Manufacturing, Design & Materials
Residual stress is a common, but often unidentified, side effect of many manufacturing processes. This locked in energy can lead to unexpected consequences, such as the early failure of a part or distortion out of required tolerances. It can also be favourable and used to stop materials from cracking or extend the life of a product. As one of the top teams in the world for evaluating, understanding, and managing residual stress within manufacturing, we benefit from access to industrial equipment via AFRC and inhouse modelling expertise.
In this project we investigated the quenching of a disc which induced distortion and residual stresses. AFRC performed all the experiments while we did modelling of quenching and distortion process using FEA. We also performed machining simulations to understand machining induced stress relaxation and distortion.
Collaborators: AFRC, Rolls Royce, Aubert & Duval
Sheet forming is an important aspect of manufacturing for most of the metal. The major industrial alloys typically used for various applications based on sheet forming are aluminium, titanium, nickel based super-alloys and various steel alloys. Sheet forming is a complex process which needs careful designing of the process parameters to successfully form the components without any thinning or fracture. This applies to both incremental and bulk sheet forming.
This project investigated the role of computational studies in designing and optimizing the sheet metal forming processes. Two different sheet metal forming processes, bulk sheet metal forming and single point incremental sheet metal forming, were investigated. Effect of different process parameters was studied.
It is aimed that these studies will help in aiding the design and optimization process for sheet metal forming die and tools. It will also help understand the effect different process parameter and material orientation during the process.
Collaborators: AFRC, Rolls Royce, Timet
The complex prototype forming of an industrial component was investigated on different aluminium and titanium alloy sheets using the incremental sheet forming (ISF) approach. Fracture, thinning and other deformation mechanisms were investigated during this work. Thinning was higher at the steeper wall angle for all the alloys, from both the experimental and finite element analysis. It is speculated that the typical tensile nature of loading and the associated thinning of the material at these regions caused plastic instability in the material thereby creating micro-cracks that resulted in the failure of the component.
Collaborators: AFRC, BOEING
Renewable Wind Energy
Integrity related anomalies on wind turbine blades can be addressed in planned outage windows however for emergent repairs, the logistics can be complex particularly for offshore wind turbines were a jack-up vessel would need to be mobilised if a blade is to be replaced. For Onshore Wind Turbines extendable modular trailers may face access challenges depending on the terrain where the turbines are installed and the weather during emergent events. According to a study conducted by NREL (2013), the annual loss of revenue associated with Wind Turbine downtime is 40.75 million USD. Additionally, there is currently a global challenge within the Wind Industry in establishing sustainable disposal and recycling techniques for blades. This project seeks to investigate in situ repairs that will restore the integrity of the blade, allowing for minimum duration reinstatement of operation, therefore reducing the number of blade replacements per life of field. The assessment of temporary repair methods may also be a key component in Life Extension assessments of Wind Farms. Documenting temporary repair methods available to Wind companies, providing guidance on the preferred methods to be implemented based on engineering design as well as cost will be some of the main benefits of undertaking this study.
Within the Oil and Gas industry it is common to have a documented Temporary Repair Management Strategy. This dissertation will also investigate if an equivalent strategy exists within the Wind Industry, highlighting any gaps and/or opportunities for transferrable knowledge and skills.
Whilst significant technology improvements and increases in installed capacity have seen wind energy become a major electricity generation technology over recent years, operations and maintenance strategies are still developing. A key part of operation and maintenance of any asset is a robust understanding of equipment integrity so that the operator can make informed decisions to maximise safe and reliable operation of its assets. Whilst there are well established methodologies for assessment of equipment defects in industries such as oil and gas, these have yet to emerge in the wind energy industry. As a result, component failures or unnecessary maintenance outages are more likely to occur.
This project aims to develop a defect assessment methodology for a wind turbine blade to allow quick and effective assessment of blade defects based on operating inspection data, similar to fitness for service methodologies used in the oil and gas industry. The project will use FEA based stress analysis of a wind turbine blade to understand the impact of differently sized and shaped defects in different areas of the blade. The intended outcome is to produce guidance to allow an operator to assess if a specific defect with a particular size and shape in a particular location on a turbine blade is tolerable or not (in which case further analysis or immediate repair will be recommended).
Collaborators: BP Wind Energy
An understanding of the long‐term performance of derogated offshore infrastructure is of significant importance for planning the decommissioning options. This depends on several factors such as the marine environment, materials, coatings, structure type, the chemical composition of fluids interacting with the structures, and relevant regulatory guidance. The rate of damage (general corrosion or perforation) may have consequences for whether structures are left in-situ or could effectively be removed, and underlying consequences for potential contamination.
