Effect of wire EDM on microstructure and fracture toughness of 7075-t6511 aluminum alloy

Abstract: This paper reports on an investigation conducted to establish the influence of Wire Electrical Discharge Machining (WEDM) on the fracture toughness of aluminum 7075-T6511. The main objective was to determine if WEDM can be used to introduce a pre-crack into a compact tension specimen instead of the ASTM E-1820-11 specified fatigue pre-crack method. Fracture tests were conducted on four specimens which were pre-cracked using the WEDM technique. The rest of the fracture toughness evaluation followed the ASTM E-1820-11 guidelines. Results obtained from the experimental data were found to be inconsistent with the theoretical expectations. The fracture toughness was found to be significantly dependent on the effect of the WEDM on the material. The WEDM introduced a Heat Affected Zone (HAZ) on the surface of the pre-crack which modifies the fracture behavior of the material. It was concluded that WEDM is not a viable alternative to create a pre-crack in a compact tension specimen to perform fracture toughness testing of aluminum 7075-T6511

Mechanical characterization of coir epoxy composites and effect of processing methods on mechanical properties

Abstract: Composite materials have now attracted wide acceptance in product development and manufacture especially in automotive and aerospace applications where weight reduction and low fuel consumption are critical product performance metrics. In most applications, glass and carbon fibre composites are used. However, natural fibre composites also offer attractive properties. They are competitive especially in terms of price and density when compared to glass and carbon fibre composites while providing similar mechanical properties. Commonly available natural fibres include coir and sisal. Resin transfer moulding (RTM) process is also an established technique for manufacturing composites as it offers good surface finish and dimensional control. The aim of this paper is to investigate the effect of resin transfer rate on the performance of the product. Coir fibre / epoxy resin composites are prepared using RTM for differing resin transfer rates and fibre fraction for treated and untreated fibres. The results obtained indicate a slight reduction in performance with reduction in resin transfer rate. However, stiffness remained unaffected. Improvement in stiffness and strength with increasing volume fraction was reported which was in agreement with literature. However, the data exhibited an optimum fibre volume fraction of 30% beyond which performance deteriorated. This investigation indicates that further work is required to optimise the production of natural fibre composites using RTM

Influence of manufacturing conditions on fatigue life of welded joints

Abstract: This paper presents a study on the influence of manufacturing conditions on the fatigue life of welded joints of high strength steels P355NL-1 and P355NL-2. Welding conditions were varied by adjusting the welding parameters and component-welding positions for a range of railway bogie welded joints. Prepared joints were then assessed for cracks and porosity defects. It was observed that an increase in welding speed resulted in an increase in crack and pore sizes. The same applied to increase in welding angle. Identified crack sizes ranged from 0.2 to 2.6 mm. Impact of such defects on fatigue life was assessed by evaluating the residual fatigue life of the component using the Paris law for stress amplitude of 150 MPa. The fatigue life of the bogie was estimated to be 6.23 × 105 instead of the required 1 × 106 cycles. It was concluded that manufacturing conditions have a significant effect on fatigue life of high strength steel welded joints. Travel speed and welding angle are critical

Improving part qualifying performance using compliance crack monitoring under rotating bending tests

Abstract: Part qualifying testing is a critical part of product development especially for mission critical components. This is more pronounced in cases where new manufacturing techniques such as high speed machining, additive manufacturing and wire electrical discharge machining are applied. Such techniques invariably modify the surface integrity of the components by introducing amongst others residual stresses and altering surface roughness. If left unattended, this may affect the performance of the product in service. Therefore, there is a need to qualify products before full commercial production and to link the manufacturing strategy to anticipate in service part performance. Endurance qualifying tests for certain products and components may include full scale endurance testing and/or a machining strategy endurance evaluation by fatigue testing either axially or in bending. Crack growth monitoring can be used to indicate the durability and performance of the product. However, crack growth monitoring during axial or rotating bending conditions is challenging and expensive. The aim of this paper is, therefore, to report on the development of a compliance based crack monitoring technique that can reduce the cost and improve the effectiveness of product qualifying tests. Tests are conducted on grade 5 titanium alloy (Ti6Al4V) specimens produced using high speed turning. These are then subjected to a rotating four point bending configuration test. Defect (crack) formation and growth (size) may then be estimated by compliance (strain) monitoring. This technique was found to be a viable low cost option for monitoring components during rotating bending conditions and to link the manufacturing technique to part performance with specific reference to dynamic loading

