Time-dependent Failures Research Articles

True triaxial shear creep behaviors of sandstone under constant normal load and constant normal stiffness conditions

The long-term stability of rocks is crucial for ensuring safety in deep engineering, where the prolonged influence of shear loading is a key factor in delayed engineering disasters. Despite its significance, research on time-dependent shear failures under true triaxial stress to reflect in situ stress conditions remains limited. This study presents laboratory shear creep measurements on intact sandstone samples under constant normal load (CNL) and constant normal stiffness (CNS) conditions, which are typical of shallow and deep engineering cases, respectively. Our investigation focuses on the effects of various lateral stresses and boundary conditions on the mechanical behaviors and failure modes of the rock samples. Results indicate that lateral stress significantly reduces shear creep deformation and decreases creep rates. Without lateral stress constraints, the samples are prone to lateral tensile fractures leading to macroscopic spalling, likely due to "shear-induced tensile" stress. This failure behavior is mitigated under lateral stress constraints. Additionally, compared to CNL condition, samples under CNS condition demonstrate enhanced long-term shear resistance, reduced shear creep rates, and rougher shear failure surfaces. These findings suggest the need to improve our understanding of rock mass stability and to develop effective disaster prevention and mitigation strategies in engineering applications.

Understanding the Mechanisms of Drilling Challenges through a Systematic Risk Assessment and Geomechanics Modeling; a Post-Drill Case Study, Balsam Field, Onshore East Nile Delta, Egypt

This case study represents an approach of applying a systematic risk assessment in combination with Post-Drilling Geomechanics modeling to properly understand the root causes of drilling challenges through Late Messenain – Early Tortunian formations, Balsam field, onshore East Nile Delta, Egypt. The aim of the analysis is to support pro-actively the operator to drill the future wells safely through the problematic formation in the field. According to the risk assessment; drilling the reservoir section experienced three major challenges including downhole losses, tight spots, and differential sticking. The case study includes two phases; phase-I (Risk Identification Phase) considers defining the drilling hazards utilizing daily drilling reports (DDR’s), meanwhile Phase-II considers (1D Geomechanics & Wellbore Stability) constructing a post-drill Geomechanics models using a licensed Software using all available E-logs, borehole image and caliper data. Post-drill geomechanics models calibrated using drilling events, borehole image, caliper data and reservoir pressure measurements. The results of both risk identification and geomechanics models confirms that tight spots and differential sticking was related to overbalance drilling with improper wellbore strengthening package of drilling fluids that results in invasion/pressure transmission and eventually thick filter cake across high permeable/depleted sandstone rock. the study results indicates that the drilling challenges might be related to certain geomechanics signs e.g. time-dependent failures, weak bedding planes and pressure transmissions. Those Geomechanics events could be related to fluids-rock interactions and lack of improper wellbore strengthening art. The study outcomes would help in minimizing drilling challenges for future wells considering both drilling practices and drilling fluids design.

Reliability evaluation of production systems with finite buffers subject to time-dependent and operation-dependent failures

Reliability evaluation of production systems with finite buffers subject to time-dependent and operation-dependent failures

A case study on time-dependent bedding plane failure

Time-delayed wellbore failures are often observed in shale formation. In some cases, cavings indicating bedding plane failure are observed a few days after initial drill-out with a gradual increase, eventually leading to wellbore collapse. Possible causes of time-delayed wellbore failure include pore pressure diffusion, and its impact can be assessed by traditional poroelastic modeling in which coupled hydraulic-mechanical processes are taken into account. Externally applied loads induce pore pressure that is dissipated according to a diffusion law. During recently conducted wellbore stability analysis targeting a particular field within a strike-slip regime, we found: (1) time-dependent bedding plane failures are significant for highly inclined wells subparallel to the maximum horizontal stress direction (bedding plane failure region gradually increases with time), (2) the Kirsch solution and the assumption of no induced pore pressure (elastic nonporous model) does not give proper mud weight limits to avoid bedding plane failures, and (3) failure regions and modes predicted by the poroelastic model are different from those based on the elastic nonporous approach, under the given situation. Results given by the poroelastic model are apparently consistent with filed observations, demonstrating pore pressure diffusion as a possible cause of observed time-delayed bedding plane failure.

