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Analysis of high strength steels in a transmission gear

Griffiths, Dewi 2018. Analysis of high strength steels in a transmission gear. PhD Thesis, Cardiff University.
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Within industry and research, engineers rely on computational simulation as it has become a day to day design tool, reducing the requirements for prototyping and extensive experimental testing. For the speed of results and cost savings compared to experimentation, the benefit of Finite Element (FE) modelling is clear. The modelling of transmission systems within FE is already established however very little attention is paid to the inclusion of the effects of heat treatment. A case layer provides resistance to high contact pressure, rolling and sliding forces but also contributes to the overall component strength. In terms of linear-elastic simulations, there is little to be gained by including specific material properties on near-surface elements to model the case layer. However, in applications where there is some plastic deformation occurring, such as those of interest to the industrial sponsor of this research, the inclusion of case properties becomes important. Through a literature review, the established methods of gear design based on experimental and computational methods within both industry and research were discussed. A summary of best practices in terms of modelling philosophy, element type, meshing, simplification and computational power was presented. A test method for the extraction of mechanical properties through the case hardened layers of steel was developed and used to establish a relationship through the case. Through a series of look up charts, the elastic and plastic material properties can be determined for use in Finite Element (FE) analyses. Such that FE models replicate the case layer in the most representative way possible, a Functionally Graded Material (FGM), based on the experimentally-measured case layer properties, is desirable. A MATLAB algorithm was developed which manipulates an ABAQUS input file, to identify near surface elements and apply the most appropriate material properties based on their depth into a case layer. To demonstrate and validate the developed FGM-based modelling approach, finite element models of both simple tensile test coupons and a more complex gear were developed, using the experimentally obtained elastic-plastic case properties applied with the FGM. Their performance was compared directly to experimental test results, and areas for further improvement identified. To summarise, this thesis contains the development of a modelling methodology for materials which have been case-hardened, using experimentally measured case properties, relevant to the design needs of the industrial sponsor, with levels of detail exceeding those found to date in the literature.

Item Type: Thesis (PhD)
Status: Unpublished
Schools: Engineering
Uncontrolled Keywords: Finite Element Analysis; Gearbox; Transmission Design; Gears; Functionally Graded Materials; Material Data; Case Hardening; Case Layer; Simulation; Non-contact Measurement; Video Strain Gauge
Date of First Compliant Deposit: 18 March 2019
Last Modified: 18 Mar 2022 02:30

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