PSI - Issue 41

Hendrik Baarssen et al. / Procedia Structural Integrity 41 (2022) 183–191 Baarsen et al. / Structural Integrity Procedia 00 (2022) 000–000

187

5

T stress < 0, is estimated as:

T stress 10 [MPa]

K c mat = 20 [MPa √ m] + ( K mat − 20) exp 0 . 019 −

(5)

where T stress is the T-stress, the second order expansion of the Williams series describing the stress field in the vicinity of the crack tip Anderson (2017). The T-stress is calculated using the formula reported in BSI (2013). The interaction curve, Kr = f ( Lr ), defining the locus of failure is here based on options 1 and 2 provided in BSI (2013). In any case, the cuto ff value L r , max is defined as:

E[ f y ] + E[ f u ] 2 E[ f y ]

L r , max =

(6)

where E[] denotes the expectation operator. Option 1 includes the following set of equations:

f ( L r ) = (1 + 0 . 5 L 2

0 . 5

r ) −

for L

r < 1

(7) (8) (9)

1 ) − 0 . 5 with λ = 1 + E ∆ ε/ f y

f ( L r ) = ( λ + 0 . 5 λ −

for L r = 1

( N − 1) / (2 N ) r

f ( L r ) = f (1) L

with N = 0 . 3(1 − f y / f u ) for 1 < L r < L r , max

f ( L r ) = 0 for L r ≥ L r , max

(10)

where E is the Young Modulus, and ∆ ε is the extent of the strain plateau. Di ff erent than option 1, option 2 requires the uniaxial tensile true stress-true strain curve at the assessment temperature up to f u . Option 2 FAD is determined by: f ( L r ) = E ε re f L r f y + L 3 r f y 2 E ε re f − 0 . 5 for L r < L r , max (11) f ( L r ) = 0 for L r ≥ L r , max (12)

where ε re f is the true strain at the true stress σ re f = L r f y .

3. Results

3.1. Tensile tests on coupon and notched plate specimens

Figure 3a depicts the engineering stress-strain diagram and the average true stress vs. true strain diagram as a result of the monotonic tensile tests on the coupon specimens. The S275JR steel plate object of this investigation has an average yield stress of f y = 307 N / mm 2 and a tensile strength of f u = 431 N / mm 2 . The average extent of the strain plateau is ∆ ε = 0 . 0225 mm / mm . The notched plate specimens, Specimens B1 to B4, have all failed on the net cross-section as a result of monotonic tensile tests. specimens B1 to B4 started to neck at the bolt hole, which initiated the failure of the net cross-section. Table 1 shows the ultimate load, N u , exp , for specimens B1 to B4. The N u , Rd is calculated value according to Equation 1, considering the measured net section area and neglecting the safety factor. Table 1 also reports the ratio between the experimental and the predicted value, confirming the results of the previous literature.