Call number: LD2668 .T4 1964 G23 / Master of Science

A commercially available bismaleimide (Compimide 353[sup]R) was blended with a toughening reactive rubber (Hycar[sup]R 1300 X 13). The rate of crosslinking as a function of rubber content and cure temperature was determined using sol-gel analysis and differential scanning calorimetry. Fourier transform infra-red was used to monitor the reaction of the maleimide group. The final degree of crosslinking was dependent on the cure temperature, for 0- 33pphr reactive rubber and independent for blends of 66-100pphr reactive rubber. The addition of a cure accelerator, diazobicyclo[ 2,2,2] octane (DABCO[sup]R) to one bismaleimide reactive rubber blend was studied. The rate and degree of crosslinking were found to be high with the addition of DABCO[sup]R. Extractable monomers present in under cured samples were studied by high pressure liquid chromatography. No detectable difference was observed in the reaction rate of the aliphatic component compared to that of the aromatic components. The mechanical properties of these materials were measured. Materials with only 33pphr reactive rubber still exhibited brittle characteristics, materials with 66pphr and 100pphr showed good tensile and fracture properties, the 66pphr blend being the preferred in terms of tensile strength, modulus and elongation. Addition of a cure accelerator (0.4-1.0% w/w) to the 66pphr material increased the fracture toughness two fold. The mechanism of DABCO[sup]R as a cure accelerator is proposed. It is suggested that the crosslinking mechanism changes from a free radical to an anionic mechanism. The morphology of cure accelerated blends changed depending on the amount of DABCO[sup]R used. Attempts were made to estimate the plastic zone size of these materials using several different methods, however, none of these methods betrayed conclusive evidence for the presence of a plastic zone. The theoretical plastic zone size and shapes were determined using the Irwin, Dugdale, von Mises and Tresca models.

A series of experiments were undertaken at the Defence Evaluation Research Agency (DERA) Farnborough, within the Aero Physics group into the phenomenon called Jet Interaction (JI). Jet Interaction (JI) is produced by the interaction of a jet with the external flow around a vehicle. This study focused on investigating the effects of a divert thruster employed to provide a vehicle with a rapid divert capability on the external flow-field and on the induced forces and moments exerted on the vehicle by the jet. The research was based on studying the effects on a hypersonic interceptor sometimes referred to as a KKV (Kinetic Kill Vehicle). There are many important parameters in JI. One of these is the jet Amplification Factor (AF). This is caused by the deflection of the free-stream around and over the jet and results in a pressure increase on the vehicle surface which adds to the divert thrust force. The experiments were carried out in the intermittent hypersonic gun tunnel, at a free-steam Mach number of 12.1. This produced a Reynolds number (based on diameter) Red of 300,000 with a one-tenth scale vehicle; these conditions correspond to a full-scale vehicle flying at an altitude of 41 km. To simulate the divertthruster, nitrogen was supplied to the model through a purpose-made force balance. Measured forces ineluded normal, axial and side as well as pitch and yawing moments. The experimental results have been compared with that of a full size vehicle featuring a 2kN divert thruster. The results have then been matched to the effective altitude as a function of the thrust coefficient (Cr). This allows the experimental data to be interpreted for a full-scale vehicle in order to answer design questions important to system engineers. The results from this investigation show that the effectiveness of a divert jet is influenced by the vehicle's altitude, achieving a negligible increase in AF with a Cr > 2.5 at an altitude > 50 km. The seeker will suffer from jet induced problems at low Cr levels for a. = 10°. An increase in Cr causes the separation region in front of the jet to extend to the nose of the tested configuration for M1 = 12.1 while complete separation is achieved at Cr > 1.2. Injection Mach number (MJ) has a small influence on AF. However it does not influence the separation region. Penetration height (h) of the jet is increased for higher Mach number injection. Both AF and the separation region are influenced by nozzle geometry. A series of different nozzle geometries were tested. These had the effect of reducing the measured amplification factor to a maximum of 1, except for the dual circular orifice combination, which doubled the measured AF achieved for a single circular orifice. The influence of nozzle geometry reduced the Cr levels required to produce a negligible increase in AF and the corresponding altitude. The angle of attack (œ) has a strong influence on AF at low Cr levels, however it becomes negligible when complete separation is achieved.