This PhD project aims to develop laboratory and modelling protocols for estimating the long‐term performance of ageing offshore structures and consequences for decommissioning. The research will involve mechanistic, experimental and numerical studies at multiple scales, to be linked within a probabilistic framework. The project will rationally quantify relevant uncertainties in material, geometric and loading characteristics, with a view to implement time-dependant reliability principles. Reference shall be made to industry experience and capabilities to confirm feasibility of removal, if required The final outcomes of the project are likely to be generalised for decommissioning projects from multiple geographies. geographical locations and depths.
Collaborators: the National decommissioning centre, NZTC, UoA, Chevron
The project is aimed at developing a framework for long-term monitoring of derogated offshore infrastructure as currently there are no clear guidelines on the implementation of post decommissioning monitoring programmes. The project is a collaborative undertaking with Shell and NDC. The team are investigating what needs monitored, why it needs monitored, and then when and how to monitor with a view to produce guidelines on long-term monitoring for both industry and the regulators.
Collaborators: the NDC, NZTC, Shell
The existing cutting techniques, such as laser, waterjet, plasma, saw, shear and explosive, used for the cutting of structural steels have their own limitations. These limitations include the thickness and size of the workpiece, the shape and environment of the cut, and have different performance measures in terms of the cutting cost, speed, precision, quality, and energy consumption. This project is aimed at the development of a new steel cutting technique for in-air and underwater applications based on the innovative concept of induced ductile to brittle transition impact. The successful completion of this project will lead to a cutting method that is cheaper, faster, and safer than the existing methods. This can have a significant contribution in reducing the manufacturing cost of steel infrastructures and marine structures as well as reducing the removal and recycling cost of offshore structures.
Collaborators: SRPE, Clockwise Technologies (Ltd)
AI & Machine Learning for Engineering Applications
Wind turbines serve a critical role in combating climate change as a source of renewable energy. The breakdown of wind turbine blades due to damages that have accumulated over time and gone undiscovered is, nonetheless, a major challenge in the wind energy industry. The goal of this thesis is to apply machine learning to anticipate damage in composite materials used in wind turbine blades. This was done by carrying out an extensive literature review on materials relevant to the subject, numerical modelling of a composite material using ABAQUS and predicting the behaviour of damage and stress components from the numerical simulation results with different ML algorithms. The results from the project work showed that using machine learning in predicting damages is very promising. Recommendations on the further work which could be carried out were discussed.
In this work, Microbiologically Influenced Corrosion (MIC) pitting depth of steel pipelines is predicted using machine learning regression models. The machine learning regression models used are Support Vector Regression (SVR) and K-Nearest Neighbours (KNN). Past works were reviewed to obtain a MIC model to generate MIC pitting depth data. The model used to generate the MIC pitting depth data was proposed by Al-Darbi et al.. The data was generated using an initial range of values for the input parameters being varied. The initial data generated was fed to the machine learning algorithms and they were used to train the algorithms. The algorithms were exposed to two different data sets, one outside the range of the initial data generate and the other within the range of the initial data. Both algorithms showed a significant drop in performance as measured by the r-squared value when exposed to the data outside the initial range while both algorithms showed very good prediction for data within its training range. The SVR algorithm showed a more consistent prediction with little drop in performance relative to the KNN algorithm.
Offshore Oil & Gas
Hydrogen being a relatively small element can reside in metals at interstitial sites or microstructural defects. Exposure to hydrogen can occur during manufacture or in service. The effect of hydrogen on austenitic stainless steel has been investigated in the past. Austenitic stainless steels can fail due to hydrogen manifesting within the theoretical framework of the hydrogen enhanced localised plasticity (HELP) and hydrogen enhance strain induced vacancy (HESIV) mechanisms. There is experimental evidence that hydrogen influences plastic deformation and fracture processes of void nucleation, growth and coalescence. These effects with consideration of the relatively slow diffusivity of hydrogen in austenitic stainless-steel crystals are not well understood. A computational framework based on the crystal plasticity theory has been developed to help fill this gap in research knowledge. The proposed model simulates hydrogen interactions with the material microstructure during deformation and the effects hydrogen will have on the fracture process of void growth. Changes in the mechanical properties of the crystal prior to fracture are governed by the interaction of hydrogen atoms and ensembles of dislocations as the crystal plastically deforms. The effects of hydrogen on void growth are considered by analysing the effect of hydrogen on the mechanical property of material bounding an embedded void. The model has been implemented numerically using the User Material (UMAT) subroutine in the finite element software (ABAQUS) and validated by comparing simulated results with experimental data. Influencing parameters have been varied to understand their effect and test sensitivities. Crystal plasticity-based finite element simulations have been done to investigate the effect of hydrogen on plastic deformation and void growth austenitic stainless steel for a wide range of stress states, Lode parameters and crystal orientations. Hydrogen was found to increase equivalent stresses and hardening responses. Hydrogen also induces higher void growth response, and this was more pronounced at high stress triaxialities. For higher stress triaxialities, hydrogen initially inhibits void growth at low strains, but promotes void growth at higher strains. The influence of hydrogen increases in magnitude with hydrogen concentration and stress triaxiality. Crystal orientation has a varied effect on hydrogen influence and void growth. Hydrogen in trap distribution is influenced by crystal orientation. Hydrogen also affects evolution of crystal rotation but does not affect the general pattern of crystal orientation evolution. The relationship between void growth and equivalent strain for a variety of stress states and hydrogen concentration has been captured in an empirical formulation which can be used to predict defect evolution.
