Progressive Failure Phenomena Research Articles

Structural behavior of steel dowel-reinforced cross-laminated bamboo and timber beams

Cross-laminated bamboo and timber (CLBT) products exemplify the efficient utilization of bamboo and timber resources, demonstrating excellent potential in sustainable structural engineering. The significant difference in mechanical properties between high-density engineered bamboo and low-density timber laminations leads to premature in-plane delamination failure and loss of ductility and energy absorption for CLBT members subjected to out-of-plane loading. This study demonstrated that vertically-driven steel dowels significantly enhanced the layer combination efficiency and addressed the above problems of CLBT. A comparison of measured critical mechanical performance parameters was presented, systematically characterizing the structural behavior of CLBT beams with steel dowels. Steel dowels in CLBT were more effective than those in cross-laminated timber at resisting high in-plane shear stress and exhibiting the progressive failure phenomenon. Although steel dowels slightly reduced the bending stiffness in some specimens, they increased the ductility and energy absorption performance, particularly in CLBT. This study provides a potential solution for improving the structural behavior of CLBT members subjected to out-of-plane loads under high in-plane shear stress conditions.

Progressive failure analysis of shallow circular tunnel based on the functional catastrophe theory considering strain softening of surrounding rock mass

Collapse mechanism for the tunnel or underground cavern is important for the support system design. This paper investigates the progressive failure phenomenon of the shallow tunnel roof under the condition of plane strain by virtue of the functional catastrophe theory. Firstly, considering the plastic strain energy as an index for the state of the studied system, the analytical solutions for the profile curves of the collapsing blocks from the shallow tunnel roof including the ‘underground’ collapse and ‘spalling’ collapse are deduced on the basis of the nonlinear power-law failure criterion. Moreover, the criterions are derived to estimate whether the progressive failure phenomena including the ‘underground’ collapses and ‘spalling’ collapses for shallow tunnel roof would occurr or not. Then, the analytical prediction obtained from this paper for the shallow tunnels is compared with the existing analytical prediction for the deep tunnels. Finally, the comparisons of the results between analytical prediction obtained from this paper and two existing model tests are conducted to demonstrate the validity of the proposed analytical methodology.

Functional Catastrophe Analysis of Progressive Failures for Deep Tunnel Roof Considering Variable Dilatancy Angle and Detaching Velocity

The phenomena of progressive failures are very common and important in geotechnical engineering. In this paper, a reliable prediction model is proposed to interpret the progressive failure phenomenon of roof collapse in deep tunnels using the functional catastrophe theory. The progressive collapse mechanisms and collapsing block shapes of deep circular tunnels under conditions of plane strain are investigated. The analytical solutions for the shape curves of the collapsing blocks of circular tunnels are derived based on the nonlinear power-law failure criterion considering variable dilatancy angle and detaching velocity. Moreover, criterions with variable dilatancy angle on progressive failure occurrence for deep tunnels are obtained. Then, the analytical predictions obtained in this paper are compared with experimental testing results, which indicate that the impacts of variable detaching velocity on the shape curves of the several continuous collapsing blocks should be considered to obtain more consistent prediction results with the corresponding experimental testing results.

SEISMIC RISK EVALUATION OF IRRIGATION TANKS: A CASE STUDY IN IBIGAWA-CHO, GIFU PREFECTURE, JAPAN

Landslides are one of earth’s most serious types of natural disasters and they are often inducedby earthquakes. Predicting the approximate landslide displacements caused by earthquakes is helpful forassessing earthquake hazards and for designing slopes to withstand future seismic shaking. In this research, theauthors firstly focus on obtaining the residual strength parameters and the peak strength parameters bymultistage procedure with the Bromhead ring shear apparatus, which are used in the slope stability analysis.The maximum vertical settlement (MVS) of a slope is determined by the Newmark method using representativedata from three earthquakes, i.e., Great Hanshin Earthquake, Chuetsu Earthquake and Iwate-Miyagi NairikuEarthquake. It is experimentally demonstrated that the MVS is very large in both Tanigumi Pond and SugoPond. Once a great earthquake occurs, the progressive failure phenomenon appears and people living in thearea will be in danger. The results presented in this paper can be applied to future landslide hazard assessmentsand used to promote reconstruction efforts by the government in the affected areas and for future disasterprevention and mitigation.

