Types Of Failure Mechanisms Research Articles

Buckling Failure Mechanism of a Rock Dam Foundation Fractured by Gentle Through-Going and Steep Structural Discontinuities

The failure mechanism analysis of dam foundations is key for designing hydropower stations. This study analyses the rock masses in a sluice section, which is an important part of the main dam of the Datengxia Hydropower Station currently built in China. The stability of the sluice rock masses is predominantly affected by gentle through-going soft interlayers and steep structural fractures. Its foundation failure mechanism is investigated by means of a numerical method, i.e., Universal Distinct Element Code (UDEC) and the geomechanical model method. The modeling principle and process, and results for the rock dam foundation are introduced and generated by using the abovementioned two methods. The results indicate that the failure mechanism of the foundation rock masses, as characterized by gentle through-going and steep structural discontinuities, is not a conventional type of shear failure mechanism but a buckling one. This type of failure mechanism is verified by analyzing the deformation features resulting from the overloading of both methods and strength reduction of the numerical method.

Load carrying capacity of inclined crossing screws in glulam-concrete composite beam with an interlayer

In many practical applications of timber-concrete composite (TCC) structures, especially in rehabilitation of timber buildings, the floorboard interlayer is utilized as formwork for pouring concrete slab. So far, few researches have been conducted to study the shear performance of inclined crossing screws in TCC beam with an interlayer. In this paper, seven groups of shear tests were conducted to study the shear performance of inclined crossing screws in glulam-concrete composite beam with an interlayer. The analyses focused on the effects of embedded length of screw into glulam, thickness of the concrete slab and screw diameter on the failure mechanism, the load-slip behavior and the load carrying capacity. Two typical failure mechanisms were observed: cone failure of the concrete layer around shear-compression screw and pull-out failure of shear-tension loaded screw. The test results demonstrated that with the increase of screw diameter and embedded length of screw into glulam, the load carrying capacity of the inclined crossing screws was enhanced. According to theoretical studies, in timber-concrete composite beams with interlayer, the calculation method for predicting load carrying capacity of inclined crossing screws was proposed, and significantly the predicted results agreed well with the experimental results.

Effects of porosity on the fatigue life of polyamide 12 considering crack initiation and propagation

Internal pores in composite materials generated during fabrication processing can induce negative influences on the physical properties. Among them, the fatigue life under repetitive loadings is one of the most detrimentally influenced properties by the undesirable pores. In this paper, we investigated the effect of pore geometries – 1) sizes and 2) aspect ratios on the fatigue life of polyamide 12 (PA12) by combining two different fatigue life prediction approaches. Considering that the typical failure mechanism of structural materials follows the initiation of the crack, propagation, and ultimate separation, the present approach counts the fatigue life until crack initiation and fatigue cycles during the crack growth until complete separation. For the prediction, a crack growth model by Castillo-Canteli-Siegele model (CCS model) with initial defects was adopted. In addition, to reflect the elastoplastic behavior better, an extended CCS model with the cyclic J-integral was used. The simulation results show that the presence of the pores in the plastic material can significantly affect the fatigue life. The characteristics of fatigue properties on the geometric conditions of pores were discussed by comparing the results. The proposed method can be seamlessly used for the evaluation of fatigue life of polymer matrix composite materials.

Variational Modelling of Strain Localization in Solids: A Computational Mechanics Point of View

Strain localization is one of the most challenging phenomena in solid mechanics. It occurs when strains concentrate in very narrow bands within a solid, typically referred to as localization bands. This behaviour is related to different types of failure mechanisms: fracture, shear bands and slip lines. Being a dissipative process, the modelling of strain localization could seem to preclude the use of variational methods. However, a sound framework to deal with this issue has been developed in the last few decades. In this contribution, we review the modelling of strain localization by means of variational methods systematically, presenting the main underlying theoretical concepts. The issue of irreversibility is approached by means of the theory of generalized standard materials, which constitutes the basis for the variational approach. Then, typical problems occurring in the modelling of strain localization are analyzed: the tendency to localize in a band of zero thickness with no dissipation, the determination of the geometry of the localization band, and the orientation bias of such band with respect to mesh alignment in finite element discretizations. We discuss solutions for these problems, focusing on the approach that tackles the description of the localization band using phase fields.

