A platform for research: civil engineering, architecture and urbanism
A platform for research: civil engineering, architecture and urbanism
The nondestructive evaluation of bonded structures
AbstractAdhesives have been used for many centuries but the stresses involved were usually very small. Often, the adhesive was a sealant or gap-filler. Modern adhesives have been used for less than 50 years, one of the first applications being in the Mosquito aircraft used in World War II. Since then, adhesive development has often been associated with advances in aviation, but structural adhesive joints are becoming an increasing feature of general modern engineering construction. Adhesives offer several advantages compared with bolts, rivets or other forms of localised connector. For instance, the stresses across the joints are more uniform (leading to lower stress concentrations), joint stiffness is increased, sealing is achieved at the same time, machining is reduced, and smoother external surfaces are attained. Dissimilar materials can be joined by bonding but not (usually) by welding, brazing etc. In the case of composite materials, their low transverse and bearing strength often precludes the use of bolts and rivets unless load-spreading inserts have first been bonded to the composite.The most common form of adhesive joint is the overlap in which the adherends may be plain or tapered to aid the smooth transfer of the loads through the structure, thus minimising the stress concentrations and maximising the joint strength. The mechanics of adhesive joints is referred to extensively in the book by Adams & Wake (1) which also covers test procedures, adhesive properties, surface preparation and so on. It has often been said that adhesives work best in shear, but in practice they are invariably strongest in compression. A major application of adhesives is in bonding the skins to the honeycomb core in sandwich structures. In this case, it is important that a fillet is formed at the junction.In a typical bonded lap joint shown in Fig. 1, it can be seen that there are many different layers. The joint strength depends on how the loads are carried by each part of this ‘structure’ and a weak link will lead to premature failure. In a well-made joint, the oxide layers, primer, and so on rarely fail. If they do, this is usually referred to as adhesion failure as it is between the adhesive and the substrate. When failure takes place in the adhesive itself, this is usually referred to as a cohesive failure.
The nondestructive evaluation of bonded structures
AbstractAdhesives have been used for many centuries but the stresses involved were usually very small. Often, the adhesive was a sealant or gap-filler. Modern adhesives have been used for less than 50 years, one of the first applications being in the Mosquito aircraft used in World War II. Since then, adhesive development has often been associated with advances in aviation, but structural adhesive joints are becoming an increasing feature of general modern engineering construction. Adhesives offer several advantages compared with bolts, rivets or other forms of localised connector. For instance, the stresses across the joints are more uniform (leading to lower stress concentrations), joint stiffness is increased, sealing is achieved at the same time, machining is reduced, and smoother external surfaces are attained. Dissimilar materials can be joined by bonding but not (usually) by welding, brazing etc. In the case of composite materials, their low transverse and bearing strength often precludes the use of bolts and rivets unless load-spreading inserts have first been bonded to the composite.The most common form of adhesive joint is the overlap in which the adherends may be plain or tapered to aid the smooth transfer of the loads through the structure, thus minimising the stress concentrations and maximising the joint strength. The mechanics of adhesive joints is referred to extensively in the book by Adams & Wake (1) which also covers test procedures, adhesive properties, surface preparation and so on. It has often been said that adhesives work best in shear, but in practice they are invariably strongest in compression. A major application of adhesives is in bonding the skins to the honeycomb core in sandwich structures. In this case, it is important that a fillet is formed at the junction.In a typical bonded lap joint shown in Fig. 1, it can be seen that there are many different layers. The joint strength depends on how the loads are carried by each part of this ‘structure’ and a weak link will lead to premature failure. In a well-made joint, the oxide layers, primer, and so on rarely fail. If they do, this is usually referred to as adhesion failure as it is between the adhesive and the substrate. When failure takes place in the adhesive itself, this is usually referred to as a cohesive failure.
The nondestructive evaluation of bonded structures
Adams, Robert D. (author)
Construction and Building Materials ; 4 ; 3-8
1990-01-01
6 pages
Article (Journal)
Electronic Resource
English
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