1.25Cr0.5Mo钢的高温疲劳-蠕变交互作用行为

通过1.25Cr0.5Mo钢高温环境应力控制的疲劳-蠕变交互作用试验,揭示和分析了1.25Cr0.5Mo钢高温疲劳-蠕变交互作用下应力循环特性以及平均应变、非弹性应变范围等参数随温度、加载历史、加载水平的变化规律,在此基础上,利用扫描电镜对试样断口进行了分析。研究表明:高温环境下,材料的应力循环特性依赖于加载水平和加载历史,平均应变、非弹性应变范围等参数依赖于温度、加载水平和加载历史,材料的断裂从以解理断裂为代表的脆性断裂过渡到以韧窝型剪切断裂为代表的延性断裂,为混合型断裂。     

通气超空泡水下射弹实验研究

利用射弹装置开展了通气超空泡水下射弹的实验研究。对水下射弹进行通气,得到了水下射弹的通气超空泡,并对空泡的形态进行了研究;得到了不同空化数条件下形成超空泡的通气率：空化数较大时较低的通气率,能形成超空泡,空化数较小时,形成通气超空泡的通气率较高;对超空泡减阻特性进行了验证,比较了同样初速度的通气超空泡射弹与不通气射弹速...     

水泥砂浆的平板撞击实验与高压状态方程研究

采用火药发射枪加载技术和PVDF应力测试技术,对强度约40 MPa含初始孔隙的水泥砂浆在平板撞击条件下的冲击特性进行了实验研究与分析。基于PVDF传感器实测的水泥砂浆试样的原始时间-电压波形,换算得到相应的时间-应力波形。结果表明:不同位置处的应力在迅速上升至波峰后均随时间衰减,冲击波峰值随传播距离而衰减,冲击速度越高衰减效应越明显,呈现出明显的黏弹性特性和耗散特性;从细观结构分析表明材料内部的微损伤缺陷是造成冲击波衰减的物理本质;再从冲击绝热数据出发,拟合了D-u与P-ρHugoniot关系,估算了砂浆的Hugoniot弹性极限,初始弹性波速及密实材料波速,对材料的冲击压缩特性采用P-α状态方程和Mie-Grüneisen型多项式状态方程分段描述,并给出了模型参数。     

界面剥离钢-混凝土组合结构应力波传播谱元法模拟研究

建立钢-混凝土组合结构截面二维谱元法模型,针对钢-混凝土界面完好以及存在界面剥离时模型在单点激励下弹性应力波场进行模拟分析,探究弹性应力波的传播规律。采用去除混凝土单元的方法反映组合结构中钢板与混凝土之间的界面剥离。通过对比分析表明界面剥离的存在对弹性应力波场以及模型上不同位置的位移响应产生影响。通过改变界面剥离程度,得到测点位移的变化规律。通过模拟,谱元法可以有效模拟钢-混凝土组合结构中弹性波的传播规律,为研究基于应力波测量的钢-混凝土组合结构界面缺陷检测机理提供帮助。     

一种新的疲劳损伤演化模型

考虑到金属构件的疲劳损伤主要属于机械损伤,则造成损伤的外因主要是应力幅,而导致损伤的内因是材料本身的性质。基于损伤力学基础理论推导的一般损伤演化方程,并结合断裂力学中经典的帕里斯公式,以有效当量应力幅和材料损伤的特性参数为控制变量得到了一种新的疲劳损伤演化模型,并以12Cr1MoV钢为例进行了实验分析。结果表明:新模型形式简单、参数少,且比Lemaitre模型与实验结果符合得更好。     

集装箱平板玻璃冲击应力分析

通过理论和实验的方法,分析集装箱中表面一块平板玻璃受到横向正面冲击的最大应力。将表面一块平板玻璃简化为四边自由均匀各向同性矩形薄板,其余玻璃作为弹性基础。通过计算,给出了最大冲击应力随集装箱正面、背面和底部缓冲材料刚度系数的变化曲线及随底部缓冲材料位置变化曲线。集装箱模型实验的结果与理论结果基本相符。无量纲最大应力响应和刚度系数曲线可供平板玻璃集装箱的结构设计参考。     

冲击载荷下铜基粉末冶金(Cu-PM)多孔材料的动态应力-应变特性研究

粉末冶金多孔材料具有较低的密度和弹性波速，对其施加动态压缩实验具有一定的难度。本文在分析该材料的各种特性后，在对该材料进行动态测试时，采用半导体应变片技术等方法，得出该材料在冲击荷载作用下的应力应变曲线。填补了该粉末冶金材料动态性能数据的空白，为工程应用提供了可靠的实验数据。     

