定、变载弯曲疲劳钢丝绳失效机理对比研究

为对比揭示定、变载弯曲疲劳钢丝绳断裂机理及磨损演化特性,运用自制钢丝绳弯曲疲劳试验机开展钢丝绳定载、变载弯曲疲劳试验,通过人工拆股统计法和VW-9000系列高速度数码显微系统对比研究钢丝绳断丝分布、断丝数、断口和磨痕形貌等断裂机理,对比分析钢丝绳未断钢丝和断丝的磨痕尺寸演化特性.结果表明:与钢丝绳定载弯曲疲劳相比,变载弯曲疲劳钢丝绳断丝出现较晚,芯股、螺旋股外层断丝数分别较多、较少,芯股外层钢丝断口挤压变形较大,芯股各层钢丝断口裂纹扩展区占比较低,芯股和螺旋股的各层钢丝磨痕尺寸总体较小,钢丝绳更易达到报废水平.     

Propagation of a longitudinal pulse in wire ropes under axial loads

Measurements of the velocity of propagation of longitudinal pulses in wire ropes as a function of applied tension are reported. Twelve 3/8-in.-diam cables are investigated which differ in configuration, i.e., number of wires per strand and number of strands, and in the material from which the wires and the core are fabricated. The velocity of longitudinal waves is found to increase with increasing tension, approaching the velocity in a solid steel bar as the applied load is increased toward the failure load of the wire rope. The material from which the wires are fabricated and the number of strands, rather than the number of wires in a strand or its core material, appear to significantly affect the velocity of longitudinal pulses.     

考虑微动磨损的钢丝微动疲劳裂纹扩展寿命预测研究

微动疲劳是矿井提升钢丝绳主要失效形式之一,在钢丝微动疲劳过程中,微动磨损严重影响钢丝微动疲劳裂纹扩展特性,进而制约钢丝微动疲劳断裂机制,故开展考虑微动磨损的钢丝微动疲劳裂纹扩展寿命预测研究至关重要. 运用自制钢丝微动疲劳试验机开展钢丝微动疲劳试验和拉伸断裂试验,通过高速度数码显微系统揭示微动疲劳过程中钢丝微动磨损演化、裂纹萌生和扩展及断裂特性,基于摩擦学和断裂力学理论,运用有限元法、循环迭代法和虚拟裂纹闭合技术建立了考虑微动磨损的钢丝微动疲劳裂纹扩展寿命预测模型,并进行试验验证. 结果表明:采用微动疲劳过程稳定阶段磨损系数预测钢丝微动磨损演化可保证预测正确性,微动疲劳过程中钢丝主要为I型裂纹扩展模式,考虑微动磨损的钢丝微动疲劳裂纹扩展寿命预测值和试验值吻合较好,验证了预测模型正确性.      

Physics-based modeling for fretting behavior of nominally flat rough surfaces

A physics-based modeling approach for fretting behavior of nominally flat rough contact is proposed. This approach employs physics-based models for partial slip of spherical contacts to formulate the contact forces at asperity tips. The individual asperity forces are added by a statistical method to obtain the fretting response of a flat rough contact. This approach suggests the plasticity index as an important parameter for studying the surface roughness effects on fretting. Fretting responses obtained by one of the models favorably compare with experimental results obtained from bolted steel lap joints. Tangential stiffness and energy loss per cycle obtained from the experiments and the model predictions deviate at higher preloads. This discrepancy is due to limitations of the modeling approach in accounting for plastic response to tangential loading.     

Some dynamic properties of axially loaded wire ropes

Results are presented on the transverse damping, the transverse fundamental natural frequency as well as the longitudinal fundamental natural frequency for axially loaded wire ropes. Twelve different wire ropes are tested. During the test, a mass is centrally attached to the rope. The results indicate an increasing transverse damping with an increasing axial load. This damping is primarily attributed to a Coulomb damping. Although core material and construction influence the transverse damping of the wire rope, no relationships are found when comparing this damping with the structural strength, the number of wires used in the rope, the alloy composition or the heat treatment of the rope materials. The transverse and longitudinal fundamental natural frequencies of the axially loaded wire ropes with a mass centrally attached has been satisfactorily modeled.     