Detection, Location and Concealment of Defective Pixels in Image Sensors

This paper presents the construction process of defective pixel detection and concealment methods, for image sensor online diagnosis and self-healing. The proposed process is based on pixel neighborhood analysis using only simple arithmetic operations on the image files. This leads to an optimization of the processing speed of the produced image. A first step in the process is to identify and locate the defective pixels on the image. Three defective pixel detection algorithms are proposed. The first one uses the distance between the pixel under test and its neighboring pixels. The second method is based on the median value of the pixel block around each pixel. The third method uses an evaluation and analysis of the local dispersion parameters in the image. The concealment of detected defective pixels is the second step of the self-healing process of image sensor. It consists of substituting the defective value by the median value of the neighborhood pixel block. In the study and learning phase, distorted images obtained by injecting random disturbances into healthy reference images are used to evaluate the defective pixel detection and concealment methods. The set of $1 176$ distorted images is constructed using 196 reference images with six types of defects, based on typical failure mechanism of image sensors. The proposed methods are compared to different state-of-the-art defective pixel detection and correction methods, in both software and FPGA implementations. The experimental results undoubtedly demonstrate that the new methods proposed in this paper perform the best results compared to the state-of-the-art.

Bearing capacity of a strip footing placed next to an existing footing on frictional soil

The ultimate bearing capacity of a single/isolated footing has been investigated intensively by many researchers. Although a lot of studies considered different aspects affecting the bearing capacity, only very few focused on the influence of an existing footing on the bearing capacity of a new footing in its close proximity. In this study, the influence of an existing footing on the ultimate bearing capacity of a recently constructed footing in a close spacing has been investigated with respect to different sizes of the footings, spacings between the footings, friction angles of the subsoil and loads applied on the existing footing. Numerical simulations based on finite-element limit analysis (FELA) are utilized to determine lower and upper bounds of the ultimate bearing capacity which bracket the exact solution from below and above. The results for isolated footings are compared with selected data from literature in terms of the bearing capacity factor Nγ indicating good agreement of both, lower and upper bound values. Accuracy of the results was enhanced by applying an adaptive mesh refinement technique which enabled a more precise approximation of the failure mechanism and a better estimation of the exact solution due to smaller differences between the lower and upper bound solutions. The results for footings placed next to an existing footing are discussed with regard to the interference factor ξγ as well as the shape and size (extend) of the failure mechanism. The results illustrate that two types of failure mechanisms may develop which either extend up to the front edge of the existing footing or pass underneath. Comparisons with previous studies revealed that interference factors have been improved significantly due to utilization of adaptive mesh refinement technique. Moreover, design charts for an estimation of ξγ are presented for variable footing width ratios, spacings between the footings, friction angles of the subsoil and loading factors of the existing footing.

Fracture Behavior of Carbon-Epoxy under Different Loading

Delamination is the common failures of composite material attributed to various reasons, most importantly the potential stiffness degradation leading to small flaws and subsequently theypropagate, and it becomes essential to characterize the new materials for interlaminar fracture. For the present study Carbon /epoxy system of IM7/8552 was investigated under mode I and mode II loading. Material was formed into unidirectional laminates with Teflon inserts at its mid length. The specimens were machined according to ASTM standards, Tests were executed on a quasi-static Intron 8225, with load control at 5 mm/ min and 2 m/min for the mode -I and mode-II respectively. The strain energy release rate was found to be GIC=0.266 kJ/m2 and GIIC=0.687 kJ/m2. Fiberbridging was prominently absent in the DCB samples Examination of the fracture surface by SEM at SAIF, in IIT{M) and the nature of the fracture surface revealed the typical failure mechanism pertaining to mode-I and mode-II failuremechanisms.

