PALSAR可检测的最大/最小地表形变梯度的统一函数模型（英文）

基于相干性和离散视数,建立PALSAR干涉可检测的最大和最小形变梯度的经验函数模型。在此基础上,采用最小二乘回归的方法拟合模型系数,建立关于相干性和视数两个参数的统一函数模型。利用汶川地区的PALSAR数据进行实验,结果表明该模型能够准确判别地表变形能否被D-InSAR技术检测到。研究结果可以帮助研究人员准确选择PALSAR数据和合理配置其干涉处理参数,对解释地表形变结果也具有重要的价值。     

焊接残余形变在工件精密装配中的仿真应用研究

基于非线性软件ABAQUS建立了某成分马氏体耐热不锈钢合金材料的喷嘴零件装配结构的焊接有限元模型,采用双椭球热源模型模拟了3种不同焊接工艺参数下其环缝处的焊接过程并进行了比较分析,得到了焊接温度场和接触应力、焊接残余应力、残余形变及焊接应变能分布规律。研究表明:不同脉冲和电流的工艺参数下所产生的拉伸残余应力最大达285 MPa,最小达225 MPa,相差60 MPa;压缩残余应力最大达95MPa,最小达75 MPa,相差20 MPa;最大压缩形变相差0.012 mm,最小稳定压缩残余形变相差0.004 mm。焊接残余应变能均匀变化在0.013~0.016之间,同时获得焊接残余形变量与配合公差之间的量化关系,为工件修复和循环使用提供焊接装配工艺理论和参数数据支撑。     

基于InSAR时序形变的矿区全盆地沉降时空演化规律分析

利用10景ALOS PALSAR影像获取山西云冈某矿区在2007年7月1日至2009年1月3日的地表时序沉降值,并使用Logistic模型拟合该矿区全盆地时序沉降。结果表明:通过交叉验证Logistic模型估计参数预测的时序沉降与InSAR监测值后发现,两者吻合较好,且其平均均值和均方根误差分别为-0.4和2.5 cm,表明在整个下沉盆地内,各点的动态沉降均符合"S"型增长,且Logistic模型能较好地描述该过程。统计该矿区全盆地Logistic模型形状参数a和b后,发现参数a和b分别服从Weibull分布和随机分布,且其数值变化较大,表明利用少量离散地表监测数据拟合的Logistic模型参数预测的全盆地动态沉降结果可靠性不高。最后,利用全盆地Logistic模型估计参数预测了该矿区2009年2月18日的地表沉降值,该值与InSAR监测结果吻合较好,均方根误差为2.15cm。     

基于PSO-SVM模型的油气管道内腐蚀速率预测

目的针对油气管道的运行安全问题,建立油气管道内腐蚀速率预测新模型,对管道的内腐蚀状况进行准确预测。方法首先对内腐蚀的原理进行简单分析,探讨引起管道内腐蚀的主要原因。对PSO(粒子群算法)、SVM(支持向量机)以及PSO-SVM模型的原理及结构进行探讨,结合文献中获取的管道内腐蚀数据,使用PSO算法对SVM算法的参数C和g进行寻优。在此基础上,对Sine函数、Sigmoidal函数和Radial basis函数三种核函数进行对比优选。最终将PSO-SVM模型与GA-SVM模型、CV-SVM模型、LS-SVM模型和FOA-SVM模型四种模型进行预测误差对比,以此证明PSO-SVM模型的先进性。结果当SVM算法的参数C=83.9243、g=0.6972,核函数选择Sine函数时,PSO-SVM模型的平均绝对误差和均方根误差最小,平均绝对误差和均方根误差分别为0.58%和0.000618,但是该模型在使用的过程中,其训练数据所使用的时间为11.26 s,与GA-SVM模型、CV-SVM模型、LS-SVM模型和FOA-SVM模型四种模型相比,其预测误差较小,但训练数据所使用的时间较长。结论利用PSO-SVM模型对油气管道内腐蚀速率进行预测是可行的,预测误差相对较小,但是由于受限于数据训练速度问题,今后仍需要对该领域进行深入研究。     

