裂纹扩展量的检测技术

本文介绍能直接测量裂纹扩展量的涡流探头自动跟踪裂纹法及裂纹扩展计法。它们的共同特点是标定曲线与试件材料无关,并具有通用性。实践表明这些方法是有效和可靠的,且精度较高,也容易实现数据采集与处理自动化。

Nonequilibrium Statistical Nature of Intergranular Brittle Fracture in Polycrystal

The brittle fracture probability and reliability are obtained in terms of dislocation mechanism of microcrack evolution. The statistical distribution functions and statistical deviations of elongation, strength, plastic work, crack extension force, fracture foughness, critical and crack length, can be derived in a unified fashion.

Nonequilibrium Statistical Theory of Fracture

Nonequilibrium statistical theory of fracture is a theory of fracture that macromechanical quantities can be derived from the microscopic atomic mechanism of microcrack(or microvoid)evolution kinetcs by means of nonequilibrium statistical physical concepts and methods. The microcrack evolution equation is the central equation in the theory.The coefficents of the equation, the microcrack growth rate and the microcrack nucleation rate,come from microscopic atomic mechanism.The solution of the equation connects with macromechanical quantities by the model of the weakest chain. All the other formulas and quantities, for instance, distribution function,fracture probability, reliability, failure rate and macromechanical quantities such as strength, toughness, life etc. and their statistical distribution function and statistical fluctuation are derived in a unified fashion and expressed by a few physical parameters. This theory can be widely applied to various kinds of fracture, such as the brittle, fatigue, delayed and environmental fracture of metals and structural ceramics. The theoretical framework of this theory is given in this paper.

Orthogonal design and numerical simulation of room and pillar configurations in fractured stopes

Room and pillar sizes are key factors for safe mining and ore recovery in open-stope mining. To investigate the influence of room and pillar configurations on stope stability in highly fractured and weakened areas, an orthogonal design with two factors, three levels and nine runs was proposed, followed by three-dimensional numerical simulation using ANSYS and FLAC3~. Results show that surface settlement after excavation is concentrically ringed, and increases with the decrease of pillar width and distances to stope gobs. In the meantime, the ore-control fault at the ore-rock boundary and the fractured argillaceous dolomite with intercalated slate at the hanging wall deteriorate the roof settlement. Additionally, stope stability is challenged due to pillar rheological yield and stress concentration, and both are induced by redistribution of stress and plastic zones after mining. Following an objective function and a constraint function, room and pillar configuration with widths of 14 m and 16 m, respectively, is presented as the optimization for improving the ore recovery rate while maintaining a safe working environment.

Breaking process and mining stress evolution characteristics of a high-position hard and thick stratum

Based on the boundary support conditions of overlying high-position,hard and thick strata,a Winkler foundation beam mechanical model was built.Computational expressions for the characteristics and position of the bending moment for high-position,hard and thick strata were constructed by theoretical analysis,and the initial breaking position of high-position,hard and thick strata was also analyzed.The breaking process and evolution law of mining stress in high-position,hard and thick strata were studied by similar material simulation tests.Studies show that:due to the foundation deformation effect of the lower strata,the initial break position in high-position,hard thick layers is in the middle of goaf;vertical tension fractures first occur under the middle surface,then tilt tension fractures form at both sides and a non-uniform thickness of the fracture structure forms and produces subsidence deformation;behind the coal wall tilt fractures extend and eventually complete the migration.Mining stress produces obvious changes before and after the breakage of the high,hard and thick stratum;high stress concentration forms in front of the coal wall before breakage and fracture stress concentration significantly reduces after migration.Coal seam mining under high-position,hard thick strata can easily induce dynamic phenomena.

