Effect of shear-induced contact area and aperture variations on nonlinear flow behaviors in fractal rock fractures

This study experimentally analyzes the nonlinear flow characteristics and channelization of fluid through rough-walled fractures during the shear process using a shear-flow-visualization apparatus.A series of fluid flow and visualization tests is performed on four transparent fracture specimens with various shear displacements of 1 mm,3 mm,5 mm,7 mm and 10 mm under a normal stress of 0.5 MPa.Four granite fractures with different roughnesses are selected and quantified using variogram fractal dimensions.The obtained results show that the critical Reynolds number tends to increase with increasing shear displacement but decrease with increasing roughness of fracture surface.The flow paths are more tortuous at the beginning of shear because of the wide distribution of small contact spots.As the shear displacement continues to increase,preferential flow paths are more distinctly observed due to the decrease in the number of contact spots caused by shear dilation;yet the area of single contacts in-creases.Based on the experimental results,an empirical mathematical equation is proposed to quantify the critical Reynolds number using the contact area ratio and fractal dimension.

TOOTH CURVES AND ENTIRE CONTACT AREA IN PROCESS OF SPLINE COLD ROLLING

In spline rolling process, the contact area between roller and workpiece plays an important role in calculating rolling-force and rolling-moment. For the purpose of studying the contact area, contact state between roller and workpiece in process of spline cold rolling based upon cross rolling is analyzed. According to the suitable hypothesis, the mathematic model of roller-tooth-curve in optional position of rolling process is established. Combing the theory of conjugate curves with the theory of envelope curve, the corresponding mathematic model of workpiece-tooth-curve is established. By utilizing establishing mathematic models, the algorithm of entire contact area in rolling process is created. On the basis of the algorithm, calculation-program is compiled under MATLAB program language environment. The calculation-program actualizes quantitative analysis and quantitative calculation of contact areas. Utilizing the calculation-program, the influence of parameters on contact area is analyzed, and the tendency is consistent with the manufacturing experience. In consideration of rolling-force optimization, the primary process parameters may be selected according to results of calculation. The result of the present study may provide basis for research on rolling-force and rolling-moment.

Double-row repair of rotator cuff tears: Comparing tendon contact area between techniques

BACKGROUND In rotator cuff repair surgery,the double-row technique is widely performed.Studies have shown that with increased contact area and pressure between tendon and bone interface,better healing is promoted.AIM To assess the different suture configurations with the double-row technique and how this influences the contact area of the rotator cuff tendon to bone.METHODS This was a controlled laboratory study where identical tears were created in 24 fresh porcine shoulders over a 1.5 cm×2.5 cm infraspinatus insertion footprint.Double-row repair techniques,with 3 to 4-suture anchors in different configurations(2 medial,2 lateral vs 2 medial,1 lateral vs 1 medial,2 lateral),were employed for three control groups.Each group consisted of eight shoulders with identical repair configurations.Footprint contact areas of the repaired tendon against the tuberosity were determined using pressure sensitive Fujifilm placed between the tendon and tuberosity.RESULTS The mean contact area between tendon and insertion footprint from the imprinted Fujifilm was obtained using computer software.The contact area measured from a standard 4-suture anchor double row repair was 75.1±9.3 mm2,whereas areas obtained for the 2 lateral-1 medial and 2 medial-1 lateral anchor configurations were 72.9±5.2 mm2 and 75.0±4.9 mm2 respectively.No statistical significance was noted between the three groups.CONCLUSION In the technique of double-row repair,using a 3-suture anchor configuration may offer a non-inferior alternative to the standard 4-anchor construct in terms of efficacy.This may also result in overall cost reduction and shorter surgical time.

