This research was commissioned and funded by The Welding Institute (TWI). The Welding Institute are a global research and development facility specialising in the joining of materials for industrial applications. The purpose of this research was to develop capability in textiles joining, particularly ultrasonic and laser welding technologies, which is relatively new to TWI. The appointed researcher adopted a ‘multi-strategy’ (Cresswell 2009) approach to the research; encompassing methods that were both familiar and unfamiliar to those usually adopted by TWI employees and researchers, whom mostly come from engineering and scientific backgrounds. The research was primarily undertaken with the adoption of a ‘craft-design’ approach that uses material investigation to explore and uncover interesting leads for investigation, which was the familiar approach of the researcher coming from a background in textile design. Material studies were carried out inquisitively without the formation of a particular hypothesis and insights were discussed with industry to identify potential commercial and functional application opportunities. Following the identification of an interest in welding stretchy fabrics Speedo agreed to become the main industry partner for the research, providing materials, access to testing equipment and validation of commercial opportunities for material samples relative to their application. The main hypothesis for the research Laser melted patterns can be used to control the elastic behaviour of stretchy textiles to have a targeted and variable compressive effect on the body developed through discussion with Speedo in response to material samples produced using transmission laser welding equipment. A predominant scientific approach was adopted during the second phase of the research to quantify and control this effect: to demonstrate repeatability and test it both on fabric and the body. Methods that were unfamiliar to the researcher prior to this research such as mechanical testing and microscopic analysis were employed. Selection of either a ‘craft design’ or ‘scientific’ approach was made pragmatically in response to the research as it developed. Through a retrospective analysis of applied methods throughout the research trajectory it has been possible to define this particular ‘multi-strategy’ project as a ‘sequential exploratory’ design (Cresswell 2009), whereby periods of subjective investigation are followed by empirical testing. The main process that has been developed by this research is a decorative method of controlling the elastic behaviour of stretchy fabrics using transmission laser welding equipment for a controlled and variable compressive effect on the body. Compression fabrics are used widely within the medical, lingerie and sportswear fields to apply pressure to the body either for an aesthetic or functional advantage. In swimwear, compression fabrics are applied to streamline the silhouette and minimise drag resistance. The technique developed by this research makes a contribution to knowledge within the field of laser processing of textiles, specifically within the field of transmission laser welding, and within the field of compression apparel. In the field of transmission laser welding a new functional capability for all-over surface patterns has been demonstrated. In the field of compression apparel a new decorative method for achieving an increasingly variable compressive effect for a smoother transition between different zones of stretch has been achieved. N.B. All redacted information throughout this thesis is confidential to Speedo.

Friction joining techniques, such as Friction Stir Spot Welding (FSSW) and high power Ultrasonic Welding (USW), could offer a solution for joining dissimilar materials combinations, such as aluminium (Al) to magnesium (Mg), where high intermetallic reaction rates make the use of conventional joining techniques problematic. Ultrasonic welds have been produced between 1 mm gauge Al 6111-T4 and Mg AZ31-H24 sheets, and the interfacial reaction has been studied as a function of welding time. For this welding system, the mechanical properties of the joints were optimised when a double reed welding system was employed to join materials that had been prepared using 800 grit SiC paper under a clamping force of 1.9 kN, and when the materials were oriented with the rolling direction parallel to the vibration direction. Welds produced between Al and Mg achieved similar peak lap shear strengths to those produced between Mg and Mg at welding times of 0.4 s, but the failure energy of the Al-Mg welds was less than half that of the parent material. In addition, the Al-Mg welds always failed at the interface between the sheets, rather than the desirable, and more energy intensive, pullout mechanism. The inferior mechanical properties were attributed to the rapid formation of a brittle intermetallic layer that initially formed as islands of the γ-Al12Mg17 phase. These islands rapidly spread and became continuous within 0.3 s of welding time, at which point a second sublayer of the β-Al3Mg2 phase began to form on the Al side of the intermetallic reaction layer. The combined layers reached a total thickness of 20 µm within 0.9 s of welding time, with the β-Al3Mg2 sublayer becoming the thicker of the two by this point. At longer welding times, interface liquation was observed at temperatures below the recognised lowest temperature eutectic reaction in the Al-Mg binary phase diagram. This was the result of the alloying elements present in the system and there was no depression in the melting point as a result of the high strain rate associated with this process, as has been proposed elsewhere. The rate of growth of the intermetallic layer during welding was higher than in static heat treatments, which was most likely due to the deformation causing microcracking in the brittle intermetallic layer, allowing short circuit diffusion to occur, and enhancing the growth rate by a factor of approximately 2. Finally, attempts were made to limit the rate of intermetallic compound (IMC) formation by applying coatings to the Mg sheet. The effect of the coatings was to reduce the overall IMC layer thickness by 50 %.

