PSI - Issue 13

Emre Özaslan et al. / Procedia Structural Integrity 13 (2018) 535–541 M.A. Güler et al./ Structural Integrity Procedia 00 (2018) 000 – 000

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5. Results 5.1. Stress concentration factor (SCF)

The effect of the W/D ratio on the stress concentration factor was investigated numerically. The stress concentration factor for a quasi-isotropic laminate was found approximately 3 when the W/D ratio equals to 6. As the W/D ratio decreased from 6 to 3, stress concentration factor increased approximately %15. It can be concluded that the laminate shows an infinite plate behavior until W/D ratio equals to 6, but after this value laminate behaves like a finite plate. The critical border of W/D ratio is shown in Fig. 4. as red dashed lines.

Fig. 4. Laminate SCF for different W/D ratios

5.2. Unnotched strength After the material characterization, the first tension test was done for unnotched specimens. The strength of unnotched specimens were used to predict the strength of notched specimens using PSC method. Also a video extensometer was used to verify the results of the finite element model for the unnotched specimen. The comparison of the results obtained using finite element analysis and test results for the unnotched specimens in terms of tension direction strain is shown in Fig. 5.

Fig. 5. Comparison of analysis and unnotched specimen strain measurements

Some of the unnotched specimens failed at grip section while others failed at gauge section. It is known that gauge section failure reflects the real strength of laminate but not the grip section failure. Therefore, unnotched strength of laminate was calculated with specimens that were failed at gauge section. The average failure strength of unnotched specimens were found to be 440 MPa. The specimens that failed at gauge section and grip section are shown in Fig. 6.