Failure Analysis Model Research Articles

Numerical simulation and fractal analysis of mesoscopic scale failure in shale using digital images

Shale rock formations often contain calcite, which is a mineral that plays an important role in the failure of shale and in fracturing the reservoir volume. This study uses digital images to characterise the mesoscopic-scale non-uniformity of shale resulting from the shape, size and distribution of calcite in the shale. The geometry of the calcite is mapped to a finite element mesh based on the meso-scale structure of the rock. The numerical failure analysis model RFPA2D-DIP, which can accurately represent the meso-scale structure of shale, is used to simulate uniaxial compression. The influence of the meso-scale structure on the compressive strength and the failure process under various loading conditions are studied. The simulation results show that the meso-scale structure has an important influence on the compressive strength and the ultimate failure mode of samples loaded in various directions α. Furthermore, the results show that the compressive strength varies significantly with the direction of the load, indicating anisotropy. Depending on the direction, the failure mode can take the form of an inverted V (α=0°, 30°, 45°), an inverted Z (α=15°), a line (α=75°), or a V (α=60°, 90°). The spatial distribution of the acoustic emissions (AE) we observed is similar to those observed in macroscopic failure modes. The fractal dimension (D) of the shale fractures under various loading conditions is calculated using the box-counting method. The fractal dimension is an effective indicator of the failure mode. The value of D corresponding to the various failure modes is as follows: for the inverted Z the maximum value is 1.688016, for the line the minimum value is 1.481904, and for both the inverted V and the V, the value is between 1.688016 and 1.481904. Therefore, the failure mode is more complex for larger values of D.

Numerical investigation of microstructure effect on mechanical properties of bi-continuous and particulate reinforced composite materials

In this paper, numerical simulations are proposed to investigate mechanical properties of bi-continuous and particulate reinforced composite materials using a non-local voxel-based discrete computational model. Special focus of this article is the effect of 3D microstructure and its heterogeneity on elastic deformation and fracture behaviors. First, a review on model formulation is presented. Model parameters are derived in terms of material constants using the concept of energy equivalency. Interface representation and numerical homogenization scheme are discussed. Following this, numerical investigations on the effects of interface properties and inclusion characteristics, i.e. the volume fraction and material constants, on homogenized elastic constants and fracture behaviors of statistically isotropic bi-phase composites are performed. The effective elastic constants predicted by the proposed model agree well with analytical results. Fracture simulation demonstrates good capability of the proposed model for the microstructure-sensitive failure analysis. Conclusions and future work are drawn based on the proposed study.

Notch effect in failure of fiberglass non-woven materials

This study is concerned with the failure characteristics of notched and unnotched specimens of a highly porous, multilayered non-woven fiber network material subjected to uniaxial tension. The network consists of glass fibers locally bonded by a polymer resin. The multilayer character of the material emerges from the manufacturing process in which the material is produced in plate form. Experiments indicate the presence of a size effect on fracture such that the net section strength of deep-notched specimens appear as higher than that of unnotched and shallow-notched specimens. For unnotched and shallow-notched specimens, failure emerges as a through-thickness delamination triggered by the failure of the interlayer bonds. The presence of notches, however, leads to a transition in deformation mechanism. For deep notches an unusual in-plane failure mode is observed where the failure plane is inclined to the notch plane. This failure mode is attributed to the fiber orientation distribution and the nonaffine characteristics of the mechanical response of the material. A computational model for the in-plane failure analysis demonstrates that failure is not defined by a fracture but rather a strength model, and this effect results from the nonaffine deformation state in the network material. The transition to the higher strength failure mode with increased notch depth results from the constraints on internal load transmission processes imposed by the notches.

Progressive failure analysis on scaled open-hole tensile composite laminates

Despite the rapid advances of numerical methods and theoretical models for progressive failure analysis of composites, it’s still a challenge to predict the strength and damage progression of composite laminates under open-hole tension (OHT). One of the main obstacles is to capture the true stress concentration at the hole edge. It has been found that the formation of longitudinal splitting at early loading stage alleviates the extremely high stress concentration. The purpose of this study is to develop an efficient progressive damage model, employing surface-based cohesive contacts for longitudinal splitting and delamination, to predict the thickness size effect of sublaminate scaled and ply-level scaled laminates under OHT. It is found that by using aligned mesh with the fiber direction for each ply, a good correlation with experimental results can be achieved for both strengths and failure modes of the laminates.