Constitutive Laws of the Underground Opening Collapse due to Dynamic Load

The constitutive laws of the collapse of underground openings in a rock massif were in-vestigated based on the results of laboratory and field experiments, and computations using ana-lytical and numerical models. It is shown that the principal mechanism of failure of underground openings over important for practice peak particle velocity amplitude range of 1 to 10 m/s is the roof and wall breakage due to the fall of key blocks. Over this load range the material crushing is of considerably less importance. The geometry of discontinuities influences mainly the stability of key blocks. Further caving depends weakly on block structure of near-tunnel zone. The mean volume of fall material is a rather stable quantity for rock massifs of different structures. Lower tunnel sta-bility in the zones of high fracturing is caused by a higher probability of the presence of the unsta-ble key blocks and the decrease of strength characteristics of fractured bounding blocks. The de-crease of average block size is a less important accompanying factor.

Statistical analysis of fracture properties based on particle swarm optimization and Pearson correlation coefficient method

Prediction of reservoir fracture is the key to explore fracture-type reservoir. When a shear-wave propagates in anisotropic media containing fracture,it splits into two polarized shear waves: fast shear wave and slow shear wave. The polarization and time delay of the fast and slow shear wave can be used to predict the azimuth and density of fracture. The current identification method of fracture azimuth and fracture density is cross-correlation method. It is assumed that fast and slow shear waves were symmetrical wavelets after completely separating,and use the most similar characteristics of wavelets to identify fracture azimuth and density,but in the experiment the identification is poor in accuracy. Pearson correlation coefficient method is one of the methods for separating the fast wave and slow wave. This method is faster in calculating speed and better in noise immunity and resolution compared with the traditional cross-correlation method. Pearson correlation coefficient method is a non-linear problem,particle swarm optimization( PSO) is a good nonlinear global optimization method which converges fast and is easy to implement. In this study,PSO is combined with the Pearson correlation coefficient method to achieve identifying fracture property and improve the computational efficiency.

Fault depth estimation using support vector classifier and features selection

Depth estimation of subsurface faults is one of the problems in gravity interpretation. We tried using the support vector classifier （SVC） method in the estimation. Using forward and nonlinear inverse techniques, detecting the depth of subsurface faults with related error is possible but it is necessary to have an initial guess for the depth and this initial guess usually comes from non-gravity data. We introduce SVC in this paper as one of the tools for estimating the depth of subsurface faults using gravity data. We can suppose that each subsurface fault depth is a class and that SVC is a classification algorithm. To better use the SVC algorithm, we select proper depth estimation features using a proper features selection （FS） algorithm. In this research, we produce a training set consisting of synthetic gravity profiles created by subsurface faults at different depths to train the SVC code to estimate the depth of real subsurface faults. Then we test our trained SVC code by a testing set consisting of other synthetic gravity profiles created by subsurface faults at different depths. We also tested our trained SVC code using real data.

Computational Fracture Analysis of an AFM-Specimen under Mixed Mode Loading Conditions

Fracture processes in ship-building structures are in many cases of a 3-D character. A finite element （FE） model of an all fracture mode （AFM） specimen was built for the study of 3-D mixed mode crack fracture behavior including modes Ⅰ,Ⅱ, and Ⅲ. The stress intensity factors （SIFs） were calculated by the modified virtual crack closure integral （MVCCI） method, and the crack initiation angle assessment was based on a recently developed 3-D fracture criterion--the Richard criterion. It was shown that the FE model of the AFM-specimen is applicable for investigations under general mixed mode loading conditions, and the computational results of crack initiation angles are in agreement with some available experimental findings. Thus, the applicability of the FE model of the AFM-specimen for mixed mode loading conditions and the validity of the Richard criterion can be demonstrated.

Estimation of main rheological parameters for Pangxidong-Jinkeng structural fracture zone and Qinzhou-Hangzhou metallogenetic belt in South China

The mylonites occurred in the fracture zones are studied by dynamically recrystallized quartz grains.The natural microstructures in mylonites are simulated and the deformation conditions of mylonitization are estimated by fractal analysis,recrystallized grain size paleopiezometer and flow laws of quartzite.Depending on fractal analysis,the deformation temperature of mylonitization is approximately 600℃,which presents high greenschist facies to low amphibolite facies.The mylonitization occurred at differential stresses of 9.1--10.7MPa(lower limits).Compared with extrapolation of quartzite flow laws and estimates of fractal analysis,the strain rate of mylonitization is under 10-13.8/s.

