Monitoring of the mechanical load and thermal history during friction stir channelling under constant position and constant force control modes

UID/EMS/50022/2019 UID/EMS/00667/2019In the present investigation, constant position and constant force process control modes; and representative process temperature measurements were analysed during the application of the friction stir channelling process. The experimental tests were carried out using rolled plates of AA5083-H111 with thickness of 15 mm. Results show that the FSC process was found not stable during the forward traverse movement stage when it is performed via position control. For both control modes, the tool was subjected to a more severe loading during the initial plunge than during the channelling period. Moreover, it was found that the tool vertical position is not significantly affected during the channelling stage when the process was force controlled. From the temperature measurements carried out, it was recorded a maximum process temperature of about 330 °C.publishersversionpublishe

The tool:workpiece interaction when machining welded hardfacing using PCBN tools

The work presented in this thesis is concerned with turning chromium carbide based hardfacings using PCBN tools. The chip formation and tool wear process was studied by quick-stop and machining tests. Cutting temperature was investigated by means of a remote thermocouple and the chip-tool interface temperature was simulated by an ANSYS Finite Element Analysis model. Cutting performance of PBN tools from different suppliers was compared in field cutting tests. Hardness, microstructure and the adhesion between the workpiece and cutting tool material were assessed.ln the turning process, saw-tooth chips were formed, with a short chip:tool contact length. Quick-stop tests revealed that the machining process involved fracture of large carbides ahead of the cutting edge in the primary zone. Temperature measurements showed that the cutting temperature for the hard facing material was lower than that with titanium alloy but much higher than that with machining mild steel. The cutting temperature predicted at the tool chip interface was in the range of 600-700°C when cutting hard facing.The tool wear process was found to involve three main progressive stages - from small scale edge chipping to large scale flaking and fracture. Four types of wear were identified: flank wear, microchipping, flaking of the rake face and delamination of the flank face. Abrasion appears to be the principal flank wear mechanism and it showed a minimum value for different speeds but increased with feedrate. The main mechanism for microchipping involved failure through the CBN particle boundaries. Flaking of the rake face occurred in the later stages and transgranular fracture was the main mechanism.In field tests, PCBN material from various sources achieved different cutting performance, which reflected the structural differences in the PBN materials. A dense structure with strong particle binding is essential for satisfactory performance of PCBN in this application

Drilling Induced Fatigue Damage in Ti-6Al-4V

The objective of this work is to develop an understanding of the relationship between hole drilling processes and the fatigue performance of the resulting part in Ti-6Al-4V. This problem is significant, as on the order of one-hundred thousand to a million holes are created in a typical large aircraft, and the limiting performance criterion is usually the fatigue lifetime. The path between the drilling process parameters and the fatigue performance has two main steps: characterization of the thermo-mechanical drill process and assessment of the relationship between the hole integrity left by the drill process and the fatigue performance. Development has been limited by the robustness of previously available thermal characterization systems, poor correlation between drill processes and physical observations of metallic effects, and limited success identifying the key hole integrity characteristics. This work develops robust novel thermal methods which enable integration into current drill process development techniques. The key integrity drivers in the hole wall are identified, characterized, and a system to assess is presented. The thermal and hole integrity trends are presented as guidance for drill process development providing significant opportunities to optimize processes. Thus, this work advances knowledge of the process to fatigue lifetime relationship by correlating the thermo-mechanical drill process to fatigue life in Ti-6Al-4V

Formation as Barrier for Plug and Abandonment of Wells

Master's thesis in Petroleum engineeringTo permanently plug and abandon (P&A) of drilled wells, permanent barrier(s) should be established. Cement is the primer material used for zonal isolation and permanent P&A as barrier material. However, it is recognized that cement may not be a suitable material. Other barrier materials are being developed and tested. The high costs of establishing barriers and durability of materials persuaded engineers to check the usability of naturally established barriers, such as creeping formations. The concept of formation as barrier (FAB) is to use earth itself as barrier material. It is desirable to exploit the displaced formation surrounding casing considering it is cost efficient, saves time and makes operation performance carried out in a safe manner. Bonded and impermeable in-situ formation (e.g. shale, salt) is known to have sufficient formation integrity and is accepted as an annulus well barrier element. The present work reviews the fundamental concept of FAB, creep process, the properties of creeping formation(s), impacts causing creep, self-healing and self-sealing capability of formations, and description of empirical and rheological models and methods that need to be utilized to find creeping formations. Due to the large deformations needed to establish a barrier through creep process, it appears that best candidates are shales with a low threshold for plastic flow and a high ability to sustain large plastic deformations. The findings show the mechanisms that may cause the gap closure process

