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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. 相似文献
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弹脆性材料的损伤本构关系及应用 总被引:8,自引:0,他引:8
本文根据连续损伤力学方法,对弹脆性材料损伤的力学响应进行一般分析。理论分析中,材料与损伤都是各向异性的。还导出了计算损伤张量、有效弹性张量、真实应力张量以及损伤能耗率张量的实用表达式。 相似文献
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A DAMAGE MECHANICS MODEL FOR FATIGUE LIFE PREDICTION OF FIBER REINFORCED POLYMER COMPOSITE LAMINA 总被引:2,自引:0,他引:2
A damage mechanics fatigue life prediction model for the fiber reinforced polymer lamina is established. The stiffness matrix of the lamina is derived by elastic constants of fiber and matrix. Two independent damage degrees of fiber and matrix are introduced to establish constitutive relations with damage. The damage driving forces and damage evolution equations for fiber and matrix are derived respectively. Fatigue tests on 0°and 90°unidirectional laminates are conducted respectively to identify parameters in damage evolution equations of fiber and matrix. The failure criterion of the lamina is presented. Finally, the life prediction model for lamina is proposed. 相似文献
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基于提高频率灵敏度的结构损伤统计识别方法 总被引:1,自引:0,他引:1
提出了一种基于反馈控制结构动力特性的损伤统计识别方法。该方法采用基于独立模态空间的反馈控制,有目的地配置闭环系统的极点,根据损伤前后闭环系统的特征值构造损伤指标。采用假设检验判断损伤是否发生,并剔除特征量中损伤程度的影响,采用统计模式识别方法识别损伤位置。Benchmark结构的数值算例表明,本文提出的损伤识别方法能够较显著地提高模态频率对刚度变化的灵敏度,准确有效地检测在噪声环境下结构小损伤是否发生以及识别损伤位置。 相似文献
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结构损伤智能诊断研究进展 总被引:1,自引:2,他引:1
综述结构损伤诊断研究的进展,主要讨论了人工神经网络在结构损伤识别中的应用,介绍了结构检测技术的发展和基于人工神经网络的诊断专家系统,最后指出了结构损伤诊断研究的发展趋势。 相似文献
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《International Journal of Solids and Structures》1999,36(12):1757-1779
Structural deterioration often occurs without visible manifestation. Continuum damage mechanics (CDM) enables one to predict the state of damage in such situations and to estimate residual strength⧹service life of an existing structure. The accumulation of damage is modeled as a dissipative process that is governed by the laws of thermodynamics. The rate of dissipation in a deformable system, R, depends on the work done on the system and the evolution of the Helmholtz free energy, Ψ. Under certain thermodynamical conditions, the first variation of Ψ vanishes, and partial differential equations for damage growth in R prior to damage localization are obtained. This approach obviates the need of introducing arbitrary dissipation potential functions with undetermined constants in the damage growth equations. All solutions use only readily available material parameters. Assuming that damage occurs isotropically under uniaxial loading, closed-form solutions are obtained for ductile damage as a function of plastic strain, for creep damage as a function of time and for fatigue damage as function of number of cycles. The models are validated with published laboratory data. 相似文献
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《International Journal of Solids and Structures》2003,40(9):2195-2213
The line crack-like damage generated within a small material volume may change the material behavior of the material volume from initially isotropic to effectively orthotropic, depending on damage orientation. Thus, the change in material behavior can be used to identify the orientation of line crack-like damage with respect to the reference coordinates. Motivated from this observation, first the equation of motion is derived for the thin uniform plate with line crack-like local damages. The locations and severities of damages are characterized by using a damage distribution function, and a damaged small material volume is represented by the effective orthotropic elastic stiffnesses, which are derived in terms of damage orientation and size. Next, a new damage identification theory is developed to identify the orientations of local damages, in addition to their locations and severities, by using the frequency response functions measured from the damaged plate. Finally, the effects of damage orientation on the vibration responses of a plate are numerically investigated, and the numerically simulated damage identification tests are conducted to verify the present damage identification theory. 相似文献
