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Investigation of thermo-mechanical behaviour in incremental sheet forming
No full textIncremental sheet forming (ISF) is an emerging flexible sheet forming process that has shown considerable advantages in manufacturing small batch or customised sheet products due to its high adaptability and reduced tooling costs. The principle of ISF is to use a computer numerical control (CNC) milling machine or a robotic system to control a hemispheric tool moving along a predefined tool path to progressively form the blank sheet into the desired shape. Conventional ISF is usually conducted at room temperature and hence exhibits limitations in manufacturing of hard-to-deform materials, e.g., magnesium and titanium alloys due to poor ductility at room temperature. To overcome this difficulty, heat-assisted ISF has been developed to further improve forming limit of hard-to-deform materials. Based on the heating source used, heat-assisted ISF can be divided into two categories, one is heat-assisted ISF by adopting an external heat source including electrical, laser, induction and hot air heating, while the other is so-called frictional stir incremental forming (FSIF), where the heating is generated by tool-workpiece interaction and frictional heat largely due to the ISF tool rotation.
FSIF has drawn considerable attention from the research community due to its low heating costs and high flexibility. However, the thermo-mechanical behaviour behind FSIF is still less understood, e.g., the tool-workpiece interfacial friction, heat generation, partition and transfer behaviour, the effect of process parameters on thermal response, and material deformation and fracture behaviour at varying forming temperatures.
This thesis investigates the thermo-mechanical behaviour in FSIF using theoretical modelling, experimental testing and finite element (FE) simulation.
Based on the PhD work, a novel theoretical thermal model is developed to correlate the relationship between friction-induced heat generation and material thermal response. The results indicate that the new theoretical model can capture the temperature distribution and variation under different processing conditions, and the results show a good agreement with the FE simulation results. A new tool path-defined straight groove test combined with mechanical and thermal detection is proposed to determine the coefficient of friction (COF) and heat partition coefficient (HPC) of aluminium alloy (AA1050) and commercially pure titanium Grade 1 (CP Ti Grade 1) sheets. The experimental and numerical results show that the determined COF and HPC values are sufficiently accurate. The interaction between friction force and thermal effect is observed by this testing method. The presented testing method and theoretical model provide an insight into the determination of the thermal-relevant parameters (COF and HPC), and the quantification of effect of friction-induced heat generation on the thermal response of AA1050 and CP Ti Grade 1.
A fully coupled thermo-mechanical FE model is developed to investigate the thermo-mechanical behaviour of AA1050 in FSIF process for the first time. Experimental testing and FE simulation are carried out to evaluate the effect of ISF process parameters on the forming temperatures and forces and to understand the heat generation mechanism. The results show a good agreement between ISF testing and FE simulation for truncated cone and pyramid parts under different process conditions. The effect of spindle speed on the formability is investigated and the forming limit under different stress states is examined. By using the developed FE model, the effect of process parameters on the friction heat and plastic work in FSIF are quantified, and the presented FE model provides an effective means to differentiate the contribution of three influential factors, i.e. the spindle speed, feed rate and plastic deformation to the total heat generation. The FE simulation results demonstrate that the spindle speed induced friction heat accounts for 95.19% of the total heat generation during FSIF process of the truncated cone part and 95.64% of the truncated pyramid part under the studied process conditions, which indicates that the spindle speed plays a predominant role in temperature increase while feed rate and plastic work have less effect on the total heat generation.
An extended micromechanics-based model with consideration of the effect of temperature due to the spindle speed induced friction heat on damage accumulation in ISF is developed to characterise ductile fracture behaviour of AA1050 at varying temperatures in ISF process under different strain states. The correlation between void evolution and damage accumulation at different temperatures is revealed, and the void volume fraction (VVF) at different deformation stages is determined by conducting microscopic in-situ tensile test. By introducing a new temperature-dependent VVF function and by determining appropriate Gurson-Tvergaard-Needleman (GTN) damage parameters, the ductile fracture at different temperatures is evaluated using FE simulation and validated by ISF experimental testing. The results show that the proposed temperature-dependent VVF function in GTN modelling is capable of predicting the ductile fracture of both the set temperature in in-situ tensile tests and the varying temperature conditions in ISF processes
Understanding the basis of differential auxin response in selected plant species
Get PDFAuxin plays a pivotal role in regulating root development and the molecular andcellular basis of this process has been well described in model plant Arabidopsis thaliana. However, our understanding of these mechanisms in other plant species remains limited. To explore the conservation of auxin responses across species, we treated three plant species - Brachypodium, rice, and foxtail millet - with varying concentrations of auxin and analysed their primary root growth response. Additionally, we conducted RNA sequencing to identify differentially expressed genes (DEGs) under one optimised auxin concentration. Comparative DEG analysis and promoter analysis revealed the conservation of the classic auxin signaling pathway while highlighting potential species-specific variations in auxin sensitivity and response
An approach on haptics and control of continuum robots
No full textThis thesis investigates solutions in the areas of force sensing, force/position control, and haptic control for continuum robots. To navigate narrow and constrained environments, continuum robots possess unique characteristics distinct from traditional rigid robots, including high flexibility, a small diameter-to-length ratio, and low stiffness. These structural and operational features introduce significant challenges in modelling, sensing, and control.
