Determination of the Adhesion Strength

For the case of rja = 1.01 (a circle-like shape of the interface), the finite-element calculations provide the stress concentration factors k = o ,maxl -o /0 = 9O°, r-rf)lcf y for the two-material combinations, TPE-PMMA 1.18 

The diagram provides the mean critical applied stress for TPE-PMMA y,critical y.critical 1.25 MPa and for TPE-PC =2.0 MPa. 

Together with the stress concentration factors, Eq. (3) provides the adhesion strength between PMMA and TPE to be cr = 1.48 MPa and between PC and TPE to be cr, = 2.34 MPa. 

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ISO 16. 1991, Determination of the adhesion strength of vulcanised rubbers to textile fabrics. ISO 6111. 1981. Analysis of multi-peak traces obtained on determinations of tear strength and adhesion strength. 

BS 901. Part A12. 1975, Determination of the adhesion strength of vulcanised rubbers to... 

This stress distribution is the basis for the determination of the adhesion strength at the interface. In such a case, the maximum stress criterion can be applied to determine the debonding strength ... 

As stated earlier, adhesion is a major concern in electronic applications involving thin polyimide films either coated on hard substrates or laminated with metal ribbons. In these cases, neither lap-shear nor die-shear techniques allow the determination of the adhesion strength this can be done by using either the 90° peel test or the island blister test whose principles are sketched in Figs 12.26 and 12.27. The 90° peel test provides reliable data for the measurement of practical adhesion, especially useful for comparing the effect of surface treatments on the interfacial adhesion. The standard peel test procedure has been modified to determine the adhesive strength of thin polyimide films coated onto 10-cm silicon wafers. The equipment illustrated in Fig. 12.26 maintains a 90° peel effort during the test conducted at room temperature with a constant rate of crosshead displacement of 2 mm min . ... 

Figure 45(d) shows the determination of the tensile strength of model agglomerates by means of the wall friction method.For this test a cylindrical pellet—sometimes with a central pin—is produced in a press. After removing the specimen from the press, it is stressed directly in the die shell. The tensile force is transmitted by adhesion between the end surfaces and the pistons as well as on the circumference and the die walls. Again, the tensile strength is defined by the quotient rupture force P divided by the cross section of the cylindrical or ring-shaped sample. 

Adhesion at the interface of the polymer-solid is a determining factor for the physical and mechanical properties of polymer composites. Many properties of particulate-filled composites are determined by the adhesion level at the filler-matrix interface. The problems involved in adhesion are very complicated and adhesion cannot be described by any single theory [1]. Many properties of particulate-filled composites are determined by the adhesion level at the filler-matrix interface [2]. However, no theory allows calculation of the adhesion strength of joints from the data on the nature of substrate and polymer or reliable calculation of the energy of the adhesive interaction. The reason for it is the number of factors that influence adhesion [3-9]. 

The reason for the lack of concordance between the theoretically and experimentally determined values of the adhesion strength lies in the fact that the process of achieving high adhesion strength is hindered by a number of phenomena that accompany the formation of adhesive-bonded joints. These factors that decrease the strength of adhesive-bonded joints can be divided into two groups ... 

The fracture stress of adhesive-bonded joints (adhesion strength) is a consequence of processes that occur in the course of their formation, but all attempts to formulate a fundamental relationship between formation and failure of adhesive-bonded joints have so far been unsuccessful. This is mainly due to the lack of methods for meastuing adhesion that would permit determination of the failure equilibrium work. Accordingly, the relationship between the experimentally determined value of the adhesion strength and the thermodynamic characteristics can be one of correlation only. 

Thus, dependence of adhesion strength on the surfactant concentration correlates with the dependence of the system surface tension. The increase of surface tension under the influence of surfactant is caused by changes in the polymer structure that determine the cohesion strength and should therefore lead to increase of the adhesion strength. 

Figure 1. Mounting and loading of the test specimens for the determination of the shear strength of the PF adhesive bondline (left), and the shape and dimensions (in mm) of the typical specimen (right).

DIN 53283 Testing of adhesives for metals and adhesively bonded metal joints determination of the shear strength of single lap joints In shear by tension loading. 

ISO 15509 2001 Adhesives - Determination of the bond strength of engineering-plastic joints... 

Neoprene—phenohc contact adhesives, known for thein high green strength and peel values, contain a resole-type resin prepared from 4-/-butylphenol. The alkyl group increases compatibiHty and reduces cross-linking. This resin reacts or complexes with the metal oxide, eg, MgO, contained in the formulation, and increases the cohesive strength of the adhesive. In fact, the reactivity with MgO is frequently measured to determine the effectiveness of heat-reactive phenoHcs in the formulation. 

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