New Creep Constitutive Model for Soft Rocks and Its Application in the Prediction of Time-Dependent Deformation in Tunnels

Creep often occurs in tunnels excavated in soft rocks and it poses a risk to the long-term stability of the excavation. To derive measures for the effective mitigation of the risk, it is important to understand the time-dependent damage mechanism governing the deformation behavior of the surrounding rocks. A new creep constitutive model for soft rocks was proposed in this study to help achieve this understanding. The new creep model was developed based on the disturbed state concept, for example, the relatively intact state of rocks was described by the Burgers model and the fully adjusted critical state was represented by the generalized Bingham model. The analytical solution from the proposed model was given and the parameter calibration based on uniaxial compression creep experimental results were described. The deformation estimated by the proposed model was demonstrated to be in better agreement with experimental data than that estimated by the Burgers model alone. In addition, a three-dimensional creep constitutive model was proposed based on the one-dimensional form with the assumption of the constant bulk modulus. A case study for a tunnel with extensive time-dependent deformations was conducted using FLAC3D with the incorporation of the proposed three-dimensional creep model. The results indicated that the proposed creep model performed well in the prediction of the time-dependent deformations and failures in the section of the tunnel being studied. This model provided a very useful tool for engineers when determining the design for excavations and ground support schemes for tunnels in soft rocks where significant creep behaviors must be considered.

Deep learning-based detection, classification, and localization of defects in semiconductor processes

Defects in semiconductor processes can limit yield, increase overall production cost, and also lead to time-dependent critical component failures. Current state-of-the-art optical and electron beam (EB) inspection systems rely on rule-based techniques for defect detection and classification, which are usually rigid in their comparative processes. This rigidity limits overall capability and increases relative engineering time to classify nuisance defects. This is further challenged due to shrinkage of pattern dimensions for advanced nodes. We propose a deep learning-based workflow that circumvents these challenges and enables accurate defect detection, classification, and localization in a unified framework. In particular, we train convolutional neural network-based models using high-resolution EB images of wafers patterned with various types of intentional defects and achieve robust defect detection and classification performance. Furthermore, we generate class activation maps to demonstrate defect localization capability of the model “without” explicitly training it with defect location information. To understand the underlying decision-making process of these deep models, we analyze the learned filters in pixel space and Fourier space and interpret the various operations at different layers. We achieve high sensitivity (97%) and specificity (100%) along with rapid and accurate defect localization. We also test performance of the proposed workflow on images from two distinct patterns and find that in order to retain high accuracy a modest level of retraining is necessary.

Simulating time-dependent quasi-brittle failures based on a multilinear releasing mechanism of viscous force (VF) fields

The time-dependent progressive failures in heterogeneous brittle materials are modeled by considering the temporal stress redistribution mechanism due to local breakages. The influence of local breakages lies in two kinds of stress redistributions: (1) Internal forces in the breaking element are assumed to release infinitely fast when compared with external loadings, and the corresponding viscoelastic deformation of the specimen happens in a finite speed. This deformation delay is implemented by introducing a VF field all over the specimen. (2) Then the gradual release of VF fields stored previously follows, resulting in the viscous recovery of the entire specimen, which is approximated as a multilinear process. The main characteristic of the present algorithm is its linearity, i.e. no nonlinear iterations are included. Numerical results of uniaxial tensile/compressive, anchor bolt pull-out and Brazilian tests show that the proposed model is capable of overcoming the over-brittle issue in existing lattice models and capturing the strain rate sensitivity, which agree well with experimental observations.

New strength metrics for containerboards: influences of basic papermaking factors

Abstract In end-use, containerboard is subjected to a variety of loading histories, such as seconds of loading/unloading, hours of vibration, days of creep load. The fundamental question is whether the commonly measured static strength represents “strength” under these conditions. Another question is, since those time-dependent failures are notoriously variable, how to describe the probabilistic aspect. This study concerns the characterisation of these different facets of “strength”. In our earlier work, we have investigated the theoretical framework for time-dependent, probabilistic failures, and identified three material parameters: (1) characteristic strength, S c {S_{c}} , representing short-term strength, (2) brittleness/durability parameter, ρ, and (3) reliability parameter, β. We have also developed a new method that allows us to determine all these parameters much faster than typical creep tests. Using the new method, we have started investigating effects of basic papermaking variables on the new material parameters. Among the samples tested, the parameter ρ varied from 20 to 50, and β from 0.5 to 1.0. This suggests that, even within the current papermaking practice, there is a wide operating window to tune these new material parameters. The future work is, therefore, to find specific manufacturing variables that can systematically change these new material parameters.

