Evaluation of Fracture Process Zone in the Flexural Response of Different Concrete Materials Using DIC Method

Shengtao Li,Xudong Chen,Shengshan Guo 대한토목학회 2020 KSCE JOURNAL OF CIVIL ENGINEERING Vol.24 No.8

In the present paper, a digital image correlation (DIC) method is used to study the development of fracture process zones (FPZ) of different concrete materials in three-point bending test. Different concrete materials including original concrete, rubber concrete, self-compacting rubber concrete and pervious concrete are investigated. Firstly, the image of the FPZ and the crack opening displacement (COD) in FPZ is obtained by acquiring strain field and displacement field information. The relationship between the development of FPZ and the mechanical properties is further studied. It is found that there is a strong correlation between the FPZ and the post-peak strength reduction of concrete. The development characteristics of FPZ of different concrete materials are analyzed. The addition of rubber will result in stronger strain concentration in pre-peak stage compared to original concrete, and the FPZ will emerges at the earlier loading stage, but it can enhance the crack resistance of concrete in the post-peak stage. Self-compacting rubber concrete was observed to have higher bearing capacity and cracking resistance during fracture than that of the others. Pervious concrete has weak resistance to fracture, and there is almost no decline of the FPZ development rate in fracture process.

Robust Control for a Class of T-S Fuzzy Systems with Interval Time-varying Delay

Shengtao Li,Yuanwei Jing,Xiaomei Liu 제어·로봇·시스템학회 2012 International Journal of Control, Automation, and Vol.10 No.4

The problem of delay-dependent stability analysis and controller design for a class of T-S fuzzy systems with interval state time-varying delay is considered. Based on Lyapunov stability theory, defining a new Lyapunov-Krasovskii functional and introducing some free-weighting matrices, a new delay-dependent criterion is given to ensure the systems asymptotically stable. The merit of the pro-posed conditions lies in the less conservativeness than the existing ones, which is achieved by consid-ering the mean of time-delay interval and the introduction of the free variables. By the concept of par-allel distributed compensation (PDC), a delay-dependent condition for the existence of a fuzzy state feedback control law with memory is proposed. Another merit is the consideration of the memory of the controller. All conditions are shown in terms of linear matrix inequalities (LMIs), which can be solved efficiently by using the LMI optimization techniques. Two numerical examples are given to il-lustrate the feasibility and validity of the proposed approach.

Experimental Study of Evolution of Fracture Process Zone in Dam Concrete under Cyclic Loading Using Digital Image Correlation

Xudong Chen,Shengtao Li,Xiyuan Cheng 대한토목학회 2022 KSCE JOURNAL OF CIVIL ENGINEERING Vol.26 No.2

In this paper, three-point bending tests were carried out o investigate the post-peak cyclic loading behavior of dam concrete under two loading rates. The fracture parameters, residual load capacity, cyclic modulus, dissipated energy, and deformation recovery were presented and analyzed. The analysis was made to understand the evolution of fracture process zone (FPZ) under post-peak cyclic loading for dam concrete by utilizing digital image correlation (DIC) technique. The results showed while the dam concrete under a higher loading rate showed an increase in maximum load, it is not necessarily the same for post-peak bearing capacity. The specimens with higher post-peak bearing capacity had higher residual stiffness, higher dissipation energy, and higher Crack Mouth Opening Displacement (CMOD) reversibility under cyclic loading. The FPZ development was investigated quantitatively, and the extension and retraction of its tip were observed. Moreover, it was found that the FPZ in specimens with higher residual stiffness developed more slowly, and FPZ had a more significant retraction rate during unloading for the specimens with higher residual bearing capacity.

Effects of Grain Boundary on {100} Recrystallization Texture of High Silicon Electrical Steel

Hongjiang Pan,Li Xiang,Shengtao Qiu 대한금속·재료학회 2018 METALS AND MATERIALS International Vol.24 No.1

In this study, high silicon electrical steel (Fe-6.5 wt% Si alloy) as-cast ingot with columnar grains was prepared bydirectional solidification. Additionally, equiaxed-grained samples with different initial grain sizes were fabricatedby casting, rolling and annealing at different temperatures. The deformation band, dislocation morphology andrecrystallization texture of these samples during subsequent rolling and annealing were investigated. The effects ofinitial grain boundary directions of columnar-grained samples and initial grain sizes (grain boundary densities) ofequiaxed-grained samples on the {100} recrystallization texture of high silicon electrical steel were analyzed. Theresults showed that the grain boundaries played an important role in the formation of the {100} recrystallizationtexture. Due to a low dislocation density (low deformation stored energy) after rolling, the samples without grainboundaries parallel to transverse direction (e.g. rolling along the axis of the columnar grains) or with small grainboundary densities (e.g. large initial grain sizes) were favorable to the formation of a {100} recrystallization textureduring annealing.

