Law of continuous damage parameter for non-ageing materials

The paper describes an experimental and theoretical study of continuous damage parameter. The results of tests of concrete elements are presented in this work. (The eight-ageing concrete may be treated as non-ageing material). The experimental results are used to formulate relation between continuous damage parameter and net stress. Proposed relation may be used for next study of damage material problems.     

A review on the law of continuous damage parameter for non-ageing materials

This paper derives the law of continuous damage parameter for non-ageing materials in the various loading programs. Compared with Piechnik and Pachla's work [5], the results obtained in this paper is more accurate in theory and simpler in evaluation.     

E1 超声造影剂的非线性参量研究

近年来对超声造影剂的研究兴趣日趋增加是由于它有可能改进超声临床诊断的效果。含有微气泡的液体可用作有效的超声造影剂。液体中气泡的存在可提高液体的非线性参量值。本文用检测二次谐波的方法实验上测定了５种超声造影剂的非线性参量：四种含气泡的液体（声振后）和半乳糖Ｅｃｈｏｖｉｓｔ３００。结果表明，含有微气泡的液体具有非常大的非线性参量值。对这种高非线性值的现象文中进行了可能的解释和讨论     

考虑剪切非线性影响的复合材料连续损伤模型及损伤参数识别

在复合材料正交各向异性连续损伤力学的基础上,引入由应变描述的连续综合变量,损伤演化方案采用综合变量的指数函数。考虑复合材料剪切非线性,通过非线性损伤因子在全局损伤出现之前将其引入本构方程。编写了VUMAT实施损伤模型,介绍连续损伤模型中材料参数的取值方法。对无法通过试验获得的损伤参数,采用遗传算法原理,定义个体适应度为试验及模拟载荷-位移曲线误差,通过编写MATLAB程序调用ABAQUS有限元模型实施参数反演方法。选择了常用铺层结构的复合材料带孔层合板进行仿真参数识别分析,验证了基于遗传算法参数识别方法的可行性。     

Non-local modelling of cyclic thermal shock damage including parameter estimation

In this paper, rate dependent evolution laws are identified and characterized to model the mechanical (elasticity-based) and thermal damage occurring in coarse grain refractory material subject to cyclic thermal shock. The interacting mechanisms for elastic deformation driven damage induced by temperature gradients and thermal damage induced by isotropic thermal expansion are combined and represented by a single variable for the total damage. The constitutive model includes the shielding of micro-structural thermal damage by the non-local elasticity-based damage developed at the macroscopic and microscopic scale. Quasi-stationary thermal experiments are used to identify the parameters used in the evolution law for thermal damage. The remaining model parameters, including a micro-structural length scale, are quantified by inverse modelling of cyclic thermal shock experiments. Longitudinal wave propagation measurements through damaged material are simulated, enabling the identification on the basis of the first and second thermal shock cycle. A third thermal shock cycle enabled the evaluation of the quality of the obtained parameter set. The set-up of the thermal shock experiments has been optimized through a parameter identifiability analysis. The damage evolution in three consecutive thermal shock cycles is investigated numerically with the optimized model.     

Size effect and continuous damage in cementitious materials

The dependence between the mechanical properties of concrete structures and their sizes is a problem addressed in this paper. Two types of size effect are distinguished: the first one is probabilistic and is related to random distributions of defects in a volume of material; the second one is purely deterministic and is related to fracture propagation in brittle heterogeneous media. These two aspects are combined in a continuous damage model. The initiation of damage is probabilistic and the evolution of damage is nonlocal. Comparisons with experiments on notched and unnotched bending beams show that the model provides a realistic prediction of the various size effects.     

Dugdale-crack in a material with continuous damage formation

A sheet containing a crack and loaded in Mode I has been studied with a one-dimensional method according to Dugdale. The material is assumed to exhibit time-independent continuous damage when loaded. The damage affects the stress in the narrow region ahead of the crack, which corresponds to the Dugdale zone. The extent of the zone is calculated. The damage at the zone boundary is found to have a great influence on the zone length.     

A continuous damage approach to the fatigue process

The fatigue process is analyzed theoretically by studying the interaction between a macroscopic crack and continuously distributed microdamage near the crack-tips. A mode I loading case is studied, using a Dugdale crack model. The results show good agreement with Paris' law for fatigue crack propagation with an exponent approximately equal to 4. The model also predicts a finite fatigue lifetime in the sense that the crack growth rate increases without limit after a finite number of load cycles.     

Measurement of the beam-beam parameter by exciting coherent betatron oscillation

Four coherent betatron oscillation modes induced by the beam-beam interaction we observed in the TRISTAN Main Ring (MR) during two e⁺ and two e⁻ bunches colliding operation. These modes are extracted using a phase mixing technique and used for measuring beam-beam parameters. The luminosity, the coupling coefficient and the emittance are estimated from the observation. The emittance agrees with the expected value to within 15% accuracy.     

