飞机舵机壳体裂纹产生原因

某飞机舵机壳体在服役过程中多次发生漏油故障,采用化学成分分析、荧光渗透检测、断口分析、金相检验等方法对漏油壳体进行检测及分析,对不同批次壳体材料进行了力学性能测试。结果表明：在脉冲油压的作用下,舵机壳体传感器孔壁萌生裂纹,并进一步扩展导致漏油;故障批次壳体材料为再结晶等轴晶组织,正常批次壳体材料为枝晶网状晶界组织,组织差异导致材料力学性能的差异,故障批次壳体材料的横向力学性能、断裂韧度以及疲劳性能等均低于正常批次壳体材料;力学性能的降低是传感器孔薄壁部位产生疲劳裂纹的主要原因。     

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。     

连杆淬火产生裂纹原因分析

采用化学成分分析、低倍组织检验、力学性能测试及其材料工艺性试验等方法对用42CrMo钢制成的发动机连杆经调质后发生的淬火裂纹问题进行了分析。结果表明,原材料中存在钨元素,导致连杆在淬火后发生淬裂。并提出相应的改进措施。     

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。     

曲轴主轴颈表面裂纹原因分析

通过对45钢曲轴主轴颈表面裂纹的综合分析,揭示了裂纹产生原因系在调质处理的淬火过程中,网状铁素体沿晶界析出,使晶界严重弱化,最终导致在中频淬火过程中形成以沿晶为主的淬火裂纹。     

齿轮轴裂纹分析

齿轮轴在淬火校直后表面出现轴向裂纹。采用化学成分、断口试验、热酸侵低倍试验、硬度试验和金相检验等方法对齿轮轴开裂件做了解剖分析。结果表明,齿轮轴纵向裂纹为由原材料缺陷引起的淬火裂纹,心部内裂纹为在解剖分析线切割加工过程中产生的应力裂纹。     

羊角锤淬火裂纹形成原因辨析

针对文献[1]提出了羊角锤淬裂原因的不同见解,即羊角锤锻后晶粒度5.5级,魏氏组织1级,不可能有粗晶粒遗传。工件厚度不均匀、羊角部位的厚度在危险尺寸范围内,钢材微量元素总量偏高、淬火加热介质有微氰化作用都与淬火裂纹的形成有关。     

六方轴表面裂纹成因分析

材料为20CrMnTi钢的六方轴渗碳淬火后,在磨削时其表面产生了严重的裂纹。采用宏观检验、金相检验以及硬度测试等方法,对六方轴表面裂纹产生的原因进行了分析。结果表明:六方轴表面裂纹是因为砂轮修理不平整以及磨削工艺参数选择不合理,使工件表面产生了严重的磨削烧伤,当磨削形变应力、热应力和组织应力综合作用超过材料的抗断强度时,就形成了裂纹。最后提出了改进措施。     

Discrete crack growth analysis methodology for through cracks in pressurized fuselage structures

A methodology for simulating the growth of long through cracks in the skin of pressurized aircraft fuselage structures is described. Crack trajectories are allowed to be arbitrary and are computed as part of the simulation. The interaction between the mechanical loads acting on the superstructure and the local structural response near the crack tips is accounted for by employing a hierarchical modelling strategy. The structural response for each cracked configuration is obtained using a geometrically non-linear shell finite element analysis procedure. Four stress intensity factors, two for membrane behaviour and two for bending using Kirchhoff plate theory, are computed using an extension of the modified crack closure integral method. Crack trajectories are determined by applying the maximum tangential stress criterion. Crack growth results in localized mesh deletion, and the deletion regions are remeshed automatically using a newly developed all-quadrilateral meshing algorithm. The effectiveness of the methodology, and its applicability to performing practical analyses of realistic structures, is demonstrated by simulating curvilinear crack growth in a fuselage panel that is representative of a typical narrow-body aircraft. The predicted crack trajectory and fatigue life compare well with measurements of these same quantities from a full-scale pressurized panel test.     

