Failure analysis used for remanufacturing of steel rolling components

The guide-pieces, used in the process line of steel rolling, were the important components. The guidepieces, which were slide contacting with the rolled-piece, had a high temperature and high speed. The wear was very serious. The results from failure analysis showed that there were three failure forms in the guide-pieces: the first was the wear during heat friction, the second was the heat fatigue under the cycle of deep heating and deep cooling, and the third was the impact rupture. Among them, the wear was the main reason. To the wear of guidepieces, there were four mechanisms, namely abrasive wear, adhesive wear, fatigue wear and corrosion wear. The failure analysis to the guide-piece laid the foundation for its remanufacturing. Foundation item: Project(50235030) supported by the National Natural Science Foundation of China     

Tribological properties and failure analysis of PTFE composites used for seals in the transmission unit

The sealing rings are one of the most important components as the sealing devices in the wet clutch unit of a heavy vehicle. The sealing ring, made from PTFE composites, was subjected to serious wear on the sealing surface, but the mating metal surface only had slight abrasion. A specialized test rig was designed for wear research and failure analysis of the sealing ring. The composition analyses of the ring material, working conditions and wear surface characteristics by visual inspection and tribological properties as well as microscopic analysis with scanning electron microscope was performed to determine the wear mechanism and failure causes. Results revealed that the wear of PTFE composites was characterized by abrasion and adhesion after a certain duration testing, and the wear mechanism changed to thermal fatigue and abrasive wear in the stage of intense wear. The thermal deformation and fatigue were primarily responsible for the rapid wear of the PTFE composites for the sealing rings.     

Experimental study on wear failure course of gas-valve/valve-seat in engine

The wear failure course of gas-valve/valve-seat in engine was investigated with a simulating tester. The results show that the failure of the contact conical surface is mainly caused by the elastic and plastic deformation and the fatigue micro-crack and spalling. The creep-deformation and corrosion atmosphere accelerated wear failure course at the high temperature. The wear failure course of the gas-valve/valve-seat in engine follows general wear rules of mechanical elements, but the rate of wear in the sharp wear stage is faster.     

Experimental study on wear failure course of gas-valve/valve-seat in engine

The wear failure course of gas-valve/valve-seat in engine was investigated with a simulating tester. The results show that the failure of the contact conical surface is mainly caused by the elastic and plastic deformation and the fatigue micro-crack and spalling. The creep-deformation and corrosion atmosphere accelerated wear failure course at the high temperature. The wear failure course of the gas-valve/valve-seat in engine follows general wear rules of mechanical elements, but the rate of wear in the sharp wear stage is faster. Foundation item: Project supported by Postdoctoral Foundation of Central South University; project (04B035) supported by the Youth Foundation of Hunan Province Education Bureau     

地质勘探钻头失效机理研究

结合地质勘探钻头破岩机理对失效的地质勘探钻头本体和合金齿(WC-Co硬质合金)进行了失效分析.通过对钻头本体的失效分析认为冲击端面失效机理为冲击疲劳,花键失效则是严重塑性变形后压渍剥落.通过对合金齿脱落、断裂、磨损三种失效形式的分析认为冲击剥落、磨粒磨损、冲击疲劳和冲击热疲劳等交叠作用是导致合金齿失效的原因,并阐明了形成的机理和主导因素.     

渐开线花键副微动磨损疲劳寿命预估

为准确预估渐开线花键副微动磨损疲劳寿命,在假设微动磨损与微动疲劳共同作用的情况下,对某型机主减速器花键副的微动损伤机理进行研究.分析国内外现有的微动疲劳预测方法,在传统SWT法预估疲劳寿命的基础上,忽略疲劳发生的位置和方向,给出花键副的损伤累积计算方法,在给定工况下预估航空花键副微动磨损疲劳寿命.结果表明:花键副微动作用过程中,微动磨损与微动疲劳互相竞争互相抑制,最终导致花键副在两种微动模式共同作用下发生疲劳失效;花键副的疲劳寿命随着SWT值的增大而减小.提出的损伤累积模型能较准确地反映微动磨损对微动疲劳的作用,为花键副的设计和维修提供了数值参考,也为进一步研究考虑齿侧间隙时的花键副微动磨损疲劳寿命预估提供了依据.     

