内爆载荷作用下不锈钢圆柱壳的断裂失效分析

在含预制裂纹的304不锈钢圆柱壳试样上进行了内爆炸试验,通过扫描电镜观察,在试样断口上发现了大量被拉长的剪切型韧窝等以局部剪切变形为主导的韧性断裂失效的典型特征.根据试验结果提出了一种应变率相关的动态断裂失效准则,采用有限元方法计算分析了圆柱壳动力响应和裂纹动态扩展过程,计算所得的最终裂纹尺度形貌与试验结果较为一致.     

FV520B钢Ⅰ-Ⅱ复合型断裂行为研究

针对离心压缩机叶轮出现的复合断裂问题,设计了I-II复合型断裂夹具和改进的紧凑拉伸试样,开展了叶轮典型材料FV520B不锈钢的试验研究。结果表明:FV520B钢I-II复合型断裂均属微孔聚集型韧性机制,只是在较大加载角度下,断口上的韧窝沿裂纹扩展方向被轻微拉长、深度变浅,主要由剪切分量占比增加所致;随加载角增加,材料总的断裂韧度增大,加载角为22. 5°和45°时较纯I型的分别增加了1. 8倍和4. 4倍,断裂韧度的I型和II型分量、及启裂角亦随之增大,采用复合型J积分断裂准则可以对试验结果进行较好地预测。本研究可为离心压缩机叶轮的复合断裂分析提供技术支撑。     

6061铝合金断裂机理的原位拉伸研究

用SEM-520原位拉伸试验对不同应力状态下6061铝合金试件的断裂过程进行研究.结果表明,不同应力状态下的铝合金试样在拉伸过程中其表面均产生了大量的滑移带,但断裂机理不同.随着三轴应力度的降低,断裂从韧窝聚合型混合剪切机制向纯剪切断裂机制过渡,试件断口也由韧窝断裂模式向剪切断裂模式演变;6061铝合金晶界处为最薄弱环节,微裂纹形核于晶界,随载荷的增加,微裂纹长大和扩展.微裂纹之间通过扩展或剪切而连接导致试样断裂;试样最小断面上的三轴应力度越小,试样断口的两个面上韧窝的取向就越明显,断口越光滑.     

薄膜微电极在热键合过程中的断裂行为研究

为了实现真正意义上的芯片实验室,金属微电极正在成为微流控芯片的重要组成部分。针对铜薄膜微电极在热键合过程中的断裂问题,利用断口分析技术研究了其断裂行为。分析了多种制备断口的方法并利用精密的自动砂轮划片机制备出了理想的断口试样,对断口试样进行宏观分析,判定该断裂是由于剪切引起的韧性断裂,利用扫描电子显微镜进行微观分析,推断出电极在热键合过程中既承受剪切力又承受拉应力,判定铜薄膜微电极在PMMA芯片热键合过程中的断裂机理是一种典型的韧窝式韧性断裂,铜薄膜微电极的断裂是由较高的热键合温度引起的。     

钛合金BT9非比例载荷低周疲劳断口显微分析

在室温下对钛合金BT9比例及非比例载荷下的低用疲劳试验后,利用扫描电镜及透射电镜对材料的疲劳变形结构进行观测.结果表明:在比例载荷条件下,疲劳断口扩展区微现形貌为等轴韧窝,随着应变强度的增加,断口韧窝密度增加,韧窝变深;在非比例载荷条件下,断口扩展区的微现形貌为准解理断裂和解理断裂.随着非比例载荷程度(相位角)的增大,断口的形貌由微孔聚集型断裂向解理断裂方向发展.     

柴油机机油泵主动轴断裂失效分析

本文利用ＡＳＭ－ＳＸ扫描电镜及ＴＮ－５５００能谱仪等现代测试手段，对１３５系列柴油机机油泵主动轴断裂失效进行了宏观和微观分析。分析结果表明，该轴为疲劳断裂。从宏观断口观察分析，断口特征不典型，属于低周疲劳断裂；从微观组织特征观察分析，断口上可见韧窝及疲劳条纹，属于韧性疲劳断裂；从使用寿命判断，属于早期疲劳失效。引起该思早期疲劳失效的原因：一晃机械加工时，键槽底部为一圆弧形直，加工粗糙形成应力集中；     

地铁转向架用P355NL1钢焊缝金属的低温冲击韧性

对地铁转向架用P355NL1钢焊缝金属进行了低温冲击试验,分析了焊缝金属的显微组织和化学成分对其低温冲击韧性的影响,并通过断口形貌观察分析了其断裂机制。结果表明:焊缝金属的显微组织包括先共析铁素体(PF)、侧板条铁素体(FSP)、细晶铁素体(FGF)以及针状铁素体(AF)等;大量的AF使其具有良好的低温冲击韧性;焊缝金属中含有硅、锰、镍等元素,促进了AF的生成并细化了晶粒;焊缝金属的韧脆转变温度为-42.70℃;-20~0℃时焊缝金属的断口形貌以韧窝为主,断裂方式为韧性断裂,断裂机理为微孔聚集型;-40℃时焊缝金属的断口形貌为韧窝和解理面相交织,断裂方式为韧-脆混合断裂;-60℃时焊缝金属的断口形貌已经完全变成解理断口,断口分布着河流状花样和解理台阶,为典型的脆性断裂。     