Metalworking fluids (MWFs) are coolants and lubricants, which are widely employed in metal cutting works. They are designed to be a long lasting product. Manufacturers have designed MWFs with lack of awareness of end-of-life disposal by including biocides, which make biological treatment challenging. Here, Syntilo 9913 was used as a case study to develop a cradle-to-grave product that was biologically stable in use but amenable to sustainable hybrid biological treatment at end-of-life. The product was reverse engineered employing factorial design approach based on a priori knowledge of the product components. From the combinatorial work, it was observed that chemical interactions can results in synergistic and antagonistic effects in terms of the toxicity and biodegradability. One of the major components of most MWFs are amines such as Triethanolamine (TEA). TEA does not biodeteriorate in single compound screening, but in combination with many other components TEA was found to cause "softening" of MWF formulations. Octylamine was found to be best for "bio-hardening" but it was not economically sustainable. Hence, the modified biocide-free synthetic MWF, Syntilo 1601, was reformulated with TEA, isononanoic acid, neodecnoic acid, Cobratec TT50S, and pluronic 17R40, which were resistant to biological treatment. Although, no change in the overall oxidation state of the MWF, metabolic activity did occur as breakdown products were observed. This suggested that both raw materials and metabolic breakdown products were recalcitrant. Thus, immobilisation agents were applied to aid further biodegradation by removing toxic bottleneck compounds. It was found that hybrid nano-iron and kaffir lime leaf performed similarly in removing chemical oxygen demand and ammonium from the system. Work in this Thesis demonstrated that the combined use of biological treatment and immobilisation agents effectively overcome the limitations of biological treatment alone by removing bottleneck compounds, which allowed greater COD reduction. This laboratory scale is a proof of principle, which needs to be tested at full scale.

Friction stir welding (FSW) and aluminium alloy 2139-T8 are currently being considered for use in future military vehicles. However, stringent regulations on weld integrity under extreme loading conditions limit the adoption of new technologies. Moreover, current finite element (FE) based methods do not give reliable predictions of strain distribution in welds, which makes it difficult to assess the performance of structures. Therefore, an extensive research program was carried out to develop a generalised finite element (FE) based methodology to predict the response of welded structures under complex loading configurations. The methodology enables the complex distribution of mechanical properties arising from welding, which is linked to microstructural variation, to be incorporated into a macro scale structural model. The method is general, and is applicable for any heat treatable aluminium alloy under a range of joining processes. To achieve this, the microstructure of 2139-T8 alloy was characterised at a range of length scales, with particular emphasis on the size and distribution of strengthening Omega precipitates. 2139-T8 was subjected to bead on plate FSW to enable characterisation of the effects of processing on the local microstructure. In addition, kinetic data for 2139-T8 was generated, allowing a simple softening model to be developed; this allowed the post-weld strength distribution to be predicted. The model was also used to recreate bulk specimens of 2139-T8 with equivalent local weld microstructure, which was verified by transmission electron microscopy. Material with equivalent microstructure was used to estimate the local mechanical property distributions across the weld, including the initial yield stress and plastic response; the mechanical properties of 2139-T8 are known to be representative of 2139-T84. From observations of this combined data, a methodology was developed to enable the estimation of the complex mechanical property distributions arising during welding. Furthermore, an automated computer program was written to implement the property distributions into FE based models. The methodology was verified using data generated for 2139-T8 and was used to simulate the response of FSW 2139-T8 loaded in uniaxial tension. The simulations were verified experimentally using digital image correlation (DIC) and the methodology was shown to demonstrate increased accuracy and reliability over existing FE methods, with respect to strain predictions. In addition, the method eliminates the need to calibrate the structural model to a particular loading configuration. Theoretically, the models are insensitive to loading and this property was tested by extending the model to simulate the strain distribution of large scale welded panels subject to explosive blast loading. The simulations were verified against blast tests where FSW 2139-T84 panels were subjected to blast loading from the detonation of plastic explosive. The results indicate that the modelling methodology developed is capable of producing accurate and reliable predictions of strain distribution in welded structures under complex loading configurations.

