It is pointed out that one approach to the problem of water treeing is (1) to analyze the degradation of the material, (2) to characterize the damage, which has an obvious mechanical aspect due to the penetration of a large amount of water, and (3) to examine the forces which might produce the damage and how the material reacts upon the stresses due to the penetration of water. It is concluded that the growth of water trees is strongly influenced by the mechanical properties and by the morphology of materials. These properties are deciding factors with regard to the response of the polymer to the penetration of water and consequently to the propagation of water trees. Because they influence the extent and the degree of the mechanical damage, they also are determining factors for the dielectric strength of the insulation. Knowledge of the driving processes for the penetration of water and ions is still poor. However, the information obtained studying water treeing from the mechanical point of view remains valid, at least to a certain extent, regardless of the water penetration process. The influence of the mechanical properties of the polymer on water treeing reveals similarities between the resistance of a material to water treeing and its resistance to certain degradations under mechanical stress. Despite the differences of range between water treeing and stress-cracking damages the observed correlations between the two phenomena have led to improved resistance of the materials to water treeing by using advanced polymer technology to improve the resistance of materials to stress cracking.
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