Impact on a water filled cylinder

The computational and experimental results of impact loading a water filled cylinder with a high speed piston are presented. Computational simulation of the impact process is performed by means of DIANA, a commercial finite element software package. In this simulation, water is modeled as a solid with very small shear modulus compared to the bulk modulus of water. The efficiency of the simulated impact is evaluated by the time dependent water pressure in the vicinity of the cylinder. Also, the shock pressure resulting from impact is detected by using a pressure transducer located in the middle of the water tube. Comparison of the computational and experimental results shows that the impact process on a water filled cylinder is well modeled. It is shown that the best way to increase the pressure peaks of the pressure profile curve is to increase the piston’s impact velocity

The Effect of Notch Tip Position on the Charpy Impact Energy for Bainitic and Martensitic Functionally Graded Steel

As stated for arrester configuration, no precise mathematical modelling was presented to correlate the Charpy impact energy of FGSs to the morphology of each layer. This is an actual gap in the literature. The main aim of the present work is to fill this gap and provide a new analytical model for the assessment of the Charpy impact energy of FGSs in the form of crack arrester configuration. Moreover, three-dimensional finite element (FE) analysis by ABAQUS software was performed to simulate the Chapry impact energy process of FGS specimens in the form of crack arrester configuration.Функционально-градиентные стали, которые относятся к группе функционально-градиентных материалов, обладающих упругопластическими свойствами, получают из аустенитной нержавеющей и малоуглеродистой ферритной сталей путем электрошлаковой переплавки. При использовании функционально-градиентных сталей можно улучшить механические свойства композитов, содержащих мартенситные и бейнитные хрупкие фазы. Представленная аналитическая модель позволяет оценить ударную энергию разрушения образцов Шарпи из бейнитно-мартенситных сталей с учетом зависимости между ударной энергией и размером пластической зоны в вершине надреза. Сравниваются величины ударной энергии для образцов Шарпи из функционально-градиентных сталей и однородного материала, соответствующего слою материала вблизи вершины надреза. С использованием программного комплекса ABAQUS выполнено трехмерное конечноэлементное моделирование данного процесса. Согласно закону Холломана для пластической зоны получены характеристики материала в различных его слоях. Рассматривалось экспоненциальное изменение характеристик материала по ширине образца. Предложенная модель позволяет получить результаты, хорошо согласующиеся с имеющимися экспериментальными данными и результатами конечноэлементных расчетов.Функціонально-градієнтні сталі, що відносяться до групи функціонально-градієнтних матеріалів із пружно-пластичними властивостями, отримують із нержавіючої сталі шляхом електрошлакової переплавки. При використанні функціонально-градієнтних сталей можно поліпшити механічні властивості композитів із мартенситними і бейн ітними крихкими фазами. Запропонована аналітична модель дозволяє оцінити ударну енергію руйнування зразків Шарпі з бейнітно-мартенситних сталей з урахуванням залежності між ударною енергією і розміром пластичної зони у вершині надрізу. Порівнюються величини ударної енергії для зразків Шарпі з функціонально-градієнтних сплавів та з однорідного матеріалу, що відповідає шару матеріалу біля вершини надрізу. Із використанням програмного комплексу ABAQUS виконано тривимірне скінченноелементне моделювання даного процесу. Згідно із законом Холломана, для пластичної зони отримано характеристики матеріалу в різних його шарах. Розглядалась експоненціальна зміна характеристик матеріалу по ширині зразка. Запропонована модель дозволяє отримати результати, які добре узгоджуються з відомими експериментальними даними і результатами скінченноелементних розрахунків

Thermo-structural Finite Element Analysis of Direct Laser Metal Deposited Thin-Walled Structures

Multilayer direct laser metal deposition is a fabrication process in which the parts are fabricated by creating a molten pool into which particles are injected. During fabrication, a complex thermal history is experienced in different regions of the build, depending on the process parameters and part geometry. The thermal history induces residual stress accumulation in the buildup, which is the main cause of cracking during the fabrication. The management of residual stress and the resulting distortion is a critical factor for the success of the process. A thermostructural finite element model (FEM) of the process is developed, and the analysis reveals different patterns of residual stress in the thin-walled structures depending on the deposition strategy and the geometry of the structures. The residual stress patterns obtained from finite element analysis (FEA) are in good agreement with the experimental results.Mechanical Engineerin

Development of functionally graded tungsten/EUROFER coating systems

Functionally graded W/EUROFER layer on EUROFER substrate is developed for first wall application. Parameters of coating systems were determined by non-linear finite element simulations. The coating system fabricated by vacuum plasma spraying has fine linear gradient and designed thickness, low porosity (< 4%), as well as a sound interface with high interface toughness. Good thermal-mechanical properties of the coating system have been assessed and analyzed

Numerical and experimental study of mechanical properties for Laser Metal Deposition (LMD) process part

Laser Metal Deposition (LMD), also called as, Laser Engineered Net Shaping (LENS), Directed Energy Deposition (DED), is a typical Additive Manufacturing (AM) technology, is used for advanced free-form fabrication. It creates parts by directly melting materials and depositing them on the workpiece layer by layer. In this process, the metal powder or fiber is melted within the melting pool by laser beam or electron beam and quickly solidifies to the deposited layer. LMD technology shows great advantages over traditional manufacturing on complex structure fabrication, including high building rates, easy material replacement and reduced material waste. These merits make the wide application of this technology in industry, such as new components fabrication and parts repairing manufacturing, coatings, rapid prototyping, tooling, repair, etc. The proposed project is to investigate the key parameters to improve the mechanical properties of different fabricate parts in LMD manufacturing by combined approach of experimental analysis and FEA simulation method. Therefore, several sets of experiments will be designed to reveal the processing parameters on properties of deposited components in the method of LMD process. The microstructure, Vickers hardness, phase identification, tensile properties of LMD parts are measured to investigate the fabricated qualities. The features of thermal stress and deformation involved in the DMD process were predicted by the FEA model. This work helps to fully study the thermal analysis to analyze the temperature profile, cooling rate and temperature gradients on microstructure and residual stress, which further influences the engineered mechanical properties of build parts --Abstract, page iv

