某加工中心刀塔芯轴断裂原因分析

某加工中心刀塔芯轴在使用过程中发生断裂。通过宏观观查、化学成分分析、冶金质量分析、金相检验、断口分析、硬度测试、芯轴尺寸及表面加工质量分析等方法对芯轴断裂的原因进行了分析。结果表明:该刀塔芯轴硬度未达到技术要求且A类夹杂物含量较高,降低了芯轴的抗疲劳性能,同时由于未设计砂轮越程槽导致退刀槽过渡圆角在砂轮打磨时被破坏,应力集中加剧,在交变载荷作用下芯轴发生了疲劳断裂。     

切胶机连接轴断裂原因分析

切胶机在投入使用不到两个月其液压缸连接轴即发生断裂。采用化学成分分析、金相检验、力学性能检测和断口分析等方法对断轴进行了分析。结果表明,该连接轴属于疲劳断裂。尽管该轴工作过程中承受着往复的拉压作用,但与一般拉压工作条件下轴的拉压疲劳断裂机理不同,导致该连接轴疲劳断裂的主要原因是工作过程产生的不断变化的弯曲应力。     

进料泵传动轴断裂分析

采用显微组织分析、扫描电镜分析和拉伸试验等方法对进料泵传动轴的断裂进行了失效分析。结果表明,泵轴断裂属疲劳失效,轴中段键槽处在制造过程中存在淬火裂纹是导致疲劳断裂的主要原因。     

调速器步进电机轴断裂失效分析

某电厂调速器步进电机轴在开机调负荷过程中发生断裂,对断裂电机轴进行了宏观检验、化学成分分析、硬度测试、金相检验和断口分析,并对步进电机轴材料进行了切应力校核。结果表明:该调速器步进电机轴断裂失效为低应力高周旋转/弯曲疲劳断裂。电机轴断裂失效的主要原因一方面是因为变径部位退刀槽位置容易造成应力集中现象,从而促使步进电机轴表面产生疲劳裂纹;另一方面是因为硫化物、碳化物等夹杂物的存在会降低材料的塑性、韧性和疲劳强度,进一步造成应力叠加,材料力学性能降低,加速疲劳裂纹的形成和扩展。     

45钢减速器轴断裂原因分析

某45钢减速器轴在使用过程中发生断裂。通过对断裂件进行宏观分析、化学成分分析、力学性能试验、金相检验以及断口微观分析,分析了该减速器轴断裂属性及原因。结果表明:减速器轴断裂属性为多源疲劳断裂,断裂主要是由轴未进行调质处理致使材料力学性能偏低、轴表面存在加工缺陷以及轴变径处存在严重的应力集中所引起。     

脱硫氧化风机轴断裂原因分析

利用金相检验、化学成分分析和力学性能测试等试验手段,结合疲劳强度校核和现场情况调研,对35CrMo钢脱硫氧化风机轴在使用过程中发生断裂的原因进行了分析。结果表明:风机轴在应力集中的键槽处产生疲劳裂纹,裂纹先沿轴向扩展,后沿轴横截面方向扩展,最终造成风机轴横向低应力高周疲劳断裂;风机轴的力学性能符合标准要求,根据疲劳强度校核,在正常载荷下,键槽处的风机轴是安全的;脱硫氧化风机运行环境恶劣,振动和长时间超负荷运行是造成该风机轴过早疲劳断裂的根本原因。     

曲柄销轴断裂分析

对曲柄销轴在采油设备上的安装配合情况进行了调查，在此基础上，分析了销轴在采油设备工作时的受力情况，并通过化学分析、金相检验和扫描电镜等方法对销轴断裂失效进行了分析。结果表明，该销轴在交变偏斜拉应力的作用下，在销轴的应力集中处——退刀槽根部产生疲劳裂纹，最终导致疲劳断裂。另外钢材质量欠佳、组织不良也促进了断裂过程的进行。     

大环件轧机用芯轴断裂分析

大环件轧机的芯轴连续发生断裂.采用断口分析、金相检验、电镜能谱分析和力学性能测定的方法对芯轴断裂的原因进行了分析.结果表明,所用材料的显微组织缺陷和耐热性能差是导致芯轴发生早期断裂的主要原因.     

42CrMo轧管机辊轴断裂分析

分析了４２ＣｒＭｏ轧管机辊轴断裂的原因。结果表明：该轴为疲劳断裂，轴中段键槽处存在的淬火裂纹是导致疲劳裂的主要原因。     

伺服机构涡轮泵转子叶片断裂失效分析

某伺服液压源涡轮泵转子在测试过程中转子叶片发生断裂,通过对失效转子的观察、测试与分析认为:转子叶片的断裂性质为疲劳断裂,断裂原因是在叶片根部存在疲劳裂纹,疲劳裂纹在动静载荷作用下失稳扩展而发生疲劳断裂.分析认为转子叶片发生疲劳破坏与其组织在锻造成型工艺过程中存在工艺缺陷,导致材料疲劳寿命下降有关.     

