EVALUATION OF THE WELD-LINE STRENGTH OF THERMOPLASTICS BY COMPACT TENSION TEST

In order to understand the relationship between processing conditions and the properties of weld-lines on a molecular level, it is necessary to evaluate the true strength of the weld-line that is not affected b y the V-shape notch on the surface of the weld-line zone. In this expe riment, the weld-line strength of several brittle, ductile, or phase-s eparated polymers was evaluated using the compact tension test by meas uring the critical stress intensity factor, K-IC, or the critical J-va lue, J(IC), and the results were compared with those obtained by tensi le testing. For brittle polymers such as poly(methyl methacrylate) (PM MA) or styrene acrylonitrile copolymer (SAN), the value of the weld-li ne factor, i.e., the strength ratio between the welded and the non-wel ded specimen, is higher than that measured by tensile testing, because of the notch sensitivity of brittle thermoplastics and the notch depe ndence of tensile strength. On the other hand, in the case of ductile polymers such as polycarbonate (PC), the weld-line factor is similar f or both the tensile and compact tension tests. However, the dependency of the weld-line factor on melt temperature is more obvious in the co mpact tension test. From these results, it seems that the compact tens ion test is more appropriate for measuring the interfacial adhesion st rength across the weld-line, which excludes the notch effect.