Modelling of Metal-Coating Delamination Incorporating Variable Environmental Parameters

A mathematical model for metal-coat delamination of degrading metal was developed incorporating multiple variable environmental parameters. Metal-coat delamination not only depends on the electrochemical reactions at metal-coat interface but also on the factors like the type of propagating metal ions and their varying concentration with annual weather changes, time of exposure of the coated objects, type of coated objects are stationary or mobile vehicles, frequency with which certain vehicles are operating in various environments e.g. controlled or uncontrolled in terms of environmental conditions. A cutting edge model has been developed to calculate the varying environmental conditions using iteration algorithm, time dependent uncertain position of objects like vehicle in various environments using stochastic approach, effect of seasonal changes on ionic compound's concentration using algebraic method and instantaneous failure probability due to varying conditions. Based on the developed model a detailed simulation study was conducted to investigate the metal-coat delamination process and the ways to regress the under coat metal corrosion

Accelerated Corrosion tests of Waste-gated Turbocharger’s Adjustable and Fixed End Links

A turbocharger which has been mounted to a heavy duty automotive diesel engine can be subjected to various aggressive environments and a range of temperatures varying from ambient to 670°C. Extreme operating environments and temperatures can initiate corrosion leading to the degradation of the components. The present research evaluates corrosion resistance of the Zinc coated and Stainless Steel waste-gate end-links based on accelerated corrosion and dust particles test, using an Environmental Test Rig. Samples were exposed to the tests for 504 hours. Images of the specimens were captured to record corrosion build-up and its progression on the surfaces during the exposure time. These results were then used to evaluate the corrosion resistance ability of both, Zinc coated Fixed and Stainless Steel Adjustable End-Links. Accumulation of corrosion and the build-up of salt deposits were observed on both End-Links during/after the experiments

A Predictive Model for Life Assessment of Automotive Exhaust Mufflers Subject to Internal Corrosion Failure due to Exhaust Gases Condensation

A study has been presented of pitting corrosion on internal walls of automotive exhaust muffler due to exhaust gases condensation. The problem mainly exists in the rear section of exhaust system close to tail end pipe such as muffler, especially when the temperature of muffler does not go up during short distance run or winter. The water vapor condenses on the muffler's inner wall in the form of water droplets. The dissolution of corrosive gases which are coming from internal combustion of engine as well as condensation of low-pH acidic vapors in the water droplet can cause severe pitting corrosion on standard exhaust steel. In this work, an experiment is reported for internal corrosion, by using mufflers as test bed subjected to different environmental conditions. Based on observations, a mechanistic model has been developed which involves three main techniques (i) the dropwise condensation technique predicts the condensation rate and is based on heat and mass transfer theory (ii) the species breakdown in the droplet is established through the main thermodynamic and chemical equilibrium (iii) the pitting corrosion involving pit depth is predicted using electrochemical kinetic reactions, species transport and chemical reactions occurring inside the droplet. Lastly, the accuracy of model has been validated by comparison between experimental and predicted results showing a good agreement

Extreme poverty and marginality in Bangladesh: Review of extreme poverty focused innovative programmes

Bangladesh has achieved notable progress in poverty reduction including reduction in extreme poverty since 1990. Still a good proportion of the people in the country are living in extreme poverty and suffering from various kinds of deprivation and marginalization. It is therefore important to look into the factors that are responsible for deprivation and marginalization and address them appropriately in order to help the extreme poor and the marginalized communities to overcome poverty. The majority of the anti-poverty programmes being implemented in the country suffer from a number of limitations, especially, with respect to addressing the needs and demands of the extreme poor groups and the marginalized communities. Given this context, it is critically important to have dedicated and innovative programmes to cater the needs of the extreme and marginalized people living in different areas in the country. Some innovations have already begun in respect of addressing extreme poverty and marginality in the country. This review of some of these programmes reveals that they have been successful in reaching and meeting the needs of the extreme poor households. However, given the fact that there are still a large number of extreme poor households who need support of this kind, efforts should be intensified to reach them and to bring them out of extreme poverty within the shortest possible time

Modeling the Effect of Residual and Diffusion-Induced Stresses on Corrosion at the Interface of Coating and Substrate

