氧化石墨烯改性碳纤维复合材料抗冲击行为研究

使用单层纳米氧化石墨烯（NGO）粒子对环氧树脂进行改性处理，采用真空辅助树脂传递模塑成型工艺制备了[±45/0/90]_2S铺层角度下的纯树脂及单层NGO改性碳纤维复合材料（CFRP）层合板。通过落锤冲击试验、超声C扫描检测、冲击后压缩试验等对纯树脂及单层NGO改性CFRP进行实验研究。结果表明，纯树脂及单层NGO改性CFRP在损伤阻抗及损伤容限实验中均存在拐点现象，且拐点出现在相同深度位置，其中纯树脂CFRP拐点位置为0.51 mm，单层NGO改性CFRP拐点位置为0.43 mm；相对于纯树脂CFRP，单层NGO改性CFRP可以显著提高复合材料的抗冲击性能及冲击后的压缩性能；通过对冲击后凹坑深度及凹坑面积进行数据模拟，可以用拟合公式实现对复合材料的损伤预测。     

高速列车转向架构架损伤、等效应力及寿命分布特性研究

为分析高速列车转向架构架损伤、等效应力及寿命分布特性，对构架疲劳关键测点进行动应力线路实测并对测点实测时域数据波形进行解析；基于实测应力时间历程及雨流计数法编制二维应力谱，利用Goodman等寿命方程将二维应力谱等效转换为一维应力谱；阐述线性累积损伤及非线性累积损伤模型的建立方法并对实测数据的线性累积损伤及非线性累积损伤进行了计算及对比分析；分别基于线性累积损伤理论及非线性累积损伤理论推导出各理论下的等效应力，基于实测数据对两种等效应力进行了计算及对比分析；通过结合非线性累积损伤及线性累积损伤理论计算的等效应力及不同可靠度下的材料S-N曲线计算并对比分析构架结构的疲劳寿命。研究结果表明，与非线性疲劳分析理论相比，线性疲劳分析理论对高速列车转向架构架的疲劳特性评估偏于保守。     

Point contact abrasive wear behavior of MAX phase materials

The room temperature abrasive wear behavior of three selected MAX phases, Ti₃SiC₂, solution strengthened Ti_2.7Zr_0.3SiC₂ and Cr₂AlC, is investigated by low velocity scratch testing using a diamond conical indentor with a final radius of 100 μm and a cone angle of 120° and applied loads of up to 20 N. All three materials showed a relatively low wear resistance in comparison to most engineering ceramics such as Al₂O_3, Si₃N₄ and SiC. For all three materials, the wear rate scaled more or less linearly with the applied load. The softer Ti₃SiC₂ with a hardness of 2.8 GPa showed the lowest wear resistance with extensive ploughing and grain breakout damage, both within and outside the direct wear track, in particular at the highest load. The hardest material, Ti_2.7Zr_0.3SiC₂, with a hardness of 7.3 GPa, showed a 5 times better wear resistance. The Cr₂AlC with a hardness of 4.8 GPa showed a wear resistance equal to or even better than that of the Ti_2.7Zr_0.3SiC₂. The wear mechanism depends on the applied load and the microstructure of the MAX phase materials tested. For the Ti₃SiC₂ sample, a quasi-plastic deformation behavior occurs below a point load of 10 N, resulting in grain bending, kink band formation and delamination, grain de-cohesion, as well as trans-and intra-granular fracture near the scratch groove. At this load, the Ti_2.7Zr_0.3SiC₂ and Cr₂AlC MAX samples display plastic ploughing, grain boundary cracks and material dislodgments.     

Progressive fracture processes around tunnel triggered by blast disturbances under biaxial compression with different lateral pressure coefficients

To investigate the progressive fracture processes around a tunnel triggered by static stress and dynamic disturbance, experiments and numerical simulations were performed. The results show that the spatial distributions of acoustic emission (AE) events become very different as lateral pressure coefficients change. The combined effect of static stress and dynamic disturbance causes the damage around the tunnel, and initial stress conditions control the damage morphology. The blast disturbance cannot fundamentally change the damaged area but will deepen the extent of damage and accelerate the failure speed. The more significant the difference between the vertical and horizontal stresses is, the higher the impact on the tunnel by the dynamic disturbance is. The AE activity recovers to a relatively stable state within a short time after the blast and conforms to power-law characteristics.     

