CORRELATION BETWEEN CREEP AND TENSILE BEHAVIOUR IN LOW ALLOY STEEL

Student Number : 9800022T - PhD thesis - School of Mechanical, Industrial and Aeronautical Engineering - Faculty of Engineering and the Built EnvironmentFor many applications, it may be useful to be able to estimate creep properties of a material from simpler testing procedures such as tensile tests than the conventional creep testing procedures. Most alloys used for creep service conditions are in a hardened condition and thus tertiary creep, controlled by micro structural degradation, is dominant. The object of the study was to investigate a reasonably simple method for estimating the creep behavior of a low alloy 1% Cr, 0.25 % Mo steel from tensile yield data. The study involved performing of series of investigations, including age hardening, tensile and creep tests. Microstructural degradation was monitored from specimens held in a furnace for different times and temperatures, which were then tested in tension at room temperatures. Tensile tests were carried out at different temperatures and strain rates and the data used to determine material parameters for use in kinetic equations describing deformation. For comparison, creep curves were obtained from both creep tests and tensile tests results. Tests on furnace aged specimens were used to quantify softening due to material degradation and formulate a structure evolution and kinetic expressions used to determine creep curves. The modified equation by Dorn was used to determine the material parameters and to predict flow characteristics. Two sets of mechanisms were observed. At low temperature and high stress (above 550MPa) dislocation by glide mechanism was investigated. At higher temperatures and low stress (below 550MPa), some form of power law creep was observed. Glide mechanism was investigated and material parameters σ ) , n and activation volume v, were calculated. The calculated value of σ ) was assumed for both plastic deformation and the softening kinetics. A reasonably good estimate of the creep behavior of the low alloy steel used in this investigation in which tertiary creep dominates can be calculated from tensile yield stress values. Furthermore, the creep rate and recovery have similar stress dependences, with the stress and temperature dependence similar to that predicted by recovery theory. The value of activation energy observed for creep for this alloy is in line with the processes which could be related to self diffusion. In order to justify the significance of this study, four existing empirical models are discussed, highlighting their merits and demerits with respect to the models used in this study. These are θ-Projection, Damage Mechanics, Estrin-Mecking and the Internal Stress Methods. Generally, in this class of alloys, recovery process occurs under an effective stress (i.e. an applied stress less the internal stress). Thus the possibility of using tensile data obtained in this study in the internals stress model was explored. The model could replicate the one used in this study if the change in internal stress value o σ is assumed to be negligible. This could be assumed to be true for tensile data at high stresses and low temperature especially during secondary creep rate when the internal stress approximates to the applied stress and at short test durations

Sustaining the shelf life of fresh food in cold chain – A burden on the environment

AbstractEnergy consumption in cold chains has been predicted to rise significantly in view of the increasing world population. Of critical attention is the increasing number of road transport refrigeration which is highly gaining enormous ground globally. In view of the fact that 40% of all foods require refrigeration, 15% of world fossil fuel energy is used in food transport refrigeration. This concern necessitates this study to examine cold chain system with the emphasis on the impact of energy consumption in sustaining the shelf life of fresh food. As the world continues to battle with the global warming occasioned by emission of carbon dioxide from fossil fuel, this study identifies alternative means of saving energy in food transportation system through minimizing energy consumption in diesel engine driven vapour compression system. Preserving perishable fresh food (mainly vegetable) under sub-zero weather is another debacle the authors envisaged in the quest to reduce fossil fuel consumption. This process requires heating the mechanical refrigeration unit in a reverse-cycle to raise the temperature at 0°C which may further result in more energy demand. The conclusion drawn from this study could be useful in re-designing food transport system for optimal energy saving

Design and Performance Evaluation of Horizontal- Shaft Palm Kernel Cracking Machine

The need to support the small and medium scale industries involved in palm kernels, led to the design, fabrication and evaluation of a horizontal shaft palm kernel cracking machine. All the materials were sourced locally in Nigeria which makes it affordable for small and medium scale farmers involved with palm kernel. The basic features of the machine include a horizontal shaft, hopper, cracking chamber, pulleys, bearings with housing, discharge outlet and electric motor (prime mover). The mean efficiency of the machine under good operating conditions is 75.5%. The production cost of the machine excluding electric motor was estimated to be one hundred and fifty-one dollar forty-sixcents (US$151.46), based on the exchange rate when it was manufactured. The cost can further be reduced, if mass-produced

Microstructural effects on properties of as-fabricated Inconel 625 with direct energy deposition process

Three-dimensional printing (3D), also known as metal additive manufacturing (MAM), fabricates parts or components from different feedstocks: wires, powders or sheets. This process differs from traditional manufacturing techniques such as casting, moulding, or subtracting existing materials. In the development and improvement or fabrication of new materials for higher strength and various applications, the type or character of a material is very important as this will ascertain the strength of the finished product. Direct energy technology can be used to fabricate and repair parts or components with the following two fabrication methods: laser wire-directed energy deposition (LW-DED) or laser powder-directed energy deposition (LP-DED). In this research, laser powder-directed energy deposition (LP-DED), a MAM process method, was employed to fabricate Inconel 625. The LP-DED process uses a laser as a heat source and rapidly melts metallic powders of different chemical compositions to fabricate complex structures, which is an innovative three-dimensional material processing technology. The as-fabricated (AF) sample specimens were investigated to determine the microstructural development, microhardness and sample defects. The microstructural features were analysed using two experimental surface microscopy methods: light optical microscopy (LOM) and scanning electron microscopy (SEM). The morphological grain structure within the samples was predominantly cellular, columnar and columnar-dendritic. Energy dispersive X-ray (EDX) and X-ray diffraction (XRD) analysis were performed to determine the chemical composition and crystallographic structures of virgin gas atomisation (GA) powder and as-fabricated sample. The XRD peaks in samples composed of face-centred-cubic (FCC) γ-nickel phase. The material microhardness was studied by performing Rockwell hardness test (HRB) with a fluctuated trend averaging 98.9 – 101.6 HRB. The relationship between processing, microstructure, grain structure and material hardness was systematically summarised and established. The study concluded with research suggestions on LP-DED of Inconel 625