TiNi形状记忆合金低速冲击性能的数值模拟

采用有限元法数值模拟了TiNi形状记忆合金(SMA)的低速冲击性能。考察马氏体相变过程中不同伪弹性模量和弹性应变极限对TiNi合金低速冲击性能的影响。结果表明,随着冲击速度的增加,4种材料的最大接触载荷和位移量都呈线性增加趋势;冲击速度相同时,3种不同伪弹性模量TiNi合金试样的最大接触载荷和位移量近似相等且都低于45#钢,TiNi合金试样产生的最大Von Mises应力和最大塑性应变都低于45#钢;超弹性模量为2.9GPa的TiNi合金产生的最大Von Mises应力和最大塑性应变均最低。TiNi形状记忆合金较低的超弹性模量和较大的弹性应变极限能够减小冲击过程中的最大Von Mises应力,抑制高塑性应变的产生并使塑性变形区域减小,从而提高TiNi合金的抗冲击性能。     

新型高强韧性高耐磨性奥氏体—贝氏体钢

以新的合金设计思想,研究了一种由奥氏体和贝氏铁素体组成的普通低合金高碳钢——奥氏体-贝氏体钢。实验结果表明,这种材料具有有很高的屈服强度、韧性与加工硬化能力,在高应力尤其是强烈冲击磨料磨损条件下耐磨性十分优异,是抗高应力、强烈冲击磨料磨损的理想材料。     

聚氨酯泡沫塑料冲击力学性能的实验研究

通过落锤冲击试验，研究了硬质聚氨酯泡沫塑料的冲击力 学性能，得到了初始应变率为１０＾１￣１０＾２ｓ＾－１的应力－应变曲线，并且同低应变率下材料的应力－应变特性进行了比较，针对不同密度的泡沫塑料，确定了它们的冲击强度模量，比较了它们的吸能特性。     

Thermo-acoustical waves in thermo-plastic materials

Summary The propagation velocities and the variation of the amplitudes of thermo-acoustical waves in thermo-plastic materials are theoretically investigated. The constitutive equations of anisotropic thermo-plastic materials are derived from the concept of imaginary decomposition of the deformation rate tensor into the elastic and plastic contributions and from that of the plastic potential. From generalized Vernotte's heat conduction law the propagation condition of the jumps of the velocity gradients and of the temperature rate is obtained. In isotropic materials and in the case of a normal stress vector on the wave front we have two purely mechanical transverse waves and two thermo-longitudinal coupled waves. Formulae for the velocities and amplitudes are quite similar with those for thermo-elastic materials. The variation of the amplitude is discussed. There are, in general, three effects on the variation, that is, the non-planar, heat conduction and plastic flow effects. The transverse waves are subjected only to the non-planar effect, while the thermo-longitudinal waves may grow or decay according to the above three effects.     

Weak shock waves in heat conducting thermoelastic materials

In this paper an attempt is made to study the propagation of weak shock waves in heat conducting materials. The equation for determining the velocities of propagation is derived and expressions for the velocities in linear elastic materials are obtained. The equations governing the growth and decay of the wave amplittude are obtained and studied for shock waves of arbitrary form in linear thermoelastic body. The stress jump in relation to the shock strength is studied for a second order material. It is shown that relationship between the stress jump and the shock strength is a type of hyperbolic relation with real asymptotes. In all the effect of the heat conduction is examined.     

Dynamic mechanical properties of polycrystalline graphites and a 2D-C/C composite by plate impact

In order to obtain dynamic mechanical properties of carbon materials, i.e., two kinds of polycrystalline graphites and a C/C composite, plate impact experiments with simultaneous three poly vinylidene difluoride (PVDF) stress gauges were conducted using a one-stage powder gun system. By this measurement system, Hugoniot curves, rarefaction wave velocities and stress–strain (S–S) curves could be obtained. The Hugoniot curves were valid, rarefaction wave velocities increased with the plateau stress in the specimen, and the slope of the S–S curve was consistent with that of the Hugoniot curve. These dynamic mechanical properties of the carbon materials are useful not only for the understanding of the dynamic behavior but also for impact fracture behavior.     

多层 U 形A瓦楞结构材料的共面力学性能

目的在不同冲击速度的共面载荷条件下,获取多层U形A瓦楞结构材料动态力学性能参数。方法建立有限元分析模型,并简化能量吸收模型,来评估其能量吸收性能。结果随着冲击速度的不断增大,均匀变形、过渡变形和动态变形等模式随之呈现。结论最佳单位体积的能量吸收主要由动态峰应力决定。在结构参数一定的条件下,共面动态峰应力取决于多层U形A瓦楞结构材料所受到的冲击速度。通过对数值结果的物理分析和讨论,提出了动态峰应力关于冲击速度的经验关系式。     

Waves in elastic materials with internal constraints

Sinusoidal waves in the elastic materials with internal constraints are investigated theoretically, where constraints of the incompressibility and the rigidity are adopted. The constitutive equations are obtained for volume-preserving and area-preserving materials and for materials with N inextensible directions. There are two kinds of waves, one is identical with waves propagating in matrix material and the other is waves depending on indeterminate parameters. The propagation velocities of the second type of waves decrease when the materials are compressed. There are some critical compressed states, where the material may be buckled. If the materials are compressed over the critical state, the stational wave can not exist.     

