Spot adhesion test

ASTM D3808-01 Standard practice for qualitative determination of adhesion of adhesives to substrates by spot adhesion test method. 

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Qualitative Determination of Adhesion of Adhesives to Substrates by Spot Adhesion Test Method, Practice for (D 3808)... 

D-3808. (See plastics, miscellaneous.) Spot adhesion test developed for plastics but may be usable with glass. 

Fig. 12. (a) Schematic of microlens array used in combinatorial JKR adhesion test with two parameters varying along orthogonal axis, (b) Experimental results from combinatorial JKR adhesion test displaying thickness dependence of critical welding temperature for polystryrene self-adhesion. Weld spots are visible features in image. The two isolated data points were collected from independent adhesion tests. Edges of microlens array are indicated by solid black lines. 

In this test, small spots of the adhesive are placed onto a substrate. Surface preparation, application procedures, and curing conditions are to be as similar as possible to those used in the quantitative test and/or the actual adhesively bonded Joint. The adhesive spots are allowed to cure according to the manufacturers specifications. To test adhesion, this ASTM standard practice recommends the use of a thin stainless steel spatula or similar probe as a prying lever to assess the relative difficulty of removing the adhesive from the substrate. If the results are acceptable, standard quantitative adhesive test procedures can be used to obtain quantitative measurement of the adhesive s performance. 

Both impact and friction were considered by Bowden and Yoffe [8, 83] to be stimuli which lead to initiation via the formation of hot spots. Insofar as no existing test is entirely free of both impulsive loads and the movement of explosive particles with respect to contiguous surfaces, both adhesion and shear may be suspected to play a role in determining sensitivity, and it is not uncommon to consider the brittleness and hardness of azides and other primary explosives when comparing their sensitivities to those of secondary explosives. 

Poor bonding arises from problems associated with the adhesive itself for example, its decreased adhesive power. The simplest method of checking on the spot for any decrease in adhesive power is to test with Bakelite samples. If the adhesive is found to have decreased adhesive power, it has probably been stored improperly. 

These three adhesion measures of molecular adhesion, in the contact make-and-break process, also allow us to test the second law of adhesion, that contaminant molecules always decrease the attraction between bodies. Consider immersing the rubber spheres in water and repeating the adhesion experiment. The results show that all three indicators of molecular adhesion (the jumping into contact, the size of the contact spot, and the pull-off force) are diminished by the presence of the water molecules. Adhesives reduce adhesion ... 

It is evident from these results that two of the adhesion proeesses (making contact and breaking contact) can be observed in the atomie force microscope. The size of the contact spot can also be deteeted if some additional technique for sensing contact spot size is used, for example, eleetrieal contact or thermal contact. Thus the three stages of adhesion can be found in the AFM. It has become clear from sueh measurements that all materials adhere in this test, verifying the first law of adhesion. These results will be considered in more detail in Chapter 4. 

This was the idea adopted by Tomlinson in 1928, to contribute to the lively debate at that time about the rate of change of molecular attractions with separation, which will be considered in detail in Chapter 5. Tomlinson heated and drew fresh fibers of fused silica to perform adhesion experiments, bringing the crossed fibers together to observe the contact point, which he estimated to have a black spot size less than 1 pm, and measuring the force of adhesion by elastic deflection of the fiber, as shown in Fig. 4.10. He also formed spherical blobs on the ends of the fibers and tested these in the same way. 

It has been shown that in comparison with spot welds, rivets and a variety of selfpiercing mechanical fastenings, toughened structural adhesives may yield single lap shear joints of superior energy absorption when used to bond aluminium alloy sheet the findings were confirmed in tests on full-size bonded vehicles (see Toughened adhesives, Structural adhesives). 

XPS (with small-area or small-spot capability) is particularly useful in adherend surface studies for identifying the chemical states of the major constituents of the surface. Areas as small as 150 xm in diameter can be analyzed routinely in modem spectrometers. This small-area capability allows rapid acquisition of XPS sputter depth profiles and facilitates failure analysis of debonded surfaces in both test and (unintentionally failed) production structures. In addition, XPS can also be used to analyze insulating samples, which is often necessary in adhesive bonding studies. Most of the oxide chemistry and bond failure analysis studies presented below were done with XPS. Some of these studies are discussed in more detail in Chapter 6. 

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