改进的 Morse 势和冲击压缩

用分子动力学方法模拟凝聚介质中一维分子链上的激波传播,以得到与冲击压缩实验相一致的结果。通过比较分子链上的孤立波解与激波的实验结果,提出对分子间Ｍｏｒｓｅ作用势进行与考虑量子效应相一致的修正,从而使分子动力学模拟得到的激波Ｕｓ－Ｕｐ关系与实验结果在波后粒子速度达到声速的范围内一致。     

Finite element modeling and optimization to prevent wire breakage in electro-discharge machining

One of the most important problems in wire electrical discharge machining is related to wire breakage. This research develops a simple finite element model and a new approach to predict the thermal distribution in the wire fairly accurately. The model can be used to optimize the different parameters of the system to prevent wire breakage. At any instant of time, the spatial heat distribution profile of the wire can be mapped on the transient analysis of any point on the wire traversing through all the heat zones from the top spool to the bottom end. Based on this principle, the finite element model and optimization algorithm are used to determine that the heat generated is the critical variable responsible for wire breakage. The model successfully predicts the thermal distribution profile accurately for various wire materials, for increased wire velocity and for reduction in heat transfer coefficient. This simple model is a precursor of development for 3-D finite element models that can describe the cross-sectional wire erosion as the workpiece cutting progresses. The modeling may lead to the development of a smart electro-discharge machining system with a sensor and feedback control to increase the cutting speed and minimize breakage.     

Analytical procedure for modelling recursively and wire by wire stranded ropes subjected to traction and torsion loads

The aim of this article is to introduce a new theoretical procedure for modelling wire ropes subjected simultaneously to tensile and torsional loads. The procedure is based upon the beam assumption and takes account wire by wire of the double helical wires on the basis of general thin rod theory developed by [Love, A., 1944. Mathematical Theory of Elasticity. Dover Publications, New York]. The proposed kinematics are based on the assumption that wires are un-lubricated and therefore that no relative sliding between adjacent wires happens.     

Numerical study of sliding wear caused by a loaded pin on a rotating disc

A computational approach is proposed to predict the sliding wear caused by a loaded spherical pin contacting a rotating disc, a condition typical of the so-called pin-on-disc test widely used in tribological studies. The proposed framework relies on the understanding that, when the pin contacts and slides on the disc, a predominantly plane strain region exists at the centre of the disc wear track. The wear rate in this plane strain region can therefore be determined from a two dimensional idealisation of the contact problem, reducing the need for computationally expensive three dimensional contact analyses. Periodic unit cell techniques are used in conjunction with a ratchetting-based failure criterion to predict the wear rate in the central plane strain region. The overall three dimensional wear rate of the disc is then determined by scaling the plane strain wear rate with a conversion factor related to the predicted shape of the wear track. The approach is used to predict pin-on-disc test data from an Al-Si coating using a tungsten carbide pin. The predicted results are found to be consistent with measured data.     

Static lateral stiffness of wire rope isolators

This paper presents an analytical model for the static lateral stiffness of Wire Rope Isolators (WRI). The wire rope isolator, which is a passive isolation device, has been widely adopted as a shock and vibration isolation for many types of equipment and lightweight structures. The major advantage of the WRI is its ability to provide isolation in all three planes and in any orientation. The WRI in the lateral roll mode, is required to possess the required lateral stiffness to support and isolate the equipment effectively. The static lateral stiffness of WRI depends mainly on the geometrical characteristics and wire rope properties. The model developed in this paper is validated experimentally using a series of monotonic loading tests. The flexural rigidity of the wire ropes, which is required in the model, was determined from the transverse bending test on several wire rope cables. It was observed that the lateral stiffness is significantly influenced by the wire rope diameter and height of the isolator. The proposed analytical model can be used for the evaluation of lateral stiffness and in the preliminary design of the WRI.     

