30Cr1Mo1V钢汽轮机转子高应力段的疲劳裂纹扩展速率

在某已服役了16 a的30Cr1Mo1V钢汽轮机转子的高应力段取样制作成紧凑拉伸试样,用MTS 810.50试验机进行室温和538℃下的疲劳裂纹扩展速率试验。结果表明：该钢疲劳裂纹稳定扩展阶段的疲劳裂纹扩展速率适用于Paris公式,室温下的疲劳裂纹扩展速率方程为da/dN=2.2101×10-8（ΔK）2.9163,538℃下的疲劳裂纹扩展速率方程为da/dN=9.8794×10-8（ΔK）2.6844;对于30Cr1Mo1V转子钢,温度升高,疲劳裂纹扩展速率加快;30Cr1Mo1V转子钢在疲劳裂纹稳定扩展阶段存在转折点,将该阶段又细分为两段,经过转折点后疲劳裂纹扩展速率的增速减慢;与原始材料相比,已服役16 a的30Cr1Mo1V钢汽轮机转子高应力段材料的疲劳裂纹扩展速率增大。     

Cohesive zone criterion for cracking along the Cu/Si interface in nanoscale components

Crack initiation and propagation along the Cu/Si interface in multilayered films (Si/Cu/SiN) with different thicknesses of the Cu layer (20 and 200 nm) are experimentally investigated using a nano-cantilever and millimeter-sized four-point bending specimens. To examine the cohesive zone model (CZM) criterion for interfacial delamination along the Cu/Si interface in nanoscale stress concentration, an exponential type of CZM is utilized to simulate the observed delamination processes using the finite element method. After the CZM parameters for the Cu/Si interface are calibrated by experiment, interface cracking in other experiments is predicted. This indicates that the CZM criterion is universally applicable for describing cracking along the interface regardless of specimen dimensions and film thickness which include the differences in plastic behavior and residual stress. The CZM criterion can also predict interfacial cracking along Cu/Si interfaces with different stress singularities.     

Crack growth characteristics of carbon nanotube-based polymer composites subjected to cyclic loading

This paper presents the characterization of crack growth in carbon nanotube (CNT)-based polymer composites under fatigue loading. Fatigue crack growth tests were performed on single-edge cracked plate specimens of CNT/polycarbonate composites at room temperature and liquid nitrogen temperature (77 K). An elastic–plastic finite element analysis was also conducted to determine the J-integral range. The crack growth rate data were expressed in terms of the J-integral range, and the effect of nanotube addition on the fatigue crack growth behavior was examined. In addition, possible mechanisms of the crack growth in the nanocomposites are discussed based on microscopic observations of the specimen fracture surfaces.     

2A50锻铝三点弯曲试验与高分辨率CT成像分析

采用高频疲劳试验机对2A50锻铝缺口试样进行了三点弯曲试验,获得了含裂纹的CT检测试样.对疲劳试样进行了高分辨率CT三维重建,分析了裂纹CT图像的损伤特点;引入了参考平面,将不同层的裂纹CT图像映射到参考平面定义了截面损伤危险度因子.CT分析结果表明:裂纹扩展过程中不同部位的疲劳损伤不均匀,三维可视化结果直观显示了裂纹...     

Examination of the Mode II fracture behaviour of wood with a short crack in an asymmetric four-point bending test

Asymmetric four-point bending tests of agathis specimens with a short crack along the neutral axis in a tangential–longitudinal system were conducted onto analyse the failure behaviour of wood with a short crack. The nominal shear strength and Mode II critical stress intensity factors of the specimens with various crack lengths were measured, and the influence of crack length on these properties was examined. The nominal shear strength of the cracked specimens was significantly lower than the strength of a crack-free specimen, even when the crack was extremely short. This finding suggests that the fracture mechanics theory is effective for analysing the failure behaviour of wood with a very short crack in this loading condition. However, the Mode II critical stress intensity factor still depends on the crack length. When the crack length was corrected with considering the formation of fracture process zone ahead of the crack tip, the critical intensity factor could be predicted effectively as well as the nominal shear strength.     

