Performance analysis of all-fiber polarimetric strain sensor for composites structural health monitoring

An improved design comprising a multifiber configuration for a polarimetric fiber optic sensor in real time structural health monitoring is presented in this paper. The sensor is in the form of a multifiber assembly composed of a high-birefringent (HiBi) sensing fiber and a single mode polarization maintaining (PM) fiber or a HiBi fiber as a lead-in and lead-out fiber, all spliced in sequence. The polarization behavior of the assembly is analyzed theoretically using Stokes matrix method for the monochromatic case. Based on this model a phase shift compensation method for multifiber sensors is proposed. The design also helps reduce the bulky optical component in the sensor. The static and dynamic responses of these multifiber sensors are experimentally evaluated to test the structural integrity of composites.     

Potential drop mapping for the monitoring of corrosion or erosion

Potential drop techniques have been employed in the power generation industry for the medium- and long-term monitoring of corrosion and/or erosion, but little quantitative data are available in the literature. The present work aims to determine how accurately the maximum depth of a defect on the far side of an inspected structure can be estimated from low-frequency potential drop measurements as a function of the shape and size of the defect itself and of the geometry of the probe. Finite Element simulations show that the electrode array configuration commonly used in existing commercial setups can lead to an underestimation of the defect depth. The novel electrode arrangement proposed in this paper overcomes this problem and is shown to give satisfactory estimates of the depth of defects as small as about twice the probe pitch. Experimental results confirm the numerical predictions and show that the quality of the reconstruction does not depend significantly on the relative position of the probe and the defect.     

Strain field analysis and sensor design for monitoring machine tool spindle bearing force

The fluctuating strain field produced by the rolling motion of the spindle bearing is analyzed by an elastic model and verified with experimental data. This strain field analysis is of considerable practical significance because of its close correlation to spindle bearing preload, cutting forces, and bearing running conditions. Based on the model, a conventional sensing scheme with strain gages mounted in a groove ground around the bearing outer ring is optimized by selecting proper sensor sizes, locations, and configurations such that signal cross-over error is minimized. In addition, the feasibility of a non-invasive sensing scheme achieved by attaching high sensitivity sensors on the outside surface of the spindle housing is studied. From the strain model, it is found that the level of strain field at the housing surface is substantially lower, and its distribution is not concentrated. Therefore, high sensitivity sensors and different sensing schemes are needed. Simulation results show that, compared with the conventional scheme, the output of this scheme requires less signal processing when the force acting on the bearing is fluctuating.     

常规铸造定向层片TiAl合金持久加载中的组织退化及改善途径

基于TiAl合金常规铸造定向层片组织与多孪晶合成晶体(polysynthetically twinned crystals,PST)的组织差别,详细讨论这些组织差别对常规铸造定向层片组织TiAl合金持久加载过程中组织退化的影响,并探讨降低这些不利影响的微合金化途径。结果表明:定向层片组织与PST晶体的差别主要包括存在层片团界和小角度取向差、Al元素成分偏析以及α_2相体积分数高于热力学平衡状态,同时,后续热等静压导致等轴γ晶粒析出和层片间距增加也是另外的明显差别。这些组织差别对定向层片组织持久加载过程中的组织退化造成不同程度的加剧作用。其中,Al元素成分偏析和α_2相体积分数过高促进了定向层片组织铸态试样的组织退化,热等静压试样中析出的等轴γ晶粒进一步加剧了其组织退化,这些均对定向层片组织持久寿命造成不利影响。而层片团界对组织退化的影响程度较小。此外,探讨了采用Zr、C、Si微合金化抑制持久加载过程中组织退化进而改善持久性能的可行性。     

Sensitivity of polymer nanoindentation creep measurements to experimental variables

Spherical indentation creep experiments were used to characterize the viscoelastic response of three polymeric materials with different elastic and viscoelastic responses. A hereditary integral formulation for creep following ramp loading was used to analyze experimental indentation data. A wide range of conditions, including different load levels and ramp times, were employed to examine sensitivity of results to the selected experimental variables. Modulus values for materials exhibiting minimal time-dependent responses were found to agree well with known values and to be invariant of experimental conditions. However, a material with substantial time-dependent deformation in the experimental time frame was found to exhibit some effect of both load level and ramp time on modulus values. Time constants measured in the experiment varied with loading rate for two of three polymeric materials examined, but time constants did not vary with peak load. The examination of the shape of experimental load–displacement responses demonstrated no appreciable plasticity in two of three materials – the same two materials with both time- and level-independent creep responses.     