黄芩苷对H2O2氧化损伤人黑素细胞的保护机制研究

目的:探讨黄芩苷对H2O2氧化损伤正常人黑素细胞的保护作用及其机制研究。方法:构建H2O2氧化损伤黑素细胞模型，通过观察不同浓度的黄芩苷处理H2O2氧化损伤正常人黑素细胞，采用倒置显微镜观察黄芩苷对黑素细胞形态的影响；cell counting kit-8（CCK-8）法检测黄芩苷对黑素细胞增殖活力作用；乳酸脱氢酶（lactate dehydrogenase,LDH）法检测黄芩苷对黑素细胞LDH表达的影响, 并通过流式细胞仪检测活性氧（ROS）水平，荧光实时定量RT-PCR检测过氧化氢酶（catalase,CAT）、谷胱甘肽过氧化物酶1（peroxidase 1,GPX1）mRNA表达情况，通过ELISA试剂盒检测黄芩苷和H2O2处理黑素细胞后分泌的热休克蛋白70（heat shock protein 70,HSP70）。结果:镜下观察黄芩苷给药后细胞较对照组形态明显改变，细胞数增多；黄芩苷作用黑素细胞后增殖率较对照组升高（P<0.05）；黄芩苷明显抑制黑素细胞中LDH表达，呈剂量-效应关系（P<0.05）。黄芩苷能显著促进CAT和GPX1 mRNA表达，且明显抑制HSP70分泌。结论:黄芩苷对H2O2氧化损伤的正常人黑素细胞具有明显保护作用，可为临床白癜风的治疗提供参考。     

西曲煤矿水文地质类型划分探讨

矿井水文地质类型划分,对煤矿的安全生产划分有着重要的意义。探讨西曲煤矿矿井水文地质类型的划分,对井田内水文地质条件及矿井充水因素进行分析,得出该矿开采受水害影响程度以及防治水工作开展的难易程度均为中等。具体为,2+3#煤层矿井水文地质类型为中等,4#煤层矿井水文地质类型为复杂,8#、9#煤层矿井水文地质类型为复杂。分析认为,该矿应加强对陷落柱的物探和钻探、本矿采空积水探放水、矿界防隔水煤柱的留设等工作,研究结果可为煤矿防治水工作提供依据,在一定程度上可确保矿井安全生产。     

Effect of retained austenite – Compressive residual stresses on rolling contact fatigue life of carburized AISI 8620 steel

In this study the rolling contact fatigue (RCF) of case carburized AISI 8620 steel was numerically and experimentally investigated. For the numerical study, a two dimensional finite element (FE) RCF model based on the continuum damage mechanics (CDM) was developed to investigate the fatigue damage accumulation, crack propagation and final fatigue life of carburized AISI 8620 steel under various operating conditions. A randomly generated Voronoi tessellation was used to model the effects of material microstructure topology. The boundaries of the Voronoi elements were assumed to be the weak planes where damage accumulates, cracks initiate and propagate to simulate inter-granular cracks. A series of torsional fatigue tests were conducted on carburized AISI 8620 steel specimens containing 0% and 35% retained austenite (RA) to determine fatigue load (S) vs. life (N) of the material. The S–N results were then used to determine the material parameters necessary for the rolling contact fatigue model. The torsional fatigue test results indicate that the carburized AISI 8620 specimens with higher RA demonstrate higher life than the specimens with lower RA. The RCF model also indicates that the material with higher level of compressive residual stresses (RS) and retained austenite demonstrates higher RCF life. In order to corroborate the results of RCF model, a three-ball-on-rod rolling contact fatigue test rig was used to determine the RCF lives of carburized AISI 8620 steels with different amounts of RA. The fatigue life and cracks evolution pattern from the numerical and experimental results were corroborated. The results indicate that they are in good agreement.     

Study on life and path of fatigue cracks in multiple site damage plates

This paper presents experimental and numerical study of the fatigue crack growth of hollowed pre-notched plates with multiple site damages (MSD). The numerical analyses were performed using finite element method. Experiments were carried out to validate the numerical results. Fatigue tests of aluminum sheets with MSD cracks were conducted to evaluate the effects of some parameters such as the thickness, hole diameter and central distance of the holes. The results show that the distance of the holes has greatest and size of the hole has little effects on the fatigue lives. Nucleation of cracks strongly depends on the thickness, distance and hole size.     

铝电解预焙阳极脱落原因分析及对策

国内某电解铝企业电解槽频繁出现脱极现象,脱极率一度达到5%,造成原铝9970率大幅下降,阳极毛耗、氟盐单耗上升,电流效率下降,生产经营指标严重下滑。本文从残极炭碗状况、残极高度、磷铁环状况、磷铁成分、铁炭压降等几个方面进行观测,并对这些现象与脱极之间存在的因果关系进行分析,制定对策加以改进,最后得以扭转。     

Multilevel approach to lifetime assessment of steam turbines

This paper presents a multilevel methodology for a steam turbine lifetime assessment based on the damage calculation, probabilistic analysis and fracture mechanics considerations. Creep-fatigue damage calculations serve as a basis for evaluating the current lifetime expenditure and for defining additional steps of analysis. The need for the use of probabilistic analysis results from the inherent uncertainty in estimating the lifetime expenditure primarily caused by scatter in material properties. Fracture mechanics considerations are helpful in determining additional safety margins for components containing cracks. This methodology has been illustrated using an example of the lifetime calculations of a high-temperature steam turbine rotor. The calculations were based on the results of 2D numerical simulations performed for steady state and transient operating conditions.