유연한 와이블 확장분포의 형상모수를 이용한 NHPP 소프트웨어 신뢰성 모형에 관한 비교연구

소프트웨어 고장분석을 위한 비동질적인 포아송과정에서 결함당 고장발생률이 상수이거나, 단조 증가 또는 단조 감소하는 패턴을 가질 수 있다. 본 논문에서는 수리시점에서도 고장이 발생할 상황을 반영하는 무한고장 NHPP 모형들을 비교 제시하였다. 소프트웨어 신뢰성분야에서 많이 사용되는 유연한 와이블 확장분포에 근거한 무한고장 소프트웨어 신뢰성모형에 대한 비교문제를 제시하였다. 그 결과 형상모수가 비교적 작은 경우가 효율적으로 나타났다. 그리고 모수 추정법은 최우추정법을 이용하였고 모형선택은 평균제곱오차와 결정계수를 이용하였다. 이 연구를 통하여 소프트웨어 개발자들은 형상모수에 따른 소프트웨어 고장현상을 파악하는데 어느 정도 도움을 줄 수 있을 것으로 사료된다. NHPP software reliability models for failure analysis can have, in the literature, exhibit either constant, monotonic increasing or monotonic decreasing failure occurrence rates per fault. In this paper, infinite failures NHPP models that repairing software failure point in time reflects the situation, was presented for comparing property. Commonly used in the field of software reliability based on Flexible Weibull extension distribution software reliability of infinite failures was presented for comparison problem. The result is that a relatively small shaping parameter was effectively. The parameters estimation using maximum likelihood estimation was conducted and model selection was performed using the mean square error and the coefficient of determination.. In this research, software developers to identify software failure property follows shape parameter, some extent be able to help is considered.

Dynamic risk analysis of offloading process in floating liquefied natural gas (FLNG) platform using Bayesian Network

The growing demand for natural gas has pushed oil and gas exploration to more isolated and previously untapped regions around the world where construction of LNG processing plants is not always a viable option. The development of FLNG will allow floating plants to be positioned in remote offshore areas and subsequently produce, liquefy, store and offload LNG in the one position. The offloading process from an FLNG platform to a gas tanker can be a high risk operation. It consists of LNG being transferred, in hostile environments, through loading arms or flexible cryogenic hoses into a carrier which then transports the LNG to onshore facilities. During the carrier's offloading process at onshore terminals, it again involves risk that may result in an accident such as collision, leakage and/or grounding. It is therefore critical to assess and monitor all risks associated with the offloading operation. This study is aimed at developing a novel methodology using Bayesian Network (BN) to conduct the dynamic safety analysis for the offloading process of an LNG carrier. It investigates different risk factors associated with LNG offloading procedures in order to predict the probability of undesirable accidents. Dynamic failure assessment using Bayesian theory can estimate the likelihood of the occurrence of an event. It can also estimate the failure probability of the safety system and thereby develop a dynamic failure assessment tool for the offloading process at a particular FLNG plant. The main objectives of this paper are: to understand the LNG offloading process, to identify hazardous events during offloading operation, and to perform failure analysis (modelling) of critical accidents and/or events. Most importantly, it is to evaluate and compare risks. A sensitivity analysis has been performed to validate the risk models and to study the behaviour of the most influential factors. The results have indicated that collision is the most probable accident to occur during the offloading process of an LNG carrier at berth, which may have catastrophic consequences.

A consistency elasto-viscoplastic damage model for progressive failure analysis of composite laminates subjected to various strain rate loadings

This paper is concerned with the development and validation of a consistency elasto-viscoplastic damage model that accounts for the strain rate-dependent plastic response and the progressive post-failure behaviour of composite materials. The model proposed is suitable for progressive failure analysis of composite materials and structures subjected to loadings at various strain rates. A strain rate-dependent yield criterion is adopted; whereas the standard Kuhn–Tucker conditions for plastic loading and unloading remain valid. Also, the plastic consistency condition for strain rate-dependent material is satisfied. The relevant strain-driven implicit numerical integration procedure for the proposed material model is developed. A tangent stiffness operator including the strain rate-dependent effects and consistent with the integration procedure developed is derived to ensure the quadratic convergence rate pertaining to the Newton–Raphson method in a finite element analysis. The implicit integration algorithm is implemented in the finite element code Abaqus through the user-defined material subroutine UMAT. The validation of the proposed model is performed on S2/8552 glass/epoxy off-axis block composite specimens subjected to compression at various strain rates. It is shown that the strain rate-dependent response of composite materials is well captured and the predicted results agree well with the experimental data reported in the literature.