A comprehensive literature review is presented, covering the primary methods and notable examples in continuum robot modelling, shape/force sensing, and position/force control. The overarching research goal is to develop a widely applicable haptic sensing and control system for continuum robots. Key technical challenges—such as interaction force measurement, hybrid force/position control, and haptic feedback control—are thoroughly explored and experimentally validated in this thesis.
To address the challenge of interaction force measurement, two novel approaches are proposed. The first is an indirect force sensing method that estimates machining forces (e.g., milling or grinding) by analysing acoustic features from the machining process. This method is applied for the first time to a semi-continuum robot and utilizes a remote microphone to capture machining sounds. Experiments were conducted using two types of tools and three types of materials to evaluate the method’s robustness under various conditions. The second approach involves the development of a novel strain gauge–based triaxial force sensor, capable of measuring forces up to 20 N with an error margin of only 0.25% in the radial direction. Both force sensing methods require minimal to no modifications to the robot, and their effectiveness has been experimentally validated.
For position and force control of multi-section continuum robots, a hybrid force/position control strategy based on direct force sensing is developed. A kinematic model employing the piecewise constant curvature (PCC) assumption is used for efficient robot control. Position tracking is achieved through a vision-based tracking system, while external forces are directly measured using the previously introduced sensor. Both position and force acquisition methods are demonstrated to be accurate and stable. A hybrid controller is then implemented to achieve simultaneous closed-loop control of position and force. Compared to other controllers that rely on indirect sensing, this approach offers higher accuracy and reduced computational complexity by leveraging direct sensing and control.
Regarding haptic feedback and control, a system is proposed to enable manual operation of continuum robots in scenarios where conventional force sensors cannot be used. This system includes components for force acquisition, teleoperation, and haptic feedback. To demonstrate its general applicability, a haptic control experiment involving machining tasks is conducted, verifying the feasibility and effectiveness of the proposed method across various use cases
Examining the impact of combining traditional and digital leadership styles on Gen Z engagement in Malaysian SMEs; a focus on employers’ perspectives
No full textThis study explores how traditional and digital leadership styles affect Generation Z (Gen Z) employees in Malaysian small and medium enterprises (SMEs), with the objective of identifying effective, balanced leadership strategies that enhance leadership effectiveness and improve Gen Z job satisfaction. As Gen Z enters the workforce with distinct expectations—valuing flexibility, purpose, feedback, and digital fluency—many SME leaders face challenges in aligning leadership practices with this generation’s needs. To address this, the study employed an inductive, qualitative research approach using semi-structured interviews with leaders across various industries and age groups. This method provided deep insight into real-world leadership behaviours and perceptions. Findings were structured around three research questions: how leadership styles impact Gen Z retention, the challenges leaders face in applying traditional and digital methods, and the strategies that can bridge these styles to create more effective leadership outcomes. The results showed that neither traditional nor digital leadership in isolation is sufficient. Traditional leadership often lacks adaptability, while digital leadership—if unaccompanied by personal connection—can result in disengagement. Two key themes emerged from the data: synergy, representing the integration of traditional and digital styles, and engagement, referring to the emotional and relational connection Gen Z expects from their leaders. Based on these themes, four strategic practices were identified: balanced communication, guided autonomy, digital integration, and human connection. Together, they form a practical leadership framework tailored to the expectations of Gen Z within Malaysian SMEs. This study not only contributes to leadership literature by addressing a clear generational gap in research but also provides actionable recommendations for SME leaders navigating the complexities of hybrid leadership and workforce diversity. It concludes by recommending further research into sector-specific leadership strategies and the impact of AI-enhanced leadership tools on Gen Z engagement and synergy in the workplace
Discrete Breathers in One- and Two-Dimensional Mechanical Lattices
