A New Approach to Estimate the Fatigue Limit of Steels Based on Conventional and Cyclic Indentation Testing

Abstract

For a reliable design of structural components, valid information about the fatigue strength of the material used is a prerequisite. As the determination of the fatigue properties, and especially the fatigue limit σw, requires a high experimental effort, efficient approaches to estimate the fatigue strength are of great interest. Available estimation approaches using monotonic properties, e.g., Vickers hardness (HV), and in some cases the cyclic yield strength, only allow a rough estimation of σw. The approaches solely based on monotonic properties lead to substantial deviations of the estimated σw in relation to the experimentally determined fatigue limit as they do not consider the cyclic deformation behavior. In this work, an estimation approach was developed, which is based on a correlation analysis of the fatigue limit σw, HV, and the cyclic hardening potential obtained in instrumented cyclic indentation tests (CIT). For this, eleven conditions from five different low-alloy steels were investigated. The CIT enable an efficient and quantitative determination of the cyclic hardening potential, i.e., the cyclic hardening exponentCHT eII, and thus, the consideration of the cyclic deformation behavior in an estimation approach. In this work, a strong correlation of σw with the product of HV and |eII| was observed. In relation to an existing estimation approach based solely on HV, considering the combination of HV and |eII| enables the estimation of σw with an enormously increased precision.

An Overview of Estimations for the High-Cycle Fatigue Strength of Conventionally Manufactured Steels Based on Other Mechanical Properties

“…In addition to regular Vickers hardness tests, Görzen et al [57] performed cyclic indentation tests while continuously monitoring the applied force F and indentation depth h. From the resulting F-h hysteresis loops, the plastic indentation depth amplitude h a,p was determined as the half width of the hysteresis loop at the mean load, as shown in Figure 10a. The definition of h a,p was made analogous to the definition of plastic strain amplitude in a stress-strain hysteresis curve (examples of which are shown in Figures 6 and 7).…”

Understanding the Fatigue Notch Sensitivity of High-Strength Steels through Fracture Toughness

“…However, it is worth mentioning that the enhanced microstructures of new high-strength steels exhibit not only high yield strength but also higher fracture toughness values [14]. These advancements challenge the traditional understanding of the relationship between fracture toughness and yield strength usually related to fatigue strength [62]. Then, the ideal materials for fatigue dimensioning parts would be located in the upper right corner of the plot.…”

Assessing Cast Aluminum Alloys with Computed Tomography Defect Metrics: A Gurson Porous Plasticity Approach

“…Focusing on localization, studies investigating defect size and the assessment of their impact on mechanical properties and fatigue life by experimental, statistical, and empirical methods have been proposed by several researchers. Gorzen et al [19] have investigated cyclic indentation test results and their correlation with fatigue life in low alloy highstrength steels. A certain defect size threshold has been observed in fatigue life estimation and crack initiation locations.…”