Different Types Of Failure Mechanisms Research Articles

Seismic bearing capacity factor [formula omitted] for a rough strip footing on sloping ground

By using the Mohr-Coulomb (MC) yield criterion, the method of stress characteristics (MOSC) has been employed to compute the bearing capacity factor Nγ in the presence of horizontal pseudo-static earthquake inertial forces for a rough strip footing over sloping ground surface. Two different types of failure mechanisms (M1 and M2) were employed. Due to rigorousness of the adopted failure mechanism, the present analysis overcomes the limitation of the existing MOSC formulation available in literature. The solutions in all the cases have also been determined based on the finite elements limit analysis (FELA). The results from the two different analyses, including the failure mechanisms, were found to be very close with each other.

(Digital Presentation) Elucidating Electrolyte-Induced Performance Decay in Sodium-Tin Batteries

Tin (Sn) anodes for sodium-ion batteries have recently been extensively investigated due to their high capacity (847 mAh/g), low average operating potential (~250 mV vs. Na/Na+), environmental benignity, and high abundance. Unfortunately, upon repeated charging/discharging, both the Sn electrode and Na metal suffers from large volume changes that rupture the solid electrolyte interphase (SEI) and initiate the onset of cell failure. To understand such complex and interrelated phenomena, we have designed a 3-electrode cell to track the evolution of the electrochemical signature of both the working and counter electrode. Additionally, we have compared the electrode morphology and electrode/electrolyte interface under different electrochemical conditions and probed these morphological/interfacial changes with cycling life performance to cultivate a holistic understanding of different types of failure mechanisms. In particular, we have discussed whether the primary reason for the shorter cycling life is the mesoscopic/macroscopic deformation of the Sn electrode caused by volume expansion/contraction or the continuous formation/breakdown of SEI. Furthermore, the effect of a localized electrochemical environment, which primarily depends on the choice of electrolytes (ether-based and carbonate-based), is also explored here.

Drill Bit Failure Forensics Using 2D Bit Images Captured at the Rig Site

Summary Identifying the root cause of damage of a pulled bit as soon as possible will aid in preparation for future drilling operations. Today, bit damage analyses are often time-consuming, delayed, subjective, and error prone. A novel automated forensics approach is presented in this paper for polycrystalline diamond compact (PDC) bit damage root cause analysis using 2D bit photos that can be easily captured on a phone or camera at the rigsite. A labeled data set consisting of 125 actual bit images and 800 synthetic images was first created with the cutters appropriately identified and labeled. Using this data set, a convolutional neural network (CNN) along with other image processing techniques was applied to first identify the individual cutters and their positions on the bit and then to quantify the damage to the cutters. A cutter detection accuracy of over 97% and a damage quantification accuracy of 97% were achieved. A separate classifier was then trained to directly identify the root cause of failure from the bit images. This classifier utilized a separate data set that consisted of multiple bit images from 25 distinct bit runs. This data set was labeled into different types of failure mechanisms through analysis by a subject-matter expert. The trained classifier developed could properly identify the root causes of failure when the bit photo quality met certain minimum standards. One key observation was that bit images are not always captured appropriately, and this reduces the accuracy of the proposed methodology. By identifying the potential root causes of PDC damage through image processing, drilling parameters can be optimized to prolong future bit life.

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.

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.

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.

Effect of competing mechanisms on fracture toughness of metals with ductile grain structures

The fracture toughness of ductile materials depends on the combined effect of plastic dissipation in the constituents and energy spent on creating new crack surfaces. The design of polycrystalline metals with improved fracture toughness requires in-depth understanding of two levels of competing mechanisms: the competition between plastic deformation and crack formation as well as the competition between transgranular and intergranular fracture. Currently, no systematic approach exists to analyze the effects of the two competitions. The fundamental challenges lie in the difficulty in separating the two forms of energy dissipation and inadequate knowledge about the correlation between fracture mechanisms and material fracture toughness. In this paper, a multiscale framework based on the Cohesive Finite Element Method (CFEM) is developed to quantify the two levels of competitions and to predict the fracture toughness of ductile materials by calculating the J-integral at the macroscale. The fracture surface energy for the crack paths associated with different types of failure mechanisms is evaluated through explicit simulation of crack propagation at the microstructure level. The calculations carried out here concern the AZ31 Mg alloy, but the overall approach applies to other materials as well. Results indicate that a proper balance between transgranular and intergranular failure can lead to optimized fracture toughness. Microstructures with refined grain sizes and balanced bonding strength in grains and grain boundaries can best promote the manifestation of favorable failure mechanisms, and as a result, enhance fracture toughness.

