Preparation of MIM213 turbine wheel with hollow internal structure

Turbine wheels fabricated by conventional ingot metallurgy suffer casting defects and compositional segregation problems, and their mechanical properties can't be fully developed. This article presents the preparation of MIM213 turbine wheels through metal injection molding in conjunction with hot isostatic pressing. The filling stages of the turbine wheel were investigated by simulation and experimental short shots, and the microstructure and mechanical properties of MIM213 superalloy were examined. It is shown that MIM is suitable for the near-net shape forming of turbine wheel with hollow internal structure and complex blade geometry. Compared with the turbine wheel with solid core structure, the turbine wheel with hollow internal structure has relatively smaller proportion of high temperature region during injection molding, resulting in smaller shrinkage stress and the elimination of shrinkage voids. The relative density of MIM213 superalloy sintered in Ar atmosphere reaches 96.6%. A high volume fraction (31%) of spherical γ′ phase with average particle size of 124 nm, discrete secondary grain boundary borides and internally precipitated MC carbides are formed in austenite matrix. The tensile properties of MIM213 superalloy are higher than that of the equivalent cast K213 superalloy.     

卧轮式分级机转子临界转速的计算

为避免卧轮式分级机在运转过程中产生共振,以卧轮式分级机实验机和工业样机转子为研究对象,采用传递矩阵法和基于ANSYS Workbench 16.0的有限元法对其临界转速进行计算,将计算结果与试验测试结果进行比较。结果表明,对于实验机,传递矩阵法与试验测试结果偏差为11.9%,有限元法与试验测试结果偏差为4.1%;对于工业样机,传递矩阵法与试验测试结果偏差为10.5%,有限元法与试验测试结果偏差为3.5%,说明有限元法计算结果准确性更高,认为对于卧轮式分级机转子临界转速的计算,更适合采用有限元法。     

飞机轮速信号测试方法研究

为解决某飞机轮速信号测试中出现的数据缺失、曲线阶梯状不平滑及数据回零问题,分析轮速信号测试原理及测试系统结构,结合待测轮速信号特性,提出轮速信号测试优化方法,包括备份设计、直流隔离、周期测试及指标优化等。并针对轮速信号地面状态特性,设计一种信号测试链路检测方案。试飞测试验证结果表明,备份数据误差低于0.5%,数据曲线平滑,可消除数据回零现象,设计的轮速信号测试链路检测方案可行,有助于试飞航前检查。     

High speed preprocessing system

In systems employing tracking, the area of interest is recognized using a high resolution camera and is handed over to the low resolution receiver. The images seen by the low resolution receiver and by the operator through the high resolution camera are different in spatial resolution. In order to establish the correlation between these two images, the high-resolution camera image needs to be preprocessed and made similar to the low-resolution receiver image. This paper discusses the implementation of a suitable preprocessing technique, emphasis being given to develop a system both in hardware and software to reduce processing time. By applying different software/hardware techniques, the execution time has been brought down from a few seconds to a few milli-seconds for a typical set of conditions. The hardware is designed around i486 processors and software is developed in PL/M. The system is tested to match the images obtained by two different sensors of the same scene. The hardware and software have been evaluated with different sets of images.     

Evaluation of shear flow in composite wind turbine blades

The present work addresses the evaluation of the shear flow as an extension of the Jourawski’s formula. This idea is developed here for the case of a multi-celled composite thin-walled section. Firstly, the explicit formulation of the shear flow due to shear forces and torsion is derived, noting the simplificative hypothesis adopted. Then, the implemented model is verified by means of a benchmark problem with a known analytical solution. Finally, this model is utilized to evaluate the shear flow on an actual blade configuration, comparing the results obtained with those of a Finite Element model of the same blade, with a similar discretization.     

Post-buckling failure in multi-delaminated composite wind turbine blade materials

This study models the inter-laminar damage due to low velocity impacts on hybrid composite materials typical of those used in wind turbine blade structures. The effect of z-pinning using natural flax yarn on the critical buckling load and post-buckling behaviour of multi-delaminated composite beams was investigated. Laminated composite beams were pinned through their thickness using natural flax yarns to control delamination failure during the post-buckling process. A multiple delamination with a triangular shape was inserted into each of the beams to simulate the damage caused by a low velocity impact e.g. ice, on composite wind turbine blades. For a laminate design of [C₉₀/G₉₀]₄, global collapse caused no delamination failure during the post-buckling test while delamination failure occurred for a laminate design of [C₀/G₀]₄. In this case, z-pinning can significantly increase the failure resistance within a composite structure and it can then postpone the failure process. The buckling process of a multi-delaminated composite beam was also simulated by finite element software ANSYS and the results were substantially verified by relevant experimental results.     