The effect of residual and diffusion induced stresses on corrosion at the interface of coating and substrate has been analysed within a multidisciplinary approach i.e. material science, solid mechanics and electrochemistry. A self-consistent equation for corrosion current density, involving the combined effect of residual stress and diffusion induced stress is developed. The influences of temperature, moduli ratio, thickness ratio, thermal mismatch ratio and residual stress gradient of coating and substrate on the corrosion current density are then discussed. Results indicate that when the thermal expansion of coating is greater than substrate, the decrease in temperature from fabrication temperature accounts for the same direction of both the residual and the diffusion stresses. This behaviour increases the deflection of coating-substrate system and results in the evolution of tensile residual stress in the coating. The tensile stress opens the pre-existing coating micro crack allowing the diffusion of corrosive agents and therefore, accelerating the corrosion damage to the coating-substrate interface. The model is based on experimental observations conducted to understand the behaviour of corrosion at the coating-substrate interface in the presence of tensile or compressive residual stresses. At the end the model has been validated against the experimental results showing a good quantitative agreement between the predicted theoretical and experimental trends

Sensor based corrosion condition monitoring of coating substrate system informed by fracture mechanics, electrochemistry and heat transfer concepts

This research investigates delamination and blistering as coating failure mechanisms due to corrosive diffusing species, residual and thermal stresses. Several mathematical models to include environmental variables as temperature, humidity ratio and atmospheric constituents have been developed and reported. During this study various coating failures have been analysed through a combination of electrochemistry, fracture mechanics and heat transfer concepts. This approach enabled the development of comprehensive mathematical models for the prediction and prognoses of coating failures applied to high value assets. The formation of blister and its propagation due to diffusion of corrosive species was investigated. Fracture mechanics concepts were utilised to study the initiation and propagation of a circular blister as an interfacial crack under the coupling affects of compressive and diffusion induced stresses along with heat transfer due to pressure gradient at the interface of coating substrate system. The direction of blister propagation was defined through a mathematical model with blister radius r and radial angle θ as initial defining parameters. Experimental work was conducted to assess the influence of varying temperatures, humidity ratios and environmental pollutants as SO2 and salt particles to investigate corrosion failures. Live condition monitoring techniques were developed to assess corrosion rate with respect to large vehicles operation frequencies to study the effects of changing environments. Three years of real time data consisted of 150K data points was acquired for investigating corrosion failures with or without coatings. Both experimental and simulation data was compared to predictive and prognostics models. There is excellent agreement between experimental and simulation results to be applied for live corrosion condition monitoring of large high value assets. A sensor based corrosion condition monitoring methodology, informed by experimental and simulation results has been developed and is presented

Predictive and prognostic modelling and simulation of coating failures due to corrosion and mechanical failures

This research presents analytical and mathematical modelling of coating failures within industrial components, structures, mobile assets and systems due to corrosive degradation and mechanical fracture. These failures lead to serval surface problems, therefore contact mechanics and electrochemistry approaches incorporating induced residual stresses have been adopted to develop a comprehensive solution for the prediction prognostic of such failures. Experimental study of film cracking and its propagation into substrates, interfacial transient behaviours and film-substrate system has been conducted. A parallel study of corrosive degradation to include cathodic delamination, cathodic blistering and tribo-corrosion of films has been conducted. Experimental and analytical studies of induced residual stresses within the coating and their effects on failure mechanisms and propagation have been completed. A detailed investigation of elastic mismatch at the interfacial contact and interfacial crack tip field has been performed and a complex stress intensity factor is presented. Mathematical derivation of oscillatory singularity, mode mix and interfacial fracture criterion to include adhesion are presented. This paper presents novel mathematical modelling incorporating interfacial crack propagating, diffusion of corrosive species and cathodic blistering for prediction and prognoses of coating failures

Slurry Erosive Wear Behavior of Hot Extruded Al6061-Si3N4 Composite

Silicon nitride possess excellent hot hardness and wear resistance coupled with very good corrosion resistance. Hence, in recent years, silicon nitride has been a serious contender as a reinforcement to develop light weight metal matrix composites for several technological applications. Al6061 is most popular matrix alloy as it possess excellent formability and in particular the quality of extrudates of Al6061 is quite high and are the most preferred in space and naval applications especially for support structures and torpedoes blades respectively. Improved corrosion and slurry erosion resistance on use of silicon nitride in nickel and aluminum alloy matrices have been reported by several researchers. In the light of the above, this paper focuses on development of Al6061- 6wt% Si3N4 by stir casting the most economical and popular route followed by hot extrusion. Hot extrusion was carried out using 200T hydraulic press at extrusion ratio of 1:10 at a temperature of 5500C. Slurry erosion tests were carried out using 3.5% NaCl solution containing silica sand particles of size 312 μm at different rotational speeds varying between 300 rpm and 1200 rpm. The sand concentration was varied from 10 g/l to 40 g/l. Under identical test conditions, hot extruded Al6061- 6wt% Si3N4 composite do possess better slurry erosion resistance when compared with matrix alloy. The mechanism involved in the material removal process during slurry erosion process will also be discussed