Open Failure Research Articles

Structural response of glass fiber-polymer composite bending-active elastica beam under long-term loading conditions

Bending-active elastica beams represent structural members which are initially installed as straight beams and then bent into arched shapes by applying horizontal displacements to one support. Designing such members for permanent structures made of fiber-polymer composites involves complex viscoelastic responses, which have not yet been thoroughly investigated. An experimental investigation of medium-scale bending-active elastica beams, consisting of pultruded glass fiber-polymer composite profiles, was thus conducted to investigate the long-term structural behavior of such members under imposed sustained bending and axial compression. The results revealed that viscoelastic responses are based on an interaction of stress relaxation and creep with their effects increased with increasing bending degree and time of exposure to sustained strains and stresses. The imposed horizontal displacement to one of the supports to maintain the bent beam shape induced sustained bending stresses in the beam. Beneficial relaxation of these stresses occurred with relaxation predicted to reach 12 % during a targeted 50-year design service life. Furthermore, the likelihood of the curved beam exhibiting in-plane deformations under sustained stresses enabled creep to occur simultaneously, with associated in-plane creep deformations and strength reduction. While creep deformations remained insignificant, progressive creep rupture occurred at highest bending degrees, exhibiting sequential creep rupture in the outer combined mat layers, delamination, crack opening and final fiber failure. Creep rupture can be prevented by postponing crack initiation in the combined mat layer beyond the targeted design service life. This can be achieved by limiting the bending degree to 50 % of the bending degree at which short-term crack initiation occurs.

Stress Characteristics and Mechanical Behavior of Rock Masses with an Opening under Complex Deep Underground Stress Conditions

In this study, the impact of principal stress states on the stress characteristics and initial failure of the rock mass surrounding a three-center arch opening was investigated using complex variable function methods and Discrete Element Method (DEM) numerical modeling. First, the mapping function of the opening was determined using the trigonometric interpolation method, and the influence of the number of terms in the mapping function on its accuracy was revealed. Based on this, the far-field stress state of the underground rock mass was characterized by the ratio of the minimum to maximum principal stress (λ) and the angle (β) between the principal stress and the vertical direction. This stress state was then converted into normal and shear stresses. Using complex variable function theory, the stress characteristics at the boundary of the opening under different stress states were analyzed. Finally, DEM numerical modeling was employed to study the initial failure characteristics at the boundary of the opening and its relationship with the stress distribution. The results indicate that the lateral pressure coefficient significantly affects the stability of the opening by influencing stress concentration around the surrounding rock. Low lateral pressure coefficients lead to tensile stress concentration at the boundary perpendicular to the maximum principal stress. As the coefficient increases, tensile stress decreases, and compressive stress areas expand. While the principal stress direction has a minor effect on stress concentration, it notably impacts stress distribution at the boundary. When λ < 1.0 and β = 45°, stress distribution asymmetry is most pronounced, with the highest compressive stress. The early failure distribution aligns with stress concentration areas, validating the use of stress analysis in predicting opening stability and failure characteristics.

An explicit finite element discrete crack analysis of open hole tension failure in composites

Developing efficient, robust methods for predicting the progressive failure of carbon fiber composites under tension is essential for optimal design, balancing weight reduction, damage tolerance, and service life. Implicit finite element (FE) methods struggle with the complex interplay of failure mechanisms, leading to a heavy reliance on costly, time-consuming experimental testing. This study introduces a novel explicit algorithm designed for laminate-level mesh models, capable of simulating cohesive cracks without predefined paths. Utilizing an explicit finite element software approach, our method effectively addresses convergence issues associated with the non-linear and unstable nature of composite failures during quasi-static loading. Contrasting with implicit FE method, this mesh-independent approach is both practical and numerically robust. The algorithm’s performance, tested on carbon-fiber reinforced composites with varying ply configurations [452/-452]s, [45n/90n/-45n/0n]s and [45/90/-45/0]ns (n=1/2/4/8), demonstrates improved simulation accuracy and efficiency over implicit FE methods, aligning well with prior experimental and simulation data. This advancement offers a promising solution for accurately simulating and understanding the complex failure behavior of these composites.

