A Novel Non-Destructive Sensing Technology for On-Site Corrosion Failure Evaluation of Coatings

The quality of coating and the resulting rate of corrosion of the underlying metal substrate can be measured by a variety of corrosion measurements (Tafel, Electrochemical Impedance Spectroscopy) by using standard laboratory electrochemical cells. However there is always a need of low cost, portable and non-destructive electrochemical cells which can be used on-site field for condition monitoring of large structures for example bridges and large infrastructures, complex operating systems as aircrafts, precision machines, petrochemical processes, automotive and locomotives. This research has developed state of the art cells and has commissioned for deploying this novel sensing technology for micro-defects detection, corrosion rate measurement and condition assessment of the defected coatings. Tafel measurement facilitated by these non-destructive cells is used to detect micro-defects and corrosion rate measurement while Electrochemical Impedance Spectroscopy measurement is facilitated to measure the coating condition. This technology has been successfully tested and commissioned on automotive, hazardous compartments with polymeric coatings and bridges to assess their coating condition in terms of their structural integrity. Post design testing involved the installation of these cells, running diagnostics, data acquisition and macrographs to predict structural defects and the resulting corrosion rate. This technology enables the design process to incorporate operational conditions and fully realize more durable and reliable solutions to be applied to high value large structures and complex interacting systems. Current developments in corrosion condition monitoring especially cost effective, non-destructive techniques to assess structural integrity beneath nonconductive and polymeric coating were long awaited. This reported development will revolutionise durability and reliability assessment techniques to enhance safety and mitigate catastrophic failures for cost savings and avoiding fatal accidents

Electrochemical Corrosion Failure Analysis of Large Complex Engineering Structures by using LPR Sensors

This paper presents the effects of three major parameters; temperature, relative humidity and hygroscopic salts contaminants on the atmospheric corrosion of large steel structures. The effects of these three parameters have been analysed by using micro-sized LPR sensors to continuously monitor the corrosion rate of a degrading large structure under varying parameters. A long term, three years study was performed by deploying LPRs on strategically selected large military vehicles (main battlefield tanks), which are stationed in the Tank Museum at Bovington, UK. These vehicles are operational and are of historic significance with cultural biography, however structural deterioration through corrosion, corrosion fatigue, stress corrosion cracking and mechanical failures are a threat to these vehicles in terms of their conservation. A set of vehicles operational (uncontrolled environment) and non-operational (controlled environment) was selected for comparative analysis in context of corrosion rate. This research is founded on a novel real-time corrosion monitoring technique that enables to better understand the relationship between varying environmental parameters and corrosion rate of large steel-based mobile structures during operation. This research provides a synthesis of real time corrosion data, which has been accumulated over a period of three years. An overview of structural deterioration is presented and derived from a significantly large data, therefore it provides a more reliable and highly accurate assessment of failures due to corrosion

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

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

Experimental Analysis and Modeling for Reciprocating Wear Behavior of Nanocomposite Coatings

This paper presents the study of wear responses of nanocomposite coatings with a steel ball under oscillatingreciprocating state. Nanocomposite coatings for this study include: Nickel-Alumina (Ni/Al2O3), Nickel-Silicon Carbide (Ni/SiC), Nickel-Zirconia (Ni/ZrO2) and Ni/Graphene. Ni/ZrO2 exhibited maximum wear rate followed by Ni/SiC, Ni/Al2O3 and Ni/Graphene respectively which was also assured by Scanning Electron Microscopy (SEM) micrographs, grain sizes, hardness, porosity, surface stresses, frictional coefficients behaviours and “Ushaped" wear depth profiles. The “U-shaped” profiles were utilised to calculate the energy distribution (Archard factor density) along the interface. A novel mechano-wear model incorporating the energy distribution equations with the mechanics equations was developed for analysing the effects of intrinsic mechanical properties (such as grain sizes, hardness, porosity, surface stresses of the nanocomposite coatings) on the wear response. The predictions showed close agreement with the experimental results. In conclusion Ni/Graphene exhibited better anti-wear properties compared to other nanocomposite coatings. The high anti-wear behaviour of Ni/Graphene composite is due to enhanced strengthening effects in the presence of graphene. The importance of this work is evident from various industrial applications which require reliable modelling techniques to predict coatings failures due to wear. This work will bring significant impact to precision manufacturing, wind turbine industries, automotive, locomotive and aerospace in overcoming critical wear failures

Internalizing and externalizing problems, empathy quotient, and systemizing quotient in 4 to 11 years-old siblings of children with autistic spectrum disorder compared to control group