Numerical modeling of plastic deformation and failure around a wellbore in compaction and dilation modes

SummaryIn many wellbore stability analyses, the ability to forecast both the occurrence and extent of plastic deformation and failure hinges upon a fundamental understanding of deformation mode and failure mechanism in the reservoir rock. This study focuses on analyzing plastic zones, localized deformations, and failures around a borehole drilled overbalanced or underbalanced through a highly porous rock formation. Based on several laboratory experiments, porous rocks are prone to deform under both shear‐induced dilation and shear‐enhanced compaction mechanisms depending on the stress state. The shapes of the deformation and failure patterns around the borehole are shown, depending on the initial stress state and the local stress paths. The inquiry of the local stress paths in the near‐wellbore zone facilitates the understanding of the reasons for different types of failure mechanisms, including the mixed‐mode and the plastic deformation structures. The modification of the 2D plane strain condition by imitating third stress in the numerical scheme helps us bring the stress paths closer to the real state of loading conditions. Our modeling reveals that the transition from isotropic to anisotropic stress state is accompanied by an increase in the deviatoric part of effective shear tensor that leads to the development of inelastic deformation, degradation, and subsequent rock failure. Particular interest is devoted to the modeling of strain localization especially in compaction mode around a wellbore and computing the amount of stress concentration at the tips of dog‐eared breakouts. Stress concentration can result in a change in irreversible deformation mode from dilatancy to compaction, elucidating the formation of the shear‐enhanced compaction phenomenon at the failure tips in the direction of the minimum horizontal stress.

Damage mechanics-based modeling approaches for cyclic analysis of precast concrete structures: A comparative study

Precast concrete frame structures are widely adopted around the world due to their various advantages, so it is important to study their seismic performance. The development of damage mechanics has enabled us to accurately investigate the typical failure mechanisms of precast structures. This paper presents three of the most commonly used modeling approaches based on damage mechanics for analysis of precast reinforced concrete structures under cyclic loading and compares the performance of the three models. Particularly, the shear behavior of the joint panel and the bond-slip behavior of the beam–column interfaces are especially considered, which are the key issues for precast concrete structures. First, the fundamental assumptions, formulations, and modeling strategies are given in detail for each approach. Then, the unified damage mechanics for concrete is introduced, and the model for reinforcement bars and the consideration of the bond-slip effect are also presented. Several benchmark cyclic tests of precast beam-to-column connections are chosen to evaluate the accuracy and efficiency of the modeling approaches. The numerical results, e.g. the capacities, deformations, and energy dissipation of the connections, are compared to the experimental results to show the ability of each approach. With this study, we can gain a further understanding of the characteristics and applicability of each modeling approach, helping us make a better decision in choosing which modeling approach is appropriate.

Predicting stress and creep life in Inconel 718 blade-disk attachments

Due to several physical and computational difficulties in Finite Element (FE) analysis of contact in fir-tree blade-disk attachments of gas turbines, there has always been a great demand for stress, fatigue and creep life assessment of fir-tree joints without modeling physical contact. However, reliability of these models is not trivial. To meet these challenges, in the current paper, three different analysis methodologies were examined for creep life assessment in a turbine engine disk. This is a significant problem for designers and operators of gas turbines. Two simple models were developed with removal of the blade from the FE domain as well as a detailed 3D model containing a blade and it’s contact details. Numerical results were compared with available experimental stress measurement. Creep material behavior models were also developed and parameters for the Liu-Murakami damage model together with the Norton creep law were determined for Inconel 718 at 620 °C. A creep subroutine was written and creep analyses of these joints were performed for typical service temperature of 620 °C and the maximum time period of 100,000 h. FE results were compared with fracture mode of service induced cracks. For the different load cases ranging from 3000 rpm to 9000 rpm, it is demonstrated that methodology based on simple models are very efficient. The equivalent pressure model always underestimates the value of peak stress whereas the virtual link model provided more realistic results. The results are discussed according to the different failure criteria for the fir-tree joints life assessment. Results presented in the paper are valuable for failure analysis of these critical components. Moreover, the stress distribution obtained from the simple realistic model can be used for the life assessment codes applicable to other types of failure mechanism.

