Simulation Of Failure Process Research Articles

Seismic triggering of landslides. Part B: Simulation of dynamic failure processes

Abstract. From field observations it is possible to establish correlations between geological conditions and landslide occurrence. However, in general, it is difficult to assess the affect of individual factors on slope instability because of their mutual interaction. In addition, the dynamic effect of propagating seismic waves significantly increases the complexity of the slope stability problem. Wave diffraction, reflection and focusing effects are dependent on local geological conditions and make it difficult to analyse dynamic sliding mechanisms using field observations alone. As a consequence, in order to examine the influence of various geological and seismic factors on slope movements, it is often necessary to produce numerical models. This paper describes the results of such models as applied to two case studies in Kyrgyzstan: the Ananevo rockslide, located in granite, and the Suusamyr debris slump-flow, situated within soft sediments (see Part A: Havenith et al., 2003). Discrete element modelling (UDEC), adapted both to the discontinuous character of fractured rock and to the heterogeneity of layered mediums, was used. This permitted simulation of deformation mechanisms, including seismically induced bending, block tilting, and slip. Particular attention was paid to the interaction between deformation mechanisms, site-specific amplification effects, and subsurface structure.

層間剥離伝播挙動解析のための連続的な応力分布を仮定したインターフェイス要素

An interface element, taking account of both the material strengths and the fracture characteristics, is proposed to numerically simulate the damage propagation process in composite laminates. Several refinements are examined for the element to ensure the smooth convergence of the solution during the calculation of the damage when incorporated in the commercially available finite element package program (MARC) through user subroutine. The element has been successfully applied to a fundamental problem of the stable crack propagation and the crack initiation. Propagation process of multiple interlaminar delaminations in circular axi-symmetric nonlinear plates subjected to a quasi-static transverse load has been solved to demonstrate the applicability and efficiency of the present element to a complex delamination propagation problem. As continuous stress distribution with respect to the surface separation along the crack path are assumed on the interface, smooth and stable convergence of the solution of the crack propagation can be realized with fairly coarse mesh compared to the modeling where discrete interface traction force is assumed only at the nodes on the interface. Since the element would be taking into account the dissipated energy during the formation of crack surface, it can be applied to the simulation of dynamic failure process.

Numerical Simulation of Rock Failure and Earthquake Process on Mesoscopic Scale

—On the basis of the lattice model of Mora and Place, Discrete Element Method, and Molecular Dynamics approach, another kind of numerical model is developed. The model consists of a 2-D set of particles linked by three kinds of interactions and arranged into triangular lattice. After the fracture criterion and rules of changes between linking states are given, the particle positions, velocities and accelerations at every time step are calculated using a finite-difference scheme, and the configuration of particles can be gained step by step. Using this model, realistic fracture simulations of brittle solid (especially under pressure) and simulation of earthquake dynamics are made.

Failure Prediction of Smeared-Crack Formulations

The smeared-crack approach of strain-softening is a popular engineering concept for the numerical simulation of tensile failure processes in concrete and rock. Despite numerous publications on the equivalent constitutive formulation of cracked solids, very little is known about the predictive value of the smeared-crack approach, particularly when nonproportional load histories are considered. To this end, two failure indicators are examined at the constitutive level in order to assess the predicted failure mode of fixed and rotating crack concepts. The directional stiffness parameter is used to examine singularities of smeared-crack formulations, which signal continuous failure due to material branching. In contrast, the localization indicator is used to examine the formation of weak discontinuities, which precede incipient failure process when the continuum degrades into a discontinuum. In this paper both failure indicators will be used to assess the failure modes of the fixed and rotating crack formulations for two loading scenarios involving pure shear and combined tension with shear.

ガラスマット強化複合材料の引張り破壊シミュレーション

A method of stochastic simulation of damage and failure process of glass mat reinforced plastics is developed, and applies to examine the relation between the strength dispersion and the damage process. A stochastic model for composites having nonuniform distribution of fracture strength is first developed by the use of finite element method. The fracture strength of each element is specified randomly to follow the normal distribution. Then, the global damage process of the material is analyzed by incorporating this model into a finite element code of anisotropic nonlinear elasticity. The damage and failure process of glass mat reinforced plastics in uniaxial tension is analyzed, and the effects of strength dispersion on inelastic behavior and fracture modes are discussed in detail.

