Environmental failure

The two principal forms of stress-corrosion failure are (a) hot salt cracking and (Z)) room-temperature cracking, the latter occurring in both aqueous and methanolic chloride environments, and in N2O4. In addition, environmental failures can occur in alloys in direct contact with some liquid and solid metals, and certain gases. 

The kinetics of environmental failure are influenced by the diffusion of water through the adhesive. This may be altered by changing the adhesive s composition... 

Table 10.1 Environmental Failure Resistance of Different Adhesive-Aluminum Joints ...

Kinloch, A.J., Environmental Failure of Structural Adhesive Joints—A Literature Survey, Explosives Research and Development Establishment, UK, ERDL Technical Note No. 95, Unlimited Distribution (AD 784 890), 1973. 

Kinloch and coworkers have developed a model to describe the mechanics of environmental failure of adhesive joints. " They have proposed a three-stage mechanism ... 

The various methods used to study the effect of environmental exposure on structural bonds have been described, pointing out that such methods provide results of a comparative nature only. There are at present few test methods that provide information useful for making predictions of durability of actual bonded structures. Most of the test methods involve the simultaneous effects of an applied load and environmental exposure some involve exposure to cyclic conditions. As explained, these conditions are much more detrimental to joint performance than is exposure to a single test condition. The tests based on fracture mechanics principles have provided some especially useful information and insights into the mechanisms of environmental failure. 

Introduction. Electrochemical corrosion of the substrate may lead to a loss of joint strength and greatly reduce the service-life. However, one has to be wary of misinterpreting any initial observations of the failed joints often signs of gross corrosion are seen on the fracture surfaces of joints which have suffered environmental attack, but such corrosion may have frequently resulted after interfacial failure had occurred due to one of the mechanisms given in Section 2.2. Thus, in such cases, corrosion of the substrates is a post-failure event, rather than a primary cause of environmental failure. 

Gledhill and co-workers [9,43] have studied the kinetics of environmental failure for epoxy/steel joints where the mechanism of attack had been found to be via the displacement of adhesive on the oxide surface by the ingressing moisture, as described in Section 2.2.1. The rate of dissociation of the interface is shown as a function of the water immersion temperature in the form of an Arrhenius... 

Thus, a visual assessment of the fracture surfaces of a joint which has been subjected to environmental attack does not indicate exactly the locus of failure and techniques such as Auger and X-ray photoelectron spectroscopy are needed to identify precisely the locus of failure. However, it does indicate that we should concentrate our attention on the interfacial regions if we are to understand and prevent such environmental failure of adhesive joints. 

Briant, C. L. (1985) Metallurgical Aspects of Environmental Failures. Elsevier, Amsterdam. 

Kinloch AJ, Little MSG, Watts JF (2000) The role of the interphase in the environmental failure of adhesive joints. Acta Mater 48 4543... 

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