孔挤压与超载复合强化对LY12CZ铝合金疲劳裂纹起始寿命的影响

研究了孔挤压与超载复合强化对LY12CZ铝合金疲劳裂纹起始寿命的影响。实验结果与分析表明,孔挤压与超载复合强化对LY12CZ铝合金的疲劳裂纹起始寿命及裂纹萌生、扩展特性的影响和孔挤压单一强化效果相同。此外还给出了复合强化后LY12CZ铝合金疲劳裂纹起始寿命的定量表达式,以及变幅载荷下LY12CZ铝合金孔挤压件疲劳裂纹起始寿命的估算新方法。     

TC4板孔冷挤压强化残余应力分布与疲劳寿命

开展了不同挤压量下TC4钛合金板孔冷挤压强化有限元仿真研究,得到了挤压强化后最小截面的切向残余应力分布规律,分析了挤压量对受载试样孔边应力分布的影响,探讨了挤压量、残余应力和疲劳增益三者之间的内在关系。采用开缝衬套冷挤压强化工艺对TC4带孔板件进行冷挤压和疲劳验证试验。研究结果表明,挤压强化后的孔边切向压缩残余应力可以有效降低孔周应力集中程度,优化受拉试样最小截面应力分布,改变裂纹源的位置并延长疲劳裂纹的萌生和扩展寿命,有效提高试样疲劳寿命。综合仿真和疲劳试验得到TC4板孔最优挤压量为4%。     

高干涉量压合衬套强化铝合金孔结构的疲劳性能

分别采用高干涉量压合衬套单侧挤压强化和两侧挤压强化两种工艺对7050铝合金孔结构进行强化,研究孔结构的残余应力和疲劳性能,并采用梯形累积法由疲劳断口定量反推出疲劳裂纹萌生寿命和扩展寿命。结果表明:孔结构中形成深度达12mm的残余压应力场,单侧挤压强化试样挤入端的残余应力显著低于挤出端的,两侧挤压强化试样挤入端和挤出端的残余应力相当;单侧挤压强化试样和两侧挤压强化试样的平均疲劳寿命比未挤压强化试样的分别提高了770%和1 500%,高干涉量压合衬套强化技术具有显著的疲劳强化效果,且双侧挤压强化的效果更好;高干涉量压合衬套强化技术可同时提高孔结构的疲劳裂纹扩展寿命和萌生寿命,且萌生寿命提高的幅度更大。     

高强度钢材料小孔孔边R冷挤压强化工艺

小孔孔边R挤压强化工艺是基于开缝衬套冷挤压理念,作为在疲劳敏感孔处延缓裂纹扩展的一种方法。该工艺利用在孔边施加一定的压力,引起材料径向塑性流动,并形成沿孔边缘向外扩展的环形残余压应力区,提高工件的抗疲劳强度。     

孔挤压强化工艺对7A12铝合金组织及疲劳性能影响的研究

研究了孔挤压强化工艺对7A12铝合金锻件的疲劳增益效果,并通过透射电镜、扫描电镜及X 射线衍射仪等设备,研究了疲劳断口的形貌特征、微观组织变化以及孔壁表层的残余应力场分布。研究结果表明,挤压过盈量为5%时,孔挤压疲劳寿命增益效果最好,是未强化的13.5倍;孔挤压后,孔壁强化层内形成了深度＆gt;9 mm 的残余压应力层,强化层内形成的位错胞状结构可以有效延缓疲劳裂纹的扩展速率,从而提高材料的疲劳寿命。     

孔挤压强化疲劳增寿效益的试验研究

为研究芯棒挤压和开口衬套挤压工艺的疲劳增寿效益,以及应力水平高低对增寿效益的影响,针对飞机结构中常用的铝合金和钛合金,设计孔表面状态分别为未挤压、芯棒挤压和开口衬套挤压的含孔细节模拟试件。通过模拟试件等幅谱下疲劳试验,获得裂纹形成、扩展和总寿命,通过对试验数据的统计对比分析,对芯棒挤压和开口衬套挤压工艺的疲劳增寿效益进行对比,研究应力水平高低对疲劳增寿效益的影响,分析在裂纹形成和扩展阶段的疲劳寿命增益。     

检测裂纹长度的高温等应变位移传感器研制

介绍了检测裂纹长度的高温等应变位移传感器的设计制造工艺,研制出了能在５５０ｏＣ下使用的高温等应变位移传感器。经常温断裂韧性和５５０ｏＣ低周疲劳裂纹扩展速率试验应用,表明研制出的高温等应变位移传感器精度高,是金属材料疲劳裂纹扩展速率和断裂韧性试验用的理想传感器件。     