Experimental and theoretical studies on inhibition performance of Cu corrosion in 0.5 M H2SO4 by three disulfide derivatives

Bochuan Tan,Shengtao Zhang,Wenpo Li,Xiuli Zuo,Yujie Qiang,Lihui Xu,Jiangyu Hao,Shijin Chen 한국공업화학회 2019 Journal of Industrial and Engineering Chemistry Vol.77 No.-

Phenyl disulfide (PDF), 2,20-dithiodipyridine (DDP), 5,5-dithiobis(1-phenyl-1H-tetrazole) (DPT) werestudied as inhibitors for Cu in H2SO4 via electrochemical methods, surface morphology analysis andtheoretical calculations. Electrochemical experiments show that PDF, DDP and DPT can exhibit excellentcorrosion inhibition performance. Their order of corrosion inhibition is DPT > DDP > PDF. Surfacemorphology analysis supports the electrochemical results. The X-ray photoelectron spectroscopy (XPS)results show that S Cu bonds are detected in PDF, DDP and DPT, and N Cu bonds are detected in DDPand DPT. PDF, DDP and DPT adsorption on the Cu surface obey the Langmuir isotherm model. The resultsof quantum chemical calculations show that DPT has more active reaction sites than DDP and PDF. Molecular dynamics simulation results show that the order of binding energies of the three corrosioninhibitor molecules on the copper surface is DPT > DDP > PDF.

Experimental Study and Analytical Modeling on Fatigue Properties of Pervious Concrete Made with Natural and Recycled Aggregates

Xudong Chen,Dandan Shi,Nan Shen,Shengtao Li,Saisai Liu 한국콘크리트학회 2019 International Journal of Concrete Structures and M Vol.13 No.1

As a solid pollutant, the recycled aggregate can be reused to replace the natural aggregate to cast pervious concrete, promoting resource recycling and reducing environmental pollution. Pervious concrete is usually applied to transportation engineering as pavements and decks, which are often subjected to fatigue loads in service. Therefore, it is essential to investigate the fatigue mechanical properties of pervious concrete. In this study, four-point cyclic bending loading test of natural aggregate pervious concrete and recycled aggregate pervious concrete were conducted under four different stress levels. By analyzing the experimental results, the mechanical performances, including hysteresis curve characteristics, damping ratio, dynamic elastic modulus and cyclic strain, of two kinds of pervious concrete under cyclic loading were revealed. Based on the improved EPF model, the relationship between fracture parameters, plastic strain and unloading strain were obtained. Besides, the relationship between the loading cycles and the ratio of plastic strain to unloading strain was received according to fatigue testing data under different stress levels. Further, the simplified fatigue model of pervious concrete was proposed and the experimental data was fitted with the model results. The fitting result reached a good agreement.

Experimental study on the dynamic behavior of pervious concrete for permeable pavement

Jingwu Bu,Xudong Chen,Saisai Liu,Shengtao Li,Nan Shen 사단법인 한국계산역학회 2018 Computers and Concrete, An International Journal Vol.22 No.3

As the concept of “sponge city” is proposed, the pervious concrete for permeable pavement has been widely used in pavement construction. This paper aims at investigating the dynamic behavior and energy evolution of pervious concrete under impact loading. The dynamic compression and split tests are performed on pervious concrete by using split Hopkinson pressure bar equipment. The failure criterion on the basis of incubation time concept is used to analyze the dynamic failure. It is demonstrated that the pervious concrete is of a strain rate sensitive material. Under high strain rate loading, the dynamic strength increases while the time to failure approximately decreases linearly as the strain rate increases. The predicted dynamic compressive and split tensile strengths based on the failure criterion are in accordance with the experimental results. The total damage energy is found to increase with the increasing of strain rate, which means that more energy is needed to produce irreversible damage as loading rate increases. The fractal dimensions are observed increases with the increasing of impact loading rate.

Optimal Timing Control of Discrete-Time Linear Switched Stochastic Systems

Xiaomei Liu,Kanjian Zhang,Shumin Fei,Haikun Wei,Shengtao Li 제어·로봇·시스템학회 2014 International Journal of Control, Automation, and Vol.12 No.4

Optimal switch-time control is the study that investigates how best to switch between different modes. In this paper, we investigate the optimal switch-time control problem for discrete-time linear switched stochastic systems. In particular, under the assumption that the sequence of active subsystems is pre-specified, we focus on the problem where the objective is to minimize a cost functional defined on the states and the switching times are the only control variables. For systems with one switching time, using calculus of variations, we firstly derive the difference formulae of the cost functional with respect to the switching time, which can be directly used to find the optimal switching instant. Then, a method is presented to deal with the problem with multiple switching times case. Finally, the viability of the proposed method is illustrated through two numerical examples.