基于腔体单元和Rebar单元的空气弹簧性能分析

建立了空气弹簧有限元离散模型,研究了空气弹簧内压-位移、容积-位移、最大外径-位移以及载荷-位移关系,仿真结果与实测结果对比表明,两者具有很好的一致性。研究了工作高度和帘线角度对空气弹簧承载能力、刚度特性以及空气弹簧在工作过程中直径变化的影响,结果表明空气弹簧的工作高度和帘线角度是影响空气弹簧性能的重要因素。

基于rebar单元的载重子午线轮胎模型建立及验证

运用ABAQUS非线性有限元分析软件并基于rebar单元建立12.00R20载重子午线轮胎有限元分析模型,同时进行装配、充气和静态加载仿真模拟分析。对比轮胎载荷-下沉量仿真模拟和试验结果,证明了模型建立的有效性。该模型有助于进一步分析轮胎的力学特性。

基于rebar单元的航空轮胎模型建立与分析

运用ABAQUS非线性有限元分析软件并基于rebar单元建立H44.5×16.5-21型航空轮胎有限元分析模型,同时进行装配、充气和静态加载仿真模拟分析。着重研究了二维轴对称模型充气后各部位产生的变形量、变形分布规律,获得了充气轮胎的断面和半径变化量。并分析了充气轮胎各层帘布和橡胶产生的应力和应变。证明了建模的有效性。

基于REBAR模型的空气弹簧有限元分析

利用 MARC非线性有限元分析软件建立空气弹簧有限元模型 ,帘线增强结构采用 REBAR单元 ,计算研究了胶囊基体和帘线增强各自的应力情况 ,分析了帘线材料参数对胶囊强度和刚度的影响。

基于Rebar实体单元的子午线轮胎加载过程模拟

利用MSC.Marc2000通用非线性有限元分析软件,用Rebar实体单元和Herrmann实体单元建立模型,仿真模拟分析215/45R17轿车子午线轮胎从安装轮辋到轮胎充气、加载和轮胎下沉全过程的情况。通过过程模拟,可以直观地观察轮胎各部位力学特性的分布及变化状况。计算结果与试验结果相近。

Explicit reinforcement models for fully-grouted rebar rock bolts

This paper investigates the explicit use of rock reinforcement in a discontinuous stress analysis model.A series of numerical experiments was undertaken to evaluate the performance of local and global reinforcement models implemented in universal distinct element code(UDEC).This was made possible by calibrating the reinforcement models to the laboratory behavior of a fully-grouted rebar bolt tested under pure pull and pure shear loading conditions.The model calibration focuses on matching different loading stages of the force-displacement curve including the initial elastic response,the hardening behavior and the bolt rupture.The paper concludes with a discussion on the suitability of the different reinforcement models in UDEC including their advantages and limitations.Finally,it addresses the choice of input parameters required for a realistic simulation of fully-grouted rebar bolts.

Bond strength improvement of GFRP rebars with different rib geometries

Based on the Canadian Standards Association (CSA) criteria,105 pullout specimens were tested to investigate the effect of different rib geometries on bond strength of glass fiber reinforced polymer (GFRP) rebars embedded in concrete. Two kinds of conventional reinforcing rebars were also studied for comparison. Each rebar was embedded in a 150 mm concrete cube,with the embedded length being four times the rebar diameter. The experimental parameters were the rebar type,rebar component,rebar diameter,rebar surface texture,rib height,rib spacing and rib width. Theoretical analysis was also carried out to explain the experimental phenomena and results. The experimental and theoretical results indicated that the bond strength of GFRP rebars was about 13%～35% lower than that of steel rebars. The bond strength and bond-slip behavior of the specially machined rebars varied with the rebar type,rebar diameter,rebar surface texture,rib height,rib spacing and rib width. Using the results,design recom-mendations were made concerning optimum rib geometries of GFRP ribbed rebars with superior bond-slip characteristics,which concluded that the optimal rib spacing of ribbed rebars is the same as the rebar diameter,and that the optimal rib height is 6% of the rebar diameter.

