Issue 57

A. Kusch et alii, Frattura ed Integrità Strutturale, 57 (2021) 331-349; DOI: 10.3221/IGF-ESIS.57.24

Notch Effect Fig. 17 shows the failure loads, normalized to A 0 =50 mm 2 , as a function of notch opening angle. There is very low scatter for samples up to  =1 mm. The root radius has a much higher influence than the angle, with the loads slightly decreasing with notch opening angle for sharp notches and with negligible difference for blunt specimens with root radius 1 mm. Lazzarin and Berto observed that the notch opening angle has no influence for R 0 /  ratios less than 0.2 [16], which means that, in this case, the notch opening angle should be irrelevant above  =0.1 mm. For  ≥ 2 mm the specimens withstand higher loads compared to smooth unnotched samples, suggesting a notch strengthening mechanism for PMMA. However, the present data is insufficient to further investigate this behavior and, being temperature and humidity uncontrolled during storage and testing there is some uncertainty whether this could be the cause for such small variation, as some previous researches demonstrate [20]. Moreover, these sets of specimens show wider scatter than the others and have a nonlinear behavior before failure.

5000

4000 4500

3500

1000 1500 2000 2500 3000

N

500

0

0

0.5

1

1.5

2

2.5

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m m

Figure 17: Normalized failure loads as a function of the notch opening angle.

Validation For linear elastic behavior, the value of the SED is directly proportional to the stress (Eqn. 3), the same is obviously true for the applied load:

2 W F 

(10)

This relationship allows to estimate the failure load valuating the SED via FEA with an arbitrary load:

2 c W W F F  (11)

2 c

Thus:

2

c c F W F W  

(12)

Tab. 5 summarizes the prediction of the failure load for the validation samples. For the sake of simplicity, only the mean value is considered. The predicted loads are always within ±15% of the measured value, in most case the discrepancy is below 10%. In this case, the plane stress condition seems to be more representative.

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