A fully coupled geomechanics and fluid flow model for proppant pack failure and fracture conductivity damage analysis

One reason for observed reductions in the conductivity of hydraulic fractures is failure of the proppant pack. Proppant deformation, crushing, or embedment can decrease the fracture width and conductivity. In this paper, the continuity and momentum balance equations were fully coupled to simulate the transient phenomena involving fluid flow through a deformable porous proppant pack. Porous media displacement, water pressure, and gas pressure were derived as primary unknowns. The governing equation was discretized using the finite element method and solved numerically. In this model, the proppant pack and formation rocks were treated as two different types of continuous porous media (Biot type). Proppant deformation, crushing, and embedment could be identified through the geomechanical model, while the damage effects on gas/oil production would be studied through the fluid-flow model. Analysis of proppant deformation and crushing was based on the proppant pack stress–strain behavior. The displacement of the fracture-formation interface represented both the deformation of proppant and rock solids around fracture surface. Mohr–Coulomb failure was used as the criterion for proppant crushing. Effects of proppant damage were evaluated on proppant pack porosity and permeability. The model can be applied generally in hydraulically fractured reservoirs with proper inputs. In this paper, we used a fractured tight sand gas reservoir as a study case. The pressure distribution as well as proppant pack deformation are illustrated in the paper. Proppant pack mechanical behavior was found to be sensitive to the fluid flow pressure. Proppant near the wellbore has a higher likelihood of being crushed.

A 2D Peridynamic Model for Failure Analysis of Orthotropic Thin Plates Due to Bending

The present paper deals with the problem of cracks propagating in thin orthotropic flat plates under bending loads. We define the mechanical behavior of an orthotropic lamina in which shear deformation can be neglected (Kirchhoff plate). The formulation follows the main ideas of bond based Peridynamics. Failure criteria limit the maximum curvatures and provide failure values which may be different in different directions. Several numerical examples show that the results obtained with the new approach are in good agreement with those obtained with more classical computational methods. Moreover the numerically computed crack patterns seem to follow in a reasonable way the orthotropic properties of the models.

Failure mechanism and control technology of longwall coalface in large-cutting-height mining method

The stability control of longwall coalface is the key technology of large-cutting-height mining method. Therefore, a systematic study of the factors that affect coalface stability and its control technology is required in the development of large-cutting-height mining method in China. After the practical field observation and years of study, it was found that the more than 95% of failures in coalface are shear failure. The shear failure analysis model of coalface has been established, that can perform systematic study among factors such as mining height, coal mass strength, roof load, support resistance, and face flipper protecting plate horizontal force. Meanwhile, sensitivity analysis of factors influencing coalface stability showed that improving support capacity, cohesion of coal mass and decreasing roof load of coalface are the key to improve coalface stability. Numerical simulation of the factors affecting coalface stability has been performed using UDEC software and the results are consistent with the theoretical analysis. The coalface reinforcement technology of large-cutting-height mining method using the grouting combined with coir rope is presented. Laboratory tests have been carried out to verify its reinforcement effect and practical application has been implemented in several coal mines with good results. It has now become the main technology to reduce longwall coalface failure of large-cutting-height mining method.

일반화 통계량에 의존한 와이블 확장모형을 이용한 NHPP 소프트웨어 신뢰성 모형에 관한 연구

소프트웨어 고장분석을 위한 비동질적인 포아송과정에서 결함당 고장발생률이 상수이거나, 단조 증가 또는 단조 감소하는 패턴을 가질 수 있다. 본 논문에서는 수리시점에서도 고장이 발생할 상황을 반영하는 무한고장 NHPP 모형들을 비교 제시하였다. 소프트웨어 신뢰성분야에서 많이 사용되는 와이블 확장분포에 근거한 무한고장 소프트웨어 신뢰성모형에 대한 비교문제를 제시하였다. 그 결과 형상모수가 비교적 큰 경우가 효율적으로 나타났다. 그리고 모수추정법은 최우추정법을 이용하였고 모형선택은 평균제곱오차와 결정계수를 이용하였다. 이 연구를 통하여 소프트웨어 개발자들은 형상모수에 따른 소프트웨어 고장현상을 파악하는데 어느 정도 도움을 줄 수 있을 것으로 사료된다. NHPP software reliability models for failure analysis can have, in the literature, exhibit either constant, monotonic increasing or monotonic decreasing failure occurrence rates per fault. In this paper, infinite failures NHPP models that repairing software failure point in time reflects the situation, was presented for comparing property. Commonly used in the field of software reliability based on Weibull extension distribution software reliability of infinite failures was presented for comparison problem. The result is that a relatively large shape parameter was effectively. The parameters estimation using maximum likelihood estimation was conducted and Model selection was performed using the mean square error and the coefficient of determination. In this research, software developers to identify software failure property follows shape parameter, some extent be able to help is considered.