Objective: This study was conducted to recognize the problems of living with a sibling with Autistic Spectrum Disorder (ASD) to improve their quality of life. Method: A total of 30 participants were selected among the 4-to11- year-old siblings of children who had referred to Tehran Psychiatric Institute due to autism spectrum disorder. For the control group, 30 children aged 4 to11years old who were the siblings of patients with chronic diseases referring to Pediatric Clinic of Rasoul-e Akram (PBUH) hospital were selected. Gilliam Autism Rating Scale-Second Edition (GARS-2) was filled out for patients and siblings participating in the study and Child Behavior Checklist was completed by their parents. Results: The mean age of the patients in this study was 4.46 ± 9.66 years (range: 1.5-22 years), and the mean age in the healthy children was 2.54 ± 8.18 years (range: 4-11 years). The mean scores of anxiety/depression, withdrawn/depressed, somatic complaints, social problems, thought problems, attention problems, and rule-breaking behavior subscale of CBCL (Child Behavior Checklist) were not significantly different between groups. Aggressive behavior was the only subscale that showed such difference (p = 0.008). Externalizing problems in children who had siblings with ASD was higher than children who had siblings with physical illness. In a group in which a sibling had ASD, sisters were more anxious/ depressed than brothers. Conclusion: Due to various psychological and social problems that siblings of children with ASD experience throughout their life, studying their psychological problems to improve their quality of life seems to be of paramount importance. © 2018 Tehran University of Medical Sciences

Internalizing and externalizing problems, empathy quotient, and systemizing quotient in 4 to 11 years-old siblings of children with autistic spectrum disorder compared to control group

Objective: This study was conducted to recognize the problems of living with a sibling with Autistic Spectrum Disorder (ASD) to improve their quality of life. Method: A total of 30 participants were selected among the 4-to11- year-old siblings of children who had referred to Tehran Psychiatric Institute due to autism spectrum disorder. For the control group, 30 children aged 4 to11years old who were the siblings of patients with chronic diseases referring to Pediatric Clinic of Rasoul-e Akram (PBUH) hospital were selected. Gilliam Autism Rating Scale-Second Edition (GARS-2) was filled out for patients and siblings participating in the study and Child Behavior Checklist was completed by their parents. Results: The mean age of the patients in this study was 4.46 ± 9.66 years (range: 1.5-22 years), and the mean age in the healthy children was 2.54 ± 8.18 years (range: 4-11 years). The mean scores of anxiety/depression, withdrawn/depressed, somatic complaints, social problems, thought problems, attention problems, and rule-breaking behavior subscale of CBCL (Child Behavior Checklist) were not significantly different between groups. Aggressive behavior was the only subscale that showed such difference (p = 0.008). Externalizing problems in children who had siblings with ASD was higher than children who had siblings with physical illness. In a group in which a sibling had ASD, sisters were more anxious/ depressed than brothers. Conclusion: Due to various psychological and social problems that siblings of children with ASD experience throughout their life, studying their psychological problems to improve their quality of life seems to be of paramount importance. © 2018 Tehran University of Medical Sciences

Analysing the Coupled Effects of Compressive and Diffusion Induced Stresses on the Nucleation and Propagation of Circular Coating Blisters in the Presence of Micro-cracks

This paper presents the delamination of coating with micro-cracks under compressive residual stress coupled with diffusion induced stress. Micro-cracks in coating provide a passage for corrosive species towards the coating-substrate interface which in turn produces diffusion induced stress in the coating. Micro-cracks contract gradually with increasing compressive residual stress in coating due to thermal expansion mismatch which blocks the species diffusion towards the interface. This behaviour reduces the diffusion induced stress in the coating while the compressive residual stress increases. With further increase in compressive residual stress, micro-cracks reach to the point, where they cannot be constricted any further and a high compressive residual stress causes the coating to buckle away from the substrate resulting in delamination and therefore initiating blistering. Blistering causes the contracted micro-cracks to wide open again which increases diffusion induced stress along with high compressive residual stress. The high resultant stress in coating causes the blister to propagate in an axis-symmetric circular pattern. A two-part theoretical approach has been utilised coupling the thermodynamic concepts with the mechanics concepts. The thermodynamic concepts involve the corrosive species transportation through micro-cracks under increasing compression, eventually causing blistering, while the fracture mechanics concepts are used to treat the blister growth as circular defect propagation. The influences of moduli ratio, thickness ratio, thermal mismatch ratio, poisson’s ratio and interface roughness on blister growth are discussed. Experiment is reported for blistering to allow visualisation of interface and to permit coupled (diffusion and residual) stresses in the coating over a full range of interest. The predictions from model show excellent, quantitative agreement with the experimental results

Optimisation of Interface Roughness and Coating Thickness to Maximise Coating-Substrate Adhesion - A Failure Prediction and Reliability Assessment Modelling

This paper addresses a novel modelling technique which is based on a multidisciplinary approach to predict the coating-substrate adhesion. It proposes new equations governing coating debondment that combines material science concepts with and solid mechanics concepts. The effects of two parameters i.e. interface roughness λ and coating thickness h on coating-substrate adhesion has been analysed. The reliability of newly developed technique has been validated by comparison with the experimental results