60Si2Mn钢壳体裂纹原因分析

目的查找某产品60Si2Mn钢关键零部件壳体,在冲压工序和超声波水浸探伤工序中,壳体底部存在裂纹疵病的原因。方法通过疵病部位宏观和微观观察、金相组织检查和验证试验等,检查壳体裂纹性质和原因。结论生产该壳体的原材料存在严重偏析现象,使壳体在热加工加热时,组织向奥氏体转变过程也产生差异,由于感应加热的时间相对较快,且感应加热时,钢材内外受感应磁场电流的不同大小的影响,内外组织变化产生不均匀性,导致在冲压过程中变形不一致,是壳体底部裂纹产生的原因。采取对壳体放慢加速度,局部回火改为整体退火等措施,能有效控制裂纹的产生。经过500发生产验证,结果未发现裂纹疵病产生。     

50 SiMnVB 钢椭圆凹坑疵病原因分析

基于某产品壳体用50SiMnVB钢在冲拔过程中毛坯内膛出现椭圆形凹坑疵病的现象,采用理化检测和工艺试验等手段对该疵病产生的原因机理进行了系统分析与验证,准确地找到了该疵病产生的原因,使生产顺利进行,有效保证了产品质量.     

某产品823钢壳体内膛疵病原因分析

目的研究某产品关键零件用壳体823钢在冲拔过程中,毛坯内膛出现侧壁拉裂和底部缩孔疵病的原因。方法通过理论分析毛坯在冲拔过程中的变形机理和金属流动规律,结合理化检测和工艺试验等手段,对该疵病产生的原因进行了系统分析与验证。结果准确找到了该疵病产生的原因。结论 823钢原材料存在缩孔残余及二次缩孔,是造成弹体毛坯底部缩孔疵病和侧壁拉裂疵病的根本原因;通过靶场射击动态考核试验和增加超声波探伤检验工序的产品,即使存在缩孔残余及二次缩孔,也不影响产品使用性能。     

某炮弹弹体内膛裂纹原因分析

目的某弹体作为某炮弾一重要零件,材料采用9260钢。研究其在冲压过程中,毛坯内膛出现侧壁拉裂和底部裂纹疵病的原因。方法利用理论分析毛坯在冲压过程中的变形机理和金属流动规律,结合理化检测等手段,对弹体疵病产生的原因进行了系统分析。结果通过对毛坯成形原理分析和理化检测分析,对裂纹产生的原因进行逐一排查,最终准确找到了该弹体疵病产生的原因。结论弹体用9260钢原材料存在缩孔残余及沿晶低熔点物质,是造成弹体毛坯侧壁拉裂和裂纹的根本原因。     

某壳体断裂原因分析

目的分析某产品壳体在靶场试验中出现断裂疵病的原因,并提出预防和改进措施。方法通过对断口进行宏微观观察、金相组织检查和化学成分分析检测、力学性能试验、验证试验及强度计算等,初步确定了壳体断裂性质和原因。结果对改进结构的壳体进行了结构强度的验证试验,经对射击试验后回收的壳体进行拆分检测,原发生断裂现象的位置无破坏、裂纹现象,变形量满足产品图定要求,改进结构的壳体结构强度满足要求。结论通过验证试验再次确定了断裂原因:壳体密封圈槽处壁厚差超差;壳体材质C元素含量偏高,材料的脆性较大;断口处材料偏析严重;结构设计强度裕度不足。根据壳体断裂原因,提出了相应的预防措施。     

航空钛锻件研制开发的回顾EI

国营三○○七厂是航空航天工业部专业化锻造厂,近十年来为满足新机研制、老机改型的需要,先后在模锻锤、摩擦压力机及环件轧制机上成功地试制了TC11、TC6、TC4、TA7钛合金飞机结构件、发动机转动部件模锻件及机匣壳体环形轧制件,模锻件的最大投影面积为2000cm^2,环形件最大直径为Φ1300mm,所开发的钛锻件项目达100余项。     

摩擦焊接技术在复合增程类壳体加工中的应用

目的某复合增程类壳体毛坯为两端盲孔结构,一直采用传统的冲压工艺方式加工,加工难度大,废品率高,材料利用率低,生产效率低,成为困扰生产的窄口。方法为彻底解决该问题,开展了壳体摩擦焊接工艺研究,即将壳体毛坯战斗部室和发动机室分开加工,再采用摩擦焊接技术进行连接,并进行小批量焊接试制、热处理、机加、理化分析及动态试验考核。结果焊接后的壳体毛坯满足制造与验收规范要求,壳体毛坯材料利用率、良品率、生产效率得到大幅度提高,大大降低了生产成本。结论该壳体采用摩擦焊接工艺方式加工可行。     