Mechanical behavior of segment rebar of shield tunnel in construction stage

In this paper, a 3D finite element （FE） program ADINA was applied to analyzing a tunnel with 9 segment tings. The loads acting on these segment tings included the squeezing action of tail brush of shield machine under attitude deflection, the jacking forces, the grouting pressure and the soil pressure. The analyses focused on the rebar stress in two statuses： （1） normal construction status without shield machine squeezing; （2） squeezing action induced by shield machine under attitude deflection. The analyses indicated that the rebar stress was evidently affected by the construction loads. In different construction status, the rebar stress ranges from -80 MPa to 50 MPa, and the rebar is in elastic status. Even some cracks appear on segments, the stress of segment rebar is still at a low level. It is helpful to incorporate a certain quantity of steel fiber to improve the anti-crack and shock resistance performance.

Electrochemical study on semiconductive properties of the passive film on rebar in concrete

The electrochemical behavior of metallic passive film on rebar in concrete is characterized by its semiconductive nature. The charge distribution at the interface between a semiconductor and an electrolyte is often determined by measuring the capacitance of the space-charge layer （Csc） as a function of the electrode potential （E）. When the space charge-layer serves as the depletion layer, the relation of Csc^-2 vs E resembles a Mott-Schottky plot （M-S plot）. The semiconductive properties of the passive film on rebar in concrete were analyzed with M-S plots to study the effect of chloride ions and mineral admixtures on rebar passive films. Some rebar electrodes were immersed in simulated concrete pore solutions, while others were embedded in concrete with/without mineral admixtures. In saturated Ca（OH）, solutions, the relation of Csc^-2-E of rebar electrodes shows linear MottSchottky relationship indicating that the passive film on rebar is a highly disordered n-type semiconductor, with donor density （ND） in the order of 10^26m^-3. After adding chloride ions （Cl wt%〈0.2%） in system solutions, the M-S plot slopes significantly decreased and ND increased, suggesting that chloride ion will cause passive film corrosion and breakdown. The M-S plots of the passive film on rebar electrodes embedded in concrete were similar to those immersed in simulated system solution. However, ND of those in concrete with mineral admixtures tended to be a little smaller, indicating that introducing proper quantity admixtures into concrete could make the rebar passive film have a thicker space-charge layer and therefore a thicker passive film layer.

Effect of Ca(OH)_2, NaCl, and Na_2SO_4 on the corrosion and electrochemical behavior of rebar

The corrosion of rebar in reinforced concrete in marine environments causes significant damage to structures built in ocean environments. Studies on the process and mechanism of corrosion of rebar in the presence of multiple ions may help to control damage and predict the service life of reinforced concrete structures in such environments. The effect of interactions between sulfate and chloride ions and calcium hydroxide on the electrochemical behavior ofrebar are also important for evaluation of structure durability. In this work, electrochemical impedance spectroscopy （EIS） plots of rebar in Ca（OH）2 solution and cement grout, including NaC1 and Na2SO4 as aggressive salts, were measured for different immersion times. The results show that corrosion of rebar was controlled by the rate of charge transfer as the rebar was exposed to chloride solution. In the presence of high concentrations of sulfate ions in the electrolyte, generation and dissolution of the passive film proceeded simultaneously and corrosion was mainly controlled by the diffusion rate. When Na2SO4 and NaC1 were added to Ca（OH）2 solution, the instantaneous corrosion rate decreased by a factor of 10 to 20 as a result of the higher pH of the corroding solution.

