高温合金不同脉宽超快激光作用下多脉冲去除阈值

实验研究了激光脉冲宽度和脉冲个数对镍基高温合金材料去除阈值的影响,分别在290 fs,1 ps和7 ps脉宽的激光下,使用1,10,50,100,300,500和1000个不同能量的激光脉冲辐照高温合金样品表面。实验结果表明,烧蚀坑尺寸会随脉冲数的增加而增加,而脉冲宽度的增加会加大脉冲个数对烧蚀坑直径的影响。通过烧蚀坑直径的平方值与激光脉冲能量之间存在的对数关系,得到了不同脉冲宽度下镍基高温合金的多脉冲材料阈值。3种不同脉宽下的高温合金多脉冲去除阈值都存在显著的累积效应。根据去除阈值计算得到290 fs,1 ps和7 ps脉宽下的累积效应系数分别为0.88,0.86和0.78。     

一种基于十字镂空结构的低频超材料吸波体的设计与制备

设计了一种十字镂空的超材料结构,与传统的铁磁吸波材料相结合,实现了低频吸收频带的扩宽.仿真结果显示,吸波体在2-4 GHz范围可以实现-10 dB以下的吸收,相比于没有加载超材料的情况,吸收带宽扩展了0.5 GHz.实验结果在2.5-5.1 GHz范围内也显示了相似的吸收曲线,低于-9 dB的吸收频带有0.48 GHz的扩宽,扩展了23%.不同结构的能量损耗密度分布表明,相比于无镂空的十字结构,镂空十字结构可以增加磁场能量损耗,加强单元结构之间的耦合,降低超材料对传统吸波材料性能的破坏.探索了传统铁磁吸波材料厚度的变化对吸波体吸收性能的影响,发现由超材料引入的附加峰位置不随着吸波材料厚度的改变而明显地移动.根据这个结果,进一步设计了由两种超材料叠加组合而成的吸波体,仿真结果和实验结果均显示,在降低了1.1 mm铁磁吸波材料层厚度的情况下,使低频吸收带宽又扩展了0.9 GHz.     

The role of superdislocations for modeling plastic deformation of lamellar TiAl

The deformation behaviour of lamellar TiAl-alloys is investigated by means of micromechanical finite element simulations. For the simulations, a lower and an upper bound periodic unit cell representing the lamellar substructure are used. Crystallographic slip is described by continuum crystal plasticity. For the simulations, 16 individual ordinary, super, and twinning systems divided into three morphological slip modes are taken into account. The strength and hardening parameters of the slip systems are determined by comparison with experimental data from room temperature compression tests of poly-synthetically twinned (PST) crystals of TiAl. The effect of the yield stress of the superdislocations is investigated by systematic parameter variations. The results show that the general anisotropy of PST-crystals can already be described with a purely morphological classification of the slip systems. Superdislocations cause a slight tension–compression anomaly if the yield stresses are higher than for the ordinary and twinning systems.     

Developments in the processing and properties of NdFeb-type permanent magnets

The composition, microstructure and processing of NdFeB-type permanent magnets are all critical factors for the successful production of high performance magnet components. Three common fabrication routes can be used to categorize these NdFeB-based bulk magnets: sintering, polymer bonding and hot deformation. Generally, the former type of magnet has a high-energy product (30–50 MGOe), full density and a relatively simple shape. Bonded magnets have intermediate energy products (10–18 MGOe), lower density and can be formed into intricate net-shapes. Hot deformed magnets possess full density, intermediate to high-energy products (15–46 MGOe), isotropic or anisotropic properties and have the potential to be formed into net shapes. This article discusses the critical issues of improved magnetic performance, environmental stability, net-shape formability and magnetization behavior for the main categories of NdFeB magnets.     

