Testing of Adhesive Joints

Testing, in general, is the evaluation of the properties of a material, either chemical, physical, mechanical, thermal, or others. In this chapter, all references to testing should be interpreted as mechanical testing. 

Mechanical testing is the determination of the behavior of a material caused by some applied loading. The material is loaded in its bulk form via a mechanical testing machine (i.e., MTS, Instron, etc.) and its properties are evaluated. Typically these include the elastic modulus or stiffness, the yield strength, the fracture stress or ultimate strength, the elongation, and Poisson s ratio. These properties depend on the mode of loading, such as tension, compression, shear, or flexure. 

The evaluation of adhesives by mechanical test methods is complex due to the state in which the adhesives are tested. Common adhesive tests require that the sample actually act as a bonded system formed by the adhesive in question and the appropriate substrates. Contrary to the usual testing of materials in their bulk form, adhesives are usually tested as one component of a system of many parts. An adhesive test actually tests the total bonded assembly, i.e., the substrates, the joint geometry, the interface, the primer coat, the surface preparation, the curing cycle, and the adhesive itself. 

The adhesive tests commonly used give valuable information for quality control, as well as providing a comparative evaluation of different adhesives. If all the conditions of the test and the techniques of bonding are kept constant, the test can provide useful information on the quality of different batches of identical adhesives, or a comparison of the properties of a group of adhesives. If the experiment is changed by varying a factor other than the adhesive, the test method can provide information about the performance of, for example, a primer or surface preparation. 

The evaluation of an adhesive by various test methods also helps in the prediction of the behavior of a joint design using the particular adhesive. However, it is difficult to translate the behavior of an adhesive from a test to its performance in actual service. This difficulty arises because most standard test techniques do not simulate actual bond geometries, environmental conditions, and stresses in the designed system. 

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Acoustic emission test of adhesive joints of the carbon plastic UKN-5000. 

ASTM D 896-84, Standard Test Method for Resistance of Adhesive Bonds to Chemical Reagents, specifies the testing of adhesive joints for resistance to solvents and... 

Groth, H., Shear lag analysis and testing of adhesive Joints with viscoelastic and viscoplastic adhesives, Proceedings of Nordic Composites and Sandwich Meeting, Royal Institute of Technology Stockholm, Nov. 19-20 1991, Organised by Nordic Industrial Fund and KTH,... 

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. 

This paper has provided an in-depth discussion on the fracture of adhesive Joints with a focus on how to deduce the intrinsic fracture parameters of the adhesive layer from experimental results. The approach of using these parameters in cohesive-zone models to predict the fracture of adhesive Joints has been outlined. By using this approach, many important issues that are frequently encountered in the fracture testing of adhesive Joints, yet are usually ignored by traditional fracture analyses, have been fully addressed and the results are presented in the... 

These data were applied on the generalized temperature-concentration diagram of the surface energy of EVA (Fig. 4), taken from Ref. [7], which includes both the operating conditions and testing of adhesive joints (curve 1), and also the conditions of the adhesive joints formation (curve 2). Traditionally [8], dependencies of the surface energy from the composition of the random copolymers describe by the simple additive function - the dotted lines. As can be seen in Fig. 4, the surface eneigies of the copolymers are close to additive values. 

Finally, the above are concerned with the design and destructive testing of adhesive joints but non-destructive testing is also an important aspect of adhesives technology and will be discussed in the present chapter. 

A range of sonic vibration techniques may be used for non-destructive testing of adhesive joints [143,147,148]. Most of these depend upon a void causing a local change in stiffness and hence a change in vibrational properties of the structure. They involve applying vibration excitation at a test point and... 

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