Peel energy

Influxes length L as the influx length increases, the influx strength a increases from zero to its maximum value CTq according to a(L) = ao(LjLc). Since the first term (in Eq. 4.25) dominates the peel energy, we see that G L2. 

Further, a large attraction exists between two smooth solid surfaces if a drop of liquid (say, water and two glass plates). It is thus obvious that the peeling energy of two plates in this system will increase if a glue or similar substance is used (instead of water). 

A well-defined amount of co-crystallization is possible across the interface of two adjacent crystals by annealing two stacked, completely wetted, solution-cast films of UHMW-PE [32]. It was found that doubling of the lamellae across the interface enhances the peel energy to such a level that the films could not be separated anymore. By contrast, pre-annealing one side of the film prohibited co-crystallization across the interface and these films could still be separated easily. It was therefore concluded that a limited amount of chain diffusion across the interface occurs during doubling of the lamellae, as facilitated by the well-defined structure of the interphase due to the adjacent reentry that occurs upon crystallization from solution. 

CONTRIBUTION OF THE ELECTROSTATIC ADHESION COMPONENTS TO THE TOTAL PEELING ENERGY OF METAL FILMS ON GLASS [43]. 

Film Work function of electrons (eV) Charge density (nC cm"2) Theoretical electrostatic adhesion energy (J m"2) Theoretical van der Waals adhesion energy (JitT2) Experimentally measured peeling energy (Jm"2)... 

One important criticism of the model proposed by Vasenin is that the energy dissipated viscoelastically or plastically during peel measurements does not appear in Eq. (23). Nevertheless, in his work, the values of coefficients K and Dj are not theoretically quantified but determined only by fitting. Therefore, it ean be assumed that the contribution of hysteretic losses to the peel energy is implicitly included in these eonstants. 

A relatively simple way to an understanding is via an energy-balance approach to the theory of peel adhesion, which is essentially an application of the first law of thermodynamics. This is developed in the article on Peel tests. For ease of illustration, consider the 90° peel of an inextensible strip. Equation 7 in the article cited gives peel energy P as... 

In some uncomplicated examples, it has been possible to analyse the results of adhesion tests to obtain numerical values associated with interfacial forces. An example of this was the work of E. H. Andrews and A. J. Kinloch, who measured the adhesion of SBR (styrene - butadiene rubber) to different polymeric substrates over a range of temperatures and test rates. Three types of tests including a 90° peel test were used. The results were analysed to evaluate the fracture energy per unit area G. (For the peel test, G was P, the peel energy.)... 

Although for many straightforward comparative purposes it is often adequate to record the results as a peel force/width, it is easy to derive an expression for the peel energy from basic mechanical principles by equating the work done by the test machine to the work done on the sample. The result forms a basis for understanding and interpreting peel tests (see also Fracture-mechanics test specimens). 

The work done on the sample can be expressed as the snm of two terms. The first is the peel energy P, which we take to be the energy (per nnit area of peeled substrate surface) dissipated in the broad region of the peel front. The second is the work done in stretching the freed strip, which will be the strain-energy density for extension to k. Here, Wx can be calculated if an expression, such as Hooke s law, for the tensile stress-strain relationship for the material is known for extensions up to k, otherwise it can be evaluated from the work done in an appropriate tensile test (Fig. 4). This can be used whether or not the yield point has been exceeded. Thus,... 

The optimal adhesive layer thickness depends on a number of factors. Some bonds, notably Tensile test specimens, are stronger when the adhesive layer thickness is redn-ced. For fracture specimens, including double cantilever beam specimens bonded with structural adhesives (see Fracture mechanics test specimens), optimal bond thicknesses have been identified, although the optimal thickness depends on the loading rate and test temperature. " Enhanced ductility plays a role in this process, and a sufficient quantity of adhesive is desired to dissipate energy (see Peel tests). This latter mechanism is also important in the peel energy of Pressure-sensitive adhesives and other systems. 

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