线接触往复运动中不同运动频率对弹流润滑特性的影响

在冲击加载条件下,应用数值分析方法,分析了线接触往复运动工况下不同的运动频率对热弹性流体动力润滑的影响.加载方式为正弦加载,行程长度为2mm.通过对计算结果的分析,发现随着往复运动中冲程频率的增加,一个周期相同瞬时的卷吸速度增加,因此油膜厚度变大,温升明显,而摩擦因数明显降低.     

表面划痕对滚子副润滑状态的影响

基于试验中观察到的滚子表面划痕现象,采用数值方法研究了不同供油条件下,划痕对滚子副润滑性能的影响,并与已有试验进行了比较,讨论了划痕长度和深度的影响.结果表明,划痕会影响滚子副的油膜压力和厚度,使得划痕中心油膜压力减小,膜厚增加;同时,划痕边缘处油膜压力增大,膜厚减小.供油层厚度越小,即乏油程度越严重,划痕边缘处的油膜压力及其梯度越大,膜厚越小.划痕越长,划痕越深,划痕中心的油膜压力越低,而膜厚越大.因此,划痕虽增大了滚子副划痕中心的膜厚,降低其压力,但同时增大了划痕附近的压力,减小了膜厚,在乏油条件下尤其如此,因此,划痕会加速滚子副的局部磨损.     

线接触热弹流润滑膜的最小膜厚公式

本文使用Ree-Eyring流变模型来描述润滑油的非牛顿性质,求得了关于线接触热弹流润滑问题的百余组完全数值解.结果显示,接触曲率半径对油膜有重要影响,但润滑剂的流变性质在大滑滚比中轻载工况下对油膜的影响不大,条件是在分析中使用准确的粘压粘温关系式.本文系统地考察了载荷、卷吸速度、滑滚比、综合曲率半径等参数对线接触热弹流润滑膜的压力分布、温度分布、摩擦系数和油膜厚度的影响,提出了最小膜厚的新公式.     

渐开线直齿轮弹流润滑数值分析及摩擦系数的研究

高速重载齿轮的载荷变化范围大,齿间润滑对其啮合过程的影响较大,包括在啮合过程中油膜厚度和油膜压力等因素,但在分析时其数值计算的难度也很大,为了提高计算的稳定性,本文采用多重网格法来求其数值解,得出了一对齿瞬时接触区的油膜厚度和油膜压力分布,并通过进一步计算,得出了一个啮合周期内的最小油膜厚度。摩擦系数是齿轮传动的重要参数,对齿轮的啮合效率有重要影响,本文结合弹流润滑理论,得出一个周期内摩擦系数的数值解,并考虑了转速的影响,得出了在不同转速下的摩擦系数曲线。     

定制边界滑移平行轴承的挤压效应(英文)

作者最近提出了一种利用滑块入口处的壁面滑移产生流体动压的新型轴承.笔者针对该类新轴承的油膜挤压问题,提出了基于滑移临界剪应力的数学模型,并给出了解析解.结果显示压力分布为分段光滑的抛物线,在滑移/非滑移边界,存在不连续的压力梯度.不同参数条件下的计算给出了不同的压力分布和壁面滑移类型.结果显示,对于代表滑块非浸润区长度的参数xt,最大压力并不总是随参数xt的减小而减小.存在一个参数xt的区间,在该区间内最大压力不变.与经典的挤压膜轴承类似,压力随膜厚的增加或趋进速度的减小而减小.笔者还发现临界剪应力的对挤压效应有重要的影响,揭示了此类新型轴承的一些内在的特性.     

陶瓷球-盘点接触弹流润滑的试验研究

工业发展对材料的要求越来越高.陶瓷材料由于其优良的机械性能得到了广泛应用.为研究陶瓷材料的润滑性能,采用光干涉技术测得了纯滚动工况下陶瓷球与玻璃盘间形成的点接触副油膜形状和厚度,讨论了卷吸速度、外载荷、润滑剂等的影响,并将陶瓷球与钢球的结果进行了比较.试验结果表明,速度、载荷和润滑剂对油膜形状和厚度均有影响.在相同条件下,陶瓷球的膜厚小于钢球,故陶瓷接触副的润滑特性并不比钢球接触副优越.     