Electron beam welding is used for fabricating critical components for the aerospace and nuclear industries which demand high quality. The cost of materials and associated processes of fabrication is also very high. Therefore, manufacturing processes in these industries are highly controlled. However, it has been found that even minor changes in the electron beam gun itself can produce large variations in beam characteristics, leading to unpredictable welding performance. Hence, it is very important to ensure the beam quality prior to carrying out welds. This requires some kind of device and process to characterise the electron beam to indicate variations. A detailed review of different technologies used to develop devices to characterise electron beams has been carried out. At this time, it is uncommon for beam measurement to be carried out on production EBW equipment. Research carried out for this thesis is focused on development of a novel approach to characterise the electron beams using a slit-probe to maintain the quality of the welds. The challenge lies in deriving relevant features from the acquired probe signal which can effectively differentiate between the beams of different quality. Wavelet transformation, with its advantages over other methods for simultaneous time and frequency localization of signals, has found its application to feature extraction in many pattern based classifications. This technique has been used to analyse probe signals considering that different quality beams will possess unique signal profiles in the form of their distribution of energies with respect to frequency and time. To achieve the aim of the thesis, an experimental approach was used by carrying out melt runs on Ti-6Al-4V plates focusing on aerospace requirements, and varying beam properties and acquiring probe signals for all beam settings. Extracted features from the probe signals have been used in classification of the electron beams to ensure these will produce welds within the tolerance limits specified by aerospace standards for quality assurance. The features vector was compiled following statistical analysis to find the significant beam characteristics. By analysing the performance of classifier for different combination of parameters of the features vector, the optimum classification rate of 89.8% was achieved by using the parameters derived from wavelet coefficients for different decomposition levels. This work showed that the use of wavelet analysis and classification using features vectors enabled identification of beams that would produce welds out-of-tolerance. Keywords: Electron beam welding, probe devices, electron beam characterisation, quality assurance, wavelet transform, features vector, linear discriminant classifier, weld profiles, weld defects.

Laser joining processes, such as brazing and welding, are a common application in industry, especially in the automotive industry. These processes are the key to lightweight and efficient design with regard to the automotive industry. There, laser brazing is used mainly for visible joints due to the superior paint adhesion and surface roughness of brazed joints compared to welds. As laser brazing is applied in the automotive industry without using any fluxes or shielding gas, this leads to a difficulty in maintaining and ensuring the quality of brazed joints.

Friction stir welding (FSW) is a well recognised method for joining aluminium alloys and other engineering materials at a temperature below their melting point. However, the microstructure of the alloys may be modified during the welding process due to frictional heat and severe plastic deformation. In this study, the microstructures of friction stir welded AA5754-H111 and AA5083-O aluminium alloys have been investigated using optical microscopy, transmission and scanning electron microscopy equipped with electron backscatter diffraction (EBSD) and energy dispersive x-ray (EDX) facilities. Typical weld zones introduced by FSW were observed. Further, a joint line remnant flaw (JLR) within the thermomechanical affected zone (TMAZ) of the welds was also revealed. The formation of the JLR is attributed to dispersion of the magnesium rich oxides within the joining line.The effect of the modified alloy microstructure on the corrosion behaviour of the welds has been investigated by corrosion susceptibility testing and ex-situ SEM examination. Both parent alloys and welds showed good exfoliation and intergranular corrosion resistance (IGC). However, severe localized corrosion was observed at joint line remnant and the weld root.Reduced hardness was recorded in the heat affected zone (HAZ) of AA5754-H111 aluminium alloy weldment. This is attributed to the heat generated during welding that led to grain coarsening. In contrast, slightly increased hardness was recorded within the TMAZ. This was related to the grain refinement as a result of the recrystallization process that took place due to the effect of the thermal cycle and the plastic deformation. Little hardness change was recorded within AA5083-O aluminium alloy weldment. This was attributed to the effect of the alloy temper condition.Thermal simulation of the service environment of the friction stir welded alloys was conducted to assess the resistance to sensitization of welds. After exposure of the welded AA5754 and AA5083 alloys at 50, 70 and 170°C for prolonged time, the resistance of the AA5083 alloy weld to the IGC drastically decreased owing to the precipitation of magnesium rich particles known as β-phase at the grain boundaries. On the contrary, the resistance of the AA5754 alloy weld to IGC remained after the thermal exposure. Thus, the level of Mg content in Al-Mg alloys plays an important role in determining the corrosion characteristics of the alloys. The precipitation of Mg rich particles (β-phase) on the grain boundary is the determining factor for the resistance of the AA5xxx alloys to IGC owing to the difference in the electrode potentials between the β-phase and the grain interior, which leads to the generation of microgalvanic cells and selective dissolution of the grain boundary.

