Acoustic Harmonic Generation Due to Thermal Embrittlement of Inconel 718

This paper describes an attempt to characterize the deterioration of a structural material's mechanical properties by nonlinear acoustics. In this particular case, the damage was caused by “thermal embrittlement” during which the material, here the nickel-based alloy Inconel 718, loses a significant fraction of its fracture toughness. Harmonic generation was the experimental method used to characterize the microstructural changes in the material as a function of exposure time at elevated temperatures. Tests were performed on two heats of Inconel 718 with slightly different chemistries, with one heat showing particular sensitivity of the fracture toughness to the elevated temperature exposure with corresponding higher changes in the nonlinearity parameter. As a mechanical measure of the fracture toughness deterioration, a small specimen punch test was used in which the ductility of a thin slice of material is determined. A clear difference between the two heats was noted in the metallographic examination, which is reflected in the harmonic generation as well as the punch test data. An explanation for the changes of the harmonic generation during the embrittlement process is speculative at the present time.     

透射式外差椭偏测量及非线性误差分析

结合激光外差干涉法和透射式椭偏测量原理,研究了一种快速、高精度测量纳米厚度薄膜光学参数的方法．给出了光学系统设计和理论分析,使用两个声光调制器产生20kHz的差频,直接比较平行分量和垂直分量外差信号的幅值和相位,得到所需要的椭偏参数．光束偏振态的椭圆化及偏振分光不完全所引起的非线性误差是影响纳米薄膜测量精度的主要因素,推导出椭偏参数非线性误差的近似解析表达式,计算结果表明由此导致的膜厚测量误差可达几个nm,相对而言,激光器和反射镜等器件产生的光束椭偏化是其主要原因．     

螺纹综合测量中测端姿态测量系统的非线性矫正

数字化轮廓包络法螺纹综合测量的关键是准确获得螺纹牙型(全牙)测端姿态的数据信息.系统采用刚性全牙测端与被测螺纹啮合,以真实反映实际螺纹旋合状态.采用高精度、高灵敏度的TESA电感测微仪、LVDT信号处理芯片AD598组成螺纹测端姿态信号采集系统.本文对该系统进行了非线性测定,并提出了以分段线性插值为原理的软件矫正算法.通过系统标定和非线性矫正,测微系统的非线性度达到0.06%.     

PZT95／5铁电陶瓷的声速及力学参数研究

本文研究了高密度PZT95／5陶瓷的声速及基本力学参数。与低密度陶瓷的研究结果对比，显示陶瓷的制备方法对陶瓷的声速影响较大：随密度增加，陶瓷的声速线性增加。极化方向对陶瓷的声速也有影响，声波方向平行于极化方向的陶瓷纵波声速最大，横波声速最小。     

Nonlinearity Measurements of High-Power Laser Detectors at NIST

We briefly explain the fundamentals of detector nonlinearity applicable to both electrical and optical nonlinearity measurements. We specifically discuss the attenuation method for optical nonlinearity measurement that the NIST system is based upon, and we review the possible sources of nonlinearity inherent to thermal detectors used with high-power lasers. We also describe, in detail, the NIST nonlinearity measurement system, in which detector responsivity can be measured at wavelengths of 1.06 µm and 10.6 µm, over a power range from 1 W to 1000 W. We present the data processing method used and show measurement results depicting both positive and negative nonlinear behavior. The expanded uncertainty of a typical NIST high-power laser detector calibration including nonlinearity characterization is about 1.3 %.     

Application of extended crystal plasticity to the modeling of glide and kink bands and of crack opening in single crystals

In this work, the influence of the development of geometrically necessary dislocations (GNDs) at a crack tip in single crystals on the hardening and crack propagation behaviour is investigated. In particular, we are interested in examining the effect of such additional hardening on the development of glide and kink bands at the crack tip as well as on the process of crack opening. To this end, following Nye and many others, local deformation incompatibility in the material is adopted as a measure of the density of GNDs. Their development results in additional energy being stored in the material, leading to additional kinematic-like hardening. A thermodynamic formulation of the model in the context of the dissipation principle facilitates the derivation of the corresponding hardening relation. Results suggest that this additional hardening retards kink-band development, but has little or no influence on glide-band development. It also influences the crack tip opening displacement (CTOD). It turns out that the simulated CTOD correlates well with experimentally determined crack-propagation rates for different crack growth direction in the crystal.     