Run-out of landslides in brittle soils

One of the factors causing the acceleration of landslides is the loss of strength of the soil involved in the potential unstable mechanism. The travelled distance and the landslide velocity, a key factor in risk analysis, will be determined by the loss of resistant forces. Brittle behaviour, commonly associated with cemented soils, overconsolidated plastic clay formations and sensitive clays, lead to the progressive failure phenomenon explained by the reduction of the strength with increasing strain. In the present study, this phenomenon has been analysed in the case of a saturated slope which becomes unstable by increasing the boundary pore water pressure. A Mohr–Coulomb model with strain softening behaviour induced by increasing deviatoric plastic strain is used. The paper focusses not only on the stability of the slope but also on the post failure behaviour (run-out and sliding velocity). A coupled hydro-mechanical formulation of the material point method has been used to simulate the whole instability process. The influence of the brittleness of the material on the triggering of instability and run-out is evaluated by means of a parametric study varying peak and residual strength. The onset of the failure and the failure geometry are controlled by both peak and residual values. Good correlations between run-outs and brittleness are found. The decay of the strength determines the acceleration of the landslides and the travelled distance.

Mechanical response features and failure process of soft surrounding rock around deeply buried three-centered arch tunnel

Due to the extreme complexity of mechanical response of soft surrounding rock (SR) around a tunnel under high geostatic stress conditions, the integration of physical and numerical modeling techniques was adopted. Based on the similarity theory, new composite-similar material was developed, which showed good agreement with the similarity relation and successfully simulated physico-mechanical properties (PMP) of deep buried soft rock. And the 800 mm×800 mm×200 mm physical model (PM) was conducted, in which the endoscopic camera technique was adopted to track the entire process of failure of the model all the time. The experimental results indicate that the deformation of SR around a underground cavern possessed the characteristics of development by stages and in delay, and the initial damage of SR could induce rapid failure in the later stage, and the whole process could be divided into three stages, including the localized extension of crack(the horizontal load (HL) was in the range of 130 kN to 170 kN, the vertical load (VL) was in the range of 119 kN to 153.8 kN), rapid crack coalescence (the HL was in the range of 170 kN to 210 kN, the VL was in the range of 153.8 kN to 182.5 kN) and residual strength (the HL was greater than 210 kN, the VL was greater than 182.5 kN). Under the high stress conditions, the phenomenon of deformation localization in the SR became serious and different space positions show different deformation characteristics. In order to further explore the deformation localization and progressive failure phenomenon of soft SR around the deeply buried tunnel, applying the analysis software of FLAC3D three-dimensional explicit finite-difference method, based on the composite strain-softening model of Mohr-Coulomb shear failure and tensile failure, the calculation method of large deformation was adopted. Then, the comparative analysis between the PM experiment and numerical simulation of the three centered arch tunnels was implemented and the relationship of deformation localization and progressive failure of SR around a tunnel under high stress conditions was discussed.

Initial and progressive failure analyses for composite laminates using Puck failure criterion and damage-coupled finite element method

In the present study, an evaluation method for the initial and progressive failure of composite laminates was proposed based on the Puck failure criterion and damage mechanics, respectively. In other words, the initial failure (crack initiation in the fiber and/or matrix) and progressive failure (crack growth in the fiber and/or matrix) were evaluated using the Puck failure criterion, and fiber- and matrix-dependent damage variables, respectively. In addition, the ABAQUS user-defined subroutine UMAT was developed based on coupling theories for the failure criterion and damage mechanics in order to efficiently analyze the progressive failure phenomenon in glass/carbon fiber-reinforced composite laminates. The developed subroutine was applied to the failure of industrial composite laminates, and the analysis results were compared to the experimental/numerical results previously reported in the literature. This comparative study confirmed that the simulation results were in good agreement with the reported composite failure results.

Multiscale modeling of metal-composite interfaces in titanium-graphite fiber metal laminates part II: Continuum scale

This study presents a multiscale numerical framework designed to predict the nonlinear constitutive behavior of metal-composite interfaces in titanium-graphite fiber metal laminates. Molecular-level property predictions derived in a separate analysis are used to parameterize a finite element model of the interface by means of a traction-separation constitutive law. Additional continuum-level energy dissipation and progressive failure phenomena are implemented into commercial finite element software through a user-defined material subroutine. Results obtained from this multiscale interface model are compared against experimental measurements of titanium-graphite fiber metal laminates in a short-beam shear loading configuration. The model predictive accuracy and its application to other bonded metal-composite systems are subsequently discussed.

Finite Element Analysis of Strain Localization under Static and Dynamic Loading Conditions Based on Cosserat Continuum Model

In the present work, the Cosserat micro-polar continuum theory is introduced into the FEM numerical model, which is used to simulate the strain localization phenomena under static and dynamic loading conditions. The numerical studies on progressive failure phenomena, which occur in a panel, characterized by strain localization due to strain softening and its development, are numerically modelled by two types of Cosserat continuum finite elements, i.e. u8ω8 and u8ω4 elements. It is indicated that both two Cosserat continuum finite elements possess better performance in simulation of strain localization. Because of the presence of an internal length scale in Cosserat continuum model a perfect convergence is found upon mesh refinement. A finite, constant width of the localization zone is computed under static as well as under transient loading conditions.