气承式充气膜结构初始形态下索膜接触分析

以半椭球形充气膜结构为例,运用通用有限元程序ANSYS,通过改变初始形态下内压、摩擦系数、膜厚,对气承式充气膜结构的初始形态进行索膜接触分析,同时将接触模型与共节点模型进行了对比分析.分析结果表明:索可以等效为边界约束,使得结构刚度增大,增强了结构的整体稳定性;合理的内压可以使索与膜面获得比较均匀的预应力;摩擦系数对膜材的选择具有一定的参考价值;膜厚对接触分析各结果的影响不同,在膜结构设计时应予以考虑;接触模型比共节点模型更合理.     

页岩气超高压往复泵工作腔压力测试与分析

以用于页岩气水平井压裂的超高压往复泵为研究对象,为探索提高泵工作性能及可靠性的解决思路,开展了泵工作腔内压力变化规律及基本特征的分析研究。根据力学基础理论,定性地分析了泵阀开启、关闭时刻点的工作腔内压力变化。搭建了全尺寸超高压往复泵工作腔压力测试台架,获得了4种柱塞冲次和5种排出管汇压力下的泵腔压力变化曲线。实验结果表明,排液冲程中柱塞冲次和排出管汇压力对工作腔压力降低的滞后时间具有显著影响,工作腔压力在临近峰值的高压区间内会产生"M"型压力冲击特征,对此特征的分析将为进一步分析阀箱内壁疲劳失效原因、优化泵阀运动机理提供解决思路及实验依据。     

火灾高温下耐火保护钢梁设计荷载的分析

研究了火灾高温环境下耐火保护钢梁温度和结构的变化,运用有限元软件ANSYS模拟不同涂料厚度的耐火保护钢梁在标准温升模型、慢速和快速温升BFD模型3种温升曲线下,荷载作用不同时的最大挠度值,并与Robertson-Ryan准则中的最大挠度值比较,确定耐火保护钢梁的设计荷载值。结果表明,采用标准火灾模型代替自然火灾模型确定的设计荷载是不安全的;钢梁最高温度越高,设计荷载越低;随着涂料增厚,温升速率的改变对设计荷载值的影响逐渐明显。     

绝热坑槽内土壤热湿迁移的实验研究

以太阳能在地下土壤蓄热为背景,通过实验研究了绝热坑槽内土壤的热湿迁移问题.实验中分别测试了不同蓄热温度、不同初始含湿量下土壤温度场和湿度场的变化过程,分析了蓄热温度和含湿量对土壤温度场和湿度场的影响,得到热湿迁移过程中温度场和湿度场变化是同步进行、相互影响的结论.当初始含湿量为0.2m3/m3时,坑槽内土壤的整体温升最大.蓄热温度越高,坑槽内土壤的整体温升越高,越有利于坑槽的蓄热.     

Assessment of compliance of dimensional tolerances in concrete slabs using TLS data and the 2D continuous wavelet transform

While several concrete waviness assessment methods are being developed to overcome the disadvantages of one assessment method over the other, the sparseness of measurements associated with each method prevents from achieving a better understanding of how elevations and undulations change across the surface. Assessing waviness over multiple one-dimensional (1D)-survey lines may not accurately reflect the actual condition or waviness of the entire floor. The methodology presented in this paper presents a compliance-checking algorithm for detecting elements where dimensions exceed specified tolerance. It also enables assessment of a concrete surface in two-dimensional (2D) domain using the synergy of Terrestrial Laser Scanning (TLS) and Continuous Wavelet Transform (CWT). 2D CWT analysis provides information not only about the periods of the surface undulation, but also the location of such undulations. The validity of the methodology is established by running a test on point clouds obtained from a warehouse project near Gresham, Oregon. A rigorous comparison between one of the existing floor waviness measurement methods, the waviness index method, and the proposed method is made. The results showed that the proposed methodology delivers accurate results that enable the localization of surface undulations of various characteristic periods. Furthermore, the proposed method is more efficient in terms of time taken for acquiring the measurements, and is, thus, more cost efficient.     

