Adhesive-Adhesive or glue is a compound in a liquid or semi-liquid state that adheres or bonds items together. Adhesives may come from either natural or synthetic source. Some modern adhesives are extremely strong and are becoming increasingly important in modern construction and industry.
The types of materials that can be bonded using adhesives are virtually limitless, but they are especially useful for bonding thin materials. Adhesives usually require a controlled temperature to cure or set. They can be electrically and thermally-conductive or nonconductive. The earliest date for a simple glue is 200,000BC and for a compound
glue 70,000 BC.
Evidence for this has been found in Sibudu Cave, South Africa and the compound glues used were made from
plant gum and red ochre. The Tyrolean Iceman had weapons fixed together with the aid of glue. 6000-year-old ceramics show evidence of adhesives based upon animal glues made by rendering animal products such as horse teeth. During the times of Babylonia, tar-like glue was used for gluing statues. The Egyptians made much
use of animal glues to adhere furniture, ivory, and papyrus.
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The Mongols also used adhesives to make their short bows and the Native Americans of the eastern United States used a mixture of spruce gum and fat as adhesives to fashion waterproof seams in their birchbark canoes. In medieval Europe, egg whites were used as glue to decorate parchments with gold leaf. The first actual glue factory was founded in Holland in the early 1700s.
There are several factors that could contribute to the failure of two adhered surfaces. Sunlight and heat may weaken the adhesive. Solvents can deteriorate or dissolve adhesive. And physical stresses may cause the separation of surfaces.
A general design rule is a relation of the type is that the material properties are greater than the function required (i.e. geometry, loads, etc.). The engineering work will consist of having a good model to evaluate the function. For most adhesive joints, this can be achieved using fracture mechanics.