Sustainability of High Temperature Polymeric Materials for Electronic Packaging Applications

Development of polymeric packaging materials for electronic devices have attracted discussions in many published works amid challenges in high speed electronic performance. In order to achieve hybrid integration in most power system, sustainable packaging materials with high thermal conductivity are needed to achieve this purpose. In this paper, attempts were made to analyse the existing packaging materials and the modification of electronics system using 2-D and 3-D dimensional packaging approaches. Also introduced in this work is the integration of polymer multi-functional block in electronic packaging which is aimed at reducing the density of electronic devices. It is hoped that the recommendation from this work will stimulate novel research and generate new interest in applications of sustainable materials for the electronics packaging industry

Process parametric optimization of spark plasma sintered Ni–Cr–ZrO2 composites using response surface methodology (RSM)

Materials properties are highly dependent on the processing parameters and technique used during sintering. The effect of Spark Plasma sintering process parameters (pressure and temperature) on the hardness and relative density of Ni–20Cr–5ZrO2 composite was investigated. Response Surface Methodology (RSM) from the design of experiment (DOE) technique was successfully employed for the experimental design, and statistical analysis was conducted on the obtained experimental results. The microstructural analysis of the sintered composite showed the presence of solid solution phases of Ni and Cr, which were confirmed by the XRD results as (Cr,Ni) alongside unreacted ZrO2 particles at sintering temperatures of 950 °C and 1000 °C. The validity of the model developed with the impact of each variable and their corresponding interaction on the responses was performed using analysis of variance (ANOVA). The relative density and hardness were the two responses considered. The actual values (experiment data) and expected values (simulated data) were subjected to statistical analysis, to develop a predictive model that synchronizes density and hardness as distinct process parameters, with material hardness and relative density serving as the responses of the specified experiment. For the responses, quantitative models were created, and 10 experimental runs were processed to ascertain the desirability of the responses. The SPS processing parameters considered the most desirable were 1000 °C sintering temperature and 50 MPa pressure. The hardness property obtained under this condition is 433.23 HV with a relative density of 98.15%

Strength Characteristics of Electrospun Coconut Fibre Reinforced Polylactic Acid: Experimental and Representative Volume Element (RVE) Prediction

Environmental conservation and waste control have informed and encouraged the use of biodegradable polymeric materials over synthetic non-biodegradable materials. It has been recognized that nano-sized biodegradable materials possess relatively good properties as compared to conventional micron-sized materials. However, the strength characteristics of these materials are inferior to fossil-based non-biodegradable materials. In this study, biodegradable polylactide (PLA), reinforced with treated coconut husk particulates (CCP) for improved mechanical properties, was fabricated using an electrospinning process and representative volume element (RVE) technique, and some of the obtained mechanical properties were compared. It was observed that the electrospun CCP-PLA nanofibre composites show improved mechanical properties, and some of these mechanical properties using both techniques compared favourably well. The electrospun fibres demonstrate superior properties, mostly at 4 wt.% reinforcement. Thus, achieving good mechanical properties utilising agro waste as reinforcement in PLA to manufacture nanocomposite materials by electrospinning method is feasible and provides insight into the development of biodegradable nanocomposite materials

Prospects of nanostructured composite materials for energy harvesting and storage

International audienceIn the 21st century, energy demand and the attendant environmental degradation, are among the most challenging issues. The concern is due to the high dependence, globally on fossil fuels as a form of energy generation. Over 6.5 billion people worldwide require approximately 13 Terawatts of energy for their day-to-day needs. In order to achieve the required energy demand, there is a need to diversify into other forms of energy; in this case, renewable energy. In so doing, there is the need to study, extensively, alternative materials and sources needed for energy generation, storage, distribution and application. There has been a significant advancement in energy generation, conversion and storage, such as fuel cells and solar cells, photovoltaic cells, supercapacitors, batteries, etc. The emergence of nanostructured and composite materials has resulted in some significant contributions towards the improvement in the energy industry development. Renewable energy, such as wind and solar energies, depend considerably, on the environmental conditions, which are not always stable. Hence, in order to harness the energy from these sources and to adequately store such energy, there is a need for a high-performance energy conversion and storage system for the energy generation process. In this regard, carbon nanomaterials, metallic sulphides, titanium oxide and many other nanostructured materials have been studied, to a large extent, for energy conversions and storage devices. The importance of nanostructured and composite materials has shown, from researches, to resolve the issues surrounding energy from generation to storage

Development and application of nanocomposite for sustainable rail vehicle with low environmental footprint

International audienceIn many developing countries, society is characterized by increasing population growth, urbanization, and industrialization, which have an effect on the environment. The growing population demands improved and safe ways of transporting people, goods, and services from one point to another at a minimal impact on the environment. The high demand for energy is another concern for any developing nation, most especially for a country where rail cars are powered by electricity. The weight of the rail cars contributes to the total carbon dioxide (CO2) emission. In order to reduce the energy demand, CO2 emission and increase return on investment, there is a need for improved composite materials. The current research focused on the production of composites made from polypropylene, sisal fiber and nanoparticle. The fiber was treated and the content was varied from 10, 20, 30 and 40 wt%, while the clay and the compatibilizer were kept constant at 3 and 5 wt% respectively. There was an improvement in the mechanical and thermal properties of the composites. Based on the improvement observed, the material can be used for the interior component of the rail vehicle