电梯钢丝绳疲劳断裂原因分析

对电梯钢丝绳断丝进行了表面形貌、显微组织、化学成分等检测分析。结果表明:电梯钢丝绳表面断丝为疲劳断裂,主要原因是钢丝绳在循环应力的作用下,受到外部挤压以及长期摩擦失油处形成疲劳应力集中点,萌生疲劳裂纹。又因钢丝绳表面挤压处产生白色马氏体,使得钢丝表面韧性弱化,加速了疲劳裂纹源的形成,故而出现了早期钢丝绳表面钢丝断裂;最后提出了相应的改进措施。     

Effect of degradation and impaired quality on wire rope bending over sheave fatigue endurance

This paper reports the outcome of a series of tests undertaken on six strand and multi-strand ropes to investigate the effects of degradation and impaired quality on the rope’s Bending-over-Sheave (BoS) fatigue endurance. The simulated degradation and quality impairment investigated were: wire breaks (internal and external); plastic wear, abrasive wear, corrosion, slack strands, slack wires and torsional imbalance. Theoretical predictions of rope fatigue endurance have been made to compare with the experimental values, using Feyrer’s equation. The investigation indicates that the bending over sheave fatigue endurance of rope is little influenced by degradation and impaired quality, which is primarily dependent on the rope construction and the diameter ratio of sheave to rope. The study establishes methodologies for assessment of the residual BoS fatigue endurance of degraded or impaired rope, which can inform the practical operation, inspection and discard of wire rope thereby enhancing safety.     

Failure Analysis of a Drilling Wire Rope

The failure of a multistrand wire rope used in drilling rig hook is investigated in this case study. The wire rope failed during the raising of the rig and caused some serious damage to the rig structure. Throughout its short time of service, the wire had been used a few times for rig up and rig down. The failure investigation is performed by metallurgical examinations and computational analyses utilizing the finite element method. The wire rope was made of AISI 1095 steel. Its chemical composition, ferrite?Cpearlite structure, and high hardness indicate that the wire is a type of extra extra improved plow steel (EEIPS) grade. The morphologies of fractured surfaces indicate tensile overloading of wires. Finite element analysis confirms the overload in core and strands, and compressive contact stresses between wires, and between wires and sheave surface. The results show that high tensile stresses due to the overload and small ratio of sheave-to-rope diameter were responsible for the failure.     

Fatigue and fracture analysis of a seven‐wire stainless steel strand under axial and bending loads

Fatigue failure of cables and strands is a common and complex problem. Failure is typically caused by different combinations of time‐variable bending and axial forces. In addition to these loads, contact stresses between wires may play an important role in the fatigue failure of cables. The present work aims to provide deep insight into the fatigue failure of a seven‐wire stainless steel strand subjected to a combination of variable axial and bending loads. To avoid side effects in the analysis, fatigue failure of the strand close to the clamps is prevented. Several tests were performed with a new device specifically designed to avoid failure near the clamps. Thus, failure is always produced at the middle length of the specimen. Test simulations were performed by employing the finite element method. The numerical results were validated via comparisons with experimental data. Finally, life prediction curves were obtained.     

Theoretical approach to the solutions of axially loaded complex ropes

Abstract

A rational analysis procedure consisting of a complete cycle of systematic calculations has been developed for the theoretical solutions of problems in describing the behavior of axially loaded complex ropes consisting of wires and strands, which were simulated as particle‐motion models. In essence, axial and rotational strains of a rope were specified. Constitutive relations of the loaded wires and strands were obtained through compatibility of motion requirements. Material law was then imposed to determine the internal force of each wire. Nonlinear equilibrium relations of wires were applied to describe the relationship among sectional stresses and external forces. The theory is used in the analysis of a 6 × 7 wire rope with an independent wire rope core (IWRC). Some solutions and comparisons to other research results have been provided. Results show that the recursive nature of the wire in the model enhanced the calculation of constitutive relations and made it easier to apply to the analysis of complex ropes having multiple orders.     