Integrated monitoring scheme for a maglev guideway using multiplexed FBG sensor arrays

In the structural monitoring of maglev guideways, electromagnetic interference (EMI) can be a significant problem, as the maglev train is powered by high-voltage electric feeding systems. Recently, researchers have successfully applied fiber optic sensors to modern railway structures, mainly because they offer EMI immunity. This study presents an integrated monitoring scheme for a maglev guideway using wavelength division multiplexing (WDM)-based fiber Bragg grating (FBG) sensors. The physical quantities such as strains, curvatures, and vertical deflections are measured in field tests. The strains are directly measured from multiplexed FBG sensors at various locations on a test bridge followed by curvature calculations based on the plane section assumption. Vertical deflections are then estimated using the Bernoulli beam theory and regression analyses. Frequency information obtained from the proposed method is compared with those from a conventional accelerometer. Verification tests were conducted on a newly developed Korean maglev test track at different vehicle speeds.     

High-temperature deformation resistance and creep resistance of a TiAl-based alloy fabricated by cold crucible directional solidification technology

In order to improve the high-temperature deformation resistance and creep resistance of TiAl-based alloys,cold crucible directional solidification (CCDS) technology was employed.A β-type TiAl-based alloy with the nominal composition of Ti44Al6Nb1Cr2V was prepared using the optimized CCDS parameters of 45 kW input power and 0.5 mm·min~(-1) solidification rate.Thermo-compression testing was utilized to evaluate the high-temperature deformation resistance and creep resistance of the CCDS Ti44Al6Nb1Cr2V alloy.Results show that the CCDS Ti44Al6Nb1Cr2V alloy billets contain aligned columnar grains and a high percentage of small-angle lamellae.Thermo-compression testing results in the radial direction of the CCDS alloy show a much higher peak stress than other reported results in similar conditions.The much higher hardening exponent and deformation activation energy are obtained,corresponding to the excellent high-temperature deformation resistance and creep resistance,which are because of the hard-oriented grains,weaker stress-strain coordination capability of lamella structure and relatively more hysteretic dynamic recrystallization.Thermo-compression testing results in the longitudinal direction of the CCDS Ti44Al6Nb1Cr2V alloy show the much higher peak stress than that in the radial direction,indicating the better high-temperature deformation resistance and creep resistance attributed to the hard-oriented lamellae in this condition.     

Injection molding process monitoring using a self-energized dual-parameter sensor

On-line monitoring of polymer melt state is critical to ensuring part quality in injection molding. This paper presents a novel, dual-parameter sensing method for simultaneous measurement of pressure and temperature variations within the mold cavity through a modulator circuit. Pressure variation during the molding cycle, which is proportional to the electrical charge output of a piezoceramic stack, is discretized into acoustic pulses that are subsequently frequency-modulated by a temperature-sensitive oscillator (TSO). The ability to measure two parameters using one sensor package without batteries and cables for data transmission provides a new platform for monitoring injection molding processes.     

Wavelet analysis of sensor signals for tool condition monitoring: A review and some new results

This paper reviews the state-of-the-art of wavelet analysis for tool condition monitoring (TCM). Wavelet analysis has been the most important non-stationary signal processing tool today, and popular in machining sensor signal analysis. Based on the nature of monitored signals, wavelet approaches are introduced and the superiorities of wavelet analysis to Fourier methods are discussed for TCM. According to the multiresolution, sparsity and localization properties of wavelet transform, literatures are reviewed in five categories in TCM: time–frequency analysis of machining signal, signal denoising, feature extraction, singularity analysis for tool state estimation, and density estimation for tool wear classification. This review provides a comprehensive survey of the current work on wavelet approaches to TCM and also proposes two new prospects for future studies in this area.     

Evaluation of a spindle-based force sensor for monitoring and fault diagnosis of machining operations

This paper presents an evaluation of a spindle-based force sensor, the force ring, which is a strong candidate for in-process monitoring and fault diagnosis of machining operations. The evaluation criteria include the effect of integration of the force ring on the dynamics of the spindle, the drift behavior due to temperature change inside the spindle, the cross-talk between the channels, and the existence and compensation of the spindle-internal forces. The application of the force ring to process model-based monitoring and fault diagnosis has been demonstrated by the determination of force calibration coefficients using the force ring and their comparison with results obtained with a platform dynamometer. It has been concluded that the force ring provides dynamometer quality force measurements.     

Longitudinal strain monitoring of rail using a distributed fiber sensor based on Brillouin optical correlation domain analysis

A fiber-optic distributed sensor system is configured to measure the longitudinal strain distribution of a rail in real time. The system is based on the Brillouin correlation domain analysis (BOCDA), in which the variation of local Brillouin frequency (ν_B) is measured that linearly depends on the strain applied to the optical fiber. In the test measurement, the longitudinal strain distribution along a 2.8 m rail is measured under different loading conditions with a spatial resolution of 3.8 cm and an accuracy of ±15 με.     

An approximate model for three-dimensional alternating current potential drop analyses using a commercial finite element code

Alternating current potential drop (ACPD) is an established technique for non-destructive testing and materials characterisation. Finite element (FE) simulation is a very useful tool for the optimisation of probes and the prediction of test results, but three-dimensional models of ACPD problems are computationally intensive. This paper presents a new, simple model in which frequency-related effects are taken into account by appropriately modifying the geometry of the modelled structure: a DC analysis can then be performed on a smaller domain, thus reducing the computational power required. The results of experimental tests for the validation of the model are also presented and discussed.     