Lomax 분포의 형상모수에 근거한 무한고장 NHPP 소프트웨어 신뢰성 모형에 관한 연구

NHPP software reliability models for failure analysis can have, in the literature, exhibit either constant, monotonic increasing or monotonic decreasing failure occurrence rates per fault. In this paper, infinite failures NHPP models that repairing software failure point in time reflects the situation, was presented for comparing property. Commonly used in business, economics, and actuarial modeling based on Lomax distribution, software reliability of infinite failures was presented for comparison problem. The result is that a relatively large shape parameter was effectively. The parameters estimation using maximum likelihood estimation was conducted and Model selection was performed using the mean square error and the coefficient of determination. In this research, software developers to identify software failure property follows shape parameter, some extent be able to help is considered.

A nonlocal finite element model for progressive failure analysis of composite laminates

Localized damage and failure of composites often lead to spurious mesh dependence and zero energy dissipation due to the lack of a length scale by using finite element analysis. Based on the variational form of the stress boundary value problem with an interface discontinuity, this paper originally proposes a finite element model on the nonlocal intralaminar damage and interlaminar delamination of composite laminates. First, strain-based initial failure criteria and damage evolution criteria are used for the fiber and matrix, and the delamination is modeled by bilinear cohesive model. It is shown two length scales are introduced into the damage evolution behaviors of the fiber and matrix to solve the localization problem of composites. Second, the global nonlocal stiffness equation is derived including the nonlocal intralaminar consistent tangent stiffness and the cohesive interface stiffness, and the node forces for bulk and interface elements. Third, numerical algorithm and finite element codes are developed by combining ABAQUS-UMAT, UEL, USDFLD subroutines and UEXTERNALDB utility subroutine to implement the proposed model, where nonlocal averaging is performed on the derivatives of the equivalent strains with respect to the strain components during each load increment which are included in the nonlocal consistent tangent stiffness. Finally, damage evolution behaviors and load responses for two [0°/90°]4s T700/8911 composite specimens with different central hole sizes are studied by nonlocal FEA. Numerical results demonstrate the ability of the proposed model to address localized deformation, strain softening and strength prediction of composites effectively.

Risk analysis of deepwater drilling operations using Bayesian network

Deepwater drilling is one of the high-risk operations in the oil and gas sector due to large uncertainties and extreme operating conditions. In the last few decades Managed Pressure Drilling Operations (MPD) and Underbalanced Drilling (UBD) have become increasingly used as alternatives to conventional drilling operations such as Overbalanced Drilling (OVD) technology. These newer techniques provide several advantages however the blowout risk during these operations is still not fully understood. Blowout is regarded as one of the most catastrophic events in offshore drilling operations; therefore implementation and maintenance of safety measures is essential to maintain risk below the acceptance criteria. This study is aimed at applying the Bayesian Network (BN) to conduct a dynamic safety analysis of deepwater MPD and UBD operations. It investigates different risk factors associated with MPD and UBD technologies, which could lead to a blowout accident. Blowout accident scenarios are investigated and the BNs are developed for MPD and UBD technologies in order to predict the probability of blowout occurrence. The main objective of this paper is to understand MPD and UBD technologies, to identify hazardous events during MPD and UBD operations, to perform failure analysis (modelling) of blowout events and to evaluate plus compare risk. Importance factor analysis in drilling operations is performed to assess contribution of each root cause to the potential accident; the results show that UBD has a higher occurrence probability of kick and blowout compared to MPD technology. The Rotating Control Devices (RCD) failure in MPD technology and increase in flow-through annulus in UBD technology are the most critical situations for kick and blowout.