Collaborators: Apache Ltd
In the current economic market, industries especially involved in petrochemical and refining process are involved in reducing the operational expenditure of the assets. The ageing of infrastructure is one of the major concerns as the cost incurred for replacement and safe operations are commercially daunting. Pressure vessels, storage tanks, and piping components are exposed to several types of damages and degradation mechanism which would compromise the structural integrity of these components. In such situations, a fitness-for-service (FFS) is performed to determine the integrity of the structure and extend the life of the damaged structure.
FFS can be described as a multi-disciplinary approach in determining if a structural component is fit for operation. Several standards are published by different organisations to perform FFS assessment in different industries. API 579-1/ASME FFS-1 is one of the widely used documentation for FFS assessment across various industries, especially in petrochemical and refining. In 2000, the American Petroleum Institute (API) published API 579 Recommended Practice for FFS assessment. Later in 2007, API with the collaboration of American Society for Mechanical Engineers (ASME) released the updated FFS assessment standard to cover wider industries with the document designation API 579-1/ASME FFS-1. Even though the API document covers assessment for various damage mechanisms and components like pressure vessels, piping, and storage tanks, the current research primarily focuses on cylindrical shells with general and local metal loss from corrosion.
As part of the research, a standalone application (PYSA 1.0) was developed using programming software PYTHON for the automation of general and local metal loss assessment based on the API 579-1/ASME FFS-1 standard. The application is capable of performing level 1 and level 2 assessments on pressure vessels and piping components, and level 3 assessment on cylindrical shells of a pressure vessel. Besides, case studies were performed using PYSA 1.0 and the results were validated against Mathcad sheets prepared with the same case studies.
Collaborators: Winkinson Coutts Ltd
A carousel is a system that allows transporting considerable lengths of a pipeline to specific locations, after positioning the product is spooled out in the desired area. To get to the desired location, it has to be transported mainly using different kinds of vessels. In the transportation process, the product and the structure of the Carousel are subject to various forces that could create problems if they are not accounted for.
This project will perform an analysis of the carousel system with product spooled on it. This analysis is focused on the storage and transportation stages of the product. The resultant forces acting on the product and the structure of the carousel will be obtained. In order to obtain a reliable result, the friction between the layers of the spooled pipeline and the base and core of the carousel are accounted for.
The project will include an analysis using an Abaqus model development based on the requirements of storage of the product in a carousel. Using the load capacity of the carousel, a model of the product on the carousel will be analysed. This analysis will include the friction and forces that each layer of the pipe provides the other layers. The forces transmitted to the core and base of the carousel will also be analysed. An important part of the analysis is to determine the distribution of the forces transmitted through all the system which has a significant impact on the integrity of the product.
With these simulations, a model that is accurate and computationally efficient has been developed. Different behaviours of the product have been simulated by applying different loads from real life scenarios. It is found that pressures are transmitted from the base to the core when the friction between the objects is lost due to the horizontal acceleration. This effect is increased when big horizontal accelerations are present. As a result of this forces, the critical points on the carousel and product are identified to be in the lower part of the core in the side where the acceleration is applied.
Stress corrosion cracking (SCC) is a very common mechanism for structures subjected to hostile environments. In defence related applications, SCC can be observed in gun barrel erosion situation in artillery systems, aging Navy aircraft fleet, cracking in components of nuclear reactors, etc. It can reduce operational effectiveness of the systems or create a risky situation for structures from safety and security point of view. Furthermore, it has a vast amount of cost on economy. In order to predict and understand the underlying mechanisms behind SCC, a novel three-dimensional multiscale and multiphysics based computational framework is developed in this project. As a computational tool, a new and powerful approach for failure simulations, peridynamics, is used. The model investigated the failure mechanisms at micro and macro level by linking two different scales.
Collaborators: Strathclyde, DSTL
Although the mechanical behaviour of composite materials is fairly well understood under static and quasi-static loading conditions, the understanding at high strain rates for shock loading conditions is rather limited. As a result of this, current designs with composite materials are very conservative which significantly reduces the weight savings advantage of these materials. It is crucial to investigate the behaviour of composite materials under high strain rate conditions. For this purpose, experimental studies are essential; however, they can be prohibitively costly. Therefore, it is important to support experimental studies with computer simulations. The objective of the proposed project was to investigate the underwater shock loading response of composite materials by using the state-of-the-art multiphysics based computational technique called peridynamics. The developed approach validated against experimental results available in the literature.
Collaborators: Strathclyde, DSTL