Get PDFIn this thesis, we investigate discrete breathers in nonlinear mechanical lattices through numerical and asymptotic methods. First, in a one-dimensional mass-in-mass Fermi–Pasta–Ulam–Tsingou (FPUT) chain with internal oscillators, we identify stable stationary breathers and long-lived weakly unstable stationary and moving breathers and breather–kinks. Second, in two-dimensional hexagonal lattices, we use multiple scales analysis, we derive the equations governing wave propagation and reduce them to Nonlinear Schrödinger (NLS) equations. We identify the ellipticity condition and a focusing condition for the exist of fully localised NLS solutions in triangular geometries, and derive (2+1)-dimensional and coupled (2+1)-dimensional NLS subsystems in honeycomb structures. The latter arise from critical points of the dispersion relation and yield existence criteria for small-amplitude breathers. These results are relevant for predictive models for energy localisation in mechanical metamaterials as they link lattice symmetry, nonlinearity and breather stability
Corporate governance in Malaysia: framework, challenges & the way forward
No full textThis paper seeks to explore the development of corporate governance in Malaysia and to provide an overview of the corporate governance framework in Malaysia in light of recent efforts to boost corporate governance amongst micro, small and enterprises in Malaysia, with a view of identifying the effectiveness and challenges of these reforms and providing recommendations to strengthen corporate governance to achieve the ultimate goals of sustainable business growth, corporate accountability, improved shareholder value and stakeholder interest protection
Waterborne debris impacts on masonry structures in extreme hydrodynamic events
No full textStructures are highly vulnerable to extreme hydrodynamic events such as tsunamis and floods. Besides water flow forces, waterborne debris impacts can also cause extensive structural damage. In this context, ASCE/SEI 7 prescribes mandatory debris impact design in flood- and tsunami-prone areas. Debris impacts generate high-magnitude impulsive forces. Therefore, low-tensile strength materials like masonry are particularly vulnerable to them, as documented in various post-disaster surveys. However research on masonry structures under waterborne debris impacts is limited. Critical knowledge gaps exist in the understanding of masonry structural behaviour in these scenarios and the development of advanced analysis methodologies. These gaps have significant practical implications given that masonry is among the most common building materials in the UK and worldwide, coupled with the recently updated tsunami risk worldwide and the increasing flood risks in climate change scenarios.
This thesis aims to achieve improved knowledge into the structural behaviour of masonry structures under waterborne debris impacts and to propose new methodologies to assess the structural performance of masonry structures in such scenarios. This work revises common assumptions in related numerical modelling and impact force calculations, i.e. the neglection of high strain rate effects in masonry material models, structural mass and structural nonlinearities. Using newly proposed high-fidelity numerical methods, this study demonstrated the limitations of all of them. Maximum strain rates exceed the critical thresholds to activate high strain rate effects in a broad range of impact scenarios. The structural mass proportionally increases the impact force for structure-to-debris mass and stiffness ratios higher and lower than critical values. Finally, the structural nonlinear behaviour of masonry structures decreases the impact force proportionally to the occurring damage. Using the data collected on the effects of the structural mass and structural nonlinearities, analytical models are proposed, for the first time, to integrate their effects in calculating the impact force-time (F-t) time diagrams of waterborne debris impacts on masonry walls. The research outputs provide new knowledge and numerical methods to assess the structural safety of masonry structures under waterborne debris impacts. Limitations remain in the absence of the fluid phase in the modelling environments and the missing coupled effects of debris and structural nonlinearities. These are critical research areas for future developments. Advanced investigations of local failure modes under debris actions are also future potential developments to identify critical impact locations at the micro-scale
Advanced Organic Geochemical Studies on the Petroleum Systems of the Nile Delta and Red Sea Basins, Egypt
No full textThe Nile Delta is a significant petroleum province in Egypt and the eastern Mediterranean. However, the origin of discovered hydrocarbons, particularly in the onshore part of the basin, was not thoroughly studied, and source-reservoir relationships remain unclear. Previous studies focused mainly on routine source rock assessment using TOC and Rock-Eval pyrolysis data, with limited investigations of the biomarker, isotopic, and molecular geochemical characteristics of the disseminated organic matter. Consequently, a more comprehensive source-reservoir correlation is essential for future exploration success.