Quantifying topography and closure deformation of rock joints

This paper presents a study for quantifying both the joint topography characteristics and the load–closure deformation of a rock joint under normal compressive loading condition. The study covers (1) laboratory measurements of rock joint surface profiles using a profilometer designed and fabricated by the research team, (2) development of a mathematical method to identify the waviness and unevenness components in joint surface profiles and the associated composite topography, (3) development of a general load–closure deformation model by using both the waviness and unevenness components in the composite topography, (4) unconfined compressive testing of rock samples with joints for the experimental load–closure deformation of joints and, (5) verification of the general load–closure deformation model by the experimental load–closure deformation results. The study leads to the following four findings: (a) the mathematical method can be used to identify the waviness and unevenness components for joint surface profiles and its composite topography. The height characteristic parameters of the complete surface topography of a joint are mainly determined by the waviness component. The texture characteristic parameters of the complete surface topography of a joint are mainly determined by the unevenness component, (b) joints can be classified into the three contact state cases using the waviness and unevenness components for both the joint surface profiles and the associated composite topography. The load–closure deformation behavior of a joint is determined by the waviness and unevenness components of the composite topography for a specific contact state, (c) the general load–closure deformation model developed in this paper is applicable to the three contact state cases. The general load–closure deformation model uses the composite topography of a joint and can take into account the effects of the contact states, the initial aperture and the waviness and unevenness components; (d) parametric studies and verifications with the uniaxial compression test results show that the general load–closure deformation model gives reasonable estimations of the load–closure deformation behavior of rock joint under compressive loading and can be reduced to those given by other researchers in the relevant literature.     

Anisotropic surface roughness and shear behaviors of rough-walled plaster joints under constant normal load and constant normal stiffness conditions

In this context,we experimentally studied the anisotropic mechanical behaviors of rough-walled plaster joints using a servo-controlled direct shear apparatus under both constant normal load(CNL)and constant normal stiffness(CNS)conditions.The shear-induced variations in the normal displacement,shear stress,normal stress and sheared-off asperity mass are analyzed and correlated with the inclination angle of the critical waviness of joint surfaces.The results show that CNS condition gives rise to a smaller normal displacement due to the larger normal stress during shearing,compared with CNL condition.Under CNL conditions,there is one peak shear stress during shearing,whereas there are no peak shear stress for some cases and two peaks for other cases under CNS conditions depending on the geometry of joint surfaces.The inclination angle of the critical waviness has been verified to be capable of describing the joint surface roughness and anisotropy.The joint surface is more significantly damaged under CNS conditions than that under CNL conditions.With increment of the inclination angle of the critical waviness,both the normal displaceme nt and shea red-off asperity mass increase,following power law functions;yet the coefficient of deternination under CNL conditions is larger than that under CNS conditions.This is because the CNS condition significantly decreases the inclination angle of the critical waviness during shearing due to the larger degree of asperity degradation.     

A dissolution-diffusion sliding model for soft rock grains with hydro-mechanical effect

The deformation and failure of soft rock affected by hydro-mechanical (HM) effect are one of the most concerns in geotechnical engineering, which are basically attributed to the grain sliding of soft rock. This study tried to develop a dissolution-diffusion sliding model for the typical red bed soft rock in South China. Based on hydration film, mineral dissolution and diffusion theory, and geochemical thermodynamics, a dissolution-diffusion sliding model with the HM effect was established to account for the sliding rate. Combined with the digital image processing technology, the relationship between the grain size of soft rock and the amplitude of sliding surface was presented. An equation for the strain rate of soft rocks under steady state was also derived. The reliability of the dissolution-diffusion sliding model was verified by triaxial creep tests on the soft rock with the HM coupling effect and by the relationship between the inversion average disjoining pressure and the average thickness of the hydration film. The results showed that the sliding rate of the soft rock grains was affected significantly by the waviness of sliding surface, the shear stress, and the average thickness of hydration film. The average grain size is essential for controlling the steady-state creep rate of soft rock. This study provides a new idea for investigating the deformation and failure of soft rock with the HM effect.     