Computerized product process: Measurement and continuous improvement

Product development has until recently been considered pure art instead of being a controllable process. However, the current competitive environment has forced companies to take a closer look in the way new products are being developed. A key element in this assessment is the development of a set of metrics, which describe the whole product development process. This article explores the data-based opportunities for continuous improvement in the product development process emerging alongside the increasing utilization of networked Information Technology (IT) applications. Based on data from information systems in the case-study companies, three different product process visualizations are presented. Each visualization is discussed both from the viewpoint of its explanatory power as well as its limitations.The results of the case-studies clearly indicate that the computerization of the engineering and design processes is generating new ways of measuring, understanding and improving product development. The appropriate measures combined with open communication and a learning environment can be used to create a cycle of continually improving the product development process.     

Measurement of the optical damage threshold in fused quartz

The damage thresholds of five different types of quartz glass used for the production of spectroscopic cuvettes for liquids were determined with single temporal and spatial mode nanosecond pulses at 532 nm. One of the glasses had a damage threshold of ?420 J/cm(2), which was more than twice that of the other glasses.     

应用MR阻尼器的连续梁桥地震损伤控制方法

基于地震作用下连续梁桥的损伤破坏机理,利用MR阻尼器控制元件,建立了基于桥墩广义水平刚度比的阻尼器出力方案,提出了连续梁桥的非线性地震损伤控制方法。对某一联三跨连续梁桥进行地震损伤控制研究,采用IDA(Increasing Dynamic Analysis)方法对控制前后桥梁结构进行损伤分析,结果表明所提出的控制方法可以有效降低桥梁损伤,并使桥墩损伤趋于均匀,显著提高桥梁的抗震性能;对采用不同控制方案和不同设计传递系数的桥梁进行地震损伤分析,结果表明半主动控制方案对墩梁残余位移和桥墩损伤的控制效果优于PON(Passive On)控制,并且设计传递系数对控制效果影响较大,需合理选用。     

Measurement of small angle fiber misalignments in continuous fiber composites

In aligned, continuous fiber composites the fibers actually wander with small angular misalignments about the mean direction. These misalignments are suspected of having a significant influence on several mechanical properties, such as longitudinal compression strength and tensile modulus. A technique is presented for measuring the volume fraction distribution of fiber misalignment angle in the range of ±10°, with an estimated resolution of ±0·25°. The method can provide a full bivariate distribution, which includes both in-plane and out-of-plane misalignments. Data from a carbon fiber composite, APC-2, are given as an illustration. Misalignment distributions for prepreg, a 0/90 laminate, and a unidirectional laminate are given. It is found that the distribution in the prepreg is axially symmetric, but changes upon laminations, the changes depending on stacking sequence. In this particular material most of the fibers are found to lie within ±3° of the mean fiber direction. Distribution standard deviations range from 0·693 to 1·936 degrees.     

A continuous damage fracture model to predict formability of sheet metal

A continuous damage fracture model, which consists of a fracture criterion and a continuum damage constitutive law was proposed in this paper to calculate formability of sheet metal. In this model, an extension of the McClintock void growth model was selected as the fracture criterion to be incorporated with a coupled damage‐plasticity Gurson‐type constitutive law. Also, by introducing a Lode angle dependent parameter to define the loading asymmetry condition, the shear effect was phenomenologically taken into account. The proposed fracture model was implemented in user defined material subroutines in ABAQUS. The model was calibrated and correlated by the uniaxial tension, shear and notched specimens tests. Application of the fracture criterion for the Limit dome height tests was discussed and the simulation results were compared with the experimental data.     

Comparison of Bayesian methods on parameter identification for a viscoplastic model with damage

The state of materials and accordingly the properties of structures are changing over the period of use, which may influence the reliability and quality of the structure during its life-time. Therefore, identification of the model parameters of the system is a topic which has attracted attention in the content of structural health monitoring. The parameters of a constitutive model are usually identified by minimization of the difference between model response and experimental data. However, the measurement errors and differences in the specimens lead to deviations in the determined parameters. In this article, the focus is on the identification of material parameters of a viscoplastic damaging material using a stochastic simulation technique to generate artificial data which exhibit the same stochastic behavior as experimental data. It is proposed to use Bayesian inverse methods for parameter identification and therefore the model and damage parameters are identified by applying the Transitional Markov Chain Monte Carlo Method (TMCMC) and Gauss–Markov–Kalman filter (GMKF) approach. Identified parameters by using these two Bayesian approaches are compared with the true parameters in the simulation and with each other, and the efficiency of the identification methods is discussed. The aim of this study is to observe which one of the mentioned methods is more suitable and efficient to identify the model and damage parameters of a material model, as a highly non-linear model, using a limited surface displacement measurement vector and see how much information is indeed needed to estimate the parameters accurately.     

A new damage parameter for fatigue life predictions under local strain analysis

A new damage parameter is proposed for fatigue life prediction using a local stress-strain approach. This parameter has a physical energy basis, and makes it possible to obtain the same accuracy as, and better life assessments than, the well-known Smith et al parameter using significantly less calculation time for load history treatment. Comparisons of life predictions obtained using the proposed parameter with experimental results and other predictions are presented.