A measurement method for distinguishing the real contact area of rough surfaces of transparent solids using improved Otsu technique

An experimental method of measuring the real contact area of transparent blocks based on the principle of total internal reflection is presented, intending to support the investigation of friction characteristics, heat conduction, and energy dissipation at the contact interface. A laser sheet illuminates the contact interface, and the transmitted laser sheet is projected onto a screen. Then the contact information is acquired from the screen by a camera. An improved Otsu method is proposed to process the data of experimental images. It can compute the threshold of the overall image and filter out all the pixels one by one. Through analyzing the experimental results, we describe the relationship between the real contact area and the positive pressure during a continuous loading process, at different loading rates, with the polymethyl methacrylate（PMMA）material. A hysteresis phenomenon in the relationship between the real contact area and the positive pressure is found and explained.

Relationship between the real contact area and contact force in pre-sliding regime

The pre-sliding regime is typically neglected in the dynamic modelling of mechanical systems. However, the change in contact state caused by static friction may decrease positional accuracy and control precision. To investigate the relationship between contact status and contact force in pre-sliding friction, an optical experimental method is presented in this paper.With this method, the real contact state at the interface of a transparent material can be observed based on the total reflection principle of light by using an image processing technique. A novel setup, which includes a pair of rectangular trapezoidal blocks, is proposed to solve the challenging issue of accurately applying different tangential and normal forces to the contact interface. The improved Otsu＇s method is used for measurement. Through an experimental study performed on polymethyl methacrylate（PMMA）, the quantity of contact asperities is proven to be the dominant factor that affects the real contact area. The relationship between the real contact area and the contact force in the pre-sliding regime is studied, and the distribution of static friction at the contact interface is qualitatively discussed. New phenomena in which the real contact area expands along with increasing static friction are identified. The aforementioned relationship is approximately linear at the contact interface under a constant normal pressure, and the distribution of friction stress decreases from the leading edge to the trailing edge.

New Equations for Describing Contact Area between Tire and Ground

New equations are proposed to describe the shapes and sizes of the contact areas between tire and ground(the contact areas)under the conditions of static load,slip,camber,and rolling.The equations are super ellipse and trigonometric function with four parameters.Results indicate that the contact areas under the conditions of static load,slip,camber can be well described by super ellipse,in the most complicated case,fourteen parameters are used.The rolling contact area can be reconstructed by the trigonometric function completely.Symmetrical and asymmetrical shapes can both be described perfectly.The suggested curves will make calculate size of the areas easily.The described shapes and sizes are in good agreement with the measured,the maximum deviation is only 2.88%.This work will provide an instrument for understanding the contact area and be helpful for analyzing tire and road.

An experimental method for quantitative analysis of real contact area based on the total reflection optical principle

The simulation of real contact area between materials is foundationally important for the contact mechanics of mechanical structures. The Greenwood and Williamson(GW) model and the Majumdar(MB) model are the basic models in this field, which are widely accepted and proven to be valid in many experiments and engineering. Although the contact models have evolved considerably in recent years, the verifications of the models are most based on the indirect methods such as electrical conductivity and contact stiffness, because of the lack of effective methods to directly measure the variation of contact surface. In this paper, the total reflection(TR) method is introduced into the verification of contact models.An experiment system based on TR method is constructed to measure the real contact area of two PMMA specimens. The comparison analysis between the results of experiment and models suggests that the experiment result has the same trend with simulation, the MB model has better agreement with the experimental result because this method can take into account the variation of radius and the merging of asperities, while the GW model has a huge deviation because of the dependence on resolution and the lack of considering the variation of radius and asperity's merging process. Taking the interaction of asperities into account could give a better result that is closer to the experiment. Our results and analysis prove that the experimental methods in this paper could be used as a more direct and valid method to quantitatively measure the real contact area and to verify the contact models.

