Hashin Failure Theory Based Damage Assessment Methodology of Composite Tidal Turbine Blades and Implications for the Blade Design

A damage assessment methodology based on the Hashin failure theory for glass fiber reinforced polymer(GFRP)composite blade is proposed. The typical failure mechanisms including the fiber tension/compression and matrix tension/compression are considered to describe the damage behaviors. To give the flapwise and edgewise loading along the blade span, the Blade Element Momentum Theory(BEMT) is adopted. In conjunction with the hydrodynamic analysis, the structural analysis of the composite blade is cooperatively performed with the Hashin damage model. The damage characteristics of the composite blade, under normal and extreme operational conditions,are comparatively analyzed. Numerical results demonstrate that the matrix tension damage is the most significant failure mode which occurs in the mid-span of the blade. The blade internal configurations including the box-beam, Ibeam, left-C beam and right-C beam are compared and analyzed. The GFRP and carbon fiber reinforced polymer(CFRP) are considered and combined. Numerical results show that the I-beam is the best structural type. The structural performance of composite tidal turbine blades could be improved by combining the GFRP and CFRP structure considering the damage and cost-effectiveness synthetically.

Monitoring damage evolution of steel strand using acoustic emission technique and rate process theory

Utilizing the acoustic emission(AE) technique, an experimental investigation into the damage evolution for steel strand under axial tension was described. The damage evolution model for steel stand relating the damage evolution to acoustic emission parameters was proposed by incorporating the AE rate process theory. The AE monitoring results indicate that damages occur in both elastic and plastic phases of steel strand. In elastic phase, AE signals are mainly sent out from the micro damage due to the surface friction among the wires of steel strand, while in plastic phase, AE signals emitted from the plastic deformation of wires. In addition, the AE cumulative parameters curves closely resemble the loading curve. The AE cumulative parameters curves can well describe the damage evolution process including the damage occurrence and damage development for steel strands. It is concluded that the AE technique is an effective and useful nondestructive technique for evaluating the damage characteristics of steel strand.

Fuzzy stochastic damage mechanics(FSDM) based on fuzzy auto-adaptive control theory

In order to fully interpret and describe damage mechanics, the origin and development of fuzzy stochastic damage mechanics were introduced based on the analysis of the harmony of damage, probability, and fuzzy membership in the interval of [0,1]. In a complete normed linear space, it was proven that a generalized damage field can be simulated through β probability distribution. Three kinds of fuzzy behaviors of damage variables were formulated and explained through analysis of the generalized uncertainty of damage variables and the establishment of a fuzzy functional expression. Corresponding fuzzy mapping distributions, namely, the half-depressed distribution, swing distribution, and combined swing distribution, which can simulate varying fuzzy evolution in diverse stochastic damage situations, were set up. Furthermore, through demonstration of the generalized probabilistic characteristics of damage variables, the cumulative distribution function and probability density function of fuzzy stochastic damage variables, which show β probability distribution, were modified according to the expansion principle. The three-dimensional fuzzy stochastic damage mechanical behaviors of the Longtan rolled-concrete dam were examined with the self-developed fuzzy stochastic damage finite element program. The statistical correlation and non-normality of random field parameters were considered comprehensively in the fuzzy stochastic damage model described in this paper. The results show that an initial damage field based on the comprehensive statistical evaluation helps to avoid many difficulties in the establishment of experiments and numerical algorithms for damage mechanics analysis.

Application of fuzzy theory on earthquake damage rate estimation of buildings

Variations between earthquakes result in many factors that influence post-earthquake building damage(e.g.,ground motion parameters,building structure,site information,and quality of construction).Consequently,it is necessary to develop an appropriate building damage-rate estimation model.The building damage survey data were recorded and constructed into files by the Architecture and Building Research Institute(ABRI),Taiwan for the 1999 Chi-Chi earthquake in the Nantou region as a basis for developing a building damage rate estimation model by applying fuzzy theory to express the fragility curves of buildings as a membership function.Empirical verification was performed using post-earthquake building damage data in the Taichung city that suffered relatively severe damage.Results indicate that fuzzy theory can be applied to predict building damage rates and that the estimated results are similar to actual disaster figures.Prediction of disaster damage using building damage rates can provide a reference for immediate disaster response during earthquakes and for regular disaster prevention and rescue planning.

