锅炉水冷壁管开裂失效分析

针对锅炉水冷壁管的开裂原因进行了失效分析。采用宏微观形貌分析、化学成分分析、金相显微组织分析等手段,分析了锅炉水冷壁管开裂的原因,结果表明,锅炉水冷壁管的开裂类型为高温蠕变开裂,使用中超温是导致该锅炉水冷壁管开裂的主要原因。     

不锈钢换热管U形部位开裂分析

针对某石化厂换热器运行较短时间后多根换热管U形部位出现环向开裂的现象,在开裂换热管开裂部位与远离开裂部位分别取样,通过宏观检查、光谱分析、显微硬度分析、金相分析、断口扫描电镜形貌和能谱分析,得出该换热管的开裂原因为:换热管在含氢环境下,产生大量氢致马氏体,导致产生氢致裂纹;裂纹在扩展的过程中,S、Cl~-及非金属夹杂物的存在对开裂起到了一定的促进作用,最终发生开裂。     

304不锈钢酸性气体压力管道开裂失效分析

针对304不锈钢酸性气体压力管道开裂的开裂原因进行了失效分析。采用宏微观形貌分析、化学成分分析、金相显微组织分析等手段,分析了压力管道失效的原因,结果表明,管道的开裂类型为晶间腐蚀开裂,不锈钢管道焊接热影响区敏化是导致该不锈钢管道开裂的主要原因。     

催化装置外取热器管程出口三通焊缝开裂失效分析

针对某催化装置外取热器管程出口三通焊缝开裂失效的情况,通过化学成分分析、有限元应力分析、扫描电镜分析等手段进行了失效分析。结果表明,三通的开裂性质为应力腐蚀开裂。     

压力表管接头焊缝开裂原因分析

分析了不锈钢压力表管接头焊缝开裂的原因,认为此种开裂具有应力腐蚀开裂、沿晶断裂特征。     

ABS工程塑料应力开裂现象综合分析及表征

ABS塑料现实使用中经常出现应力开裂现象。为了解决此问题,本项目对有应力开裂的ABS试样和无应力开裂的ABS试样进行拉伸实验、冲击性能测试、红外光谱分析、热分解实验、扫描电镜和感偶等离子原子发射光谱分析。通过分析比较,找出开裂原因,指导材料的应用。试验结果表明：无应力开裂试样的拉伸强度是有应力开裂试样的约1／3,但断裂伸长率却是有应力开裂试样的约5．6倍;应力开裂试样的抗冲击强度下降了。无应力开裂的试样中无机填料量较少（质量分数约为3．07％）、颗粒较小、且分散均匀;而有应力开裂的试样无机填料质量分数约为5．29％。无应力开裂试样中Ti的质量分数24．33％,有应力开裂试样的Ti的质量分数35．77％,由于Ti的量增大,且颗粒较细,比表面积增大而不易分散均匀,出现团聚现象,形成应力集中。     

法兰不锈钢垫片开裂的失效分析

通过化学成分分析、金相检查和断口分析等手段,对一法兰不锈钢垫片的开裂进行了失效分析。实验测试和数据分析表明,该垫片开裂的主要原因为氯离子引起的应力腐蚀开裂。     

制氢转化炉TP321H猪尾管开裂原因分析

采用宏观形貌分析、金相显微组织分析及EDS能谱成分分析等手段,对某制氢转化炉TP321H猪尾管开裂原因进行分析。结果表明,猪尾管开裂机理为敏化态奥氏体不锈钢的氯化物应力腐蚀开裂,是在拉应力和腐蚀介质的联合作用下导致的沿晶型开裂。     

裂解汽油加氢二段反应器急冷剂管道开裂原因分析及对策

对裂解汽油加氢二段反应器急冷剂管道因化学腐蚀和应力腐蚀引起的开裂进行了溯源分析。通过对1号外管宏观及低倍金相检验、样管化学成分分析、样管显微组织分析、电镜观察及能谱分析等方式进行综合分析急冷剂管道开裂原因。确定氯离子应力腐蚀开裂起主导作用,焊缝及热影响区敏化加速了开裂进程,采取相应对策有效地防止管道开裂发生,为乙烯裂解汽油加氢装置长周期安全稳定运行提供了保障。     

汽车用天然橡胶衬套开裂的失效分析

通过表观形貌观察、表面元素分析、热重分析、密度测定以及裂解气相色谱-质谱的有机成分检测,分析汽车用天然橡胶(NR)衬套开裂失效的原因。结果表明:汽车用NR衬套发生开裂的原因是热氧老化;与未发生开裂样品相比,开裂样品的表面氧元素含量增大,热分解温度升高,密度增大,酚类抗氧剂消失。     

乙烯装置氢气加热器U形弯管失效分析

某乙烯装置氢气加热器系外置式夹套换热器。该设备在检修时发现,U形弯管内侧有泄漏现象。通过取样进行化学成分、金相和腐蚀产物分析发现,U形弯管上存在的外表面裂纹是由内壁向外扩展至外壁所形成的,且呈多源裂纹特征,裂纹呈树枝状扩展,系典型的应力腐蚀裂纹。     

Hertzian crack analysis in alumina–chromium composites

Ceramic metal composites are of interest for their good resistance to crack propagation. We have prepared different kinds of alumina chromium composites, observed their microstructures and made an analysis of Hertzian cracks in order to identify the principle parameters of crack propagation in relation with the metallic phase size and distribution in the matrix. The crack is analysed at two scales, a macroscopic one to estimate the fracture toughness from the overall crack and a microscopic one to study, at the local level, the influence of the metallic phase on crack propagation. Using macroscopic models the fracture toughness estimation highlights the benefit of the presence of chromium particles. Observations and measurements made on the crack path and metallic phase, from the microstructure analysis, combined with the knowledge of the residual stress state, provide the principal parameters governing crack propagation in these composites.     