Evolution of real contact area during stick-slip movement observed by total reflection method

We build an experiment system based on total reflection(TR) method to observe the evolution of real contact area of polymethyl methacrylate(PMMA) in the continual stick-slip movement. The bilateral friction is adopted to overcome the bending moment in the lateral friction movement. Besides some classical phenomena of stick-slip movement such as periodical slow increase of frictional force in sticking phase and a sudden drop when slipping, a special phenomenon that the contact area increases with the tangential force is observed, which was called junction growth by Tabor in 1959.Image processing methods are developed to observe the variation of the junction area. The results show that the center of the strongest contact region will keep sticking under the tangential force until the whole slipping, the strongest point undergoes three stages in one cycle, which are named as sticking stage, fretting stage, and cracking stage, respectively. The combined analysis reveals a physical process of stick-slip movement: the tangential force causes the increase of the real contact area, which reduces the pressure between the contact spots and finally leads to the slipping. Once slipping occurs,the real contact area drops to the original level resulting in the pressure increase to the original level, which makes the sticking happen again.

Simulation model optimization for bonnet polishing considering consistent contact area response

Simulation model optimization plays a crucial role in the accurate prediction of material removal function in bonnet polishing processes,but model complexity often poses challenges to the practical implementation and efficiency of these processes.This paper presents an innovative method for optimizing simulation model parameters,focusing on achieving consistent contact area and the accurate prediction of the material removal function while preventing increase in model complexity.First,controllable and uncontrollable factors in bonnet simulations are analyzed,and then a simplified contact model is developed and applied under constant force conditions.To characterize the bonnet's contact performance,a contact area response curve is introduced,which can be obtained through a series of single spot contact experiments.Furthermore,a rubber hyperelastic parameter optimization model based on a neural network is proposed to achieve optimal matching of the contact area between simulation and experiment.The average deviation of the contact area under different conditions was reduced from 22.78%before optimization to 3.43%after optimization,preliminarily proving the effectiveness of the proposed simulation optimization model.Additionally,orthogonal experiments are further conducted to validate the proposed approach.The comparison between the experimental and predicted material removal functions reveals a high consistency,validating the accuracy and effectiveness of the proposed optimization method based on consistent contact response.This research provides valuable insights into enhancing the reliability and effectiveness of bonnet polishing simulations with a simple and practical approach while mitigating the complexity of the model.

A consecutive joint shear strength model considering the 3D roughness of real contact joint surface

A consecutive joint shear strength model for soft rock joints is proposed in this paper,which takes into account the degradation law of the actual contact three-dimensional(3D)roughness.The essence of the degradation of the maximum possible dilation angle is the degradation of the 3D average equivalent dip angle of the actual contact joint asperities.Firstly,models for calculating the maximum possible dilation angle at the initial and residual shear stress stages are proposed by analyzing the 3D joint morphology characteristics of the corresponding shear stages.Secondly,the variation law of the maximum possible dilation angle is quantified by studying the degradation law of the joint micro convex body.Based on the variation law of the maximum possible dilation angle,the maximum possible shear strength model is proposed.Furthermore,a method to calculate the shear stiffness degradation in the plastic stage is proposed.According to the maximum possible shear strength of rock joints,the shear stress-shear displacement prediction model of rock joints is obtained.The new model reveals that there is a close relationship between joint shear strength and actual contact joint roughness,and the degradation of shear strength after the peak is due to the degradation of actual contact joint roughness.

MD simulation of the effect of contact area and tip radius on nanoindentation

Molecular dynamics simulations of nanoindentation are performed on monocrystal copper. A new contact atoms method is presented for calculating the contact area. Compared with conventional methods, this method can provide the contact area more accurately not only for sink-in but also for pile-up situation. The effect of tip radius on indentation is investigated too. The results indicate that the measured hardness of the material will become higher as the tip radius increases.

Concussion in contact sport:A challenging area to tackle

1.The problem The term'concussion'refers to a common form of traumatic brain injury,which typically occurs after a blow or injury to the head.It has been described as a'complex pathophysiological process affecting the brain,induced by biomechanical factors',and shear forces induced by rotational acceleration are believed to be the primary mechanism of injury in concussion.~1The incidence of concussion in the UK has been shown to be

A Study on Law of Change of Real Contact Area of Friction during Transition Process

Mechanism of frictional vibration and the difference of kinctic-static friction is an open question. Research shows that the change of real area of contact during transition process of friction results in the phenomena mentioned above. In substance, the F-Vr, descent and F-T ascent characters are caused by A-Vr, and A-T characters respectively. Based on ultrasonic experiment the mechanism of the phenomena is explained and the frictional formulas using the parameter-real area of contact are given in this article.

