Numerical modelling of additive manufacturing process for stainless steel tension testing samples

Nowadays additive manufacturing (AM) technologies including 3D printing grow rapidly and they are expected to replace conventional subtractive manufacturing technologies to some extents. During a selective laser melting (SLM) process as one of popular AM technologies for metals, large amount of heats is required to melt metal powders, and this leads to distortions and/or shrinkages of additively manufactured parts. It is useful to predict the 3D printed parts to control unwanted distortions and shrinkages before their 3D printing. This study develops a two-phase numerical modelling and simulation process of AM process for 17-4PH stainless steel and it considers the importance of post-processing and the need for calibration to achieve a high-quality printing at the end. By using this proposed AM modelling and simulation process, optimal process parameters, material properties, and topology can be obtained to ensure a part 3D printed successfully

Laser Cladding for use in Extreme Tribological Interfaces

Coatings are common in engineering applications for protecting the surface of components, either from exposure to environmental conditions or from contact with other components. Laser cladding is a coating technique which allows for thicker coatings of various alloys that enable high load bearing interfaces to operate at a wider range of loads or for longer, for example by increasing durability. This is of great benefit to the railways industry as well as other heavy industries, such as the steel industry. Laser clad coatings have been used extensively in other industries such as oil and gas for increasing the durability of drilling components; in mining and earth moving equipment, for increasing the durability of the components that come in contact with hard soil and rocks. Both are extreme interfaces. In this study, new interfaces and extreme conditions for new industries are investigated, by highlighting the laser clad coating advantages, when used under extreme conditions. The extreme test conditions have not been investigated in published literature, especially with the use of laser clad coatings. This project evaluated the performance of laser cladding coatings on railway components such as the wheel and rail. Other interfaces found in machinery in the steel industry were considered, specifically in the rolling of steel. A variety of interfaces were evaluated by modelling and testing, such as rolling-sliding, high pressure water jet erosion and impact. Three clad materials were identified as suitable for the chosen interfaces, martensitic stainless steel (MSS), Stellite 6 (Co-Cr) and a two-layer clad of Inconel 625 with Technolase. The clad parameters were fixed, resulting in constant material grades, allowing the coatings used in different interfaces to be comparable. The materials choice was based on published research on similar interfaces. Tests were performed on existing test rigs for rolling-sliding and bending tests. The impact test was performed on a rig modified specifically for this study, while a bespoke rig was built for the erosion test. Metallographic techniques were used for all materials, to prepare the samples for characterisation using optical and electron microscopy, as well as nanoindentation and microhardness. Pre- and post-test material analysis was performed. The use of computer modelling was considered mainly for the generation of test parameters, while the results from testing were compared to existing data. Key findings highlight that the use of the selected clad materials under the chosen extreme interfaces can have a positive effect on the durability of the coating, mainly by increasing the wear resistance properties of the coating. Furthermore, the two-layer clad coating showed promising results in stopping crack propagation to the substrate. The test results can be used in predictive tools by researchers in academia, as well as in industry, as a way of introducing laser cladding applications to interfaces of engineering products. Furthermore, the performance of the chosen materials indicates that this study may be used as the basis for selecting similar clad coatings for pilot trials or large scale testing

Infrastructure Design, Signalling and Security in Railway

Railway transportation has become one of the main technological advances of our society. Since the first railway used to carry coal from a mine in Shropshire (England, 1600), a lot of efforts have been made to improve this transportation concept. One of its milestones was the invention and development of the steam locomotive, but commercial rail travels became practical two hundred years later. From these first attempts, railway infrastructures, signalling and security have evolved and become more complex than those performed in its earlier stages. This book will provide readers a comprehensive technical guide, covering these topics and presenting a brief overview of selected railway systems in the world. The objective of the book is to serve as a valuable reference for students, educators, scientists, faculty members, researchers, and engineers

Incorporating automated rail fatigue damage detection algorithms with crack growth modelling

