Austempered Ductile Iron (ADI) for gears: Contact and bending fatigue behavior

Abstract Austempered Ductile Iron (ADI) represents an alternative solution for the manufacturing of the housing of small planetary gearboxes, with the gear teeth obtained directly on the housing itself: such solution combines a cost-effective process with the possibility of obtaining complex geometry of the case. With respect to most traditional solutions, by means of ADI the requirements of strength and accuracy of the gear teeth can be satisfied without an additional finishing step after the heat treatment: the teeth can be obtained by broaching and, thanks to the low distortion which can be granted by the austempering process, a subsequent finishing operation is not needed. For these reasons, ADI has been selected for the application to a family of small gearboxes for automation. Due to the limited experience and data available for such material, to improve the design and rating processes, a testing campaign has been performed. The aim was to obtain strength data for bending and contact fatigue, considering the specific manufacturing and heat treatment processes. The paper describes the test procedures adopted and the test results, which have been obtained on gears specimens by means of Single Tooth Fatigue (STF) and pitting tests on a FZG type bench respectively. The tests are supported by metallurgical investigations on the failed teeth, to describe and understand the failure mechanisms. The results are then compared with the data and the shape curves provided by the international standards

Fracture locus of a CORTEN steel: Finite Element calibration based on experimental results

Abstract In order to protect low-alloy steel from corrosion in outdoor applications, it is common practice to use surface treatments e.g. painting or galvanization. The costs of these specific treatments and further maintenance can be reduced by exploiting weathering steel, the so-called CORTEN steel. The rust of this material forms a protective layer, adherent and self-regenerative, capable to stop the oxidation of the raw material. This characteristic, called self-passivation, is achieved by adding Cu, Cr and P in the alloy. Furthermore, its natural rust-color inspired architects, artists and civil engineers that start using CORTEN for bridges, building facades, artworks etc.. The harmony of CORTEN with natural environments boosts its application for guardrails (safety barriers) along the highway and alpine roads of the South-Tyrolean region. These components, in addition to aesthetic characteristics, have to fulfill safety requirements, especially during crash events. During an impact, the main goal of guardrails is to absorb and dissipate energy. Large deformations take place. Therefore, the most important mechanical characteristic for guardrails' materials is the tenacity related to the ductile behavior. However, despite CORTEN guardrails are homologated through experimental tests, in some specific conditions the passivation process could fail. Therefore, its energy absorption capabilities can be jeopardized by corrosion. In order to verify and/or optimize specific guardrails' geometries for safety applications, it is important to be able to model the ductile behavior and fracture locus of CORTEN within finite elements. The goal of this paper is to characterize the ductile behavior of CORTEN through experimental quasi-static tests with different geometries, thus different level of triaxiality. The test configurations were numerically reproduced, to retrieve the actual stress state, quantify the plastic strain at failure and calibrate a ductile damage model

Numerical and experimental assessment of the static behavior of 3D printed reticular Al structures produced by Selective Laser Melting: progressive damage and failure

Abstract In recent decades, the interest of the manufacturing industry towards additive manufacturing techniques has increased considerably. Speed and ease of implementation are just some of the factors that helped making this type of production one of the most developed in the world, considering also the possibility of creating complex geometries. The present research uses of a series of Al A357 specimens produced by SLM method. The experimental measurements on a first geometry have been used to calibrate the ductile damage model implemented in the FE code. The material model is based on both classical incremental model of plastic response with isotropic hardening and phenomenological concept of damage in continuum mechanic. The result of the calibration process was verified through the comparison of FE simulation of reticular specimens with the measured experimental response. Comparison between experimental data and numerical results will be discussed

CFD simulations of gearboxes: implementation of a mesh clustering algorithm for efficient simulations of complex system's architectures

AbstractIn the last decade, computer-aided engineering (CAE) tools have become a determinant factor in the analysis of engineering problems. In fact, they bring a clear reduction of time in the design phase of a new product thanks to parametrical studies based on virtual prototypes. The application of such tools to gearboxes allowed engineers to study the efficiency and lubrication inside transmissions. However, the difficulties of handling the computational domain are still a concern for complex system configurations. For this reason, the authors maintain that it is fundamental to introduce time efficient algorithms that enable the effective study of any kind of gear, e.g., helical and bevel configurations. In this work, a new mesh handling strategy specifically suited for this kind of studies is presented. The methodology is based on the Global Remeshing Approach with Mesh Clustering (GRAMC) process that drastically reduces the simulation time by minimizing the effort for updating the grids. This procedure was tested on spur, helical, and bevel gears, thus demonstrating the flexibility of the approach. The comparison with experimentally measured power losses highlighted the good accuracy of the strategy. The algorithm was implemented in the opensource software OpenFOAM®