自动液力变速器高速开关阀动态仿真与优化

高速开关电磁阀的响应时间对自动液力变速器性能的影响很大,为了减小开关阀的响应时间,运用AMESim软件建立了动态性能仿真模型,提出基于ITAE准则创建目标函数,采用遗传算法寻优,对阀的线圈匝数、工作行程等参数进行优化,并分析了优化结果。研究结果表明:动态性能模型的仿真结果与性能检测试验数据相对比,响应误差为3.3%,仿真模型能够比较准确地描述开关阀的动态性能;经参数优化,高速开关阀的响应时间缩短了38.16%,满足了快速响应性能的要求。该研究为进一步提高自动液力变速器的性能提供了理论参考。     

基于Matlab和AMESim的M8阀组的建模与仿真

以力士乐的M8阀为研究对象,对其进行测量,获得相关几何参数。推导了M8阀的半圆形、U形节流槽的最小过流面积,并利用Matlab对其相应函数表达式进行了编程。将M8阀P-A口的节流槽几何参数代入Matlab编辑的函数表达式得到了半圆形、U形节流槽的过流面积与阀芯位移的特性曲线。分析了M8阀的工作原理并根据其原理建立AMESim HCD模型,以三联M8阀分别控制挖掘机的动臂、斗杆及铲斗油缸建立挖掘机工作装置的AMESim HCD仿真模型,以某企业大型挖掘机的相关参数对仿真模型进行参数设置。通过仿真得到模型工作装置中相关液压元件的压力、流量相关参数,给出了动臂联的压力、流量等相关参数曲线。最后用实测数据和仿真结果进行了对比,结果证明该方法是可行的。     

基于Mel的仿真模型干涉检测方法研究

虚拟环境下完成生产线设备模型建立并进行布局仿真,改善现有图纸化设计方法直观效果差、验证困难等缺陷,可以有效提高生产线的设计质量。针对生产线设备位置关系复杂,虚拟环境下布局仿真时模型实体缺少有效干涉检测方法的问题,采用对象分解的干涉检测算法,研究了基于Mel Script在Maya仿真环境中进行模型实体干涉检测的方法。仿真结果表明,该检测方法可以准确检测出实体间的干涉现象,对生产线虚拟仿真过程有重要的参考价值。     

基于动态惯性权重粒子群算法的磨削低能耗加工方法

利用三层误差反向传播(back propagation, BP)神经网络建立磨削能耗预测模型,以砂轮线速度、进给速度和磨削深度为影响因素设计125组全因子试验,并取其中的75组试验数据作为该预测模型的训练样本与测试样本。采用动态惯性权重改进粒子群算法(adaption particle swarm optimization, APSO),以BP神经网络的预测作为适应度函数,以最小能耗为目标进行迭代寻优获取最优工艺参数。结果表明:模型预测结果较为准确,采用优化后的工艺参数能够有效降低磨削能耗。      

五轴数控机床旋转轴误差辨识及补偿

五轴数控机床刀具与工件接触点(切削点)相对位置不变的旋转运动控制称为RTCP(Rotated Tool Centre Point),该功能对五轴数控机床曲面加工精度具有重要影响。为了提高五轴数控机床RTCP精度,分析了五轴数控机床RTCP运动过程中旋转轴结构参数误差与刀尖点误差关系,建立了刀尖点误差与旋转轴结构参数误差映射模型,根据刀尖点误差数据建立了旋转轴结构误差辨识方程组,通过矩阵最小二乘实现五轴数控机床旋转轴结构参数误差求解,用于五轴数控机床旋转轴结构参数误差补偿。结果表明:该误差辨识模型可准确计算出旋转轴结构参数误差,提高了旋转轴几何误差检测效率和精度,对提升数五轴控机床加工精度具有重要的意义。     

伺服阀控液压马达系统的参数模型辨识

在对液压控制系统进行建模过程中,由于液压伺服系统普遍存在非线性,使用传统的机理建模方法就难以建立准确的数学模型,也就不能准确地反应系统实际情况.而过程的输入输出数据一般都是可以测量的,且过程的动态特性必然表现在实验结果数据之中,因此可通过系统辨识的方法,利用这些数据建立对象的数学模型.本文作者确定出模型的结构,然后利用最小二乘法辨识出了阀控马达系统参数模型,仿真证明此模型是比较精确的.     