Wear resistant surfaces with high toughness and impact resistant properties are to be created to improve the life cycle cost of brake discs for trains. A potential solution to this industrial problem is to use an arc cladding process. This work describes the application of gas tungsten arc welding (GTAW) for a structural ceramic Metal Matrix Composite (MMC) on steel. The structure of the two ceramics examined indicates the possibility of development of a wear resistant surface, which would extend the life of the brake disc. Silicon Carbide (SiC) and Tungsten Carbide (WC) ceramics were studied to embed them in a steel matrix by an advanced GTAW method. WC particles penetrated the liquid weld pool and also partially dissolved in the steel matrix, whereas, SiC because of the physical properties never penetrated deeper into the weld pool but segregated on the surface. Successful embedding and bonding of WC led to the decision to exercise an in-depth analysis of the bonding between the WC particles and the matrix. Chemical analysis of the matrix revealed more WC dissolution as compared to particle form within the clad. It was observed that WC reinforcement particles built a strong chemical bond with the steel matrix. This was shown by electron backscatter diffraction (EBSD) analysis. The hard clad layer composed of WC reinforced steel matrix gave an matching friction coefficient to high-strength steel in cold wear conditions through Pin-on-Disc wear and friction testing. A prototype railway brake disc was created with the established GTAW parameters to find out the difficulties of producing industrial scale components.

Preferential weld corrosion (PWC) remains a major operational challenge that jeopardizes the integrity of oil and gas production facilities. It is the selective dissolution of metal associated with welds, such that the weld metal (WM) and / or the adjacent heat-affected zone (HAZ) corrode rather than the parent metal (PM). Corrosion inhibition is conventionally used to mitigate this problem however several indications suggest that some corrosion inhibitors may increase PWC. Furthermore, it is not possible to detect systems that are susceptible to PWC and or to understand the apparent ineffectiveness of some corrosion inhibitors at high flow rates. Consequently, the aim of this research is to assess the suitability of submerged jet impingement method to study flow accelerated preferential weld corrosion, which is critical to safe and economic operations of offshore oil and gas facilities. In this research, a submerged jet-impingement flow loop was used to investigate corrosion control of X65 steel weldment in flowing brine, saturated with carbon dioxide at 1 bar, and containing a typical oilfield corrosion inhibitor. A novel jet-impingement target was constructed from samples of parent material, heat affected zone and weld metal, and subjected to flowing brine at velocities up to 10 ms- 1 , to give a range of hydrodynamic conditions from stagnation to high turbulence. The galvanic currents between the electrodes in each hydrodynamic zone were recorded using zero-resistance ammeters and their self-corrosion rates were measured using the linear polarisation technique. At low flow rates, the galvanic currents were small and in some cases the weld metal and heat affected zone were partially protected by the sacrificial corrosion of the parent material. However, at higher flow rates the galvanic currents increased but some current reversals were observed, leading to accelerated corrosion of the weld region. The most severe corrosion occurred when oxygen was deliberately admitted into the flow loop to simulate typical oilfield conditions. The results are explained in terms of the selective removal of the inhibitor film from different regions of the weldment at high flow rates and the corrosion mechanism in the presence of oxygen is discussed.