Main Gas Pipelines： Fracture Resistance Assessment of Pipes

This paper proposes an estimation method of fracture resistance of oil ＆ gas pipes, based on the results of full scale hydraulic pressure pipe testing with the artificial notch, made by the authors at 2002-2006. It shows that the fracture process at the stage of stripping （initialization） of crack can be characterized by Critical Fracture Diagram （CFD）. Calculating and experimental way to construct CFD is suggested and discussed. The fracture resistance requirements for oil ＆ gas pipes in terms of fracture mechanics （Kc, Lc） are formulated and proved. The results of full scale hydraulic pressure pipe testing, based on metal testing data of the standard Charpy specimens （KCV） and pipe＇s specification requirements are interrelated. The way to estimate the admissible temperature operation conditions of oil ＆ gas pipes by means of based metal ＂KCV-temperature＂ dependence is proposed.

Mechanistic study on the cellulose dissolution in ionic liquids by density functional theory

Ionic liquids （ILs） have attracted many attentions in the dissolution of cellulose due to their unique physicochemical properties as green solvents. However, the mechanism of dissolution is still under debate. In this work, computational investigation for the mechanisms of dissolution of cellulose in [Bmim]Cl, [Emim]C1 and [Emim]OAc ILs was performed, and it was focused on the process of breakage of cellulose chain and ring opening using cellobiose as a model molecule. The detailed mechanism and reaction energy barriers were computed for various possible pathways by density functional theoretical method. The key finding was that 1Ls catalyze the dissolution process by synergistic effect of anion and cation, which led to the cleavage of cellulose chain and formation of derivatives of cellulose. The investigation on ring opening process ofcellobiose suggested that carbene formed in ILs played an important role in the side reaction of cellulose, and it facilitated the formation of a covalent bond between cellulose and imidazolium core. These computation results may provide new perspective to understand and apply ILs for pretreatment of cellulose.

Slip Rates of the Major Faults on the Mid-southern Section of the North-South Seismic Belt Calculated from the Block Theory

In this paper, using the 1999 ~ 2007 GPS velocity field data, and by choosing the optimal block model, we obtained the deformation models applicable to the boundary zones of major blocks and the slip rates of block boundary faults on the mid-southern segment of the North-South Seismic Belt. The results show that： on the Longmenshan fault zone, the tensional and compressive slip rate is small on the Baoxing-Wenchuan segment, about 0. 5 ~ 1.8mm·a^-1, and the rate is relatively significant on the segment of the Wenchuan--Maoxian, as 1.8 ~3.8mm·a^-1; on the Xianshuihe fault belt, there is a certain difference in spatial distribution between the tensional slip rag.e and strike-slip rate： the tensional slip rate （ 8. lmm^a-1） is bigger than the sinistral strike-slip rate （ 4.8mm·a^-1） at the north of the Luhuo region; the tension and compression slip rate is basically the same as the strike-slip rate at Luhuo-Dawu; the Dawu-Kangding section presents a trend of decreased strike-slip rate and increased tensional slip rate; the Kangding-ghimian segment shows a strike-slip nature; the strike-slip rate is significantly greater than the tension/compression rate on the Xiaojiang fault zone; the slip rate on the Red River fault zone shows obvious spatial segmentation, the slip rate is smaller in its northwest part, but with a certain amount of tensional/compression component, 4. 7mm·a^-1 on the Jingdong segment. The segment east of Jingdong （ western Gejiu） is mainly of strike-slip, with a slip rate of 4. 5mm·a^-1.

Study on the Recurrence Probability of Strong Earthquakes of Faults

Based on the physical model of Brownian passage time,the probabilities of recurrence of strong earthquakes on the major active faults in China are calculated in different predictive time spans,based mainly on the analysis of the earthquake preparation process before a strong earthquake occurs. Furthermore,the seismic risks on active faults are studied. The results show that the earthquake probabilities on the Xianshuihe fault,the Altyn Tagh fault,the east Kunlun fault and Xiaojiang fault are significantly greater than other faults in the Chinese mainland,which indicates that the level of stress accumulation on these faults are higher than on other faults. Therefore,these faults may have a seismic risk for strong earthquake in future.

