14 T. Sasaki et al. fatigue damage due to the pre-fatigue load influenced elastic deformation behavior as well as the acoustic velocity. However, the acoustic measurement suggests the increase in the elasticity along the tensile direction by compressive residual stress (Fig. 2.6), and this is inconsistent with the increase in the elastic compliance d"yy/dF. The discrepancy between the acoustic and the optical measurement can be explained by taking into consideration the effect of internal force by residual stress field described in another work [13]. The neck part of specimen is initially compressed by the surrounding region including both grip of specimen. When the specimen is stretched, the restoring force acts on the compressed region, resulting in decreasing the external tensile force. Consequently, the value d"yy/dFin the compressed region decreases. At the same time, the heterogeneity of residual stress in both side of the neck part of specimen may cause bending deformation. In the latter fatigue stage of NP > 10 3, the residual stress is released by crack initiation, leading to the predominant shear deformation (Fig. 2.11). 2.4 Conclusion The influence of fatigue damage on the elastic response of aluminum alloy has been investigated through acoustic wave velocity measurement and visualization of macroscopic deformation behavior using ESPI. In the earlier fatigue stage of prefatigue cycle NP < 10 3, the change in the acoustic velocities suggested an increase of compressive residual stress along the tensile direction induced by the localized plastic deformation. On the other hand, the visualization of macroscopic deformation using ESPI demonstrated that strain heterogeneity in the macroscopic elastic regime was enhanced with increasing the pre-fatigue cycle, NP. We infer that the residual stress induced by the fatigue cyclic load influenced to the macroscopic deformation behavior. These results indicate that the fatigue damage at the earlier fatigue stage due to the localized plastic deformation can be detected by the macroscopic deformation behavior using ESPI. References 1. Ogura, K., Miyoshi, Y., Kayama, M.: A study of X-ray analysis of fatigue fracture surface. Eng. Fract. Mech. 22, 123 (1985) 2. Steuwer, A., Edwards, L., Pratihar, S., Ganguly, S., Peel, M., Fitzpatrick, M.E.: In situ analysis of cracks in structural materials using synchrotron X-ray tomography and diffraction. Nucl. Instrum. Methods Phys. Res. B. 246, 246 (2006) 3. Steuwer, A., Rahman, M., Shterenlikht, A., Fitzpatrick, M.E., Edwards, L., Withers, P.J.: The evolution of crack-tip stresses during a fatigue overload event. Acta Mater. 58, 4039 (2010) 4. Moorth, V., Jayakumar, T., Raj, B.: Influence of microstructure on acoustic emission behavior during stage 2 fatigue crack growth in solution annealed, thermally aged and weld specimens of AISI type 316 stainless steel. Mater. Sci. Eng. A212, 212 (1996) 5. Hasegawa, S., Sasaki, T., Yoahida, S., Hebert, S.L.: Analysis of fatigue of metals by electronic speckle pattern interferometry. Conf. Proc. Soc. Exp.Mech. 3, 127 (2014) 6. Sasaki, T., Hasegawa, S., Yoahida, S.: Fatigue Damage Analysis of Aluminum Alloy by ESPI. Conf. Proc. Soc. Exp. Mech. 9, 147 (2015) 7. Stratoudaki, T., Ellwood, R., Shrples, S., Clark, M., Somekh, M.G.: Measurement of material nonlinearity using surface acoustic wave parametric interaction and laser ultrasonics. J. Acoust. Soc. Am. 129(4), 1721 (2011) 8. Rivière, J., Remillieux, M.C., Ohara, Y., Anderson, B.E., Haupert, S., Ulrich, T.J., Johnson, P.A.: Dynamic acousto-elasticity in a fatiguecracked sample. J. Nondestruct. Eval. 33, 216–225 (2014). doi:10.1007/s10921-014-0225-0 9. Su, Z., Zhou, C., Hong, M., Cheng, L., Wang, Q., Qing, X.: Acousto-ultrasonics-based fatigue damage characterization: linear versus nonlinear signal features. Mech. Syst. Signal Process. 42, 25 (2014) 10. Eira, J.N., Vu, Q.A., Lott, M., Payá, J., Garnier, V., Payan, C.: Dynamic acousto-elastic test using continuous probe wave and transient vibration to investigate material nonlinearity. Ultrasonics. 69, 29 (2016) 11. Yoshida, S., Sasaki, T., Craft, S., Usui, M., Haase, J., Becker, T., Park, I.-K.: Stress analysis on welded specimen with multiple methods. Conf. Proc. Soc. Exp. Mech. 3, 143 (2015) 12. Toda, H., Fukuoka, H., Aoki, Y.: R-value acoustielastic analysis of residual stress in a seem plate. Jpn. J. Appl. Phys. 23, 86 (1984) 13. Yoshida, S., Miura, F., Sasaki, T., Rouhi, S.: Optical analysis of residual stress with minimum invasion. In: Conference and Exposition on Experimental and Applied Mechanics, Indianapolis, USA, #141 (2017) Tomohiro Sasaki Associate professor, The topics includes fatigue analysis, measurement of welding induced residual stress metals, using optical and acoustical techniques.
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