Numerical analysis of the influence of material mismatching in the transition curve of welded joints

In this paper finite element simulations of mismatched welded joints at different temperatures have been performed in order to analyse the influence of temperature on their fracture behaviour and to obtain their transition curves. Cleavage is described by means of the Beremin micromechanical model. The ductile failure model is based on the so-called complete Gurson model. Both fracture mechanisms have been implemented in FORTRAN and introduced in ABAQUS by two user subroutines. The weld configuration significantly affects the stress and strain fields and different transition curves are obtained for the different configurations. The highest transition curve is obtained for the narrowest overmatched weld, being its transition temperature the lowest.     

60Si2Mn弹簧钢连续冷却组织调控研究

该文基于Gleeble3800热模拟试验机,运用热压法研究60Si2Mn弹簧钢连续冷却过程中的冷速和温度转变曲线,依据曲线斜率变化获取相变点和临界冷却速率,进而绘制60Si2Mn弹簧钢连续冷却转变(continuous cooling transition,CCT)曲线。根据CCT曲线,选择合理的斯太尔摩工艺冷却控制参数,并通过实际生产验证工艺效果。结果表明,CCT曲线与组织演化规律具有很好的对应关系。当冷却速度介于1~10℃/s时,组织为铁素体和珠光体组织,并且随着冷却速率的增加,铁素体含量逐渐减少,珠光体含量有所增加。为实现表面脱碳和铁素体分布的良好控制,要将冷速控制5~8℃/s,所有规格弹簧钢试样表面脱碳控制在180μm以内,同时铁素体分布趋于均匀,为后续深加工创造有利条件。该文工作为60Si2Mn弹簧部件的组织控制、性能优化等方面提供科学依据与理论支撑,对提升60Si2Mn使用寿命具有工程应用价值。     

奥氏体不锈钢凝固相转变规律曲线(SPT曲线)建立

利用自行设计的高温凝固相转变测定实验装置,研究了304奥氏体不锈钢在不同冷却速度下的高温凝固相转变过程,得到了凝固过程中液相（ L）到高温铁素体（δ）到奥氏体（γ）的相变温度。在此基础上分析了304奥氏体不锈钢在不同冷却速度下的高温凝固相转变规律,从而建立了304奥氏体不锈钢的低冷速凝固相转变规律曲线—SPT（Solidification phase transforma?tion）曲线。结果表明：对试样进行液氮酒精淬火有效地保留了试样高温时各相的状态。可以清楚的显示在不同冷速下的不同温度淬火时液相和固相的各相成份比例及在不同淬火温度下各成份体积比例的变化。通过研究体积比例变化,可以得到304奥氏体不锈钢在不同冷速下的液相线、固相线及各种反应开始和结束的转变温度（即SPT曲线）。由SPT曲线也可以看出,随着冷却速度的增大,相转变模式会发生变化,相图会向左移动,各相变反应的温度区间减小。     

Computer modeling of the write process in perpendicular recording

A self-consistent computer simulation model utilizing a ring head and single layer recording medium has been developed to study perpendicular recording. In the model it is assumed that the medium switches uniformly following the volume averaged field. The optimum recording field obtained from the model calculation at various head-medium spacings permits an estimation of head saturation limitations. The roll-off curve, which is the linear superposition of the alternating voltage pulses, is in good agreement with experimental data. The write spacing loss is spacing dependent and is 120d/λ (dB) at contact for a typical recording case. For contact recording the imaging effect is important in the write process. Optimum recording at contact is shown to produce a high overshoot and sharp leading edge in the transition while leaving the magnetization level below the coercivity; this yields an apparent "negative" transition length in terms of the arctangent transition model.     

具有双峰反应特性的高韧性双马来酰亚胺树脂固化动力学和TTT图

以全动态DSC扫描实验为基础,结合半经验的唯象模型获得了基于唯象模型的具有双峰反应特性的高韧性双马来酰亚胺5429树脂的固化动力学参数,建立相应的唯象动力学模型。以5429树脂在180℃条件下,恒温不同时间的DSC实验数据为基础,利用DiBenedetto方程研究等温条件下固化度与加热时间的关系并得到玻璃化转变温度与固化时间的关系表达式,并采用凝胶盘法得到5429树脂不同温度下的凝胶时间,建立了凝胶时的固化度和玻璃化转变温度之间的函数关系,在此基础上绘制了TTT图,从TTT图中得到的5429树脂的最优固化工艺曲线与其标准固化工艺曲线一致。     

Conformation transition of Bombyx mori silk protein monitored by time-dependent fourier transform infrared (FT-IR) spectroscopy: effect of organic solvent

The conformation transition from random coil and/or helix to β-sheet of silk protein is the most important step in the formation of silk fiber in nature as well as by artificial spinning. Time-dependent Fourier transform infrared (FT-IR) spectroscopy was used in this research to monitor such a conformation transition process induced by the organic solvents methanol, ethanol, propanol, isopropanol, and acetone. The kinetics of β-sheet formation of regenerated Bombyx mori silk fibroin in these organic solvents was obtained by the Δabsorbance-time curve from the time-dependent difference infrared spectra. The results showed that the conformation transition rate of silk fibroin was methanol > ethanol > acetone > propanol > isopropanol, which is in accordance with the polarity of these organic solvents. In connection with the mechanical properties and morphologies of regenerated silk fibers using these organic solvents as coagulation bath reported in the literature, we may conclude that the conformation transition rate of silk protein in the organic solvent is very important in wet-spinning to produce high-performance regenerated silk fibers.     