Short failure localization in advanced package using optoelectronic sampling terahertz time domain reflectometry and deconvolution method

Failure localization in advanced packaging is a challenging task. Optoelectronic sampling Terahertz time-domain reflectometry (OES THz TDR) employs ultrafast lasers to generate high-frequency THz pulse. The THz pulse is coupled into advanced package trace using radio frequency probe. When there is an open or short failure in the circuit, TDR signal could be captured. Deconvolution processing method was introduced to remove noise from multiple reflections of the remaining circuit. A short failure model with remaining circuit was studied. After deconvolution, the TDR localization accuracy improves from 573 μm to 12 μm, and the correlation coefficient improved from 99.612 % to 99.955 %. Advanced package sample including substrate, C4 bump, interposer, and micro bump was analyzed. By comparing the TDR waveform of short failure sample and references, the short failure is localized inside of the die. By destroying the failure sample and measuring the current-voltage curve, the short failure location is verified.

Control and fault diagnosis for two-interleaved boost converter associated with to PEMFC

This paper presents an enhanced control and fast fault detection method, localisation and isolisation for a two-phase interleaved boost DC/DC converter specifically designed for fuel cell applications. Fuel cells are known for their rapidly changing output voltage and current due to fluctuating load demands. Conventional converters might not be able to respond fast enough to maintain stable operation under such conditions.The two-phase interleaved design offers significant advantages. such as reduced ripple current delivered by dividing the Input current, the converter significantly lowers input and current ripple compared to single-phase designs. Each phase handles a smaller portion (1/N) of the total current, leading to reduced stress on individual components and enhanced reliability and operating margins. Additionally, Interleaving minimizes conduction losses by dividing the current among multiple converter stages. This work presents a model of a two-phase interleaved boost DC/DC converter and implements a PI controller for its output voltage regulation. This control method guarantees good performance even under varying reference voltages and load conditions. The proposed algorithm addresses the challenge of open circuit switch failures by utilizing current slopes for swift fault detection and rapid corrective action. This ensures accurate reference tracking, desired dynamic response, and timely fault detection and localization. The entire system was rigorously tested using MATLAB/Simulink software under various conditions, including reference voltage and load variations, as well as open circuit switch faults. The results showcase the proposed system's superior performance in terms of: Dynamic performance: The system exhibits rapid response to changes in operating conditions. Fast fault detection, localization and isolation.

A fatigue test based on inclined loading block concept to benchmark delamination growth considering loading history and [formula omitted]-curve effect

The main objective of this paper is to present a delamination benchmark test concept for composite materials that develop non-self-similar delamination in characterization specimens. The non-self-similar delamination is induced by rotating the loading blocks. The simplicity of the test allows for analyzing the loading mode history by concatenating different loading conditions, such as static and fatigue loading, under multiple loading modes. The methodology introduced in this paper can be particularized for any given composite material set and any sequence of loading conditions. To demonstrate the capabilities of the benchmark test, a case study is presented using AS4D/PEKK-FC thermoplastic composite material, which exhibits strong R-curve behavior. A sequence of opening and shear failure modes was applied under static and fatigue loading, providing an experimental data set that is ready to be used as a part of the validation of numerical predictive delamination models. The delamination process was monitored by X-ray radiography, and the final fracture surfaces were analyzed with scanning electron microscopy (SEM), giving a physical insight into the contribution of the fracture mechanisms to the delamination process.

Internal Bump Cracking Risk Assessment for Flip Chip Ball Grid Array Package During Board Level Reliability Test Through Finite Element Analysis

The performance of semiconductor devices during board-level reliability (BLR) thermal cycling tests continues to be a concern in different applications. The primary focus of those BLR tests is to evaluate the fatigue life of external solder joints between the package and printed circuit board (PCB). For flip-chip ball grid array (FCBGA) package technology, internal solder bumps can also crack and result in open electrical failure. This type of BLR failure has yet to be widely reported in the literature. This article presents failures due to internal solder bump cracks during the BLR test. Failure analysis (FA) clearly shows the cracking location strongly depends on bump density. Finite Element Analysis (FEA) based simulation is performed to understand the failure mechanism. Unlike the standard BLR modeling approach, which focuses on predicting external solder joint fatigue life with correlated data, simulation here has to capture the entire internal bump pattern in the global BLR model. The need to capture the entirety of the bump scheme poses a significant challenge to managing the global model size with a reasonable meshing count and running time. Therefore, a customized post-process approach is developed to analyze bump density impact and enable design optimization.