Flow Stress Prediction of SiCp/Al Composites at Varying Strain Rates and Elevated Temperatures

With isothermal compression tests in the Gleeble-3500 system, the hot deformation behaviors of SiCp/Al composite were studied at a wide range of temperatures from 623 K to 773 K, and strain rates ranging from 0.001 s^?1 to 10 s^?1. Four different modeling methods such as the modified Zerilli-Armstrong model, the strain compensation Arrhenius-type model, the double multivariate nonlinear regression (DMNR) and the artificial neural model (ANN) were used to predict the flow stress. The suitability levels of these models were evaluated by contrasting both the correlation coefficient R _C and the average absolute relative error. The results show that the predictions of these four models can adequately meet the accuracy requirement according to the experimental data of this composite. With the increasing of the numbers of determined material constants and the complexity of computing methods, the predictability of these four methods is enhanced. The deformation parameters in the selected ranges such as strain rate and temperature have non-ignorable effect on predicted results of the previous two methods, while they have slight influence on DMNR and ANN.     

Fracture in strain gradient elasticity

Recent experiments have shown that the microscale material behavior is very different from that of bulk materials, and displays strong size effects when the characteristic length associated with the deformation is on the order of microns. Conventional continuum theories, however, can not predict this size dependence because they do not have an intrinsic length in their constitutive models. A new continuum theory, namely the strain gradient theory, has been proposed to investigate the deformation of solids at the microscale. For materials undergoing plastic deformation, the basis of strain gradient theory is the dislocation theory in materials science, and strain gradient plasticity has agreed remarkably well with experiments. For elastic materials with microstructures, it has also been established that the material behavior can be represented by an elastic strain gradient theory. A general approach to investigate fracture of materials with strain gradient effects is established. Both the near-tip asymptotic fields and the elastic full-field solutions are obtained in closed form. Due to stain gradient effects, stresses ahead of a crack tip are significantly higher than those in the classical K field. The plastic zone size surronunding a crack tip is estimated by elastic near-tip fields, as well as by the Dugdale model. It is established that the plastic zone is, in general, much more round and larger than that estimated from the classical K field.     

物理基本构模型和BP人工神经网络模型预测AZ80镁合金高温流动应力的比较研究

基于变形温度250~400 ℃和应变速率0.001~1 s^-1条件下的铸态AZ80镁合金的热压缩试验数据,建立了基于应力位错关系和动态再结晶动力学的物理基本构模型以及前馈反向传播算法的人工神经网络（ANN）模型来预测AZ80镁合金的热变形行为。采用相关系数（R）、平均绝对相对误差（AARE）、相对误差（RE）3种统计学指标来验证2种模型的预测精度。结果表明,2种模型均可以准确预测AZ80镁合金的热变形行为。其中,ANN模型预测的应力值与实验数据更为吻合,其R和AARE分别为0.9991和2.02%,而物理基本构模型预测的R和AARE分别为0.9936和4.52%。ANN模型较好的预测能力归功于它擅长处理复杂的非线性关系,而物理基本构模型的预测能力是基于模型具有一定的物理意义,模型参数的确定充分考虑了热变形过程中的加工硬化（WH）、动态回复（DRV）和动态再结晶（DRX）的热动力学机制。最后,对这2种本构模型的优缺点及适用范围进行了比较讨论。     

Finite Element Modeling of Roller Burnishing Process

Hard roller burnishing is a cost effective surface enhancement process where a ceramic ball rolls on the machined surface under a high pressure and flattens the roughness peaks. It not only improves surface finish but also imposes favorable compressive residual stresses and raises hardness in functional surfaces, which can lead to long fatigue life. Most research in the past focused on experimental studies. There is still a special need for a reliable finite element (FEM) model that provides a fundamental understanding of the process mechanics. In this study, 2D and 3D FEM models for hard roller burnishing were established. The simulation results (i.e. surface deformation and residual stress) were evaluated and compared between initial hard turned and burnished surfaces. The predicted residual stress was validated with the experimental data obtained from the literature.     

