Applied Problems in the Mechanics of Strain Hardening of Structural Metallic Materials

Some applied problems of the mechanics of strain-hardening processes in metallic materials are considered. To solve these problems, the concept of loading surface, which separates the elastic and elastoplastic domains in the stress space, is used. Strain-hardening models are analyzed. For a wide range of steels and alloys, the most commonly used hypothesis of isotropic-and-kinematic hardening is experimentally justified __________ Translated from Prikladnaya Mekhanika, Vol. 41, No. 10, pp. 12–51, October 2005.     

准脆性材料黏聚阻裂的计算与实验

工程常用材料铸铁混凝土等,在裂缝前端区域有微观及宏观缺陷的变化及能量耗散,表现为准脆性损伤断裂特点.若把该阻止裂缝扩展与张开的损伤发展区简化成虚拟裂纹,将存在裂纹黏聚分布力与变形或张开位移;讨论了与此相关的黏聚裂纹力学模型及方程解答说明.相应于黏聚张开位移有微细观测图与实验测试数据,给出黏聚裂纹模型的解析计算方法,并将理论计算与实验测试数据进行了对比.以双K断裂准则和黏聚模型为基础,给出对含裂纹结构的承载力的预估计算.理论计算比较符合实验结果.     

蜂窝夹层复合材料老化强度与疲劳性能的试验研究

本文对蜂窝夹层复合材料老化强度和疲劳试验进行了研究。通过对该材料在老化前后的拉伸、压缩、面内剪切机械性能测试,以及在不同应力水平下的疲劳试验,分析试验结果,得出了标准老化环境对试件的拉伸、压缩承载能力影响不大,而蜂窝夹芯的排列方向对面内剪切试件的强度和疲劳寿命将产生一定的影响等一些对实际工程应用的问题有参考价值的结论和看法。本文还就蜂窝夹层复合材料老化强度和疲劳试验中的一些试验方法、试件的破坏形式、试验件的胶接方法进行了探讨。     

利用结构基因法研究非线性周期性板结构的等效力学性能

非线性周期性板结构是一类在智能复合材料领域具有巨大应用潜力的结构,因其构成材料的非线性特性,以及结构中经常包含增强纤维、肋板和空洞等复杂微结构导致的材料几何非线性,利用常规的有限元方法进行建模和分析较为困难.本文提出了一种结构基因法,通过提取非线性周期性板结构的最小模型单元作为其结构基因,将异质周期性板结构等效为均质板结构,便捷地求解了非线性周期性板结构的微观力学性能和整体等效力学性能.算例表明,结构基因方法可用来分析复杂非线性复合材料结构问题,计算结果精度足够,为复合材料微观力学研究提供了有价值的参考.     

炸药参数对高锰钢爆炸硬化性能的影响

为了研究炸药参数对高锰钢爆炸硬化效果的影响,对两种不同密度的炸药进行爆速测试,并利用该炸药分别对高锰钢试样进行爆炸硬化实验,测试了从硬化表面向材料内部的硬度、抗拉强度和冲击韧性随深度的变化。测试结果表明:高锰钢试样在相同深度下,经过密度1.38 g/cm3炸药3次爆炸硬化得到的硬度大于密度1.48 g/cm3炸药2次爆炸硬化后的硬度,而冲击韧性小于密度1.48 g/cm3炸药作用后的冲击韧性;从爆炸硬化表面向下15 mm内,经过密度1.38 g/cm3炸药3次爆炸硬化得到的抗拉强度大于密度1.48 g/cm3炸药2次爆炸硬化后的抗拉强度,但深度大于15 mm时,经过密度1.38 g/cm3炸药3次爆炸硬化得到的抗拉强度小于密度1.48 g/cm3炸药2次爆炸硬化后的抗拉强度。从硬化后试件的硬度、抗拉强度以及冲击韧性这3方面考虑,使用单次爆炸冲量较小的炸药进行多次爆炸硬化效果较好。     

结构非线性振动及其控制系统的等效力学模型研究

研究了结构非线性振动及其控制系统的等效力学模型建立问题,对结构进行等效线性化处理;对状态变量的观测,仅测量结构的前几个位移。将随机激励和观测噪声等维化处理后,导出了结构非线性振动及其控制系统的等效力学模型。通过等效力学模型的应用研究,得出了多高层结构在风与地震作用下的多维与一维等效力学模型、等效振型力学模型及其线性力学模型,给出了等效力学模型在多高层结构自适应抗风抗震控制中的应用。     

