Godefroid, Leonardo BarbosaBernardes, Américo TristãoMuniz, Tainan FerreiraVilela, Jefferson JoséMachado, Fabiano Alcântara2023-08-172023-08-172023GODEFROID, 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. 2023.2176 1523http://www.repositorio.ufop.br/jspui/handle/123456789/17229This 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.en-USabertoCrack closureDriving force parametersSteels for automotive industryArtigo publicado em periodicoThis is an Open Access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Fonte: PDF do artigo.http://dx.doi.org/10.4322/2176-1523.20222767