Adhesive bonding joint geometry

The value of 6ic can be used not only as a comparative but also tis an estimated characteristic of the cracking resistance of adhesive-bonded joints. For this purpose it is necessary to find a relationship between the displacements 6i, load, body geometry, and crack length. The relationship for a crack with yield zone localized within its plane can be written... 

Joint geometry. The ideal adhesive-bonded joint is one in which under all practical loadii conditions the adhesive is stressed in the direction... 

A critical issue when designing adhesively bonded joints mating pipes is when the joint undergoes torsion, which could often be experienced by pipes and risers in their service lives. Again, without elaborate mathematical derivations, the distribution of the shear stress in the adhesive with reference to the geometry shown in Fig. 18.8 can be evaluated by the following equation ... 

The stresses in an adhesive joint depend, once a constitutive model is chosen, on the geometry, boundary conditions, the assumed mechanical properties of the regions involved, and the type and distribution of loads acting on the joint. In practice, most adhesives exhibit, depending on the stress levels, nonlinear-viscoelastic behavior, and the adhetends exhibit elastoplastic behavior. Most theoretical studies conducted to date on the stress analysis of adhesively bonded joints have made simplifying assumptions of linear and elastic and/or viscoelastic behavior in the interest of tracking solutions. 

Only recently, work involving the time-dependent fracture characteristics of adhesively bonded joints has been under way. Francis et discussed the effects of a viscoelastic adhesive layer, geometry, mixed-mode fracture response, mechanical load history, environmental history, and processing variations on the fracture processes of adhesively bonded joints. However, their finite-element analysis includes only linear elastic fracture mechanics. 

To demonstrate the T-stress effect and to understand other factors affecting crack path selection, the authors and their coworkers [13,25,31,32] carried out a series of experimental studies with adhesively bonded joints to determine the effects of T-stress, specimen geometry, external loading conditions, surface pretreatment. 

Chen, B., Dillard, D.A., Dillard, J.G. and Clark, R.L. Jr., Crack path selection in adhesively bonded joints the roles of external loads and specimen geometry. Int. J. Fract., 114, 167-190 (2002). 

The objective here is to understand the damping properties of joints bonded with various adhesives and to see how this might affect the overall damping of a structure. Some variables to be examined are the effects of adhesive properties, joint geometry, and temperature on the overall damping performance of a joint. 

Shear tests are very common because samples are simple to construct and closely dupUcate the geometry and service conditions for many structural adhesives. As with tensile tests, the stress distribution is not uniform and, while it is often conventional to give the failure shear stress as the load divided by the bonding area (Table 11.1), the maximum stress at the bond line may be considerably higher than the average stress. The stress in the adhesive may also differ from pure shear. Depending on such factors as adhesive thickness and adherend stiffness, the failure of the adhesive shear joint can be dominated by either shear or tensioa ... 

Adhesive materials are applied as thin layers of polymeric materials capable of transmitting stresses between two substrates. They can be classified according to their functions into physical or chemical adhesive forms. Adhesives must behave as fluids before they set and become solid. Thus, the solid adhesive is formed from (a) its solution by solvent evaporation, (b) hot-melting by coohng and (c) reactive liquid precursor by in-situ thermosetting reactions. The purpose of adhesives is the transmission of forces from one adherent to the other. Thus, adhesive performance is always described in terms of mechanical adhesion in which the strength of the polymer interface with the adherents is evaluated. The distribution of stresses in bonded joints depends on the overall bond geometry and on the loads applied to the bonded structnre. The initiation and development of failure is most certainly associated with stress distribntion. 

In the application of the hybrid joint in the wheel system, it was observed that the joint geometry played a relevant role on its performances. The presence of the disc flange angle and the deformability of the rim well created zones of clearance inside the joint. The more the interference the less the quantity of adhesive penetrated inside the clearance. The extent of the bonded area strongly affected the total static resistance of the hybrid joint. On the contrary, the fatigue life of the bonded wheel seemed to be independent to its resistance to the decoupling, and to depend on the interference level to a large extent. 

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