Joint design methods

Design. Detailed adhesively bonded joint design and analysis methods are discussed elsewhere in this volume. General issues associated with bonded assembly design will be considered here. 

Reference [20] notes that any such system should be easy to learn and use, accurate, easy to update, flexible, well based and linked to existing design methods and tools. It should recognise innovation, include diverse environments and be acceptable to all partners in the construction process. The authors point out that the clear statement of assumptions enables them to limit the number of factors. Apart from the environment and the material, joints, contact with other materials and local movement all provide sites for degradation. Protective layers help provided that they remain intact, but degradation proceeds rapidly once they are penetrated. 

ASTM D 1144 provides a recommended practice for determining the rate of bond strength development for either tensile or lap shear specimens. However, peel and can-teliever tests can also be used effectively. Measured bond strength values of partially cured test specimens are compared with those of a reference (i.e., fully cured adhesive joint) to assess the extent of cure. This method may suit some applications, but it is limited in accuracy because it does not directly measure the degree of cure in the adhesive, and the effect on the joint design and substrates may override the effect of cure development. 

More recently, methods to design control chart parameters jointly with system logistics control parameters have been developed (Colledani and Tolio 2011). In particular, methods to jointly design control charts and... 

V Crupi, E Guglielmino, M Maestro, and A Marino. Fatigue analysis of butt welded AH36 steel joints Thermographic method and design S—N curve. Marine Structures, 22(3) 373—386, 2009. 

The Asphalt Institute deflection procedure for asphalt overlay design over rigid pavements is considered as a supplement to the effective thickness design method. It is used to determine if corrective actions to minimise pavement deflection, particularly at the joints, should be initiated prior to overlay construction this is only in the case when rubblisation, or crack (brake) and seat, has not been selected. 

Procedures for the determination of important properties are essential for the selection of an appropriate product and for joint design and analysis. We have seen that adhesive polymers are sensitive to temperature and moisture, and to the rate at which stress is applied. Their bondline behaviour in joints depends greatly upon the system stiffness, and upon more subtle variations such as bondline thickness. It is therefore important that test methods are relevant to the real application, the fabrication conditions, the actual materials to be joined, and so on. Many standard test methods exist, for both strength and durability assessment, and these were discussed in Chapter 4. 

When bonding elastic material, forces on the elastomer during cure should be carefully controlled, as too much pressure will cause residual stresses at the bond interface. Stress concentrations may also be minimized in rubber-to-metal joints by elimination of sharp comers and by the use of metal adherends sufficiently thick to prevent peel stresses that may arise with thinner-gauge metals. As with all joint designs, polymeric joints should avoid peel stresses. Figure 7.16 illustrates methods of bonding flexible substrates so that the adhesive will be stressed in its strongest direction. ... 

This is an extremely complicated subject and will oidy be touched upon here. The ultimate objective is to develop a design method for bonded construction based on the principles of mechanics and rational engineering design so that joint behavior can be predicted. 

P(l) Two design methods are given for the design of lap and strap Joints a simplified procedure and a rigorous procedure (5.3.5.4 and 5.3.5.5 resnertiveivl In both nmcediires Ian and stran inints are treated... 

The methods to reduce Joint peak stresses described in 5.3.1.3 should be applied to the bonded insert Joint design when practical. 

The rigorous design method is based on generally accepted closed-form models. The adhesive behaviour in the models is assumed to be linearly elastic. Only the formulae used in the calculation of the temporary maximum joint resistance require the complete shear stress—shear strain curve or the elastic—plastic model of the adhesive to be known. As adhesives typically have a non-linear shear behaviour, using only the linear part of the stress—strain curve brings added conservatism to the models with respect to the actual joint resistance. 

When practical, the methods described in 5.3.1.3 to reduce joint peak stresses should be applied to moulded joint design. 

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