Bonds joint design

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. 

In the bonded joint design the most basic problems are the unavoidable shear stress concentrations and the inherent eccentricity of the forces causing peel stresses both in the adhesive and in the adherends. At the ends of the overlap both the peel and shear stresses reach their maximum values, resulting in reduced load-bearing capacity of the joint, see Figure 5.28. 

P(l) The loads for the bonded joint analysis shall be obtained from the global analysis of the structure. The bonded Joint design ensures that the bondline is capable of transferring the applied loads between the Joint members and that the joints members (adherends) are capable of withstanding the Joint-induced internal loadings. The basic strength of the components to be Joined under the applied external loads shall be evaluated as a part of the component design process (Chapter 4). 

There are certain fundamental rules in the bonded joint design that have to be followed throughout the design. These rules, or principles, also form the basis to how the different Joining techniques are dealt with in the EUROCOMP Design Code and, more generally, how the bonded Joint sections of the Code are structured. The main joint design principles are listed below, followed by further explanations ... 

It is important to realise that the bonded joint design may only ensure that the joint is capable of withstanding the external loads assumed in the design. Further on, in the case of certain configurations with highly eccentric load paths, such as lap and strap joints, it... 

Bigwood D A and Crocombe A D (1990), Non-linear adhesive bonded joint design analyses , Int J Adhes Adhes, 10(1), 9. 

Some researchers have also measured what they perceive to be fracture-mechanics properties under up to three modes, the first being crack-opening, and the second shear, thinking that these properties could form the basis of bonded joint design. The author has yet to see any successful joint designed using these properties and will not discuss them further. No such... 

When the scanning of the adhesive bonded joint between the shells on the leading edge is complete, the rotor blade is rotated 180° and another special designed Y-module is applied for inspection of the trailing edge of the rotor blade in set-up 3, illustrated on figure 5. 

L. J. Hart-Smith, Design of Adhesively Bonded Joints, in Joining Fibre-Reinforced Plastics, F. L. Mathews (Editor), Elsevier Applied Science, London and New York, 1987, pp. 271-311. 

Tong, L., et al., Analysis Design of Structural Bonded Joints, Kluwer, 1999. 

Dillard D A, Leichti K M, Lefebvre D R, Lin C, Thornton J S. Adhesively Bonded Joints, Testing, Analysis and Design, Baltimore, 1986, Proceedings p 83. 

The best approach to achieving good performance in bonded joints is to select the proper adhesive, design the joint properly for the specific application, and maintain rigid process control. One disadvantage in the use of adhesives is the absence of good non-destructive tests to determine the strength of adhesive-bonded joints in a wide variety of ord applications... 

Important Processing Issues. As with conventional adhesive bonding, there are several important issues that cannot be overlooked with weldbonding. Two of the most important issues are joint design and surface preparation. 

Adherend stresses in weldbonded joints are lower and more uniform than those for comparable spot welded joints. This provides increased in-plane tensile shear and/or compressive buckling load-carrying ability for a given joint design. The presence of the spot weld provides enhanced out-of-plane load-carrying capability compared to adhesive bonding only. 

Morris, C. E. M., Strong, Durable Adhesion Bonding Some Aspects of Surface Preparation, Joint Design, and Adhesive Selection, Materials Forum, vol. 17, 1993, pp. 211-218. 

Certain specifications and standards provide excellent tutorials on adhesives and sealants. For example, MIL-HDBK-691 offers a complete handbook on adhesive bonding, and MIL-HDBK-725 provides a guide to the properties and uses of adhesives. ASTM C 962 provides an excellent source of information regarding sealant joint design and the types of sealants that are appropriate for various substrates. Although this specification is primarily for construction sealants, much of the information that it contains is generally useful for other sealant applications. 

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. 

Anderson, G. P., et al., Effect of Removing Eccentricity from Button Tensile Adhesive Tests, Adhesively Bonded Joints Testing, Analysis, and Design, ASTM STP 981, W. S. Johnson, ed., American Society of Testing and Materials, Conshohocken, PA, 1988. 

Tong L, Steven GP, Analysis and design of structural bonded joints, Kluwer Academic, 1999. 

The difference between expansion joint design and location in floors protected with bonded tile or brick, and monolithic toppings and surfacings, and in floors protected by "acid brick" laid with chemically-resistant mortars over an impervious membrane. 

Bonded joints have to be designed in a way that forces applied cannot result in peeling or cleavage in the adhesive layer (Figure 11.1). 

In conclusion, the following principles apply to the constructive design of bonded joints ... 

---