Fluxes in a full-flooded lubricated Tapered Roller Bearing: Particle Image Velocimetry measurements and Computational Fluid Dynamics simulations

The acquisition of complex fluxes inside a Tapered Roller Bearing (TRB) via Particle Image Velocimetry (PIV) is an experimental challenge. This can be successfully performed by exploiting a special test rig having the outer ring manufactured with sapphire. In the present paper, the velocity field in the region between cage, rollers and outer race have been captured via PIV in a fully flooded lubricated TRB. The experimental conditions have been reproduced numerically via Computational Fluid Dynamics (CFD). The comparison of PIV results with CFD ones showed excellent consistency. It has been observed that, in the target domain, the tangential velocity of the lubricant is greater than those of the cage. In addition, in the proximity of the edges of the rollers, squeezing effects due to high gradients of pressure have been recorded. The distribution of flow rates due to the pumping effect in different regions of the TRB have been estimated

Ductile damage model of an alluminum alloy: experimental and numerical validation on a punch test

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experimental testing and numerical modelling of a kevlar woven epoxy matrix composite subjected to a punch test

Abstract The paper investigates the penetration mechanics of thick-section composites. For this purpose, a series of quasi-static penetration tests on Kevlar 29 (plane wave) /epoxy panels with a nominal thickness of 6.5 mm (14 layers) were designed and conducted. The experiments were performed at different support spans using a blunt geometry for the punch. During the tests, the punch displacements and the applied force on the punch were measured. Finite element (FE) models were created to replicate the quasi - static punch test using the LS-DYNA solver and exploiting a material damage model that allows the reproduction of all the different types of failure occurring during the tests (fibre failure, matrix failure, delamination). The focus is placed on the capability of the model to mimic the experimental damage in order to have a reliable virtual tool able to provide, with high accuracy, the penetration mechanisms and the trend of the absorbed energy during the different phases of penetration. The comparison between experimental data and numerical results is discussed

bending fatigue behaviour of 17 4 ph gears produced via selective laser melting

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Preliminary evaluation of the influence of surface and tooth root damage on the stress and strain state of a planetary gearbox : an innovative hybrid numerical-analytical approach for further development of structural health monitoring models

Wind turbine gearboxes are known to be among the weakest components in the system and the possibility to study and understand the behavior of geared transmissions when subject to several types of faults might be useful to plan maintenance and eventually reduce the costs by preventing further damage. The aim of this work is to develop a high-fidelity numerical model of a single-stage planetary gearbox selected as representative and to evaluate its behavior in the presence of surface fatigue and tooth-root bending damage, i.e., pits and cracks. The planetary gearbox is almost entirely modelled, including shafts, gears as well as bearings with all the rolling elements. Stresses and strains in the most critical areas are analyzed to better evaluate if the presence of such damage can be somehow detected using strain gauges and where to place them to maximize the sensitivity of the measures to the damage. Several simulations with different levels, types and positions of the damage were performed to better understand the mutual relations between the damaged and the stress state. The ability to introduce the effect of the damage in the model of a gearbox represents the first indispensable step of a Structural Health Monitoring (SHM) strategy. The numerical activity was performed taking advantage of an innovative hybrid numerical–analytical approach that ensures a significant reduction of the computational effort. The developed model shows good sensitivity to the presence, type and position of the defects. For the studied configuration, the numerical results show clearly show a relation between the averaged rim stress and the presence of root cracks. Moreover, the presence of surface defects seems to produce local stress peaks (when the defects pass through the contact) in the instantaneous rim stress

A New Integrated Approach for the Prediction of the Load Independent Power Losses of Gears: Development of a Mesh-Handling Algorithm to Reduce the CFD Simulation Time

To improve the efficiency of geared transmissions, prediction models are required. Literature provides only simplified models that often do not take into account the influence of many parameters on the power losses. Recently some works based on CFD simulations have been presented. The drawback of this technique is the time demand needed for the computation. In this work a less time-consuming numerical calculation method based on some specific mesh-handling techniques was extensively applied. With this approach the windage phenomena were simulated and compared with experimental data in terms of power loss. The comparison shows the capability of the numerical approach to capture the phenomena that can be observed experimentally. The powerful capabilities of this approach in terms of both prediction accuracy and computational effort efficiency make it a potential tool for an advanced design of gearboxes as well as a powerful tool for further comprehension of the physics behind the gearbox lubrication