随焊冲击旋转挤压控制LD10薄板件焊接变形和热裂纹的研究

LD10铝合金薄板在焊接过程中易产生焊接热裂纹,焊后薄板件易产生较大的焊接变形。采用冲击旋转挤压头对焊缝及相邻区域施加一定频率的冲击旋转挤压作用,使焊缝及近缝区产生塑性延展;对LD10常规焊接件和随焊冲击旋转挤压件的焊接残余变形与焊接残余应力进行测量,对比分析了常规焊接件和随焊冲击旋转挤压件的拉伸试验、维氏硬度、断口分析和金相组织,明确了随焊冲击旋转挤压工艺对焊接件组织及性能的影响。试验结果表明,随焊冲击旋转挤压处理后,工件的残余应力被降低到较低水平,随焊冲击旋转挤压工艺起到控制焊接残余应力和变形的作用,并且抑制了焊接热裂纹的产生。     

某超高强度钢零件小孔挤压强化工艺研究

起落架与机体同寿命是现代高寿命飞机的普遍要求。对于起落架主要承力件,除优化设计外,在选材上应选用300M、A100超高强度钢及钛合金等高强度、高韧度材料,并采用先进的表面强化技术及先进工艺等。小孔挤压强化技术是通过在孔周围施加一定的残余应力,从而显著地提高带孔零件的疲劳寿命。通过对超高强度钢零件薄壁上小孔内表面进行挤压强化工艺的研究,针对超高强度钢小孔孔壁挤压强化的工艺方法,找到了合理的挤压参数,并应用于产品的加工。     

喷丸成形及强化工艺对铝合金疲劳性能及裂纹扩展的影响

采用数控喷丸机对2024-T351铝合金进行畸形喷丸成形及强化工艺试验,采用MTS880设备对板材进行轴向疲劳性能测试,同时对原始状态、喷丸强化及喷丸成形下的板材进行裂纹扩展速率的测试.通过对比不同方式下裂纹扩展的速率的对数图,得知经过喷丸成形及强化后试件的裂纹扩展速率大大减小,比原始状态降低30％左右.     

Low cycle fatigue and strengthening mechanism of cold extruded large diameter internal thread of Q460 steel

large diameter internal thread of high-strength steel(LDITHSS) manufactured by traditional methods always has the problems of low accuracy and short life. Compared with traditional methods, the cold extrusion process is an effective means to realize higher accuracy and longer life. The low-cycle fatigue properties of LDITHSS are obtained by experiments, and the initiation and propagation of fatigue cracks are observed by scanning electron microscope(SEM). Based on the mechanical properties, surface microstructure and residual stress, the strengthening mechanism of cold extruded large diameter internal thread(LDIT) is discussed. The results show that new grains or sub-grains can be formed on the surface of LDIT due to grain segmentation and grain refinement during cold extrusion. The fibrous structures appear as elongated and streamlined along the normal direction of the tooth surface which leads to residual compressive stress on the extruded surface. The maximum tension stress of LDIT after cold extrusion is found to be 192.55 k N. Under low stress cycling, the yield stress on thread increases, the propagation rate of crack reduces, the fatigue life is thus improved significantly with decreasing surface grain diameter and the average fatigue life increases to 45.539×10~3 cycle when the maximum applied load decreases to 120 k N. The low cycle fatigue and strengthening mechanism of cold extruded LDIT revealed by this research has significant importance to promote application of internal thread by cold extrusion processing.     

A study on chevron crack formation and evolution in a cold extrusion

A numerical algorithm based on the element deletion method and rigid-viscoplastic finite element approach depending on Cockcroft-Latham and specific plastic work fracture criteria was applied to predict formation and evolution of possible cracking in a cold extrusion of aluminum and steel alloys. The Cockcroft-Latham fracture criterion induced an internal crack while an external crack occurred owing to the specific plastic work criterion in simulations. As a result, the Cockcroft-Latham criterion was found to be valid for predicting chevron cracking in comparison with the experimental observation available in the literature. Using the Cockcroft-Latham criterion, cracking was carefully investigated in terms of the size of the crack and gap distance between cracks depending on the number of elements and boundary condition at the punch interface. The critical damage values for the Cockcroft-Latham fracture criterion were also calculated based on the tensile instability and fracture conditions to investigate their effect on possible cracking. Finally, a processing map based on the Cockcroft-Latham fracture criterion for preventing chevron cracking in the cold extrusion of commercially available steel alloy was developed by considering processing parameters such as reduction in area and semicone angle. According to this investigation, the developed element deletion method with the Cockcroft-Latham fracture criterion was reasonably accurate for carrying out chevron cracking analyses in the cold extrusion with proper selection of a critical damage value.     