Multiscale Hierarchical Structure and Laminated Strengthening and Toughening Mechanisms

Metal matrix composites with multiscale hierarchical structure and laminated structure have been developed to provide a novel route to achieve high strength, toughness and ductility. In this chapter, a lot of scientific research has been carried out in the preparation, processing, properties and application of metal matrix composite. Many toughening mechanisms and fracture behavior of composites with multiscale hierarchical structure and laminated structure are overviewed. It is revealed that elastic property and yield strength of laminated composites follow the “rule of average.” However, the estimation of fracture elongation and fracture toughness is complex, which is inconsistent with the “rule of average.” The fracture elongation of laminated composites is related to the layer thickness size, interface, gradient structure, strain hardening exponent, strain rate parameter and tunnel crack, which are accompanied with crack deflection, crack blunting, crack bridging, stress redistribution, local stress deformation, interfacial delamination crack and so on. The concept of laminated composites can be extended by applying different combination of individual layer, and provides theoretical as well as experimental fundamentals on strengthening and toughening of metal matrix composites

Thermal analysis of wood-steel hybrid construction

Main goal of this work is to present a numerical model to study the thermal necrosis due a dental drilling process, with and without water irrigation. Also an experimental methodology is used to measure the thermal occurrence in a pig mandible. Motivation, the assessment of bone damage, using the temperature criterion (above 55ºC

Study of local creep deformation behavior of heterogeneous weld configurations involving ferritic Chrome-Molybdenum steel and austenitic Ni-base alloys

Dissimilar Metal Welds (DMWs) made between ferritic low alloy steel (BCC) and austenitic alloys (FCC) are widely used in the high temperature components of power plants. Ex-service data from power plants suggests these bimetallic welds fail prematurely by creep mechanism, with lifetimes much lesser than the creep lives of either of the base materials. Earlier creep studies have demonstrated that failures are associated with creep cavities along the ferritic steel HAZ close to BCC/FCC boundary, due to the local detrimental microstructure. Structure-property relationships have not been established for these heterogeneous materials due to the limitation in the spatial measurement of creep strain rates. Hence, the objective of this research study is to develop a methodology to extract the local creep constitutive properties from heterogenous weld configurations and correlate these properties with the underlying microstructure. The following heterogeneous weld configurations were considered:I. Conventional DMWs made between 2.25Cr-1Mo steel and Alloy 800H base materials using Inconel weld consumable,II. Graded Transition Joints (GTJs) made between 2.25Cr-1Mo steel and Alloy 800H base materials using each of the three candidate filler metals viz., (i) Inconel 82, (ii) P87, and (iii) 347HLocal creep studies discretized the heterogeneous creep behavior in both these welded configurations. Global creep strain from both these welded configurations was a result of creep strain evolution from the 2.25Cr-1Mo base material and regions inside 2.25Cr-1Mo HAZ, while the other austenitic regions showed negligible creep formation. In both DMWs and GTJs, creep strain was accumulating inside 2.25Cr-1Mo HAZ and was driving the premature failure in these welded joints.Research findings from these local creep studies were summarized as follows:1. In DMWs, creep strain accumulation and the creep damage occurred close to BCC/FCC boundary due to the localized decarburization (depletion of carbides) in those regions,2. In all the GTJs, creep strain accumulation and the creep damage occurred in the FGHAZ at 3.5mm away from the weld interface, as a result of carbide coarsening during weld processing.Microstructure based creep model framework was developed to model the discrete creep strain rates with the local microstructures of 2.25Cr-1Mo steel

Laser direct metal deposition of dissimilar and functionally graded alloys

The challenges in the deposition of dissimilar materials are mainly related to the large differences in the physical and chemical properties of the deposited and substrate materials. These differences readily cause residual stresses and intermetallic phases. This has led to the development of functionally graded materials which exhibit spatial variation in composition. Laser direct metal deposition due to its flexibility, it offers wide variety of dissimilar and functionally graded materials deposition. Despite considerable advances in process optimization, there is a rather limited understanding of the role of metallurgical factors in the laser deposition of dissimilar and functionally graded alloys. The aim of this work is to understand and explain mechanisms occurring in diode laser deposition of dissimilar materials and functionally graded materials. The first part of this work addressed diode laser deposition of Inconel 718 nickel alloy to Ti-6Al-4V titanium alloy. Here, the effect of laser pulse parameters and powder mass flow rates on the stress formation and cracking has evaluated by experiment and numerical techniques. Results showed that the clad thickness was an important factor affecting the cracking behaviour. In the second part of this study, an image analysis technique has been developed to measure the surface disturbance and the melt pool cross section size during laser direct metal deposition of Inconel 718 on a Ti-6Al-4V thin wall. It was noted that under tested conditions the overall melt pool area increased with the increase in powder flow rate; the powder carrier gas flow rates also seemed to play important roles in determining the melt pool size. In the third part of this study, a parametric study on the development of Inconel 718 and Stainless steel 316L continuously graded structure has been carried out. Results suggested that microstructure and other mechanical properties can be selectively controlled across the deposited wall. The results presented in this dissertation can be used as a metallurgical basis for further development of dissimilar and functionally graded manufacturing using LDMD technique, guiding future manufacturing engineers to produce structurally sound and microstructurally desirable laser deposited samples.EThOS - Electronic Theses Online ServiceGBUnited Kingdo