电梯曳引系统摩擦磨损的分析

通过对曳引轮和曳引绳摩擦副的失效形式、润滑状态、摩擦类型和磨损机制的分析,认为电梯曳引系统的失效主要是由表面接触疲劳、磨粒磨损、氧化磨损等摩擦磨损的逐步累加所致,曳引轮和曳引绳主要失效形式是表面接触疲劳和磨粒磨损.分析结果还提出了曳引轮、曳引绳的选材方向和减少摩擦磨损的方法.     

Effect of Carbon Nanotube on the Oscillating Wear Behaviour of Metal-PTFE Multilayer Composites

Two kinds of metal-PTFE multilayer composites, which were composed of a steel backing, a middle layer of sintered porous bronze and a surface layer of polytetrafluoroethylene(PTFE) filled by carbon nanotubes(CNTs) or not, were prepared. The wear properties of metal-PTFE multilayer composites oscillating against 45 carbon steel under dry condition were evaluated on an oscillating wear tester, and the effect of CNTs on wear behaviour of metal-PTFE multilayer composites was studied. The results showed that the worn surface of metal-PTFE multilayer composites was characterized by adhesive wear, abrasive wear and fatigue wear. The CNTs greatly increased the adhesion strength of PTFE in the metal-PTFE composites and thereby greatly reduced puck, ploughing, and fatigue failure of PTFE during wearing. The PTFE filled with CNTs prevented direct contact between the mating surfaces and served as fine self-lubricating film, in which the oscillating wear mechanism of the composites was changed to a slightly adhesive wear. Therefore, the CNTs significantly decreased the weight loss and obviously increased the wear resistance of metal-PTFE multilayer composites.     

GH80A镍合金电子束焊接接头旋转弯曲高周疲劳行为研究

随着镍合金电子束焊接在工业中的大量应用,尤其是在航空发动机和燃气轮机等关键长寿命服役设备中的使用,有必要对镍合金电子束焊接接头的高周疲劳属性和断裂机理进行系统的分析研究。本文利用旋转弯曲高周疲劳试验机进行疲劳试验,获得了母材和焊接接头的应力-寿命(S-N)曲线和疲劳断口,同时利用扫描电镜（Scanning Electron Microscope,SEM）对疲劳断口进行了微观特征分析,确定了母材和焊接接头在不同应力幅下的疲劳裂纹萌生区和扩展区,分析了裂纹萌生区位置与应力幅的相互关系。最后,利用有限元分析了焊接接头热影响区微裂纹位置与大小对材料疲劳性能的影响。从现有的试验和模拟结果可以得到：1)母材和电子束焊接接头应力-寿命(S-N)曲线分布趋势一致,但焊接接头疲劳强度要低于母材,在靠近107周次时,两者疲劳强度差距最小;2)在高应力幅（低周疲劳寿命阶段）母材和焊接接头的疲劳裂纹均起源于试件表面并且都是多点萌生断裂,焊接接头疲劳断口位置位于焊接熔合区或热影响区;3)在低应力幅（高周疲劳寿命阶段）疲劳裂纹在试件次表面萌生,焊接接头疲劳断口位于热影响区或焊接母材靠近热影响区处;4) 通过有限元模拟发现微裂纹的存在有利于裂纹的扩展。在拉应力作用下,横向微裂纹更优于纵向裂纹沿着应力方向进行裂纹扩展;随着微裂纹尺寸增大,微裂纹间更易于相互贯通,形成更长的裂纹,从而降低了材料的疲劳性能。综上可知,电子束焊接仅仅影响材料的疲劳强度。疲劳断裂机理和母材一致都为穿晶解理断裂,疲劳裂纹萌生区域位置也和母材一样都受应力幅的直接影响。     