This study assesses potential source rocks from the Nile Delta Basin and examines the discovered hydrocarbons to better understand source-reservoir relationships with a greater focus on the onshore part of the basin, which received little attention. A comprehensive geochemical evaluation of Oligocene-Pliocene source rocks and discovered hydrocarbons from the onshore Nile Delta was conducted. Molecular and isotopic compositions, biomarker distributions, and multivariate statistical techniques (chemometrics) were applied to classify hydrocarbons into genetic families and conduct oil-source correlations. The quantity, quality, thermal maturity, sources, and depositional palaeoenvironment of the disseminated organic matter were also investigated.
Geochemical signatures of onshore Nile Delta condensates suggest non-marine waxy oils derived from clay-rich source rocks dominated by Type-III terrigenous organic matter, deposited in oxic fluvio-deltaic settings. The molecular and isotopic results indicate that Oligocene-Miocene natural gases are wet-thermogenic, generated by secondary cracking of associated oils derived from Type-III, Type-II/III, or Type-II kerogen. The condensate and associated gas samples from Oligocene pay zones have different geochemical signatures than those from Miocene reservoirs, suggesting derivation from different source rocks with variable levels of thermal maturity or the presence of multiple charge systems from a common source in the onshore Nile Delta.
Oligocene–Pliocene potential source rocks in onshore Nile Delta exhibit fair to good organic richness (TOC ~1 wt.%) and are predominantly gas-prone, containing Type-III kerogen with minor contributions from Type-II/III and Type-IV kerogens. Molecular and biomarker results indicate mixed organic matter contributions from higher plants, algae, bacteria, and plankton, deposited under suboxic to anoxic nearshore marine or lacustrine environments. Isotopic and molecular compositions of Oligocene-Pliocene mud gases reflect gases with complex origins and mixing histories, ranging from primary microbial to pure thermogenic, with pre-Miocene intervals dominated by thermogenic processes. Chemometric analyses reveal no definitive correlation between Miocene-Pliocene rocks and condensates or oils in the onshore Nile Delta, implying that deeper pre-Miocene rocks are the most probable source for hydrocarbons in the onshore Nile Delta. However, Cretaceous-Eocene intervals examined in the western offshore Nile Delta primarily contain Type-II marine-algal organic matter and show no similarity to the discovered condensates, based on n-alkane and isoprenoid ratios.
Unlike the Gulf of Suez and Western Desert petroleum provinces, the Red Sea Basin remains underexplored in Egypt, with limited understanding of its petroleum systems. To investigate the effect of pressure on hydrocarbon generation from Type-I kerogen source rocks, high water-pressure pyrolysis experiments were conducted on an immature Type-I kerogen oil shale sample from the Duwi Formation, Red Sea Basin. The sample was pyrolysed under anhydrous, low-pressure hydrous (110–160 bar), and high water-pressure (500–900 bar) conditions at 320 °C (end of bitumen generation) and 350 °C (oil-generation window) for 6 and 24 h, respectively, contributing to a broader understanding of Type-I kerogen source rocks and how pressure in geological basins affects petroleum generation from these rocks.
Results indicate that high water pressure retards oil, gas, and bitumen generation from Type-I kerogen source rocks, with oil generation being most affected. Compared to previously studied Type-II and Type-IIS kerogens, the retardation effect on oil generation from the Duwi Formation is more pronounced, while gas generation is less impacted at 350 °C. This is because high water pressure retards bitumen-to-oil conversion or oil expulsion from the rock, and the retained oil in the rock could be directly cracked into gas in the presence of clay minerals. This has significant implications for overpressured basins, where oil yields may be lower, while unconventional gas resources are likely to be more abundant. Consequently, the Duwi Formation should not only be regarded as an oil source but also as a potential candidate for unconventional gas exploration, particularly in overpressured areas of the Red Sea Basin.
In addition to the effect of pressure on hydrocarbon generation, pyrolysis experiments on the Duwi Formation were utilised to examine the impact of pressure on biomarker evolution, which has not been studied previously. Results show that extracted bitumens exhibit higher maturity under anhydrous conditions than under low-pressure hydrous conditions, with more pronounced differences at 350 °C. Biomarker ratios further reveal that the extracted bitumen is consistently more mature than the corresponding generated oil, likely due to the catalytic effects of clay minerals on bitumen within the rock. In contrast, δ¹³C values were similar for extracted bitumen and the corresponding generated oil under identical experimental conditions. At 320 °C, C31‒C35 hopane isomerisation, Ts/Tm, Ts/H30, and C29Ts/H29 ratios consistently decreased with increasing pressure, while sterane ratios remained unaffected. However, at 350 °C, the dominant influence of temperature over pressure resulted in more complex and variable trends, suggesting that biomarker-based maturity assessments should be applied cautiously in overpressured basins.
