Mechanical adhesion tests

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. 

Combination of Eq. 7 or Eq. 8 with the Young-Dupre equation, Eq. 3, suggests that the mechanical work of separation (and perhaps also the mechanical adhesive interface strength) should be proportional to (I -fcos6l) in any series of tests where other factors are kept constant, and in which the contact angle is finite. This has indeed often been found to be the case, as documented in an extensive review by Mittal [31], from which a few results are shown in Fig. 5. Other important studies have also shown a direct relationship between practical and thermodynamic adhesion, but a discussion of these will be deferred until later. It would appear that a useful criterion for maximizing practical adhesion would be the maximization of the thermodynamic work of adhesion, but this turns out to be a serious over-simplification. There are numerous instances in which practical adhesion is found not to correlate with the work of adhesion at ail, and sometimes to correlate inversely with it. There are various explanations for such discrepancies, as discussed below. 

Fundamental mechanisms of adhesion. All classical adhesion tests involve a rheological component, in the deformation of the near-interface material, and a surface chemical component. With the recent availability of microscopic techniques to study surface forces, one can possibly go after the surface chemical component, separately from the rheological component. More generally, the configurational and dynamic behavior of macromolecular interfacial regions remains a very rich area. 

In the case of direct application of E-coat to IVD specimens (one of the systems that showed excellent adhesion performance in both the tape test and the accelerated adhesion test), due to the high throw power of the E-coating process, the deep penetration of E-coat into the porous IVD structure creates mechanical interlocking and thus strong adhesion. Because of this development of mechanical interlocking, neither the tape test nor the accelerated adhesion test could distinguish the effect of plasma treatment on adhesion performance. 

Fracture mechanics characterisation tests have been performed to determine the mixed mode fracture envelope of an epoxy bonded glass/epoxy composite. Analysis of lap shear, and L-stiffener geometries has shown that for this relatively brittle adhesive reasonable first estimations of failure loads can be obtained for both cracked and uncracked specimens. An image analysis technique has been developed which enables failure mechanisms to be... 

Physical properties were evaluated using standard DIN or ASTM specifications. The sealants were filled into Teflon molds to form homogeneous test pieces of comparable thickness. The specimens were then moisture cured and conditioned at 25 °C and 50% relative humidity for 14 days before mechanical property testing. The hardness of the cured sealant samples was measured by Shore A. Shelf life at 50 °C was determined for a maximum of 21 days. Tack-free times were determined by finger touch under ambient conditions. For adhesion testing the substrates were first wiped with either methyl ethyl ketone (aluminum, steel, glass, concrete, wood) or methanol (PVC, PMMA, ABS, polystyrene), then washed with detergent, rinsed with distilled water, and allowed to air dry prior to preparation of the test specimens. Specimens were cured for 14 days at ambient conditions. 

The mechanical troweling apparatus for preparation of adhesion test specimen of plastering materials to concrete substrate has been proposed by R.NANIWA. Workability of PLCM were estimated by 3 rheological characteristics horizontal reaction force Ftr, vertical reaction force Fnr and reaction moment Mr at the grip (supporting point) were measured. Fig. 5 shows the schema of troweling motion and the apparatus in this test method. Some examples of test... 

Hada, K et al. (1994) Mechanical Troweling Apparatus for preparation of Adhesion Test Specimen of Plastering Materials. Annual Convention of Architectural Institute of Japan, PP. 1345-1346. 

The adhesion tests were conducted with flat, well-mated substrate specimens to minimize the effect of mechanical interlocking of the adhesive to the substrate. However, with bone containing surface pits, greater tensile adhesion values were obtained. Bone etched with 37% phosphoric acid prior to applying the adhesive did not improve joint strength. 

After plating, the first test of deposit was controlling the mechanical adhesion of Cu layers using the adhesive tape test. All films passed successfully this test whereas films obtained from an acid CUSO4 solution never passed the same test. The excellent mechanical properties of Cu films deposited from alkaline cyanide solutions is therefore presumably related to some specific interactions between the CN ions and the Si surface as recently observed for the electrodeposition of gold on n-Si from KAu(CN)2 solutions (6). 

In PP compoimds (which is the main use of mica in TP reinforcement), the mechanical and thermal properties are considerably enhanced by modifying the PP with a maleic anhydride compatibilizer, which improves adhesion. Test results suggest that the improvement continues with increasing amounts of maleic anhydride. 

An aqueous chemical pretreatment for unfilled polyetherimide substrates is described. The process includes the use of a chemical impregnator to increase the mechanical adhesion component and avoid metal lymer delamination during the initial electroless metallization step. Excellent adhesion was achieved for copper or nickel to both injection-molded plaques and extruded films. The metalA>olymer bond was found to be durable in thermal environments (dry and moist) as well as in simulated solder tests. Failure occurred within the polymer substrate during 90° peel testing. The process was found to be applicable to filled substrates as welt. 

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