用湿摩擦值法评价Lyocell纤维原纤化程度

从Lyocell纤维在湿态下受到摩擦应力时的变化 ,阐述了用湿摩擦值表征原纤化程度的可能性。根据原纤化产生的条件 ,自行设计了测定原纤化程度的设备。通过对诸如包绕用布、湿度、磨辊的平稳度等影响因素的控制 ,可以得到重复性较高的测定结果。基于实验得出的丝束纤度对湿摩擦值影响呈线性关系 ,提出了合理简便的制样方案。

聚四氟乙烯支座滑动摩擦值的安全系数

六十年代中期以来安装了大量(聚四氟乙烯、合成橡胶和特殊钢)的支座,越来越多地被使用,但最初评定聚四氟乙烯滑动摩擦值试验,忽略了摩擦值随着桥梁运营次数增加而增大的因素。从设计观点看,采用聚四氟乙烯支座,其滑动摩阻系数应具有充分的安全系数。

路面抗滑值测定方法对比及相关关系分析

通过对摆式仪法和双轮式横向力摩擦系数测试车观测法进行对比分析,力求回归分析BPN和SFC测试结果的相关性、建立两种试验方法间的换算公式,从而指导实际施工中两种观测结果的有效结合和换算。

不同密度原棉滑动摩擦分析

为了研究原棉摩擦力变化规律,以原棉为原料,利用提拉装置夹持原棉,数显推拉力计采集原棉与亚克力筒的摩擦力值,分析不同密度、不同接触面积以及不同电机频率条件下原棉与筒壁的摩擦力变化。

具有非单调摩擦热弹性接触问题的有限元法

给出了一个变形体和刚性基础之间用双边摩擦表达其接触性质的、静态热弹性问题的方程式及其近似解法.以非单调、多值性表示该摩擦定律.忽略了问题的耦合效应,则问题的传热部分与弹性部分各自独立处理.位移矢量公式化为非凸的次静态问题,用局部Lipschitz连续函数来表示变形体的总势能.用有限单元法近似求解全部问题.

交联处理对Lyocell纤维抗原纤化性能的影响

对尚未干燥过的初生Lyocell纤维进行交联处理,并分析了各种交联条件下所制得的Lyocell纤维的原纤化性能。研究结果表明,交联剂的浓度及浸润时间、碱剂的浓度及处理时间都会对控制最终纤维的原纤化程度产生一定的影响。在研究范围内,当交联剂的体积质量浓度为40g/L、浸润时间为40min,且碱剂的体积质量浓度为30g/L、处理时间为30min时,最终所得Lyocell纤维的抗原纤化能力比未处理的普通Lyocell纤维提高了约7倍,由此表明交联处理是提高Lyocell纤维抗原纤化性能的一种有效途径。对纤维微观结构的分析结果进一步表明,经交联处理后,Lyocell纤维的基纤及基纤聚集束的尺寸减少且含量增加,这是导致纤维抗原纤化能力提高的关键结构原因。

TAHT交联对Lyocell纤维抗原纤化性能的影响

采用1,3,5-三丙烯酰基-六氢化-1,3,5-三嗪(TAHT)交联后处理的方法提高Lyocell纤维的抗原纤化性能;用湿摩擦值表征纤维的抗原纤化能力,研究了TAHT交联条件对Lyocell纤维抗原纤化能力及力学性能的影响规律。结果表明:最佳实验条件为采用交联剂和催化剂分别溶解、共同浸渍纤维的方法,TAHT质量浓度30 g/L,交联温度70℃,浸渍时间3 min,汽蒸时间3 min,磷酸三钠质量浓度20 g/L;改性后的Lyo-cell纤维抗原纤化能力提高100倍以上,断裂强度下降18%;红外光谱表明Lyocell纤维与TAHT发生了迈克尔加成反应,生成二次价键,使纤维的抗原纤化能力明显提高。

非极限状态挡土墙土压力计算

在考虑摩擦角发挥值与墙体位移关系的基础上,利用薄层单元法对未达到极限状态的挡土墙非极限状态主动土压力进行研究。取挡土墙后滑动楔体沿平行于填料坡面的水平薄层作为微分单元体,通过作用在水平薄层的力和滑动楔体力矩平衡条件,建立关于一般挡土墙非极限状态主动土压力的微分方程,得到非极限状态土侧压力系数、土压力强度、土压力合力和作用点的理论公式。对墙土摩擦角发挥值和填土内摩擦角发挥值进行讨论,并分析填土内摩擦角和挡土墙位移比对土侧压力系数、土压力分布和作用点的影响。对计算值与实测模型试验值进行对比分析。研究结果表明,采用库仑理论计算平动刚性挡土墙倾覆力矩偏于不安全。本文方法计算主动土压力结果与实测值的变化规律基本一致,主动土压力分布曲线吻合良好,具有一定的理论意义和工程实用价值。