Reliability assessment for final elements of SISs with time dependent failures

Reliability assessment for safety-instrumented systems (SISs) plays a vital role in improving the design of SISs. Traditional methods for SIS reliability assessment that assume constant failure rates are, however, not realistic for many final elements of SISs, e.g. electro-mechanical and hydraulic/mechanical actuators that are subject to degradation. This paper presents an approach for reliability assessment of SIS final elements with time dependent failure rates. Different operational issues, such as partial and full testing, are investigated for their effects on reliability of SISs. Approximation formulas for evaluation of average probability of failure on demand (PFDavg) involving degradation are developed within different subsequent proof testing intervals, and Weibull distributions are adopted to model the degradation processes of the final elements. The corresponding numerical results of PFDavg from the set of the derived formulations are validated by Petri nets models that are developed for different scenarios. Shutdown valves installed as part of a high integrity pressure protection system are analyzed as the case, to illustrate the feasibility of the proposed approach, and also demonstrate that the approximation can provide possibilities for testing strategies design and optimization.

Lateral unicompartmental knee replacement: a systematic review of reasons for failure.

Currently, individual studies lack the power to successively illustrate different failure modes; therefore, we undertook a systematic review to examine lateral unicompartmental knee replacement (lat UKR) failure modes. Furthermore, we compared early with midterm and late failures and fixed-bearing with mobile-bearing implants. A search using the databases of PubMed, EMBASE, Cochrane, and annual registries was performed to search for failed lat UKRs. Studies were included when they reported more than four failures,described failure modesandwere minimum level IV studies. Data was analysed based on overall failure modes, fixed- vs. mobile bearing andearly (<5years) vs. midterm (5-10years) vs. late failures (>10years). Fourteen cohort studies and two registry-based studies were included. A total of 336 overall failures, 87 time-dependent failures, and 175 implant-specific failures were identified. The main overall causes of failure were osteoarthritis (OA) progression (30%) and aseptic loosening (22%). These were followed by less common causes such as instability (7%), unexplained pain (5%), infection (5%), polyethylene wear (5%), and bearing dislocation (5%). Bearing dislocation was the most common early failure (29%) and also the most common failure among mobile-bearing implants (27%). In midterm and late failures, OA progression had the highest rates (59% and 78% respectively) and was also the most common type of failure in fixed-bearing implants (44%). Progression of OA and aseptic loosening are the major overall failure modes in lat UKR. Bearing dislocation was the main failure mode in early years and in mobile-bearing implants, whereas OA progression caused most failures in late years and in fixed-bearing implants. Systematic Review of minimum level IV studies.

ON-state Reliability of Cu Atom Switch Under Current–Temperature Stress

The dc current-stress tolerance of the ON-state Cu atom switch is evaluated at elevated temperature. It is revealed that the reset-direction current stress causes time-dependent failures, which originate from the $E$ -field-driven diffusion of Cu in the conducting bridge. A new empirical lifetime estimation model, including the Joule heating effect, gives an allowable maximum current per atom switch of $I_{{\textrm {max}}}= 115~\mu \text{A}$ , which is large enough to satisfy the requirements for signal routing under currents that are average (18 $\mu \text{A}$ ) and peak (63 $\mu \text{A}$ ) in the reconfigurable switch block operated at 500 MHz at 125 °C.

Performance Evaluation of Preventive Maintenance Considering Transportation Delays

This paper considers a production system of a single product, with constant transportation delays of items, between the machine and the buffer and between the buffer and the customer. The demand arrives with a constant rate. The system is modeled by a continuous-flow model. The machine is subject to time-dependent failures and the piloting policy is of hedging point type. We employed a preventive maintenance policy that is realized at each certain period. A performance evaluation of the system is made by simulation.

Perturbation analysis and optimisation of continuous flow transfer lines with delay

This paper addresses the optimisation of failure-prone transfer lines with delays for material transfer and with a constant demand. A continuous flow model with delays is proposed. Compared with traditional continuous flow models in which materials flow from one station to another instantaneously, material flowing out a machine waits a period of time called a delay before arriving at its downstream buffer. Machines are subject to time-dependent failures. Times between failure and times to repair are random variables with a general distribution. The production of each machine is controlled by a base stock policy. We propose a simulation-based optimisation method for determining optimal base stock levels in order to minimise the long-run average cost incurred by inventory holding and demand backlogging. It is based on an infinitesimal perturbation analysis for the estimation of gradients along the simulation. The unbiasedness of the gradient estimators is established.

MODELING MANUFACTURERS' AND CUSTOMERS' COSTS FOR COST SHARING LIFETIME WARRANTY

Lifetime warranties are becoming more popular as these types of warranties provide assurance for a longer reliable service life, protection of customers against poor quality and the potential high cost of failure occurring during the long uncertain life of products. Chattopadhyay and Rahman (2008) proposed taxonomy for Lifetime warranty policies and developed cost models for Free rectification lifetime warranty (FRLTW) policies. In line with Chattopadhyay and Rahman, in this paper, stochastic models for two most potential and currently practiced Cost sharing lifetime warranty (CSLTW) policies, Specific parts excluded lifetime warranty and Limit on individual cost lifetime warranty have been developed to estimate the customers' and manufacturers' costs. The developed models capture the uncertainties of lifetime warranty coverage period and implication in offering such warranties on both manufacturer and customers. The developed models are analyzed using illustrative examples considering products with time-dependent failures.