Wind turbine blade trailing edge failure assessment with sub-component test on static and fatigue load conditions

Wind turbine blades present different types of failure mechanisms and modes which are associated with specific loading conditions. Trailing edge failure mode has been documented in full-scale blade tests as one of the failure types observed in blades on service. Trailing edge failure is characterized by failure of the trailing edge adhesive joint and the buckling of the trailing edge sandwich panels. This failure is governed by the contribution of edgewise, flapwise and torsion moments, with edgewise moments being the main driver. This paper describes a blade sub-component test setup suitable for studying trailing edge failure on static and fatigue load conditions, which is an improvement in the experimental verification of a trailing edge blade design. The test setup and design drivers are described and studied via FE models. Static and fatigue test results are reported for a full-scale blade section sub-component obtained from a 34 [m] wind turbine blade. Moreover, experimental results are discussed and compared with FE models to describe and study the trailing edge failure mechanism.

Acoustic emission characteristics of fracture modes in masonry materials

Acoustic emission (AE) is a powerful technique for detection and analysis of the elastic waves produced by the failure mechanisms in construction materials such as masonry. In this study, the different fracture mechanisms are studied in relation to the properties of bricks and mortars. The fracture process is being evaluated using the combination of AE and Digital Image Correlations (DIC) techniques. The isolation of the AE signatures of different types of failure mechanisms is done by testing bricks in flexure and brickwork couplets in compression. AE data are analyzed with a simplified AE parameter-based approach aiming to characterize the fracture mode. This is one of the first times where the relation between the shear and the longitudinal strain field is correlated in masonry with AE. This offers new insight in the material's behavior especially in relation to complicated structural geometries where the dominant stress mode is not known a priori.

An experimental and numerical study of the dynamic response of composites under impact at low temperatures

ABSTRACTAn analytical method was applied to investigate the effects of strain rate, low temperature, and impact direction on the energy absorption of composite specimens. The performance of an analytical model was found to be adequate for modeling composites before failure initiation. Results indicated that impact performance of composites is affected over the range of temperatures. Failure mechanism was changed from matrix cracking at room temperature to delamination and fiber breakage at low temperatures. Moreover, it was shown that about 70% of total energy absorbed by a specimen was used to destroy the composite under different types of failure mechanisms.

Discrete element study of viscous flow in magnetorheological fluids

Using discrete element simulations, we gain insight into the structure of a magnetorheological fluid (MRF) under shear. In simulations with flat walls, the particles arrange in chains, sheet-like structures, or columns along the magnetic field lines, depending on the strength of the applied external magnetic field. Corresponding to the structure formation, three different types of failure mechanisms can be identified. For the characterization of the different regimes, specific particle coordination numbers are introduced. The three structural regimes can be distinguished and described by means of these coordination numbers. To analyze the contact between the MRF particles and the walls of the shear cell, additional simulations with rough walls have been conducted. The resulting structure formation could be successfully classified by the introduced coordination numbers. Based on the analysis of the shear stress transmission both in the case of flat and rough walls, possibilities for shear stress enhancement for technological applications are discussed.

Classification of wavelet decomposed AE signals based on parameter-less self organised mapping

Composite materials are characterised by different types of failure mechanisms which are typically associated with matrix cracking, fibre-matrix debonding and fibre breakage. These three mechanisms result in a different AE signature, which can be often recognised. In certain cases it is necessary to classify and map the damage types so as to be able to evaluate the accumulated damage and remaining strength of the material. In this framework, neural networks are widely used for damage characterisation. The classical approach involves recording waveform features and tries to associate them with the underlying damage source. Nevertheless, very often, it is very hard to draw definite conclusions based on these features. In this study, we have used a new type of a neural network which is called parameter-less self organised mapping. It is based on Kohonen neural networks but it is not bound to the naturally subjective learning rate, neighbourhood function and their annealing with the training progress. Moreover, for the training of the NN and the subsequent classification, we have successfully used wavelet decomposed AE signals.

Development of a Comprehensive Oxide Scale Failure Diagram

This paper describes a new approach towards the development of a comprehensive oxide scale failure diagram (OSFD) that delineates the mechanical limits of scales for the different types of failure mechanisms. While former diagrams of a similar type were based on relating the critical strain to scale failure to oxide scale thickness, the new approach replaces scale thickness with a comprehensive operational parameter ωo that summarizes in a multi-level treatment all contributing factors, e.g. physical defect size, interface roughness, scale thickness, Young’s modulus, fracture toughness, etc., that influence failure strain. While this approach should ideally be based on a comprehensive treatment of ωo using fully implemented coding, further considerations based on the identification of “low-impact” and “high-impact” parameters lead to a simplified OSFD where only the physical defect size is needed. This simplified approach can be used to assess the strain tolerance of oxide scales in industrial operation once the particular diagram has been established from laboratory data.