飞机舵机失效分析及首断件判定

某飞机舵机在地面随机振动试验后其电传功能失效,分解发现其中的电门支架和传感器支架均已断裂。采用断口分析、化学成分分析、硬度测试和金相检验等手段对该舵机失效原因及首断件进行了分析。结果表明:电门支架为该失效舵机各断裂件中的首断件,电门支架断裂的主要原因是其断裂处在振动试验前就已存在裂纹;舵机失效过程为电门支架首先发生准解理断裂后,其中一块断口由于失去固定作用对传感器支架产生撞击,进而又引起传感器支架发生疲劳断裂。     

5083铝合金支架开裂失效分析

结合产品运行工况,通过对失效件进行化学成分、金相以及断口分析,对某5083铝合金支架的开裂原因进行了分析。结果表明:高的循环应力和环境腐蚀,导致了支架疲劳开裂;另材料中较多的夹杂物加速了支架的疲劳开裂。提出了通过改进产品结构、确保其使用寿命的方案。     

烟囱焊接开裂分析

经焊接后的SUS430不锈钢烟囱在制造弯曲过程中出现开裂。对开裂件进行了化学成分分析、宏微观检验和力学性能测定。结果表明,材料在焊接过程中由于热影响区晶粒异常长大,并伴随α脆性相出现,导致材料的塑性降低,在后续工艺中冷变形作用下发生开裂。探讨了SUS430焊接过程中的热处理工艺。     

耐久道路试验中钢支架断裂原因分析

某汽车用钢支架,在耐久道路试验过程中发生断裂失效。通过化学成分分析、静拉伸试验、金相检验和断口分析,对比了耐久道路试验的失效件和合格件,分析了该钢支架的断裂原因。结果表明:失效支架材料中的碳含量很低,材料的晶界强度较弱;支架断裂部位发生了较大冲压形变,导致应力较大;二次加工脆性是支架沿晶疲劳断裂的根本原因。     

12Cr1MoV联箱与支管焊缝裂纹分析

为研究某厂联箱与支管运行1.4×105h后发生开裂的原因,采用宏观渗透及光学显微镜、扫描电镜、能谱仪、显微硬度计等测试方法对失效管进行检测.研究表明:焊后存在焊接缺陷,大量的裂纹垂直于焊缝,加速裂纹的扩展,改变应力分布状态;部分夹杂物沿直线分布,使材料受力具有方向敏感性,导致材料开裂失效;断口表面主要是Fe的氧化物,焊件长期过热,外表面形成不均匀氧化层,产生应力集中,致使焊缝从管壁外侧开裂;母材硬度超标.优化焊接工艺方案,焊前预热焊后回火,消除管件外壁的氧化层及减少设备停机次数均能有效防止同类焊接结构开裂失效.     

某压缩机法兰与钢管焊接接头焊缝开裂失效分析

某平台湿气压缩机法兰与钢管焊接接头焊缝发生开裂失效,采用宏观观察、化学成分分析、金相检验、力学性能试验、扫描电镜分析和能谱分析等方法对焊缝的开裂原因进行了分析。结果表明:焊接接头结构的不合理和焊缝内部的未熔合缺陷造成局部应力集中,并导致焊接接头的疲劳极限下降,在应力作用下法兰一侧切口处焊缝根部与未完全熔合的法兰母材交界处形成裂纹源;在外部循环载荷作用下,裂纹逐渐向外表面扩展,当达到焊接接头的疲劳极限时,焊缝即发生开裂。     

变速箱悬置支架开裂失效分析

某变速箱A380铝合金悬置支架在整车生产线的螺栓安装时发生了开裂失效。通过宏观检查、化学成分分析、金相检验、断口分析、硬度和密度测试等对悬置支架开裂失效原因进行了分析;在不同工艺条件下进行了模拟,确定了造成开裂的工艺条件。结果表明:悬置支架在铸造过程中,由于脱模剂混入其内部形成大量铝的氧化物,该氧化物造成材料强度降低是引起悬置支架发生开裂的主要原因。该氧化物是在冷模状态下大量的脱模剂与快速压铸的铝液反应形成的铸造缺陷。     

