Structural changes in polyamide 6 (PA6) with temperature and moisture absorption were examined by 1H pulsed NMR. The spin-spin relaxation times (T2) and the fractions were measured by the solid

The interface stress distributions in scarf adhesive joints with similar adherends under static tensile loadings are analyzed using two-dimensional and three-dimensional finite element calculations for the two cases where the adhesive length is held constant and where the width of the adherends is held constant. The effects of adhesive Young's modulus, the scarf angle and the adhesive thickness on the interface stress distributions are examined. In addition, the joint strength is predicted using the interface stress distributions based on the maximum principal stress theory and von Mises' stress. It is found that when the scarf angle is around 60 degrees, the singular stress at the edges of the interfaces is minimal in the 3-Dimensional FEM calculations while the singular stresses vanish at 52 degrees in the 2-dimensional FEM calculations. The value of the singular stress at the edges of the interfaces obtained from 3-D FEM is larger than that from 2-D FEM. It is found that the singular stress increases at the edge of the interfaces as the scarf angle decreases. In addition, the effect of the adherends where the width is held constant is demonstrated. For verification of the FEM calculations, the strains in the adherends and the joint strengths were measured. The measured strains are in a fairly good agreement with those obtained from the 3-D FEM calculations. Also, the measured joint strength is fairly consistent with the predicted results based on the maximum principal stress theory. As the result, the maximum joint strength was observed when the scarf angle was around 60 degrees. The difference in the interface stress distributions is demonstrated between the two cases.

The objective of this study is to clarify the factor which influences the rising of tack with contact time in a pressure-sensitive adhesive tape. For this purpose, butyl acrylate-acrylic acid random copolymer with acrylic acid content of 5mol% was crosslinked with various crosslinking agent amounts. Contact time dependencies of tack and fracture energy (work of adhesion) were measured by probe tack test with two different peel rates. In the case of 10mm/s, tack increased with contact time, whereas decreased with an increase in the crosslinking agent amount. The rising rate of tack with contact time decreased with an increase in the crosslinking agent amount. The similar tendency was obtained for the fracture energy. On the contrary, the tendency for 1mm/s was quite different from that for 10mm/s. It was found that the rising of tack with contact time is greatly affected by the crosslinking and the difference in the relative contribution of interfacial adhesion and cohesive strength. Moreover, it was useful to plot the relation between the values of tack and fracture energy for various peeling rate in order to clarify the tack properties.