罕遇地震下自复位钢框架抗震性能参数分析

分析研究对梁腹板带有摩擦阻尼器的自复位钢框架结构抗震性能起主要影响作用的钢绞线初始预应力值和摩擦阻尼器的摩擦力值这两项参数。首先,采用ABAQUS有限元软件的连接单元法建立结构分析模型。然后,对结构分析模型的计算参数进行取值。最后,分析了预应力钢绞线的初始预应力值和摩擦阻尼器的摩擦力值这两项参数对自复位钢框架结构抗震性能的影响。

Visualization and simulation of plastic material flow in friction stir welding of 2024 aluminium alloy plates

Thin copper sheets as marker material were embedded into weld path of 2024 aluminium alloy plates and their final position after friction stir welding was examined by metallographic techniques. Referring to the visualized material flow patterns, a three-dimensional model was developed to conduct the numerical simulation of the temperature profile and plastic material flow in friction stir welding. The calculated velocity contour of plastic flow in close proximity of the tool is generally consistent with the visualized results. As the tool rotation speed increases at a constant tool travel speed, the material flow near the pin gets stronger. The predicted shape and size of the weld nugget zone match with the experimentally measured ones.

浅谈乳化沥青稀浆封层在砂石路中的应用

本文概述了在砂石路上铺洒乳化沥青稀浆封层的施工工艺及封层材料的有关要求。实施效果较好。是改善砂石路面的有效途径。

Numerical simulation of friction stir butt-welding of 6061 aluminum alloy

A two-dimensional computational fluid dynamics model was established to simulate the friction stir butt-welding of 6061 aluminum alloy. The dynamic mesh method was applied in this model to make the tool move forward and rotate in a manner similar to a real tool, and the calculated volumetric source of energy was loaded to establish a similar thermal environment to that used in the experiment. Besides, a small piece of zinc stock was embedded into the workpiece as a trace element. Temperature fields and vector plots were determined using a finite volume method, which was indirectly verified by traditional metallography. The simulation result indicated that the temperature distribution was asymmetric but had a similar tendency on the two sides of the welding line. The maximum temperature on the advancing side was approximately 10 K higher than that on the retreating side. Furthermore, the precise process of material flow behavior in combination with streamtraces was demonstrated by contour maps of the phases. Under the shearing force and forward extrusion pressure, material located in front of the tool tended to move along the tangent direction of the rotating tool. Notably, three whirlpools formed under a special pressure environment around the tool, resulting in a uniform composition distribution.

Frictional heat analysis of mine hoist and numerical simulation on temperature field of gasket

The frictional performance of gaskets is greatly affected by frictional heat in operational mine hoists. Based on frictional mechanism and heat transfer theory, the mathematical model of the temperature field of the PVC gasket in an operational mine hoist was investigated, a numerical simulation using ANSYS is presented and the distribution of the temperature and heat flux were studied under basic assumptions. The results show that the temperature gradually decreases as the radius of the model increases and the isotherms are arcs of concentric semi-circle. The heat flux is of bilateral symmetry in the model and decreases radially. The theoretical values correspond with the measured values for a short time (τ≤ 100 s) when the steel wire rope slides.

Frictional contact algorithm study on the numerical simulation of large deformations in deep soft rock tunnels

There exist three types of nonlinear problems in large deformation processes of deep softrock engineering, i.e., nonlin- earity caused by material, geometrical and contact boundary. In this paper, the numerical method to tackle the nonlinear eontact and large deformation problem in A Software on Large Deformation Analysis for Soft Rock Engineering at Great Depth was presented. In the software, based on Lagrange multiplier method and Coulomb friction law, kinematic constraints on contact boundaries were introduced in functional function, and the finite element equations was established for two incremental large deformation analyses models, polar decomposition model and additive decomposition model. For every incremental loading step, by searching for the contact points in the potential contact interfaces （the excavation boundaries）, the Lagrange multipliers, i.e., contact forces are cal- culated iteratively by Gauss-Seidel method, and justified through satisfy the inequalities of static constraint on contact boundaries. With the software, large deformation and frictional contact of a transport roadway were analyzed numerically by the two models. The numerical examples demonstrated the efficiency of the method used in the software.

