Applications to Adhesive Bonding

This equation can be used to generate expressions applicable to adhesive bonds. Figure 13 shows a situation where two thick adherends are used to make a simple adhesive bond. Equation (63) follows from simple beam theory, ... 

Surface-sensitive techniques for use in the study of adhesive bonding are discussed, including X-ray photoelectron spectroscopy and auger electron spectroscopy/scanning auger microscopy. Data analysis is considered, with reference to quantification, chemical-state information, depth-distribution information and surface-behaviour diagrams. Applications to adhesive bonding are described, particularly failure analysis, hydration of phosphoric acid-anodised aluminium and adsorption of hydration inhibitors. 100 refs. 

The inception of epoxy adhesives occurred almost simultaneously with the commercialization of epoxy resins. This is due to the fact that all the unique handling, application, and performance properties of epoxy resins are especially important when it comes to adhesive bonding. 

Adhesives have been used successfully in a variety of applications for centuries. Today, adhesives are more important than ever in our daily lives, and their usefulness is increasing rapidly. In the past few decades there have been significant advances in materials and in bonding technology. People now routinely trust their fortunes and their lives to adhesively bonded structures and rarely think about it. 

For applications in adhesive bonding research or technology, ellipsometry is useful for the quantitative determination of film thicknesses. Especially aluminum is a metal that has been studied extensively. It lends itself well to oxide thickness measurements because AI2O3 is transparent, whieh is a requirement. The thickness of the oxide formed in certain media can be determined [92]. Other studies reported on the use of ellipsometry to investigate the corrosion or rate of oxide film dissolution in certain environments in situ. As the film dissolves, the formation of pores and differences between the densities of different layers in the oxide film ean be distinguished and related to the conditions of the anodizing process [93]. 

New applications of adhesive bonding can be expected where the specific advantages of this joining technique will be usable. Due to lightweight construction, which will be more and more important, outside panels must be used as supporting parts of the body structure. Conventional sheet steel constructions often show welded joints at the visible... 

In all of these applications the adhesive bond must remain sufficiently strong and stiff over the 20-40 year life of the rolling stock the adhesive itself must also remain sufficiently flexible to allow joint deformation under impact loading. In these respects British Rail have favoured two-part acrylics, at least for use with zinc-coated steels. 

Many tests, for example Tensile tests and Shear tests, measure a critical stress rather than an energy of fracture. Good has pointed out that this critical stress will also depend on the fracture energy. He adapted the Griffith - Irwin theory of fracture for application in adhesive bonds. According to this theory, the fracture stress Of of material of modulus E will be given by... 

The importance of the surface condition prior to adhesive bonding of metal substrates has been widely reported in the literature. A number of separate articles are provided, which arc cross-referenced in this article or listed at the end. Here are presented a number of general comments that are applicable to all metal bonding pre-treatment procedures. The aim of the following section is, firstly, to describe the role of a metal pre-treatment and, secondly, to aid in the selection of a particular process. 

In Thermal spray processes the nature of the process was described here, applications to adhesion are presented. Thermal spray coatings for applications involving adhesion are in three general areas, metallic bond or anchor coating, ceramic bond coat, and sprayed polymer as the adhesive. In many cases, the surface modification by the deposition of a thermally sprayed coating is an alternative to environmentally hazardous methods. The thermal spray process is a dry process in which the effluent is collected in a dry cartridge system and usually recycled. 

Nondestructive Testing of Adhesive Joints. Many commercially available adhesives are based on polymers. NDT of adhesive joints (180) poses challenges because of (2) the small size of possibly deleterious defects (eg, porosity), (2) the thinness of the adhesive layers, and (3) sometimes, the size, shape, and material of the adherends. Acousto-ultrasonics (181) and various types of ultrasonics (182,183) are applicable to adhesive joints. Ultrasonics can be combined with noncontact optical methods (184) and pulsed thermography (185). However, the assessment of the quality or of the quantitative strength of the adhesive bond based on the NDT data often proves difficult. 

EN ISO 8504-1 Preparation of steel substrates before application of paints and related products. Surface preparation methods. General principles. ISO 17212 Structural adhesives. Guidelines for the surface preparation of metals and plastics prior to adhesive bonding. 

The successful and cost-effective application of adhesive bonding technology is crucially dependent on correct joint design. The adhesive joint must be adequately dimensioned for the forces to transmit. Large static loads should be avoided wherever possible - especially where the joint is exposed to higher temperatures. In such cases, joints should be optimised to provide additional support. Similar measures should be taken to counteract peeling stresses (Fig. 24). Some examples are illustrated in the chapter Technical Characteristics in Volume 1. 

Phosphoric acid anodization (PAA)( > is a common method of surface preparation of aluminum adherends prior to adhesive bonding for aerospace applications. PA A surfaces are microscopically rough(6) and are more resistant to hydration than aluminum surfaces prepared by other treatments.(2,90) The microroughness provides for mechanical interlocking with the primer or adhesive, which results in a strong adhesive bond, while the environmental stability of the oxide (together with its porosity) results in excellent bond durability in hot, humid environments. 

G. A. Alers and R. K. Elsley, Application of quantitative ultrasonic signal analysis to adhesive bond strength prediction. Structural Adhesives and Bonding, pp. 119-137 (March 13-15, 1970). 

---