Fracture analysis of cortical bone under the condition of cement line debonding and osteon pullout

Cortical bone consists of osteons embedded in interstitial bone tissue and there is a thin amorphous interface, named cement line, between osteon and interstitial bone. Due to fatigue and cyclic loading, the pullout or debonding phenomenon often occurs in osteonal and interstitial tissue bone. The study aims to construct a fiber-reinforced composite material debonding model for cortical bone, in which the bonding condition along the osteon, cement line and interstitial tissue bone are assumed to be imperfect. In the study, we used the complex variable method to obtain series representations for stress fields in the osteon, cement line and the interstitial tissue bone with a radial crack. The effects of material properties of osteon and cement line, crack position, and varying degrees of debonding on the fracture behavior were investigated by computing the stress intensity factor （SIF） in the vicinity of the microcrack tips. The investigation results indicated that the cement line was important for controlling the fracture toughening mechanisms and that the level of imperfect bonding among osteon, cement line and interstitial tissue bone had a pronounced effect on the crack behavior and should not be ignored.

Direct estimation of rupture depths of earthquake faults from coseismic surface deformation

The rupture dimensions of earthquake faults are important parameters for characterizing earthquake ruptures and ground motions. Two key parameters to be determined are the rupture depth and dip angle of earthquake faults. Dislocation theory in an elastic half space indicates that if a seismic rupture directly runs up to the ground surface, there exist zero points of horizontal strain in the surface deformation, which correspond to the rupture depths, except for pure strike-slip faults. In this study, we use numerical simulations to investigate the possibility of inferring rupture depths from zero-strain points for cases of buried faults and heterogeneous media. The results show that the correspondence of zero-strain points to the rupture depths can be influenced by the heterogeneity of the underground media and the stress field. For buried faults, the correspondence relationship is approximately valid when the fault depth is <1 km. In addition, the range of earthquake fault dip angles can be estimated by horizontal displacements on the ground. We also study how to determine the rupture depths of faults from InSAR data after large earthquakes, and successfully apply the method to the 2008 Wenchuan earthquake. The method proposed here, which determines the parameters of fault geometry according to surface deformation, is simple and easy to perform. With independent of aftershocks, it can provide valuable constraints to kinematic inversions.

Rational design of sustainable polyurethanes from castor oil: towards simultaneous reinforcement and toughening

Sustainable polyurethanes prepared from castor oil and diisocyanates show very low strength and toughness, due to the highly cross-linked and flexible structure. Herein, we report a new strategy to simultaneously reinforce and toughen castor oil-based polyurethane via incorporating a stiff component （isosorbide, IS） to enhance network stiffness and reduce crosslink density. The crosslinking degree de- creases while the strength, moduli, ductility and heat re- sistance significantly increase accordingly with increasing IS content. The tensile behaviors are tunable over a broad range （either as elastomers or as plastics） depending on the com- positions. The polyurethanes show excellent thermal stability with onset decomposition temperature higher than 280℃. The investigation provides a new hint for future design and fab- rication of high performance sustainable polymers from other vegetable oils.

On-line diagnosis method of crack behavior abnormality in concrete dams based on fluctuation of sequential parameter estimates

Research on on-line diagnosis method of crack behavior abnormality in concrete dams can provide support for timely grasping abnormality state of the crack itself and achieving real-time monitoring of the dam safety.Considering that samples of crack effects in concrete dams increase actually over monitoring time,a superiority criterion for the on-line diagnosis is determined so as to detect the abnormality moments timely and reliably.By integrating the safety monitoring statistical model of crack effect variable with change point theory,a fluctuation method of regression coefficients is established for the on-line diagnosis.In addition,each abnormality moment is detected by the cumulative sum of regression model residuals.Results indicate that abnormality of crack behavior in concrete dams can be characterized by structural instability of crack monitoring model.And causes of crack behavior abnormality can be analyzed by the established method,which will play an important role in dam safety monitoring.Further,taking the crack in a concrete gravity-arch dam as an example,the scientific rationality and validity of the established on-line diagnosis method are confirmed.