Optimization of a Failure – prone Manufacturing System with Regular Preventive Maintenance: an IPA Approach

AbstractThis paper addresses the optimization of a single-stage single-product manufacturing system with a constant demand and a systematic preventive maintenance policy. The manufacturing system is modeled by a continuous-flow model. The machine is subject to time-dependent failures and its production speed is given by a hedging point policy. Times to failure and times to repair are random variables with exponential distribution. We propose a simulation-based optimization method for determining the optimal buffer level in order to minimize the long run average cost including inventory holding cost, backordering cost and corrective and preventive maintenance costs. The optimization algorithm is based on the Infinitesimal Perturbation Analysis (IPA) technique for estimation of gradients along the simulation. The unbiasedness of the IPA estimators is established. Numerical results based on the simulation algorithm are proposed to determine the optimal buffer level and to derive the optimal value of the period of the systematic preventive maintenance.

Failure models and throughput rate of transfer lines

This paper addresses the impact of failure models on the performance of transfer lines composed of N machines separated by N − 1 buffers. The two most used failure models, operation-dependent failures (ODF) and time-dependent failures (TDF), are considered. A machine subject to TDF can fail even it is not working on a part. A machine subject to ODF cannot fail if it is not working on a part. A transfer line considered in this paper contains both machines subject to TDF and machines subject to ODF. Up times, repair times and processing times are continuous random variables of general distribution. We prove that modelling a machine subject to ODF of a transfer line as a machine subject to TDF, as usually done in the literature, leads to under-estimation of the throughput rate if the time between failures of the related machine is exponentially distributed while all other times are general random variables. We then propose a timed Petri net approach for performance evaluation and simulation of transfer lines with both machines subject to TDF and machines subject to ODF. Numerical results show that this result holds under more general conditions.

Simulation-based optimization of a single-stage failure-prone manufacturing system with transportation delay

This paper addresses the optimization of the continuous-flow model of a single-stage single-product manufacturing system with constant demand and transportation delay from the machine to the inventory. The machine is subject to either time-dependent or operation-dependent failures. The production is controlled by a hedging point policy. The goal is to determine the optimal hedging point, which minimizes the long-run average inventory holding and backlogging cost. Sample path analysis shows that the cost function is convex and sample gradient estimators are derived. A bi-section search algorithm based on simulation and sample gradients is proposed to determine the optimal hedging point.

Comparisons of two-machine line models in throughput analysis

Throughput analysis is important for the design, operation and management of manufacturing systems. Due to the large state space, exact analytical results only exist for two-machine serial lines. To analyse longer lines or more complex systems, the two-machine line model becomes the building block for further development. Therefore, many two-machine line models have been presented in the literature. A thorough understanding of the nature and differences of the various two-machine line models is critical for future analysis and development. In this paper, we study eight different two-machine models, categorized by synchronous and asynchronous lines with both time-dependent and operation-dependent failures, respectively. For each model, we introduce and compare the assumptions, calculation formulae, and their performance in system throughput. The results show that all the models exhibit similar performance with small differences, comparable to (or less than) the accuracy of data collection on the factory floor.

OPTIMIZATION OF CONTINUOUS-FLOW TRANSFER LINES WITH DELAY USING IPA

This paper addresses the optimization of failure-prone transfer lines with delays and constant demand. For this purpose, we propose a new continuous flow model. Machines are subject to time-dependent failures, times to failure and times to repair are random variable with general distribution. Material flowing out a machine waits a period of time called delay for material transfer before arriving at its downstream buffer. We present a simulation-based optimization method for determining optimal buffer levels in order to minimize the long run average cost. The optimization algorithm is based on the Infinitesimal Perturbation Analysis for estimation of gradients along the simulation.

Evaluation and Optimization of Two-Stage Continuous Transfer Lines Subject to Time-Dependent Failures*

This paper addresses the performance evaluation and optimization of continuous flow transfer lines composed of two machines separated by a buffer of finite capacity. Machines are subject to time-dependent failures. Times to repair and times to failure of the machines are random variables with general distribution. For the purpose of performance evaluation, a set of evolution equations that determines continuous state variables at epochs of discrete events is established. Based on the evolution equations, we prove the concavity of the throughput rates of the machines and derive gradient estimators. Unbiasedness and strong consistency of the gradient estimators are proved. Finally, an design optimization problem that maximizes a concave function of throughput rate and a design parameter is addressed.