Preparation and properties of a new cutting pick of coal shearers

Reliability and wear resistance of cutting picks play a significant role in coal mine exploitation with coal shearers.Tool bit separation,blade breaking,severe erosion of the cutting body and fatigue fractures are the main reasons for failure of cutting picks.We carried out carburization on a 30CrMnMo alloy to synthesize a new cutting pick material with improved mechanical properties and high wear resistance.The results indicated that carburization can effectively strengthen the surface of the30CrMnMo alloy by forming a thick carburized layer and thus significantly improve the surface hardness and wear resistance.In addition,the excellent toughness of 30CrMnMo alloy as a substrate of cutting picks can prevent brittle ruptures and fatigue fractures under high impact stress conditions.The significant decrease in both frictional coefficient and rate of erosion of this carburized 30CrMnMo alloy suggests that this alloy is a potential material for cutting picks of coal shearers after rational carburization.     

换热器疲劳寿命的可靠性分析

针对换热器的疲劳失效分析, 以概率论为基础, 结合确定性的疲劳断裂力学估算方法, 推导了换热器零部件的疲劳裂纹扩展寿命的计算公式。考虑到主要评定参数:初始裂纹尺寸、工况载荷、断裂韧性、机械强度、系数等的不确定性和随机性, 应用蒙特卡罗模拟法对这些具有某种特定分布的随机变量进行了随机抽样计算。并利用数值积分法编制了计算机程序, 求出在一定可靠度和置信度下的疲劳寿命, 并与理论计算方法求得的疲劳寿命进行了比较。还比较了不同初始裂纹尺寸和断裂韧性对疲劳寿命的影响, 并给出了算例。分析结果表明, 蒙特卡罗模拟法真实地反映评定参数客观存在的不确定性, 克服了确定性评定方法的缺点, 具有良好的工程指导意义。     

钢砼组合结构PBH剪力键的疲劳性能

为了研究钢箱-砼组合结构中PBH剪力键在反复荷载作用下的疲劳性能,设计制作了PBH剪力键试验模型,进行了24万次疲劳推出试验。在疲劳破坏形态和试验滑移及应变数据分析的基础上,利用数值工具开展肋板开孔孔径、穿入钢筋直径、混凝土强度3个参数的PBH剪力键疲劳寿命影响因素分析。研究表明：PBH剪力键的疲劳破坏形态与静载破坏相似,表观表现为混凝土面多处斜向劈裂裂缝、内部榫孔混凝土压碎、穿入钢筋局部屈服;疲劳破坏演化过程分为疲劳损伤开始、发展、破坏3个阶段,其中疲劳发展阶段占整个疲劳阶段的91.7%,结构刚度在疲劳损伤开始和发展阶段退化较慢,在疲劳破坏阶段退化较快;肋板开孔孔径、穿入钢筋直径、混凝土强度3个参数对PBH剪力键疲劳寿命影响均有明显影响,其中穿入钢筋直径对疲劳寿命的影响尤为突出。     

热处理对铜基化学镀镍层结构和性能的影响

采用化学镀技术在紫铜表面制备化学镀镍层,结合OLYMPUS、XRD、HVS-1000等方法研究不同热处理温度对镀层结构和性能的影响,分析不同热处理温度与镀层表面形貌、微观结构、显微硬度和耐磨性的关系。结果表明,经500℃热处理后,镀层出现明显晶界,形成了大量与Ni相共格的高硬质相Ni3P,镀层硬度和耐磨性均达到最佳,此时镀层显微硬度为1 284 HV,磨损量为2.6 mg。     

钢的高温性能和模具的失效分析

本文简要介绍了新型热作模具钢(HD)的高温性能,这种钢的高温强度和热疲劳热磨损抗力优于3Cr2W8V钢,对其原因进行了适当的分析。同时,对铜管热挤压底模进行了失效分析和硬度检验、表层组织分析以及热疲劳热磨损形貌观察,结果表明模具的变形和拉毛失效均与模具材料的高温强度、组织稳定性以及均匀性密切相关,从而说明了HD钢模具使用寿命高的机制。     