Research on Key Test Methods of the Smart Meter Software Based on Failure Modes

Software quality has become a key factor affecting the overall quality of the smart meter. To improve the reliability of the smart meter software, analyzed the typical failure modes and mechanism based on actual failure cases of smart meters. For different software failure modes, the test techniques were studied from the perspective of the software development cycle. Designed a test program of the smart meter software and provided automated test tools to improve the breadth and depth of the software test and improve the product reliability.

Seismic Performance Analysis of Highway Subgrade Retaining Structure

Subgrade retaining structure is the most common structure of highway, once it is damaged by earthquake, its damage is universal. Under the action of seismic load, whether the subgrade retaining structure cracks or collapses, and the failure mechanism is one of the key problems in the design of retaining structure in earthquake area. Therefore, it is necessary to systematically study the typical failure mode, failure mechanism and seismic earth pressure of highway retaining structures. In this paper, through the investigation and analysis of earthquake damage law and failure mode of highway retaining structure, combined with numerical model test, the seismic damage mode of highway retaining structure is summarized, and effective seismic reinforcement method is put forward, which provides a certain basis for post-disaster reconstruction of highway structure.

Seismic vulnerability of historical orthodox churches in Romania: numerical modelling and retrofit solutions

Historical orthodox churches in Romania are generally masonry structures, built without a clear understanding of earthquake demands. Past earthquakes have shown specific damage patterns for these buildings: damages in domes and bell towers, damages of the church nave (particularly a general longitudinal dislocation), damages of the infrastructure. As some of the existing buildings have high architectural or historical value, their structural strengthening is important. Typical failure mechanisms for churches under earthquake loads are identified. Based on these mechanisms, the methods for assessing the seismic vulnerability of existing churches are discussed. A historical listed church is considered as case study. The considered numerical model is presented. Qualitative and quantitative results obtained from the numerical model for the un-retrofitted building are analysed. A retrofit solution is proposed. Comparisons are made between the expected structural behaviour of the church in its present state and after structural strengthening. Conclusions are drawn regarding the seismic vulnerability of this type of buildings.

Typical characteristics of large-scale landslides in the transition belt between the Qinghai-Tibet Plateau and the Loess Plateau

The transition belt between the Qinghai-Tibet Plateau and the Loess Plateau is an area where geohazards occur frequently. To develop a basic understanding of the geohazards in this region, a detailed field investigation of large-scale landslides (i.e., > 106 m3 in volume) has been performed. The results show that 259 large-scale landslides have occurred in this region, of which 254 landslides are rock landslides and the others are soil landslides. These landslides have an average volume of 20.6 Mm3, are mainly concentrated along rivers, and have a linear density that reaches 0.45 landslides/km. Furthermore, more than 90% of the landslides are located within 5.0 km of a fault and more than 80% of the landslides are located at elevations of 1000–2600 m. With increasing landslide volume, the mobility increases, and approximately 45% of the landslides are sturzstrom-type landslides. Large-scale landslides are mainly concentrated along faults, especially around fault intersections. The typical failure mechanisms of the studied landslides are clearly influenced by the regional structure, earthquakes, and river incision.

Stability of dual square tunnels in rock masses subjected to surcharge loading

The stability of dual unlined square tunnels subjected to surcharge loading in rock masses, obeying Generalized Hoek-Brown (GHB) failure criterion, is investigated by adaptive finite element limit analysis (AFELA) under plane strain conditions. Both upper bound (UB) and lower bound (LB) of the dimensionless stability number N are obtained, with the relative errors being found within 7%. Extensive parametric studies are conducted to investigate the effects of the center-to-center distance ratio, cover depth ratio, geological strength index (GSI) and material constant for intact rock (mi). The results are presented in the form of dimensionless stability tables and charts for engineers to use, and typical failure mechanisms are discussed. The results obtained in this study compare reasonably well with the solutions reported in the literature.