工业管道应力腐蚀裂纹的检验

概述了金属材料应力腐蚀裂纹的特点,提出了工业管道对其检验的内容和方法,通过对应力腐蚀裂纹宏观和微观特征的检查和分析,基本可以区别应力腐蚀裂纹和其他裂纹.应力腐蚀裂纹是比较危险的缺陷,因此在管道检修和设计时应采取必要的改进措施,防惠于未然.     

Indentation Crack Initiation and Propagation in Tempered Glass

Indentation crack initiation and propagation in tempered glass surfaces are examined and the results compared to those in annealed and in ion-exchange-strengthened glasses. The presence of surface compression due to tempering inhibits median crack initiation during the loading cycle of the indentation and depresses the radial crack initiation load during unloading. However, the extent of lateral cracking is enhanced in tempered glass surfaces. In situ crack propagation experiments reveal that the compressive stress tends to weakly stabilize crack extension prior to failure. The degree of crack stabilization is considerably lower than expected from a theoretical analysis.     

Analysis of Effect of Crack Interaction on Nature of Strength Loss in Thermally Shocked Brittle Ceramics

A fracture mechanics analysis is presented to study the effect of collinear crack interaction on the crack stability and propagation behavior in a brittle material subjected to thermal stress failure. It is shown that collinear crack interaction may result in crack coalescence and complete failure.     

The acoustic emission analysis of the crack processes in alumina

The crack processes in single-phase alumina specimens have been investigated by acoustic emission (AE) analysis with regard to the increase of the crack resistance. During loading of a notched specimen, individual AE signals are observed at first, which are probably due to the generation of microcracks in a process zone around the notch. At higher loads signal clusters are found, which should be due to the coalescence of microcracks. By these coalescence events the main crack is formed. At macroscopic crack propagation most AE events are located within the crack tip zone. However, up to about 20% of all events are located within the crack flank zone behind the crack tip. Thus, it can be concluded that there is an energy dissipation at the crack tip at beginning of the loading, which determines the starting value of the crack resistance. At macroscopic crack propagation crack flank interactions contribute to the increase of crack resistance, too. However, it cannot be decided from AE if the contribution of the process zone at the crack tip or of the crack flanks in the wake of the crack tip play the major role in increasing the crack resistance.     

Micromechanical Analysis of Short Cracks in Fiber-Reinforced Ceramics

The finite-element method is used to perform a micromechanical analysis of a crack in a fiber-reinforced ceramic, when the crack length is the same order of magnitude as the fiber spacing. The stress intensity factor is calculated under mode-I loading for various crack lengths and fiber volume fractions. Cracks with and without fibers bridging the faces of the crack are analyzed.     

Thermally Induced Fast Fracture in a Glass Double-Cantilever-Beam Specimen

Rapid crack propagation and arrest in a soda-lime glass double-cantilever-beam specimen subjected to a thermal shock loading are investigated. The crack growth-time history is measured and compared with that predicted by a one-dimensional dynamic fracture model. Good correlations between predicted and measured crack speeds and crack lengths at arrest were obtained. Inertial effects can be sufficient to produce complete fracture of the specimen. The predicted initial crack driving force required to produce this failure agreed with the observed value. These results are contrasted with the predictions of a quasi-static analysis that always predicts crack arrest and underestimates the arrested crack length.     

Correlation between Long and Short Crack R-curves in Alumina Using the Crack Opening Displacement and Fracture Mechanical Weight Function Approach

Both fine grain sized and coarse grain sized alumina has been used as a model material to correlate short crack R - curves by the surface-flaw-in-flexure method with long crack R -curves from a compact tension specimen. The analysis has been made using the crack opening displacement from long cracks combined with the appropriate weight function to compute the crack closure stresses by crack bridging as a function of crack opening displacement. Then the long crack R - curve, the short crack curve, as well as the crack opening displacement for short cracks are computed. The agreement with the experimental data is within an absolute value of about 0.3 MPa and attributed to uncertainties in determining the crack tip toughness and effects due to subcritical crack growth.     

Edge-Crack Resistance Curves in Supercritical Ceramics

The growth of edge cracks in zirconia-reinforced ceramics is analyzed theoretically with the „supercritical” transformation model. The injection of an initial edge crack by a damage process is modeled in an approximate manner. Subsequent crack growth under the application of a remote tensiles stress models the evolution of the transformed region as the crack advances. For the range of initial crack sizes considered, „nominal” resistance curves depend strongly on a transformation-toughening parameter. The analysis may have a bearing on the indentation/bend method of testing fracture toughnesses.