Service life estimation of extrusion dies by numerical simulation of fatigue-crack-growth

In this study, fatigue behavior of cold extrusion dies is investigated analytically. Experimental studies and practical experience have shown that fatigue cracks occur at the inlet radius of die shoulders. The highest stress concentration is found also at the same location. For this reason, effective stress intensity factors at different locations of the die-shoulder inlet of a typical axisymmetric extrusion die have been calculated by using the finite element method. The crack growth has been simulated by applying the Paris/Erdoĝan fatigue law to the computed data. Finally, service life of the extrusion die has been estimated from the crack-growth-rate. Agreement of theoretical estimations with available data is found to be satisfactory within the limits of experimental uncertainties. Furthermore the experimental behavior of the crack growth (stable-unstable-stable growth with final fracture) is simulated correctly. It has been shown that the unexplained behavior is caused by decrease of stress concentration with increasing crack-length.     

单试样测试材料JId值方法的比较

利用示波冲击试验，以小角度多试样冲击试验结果为标准，对几种单试样测试材料动态弹塑性断裂韧度JId值的方法进行了比较。结果表明：最大载荷前能量方法只适用于测试启裂后无显著形变强化的高强钢；柔度变化率方法不宜于测试撕裂阻力较高的材料；而对于裂尖钝化时近似呈半圆形的材料，利用饱和伸张区宽度方法可以方便地得到材料的JId值。     

星形套冷挤压成形有限元方法研究

利用高级非线性软件MSC．Marc，采用弹塑性热机耦合分析对行星套冷挤压过程进行了模拟，得出了塑性成形的流动规律和模具的应力分布，比较了不同建模方法对模拟结果的影响，比较全面地阐述了冷挤压塑性成形的有限元仿真技术。研究结果对冷挤压成形的有限元仿真以及塑性成形工艺控制和提高模具寿命具有指导意义。     

A Study on the Extrusion by a two-step process for manufacturing helical gear

Much research has been carried out in the manufacturing of helical gears by cold forging or by extrusion. Although cold forging is applied to some bevel, spur, and helical gears, problems in connection with the reduction forming load and tool life still make it difficult for these methods to be commercialized. In this study, focusing on reducing a load in forming helical gears, the extrusion of helical gears by two-step process is proposed. This process is composed primarily of extruding a billet to a spur gear and then twisting the previous spur gear extruded to a helical gear. Cylindrical billets of Cr-Mo steel(SCM 415) and aluminium alloy(Al60 series) were used as specimen materials for the experiments. The maximum loads obtained by upper-bound analysis and FEM are compared with the results of experiments. The loads of the analysis have good agreements with those of the experiment. The newly proposed method can be used as an advanced technique that remarkably reduces the forming load and replaces the conventional forming.     

差速器行星齿轮冷挤压工艺及制造研究

结合开发差速器行星齿轮冷挤加工,根据该零件的技术要求,依据冷挤压理论,分析研究了该零件的冷挤压工艺及制造方案,特别对冷挤压工艺中的几个主要问题进行了研究.通过研究得到,冷挤压加工是该齿轮最合适的生产方式,它具有以下独特优势:降低生产成本,提高原材料利用率,提高齿轮质量,提高生产效率,降低环境污染,有利于可持续发展,是值得推广的低碳锥齿轮加工技术.     

Improved anticontaminator for cryo-electron microscopy with a Philips EM 400

Electron microscopy of frozen-hydrated specimens is frequently impaired by atmospheric humidity, introduced together with the cold specimen and subsequently condensing on it. This effect can be prevented in the Philips 400 electron microscope operating with the cold stage PW6591 by an improved anticontaminator described in this note. The retractable anticontaminator is formed by two adjustable liquid-nitrogen cooled blades placed just above and below the specimen. It does not interfere with any other feature of the microscope.     

摆杆体冷挤压成形工艺及模具设计

通过对摆杆体进行冷挤压工艺分析,介绍该零件冷挤压毛坯的制备、表面处理及冷挤压工艺流程,并对冷挤压模具的结构特点及硬质合金凹模的制造要点进行了阐述.