A comprehensive experimental study of fountain flow has been completed. The study was concerned with the characteristics and effects of the flow domain below an idealised small-scale model of the underside of the fuselage of a vertical take-off or landing aircraft with a pair of matched jets. The fountain flow was generated by the normal impact of the jets with a ground board and it in turn impacted with a rectangular blocking tray representing the undersurface of a fuselage. A range of test programmes were carried out. After having examined the fountain flow pressure field and conducted simple flow visualisation tests, a series of tests were undertaken on a range of blocking trays to determine the magnitude and variation of the normal forces on the trays due to the effect of impinging fountain flows. A few tray force tests were carried out with a heated compressed air supply to the jets' nozzles. Following these tests, programmes of pressure distribution tests were carried out on a 'long' tray and on a 'short' tray. Temperature distribution tests were conducted on a long tray, these tests were exploratory only and could form the basis for future experimental studies. The test facility was appraised for jets flowing at high subsonic velocities and found to be suitable but no further tests were undertaken. Finally use was made of computational fluid dynamics (CFD) theoretically to solve the governing Navier-Stokes fluid flow equations for domains which simulated the experimental studies just completed and analysed. The analyses of the data obtained from the test programmes revealed that fountain flow caused towards 20% of jet lift augmentation at maximum with good correlation between direct tray force measurements and integrated tray pressure measurements. A useful plot of the variation of tray force against tray height was obtained from moving ground board tests but the velocity of vertical movement of the board towards the nozzles and tray was found not to make a significant difference for the given range of velocities. The plot displayed a distinct peak when the gap between the tray and the ground board was about 2% jet nozzle diameters. At smaller gaps the tray force fell steeply to a suckdown value approaching 20% of jet lift reduction. A reasoned explanation of this phenomenon is presented. The tray force tests using hot jets indicated that slightly lower tray forces occurred than for jets at ambient temperature, everything else being equal. For the general configuration of the model it was concluded that hot gas tests were not necessary as tests at room temperature gave more useful results for design purposes. The CFD computations were particularly effective in obtaining a qualitative impression of the flow patterns in the blocked fountain flow domain. A useful insight was also gained into entrainment into the domain. The tray force computaions were less satisfactory, however, resulting in underestimations of about 30% although the general pattern of pressure distributions across and along the tray were quite similar experimentally determined patterns. Overall it was concluded that the use of small scale model tests had been shown to be effective for certain design purposes for full-scale aircraft and that a dual approach using CFD and model tests could be more rewarding than either the one or the other technique in isolation.

The brittle nature of the most of fibre reinforced polymer (FRP) composites causes they show high capability in absorbing the impact energy in vehicular structures. This energy absorption is introduced by various fracture mechanisms. In this regard, the fracture study is one of the most important areas to be considered in investigating the energy absorption capability of composite box structures. Various fracture mechanisms such as fibre breakage and buckling, matrix cracking and crushing, debonding at the fibre-matrix interface and especially plies delamination play important roles in progressive failure mode and energy absorption of composite tubes. Delamination occurs as results of shear and tensile separation between fronds. The main objective of this research is to study the effects of interlaminar fracture toughness on the progressive energy absorption of composite structures under quasi-static loading. In this regard, Mode-I, Mode-II and mixed-Mode I/II interlaminar fracture toughness of various types of FRP composites with various laminate designs are studied experimentally to investigate the relationship between interlaminar crack propagation and the energy absorption capability and crushing modes of composite structural elements. The combination of brittle fracture, lamina bending, local buckling and transverse shearing crushing modes was found from experimental studies. New analytical solutions based on friction, bending and fracture mechanisms were proposed to predict the mean crushing force for each of these failure modes. The crushing process of composite boxes was also simulated by finite element software LS-DYNA and the results were verified with the relevant experimental and analytical results.

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Global markets are continuously developing and becoming extremely competitive. The manufacturing organisations are improving their capabilities and responsiveness to satisfy their customer demands. Due to this dynamic change, most of the developed countries, particularly the United Kingdom, Europe and the United States have witnessed a sharp increase in outsourcing. A literature search revealed weakness in outsourcing, due to the lack of suitable decision models and frameworks. However, limited research has been carried out in the area of outsourcing of manufacturing in small and medium sized companies. The main aims of this research are formulating appropriate decision models for small and medium sized companies; in particular, those that have been outsourcing, or planning to outsource, their manufacturing activities. The outsourcer's criteria for outsourcee selection for small and medium sized manufacturing companies are chosen after analysing the data obtained through the literature survey, questionnaire survey and personal interviews. Next, a model is formulated for numerical evaluation of outsourcer's criteria for outsourcee selection. Then, a second model for outsourcee (supplier) selection is formulated. The model comprises analytical hierarchy process, cluster analysis and criteria scoring of outsourcee. In the selection process of the most appropriate outsourcee, three elements has to be considered; the previously defined i) vector of important criteria resulted from the information analysis of literature survey, questionnaire and interviews, ii) the specific criteria ranking scoring identified by a particular outsourcer company and iii) the fulfilment of both general criteria (business / market) and specific criteria (outsourcer company) by the potential outsourcees. The outsourcee that achieves the highest total score based on the priority weights of each criterionand sub-criterion in the model may be considered the most suitable. The numerical results of the second model are compared against the empirical outcome of a test case is satisfactory. The developed method is consistent, faster and objective. A further model for drawing up and implementing a manufacturing level agreement was formulated, based on the information collected through the literature survey, questionnaire survey and interviews. The above models were presented to the managers of the companies and are found to be useful according to the feedback provided by them. They will be using the models in stages, subject to the resource availability.

