Tensile adhesion measurement

A variety of techniques has been developed to measure the condition of a coating so that some evaluation of its protective ability can be made. Many of these are based on electrochemical measurements [2]. The four techniques used in this study are (1) corrosion potential, (2) AC conductance, (3) tensile adhesion, and (4) weight gain. 

The adhesion was measured by fastening a lead anchor of known area (2,84 cm ) to the coating with a cyanoacrylate adhesive (Loctite 414) and after curing, pulling it off normal to the surface with a Dillon tensile tester. The force to remove the coating was divided by the area of attachment to convert it to a normalized tensile adhesion value. 

It should be noted that the electrochemical measurements (corrosion potential and conductivity) for the two novolac epoxies cured with an aromatic amine from different sources showed good agreement, although the tensile adhesion and weight gain values were not as reproducible. 

The metallic layers were examined either by conventional or cross-section TEM in a Jeol 200 Cx microscope. For the cross section preparation a sandwich of two laminates is made, glued face to face with an epoxy, cut in small pieces, mechanically polished, and then ion milled to a final TEM observation thickness. The plane section TEM sample are prepared by dissolving the PET in trifluoroacetic acid for 5 to 10 mn. The area observed, on plane section TEM, for the grain size calculation is close to 0.2 urn. For the adhesion measurements, test pieces consist of aluminum support (1 mm thick) double sided tape (Permacel P-94) PET (12pm) / evaporated aluminum/ ethylene acrylic acid (EAA) copolymer film. These laminates are prepared for the peel test by compression under 1.3 105 N.m2 at 120°C for 10 seconds. The peel test is performed by peeling the EAA copolymer sheet from the laminate in an INSTRON tensile tester at 180° peel angle and 5 cm min peel rate. 

The viscoelastic contribution to the fractnre energy in an adhesion test is, in principle, rate and temperatnre-dependent. Where this contribution is significant, it has been possible to nationalise adhesion measurements using the WLF transform-see Adhesion - fundamental and practical. Pressure-sensitive adhesives - adhesion properties and Tensile... 

Split cell testers Tensile strength measurements may also evaluate internal adhesion properties, independent of the mechanical interaction of shear plane, because T is measured at zero shear. Warren Springs Laboratories (WSL) designed two instruments one to measure the cohesive strength of powders at varied states of compaction and the other to measure tensile strength. The tensile strength measurement equipment, developed by WSL, was the WSL tensile tester, a diametrically divided split shallow circular cell. 

As a conclusion to this section on adhesion measurements, we can say that the despite the importance of this topic only a limited number of relevant techniques is available. When selecting a method it is important to use a method with a relevant force mode (shear, tensile, or a combination) and relevant conditions. 

Table 10 is derived, with change of units, from Kuenzi and Stevens (1963) and gives inter alia modulus figures of adhesives measured in joints formed by bonding aluminium washers or tubes and subjecting them to tensile or torsional stress. Table 11 gives further figures derived from various sources. 

ASTM C-1135 can be used to determine the tensile adhesion strength of a sealant bond. Although no ASTM standards that specifically address the measurement of the adhesion or bond strength of sealants loaded in shear, the standards in place for adhesive bonds can be used (single lap shear - ASTM D-1002, notched lap shear - ASTM D-3165, and double lap shear - ASTM D-3528). Much of the adhesion testing that is performed in the industry is testing to determine the effects of environmental and chemical exposure on sealant adhesion. This exposure can be either static or cyclic (Gutowski and Cerra 2009). 

Since adhesives are plastic materials, they may creep under high loads and therefore the expected static load is a determining factor for the durability. Compared to lap shear strength or tensile strength measured with shouldered test bars, the resistance toward static load is significantly lower. It is recommended to use only in the range of 3% to a maximum 10% of the maximum lap shear strength for the calculation of the sustainable permanent static loads for the use phase. 

The 2SiPAS films to be used for tensile strength measurement, surface analysis, and platelet adhesion experiments were cast from 10 wt% DMAc solution. 2SiPAS solution was slowly evaporated with heat-light at 60 C for 5 days. After that, the film was dried at room temperature for 24 h under a vacuum. 

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. 

In addition to transport properties, the adhesive properties are characterized by tensile measurements. For instance, the peel strength is deterrnined by measuring the force required to pull the adhesive from a substrate at a constant speed in a controUed temperature and humidity environment. 

Fig. 16. The results of Dyckerhoff and Sell for inlerfacial strengths measured hy butt-tensile tests for various lacquers (adhesives) against various plastics as a function of the surface energy, ys of the plastics. Arrows indicate the surface tensions of the adhesive, y, used in the generation of each curve, showing rough agreement with the requirement that a maximum in adhesion is achieved when yt ys (I kp/cm- 0.1 MPa). Redrawn from ref. [71. ...

The strength and adhesion of sprayed metal coatings are extremely difficult to measure with precision, and the properties of sprayed metals vary greatly with the spraying conditions and with the conditions of test. It is difficult, therefore, to correlate the values taken from the literature on the subject. For instance, American workers produce tensile test pieces by depositing on to 9-5 mm (0-375 in) steel tube and then machining out the tube. By this method the results shown in Table 12.7 were obtained. 

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