Adhesion test , description

The preceding has been a description of our efforts to develop a screening test for adhesives which will be used on steel or monel substrates which are maintained at a cathodic potential, immersed in... 

FIGURE 13.9 Descriptions of simple tensile detachment (a) and simple lap shear (b) assemblies for testing adhesion. 

A standard test report usually documents the resulting measurements, such as tensile shear strength and peel strength. It should also indicate all the pertinent conditions that are required to ensure reproducibility in subsequent testing. It is often very useful to describe the failure mode of the tested specimens. An analysis of the type (or mode) of failure is an extremely valuable tool to determine the cause of adhesive failure. The failed joint should be visually examined to determine where and to what extent failure occurred. The percent of the failure that is in the adhesion mode and that in the cohesion mode should be provided. A description of the failure mode itself (location, percent coverage, uniformity, etc.) is often quite useful. The purpose of this exercise is to establish the weak link in the joint to better understand the mechanism of failure. 

Numerous standard test methods have been developed by various government, industrial, and university investigators. Many of these have been prepared or adopted under the auspices of the ASTM Committee D 14 on Adhesives or other professional societies. Reference to the appropriate standards will adequately equip one with the background necessary to conduct the test or a version of it. Several of the more common standard tests are described in this section. Numerous variations exist for specific applications or materials. In these descriptions, the emphasis is on understanding of the reasons for the test, its relationship to a specific adhesive property, advantages and limitations of the test, and possible variations or extrapolations of the test method. The detailed description of the test mechanics is kept to a minimum, since they are adequately covered in the existing standards and specifications. 

In this paper, we present test results of two methods for surface pretreatment which are generally applicable under atmospheric conditions and which can be integrated in the production line. Pragmatic approaches for the numerical description of the material behavior of adhesives according to specific loading conditions are given. Furthermore, we present model parameters for some commercial adhesive systems which were tested in relevant conditions. A concept of knock-down factors and characteristic values which is widely used in component design will be discussed. Experimental results were used to manufacture a fuUy bonded structural component of a rail vehicle. Test results are compared with FE-model predictions. 

Under normal service conditions, stresses due to cyclic loading are small and deformations can therefore be considered to be elastic. However, cyclic loading may cause fatigue of the adhesive. A conventional fatigue testing technique involves determination of so-called S-N curves, where S is the stress amplitude and N is the number of cycles to failure. At this point, it would be useful to define some important parameters that are used in the phenomenological description of the fatigue phenomenon. Based on Fig. 33.5, the stress amplitude can be defined as in Eq. (3) we use t since samples were loaded in shear. 

Beyond the particular process of cure in this case, the important problem which should not be neglected is the bonding of the rubber to the metal. This problem of adhesion of rubbers to metals is very weU covered in Reference [27] where a full description of the various tests is given. Another case of interest appears with the cure of a rubber when the cure is bound to various fabrics in order to get proofed materials such as hose. 

Acrylics, s poly methyl methacrylate Acitainer, 255 description, 256 design considerations, 258 development, 257 material selection, 263 production details, 267 testing, 269 Adhesives... 

In conclusion, a description of a wide variety of test techniques can provide direction in choosing an appropriate test. The tests described in this section are under the jurisdiction of ASTM Committee D-14 on adhesives. It is suggested that before applying any of these test techniques, references should be made to the specific ASTM standard for detailed procedures. 

For detailed descriptions of these test specimens, the test methods, and sample fabrication procedures, reference should be made to ASTM D3433-75. Another test specimen designed to test structural adhesives in mode I is the cleavage specimen for metal-to-metal bonds as described in ASTM D1062-78. 

Tack. Tack is in many ways similar to peel adhesion in that a bond is formed and then broken in a lifting manner. When dealing with theoretical descriptions of tack, all of the same considerations that are involved with peel adhesion mechanics are employed. In a practical sense, however, the bond formed in a tack test typically exists for only a short time and is formed with a relatively light amount of force when compared to a peel test. In addition, the test is typically performed with the tape held fixed and a probe or ball being used to contact the tape. 

Role of polymer Adhesive/coating/consoli-dant/moulding material A brief description of the tested conservation application is valuable Cellulose acetate was rejected as a picture varnish... 

However, it is also necessary to discuss how broadband bulk, shear and Poisson s ratio are measured. The measurement of the broadband shear modulus is easily accomplished using the time-temperature-superposition-principle (TTSP) and a torsion test. See Kenner, Knauss and Chai (1982) for a description of a simple torsiometer and the measurement of a master curve for a structural epoxy adhesive, FM-73, at 20.5° C. 

The strength of an adhesive joint is a system property dependent on the properties of the adhesive, the adherend(s), and the interphase and requires an understanding of mechanics, physics and chemistry. Accordingly, this chapter will provide a brief overview into proposed mechanisms (or molecular models) responsible for adhesion before embarking on a description of a number of test methods and discussing the meaning of some test results. 

The fundamental mechanism that determines how one material adheres to another material has not been unambiguously identified. Indeed, it appears that different mechanisms might be active in different adhesive joints depending on a variety of factors. Despite extensive and careful research, no definitive, universally accepted relationship has been established between specific atomic or molecular parameters at or near an interface and the strength of an adhesive bond. While the purpose of this chapter is to explore the measurement of mechanical properties of joints, a brief description of proposed mechanisms, or theories, responsible for adhesion is presented to provide insight into the interpretation of physical test results. Details of these theories are available in references [1-4], The following six theories are perhaps the most widely accepted mechanisms for one material adhering to another. 

On the use of nomenclature, it should be noted that there are obviously many failure paths available to a crack in an adhesive joint, and frequently the adhesive is also tested as a bulk, homogeneous material. To avoid the use of too many subscripts, etc. the symbols G and K will be used freely to represent any of the possible options mentioned above and, hopefully, the text will make clear the type of test and locus of failure. Where confusion might arise then a suitable subscript or bracketed description will be used in that part of the text. 

The stresses in joints are discussed extensively so that the engineer can get sufficient philosophy or feel for them, or can delve more deeply into the mathematics to obtain quantitative solutions even with elasto-plastic behaviour. A critical description is given of standard methods of testing adhesives, both destructively and non-destructively. The essential chemistry of adhesives and the importance of surface preparation are described and guidance is given for adhesive selection by means of check lists. For many applications, there will not be a unique adhesive which alone is suitable, and factors such as cost, convenience, production considerations or familiarity may be decisive. A list of applications is given as examples. 

Abstract This chapter gives a brief description of special mechanical tests for various types of materials and sample geometries, such as blister tests for membranes/adhesives/coatings, tensile tests and shear tests for sealants/foam adhesives, indentation and scratch tests for coatings, tack tests for pressure-sensitive adhesives (PSAs), and bimaterial curvature tests for characterizing residual stress, stress-free temperature (SFT), and coefficient of thermal expansion (CTE) of adhesives bonded to substrates of interest. In addition, some applications of these tests, including the nano-/micrometric scale, are also described in this chapter. 

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