Early Crack Propagation in Single Tooth Bending Fatigue: Combination of Finite Element Analysis and Critical-Planes Fatigue Criteria

Abstract

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.

Numerical Study of the Impact of Shot Peening on the Tooth Root Fatigue Performances of Gears Using Critical Plane Fatigue Criteria

“…The most critical point and the severity of the damage were evaluated for both conditions exploiting the Findley fatigue criterion (Figure 6). The results for the reference non-treated gear are coherent with the experimental findings [57] showing a nucleation site in the "critical section" as defined by the ISO standard and with an early propagation direction of γ NP = 43 • . The shot-peened gear shows quite a different behaviour.…”

“…The most reliable and effective method to take into account all these differences, is to use advanced fatigue criteria. This procedure was already used by the authors for determining the relation between STBF tests and real gears [23,[56][57][58][59].…”

Gear Tooth Root Bending Strength Estimation under the Assumption of Fatigue Limit Existence

“…Material Design & Processing Communications case and the actual case [23, 36-39, 52, 53]. On the one hand, the lack of the rolling/sliding condition implies that the loading condition occurring within the toot root is different [11,54,55]. On the other hand, the fact that the tests are performed on the teeth rather that gear implies a statistical difference [17,18].…”

Experimental Study on Vibration Fatigue Behavior of Aircraft Aluminum Alloy 7050

“…The results revealed the relationship between the accelerations and the fatigue damage, as well as the mentioned characteristic parameters of the system. Franco Concli [ 31 ] evaluated the accuracy of five different criteria by applying them to different fractured gear specimens. The results showed that the criteria of the mechanical components agreed with determining the most critical node for gear geometries.…”