K18C镍基高温合金光谱标准样品的研制

采用二次冶炼的方法炼制出K18C镍基高温合金光谱标准样品,其中包含C,Cr,Fe等16种元素。对标准样品的均匀性与稳定性进行了考察。结果表明所研制的K18C镍基高温合金标准样品成分均匀,稳定性优良,5年内各成分量值无变化。委托多家实验室进行协作定值,选择了合适的统计学方法对各协作单位的数据进行检验和计算,获得标准样品的标准值及其扩展不确定度。     

可视滴定法测定铝钒中间合金中的钒时称样量和滴定液浓度的优化

用可视滴定法测定铝钒中间合金中的钒时,对称样量和硫酸亚铁铵滴定液浓度的关系进行了探讨。实验发现,基体铝对于铝钒合金中钒的测定无影响。常见的铝钒合金范围为50%～60%,低于50%和高于标准上限0.5%钒含量的合金没有实验样品,通过向样品溶液中加入钒标准溶液可模拟铝钒合金试样。依据化学分析等物质量反应定律,选择不同钒含量的试验样品,对钒的称样量和滴定液浓度进行优化,确定了硫酸亚铁铵滴定液的浓度与滴定液消耗体积的合适关系。     

The influence of thermodynamic gas parameters on laser-induced bubble dynamics in water

The oscillating properties of laser-induced cavitation bubbles in water are investigated by means of a fiber-optic sensor based on optical beam deflection. The experimental results show two important points. One is that the smaller the bubble radius the more quickly the bubble surface moves. Thus, the variations of the temperature and the pressure inside the bubble will be close to those of an adiabatic process. The other is that the high-energy vapor inside the newborn bubble diffuses and coagulates rapidly through violent expansion and thermal conduction. Thus, the gas content of the bubble reduces significantly in the first oscillation. Numerical simulation is made for the bubble model with consideration of liquid viscosity, surface tension, and gas content. Through modification of the polytropic index and the gas content parameter, two parameters of this model, the numerical results fit the experimental results well.     

Low cycle fatigue behavior of single crystal superalloy with temperature gradient

In present study, low cycle fatigue model based on rate dependent constitutive formulation with kinematic hardening and fatigue damage rule is introduced to investigate the fatigue behavior of single crystal superalloys with temperature gradient. Low cycle fatigue tests with uniform temperature and with temperature gradient are carried out to investigate the influence of temperature gradient. The microstructure reveals that the slip deformation is a principal mechanism of low cycle fatigue with temperature gradient. Complex stress experiments of low cycle fatigue are carried out to verify the life prediction rule. Bauschinger effect, ratcheting effect and fatigue damage of single crystal superalloy at different temperatures are studied. Special attention is placed on the simulation of low cycle fatigue behavior with temperature gradient. The simulation results show that the ratcheting effect at high temperature is more remarkable than that at low temperature due to the influence of temperature gradient, which results in the difference of damage evolution between high temperature zone and low temperature zone. Comparison between experiments and simulations with temperature gradient proves that the predicted model based on the damage of the second cycle is reasonable.     

半无限板边缘裂纹的权函数解法与评价

权函数法是求解裂纹体在任意受载条件下的应力强度因子和裂纹面位移等断裂力学参量的高效、高精度方法,与有限元等数值方法相比,在求解效率和可靠性方面均具有明显优势.针对半无限板边缘裂纹,系统分析了在国际断裂力学界较有代表性的Wu-Carlsson、Glinka-Shen和Fett-Munz三种解析形式的权函数法,进而以在远端均匀加载下的半无限板边缘裂纹面位移Wigglesworth解析解导得的权函数及其对应的格林函数解(即裂纹面受一对单位集中力作用下的应力强度因子)为基准,沿整个裂纹长度对3种权函数的精度逐点进行比较,并与文献中基于其他方法求得的权函数做了广泛对比,包括Bueckner,Hartranft-Sih以及Wigglesworth利用不同解析方法推导出的高精度的权函数.研究了3种参考载荷(均布/正反向线性分布应力、集中力)及其不同组合,以及裂纹嘴位移的几何条件对权函数精度的影响.结果表明,基于一种参考载荷下的裂纹面张开位移比基于两种参考载荷下的应力强度因子所得到的权函数具有更高的精度,而且后一种方法的精度明显受到所选参考载荷组合的影响;裂纹面位移在裂纹嘴处三阶导数等于零的条件对基于一个参考解的权函数精度的改进效果较小.最后给出了利用各种权函数方法计算得到的4种载荷条件下的应力强度因子,并对结果进行了比较.