履带行走式机械驱动链轮的动力学仿真与疲劳分析

应用Solid Works软件对履带行走式机械驱动链轮进行了三维建模,通过ADAMS软件进行系统运动学/动力学仿真与分析,得出驱动链轮轮齿载荷谱。根据载荷谱应用MSC PANTRAN与MSC FATIGUE软件对链轮轮齿进行疲劳寿命分析,为驱动链轮的修复与再制造提供理论依据。     

Synthesis of mullite aggregates from fly ash: effect on thermomechanical behaviour of low cement castables

Abstract

Refractory aggregates were synthesised from beneficiated fly ash by reaction sintering with calcined alumina at 1600°C, and 83% mullite yield was achieved. The aggregates had low porosity, low thermal expansion and good refractoriness. To study compatibility in castable refractories, the aggregates were used in high alumina cement based low cement castables and their thermomechanical behaviour was studied. Microstructural characterisation revealed that the emergence of new bond phases such as mullite and calcium hexa-aluminate had a beneficial effect on the hot modulus of rupture and creep resistance of castables. An attempt was made to establish a structure–property relationship.     

Themo-elasto-viscoplastic modelling of friction stir welding

Abstract

A coupled two-dimensional Eulerian thermo-elasto-viscoplastic model has been developed for modelling the friction stir welding process. First, a coupled thermo-viscoplastic analysis is performed to determine the temperature distribution in the full domain and the incompressible material flow around the spinning tool. Next, an elasto-viscoplastic analysis is performed outside the viscoplastic region to compute the residual stress. Both frictional heat and plastic deformation heat generation are considered in the model. Furthermore, this is the only known model computing residual stress accounting for plasticity caused by both thermal expansion and mechanical deformation due to material spinning. The computed residual stress is verified by comparing to experimentally measured data.     

Effect of microstructure on mechanical properties for A356 casting alloy

Abstract

A quantitative study of the relationship between microstructural features such as secondary dendrite arm spacing (DAS), eutectic structure and mechanical behaviours of A356 casting alloys has been conducted. In the condition of minimising casting defects, the influence of microstructural features on the mechanical performance becomes more pronounced. Depending on the cooling rate affecting the primary and eutectic microstructure, the tensile properties were changed upon experimental conditions, i.e. both of tensile strength and elongation were increased with decreasing DAS, also the results were the same at high temperatures. The increase in both of room temperature high cycle fatigue and high temperature low cycle fatigue lives with decreasing DAS was observed, mainly due to homogeneous deformation owing to the fine size of eutectic silicon and Fe intermetallic particles. The observation of fracture surfaces was conducted to find the effect of microstructure on mechanical properties by a scanning electron microscope.     

Long fatigue crack growth behaviour of ferritic steel weld metal

Abstract

Single edge notched weld joint specimens were tested at different stress levels to study the long fatigue crack growth behaviour of a ferritic steel (nuclear grade SA333 Grade 6 steel) weld metal at two stress ratios R of 0·1 and – 1. A two slope behaviour was noticed in the crack growth rate versus stress intensity factor range plots at both stress ratios. Different parameters were employed to generalise the load ratio effect on fatigue crack growth rate.     

Effect of microstructure on tensile and fatigue properties of cast Mg–10Gd–2Y–0·5Zr alloy

Abstract

The microstructure and its effect on tensile properties and fatigue properties of a Mg–10Gd–2Y–0·5Zr (wt-%) cast alloy have been studied. The microstructures of as-cast, solution treated and T6 treated specimens were examined by optical and scanning electron microscopy (SEM). Tensile properties and fatigue properties of the specimens were determined and fractography was carried out. The SEM examination showed that the precipitates after T6 treatment were mainly distributed at grain boundaries, which accounts for the intergranular brittle fracture observed. The average grain size of the specimens measured after solution treatment varied from 87 to 128 μm. The mechanical tests showed that the tensile strength and low cycle fatigue strength increase with decreasing average grain size, whereas high fatigue strength is less sensitive to grain size. The fractography indicated that ductile and brittle fracture patterns coexist.     

Influential microstructural changes on rolling contact fatigue crack initiation in pearlitic rail steels

Abstract

Rail life is controlled by the balance between wear and fatigue damage due to in service loading. To model and optimise rail life, knowledge of the fatigue crack initiation mechanism is required. This paper reports the effect of in service loading on microstructural changes in the subsurface layer of pearlitic rail steels and observations of early stage (10–50 μm length) fatigue crack formation. Micro and nanohardness measurements are reported, along with microstructural observations, showing differential work hardening in the proeutectoid ferrite and pearlite phases. It is proposed that the differential straining results in ductility exhaustion in the proeutectoid ferrite and therefore fatigue crack initiation and initial growth in the proeutectoid ferrite phase. Observations of short (<50 μm) cracks in rails taken out of service containing significant amounts of proeutectoid ferrite (≈20%) confirm the proposed mechanism.     

Effect of thermomechanical treatment on spray formed Cu – Ni – Si alloy

Abstract

The heat treatment response of a spray formed Cu – 2.4Ni – 0.6Si (wt-%) alloy has been investigated. The spray formed alloy was given various thermomechanical treatments prior to isothermal aging. These treatments included solutionising and/or cold rolling with different reductions in original thickness. The variation in hardness and electrical conductivity of the alloys was measured as a function of the aging time. The results indicated the highest peak hardness value of ~250 kg mm^-2 for the alloy aged after solution treatment and cold rolling to 40% reduction in thickness, compared with the maximum hardness of 220 kg mm^-2 for specimens aged directly in the as spray formed condition. However, the electrical conductivity after aging was observed to be a maximum of 65%IACS (International Annealed Copper Standard) in specimens cold rolled to 80% reduction in thickness before aging. The aging response was observed to accelerate with the degree of cold working. Optical, scanning electron and transmission electron microscopy were used for microstructural characterisation of the materials. Precipitation of the second phase was observed to dominate in deformation bands. The alloy showed evidence of discontinuous precipitation, particularly when the alloys were cold rolled before aging. The onset of discontinuous precipitation led to a drastic deterioration in hardness of the alloys. The precipitation behaviour of the alloy is discussed in the light of microstructural characteristics associated with various processing conditions of the alloy.     

基于有限元法的机械疲劳寿命预测方法的研究

介绍了一种采用疲劳有限元分析软件MSC．FATIGUE来对结构件进行疲劳寿命预测的方法。以一阶梯轴为研究对象,在指定的载荷工况下,用有限元法分析了轴上的应力分布情况,并估算危险点处的疲劳寿命。该方法对设计制造过程中机械零部件的疲劳强度分析具有一定的参考价值。