Projects
Projects: Projects for Investigator |
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| Reference Number | EP/M000966/1 | |
| Title | Dislocation-Microstructure Interaction at a Crack Tip - In Search of a Driving Force for Short Crack Growth | |
| Status | Completed | |
| Energy Categories | Not Energy Related 50%; Other Power and Storage Technologies(Electric power conversion) 50%; |
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| Research Types | Basic and strategic applied research 100% | |
| Science and Technology Fields | ENGINEERING AND TECHNOLOGY (Mechanical, Aeronautical and Manufacturing Engineering) 100% | |
| UKERC Cross Cutting Characterisation | Not Cross-cutting 100% | |
| Principal Investigator |
Dr L Zhao No email address given Sch of Mechanical and Manufacturing Eng Loughborough University |
|
| Award Type | Standard | |
| Funding Source | EPSRC | |
| Start Date | 24 October 2014 | |
| End Date | 23 April 2019 | |
| Duration | 54 months | |
| Total Grant Value | £401,631 | |
| Industrial Sectors | Aerospace; Defence and Marine; Manufacturing | |
| Region | East Midlands | |
| Programme | NC : Engineering | |
| Investigators | Principal Investigator | Dr L Zhao , Sch of Mechanical and Manufacturing Eng, Loughborough University (99.998%) |
| Other Investigator | Professor V Silberschmidt , Sch of Mechanical and Manufacturing Eng, Loughborough University (0.001%) Dr A Roy , Sch of Mechanical and Manufacturing Eng, Loughborough University (0.001%) |
|
| Industrial Collaborator | Project Contact , DSTL - Defence Science and Technology Laboratory (0.000%) Project Contact , Alstom Ltd (UK) (0.000%) Project Contact , Rolls-Royce PLC (0.000%) |
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| Web Site | ||
| Objectives | ||
| Abstract | Nickel-based superalloys are particularly used in applications involving high temperatures and stresses, such as the critical gas-turbine blades and discs in aerospace and power-generation industries. The behaviour of short cracks in nickel superalloys is of particular importance for component design and life prediction, as a large proportion of service life is spent in the growth of small cracks before final failure. Due to the strong influence of local microstructure and heterogeneous stress/strain fields, short cracks are known to grow anomalously under fatigue and tend to exhibit high, irregular and scattered growth rates. The physical driving force for short crack growth is still not well understood yet despite intensive research effort, mainly due to the limited understanding of crack-tip behaviour.This proposal aims to investigate the fundamental deformation mechanism at the tip of a short crack for nickel-based superalloys under fatigue at a range of temperatures. The research will focus on the influence of evolving local plasticity, induced by dislocation dynamics at the crack tip, on short crack growth. The interaction between dislocation and material microstructure is the major source for heterogeneous plasticity and internal stress concentration, leading to initiation and growth of short cracks. Short crack growth testing in a controlled environment will be carried out to study the anomalous behaviour of short crack growth in these alloys under fatigue, which is the expertise of UoS. Temperature will be varied in order to observe the critical effect of temperature change on the slip behaviour near the crack tip. Following crack growth tests, post-mortem transmission-electron-microscopy analyses of crack-tip zone will be performed to reveal the detailed mechanisms for nucleation and multiplication of dislocations, pile-up and penetration of dislocations at phase/grain boundaries and the influence of grain misorientations on dislocation behaviour. In particular, match-stick samples will be extracted from the crack-tip fracture process zone of fatigue-tested specimens to allow in-situ measurements of crack tip deformation under fatigue, which are the established techniques at UoM. In this case, high resolution digital image correlation, with the assistance of grain orientation mapping and scanning-electron-microscopy imaging of gold remodelled surfaces, will be used to quantify shear strain in slip traces formed near the crack tip during fatigue loading. In addition, high energy synchrotron X-ray diffraction studies will be carried out to measure the elastic strain response and load transfer between different phases around the crack tip, which will provide insight regarding the penetration of dislocations into the gamma-prime precipitates. To physically simulate the material plasticity behaviour, a three-dimensional discrete-dislocation-dynamics (DDD) approach will be developed to model the interaction between dislocations and materialmicrostructures, which is the strength of LU, based on experimental results. The DDD model will be interfaced with viscoplasticity and crystal plasticity models, and further applied to investigate the role of dislocation dynamics in depicting short crack growth. A multi-scale finite element method will be established for the crack-tip deformation analyses, which aims to identify a micromechanics-based driving force for short crack growth. Computational simulations will be thoroughly validated against local strain measurements (at both mesoscale and microscale), in-situ and post-mortem measurements as well as X-ray tomography of extracted match-stick samples. The ultimate goal is to deliver an efficient finite element procedure to predict short crack growth, with full validation against the experimental data, for end users | |
| Publications | (none) |
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| Final Report | (none) |
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| Added to Database | 09/12/14 | |