三销轴叉精整底部裂纹产生和防护

三销轴叉精锻件是汽车等速传动系统中的关键零件,其头部内、外腔形状复杂,尺寸精度要求高,故一般采用温锻预成形+冷精整成形复合成形技术,而预成形温锻件设计不合理,在冷精整成形中,存在内腔底部薄壁处出现裂纹的问题。利用数值模拟技术,分析了三销轴叉冷精整型腔底部区域成形过程的成形力、应力、应变的变化,对预成形温锻件进行了优化,设计了不同的入模角,入模角的起始点位于内腔基准平面之上。工程实践后,优化后的预成形温锻件在冷整形后,口部内腔底部没有裂纹产生,流线连续,获得较为理想的精锻件。证明优化后的预成形温锻件,经冷精整成形后,精锻件产品质量显著提高,可有效防止裂纹产生。     

6061铝合金飞机溢油口拉深成形研究

目的 掌握深腔薄壁溢油口拉深成形工艺,解决拉深成形过程中起皱和破裂问题,研究各参数对拉深成形的影响规律,最终成形出合格产品。方法 以6061铝合金飞机溢油口为主要研究对象,采用Dynaform有限元数值模拟软件建立有限元模型,分析成对拉深成形对材料流动的影响并与单一拉深成形进行对比,通过改变毛坯外形尺寸、凹凸模间隙和压边力等参数进行拉深成形模拟试验研究,最终通过拉深成形试验验证成形方法及各参数设置的合理性。结果 成对拉深成形能限制单一拉深成形圆弧开口位置材料收缩,改善开口处起皱和变形缺料的现象。随着凹凸模间隙的增大,最大减薄率逐渐降低而后升高,最佳成形凹凸模间隙为1.05t;随着压边力的增大,最大减薄率逐渐升高,最大增厚率逐渐降低,最佳成形压边力为50 kN;凹模圆角半径小于7 mm 时,板料最大减薄率逐渐减小,半径为4 mm时,最大减薄率下降最快,半径在7~8 mm范围内,板料最大减薄率趋于平稳,最佳成形凹模圆角半径为7 mm。结论 模拟得到了毛坯外形尺寸、凹凸模间隙和压边力等参数对拉深成形的影响规律,最终制造出了满足设计要求的产品,验证了各参数设置的合理性。     

特种机械中杆类零件的局部成形工艺及模具设计

以某产品的机头体为例,原采用开式模锻工艺,材料利用率低,机加定位难度大。为了提高毛坯的净化程度和降低生产成本,需要更高效的加工方式。通过对电镦过程的工艺参数摸索,根据已有设备改进工装模具,并借助有限元模拟分析,最终设计采用了一次加热下同时完成局部镦粗再挤压成形的工艺。该工艺难点是控制镦粗的形状,以及砧子和挤压模的材料选择。经计算,该毛坯材料利用率提高到95.4%,并且由于杆部未变形,外形更利于后期机加定位夹持。     

发动机连杆热锻模具结构分析及优化设计

目的以1KD发动机连杆的热锻模具为研究对象,对其进行结构分析和优化设计。方法采用DEFORM3D模拟1KD连杆热锻成形过程,重点关注与模膛布局相关的中心飞边仓深度、模膛的中心距和旋转角度等3个参数,对成形载荷、锻件折叠和模具磨损的影响。结果采用两次预锻加终锻的生产工艺,可以达到分配坯料质量、降低载荷的目的;模膛中心距和模膛旋转角是影响成形载荷的主要因素,而中心飞边仓深度对模具磨损有显著的影响。结论最终获得了3个参数的优化组合:模膛中心距为32 mm,模膛旋转角为12°,中心飞边仓深度为10 mm,对模具设计和实际生产有一定的参考价值。     

