PSI - Issue 17

Konstantinos Kouzoumis et al. / Procedia Structural Integrity 17 (2019) 347–354 Konstantinos Kouzoumis / Structural Integrity Procedia 00 (2019) 000 – 000

351

5

In the case of k=1 the failure stresses measured were very low and did not seem to be fully responsible for the failure of the specimen. According to the original report the specimen appeared to have an inhomogeneous temperature field across the crack vicinity, which has been assumed to result in secondary thermal stresses of 110MPa magnitude. The results of the Option 1 basic assessment are shown in Figure 2. It should be noted that equation (4) gives the same results with the reference stress solution used in the constraint effect associated clauses of BS 7910 (Annex N) and R6 (Section IV.5) , for both centre cracked equibiaxially and uniaxially loaded plates. In the uniaxial case it is also equivalent to the Von Mises plane strain solution used for the A assessment of k=0 . For biaxiality ratios of k=1 and k=0.5 the B assessments have significantly decreased values of L r , while for k=2 L r has increased. The latter case causes concern, since the limit load for a uniaxially loaded plate might not give safe results and would be worth exploring further if there were experimental data that captured failure at k=2 .

1.8

k=1 - A

k=0 - A k=0 - B

1.6

k=1 - B

1.4

1.2

k=0.5 - A

k=0.5 - B

1

K r

k=2 - B

0.8

k=2 - A

0.6

0.4

0.2

Option 1 FAL

0

0

0.2

0.4

0.6

0.8

1

L r

Figure 2: Option 1, A & B assessments

Overall, apart from the specimen loaded with a ratio of k=2 , which didn’t fail during testing (plotted with open symbols in Figure 2), all the failed specimens have been safely predicted to be in the unsafe zone of the FAD. This supports the use the conservative 5% Master Curve values for the calculation of K r in Option 1 assessments that disregard biaxiality. Given that all assessment points lie in the fracture dominated zone and above the FAL there cannot be a definitive conclusion about equation (4) and it would be worth testing the limit load equation applied on the B assessments on tests conducted in the collapse dominated zone (high values of L r ).

4.2. Option 3 assessments

An option 3 failure assessment line is given by equation (5)

J

f L

( ) r

=

e

J −

(5)

el pl

where J e is the value from the J-integral from the elastic analysis and J el-pl is the value from the J-integral from the elastic-plastic analysis. For the calculation of these variables, FEA is invoked. Overall, three FEA are run for each specimen, these include: • an elastic analysis, with an elastic modulus of 212GPa and a Poisson ratio of 0.3, for J e .

• an elastic plastic analysis, containing the whole tensile curve, for J el-pl • an elastic perfectly plastic, with the properties of Table 2, for the limit load