PSI - Issue 47

Mario A. Sánchez Miranda et al. / Procedia Structural Integrity 47 (2023) 310–324 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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respectively (corresponding to Figure 7a and 7b). The confrontation of Figures 10 against 11 leads to following remarks:

Figure 10. a) Fracture surfaces of specimen 1112, b) Fracture surface of specimen 2525.

Figure 11. a) Fracture surfaces of parent material UHMWPE , b) Fracture surface of parent material PP.

Considerable plastic deformation is observed on Figures 11a and 11bm which is related to high elongation on the parent materials, and characterized by the formation of small and elongated fibers before fracture [41]. The ductile behavior is absent on the fracture surfaces of dissimilar welding (Figures 8a, 8b, 8c and 8d), where fracture surfaces present brittle behavior [41,42]. Some investigation about the transition from brittle to ductile fracture behavior on thermoplastics welded using FSW have led to the following conclusions: low heat generation induces insufficient melting of materials and rigid polymeric chains, which characterize brittle fracture under tensile tests. On the other hand, high heat generation ensure the mixing of materials and the softening of polymeric chains, but increases the generation of some welding defaults [41]. In Figure 12 are plotted the zones of transition from laminar to turbulent flow and from brittle to ductile fracture behavior in function of tool pin temperature, during the welding process of these dissimilar thermoplastics. Lower temperature of 44 – 46  C in the tool pin was measured on the specimen 1112, for the lower rotating speed (1100 rpm); whereas this temperature rises to 49 – 52  C for the specimen 1525, 54 - 56  C for the specimen 2025 and 56 - 58  C for the 2525.