A Carbonation and Chloride Induced Corrosion Model for Hot-dip Galvanised Reinforcement Bar Material in Concrete

This paper focuses on methodological issues relevant to corrosion risk prediction models.A model was developed for the prediction of corrosion rates associated with hot-dip galvanised reinforcement bar material in concrete exposed to carbonation and chlorides in outdoor environment.One-year follow-up experiments,over five years,were conducted at various carbonation depths and chloride contents.The observed dependence of corrosion rate on the depth of carbonation and chloride content is complex indicating that the interaction between the carbonation and chloride influencing the corrosion.A non-linear corrosion model was proposed with statistical analysis to model the relationship between the corrosion rate and the test parameters.The main methodological contributions are(i)the proposed modeling approach able to take into account the uncertain measurement errors including unobserved systematic and random heterogeneity over different measured specimens and correlation for the same specimen across different measuring times,which best suits the measurement data;(ii)the developed model in which an interaction parameter is introduced especially to account for the contribution and the degree of the unobserved carbonation-chloride interaction.The proposed model offers greater flexibility for the modelling of measurement data than traditional models.

Mechanistic modeling of copper corrosions in data center environments

Air-side economizers are increasingly used to take advantage of“free-cooling”in data centers with the intent of reducing the carbon footprint of buildings.However,they can introduce outdoor pollutants to indoor environment of data centers and cause corrosion damage to the information technology equipment.To evaluate the reliability of information technology equipment under various thermal and air-pollution conditions,a mechanistic model based on multi-ion transport and chemical reactions was developed.The model was used to predict Cu corrosion caused by Cl_(2)-containing pollutant mixtures.It also accounted for the effects of temperature(25℃and 28℃),relative humidity(50%,75%,and 95%),and synergism.It also identified higher air temperature as a corrosion barrier and higher relative humidity as a corrosion accelerator,which agreed well with the experimental results.The average root mean square error of the prediction was 13.7Å.The model can be used to evaluate the thermal guideline for data centers design and operation when Cl_(2)is present based on pre-established acceptable risk of corrosion in data centers’environment.

Risk Based Optimal Inspection and Repair Planning for Ship Structures Subjected to Corrosion Deterioration

A framework of risk based inspection and repair planning was presented to optimize for the ship structures subjected to corrosion deterioration. The planning problem was formulated as an optimization problem where the expected lifetime costs were minimized with a constraint on the minimum acceptable reliability index. The safety margins were established for the inspection events, the repair events and the failure events for ship structures. Moreover, the formulae were derived to calculate failure probabilities and repair probabilities. Based on them, a component subjected to corrosion is investigated for illustration of the process of selecting the optimal inspection and repair strategy. Furthermore, some sensitivity studies were provided. The results show that the optimal inspection instants should take place before the reliability index reaches the minimum acceptable reliability index. The optimal target failure probability is 10 -3 . In addition, a balance can be achieved between the risk cost and total expected inspection and repair costs by means of the risk-based optimal inspection and repair method, which is very effective in selecting the optimal inspection and repair strategy.

Damage model of fresh concrete in sulphate environment

A model of damage to fresh concrete in a corrosive sulphate environment was formulated to investigate how and why the strength of corroded concrete changes over time. First, a corroded concrete block was divided into three regions: an expanded and dense region; a crack-development region; and a noncorroded region. Second, based on the thickness of the surface corrosion layer and the rate of loss of compressive strength of the corroding region, a computational model of the concrete blocks' corrosion-resistance coefficient of compressive strength in a sulphate environment was generated. Third, experimental tests of the corrosion of concrete were conducted by immersing specimens in a corrosive medium for 270 d. A comparison of the experimental results with the computational formulae shows that the calculation results and test results are in good agreement. A parameter analysis reveals that the corrosion reaction plays a major role in the corrosion of fresh concrete containing ordinary Portland cement,but the diffusion of the corrosion medium plays a major role in the corrosion of concrete mixtures containing fly ash and sulphate-resistant cement. Fresh concrete with a high water-to-cement ratio shows high performance during the whole experiment process whereas fresh concrete with a low water-to-cement ratio shows poor performance during the late experiment period.

