PSI - Issue 17

C P Okeke et al. / Procedia Structural Integrity 17 (2019) 589–595 C P Okeke et al / Structural Integrity Procedia 00 (2019) 000 – 000

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Among the three frequency based fatigue formulations used, Wirsching is considered more accurate than Steinberg and Narrow band formulations as it has a 99% match to the experimental fatigue life. Both Steinberg and Narrow band are conservative in predicting the fatigue life, this has also been observed by Rahman et al (2000).

6. Conclusion

The fatigue life of PMMA polymer material under an accelerated random vibration loading has been assessed with consideration to material nonlinearity. The fatigue life based on initial elastic modulus and secant modulus is predicted using ANSYS software and compared to the experimentally obtained fatigue life. Three frequency based fatigue life prediction models, Steinberg, Narrow-Band and Wirsching were used. Twelve specimens cut-out from injection moulded optical blades of PMMA were tested to obtain the fatigue life. The average experimental fatigue life was obtained from the twelve specimens tested. With Wirsching formulation, the use of initial elastic based modulus gives fatigue life that is 52% of the average experimental result, while for the secant modulus based analysis, the fatigue life accurately matches the experimental result with only 1% difference. Steinberg and Narrow Band formulations are conservative in fatigue life prediction, with difference of 28% and 24% respectively to the result of secant modulus based Wirsching formulation. The significant error in the result of initial elastic modulus clearly reflects the evidence of material non-linearity. It is apparent in this study that even without using nonlinear model, the fatigue life of nonlinear material can be accurately predicted using secant modulus based linear model. This ultimately saves significant simulation time and accelerates product development.

Acknowledgements

This research has been funded by Wipac Ltd.

References

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