An investigation of hot forming quench process for AA6082 aluminium alloys

This thesis is concerned with the mechanical properties and microstructure evolution during the novel solution Heat treatment Forming cold die Quenching (HFQ) process. HFQ is a hot sheet forming technology which incorporates the forming and quenching stages to produce high strength and high precision Al-alloy sheet parts. The work in the thesis divided into three main sections: Firstly, viscoplastic behaviour of AA6082 at different deformation temperatures and strain rates was identified through analysis of a programme of hot tensile tests. Based on the results from the hot tensile tests, a set of unified viscoplastic-damage constitutive equations was developed and determined for AA6082, providing a good agreement with the experimental results. SEM tests were carried out to investigate the damage nucleation and failure features of the AA6082 during hot forming process and the results are discussed. Secondly, the viscoplastic-damage constitutive equations were implemented into the commercial software ABAQUS via the user defined subroutine VUMAT for the forming process simulation. An experimental programme was designed and testing facilities were established for the validation of the FE process modelling results. A fairly good agreement between the process simulation and the experimental results was achieved. This confirms that the established FE process simulation model can be used for hot stamping of AA6082 panel parts. Further process modelling work was carried out to identify the optimal forming parameters for a simplified representation of a panel part. Finally, a precipitation hardening model was developed to predict the post-ageing strength of AA6082 panel parts, having varying amounts of forming-induced plastic strain. The model was tested against results of experiments which were carried out to investigate the effect of pre-deformation on the ageing kinetics of AA6082. The model is shown to fit and can be used to explain changes in the strength of the material. This set of equations was implemented in the VUMAT, in combination with the viscoplastic damage constitutive equation set, to model the whole HFQ process. The FE model was tested with experimental ageing and hardness results providing good agreements, which are discussed in light of the future development of the HFQ process

A new approach to improve ill-conditioned parabolic optimal control problem via time domain decomposition

In this paper we present a new steepest-descent type algorithm for convex optimization problems. Our algorithm pieces the unknown into sub-blocs of unknowns and considers a partial optimization over each sub-bloc. In quadratic optimization, our method involves Newton technique to compute the step-lengths for the sub-blocs resulting descent directions. Our optimization method is fully parallel and easily implementable, we first presents it in a general linear algebra setting, then we highlight its applicability to a parabolic optimal control problem, where we consider the blocs of unknowns with respect to the time dependency of the control variable. The parallel tasks, in the last problem, turn "on" the control during a specific time-window and turn it "off" elsewhere. We show that our algorithm significantly improves the computational time compared with recognized methods. Convergence analysis of the new optimal control algorithm is provided for an arbitrary choice of partition. Numerical experiments are presented to illustrate the efficiency and the rapid convergence of the method.Comment: 28 page

3D direct and inverse solvers for eddy current testing of deposits in steam generator

We consider the inverse problem of estimating the shape profile of an unknown deposit from a set of eddy current impedance measurements. The measurements are acquired with an axial probe, which is modeled by a set of coils that generate a magnetic field inside the tube. For the direct problem, we validate the method that takes into account the tube support plates, highly conductive part, by a surface impedance condition. For the inverse problem, finite element and shape sensitivity analysis related to the eddy current problem are provided in order to determine the explicit formula of the gradient of a least square misfit functional. A geometrical-parametric shape inversion algorithm based on cylindrical coordinates is designed to improve the robustness and the quality of the reconstruction. Several numerical results are given in the experimental part. Numerical experiments on synthetic deposits, nearby or far away from the tube, with different shapes are considered in the axisymmetric configuration.Comment: 3

Thermodynamic analysis of indirect injection diesel engine operation

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Shear Strength of Fiber Reinforced Concrete (FRC) Beams without Stirrups

This paper presents the results of twelve shear tests carried out on simply supported rectangular beams, with a shear span to depth ratio (a/d) of 2.4, under a single concentrated load. Six of the beams contained conventional stirrups and six beams were reinforced with steel fibers as web reinforcement. The parameters were: the effect of fiber volume content (0, 0.5, 1.0, and 1.5%), fiber type (end-hooked or corrugated), and the presence of minimum stirrups. The beam span, beam dimensions, shear span to depth ratio (a/d), and percentage of longitudinal reinforcement were all kept constant. Beam deflection, steel strains, crack propagation, and failure modes were recorded for all the tested beams. The test results showed that the stress at shear cracking and the ultimate shear stress increased with increasing the fiber volume content. When steel fibers with a content of 1.5% were added to the beams with minimum stirrups, the brittle shear failure was changed to ductile flexure failure. The test results were used to evaluate existing empirical equations estimating the shear strength of steel fiber-reinforced concrete beams without stirrups. The evaluation indicated that the equations proposed by Narayanan and Darwish 1987 and Kara 2013 provided the most accurate estimation when compared to the test results

Assessment of thermal and visual micro-climate of a traditional commercial street in a hot arid climate

PhD ThesisIn the hot arid contexts, the impact of urban climate is often associated with negative effects on outdoor thermal comfort and an increase in the urban heat island (UHI) effect. The primary aim of this research is to investigate the outdoor thermal performance of traditional commercial urban streets located in the hot arid context of Cairo in Egypt. A number of methods were used including field measurements and social surveys. Consequently, urban air flows, temperature and daylight simulations to assess existing and possible improvement scenarios to extend pedestrian thermal and visual comfort were tested. The field measurements were conducted in order to first assess the UHI intensity in the urban street, and to investigate the effectiveness of the traditional design solutions in ensuring comfortable outdoor conditions based on human-biometeorological assessment methods. Validation of results was carried out by comparing measured and simulated results of thermal conditions in the commercial spine ENVI-met is a three dimensional microclimatic model based on computational fluid dynamics (CFD) models and is designed to simulate surface-air interactions in urban environments. It was used to calculate the mean radiant temperature and obtaining the microclimatic maps with problematic areas concerning the pedestrian's thermal comfort for the existing urban configurations. Outdoor thermal comfort was assessed based on a thermal sensation survey and the physiological equivalent temperature (PET), with a comfort range of (24oC - 32oC). To improve outdoor thermal conditions at pedestrian level seven different shading scenarios addressing the form and the opening of shading devices were simulated using CFD Fluent, based on two dependant variables including air temperature distribution and wind velocity. The daylight analysis software (DIVA) was used to evaluate the solar access for the tested cases. The findings show that typology and the opening locations are one of the paramount factors in providing a temperature reduction in the urban scale. As the air temperature was reduced by (2.3oC) for the best case compared to the base leading to a lower PET for the best case recording 32.9oC against 35oC for the base case

Breeding Biology of the Sardinian Warbler (Sylvia melanocephala melanocephala) in the North-East of Algeria

This work examined the reproductive phenology of the Sardinian warbler (Sylvia melanocephala melanocephala) in North-eastern Algeria, which is its main geographical nesting area. Twenty-eight (28) nests were studied during two successive seasons (2016 and 2017). The results obtained in this study confirm that the nests were constructed at an average height of (01.97±01.04 m) from the ground. The laying period lasted eight (08) weeks (mid-March to the beginning of the second week of May), so fifty-four (54) days. The mean clutch size is (4.14±0.97) eggs per brood. The recorder traits were previously observed in European populations. The average of hatching success was (47.38 %) and mean reproductive success (45.24 %) were relatively low compared to European populations