Metallurgical Investigation of Failed Locked Coil Track Ropes Used in a Mining Conveyor

A locked coil track rope (LCTR) is essentially composed of wires (round and rail-shaped) laid helically in different layers. These wire ropes are sometimes used in conveyors carrying empty and loaded buckets in mining areas. During service, such wire ropes may fail prematurely due to disintegration/failure of individual groups of wires. To understand the genesis of LCTR wire failures, a detailed metallurgical investigation of failed rope wires was made and included visual examination, optical microscopy, scanning electron microscopy (SEM), and electron probe microanalysis (EPMA). Two types of failed wires were investigated; one is from a 40 mm diameter locked coil track rope and the other from a 53 mm locked coil track rope. Optical microscopy of failed round wires in the 53 mm diameter rope clearly revealed fully decarburized layers at the surface and a few grain-boundary cracks. From the location of the failure, it was clear that apart from static tensile loads, the wire ropes had been subjected to bending and unbending loads near the saddle, as fully loaded or empty buckets traveled access the conveyor. The SEM studies confirmed that the fracture had been caused by initiation of fatigue cracks in the decarburized zone under conditions of repeated bending and unbending stresses superimposed on the static tensile load.     

Failure Analysis of Failed Wire Rope

Failure of an old rope from a stringing lattice transmission towers occurred in winter while the rope was being removed to make way for a new rope. Fracture took place around mid-span. At that time, ambient temperature was −22 °C. Wire rope was in service for nearly 50 years. We were given the mandate to determine the reasons for the fracture of the wire rope and also to suggest measures to prevent such failures from occurring. The study involved laboratory testing (mechanical and metallographic) of representative wire rope samples. The effect of low temperature (from room temperature to −40 °C) on the tensile behavior of wires and wire rope samples was evaluated. In addition, we designed an instrumented impact test to assess the effect of notches, low temperatures and dynamic loading on the fracture behavior; however, no standards were available for direct comparison. Optical metallography was used to judge the extent of corrosion and the nature of microstructure and the cleanliness of the steel. The fracture morphology of broken tensile and impact specimens was carried out using scanning electron microscopy to establish relations between test parameters and fracture modes. Results indicate that considerations have to be given to the occurrence of corrosion, notches, low temperatures, and dynamic loading conditions when replacing wire ropes and this may necessitate the replacement of wire rope earlier than the time dictated by the criterion of 10% loss in breaking strength. Results also indicate that impact testing is a better evaluator of the susceptibility of wire ropes to brittle fracture than tensile tests.     

The use of fracture mechanics in failure analysis in the offshore diamond mining industry

This paper considers two major failures of offshore diamond mining equipment, which should not have occurred had both fracture mechanics aspects and materials behaviour been more fully understood. The two case studies include (a) failure of a wire rope swivel, and (b) failure of a load cell (used for monitoring rope load). In case (a) the swivel shank had failed in reverse bending fatigue, although it was thought initially to experience only tensile stresses. The linkage system to the haul rope, through a form of clevis plates, led to high bending fatigue stresses, and the failure was exacerbated by inappropriate remedial changes, including poor choice of material, as well as stress concentrating effects induced by a shrink fit stainless steel collar. In case (b), complete collapse of a gantry, sheave wheel system and partial A frame support resulted from the prior brittle failure of the load cell, and this could be attributed to incorrect heat treatment of the load cell material. In both cases quantitative use is made of fracture mechanics in the failure assessment.     

Life Cycle Assessment of Wire Rope Used in Crane Application in a Steel Plant

Journal of Failure Analysis and Prevention - Wire rope is an important part of any crane. Failure of wire rope may lead to major loss in terms of life and cost. Wire rope failures are attributed by...     

Failure analysis of coal pulverizer mill shaft

Failure of a ball and race type coal pulverizer mill shaft has been analysed. It was found that the shaft, made of EN 25 steel, failed by fatigue. The fatigue cracks originated from the keyway area, unusually from the top edge. The presence of elongated manganese sulphide inclusions due to improper heat treatment had reduced the ductility and CVN toughness of the material, and thus made the material more prone to failure.     

起重钢丝绳通也滑轮的偏角和包角对钢丝绳寿命的影响

在缆索起重机等高效的起重设备设计中,很重要的问题是必须采取多方面的措施来增加所用钢丝绳的使用寿命。这些措施包括应在导绕系统中钢丝绳通过滑轮时采用尽可能小的偏角和适当的包角,以求达到使钢丝绳具有较长的疲劳寿命的目的。本文将对这两方面加以阐述,特别是对偏角和包角影响钢丝绳疲劳寿命的机理作出解释。     

Failure analysis and fatigue performance evaluation of a failed connecting rod of reciprocating air compressor