多层多级介质过渡线圈整体密封工艺

针对感应线圈承受冲击、过载、浸水试验后可能出现的开裂、断线及密封、绝缘失效等问题，提出了多层多级介质过渡线圈整体密封工艺。就是利用密封接触面及密封胶的热胀冷缩效应，由多种密封材料合理搭配形成介质过渡，通过线孔密封、线圈与壳体槽之间的密封、线圈的层间密封和外层密封等，实现线圈在小体积结构中的密封、强度和绝缘保护。验证试验结果表明：多层多级介质过渡线圈整体密封工艺用于小口径感应装定引信，经过温冲、浸水、锤击等试验后，未出现密封失效、结构开裂、绝缘失效等现象，有效地解决了弹上感应线圈的密封设计、绝缘设计和强度设计的技术难题。该工艺为国内小型感应装定引信信息交联电磁线圈的密封、强度及绝缘设计提供了借鉴。     

滑油散热器进油管嘴裂纹分析

某直升机用主减速器滑油散热器装机使用一段时间后,在进油管嘴与散热器焊接处出现渗油,检查发现该处存在裂纹。通过断口宏、微观形貌观察以及焊缝截面金相检验,确定了进油管嘴的开裂性质和开裂原因。结果表明:主减速器滑油散热器进油管嘴的裂纹性质为高周疲劳裂纹,管嘴开裂与其结构设计不合理有关;通过减小管嘴长度和增加端盖厚度,可以有效地避免进油管嘴的开裂失效。     

汽车内饰镀铬框开裂失效的原因分析

某汽车零件厂的镀铬件面框开发过程中经100℃高温烘烤与气候交变试验后其下部120℃转角处均出现开裂。通过X射线测厚法、显微镜、冰醋酸内应力分析、计算机仿真模拟等方法对镀铬面框的开裂缺陷进行了深入分析。结果表明:由于外罩与内框局部焊接力过大,限制了内框和镀铬框在高温状态下的膨胀,使镀铬框受到较大的膨胀力,从而导致应力较为集中的区域出现开裂。通过对外罩盖与内框焊点的优化,降低了焊接力,给予了内框一定的膨胀空间,成功解决了故障现象,满足了产品的质量要求。     

扭力梁式后悬架模态与疲劳实验研究

扭力梁式后悬架是汽车行驶系统中重要的承重构件,在不同的行驶工况下,会受到不同幅值和不同频率的激励。在激励频率和扭力梁式后悬架固有频率接近或相同时,会产生共振,进而发生疲劳断裂。通过对扭力梁式后悬架进行模态实验,获得该结构的固有频率和模态振型。对同一型号的扭力梁式后悬架进行弯曲、扭转疲劳实验,得到其疲劳破坏的具体形式。对产生破坏的扭力梁式后悬架进行模态实验,对未损坏和损坏的扭力梁式后悬架各自的固有频率和模态振型进行对比分析,发现产生疲劳破损的扭力梁式后悬架在某一阶频率下的模态振型有较大变化,结构的固有频率值和固有频率分布的变化并不很大。     

Composite integrated rear suspension

Fiber reinforced plastics are undergoing extensive studies as potential structural materials for automotive applications. This paper describes the design, fabrication, weight analysis and testing of a composite integrated rear suspension in a Ford Escort vehicle. This suspension utilizes a transverse FRP leaf spring to integrate the functions of the production Escort stamped steel lower arms and coil springs. The spring was designed using previously developed composite design procedures. The results show concept feasibility, a vehicle weight saving of 7 lb, good ride, noise, vibration and harshness (NVH) characteristics. A reduction in roll stiffness points out the need for development in the design of the center clamp attachment to the body structure. This study demonstrates the viability and potential of fiber reinforced composites in automotive suspension systems.     

Failure analysis of the suspension spring of a light duty truck

In this paper the failure of the rear suspension spring is analyzed in detail. The rear axle suspension system of the truck and fractured flat spring is investigated. Fracture surface, mechanical and chemical properties and microstructure of the spring material is analyzed. Forces acting on the spring is determined and strength calculations are carried out. Later, failure behaviour and cause of fracture is revealed after carefully analysis of microstructure and results of calculations. At the end precautions to be taken to prevent a similar failure is recommended.     