This thesis examines the feasibility of incorporating Non Destructive Testing (NDT) of rail surface damage by means of combining image processing with damage prediction models. As rail traffic and adherence to safety measures become increasingly strict on the network, the associated maintenance cost of rail infrastructure must be kept at a minimum. Proactive maintenance is crucial to maintaining the competitive advantage of rail transport. A considerable amount of research has been done on improving the practical tediousness associated with popular condition monitoring techniques in rail industry e.g. Ultrasonic, and Eddy current method. This thesis aims to fill the gap of yet to be explored benefit, of combining detection and prediction of RCF damage. This research project will contribute to the rail industry by simplifying maintenance operations and support decision making. In this thesis, a summary of existing image-based NDT and crack growth models is presented as a foundation on which the novel application is built.It could be said that similar research mainly focuses on quantifying severity of damage without predicting crack behaviour. The simulated results of the proposed image processing algorithm confirm superiority of local illumination invariant enhancement, multi-window segmentation, and cascaded feature extraction. The influential parameters of these methods are consistent within each image data set but differ across all sets. This is observed to be as a result of difference in environmental and reflection properties of acquired images.A sensitivity analysis of the proposed algorithm on data set 2 suggests a non-linear relationship between severity of damage and pixel mean intensity including variance. Taking to account fracture mechanics aspect of this thesis, the influence of crack geometry on growth rate and path has been established by case study of newly initiated and critically grown cracks. It was further established that larger cracks are observed to grow faster than smaller ones. In addition, the influence of track curve radius and supporting structures on wheel rail contact dynamics is well understood from the structural mechanic’s tests related to contact forces and bending moment. These translate to increase or decrease in contact stresses, strains, and the propagation rate of defects. Unlike other predictive models, the method developed in this thesis focuses on replicating the actual surface condition of the rail prior to estimating the fracture parameters (using detailed 3D Finite Element model) that dictate residual life of the rail asset. The model makes it possible to combine two separate maintenance activities i.e. detection and prediction without inducing down time of the service. A direct impact of this novel application is the utilisation of the actual crack boundary for prediction of fracture behaviour. It is insinuated that stress distribution of actual crack boundary differs from elliptical equivalent assumptions. Further work would include improving detection aspect of the novel application to avoid intersecting boundary coordinates, which are not readily imported into the Linear Elastic Fracture Mechanics (LEFM) prediction model. It is also beneficial to expand the prediction aspect of the research work to include influence of neighbouring cracks and fluid entrapment for more flexible analysis of other environmental and contact conditions. To improve on current work, it will be useful to conduct laboratory investigations on the influence of Image Acquisition System (IAS) light source in relation to illumination inequality within the captured image. Also fracture mechanics experimental validation can be used to assert the accuracy of the metho

Micro-CT Scanning in the Investigation of Squat Defects in Rail Steel

This thesis contains the results from an investigation into Squats, a discrete rail steel defect. Micro-computed tomography (micro-CT) scanning was used to scan the entire structure of four out of five defects removed from railway track. The fifth was not scanned as it shelled in track. The difficulty turning these raw X-ray images into a segmented 3D model were overcome by developing a new technique. Isolating separate regions of the scans created areas where voxel value variation was at a minimum (i.e. the histogram became one narrow peak rather than multiple broad peaks). This allowed the automatic crack segregation module to work fairly well, and then enhanced using the region growing modules within the software. These scan results were then verified to be accurate using metallographic sample preparation, optical and electron microscopy. Micro CT scanning was performed on a custom 450KeV scanner, allowing the capture of the first entire Squat crack network morphology. Full defect imaging allowed the different defects to be compared to each other, highlighting differences and similarities. The defects came from metro, mixed and high-speed railways and one was found within an aluminothermic weld. The verification process and investigations of the scan volumes yielded further information about the defect’s origins. These origins were used to determine that, for the five defects investigated, there were four different causes. The two that shared a cause were from the same track section. Based on the causes, the defects were identified as a Stud, two Grinding Induced Squats (GIS), a Squat (caused by the legacy issue of MnS inclusions) and possibly a Squat or Stud in a slightly contaminated weld. None of the defects were considered to be a classic Squat, which is caused by Rolling Contact Fatigue (RCF), because there were other factors in their initiation. One of the defects contained a transverse defect, which is a crack that grows down through the railhead and can break the rail. This transverse defect was ~9mm deep into the rail when it was removed, meaning it would not have returned to the surface to shell. A high-resolution volume of the transverse defect region was created and its origin gives an important insight into the potential causes of rail-breaking defects. The origin of this transverse defect was a cluster of debris-filled voids that had formed due to the corrosion and cyclic loading (fretting) of a crack branch. These voids aligned with a deep grinding mark on the surface of the rail, which acted as a stress raiser. Because corrosion is a factor in this transverse defect case, the age of a rail and its environment are factors for defect development as well as traffic volume, given the correlation of corrosion with time. Results of this work highlight both the importance of a good surface finish and the diversity of causes found within the term “Squat”. Thus the identification of the Stud variant may be the beginning of a more comprehensive group of Squat type defects being established. This refining of the category could lead to fruitful big data analyses of the Squat type defect occurrences. The CT volumes of the defects created in this work can easily be stored for comparison in future investigations. The virtual nature of the volumes allows the sharing of defect information more readily than physical and sectioned defects, which deteriorate with time and require physical storage and transport

