Peel test

When this method is applied to MID It is important to bear in mind that a comparatively large test metallization is needed. Empirical experience indicates that connectors for peel-off testing should be more than 800 pm in width. The metallization should be at least 17 pm thick in order to withstand the necessary tensile forces. The common metallizations such as LPKF-LDS plating therefore often require galvanic overplating to bring them up to the necessary thickness. The thickness of the metallization influences the result, and this has to be taken into account. Deformation of the metal layer factors into the measurement result. Consequently, the result cannot be applied one-to-one to combinations of materials other than that tested. 

Failure modes at surfaces of loading and substrate fixtures. 

According to Sexsmith, Troczynski and Breslauer (1997), the frictional force/ can further be described by/= yti-F, where yit is the coefficient of rolling friction. Furthermore, the plastic work of bending is a function of the applied force and also proportional to the foil width w. Then Eq. (7.2) can be rewritten as 

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The usual practical situation is that in which two solids are bonded by means of some kind of glue or cement. A relatively complex joint is illustrated in Fig. XII-14. The strength of a joint may be measured in various ways. A common standard method is the peel test in which the normal force to separate the joint... 

Fig. XII-15. Diagram of peel test. A and B, adhesive joint C, double Scotch adhesive tape and D, rigid support. (From Ref. 107. By permission of IBC Business Press, Ltd.)...

Fig. 2. Illustrations of forces to which adhesive bonds are subjected, (a) A standard lap shear specimen where the black area shows the adhesive. The adherends are usually 25 mm wide and the lap area is 312.5 mm. The arrows show the direction of the normal apphcation of load, (b) A peel test where the loading configuration, shown by the arrows, is for a 180° peel test, (c) A double cantilever beam test specimen used in the evaluation of the resistance to crack propagation of an adhesive. The normal application of load is shown by the arrows. This load is appHed by a tensile testing machine or other...

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. 

A sealant s adhesion is commonly studied by 180 degree peel tests such as ASTM C794 or by tensHe/adhesion joints tests such as ASTM C719. The adhesion test protocol should simulate actual field conditions as closely as possible. Sealants often have good adhesion to dry substrates, but this adhesion may be quickly destroyed by water. Because most sealants are exposed to water over their lifetime, adhesion testing should include exposure to water for some length of time. ASTM C719 is one of the better tests to determine a sealant s adhesion durabHity as it exposes sealants to seven days of water immersion. 

Another distinction to be made is illustrated with the peel test shown in Fig. 1. Application of stress may cause the joint to fail either adhesively or cohesively . Adhesive failure, shown in Fig. la, is thought ideally to correspond to a perfect... 

Fig. 1, Schematic of commonly u.sed methods for testing the strength of adhesive joints, (a) Peel test. Note that the peel angle can be changed depending on the test requirements, (b) Double overlap shear test. In this test, the failure is predominantly mode II. (c) Single overlap shear test. In this test the failure mode is mixture of mode I and mode II. (d) Blister test.

Fig. 2. Schematic of energy dissipation in a commonly used peel test. The energy dissipation can occur in the adhesive and/or the adherends. The extent of energy dissipation depends on the elasto-plastic properties of the adhesive and the adherends under the test conditions as well as the local stresses and strains near the crack tip.

The experimental and theoretical procedure used by Tirrell et al. is similar to that of Brown and coworkers. Tirrell et al. compared their results from the JKR experiments to 90° peel tests. The details of the experiment may be obtained from the original papers. The obser ations of Tirrell et al. can be summarized as follows ... 

Fig. 17. Adhesion energy G measured as a function of the surface density of the interfacial chains. It may noted that the strength measured in a peel test (a) is about 5 times larger than that measured using the JKR method (b). Further, a maximum exists in the value of G as function of the surface chain density. This is because of swelling effects at larger values of surface chain density. The open symbols represent the data for elastomer molecular weight Mo = 24,000 and the closed symbols represent the data for Mo = 10,000.

