龙滩碾压混凝土坝随机损伤力学分析的模糊自适应有限元研究

在分析了损伤、概率、模糊隶属度在[0,1]区间内度量协调一致性基础上,为了更深刻理解和更本质地描述与研究损伤力学提出发展模糊随机损伤力学的观念。探讨损伤变量广义不确定性实质,进而构造并解释三类损伤变量的模糊性态,提出对应的模糊映射分布形式,即降半分布、"秋千"分布和组合"秋千"分布,三者可以分别探讨不同形式下随机损伤的模糊演变过程,实现了随机损伤变量的模糊化自适应生成与构建。分析并论证损伤广义概率特性,根据扩张原理及随机损伤变量满足β概率分布的理论和定义,对模糊集上随机损伤变量的概率分布函数和概率密度函数积分进行修正,结合当量正态理论,将三类模糊随机损伤泛函引入本构方程完成模糊随机有限元可靠度与模糊随机损伤的同步分析,实现了损伤模型的清晰化过程。借助自主研制的模糊随机损伤有限元程序,对龙滩碾压混凝土坝进行三维模糊随机损伤场力学性态的分析与研究,从而把随机场参数的统计相关性、非正态分布性全面融入模糊随机损伤分析的模型中,把损伤变量的不确定性做了完善的延拓、将模糊和随机两种不确定因素合理有效地引入连续损伤力学的分析与建模中。该研究工作对非确定损伤力学研究及结构可靠度分析都提供了一定的参考价值。

岩石边坡模糊随机损伤可靠性研究

目的延拓非确定损伤理论研究以揭示损伤力学蕴涵的复杂机理.方法基于损伤、概率、模糊隶属度在[0,1]区间上协调一致性,提出了模糊随机损伤力学观念;构造解释了3类损伤变量模糊性态及对应模糊映射分布,即降半分布、"秋千"分布和组合"秋千"分布,实现了随机损伤变量模糊化自适应生成与构建;依据扩张原理及随机损伤变量满足β概率分布,对模糊集上随机损伤变量的CDF、PDF积分修正,结合当量正态理论,将三类模糊随机损伤泛函引入本构方程,完成了模糊随机有限元可靠度与模糊随机损伤同步分析.结果分析表明,基于全面统计评价的初始损伤场建立,避免了常规损伤力学分析中试验及模型构造的困难.结论借助可靠度理论所得的模糊随机损伤力学模型,可全面揭示复杂工程对象在损伤模糊演变过程中具有的随机变异本质,实现局部损伤发育与结构宏观可靠度的耦合分析.

基于模糊随机损伤力学的模糊自适应有限元分析

为延拓非确定损伤理论研究以揭示损伤力学本质,基于损伤、概率、模糊隶属度在[0,1]区间上协调一致性提出模糊随机损伤力学观念。构造解释了3类损伤变量模糊性态及对应模糊映射分布,即降半分布、"秋千"分布和组合"秋千"分布,实现了随机损伤变量模糊化自适应生成与构建。依据扩张原理及随机损伤变量满足β概率分布,对模糊集上随机损伤变量的CDF、PDF积分修正,结合当量正态理论,将3类模糊随机损伤泛函引入本构方程,完成模糊随机有限元可靠度与模糊随机损伤同步分析。用自主研制分析软件对龙滩碾压混凝土坝做三维模糊随机损伤场力学性态研究,由复杂随机场与模糊随机损伤分析的成功融合证明分析方法是适用的、可行的、必要的。

腹部多器官与单器官伤的损伤与救治情况比较

我院从1973年4月至1994年6月共收治各种损伤7591例。腹部损伤367例,其中腹部多器官伤124例,单器官伤243例。本文通过比较,重点讨论腹部多器官伤的临床特点和救治要点。 1 临床资料 1.1 腹部器官损伤数:本组1器官伤243例,2器官伤77例,3器官伤23例,4器官伤12例,5器官伤7例,6器官伤2例,7器官伤3例。本文所列腹部器官伤不包括腹壁软组织损伤、单纯性腹膜后血肿以及肠系膜和大网膜损伤。