Effects of Deformation Conditions on Dynamic Recrystallization of a Nb Microalloyed Anti-seismic Rebar

The hot deformation behavior of a Nb microalloyed anti-seismic rebar was investigated at deformation temperatures of 950-1 100 ℃ and strain rates of 0. 01-0. 1 s- 1 on a Gleeble-3800 thermo-mechnical simulator. The flow stress-strain curves show the typical dynamic recrystallization with a peak,before reaching the steady state flow at higher deformation temperatures and lower strain rates. The constitutive equation governing the dynamic recrystallization( DRX) was obtained and the average activation energy of deformation was calculated as Q = 389. 5 kJ / mol by the regression analysis. The DRX grain size was also found to decrease with the increasing strain rate and the decreasing deformation temperature. The austenite grain size was refined from 118. 0 μm to 15. 07-40. 01 μm by DRX. The DRX grain size under diverse deformation conditions predicted by mathematical model agrees well with experimental results.

Improvement to anti-rust property of hot rolled rebar by compact oxide scale

A method was proposed to improve the anti-rust property of hot rolled rebar, which uses oil–water emulsion cooling instead of water cooling after hot rolling. The experiments were carried out by two cooling methods, one cooled by water, the other cooled by oil–water emulsion. The results of wet/dry cyclic accelerated corrosion test showed that the anti-rust property of rebar cooled by oil–water emulsion was better than that by water obviously. The results of OM, SEM and EPMA analysis indicated that these two scales contained three layers: an outer Fe_3O_4 layer, an intermediate Fe O layer with island-shaped pro-eutectoid Fe_3O_4, an inner eutectoid Fe_3O_4 layer. For the water cooled rebar, all three layers of oxide scale were relatively thin. Moreover, the scale had plenty of defects such as porosity, and crack. However, for the oil–water emulsion cooled rebar, all three layers of oxide scale were relatively thick and compact, which played an important role in protecting the rebar from atmospheric rust.

Experimental research on bond strength of deformed GFRP rebars with different surface configurations

Based on the Canadian Standards Association(CSA) criterion,experiments on 30 pull-out specimens were conducted to study the bond strength of deformed GFRP rebars with 8 different surface configurations.Each rebar was embedded in a 150 mm concrete cube,and the test embedded length was four times of the rebar diameter.Relationship between the mode of failure,the average bond strength and the average bond strength-slip for each rebar was analyzed.Results show that the failure mode of all specimens is the shearing off or desquamation of ribs,no splitting cracks appear on the cube specimens.The bond stress of deformed GFRP rebars mainly depends on the mechanical interaction between the ribs of the bar and the surrounding concrete,and the bond strength of deformed GFRP rebars is improved obviously.The optimal rib spacing is less than 2.5 times of the rebar diameter,and the rib height is more than 3% of the rebar diameter.

基于RebarSmart的廊道结构数字化钢筋设计

RebarSmart是成都勘测设计研究院有限公司基于CATIA平台开发的混凝土结构钢筋数字化设计软件,可用于电水利工程的配筋设计,具有直观准确的优点。文章以某水电工程的基础廊道为例,介绍了三维钢筋软件RebarSmart在水电工程中的应用。

Effect of temperature on the passivation behavior of steel rebar

Steel rebar normally forms an oxide or rusty skin before it is embedded into concrete and the passivation properties of this skin will be heavily influenced by temperature. To study the effect of temperature on the passivation properties of steel rebar under different surface conditions, we conducted scanning electron microscopy （SEM） observations and electrochemical measurements, such as measurements of the free corrosion potential and polarization curves of HPB235 steel rebar. These measurements identified three kinds of surfaces： polished, oxide skin, and rusty skin. Our results show that the passivation properties of all the surface types decrease with the increase of temperature. Temperature has the greatest effect on the rusty-skin rebar and least effect on the polished steel rebar, because of cracks and crevices on the mill scale on the steel rebar＇s surface. The rusty-skin rebar exhibits the highest corrosion rate because crevice corrosion can accelerate the corrosion of the steel rehar, particularly at high temperature. The results also indicate that the threshold temperatures of passivation for the oxide-skin rebar and the rusty-skin rebar are 37℃and 20℃, respectively.

