Mian Hammad Nazir

Optimisation of interface roughness and coating thickness to maximise coating–substrate adhesion – a failure prediction and reliability assessment modelling

A mathematical model for failure prediction and reliability assessment of coating–substrate system is developed based on a multidisciplinary approach. Two models for diffusion and bending of bi-layer cantilever beam have been designed separately based on the concepts of material science and solid mechanics respectively. Then, these two models are integrated to design an equation for debonding driving force under mesomechanics concepts. Mesomechanics seeks to apply the concepts of solid mechanics to microstructural constituent of materials such as coatings. This research takes the concepts of mesomechanics to the next level in order to predict the performance and assess the reliability of coatings based on the measure of debonding driving force. The effects of two parameters i.e. interface roughness and coating thickness on debonding driving force have been analysed using finite difference method. Critical/threshold value of debonding driving force is calculated which defines the point of failure of coating–substrate system and can be used for failure prediction and reliability assessment by defining three conditions of performance i.e. safe, critical and fail. Results reveal that debonding driving force decreases with an increase in interface roughness and coating thickness. However, this is subject to condition that the material properties of coating such as diffusivity should not increase and Young’s modulus should not decrease with an increase in the interface roughness and coating thickness. The model is based on the observations recorded from experimentation. These experiments are performed to understand the behaviour of debonding driving force with the variation in interface roughness and coating thickness.

Modelling of metal-coating delamination incorporating variable environmental parameters

A mathematical model for metal-coating delamination of degrading metal was developed incorporating multiple variable environmental and physical parameters. Metal-coating delamination not only depends on the electrochemical reactions at metal-coating interface but also on the factors like the type of propagating metal ions and their varying concentration with annual weather changes (summer and winter), time of exposure of the coated objects, type of coated objects, i.e. stationary or mobile vehicles and 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 (controlled and uncontrolled) using stochastic approach, effect of seasonal changes (summer and winter) on ionic compounds 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-coating delamination process and the ways to regress the under coating metal corrosion.

A unified mathematical modelling and simulation for cathodic blistering mechanism incorporating diffusion and fracture mechanics concepts

A novel mathematical model has been developed to understand the mechanism of blister initiation and propagation. The model employs a two-part theoretical approach encompassing the debondment of a coating film from the substrate, coupled with the design components incorporating diffusion and fracture mechanics, where the latter is derived from equi-biaxial tensile loading. Integrating the two components, a comprehensive mathematical design for the propagation of blister boundaries based on specific toughness functions and mode adjustment parameters has been developed. This approach provided a reliable and efficient prediction method for blister growth rate and mechanisms. The model provided a foundation for holistic design based on diffusion and mechanic components to enable better understanding of the debondment of thin elastic films bonded to a metallic substrate.

A holistic mathematical modelling and simulation for cathodic delamination mechanism – a novel and an efficient approach

This paper addresses a holistic mathematical design using a novel approach for understanding the mechanism of cathodic delamination. The approach employed a set of interdependent parallel processes with each process representing: cation formation, oxygen reduction and cation transport mechanism, respectively. Novel mathematical equations have been developed for each of the processes based on the observations recorded from experimentation. These equations are then solved using efficient time-iterated algorithms. Each process consists of distinct algorithms which communicate with each other using duplex channels carrying signals. Each signal represents a distinct delamination parameter. As a result of interdependency of various processes and their parallel behaviour, it is much easier to analyse the quantitative agreement between various delamination parameters. The developed modelling approach provides an efficient and reliable prediction method for the delamination failure. The results obtained are in good agreement with the previously reported experimental interpretations and numerical results. This model provides a foundation for the future research within the area of coating failure analysis and prediction.

The Implications of Wet and Dry Turning on the Surface Quality of EN8 Steel

This paper, by experimental and investigation, examines the effects of dry and flood cutting conditions by comparing the rate of tool wear during metal turning and the produced surface roughness to determine if dry cutting can be a cost effective solution. For efficient manufacturing, the surface roughness of the turned parts should be dependent on their intended application, factors such as environment of operation or further manufacturing processes will determine this level of surface roughness required, as the performance and mechanical properties of the material can be affected. EN8 steel has been selected as the work material for its popularity and low hardness. The results show both wet and dry conditions have their benefits in relation to the intended application of the part, but mostly dry turning produces competitive surface roughness when finished by turning when compared to wet, and acceptable levels of tool wear while rough cutting. It would be recommended that in most circumstance for rough cutting, dry conditions should be employed with the knowledge of slight increased tool wear and possibly shorter life but with reduced manufacturing costs and environmental hazards.