Improving the response of a wheel speed sensor by using frequency-domain adaptive filtering

In this paper, a frequency-domain least-mean-square adaptive filter is used to cancel noise in a wheel speed sensor embedded in a car under performance tests. In this case the relevant signal is buried in a broad-band noise background, where we have little or no prior knowledge of the signal or noise characteristics. The results of the experiments show that the signal of interest and the noise (all forms of interference, deterministic, as well as stochastic) share the same frequency band and that the filter used significantly reduced the noise corrupting the information from the sensor while it left the true signal unchanged from a practical point of view. In this paper, a signal-to-noise ratio improvement higher than 40 dB is achieved. The results of the experiment show the importance of using digital signal processing when dealing with a signal corrupted by noise.     

Particle swarm-based structural optimization of laminated composite hydrokinetic turbine blades

Composite blade manufacturing for hydrokinetic turbine application is quite complex and requires extensive optimization studies in terms of material selection, number of layers, stacking sequence, ply thickness and orientation. To avoid a repetitive trial-and-error method process, hydrokinetic turbine blade structural optimization using particle swarm optimization was proposed to perform detailed composite lay-up optimization. Layer numbers, ply thickness and ply orientations were optimized using standard particle swarm optimization to minimize the weight of the composite blade while satisfying failure evaluation. To address the discrete combinatorial optimization problem of blade stacking sequence, a novel permutation discrete particle swarm optimization model was also developed to maximize the out-of-plane load-carrying capability of the composite blade. A composite blade design with significant material saving and satisfactory performance was presented. The proposed methodology offers an alternative and efficient design solution to composite structural optimization which involves complex loading and multiple discrete and combinatorial design parameters.     

High speed microcompression of paper coatings

A novel high speed microcompression platen tester was developed in order to measure the out-of-plane compressive modulus of thin materials. The instrument is capable of subjecting a sample of thickness 20 μm or greater to a transverse compressive pulse over a time interval ranging from approximately 2 ms to several seconds, and can therefore be used to collect data under conditions representative of those in a high speed calender nip. In this study, free layers of coating formulations normally used to coat paper were prepared and tested using the microcompression platen tester described above. Tests were conducted at high speeds, with a pulse duration of 2 ms during the compressive stroke, and at 23 °C to simulate room temperature calendering conditions. The compressive modulus of the coating did not correlate strongly with the modulus of its constituent latex. Latex content, however, strongly affected coating compressive modulus. A sharp increase in the compressive modulus was observed at the coating critical pigment volume concentration (CPVC)—essentially the latex concentration at which the coating layer porosity is reduced to zero. Pigment size distribution and pigment morphology also affected the compressive modulus of coating in a manner consistent with packing theory.     

氦透平膨胀机特性分析及转速控制方法

介绍了透平的几个重要特性:效率、特性比、制动方式以及制冷量的调节,并分析了各个特性的特点和意义。结合理论,给出了4种氦透平膨胀机的转速控制方法,详细说明了转速设定值的计算方法、计算流程及参数确定的方法,并分析说明了其优缺点。最后总结对比分析了几种方法在控制过程中设定值、控制器、执行机构上的差异,为实现氦透平膨胀机的PLC控制提供参考。     

High speed flexible disk - head interface

Progress toward the use of high speed flexible disks in recording systems has been made possible by a better understanding of stabilization requirements. Benson and Bogy [1], and Greenberg [2] have described the overall response to a localized load on a flexible disk. Greenberg describes the head/disk interface with an expression that uses Reynolds equation for loading. This study examines the flying height behavior between a high speed flexible disk and a spherical head using white light interferometry. Geometric parameters determining optimum flying characteristics are discussed, and stable, relatively uniform air bearing spacings in the sub-micron region are described at a surface speed of 40 m/sec. Correlation is established with a computer model which couples the solution of the Reynolds equation for the air bearing with a simplified treatment of a localized region of the disk. This portion of the disk is considered as a membrane on an elastic foundation. Steady state tension and elasticity parameters are used to model rotational stresses and axial compliance.     

High speed scanning calorimetry for amorphous alloys

A high speed scanning calorimeter has been developed for simultaneous measurements of heat capacity and electrical resistivity of thin strips. The system was designed for amorphous alloys but can be used for other materials as well. The specimen is heated by an electrical current at rates ranging from 250 to 40,000 K·s^–1, and the temperature is sensed by an IR pyrometer ranging down to room temperature. The maximum data acquisition rate is 50 kHz. Operational characteristics of the system are given, and various phenomena that affect design and operation are discussed. Data are taken for some Metglas alloys. Glass transition and crystallization temperatures as well as rough viscosity data are evaluated. At high heating rates the glass transition is spread over a wide temperature range. The formation of metastable crystalline phases can be bypassed so that stable phases form directly from the amorphous state.