Peel tests stress distribution

Figure 6.27 (a) Schematic diagram of a peel test, (b) Distribution of normal stresses in the adhesive layer ahead of the advancing peel front [92]. 

The test was investigated by Painter13 who showed that the stress is concentrated at the tips of the cones. The stress distribution is not even and the action is not pure tension but involves peel and shear forces. Painter s results showed that failure occurred at the interface rather than in the rubber... 

Fig. 22.3 Schematic of a peel test (after Ref [2]) showing (a) the stress distribution as a function of position under the peel front and (b) schematic of a force-time curve obtained from a probe test.

The characteristic beam on elastic foundation stress distribution, as shown in Fig. 2 for the applied moment case, is frequently encountered in a wide range of adhesive bond situations. In addition to lap joints mentioned earlier, peel tests, moisture-induced stresses, and curvature mismatch situations all tend to exhibit this characteristic distribution. Clearly, the beam on elastic foundation has important qualitative and, in many cases, quantitative applicability to a host of adhesively bonded joints. 

As mentioned, shear tests will usually produce nonuniform stress distributions in the bonded joint. This deviation from a pure shear condition results in misleading adhesive strengths. To determine the shear strength and modulus of a bonded system in which peel stresses, bending stresses, and other nonuniformities are eliminated, ASTM E229-70 has been... 

Keywords Adhesive modulus Adhesys expert system Co-axial joints Compression Concealed joints Creep Elastic limit Epoxy Epoxy composite Einite element analysis Glue line thickness Goland and Reissner Hart-Smith Heat exchanger Hooke s Law Joint designs Joint thickness Lap shear strength Peel Plastic behaviour Polyurethane Pipe bonding Shear stresses Shear modulus Stress distribution Thick adherend shear test Tubular joints Volkersen equation Young s modulus... 

Adams et al. [6] detailed axisymmetric analysis of a butt-tension joint and considered the influence of the detailed geometry at the edges of the joint on the stress distribution. The single lap joint was further analysed by Crocombe and Adams [7] using the finite element method and the effect of the spew fillet was included which was seen to significantly redistribute, and decrease, the stresses at the ends of the adhesive layer. In complementary work, Crocombe and Adams [8,9] analysed the mechanics of behaviour of the peel test and included the effects of non-linear deformations and also plasticity in their work. Harris and Adams [10] extended this work and accounted for the non-linear behaviour of the single lap joint. Crocombe et al. [11] quantified the influence of this non-linearity, both material and geometric. 

The stress distribution in a peel test is complex and dependent on the material properties of the adherends and adhesive as well as the specimen dimensions. In general, the stress distributions in peel tests are not well understood. A simple and easy to perform peel test using a length of household cellophane tape is again... 

The analytical methods of fracture mechanics (both cohesive and adhesive) are described in a number of references [21-24] and will not be repeated here. However, a brief outline of one simple approach provides some insight into the concepts, principles, and methodologies involved for the reader who is not familiar with fracture mechanics. In the previous discussion of peel tests, it was noted that Gent and Hamed [ 18-20] had performed some extremely informative fracture mechanics tests using peel specimens. We consider a simplified fracture mechanic analysis of the 90° peel test shown in Fig. 17. Here we assume that the substrate is rigid and the peel adherend is very flexible and perfectly elastic. The stress distribution in the vicinity of the 90° bend is complex and difficult to determine. If the material is perfectly elastic, however, this stress distribution is... 

Dom and Liu (1993) investigated the influence of the spew fillet in plastic/metal joints. The study includes an FE analysis and experimental tests and they conclude that the spew fillet reduces the peak shear and peel adhesive stresses and decreases stress and strain concentrations in the adherends in the most critical regions. They also studied the influence of different adhesive and different metal adherends. A ductile adhesive and a more balanced joint (aluminum/plastic instead of steel/plastic) give a better stress distribution. 

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