- Title
- Development of a constitutive model for energy factors in erosive wear models to predict the service life of ductile metals
- Creator
- Biswas, Subhankar
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2016
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- To gain a better understanding of the surface behaviour and its influence on erosion mechanisms, erosion tests were performed using a micro-sandblaster under a constant particle flux with a range of impact velocities and angles. Two different sizes of angular SiC and Al₂O₃ particles were entrained into a stream of compressed air to impact on commercial grade mild steel and aluminium surfaces. Both the surface materials were ductile with the erodents hard and angular. The erosion rates for different impact angles and particle velocities were determined following the experimental methodology outlined in the ASTM G76 standard procedure. It was found that impact velocity, angle, as well as particle size, reflected the severity of erosion. The particle flux effect on the scar area revealed that the particle flux increased as impact angle increased. Erosion testing events were further analysed to study the different mechanisms of material removal and to examine the characteristics of surface and subsurface wear in ductile materials. Scanning electron microscopy results confirmed that at shallow impact angles, erosion was dominated by the cutting wear mechanism; however, at higher angles, erosion was dominated by the deformation wear mechanism. At shallow impact angles, materials were removed through cutting, ploughing and the formation of lips. Surface analysis also showed that at higher impact angles, the ductile material surfaces underwent severe deformation. It was also evident that surface deformation was accompanied by substantial heat affects that modified the surface and altered the material removal mechanism. Additionally, investigated impact angles (from 15° to 90°) also confirmed that material was removed through surface and subsurface cracking and damage. These subsurface cracking and damage were observed up to a certain depth from the worn surface. It was also apparent that both the depth of subsurface cracking and subsurface damages increased when impact velocity increased. The variation was consistent with an increase in surface and subsurface temperature (heating) at higher velocities. With increased temperature, the depth of the heat affected zone increased and the work hardening layer thickness also increased. It was also evident that the subsurface microstructure of the material plays a significant role in the erosion process. Subsurface microstructural damage was consistent with attainment of higher temperature and can be explained by the high strain-rate deformation and thermo-physical properties of the surface. A comprehensive study on erosion in ductile surfaces and their affects on the surface and subsurface were shown that there are some satisfactory predictive models developed for erosion. However, there are still many unknown factors that contribute to the erosion process; for example, in many instances even the mechanisms of material removal is unclear and the manner in which energy factors are involved in the wear system has not been adequately described. Further, the influence of the dissipation of kinetic energy to the surface at different impact angles was not apparent in the described models. Thus, there was a gap in the literature in relation to the dissipation of kinetic energy to the surface material during erosion and a need to study the relevant surface parameters such as coefficient of restitution, elastic-plastic properties, microstructure and surface heating. In this thesis, a new empirical erosion model was developed based on surface material properties, impact parameters and energy factors as described below: [formula could not be replicated] In which W is the erosion rate in units of mass loss, ϕ is the cutting energy factor, ε is the deformation energy factor, α is impact angle and KEpd is the dissipated kinetic energy in the surface material as is expressed below: [formula could not be replicated] Where, m is the total mass of impacting particles, vi is impact velocity, pd is dynamic pressure during impact, E1 and E2 are the elastic modulus of impacting particle and surface material respectively, γ1 and γ2 are the Poisson’s ratio for impacting particle and surface material as well as R is the radius of the impacting particle. This study has shown that the erosion model can be used successfully at various impact conditions. Validation studies on a larger scale were also performed for independent validation. It was shown that the erosion rate is independent of a certain velocity and impact angles. The model was also able to determine the dynamic pressure, strain rate and coefficient of restitution and the useful parameters for determining erosion mechanism.
- Subject
- erosion rate; predictive erosion model; unit energy factors; erosion mechanism; impact velocity; impact angle
- Identifier
- http://hdl.handle.net/1959.13/1317966
- Identifier
- uon:23547
- Rights
- Copyright 2016 Subhankar Biswas
- Language
- eng
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| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | ATTACHMENT01 | Thesis | 8 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 217 KB | Adobe Acrobat PDF | View Details Download |