超低碳贝氏体钢埋弧焊焊缝金属的组织与力学性能

针对超低碳贝氏体钢HQ785DB的焊接特点,在低碳钢焊丝的基础上设计了一种埋弧焊用焊丝,将该焊丝匹配氟碱型SJ101焊剂对该钢进行焊接,研究了焊缝金属的显微组织、力学性能及冲击断口形貌。结果表明:焊缝金属组织以针状铁素体和板条贝氏体为主,另有少量弥散分布的粒状贝氏体;焊缝金属的抗拉强度为806.25 MPa,伸长率为16.78%,20℃时的冲击吸收功为183.25J;冲击断口上存在大量韧窝,以微孔聚集型的韧性断裂为主。     

介观尺度磷青铜薄板韧性断裂和变形行为的尺寸效应

借助单轴微拉伸试验研究了磷青铜薄板力学性能和韧性断裂的尺寸效应。结果表明,屈服强度与材料厚度t、晶粒尺寸d之间均存在着第Ⅱ类尺寸效应,但与t/d之间却存在着第Ⅰ类尺寸效应。断口形貌显示,随着t的减小,断裂机制由韧窝-微孔聚集断裂向滑移分离过渡;随着d的增大,韧窝逐渐变大变深,但当t/d<1时,拉伸过程过早形成微裂纹,导致试样迅速断裂。最后,基于表面层模型构建了介观尺度磷青铜薄板的混合本构方程。     

不同温度固溶处理后FeMnSiCrNi形状记忆合金的力学性能和断裂特征

采用组织观察和拉伸试验等手段研究了经不同温度固溶处理后FeMnSiCrNi合金的力学性能与断裂行为.结果表明:经一定温度固溶处理后,铁基合金标准拉伸试样的拉伸断裂过程具有应力诱发马氏体相变和马氏体自身滑移两个塑性变形阶段;当固溶处理温度为1000℃时,该合金具有优良的综合力学性能;其拉伸试样的断裂机制为微孔聚集型延性断裂,断口特征主要表现为大量的韧窝.     

椭球封头圆柱形爆炸容器振动特性研究

对椭球封头圆柱形爆炸容器在中心点爆炸状态下的 19次有效炮实验给予了介绍并对实验结果的壳体振动特性进行了分析。理论和实验分析表明 ,在封闭容器内爆炸冲击载荷具有明显的脉冲激励特征 ;容器壳体的振动频谱主要受前 10阶固有频率的影响 ;随着冲击载荷的增加 ,其壳体的主振频率将趋于相应壳体的呼吸频率 ,其应变增长具有减少的趋势 ;联接螺栓的振动模态主要受相应圆柱壳体和封头轴向振动模态的影响 ,并出现了在时域上其振动模态在圆柱壳振动模态和封头轴向振动模态间跳变的现象。     

Research on the dynamic mechanical characteristics and turning tool life under the conditions of excessively heavy-duty turning

The dynamic mechanical characteristics of excessively heavy-duty cutting were analyzed based on the cutting experiments with 2.25Cr-1Mo-0.25V steel used in hydrogenated cylindrical shells. By investigating the influence of dynamic mechanical characteristics on the tools’ failure in limited heavy-duty cutting processes, the model of dynamic shearing force in the cutting area was established. However, the experimental results showed that the dynamic shear flow stress in the cutting area greatly influenced the tools’ fatigue. The heavy-duty cutting tool was damaged in the form of a shearing fracture. Through a comprehensive analysis of the theory, the critical condition of the tools’ fracture under extreme loading was established.     

Transverse shear and rotary inertia effects on the stability analysis of functionally graded shells under combined static and periodic axial loadings

The effect of transverse shear and rotary inertias on the dynamic stability of functionally graded cylindrical shells subjected to combined static and periodic axial forces is investigated in this paper. Material properties of functionally graded cylindrical shells are considered temperature-dependent and are graded in the thickness direction according to a power-law distribution in terms of the volume fractions of the constituents. Numerical results for silicon nitride-nickel cylindrical shells are presented based on two different methods: the first-order shear deformation theory (FSDT) which considers the transverse shear strains and the rotary inertias, and the classical shell theory (CST). The results obtained show that the effect of transverse shear and rotary inertias on the dynamic stability of functionally graded cylindrical shells subjected to combined static and periodic axial forces is dependent on the shell’s material composition, environmental temperature, amplitude of static load, deformation mode, and the shell’s geometry parameters.     