Evolution of force chains in shear bands in sands

Precise knowledge of the post-peak constitutive response occurring within shear bands in sands is of keen interest in geomechanics, particularly for accurate modelling of progressive failure phenomena. There is mounting evidence that the displacement field within shear bands in sands is non-uniform and distinguished by distinct meso-scale features: namely, particle force chains. Experimental validation of such features will help elucidate the precise nature of the deformation field within shear bands. This paper presents experimental evidence of the kinematic signatures of force chain activity within shear bands in sands. The meso-scale kinematics are quantified from digital-image-correlation-based, grain-scale displacement analyses performed on digital images of specimens undergoing plane strain compression. As in previous work, the data reveal distinct, systematic patterns in the kinematics along the length of the shear band, which serve as indirect evidence of force chain build-up and collapse. Herein, local volume changes are shown to integrate into this pattern. Temporal changes in these patterns with the progress of deformation are also tracked. It is argued that the changes observed in the kinematics from softening to critical state provide a physical, meso-scale explanation for the progress of global stress–strain response through the post-peak regime.

Stochastic Modeling of Progressive Failure in Heterogeneous Soil Slope

Accurate and efficient simulation of the slope stability, certainly gives the reliable approach for the hazard preparedness. However, inherent difficulties associated with the slope failure make the situation very difficult. First, the computation of fracture path based on the strict mathematical formalism is cumbersome especially for the progressive failure phenomenon. Second, due to the lack of reliable knowledge on material properties, stochastic simulation is necessary. Stochastic modeling together with the progressive failure phenomenon is apparently difficult task. In this paper, heterogeneous slope is simulated considering the progressive failure phenomenon using the modified finite element method introducing the fracture along the edge of the meshes thus incorporating the time evolution of the fracture surface. This is achieved by restructuring the tessellation in every fracture stage. Unlike remeshing this technique only increases the number of total nodes while number of meshes remaining same, which is simple and natural. Further, in this research, effect of uncertainty in the material properties upon the uncertainty in the response of soil slope has been evaluated, hence giving the reliable probabilistic estimation of the factor of safety, failure surface and deformation of the slope. Thus the simulation based on the more reliable understanding of the material properties and the efficient numerical procedure for the progressive failure phenomenon can give the reliable result of the simulation for the heterogeneous soil slope thus enabling the more accurate way for hazard preparedness.

A strain-rate dependent 3-D micromechanical model for finite element simulations of plain weave composite structures

Abstract A new 3-D constitutive model is developed for finite element simulations of plain weave composites (PWC) structures and implemented in the explicit finite element software DYNA3D. The aim of this work is to develop a material model for PWC which incorporates their significant deformation characteristics like strain rate sensitivity, progressive failure phenomena, and nonlinearity in shear and yet is computationally efficient. The constitutive relations are obtained using micromechanical analysis of a simple representative unit cell developed earlier in [1] to predict the mechanical properties of PWC. The matrix is modeled as a viscoplastic strain-rate dependent material, thereby incorporating strain-rate sensitivity in the composite model. Nonlinearity in shear is modeled using an explicit strain dependent relation for shear moduli of the constituents. A set of strain based failure criteria and corresponding stiffness degradations is used to model the progressive failure behavior. The constituents are checked for various modes of failure at each time step and if found to have failed, their moduli are reduced based on the mode. Only fiber breakage is assumed as ultimate failure of the composite. Initially, the yarns and the matrix are assumed to be transversely isotropic and isotropic materials respectively. They become orthotropic with the advent of initial failure. Experimental results available in the literature are used to verify the model’s predictions.

Large deflection analysis of composite laminates

A B-spline finite strip model is developed to simulate large deflection and delamination behaviour of laminated composite plates subjected to transverse loading. The model is based on a layer-wise plate theory. The geometrical non-linearity is included through use of von Karman’s non-linear strain–displacement relationship. In order to model progressive failure phenomena of composite laminates, both stress-based criteria and fracture-mechanics-based criteria are employed, and the former for delamination initiation whilst the later for delamination propagation. Comparison is made between the calculations of the present model and available analytical and experimental results.

Embankment on Soft and Sensitive Clay Foundation

A test embankment built on a soft sensitive clay foundation has failed at a computed safety factor higher than one, thus confirming the allegation that the field vane test overestimates the shear strength in this type of clay. The increased shear strength values measured by the vane, as compared to the shear strength mobilized at failure, are explained by the affect of the rate of loading (time effect) and by the anisotropy of the clay. However, correcting the measured vane shear strength for these two factors, as recommended by Bjerrum (1973), results in a computed safety factor at failure still higher than one. This is due to the progressive failure phenomenon, which tends to develop in sensitive clays (liquidity index higher than one). Pore pressure and deformation measurements carried out during construction have confirmed the development of this progressive failure. The writers recommend the use of semi-empirical correction factors as functions of the plasticity index, anisotropy, and progressive failure.