钢丝绳模型比较研究

将现有的各种钢丝绳计算模型进行比较研究，通过将数值结果与现有的实验数据进行比较可以看出，考虑绳芯变化并结合Love曲杆理论的JW和KC模型更适用于实际的钢丝绳结构。     

矿用钢丝在腐蚀介质环境下的微动行为研究

钢丝绳中钢丝的锈蚀、磨损或断裂是造成矿井用钢丝绳失效的主要形式。以6×19点接触式提升钢丝绳为研究对象,在自制的微动摩擦磨损试验机上开展钢丝在腐蚀介质环境下的微动磨损试验研究。考察钢丝在模拟矿井淋水腐蚀介质中的微动运行特性,通过磨痕测量微动磨损量,采用光学显微镜、扫描电镜和能谱仪对钢丝的微动损伤机理进行分析。结果表明：腐蚀介质影响钢丝的微动运行区域,在干摩擦和中性腐蚀介质下运行于混合区,而在酸性和碱性腐蚀介质下运行于滑移区;腐蚀介质明显降低钢丝的摩擦系数,其中酸性介质下的摩擦系数最小,约为0.36;腐蚀与磨损的交互作用显著加速了材料的流失,酸性腐蚀介质下钢丝的磨痕深度最大;钢丝在干摩擦条件下的损伤机制以材料的塑性变形、粘附涂抹和摩擦氧化为主,而在腐蚀介质环境下的损伤机制转变为磨粒磨损和化学腐蚀。     

Stabilized finite element solution to handle complex heat and fluid flows in industrial furnaces using the immersed volume method

We consider the numerical simulation of conjugate heat transfer, incompressible turbulent flows for multicomponents systems using a stabilized finite element method. We present an immersed volume approach for thermal coupling between fluids and solids for heating high‐alloy steel inside industrial furnaces. It consists in considering a single 3D grid of the furnace and solving one set of equations with different thermal properties. A distance function enables to define precisely the position and the interface of any objects inside the volume and to provide homogeneous physical and thermodynamic properties for each subdomain. An anisotropic mesh adaptation algorithm based on the variations of the distance function is then applied to ensure an accurate capture of the discontinuities that characterize the highly heterogeneous domain. The proposed method demonstrates the capability of the model to simulate an unsteady three‐dimensional heat transfers and turbulent flows in an industrial furnace with the presence of three conducting solid bodies. Copyright © 2010 John Wiley & Sons, Ltd.     

Analytical solutions for bending and flexure of helically reinforced cylinders

There has been a great deal of interest in the problems of modelling cables and ropes. A recent review by Cardou and Jolicoeur [Appl. Mech. Rev. 50 (1997) 1] considers the modelling of a cable which consists of a central core surrounded by one or several helically wound wire layers. One approach has been to consider the deformations of an individual helical wire and to synthesise the model of a cable by using contact conditions between the various wires. Other authors have adopted a continuum approach regarding each layer as a transversely isotropic material whose principal direction is along a helix surrounding the central axis of the cable. In each layer the helix angle is constant so that, when referred to cylindrical polar co-ordinates, the cylinder has a constant stiffness matrix in each layer. The intention in this paper is to use the continuum approach and describe the analytical solutions that govern the simple bending, flexure, or bending under a uniform load, of an anisotropic elastic cylinder consisting of a single material of this type. The extension of this work to a composite cylinder consisting of several concentric layers, surrounding a central core, which are either bonded together or make a frictionless contact, is briefly described.     