A whole process damage constitutive model for layered sandstone under uniaxial compression based on Logistic function

Bedding structural planes significantly influence the mechanical properties and stability of engineering rock masses.This study conducts uniaxial compression tests on layered sandstone with various bedding angles(0°,15°,30°,45°,60°,75°and 90°)to explore the impact of bedding angle on the deformational mechanical response,failure mode,and damage evolution processes of rocks.It develops a damage model based on the Logistic equation derived from the modulus’s degradation considering the combined effect of the sandstone bedding dip angle and load.This model is employed to study the damage accumulation state and its evolution within the layered rock mass.This research also introduces a piecewise constitutive model that considers the initial compaction characteristics to simulate the whole deformation process of layered sandstone under uniaxial compression.The results revealed that as the bedding angle increases from 0°to 90°,the uniaxial compressive strength and elastic modulus of layered sandstone significantly decrease,slightly increase,and then decline again.The corresponding failure modes transition from splitting tensile failure to slipping shear failure and back to splitting tensile failure.As indicated by the modulus’s degradation,the damage characteristics can be categorized into four stages:initial no damage,damage initiation,damage acceleration,and damage deceleration termination.The theoretical damage model based on the Logistic equation effectively simulates and predicts the entire damage evolution process.Moreover,the theoretical constitutive model curves closely align with the actual stress−strain curves of layered sandstone under uniaxial compression.The introduced constitutive model is concise,with fewer parameters,a straightforward parameter determination process,and a clear physical interpretation.This study offers valuable insights into the theory of layered rock mechanics and holds implications for ensuring the safety of rock engineering.

全封闭舱内爆炸载荷作用下薄板变形研究

在内爆炸载荷作用下,舱室内部长时程准静态压力载荷会对结构极限变形产生重要影响,使得其结构响应与敞开环境空爆下的情况有较大区别。计算分析了方形薄板在内爆炸载荷作用下动态响应,基于薄板在冲击载荷作用下的变形规律,提出了用于评估结构在内爆炸载荷作用下极限变形的无量纲损伤数。该无量纲损伤数考虑了舱室体积、炸药能量、结构几何尺寸及屈服强度等因素对内爆炸载荷作用下结构变形响应特性的影响。薄板变形的分析结果表明,结构极限变形与板厚比和无量纲损伤数之间存在明显线性关系,可通过拟合获得舱内爆炸载荷作用下结构极限变形的快速预报经验公式。提出的无量纲损伤数考虑了板大变形响应过程中的中面膜力效应和板厚影响,更加适合于分析薄板在内爆炸载荷作用下的塑性大挠度变形值。

关于结构塑性动力失效若干问题的研究进展

重点分析常见工程结构元件（如梁、板、圆柱壳、圆环和夹层及复合材料结构）在强动短时载荷下塑性动力失效的研究方法、进展及尚待解决的问题，这些结构元件的失效模式及分析方法具有普遍意义，建议借用无量纲数──损伤数（ｄａｍａｇｅｎｕｍｂｅｒ）──来统一表征结构塑性动力失效的判据，最后以海洋平台和桁架为例简单介绍工程中复杂结构动力失效分析的情况。

传动装置齿轮耐久性台架试验方法研究

为了使履带车辆传动装置结构设计、试验校核更加符合车辆现场实际使用情况,结合履带车辆左输出轴齿轮样车测试扭矩载荷数据,提出了基于现场样车载荷测试的履带车辆传动装置耐久性旋转台架试验方法.结合车辆传动装置性能试验台架扭转加载特点,对左输出轴齿轮实测转速和扭矩载荷数据按挡位进行分类,然后利用损伤切片累计图法计算左输出轴齿轮累积损伤.根据试验样本数据与设计里程占比,对累积损伤进行相应比例的放大,同时,考虑到驾驶员之间的差异性,以适当的精度对累积损伤进行了外推,进而依据试验室台架模拟试验与现场实际试验损伤数等效的原理,计算出传动装置台架试验目标损伤数.分别在累积损伤分布图和转速幅值概率密度分布函数上确定台架所需加载的扭矩和转速.结果表明,该方法制定传动装置耐久性台架试验方案可行,能够反映现场实际使用条件.