Discussion on bearing capacity of soft rock ground based on in situ load test

This paper explores five methods of bearing capacity of soft rock foundation based on in-situ load test, namely, point of contraflexure method, relative settlement method, rebound method based on elastoplasticity theory, hyperbola fitted method and minimum curvature radius method. The suitability of various methods was discussed on the basis of the typical results from in-situ load test of Renshou mansion and Caifu plaza in YueYang. It shows that the bearing capacity can be obtained by the proportion load and limit load from p-s curve with first and second point of contraflexure easily. The accurate value of bearing capacity could be obtained by hyperbola fitted method and minimum curvature radius method theoretically, so it is recommended. The rebound method is clear in principle, in which the elastoplasticity characteristic was thought about, and it is recommended, too. Out of consideration for the unsteadiness and unobviousness of bearing capacity from relative settlement method, it can be only adopted as reference. So bearing capacity of soft rock foundation should be decided by weathering condition of soft rock and curve type.     

GIS环境下缓和曲线绘制方法研究

缓和曲线是构成交通线路中线平面线形的基本要素之一。从分析缓和曲线几何特征和数学模型出发,根据计算机图形学中曲线离散化表达的基本原理,用折线拟合的方法实现了GIS环境下缓和曲线对象的准确绘制。基于数值积分的复化梯形公式,推导出了缓和曲线拟合折线分段数计算的严密数学公式。进一步给出了缓和曲线上任意点坐标与里程间的转换方法,使研究成果更具实用性。该方法在SuperMap GIS平台上实现,其绘图精度和效率能满足应用需求。     

Analysis of the temperature dependence of the fracture stress of sharp notched bending specimens of a structural steel with respect to intermediate transitions

The flow and fracture stresses, σ_y^g and σ_f^g (δ = crack tip displacement), of sharply notched bending specimens of a structural steel U St 37-1 are measured in the temperature range from full scale to small scale yielding. The best adaption of the experimental results for σ_f^g is obtained by a curve which exhibits an intermediate transition, i.e. which follows in a temperature range between an upper, T_tM¹ and a lower, T_tl¹, transition temperature to the curve σ_y^g(T) for the flow stress with a constant δ = δ₁. This transition corresponds to that of the slip to the twin nucleated fracture. Two analyses [3,5] according to the local fracture stress, σ_f^*, concept show that the amount and the temperature dependence of σ_f^* are somewhat different for both methods, but that both exhibit an increase of σ_f^* in the transition range. It is concluded that each transition in the nucleation mode of the fracture is connected with such a transition in the fracture stress. It may, however, become indistinct or even be covered by the scatter of the experimental points.     

The mechanism of creep behaviour in glassy polymers

A model is presented to describe the creep behaviour of glassy polymers below the glass transition temperature. It consists of a Hookean spring in series with a non-Newtonian dashpot having an entropy spring in parallel. The shape of the response of this spring is deduced from a master curve, giving the extension as a function of logarithm of time, built from creep data, reported here and obtained on polycarbonate over a wide range of times and temperatures. The model takes into account a number of aspects of creep behaviour and predicts a threshold stress beneath which delayed yielding no longer occurs. Torsional creep data, obtained on Polyvinylchloride by Mallon and Benham are found to be in excellent agreement with the proposed model.     

Kinetics of two-stage crystallization in Metglas 2826A

Crystallization kinetics of MSI and MSII stages in Metglas 2826A has been investigated by quantitative transmission electron microscopy. The volume fraction of crystallization against time curve has been found to show a plateau in the lower temperature region of annealing. It has been found that the glass transition temperature, T _g, has no effect on the sequence reversal of the crystallization reaction. It has been shown that the sequence reversal of transformation stages occurs due to the large difference in the activation energy of crystallization of MSI and MSII. In addition, the change in the morphology of the crystals obtained by annealing the amorphous alloy below and above the glass transition temperature, T _g, is reported.     

汽车半轴中频感应淬火的质量实时控制

利用RAYTEK红外测温仪测量了汽车半轴中频感应淬火时不同电参数情况下的表面温升曲线.并对有效硬化层深、过渡区层深、表面硬度变化以及金相组织进行了研究.得到了性能随电参数变化的规律.把所有金相以及硬度和层深分布都合格的样品与淬火时实时测量的表面温升曲线相对应,得到了质量合格区.从而实现了用测温仪在线实时控制,当温升曲线进入合格区时即可停止加热并立即淬火.     

