Damage spreading in a gradient

We propose a new method of analyzing the frozen-chaotic transition in a cellular automaton by propagating damage in a gradient. We obtain estimations forp _c and for the critical exponents for the Kauffman model and the mixture of OR and XOR rules.     

Damage spreading in a driven lattice gas model

We studied damage spreading in a Driven Lattice Gas (DLG) model as a function of the temperature T$T$, the magnitude of the external driving field E$E$, and the lattice size. The DLG model undergoes an order–disorder second-order phase transition at the critical temperature _Tc(E)$T_c\left(E\right)$, such that the ordered phase is characterized by high-density strips running along the direction of the applied field; while in the disordered phase one has a lattice-gas-like behavior. It is found that the damage always spreads for all the investigated temperatures and reaches a saturation value _Dsat$D_{sat}$ that depends only on T$T$. _Dsat$D_{sat}$ increases for T<_Tc(E=∞)$T<T_c(E=\infty )$, decreases for T>_Tc(E=∞)$T>T_c(E=\infty )$ and is free of finite-size effects. This behavior can be explained as due to the existence of interfaces between the high-density strips and the lattice-gas-like phase whose roughness depends on T$T$. Also, we investigated damage spreading for a range of finite fields as a function of T$T$, finding a behavior similar to that of the case with E=∞$E=\infty$.     

Damage of beryllium surface under irradiation with a high-current electron beam

Radiation damage of a beryllium surface by a high-current electron beam at the GSEP-3 accelerator is considered. The degree of damage of beryllium samples has been determined. The temperature fields inside the sample and the distributions of thermal stresses have been calculated. The reasons for beryllium surface cracking formation have been found. The concentrations of point defects have been calculated. The possible reasons for an increase in microhardness of the irradiated beryllium surface layer are discussed.     

Damage detection of a rectangular plate by spatial wavelet based approach

This paper presents a technique for structure damage detection based on spatial wavelet analysis. Many damage detection methods require modal properties before and after damage. This method only needs the spatially distributed signals (e.g. the displacements or mode shapes) of the rectangular plate after damage. First, spatially distributed signals of the rectangular plate with damage are obtained by finite element method. The damaged region is represented as the elements with reduced stiffness. Then these spatially distributed signals are analyzed by wavelet transformation. It is observed that distributions of the wavelet coefficients can identify the damage position of rectangular plate by showing a peak at the position of the damage. It is also demonstrated that this method is very sensitivity to the damage size.     

Damage track detectors in radioprotection dosimetry: a novel approach

Limited sensitivity and unpredictable background are the major drawbacks of damage track detectors in the assessment of low neutron doses and low concentrations of alpha emitters in biological and environmental samples. The simplest way to increase the sensitivity of the damage track detectors is to increase both the exposure time and the detector area. However, the strong variability of the background may make this task often impossible. This background problem has been finally solved by a new registration method based on counting coincidence spots in geometrically matched pair of detectors. By using spark counting and electrochemical etching, both of which produce spots visible at low magnification, coincidences induced in two matched detector-surfaces by a few-microns-long tracks can be easily seen. This novel counting approach can be considered just the converse of those used in the past with Bi-fission detectors and cosmic ray stacks.     

Damage in lithium niobate induced by a high-power proton-carbon beam

Surface damage in lithium niobate LiNbO₃ induced by a high-power proton-carbon beam was investigated. Typical damage patterns were observed. The effect of thin metal surface coating on the damage was considered.     

532nm皮秒脉冲激光对单晶硅的损伤特性研究

随着光电对抗和超短脉冲激光技术的发展,研究超短脉冲激光与单晶硅相互作用具有非常重要的理论和实际意义.为了进一步明确532 nm皮秒脉冲激光对单晶硅的损伤机理,本文开展了532 nm皮秒脉冲激光辐照单晶硅的损伤效应实验研究,测定了损伤阈值,明确了损伤机理,探讨了低通量下的脉冲累积效应.首先,利用波长为532 nm、脉冲宽...     