基于裂纹附加模态Timoshenko梁的裂纹损伤识别

将梁中横向裂纹等效为无质量扭转弹簧，并忽略其对梁剪切变形的影响，得到的具有任意裂纹数目Timoshenko 梁自振模态的统一显示解析表达式．将裂纹梁的自振模态分为基本模态和裂纹附加模态，利用最小二乘拟合，建立了利用裂纹附加模态函数的梁裂纹损伤识别方法．通过数值模拟开展了简支单裂纹梁以及悬臂和固支双裂纹梁等的裂纹损伤识别，考察了测量误差对损伤识别的影响，数值结果表明本文所提出的裂纹损伤识别方法对裂纹位置的识别精度高于对裂纹损伤程度的识别精度；随着测量误差的增加，裂纹位置及裂纹损伤程度的识别误差增加，但仍在可接受的范围内，故该裂纹损伤识别方法在实际工程中具有一定的应用价值．     

Influence of the Asymmetry of Static Loads on the Vibration Characteristics of Planetary Gearings

A model of planetary double-reduction gearing is used to study how the asymmetry of dynamical loads affects its vibration characteristics. Design methods for reducing the asymmetry of static loads are shown to be efficient     

Effect of Processes at the Compression Pulse Front on Spalling Strength of a Material and Resistance to High-Velocity Penetration

Tests on backward spalling of 38KhN3MFA structural steel, D-16 aluminum alloy, M-2 copper, 02Kh18K9M5-VI maraging steel, KhN75VMYu alloy, beryllium, and other materials show that spalling strength correlates with the threshold of structural instability of a material to compression at the leading edge of the compression pulse. It is shown that the threshold of structural instability to compression obtained in experiments on uniaxial deformation of flat targets determines the strength of resistance to high-velocity penetration in the Alekseevskii–Tate model.     

A combined isotropic-kinematic hardening model for the simulation of warm forming and subsequent loading at room temperature

A coupled isotropic-kinematic hardening material model was developed based on phenomenological observations of performed two stage experiments on a medium carbon steel – SAE 1144, where the first deformation is performed at elevated temperatures and the second deformation at room temperature. Above all, deformations with orthogonal loading at various temperatures were investigated in order to determine the influence of the loading direction as well as of the temperature. Bergström’s theory of work hardening as well as the nonlinear kinematic hardening of an Armstrong–Frederick type were used as a basis for the model development. In the proposed model a relationship between material coefficients of the classical Bergström model and temperature was investigated. The aim of the new material model was to introduce the least possible amount of new parameters as well as to facilitate the mathematical determination of parameters during the fitting of the model with experimental data. The developed model was implemented in an in-house FE-Code in order to simulate the material behavior due to the dynamic strain aging and the hardening behavior after the dynamic strain aging process. Representative simulation results were compared with the experimental data in order to validate the efficiency and the application range of the model.     

基于可变形蜂窝的柔性蒙皮力学性能分析与结构设计

变体飞机可以在飞行中充分改变外形获得最佳气动效率以适应变化的任务环境.覆盖在结构表面的蒙皮不仅要具有良好的面内方向柔性,产生满足设计变形量的光滑连续变形,同时要提供足够的垂直平面方向刚度,维持气动构型,并将气动载荷传递到下层结构.论文提出一种在十字形可变形蜂窝表面覆盖硅胶表层的结构作为柔性蒙皮,理论分析了该柔性蒙皮在面内方向的变形机理以及十字形可变形蜂窝的形状参数对其力学性能的影响,并与仿真和试验结果进行了比较.根据后缘变弯度机翼的设计要求,给出了柔性蒙皮的设计参数范围.结果表明该柔性蒙皮具有足够的面内方向变形能力和垂直平面方向承载能力,满足变弯度机翼后缘设计要求.     

On A. D. Kovalenko's Research Works on the Thermomechanics of Coupled Fields in Materials and Structural Members and Its Further Development

A brief review is given to the research works of Academician A. D. Kovalenko that laid the foundations of the thermomechanics of coupled fields in inelastic materials and structural members under monoharmonic loading. The developments of Kovalenko's ideas by the associates of the Thermoelasticity Department founded by him are pointed out __________ Translated from Prikladnaya Mekhanika, Vol. 41, No. 9, pp. 16–25, September 2005.     

水分及冻融循环对红砂岩物理力学特性的影响

将干燥红砂岩进行饱水及开放系统下的冻融循环实验,并对干燥、饱水及经历一定冻融次数后的试样进行单轴压缩实验,系统地研究了红砂岩的遇水软化性及冻融损伤劣化特性,分析了岩石的弹性模量、强度、应力-应变关系的变化规律。结果表明：在水分的作用下,红砂岩的弹性模量及强度显著降低,且强度受水分影响引起的损伤较弹性模量大;水分及软弱结构面的存在促进了岩石的冻融损伤劣化,并伴随着岩石延脆性性质的改变,最终在冻融循环的作用下完全崩解;在寒区岩体工程设计和施工过程中,必须考虑水分和温度对工程稳定性的影响,采取加强防排水及隔热保温技术等综合防治措施减少冻融灾害。     