基于扭矩控制的导管内径滚压连接成形特征分析

钛合金导管内径滚压连接技术主要用于飞机液压管路系统中,具有耐高压和高密封性,能够提升飞机液压管路系统的高可靠性能,满足飞机轻量化和长寿命的需求,成为航空管件连接技术的首选方案.本文以理论分析、有限元模拟和试验相结合的方法,从导管滚压连接胀形器各组件的运动状态、接触状况、受力分析以及管材节点位移变化等方面,探讨了基于扭矩控制的导管内径滚压连接成形机理及特征.研究表明,成形过程中芯轴主动转动,滚柱带动保持架周向随动转动;芯轴与滚柱之间有较大的径向挤压力和切向摩擦力,在这两个力的合力作用下,产生轴向进给力,使芯轴自动进给,导管、滚柱和芯轴之间接触面和接触力逐渐增大,成形扭矩随之增加,导管材料逐渐嵌入管套凹槽,完成连接成形,这是扭矩控制的导管内径滚压连接机理所在.理论分析与有限元模拟及试验结论吻合较好,研究结果对工程应用中的质量控制和工艺优化具有一定的指导作用.     

厚壁结构管件刚模塑性成形过程的数值模拟与工艺研究

基于刚塑性有限元法,忽略了回弹和管坯与模具、芯轴的间隙的影响,建立了简化的有限元模型,对厚壁管压弯、压扁成形过程进行了数值模拟,得到了各场量的分布。根据应力分布结果,对起皱和破裂等缺陷进行分析预测,并根据截面变化情况,研究了芯轴对截面畸变的作用与影响。该研究对厚壁管件弯曲和扁化过程的工艺方法提供了依据。     

模具间隙对薄壁管绕弯成形的影响规律

详细分析了薄壁管绕弯成形过程及其变形特点,基于有限元法对绕弯成形模具芯棒与管坯间隙,压块与管坯间隙,防皱块与管坯间隙以及弯曲凹模与管坯间隙等4个因素与薄壁管成形质量、回弹量的影响显著程度进行了四因素三水平的正交试验分析。结果表明:芯棒与管坯的间隙对成形后薄壁管壁厚及回弹的影响最显著,弯曲凹模与管坯间隙对回弹影响也较显著。     

Influence of Mandrel on the Performance of Titanium Tube with Cold Rotary Swaging

Rotary swaging is a process to reduce the diameter of tubes and/or rods. It can be used to produce tubes or rods with a variety of external and internal diameters and shapes. Mandrel is an important part of the forming process. In this work, the influence of mandrel on tube performance is discussed. Data show that larger mandrels provide better forming results. Wall thickness standard deviation can be reduced from 0.108 (without mandrel) to 0.031 (7.4 mm diameter) and the hardness of the tube can be increased from 273.5 HV (original material) to 328.5 HV (7.4 mm diameter). Surface toughness can also be improved. Analysis shows that the microstructure is distinctly different from that of the original material and it varies by changing the mandrel. This research validates the use of cold swaging as an efficient method of forming titanium.     

热轧钢管用限动芯棒表面失效形貌分析

利用数码相机、光学显微镜、扫描电镜以及能谱仪等仪器,对某参与钢管轧制后失效报废的限动芯棒进行了解剖分析,对失效芯棒的各种表面缺陷进行了观察和分类,并探讨了缺陷产生的原因。结果表明:限动芯棒经过轧制后产生的表面缺陷主要有片状脱落、网状裂纹、沟状缺陷和环状裂纹等,高温氧化和高温磨损是限动芯棒表面失效的主要原因;在轧制初期,芯棒头部和中部表面的镀铬层被磨损,随后形成氧化膜,氧化膜在压力、摩擦力及热应力的作用下发生起泡乃至开裂、脱落;裂纹首先从表面萌发,逐渐向芯棒心部扩展、交汇,在摩擦或内应力的作用下极易脱落,甚至形成大面积的严重磨损;芯棒表面的网状缺陷或大面积的氧化膜剥落进一步恶化,裂纹逐渐变宽,伴随着表层的块状脱落,形成了较深的磨损沟,并且在高温、润滑剂以及腐蚀液的作用下,沟状缺陷的内表面发生氧化,这些氧化皮的破裂和脱落加速了裂纹的扩展和局部脱落,因此当限动芯棒表面出现沟状缺陷时,意味着其失效速度将明显加快。     