An electroanalytical sensor for monitoring alumina concentration in cryolite-alumina baths

Conclusions  Although the scientific feasibility for this new electroanalytical sensor concept is partially demonstrated by the family of current/voltage curves in Figure 1, considerable further work is needed to demonstrate commercial viability of the concept. Further intensive laboratory investigation, including the following actions is necessary before inplant, proof-of-principle tests can be undertaken.

Double electrolyte sensor for monitoring hydrogen permeation rate in steels

An amperometric hydrogen sensor with double electrolytes composed of a gelatiniform electrolyte and KOH solution has been developed to determine the permeation rate of hydrogen atoms in steel equipment owing to hydrogen corrosion. The gelatiniform electrolyte was made of sodium polyacrylate (PAAS), carboxyl methyl cellulose (CMC) and 0.2 mol dm⁻³ KOH solution. The results show that the gelatiniform electrolyte containing 50 wt.% polymers has suitable viscosity and high electrical conductivity. The consistent permeation curves were detected by the sensor of the double electrolyte and single liquid KOH electrolyte, respectively. The developed sensor has good stability and reproducibility at room temperature.     

基于光电传感器的模具废料监测系统设计

为避免因修边废料堆积而损坏模具,采用光电传感器建立了模具废料状态监测系统,介绍光电传感器监测的工作原理与系统的功能,并阐述了传感器的监测点布置和安装方法。实际生产表明,废料监测系统可准确监测冲模废料状态,以便采取相关措施,避免模具损坏。     

径向流磁流变阀压降性能分析

提出并设计了一种径向流磁流变阀,并加工了样机进行压降性能分析.该径向流磁流变阀的液流通道由2个中心小孔、1个圆环通道和2个径向圆盘通道串联组合而成.采用ANSYS/Emag电磁场仿真软件搭建了径向流磁流变阀有限元仿真模型,并进行了磁场仿真分析以获取理想的仿真压降.搭建了压降性能测试试验台,在不同的加载电流和模拟负载下对所设计的径向流磁流变阀压降性能进行了试验分析.试验压降和仿真压降趋势一致.     

2324铝合金蠕变时效成形有限元分析

蠕变时效成形技术是利用金属的蠕变特性,将成形与时效同步进行的一种成形方法。该成形方法适于成形可时效强化型合金的整体带筋和变厚度大曲率复杂外形和结构的整体壁板构件,被认为是下一代大型民用飞机特别重要的金属成形工艺之一。文章根据蠕变试验数据,确定了2324铝合金蠕变本构方程中的材料常数,并应用有限元软件ABAQUS/Standard,通过编写蠕变子程序,对2324铝合金板单曲率弯曲、蠕变和回弹进行了有限元分析。     

Application of a novel type Barkhausen noise sensor to continuous fatigue monitoring

A novel Barkhausen noise (BN) sensor with no need for external magnetization was tested and applied to continuous fatigue monitoring of mild steel and high strength steel specimens. This new type of sensor indicated an increase in the BN rms value under maximum tensile stress during one cycle in cyclic bending tests with increasing stress amplitude. The BN rms value under maximum compressive stress stayed, however, approximately constant. The reason for this behaviour was the stress-induced anisotropy of the BN. Bending fatigue experiments with constant stress amplitude and R=−1 were conducted at different stress levels. In addition to the BN also the acoustic emission of the specimen was measured. In the mild steel specimens the BN amplitude stayed constant after the initial saturation period, but just prior to the failure of the specimen the amplitude increased meaningfully. This increase occurred at the same time as the increase in the acoustic emission signal indicating the beginning of crack initiation and growth. In the high strength steel specimens the BN amplitude decreased after the initial saturation period. The increase of the BN signal started well before the failure of the specimen and even before the increase in the acoustic emission signal.     

The computer-aided analysis of directional solidification processes

Computer-aided modeling and simulation has become a viable tool in enhancing the physical understanding of solidification processes. This tool also has the unique capability of enabling the user to extrapolate a given materials processing technique from a small-sized laboratory set-up to a large production size, yielding improved process design. However, most solidification processes are very complicated in nature; both physical models and geometrical complexities pose stringent computing requirements. Recent progress made in modeling, computing, and process simulation is highlighted in this article.     

T形接头机器人GO2焊接过程实时监控

针对T形接头的机器人CO2焊接,建立了焊接过程的实时监控系统,对电弧传感器采集的焊接电参数信息实施在线处理与特征提取.构建焊接电流瞬时值标准差、峰度和变异系数的三维特征矢量,描述正常焊接过程与受到干扰的焊接过程之间的区别.将三维特征矢量作为模糊Kohonen聚类神经网络系统的输入,对焊接过程进行识别,为实时监控机器人CO2焊接过程奠定了基础.