化学腐蚀对混凝土材料力学特性影响的试验研究

对不同水化学环境腐蚀过程中砂浆试样物理力学性质进行了试验研究,分析了溶液pH值、浓度及水化学成分对砂浆的腐蚀程度,探讨了砂浆试样的化学腐蚀机制。试验结果表明:在相对封闭的环境条件下,无论是哪种水化学溶液,随着化学侵蚀时间的加长,溶液的pH值均趋于碱性;同时,溶出的Ca2+、Mg2+离子具有累积性特点。在其他条件相同的情况下,水化学溶液的离子成分对砂浆试样的腐蚀程度各不相同。酸性条件下,Na2SO4溶液砂浆试样物理化学性质的影响要比NaHCO3溶液大;中性条件下,与纯净的蒸馏水相比,Na2SO4溶液对砂浆试样的腐蚀作用要强一些。     

Study on mechanical characteristics and safety evaluation method of steel frame structure after fire

Mechanical characterization of steel frame structure after fire are analyzed based on fire dynamics, heat transfer theory, structural mechanics, and finite element theory. We study the temperature characteristics and mechanical properties of steel frame structure under different fire locations and propose a safety evaluation method. We also analyze damage level of main frame components, maximum temperature of fire, thermal characteristics of frame components, firing duration, etc. to provide useful information for fire resistance design of the steel frame structure and post-disaster safety evaluation.     

钢纤维掺量对活性粉末混凝土力学性能的影响

通过实验研究了活性粉末混凝土的基本力学性能(抗压强度、劈拉强度和抗折强度),分析了钢纤维掺量对活性粉末混凝土力学性能的影响,拟合得到了抗折强度与劈拉强度之间的关系表达式。在实验分析的基础上,建立了不同钢纤维体积含量活性粉末混凝土受压应力-应变全曲线的数学表达式。研究结果表明：钢纤维体积含量在1.0%～3.5% 之间时,活性粉末混凝土的抗压强度、劈拉强度和抗折强度均随着钢纤维掺量的增加而增大;当钢纤维体积含量超过3.5% 后,活性粉末混凝土抗压强度下降,劈拉强度略有提高,而抗折强度仍有明显的提高。     

单元类型和尺寸对裂尖疲劳塑性数值模拟的影响研究

本文采用Jiang-Sehitoglu循环塑性模型和多轴疲劳准则对紧凑拉伸式样裂尖的循环塑性变形、裂纹扩展速率和残余应力进行了有限元数值模拟,着重考察了单元的类型和最小单元尺寸对裂尖循环塑性和裂纹扩展速率的影响.紧凑拉伸试样的材料为1070钢,数值模拟采用了线性单元(四节点)和二次单元(八节点)两种单元,裂尖附近有限元单元的最小尺寸从0.007mm到0.24mm不等.文中将裂纹扩展速率的预测值与实验值进行了比较,通过对裂纹扩展速率的比较,确定在疲劳塑性分析时对单元类型和尺寸进行合理选取.     

Influence of the coupling of mechanical and thermal fields on the amplitude-frequency characteristics of a cylinder

A dynamic boundary-value problem of coupled thermoelasticity for a finite cylinder with mixed boundary conditions is solved. The problem is reduced to a system of four singular integral equations solved by the mechanical-quadrature method. A numerical experiment is conducted to obtain amplitude-frequency characteristics for finite cylinders with different cross sections. The effect of thermoelastic coupling on stress distribution is assessed __________ Translated from Prikladnaya Mekhanika, Vol. 42, No. 10, pp. 86–95, October 2006.     

孔隙度对湿式离合器局部润滑及摩擦特性影响研究

针对湿式离合器局部润滑及摩擦特性的影响因素,建立了摩擦副微观混合润滑模型.考虑了微凸峰接触和局部温升的影响,分析了孔隙度对湿式离合器局部压强分布、油膜和微凸峰承压比、实际接触面积、局部温升的影响.同时,利用摩擦磨损试验机(UMT)进行小试样销-盘试验,分析了不同孔隙度下离合器摩擦副局部摩擦系数的变化.结果表明:在混合润滑中,随着孔隙度的增大,润滑油膜动压作用减小,局部微凸峰接触压强增大,微凸峰法向压力承载比增大,摩擦副实际接触面积增加,因此摩擦系数增大.     

活性粉末混凝土力学性能及冻融性能研究

活性粉末混凝土具有优异的力学性能和耐久性,本文按照正交设计方法设计了9组不同配合比的活性粉末混凝土,通过试验研究了其基本力学性能及抗冻融性能,分析了水胶比、硅灰水泥比和钢纤维含量等因素对活性粉末混凝土力学性能及抗冻融性能的影响规律。研究表明,水胶比是影响活性粉末混凝土力学性能及抗冻融性能最主要的因素,钢纤维含量对活性粉末混凝土抗折和劈裂强度影响较为显著,对其抗压强度和抗冻融性能的影响不明显。本文根据试件破坏的现象对钢纤维作用的机理做了初步的探讨。