Лако-красочные материалы — производство

Adhesives and adhesive bonds are very weak in peel, so that peel tests can discriminate rapidly between different surface pretreatments, particularly after, or during, environmental exposure (e. g. Brockmann(53)). Various forms of the peel test are described in several texts (5, 25, 37, 54-56), which are all essentially variations on the common theme depicted in Fig. 4.13, with the peel angle as the main variable. Adams and Wake(5) state that the key factor in determining fracture is the bending moment, M, at the tip of the propagating crack which is reacted over a very short length of adhesive, resulting in large local stresses, particularly in a direction across the adhesive thickness. However, the load measured by the peel test is not proportional to the ‘strength’ of the adhesive, but

rather is influenced by its strain to failure, the bondline thickness, and the stiffness of the peeling adherends. The damped sine-wave pattern of stresses in a T-peel joint was illustrated in Fig. 4.1(d), from the work of Kaelble. Clearly the pattern of stresses is quite complex, but Adams and Wake showed that joint strength is predictable from bulk adhesive tensile properties, at least for a rubber-modified epoxy with a high strain to failure.