Processing TiAl-Based Alloy by Elemental Powder Metallurgy

TiAI-based alloys with various compositions (including Ti-48Al, Ti-47Al-2Cr-2Nb, Ti-47Al-2Cr-2Nb-0.2B and Ti-47Al-3Cr, in mole fraction) had been prepared by elemental powder metallurgy (EPM). The results have shown that the density of the prepared Ti-48AI alloy increases with increasing hot pressing temperature up to 1300℃. The Ti-48AI alloy microstructure mainly consisted of island-like Ti3Al phase and TiAl matrix at hot pressing temperature below 1300℃, however, coarse α2/γ lamellar colonies and γ grains appeared at 1400℃. It has also indicated that the additions of elemental Cr and B can refine the alloy microstructure. The main microstructural inhomogeneity in EPM TiAI-based alloys was the island-like α2 phase or the aggregate of α2/γ lamellar colony, and such island-like structure will be inherited during subsequent heat treatment in (α＋γ) field. Only after heat treatment in a field would this structure be eliminated. The mechanical properties of EPM TiAl-based alloys with various compositions were tested, and the effect of alloy elements on the mechanical properties was closely related to that of alloy elements on the alloy microstructures. Based on the above results, TiAI-based alloy exhaust valves were fabricated by elemental powder metallurgy and diffusion joining. The automobile engine test had demonstrated that the performance of the manufactured valves was very promising for engine service.

Influence of vibration mode on the screening process

The screening of particles with different vibration modes was simulated by means of a 3D discrete element method (3D-DEM). The motion and penetration of the particles on the screen deck were analyzed for linear, circular and elliptical vibration of the screen. The results show that the travel velocity of the particles is the fastest, but the screening efficiency is the lowest, for the linear vibration mode. The circular motion resulted in the highest screening efficiency, but the lowest particle travel velocity. In the steady state the screening efficiency for each mode is seen to increase gradually along the longitudinal direction of the deck. The screening efficiency increment of the circular mode is the largest while the linear mode shows the smallest increment. The volume fraction of near-mesh size particles at the underside is larger than that of small size particles all along the screen deck. Linear screening mode has more near-mesh and small size particles on the first three deck sections, and fewer on the last two sections, compared to the circular or elliptical modes.

Simulation-Based Construction of Three-Dimensional Process Model for Punching Cartridge Cases

A method of constructing three-dimensional process model for the punching cartridge cases is presented based on DEFORM simulation analysis. Using DEFORM software,the finite element simulation models for the punching and forming process of cartridge cases are established,and the corresponding simulation result model of each intermediate procedure is obtained by continuously performing the forming process simulation. The simulation model cannot annotate size and process information due to poor interface between DEFORM software and CAD software. Thus,a 3D annotation module is developed with secondary development technology of UG NX software. Consequently,the final process model with dimension and process information is obtained. Then,with the current 3D process management system,the 3D punching and forming process design of cartridge cases can be completed further. An example is also provided to illustrate that the relative error between the simulation process model and the physical model is less than 2%,which proves the validity and reliability of the proposed method in this study.

Finite element modeling of consolidation of composite laminates

Advanced fiber reinforced polymer composites have been increasingly applied to various structural components. One of the important processes to fabricate high performance laminated composites is an autoclave assisted prepreg lay-up. Since the quality of laminated composites is largely affected by the cure cycle, selection of an appropriate cure cycle for each application is important and must be optimized. Thus, some fundamental model of the consolidation and cure processes is necessary for selecting suitable parameters for a specific application. This article is concerned with the ＂flow-compaction＂ model during the autoclave processing of composite materials. By using a weighted residual method, two-dimensional finite element formulation for the consolidation process of thick thermosetting composites is presented and the corresponding finite element code is developed. Numerical examples, including comparison of the present numerical results with one-dimensional and twodimensional analytical solutions, are given to illustrate the accuracy and effectiveness of the proposed finite element formulation. In addition, a consolidation simulation of AS4/3501-6 graphite/epoxy laminate is carded out and compared with the experimental results available in the literature.

AN INVESTIGATION ON THE LOW TEMPERATURE RELAXATION OF POLYETHERETHERKETONE

The temperature spectra of internal friction of polyetheretherketone (PEEK) are investigated from 130K to 250K with a multi-function torsion pendulum in the frequency range of 0.1 Hz to 5 Hz. A relaxation process, γ relaxation, appears in the temperature range of the measurement. Its relaxation time distribution in terms of a Gaussian distribution, and the relation between molecular motion mechanism and the distribution characteristic are discussed. The element process of γ relaxation is found to be a disordering one.

Design of Efficient Router with Low Power and Low Latency for Network on Chip

The NoC consists of processing element (PE), network interface (NI) and router. This paper proposes a hybrid scheme for Netwok of Chip (NoC), which aims at obtaining low latency and low power consumption by concerning wired and wireless links between routers. The main objective of this paper is to reduce the latency and power consumption of the network on chip architecture using wireless link between routers. In this paper, the power consumption is reduced by designing a low power router and latency is reduced by implementing a on-chip wireless communication as express links for transferring data from one subnet routers to another subnet routers. The average packet latency and normalized power consumption of proposed hybrid NoC router are analyzed for synthetic traffic loads as shuffle traffic, bitcomp traffic, transpose traffic and bitrev traffic. The proposed hybrid NoC router reduces the normalized power over the wired NoC by 12.18% in consumer traffic, 12.80% in AutoIndust traffic and 12.5% in MPEG2 traffic. The performance is also analyzed with real time traffic environments using Network simulator 2 tool.

A Review of Residual Stress and Deformation Modeling for Metal Additive Manufacturing Processes

A metal additive manufacturing process results in a nearly net-shaped fabrication of parts directly from digital data.A local heat source melts the deposited material,and a part is built layer-by-layer.Residual stress and de-formation are critical issues experienced by additively manufactured parts.Modeling the additive manufacturing process provides important insights and can help determine an optimal build plan so as to minimize residual stress formation.Various approaches have been used for modeling of residual stresses,ranging from high-fidelity models to simplified models,for quicker results.This paper provides a state-of-the-art review of the approaches used to numerically model residual deformation and stresses in structures built using additive manufacturing.Fur-thermore,it describes the physical causes of residual-stress generation in an additively manufactured structure.

Numerical simulation of the sticking process of glass-microparticles to a fiat wall to represent pollutant-particles treatment in a multi-channel cyclone

Ultrafine particles are dangerous to human health and are usually difficult to separate from airflow because of their low inertia, which helps them to stick easily to surfaces because of adhesive forces. This characteristic provides opportunities for adhesive ultrafine particle separation by designing air-cleaning devices that exploit the sticking ability. To understand governing effects in such air-cleaning devices, which can be designed as multi-channel cyclones, the sticking of adhesive spherical glass particles under oblique impact has been investigated numerically by using the discrete element method. An adhesive dissipative contact model was applied by implementing different interaction forces for various-sized ultraflne pollutant particles. Normal loading is represented by the elastic Hertz contact model, whereas viscous damping is described by the modified nonlinear Tsuji model. The influence of deformation- dependent adhesive forces for a range of ultrafine particle sizes is illustrated during the sticking process. Dissipative oscillations during the sticking process were observed because of the influence of viscous damping forces.