NMR research on deterioration characteristics of microscopic structure of sandstones in freeze-thaw cycles

In order to study the deterioration characteristics of the microscopic structure of sandstones in freeze-thaw cycles, tests of180 freeze-thaw cycles were performed on sandstone specimens. The nuclear magnetic resonance （NMR） technique was applied tothe measurement of sandstone specimens and analysis of the magnetic resonance imaging. Then, the fractal theory was employed tocompute the fractal dimension values of pore development of rocks after different freeze-thaw cycles. The results show that the massand porosity of rocks grow with the increase of freeze-thaw cycles. According to the NMR T2 distribution of sandstones, the poresizes of rock specimens increase after 180 freeze-thaw cycles, especially that of the medium-sized and small-sized pores. The spatialdistribution of sandstone pores after freeze-thaw cycles has fractal features within certain range, and the fractal dimension ofsandstones tends to increase gradually.

Experimental Study on Damage Properties of Rocks Under Dynamic Loading

The damage properties of two types of rocks under dynamic loading are studied. The shock induced experiments are done using planar impact technique on the one? stage light gas gun, and the ultrasonic tests on the damaged rocks have been made by use of the ultrasonic pulse? transmission method. The shock induced damage of rock is related to the shock speed and the attenuation coefficient of sonic wave, and the latter reflects the damage degree in rock fairly well. The attenuation coefficient α can be used as main damage parameter for constructing damage model of rock under dynamic loading.

Fatigue reliability quantitative analysis of cement concrete for highway pavement under high stress ratio

In order to obtain the change law of the fatigue reliability of cement concrete for highway pavement under high stress ratios, first, the probability densities of monotonic random variables including concrete fatigue life are deduced. And then, the fatigue damage probability densities of the Miner and Chaboche-Zhao models are deduced. By virtue of laboratory fatigue test results, the fatigue damage probability density functions of the two models can be obtained, considering different stress ratios. Finally, substituting load cycles into them, the change law of cement concrete fatigue reliability about load cycles can be acquired. The results show that under the same stress ratio, with the increase in the load cycle, the fatigue reliability declines from almost 100% to 0% gradually. No matter under what stress ratio, during the initial stage of the load action, there is always a relatively stable phase for fatigue reliability. With the increase in the stress ratio, the stable phase gradually shortens and the load cycle corresponding to the reliability of 0% also decreases. In the descent phase of reliability, the higher the stress ratio is, the lower the concrete reliability is for the same load cycle. Besides, compared with the Chaboche-Zhao fatigue damage model, the Miner fatigue damage model is safer.

MINER RULE CONSIDERING FUZZINESS OF STRESS DAMAGE UNDER DIFFERENT LOAD SEQUENCES

Since the traditional Miner rule ignores the influence of the load sequence on the fatigue life, the fuzzy rules are used to analyze the fuzziness of the fatigue damage caused by the stress nearby the fatigue limit under different load sequences. The improved fuzzy Miner rule can reflect the influence of the load sequence on the fatigue life. Results of the example show that the prediction error can be reduced from 61.6% to 21.7%.

