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Self-restraint stress produced in early age is a matter of interest associated with cracking of concrete. Mesoscopic modelling nowadays is one of the effective approaches to investigate internal stresses, deformation, damage of concrete at much smaller scale. However, grid discretization and mesoscopic properties calibration are still challenging issues that prevent fast pre-processing and require extremely dense meshes for accurate solutions. In this paper, a thermo-mechanical model required only regular-element discretization is proposed by developing a diffuse meshing technique to analyze the evolution of self-restraint stress. Cross-scale numerical validations are carried out to calibrate the mesoscopic parameters, along with verifying the feasibility of the proposed model. Furthermore, the effect of simplified aggregate mesostructure on the thermo-mechanical behavior of concrete is evaluated through comparisons with the results obtained by considering complex-shaped aggregate using the proposed diffuse element model. The results show the thermo-mechanical mismatch between different components is the main reason for producing the self-restraint stress, and aggregate meso-structure have nonnegligible influence on the global response or local behavior.

Chloride ions in marine environment can cause corrosion of steel reinforcement in reinforced concrete (RC) structures and result in structure deterioration. This study investigates a dual-functional intervention method, i.e. impressed current cathodic protection – structural strengthening (ICCP-SS) method, using carbon fibre reinforced polymer (CFRP) as both the anode material for impressed current cathodic protection and strengthening material for structural strengthening system. The effectiveness of the ICCP-SS method on the improvement of durability of RC structures is considered in a long-term timeframe. An experimental programme comprising nine simply supported beams is presented in this paper. The beams experienced 360-day accelerated corrosion and 180-day cathodic protection, followed by four-point bending tests. Flexural behaviour and capacities of the degraded beams repaired by using ICCP technology, structural strengthening technology and ICCP-SS technology were obtained. After the tests, the steel reinforcement bars inside concrete were taken out and cleaned to measure the section reduction due to corrosion. Results showed that the ICCP-SS technology can prevent the corrosion of the steel reinforcement effectively and increase the capacities of the beams at the same time. Finally, the appropriateness of existing design approaches for the intervened beams was also discussed in the paper. The ICCP-SS intervention method is found to be beneficial for the durability of RC structures in marine environment.

Combining the theoretical derivation and numerical calculations, the characteristic changes of the tensile constitutive relation of corroded steel bars and their underlying mechanisms are studied. Corroded steel bars are regarded as a combination of three parts, which include uncorroded part, corroded part with variable cross section, and uniform corroded part. It is assumed that in all three parts the steel material follows a simplified trilinear constitutive relation of a mild steel material (elasticity, yielding, and hardening), from which an analytical model describing the overall tensile constitutive relation of the corroded steel bar is developed. Based on the experimental data of slotted steel bars, the validation of the present analytical model is provided. The results show that the trilinear model can give relatively accurate prediction of the characteristic parameters of corroded steel bars. The influences of corrosion rate on the mechanical properties of corroded steel bars are examined using the proposed model.

Porous aerostatic bearings as a new type of supporting component used in ultraprecision equipment. The study of porous models is essential as they are a basis for porous aerostatic bearings. However, the effects of micropore structure and flow state inside a material have not been addressed in previous studies. Herein, we propose a high-accuracy and low-cost method using deep learning to reconstruct a three-dimensional (3D) porous model and obtain the 3D flow state inside a porous material. It can reveal richer flow states such as the flow track and movement in three directions, which have not been revealed previously. This new method is effective for studying the properties of porous materials, micro-flow state, and simulation of parameters in detail.

The results of this study showed the beneficial effect of chloride ion to enhance the corrosion inhibition and prevent direct oxidation of carbon fibres under anodic polarization. The corrosion rate of carbon fibre sharply decreased after introducing chloride ions. Uniaxial tensile test performed after the simulated ICCP tests showed that the tensile strength of the carbon fibre bundles was higher when the electrolyte contained chloride ions. The application of carbon fibre as the anode material is found to be particularly well suited for coastal reinforced concrete structures.

An analytical model was developed to predict the tensile behaviour of a corroded steel bar. The model was established based on cross sectional analysis and was validated using experimental data for slotted steel bars and electrochemically corroded steel bars. The model was further used to predict the tensile behaviour of a corroded steel bar. The corrosion mode of the steel bar was supposed to be pitting corrosion and the distribution of the corroded section was supposed to follow a lognormal distribution. A power law between the parameters of the lognormal distribution and the average corrosion rate of the steel bar was used to predict the statistical distribution of the cross section area of a corroded steel bar. Based on these assumptions, the yield strength, ultimate strength and ductility of a corroded steel bar were predicted with different corrosion rates. The predicted behaviours are compared to collected experimental results from various sources. It is found that the numerical results of yield strength and ultimate strength agree well with the collected experimental results. The model slightly underestimates the ductility of the corroded steel bars. The result of the model would be helpful for the prediction of the tensile behaviour of reinforced concrete member subjected to chloride induced corrosion.

International audience; The understanding of rail braking is irrevocably dependent on the tribological analysis of contacts such as the wheel/rail contact or the wheel/brake disc contact. Because it is very complex to experimentally analyze the inside of a contact, a numerical approach based on discrete element modeling was used to model a third body composed of copper and graphite, the main elements present in sintered brake materials. Simulations were analyzed by measuring several global quantities as a function of the proportion of copper and the local properties of the material to determine the extent to which local parameters influence the electrical and tribological properties of the third body. Among the results noted was the fact that a certain proportion of mixture makes it possible to achieve a balance between electrical and tribological properties.

Continuous reinforced concrete (RC) beams are popular structural components. However, RC structures in corrosive environments can be degraded due to steel reinforcement corrosion. In this study, a dual-functional intervention method, i.e., impressed current cathodic protection and structural strengthening (ICCP-SS), is adopted to repair degraded beams. The carbon fabric-reinforced cementitious matrix (C-FRCM) composite serves dual functions in the intervention method. The effects of reinforcement corrosion, cathodic protection and the C-FRCM strengthening system on the behaviors of continuous beams should be investigated. This study provides experimental data on continuous RC beams rehabilitated by ICCP-SS in corrosive environments and investigates the structural responses, moment redistributions and design rules of these beams. The electrochemical monitoring results showed that steel reinforcements in continuous beams under corrosive environments are successfully protected. Five-point bending test results showed that beams strengthened with C-FRCM composites have higher yielding loads and ultimate loads than corroded beams without protection. Comparison of the predicted and measured moment capacities at the central support and midspan showed that the design methods generally underestimate the moment capacities of unstrengthened sections and overestimate those of strengthened sections.

International audience; Recent developments in powder technology gave birth to a new lubricant – powder lubricant. Compared to liquid lubricant, powder lubricant like graphite powder has several advantages, such as good electrical conductivity and good thermal resistance. Such advantages are especially appreciated in sliding electrical contacts. Thus, the study of the electrical transmission ability of a shearing powder layer under different dy-namical constraints appears to have a great interest. Recent works allowed to model the coupling of mechanical and electrical effects in a discrete medium. This algorithm was extended to study the electrical properties of a shearing powder layer with Discrete Element Method. The mechanical and electrical behaviors of the sample were studied in different dynamical regimes, characterized by the inertial number I. The results exhibit an interesting relationship between the average contact resistance and the inertial number I. An exponential increase of the sample's electrical resistance as well as the induced electrical noise are observed closed to the dense flow limit. Such observations underline the fact that to ensure the electrical transmission ability of the powder layer, one must keep the particle size and shear rate small, and a sufficiently large pressure.