Numerical simulation of failure processes in brittle rock : Kuijpers, J S Proc Conference on Fractured and Jointed Rock Masses, Lake Tahoe, 3–5 June 1992P656–664. Publ California: Lawrence Berkeley Laboratory, 1992

Numerical simulation of failure processes in brittle rock : Kuijpers, J S Proc Conference on Fractured and Jointed Rock Masses, Lake Tahoe, 3–5 June 1992P656–664. Publ California: Lawrence Berkeley Laboratory, 1992

Computer Simulation of Materials Failure Processes in a Thermal or Radiational Environment

Computer Simulation of Materials Failure Processes in a Thermal or Radiational Environment

A transient stochastic failure model for unidirectional composites under impact loading

A dynamic failure model is unidirectionally reinforced composites under impact loading. It comprises two parts the first of which involves double-edge notched composites with a matrix split. The second part is a complete stochastic simulation of sequential failure processes for various coefficients of variation of fibre strength. The predicted final fracture surfaces for both CFRP and GRP are consistent with observations from previous experimental work on tensile impact of composites.

Examinations on Dynamic Strength Distribution and Macromodel

The present paper introduces a probabilistic failure model and aims at establishing a general assessment system to predict a decrease in reliability of composite materials due to cumulative damage. The failure model used in this system requires a good actuality and utility, i. e. : 1) Actuality-the model should represent more acurately the actual failure process of composites ; 2) Utility-the constructed model should give a good approximation to actual strength properties of composites when the program is run with currently used specimen sizes. In the previous third report, a statistical analysis on the dynamic failure process simulation model was proposed and compared with the static failure process simulation (1 st report).In this report, a statistical analysis is made based on the dynamic failure model and compared with the static one in terms of the different strength parameters. It shows that both static and dynamic simulation give little difference as far as the average values of tensile strength and maximum strain are concerned, but that the dynamic simulation gives a better estimation in terms of the dispersion of strength data and the actual failure pattern.A macro model is also proposed in this report, which is a new cumulative failure model composed of elements of micro models based on the previous dynamic failure process simulation models.A macro model is successfully used in estimating the statistical nature of strength properties of composite materials of actual size. It shows that the strength of composites depends clearly on the length but not on the width of a specimen.

Establishment of Dynamic Failure Model and Examination on Dynamic Failure Process

The present paper proposes a new dynamic failure process simulation model considering the effect of matrix shear failure as well as random fiber breaks based on a shear-lag theory in which an additional time variable is also incorporated by taking the mass of fiber and matrix elements into account. An exact time-dependent stress redistribution process in a composite failure model is evaluated by means of a finite difference scheme based on an increment method for unidirectional carbon (C) and carbon (C) /glass (G) hybrid FRP models.It is observed that the time-dependent stress concentration factor evaluated by the simulation is in good accordance with the Hedgepeth's analytical solution. It is also clarified that the stress in carbon fiber is relieved to some extent due to the presence of neighbouring glass fibers in hybrid C/G hybrid FRP models.The stress wave propagation is successfully simulated by visualizing a time-dependent change in nodal displacements as well as pursuing a dynamic failure process of a composite failure model. These simulations are shown to be effective in characterizing different failure processes and stress wave propagation behaviors of unidirectional CFRP under varied higher strain rates.Finally, a simple damping term is taken into account in the dynamic failure process simulations. It is shown that a clear difference exists in the dynamic failure process and the resulting tensile stress-strain diagram of CFRP and C/G hybrid FRP under varied higher strain rates.

一方向ハイブリッド繊維強化材の動的引張破壊過程のシミュレーション

The authors proposed a new failure process simulation model considering interfacial debonding between fibers and matrix as well as random fiber breaking based on a shear-lag theory, in which not only fiber elements but also matrix elements are included. The failure model was applied to characterize not only the static tensile failure process but also the statistical nature of hybrid effect of several types of unidirectional hybrid FRP in the previous reports.The present paper proposes a new dynamic failure process simulation model in which an additional time variable is also incorporated by taking the mass of fiber and matrix elements into account. An exact time-dependent stress redistribution process in a new composite failure model is evaluated by means of a finite difference scheme based on an increment method. The numerical results are shown and discussed for two types of unidirectional carbon (C)/glass (G) hybrid FRP models.As the results, it is shown that a time-dependent stress concentration factor is exactly evaluated by the simulation which is in good accordance with Hedgepeth's solution and that the stress in a carbon fiber is relieved to some extent due to the presence of glass fiber in hybrid C/G FRP. It is also shown that a clear difference exists between the static and dynamic tensile failure patterns for both types of hybrid FRP. It is furthermore shown that the dynamic stress-strain behavior and the acoustic emission are successfully simulated by taking the stress drop and the released strain energy due to fiber and matrix failures into consideration, which gives a more realistic behavior than the static simulation.