Over the recent years, a considerable growth in the number of vehicles on the roads has been observed. This increases importance of vehicle safety and of minimization of fuel consumption, subsequently prompting manufacturers of cars to equip their products, with more advanced features such as Adaptive Cruise Control (ACC) and Collision Avoidance and Collision Warning System (CWS). In this thesis we concentrate on new methods for ACC. This work will include: Design of the simulation models suitable for this application, Investigation and design of suitable hybrid control algorithm by using classical and advanced control algorithm's consisting of the gain scheduling PI and Linear Quadratic (LQ) controllers, Design of the Nonlinear Model Predictive Control (NMPC) and the nonlinear Balance-Based Adaptive Control (B-BAC), Real-time implementation and tests of the algorithms by using NI Lab View Starter Kit Robot from National Instruments, Implementation and tests of the models and the controllers in MA TLAB/Simulink(R). The applications of the different control methods in the ACC are tested and compared against different traffic scenarios considering both velocity tracking (CC) and distance tracking (ACC) modes. Judging about the performance of ACC by utilizing the two advanced control methods; B-BAC and NMPC includes trade-offs between tracking-distance and velocity and the vehicle acceleration. However, both the B-BAC and the NMPC has demonstrated significantly smoother responses in controlling the throttle and the brake compared to PI control and linear MPC which in tum could improve the vehicle acceleration and fuel efficiency. The methods in order of producing better performance in terms of the values of control errors and their influences on fuel saving; NMPC, B-BAC, linear MPC and PI control. Improvement of fuel efficiency is investigated in this thesis through two approaches; first, by calculating the optimal control actions corresponding to the throttle and the brake signals through utilising the advanced control methods, second, by reducing the engine speed to idle speed during coast phase of the vehicle which causes the engine friction to be reduced. The engine speed can be reduced through transition between locked and unlocked states of the torque convertor. Possibility of achieving fuel efficiency through coasting in the vehicle has been investigated in the simulation and it has been demonstrated that longer coasting duration could be achieved i.e. more distance can be covered, and the fuel efficiency could be improved.

The sponsors of this project have been using the rigid heavily-crosslinked polyurethane foam detailed in this study for load-bearing applications. One of the main requirements of this material is that it must possess excellent recovery properties following extensive compressive periods over several years. For such long loading regimes, there is need for detailed understanding of the compressive behaviour of this material, and its subsequent recovery upon release. More recently, there has been a growing interest in replacing the polyurethane foam with an alternative cellular plastic that possesses similar, if not identical, compressive recovery and behaviour. Attention was focused on the other primary polymer contingent, a polyethylene foam. A polyimide foam was also considered as it was already being used in applications similar to those of the polyurethane foam. The structures of the foams were investigated by means of Differential Scanning Calorimetry, Scanning Electron Microscopy and Image Analysis. The deformation mechanisms that occur during the application of a compressive force were examined visually via a scanning electron microscope compression rig. The mechanical analysis involved stress-strain testing whereby three stages of compression were identified (‘linear elastic, stress plateau and densification’), as described in the literature. Quadratic relationships were found to exist between the foam density and the ‘elastic modulus, plateau modulus and the compressive strength’ respectively. Such relationships had previously been found to exist in the literature, but not for the rigid variety of foam at such a broad range of densities. Further analysis included a detailed study of the recovery of the polyurethane (100 kg m[sup]-3 to 800 kg m[sup]-3) foams, a lightly-crosslinked polyethylene foam and a non-crosslinked polyimide foam. The foam samples were compressed by strains which spanned their linear elastic and stress plateau regimes i.e. by 2.5% to 35% for periods ranging from 3 days up to one year at ambient temperature. This analysis was also undertaken at elevated temperature as a means of accelerating the ageing process. Recovery of all of the samples was monitored for a minimum of 100 days at ambient temperature following release. Recovery of all of the foams tested was found to occur in two stages; an initial rapid recovery within the first day following release followed by a much slower recovery phase over a period of approximately 100 days. The initial rapid recovery was attributed to the recovery of the bulk polymer whilst the recovery of the cellular structure was associated with the ensuing slower recovery phase. In addition, recovery of the foams was found to be dependent more upon the compressive strain than on other parameters, such as compressive period and foam density. For compressive periods exceeding two weeks, recovery is almost independent of the latter parameters.