PSI - Issue 61

Jignesh Nakrani et al. / Procedia Structural Integrity 61 (2024) 188–194 Jignesh Nakrani et al. / Structural Integrity Procedia 00 (2019) 000 – 000

192

5

2  + P



(

)

2 0.886 4.64 13.32 14.72 5.6     + − + − 3 4

K  =

(1)

(

)

3/2

B W

1

−



where α = a / W , W and B represent the width and thickness of the CT specimen, respectively, N denotes number of cycles, ∆ P denotes the load range, a represents crack length. Results of fatigue crack propagation rate were fitted to the Paris law given in Paris and Erdogan (1963) as per Eq (2).

da dN

( ) m

(2)

C K

= 

where C denotes the Paris constant and m denotes Paris exponent.

Table 3. Paris’ constant s Specimen C

m

SS304 Al5083

2 × 10 -8 7 × 10 -12 1 × 10 -18 3 × 10 -9

3.68 4.54

FSW Interface

12.14

FSW Offset

3.99

From Fig. 3, the slowest crack growth rate is noticed for the SS304 base material. This is indicated by the smaller Paris exponent, m = 3.68 (Table 3) in comparison to Al5083 and the FSW joint cases. For Al5083 alloy, the crack propagated faster than the SS304 alloy. Crack growth rate in Al5083 was more than the FSW cases in the initial Δ K region (Δ K below 16 MPa.m 0.5 ). Crack growth rate for a FSW interface notch specimen was observed to be higher than the Al5083 when Δ K is higher than 16 MPa.m 0.5 . The crack growth rate in the FSW interface is 3 times and 2.5 times than the crack growth rates in SS304 and Al5083, respectively as reflected with m values in Table 3. The Paris constant, C was lowest for the FSW interface case, followed by Al5083. The lower C and higher m values for the FSW interface case suggest that initially, crack propagation was slower, but accelerated rapidly once it began. Conversely, the FSW offset exhibited a lower C value, indicating a comparable crack propagation rate with Al5083 in the initial stage. Throughout the test, the crack growth rate for the FSW offset case consistently stayed lower than that observed for Al5083. Fig. 4 shows the crack path trajectories of FSW specimens. For FSW interface case, the crack followed a straight path along the Al- SS interface. It’s important to note that the interface within dissimilar joints comprises secondary phase particles, which have the potential to generate micro-cracks and facilitate an accessible pathway for fatigue crack propagation Cortés et. al (2019). This would lead to higher crack growth rate for the FSW interface case, observed in the current study. Conversely, for FSW offset case, the crack traveled towards Al5083. This deviation in the crack path towards Al5083 resulted in an FCGR slope that closely resembled that of Al5083. For a more in-depth analysis of crack growth behavior, fracture samples of FCGR specimens were examined using scanning electron microscopy (SEM).

Fig. 4. Crack path trajectories for (a) FSW Interface and (b) FSW Offset cases.