An investigation of cochlear dynamics in surgical and implanation processes

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The aim of this research is to improve the understanding of the impact on the cochlear dynamics corresponding to surgical tools, processes and hearing implants such that these can be designed more appropriately in the future. The results suggest that enhanced performance of implants can be achieved by optimisation of the location with respect to the cochlea and have shown that robotic surgical tools used to enable precise, simplified processes can reduce harm and offer other benefits. With an ageing population, and where exposure to noise on daily basis is increased rather than industrial settings, at least two factors of age and noise, will contribute to a greater incidence of hearing loss in the population in the future. In the research a mathematical model of the passive cochlea was produced to increase understanding of the sensitivity and behaviour of the fluid, structure and pressure transients within the cochlea. The investigation has been complemented by an innovative experimental technique developed to evaluate the dynamics in the cochlear fluids while maintaining the integrity of the cochlear structure. This technique builds on the success of the state-of-the-art surgical robotic micro-drill. The micro-drill enables removal of bone tissue to prepare a consistent aperture onto the endosteal membrane within the cochlea. This is known as preparing a ‘Third window’. In this technique the motion of the exposed endosteal membrane is treated as the diaphragm element of a pressure transducer and is measured using a Micro- Scanning Laser Vibrometer operating through a microscope. There are two principal outcomes of the research: First, the approach has enabled disturbances in the cochlea to be contrasted for different surgical techniques, which it is expected to allude preferential methods in future surgery in otology. In particular it was shown that when using the robotic micro-drill to create a cochleostomy that the disturbance amplitude reduces to 1% of that experienced when using conventional drilling. Secondly, an empirically derived frequency map of the cochlea has been produced to understand how the location of implants affects maximum power transmission over the required frequency band. This has also shown the feasibility of exciting the cochlea at a third window in order to amplify cochlear response

Current research in cavitating fluid films

A review of the current research of cavitation in fluid films is presented. Phenomena and experimental observations include gaseous cavitation, vapor cavitation, and gas entrainment. Cavitation in flooded, starved, and dynamically loaded journal bearings, as well as squeeze films are reviewed. Observations of cavitation damage in bearings and the possibility of cavitation between parallel plates with microasperities were discussed. The transcavity fluid transport process, meniscus motion and geometry or form of the film during rupture, and reformation were summarized. Performance effects were related to heat transfer models in the cavitated region and hysteresis influence on rotor dynamics coefficients. A number of cavitation algorithms was presented together with solution procedures using the finite difference and finite element methods. Although Newtonian fluids were assumed in most of the discussions, the effect of non-Newtonian fluids on cavitation was also discussed

Solid rocket motor internal insulation

Internal insulation in a solid rocket motor is defined as a layer of heat barrier material placed between the internal surface of the case propellant. The primary purpose is to prevent the case from reaching temperatures that endanger its structural integrity. Secondary functions of the insulation are listed and guidelines for avoiding critical problems in the development of internal insulation for rocket motors are presented

Parametric study of the orthogonal cut machining in composite

Nowadays machining fiber reinforced plastic (FRP) composite materials is a compulsory process to satisfy functional requirements of the component. However, the fracture mechanics involved in the material removing process are quite complex. Since up to date the knowledge about this field is considerably poor, industrial machining process of FRP is not optimized yet. This results in low quality machined components where fiber pullouts or matrix delaminations are present. A experimental parametric study of orthogonal machining in multidirectional FRP laminates has been performed looking for the optimum cutting conditions where the machined quality is maximized. Cutting parameters such as cutting speed, depth of the cut or tool geometry have been studied. The influence of these parameters have been evaluated through force measurements, temperature monitoring and a complete damage inspection (external and internal). A meticulous analysis in each cutting condition has been performed and finally it was concluded that the optimum cutting condition was the maximum cutting speed, 200m/min, at the minimum depth of the cut, 0.05mm.Ingeniería Aeroespacia

Collapse Behaviour of Cold-Formed Steel Structure at Elevated Temperatures

This thesis describes a full-scale fire test and finite-element (FE) modelling carried out on a cold-formed steel structure. The structure was collapsed with an inwards asymmetrical collapse mechanism. The FE model was validated against the full-scale fire test results where the comparison shows that the FE results were in good correlation with the full-scale fire test results. The results presented in this thesis can contribute to practical design guidance for fire safety engineering

Quantification of drilling quality and mechanisms in CFRP composites

Drilling on fibre reinforced composites is a crucial process in fabrication of airframes in aircraft industry. In this research, an extensive experimental investigation on drilling and machining CFRP laminates using different tools is carried out to analyse effects of processing parameters on drilling performance. Drilling performance and quality of circular holes on a commercial aircraft CFRP laminate are investigated, using drill bit with three different configurations made of solid carbide, namely GT50 dagger drill, GT15 reamer drill, and twist drill. Back support of different geometry, as full support, partial support and no support, is employed during drilling at spindle speeds of 500, 1000, and 2000 rpm, and feed rate of 50 mm/min. Thrust force and torque, are measured. Quantification of the quality and holes integrity is accomplished by evaluating surface roughness, heat distribution, drilled hole roundness or circularity, chip size, and damage factor. The second major study is an energy-based analysis based on the energy balance model established by William’s on cutting polymers is presented by addressing Mode I fracture as a key mechanism in different cutting directions in a unidirectional CFRP laminate, induced by orthogonal cutting. Then, tool wear and tool life of dagger and reamer drill bits are investigated, evaluating blunting and wear of the tools. With that, assessment on tool wear and tool life are made by addressing their significant influence on thrust force and torque during drilling, delamination factor in the CFRP laminates, fibre peel-up and push-down mechanisms, surface roughness and temperature increase. Lastly, finite element analysis is added to explore and predict the drilling mechanism and chip removal mechanism as a function of failure criteria. With all that has been addressed above, this study plays a critical role for selection of the optimal drilling conditions for minimising production cost and maximising productivity