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线性疲劳累积损伤准则适用性评估 总被引:3,自引:0,他引:3
本文将线性疲劳累积损伤理论分为3类:(1)等损伤线性疲劳累积损伤理论;(2)变损伤线性疲劳累积理论;(3)等损伤线性分阶段疲劳累积损伤理论.对每类理论分别从理论基础、材料常数、引入的参量及工程应用等方面进行分析,归纳出典型模型,并利用金属材料的两级谱、多级谱和随机谱试验数据进行了评估.最后,从理论基础和数据评估两方面进行综合评述,得出了不同类型的模型的适用范围和计算效果,对工程实践具有参考价值. 相似文献
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A general anisotropic damage theory of cracked laminates is formulated here. The deformation of composite laminates is composed
of matrix elastic strains, pseudo-elastic damage strains due to cracking and permanent damage strains due to interlaminar
slip. The surface of damage initiation is constructed according to the concept of linear elastic fracture mechanics for the
virgin material. After the initial damage, a pesudo-elastic damage can be used to describe the damage behaviour if interlaminar
slip is negligible. Damage evolution, load induced anisotropy and interlaminar intralaminar interaction for composite laminates
are examined; the latter can perturb the normality structure of damage strain rate. Explicit expressions are given for pseudo-elastic
(or secant) moduli of the damaging composite laminates, under a non-interacting assumption imposed on the cracks between different
families. 相似文献
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本文利用Mazars和Lemaitre提出的混凝土脆性损伤模型,求得了裂纹尖端应力、应变及损伤的局部解.对手Ⅲ型及不可压缩平面应变Ⅰ型裂纹,其尖端场的构造和理想塑性材料相类似.指出由于丧失了应力全连续条件,从而损伤边界不能由局部解定出. 相似文献
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Wavelet packet based damage identification of beam structures 总被引:3,自引:0,他引:3
Jian-Gang Han Wei-Xin Ren Zeng-Shou Sun 《International Journal of Solids and Structures》2005,42(26):6610-6627
Most of vibration-based damage detection methods require the modal properties that are obtained from measured signals through the system identification techniques. However, the modal properties such as natural frequencies and mode shapes are not such a good sensitive indication of structural damage. The wavelet packet transform (WPT) is a mathematical tool that has a special advantage over the traditional Fourier transform in analyzing non-stationary signals. It adopts redundant basis functions and hence can provide an arbitrary time-frequency resolution. In this study, a damage detection index called wavelet packet energy rate index (WPERI), is proposed for the damage detection of beam structures. The measured dynamic signals are decomposed into the wavelet packet components and the wavelet energy rate index is computed to indicate the structural damage. The proposed damage identification method is firstly illustrated with a simulated simply supported beam and the identified damage is satisfactory with assumed damage. Afterward, the method is applied to the tested steel beams with three damage scenarios in the laboratory. Despite the noise is present for real measurement data, the identified damage pattern is comparable with the tests. Both simulated and experimental studies demonstrated that the WPT-based energy rate index is a good candidate index that is sensitive to structural local damage. 相似文献
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《International Journal of Plasticity》2007,23(10-11):1826-1859
This work gives the thermodynamically consistent theoretical formulations and the numerical implementation of a plasticity model fully coupled with damage. The formulation of the elasto-plastic-damage behavior of materials is introduced here within a framework that uses functional forms of hardening internal state variables in both damage and plasticity. The damage is introduced through a damage mechanics framework and utilizes an anisotropic damage measure to quantify the reduction of the material stiffness. In deriving the constitutive model, a local yield surface is used to determine the occurrence of plasticity and a local damage surface is used to determine the occurrence of damage. Isotropic hardening and kinematic hardening are incorporated as state variables to describe the change of the yield surface. Additionally, a damage isotropic hardening is incorporated as a state variable to describe the change of