Adherend definition

The definition of an adhesion promoter in its most literal sense may be stated as any substance which when placed between two adherends results in a measurable increase in the force required to separate the two materials. This definition does not address the basic mechanism responsible for the increased adhesion nor does it concern itself with the mode by which the promoter is contacted with the adherend surface, i.e. as primer, by in situ incorporation into an adhesive or coating, or by other means. 

Adhesives, non-scientifically, are materials which provide adhesion as a result of mechanical interlocking with the basic roughness of the adherend surfaces. A precise definition of an adhesive describes it as a substance capable of holding materials together by surface attachment. 

Structural bond—A bond that stresses the adherend to the yield point, thereby taking full advantage of the strength of the adherend. On the basis of this definition, a dextrin adhesive used with paper (e.g., postage stamps, envelopes) which causes failure of the paper, forms a structural bond. The stronger the adherend, the greater the demands placed on the adhesive. Thus, few adhesives qualify as structural for metals. A further requirement for a structural adhesive is that it be able to stress the adherend to its yield point after exposure to its intended environment. 

The fibre orientation on the bond surface should be parallel to the primary loading direction. Otherwise it is likely that the Joint will fail due to adherend failure at a relatively low loading level. Owing to a great variety of possible laminate structures and applications, it is unrealistic to require that the fibre orientation on the bond surface and the primary loading direction should be parallel in all connections. This requirement is essential for primary structural connections (see 5.1.1 for definition) and for other connections it is a recommendation. The requirement allows the use of fabrics, woven rovings and uni directional reinforcements on bond surfaces when at least half of the fibres are parallel to the loading direction. In primary structural connections mats are not allowed to be used on bond surfaces. 

The often used FPL etdi of an aluminum-lithium alloy bonded with polysulfone leads to interfacial (at the metal oxide/polymer interface) failure (38) which is a surprisingly uncommon type of failure. The results leading to this assignment are shown as XPS C Is and O Is narrow scan spectra in Figure 15. This definitive assignment of failure mode is based on the fact that one failure surfece has an oi gen photopeak similar to the pretreated adherend before bonding and the other failure surfece has an 0 gen photopeak similar to the adhesive. 

An adhesive is a substance capable of holding substrates (adherends) together by surface attachment A material merely conforming to this definition does not necessarily ensure success in an assembly process. For an adhesive to be useful, it must not only hold materials together but also withstand operating loads and last the hfe of the product... 

If the adherends have different elastic properties, then a rigorous definition of the nominal phase angle should include a length scale to account for the oscillatory nature of the elastic stresses at the crack tip. 

Abstract This introductory chapter gives a brief description of adhesive bonding and adhesion-related phenomena. The major definitions of the terms associated to this technology such as adhesion, cohesion, adhesives, sealants, and adherends are given so that there is uniformity of language throughout the handbook. The reasons that drove the editors to prepare this book are explained. Finally, the organization of the book is described. 

The parameter definitions in the above equation can be found in Oplinger (1994) and are not given here due to complexity. In O Eq. 24.31, the overlap geometric nonlinearity and the adhesive shear, but not peel strain, are considered. In O Eqs. 24.30 and O 24.31, the adherends are modeled as Euler beams and thus the transverse shear stiffiiess is not modeled. 

Bulk tensile testing has shown that adhesives generally exhibit plasticity and, hence, nonlinear material properties are required to model their behavior over the fiill load range. Nonlinear properties may also be required for adherends. Thus, a combination of elasto-plastic material models may be used to predict the behavior of adhesive joints under load. The definition of the yield surface is important when using elasto-plastic material models. Von Mises yield surface is commonly used for the analysis of metals, which assumes that the yield behavior is independent of hydrostatic stress. As a result, the yield surface is identical in tension and compression. However, the yield behavior of polymers has been shown to exhibit hydrostatic stress dependence (Ward and Sweeney 2004) as the yielding starts earlier in tension than in compression. Thus, a yield criterion which includes hydrostatic stress effects should be used to determine the yield surface. Various yield criteria with hydrostatic stress dependence such as Drucker-Prager, Mohr-Columb, and modified Drucker-Prager/cap plasticity model have been implemented in commercially available finite element software. 

Whatever the definition might be, for space applications, the loads taken into account for the design are those calculated, increased by the margin factor for the considered application, and the cohesive failure mode (in the adhesive or in the adherends) will be the mode expected. 

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