Acoustic response of aluminium and Duroid plates to hypervelocity impacts

The growing need for real-time impact sensors for deployment on both space vehicles and space habitats (in orbit or on the surface of atmosphere-less bodies such as the Moon) has stimulated sensor development programmes. The sensors should be low mass, low power, easily read-out electronically, cover large areas and be sensitive to impacts which can cause damage up to and including penetration. We propose that piezo-strain acoustic sensors can play an important role in this work. Accordingly we report on a series of hypervelocity impact tests of acoustic sensors mounted on thin plates (aluminium and Duroid plates). The acoustic sensors gave strong signals for impacts of sub mm-mm scale projectiles. We investigated dependences on impactor speed and size, angle of incidence and tested the difference between cratering and penetrating impacts.     

螺纹的综合测量和单项测量

简要介绍了螺纹测量的现状和目前存在的问题,讨论了螺纹测量需要研究的几个问题,分析了螺纹单项参数测量和综合测量的关系以及螺纹量值传递技术.具体介绍了实现内螺纹中径参数测量的测量原理、测量方法和测量中的问题.     

Acoustic Thermometry Results from 271 to 552 K

The NIST acoustic thermometer determines the thermodynamic temperature from measurements of ratios of the speed of sound of argon in a nearly spherical cavity. We report recent results for T − T ₉₀ on 12 isotherms spanning the range 271–552 K. (T is the thermodynamic temperature and T ₉₀ is the temperature on the International Temperature Scale of 1990.) The results are in excellent agreement with recent acoustic thermometry results reported by Benedetto et al. in the range from 273 to 380 K and with our previously reported results at 303, 430, and 505 K. The combined data sets are sufficiently redundant and sufficiently distributed over the temperature range to support a re-determination of the reference function for standard platinum resistance thermometers for a future temperature scale. The isotherms were analyzed using several methods; the T−T ₉₀ results and related uncertainties are insensitive to the method chosen. The thermal expansion of the stainless-steel resonator was deduced from the frequencies of the microwave resonances of the cavity. To clearly identify two nearly degenerate eigenmodes in our nearly axially symmetric resonator, two phased coupling probes were used to control the azimuthal angle of the microwave excitation.     

Variational projection methods for gradient crystal plasticity using Lie algebras

A computational method is developed for evaluating the plastic strain gradient hardening term within a crystal plasticity formulation. While such gradient terms reproduce the size effects exhibited in experiments, incorporating derivatives of the plastic strain yields a nonlocal constitutive model. Rather than applying mixed methods, we propose an alternative method whereby the plastic deformation gradient is variationally projected from the elemental integration points onto a smoothed nodal field. Crucially, the projection utilizes the mapping between Lie groups and algebras in order to preserve essential physical properties, such as orthogonality of the plastic rotation tensor. Following the projection, the plastic strain field is directly differentiated to yield the Nye tensor. Additionally, an augmentation scheme is introduced within the global Newton iteration loop such that the computed Nye tensor field is fed back into the stress update procedure. Effectively, this method results in a fully implicit evolution of the constitutive model within a traditional displacement‐based formulation. An elemental projection method with explicit time integration of the plastic rotation tensor is compared as a reference. A series of numerical tests are performed for several element types in order to assess the robustness of the method, with emphasis placed upon polycrystalline domains and multi‐axis loading. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis,characterization and properties of ferroelectric rubidium hydrogen tartrate single crystals

Rubidium hydrogen tartrate single crystals were grown in silica hydrogel. Controlled reaction was employed between tartaric acid and rubidium chloride solutions by slow diffusion process in the gel medium. Colourless transparent crystals were grown at room temperature. The average density of crystals measured pyknometrically was 2·263 g cm⁻³. Thermal stability of the materials was studied. Chemical etching was employed to determine the perfection of these crystals.     

Cyclic transition of deformation in {1 2 3}<6 3 4> single crystal processed by accumulative roll-bonding

In this study, the crystal plasticity finite element method model was used to study the deformation in a single crystal aluminium processed by accumulative roll-bonding (ARB). The predicted textures match well with the experimental observations up to nine cycles. The texture and slip activities in representative layers were investigated, and cyclic transition of them was observed. It was found that the thickness position change caused by cutting and stacking was a basic reason for the cyclic transition. Finally, the effect of shear deformation to this transition was discussed.     