The study of acid-base interaction is an important branch of interfacial science. These interactions are widely exploited in several practical applications such as adhesion and adsorption processes. Most of the current studies in this area are based on calorimetric studies or wetting measurements or peel test measurements. While these studies have been instrumental in the understanding of these interfacial interactions, to a certain extent the interpretation of the results of these studies has been largely empirical. The recent advances in the theory and experiments of contact mechanics could be potentially employed to better understand and measure the molecular level acid-base interactions. One of the following two experimental procedures could be utilized (1) Polymers with different levels of acidic and basic chemical constitution can be coated on to elastomeric caps, as described in Section 4.2.1, and the adhesion between these layers can be measured using the JKR technique and Eqs. 11 or 30 as appropriate. For example, poly(p-amino styrene) and poly(p-hydroxy carbonyl styrene) can be coated on to PDMS-ox, and be used as acidic and basic surfaces, respectively, to study the acid-base interactions. (2) Another approach is to graft acidic or basic macromers onto a weakly crosslinked polyisoprene or polybutadiene elastomeric networks, and use these elastomeric networks in the JKR studies as described in Section 4.2.1. 

Adhesion of copper films to PMDA/ODA polyimide was determined by peel tests conducted on samples that were prepared by vapor-depositing a thin layer of copper onto the polyimide and then building the thickness of the metal layer to about 18 p,m by electrodeposition of copper. Results of the adhesion measurements correlated well with substrate pretreatment. When the substrate... 

Fig. 1. PSA te.sling. (a) 180° Peel test (radius exaggerated), (b) Shear holding power test, front and side view.

While detail may be found in the ASTM D-3330 or PSTC-1 and PSTC-2 standards, the peel test is typically carried out as follows The tape is conditioned at 23°C and 50% relative humidity for 1 day. Next, the tape is rolled down with a weighted standard roller onto a clean test substrate (usually polished 302 stainless steel), allowed to dwell for a specified time (usually 1 min), and then clamped with the testing fixture in the test machine and peeled at a specified rate. 

PSA peel testing is sensitive to a variety of factors and careful testing is necessary to get reproducible results. Critical variables include the following ... 

A loop tack (Fig. 2c) test consists of allowing a tear-shaped loop of conditioned tape to drape into contact with a test surface of specified area (usually 25.4 x 25.4 mm), with the force of contact limited to the weight of the tape itself (ASTM Ref. D-6195). The ends of the loop are held in a tensile tester. After a momentary contact time the tester is engaged and the tape is removed at a specified speed. The maximum in the removal force is ordinarily observed just at the point where the two peel fronts Join. The value is reported in a force per area of tape width, or lb in. -. While this tack test has some popularity, it is perhaps more of a very short dwell time peel test, and it has variables more associated with that test, especially backing effects, since heavier backings lead to higher tack values. 

Adhesive strength refers to the bond produced by contact of an adhesive to a surface. It used to be measured by peeling tests. This ultimate strength depends on temperature, applied pressure and time of contact. 

Both static and dynamic tests are employed to evaluate the adhesion strength of cord-mbber composites. The major static tests used in tire industry are H-adhesion, 90/180° peel test, tire cord adhesion test (TCAT) and co-axial shear pull-out test (CSPT). Although these methods are... 

FIGURE 23.17 Styrene-butadiene copolymer (SBR) peel adhesion test piece after first appl3nng a gas decompression (GD) procedure and then peel testing. 

Peel Strength. Samples were prepared by cutting 2.5" (63.5 mm) wide radial sections, bead to bead. The sample was then sectioned into two 1.25" (31.75 mm) radial strips, which were each cut circumferentially at the centerline of the tread resulting in four test specimens (2-SS and 2-OSS). Each sample was cut with a razor knife for a length of 1" (25.4 mm) from the skim end of the test strip, midway between the belts, to facilitate gripping the ends in the T-2000 stress-strain tester jaws. The sides of each specimen were scored midway between the belts, to a depth of 1/8" (3.175 mm) radially from the end of the gripping surface to the end of belt 2 in the shoulder area, providing a 1" wide peel section. The peel test was performed at 2"/min (50.8 mm/min) at 24°C. 

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