芯轴摩擦系数对推压-拉拔复合缩径的影响

推压-拉拔复合缩径工艺是管坯减径的新方法,芯轴外表面与管坯内表面之间摩擦系数对工艺有重要的影响。通过建立推压-拉拔复合缩径变形过程中变形管坯的力学模型,分析了芯轴外表面与管坯内表面之间摩擦系数对成形的影响规律。针对某载重6.5 t胀压成形汽车桥壳管件的第一道次推压-拉拔复合缩径,设定不同的芯轴摩擦系数,进行了有限元仿真,得到了芯轴摩擦系数对管坯变形的影响规律,并基于管坯传力区不失稳以及变形所需凹模推力和芯轴拉拔力较小,给出了芯轴摩擦系数的设定范围。进行了缩径实验,实验和有限元模拟的结果接近。较小的芯轴摩擦系数可能造成管坯起皱失稳,而较大的芯轴摩擦系数,有利于降低管坯轴向压应力、凹模推力和芯轴拉拔力,但可能造成管坯表面划伤。     

External Pressure Forming and Buckling Analysis of Tubular Parts with Ribs

Buckling and forming processes of tubes with varying slenderness ratio （ratio of length to diameter） under external hydraulic pressure were analyzed with three-dimensional finite element method （FEM） for studying tube external pressure forming （EPF）. Buckling pressures for different tube blanks without mandrel were predicted, and an EPF of a carbon steel tube onto a mandrel with six ribs was simulated. Both thickness distribution and buckling pressure from the simulations were found to be in agreement with those from experiments. Buckling pressures are shown to be a function of the slenderness ratio. The tubular part with six ribs produced by EPF has a uniform thickness distribution, whose maximum thinning rate is only 5.9%.     

Metallurgical Observations on Fatigue Failure of a Bent Copper Tube

Deoxidized high phosphorus copper (C12200, DHP-Cu) is the principal construction material in hydraulic and HVAC installations due to its superior thermal/electrical conductivity, formability, corrosion resistance, and antibacterial properties. However, design and installation deficiencies or aggressive environmental conditions lead very often to unexpected failures due to abnormal operation or improper handling of material during construction. Copper water tubes experiencing leakage at the bend area, after short-time period in service, were disconnected from a hydraulic installation and brought for failure investigation. Optical and scanning electron microscopy, employed for microstructural and fractographic evaluation, were used as the principal analytical techniques in the context of the present investigation. Failure analysis findings suggest strongly that the leakage was caused by low-cycle fatigue failure (<10⁴ cycles), initiated from the tube outer surface and followed by brittle intergranular fracture. Final fracture occurred via the brittle intergranular failure process, when the remaining tube wall thickness reaches a critical size. The crack then becomes unable to sustain the operating load. Review of the design and installation conditions along with the special attention to material handling to avoid surface flaws (pits, scratches, gouges, etc.), which might be potential fatigue crack initiation sites due to increased stress concentration, are suggested as preventive actions to minimize the potential for further fatigue damage.     

Tube cyclic expansion-extrusion (TCEE) as a novel severe plastic deformation method for cylindrical tubes

Tube cyclic expansion-extrusion (TCEE) is proposed as a novel severe plastic deformation method for processing cylindrical tubes. TCEE is capable of imposing large strains to cylindrical tubes without dimensional and geometrical changes. In TCEE process, peripheral small shallow grooves were devised on mandrel and inner surface of the chamber. The grooves allow tubular specimen to initially expand and then extrude to the initial thickness while it is deformed between mandrel and chamber. TCEE was first trialed on commercial AZ91 magnesium alloy and substantial grain refinement was recorded. Mean grain size of 1 μm was achieved after two cycles of TCEE. Microhardness assessment across tube thickness demonstrates good homogeneity of hardness distribution; microhardness of the initial tube increased from 65 to 90 Hv after two processing cycles of TCEE. After two processing cycles of TCEE, yield and ultimate strengths were increased by 2.9 and 2.6 times compared to those in as-cast condition. The elongation to failure was also increased from initial value of 1.6 % to about 8.1 %. The process was also numerically simulated by commercial FE code of ABAQUS/explicit to further investigate strain accumulation in TCEE process.     

芯棒对铝合金矩形管绕弯回弹作用的数值模拟

为掌握芯棒参数对薄壁矩形管绕弯成形回弹的影响规律,从而为芯棒参数的选取与设计提供依据,基于ABAQUS有限元软件建立了3A21铝合金薄壁矩形管弯曲成形及回弹三维有限元模型,试验验证了所建模型的可靠性.基于所建模型,研究了芯棒参数如芯棒/芯头与管坯摩擦(μm)、芯棒/芯头与管坯间隙(δm)、芯头个数(n)及芯棒伸出量(em)对回弹角的影响.结果表明:抽芯是一个应力预卸载过程,可显著减小回弹;随着芯棒/芯头与管坯摩擦系数(μm)的增加,回弹减小;随着芯棒/芯头与管坯间隙(δm)的增加,回弹增加;随着芯头个数(n)的增加,回弹减小;随着芯棒伸出量(em)的增加,回弹先增大后减小.