Comparison of Biotribology of Swine Compact Bone Against UHMWPE

A pin-on-disk tribometer was used, in a comparative test to observe the tribological behavior of the swine femoral bone against UHMWPE with dry friction, physiological water and human plasma lubrication. The wear mechanisms of swine bones and UHMWPE were investigated by SEM. The experimental results of these wear tests demonstrated that both the friction coefficient and wear rate of UHMWPE were the lowest when human plasma lubrication was used. The wear mechanism of the compact bone was mainly fatigue wear with dry friction, corrosive wear under physiological water lubrication and abrasive wear with human plasma lubrication. For UHMWPE, the wear mechanism was adhesive wear and plastic deformation with dry friction, serious ploughing and fatigue fracture wear under physiological water lubrication, fine ploughing and plastic deformation with human plasma lubrication. An analysis of nitrogen elements on the wear surface of UHMWPE indicated that the content of nitrogen in worn areas was 16 times higher than that in unworn areas, which proved that serum protein deposition occurred on worn areas.     

H3Cr5WMoV埋弧堆焊合金层的组织与性能

利用自动埋孤焊在Q235钢基材表面得到H3Cr5WMoV合金堆焊层，并对合金堆焊层进行了回火处理。比较研究了堆焊层在焊态和回火态的组织、硬度、耐磨性及抗热疲劳性能。结果表明，堆焊层组织为板条马氏体加残余奥氏体。回火态堆焊层的硬度和耐磨性同于焊态堆焊层，回火态堆焊层的抗热疲劳性能也好于焊态堆焊层。     

OPI-1800AWS柱塞泵柱塞失效分析

用扫描电镜（SEM）分析方法对柱塞泵柱塞表面进行失效分析。分析表明,国产柱塞主要失效形式为磨料磨损,伴随轻度腐蚀和疲劳;美国柱塞主要失效形式为表面严重腐蚀、疲劳和化合物剥落。国产柱塞表层堆焊的镍基合金,含Ni量高,晶粒细,具有较好的耐腐蚀性能,可用于酸化压裂作业;美国柱塞表层复合碳化物的含量高,晶粒粗大,硬度高,耐磨料磨损的性能高,可用于加砂压裂作业。在设计柱塞时,必须提高柱塞强化表面的耐磨和耐腐蚀性能,同时还应当考虑使用防砂结构。     

接触疲劳磨损理论用于激光熔覆层的寿命预测

利用接触疲劳磨损理论讨论激光熔覆试样的疲劳磨损寿命问题，试验结果表明，在本试验条件一，接触疲劳磨损理论用于激光熔覆层的寿命估算是可行的。     

高镍铸铁排气歧管低周热疲劳研究

针对某新开发的车用高镍铸铁排气歧管进行了低周热疲劳寿命预测研究,为获取准确的热边界条件,采用STAR-CCM＋与有限元软件进行基于疲劳寿命试验条件的非稳态耦合传热分析,得到了排气歧管的对流换热系数和温度场,建立了具有真实装配关系并施加螺栓预紧力的排气歧管有限元模型,在对等效塑性应变分析的基础上,结合Coffin-Manson公式进行寿命预测。结果表明,在排气歧管开发过程中,采用该方法可以快速对其热疲劳寿命进行评估。     

经激光表面熔凝处理的Mg-11Y-2.5Zn合金的显微组织和摩擦学性能

用X-ray衍射和激光共聚焦扫描显微镜对经激光表面熔凝处理的Mg-11Y-2.5Zn合金进行显微组织和相组成分析,并测量改性层硬度变化。研究结果表明,经激光表面熔凝处理后,改性层由熔化区和热影响区组成,熔化区的显微组织明显细化,硬度有所改善。研究了经激光表面处理和铸态Mg-11Y-2.5Zn合金的摩擦学性能,滑移速率为0.785m/s,载荷范围为20～320N。两者的摩擦因子无显著差异,但经激光表面处理的Mg-11Y-2.5Zn合金表现出较低的磨损率,归结于熔凝区的组织细化和硬度增加。SEM磨损表面形貌分析表明,激光表面熔凝处理的合金与未处理合金的磨损机制基本相同,轻微磨损阶段为磨粒磨损和剥层磨损,严重磨损阶段为表面热软化和熔化磨损。