T peel test

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 typical load curve of the t-peel test is shown in Fig. 20.8. Peel strength is taken as the average value of the center portion of the curve, usually over at least a 5-in length. 

The t-peel test is described in ASTM D 1876 and is the most popular of all peel tests. The t-peel specimen is shown in Fig. 20.7. Generally, this test method is used when both adherends are flexible. Because the angle of peel is controlled by the properties of the adherends and the adhesive, the test is less reproducible than other peel tests. A sample population of at least 10 is required, whereas most other ASTM tests require a minimum of 5. 

A variation of the t-peel test is a 180° stripping test, described in ASTM D 903. This method is commonly used when one adherend is flexible enough to permit 180° turn near the point of loading. This test offers more reproducible results than the t-peel test because the angle of peel is kept constant, although it is dependent on the nature of the adherend. 

D 1876 Test Method for Peel Resistance of Adhesives (T-Peel Test)... 

Typical force versus time traces obtained from T-Peel tests are shown in Fig. 11. As can be seen, the peel load reaches a nearly constant value for both substrate materials, with some minor fluctuations superimposed on the results. These values have been used in an analytical model to calculate the adhesive facture energy, Gc [8]. For all the tests performed the crack propagated cohesively in the adhesive layer. The peel load was found to depend on the alloy type and on the thickness of the substrates, since most of the energy during the test is dissipated by plastic deformation of the arms. Numerical FV work is in progress. 

Fixed arm peel and T-peel test procedures are used to measure peel strength for flexible laminates. Analysis of the contributions from elastic and plastic deformations of the peel arms during these tests enables the energy contribution from plastic effects to be subtracted from the energy required to peel the laminate. In this way, the adhesive fracture toughness is determined. 

The same laminate system was used by all laboratories, namely a laminar structure with five layers based on polypropylene (PP), an adhesive, an ethylene vinyl alcohol (EVOH) layer another adhesive and another polypropylene layer. This is designated PP/adh/EVOH/adh/PP and was used in both fixed arm peel tests and T-peel tests. Peel specimen were 15 mm in width and a notional 100 mm in length. The peel arms were PP/adh (with a thickness of 51pm) and EVOH/adh/PP (with a thickness of 75pm). Although there is no rigorous value for modulus for such multi-layered arms, we have obtained a tensile modulus value for each arm and assumed the materials of the arms to be uniform for the purposes of our calculations. 

Table 2 Peel results at 23"C for copper laminates from fixed arm and T-peel tests.

The testing of the peel resistance occurs according to the standard DIN EN 1464 Adhesives - determination of peel resistance of high-strength bonded joints - climbing drum peel test (respectively, T-peel test) and serves the determination of the resistance of bonded metal joints to peeling forces (Figure 10.5). 

Fig. 22.2 Edge view by scanning electron microscopy of a T-peel test done on a block copolymer based PSA. Photo courtesy of Ken Lewtas (Exxon Mobil Chemical).

FIGURE 3.77 Test panel and T-type test (T-peel test) specimen for peel resistance of adhesives (standard test method ASTM D1876-95). The bent, unbonded ends of test specimen are clamped in test grips of tensile testing machine and load applied at a constant head speed of 254 mm (10 in.). Average peeling load (in pounds per inch of specimen width) is determined for the first 127 mm (5 in.) of peeling after the initial peak. 

Figure 8 Some standard peel test geometries (a) T-peel test specimen, ASTM D-1876 (b) typical testing jig used in ASTM D-1876 (c) climbing drum peel test, ASTM D-1781 (d) 180° peel test, ASTM 903.

The test methods presently used to evaluate the adhesion of pressure-sensitive adhesives to release liners are modified adhesion tests, such as the 180° or 90° peel test, with the liner adhered to a test panel, or a T-peel test, where the sample is freely suspended while the tape is peeled at a controlled rate from the release liner. The values obtained by the latter method are alfected considerably by the stiffness of the liner, which alters the angle of peel. 

The main conclusion of that work was that the toughness of the adhesive joint could be defined thermodynamically as the work of adhesion W. Of course, this definition was only applicable in certain special equilibrium circumstances, when the materials were elastic and when the fracture occurred very slowly. The toughness W was measurable in a T peel test shown in Fig. 15.4. This idea explained the force F required to peel two sheets apart, depending only on W and the width of the strips b (see Section 7.7). 

Figure 15.4. Measurement of joint toughness in a T peel test.

ASTM D1876-72(83). Peel Resistance of Adhesives (T-Peel Test), Annual Book of Standards, 15.06, American Society for Testing and Materials, 1986,... 

PhE was also measured during T peel tests of two-ply Kevlar-epoxy panels. The entrance to the photomultiplier was approximately 2 cm from the "crack," and directed toward it. PhE was observed only during separation of the plys and decayed immediately upon release of the stress. For a... 

Pig. 33. EE from T-peel testing of Aluminum/epoxy interface for adhesive and adhesive plus cohesive failure. 

---