装配式刻槽道面宏观构造特征参数研究

本文以A320主起落架轮胎与装配式道面板为研究对象,首先,基于能量损耗理论及摩擦学基本原理,建立轮胎与道面之间的能量耗散方程,从而得出道面宏观构造特征参数与摩擦耗散之间的量化关系。其次,利用ABAQUS建立飞机轮胎-道面板相互作用动力仿真模型。最后,通过仿真实验得到最优的装配式刻槽道面的构造特征参数(刻槽深度、刻槽宽度、刻槽倒角),结果表明:当刻槽宽度为30 mm、刻槽深度为2 mm、刻槽倒角为45°时,装配式道面板可以显著增强道面抗滑性能,具有良好的摩擦耗散性能,与轮胎接触面更大,抓地性能更好,可以提高装配式道面板的耐久性。

半无限区域雪壤与车轮交互作用接触动力学特性分析

车轮与雪壤交互作用是车辆在高原、极地等环境下安全行驶的基础。为构建准确表征车轮与雪壤接触过程的车轮-雪壤交互动态模型,建立圆盘加载仿真模型,获取典型雪壤的压力-沉陷关系;基于硬质雪壤建立车轮-雪壤交互数值仿真模型,对车轮-雪壤交互接触作用力进行数值仿真。利用圆盘加载试验结果和实车试验结果,对建立的数值模型进行有效性验证。基于车轮-雪壤交互平均接触应力关系建立车轮-雪壤交互接触作用力解析模型,利用仿真结果对解析模型进行验证。研究结果表明:半无限区域下的圆盘加载数值仿真模型能够有效反映雪壤的压力-沉陷特性,车轮-雪壤交互数值仿真结果与实际车轮行驶的下陷量、运动阻力系数有较好的一致性;车轮行驶滑移率为正时,车轮载荷-沉陷关系和车轮-雪壤交互接触作用力趋于稳定,车轮行驶滑移率为负时,车轮下陷量变大,由此导致垂向支持力正应力部分和运动阻力增加;车轮行驶滑移率为正时,车轮-雪壤交互解析模型可以准确预测车轮-雪壤交互接触作用力的变化趋势。

Experimental Study on the Effect of Fine-Grained Soil Content on the Freezing Strength of Aeolian Sand-Cement Interface

In cold regions,understanding the freezing strength of the interface between soil and structure is crucial for designing frost-resistant foundations.To investigate how the content of cement powder in aeolian sand affects this strength,we conducted direct shear tests under various conditions such as different fine-grained soil content,normal stress,and initial moisture content of the soil.By analyzing parameters like soil properties,and volume of ice content,and using the Mohr-Coulomb strength theory to define interface strength,we aimed to indirectly measure the cementation strength of the interface.Our findings revealed that as the particle content increased,the interface stress-strain curves became noticeably stiffer.We also observed a positive linear relationship between freezing strength and silt content,while the initial moisture content of the soil did not significantly impact the strengthening effect of fine-grained soil on freezing strength.Moreover,we discovered that as the powder content increased,the force binding the ice to the interface decreased,while the friction angle at the interface increased.However,the cohesion force at the interface remained relatively unchanged.Overall,our analysis suggests that the increase in freezing strength due to fine-grained soil content is primarily due to the heightened friction between aeolian sand and the interface.