the damage surface. The hardening conjugate forces (stress-like terms) are general nonlinear functions of their corresponding hardening state variables (strain-like terms) and can be defined based on the desired material behavior. Various exponential and power law functional forms are studied in this formulation. The paper discusses the general concept of using such functional forms. however, it does not address the relevant appropriateness of certain forms to solve different problems. The proposed work introduces a strong coupling between damage and plasticity by utilizing damage and plasticity flow rules that are dependent on both the plastic and damage potentials. However, in addition to that the coupling is further enhanced through the use of the functional forms of the hardening variables introduced in this formulation.The use of this formulation in solving boundary value problems will be presented in future work. The fully implicit backward Euler scheme is developed for this model to be solved in a Newton–Raphson solution procedure. 相似文献
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多轴随机载荷下的疲劳寿命估算方法 总被引:5,自引:0,他引:5
现代工业的发展使得更多的构件承受着复杂的载荷形式, 将单轴疲劳模型应用到多轴载荷情况已不能满足现代工业的设计要求, 多轴随机载荷下的疲劳寿命计算日益引起人们的重视. 多轴随机载荷的寿命预测中, 如何计算载荷循环次数是其基础,目前广泛使用的是雨流计数方法, 现在已能成功的应用于多轴载荷的情况. 累积的疲劳损伤分析在各种构件和结构的载荷历史中都起着重要的作用. 自从线性损伤律提出以来已发展了数十种损伤律, 变幅载荷引起的疲劳损伤可以由许多不同的累积损伤律来计算, 虽然发展了许多损伤模型, 由于问题的复杂性, 每个模型的应用范围也是随具体情况而定. 线性损伤律方法尽管有很多不足之处, 但在设计使用中仍占有重要的位置. 两载荷水平及模式下的损伤累积以及损伤与物理机制的关系在本文中也做了介绍. 针对近年来提出的描述多轴随机载荷下疲劳寿命估算方法进行了详细的评述, 对各模型的应用范围和预测能力进行了讨论, 并对今后的工作提出了建议. 相似文献
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《International Journal of Solids and Structures》2003,40(12):2957-2974
The present paper presents a model of damage coupled to wear. The damage model is based on a continuum model including the gradient of the damage variable. Such a model is non-local in the sense that the evolution of damage is governed by a boundary-value problem instead of a local evolution law. Thereby, the well-known mesh-dependency observed for local damage models is removed. Another feature is that the boundary conditions can be used to introduce couplings between bulk damage and processes at the boundary. In this work such a coupling is suggested between bulk damage and wear at the contact interface. The model is regarded as a first attempt to formulate a continuum damage model for studying crack initiation in fretting fatigue.The model is given within a thermodynamic framework, where it is assured that the principles of thermodynamics are satisfied. Furthermore, two variational formulations of the full initial boundary value problem, serving as starting points for finite element discretization, are presented. Finally, preliminary numerical results for a simple one-dimensional example are presented and discussed. It is qualitatively shown how the evolution of damage may influence the wear behaviour and how damage may be initiated by the wear process. 相似文献
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Miao Zhang · Qing-Chun Meng · Xing Zhang · Wei-Ping Hu Division School of Aeronautic Science Engineering Beihang University Beijing China 《Acta Mechanica Sinica》2011,27(3):416-425
Based on the theory of continuum damage mechanics,a bi-variable damage mechanics model is developed,which,according to thermodynamics,is accessible to derivation of damage driving force,damage evolution equation and damage evolution criteria. Furthermore,damage evolution equations of time rate are established by the generalized Drucker’s postulate. The damage evolution equation of cycle rate is obtained by integrating the time damage evolution equations,and the fatigue life prediction method for smooth specimens under repeated loading with constant strain amplitude is constructed. Likewise,for notched specimens under the repeated loading with constant strain amplitude,the fatigue life prediction method is obtained on the ground of the theory of conservative integral in damage mechanics. Thus,the material parameters in the damage evolution equation can be obtained by reference to the fatigue test results of standard specimens with stress concentration factor equal to 1,2 and 3. 相似文献