岩石爆破分形损伤模型研究

在Ｋｕｓ和Ｔｈｏｒｎｅ等人研究基础上，利用分形理论及应用成果提出了一种新的岩石爆破损伤模型。新模型将岩体中各种结构弱面视为初始损伤，并将其分形维数作为岩石性质的主要参量，用损伤能量耗散率及与分形维数的关系表征爆破过程中的岩石损伤演化规律，从而弥补了现有模型未考虑初始损伤影响和将损伤演化归结为体积应变函数的不足。还通过模拟试验等手段验证了新模型的如上观点。     

HOMOTOPY CONTINUATION ALGORITHM FOR STRUCTURAL DAMAGE IDENTIFICATION

I. INTRODUCTIONStructural damages due to the loss of sti?ness such as crack, localization bulking have remarkablein?uences on the physical properties of structure such as deformation, stress, frequency and modelshape. So the change of these properties can be used to identify the damage location and degree ofstructures. The damage identification techniques based on these properties’ changes have attractedmuch attention in recent years, and many approaches have been developed[1??5].Nowaday…     

基于小波包变换的梁式结构损伤定位方法

本文针对梁式结构,基于小波包变换理论,提出一种新的损伤定位方法。该方法利用小波包变换将结构的响应分解到不同的模态,引入曲率公式定义了新的小波能量指标,使得能量指标对损伤位置更加敏感。根据工程实际,构造了对应于结构区域的损伤指标。利用D-S证据理论对得到的各阶损伤指标进行数据融合,从而优化了识别结果。通过数值模拟和实验,对新提出的方法进行了验证,结果表明该方法有效,并可应用于工程实际。     

基于Ottosen本构关系的混凝土三维损伤模型

提出基于混凝土已有本构模型建立混凝土三维损伤模型的方法，该方法无需再进行新的参数标定，计算损伤不必通过对损伤演化方程的积分获得。基于Ottosen本构模型建立了相应的损伤模型，就损伤参量和Ottosen非线性指标的不同选取方式，对典型比例加载情形的全过程进行损伤分析，发现基于刚度下降和基于变形能力损失的两种不同损伤描述具有互补性，非线性指标采用比例增大法计算较为简单合理。     

Strength of damaged polycarbonate after fatigue

A fatigue damage model is proposed to establish a predictive formula for the fatigue service life of polycarbonate (PC) materials. A damage variable is introduced in terms of remaining fracture strain, and a new fatigue damage evolution relation is derived to characterize the extent of fatigue damage after a certain number of loading cycles. Fatigue tests were conducted to construct the stress amplitude versus the fatigue life curve. After different numbers of cycles of fatigue, the new damage variable for PC materials was measured by pulling damaged specimens to fracture under monotonic loading. Experimental results on damage evolution and fatigue life have a good agreement with those predicted by the proposed damage model.     

应力波衰减基础上的岩石爆破损伤模型

在TCK损伤模型基础上 ,考虑岩石冲击损伤过程的声波测试衰减规律 ,构造新的岩石爆破损伤模型。将该模型装进LS DYNA3D动态有限元程序 ,通过岩石冲击损伤实验验证该程序的计算结果 ,并用新模型实现了岩石台阶爆破数值计算。     

基于微态方法的耦合韧性损伤的弹塑性本构模型

基于广义连续介质力学提出了一个热力学一致性的耦合微态韧性损伤的弹塑性本构模型。该模型遵循Forest的微态方法,在有限变形中提出引入额外的微态损伤因子及其一阶梯度以考虑材料的内部特征尺度。通过广义虚功原理得到了微态损伤的补充控制方程,对亥姆霍兹自由能进行扩展,得到了新的包含微态损伤变量的损伤能量释放率,在微态损伤的正则化作用下,采用隐式迭代更新局部损伤和应力等状态变量。基于Galerkin加权余量法,推导了以传统位移和微态损伤为基本未知量的有限元列式。利用该数值模型,对DP1000材料的单向拉伸实验和十字形零件的冲压实验进行了应变局部化与材料断裂的有限元分析。结果表明,该微态弹塑性损伤模型可以得到一致的有限元模拟响应曲线并收敛到实验曲线,从而避免发生网格依赖性问题。     