The effect of material behaviour on the analysis of single crystal turbine blades: Part I – Material model

ABSTRACT This paper describes a slip system model developed for the analysis of modern single crystal superalloys – specifically, the first generation alloys RR2000 and SRR99, and the second generation alloy CMSX‐4. The single crystal model is implemented as an ABAQUS User MATerial (UMAT) subroutine, the framework is based on the classical theory of single crystal plasticity. The constitutive equations used have different formulations based on the micromechanisms of deformation and experimental measurements. The emphasis is on the effect of incorporating the micromechanisms of material behaviour on predicted macroscopic results. Several important phenomena and mechanisms, which are required for explaining creep properties as a function of stress, temperature and orientation are identified and included in the model. These include: activation of < 101 > {111} and < 112 > {111} slip systems, rigid body rotation, continuum damage, slip system softening, dislocation interaction, threshold behaviour and rafting. Model simulations are compared with experimental data in various deformation regimes. In a later part of the paper, the model is used to analyse the performance of a single crystal turbine blade. This enables the effect of the micromechanisms of deformation on overall component behaviour to be quantified.     

基于位错密度的晶体塑性有限元方法的数值模拟及参数标定

运用ABAQUS有限元分析软件对基于位错密度的晶体塑性有限元方法(CPFEM)及其晶体塑性参数进行了深入的研究。结果表明,CPFEM晶体塑性本构可以准确地体现材料的力学性能。通过讨论不同晶体塑性参数,得到各个参数可以分别控制材料的屈服强度、硬化过程、剪切应变速率、极限强度等性能。此外,为了标定材料的晶体塑性参数引入多晶的代表体积单元(RVE)模型,并讨论了晶粒数以及晶粒规整度对于RVE模型的影响。结果表明,RVE模型的晶粒数达到临界值750个时能够体现等轴晶的宏观各向同性。结合晶体塑性RVE模拟和拉伸试验结果,对Inconel 718合金的晶体塑性参数进行标定,晶体塑性有限元的模拟结果和实验结果的误差小于5%。证明经过标定的晶体塑性参数可以准确反映Inconel 718的力学性能,也使得进一步研究该合金介观晶粒尺度的力学性能成为可能。     

非线性超声检测的因素探讨及其在HR3C烟侧腐蚀的应用

基于对影响非线超声性检测因素的探讨,考察了应用非线性检测无损评价HR3C烟侧腐蚀的可行性。结果表明:脉冲激励串个数n≤2df/c,加汉宁窗有助于降低系统干扰,此外,样品表面粗糙度对非线性系数β产生显著的影响。随腐蚀时间的延长,非线性系数呈现阶段性的递增趋势。腐蚀初期(腐蚀时间在50h以内),非线性系数增幅不足20%;然而,腐蚀至150h,非线性系数显著增加;相对于未腐蚀样品,腐蚀200h时的非线性系数增幅达260%。非线性系数的单调变化与腐蚀损伤的加剧相一致,因此,应用超声非线性无损评价HR3C的烟侧腐蚀是可行的。     

Subsurface crack formation and propagation of fretting fatigue in Ni‐based single‐crystal superalloys

The fretting fatigue crack formation and propagation behaviors of Ni‐based single‐crystal (NBSX) superalloys are investigated in this paper. Subsurface crack formation process is revealed by in situ fretting fatigue experiment. The crack is observed to form on subsurface area, then propagates to the contact surface. Inclusions in materials are found to have obvious effects on crack propagation, and slip lines are closely related to the crack propagation direction. Crystal plastic finite element method (CPFEM) simulation is used to simulate crack formation position. The accumulative plastic strain peaks at the edge of contact zone and the subsurface area. The results show that the CPFEM simulation and in situ observation achieve good agreements.     

单晶材料X射线应力测定原理与方法

结合单晶X射线应力测定基本原理,通过必要的理论分析,对现有单晶应力测定方法进行必要的改进和优化。基于工程实际应用需要,精简了单晶应力测定步骤并拓宽其应用范围,即不需要事先精确已知200,只需改变空间方位角驴和驴,再通过多元线形回归分析方法即可计算出各应力分量。最后给出了单晶应力测定的典型实例,即对同一部位重复测定应力,证实测量误差不超过±20MPa,说明该方法具有较高的测量精度和可靠性。