Study on Reliability Assessment System of Composite Materials (2nd Report)

From a microscopic point of view, composite materials generally contain innumerable defects in itself, but even if they have some defects, many of them are sometimes almost harmless depending upon types, locations and applied conditions. On the other hand, in a stress concentrated region, even a very minute defect often causes a crack growth and then arrives at a fatal size. So it is impossible to estimate the strength reliability of composite materials until the extent that every type of defect takes part in a catastrophic fracture is predicted and examined.For this purpose, the present paper aims at estimating the strength reliability of composite materials containing defects in itself on the basis of a stochastic tensile failure process simulation of unidirectional fiber reinforced composites which was described in the previous report. Each type of defect modes of composite materials has been classified and modelized systematically, and the damage tolerance has been examined as follows : a goodness of fit has been investigated for statistical distributions on each type of defect mode, which gives the difference in goodness of fit due to the number of included defects or the sample size. As for a decrease in the strength reliability due to defects, the effect of fiber and matrix defects has been examined in detail. And finally, a comparison has been tried among each type of defect modes by means of the PDF curve, which has been shown to be useful to a certain extent in discriminating a defect mode.

ハイブリッド効果に関する統計的考察および材料設計

The importance of hybrid composites is related to (1) the wider range of spectrum on materials properties, (2) the good balance between strength, rigidity and toughness of composites, and (3) the possibility of obtaining a more complicated multi-load-path structure. The present paper is concerned with a statistical characterization of tensile failure behavior of hybrid composites with unidirectional carbon/glass hybrid fiber reinforced composites as an example based on the new failure process simulation model which was previously proposed by the authors. The effects of fraction and dispersion pattern of carbon fibers on tensile failure characteristics of hybrid composites are systematically analyzed and the results are statistically examined.As results, it is verified that the hybrid effect in a broader sense exists: the composition effect is apparently larger than that estimated by the rule of mixture as far as strength, elongation and absorped energy of hybrid composites are concerned. It is furthermore shown that the hybrid effect in a narrower sense, which is defined as the net hybrid effect, that is, the initial failure strain enhancement from which the statistical size effect is subtracted, is also statistically valid: the relation between the hybrid effect and the carbon fiber fraction or the dispersion of hybrid composites is clarified. Thus these results give a fundamental guideline for the materials design of hybrid composites.

一方向ハイブリッド繊維強化材の引張破壊過程のシミュレーション

The failure process of fiber reinforced composites is a complicated accumulation process of damage due to random failure of fibers, matrix and interfaces, which leads to a catastrophic fracture. A Monte Carlo simulation is one of the most effective methods to analyze such a complicated probabilistic phenomenon as a failure process of composites, and several investigations have been carried out in the past. In most of the past investigations, a simple failure model has been applied in which only random fiber break and stress concentration in the nearest fiber to the broken fiber are taken into consideration. This formulation, however, leads to no more than a flat cleavage plane of a specimen, which does not apparently agree with an actual observed phenomenon.The present paper proposes a new failure model considering interfacial debonding between fibers and matrix as well as fiber breakage. A tensile failure process simulation was carried out for unidirectional carbon fiber (C)/glass fiber (G) hybrid composites with two different kinds of hybrid constitution (concentrated versus dispersed) based on the proposed failure model. The simulation was compared with the observed results of hybrid model experiments based on an acoustic emission (AE) method.The present simulation showed a complicated zigzag cleavage plane in the specimen and also the clear difference in failure process depending upon hybrid constitutions. Furthermore, the simulated results agreed well in tendency with the model experiments in regards to the characteristic shape of stress-strain diagrams and AE properties.

Mathematical simulation of failure processes of composite materials reinforced with brittle fibers

1. It is concluded on the basis of an analysis of experimental data and also from theoretical investigations with respect to stress redistribution upon the breaking of fibers that the successive breaking of a number of fibers, caused by the overload from the breaking of individual fibers, is one of the principal mechanisms according to which the complete failure of a material reinforced with brittle fibers takes place.