绝热剪切损伤和破坏的数值模拟研究

绝热剪切破坏是冲击载荷作用下金属材料中经常出现的一种重要破坏模式,尽管已经在实验中观察到了绝热剪切带内部的损伤现象,但是在理论和计算模型中往往还只是考虑它的热软化效应,对与之伴随的损伤破坏效应却鲜有讨论．该文在前人实验的基础上,提出了一个适用于绝热剪切带内部微孔洞损伤发展的演化方程,并在本构方程中同时考虑了温度和损伤对材料的影响,成功地模拟出了绝热剪切带的热软化效应和损伤破坏效应．     

多轴非比例加载低周疲劳寿命预测方法的研究

在分析多轴损伤临界面上的能量变化特性的基础上,提出一种基于临界平面方法的多轴疲劳损伤参量,该损伤参量将表征附加强化的非比例度作为摩擦系数引入其中,利用线性累计损伤准则建立了该损伤参量最大值和疲劳循环周次的关系,进而获得一种预测多轴非比例低周疲劳寿命的方法。经试验验证,结果是令人满意的。     

航空发动机涡轮盘裂纹萌生寿命的估算方法

针对航空发动机涡轮盘裂纹萌生寿命的估算问题，给出一个全新的损伤参量。该损伤参量结合了分析多轴疲劳的临界面方法，“应力功”的概念和疲劳破坏的微观机制。依据该损伤参量，利用有限元程序和自编程序计算得出损伤参量和疲劳循环次数的关系，建立以这一损伤参量为基础的疲劳损伤累积模型，进而估算涡轮盘裂纹萌生寿命。     

Damage Assessment of Reinforced Concrete Structures Using Fractal Analysis of Residual Crack Patterns

Currently, assessing the performance and safety of reinforced concrete structures relies on routine-based visual inspection (VI). Cracks width measurements are commonly used as a convenient indicator of damage; however other factors, such as distribution and pattern of the cracks should be considered equally important in measuring the extent of damage present in the structure. As a result, condition assessed by VI is subjective in nature and depends on the experience, knowledge, expertise, and judgment of the inspector carrying out the assessment. A new approach based on the fractal analysis of residual crack patterns is proposed in this paper to assess the structural integrity of reinforced concrete elements. A new damage index is presented to quantitatively perform a damage classification. The methodology is validated through experimental studies on two large-scale reinforced concrete shear walls subjected to a displacement controlled reversed cyclic loading. Damage grades are also identified based on width of cracks and proposed damage index (DI). The results demonstrate a more accurate estimation of damage grades using DI. Furthermore, it is demonstrated that the DI can estimate the relative stiffness loss of the specimens with acceptable accuracy.     

Multidimensional Damage Identification Based on Phase Space Warping: An Experimental Study

A multidimensional damage identification scheme developed in previous work is modified and investigated experimentally. An experimental apparatus consists of a driven two-well magneto-elastic oscillator, where a cantilever beam vibrates in a magnetic potential field perturbed by two electromagnets. These electromagnets are activated by a computer controlled power supply and their terminal voltages are considered a two-dimensional damage variable. The effect of total change in the supply voltage of the electromagnets is approximately 4% shift in the experimentally measured natural frequencies of small oscillations in each well of the potential. Experimental runs are started in a nominally chaotic regime. The battery voltages are altered on specific trajectories in the damage (voltage) phase space. Damage identification is accomplished based on the elastic vibration data collected using laser vibrometers and a accelerometer. The phase space warping based damage tracking feature vectors are estimated using a new phase space partitioning scheme. The damage identification is achieved by applying smooth orthogonal decomposition to the obtained statistics. The effect of the data record size on the quality of reconstructed damage trajectory is investigated in a series of experiments. It is also demonstrated that the new partitioning scheme considerably improves signal-to-noise ration of the identified damage states.     