Freeze-thaw damage mechanism of elastic modulus of soil-rock mixtures at different confining pressures

As a frequently-used roadbed filler,soil-rock mixture is often in the environment of freeze-thaw cycles and different confining pressures.In order to study the freeze-thaw damage mechanism of elastic modulus of soil-rock mixtures at different confining pressures,the concept of meso-interfacial freeze-thaw damage coefficient is put forward and the meso-interfacial damage phenomenon of soil-rock mixtures caused by the freeze-thaw cycle environment is concerned;a double-inclusion embedded model for elastic modulus of soil-rock mixtures in freezing-thawing cycle is proposed.A large triaxial test was performed and the influences of confining pressure and experimental factors on elastic modulus of soil-rock mixtures were obtained,and then the accuracy of the double-inclusion embedded model to predict the elastic modulus of soil-rock mixtures in freezing-thawing cycle is verified.Experiment results showed that as to soil-rock mixtures,with the increase of confining pressure,the elastic modulus increases approximately linearly.The most crucial factors to affect the elastic modulus are rock content and compaction degree at the same confining pressure;the elastic modulus increases with the increase of rock content and compactness;as the number of freeze-thaw cycles increases,the freeze-thaw damage coefficient of meso-structural interface and the elastic modulus decrease.

Numerical Analysis of Structural Progressive Collapse to Blast Loads

After the progressive collapse of Ronan Point apartment in UK in 1968, intensive research effort had been spent on developing guidelines for design of new or strengthening the existing structures to prevent progressive collapse. However, only very few building design codes provide some rather general guidance, no detailed design requirement is given. Progressive collapse of the Alfred P. Murrah Federal building in Oklahoma City and the World Trade Centre (WTC) sparked again tremendous research interest on progressive collapse of structures. Recently, US Department of Defence (DoD) and US General Service Administration (GSA) issued guidelines for structure progressive collapse analysis. These two guidelines are most commonly used, but their accuracy is not known. This paper presents numerical analysis of progressive collapse of an example frame structure to blast loads. The DoD and GSA procedures are also used to analyse the same example structure. Numerical results are compared and discussed. The accuracy and the applicability of the two design guidelines are evaluated.

Identification of damage mode in AZ31 magnesium alloy under tension using acoustic emission

In order to characterize different damage modes, real-time detection of the tensile cracking process for AZ31 magnesium alloy was performed using acoustic emission （AE） technique. Results showed that elastic deformation, plastic deformation, microcracking, stable and unstable propagation occurred during crack damage. Four damage modes were determined using AE multiparameter analysis. Dislocation motion signals with amplitudes 〈70 dB and twinning signals with 70-100 dB were found. Microcrack signal energy was concentrated from 2400 aJ to 4100 aJ, mainly at a rise time of less than 800 gs. A stable crack propagation signal had high peak to counts in the 20 to 50 range, whereas its ring count was in the 20 to 2000 range. The average frequency of unstable propagation signals was approximately 100 kHz, with duration from 2000 gs to 10s gs. The damage mechanisms and AE resources from different crack propagation steps were discussed. Various damage modes could be characterized by different AE signal parameters when they appeared simultaneously during crack propagation.

Mechanics of rib spalling of high coal walls under fully-mechanized mining

In order to solve the problem of rib spalling of high coal walls in fully-mechanized（HCWFM）mines,we used the principle of damage mechanics to analyze coal wall rib spalling.The results show that coal wall rib spalling is,to a certain degree,a macro-performance of the development of micro-cracks.We built a mechanical model to simulate the damage to the front of coal walls,carried out theoretical calculations of the damage parameters,analyzed the effect of mining height,original cracks,seam strength,horizontal stress,vertical displacement of the coal walls and other parameters on coal wall rib spalling, which conform well with the results of our field measurements and numerical simulation.The key to control coal wall rib spalling is to control the development of cracks in coal walls.Accelerating the speed of advancing the working face,improving the setting load of support and the horizontal force of the guard board,strengthening coal walls and other technical measures can effectively reduce the degree of damage to the coal walls and control coal wall rib spalling at HCWFM faces.

