高铬铸铁耐磨衬板断裂分析

采用宏观分析、化学成分分析、金相检验、力学性能测试以及断口微观分析等方法,对某高铬铸铁耐磨衬板在安装过程中发生断裂的原因进行了分析。结果表明:该衬板断裂为穿晶脆性断裂,疏松、缩孔、铸造裂纹等铸造缺陷是造成衬板断裂的主要原因;衬板组织不均匀,碳化物粗大并有尖锐的棱角,表现出硬而脆的特征,未能抑制裂纹的扩展,最终导致衬板在安装外力作用下发生脆性断裂。     

采用电子扫描显微镜分析弹簧镀锌后断裂的原因

我厂产品中65Mn材料的簧片,厚0.4毫米。图纸规定材料硬度为HRC42—47,镀锌14～20微米。技术要求此件冲压成型后要经淬火→回火→酸洗→镀锌→除氢→钝化等工序。但簧片装配后使用时大部分断裂,严重影响产品质量。为了分析簧片断裂原因,我们将簧片断口在金相显微镜下进行观察,但对其断裂原因无法下结论。又将半成品件中经过热处理而未镀锌的簧片和已经镀锌的簧片抽样按簧片技术要求进行氢脆性试验(压合和张开一定的角度):发现没镀锌的簧片没有断裂的现象,而镀锌的簧片有30%     

JZC-1M/027-01继电器失效机理分析

通过对JZC-1M/027-01继电器进行失效分析,认为继电器失效原因是由于中簧片在焊接部位产生断裂,导致中簧片不能回弹,在继电器加电时中簧片与常开簧片接触,断电后不能复位,使中簧片与常开簧片为短路状态.断裂簧片脆性断裂的原因是簧片在焊接过程中曾经较长时间受到较高温度的作用,导致热影响区(断裂部位)晶粒长大,晶界变粗且弱化,在继电器工作过程中,由于该部位多次受到应力作用而产生脆性断裂.正常簧片在热影响区未发现类似现象.     

发电厂锅炉引风机叶柄断裂原因分析

本文采用金相显微镜、扫描电镜和能谱仪对引风机叶柄断裂原因进行了分析。叶柄断裂位置螺纹根部可见明显的加工刀痕,在尖锐处存在应力的最大值,引起应力集中。在拉应力、弯曲及扭转应力作用下,可能导致裂纹的萌生。另外,风机在运行过程中振动疲劳与旋转弯曲疲劳联合作用,亦将引起叶柄断裂的扩展,导致叶柄最终断裂。     

高压燃油管开裂分析

采用断口分析,金相分析和化学成分分析等方法,对高压燃油管开裂原因进行了分析.结果表明,宏观断口上有明显的贝纹线花样,微观断口上有典型的疲劳辉纹,表明高压燃油管的裂纹为疲劳裂纹.疲劳裂纹源产生于油管冷镦时内孔壁上留下的凹坑环残迹处,金相分析表明此处的显微组织严重变形,存在较大的内应力,是应力集中点.裂纹在此产生并扩展,直至穿透管壁而开裂.     

残余压应力场中疲劳裂纹的止裂

20Cr钢在不同缺口尖锐度下滚压后疲劳试验结果表明,滚压强化明显提高缺口试样的疲劳极限,其作用高于光滑试样,缺口越尖锐强化效果越显著。在缺口滚压试样疲劳断口上出现裂纹扩展速率快—慢—快的变化。缺口试样滚压后在疲劳极限下运行出现非扩展裂纹。     

调整螺母裂纹成因分析

调整螺母在调质处理后探伤时发现有裂纹,采用宏观检验、化学成分分析、金相检验等方法对其开裂原因进行了分析。结果表明：该批调整螺母开裂是由于明显的带状偏析和较多的夹杂物引起的淬火裂纹,同时由于回火温度过高,使得裂纹两侧脱碳出现网状铁素体。     

