Riveting with carbon

A recent successful application of carbon/carbon composites is the tool for superplastic forging of titanium illustrated by Figure 6 tubes up to 1.5 m in length can be forged at temperatures up to 1000°C, thus offering a rapid alternative fabrication technique to present production methods, e.g., riveted tubes (15). Contact brushes for electrical commutators, made with carbon fibers and carbon/carbon composites (16), are opening another new field of application. Furthermore, pistons in diesel engines have been proposed to be made from carbon/carbon composites (17). 

Use of dissimilar metals such as aluminum and carbons steel can result in galvanic corrosion. The entire HMMWV vehicle is secured with more than 2800 rivets, and this design affords the vehicle high-strength-weight ratio each rivet is a preferential site for corrosion. 

E6.2. Predict whether or not galvanic corrosion will cause the following alloys to be subjected to leaching (i) carbon and carbon steel alloys in an oxidizing atmosphere, (ii) steel rivets in aluminum drain gutters, (iii) copper-nickel alloy in refinery condenser tubes, (iii) graphite fiber-reinforced aluminum composites, (iv) brass in water, (v) iron-chromium alloys, and (vi) carbon steel pipe in contact with the weld to stainless steel pipe. 

Materials of Construction. The principal materials of construction are ferrous throughout, but different grades are used for the different components. Casings usually are in cast iron or cast steel, and impellers may be in the same materials or in fabricated steel. Early designs of centrifugal compressors used riveted assembly for impellers castings or welded construetions are preferred today. Shafts usually are of carbon steel with hardened or stainless steel sleeves at points where erosion is likely. The selection of materials for smaller components that may be subject to friction is particularly important because of the danger of comlnistion. 

Scrap materials often can be put to good use. When using scrap, however, it is best to weld with a low-hydrogen E7016-18 type of electrode, since the analysis of the steel is unlikely to be known, and some high-carbon steels may be encountered. Low-hydrogen electrodes minimize cracking tendencies. Structural scrap frequently comes from dismantled structures such as elevated railroads, which used rivet-quality steel that takes little or no account of the carbon content. 

As a result, ultra high modulus carbon fibers are preferred to others for their high stiffness/ density ratio for a low CTE compared with titanium or aluminum. Since composites are preferred to metal parts, bonding becomes the mandatory technology for fastening parts, because drilling and the bolt/nut/rivet principle require holes which affect the mechanical properties of the joint due to concentrations of loads around sectioned fibers. 

Rivets made from LCP materials offer many good qualities compared to metal fasteners. LCP rivets used to fasten carbon fibre/epoxy composites are cheaper and lighter than, for example, titanium fasteners and given fewer corrosion problems than aluminium. LCP rivets are also favourable in connection with aluminium panels. 

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