@article{6278dc978b54428baf189ceeeab9fef0,
title = "In situ nonlinear ultrasonic characterization of slip irreversibility and material hardening in stainless steel 316L",
abstract = "This work uses in situ nonlinear ultrasound measurements to study the relationship between the acoustic nonlinearity parameter β and the low cycle fatigue behavior of stainless steel 316L. The measured β shows a rapid decrease during hardening followed by a transition to a slower decrease in β as a function of fatigue cycles. Measurements show this trend is consistent at two different strain amplitudes. By comparing our results with prior work on dislocation characterizations in the same material, we hypothesize that the transition in slopes of β coincides with the planar-to-wavy transition that occurs at the end of hardening. Further, measurement results show that the parameter Δβt-c, the difference between β measured after the tension and compression portions of the fatigue cycle, depends on strain amplitude. The dependence of Δβt-c on strain amplitude is related to fatigue life through a power law relationship, similar to slip irreversibility. Overall, the results provided in this work suggest that β correlates with characteristics of low cycle fatigue, and thus supports the idea that in situ NLU measurements can eventually be used as a quantitative measure to predict fatigue life.",
keywords = "Low cycle fatigue, Nonlinear ultrasound, Plastic deformation, Rayleigh wave, Second harmonic generation, Slip irreversibility",
author = "Changgong Kim and Hyelim Do and Matlack, {Kathryn H.}",
note = "Secondly, we hypothesize that the tendency toward wavy slip determines the slope of \u03B2 in the softening stage. In Fig. 10, the decrease in \u03B2 during softening is more significant for 0.5 % strain amplitude. Pham et al. observed that after reaching a critical value of dislocation density, i.e., the end of hardening, frequent secondary slip and cross slip facilitate dislocation interactions, which result in dislocation annihilation and rearrangement [21,31]. These interactions promote the transformation of planar-type dislocations to wavy-type dislocations, which are characterized by walls and channels. The walls and channels are not well-defined for a smaller strain amplitude due to the ease of cross slip and secondary slip, which is the reason that the planar-to-wavy transition depends on strain amplitude. This means that the transition to wavy slip will be more prominent for 0.5 % strain amplitude yet both strain amplitudes will have essentially reached dislocation saturation; this aligns with the NLU results, where the decrease in \u03B2 during softening is more significant for 0.5 % compared to 0.3 % strain amplitude. These comparisons support the hypothesis that the evolution of \u03B2 relates to macroscopic hardening/softening behavior, which represents the evolutionary characteristics of dislocations during LCF. In summary, our results suggest the following hypotheses that should be further studied: (1) a rapid decrease in \u03B2 during early fatigue cycles relates to macroscopic hardening, and (2) the change in the slope of \u03B2 during softening coincides with the planar-to-wavy transition that occurs near the end of the hardening stage.The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Changgong Kim reports financial support was provided by National Science Foundation. Kathryn Matlack reports a relationship with National Science Foundation that includes: funding grants. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.This material is based upon work supported by the National Science Foundation under Grant No. CMMI-20-15599. Experimental measurements were carried out in part in the Advanced Materials Testing and Evaluation Laboratory, University of Illinois. This material is based upon work supported by the National Science Foundation under Grant No. CMMI-20-15599. Experimental measurements were carried out in part in the Advanced Materials Testing and Evaluation Laboratory, University of Illinois.",
year = "2025",
month = sep,
doi = "10.1016/j.ndteint.2025.103401",
language = "English (US)",
volume = "154",
journal = "NDT and E International",
issn = "0963-8695",
publisher = "Elsevier Ltd",
}