behavior of the adhesive layer itself is neglected and only the adherents are considered. Failure will also very much depend on the opening mode of the joint. Mode I is an opening or tensile mode where the loadings are normal to the crack. Mode II is a sliding or in-plane shear mode where the crack surfaces slide over one another in direction perpendicular to the leading edge of the crack. This is typically the mode for which the adhesive exhibits the highest resistance to fracture. Mode III is a tearing or antiplane shear mode. As the loads are usually fixed, an acceptable design will result from combination of a material selection procedure and geometry modifications, if possible. In adhesively bonded structures, the global geometry and loads are fixed by structural considerations and the design procedure focuses on the material properties of the adhesive and on local changes on the geometry. Increasing the joint resistance is usually obtained by designing its geometry so that: The bonded zone is large It is mainly loaded in mode II Stable crack propagation will follow the appearance of a local failure. Shelf life Some glues and adhesives have a limited shelf life. Shelf life is dependent on multiple factors, the foremost of which being temperature. Adhesives may lose their effectiveness at high temperatures, as well as become increasingly stiff. Other factors affecting shelf life include exposure to oxygen or water vapor. See also Impact glue References Bibliography Kinloch, Anthony J. (1987). Adhesion and Adhesives: Science and Technology. London: Chapman and Hall. External links Educational portal on adhesives and sealants RoyMech: The theory of adhesive bonding 3M's Adhesive & Tapes Classification Database of adhesives for attaching different materials Visual arts materials 1750 introductions Packaging materials