This thesis is based on the PhD work of investigating the Friction Stir Welding process (FSW) with numerical and Artificial Neural Network (ANN) modelling methods. FSW was developed at TWI in 1991. As a relatively new technology it has great advantages in welding aluminium alloys which are difficult to weld with traditional welding processes. The aim of this thesis was the development of new modelling techniques to predict the thermal and deformation behaviour. To achieve this aim, a group of Gleeble experiments was conducted on 6082 and 7449 aluminium alloys, to investigate the material constitutive behaviour under high strainrate, near solidus conditions, which are similar to what the material experiences during the FSW process. By numerically processing the experimental data, new material constitutive constants were found for both alloys and used for the subsequent FSW modelling work. Importantly no significant softening was observed prior to the solidus temperature. One of the main problems with numerical modelling is determining the values of adjustable parameters in the model. Two common adjustable parameters are the heat input and the coefficients that describe the heat loss to the backing bar. To predict these coefficients more efficiently a hybrid model was created which involved linking a conventional numerical model to an ANN model. The ANN was trained using data from the numerical model. Then thermal profiles were abstracted (summarised) and used as inputs; and the adjustable parameters were used as outputs. The trained ANN could then use abstracted thermal profiles from welding experiments to predict the adjustable parameters in the model. The first stage involved developing a simplified FE thermal model which represents a typical welding process. It was used to find the coefficients that describe the heat loss to the backing bar, and the amount of power applied in the model. Five different thermal boundary conditions were studied, including both convective and ones that included the backing bar with a contact gap conductance. Three approaches for abstracting the thermal curves and using as inputs to the ANN were compared. In the study, the characteristics of the ANN model, such as the ANN topology and gradient descent method, were evaluated for each boundary condition for understanding of their influences to the prediction. The outcomes of the study showed that the hybrid model technique was able to determine the adjustable parameters in the model effectively, although the accuracy depended on several factors. One of the most significant effects was the complexity of the boundary condition. While a single factor boundary condition (e.g. constant convective heat loss) could be predicted easily, the boundary condition with two factors proved more difficult. The method for inputting the data into the ANN had a significant effect on the hybrid model performance. A small number of inputs could be used for the single factor boundary condition, while two factors boundary conditions needed more inputs. The influences from the characteristics of the ANN model were smaller, but again thermal model with simpler boundary condition required a less complex ANN model to achieve an accurate prediction, while models with more complex boundary conditions would need a more sophisticated ANN model. In the next chapter, the hybrid method was applied to a FSW process model developed for the Flexi-stir FSW machine. This machine has been used to analyse the complex phase changes that occur during FSW with synchrotron radiation. This unique machine had a complex backing bar system involving heat transfer from the aluminium alloy workpiece to the copper and steel backing bars. A temperature dependent contact gap conductance which also depends on the material interface type was used. During the investigation, the ANN model topologies (i.e. GFF and MFF) were studied to find the most effective one. Different abstracting methods for the thermal curves were also compared to explore which factors (e.g. the peak temperature in the curve, cooling slope of a curve) were more important to be used as an input. According to close matching between the simulation and experimental thermal profiles, the hybrid model can predict both the power and thermal boundary condition between the workpiece and backing bar. The hybrid model was applied to six different travel speeds, hence six sets of heat input and boundary condition factors were found. A universal set was calculated from the six outcomes and a link was discovered between the accuracy of the temperature predictions and the plunge depth for the welds. Finally a model with a slip contact condition between the tool and workpiece was used to investigate how the material flow behaviour was affected by the slip boundary condition. This work involved aluminium alloys 6082-T6 and 7449-T7, which have very different mechanical properties. The application of slip boundary condition was found to significantly reduce the strain-rate, compared to a stick condition. The slip condition was applied to the Flexi-stir FSW experiments, and the results indicated that a larger deformation region may form with the slip boundary condition. The thesis successfully demonstrates a new methodology for determining the adjustable parameters in a process model; improved understanding of the effect of slip boundary conditions on the flow behaviour during FSW and insight in to the behaviour of aluminium alloys at temperatures approaching the solidus and high strain-rates.