某63CY-104型斜盘柱塞泵壳体开裂原因

某63CY-104型斜盘柱塞泵壳体经常发生开裂,导致液压油泄漏。采用金相检验、断口分析和有限元分析等方法,分析了柱塞泵壳体开裂的原因。结果表明：柱塞泵壳体组织中平直、粗大且两端尖锐的C型石墨是导致壳体发生开裂的主要原因;柱塞泵在工作过程中受振动较大,壳体3,4,5阶模态振型变化较大,容易发生共振,使壳体产生裂纹。     

给水泵轴横向裂纹分析

某厂生产的给水泵轴在车削加工过程中发现轴中央部位有一条横向裂纹。采用化学成分分析、金相检验和断口分析等方法对裂纹产生的原因进行了分析。结果表明:该裂纹为锻造裂纹,锻造温度偏高可能是引起裂纹的重要原因。     

卡爪高频淬火开裂分析

对卡爪高频淬火过程中产生的裂纹进行了分析。认为,淬火过程中产生的局部拉应力加上尖锐Ｖ型槽上起的应力集中是造成开裂的主要原因,此外,夹杂物及其分布方向的影响也不可忽视。     

Bridging crack model for fracture of spruce

An analysis is presented of how cracking in wood can be predicted using fracture mechanics. In situ, real-time, scanning electron microscopy was used as a tool to estimate the physical mechanism of fracture in softwoods using end-tapered double cantilever beam specimens. It was found that bridging behind the crack tip is the main toughening mechanism, which contributes to non-linear wood behavior in the presence of stress concentrations. A new bridging crack model is presented that mimics the observed cracking mechanism. Intrinsic flaw size is found to correspond to the fiber length of spruce.     

Measuring and calculating GTOD and the J-integral with a double clip gauge

This paper describes a technique for measuring and calculating CTOD (crack tip opening displacement) arid the J-integral with double clip gauge. CTOD (or δ) and the rotation factor (r), the relation between δ and J-integral, as well as the R-curves δ - Δa and J. Δa are discussed. From the measurements with double clip gauge, one can calculate CTOD and J througout the entire loading process. The present technique seems to be a better approach than DD19, in which r is taken as a constant (r = 1/3).     

Toughening of polyester resins by rubber modification

The microstructures of two polyester resin systems, with reactive liquid rubber additions incorporated, were investigated using electron microscopy. Fracture surface morphologies of failed fracture toughness specimens were examined using scanning electron microscopy. The fine structures of unfractured toughened resins were examined by imaging ultra thin sections in the transmission electron microscope. Three of the four rubber additives investigated produced, upon curing, a dispersion of second-phase rubber-rich particles in the polyester resin matrix. The fourth additive, which was more compatible with polyester than the other three, did not produce any detectable particle dispersion upon curing, even at relatively high concentrations. The fine structures of the particle distribution were found to be highly dependent upon both rubber and resin formulations. Rubber additions modified the mode of fracture observed in double torsion tests of polyester resins, from continuous crack propagation to slip-stick, and distinctive changes in fracture surface morphology were observed. In zones of crack arrest and slow stable crack growth, crack blunting occurred and highly deformed structures were seen on the fracture surface. In one system, this zone was split into two distinct regions, due to crack blunting and the initiation of new, sharp cracks. In zones of rapid crack growth, there was no evidence of crack blunting. The amount of crack blunting was highly dependent upon speed of testing.     

Q345B中厚板表面的纵裂纹分析

采用金相检验和扫描电镜及能谱分析等手段对热轧Q345B中厚板表面纵裂纹进行了分析.结果表明,热轧Q345B中厚板表面纵裂纹是由于铸坯中存在夹杂物及铸坯纵裂引起的.通过对炼钢生产过程的观察,提出了改进连铸工艺等相关措施,取得了良好的效果.     

Fatigue crack growth behavior of the simulated HAZ of 800 MPa grade high-performance steel

The present study focuses on the fatigue properties in the weld heat-affected zone (HAZ) of 800 MPa grade high-performance steel, which is commonly used in bridges and buildings. Single- and multi-pass HAZs were simulated by the Gleeble system. Fatigue properties were estimated using a crack propagation test under a 0.3 stress ratio and 0.1 load frequencies. The microstructures and fracture surfaces were analyzed by optical microscopy, scanning electron microscopy, and transmission electron microscopy. The results of the crack propagation test showed that the fatigue crack growth rate of coarse-grained HAZ (CGHAZ) was faster than fine-grained HAZ (FGHAZ), although both regions have identical fully martensite microstructures, because FGHAZ has smaller prior austenite grain and martensite packet sizes, which can act as effective barriers to crack propagation. The fatigue crack growth rate of intercritically reheated CGHAZ (ICCGHAZ) was the fastest among local zones in the HAZ, due to rapid crack initiation and propagation via the massive martensite-austenite (M-A) constituent.     

