Adhesive bonding joint design

Bonding Adhesives for Design of Structural Joints D 5677 Specification for Fiberglass (Glass Fiber Reinforced Thermosetting Resin)... 

In selecting an adhesive system, one must calculate the strength required. If, for example, you wish to design an adhesive-bonded lifting device for a 50 lb (23 kg) machine component, you can use an adhesive with a 100 psi (0.689 MPa) shear strength and make the bond area 0.5 in (3.2 cm ). You must use this type of joint-strength analysis in all adhesive-joint designs [Ref. 4, pp. 171-172]. 

Techniques Adhesive Bonding, Solvent Bonding, and Joint Design, Supplier Technical Report ( SR-401A), Borg-Wamer Chemicals, Inc., Parkersburg, WV, 1986. 

P(6) For an adhesively bonded connection and a bonded insert joint designed by testing, the following partial material safety factors shall be used ... 

The long-term durability of an adhesively bonded connection, i.e. its ability to function effectively throughout its design life, is a vital prerequisite for the successful use of adhesives. Tests and experience are important to evaluate the long-term durability of a correctly bonded adhesive joint. 

From the viewpoint of the adhesive technologist, plastics are an anomaly bonded joints can be made in which the plastic fails before the adhesive, but certain plastics are very difficult to bond. Although plastics often present difficulties in adhesive bonding (Table 4.2), all can be joined successfully with the correct choice of adhesive, joint design, and surface preparation [28] ... 

OPTIMIZING ADHESIVE BONDING THROUGH JOINT DESIGN—A PRACTICAL APPROACH... 

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. 

Adhesive Disadvantages. There are some limitations in using adhesives to form assemblies. The major limitation is that the adhesive joint is formed by means of surface attachment and is, therefore, sensitive to the substrate surface condition. Another limitation of adhesive bonding is the lack of a nondestructive quality control procedure. Finally, adhesive joining is still somewhat limited because most designers of assemblies are simply not familiar with the engineering characteristics of adhesives. 

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. 

Much of what we know about bonding to composite materials has come through the aerospace industries. The early studies on adhesives, surface preparation, test specimen preparation, and design of bonded composite joints reported for the PABST Program76 gave credibility to the concept of a bonded aircraft and provide reliable methods of transferring loads between composites and metals or other composites. 

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. 

Our research builds on this limited body of work concerning diffusion at the interface of adhesive joints. We have measured the interfacial diffusion process of acetone into a bonded pressure sensitive adhesive tape bj employing single frequency capacitance measurements and a novel interdigitated electrode sensor design. 

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