PSI - Issue 10

I.D. Gavardinas et al. / Procedia Structural Integrity 10 (2018) 18–24 I.D. Gavardinas and A.E. Giannakopoulos / Structural Integrity Procedia 00 (2018) 000 – 000

22

5

The hardness number H M relates explicitly to the applied force P (in N) and the indentation depth h (as a ratio h/b ). ( H M : M-type Shore durometer hardness reading (0< H M <100)).

  0.324 0.0044 M P H N  

(4)

Applied force:

100 M H

h b

12.941 1

Indentation depth:

(5)



   

/ 1 2

a b             

   

2

h a

b a        

a b



  

1

arcsin

cos









  1

(6)

tan



2

First, the hardness number H M , is measured. Then, the applied load P and the ratio h/b are estimated, through equations (5) and (6), respectively. From the value h/b , the values a/b and 3P/(8E o b 2 ) are obtained. Finally, E 0 and a are calculated. A graphical explanation is provided in Fig.4.

Fig. 4. Graphical explanation for the indentation methodology.

First, we plot the anticipated curves for a/b and 3P/(8E o b 2 ) . On the horizontal axis we locate the value h/b (point A1 (or A2 for the second patch), go up to point B1 (or B2 for the second patch), and obtain the value a/b on the left vertical axis, i.e. point C1 (or C2 for the second patch). We continue up to point D1 (or D2 for the second patch) and obtain the relevant value on the right vertical axis, i.e. point E1 (or E2 for the second patch). From the two readings we obtain E 0 and a . The black solid line (connecting points A1, B1, C1, D1, E1) corresponds to the bovine patch 1, while the blue dotted line (connecting points A2, B2, C2, D2, E2) to the bovine patch 2. The results for the bovine patches are summarized in Table 1. Results for a rubber with known properties are also included for comparison.

3. Results and discussion

The proposed methodology furnishes several mechanical material parameters. The hardness number is H M =69.40 and 62.90 for the first and second sample, respectively, while the corresponding elastic moduli are E =6.356 and 4.701 MPa. The corresponding forces are 0.6294 N and 0.60076 N and the indentation depths 0.6294 mm and 0.60076