Rivet-bonding

When materials with different coefficients of linear thermal expansion (CLTE) are bolted, riveted, bonded, crimped, pressed, welded, or fastened together by any method that prevents relative movement between the products, there is the potential for thermal stress. Most plastics, such as the unfilled commodity TPs, may have ten times the expansion rates of many nonplastic materials. However there are plastics with practically no expansion. Details are reviewed in Chapter 2, THERMAL EXPANSION AND CONTRACTION. 

Interestingly, a process similar to the practice of using nails to tack wood members together while the glue cured also survived the transition to metal substrates and was known as rivet-bonding. In this practice adhesive was applied between metal details and fasteners installed to hold the two together while the adhesive was cured, either in an oven or at room temperature. The fasteners did double duty as the means of applying bond pressure as well as to carry loads in service. Because of the very non-uniform bond pressure, this method had the potential to introduce voids that in some cases became sites for corrosion initiation and delamination. 

The primary desired method of load transfer through an adhesive bonded joint is by shear. This means that the design mnst avoid peel, cleavage, and normal tensile stresses. One practical apphcation of a method avoiding other than shear stresses is the nse of a rivet bonded construction (Fig. 4.35). The direction of the fibers in the onter ply of the composite (against the adhesive) should not be 90° to the expected load path. 

ADHERENO STRESS DISTRIBUTIONS (OIREa OR SHEAR) Figure 4.35 Load transfer in rivet-bonded construction. (From Ref. 45)... 

Rivet bonding the combination of a small number of rivets and a structural adhesive can usually give a much stronger assembly than a large number of rivets used alone [3]. This process has been widely used in the assembly of school buses for many years... 

Pirondi A, Moroni F (2009) Clinch-bonded and rivet-bonded hybrid joints application of damage models for simulation of forming and failure. J Adhes Sci Technol 23 1547... 

Transition Joints. Use of explosion-clad transition joints avoids the limitations involved in joining two incompatible materials by bolting or riveting. Many transition joints can be cut from a single large-area flat-plate clad and deflvered to limit the temperature at the bond interface so as to avoid undesirable diffusion. Conventional welding practices may be used for both similar metal welds. 

Ceramics cannot be bolted or riveted the contact stresses would cause brittle failure. Instead, ceramic components are bonded to other ceramic or metal parts by techniques which avoid or minimise stress concentrations. 

It is clear that European civil aircraft manufacturers adopted adhesive bonding for major structural elements much more rapidly than their American counterparts, but it is difficult to determine exactly why. Certainly a number of contributing factors are obvious. One was a history of success in incorporating adhesively bonded structure in military aircraft such as the Mosquito. Although the Mosquito was the most unusual and extreme example of adhesively bonded structure, other European wartime aircraft contained bonded structure as well. American military craft of the time were almost exclusively riveted aluminum structure. 

Local repair of delamination originally caused by non-durable surface treatment is only temporarily successful at best. The surface treatment on the unrepaired portion of the assembly remains susceptible to attack and the area of delamination will likely continue to grow once the assembly is put back into service and exposed to moist conditions. Replacement or complete remanufacture of the component is the only way to permanently address this type of damage. However, time-limited repairs using bonded or mechanical methods can be used to extend the life of the component until a major overhaul is scheduled. In some cases such as widespread disbond of fuselage doublers, mechanical repairs (rivets and fastened doublers) and continued inspection are used to extend the life of the skin indefinitely because of the high cost of replacement. 

The first type of bonded design for this application was the beaded doubler panel (Fig. 28). This design was fairly successful at addressing the problems with simple riveted structure but had two primary drawbacks. The area under the beads remained a single thickness sheet and was still prone to fatigue. Reducing the unbonded areas under the beads was not a solution because it reduced the overall stiffness of the panel. Secondly, tooling for these panels was complex and not very robust. Autoclave pressure applied to the beaded areas of the doubler would cause them to collapse, so thick frames were fabricated with cutouts for the beads to protect them. A rubber layer bonded to the surface of the frames... 

Bonding enables stresses to be distributed over large areas in the joint, thus avoiding the local stress concentrations present in riveted or spot-welded joints which can reduce fatigue resistance. 

Bonding can eliminate crevices that often lead to crevice corrosion in riveted joints. 

A new approach was proposed for making effective helmets which could replace the former British army steel helmet. Essentially the new helmet used modified phenolic resins reinforced with nylon, and the crown cap inside was thermoformed from polyethylene. Formerly the crown cap was attached to the steel by rivets—not an appropriate method for fixing polyethylene to reinforced plastics. Instead a method was developed with a hot-melt adhesive based on ethylene-vinyl acetate copolymers cast as film on release paper. For assembly, the cast film is cut in advance to match the intricate shape required and activated by heat to bond under light pressure subsequently, a further heat activation is employed to fix the crown cap in place (Figure 52 illustrates this). 

Where neither a load-carrying component nor a less critical component can be completely manufactured from the reservoir material, a useful alternative is to bond, rivet or press composite onto the surface of a metal component, or to incorporate inserts of the composite in a machine component. Many applications of this technique have been developed, and a few examples will serve to illustrate it. 

The retainer may be completely fabricated from a composite material, or may consist mainly of a composite with reinforcement by metal rings. Alternatively it may be conventionally fabricated of steel or other suitable metals, with composite components bonded, rivetted or pressed onto it, or with holes or grooves filled with the lubricant composite. 

C. A. Rivet, and E. D. Smith. Anal. Chem. 23, 730-2 (1951). Correlation of chromatographic adsorption with H bond interactions. 

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