Simulation of Corrosion-Induced Cracking of Reinforced Concrete Based on Fracture Phase Field Method

Accurate simulation of the cracking process caused by rust expansion of reinforced concrete(RC)structures plays an intuitive role in revealing the corrosion-induced failure mechanism.Considering the quasi-brittle fracture of concrete,the fracture phase field driven by the compressive-shear term is constructed and added to the traditional brittle fracture phase field model.The rationality of the proposed model is verified by a mixed fracture example under a shear displacement load.Then,the extended fracture phase model is applied to simulate the corrosion-induced cracking process of RC.The cracking patterns caused by non-uniform corrosion expansion are discussed for RC specimens with homogeneous macroscopically or heterogeneous with different polygonal aggregate distributions at the mesoscopic scale.Then,the effects of the protective layer on the crack propagation trajectory and cracking resistance are investigated,illustrating that the cracking angle and cracking resistance increase with the increase of the protective layer thickness,consistent with the experimental observation.Finally,the corrosion-induced cracking process of concrete specimens with large and small spacing rebars is simulated,and the interaction of multiple corrosion cracking is easily influenced by the reinforcement spacing,which increases with the decrease of the steel bar interval.These conclusions play an important role in the design of engineering anti-corrosion measures.The fracture phase field model can provide strong support for the life assessment of RC structures.

The Effect of Initial Defects on Overall Mechanical Properties of Concrete Material

Considering the fact that the initial defects,like the imperfect interfacial transition zones(ITZ)and the micro voids in mortar matrix,weaken the mechanical properties of concrete,this study develops corresponding constitutive models for ITZ and matrix,and simulates the concrete failure with finite element methods.Specifically,an elastic-damage traction-separation model for ITZ is constructed,and an anisotropic plastic-damage model distinguishing the strength-difference under tension and compression for mortar matrix is proposed as well.In this anisotropic plastic-damage model,the weakening effect of micro voids is reflected by introducing initial isotropic damage,the distinct characteristic of tension and compression which described by decomposing damage tensor into tensile and compressive components,and the plastic yield surface which established on the effective stress space.Furthermore,by tracking the damage evolution of concrete specimens suffering uniaxial tension and compression,the effects of imperfect status of ITZ and volume fraction of initial voids on the concrete mechanical properties are investigated.

Effect of Reinforcement Corrosion Sediment Distribution Characteristics on Concrete Damage Behavior

Reinforcement corrosion directly affects the mechanical behavior of reinforced concrete structures.An electric corrosion test was conducted on a reinforced concrete test specimen,and a finite element model of the reinforcement corrosion damage was established.In addition,the damage behavior of reinforced concrete under different corrosion sediment distribution characteristics and different corrosion rates was studied.It was noted that when corrosion sediments are in a“semiellipse+semicircle”distribution,the results of numerical calculation are consistent with those obtained experimentally,reflecting the damage characteristics of reinforced concrete test specimens.Further,the results showed that the distribution characteristics of corrosion sediments greatly influence the damage behavior of reinforced concrete.In particular,when the corrosion sediments demonstrate a“semiellipse”distribution,reinforced concrete members may easily suffer from reinforcement damages.In the case of“semiellipse+semicircle”and“circle”distributions,the cohesive force between the reinforcements and concrete decreases:With the same corrosion rate,the damaged area expands with the increase in the number of reinforcements,which indicates a reduction in the cohesive force and thus,a reduction in the damage in the reinforcement area.This paper analyzes in-depth the effects of reinforcement corrosion expansion on the concrete damage behavior,provides references for practical engineering.

一种基于领域自适应的跨工况滚动轴承故障诊断新方法

机械设备在运转时,不同状态下滚动轴承监测数据存在较大分布差异且难以获取带标签的数据,导致现有模型在跨工况条件下故障诊断准确率低.针对滚动轴承跨工况诊断难题,论文提出一种基于领域自适应的跨工况滚动轴承故障诊断方法,该方法首先提取振动信号故障敏感特征,并将其嵌入Grassmann流形空间,避免直接进行特征变换导致特征失真;其次利用动态分布对齐自适应调整源域和目标域分布差异,并通过增加类内散度正则化项最小化类内距离,增加类的可分性;最后,根据结构风险最小化原则建立域不变分类模型.在不同工况下的滚动轴承数据集上与现有方法进行了比较实验,结果表明论文提出的方法能有效提高分类准确率.

A macro-meso constitutive law for concrete having imperfect interface and nonlinear matrix

The overall behavior of concrete depends on its meso structures such as aggregate shape, interface status, and mortar matrix property. The two key meso structure characters of concrete, bond status of interface and nonlinear property of matrix, are considered in focus. The variational structure principle is adopted to establish the macro-meso constitutive law of concrete. Specially, a linear reference composite material is selected to make its effective behavior approach the nonlinear overall behavior of concrete. And the overall property of linear reference composite can be estimated by classical estimation method such as self-consistent estimates method and Mori-Tanaka method. This variational structure method involves an optimum problem ultimately. Finally, the macro-meso constitutive law of concrete is established by optimizing the shear modulus of matrix of the linear reference composite. By analyzing the constitutive relation of concrete established, we find that the brittleness of concrete stems from the imperfect interface and the shear dilation property of concrete comes from the micro holes contained in concrete.

Bond-associated non-ordinary state-based peridynamic model for multiple spalling simulation of concrete

The non-ordinary state-based peridynamic(NOSB PD)model has the capability of incorporating existing constitutive relationships in the classical continuum mechanics.In the present work,we first develop an NOSB PD model corresponding to the Johnson–Holmquist II(JH-2)constitutive damage model,which can describe the severe damage of concrete under intense impact compression.Besides,the numerical oscillation problem of the NOSB PD caused by zero-energy mode is analyzed and hence a bond-associated non-ordinary state-based peridynamic(BA-NOSB PD)model is adopted to remove the oscillation.Then,the elastic deformation of a three-dimensional bar is analyzed to verify the capability of BA-NOSB PD in eliminating the numerical oscillation.Furthermore,concrete spalling caused by the interaction of incident compression wave and reflected tension wave is simulated.The dynamic tensile fracture process of concrete multiple spalling is accurately reproduced for several examples according to the spalling number and spalling thickness analysis,illustrating the approach can well simulate and analyze the concrete spalling discontinuities.