超薄镜破坏阈值的研究

新一代空间相机的非球面主镜由一些超轻超薄的分块镜组成，由于目前通用的空间光学反射镜材料非常有限且大部分均为脆性材料，在力的作用下产生强制性的变形将引起镜体大的应力甚至破碎，所以必须研究超薄镜的破坏阈值。首先将弹性力学中应力强度因子的概念引入主动光学中，证明了应力强度因子即传统意义的材料破坏阈值。提出材料表面的微裂纹是材料脆性断裂的根本原因。介绍了一种计算材料应力强度因子的方法。最后针对超薄平面镜模型进行了实例计算，得到了超薄镜的破坏阈值与其尺寸、厚度、支承条件、表面粗糙度之间的关系。     

Damage detection by mode shape squares extracted from a passing vehicle

The success of damage detection heavily depends on the quality of damage features, such as mode shapes and power mode shapes, etc. However, these features are usually difficult and inconvenient to be accurately obtained in practice. To solve this problem, this paper develops a simple method to approximately extract structural mode shape squares from the acceleration of a passing tapping “vehicle”, which serves as a “message carrier” of the dynamic properties of the structure. Based on the approximately obtained mode shape square, a new damage index is proposed to improve the sensitivity to damage. Numerical simulations and simple experiments demonstrate the validity of the proposed method. Compared with traditional methods, it is easier to be implemented and more accurate in noisy environment, because it requires neither pre-installing many sensors on the structure, nor solving eigenvector or singular value problems and uses only the information of point impedance. In addition, the density of measurement points can be flexibly adjusted since the tapping vehicle scans the structure continuously.     

一种高分子粘结炸药代用材料的微观结构及损伤演化的研究

 利用扫描电子显微镜及加载系统，观察测定了一种代号为D-90033的高分子炸药替代品的微观结构及压缩性能。电镜下观察到该材料的两种主要组分，一种呈粒状结构，另一种是片层结构。同时还观察到在单向压缩荷载作用下该材料的主要损伤与破坏机制是沿两相边界产生并扩展的纵向裂纹。     

Damage to a Multilayer Woven Composite by Low-Velocity Indentation with a Rigid Spherical Indenter

The results of experimental studies of damage to a layer of a woven composite by pressing steel spherical indenters are presented. The effect of the indenter-curvature radius on the structure of the localdamage area of the composite and the effect of the local damage on the strength of initially equistrength composites under tension along the principal directions of layer reinforcement are determined.     

Damage rate experiments inAuIn

In stage III of Au divacancies are thermally mobilized at lower temperatures than monovacancies. Dependent on the temperature, the formation of In-vacancy complexes is studied by PAC during damage rate experiments. The differences between H⁺- and Au⁺⁺- irradiation demonstrate the athermal formation of divacancies during low temperature irradiations.     

Damage evaluation of reinforced concrete frame based on a combined fiber beam model

In order to analyze and simulate the impact collapse or seismic response of the reinforced concrete(RC)structures,a combined fiber beam model is proposed by dividing the cross section of RC beam into concrete fiber and steel fiber.The stress-strain relationship of concrete fiber is based on a model proposed by concrete codes for concrete structures.The stress-strain behavior of steel fiber is based on a model suggested by others.These constitutive models are implemented into a general finite element program ABAQUS through the user defined subroutines to provide effective computational tools for the inelastic analysis of RC frame structures.The fiber model proposed in this paper is validated by comparing with experiment data of the RC column under cyclical lateral loading.The damage evolution of a three-dimension frame subjected to impact loading is also investigated.     

