Effect of R load ratio on fatigue crack growth resistance of steels used in automotive applications : experimental results and use of performance prediction models.
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2023
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This research consisted in comparing the fatigue crack growth (FCG) performance of four HSLA/ AHSS steels used
in automotive applications and with different microstructures, and the application of some prediction models for the da/dN
versus ΔK traditional sigmoidal curve as a function of the R load ratio. FCG tests were carried out on C(T) test specimens
with R-ratios varying between 0.03 and 0.7. Using the original and empirical methodology proposed by Paris and Erdogan
to describe the da/dN-ΔK relationship, the results showed significant differences in function of microstructure, and a
deleterious effect of R-ratio increase on the crack growth rate. In order to check existing methodologies based on physical
considerations for predicting the fatigue behavior of materials and the effect of the R-ratio mainly in the fatigue threshold
ΔKth region, the well-known crack closure model proposed by Elber, an approach using two parameters as a driving force
for the crack growth proposed by Vasudevan and co-authors and a combination of these two models recently proposed
by Zhu and co-authors were compared. The manifestation of crack closure and its qualitatively expected dependence on
the R-ratio were verified for the studied steels, but the Elber model was not able to provide a master curve that accurately
summarized the effect of the R-ratio on the sigmoidal fatigue curve of steels. The combined use of two critical thresholds,
ΔKth* and Kmax*, for predicting fatigue crack growth according to the Vasudevan model also did not provide accurate
results in evaluating the effect of the R-ratio. Regardless of the verified dispersions, there is a connection between the
two-parameter methodology and crack closure, hence the model by Zhu and co-authors could be a promising alternative.
However, this model also showed significant dispersions and was unable to create a master curve to adequately predict the
effect of R-ratio on crack growth. Thus, it can be concluded that this research topic is still open, requiring a more in-depth
phenomenological knowledge to predict the effect of the R-ratio on FCG.
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Crack closure, Driving force parameters, Steels for automotive industry
Citação
GODEFROID, L. B. et al. Effect of R load ratio on fatigue crack growth resistance of steels used in automotive applications: experimental results and use of performance prediction models. Tecnologia em Metalurgia, Materiais e Mineração, v. 20, artigo e2767, 2023. Disponível em: <https://www.tecnologiammm.com.br/article/10.4322/2176-1523.20222767/pdf/tmm-20-e2767.pdf>. Acesso em: 06 jul. 2023.