A connecting rod of a reciprocating air compressor is subjected to complex dynamic loads therefore it is of a critical machine element. Failure of this type of connecting rod was reported to occur at the rounded fillet of the big connecting rod end. The present investigation is aimed to identify the cause of failure and to evaluate fatigue performance of the failed connecting rod. Factors affecting failure including structural design, type of material and dynamic loads were assessed using standard failure analysis method. This method included analysis of chemical composition, microstructural examination using optical microscopy, hardness and tensile tests, scanning electron microscopy (SEM) fractography and stress analysis. To evaluate fatigue performance, fatigue crack growth rate (FCGR) test was performed using a sinusoidal load with a constant load amplitude. Results of this investigation suggest that the cause of failure was low cycle fatigue and the initial crack location was consistent with high stress concentration, i.e. fillet radius. From metallurgical point of view, the connecting rod was made of cast steel, not forged steel, with a considerable number of non metallic inclusions such as Al₂O₃, SiO₂ and FeO. These inclusions which were present near the surface of the rounded fillet seemed to act as stress raiser and they were responsible for crack initiation. In addition, the presence of inclusions could increase fatigue crack growth rate, da/dN (in m/cycle) as indicated by a high value of Paris’ constant (n), typically of 5.2141.     

Theoretical and experimental investigation of effects of failures on the tensile endurance of elevator ropes

Elevators have an important place in human life just after uprising demands in high rise buildings, skyscraper and luxury residence concepts have surged. Steel wire ropes provide permanent working safety and reliability in the elevator installations. Due to this reason steel wire ropes are one of the vital components of elevators. In this study, effects of discard criteria such as wire breaks, abrasive wear and corrosion where extents of those failures are defined by ISO 4344 standard on the tensile endurance of 6×19 Seale and 8×19 Warrington elevator ropes have been investigated theoretically and experimentally. Tensile endurances of rope samples that have different extents of failure have been determined by using tensile testing machine and comparison is made by undamaged samples for each rope separately. In addition, stress and strain values occurred on the elevator ropes investigated have also been presented. The most critical failure type has been found to be 24 wire breaks for 6×19 Seale rope with fiber core where lifting capacity reduced by 25.99 %. The most critical failure type has been found to be abrasive wear which is 0.1 mm in depth along 100 mm length for 8×19 Warrington rope with independent wire rope core where lifting capacity reduced by 7.93 %.     

Effect of corrosion on the fatigue life and fracture mechanisms of 6101 aluminum alloy wires for car manufacturing applications

An innovative solution for the automotive industry is to replace the copper used for wiring harnesses with aluminum alloys, such as the aluminum–magnesium–silicon 6101 alloy. Wiring harnesses are composed of thin strand arms obtained by a wire drawing process. These strands are susceptible to exposure to a corrosive environment and fatigue solicitations simultaneously. The fatigue endurance of this alloy was studied using the stress-life approach for three metallurgical states representative of three cold-drawing steps. Fatigue tests performed in corrosive media tests highlighted a strong decrease of the 6101 alloy lifetime due to fatigue–corrosion interactions and a modification of failure modes.     

Failure Analysis of Wire Rope Used for Hoisting in Mining: A Case Study

Wire ropes are used in vast range of applications and many of the applications are safety critical. In the mining industry wire ropes are extensively used for hoisting/haulage. Due to the hostile operating load conditions, many wire ropes degrade in service. Fatigue of wires in rope in combination with other detrimental factors is frequently responsible for rope deterioration and premature failure during operation. In this paper the causes of failure of a wire rope used for hoisting in an Indian mine are determined with only a minimum level of information provided by the customer. Samples of the failed rope were obtained and analyzed and potential remedial measures to prevent such degradation are discussed. Reprinted with permission from Proceedings of AIME 2006, held on January 20–21, 2006 organized by Jamia Milia Islamia (a central university) New Delhi-110025, pp. 122–132.     

Effect of terminal mass on fretting and fatigue parameters of a hoisting rope during a lifting cycle in coal mine

The effect of terminal mass on fretting and fatigue parameters of the hoisting rope during a lifting cycle in coal mine was investigated in this study. Static analyses of the rope were performed at the start and end of the lifting cycle as compared to dynamic analyses during lifting. Correlation models between rope tensions and fretting and fatigue parameters were established. The results show that overall ranges of wire tension, relative displacement and contact load between wires in the rope are 1.5–175.6 N, 0.9–99.6 μm, and 0.2–452.9 N with the terminal mass increasing from 1000 to 1700 kg. Increases of fretting and fatigue parameters shorten the rope life.     