An analytical study of the effect of slamming pressures on the interlaminar behaviour of composite panels

This paper discusses the effect of material properties on the interlaminar behaviour of ship panels made of composite materials under stress waves caused by slamming loads. First, a brief reference to the analytical model developed to simulate the propagation of stress waves caused by slamming impact on composite materials which has been recently published in Composite Structures is made. Then, some parametric studies are done, discussing the influence of material Young’s modulus on the interlaminar peak stresses. The influence of strain rates is also discussed.     

Reflection of piezothermoelastic waves from the charge and stress free boundary of a transversely isotropic half space

The present paper concentrates on the study of propagation and reflection characteristics of waves from the stress free, thermally insulated/isothermal boundary of a piezothermoelastic half space. The non-classical (generalized) theories of linear piezo-thermoelasticity have been employed to investigate the problem. In the two-dimensional model of the transversely isotropic piezothermoelastic medium, there are three types of plane waves quasi-longitudinal (QL), quasi-transverse (QT) and thermal wave (T-mode), whose velocities depend on the angle of incidence and frequency. These waves are dispersive in character and are also affected by piezoelectric as well as pyroelectric properties of the materials. The low and high frequency approximations for the speeds of propagation and the attenuation coefficients of these waves have been obtained. The quasi-longitudinal (QL), quasi-transverse (QT) and thermal wave (T-mode) incident cases at the stress free, thermally insulated or isothermal open circuit boundary of a transversely isotropic piezothermoelastic half space are considered to discuss the reflection characteristics of various waves. The amplitude ratios of reflected waves to that of incident one in each case have been obtained. The special cases of normal and grazing incidence are also derived and discussed. Finally, the numerical computations of reflection coefficients are carried out for cadmium Selenide (CdSe) material by using Gauss elimination procedure. In addition the phase velocities and attenuation coefficients are also computed along various directions of wave propagation. The obtained results in each case are presented graphically.     

On pressure-shear plate impact for studying the kinetics of stress-induced phase transformations

Pressure-shear plate impact experiments are proposed for studying the kinetics of stress-induced phase transformations. The purpose of this paper is to determine loading conditions and specimen orientations which can be expected to activate a single habit plane variant parallel to the impact plane, thereby simplifying the study of the kinetics of the transformation through monitoring the wave profiles associated with the propagating phase boundary. The Wechsler-Lieberman-Read phenomenological theory was used to determine habit plane indices and directions of shape deformation for a Cu---Al---Ni shape memory alloy which undergoes a martensitic phase transformation under stress. Elastic waves generated by pressure-shear impact were analyzed for wave propagation in the direction of the normal to a habit plane. A critical resolved shear stress criterion was used to predict variants which are expected to be activated for a range of impact velocities and relative magnitudes of the normal and transverse components of the impact velocity.     

Recent developments in velocity and stress measurements applied to the dynamic characterization of brittle materials

The synthesis of novel brittle materials with tailored microstructures requires the understanding of new physical phenomena related to the failure of these materials. Observation capabilities with spatial resolution of atomic dimensions, e.g., scanning tunneling microscopy (STM) and high resolution electron microscopy (HREM), have opened new frontiers in the mechanical characterization of these advanced materials. The challenge is to design experiments capable of loading the material in a controlled fashion such that defects, resulting in well defined macroscopic stress and velocity features, are produced. In this article, techniques for the measurement of surface and in-material particle velocities and in-material axial and transverse stress measurements are reviewed. Examples on the usefulness of these techniques in the study of brittle failure are provided. A variable sensitivity displacement interferometer is used in the measurement of normal and in-plane motion in pressure–shear recovery experiments conducted on fiber composite materials. In-material stress measurements with piezoresistance gauges are used in the identification of so-called failure waves in glasses.     

Thermo-acoustical waves in linear thermo-elastic materials

Summary Coupled waves of thermal and mechanical jumps in linear thermo-elastic materials are analysed. General linear anisotropic constitutive equations of thermo-elastic materials are derived from the Clausius-Duhem inequality and Vernotte's heat conduction law is adopted. The waves are defined to have jumps in acceleration and in temperature rate and the four-dimensional thermo-acoustical propagation condition is obtained. The differential equations which govern the variation of the wave amplitudes are obtained. For waves in linear isotropic thermo-elastic materials, there are four principal waves. Two shear waves are purely mechanical and propagate with constant amplitude, while two thermo-longitudinal waves have different propagation velocities: one is larger and other smaller than the purely mechanical longitudinal wave velocity, and their amplitudes decay, in general, exponentially in time.