基于多体动力学递推算法的电动汽车建模与仿真分析

运用多体动力学理论建立整车动力学模型已成为汽车动力学研究的重要手段。以大连理工大学汽车学院研制的某电动汽车为对象,运用多体动力学递推算法建立了包含前后悬架、车身及车轮在内的多体仿真分析模型,将前后悬架视为3个子系统,引入哑体,实现对各子系统的单独处理;同时完成了整车的快速建模与分析;将MATLAB整车仿真程序的结果与ADAMS仿真结果进行比对,二者吻合较好,验证了所建模型及求解算法的正确性。     

Hydraulic fracture in poro-hydro-elastic media

The prediction of fluid-driven crack propagation in deforming porous media has achieved increasing interest in recent years, in particular with regard to the modeling of hydraulic fracturing, the so-called “fracking”. Here, the challenge is to link at least three modeling ingredients for (i) the behavior of the solid skeleton and fluid bulk phases and their interaction, (ii) the crack propagation on not a priori known paths and (iii) the extra fluid flow within developing cracks. To this end, a macroscopic framework is proposed for a continuum phase field modeling of fracture in porous media that provides a rigorous approach to a diffusive crack modeling based on the introduction of a regularized crack surface. The approach overcomes difficulties associated with the computational realization of sharp crack discontinuities, in particular when it comes to complex crack topologies including branching. It shows that the quasi-static problem of elastically deforming, fluid-saturated porous media at fracture is related to a minimization principle for the evolution problem. The existence of this minimization principle for the coupled problem is advantageous with regard to a new unconstrained stable finite element design, while previous space discretizations of the saddle point principles are constrained by the LBB condition. This proposed formulation includes a generalization of crack driving forces from energetic definitions towards threshold-based criteria in terms of the effective stress related to the solid skeleton of a fluid-saturated porous medium. Furthermore, a Poiseuille-type constitutive continuum modeling of the extra fluid flow in developed cracks is suggested based on a deformation-dependent permeability, that is scaled by a characteristic length.     

Small and Moderate Prandtl Number Chaotic Convection in Porous Media in the Presence of Feedback Control

Feedback control on thermal convection in a fluid-saturated porous medium is investigated based on the dynamical systems approach. A low dimensional Lorenz-like model was obtained using the Galerkin-truncated approximation. The possible suppression or enhancement of chaotic convection is demonstrated when the fluid layer is subjected to feedback control in a low-dimensional framework.     

基于非齐次复合Poisson过程的正交异性钢桥面板细节疲劳裂纹随机扩展研究

传统的正交异性钢桥面板疲劳损伤评估常采用确定性和可靠性分析方法,忽略了疲劳裂纹扩展的随机性影响,针对这一问题,提出钢桥面板细节疲劳随机扩展分析方法。本文以南溪长江大桥为工程背景,基于长期车辆荷载监测数据,建立了车辆荷载非齐次复合Poisson过程模型。建立钢桥面板有限元模型,采用瞬态分析方法将随机车辆荷载转化成细节疲劳应力,基于线弹性断裂力学理论推导U肋-顶板焊接细节疲劳裂纹扩展时变微分方程,实现宏观关系式疲劳应力幅次数-疲劳损伤至微观表达式应力时间序列-疲劳损伤转换,讨论了车载次序及超载对疲劳裂纹扩展的影响。研究结果表明,非齐次复合泊松过程模型能够较好描述随机车流运营状态,车辆荷载的次序对疲劳裂纹扩展速率的影响不可忽略,重车排序靠前时能够促使疲劳裂纹扩展增速,南溪长江大桥细节点的车辆超载迟滞效应修正系数取值0.804。     

Nonlinear state-observer control for projective synchronization of a fractional-order hyperchaotic system

In this paper, we consider an observer-based control approach for manipulating projective synchronization of nonlinear systems in high dimensional. Based on the stability theory of the fractional-order dynamical system, a nonlinear state observer is designed which can achieve projective synchronization in a class of high dimensional fractional-order hyperchaotic systems without restriction of partial-linearity and calculating the Lyapunov index of system. Simulation studies are included to demonstrate the effectiveness and feasibility of the proposed approach and synthesis procedures.