony content ductiUty decreases. Low percentages of antimony (3—7%) and copper (2—4%) provide maximum resistance to fatigue cracking in service. Since these low alloy compositions are relatively soft and weak, compromise between fatigue resistance and compressive strength is often necessary. 

For high, fatigue strength in automotive bearings, a very thin layer of babbitt is desirable so that much of the load is taken on a stronger backing material. Relative improvement in fatigue resistance was found to be as follows with tin babbitt (14) ... 

With binary copper—lead, the continuous copper phase provides the primary load support while pockets of 20—50% lead supply a continuous lead surface film. Tin content of 3—5% is commonly incorporated with the lead to minimi2e corrosion. Copper—lead alloys, either cast or sintered on a steel back, provide good fatigue resistance for heavy-duty main and connecting rod bearings for auto, tmck, diesel, and aircraft engines. 

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