To further investigate the hydrocarbon potential of the Duwi Formation in the underexplored Red Sea Basin, chemometric analysis was conducted on pyrolysis-generated oils and natural oils from the Gulf of Suez. The results indicate that artificially generated oils and South Malak-1 oils from southwestern onshore Gulf of Suez are quite different, and both groups differ significantly from other natural oils. This similarity between 350 °C and South Malak-1 oils suggests that the Duwi Formation could be a key petroleum source in the underexplored Red Sea Basin when considering mixing and migration effects under natural conditions.
This study provides valuable insights into the petroleum systems of the Nile Delta and Red Sea basins, improving the understanding of source-reservoir relationships. Moreover, it enhances the understanding of how high pressure affects biomarker evolution and petroleum generation from Type-I kerogen source rocks in geological basins. These findings offer valuable implications for petroleum exploration and biomarker-based maturity assessments, particularly in deep petroleum systems and overpressured basins
Shear performance of reinforced concrete (RC) beams strengthened with mortar-based composites under monotonic and fatigue loading
Get PDFReinforced concrete (RC) beams form the backbone of modern structures, yet their performance is increasingly compromised by aging, environmental degradation, outdated design standards, unauthorised modifications, increased load demands, impact damage, poor construction quality, and corrosion. These challenges have significantly heightened the demand for effective structural maintenance and strengthening strategies. While fibre-reinforced polymers (FRPs) are widely adopted due to their high strength-to-weight ratio and design flexibility, their limitations—such as poor fire resistance, environmental toxicity, and incompatibility with concrete substrates—restrict their applicability. In this context, mortar-based composites, including Steel-Reinforced Grout (SRG) and High-Performance Fibre-Reinforced Concrete (HPFRC), have emerged as promising alternatives for enhancing the shear capacity of RC beams. Despite their potential, research on SRG and HPFRC systems remains limited, particularly under cyclic and fatigue loading conditions.
This study aims to evaluate the application of SRG and HPFRC jacketing for the shear strengthening of RC beams. The research begins with a comprehensive literature review and the establishment of a database containing 218 samples of RC beams strengthened with mortar-based composites. This database facilitates the analysis of key design parameters influencing shear strengthening performance and assesses the accuracy of traditional empirical models for shear capacity prediction.
Subsequently, experimental investigations evaluate the static and fatigue performance of SRG-strengthened beams, with comparative analyses including Carbon Fabric Reinforced Cementitious Matrix (CFRCM) and Steel-Reinforced Polymer (SRP) systems. Unlike these systems, HPFRC, which lacks textile reinforcements, is studied independently to account for its unique mechanical properties. Key parameters, such as shear span-to-depth ratio (a/d), textile density, jacket configuration, and mortar properties, are systematically explored. Results confirm the effectiveness of all strengthening systems in enhancing shear capacity, with fully wrapped SRG systems uniquely capable of transforming failure modes from brittle shear to ductile flexural behaviour. Predictive models for shear capacity and fatigue life were developed for SRG and HPFRC systems based on experimental findings.
In addition, nine machine learning (ML) models were developed to predict the shear capacity of FRCM-strengthened beams, with XGBoost achieving the highest accuracy and stability. Shapley Additive Explanations (SHAP) and Partial Dependence Plots (PDP) were employed to enhance model interpretability and identify key factors influencing shear capacity, such as beam depth, concrete compressive strength, and mortar thickness. A novel finite element analysis (FEA) model for SRG systems was also proposed, addressing limitations in existing methods by independently modelling the behaviours of mortar and textile components. This innovation enables accurate simulation of premature delamination in high-density SRG systems, providing a robust framework for future design optimization.
This research validates the efficacy of mortar-based composites for shear strengthening of RC beams, advancing understanding and application in both static and fatigue contexts. The findings bridge critical knowledge gaps in the performance of SRG and HPFRC systems, enhance the predictive accuracy of design models, and offer innovative tools and methodologies to improve the resilience of aging infrastructure
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