Cr9Mo钢热压缩试验结果的标定及验证

在Gleeble 1500D热模拟机上进行了Cr 9Mo钢的热压缩试验。通过对变形前后试样轮廓尺寸的定量分析发现,仅考虑摩擦的影响来进行试验结果的标定是不充分的,标定结果存在较大误差,因为试样上温度梯度的影响不可忽略。使用平均摩擦系数和试验中监测的温度梯度参数,通过有限元软件模拟不同变形条件下的热压缩过程,进而使用迭代法标定了试验结果。对物理试验和有限元数值模拟的结果比较证明,在进行热压缩试验数据标定时,同时考虑摩擦和温度梯度两个因素,可取得较高精度的结果。     

大型小曲率部件自动制孔设备柔性导轨设计

针对飞机装配制造中大型小曲率部件自动制孔设备中柔性导轨自身的特性开展导轨的优化设计方法的研究.该方法通过对柔性导轨特性的分析,提出以导轨极限弯曲半径为目标、弹性和局部刚性为约束、导轨结构参数为设计变量的设计优化模型.基于子问题近似算法和共轭梯度算法,运用Ansys软件的APDL语言编程实现柔性导轨的优化设计.对优化结果进行仿真验证,仿真结果与优化结果相吻合,证明该优化设计方法对指导柔性导轨的开发具有工程参考价值.     

Deformation mechanism maps of magnesium lithium alloy and their experimental application

Deformation mechanism maps for binary Mg-(8-9) Li(mass fraction,%) alloy at 423-623K were constructed in order to elucidate the internal meaning of mechanical experimental data at elevated temperatures,The models and data source used for constructing maps and constructe results are presented.It is determined through comparison of mechanical experimental data with constructed deformation mechanism maps that the dominant deformation mechanism for such alloy at 423-623K is lattice diffusion controlled grain boundary sliding.The difference of such deformation mechanism maps from former ones in that dislocation quantity inside the grains participates in the model calculation,which reveals the dislocation features of different deformation mechanisms.     

Material Constitutive Models for Creep and Rupture of SiC/SiC Ceramic-Matrix Composites (CMCs) Under Multiaxial Loading

Material constitutive models for creep deformation and creep rupture of the SiC/SiC ceramic-matrix composites (CMCs) under general three-dimensional stress states have been developed and parameterized using one set of available experimental data for the effect of stress magnitude and temperature on the time-dependent creep deformation and rupture. To validate the models developed, another set of available experimental data was utilized for each model. The models were subsequently implemented in a user-material subroutine and coupled with a commercial finite element package in order to enable computational analysis of the performance and durability of CMC components used in high-temperature high-stress applications, such as those encountered in gas-turbine engines. In the last portion of the work, the problem of creep-controlled contact of a gas-turbine engine blade with the shroud is investigated computationally. It is assumed that the blade is made of the SiC/SiC CMC, and that the creep behavior of this material can be accounted for using the material constitutive models developed in the present work. The results clearly show that the blade-tip/shroud clearance decreases and ultimately becomes zero (the condition which must be avoided) as a function of time. In addition, the analysis revealed that if the blade is trimmed at its tip to enable additional creep deformation before blade-tip/shroud contact, creep-rupture conditions can develop in the region of the blade adjacent to its attachment to the high-rotational-speed hub.     

Analytical modelling of functionally graded NiTi shape memory alloy plates under tensile loading and recovery of deformation upon heating

This paper presents an analytical model describing the deformation behaviour of functionally graded NiTi plates under tensile loading and their shape recovery during heating. The property gradient of the plate is achieved by either a compositional gradient or microstructural gradient through the thickness. Closed-form solutions are obtained for nominal stress–strain variations of such plates under uniaxial loading at different deformation stages. It is observed that the martensitic transformation occurs partially over the nominal stress gradient, unlike typical NiTi shape memory alloys. The curvature–temperature relations are established for complex shape memory effect behaviour of such plates during the recovery period. The analytical solutions are validated with relevant experimental results.     

Microstructure-based multiscale modeling of elevated temperature deformation in aluminum alloys

A multiscale model for predicting elevated temperature deformation in Al–Mg alloys is presented. Constitutive models are generated from a theoretical methodology and used to investigate the effects of grain size on formability. Flow data are computed with a polycrystalline, microstructure-based model which accounts for grain boundary sliding, stress-induced diffusion, and dislocation creep. Favorable agreement is found between the computed flow data and elevated temperature tensile measurements. A creep constitutive model is then fit to the computed flow data and used in finite-element simulations of two simple gas pressure forming processes, where favorable results are observed. These results are fully consistent with gas pressure forming experiments, and suggest a greater role for constitutive models, derived largely from theoretical methodologies, in the design of Al alloys with enhanced elevated temperature formability. The methodology detailed herein provides a framework for incorporation of results from atomistic-scale models of dislocation creep and diffusion.