Failure analysis of a cableway rope

This study is focused on the failure analysis of a cable way rope composed by different wires in which the magnetoscopic analysis has pointed out a significant and abnormal number of failure indications after a relatively short time of service. Such a phenomenon has taken place in one of the longest worldwide cableway plant and it is interesting that the performed microstructural analysis has clearly indicated that the applied steel seems featured by a good soundness of the very fine perlite micro-structure that has not been interested in any way by the decarburation phenomena. Moreover, the realized micro-hardness tests indicate a reliable homogeneity of the strength properties featuring the steel along the wire section. On the other hand, the fractographic analysis clearly indicates that the source of the failure mechanism is the initiation of the cracks in the surface of the z-shaped wire of the outer wire layer in contact with the wires of the inner layer. The coupling of the different results seems to indicate that the most probable cause of the failure mechanism has to be found in the excessive pressure applied on the rope and to the consequent sliding between the external wire layer and the inner adjacent one that produces debris and the nucleation of the crack.     

超深矿井提升机卷筒动态应力与疲劳寿命研究

超深矿井提升机卷筒在钢丝绳多层缠绕时所受钢丝绳的缠绕力错综复杂,在长期作业过程中卷筒结构可能会萌生裂纹进而发生疲劳破坏,所以有必要对卷筒结构在多层缠绕实际工作条件下的疲劳寿命展开研究。基于板壳理论,将超深矿井提升机卷筒视为均匀受压的旋转对称壳体,通过对卷筒结构负荷构成进行分析,建立了钢丝绳对卷筒作用力的数学模型,并根据提升系统动力学原理建立了钢丝绳满载上提和空载下放的动力学模型,确定了卷筒结构的动态载荷。通过对卷筒结构作业过程强度分析得出卷筒结构在整个工作循环中的应力-时间历程曲线。结合不同存活率的S-N曲线和累积损伤理论,分析了卷筒结构在不同负载下的疲劳寿命。研究结果表明：提升机满载上提和空载下放过程中卷筒结构的最大等效应力均出现在等速阶段,且其最大等效应力出现在卷筒内壁支轮与支环的中部;在给定的存活率下卷筒结构的疲劳寿命与工作负载密切相关。研究结果为多层缠绕复杂工况下卷筒的力学分析与科学设计提供了理论支撑。     

Effect of abrasive wear on the tensile strength of steel wire rope

Known amounts of external abrasive wear were introduced into a new 6-strand steel wire rope and the effects of this wear on the tensile strength of the rope examined against the rope discard criteria for wear stated in ISO 4309: 1990 and other selected international standards. The variations of strength with degree of wear in the test rope were compared with continuous observations on two haulage ropes which were in service under abrasive wear conditions up to the stage of failure. The results point to a need for greater caution in applying available discard criteria for wear. The results also indicate the existence of two different rapid strength deterioration regimes in strand wire rope under increasing amounts of external abrasive wear and they direct towards test parameter levels which signal the onset of these regimes.     

基于内部失效机理预测评估渗碳Cr-Ni齿轮钢的超高周疲劳强度

对渗碳Cr-Ni齿轮钢进行应力比为0和0.3的室温超高周疲劳实验,观测试样中诱发裂纹萌生的夹杂和疲劳断口形貌,以全面评估渗碳Cr-Ni齿轮钢疲劳性能。将疲劳失效模式分为有细颗粒区(Fine granular area,FGA)的内部疲劳失效和有表面光滑区(Surface smooth area, SSA)的表面疲劳失效,并阐明了渗碳Cr-Ni齿轮钢的超高周内部疲劳破坏机制。基于累积损伤和位错能量法并结合细颗粒区形成机理和夹杂的最大评估尺寸,分别构建了两种渗碳Cr-Ni齿轮钢内部疲劳强度的预测模型。利用FGA尺寸与夹杂尺寸的比值和夹杂应力强度因子及应力比之间的关系,修正所提出的两种疲劳强度预测模型并给出了最大夹杂尺寸下的l_FGA-S-N曲线。结果表明,基于累积损伤法和位错能量法分别构建的疲劳强度预测模型都可用于预测评估渗碳Cr-Ni齿轮钢在多种应力比下的内部疲劳强度,基于位错能量法的强度预测模型精度较高。