Effects of wire electrical discharge machining on fracture toughness of grade 5 titanium alloy

Grade 5 titanium (Ti6Al4V) is considered as the workhorse material when it comes to automotive and aerospace applications. It is widely referred to as an aerospace alloy and is relatively a new engineering material. The main attraction of this material is its high strength to weight ratio when compared to such common engineering materials such as steel and aluminum alloys. One of the major challenges in the use of this aerospace material is its machinability. Its high strength which is maintained at elevated temperatures, low thermal conductivity, low elastic modulus and high reactivity with oxygen is a perfect recipe for machining challenges. This leads to high tool wear and long production times. Such challenges are sometimes overcome by electrical discharge machining (EDM). Given that titanium is usually applied to mission critical components (gears, shafts, wing sections), it is important to understand the possible effect of wire EDM on their structural performance. One of the structural integrity indicators in such applications is fracture toughness. Fracture toughness is widely used for damage tolerance analysis of aerospace components in which critical crack sizes are computed for given loading conditions to arrive at safe inspection and maintenance intervals. It is therefore the purpose of this paper to conduct a study on the effect of wire EDM on the fracture toughness of this aerospace material. Standard test procedure using compact tension (CT) specimen is used to measure the fracture toughness. Four specimens are produced using wire EDM. This includes the pre-crack which is usually produced by fatigue cycling. Obtained results indicate a slight decrease in fracture toughness compared to that reported in literature. In addition, it can also be concluded that wire EDM can be used as an alternative to fatigue pre-cracking in fracture toughness testing of titanium alloys

Effect of HHO on four stroke petrol engine performance

Contemporary research into alternative sources of energy for transportation focuses mainly on electric/battery, hybrid and hydrogen powered vehicles. Such focus assumes that the current technology has to be discarded and cannot be improved. However, it is possible to introduce interim technology to alleviate the current challenges arising from continued reliance on fossil fuels. Such challenges include increased greenhouse gas (GHG) emissions with consequent global warming and climate change impacts. The purpose of this research work is to determine if the partial inclusion of hydrogen gas (HHO) in a petrol fuelled spark ignition (SI) internal combustion (IC) engine would improve engine performance. If this is possible, old SI technology can be modified to reduce GHG emissions and improve utilisation of fossil fuels which are expected to dominate the transport energy source for at least the next half century. An HHO generator was designed, constructed and mounted in the engine compartment of a 1989 Ford Laser vehicle. This system allowed partial inclusion of HHO gas on demand into the combustion process through the air supply stream. Detailed and comprehensive experimental investigations were conducted for engine speeds ranging from 1000 to 3500 rpm while parameters such as the power output, exhaust gas emissions and fuel consumption were monitored. Results obtained indicated a decrease in hydrocarbon emissions and an increase in power output with an increase in the HHO gas for certain engine operating conditions. However, performance improvement cannot be claimed for all operating conditions, especially under higher loads where the engine ran with a rich fuel mixture. Hence, further work is required, through HHO generator refinement alongside better engine management, to improve the experimental performance and hence further understanding of this technology