Railway Research

This book focuses on selected research problems of contemporary railways. The first chapter is devoted to the prediction of railways development in the nearest future. The second chapter discusses safety and security problems in general, precisely from the system point of view. In the third chapter, both the general approach and a particular case study of a critical incident with regard to railway safety are presented. In the fourth chapter, the question of railway infrastructure studies is presented, which is devoted to track superstructure. In the fifth chapter, the modern system for the technical condition monitoring of railway tracks is discussed. The compact on-board sensing device is presented. The last chapter focuses on modeling railway vehicle dynamics using numerical simulation, where the dynamical models are exploited

Active thermography for the investigation of corrosion in steel surfaces

The present work aims at developing an experimental methodology for the analysis of corrosion phenomena of steel surfaces by means of Active Thermography (AT), in reflexion configuration (RC). The peculiarity of this AT approach consists in exciting by means of a laser source the sound surface of the specimens and acquiring the thermal signal on the same surface, instead of the corroded one: the thermal signal is then composed by the reflection of the thermal wave reflected by the corroded surface. This procedure aims at investigating internal corroded surfaces like in vessels, piping, carters etc. Thermal tests were performed in Step Heating and Lock-In conditions, by varying excitation parameters (power, time, number of pulse, ….) to improve the experimental set up. Surface thermal profiles were acquired by an IR thermocamera and means of salt spray testing; at set time intervals the specimens were investigated by means of AT. Each duration corresponded to a surface damage entity and to a variation in the thermal response. Thermal responses of corroded specimens were related to the corresponding corrosion level, referring to a reference specimen without corrosion. The entity of corrosion was also verified by a metallographic optical microscope to measure the thickness variation of the specimens

Numerical Computation, Data Analysis and Software in Mathematics and Engineering

The present book contains 14 articles that were accepted for publication in the Special Issue “Numerical Computation, Data Analysis and Software in Mathematics and Engineering” of the MDPI journal Mathematics. The topics of these articles include the aspects of the meshless method, numerical simulation, mathematical models, deep learning and data analysis. Meshless methods, such as the improved element-free Galerkin method, the dimension-splitting, interpolating, moving, least-squares method, the dimension-splitting, generalized, interpolating, element-free Galerkin method and the improved interpolating, complex variable, element-free Galerkin method, are presented. Some complicated problems, such as tge cold roll-forming process, ceramsite compound insulation block, crack propagation and heavy-haul railway tunnel with defects, are numerically analyzed. Mathematical models, such as the lattice hydrodynamic model, extended car-following model and smart helmet-based PLS-BPNN error compensation model, are proposed. The use of the deep learning approach to predict the mechanical properties of single-network hydrogel is presented, and data analysis for land leasing is discussed. This book will be interesting and useful for those working in the meshless method, numerical simulation, mathematical model, deep learning and data analysis fields