Ultra low-k die crack study for lead free solder bump flip-chip packaging

Ultra low-K (ULK) dielectric has lower mechanical strength (E < 8 GPa), lower cohesive strength and lower adhesion (<5 J/m²) than low-K and SiO₂ dielectric material. The packaging reliability test has shown that delamination between copper (Cu) and ULK is a major concern. In addition to the Cu and ULK delamination issue, the ULK die crack after temperature cycling test (TCT) showed die crack failure to be another issue. ULK die crack failure can be detected by C-mode scanning acoustic microscopy (CSAM). The CSAM image of the die crack mostly shows a crescent moon shape. The crack initiates at the upper edge of the underfill fillet penetrating the sidewall of the die, and then propagates toward the inside of the die. Finite element simulation indicates that the die crack failure starts at the backside edge of the die. The ULK die crack is caused by two mechanisms. First is the bending stress at the backside of the die, which is the result of the coefficient of thermal expansion (CTE) mismatch between the silicon die and the organic substrate. Second is the thermo-mechanical stress, which is the result of the local CTE mismatch between the silicon die and the underfill. The finite element simulation parametric study performed in this paper shows that a low underfill fillet height and a small fillet tip angle reduce the thermo-mechanical stress. In addition, attaching a heat sink to the surface of the flip-chip die increases packaging stiffness and resists the bending stress induced by the shrinkage of the substrate. Experimental results demonstrate that lowering the height of the underfill fillet, reducing the angle of the fillet tip and attaching a heat sink to the flip-chip die are effective ways to solve the ULK die crack issue.     

Residual strength analysis using CTOA criteria for fuselage structures containing multiple site damage

An extensive experimental program was conducted by the Boeing Company under the funding of the Federal Aviation Administration (FAA), National Aeronautics and Space Administration (NASA), and the United States Air Force Research Laboratory (USAF/RL) to investigate the effects of multiple-site damage (MSD) on the residual strength of typical fuselage splice joints. The experimental results were used to validate the analytical prediction using various methodologies, including STAGS (a generalized shell finite element code) with the crack-tip-opening angle and T^* fracture criteria.The test specimens consisted of large flat panels, curved panels, and an aft pressure bulkhead. The flat panel specimens included three types of longitudinal splice joints and one type of circumferential splice joint. For each type, one panel contained only a lead crack and the other two panels contained MSD 1.3 and 2.5 mm in size, respectively, at the fastener holes ahead of the lead crack. The curved panels were tested under simulated loads of combined cabin pressure and fuselage down bending. Two skin splice types were tested. For each splice type, one panel contained a lead crack only and the other had a lead crack with various sizes of MSD. A section of an aft fuselage containing a large lead crack and MSD in the pressure dome was also tested to demonstrate the capabilities of the methodologies in analyzing actual aircraft structures. This paper presents the analytical approaches and the comparison of predictions with the experimental results in terms of crack linkup stress and residual strength.     

Crack growth in a mixed-mode loading on marble beams under three point bending

A combined theoretical and experimental study of a crack growth in a mixed-mode I–II loading is presented. A 160×40×20 mm marble beam, with an artificial crack 8 mm and 10 mm long each, was subjected to three point bending. The crack was located vertically to the beam's lower longitudinal fiber, through the whole width of the beam. The position of the crack was displaced from the center of the beam to one of the supporting points. The vertical force P, placed on the middle of the upper fiber of the beam, imposed the combination of the opening (mode I) and the sliding (mode II) modes on the crack mouth, creating the mixed-mode I–II loading case. The stress intensity factors K _I and K _II, which describe the local stress and strain field around the crack tip, were determined by a suitable finite element program. The crack growth was defined by two classical fracture criteria of LEFM; the minimum strain energy density and the maximum circumferential stress criteria. The initial crack growth angle () was calculated from both criteria and the critical load (P _c) from the minimum strain energy density (SED) criterion. These theoretical predictions were compared with some experimental results found from three marbles with different elastic constants; the Krystallina of Kavala, the Snow-white of Thassos and the White of Piges Drama. The theoretical results showed the same trend of and P _c as the experimental ones and they are in good agreement.Presented at Fourth Greek National Congress on Mechanics, 26–29 June 1995, held at Xanthi, Greece.     

Stress Intensity Factors of partly circumferential surface cracks at the outer wall of a pipe

By means of the finite element method stress intensity factors were calculated for partly circumferential surface cracks at the outer wall of a pipe. The crack shape considered can be described as curved rectangular shape. The cracks considered have crack depths between 20 and 80 percent of the wall thickness of the pipe and crack lengths (defined by the angle of circumference φ) between φ = 10° and φ = 60°. The pipe is loaded by a constant axial tensile stress σ₀ (equal to 136 Nmm^?2 in the numerial calculations), and the wall thickness to inner radius ratio of the pipe was chosen to 0.1. A wall thickness of 20 mm was used for the numerical calculations.     