预应力FRP加固RC梁界面疲劳裂纹扩展行为研究

以预应力纤维增强复合材料（FRP）片材加固钢筋混凝土（RC）梁为研究对象,探讨了该类加固梁中FRP与混凝土之间界面疲劳裂纹的扩展规律。基于界面裂纹尖端的力学分析模型,理论推导了三点弯曲加固梁的界面裂纹应力强度因子（SIF）的计算公式,分析了FRP预应力水平对SIF的影响,并结合加固梁的界面裂纹扩展实验,提出了该类加固梁...     

注塑机模板断裂的原因及预防

分析各种注塑机模板断裂的主要原因,介绍如何选用注塑机,以及在使用如何防止注塑机模板的断裂。     

Numerical Evaluation of Toughening by Crack-Face Grain Interlocking in Self-Reinforced Ceramics

Crack bridging associated with the pull-out process of interlocking grains in self-reinforced ceramic materials is studied through a micromechanical simulation. The pullout of a single inclined grain is modeled via the numerical solution of a general contact problem. The bridging-force versus crack-opening-distance curve indicates a nonlinear, springlike response for the pullout of interlocking grains. The sliding friction along the debonded interface, induced by highly localized contact stresses, dominates the total bridging force. The bridging force increases with grain inclination until eventual bridge failure. The pullout of misaligned grains mainly affects short-crack toughening, with a rising R -curve, whereas aligned grains contribute to long-crack toughening. The residual stresses of the thermal expansion anisotropy play a minor role in the pull-out process of grain interlocking and the resultant toughening. The proposed mechanism is operative in both single-phase and composite ceramics in which pullout of elongated grains/reinforcements occurs.     

Solidification crack characteristics and sensitivity of peritectic steel

The characteristics and sensitivity of solidification cracks in peritectic steels were investigated using directional solidifi-cation technology.Interdendritic cracks were observed in both hypoperitectic steels(12CrlMoV,15CrMo)and hyper-peritectic steel(20CrMo)during solidification at growth velocities of 15,50,and 80 pm/s.At the dendritic boundaries,sulphide precipitates were found,promoting crack formation.Based on the statistical analysis of interdendritic cracks in peritectic steels,the area ratio(RA)of interdendritic cracks in a directional solidification structure was proposed to evaluate the crack sensitivity of peritectic steels.Furthermore,the crack sensitivities of peritectic steels(12CrlMoV,15CrMo,and 20CrMo)were tested,evaluated,and compared with the surface crack rates of three types of steels produced from a steel plant.The results demonstrated that RA was in good agreement with that of the steel plant,and the crack sensitivity of 12CrlMoV steel was the strongest,followed by that of 15CrMo and 20CrMo steels.Thus,RA can be used to evaluate the crack sensitivity of peritectic steel.     

Correlation between longitudinal crack occurrence and mold heat transfer in continuous casting based on process data mining

The correlation between the longitudinal crack occurrence and integrated heat transfer of the mold with data mining methods was investigated.Firstly,three kinds of support vector machine models based on principal component analysis with different input features were established to explore the effect of integrated heat transfer on the accuracy of the prediction model for the longitudinal crack.The results show that the accuracy was improved while features including mean and standard deviation of integrated heat transfer were added.Then,the difference in integrated heat transfer between defect and normal samples under the same process parameters was quantitatively compared.Compared with normal samples,the temperature difference of cooling water for defect samples decreased by 0.65％,and the temperature dif-ference fluctuation increased by 31.1％.Finally,the literature data were used to provide support for the quantitative correlation according to defect formation mechanism.A new criterion for the prediction of longitudinal crack and a discovering method for correlation between product quality and process parameters in the manufacturing industry have been provided.