Failure Evaluation of Reinforced Concrete Beams Using Damage Mechanics and Classical Laminate Theory

The prediction of the behavior of reinforced concrete beams under bending is essential for the perfect design of these elements.Usually,the classical models do not incorporate the physical nonlinear behavior of concrete under tension and compression,which can underestimate the deformations in the structural element under short and long-term loads.In the present work,a variational formulation based on the Finite Element Method is presented to predict the flexural behavior of reinforced concrete beams.The physical nonlinearity due cracking of concrete is considered by utilization of damage concept in the definition of constitutive models,and the lamination theory it is used in discretization of section cross of beams.In the layered approach,the reinforced concrete element is formulated as a laminated composite that consists of thin layers,of concrete or steel that has been modeled as elastic-perfectly plastic material.The comparison of numerical load-displacement results with experimental results found in the literature demonstrates a good approximation of the model and validates the application of the damage model in the Classical Laminate Theory to predict mechanical failure of reinforced concrete beam.The results obtained by the numerical model indicated a variation in the stress-strain behavior of each beam,while for under-reinforced beams,the compressive stresses did not reach the peak stress but the stress-strain behavior was observed in the nonlinear regime at failure,for the other beams,the concrete had reached its ultimate strain,and the beam’s neutral axis was close to the centroid of the cross-section.

Embankment deformation analyzed by elastoplastic damage model coupling consolidation theory

The deformation of embankment has serious influences on neighboring structure and infrastructure.A trial embankment is reanalyzed by elastoplastic damage model coupling Biot's consolidation theory.With the increase in time of loading,the damage accumulation becomes larger.Under the centre and toe of embankment,damage becomes serious.Under the centre of embankment,vertical damage values are bigger than horizontal ones.Under the toe of embankment,horizontal damage values are bigger than vertical ones.

Structural damage assessment using improved Dempster-Shafer data fusion algorithm

As an efficient tool in handling uncertain issues, Dempster-Shafer evidence theory has been increasingly used in structural health monitoring and damage detection. In applications, however, Dempster-Shafer evidence theory sometimes leads to counter-intuitive results. In this study, a new fusion algorithm of evidence theory is put forward to address various counter-intuitive problems and manage the reliability difference of the evidence. The proposed algorithm comprises the following aspects:(1) Dempster's combination rule is generalized by introducing the concept of evidence ullage. The new rule allows classical Dempster's rule and can resolve counter-intuitive problems cause by evidence conflict and evidence compatibility;(2) a reliability assessing method based on a priori and posterior knowledge is proposed. Compared with conventional reliability assessment, the proposed method can reflect the actual evidence reliabilities and can efficiently reduce decision risk. Numerical examples confirm the validity and utility of the proposed algorithm. In addition, an experimental investigation on a spatial truss structure is carried out to illustrate the identified ability of the proposed approach. The results indicate that the fusion algorithm has no strict request on the accuracy and consistency of evidence sources and can efficiently enhance diagnostic accuracy.

Reliability Analysis Based on a Nonlinear Fatigue Damage Accumulation Model

A modified nonlinear fatigue damage accumulation model based on the Manson-Halford theory was presented,and the new model was developed for fatigue life prediction under constant and variable amplitude loading, which took the effects of the load interactions and the phenomenon of material's strength degradation into account. The experimental data of the 30 Cr Mn Si A and the LY-12 cz from literature were used to verify the proposed model. And from the good agreement between the experimental data and predicted results,we can see it clear that the proposed method can be applied to predicting fatigue life under different loadings.

Rheological property of low-damage,ideal packing,film-forming amphoteric/sulfonation polymer drilling fluids

Low-permeability dense reservoirs,including micro-fractured reservoirs,are commonly characterized by high content of clay substances,high original water saturation,high sensitivity to invasive fluids,high capillary pressure,complicated structure and anisotropic,high flow-resistance and micro pore throats etc,.Generally they also have lots of natural micro fractures,probably leading to stress sensibility.Main damaging factors in such reservoirs are water-sensibility and water-blocking caused by invasive fluids during drilling and production operations.Once damaged,formation permeability can rarely recovered.Numerous studies have shown that damaging extent of water-blocking ranges from 70% to 90%.Main damaging mechanisms and influencing factors of water-blocking were systematically analyzed.Also some feasible precaution or treating approaches of water-blocking were put forward.In a laboratory setting,a new multi-functional drilling fluid composed mainly of amphion polymer,sulfonation polymer,high effectively preventive water-blocking surfactants,ideal packing temporary bridging agents(TBA) and film-forming agents,etc.,were developed.New low-damage drilling fluids has many advantages,such as good rheological properties,excellent effectiveness of water-blocking prevention,good temporary plugging effect,low filtration and ultra-low permeability(API filtration≤5 mL,HTHP filtration≤10 mL,mud cake frictional coefficient≤0.14,permeability recovery>81%),can efficiently prevent or minimize damage,preserve natural formation and enhance comprehensive development-investment effect in TUHA Jurassic dense sandstone reservoir formation with low-permeability,the only one developing integrated condense gas field.Some references can be provided to similar reservoir formations.