A circumferential crack in a pressurized cylindrical shell

Following an earlier analysis of an axial line crack in a cylindrical shell, the stresses for a finite circumferential crack are presented. The inverse square root singularity of the stresses peculiar to crack problems is obtained in both the extensional and bending components. Furthermore, the initial curvature may be related to that found in an initially flat plate by a factor of the form

$$\frac{{{}^\sigma shell}}{{{}^\sigma plate}} \approx 1 + (a + b \ell n \frac{c}{{\sqrt {Rh} }})\frac{{c^2 }}{{Rh}} + ...$$     

The Effect of Wave Formation and Wetting Angle on the Thermocapillary Breakdown of a Falling Liquid Film

An experimental investigation is performed of the breakdown of a liquid film flowing down a vertical plate with a heater sized 150×150 mm. The main parameters which are varied in the experiment are the Reynolds number Re = 0.47 to 331 and the heat flux q = 0 to 1.92 W/cm². It is found that the effect of the heat flux on the wave motion of the liquid film causes the formation of a jet flow. Dry spots are formed in the region of thin film between the jets. For the purpose of investigating the effect of wave formation on the film breakdown, the distance between the nozzle and heater is varied from 41.5 to 200 mm. It is found that the distance between the nozzle and heater defines the hydrodynamics of the liquid at relatively low heat fluxes, but has no appreciable effect on the heat flux at which the film breakdown occurs. Different working liquids and coatings of the working surface are used in the experiments to investigate the effect of the wetting angle on the film breakdown. The equilibrium wetting angle is measured by the "bubble" method. No effect of the equilibrium wetting angle on the nonisothermal breakdown of the film was revealed.     

一种软包装边角式折叠成型结构与工艺研究

目的针对现有热成型真空包装产品出现的下膜不能预印刷以及需要贴标签等问题,探讨设计一种软包装折叠成型的包装结构及工艺。方法采用边角式折叠成型方式,该包装结构由上下膜组成,下膜通过边角折叠点封固定,同时对下膜进行参数化设计。结果得出了纵向折叠收缩量与折角成正切函数关系,当折角取90°时,纵向折叠收缩量最大;获得了推压折角与折角的函数关系,结果显示折角比率一定时,随着推压折角的增加,折角逐渐减小。结论解决了边角式折叠参数关系,并提供了一种折叠工艺方案,流程为纵向折叠成型—边角折叠—横向折叠成型—边角点封定型—充填产品—抽真空热封和模切,为进一步实现产品的自动化包装和生产提供理论支撑。     

Fractal effects of crack propagation on dynamic stress intensity factors and crack velocities

Crack extension paths are often irregular, producing rough fracture surfaces which have a fractal geometry. In this paper, crack tip motion along a fractal crack trace is analysed. A fractal kinking model of the crack extension path is established to describe irregular crack growth. A formula is derived to describe the effects of fractal crack propagation on the dynamic stress intensity factor and on crack velocity. The ratio of the dynamic stress intensity factor to the applied stress intensity factor K(L(D, t), V)/K(L(t), 0), is a function of apparent crack velocity V_o, microstructure parameter d/a (grain size/crack increment step length), fractal dimension D, and fractal kinking angle of crack extension path . For fractal crack propagation, the apparent (or measured) crack velocity V_o, cannot approach the Rayleigh wave speed Cr. Why V_o is significantly lower than Cr in dynamic fracture experiments can be explained by the effects of fractal crack propagation. The dynamic stress intensity factor and apparent crack velocity are strongly affected by the microstructure parameter (d/a), fractal dimension D, and fractal kinking angle of crack extension path . This is in good agreement with experimental findings.     

Modeling and Failure Analysis of a Broken Railway Axle: Effects of Surface Defects and Inclusions

In the present work, the fatigue behavior of an axle was analyzed using modeling and experimental approaches. A failed axle was used for experimental studies. The experimental results were then analyzed in order to model and predict the fatigue life of axle. The three-dimensional finite element analysis was used to simulate the fatigue behavior of axle. The growth of a machining defect, 2 μm initial crack length, was simulated versus applied cycles. The changes in the stress intensity factor as a function of crack length were modeled as well. The model predicted that after about 5 × 10⁸ cycles there was an abrupt increase in the crack length, reaching a critical value of about 65 mm at around N _f = 5 × 10⁹ cycles, indicating that the longer the crack, the higher its growth will be. The experimental results were then compared with the modeling predictions. It is shown that the latter are in a good agreement with the former. The results obtained in this study do give a basis for evaluation of single scratch or notch produced by improper machining.