PSI - Issue 14

9

Santosh Kumar et al. / Procedia Structural Integrity 14 (2019) 872–882 Santosh / Structural Integrity Procedia 00 (2018) 000–000

880

Fig. 14. SEM image of Charpy test specimen fracture surface A1) SF Longitudinal A2) SF Transverse B1) CR longitudinal B2) CR Transverse

5.2 Fractography of fracture toughness test

A typical fractured (K IC test) surface consisting precrack and final fracture regions with corresponding fracture pattern is shown in Fig. 15.

Fig. 15. SEM image of K IC sample fracture surfaces for (A) SF (B) CR material

Precrack region for both materials shows the stepwise striation crack growth. A cleavage type of fracture is observed in the said region for both route materials. In final fracture region of SF material, a cleavage mode of fracture (brittle) is observed but, the same in case of CR material is Quasi-cleavage (mixed mode – ductile + brittle) type of fracture. This confirms the higher fracture toughness value for CR material. 6. Discussion Tensile test results show that, both route materials possess similar YS and UTS in respective hardness ranges. Generally, strength of a material is influenced by its microstructure i.e. phases and their distribution, grain size etc.