Application of J Integral for the Fracture Assessment of Welded Polymeric Components

For many demanding applications of engineering plastics, fracture behaviour under various loading conditions is of prime practical importance. It is well known that fracture properties of plastics are significantly affected by the loading rate, temperature and both local and global stress states. The limitations associated with conventional fracture test methods may, at least in principle, be overcome by the use of appropriate fracture mechanical approaches, which properly account for the temperature and rate dependence of the mechanical behaviour of plastics and should provide geometry-independent fracture toughness values. To provide an additional contribu-tion to this application, fracture tests were performed on both 15- and 20-mm-thick bulk-extruded sheets of a polypropylene random copolymer (PP(RC)) and on four different configurations of their welded joints. The fully ductile fracture range was determined by rate-dependent tests on single CT specimens, and fracture toughness values were derived at the peak loads ( J Fmax and CTOD Fmax ). Fracture toughness values were determined for stable crack extension based on the J- Δ a and/or CTOD- Δ a R -curves using single and multiple specimens in terms of various definitions of the crack initiation ( J 0.2 , J 0.2BL or δ 0.2 ) toughness values. As expected, both methods revealed distinct differences between the bulk materials and the welded joints. These differences were found to depend on the loading rate, the weld configuration and on the data reduction method ( J integral or CTOD ).