The Possibility of a Visual Analysis of the Failure of Butt Adhesive Joints Made with Different Glues

The results of conducted by the authors of the article numerical analyzes, indicate the importance of normal stresses, perpendicular to the adhesive joint, during the impact destruction of block adhesive samples. This kind of stresses are responsible for the occurrence of tearing or chipping in a joint. The very significant influence of adhesion in the impact-bonded adhesive joint was the reason for testing this parameter in joints made with adhesives with different Young’s modulus. It was assumed that adhesives differing in stiffness will have different adhesive properties, which should affect the impact strength of the adhesive joints. It was also assumed that the adhesion in the joint can be assessed by analyzing the surfaces of joint damage. Cylindrical butt joints connected with various adhesives were used to carry out the tests, in which they were loaded on tear-off. The nature of tested joints damage was usually cohesive or cohesive-adhesive. The assessment of the nature of joint damage allowed to determine whether they were the result of the loss of cohesion by the adhesive (cohesive damage) or the effect of poor adhesion between the hardened joint and adherends (adhesive damage). The assessment of the nature of the destruction was carried out by three methods: visual, using an optical microscope and using an electron microscope. As a result of the carried out observations, it was found that the visual method is the least useful and not very reliable, especially in the case of transparent or low-contrast in relation to the glued material joints. The use of electron microscope allows to obtain the most reliable results, however, the possible magnification is too large and the assessment of the entire weld fracture is difficult because it does not fit in the field of observation. Observations conducted using optical microscopy at a slight magnification (5-10 times), in most cases allow to determine the nature of the destruction to a satisfactory degree, with limitations such as in the visual method.