Fatigue Life Prediction of a Rubber Mount Based on the Continuum Damage Mechanics

Abstract

Failure analysis and fatigue life prediction are important steps in the design procedure of industrial products to assure the safety and reliability of their components. A new methodology to predict the fatigue life of a rubber mount based on the continuum damage mechanics is proposed in this study. The hyperelastic constitutive model of the natural rubber material in the mount was fitted using the three parameter Mooney-Rivlin model. A damage variable was introduced and the evolution function of cumulative damage in the rubber material was derived. The parameters in the damage function were acquired based on uniaxial tensile tests and fatigue life tests of the natural rubber specimens. Then the finite element analysis (FEA) models of the rubber mount for loads in the X and Y directions were established and the strain contours and the maximum principal strains of the rubber mount under various loads were calculated. The maximum principal strain was used as the fatigue parameter, which was substituted into the natural rubber’s fatigue life damage function to predict the fatigue life of the rubber mount. Finally, the fatigue lives of the rubber mount under various loads were measured on a fatigue test rig to validate the accuracy of the fatigue life prediction method. The test results indicated that the fatigue lives predicted agreed fairly well with the test results and the fatigue prediction method should be applicable to both rubber and other types of components.     

Damage detection of cracked thick rotating blades by a spatial wavelet based approach

This paper presents a technique for blade damage detection based on spatial wavelet analysis. The wavelet transform is used to analyze spatially distributed signals (e.g. mode shape) of cracked thick rotating blades. First, a finite element model is applied to the vibration of a thick rotating blade with a single edge crack. The effects of transverse shear deformation and rotatory inertia are taken into account. Then the mode shapes of the cracked rotating blade are analyzed by wavelet transformation. The effects of crack locations and sizes on the wavelet coefficients are studied. It is found that the distributions of the wavelet coefficients can identify the crack position of the rotating blades by showing a peak at the position of the crack. Then the signals are analyzed by wavelet transform. It is found that the distributions of the wavelet coefficients can identify the crack position. Assumed measurement errors are added to nth mode shape for evaluating the effect of measurement errors on the capability of detecting crack position. The moving average method is used to process the data with assumed measurement errors. The crack positions can also be identified when there exist assumed measurement errors.     

Damage Spreading in the Ising Model with a Special Metropolis Dynamics Approach

The time evolution of the Hamming distance (damage spreading) for the S=1/2 and S=1 Ising models on the square lattice is performed with a special metropolis dynamics algorithm. Two distinct regimes are observed according to the temperature range for both models: a low-temperature one where the distance in the long-time limit is finite and seems not to depend on the initial distance and the system size; a high-temperature one where the distance vanishes in the long-time limit. Using the finite size scaling method, the dynamical phase transition (damage spreading transition) temperature is obtained as T_c≌1.675±0.025 for the S=1 Ising model.     

砷化镓光导开关的损伤形貌研究北大核心CSCD

制作了同面型砷化镓光导开关,并测试了其导通性能。在偏置电压8 kV、激光能量10 mJ、重复频率10 Hz的条件下,研究了光导开关触发104次后器件表面的损伤形貌。利用激光扫描共聚焦显微镜,对电极边缘及电极间的损伤形貌进行分析,研究发现阳极边缘由于热积累形成热损伤,而阴极边缘的热损伤来源于热应力,并对电极间损伤形貌进行细致表征及分类。     

激光引起玻璃表面的破坏

探讨了高功率激光对玻璃表面的破坏。测量了在２００ｐｓ激光正入射照射下Ｋ８玻璃的破坏阈值。解释了样品输入面和输出面破坏阈值不同的原因。     

Numerical Analysis of Damage Thermo-Mechanical Models

In this paper, we present numerical computational methods for solving the fracture problem in brittle and ductile materials with no prior knowledge of the topology of crack path. Moreover, these methods are capable of modeling the crack initiation. We perform numerical simulations of pieces of brittle material based on global approach and taken into account the thermal effect in crack propagation. On the other hand, we alsopropose a numerical method for solving the fracture problem in a ductile material based on elements deletion method and also using thermo-mechanical behavior and damage laws. In order to achieve the last purpose, we simulate the orthogonal cutting process.