Vibration and buckling of cross-ply laminated composite circular cylindrical shells according to a global higher-order theory

Natural frequencies and buckling stresses of cross-ply laminated composite circular cylindrical shells are analyzed by taking into account the effects of higher-order deformations such as transverse shear and normal deformations, and rotatory inertia. By using the method of power series expansion of displacement components, a set of fundamental dynamic equations of a two-dimensional higher-order theory for laminated composite circular cylindrical shells made of elastic and orthotropic materials is derived through Hamilton's principle. Several sets of truncated approximate higher-order theories are applied to solve the vibration and buckling problems of laminated composite circular cylindrical shells subjected to axial stresses. The total number of unknowns does not depend on the number of layers in any multilayered shells. In order to assure the accuracy of the present theory, convergence properties of the first natural frequency and corresponding buckling stress for the fundamental mode r=s=1 are examined in detail. The internal and external works are calculated and compared to prove the numerical accuracy of solutions. Modal transverse shear and normal stresses can be calculated by integrating the three-dimensional equations of equilibrium in the thickness direction, and satisfying the continuity conditions at the interface between layers and stress boundary conditions at the external surfaces. It is noticed that the present global higher-order approximate theories can predict accurately the natural frequencies and buckling stresses of simply supported laminated composite circular cylindrical shells within small number of unknowns.     

轴向冲击载荷下圆柱壳动力屈曲的计算机仿真

圆柱壳是工程中最常用的结构元件之一,对圆柱壳在各种基本载荷以及在不同类型载荷的联合作用下的屈曲问题研究一直是应用力学界和结构工程界十分关注的课题,与静力屈曲相比,圆柱壳的动力屈曲问题的研究还不尽完善.文章通过有限元软件ANSYS研究圆柱壳轴向冲击下的动力屈曲问题.     

On the creep buckling of circular cylindrical shells

Approaches to the creep buckling of clamped circular cylindrical shells subjected to axial compression combined with internal pressure are investigated with special emphasis on the concept of creep stability and the accuracy of the analysis. The instability in creep is discussed first, and it is elucidated that the pertinent phenomena can be analysed by a quasi-static method. Then, the formulation of the problem and the method of calculation of the resulting equations are studied. The influence of the creep laws and the non-linearity in field equations on the creep buckling of shells are also discussed.     

Energy dissipation in braced cylindrical shells

This paper presents an experimental and numerical investigation of the energy dissipation characteristics of mild steel cylindrical shells subjected to large deformations under line loadings acting parallel and perpendicular to the shells' longitudinal axes. The effects of diametrical bracing, cylinder length and external loading orientation on the deformation patterns and energy dissipation capacities are described. The results are applied to the design of a new impact attenuation system used in highway safety applications.     

钢管混凝土构件的爆炸荷载试验研究

针对钢管混凝土结构构件在爆炸冲击荷载作用下的动力响应进行研究,试验对象为相同管径三种不同壁厚的钢管混凝土结构构件在简支状态下,受到两种不同爆炸冲击荷载的作用,测量了两种不同爆炸空气冲击波的压力时间曲线、构件跨中的应变时间曲线和构件跨中的最终挠度值,并对测量结果进行分析,为钢管混凝土构件的抗爆炸荷载设计提供有益的试验成果,也为后续进一步研究提供有效的基础数据和可靠的对比参照.     

Dynamic buckling of suddenly loaded imperfect hybrid FGM cylindrical shells with temperature-dependent material properties under thermo-electro-mechanical loads

Only static buckling of the hybrid functionally graded material (FGM) cylindrical shells has been investigated so far. In the present paper, dynamic buckling of imperfect FGM cylindrical shells with integrated surface-bonded sensor and actuator layers subjected to some complex combinations of thermo-electro-mechanical loads is investigated. The general form of Green's strain tensor in curvilinear coordinates and a high-order shell theory proposed earlier by the author are used. The complicated nonlinear governing equations are solved using the finite-element method. Buckling load is detected by a modified Budiansky's criterion proposed earlier by the author. Effects of temperature dependency of material properties, volume fraction index, load combination, and initial geometric imperfections on thermo-electro-mechanical post-buckling behavior are evaluated. Results reveal that the volume fraction index, temperature gradient, layer sequence, and the adaptive feedback control somewhat may affect the buckling load.     

Theory and comparison of the effect of composite and shape memory alloy stiffeners on stability of composite shells and plates

The effects of composite and shape memory alloy stiffeners on stability of composite cylindrical shells and rectangular plates subjected to a compressive load are compared. The governing equations for reinforced cylindrical shells are developed based on the Love first approximation theory and smeared stiffeners technique. It is shown that composite stiffeners are more efficient in cylindrical shells, while shape memory alloy stiffeners may be preferable in plates or in long shallow shells. It is also proven that shape memory alloy stiffeners increase the upper and lower buckling loads, i.e. the linear buckling load and the minimum postbuckling load-carrying capacity of cylindrical shells modeled as single-degree-of-freedom systems by the same amount.