贝氏体钢内水冷穿孔顶头的粘钢及防止措施

从顶头生产工艺控制的角度,分析了贝氏体钢内水冷穿孔顶头产生粘钢的原因、特点和机制,指出掉鼻、缺肉是顶头粘钢的另一种更为严重的失效形式,强化熔炼工艺控制和保证夹杂物总量在A0.5B1C0.5D1级水平,粘钢问题可以得到有效控制。     

Sliding wear behavior of salt bath nitrocarburized medium carbon steel

Salt bath nitrocarburizing is a well-known thermochemical diffusion process for enhancing the tribological and corrosion properties of ferrous components. The current work describes the role of a compound layer developed during nitrocarburizing, both in the ferritic and austenitic regimes of Fe-N-C system, on the sliding wear behavior of a medium carbon steel. The wear behavior of the nitrocarburized steel discs was assessed by the pin-on-disc tests (ASTM G 99-99) under different normal loads running against a hardened SAE52100 pin. It was observed that the compound layer on the surface not only controlled the wear rate but also resisted the adhesive wear/transfer of material from pin to disc, aside from providing low-friction coefficients.     

应用ATV71变频器有效解决给粉机变频器低电压跳闸问题

本文分析了给粉机变频器低电压跳闸的原因和解决办法，为解决给粉机变频器低电压跳闸，消除设备隐患提供了经验。     

高能超声处理Al-1Si合金凝固组织分析

采用高能超声处理Al-1Si合金熔体,借助金相显微镜和电子探针进行组织分析,并测定合金的熔化潜热,分析了熔体中超声空化效应和声流效应影响凝固过程的机理。结果表明,试样晶粒平均尺寸由超声处理前的94μm减小到超声处理后的34μm;合金试样的熔化吸热量由263.90J/g降低为159.81J/g,在熔体中施加高能超声显著改善了合金成分的均匀性并细化了晶粒。     

Variable-gain up-converter with current reuse for 5-GHz WLAN applications

A variable-gain up-conversion mixer for 5-GHz WLAN applications is presented, whose input stage is based on a novel variable gain transconductor. The proposed topology features reduced power consumption by exploiting dc current reuse for mixer biasing. Moreover, a new low-consumption control circuit is introduced, which achieves a temperature-stable and linear-in-dB characteristic, providing a 40-dB dynamic range within ±1 dB gain error.     

Dynamic Effects in Hopkinson Bar Four-Point Bend Fracture

Hopkinson bar techniques have played an important role in the study of high-rate deformation and fracture behavior of materials. In the current work, a split Hopkinson pressure bar was developed for dynamic four-point bend fracture testing, referred to as a “two-bar (incident and transmitted bars)/four-point” (2-bar/4-pt) bend test. To further understand some fundamental issues regarding stress wave propagation in this 2-bar/4-pt bend testing system, dynamic fracture tests were performed in pulse-shaped and unshaped pulse testing conditions. The effect of the pulse shaper on the incident pulse characteristics (rise time and duration), specimen’s dynamic response (load and loading point displacement), crack initiation time and stress-state equilibrium were investigated experimentally in the current work. The present results show that stress state equilibrium can be achieved prior to fracture initiation in notched and precracked specimens. In the pulse-shaped bending test, the specimen is more likely to attain stress-state equilibrium than in an unshaped incident pulse test. The crack initiation time was extended and the time required for attaining stress equilibrium was reduced by pulse shaping due to the tailored incident pulse having a longer rise time, which ensures that stress equilibrium is achieved prior to crack initiation. This article is based on a presentation made in the symposium entitled “Dynamic Behavior of Materials,” which occurred during the TMS Annual Meeting and Exhibition, February 25–March 1, 2007 in Orlando, Florida, under the auspices of The Minerals, Metals and Materials Society, TMS Structural Materials Division, and TMS/ASM Mechanical Behavior of Materials Committee.     

Modeling of Bolt Joint Behavior of Cast Aluminum Alloy (A380-T5) by Coupling Creep and Plasticity in Finite Element Analysis

Aluminum casting alloys exhibit creep behavior when the materials are exposed to high temperature and load. In this article, the stress- and temperature-dependent creep behavior of a die casting A380-T5 aluminum alloy was simulated using a classical constitutive model. The bolt-load retention behavior of the material was analyzed in a head bolt joint in an aluminum engine under thermal cycle condition using the finite element method. In this simulation, transient thermal analysis was performed first to calculate the metal temperature at the head bolt joint as a function of time during engine thermal cycling. This temperature was then input as the thermal loading in the subsequent structural analysis to calculate its effect on the bolt-load retention. The finite element analysis (FEA) model for the bolt-load retention simulation includes not only the plasticity in all metal components but also the creep properties of head bolt threads in the cast aluminum engine block. The FEA model was validated by good correlation between the predicted head bolt-load loss and the experimental measurement during engine thermal cycling. The simulation results also indicated that creep in the head bolt threads of cast aluminum engine block was mainly responsible for the load loss in the head bolt joint. This article is based on a presentation given in the symposium entitled “Simulation of Aluminum Shape Casting Processing: From Design to Mechanical Properties” which occurred March 12–16, 2006 during the TMS Annual Meeting in San Antonio, Texas under the auspices of the Computational Materials Science and Engineering Committee, the Process Modeling, Analysis and Control Committee, the Solidification Committee, the Mechanical Behavior of Materials Committee, and the Light Metal Division/Aluminum Committee.