节理研究进展及在非贯通节理岩体研究的应用

节理的表面形貌可按其规模大小分为起伏度和粗糙度两类.节理面的几何和力学特性对非贯通节理岩体扩展贯通有重要影响.典型节理面的粗糙形貌可以模拟为一系列非规则的、齿形凸台形貌.综述了贯通节理破坏理论新的进展,并探讨了节理破坏理论的适用性.结合非贯通节理岩体研究的现状,提出了考虑节理的粗糙度和起伏度情况下研究非贯通节理岩体扩展贯通强度和变形特性的新思路.     

Sand–concrete interface response: The role of surface texture and confinement conditions

Sand–concrete interface direct shear tests were used to investigate the effects of surface roughness, surface waviness, mean sand diameter and relative density on interface strength and behavior under different confinement conditions. Extreme concrete surface textures, including smooth, rough and rough–wavy textures, were reproduced. Surface plowing was assessed via image analysis, laser scanning and extended multifocal micrographs. The experimental results showed that smooth concrete surfaces exhibited high values of interfacial–to–internal friction angle ratios, ranging 88–90%, due to the angular shape of sand particles. The rough concrete surfaces generated higher interface strength than smooth concrete surfaces; however, the interface strength was still inferior to the surrounding sand strength. Surface plowing, which identified a mixed shear plane at the sand–concrete interface, was developed as particles were detached from the surface, thus inhibiting the interface friction angle from reaching the sand friction angle. Higher sand–concrete interface strength was achieved as surface waviness increased, and interface friction angles greater than the surrounding sand friction angle were reached. Under a constant normal stiffness condition, significantly high interface strength is achieved due to the increase of the current normal stress, which was directly influenced by the initial normal stress, stiffness, surface roughness, mean sand diameter and relative density; surface waviness did not have a marked effect on the normal stress variation. Based on these results, multiple regressions were proposed to estimate the sand–concrete interface strength by the interfacial–to–internal friction angle ratio and the effect of the constant normal stiffness condition.     

运用弹流理论设计无划伤钢筋矫直机

本文根据道森－希金森弹流理论，提出了在圆钢盘矫直过程中，用弹流油膜避免钢筋表面划伤的新方法。并介绍 了使弹流油膜易于形成的矫直方案及结构参数的 确定和力能参数的计算方法。     

轧制力对静压支承油膜厚度的影响

静压支承是一种广泛用于各种机械设备的新型支承结构,文章概述了静压支承原理,通过实验,讨论了静压支承的三个重要参数:承载能力,油膜厚度、供油压力,并给出了不同供油压力下轧制力与油膜厚度的关系曲线,阐述了油膜刚度与供油压力的关系。     

消防泡沫在液体燃料上的铺展性能试验研究

摘 要：扑救易燃液体火灾往往存在扑救时间长、火情易反复的现象。根本原因在于缺乏泡沫对液体燃料火灾灭火过程的深入认识。泡沫在易燃液体表面的铺展可能是抑制火灾最重要的因素,研究泡沫灭火剂在燃油表面灭火过程中的铺展覆盖情况至关重要。选用3%AFFF、3%AFFF/AR和3%FP 3种灭火剂在矩形流道内研究了泡沫铺展性能。研究表明,由于3%AFFF和3%AFFF/AR在燃料表面的剪切应力较小,其铺展速度比3%FP较快。由于3%AFFF和3%AFFF/AR可以在溶剂油表面形成水膜,其铺展速度与在水表面相似。3%FP在溶剂油表面不能形成水膜,比在水表面铺展慢。     

压缩空气泡沫扑灭变压器全液面溢油火灾试验研究

从变压器溢油火灾的产生原因出发,开展压缩空气泡沫灭变压器全液面溢油火的缩尺实验,对压缩空气泡沫喷淋系统和泡沫枪两种灭火方式进行了研究,考察了压缩空气泡沫扑灭此类火灾的优势以及火灾变化规律。研究表明,成膜型压缩空气泡沫扑灭变压器全液面溢油火是有效的,能够在高温油面形成稳定覆盖层,防止沸溢喷溅;冷却降温是灭火的关键因素,将油温降低到燃点以下,可扑灭溢油火灾并防止发生复燃。