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1.
混凝土材料声发射技术研究综述   总被引:10,自引:0,他引:10       下载免费PDF全文
本对混凝土材料声发射技术研究的历史,现状及涉及的领域进行了概括与总结。对混凝土材料声发射机理,声发射参数与力学参数间的关系。声发射在断裂力学中的应用,混凝土材料的凯塞效应与应用以及现代非线性理论和方法与声发射技术的结合等问题进行了评价与展望。  相似文献   

2.
 对镀制强激光薄膜的光学元件在外界环境中时,表面面形发生的变化进行了研究。理论分析了表面面形的变化机制,明确水致应力具有物理和化学两种形成机制,是改变镀膜元件面形的主要因素;实验研究了镀制激光高反膜的K9材料元件存放过程中面形变化趋势,发现这种趋势变化具有时间效应和湿度效应。  相似文献   

3.
Al-Cu多晶锯齿形屈服现象中的尺度效应   总被引:2,自引:0,他引:2       下载免费PDF全文
对Al-Cu多晶合金锯齿形屈服现象中各特征物理量(应力跌幅、跌落时间和再加载时间)随应变演化的规律进行了系统研究,讨论了不同厚度试件演化结果的区别.同时,这种尺度效应还表现为相同加载条件下1,2mm厚度试件与3mm厚度试件的Portevin-Le Chrtelier (PLC)类型的差异.利用非线性时间序列分析的方法对前者在相空间中吸引子的几何特性进行了描述,并通过主分量分析的方法初步判定其中存在着混沌行为.后者演化过程中应力跌落事件按跌落幅度统计分布符合幂律规律,具有自组织临界性特征.最后,借助自组织 关键词: 锯齿形屈服 尺度效应 Al-Cu合金  相似文献   

4.
张辉  曾德长 《物理学报》2010,59(4):2808-2814
研究了Terfenol-D材料中巨磁致伸缩的逆效应,即磁机械效应.基于Stoner-Wohlfarth(SW)模型,考虑磁晶各向异性和应力各向异性能,依据自由能极小原理,获得了退磁态下Terfenol-D单晶中磁化强度方向和压应力的关系.采用数值方法求解了平衡条件下的非线性方程组.理论结果表明,Terfenol-D巨磁致伸缩单晶中的磁各向异性取决于磁晶各向异性和应力各向异性之间的竞争.在压应力的作用下,Terfenol-D单晶中的磁各向异性由立方向单轴转变.理论和实验结果的比较表明,存在一个临界压应力,使磁致伸缩效应达到极大值.该理论结果还解释了压应力使得Terfenol-D单晶材料难于磁化和磁致伸缩效应出现极大值的实验事实.理论计算不仅为研究这类问题提供了一个更准确的方法,而且其结果也有助于理解类似材料中的磁化过程. 关键词: Terfenol-D 磁机械效应 巨磁致伸缩效应 磁各向异性  相似文献   

5.
张辉  曾德长 《中国物理 B》2010,19(4):2808-2814
研究了Terfenol-D材料中巨磁致伸缩的逆效应,即磁机械效应.基于Stoner-Wohlfarth(SW)模型,考虑磁晶各向异性和应力各向异性能,依据自由能极小原理,获得了退磁态下Terfenol-D单晶中磁化强度方向和压应力的关系.采用数值方法求解了平衡条件下的非线性方程组.理论结果表明,Terfenol-D巨磁致伸缩单晶中的磁各向异性取决于磁晶各向异性和应力各向异性之间的竞争.在压应力的作用下,Terfenol-D单晶中的磁各向异性由立方向单轴转变.理论和实验结果的比较表明,存在一个临界压应力,使磁致伸缩效应达到极大值.该理论结果还解释了压应力使得Terfenol-D单晶材料难于磁化和磁致伸缩效应出现极大值的实验事实.理论计算不仅为研究这类问题提供了一个更准确的方法,而且其结果也有助于理解类似材料中的磁化过程.  相似文献   

6.
 在引入材料损伤软化、温度软化效应的基础上,对一维柱对称内聚爆加载管壳中应力波的传播、材料的变形和层裂问题开展了研究。成功地通过自编写有限元代码,完成了系列数值模拟计算,得到了管壁中与物理事实一致的应力波传播图像和材料的变形、损伤、层裂的发展规律,成功模拟了内聚爆加载管壳的多次层裂现象。  相似文献   

7.
退火铝合金中Portevin-Le Chatelier效应的数值模拟研究   总被引:2,自引:0,他引:2       下载免费PDF全文
通过综合考虑沉淀动力学和动态应变时效机理,建立了一套具有明确物理内涵的唯象本构模型.并在对不同加载应变率下的单轴拉伸实验的数值模拟中,得到了3种类型的Portevin-Le Chatelier效应应力曲线.计算结果与实验数据的较好吻合,验证了该模型的有效性. 关键词: Portevin-Le Chatelier效应 动态应变时效 数值模拟  相似文献   