35CrMo圆钢零件调质开裂原因分析

35CrMo圆钢零件在调质后出现了开裂现象,通过宏观检验、化学成分分析及金相检验等方法对开裂原因进行了分析。结果表明:加工工艺不当使圆钢疏松部分被使用,诱发裂纹产生,而调质过程中冷却速度过快促进了裂纹的扩展。     

Modeling of Coalescence of Dispersed Surface Cracks. Part 1. Probabilistic Model for Crack Coalescence

A probabilistic model was developed for coalescence of cracks randomly dispersed on the surface and having uniform orientation and statistically nonuniform length. The model makes it possible to calculate the probability of coalescence of any pair of closely located cracks with allowance for the interaction of the strain fields. The model has been modified for the case of coalescence of cracks having the biggest length in the sample. The initial parameters for determining the probability of coalescence are: mathematical expectation of the length of cracks, their surface density, the magnitude of the damaged area of the material (size-scale factor), and the level of the acting stress. The model obtained can be used to predict the life of a component from the criterion of formation of critical cracks by coalescence of dispersed defects.     

某产品零件导气箍锻造裂纹问题分析

分析了导气箍裂纹的原因是锻造缺陷所致。由于锻造缺陷是锻造过程常见的缺陷,难以避免,因而提出了采用打磨等方法消除微裂纹的补救措施和采用探伤检查剔除裂纹零件等排除法来解决锻造裂纹问题,经实际应用证明解决措施可行。     

基于折页模式与折页单元组配关系的折页机工作效能分析方法

分析了折页模式的描述格式,根据印张折痕的位置关系及变向特性对折页模式进行了分解,将复杂折页模式分解为了一系列平行折的顺次组合。结合平行折研究了折页模式与折页单元之间的组配关系,归纳了折页模式与折页单元的组配规则。以JDF定义的85种常用折页模式为参照,提出了一种基于折页模式与折页单元组配的折页机工作效能分析方法。     

Method of Stressed State Analysis of Thick-Walled GTE Shells from Composite Materials

Methodical aspects of the calculation of thick-walled GTE shells from composite materials have been studied. A method is proposed for calculating ring-shaped elements of non-small curvature, as well as short shells, unfastened and loaded by bending moment at the left face and normal pressure at the median surface. Based on these solutions, applicability limits of the theory of thick-walled shells have been set.     

Modal analysis of multi-cracked beams with circular cross section

This paper proposes a numerical model that combines the finite element and component mode synthesis methods for the modal analysis of beams with circular cross section and containing multiple non-propagating open cracks. The model virtually divides a beam into a number of parts from the crack sections and couples them by flexibility matrices considering the interaction forces that are derived from the fracture mechanics theory. The main feature of the presented approach is that the natural frequencies and mode shapes of a beam with an arbitrary number of cracks and any kind of two end conditions can be conveniently determined with a reasonable computational time. Three numerical examples are given to investigate the effects of location and depth of cracks on the natural frequencies and mode shapes of the beams. Moreover, it is shown through these examples that the evaluation of modal data obtained by the proposed model gives valuable information about the location and size of defects in the beams.     

野营折叠网壳结构表面定常风场的数值模拟研究

基于流体动力学基本原理和大气边界层基本理论,运用计算流体动力学软件Fluent6.3对野营折叠网壳结构表面风压分布进行数值模拟技术的基础性研究,对比与风洞试验数据,确定复杂体型结构数值模拟时的计算域尺寸、网格划分方式、网格数量、湍流模型等基本参数设定,得到野营折叠网壳在不同风向角下的表面风压分布及其结构体形系数,同风洞试验结果对比,吻和较好。分析表明风速对结构风荷载体形系数影响较小,而风向角对风荷载体形系数的影响较大;所得结构的体形系数,为类似体型结构的抗风设计提供依据。     

一种下拉杆（SZ804）零件的热处理工艺研究

东方红大轮拖SZ804下拉杆材料60Si2Mn,形状为板条状,技术要求HRC37~42要求校平,生产中出现淬火硬度不足及校平中多次出现断裂情况,这个问题长期困扰着我们,通过改进工艺把原来油淬改为水淬,增加回火时间,消除淬火应力。有效地控制了淬火硬度不足,校平断裂等,使问题得到了解决。