接触面积对H62/T2弹性接触载流摩擦副性能的影响

针对接触条件对电连接器热插拔条件下性能影响不明的问题,采用H62/T2弹性接触摩擦副,在微-滑动摩擦试验机上,对其进行往复滑动载流摩擦实验,研究了接触面积对H62/T2载流摩擦磨损性能的影响。结果表明:在给定电流为2 A、4 A、6 A条件下,随接触面积的增加,摩擦系数波动性降低,即摩擦过程的稳定性提高,平均摩擦系数和总磨损体积均呈现增大趋势;在电流为2 A条件下,当圆弧半径从1.5 mm增加至5.5 mm时,电流波动性减小,载流稳定性提高,载流效率η从98.26%提高至99.73%。摩擦副的摩擦磨损机制包括磨粒磨损、粘着磨损、电弧侵蚀且多机制耦合作用,随接触面积的增加,以熔融和喷溅为主的电弧侵蚀减少,以犁沟和粘着为主的机械磨损加剧。

元白话语言接触研究综述

由于元代特殊的社会文化背景,使得元白话表现出独特的语言接触面貌。目前在语法和词汇方面,学界对其研究可以说表现为从断代的静态描写到历时的动态描写,从文献的混同分析到分类对照考察,且逐渐兼顾汉语本身演变规律和语言融合因素的双重影响。不过研究成果虽多,但也存在研究广度欠缺、研究视域狭窄,对内在机制动因挖掘不够深入等问题。站在长城地带北方话语言接触底层研究的视角上,认为“汉儿言语”并非某个朝代所独有,至少在魏晋南北朝以来不断发展递变,在长城内外已构成“汉儿言语联盟”。站在北方话发展历史的角度观照“汉儿言语”“辽代汉儿言语”“蒙式汉语”“满式汉语”等均是其不同时代的变体。理清这一汉语发展脉络,对我们认识汉语基础方言的演变、认识中华民族多元一体化格局的形成,无疑具有重要的历史和现实意义。

Analysis and Numerical Simulation of Rolling Contact between Sphere and Cone

In non-conforming rolling contact, the contact stress is highly concentrated in the contact area. However, there are some limitations of the special contact model and stress model used for the theoretical study of the phenomenon, and this has prevented in-depth analysis of the associated friction, wear, and failure. This paper is particularly aimed at investigating the area of rolling contact between a sphere and a cone, for which purpose the boundary is determined by the Hertz theory and the geometries of the non-conforming surfaces. The phenomenon of stick-slip contact is observed to occur in the contact area under the condition of no-full-slip（Q 〈 μ·P）. Using the two-dimensional rolling contact theory developed by CARTER, the relative positions of the stick and slip regions and the distribution of the tangential force over the contact area are analyzed. Furthermore, each stress component is calculated based on the Mc Ewen theory and the idea of narrow band. The stress equations for the three-dimensional rolling contact between the sphere and the cone are obtained by the principle of superposition, and are used to perform some numerical simulations. The results show that the stress components have a large gradient along the boundary between the stick and slip regions, and that the maximum stress is inversely proportional to the contact coefficient and proportional to the friction coefficient. A new method for investigating the stress during non-classical three-dimensional rolling contact is proposed as a theoretical foundation for the analysis of the associated friction, wear, and failure.

射频连接器装配位移的机电耦合建模及实验

射频连接器是射频和微波系统中必不可少的器件。在射频连接器装配过程中,装配位移的变化会导致接触状态变化,进而影响传输信号完整性。针对互连射频连接器的装配位移变化影响传输电性能这一问题,通过搭建射频连接器的装配位移与散射参数测量实验平台,研究装配位移对电信号的影响。基于微波网络理论分析,引入接触区域的等效电路,将接触区域等效电路转化为端口网络与射频连接器端口网络级联,构建装配位移影响下互连射频连接器的场路耦合模型。根据该模型搭建实验平台,测量射频连接器不同装配位移下的散射参数,由实验数据拟合装配位移和接触区域阻抗的映射关系,最后构建出射频连接器装配位移的机电耦合模型。通过搭建装配位移实验平台,验证了耦合模型的有效性。