Thick adherend test

Results from EUROCOMP test programme at Helsinki University of Technology ) Napkin ring torsion tests Thick adherend test Sections in EUROCOMP Handbook... 

ASTM D 3983-81—Measuring strength and shear modulus of nonrigid adhesives by the thick adherend tensile lap specimen [thick adherend test]... 

Thick adherend test data suggests FM 400 is superior. 

A recently developed method is the so-called thick adherend test , (ASTM D 3983-81) in which it is attempted to minimize the effects of differential straining using stiff, thick, metallic or wooden adherends. In this form of joint, there is a considerable increase in the flexural stiffness of the adherends. The combination of these two properties has led to the popular belief that the adhesive is now in a state of uniform shear and there are no significant transverse peeling loads (but see Renton, 1976). 

Although the thick adherend test piece may be a cheaper and more simple joint to manufacture than the napkin ring test piece, it has a number of limitations to its applicability that appear to be not generally recognized. In particular, the measurement of the small glue-line deformations requires considerable experimental care and accuracy, if reliable results are to be obtained. 

The stress-strain curves of adhesive layers under a close-to-uniform state of deformation, as in O Fig. 44.1, are customarily measured on a thick-adherend test coupon using very sensitive displacement extensometers, developed by Krieger (1988), as shown in O Fig. 44.5. Each aluminum adherend is typically 9.5 mm (0.375 in.) or 12.7 mm (0.5 in.) thick to enforce a close-to-uniform shear strain in the adhesive. 

The various forms of lap joint described in Section 3.2.1 do not really provide a true measure of the adhesive shear properties, with the possible exception of the thick adherend test, although this cannot give the ultimate shear strength. 

Peel tests are accompHshed using many different geometries. In the simplest peel test, the T-peel test, the adherends are identical in size, shape, and thickness. Adherends are attached at thek ends to a tensile testing machine and then separated in a "T" fashion. The temperature of the test, as well as the rate of adherend separation, is specified. The force requked to open the adhesive bond is measured and the results are reported in terms of newtons per meter (pounds per inch, ppi). There are many other peel test configurations, each dependent upon the adhesive appHcation. Such tests are well described in the ASTM hterature. 

Fracture mechanics (qv) tests are typically used for stmctural adhesives. Thus, tests such as the double cantilever beam test (Fig. 2c), in which two thick adherends joined by an adhesive are broken by cleavage, provide information relating to stmctural flaws. Results can be reported in a number of ways. The most typical uses a quantity known as the strain energy release rate, given in energy per unit area. 

There is a need for an accurate assessment of the mechanism of cathodic debonding of thick adherends. This would contribute to better control over the selection of formulations resistant to attack. One of the objectives of this work was to develop an accelerated screening test. The screening test was used to evaluate the relative performance profiles of a number of commercial adhesives which were recommended for marine applications. It is hoped that a screening test such as this one could be used to isolate measurable primer properties which can be related to the long term prospectus of the primer, and the variability of this prospectus under permutation of substrate type or additives. 

Adhesives by the Thick Adherend Tensile Lap Specimen D 4027 Test Method for Measuring Shear Properties of Structural Adhesive by the... 

To enable the determination of almost pure strength values for the adhesive layer, the parameters eccentric application of load and adherend extension/ deformation must be eliminated. This is the case in the test piece geometry depicted in Figure 10.4 according to the standard ISO 11003-2 Shear testing method for thick adherends . 

Rg. A6. Thick adherend shear test (TAST) specimen. 

For thick adherend lap shear test specimens a surface treatment was performed. The aluminium adherends were 10 mm thick and 25 mm wide. After the specimens were cured and postcured, the adherends were cut to form a test area with an 8 mm lap length. 

Thick adherend lap shear tests (TALST) were not based on any standard. However, standard practice used in the tests was followed. The displacement rate used was 0.3 mm/min. The adhesive layer displacement was measured using two in-house built KGR-1 type extensometers. 

Astm D5656-01. (2001). Standard test method for thick-adherend metal lapshear joints for determination of the stress-strain behavior of adhesives in shear by tension loading. 

Several testing techniques are possible which use different specimen configurations, different loading modes, and various loading frequencies. Marceau et al. have described results for thick adherend lap shear and double cantilever beam (DCB) specimens exposed to 140 F/100%... 

An adhesively bonded structure is considered in shear when the applied loads act in the plane of the adhesive layer. The loads tend to produce sliding of the adherends and this results in sliding or shearing of the adhesive. These shear stresses should not be confused with pure shear stresses, which are typical of uniform blocks of a homogeneous material. Interactions between adhesive thickness, adherend thickness and yield strength, and bond geometry produce nonuniform stresses. When this occurs, the shear bond may actually be dominated by tensile stresses rather than shear stresses. However, in service, adhesive structures rarely encounter these pure shear conditions. Therefore, standard shear tests provide adequate duplication of conditions which may exist in an actual structural adhesive application. 

Samples for the floating roller peel test can be a bonded honeycomb type or any adhesive assembly consisting of a rigid adherend and a relatively flexible adherend. Test specimens are typically aluminum with the flexible adherend being 0.025 inch thick and the rigid adherend at 0.064 inch thickness (see Figure 16). Samples are tested in a tensile machine at a crosshead speed of 6 inches/min for three inches of peel distance. Peel strengths are reported in pounds per inch of peel width. 

Test Method for Measuring Strength and Shear Modulus of Nonrigid Adhesives hy the Thick-Adherend Tensile-Lap Specimen-, and ASTM D2979, Standard Test Method for Pressure-Sensitive Tack of Adhesives Using an Inverted Probe Machine. 

BSl (2011), BS EN 14869-2 2011 Structural adhesives. Determination of shear behaviour of structural bonds. Thick adherends shear test, 2011 edn. London British Standards Institution. 

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