8.
单粒子效应是航天电子器件失效的重要原因,研究其物理过程对航天电子器件寿命预测、器件抗辐照加固有着重要的意义。现有的模型多从线性能量沉积的角度来解释单粒子翻转,因此无法解释单粒子效应地面实验模拟过程中的温度效应。建立了一个新模型,从高能带电离子与材料相互作用的物理过程出发,通过解三维的热扩散方程,计算出能量在材料中沉积、交换、扩散,得到电子和晶格温度的空间分布以及时间演化过程。推断出离子辐照过程中导致的自由电子浓度和收集电荷随LET的变化关系。此模型解释了单粒子效应中随着器件温度升高,单粒子效应截面增加的现象。  相似文献   

9.
粘塑性介质中球形孔洞的动态增长   总被引:1,自引:0,他引:1       下载免费PDF全文
 提出了一个新的粘塑性介质中球形孔洞在高加载率作用下的演化方程。方程中考虑了应变率、局部惯性和介质的硬化效应,并对这些影响进行了数值分析和讨论。数值分析结果表明:孔洞的增长对外加载率和应变率十分敏感,在高加载率条件下局部惯性效应对孔洞增长有着重要影响,随着加载率的增加,这种影响增大。另外,得到了使孔洞增长的临界应力值的表达式。  相似文献   

10.
洪杰  刘宝龙  张大义  马艳红 《物理学报》2012,61(16):168102-168102
将传统金属橡胶制备工艺和形状记忆合金材料相结合, 研制了一种新型智能阻尼材料——-记忆合金金属橡胶, 并对其成型工艺、形状记忆效应、热弹性力学性能及参数影响规律进行了试验研究. 研究表明, 作为一种特殊的金属橡胶, 该材料不仅具备普通金属橡胶高阻尼、低密度、孔隙度可控等优点, 同时具备普通金属橡胶所不具备的智能材料特征: 1)良好的单程形状记忆效应, 该材料在大载荷加载后的残余塑性变形可以在升温过程中完全恢复; 2) 弹性模量和损耗因子具有温变特性, 在相变温度区间内弹性模量和损耗因子随温度近似线性变化. 由于同时具备金属橡胶和形状记忆合金两大金属类功能材料的优点, 形状记忆合金金属橡胶成为一种可应用于振动主动控制、 集良好承载能力和阻尼特性于一身、具有结构功能一体化优 势的新型智能阻尼材料.  相似文献   

11.
差分吸收光谱仪测量上下限的确定   总被引:9,自引:2,他引:7  
给出差分吸收光谱仪(DOAS)系统对测量上下限的确定方法,由于测量原理Beer-Lambert的线性适用范围限制了系统的测量上限,系统的噪声,被测气体的差分吸收截面以及测量的数据点数共同决定了系统的测量下限,通过理论分析与实际测量确定了DOAS系统的测量上下限。  相似文献   

12.
Accepted views concerning Poisson's ratio for central-force polycrystals are amended. For pulycrystals the ratio can vary from 1/4, which is actually a lower limit. An upper limit of Poisson's ratio exists also. Both limits can be calculated from single-crystal elastic data. The limits correspond to Voigt's and Reuss's states of uniform local strain and of uniform local stress, respectively.  相似文献   

13.
An analysis of experimental data on the critical diameter for burning of nitroglycerin-based propellant NB and on the temperature profiles in the combustion wave on a propellant sample in a heat-absorbing confinement was performed. It was demonstrated that, for cylindrical samples placed into a heat-absorbing confinement, there are two values of the critical diameter. The smallest value of the critical diameter (lower extinction limit) is associated with heat losses from the heat conduction zone and reaction zone of the condensed phase. The largest value of the critical diameter (upper extinction limit) is determined by heat losses from the condensed and gas phases. It was demonstrated that the value of the critical diameter is controlled by the maximum size of hotspots on the burning surface. For example, the mean critical diameter equals approximately twice the maximum hotspot size. Critical diameters characteristic of the range between the lower and upper limits range from a quarter to a half of the maximum hotspot size, with the process of extinction in this interval being of stochastic character.  相似文献   

14.
 非晶材料的高强度及其对温度的敏感性,导致爆炸复合制备非晶块体时下限较大而上限较小,使得焊接窗口较窄。通过对非晶薄带涂铜以降低表面硬度,分析表明其不仅能降低下限,同时使高速撞击产生的热量主要集中在涂层上,减小非晶薄带的受热影响区域;再利用损伤力学的思想,在装置设计时采用增设缺陷的方法,以削弱到达焊接界面的反射拉伸波强度,提高焊接上限;降低的下限和提高的上限能使焊接窗口有效地扩大,从而使爆炸复合制备非晶块体易于实现。  相似文献   