A progressive failure analysis model for composite structures in hygrothermal environments

A progressive failure analysis model involving hygrothermal effects is presented for predicting failure of composite structures in hygrothermal environments. The model introduces a constitution equation accounting for the hygrothermal strains. Synchronously, the temperature-induced modification of stiffness and strength parameters are involved in the stress analysis model, failure criterion and material degradation rules. A user defined subroutine was developed and embedded into a FEA package to perform the failure analysis of composite structures in hygrothermal environments. To verify the proposed model, specimens made of carbon/bismaleimide composites with two typical lay-ups were tested under tension and compression loadings, respectively, in which both dry and moisture specimens were tested at 25°C, and only moisture specimens were tested at 75°C and 105°C. The good consistency between the numerical and experimental results, either the failure load or failure pattern, validates the proposed model. It follows that hygrothermal environments can hardly affect the tensile mechanical properties while significantly reduce the compressive behaviors of laminated composite structures. In addition, the failure mechanisms of typical tension and compression specimens are disclosed.

유한 및 무한고장 지수파우어 NHPP 소프트웨어 신뢰성모형에 대한 비교 연구

NHPP software reliability models for failure analysis can have, in the literature, exhibit either constant, monotonic increasing or monotonic decreasing failure occurrence rates per fault. In this paper, finite failure NHPP models that assuming the expected value of the defect and infinite failures NHPP models that repairing software failure point in time reflects the situation, were presented for comparing property. Commonly used in the field of software reliability based on exponential power distribution software reliability model finite failures and infinite failures were presented for comparison problem. As a result, finite fault model is effectively infinite fault models, respectively. The parameters estimation using maximum likelihood estimation was conducted. In this research, software developers to identify software failure property some extent be able to help is considered.

Failure analysis and permeation modelling of photovoltaic module sealing material in Hot and humid conditions

Hot and humid conditions are one of the most typical working environments of photovoltaic module. Studying the aging and failure mechanisms of photovoltaic module and their reactions with steam in these conditions is needed to increase the reliability of photovoltaic module products. In this paper, the IR spectrum was used to analyse ethylene-vinyl acetate in different aging states and determine the reaction process of ethylene-vinyl acetate on the aging process in hot and humid conditions. In this study, a mathematical model was developed to extrapolate the factors that influenced the steam permeation and time constant in this process. The results will benefit sealing materials selection, design and enhancement of anti-permeation abilities, decrease the risk of failure by steam permeation, and improve the reliability of photovoltaic module.

Coupled thermo–mechanical interface model for concrete failure analysis under high temperature

A thermo–mechanical interface model for failure analysis of concrete subjected to high temperature is presented in this work. The model is an extension of a fracture energy-based interface formulation which now includes thermal damage induced by high temperature and/or fire. The coupled thermal–mechanical effect in the interface model is taken into account through the formulation of a temperature dependent maximum strength criterion and fracture energy-based softening or post-cracking rule. In this sense, the strong variation of concrete ductility during failure processes in mode I, II or mixed types of fracture is described through the consideration of temperature dependent ductility measures and of the specific work spent in softening. Moreover, a temperature-based scaling function is introduced to more accurately predict the thermal effect affecting the interface strength and post-cracking response. After outlining the mathematical formulation of the interface model, numerical analyses are presented to validate its soundness and capability. A wide range of experimental results, available in the scientific literature, are analyzed at both material and structural scale of analysis using the proposed interface model and in the framework of the discrete crack approach. The results demonstrate the predictive capabilities of the proposed interface constitutive theory for temperature dependent failure behavior of concrete.

Weak coupling of shell and beam computational models for failure analysis of steel frames

A hierarchical modeling of planar steel frames that is based on a weak coupling of shell and beam computational models is studied in detail. A shell finite element is used to compute failure response of a representative part of each column and each beam of a frame under consideration; elasto-plasticity, geometrical nonlinearity and material softening (along with a localization limiter) are taken into account. The computed results, which naturally include local buckling and/or localized material failure effects, are further incorporated into a beam inelastic stress-resultant constitutive model; the embedded-discontinuity-in-rotation Euler–Bernoulli finite element is considered in this work. The designed beam finite element formulation can be effectively used for the failure analysis of the steel frame. Important issues of such weak coupling concept are presented and results of several numerical simulations are discussed.

A new progressive failure analyses model: development, implementation, parametric study and validation

A model for composite failure analysis was developed based on the theory of action plane of failure. A Weibull curve jointly with a non-local criterion was used to model fibre failure. Routines were implemented in finite element code and an extensive parametric evaluation, which included identification and sensibility analysis, was performed from the results of elementary coupons. Key parameters and their influence over the response are presented. Finally, the model was validated against experimental data obtained from the tests performed on large composite plates presenting stress concentrator and consistent results were obtained for both structures analysed (notched and circular hole).