Developing accurate design data to enable the effective use of new materials is undoubtedly an essential goal in the gear industry. To speed up this process, Single Tooth Bending Fatigue (STBF) tests can be conducted. However, STBF tests tend to overestimate the material properties with respect to tests conducted on Running Gears (RG). Therefore, it is common practice to use a constant correction factor $f_{korr}$, of value 0.9 to exploit STBF results to design actual gears, e.g., through ISO 6336. In this paper, the assumption that this coefficient can be considered independent from the gear material, geometry, and loading condition was questioned, and through the combination of numerical simulations with a multiaxial fatigue criterion, a method for the calculation of $f_{korr}$ was proposed. The implementation of this method using different gear geometries and material properties shows that $f_{korr}$ varies with the gears geometrical characteristics, the material fatigue strength, and the load ratio (R) set in STBF tests. In particular, by applying the Findley criterion, it was found that, for the same gear geometry, $f_{korr}$ depends on the material as well. Specifically, $f_{korr}$ increases with the ratio between the bending and torsional fatigue limits. Moreover, through this method it was shown that the characteristics related to the material and the geometry have a relevant effect in determining the critical point (at the tooth root) where the fracture nucleates.

Mechanical components, such as gears, are usually subjected to variable loads that induce multiaxial non-proportional stress states, which in turn can lead to failure due to fatigue. However, the material properties are usually available in the forms of bending or shear fatigue limits. Multiaxial fatigue criteria can be used to bridge the gap between the available data and the actual loading conditions. However, different criteria could lead to different results. The main goal of this paper is to evaluate the accuracy of different criteria applied to real mechanical components. With respect to this, five different criteria based on the critical plane concept (i.e., Findley, Matake, McDiarmid, Papadopoulos, and Susmel) have been investigated. These criteria were selected because they not only assess the level of damage, but also predict the direction of crack propagation just after nucleation. Therefore, measurements (crack position and direction) on different fractured gear samples tested via Single Tooth Bending Fatigue (STBF) tests on two gear geometries were used as reference. The STBF configuration was numerically simulated via Finite Elements (FE) analyses. The results of FE were elaborated based on the above-mentioned criteria. The numerical results were compared with the experimental ones. The result of the comparison showed that all the fatigue criteria agree in identifying the most critical point. The Findley and Papadopulus criteria proved to be the most accurate in estimating the level of damage. The Susmel criterion turns out to be the most conservative one. With respect to the identification of the direction of early propagation of the crack, the Findley criterion revealed the most appropriate.

The characterization of new materials for enabling gear design is definitely a fundamental objective in the gear industry and research. Single Tooth Bending Fatigue (STBF) tests can be performed to speed up this process. However, it is well known that STBF tests tend to overestimate material strength compared to tests performed directly on meshing gears (MG) which, in turn, require an excessively long test time. Therefore, it is common practice to use a constant correction factor $f_{korr}$ of 0.9 to translate STBF results for designing actual MG (e.g., via ISO 6336). Recent works involving a combination of Finite Element Models (FEM) and multiaxial (non-proportional) fatigue criteria based on the critical plane concept have highlighted that the assumption of considering $f_{korr}$ as a constant independent of the gear design parameters leads to inaccurate results. However, in previous studies, no correlation between $f_{korr}$ and gear design parameters has emerged. In the present paper, the influence of the normal pressure angle (${\alpha }_n$), the profile shift coefficient ($x^{*}$), and the normal module ($m_n$) on $f_{korr}$ was investigated by analyzing FEM simulations with the Findley fatigue criterion. 27 gear geometries were studied by varying the above 3 parameters in 3 levels (full factorial DOE). These geometries were simulated in both MG and STBF configurations. The results of the 54 FEM simulations were analyzed by applying the Findley fatigue criterion and the corresponding $f_{korr}$ were calculated. The correlation between $f_{korr}$ and ${\alpha }_n$, $x^{*}$ and $m_n$ was investigated using the Analysis of Variance (ANOVA) technique. The results show that the only gear design parameter influencing $f_{korr}$ is $x^{*}$ hence, a regression model for $f_{korr}$ including $x^{*}$ has been developed. This latter has been then adopted for calculating and comparing $f_{korr}$ values from other combination of the parameters found in literature, giving good correspondence.

In the last years, additive manufacturing has become a widespread technology which enables lightweight-design based on topological optimization. Therefore, generation of lattice structures with complex geometries and small thicknesses is allowed. However, a complete metallurgical and mechanical characterization of these materials is crucial for their effective adoption as alternative to conventionally manufactured alloys. Industrial applications require good corrosion resistance and mechanical strength to provide sufficient reliability and structural integrity. Particularly, fatigue behavior becomes a crucial factor since presence of poor surface finishing can decrease fatigue limits significantly. In this work, both the low-cycle-fatigue and high-cycle-fatigue behaviors of Inconel 625, manufactured by Selective Laser Melting, were investigated. Fatigue samples were designed to characterize small parts and tested in the as-built condition since reticular structures are usually adopted without any finishing operation. Microstructural features were studied by light-optical microscopy and scanning-electron microscopy. Finally, fatigue failures were deeply investigated considering fracture mechanics principles with the Kitagawa–Takahashi diagram.

Winter sports have significantly developed in the last century. Among others, skiing is a winter-sport branch in which the equipment makes the difference in the performances. While in the beginning of the last century skis were simply made of wood, nowadays the increasing demand of performances and weight reduction has promoted the adoption of composite materials. However, no significant progress has been made in the engineering approach to design such equipment which are very often still designed on the basis of several physical prototypes and trials. This is particularly true in the niche sector of ski mountaineering, where the production batches are significantly smaller with respect to those of alpine skis and at the same time the weight reduction plays a determinant role. In this context, finite elements analysis (FEA) could represent an important tool to shorten the development times and costs leading to a more effective design process. The aim of this research is the development of an accurate virtual model of an existing mountaineering ski, capable of reproducing the behavior of the real component under operation. A preliminary characterization of all the materials used for the different layers of the ski was performed via tensile tests on flat dog-bone-shaped samples in combination with digital image correlation (DIC) techniques. Samples were laser cut from sheets. The tensile tests were performed in the two principal directions for each material. In combination with DIC, these tests allowed us to estimate the four in-plane (XY) elastic properties, namely, the two elastic modules, the shear module, and the Poisson ratio (Ex, Ey, Gxy, νxy). The DIC acquisitions were elaborated with the free software GOM-Correlate. The digital model of the ski was created and simulated in an open-source environment: Code_Aster/Salome-Meca. The reason for using an open-source software is the possibility to parallelize the calculation without restrictions due to licenses and to customize the code according to the specific problem of interest. These aspects underline the potential of open-source software to improve the design process. The results of the simulations were compared with the response of the real ski in a three-point bending and a torsion-bending tests. Differences of 2.5–10% with respect to the real ski were observed for the different modeling techniques. Moreover, the validated virtual model of the ski was used to study the behavior of the ski when interacting with the snow for different roll angles and loads.