Heat transfer and friction factor of Therminol liquid phase heat transfer fluid in a ribbed tube

Experiments and simulations on flow and heat transfer behavior of Therminol-55 liquid phase heat transfer fluid have been conducted in a ribbed tube with the outer diameter and inner diameter 25.0 and 20.0 mm,pitch and rib height of 4.5 and 1.0 mm.respectively.Experimental results show that the heat transfer and thermal performance of Therminol-55 liquid phase heat transfer fluid in the ribbed tube are considerably improved compared to those of the smooth tube.The Nusselt number increase with the increase of Reynolds number.The increase in heat transfer rate of the ribbed tube has a mean value of 2.24 times.Also,the pressure drop results reveal that the average friction factor of the ribbed tube is in a range of 2.4 and 2.8 times over the smooth tube.Numerical simulations of three-dimensional flow behavior of Therminol-55 liquid phase heat transfer fluid are carried out using three different turbulence models in the ribbed tube.The numerical results show that the heat transfer of ribbed tube is improved because vortices are generated behind ribs,which produce some disruptions to fluid flow and enhance heat transfer compared with smooth tube.The numerical results prove that the ribbed tube can improve heat transfer and fluid flow performances of Therminol liquid phase heat transfer fluid.

Enhanced heat transfer in a heat exchanger square-duct with discrete V-finned tape inserts

The article presents an experimental and numerical study on thermal performance enhancement in a constant heatfluxed square-duct inserted diagonally with 45° discrete V-finned tapes(DFT).The experiments were carried out by varying the airflow rate through the tested square duct with DFT inserts for Reynolds number from 4000 to 25000.The effect of the DFT with V-tip pointing upstream at various relative fin heights and pitches on heat transfer and pressure drop characteristics was experimentally investigated.Both the heat transfer and pressure drop were presented in terms of Nusselt number and friction factor respectively.Several V-finned tape characteristics were introduced such as fin- to duct-height ratio or blockage ratio(R_B=e/H = 0.075,0.1,0.15 and 0.2),fin pitch to duct height ratio(R_P= P/H=0.5,1.0,1.5 and 2.0) and fin attack angle,α = 45°.The experimental results reveal that the heat transfer and friction factor values with DFT inserts increase with the increment of R_B but the decrease of R_P.The inserted square-duct at R_B = 0.2 and R_P = 0.5 provides the highest heat transfer and friction factor while the one with R_B= 0.1 and R_P= 1.5 yields the highest thermal performance.Also,a numerical simulation was conducted to investigate the flow structure and heat transfer mechanism inside the tested duct with DFT inserts.

Study for reasonable value of friction coefficient between main cable and saddle

The value of friction coefficient between the main cable and saddle, relates to not only the anti-slippage stability of three-tower suspension bridge, but also the reasonable stiffness of the middle tower and the magnitude of rigidity of the whole bridge. First, the paper does some comparative studies about the relevant provisions of international norms, and then, summarizes the relevant load test results both at home and abroad. Finally, the paper draws the appropriate anti-slippage safety factor for the most unfavorable load in accordance with international load standards, and discusses the rationality and feasibility of the friction coefficient of 0.2 between main cable and saddle.

Seismic Performance of Dry-Friction Devices in Shear-Frame Buildings

In recent years the application of friction-based passive energy dissipation devices have been proven very effective in reducing structural response to earthquake excitations and also implemented for a large number of buildings. Their design heavily relies on numerical simulations to model the influence of the energy dissipation devices. The modeling of friction forces must be accurate for realistic simulation of the influence of these devices. In state-of-the-practice, the hysteretic behavior of friction devices has been typically modeled with Coulomb friction having a constant coefficient of friction. However, the basic laws for typical sliding materials and experimental investigations show non-linear relationship between friction and sliding velocity, which includes stiction and Stribeck effect. The influence of stiction and Stribeck effect may be significant and can not be ignored in simulating the dynamic responses of structures with friction-based energy dissipation devices. In this paper the optimal performance of dry friction device in shear-frame buildings when subjected to earthquake ground motions has been investigated. The focus of this paper is on the optimal minimization of response of the shear-frame building. Since buildings with friction devices behave in a highly nonlinear manner, nonlinear response-history analysis considering comprehensive sliding friction models has been carried out. The performance has also been evaluated using the various response measures： the maximum absolute acceleration, the maximum base shear, and the maximum inter-story drift. Different performance indices have been used to quantify the influence of the device properties.

Turbulence Model Investigations on the Boundary Layer Flow with Adverse Pressure Gradients

In this paper, a numerical study of flow in the turbulence boundary layer with adverse and pressure gradients （APGs） is conducted by using Reynolds-averaged Navier-Stokes （RANS） equations. This research chooses six typical turbulence models, which are critical to the computing precision, and to evaluating the issue of APGs. Local frictional resistance coefficient is compared between numerical and experimental results. The same comparisons of dimensionless averaged velocity profiles are also performed. It is found that results generated by Wilcox （2006） k-co are most close to the experimental data. Meanwhile, turbulent quantities such as turbulent kinetic energy and Reynolds-stress are also studied.