This work presents a review of several investigations on the topic of adhesive bonding at high and low temperatures. Durability and strength at extreme temperatures have always been a major limitation of adhesives that, given their polymeric nature, exhibit substantial degradation at temperatures where other structural materials (such as metals for example) have minute changes in mechanical properties. However, due to the inherent advantages of bonding, there is a large and continued effort aiming to improve the temperature resistance of adhesive joints, and this effort has been spread among the various topics that are discussed in this review. These topics include adhesive shrinkage and thermal expansion, adhesive properties, joint geometry optimization, and design techniques, among others. The findings of these research efforts have all found use in practical applications, helping to solve complex problems in a variety of high-tech industries where there is a constant need to produce light and strong components that can withstand large temperature gradients. Therefore, the final sections of this work include a discussion on two specific application areas that demonstrate the strict demands that extreme temperature use imposes on adhesive joints and the methods used to improve their performance.

This paper describes the influence of the curing temperature on the physical and mechanical properties of three structural adhesives. This work was undertaken to improve the understanding of the effect of curing temperature in the glass transition temperature, T _g , and stiffness of epoxy adhesives. The mechanical properties (Young's modulus and yield strength) of the adhesives were measured in bulk specimens. T _g was measured by a dynamic mechanical analysis using an in-house developed apparatus. The curing process was the same for all tests, consisting of a curing stage followed by a post cure stage. The initial stage was performed at different temperatures. T _g and the mechanical properties was found to vary as a function of the cure temperature of the adhesive. When cured below the cure temperature, T _cure , at which the T _g of the fully cured network, T _{g ∞}, is achieved, the strength and stiffness of the adhesive increase as the cure temperature increases and the T _g is higher than the cure temperature. When cured above the T _cure at which the T _{g ∞} is achieved, the strength and stiffness decrease as the cure temperature increases and the T _g is higher than the cure temperature.

Aircraft face damage from impact with objects or birds or due to ageing that leads to fatigue cracks. The conventional methods of repairing aircraft metallic structures generally include the use of a plate joined by screws or rivets. Although these methods are efficient in the short term, they introduce stress concentrations leading to the initiation of new cracks that are difficult or impossible to detect by non-destructive methods. For these reasons, it is necessary to develop new methods to improve the behaviour of the structure (especially for long term) and its manufacture cost. One of the solutions that have been studied by the aeronautical industry is the use of patches bonded with structural adhesives. However, adhesively bonded patches have problems of stress concentration at the edges where crack initiation is prone to occur. This problem can be reduced by the use of a taper and a spew fillet at the end of the patch and by the use of a mixed adhesive technique where a ductile adhesive is placed at the edges of the patch. Double strap specimens from 3 mm thick 6063-T6 aluminium alloy sheet were analysed. Aluminium and straps (or patches) with an internal taper, an adhesive spew fillet, and dual adhesives were experimentally tested. The results obtained were explained by a finite element analysis. A taper angle is beneficial only for the brittle adhesive. The use of two adhesives is advantageous for the taperless configuration.

The study of the behaviour of adhesive joints under impact loadings is a very active field of research, driven by significant industrial interest. Many industries, such as the automotive industry, are currently employing adhesive joints extensively, making use of the inherent properties of adhesive joints to improve the mechanical behaviour, reduce weight, and simplify manufacturing. Reduced structural weight is achieved by combining multiple lightweight materials, which is made possible by using adhesive joints. Impact strength is also a major factor, as vehicles must be able to provide adequate safety levels for their occupants during collisions. Another example of industrial application is the defence industry, which uses bonded structures to withstand ballistic impacts, with extremely high impact velocities. Understanding the behaviour of adhesive joints under impact is, therefore, crucial for designing stronger and safer structures. This document aims to review the research that has been previously undertaken in this field. Discussed research topics include high strain rate property determination, adhesive joint testing, effects of coupling environmental conditions with impact loads, and sections on numerical and constitutive modelling procedures. The final sections describe some practical applications of adhesive joints under large strain rates and relate them to the fundamental concepts previously discussed.