Mechanism of micro-waviness induced KH_2PO_4 crystal laser damage and the corresponding vibration source

The low laser induced damage threshold of the KH2PO4 crystal seriously restricts the output power of inertial confinement fusion.The micro-waviness on the KH2PO4 surface processed by single point diamond turning has a significant influence on the damage threshold.In this paper,the influence of micro-waviness on the damage threshold of the KH2PO4 crystal and the chief sources introducing the micro-waviness are analysed based on the combination of the Fourier modal theory and the power spectrum density method.Research results indicate that among the sub-wavinesses with different characteristic spatial frequencies there exists the most dangerous frequency which greatly reduces the damage threshold,although it may not occupy the largest proportion in the original surface.The experimental damage threshold is basically consistent with the theoretical calculation.For the processing parameters used,the leading frequency of micro-waviness which causes the damage threshold to decrease is between 350-1 μm-1 and 30-1 μm-1,especially between 90-1 μm-1 and 200-1 μm-1.Based on the classification study of the time frequencies of microwaviness,we find that the axial vibration of the spindle is the chief source introducing the micro-waviness,nearly all the leading frequencies are related to the practical spindle frequency（about 6.68 Hz,400 r/min） and a special middle frequency（between 1.029 Hz and 1.143 Hz）.

A damage-based constitutive model for rock under impacting load

Using the Splitting Hopkinson Pressure Bar(SHPB) experimental system, investigations were made into the dynamic mechanical performances of underground soft rocks. The experiments proved that the measured stress–strain curves display the characteristics of plastic deformation. By making use of a revised overstress constitutive formula for the stress model and by taking into account that the strain rate and strain are a function of 1 E(t)/E0, a revised overstress constitutive formula for the stress model was simplified by applying dimensional analysis and consequently, a simplified overstress formula was obtained for the stress model. Then, by taking into consideration the effects of damage under a dynamic load on the dynamic loading strength of the rock, the continuous damage theory and the statistical strength theory were introduced into the development of the simplified overstress constitutive formula for the stress model. Hence, a damage-based constitutive formula for an overstress model, which can be appropriately applied to the analysis of full dynamic stress–strain curves, was developed. By using the simplified damage-based constitutive formula for an overstress model, the actually measured curves are fitted, indicating that the fitting curves and those actually measured are in good agreement.

Calculation Model and Simulation of Warship Damage Probability

The combat efficiency of mine obstacle is the focus of the present research. Based on the main effects that mine obstacle has on the target warship damage probability such as: features of mines with maneuverability, the success rate of mine-laying, the hit probability, mine reliability and action probability, a calculation model of target warship mine-encounter probability is put forward under the condition that the route selection of target warships accords with even distribution and the course of target warships accords with normal distribution. And a damage probability model of mines with maneuverability to target warships is set up, a simulation way proved the model to be a high practicality.

Analysis of damage localization for ductile metal in process of shear band propagation

Distribution of localized damage in shear band can’ t be predicted theoretically based on classical elastoplastic theory. The average damage variable in shear band was considered to be a non-local variable. Based on non-local theory, an analytical expression for the localized damage in strain-softening region of shear band in the process of shear band propagation was presented using boundary condition and symmetry of local damage variable, etc. The results show that dynamic shear softening modulus, dynamic shear strength and shear elastic modulus influence the distribution of the localized damage in shear band. Internal length of ductile metal only governs the thickness of shear band. In the strain-softening region of shear band, the local damage variable along shear band’s tangential and normal directions is non-linear and highly non-uniform. The non-uniformities in the normal and tangential directions of shear band stem from the interactions and interplaying among microstructures and the non-uniform distribution of shear stress, respectively. At the tail of the strain-softening region, the maximum value of local damage variable reaches 1. This means that material at this position fractures completely. At the tip of shear band and upper as well as lower boundaries, no damage occurs. Local damage variable increases as dynamic shear softening modulus decreases or shear elastic modulus increases, leading to difficulty in identification or detection of damage for less ductile metal material at higher strain rates.