Linking the effect of localised pitting corrosion with mechanical integrity of a rare earth magnesium alloy for implant use

This study presents a computational framework that investigates the effect of localised surface-based corrosion on the mechanical performance of a magnesium-based alloy.A finite element-based phenomenological corrosion model was used to generate a wide range of corrosion profiles,with subsequent uniaxial tensile test simulations to predict the mechanical response to failure.The python-based detection framework PitScan provides detailed quantification of the spatial phenomenological features of corrosion,including a full geometric tracking of corroding surface.Through this approach,this study is the first to quantitatively demonstrate that a surface-based non-uniform corrosion model can capture both the geometrical and mechanical features of a magne-sium alloy undergoing corrosion by comparing to experimental data.Using this verified corrosion modelling approach,a wide range of corrosion scenarios was evaluated and enabled quantitative relationships to be established between the mechanical integrity and key phenomenological corrosion features.In particular,we demonstrated that the minimal cross-sectional area parameter was the strongest predictor of the remaining mechanical strength(R2=0.98),with this relationship being independent of the severity or spatial features of localised surface corrosion.Interestingly,our analysis demonstrated that parameters described in ASTM G46-94 showed weaker correlations to the mechanical integrity of corroding specimens,compared to parameters determined by Pitscan.This study establishes new mechanistic insight into the performance of the magnesium-based materials undergoing corrosion.

溶蚀丘陵型岩溶流域概念性水文模型及其应用

为弥补传统概念性水文模型在岩溶水文模拟上的缺陷,基于三水源新安江模型,采用多个线性水库表达岩溶地下系统的异质性,同时引入流域虚拟面积系数修正岩溶流域的非闭合性。将改进的概念性水文模型应用于湘中南典型溶蚀丘陵型岩溶流域,并在此基础上探讨岩溶流域非闭合性的动态变化。研究结果表明:①改进模型的日径流模拟精度提高11.21%,水量平衡误差及低水误差分别降低23.29%、27.64%;②岩溶地下汇流系统的多向性导致流域非闭合状态具有双重性;③地下汇流面积与时段降雨量呈正相关,然而受地下饱和程度的制约,地下汇流面积的变化率随时段降雨量的增大而减小;④由于岩溶地貌的蓄水滞水作用,地下流域受外侧补给的过程存在滞后性。模型的改进与拓展研究可为岩溶水文模拟提供新思路。

Experimental and numerical investigation on the thermal and mechanical behaviours of thermal barrier coatings exposed to CMAS corrosion

Calcium-magnesium-alumino-silicate(CMAS)corrosion is a critical factor which causes the failure of thermal barrier coating(TBC).CMAS attack significantly alters the temperature and stress fields in TBC,resulting in their delamination or spallation.In this work,the evolution process of TBC prepared by suspension plasma spraying(SPS)under CMAS attack is investigated.The CMAS corrosion leads to the formation of the reaction layer and subsequent bending of TBC.Based on the observations,a corrosion model is proposed to describe the generation and evolution of the reaction layer and bending of TBC.Then,numerical simulations are performed to investigate the corrosion process of free-standing TBC and the complete TBC system under CMAS attack.The corrosion model constructs a bridge for connecting two numerical models.The results show that the CMAS corrosion has a significant influence on the stress field,such as the peak stress,whereas it has little influence on the steady-state temperature field.The peak of stress increases with holding time,which increases the risk of the rupture of TBC.The Mises stress increases nonlinearly along the thick direction of the reaction layer.Furthermore,in the traditional failure zone,such as the interface of the top coat and bond coat,the stress obviously changes during CMAS corrosion.