PSI - Issue 14

Mohd Tauheed et al. / Procedia Structural Integrity 14 (2019) 354–361 Mohd Tauheed/ Structural Integrity Procedia 00 (2018) 000–000

358

5

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(3)

A direct method was implemented for the determination of TSL. In this method, the evolution of mode I strain energy release rate, G I was plotted against crack tip opening displacement for the DCB specimen at a specific crack length as shown in the Fig. 3 (a). Then a 6 th degree polynomial was fit to the evolution of G I with separation. For individual crack length, a set of images were taken at the crack tip location during loading of the DCB specimen. In each image, the normal separation was determined using DIC technique. Two reference points, one at upper and one at the lower end of the adhesive layer were used to determine the separation Mode I traction-separation law for individual crack length was obtained by differentiating the 6 th degree polynomial equation of G I and separation in the DCB specimen and bilinear approximations for these experimentally obtained mode I traction-separation laws are shown in Fig. 3 (b). The criteria for approximation is the area under the curve which corresponds to the critical fracture toughness G IC and equal maximum separation for a crack length. 3. End notch flexure (ENF) test An ENF specimen is widely used to determine pure mode II fracture parameter. ASTM D7905 standard test method was followed in ENF specimen preparation as shown in Fig. 4. Figure 5 shows an experimental setup used for testing for ENF specimens and determination of G IIC are given as follows: ��� � �� � �� �� � �� �� (4)

Fig. 4. Geometry of the ENF specimen

Load cell

ENF specimen

Vertical slide

ENF Fixture Camera & lens

Fixture for camera

Fig. 5. Experimental setup for ENF test