Influence of Damage Evolution on the Failure Surface of Concrete

The damage which represents the alternation of internal slate of material was introduced to concrete strength theory according to the theory of mechanics of continuous medium and the failure criterion of deteriorated concrete was diseussions. In the tests, ultrasonic velocity is used to establish the damage variable and to establish the damage-eoupled failure criterion of concrete under freeze-thaw. The results show that the failure surface is gradually shrinking with the increase of freeze-thaw times. Furthermore, by the comparison between the theoretical data and the testing data from the literature, the rationality of strength theory proposed in the paper acquire confirmation. The damage-coupled failure criterion presented here can indicate the influence of damage evolution on the failure surface of concrete.

Elasto-plastic postbuckling of damaged orthotropic plates

Based on the elasto-plastic mechanics and continuum damage theory, a yield criterion related to spherical tensor of stress is proposed to describe the mixed hardening of damaged orthotropic materials. Its dimensionless form is isomorphic with the Mises criterion for isotropic materials. Furthermore, the incremental elasto-plastic damage constitutive equations and damage evolution equations are established. Based on the classical nonlinear plate theory, the incremental nonlinear equilibrium equations of orthotropic thin plates considering damage effect are obtained, and solved with the finite difference and iteration methods. In the numerical examples, the effects of damage evolution and initial deflection on the elasto-plastic postbuckling of orthotropic plates are discussed in detail.

A method for calculating damage evolution in adiabatic shear band of titanium alloy

A method for calculating the evolution of the local damage variable at the adiabatic shear band(ASB)center was proposed.In the present method,the JOHNSON-COOK model and the nonlocal theory were adopted,and the damage variable formula applicable for the bilinear(linearly elastic and strain-softening)constitutive relation was further generalized to consider the plastic deformation occurring in the strain-hardening stage.Aiming at Ti-6Al-4V,the effect of strain rate on the evolution of the local damage variable at the ASB center was investigated.In addition,a parametric study was carried out,including the effects of strain-hardening exponent,strain rate sensitive coefficient,thermal-softening exponent,static shear strength,strain-hardening modulus,shear elastic modulus,work to heat conversion factor,melting temperature and initial temperature.The damage extent at the ASB center in the radial collapse experiment was assessed.It is found that at higher strain rates the damage in the ASB becomes more serious at the same average plastic shear strain of the ASB.

An Optimized Damage Identification Method of Beam Using Wavelet and Neural Network

An optimized damage identification method of beam combined wavelet with neural network is presented in an attempt to improve the calculation iterative speed and accuracy damage identification. The mathematical model is developed to identify the structure damage based on the theory of finite elements and rotation modal parameters. The model is integrated with BP neural network optimization approach which utilizes the Genetic algorithm optimization method. The structural rotation modal parameters are performed with the continuous wavelet transform through the Mexico hat wavelet. The location of structure damage is identified by the maximum of wavelet coefficients. Then, the multi-scale wavelet coefficients modulus maxima are used as the inputs of the BP neural network, and through training and updating the optimal weight and threshold value to obtain the ideal output which is used to describe the degree of structural damage. The obtained results demonstrate the effectiveness of the proposed approach in simultaneously improving the structural damage identification precision including the damage locating and severity.

Damage Detection of Offshore Jacket Structures Using Frequency Domain Selective Measurements

损坏察觉技术为的发展近海夹克衫结构是重要的阻止灾难的事件。这份报纸使用频率回答为监视的结构的健康的目的基于的方法。在完成这项任务的努力，最小的等级不安理论的概念被利用了。现在的文章介绍有希望的方法论有效地选择频率点。达到这个目标，每个成员的形式的紧张精力比率在结构的不同自然频率被评估以便为损坏察觉识别敏感频率领域。建议方法论开创大得多的察觉效率的可能性。另外，建议方法的表演在与多重损坏的关系被评估。上述的点用二个维的夹克衫平台的数字学习被说明，并且结果证明了令人满意利用建议方法论。

水液相下羟自由基与谷氨酸分子反应机理的量子化学研究

采用密度泛函理论的M06-2X和MN15方法,结合自洽反应场理论的SMD模型方法,研究了水液相下羟自由基(OH)与谷氨酸分子(Glu)反应的机理。研究发现:Glu的损伤可通过OH抽取其不同位置的H原子、OH加成到羧基和去质子羧基C以及单电子从Glu分子向OH转移3个途径实现。势能面计算表明:OH加成到羧基和去质子羧基C的反应通道最具优势,反应无势垒;OH抽取质子化氨基H、α-H、β-H、γ-H和羧基H的最低能垒分别是28.7、17.6、8.0、18.3和29.0 kJ/mol;电子从Glu分子向OH转移为劣势通道,反应能垒是255.2 kJ/mol。结果表明,水液相下OH加成和抽H均可诱导Glu分子损伤,损伤的Glu绝大多数难以修复,Glu具有清除羟自由基的能力。