A Comprehensive Review Toward the State-of-the-Art in Failure and Lifetime Predictions of Power Electronic Devices

This paper discusses various types of failure mechanisms, precursor parameters, and accelerated aging-based procedures to estimate the remaining life of power electronic devices. Special attention has been given to summarize the different techniques typically used for measuring the junction temperature, because it plays a vital role during accelerated aging and condition monitoring. We reviewed more than 250 papers, and the references list 139 of them in order to explain and address the advantages and disadvantages of various techniques toward the reliability prognosis. Thus, this paper can be considered as an expedient reference to conduct future research on lifetime prediction of existing power electronic devices.

Stability of two circular tunnels at different depths in cohesive-frictional soils subjected to surcharge loading

Adaptive finite element limit analysis (AFELA) is employed to investigate the stability of two circular tunnels at different depths in cohesive-frictional soils subjected to surcharge loading. The upper and lower bounds of the tunnel stability numbers are obtained, with the relative errors being found within ±5%. Five parametric studies are conducted to evaluate the effects of the horizontal and vertical spacing ratio, overburden stress factor, cover depth ratio and soil internal friction angle on the tunnel stability numbers. Design tables and charts are provided to facilitate engineers’ use. In addition, typical failure mechanisms are discussed and examined.

Notch tip fields in amorphous films resting on ductile substrates

The architecture consisting of films resting on a ductile substrate is ubiquitous in a wide variety of applications. A typical failure mechanism of such a structure is cracking of the films. In this study, the calculations for the notch tip fields in a metallic glass film deposited on a ductile substrate are carried out to explore the fracture mechanisms of the amorphous films. The amorphous film is characterized by an isotropic elastic-plastic model which captures the pressure sensitive yielding and post-yield strain softening behavior of metallic glasses, and the substrate is taken to be an elastic-plastic solid with the flow rule given by von-Mises flow theory. It is found that the thick amorphous films exhibit high opening stress and small plastic deformation, indicating that brittle cracking of the films tends to be the dominant fracture mode. Whereas, the low opening stress is observed and shear bands develop in the case of thin amorphous films, implying that the cracking caused by shear bands governs the fracture of films. We further revealed that the pressure sensitive yielding plays an important role in the fracture of amorphous films; large degree of pressure sensitivity enables low opening stress and enhanced plastic deformation in the films, increasing the propensity of formation of shear bands. The findings of this study provide plausible explanations for the experimentally observed fracture behavior of amorphous films on ductile substrates, and shed new light on the fracture mechanisms of such a structure.

Stability of dual circular tunnels in a rock mass subjected to surcharge loading

This paper investigates the stability of dual circular tunnels in a rock mass subjected to surcharge loading using adaptive finite element limit analysis (AFELA). The tunnels are modelled under plain-strain conditions, and the rock mass is assumed to be a homogeneous and isotropic material obeying the Hoek-Brown failure criterion. For the studied problem, numerical kinematic and static approaches are employed to calculate the rigorous upper and lower bounds of the stability number N, which has been bracketed within ±5% from above and below. The calculated results are presented in the form of dimensionless stability charts, and the typical failure mechanisms are discussed through parametric studies of the problem variables using the visualized results of AFELA.

A Failure Mechanism Cumulative Model for Reliability Evaluation of a k-Out-of-n System With Load Sharing Effect

In this paper, we propose a failure mechanism cumulative model that considers the loading history of the load sharing effect in a k-out-of-n system. Three types of failure mechanisms are considered, continuous degradation, compound point degradation, and sudden failure due to shock. By constructing a logic diagram with functional dependence gate, the load-sharing effect can be explained from the failure mechanism point of view using a mechanism-acceleration gate that shows that when one component fails, the failure mechanisms of the other surviving components will be accelerated. By deriving the total damage equation and a constructing failure behavior model, the system reliability of a k-out-of-n system with different types of failure mechanisms were evaluated. A voltage stabilizing system that contains a 1-out-of-2 subsystem, or a 2-out-of 3 subsystem was used to illustrate the practical applicability of the proposed approach. A combined Monte Carlo and binary decision diagram method was used in the numerical simulation process.