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 analyzed within a multidisciplinary approach, i.e., material science, solid mec...

Life assessment prognostic modelling for multi-layered coating systems using a multidisciplinary approach

ABSTRACT The multidisciplinary approach has been adopted to model the formation and propagation of blistering effect for evaluation of useful coating life in the multi-layered coating–substrate system. A prognostic model of de-bonding driving force has been formulated as a function of material science, solid mechanics and fracture mechanics properties to estimate critical, safe and fail conditions of the coating–substrate system. The blister growth velocity rate is also included in the developed model to estimate the blister propagation as a function of diffusion-induced stress and residual stress. The proposed prognostic modelling for the formation and propagation of blistering effect are combined to form an assessment model for the evaluation of useful coating life of the multi-layered coating–substrate system and validated through experimental observation.

Analyzing and Modelling the Corrosion Behavior of Ni/Al2O3, Ni/SiC, Ni/ZrO2 and Ni/Graphene Nanocomposite Coatings

A study has been presented on the effects of intrinsic mechanical parameters, such as surface stress, surface elastic modulus, surface porosity, permeability and grain size on the corrosion failure of nanocomposite coatings. A set of mechano-electrochemical equations was developed by combining the popular Butler–Volmer and Duhem expressions to analyze the direct influence of mechanical parameters on the electrochemical reactions in nanocomposite coatings. Nanocomposite coatings of Ni with Al2O3, SiC, ZrO2 and Graphene nanoparticles were studied as examples. The predictions showed that the corrosion rate of the nanocoatings increased with increasing grain size due to increase in surface stress, surface porosity and permeability of nanocoatings. A detailed experimental study was performed in which the nanocomposite coatings were subjected to an accelerated corrosion testing. The experimental results helped to develop and validate the equations by qualitative comparison between the experimental and predicted results showing good agreement between the two.

Dynamic Frame Sizing with Grouping Slotted Aloha for UHF RFID Networks

Tag collision in a radio frequency identification system (RFID) is an important parameter that affects the overall system performance. Different algorithms have been proposed to efficiently utilize the slots during data transmission between reader and tags that need to be identified. Dynamic Frame slotted Aloha is a widely used anti collision algorithm that can be further divided into two main categories depending upon how the frame selection is performed. It has been found that dynamic frame sizing with grouping yields highly efficient results. In this study, the proposed algorithm modifies the mechanism used for dynamic grouping as implemented in the EPC global class 1 generation 2 algorithm and results have been presented showing improvement in the number of slots utilization and iterations required to successfully detect different number of tags. General Terms Algorithms, RFID Anti collision

Condition monitoring and predictive modelling of coating delamination applied to remote stationary and mobile assets

The ambiguous nature of meteorological parameters in uncontrolled environmental conditions makes it difficult to determine the structural integrity of stationary and mobile assets. The weather conditions for large vehicles, at The Tank Museum at Bovington, UK, which are operating in controlled and uncontrolled environmental conditions are investigated through weather history and corrosion monitoring techniques applied to large military vehicles by using linear polarisation resistance method. Corrosion initiation and propagation was found on several occasions during the operation of large vehicles within uncontrolled environment due to critical level of metrological parameters including salinity, relative humidity and rainfall. Comprehensive solutions have been proposed to detect damage initiation at the earliest possible stage to prompt maintenance professionals to take necessary actions to avoid damage. Early detection techniques will help to prolong the service life of large vehicles or metal structures which are operating or installed remotely. The analysis of diffusion of salt particles into coating during summer and winter season is also presented by estimating the salt concentration by taking linear relationship between wind speed and salt deposition rate based on ISO classification of airborne salinity. The proposed solutions can be applied to valuable assets operating in coastal, non-coastal and near the sea regions to predict and estimate the damage. The research will directly impact the maintenance and reliability of the automotive, oil and gas pipelines, aerospace and defence applications through remote condition monitoring technique.