Determining optimum parameters for manual compaction of loose biomass

Abstract: Significant amounts of loose biomass are produced annually through agricultural and forestry activities. It is common practice to burn these loose biomass deliberately after harvesting or in accidental veld fires in the case of forestry. This energy could be harnessed for cooking and heating. The challenge with the use of loose biomass lies in its low density and hence low energy content which can be improved through densification. The aim of this paper is to determine the optimum densification parameters that can be used to develop manual briquetting technologies to empower poor communities to harness the energy available in loose biomass that they dispose annually. This forms part of a larger project aimed at developing off grid biomass value chain technologies. Using loose grass and loose leaves, experimental data revealed an optimum density of 1250 kg/m3 and a corresponding densification pressure of 40 MPa. In addition, a comparison of the thermal profile of solid round and round hollow briquettes showed more superior performance of the round hollow briquette based on recorded maximum combustion temperatures. Briquettes with a hole in the middle are therefore preferred to solid briquettes

Design of chilled ceiling displacement ventilation for direct expansion HVAC system

Abstract: Displacement ventilation is a low cost ventilation technique used in distributing conditioned air in Heating, Ventilation and Air Conditioning (HVAC) systems. This is a ventilation strategy well suited to significantly reduce building energy consumption in this age of high energy costs, global warming and climate change. This is achieved through the leveraging of natural buoyancy driven flow in the conditioned space in a way that minimizes energy expenditure in supply and extraction fans. In addition, the conditioned air is supplied at higher temperature implying lower energy demand for cooling units. The global legislative move towards greener buildings demands the use of sustainable and energy efficient air conditioning systems of which displacement ventilation makes a major contribution. One of the challenges in using displacement ventilation is the stratified temperature distribution in the conditioned space. The temperature gradients between the ceiling and the floor can lead to decreased comfort conditions. One approach to overcome this problem is to use the chilled ceiling. How does one size the chilled ceiling system in such cases? The purpose of this paper is to present a detailed design analysis of a displacement ventilation chamber that includes chilled ceiling. The chamber utilizes an under floor air supply system into a conditioned space configured to represent typical office space. The construction and performance testing of the displacement ventilation testing chamber is then reported in a subsequent paper

Coal combustion models: a review

Abstract : Computational Fluid Dynamics has been used for optimisation of industrial applications with some level of success. The modest accuracy provided by some of the combustion models in use has left some room for research and improvement. Coal is presented as a fuel with complex chemical properties due to its fossil fuel nature. The devolatilization process of coal is investigated with special attention to the best models that can handle heavy and light volatiles found in coal. The heterogenous char combustion is also presented paying attention to the nature of the char particle during the combustion process. The other processes such as drying, homogenous volatile combustion, radiation models, particle tracking models and turbulent models are investigated in a general manner as they rarely vary with the type of fuel being investigated. A summary of the industrial applications that have successfully utilised the CFD models for optimisation of coal combustion are presented thus helping in drawing the final conclusion

Experimental investigation of water leakages through a longitudinal crack due to expansion of the pipe material under pressure

Abstract: The effect of the pipe material plays a preeminent role in the overall water leakage behaviour of cracks, and specifically of longitudinal cracks for pipes composing Water Distribution Systems. Due to pipe material properties, a longitudinal crack on a pipe exhibits expansion behaviour under internal pressure increases, taken up by hoop stresses, which cause high stress concentration around the crack, provoking the expansion of cracked areas. With the aim of assessing the increment of water leakages through longitudinal cracks, caused by pressure increase, in this paper results from experimental tests of a longitudinal crack on a pipe wall were analysed and discussed. This is achieved by subjecting several plates with different length of cracks to tension and monitoring the opening of the cracks. A mathematical model for longitudinal crack opening is derived using the orifice equation, as a function of pressure, pipe material properties, pipe geometry and fluid properties for uni-axial stress state. Subsequently, an equation describing the increase of the leakage flow rate as function of the increase of the crack area in uni-axial stress state is determined. The derived model (Ilunga’s Equation) contradicts the Torricelli’s orifice equation which assumed that the orifice area is fixed, but variable with the change in pressure due to pipe material properties