汽车主动悬架模糊自适应控制研究

在建立的整车主动悬架系统动力学模型基础上,利用自适应模糊控制方法,分别设计了前轮和后轮的主动悬架模糊自适应控制系统,将前轮的路面激励信号引入到后轮处主动悬架控制策略之中,使得主动悬架可以根据路面和车身姿态的变化而改变特性,以适应当前车辆运行工况的需求,分别进行了随机路面输入和正弦波凸起输入的仿真计算和分析,结果表明,相对于传统的被动悬架系统,模糊自适应控制主动悬架系统车辆的质心垂直加速度峰值和标准差分别下降了38.9%和36.5%;车辆以5m/s速度驶过正弦波凸起时,主动悬架的后轮处车身加速度峰值比被动系统减少了43.9%,有效提高了汽车的行驶平顺性。     

蒸汽过热器管断裂失效分析

某奥氏体不锈钢制蒸汽过热器管在加碱煮炉过程中发生断裂。采用力学性能测定、宏微观检验及能谱分析,对该断裂管进行了分析研究。结果表明,蒸汽过热管断裂失效是由碱脆造成的。     

地铁列车转向架断裂原因分析

地铁列车转向架是由钢板焊接而成，在服役一年后断裂，对断裂件进行了断口形貌、金相组织、化学尬发分析及硬度测定。结果表明，断口显示出疲劳断裂痕迹，焊接缺陷是引起疲劳裂纹萌生及扩展的主要原因，而热影响区粗大的贝氏体及低碳马氏体组织的存在加速了疲劳断裂过程，最终导致转向架早期疲劳断裂。     

考虑随机因素的汽车悬架参数多目标稳健优化

为了稳健地提高汽车平顺性,减少轮胎对路面破坏。以某载货汽车的四自由度悬架模型为研究对象,同时考虑制造精度的影响,以车身垂直加速度、前后轮胎动载荷的均方根值的统计均值和方差为目标函数,采用蒙特卡罗抽样法和自适应多目标遗传算法对悬架参数进行稳健优化。结果表明：优化后的悬架弹簧刚度减少而阻尼系数增大,性能有大幅度改善,与传统的优化设计相比更符合实际情况,且具有更强的抗干扰能力。     

Failure Analysis of Welded Radiant Tubes Made of Cast Heat-Resisting Steel

Radiant tubes made of cast heat-resisting steels were cracked after 4 years of operation at 1020 °C temperature in hydrocarbon cracking furnace. Optical microscopy of the tubes showed that there was extensive precipitation and intermetallic compound formation especially as brittle networks with progressive reduction in toughness and resistance to thermal and mechanical stresses. SEM and EDS analysis proved both decarburization and oxidation on interior and exterior surfaces. Apart from cracking due to long-term heating, the tubes experienced high temperature creep. HAZ cracking after welding of cracked and/or creeped tubes due to formation of brittle carbide networks was overcome by localized solution heat treatment followed by fast dry air cooling. Localized dissolution of carbide networks and intermetallic compounds resulted in lower strain microstructures and enhanced resistance of parts to thermal and mechanical stresses during repair welding. It is evident that localized solution heat treating other than lowering strains can cause the precipitates to be more uniformly and finely distributed. Fast dry air cooling rate after solution heat treating and similar cooling after welding can help to control precipitation of carbides. Detailed non-destructive testing after welding along with tensile testing proved that post-weld cracking was controlled.     

In‐Field Measurement of Forces and Deformations at the Rear End of a Motorcycle and Structural Optimisation: Experimental–Numerical Approach Aimed at Structural Optimisation

Abstract: The present study concerns the analysis of the asymmetric displacement behaviour of the rear part of a motorcycle. Stylistic reasons led to the design of a vehicle with only one suspension located on the left‐hand side. Experimental tests performed on a circuit with seven obstacles along a straight line confirmed that the bending displacement is higher on the right‐hand side than on the left. This study aimed to perform a structural optimisation of the components involved at the rear end of the motorcycle, to find a solution to the problem. A hybrid approach is applied: the force acting on the suspension and bending displacements at the rear end were simultaneously measured in working conditions; a finite‐element method model was then set up, validated and applied for design optimisation purposes. Both methodological aspects and applicative results are presented and discussed. Finally, a solution in accordance with design specifics is proposed.     

齿轮轴退火开裂分析

用理化分析方法,对２０ＣｒＭｎＴｉ钢制齿轮轴退火开裂进行了分析,结果表明,该齿轮轴铬,锰含量超标,齿轮轴热处理退火后出现较大应力,导致齿轮轴开裂。