STUDY ON CORROSION RESISTANCE OF REBAR IN HYBRID GRINDING FLY ASH -LIME SILICATE CONCRETE

The corrosion resistance of rebar in fly ash-lime silicate concrete as well as its macro properties and pore distribution is investigated. The results show that the fly ash is activated, the compressive strength of the silicate concrete is strengthened and its pore structure is modified after fly ash and lime being hybrid ground. Also the corrosion resistance of rebar in the silicate concrete is improved. (Author abstract) 3 Refs.

Tensile Fracture Mechanism of Claviform Hybrid Composite Rebar

Based on the shear-lag theory, a hexagonal model of fiber bundles was established to study the tensile fracture mechanism of a claviform hybrid composite rebar. Firstly, the stress redistributions are investigated on two conditions： one condition is that interfacial damage is taken into account and the other is not. Then, a micro-statistical analysis of the multiple tensile failures of the rebar was performed by using the random critical-core theory. The results indicate that the predictions of the tensile failure strains of the rebar, in which the interfacial damage is taken into account, are in better agreement with the existing experimental results than those when only elastic case is considered. Through the comparison between the theoretical and experimental results, the shear-lag theory and the model are verified feasibly in studying the claviform hybrid composite rebar.

Effect of Chromium Micro-alloying on the Corrosion Behavior of a Low-carbon Steel Rebar in Simulated Concrete Pore Solutions

A new low-cost corrosion-resistant rebar（HRB400 R） was designed and fabricated by chromium micro-alloying. The effects of Cr on the passivation and corrosion behavior of this rebar in the simulated concrete pore solutions were studied systematically, and its improved corrosion resistance was revealed. In the Cl--free saturated Ca（OH）_2 solution, the HRB400 R rebar presented nearly the same passive film and similar passivation ability compared to the common carbon steel rebar. In the long-term immersion corrosion test in the Cl--contained Ca（OH）_2 solution, the HRB400 R rebar presented improved corrosion resistance and obvious longer passivation-maintaining period. Micro-alloying of Cr element in the rebar matrix enhanced its corrosion resistance against Cl--attack and retarded the corrosion initiation in the matrix. In the alkaline Na Cl salt spraying test, the HRB400 R rebar also presented obviously lower mass-loss rate. The enrichment of Cr element in the rust layer improved its retardant effect to the penetration of aggressive medium, and decreased the corrosion propagation rate of the rebar.

Strengthening of High Strength Rebars

The influence of alloying elements and cooling conditions after rolling on the microstructures and mechanical properties of a series of medium carbon Si-Mn-Mo-V high-strength precision-formed rebars were investigated.It is found that steel with combined addition of Mo and V appears to be the most promising one than those containing V and Nb or containing V alone under the same pro- cessing conditions.From CCT curve of the steel and the cooling curve of the bar determined by sim- ulating the cooling rate in mill practice,the reason why 40Si2MnMoV bar has excellent combination of strength and ductility is clarified.

Chest, pericardium, abdomen, and thigh penetrating injury by a steel rebar: A case report

BACKGROUND Combined penetrating trauma involving the chest, pericardium, abdomen, and thigh is rare and lethal. It is difficult to quickly rescue patients with penetrating injuries from long steel bars.CASE SUMMARY A previously healthy 56-year-old male worker presented with a length of rebar that penetrated the chest-abdomen-pelvic cavity and was palpable on the anterior side of the neck and thigh. On radiological imaging, the left chest wall-left chest cavity-mediastinum-abdominal cavity-right groin area-right thigh demonstrated a strip-like density shadow, about 1.5 cm thick, with the heart, stomach wall, and part of the intestine involved. There was a left-sided pleural effusion, left lung compression of about 50%-60%, and a small amount of left pleural effusion/blood accumulation;possible perforation of hollow organs;and double multiple ribs fractures on the side. An emergency green channel was opened to provide a rescue process for smooth and timely diagnostic and treatment to save the patient's life. The patient was followed at 4 mo after discharge and showed good recovery.CONCLUSION For pre-hospital emergency treatment in locations that are not fully prepared for surgery, we do not recommend cutting the steel bars outside the body. We advocate pulling out foreign bodies intact to reduce secondary injuries.