15.
A close study of Heisenberg uncertainty principles reveals many significant facts, and all four major physical quantities, energy, time, momentum and length, have both lower and upper limits. Now, many questions come up. What are these limits? Some answers may lead to the understanding of the development of our universe. What is the shortest limit of time? At the beginning of big bang, there exists a tremendously short time, the Planck time. This may be just the shortest time limit in our universe. The longest time limit might be the lifetime of our universe. The longest length might be the final diameter of our expanding universe. All these lead to a finite universe. Two more coupling formulae are formed for the other two pairs of physical quantities, mass and speed, thermal energy and temperature. These four physical quantities must also have limits. We already knew that speed has upper limit and temperature has lower limit. By these two formulae, Planck and Einstein equations are derived directly. Since most other physical quantities are somewhat related to these major physical quantities, it seems that there exists a principle of limitation of physical quantities. A quantitative sketch of big bang is described. It also shows that our universe will contract back to another big bang. The principle of limitation opens up some fields of investigation. It may bring nature back to the harmony and determined world described by classical physics.  相似文献   

16.
Inter-spin distances between 1 nm and 4.5 nm are measured by continuous wave (CW) and pulsed electron paramagnetic resonance (EPR) methods for a series of nitroxide-spin-labelled peptides. The upper distance limit for measuring dipolar coupling by the broadening of the CW spectrum and the lower distance limit for the present optimally-adjusted double electron electron resonance (DEER) set-up are determined and found to be both around 1.6-1.9 nm. The methods for determining distances and corresponding distributions from CW spectral line broadening are reviewed and further developed. Also, the work shows that a correction factor is required for the analysis of inter-spin distances below approximately 2 nm for DEER measurements and this is calculated using the density matrix formalism.  相似文献   

17.
Photon correlation spectroscopy (PCS) is a technique to measure rapidly particle size in the sub-micrometre region. The use of PCS is, however, limited by concentration. The upper limit is due to multiple scattering of the incident light and the lower limit is determined by the fact that fluctuations of the number of particles in the measuring zone have a significant influence on the apparent diffusion coefficient. In this paper a signal processing method is described which differentiates this influence. With this system the lower limit is no longer limited to about 100 particles in the measuring volume corresponding to a concentration of 109 particles/cm3. The limitation is now the intensity of the scattered light, which becomes too weak at a concentration of about 50 particles/cm3. As a consequence of this work, a revision to the basic theory of PCS may be necessary. Moreover, the new processing method also permits the measurement of the particle concentration in the sample.  相似文献   

18.
The applicability of the quantum theory of a weak gravitational field (Gupta's theory) is examined on the basis of the quasiclassical generally relativistic point of view. It is shown that in standard quantum theory the energy of a particle cannot be arbitrary but is bounded both below and above. These bounds arise because it is impossible to treat the region of interaction of elementary particles as a part of flat space. The lower limit depends on the curvature tensor of the external gravitational field, while the upper is determined by the gravitational field of the particle itself.  相似文献   

19.
《Physics letters. A》2020,384(34):126867
Traffic congestion is increasingly deteriorating people's travel experience, and accordingly the relationship between travel mode selection and subjective well-being has become a hot issue of concern. Motivated by this, an incentive mechanism combining both reward and punishment is proposed to characterize the evolution of subjective well-being. Two psychological thresholds are introduced: payoff higher than the upper limit will result in rewarding while that lowers than the lower limit leads to punishment. Results show that when the upper and lower limits are close enough, cooperative behavior can be dramatically promoted, that is, more travelers choose low-carbon transportation mode. Moreover, we find that punishment is superior to rewarding in stabilizing high cooperative level. It also shows that whether to choose low-carbon transportation mode depends sensitively on the changes of the upper and lower limits as well as the heterogeneity of self-interest. This study is helpful to promote the formulation of green travel management policies in the future.  相似文献   

20.
Six models of contrast microbubbles are investigated to determine the excitation threshold for subharmonic generation. The models are applied to a commercial contrast agent; its characteristic parameters according to each model are determined using experimentally measured ultrasound attenuation. In contrast to the classical perturbative result, the minimum threshold for subharmonic generation is not always predicted at excitation with twice the resonance frequency; instead it occurs over a range of frequencies from resonance to twice the resonance frequency. The quantitative variation of the threshold with frequency depends on the model and the bubble radius. All models are transformed into a common interfacial rheological form, where the encapsulation is represented by two radius dependent surface properties-effective surface tension and surface dilatational viscosity. Variation of the effective surface tension with radius, specifically having an upper limit (resulting from strain softening or rupture of the encapsulation during expansion), plays a critical role. Without the upper limit, the predicted threshold is extremely large, especially near the resonance frequency. Having a lower limit on surface tension (e.g., zero surface tension in the buckled state) increases the threshold value at twice the resonance frequency, in some cases shifting the minimum threshold toward resonance.  相似文献   

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