PSI - Issue 21

Amir H. Benvidi et al. / Procedia Structural Integrity 21 (2019) 12–20 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

17

6

hyperelastic material models with the stress-strain graph from the uniaxial tensile test, the second-order Ogden material model for EPDM rubber was selected. The general form of Ogden hyperelastic material model in conjunction with the obtained constants for the EPDM rubber is presented in the following:

2

i 

N



3 

1 



(

3)

W

2   



  

2

1

2

3

i 

1

i



5.18 03 E 

1.349

1 



2 



(4)

6.121

2.350

1 



2 

 

Fig. 4 shows the predictions of the Ogden model with corresponding experimental data. As it is clear from this figure, good correlation exists between the predictions of this model and the experiments.

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Test data

Eng Stress (Mpa)

Ogden-N2

0

0.5

1

1.5

2

2.5

Eng Strain

Fig. 4. The experimental stress-strain diagram of EPDM rubber with predictions of Ogden model

As described in Section 2, the nature of stress field around the notch tip should be evaluated in the tested V-notched components. To do this, the maximum and minimum values of principal stresses through a circular path, close to the notch tip, were obtained via finite element modeling (FEM). Afterwards, the ratio of maximum to minimum stress values was achieved and the result is drawn in Fig. 5. As can be seen from this figure, the ratio is always larger than 17. As a result, it can be inferred that the stress field near a rounded tip notch in rubber-like materials is also almost uniaxial. Therefore, the methods presented in Section 2 can also be utilized for V-shaped notch rubbers. In other words, the critical value of SED obtained from the uniaxial tensile test can be considered as the critical SED of notched specimens. In this study, the shape of the control volume was considered crescent- shaped, like that utilized for brittle material. Now, we can adopt the ASED criterion for rupture assessment of notched rubbers. To obtain the value of , the final stretch of rubber in the uniaxial tensile test ( =3.051) can be substituted into relations (3) and (4). By doing so, the critical SED ( ) is obtained to be equal to 3 2.499 / MJ m .