Unstable cracking of medium density polyethylene

The ductile instability characterization of medium density polyethylene (MDPE) has been studied with theJ integralR curve method. The loading of variously notched samples in three-point bending using a compliant test fixture showed that sudden unstable cracking occurred after the commencement of stable ductile cracking. The tearing modulus which is obtained from theR curve can describe the transition from stable to unstable crack. Instability occurs when an applied situation depending on loading system and/or sample geometry exceeds the tearing modulus of MDPE.     

Calculation of Phase Equilibria between Solid Solutions with Magnetic Transition by the Cluster Variation Method

By using the geometric analysis of grand potential, the molar grand potential-effective chemical potential curve of solution with magnetic transition can be obtained from the relevant molar free energy diagram, and it is shown that the grand potential and effective chemical potential can be separated into paramagnetic and magnetic terms. In addition. the CVM has been combined with the present magnetic transition free energy model such as M .Hillert and T.Nishizawa's models to calculate phase equilibria between solutions with magnetic transition, and this combined method has been applied to the α/γ phase equilibrium in the Fe-Mn binary system and found to be feasible.     

分段线性减振系统的防跳跃及减振性能

为分析一类单自由度分段线性减振系统性能。先用平均法求得系统在主共振激励下的幅频响应方程,并基于约束分岔理论计算转迁集。再定性地分析转迁集各区域系统的幅频响应类型,得到避免跳跃的参数临界条件。数值计算验证了理论分析的可靠性。此外还讨论了阻尼比和激励幅值在非跳跃参数区域变化时,对系统力传递率及系统幅频响应峰值点力传递率的影响。研究结果证明较小激励情况下,阻尼比越大,减振系统的抗振动性能越好。     

Comparison of the static and dynamic fracture behaviour of an AE-460 structural steel

The ductile-to-brittle transition curves of a structural steel under low strain rate (static conditions) and impact (dynamic conditions) are compared in this work, and the influence of the geometry of the initial defect that promotes fracture (notch or crack) is evaluated. The toughness of the precracked specimens was characterised by the J-integral parameters obtained at the initiation of the stable crack growth, J_c, and when the unstable fracture takes place, J_u. The different methods used in dynamic tests in order to calculate the dynamic J-integral parameter, J_d, were evaluated. The use of cracked specimens, instead of notched ones, modifies the transition curve to higher temperatures and, finally, the transition temperature shift between static and dynamic test results is also quantified     

Transition to Turbulence in Pipe Flow

We review the results of recent experimental investigations into transition to turbulence in fluid flow through a circular straight pipe, at room temperature. The stability of Hagen–Poiseuille flow was investigated using impulsive perturbations by either injecting or sucking small amounts of fluid through holes in the wall of the pipe. The evolution of the induced patches of disturbed flow were observed using flow visualization and laser Doppler velocimetry. The principle result obtained was a finite amplitude stability curve where the critical amplitude of the disturbance required to cause transition is found to be inversely proportional to the Reynolds number. Estimates for the lower threshold value of Reynolds number which is required to sustain turbulence were also measured.     

添加AP的乳化炸药基质的热分解研究

利用C80微热量热仪研究了分析纯硝酸铵、典型配方的乳化炸药基质以及含有高氯酸铵(AP)的乳化炸药基质的热分解过程。通过C80热流曲线所得出的结果,采用单一非等温曲线法,求出了相应的动力学参数。结果表明:AP不但可以消弱AN晶变的热效应,而且具有稳定AN晶型的作用;AP对乳化炸药基质的热分解具有一定的催化作用,但催化作用不显著。     

添加AP的乳化炸药基质的热分解研究

利用C80微热量热仪研究了分析纯硝酸铵、典型配方的乳化炸药基质以及含有高氯酸铵(AP)的乳化炸药基质的热分解过程。通过C80热流曲线所得出的结果,采用单一非等温曲线法,求出了相应的动力学参数。结果表明:AP不但可以消弱AN晶变的热效应,而且具有稳定AN晶型的作用;AP对乳化炸药基质的热分解具有一定的催化作用,但催化作用不显著。     

Investigation of forced flow boiling of nitrogen in a long vertical tube

The results of experimental investigations of nitrogen boiling in a vertical tube 1850 mm long id 10 mm, are presented. It has been established that compared with pool boiling, heat flux and pressure effects are somewhat less pronounced and the boiling curve hysteresis phenomenon is missing. The transition from the subcooled boiling region to saturated boiling is shown not to be accompanied by a change of heat transfer intensity. Experimental data obtained over the entire range of parameters (p = 1.8–7.0 bar, G = 170–750 kg m^?2 s^?1, q = 10 200-42 720 W m^?2) are correlated by an equation.