Numerical investigation of effect of eccentric decoupled charge structure on blasting-induced rock damage

Eccentric decoupling blasting is commonly used in underground excavation.Determination of perimeter hole parameters(such as the blasthole diameter,spacing,and burden)based on an eccentric charge structure is vital for achieving an excellent smooth blasting effect.In this paper,the Riedel-Hiermaier-Thoma(RHT)model was employed to study rock mass damage under smooth blasting.Firstly,the parameters of the RHT model were calibrated by using the existing SHPB experiment,which were then verified by the existing blasting experiment results.Secondly,the influence of different charge structures on the blasting effect was investigated using the RHT model.The simulation results indicated that eccentric charge blasting has an obvious pressure eccentricity effect.Finally,to improve the blasting effect,the smooth blasting parameters were optimized based on an eccentric charge structure.The overbreak and underbreak phenomena were effectively controlled,and a good blasting effect was achieved with the optimized blasting parameters.

Degradation mechanism of rock under impact loadings by integrated investigation on crack and damage development

Failure of rock under impact loadings involves complex micro-fracturing and progressive damage. Strength increase and splitting failure have been observed during dynamic tests of rock materials. However, the failure mechanism still remains unclear. In this work, based on laboratory tests, numerical simulations with the particle flow code(PFC) were carried out to reproduce the micro-fracturing process of granite specimens. Shear and tensile cracks were both recorded to investigate the failure mode of rocks under different loading conditions. At the same time, a dynamic damage model based on the Weibull distribution was established to predict the deformation and degradation behavior of specimens. It is found that micro-cracks play important roles in controlling the dynamic deformation and failure process of rock under impact loadings. The sharp increase in the number of cracks may be the reason for the strength increase of rock under high strain rates. Tensile cracks tend to be the key reason for splitting failure of specimens. Numerical simulation of crack propagation by PFC can give vivid description of the failure process. However, it is not enough for evaluation of material degradation. The dynamic damage model is able to predict the stress-strain relationship of specimens reasonably well, and can be used to explain the degradation of specimens under impact loadings at macro-scale. Crack and damage can describe material degradation at different scales and can be used together to reveal the failure mechanism of rocks.

State Representation Methodology （SRM） for Bridge Condition Assessment in SHM

This paper introduces a new concept of ＂State Representation Methodology （SRM）＂ which is a kind of bridge condition assessment method for structural health monitoring system （SHM）. There are many methods for system identification from the simplicity comparison of damage index to the complicated statistical pattern recognition algorithms in SHM. In these methods, modal analysis and parameters identification or many defined indices are common-used for extracting the dynamic or static characteristics of a system. However, there is a common problem： due to the complexity of a large size system with high-order nonlinear characteristics and severe environment interference, it is impossible to extract and quantify exactly these modal parameters or system parameters or indices as the feature vectors of a system in damage detection in an easy way. The SRM considered a more general theory for the non-parametric description of system state.

Modal Strain Energy Based Structural Damage Localization for Offshore Platform using Simulated and Measured Data

Modal strain energy based methods for damage detection have received much attention. However, most of published articles use numerical methods and some studies conduct modal tests with simple 1D or 2D structures to verify the damage detection algorithms. Only a few studies utilize modal testing data from 3D frame structures. Few studies conduct performance comparisons between two different modal strain energy based methods. The objective of this paper is to investigate and compare the effectiveness of a traditional modal strain energy method(Stubbs index) and a recently developed modal strain energy decomposition(MSED) method for damage localization, for such a purpose both simulated and measured data from an offshore platform model being used. Particularly, the mode shapes used in the damage localization are identified and synthesized from only two measurements of one damage scenario because of the limited number of sensors. The two methods were first briefly reviewed. Next, using a 3D offshore platform model, the damage detection algorithms were implemented with different levels of damage severities for both single damage and multiple damage cases. Finally, a physical model of an offshore steel platform was constructed for modal testing and for validating the applicability. Results indicate that the MSED method outperforms the Stubbs index method for structural damage detection.