基于构型力内变量的界面损伤问题研究

本文基于材料构型力的基本理论和损伤力学中含有内变量的热力学框架,提出了新的损伤变量定义方式,为研究界面损伤问题提供了一种新思路。首先,基于双相弹性体的能量分析,给出界面材料构型力表达式,通过构型力的离散化方法,实现了其在有限元中的数值计算。其次,定义构型力为界面损伤内变量,进而提出一种新的损伤演化模型,并采用刚度劣化的方法,对该界面损伤模型进行数值实现。最后,通过对复合材料界面损伤问题（有裂纹或无裂纹）进行数值模拟,分析了其界面损伤发展趋势,探讨了此模型的合理性和优越性。基于构型力内变量的界面损伤模型,可为研究复合材料的界面损伤失效问题提供一种普适性的方法。     

一个新的普遍形式的局部损伤断裂准则

利用损伤函数概念，建立了一个普遍形式的局部断裂准则。该准则考虑了局掊应力，应变和损伤历史对断裂的影响，根据损伤力学理选取了一个新的连续损伤函数，从而导出一个新的连续损伤断裂准则。新的临界断裂参数ＷＤＣ，具有明显的物理意义，且易通过试验测得，是一个不依赖于应力状态的材料九。文中还从细观力学理论和有关的试验资料出发，选取了相应的损伤函数，再现了前人的细观力学准则和经验准则。     

Assessment of structural damage using natural frequency changes

The present paper develops a new method for damage localization and severity estimation based on the employment of modal strain energy. This method is able to determine the damage locations and estimate their severities, requiring only the information about the changes of a few lower natural frequencies. First, a damage quantification method is formulated and iterative approach is adopted for determining the damage extent. Then a damage localization algorithm is proposed, in which a damage indicator is formulated where unity value corresponds to the true damage scenario. Finally, numerical studies and model tests are conducted to demonstrate the effectiveness of the developed algorithm.     

Damage detection by system identification. An application of the generalized singular value decomposition

Summary A new method of damage detection is introduced. The mathematical formulation of the dynamical system is based on a state-space model. The physical system is measured and described by parameters of the state-space realization, which are estimated by the generalized singular value decomposition. Influence coefficients, evaluated from the parameters of the mathematical model, allow for damage detection. The suitability of the new method is demonstrated by an experimental model.     

A new free energy for plastic damage analysis

This work presents a new free energy for the ductile plastic damage analysis. The derivation here is based on the ductile plastic damage model proposed by Lemaitre and the examination of the plastic strain of a damaged material. The result given here can be used for the damage evolution law derived from the potential of dissipation.     

Investigation of the damage variable basic issues in continuum damage and healing mechanics

Consistent mathematics and mechanics are used here to properly interpret the damage variable within the confines of the concept of reduced area due to damage. In this work basic issues are investigated for the damage variable in conjunction with continuum damage and healing mechanics. First, the issue of the additive decomposition of the damage variable into damage due to voids and damage due to cracks in continuum damage mechanics is discussed. The accurate decomposition is shown to be non-additive and involves a term due to the interaction of cracks and voids. It is shown also that the additive decomposition can only be used for the special case of small damage. Furthermore, a new decomposition is derived for the evolution of the damage variable. The second issue to be discussed is the new concept of independent and dependent damage processes. For this purpose, exact expressions for the two types of damage processes are presented. The third issue addressed is the concept of healing processes occurring in series and in parallel. In this regard, systematically and consistently, the equations of healing processes occurring either consecutively or simultaneously are discussed. This is followed by introducing the new concept of small healing in damaged materials. Simplified equations that apply when healing effects are small are shown. Finally, some interesting and special damage processes using a systematic and original formulation are presented.