抽油机人字齿轮表面裂纹分析

采用金相和扫描电镜等手段,对抽油机人字齿轮轴孔及外圆表面裂纹进行了分析,结果表明,退火温度过高,导致齿轮出现严重过热,在淬火应力的作用下使齿轮沿过热晶界开裂,形成表面裂纹。     

Fatigue crack nuclei in austempered ductile cast iron

ABSTRACT Short fatigue crack nuclei in austempered ductile cast iron have been studied using optical microscopy, scanning electron microscopy, atomic force microscopy and X‐ray microtomography and by electron backscatter diffraction analysis. Fatigue cracks nucleate at graphite nodules and shrinkage microporosity. The crack nuclei are arrested and retarded by barriers in the microstructure, by either blocking of slip at boundaries or owing to the requirement for tilt and twist of the stage I crystallographic crack at grain boundaries. These observations indicate that both the size of the defects, such as graphite nodules and microporosity, and the size of the prior austenite grains control the largest crack nucleus that can develop, and hence determine the component fatigue limit.     

On the Toughness Response of iPP and sPP/MWNT Nanocomposites

Nanocomposites based in polypropylene (both syndiotactic and isotactic) and multiwall carbon nanotubes (MWNTs) directly blended in the melt via micro‐extrusion, were studied. The aim was to determine the role of MWNTs, on the creation of the plastic zone and crack propagation in double‐cracked tensile specimens. Essential work of fracture toughness testing was performed on these nanocomposites. In all cases, the effect of MWNT weight fraction on the above properties was extensively studied. Data obtained have shown a non‐linear relationship of almost all properties with MWNTs content. Scanning electron microscopy revealed that a micro crack/craze bridging mechanism can be detected in polymer matrix/ MWNT nanocomposites. This mechanism was observed in the fibrillated areas of the specimens' fractured surfaces. The results obtained showed a promising role of the nanotubes as tougheners for future nanocomposites' applications. Ductile‐to‐brittle transition was confirmed for MWNT contents above 1 wt%.     

Experimental characterization of short crack nucleation and growth during cycling in lean duplex stainless steels

Considering that many applications of Lean Duplex Stainless Steels (LDSSs) involve cyclic loading, the aim of this paper is to study short crack initiation and growth during low (LCF) and high cycle fatigue (HCF) in AL 2003 (UNS S32003). Electron Backscattered Diffraction (EBSD) analysis of plastically active grains allows to determinate the slip systems and their associated Schmid factor (SF). Additionally, the dislocation structure developed during cycling is observed by transmission electron microscopy (TEM). Whereas in HCF cracks nucleate at grains boundaries, during LCF cracks nucleate along intrusion/extrusions in ferritic grains and as they reach austenitic grains grow along active slip systems or by double slip system. Moreover, phase boundaries and grain boundaries act as effective barrier against crack propagation.     

Application of optical deformation analysis system on wedge splitting test and its inverse analysis

An alternative approach of fracture tests evaluation based on optical measurements of displacements is investigated in this paper. The non-linear hinge model based inverse analysis outgoing from the optically measured crack mouth opening displacements is introduced for the wedge splitting test. Results of the inverse analysis are compared with traditional inverse analysis based on clip gauge data. Then the optically measured crack profile and crack tip position are compared with predictions done by the non-linear hinge model and a finite element analysis. It is shown that the inverse analysis based on the optically measured data can provide material parameters of the fictitious crack model matching favorably those obtained by classical inverse analysis based on the clip gauge data. Further advantages of using of the optical deformation analysis lie in identification of such effects as aggregates bridging and crack branching. These effects would remain hidden if the crack profile is simulated by a model based on the fictitious crack model.