Coupling effect between electromigration and joule heating on the failure of ball grid array in 3D integrated circuit technology

Ball Grid Array (BGA) packaging method has been widely used in microelectronic devices, and electromigration (EM) in BGA is a crucial reliability issue, determining the performance of the products. Herein, we report a new failure mode induced by a coupling effect of EM and Joule heating in BGA structure. The test sample consists of a roll of 500 μm-BGA solder joints with upper and lower Cu under-bump-metallization (UBM) of different thicknesses, 16 μm, and 68 μm, respectively. Open failures of the thinner cathodic Cu UBM at the contacting area with solder joint were observed under four different EM conditions (130 °C-3000 A/cm2, 160 °C-2300 A/cm2, 160 °C-3000 A/cm2, and 160 °C-4600 A/cm2). Infrared (IR) results reveal the temperature at the thinner Cu UBM is higher than that in the solder joint as well as at the thicker Cu UBM. Simulation results elucidate the current density at the contacting area is about 22 times higher than the average density in the solder joint, so the effect of current crowding can be very serious in the failure site. Furthermore, severe current crowding and Joule heating promote the nucleation rate of voids at the joint location, which can further increase the current density and temperature, leading to a positive feedback effect until an open failure occurs in the circuitry. Our analysis enables the discussion of a coupling failure mode of EM and Joule heating in BGA, and provides a valuable guide of device design against EM failure in consumer electronic products.

Stability analysis of energy dissipation mechanisms in rocks surrounding circular opening

This study analyzes the stability of surrounding rock for a circular opening based on the energy and cavity expansion theory, and regards the surrounding rock failure of circular opening as an unstable state driven by energy. Firstly, based on the large-strain cylindrical cavity contraction and energy dissipation method, the deformation caused by the excavation of surrounding rock is regarded as the cylindrical cavity contraction process. By introducing the energy dissipation mechanism, the energy dissipation solution of cylindrical cavity contraction is obtained. The energy dissipation process of surrounding rock is characterized by the strain energy changes in the elastic and elasto-plastic regions of this cavity contraction analysis. Secondly, the deformation control effect of support and surrounding rock parameters on the energy dissipation of surrounding rock is studied based on the energy dissipation solution of surrounding rock under support conditions. Finally, the effectiveness and reliability of the analytical approach was demonstrated by comparing the support design results with those in the literature. The research results indicate that the three-dimensional mechanical properties and dilatancy angle of rock and soil mass have a significant impact on the energy support design of surrounding rock. This study provides a general analysis method for the stability analysis of surrounding rock of deep buried tunnels and roadway.

Results of Eustachian tube balloon dilation measured using the nine-step test

Suggested several decades ago, the nine-step test is an intuitive test of Eustachian tube function. However, studies employing the nine-step test to assess the results of Eustachian tube balloon dilation (EBD) are limited. We aimed to objectively evaluate the efficacy of EBD in opening failure patients with decreased maximal peak pressure difference (MPD) using the nine-step test. Patients who had MPD values ≤ 13 daPa in the nine-step test were enrolled. The patients were categorized into two groups according to treatment decisions after discussion with a clinician: an EBD group (N = 26) and a medication group (N = 30). One month after treatment, the seven-item Eustachian Tube Dysfunction Questionnaire (ETDQ7) and the nine-step test were administered to all participants and subgroups of symptomatic participants (ETDQ7 > 15). MPD improved (increased) in both the EBD group and the medication group. ETDQ7 values improved (decreased) in the EBD group, but not in the medication group. In subgroup analysis, MPD and ETDQ7 values improved only in the symptomatic EBD group. According to the nine-step test, EBD can normalize 53.8% of decreased MPD. Posttreatment MPD and ETDQ7 scores were significantly better in the EBD group than in the medication group. However, EBD in patients with abnormal nine-step test results seemed less efficacious when the treatment results of the medication group were considered.

Prediction of the critical energy release rate for rat femoral cortical bone structure under different failure conditions

Background and ObjectiveCritical energy release rate is a global fracture parameter that could be measured during the failing process, and its value may change under different failure conditions even in the same bone structure. The aim of this study was to propose an approach that combined the experimental test and finite element analysis to predict the critical energy release rates in the femoral cortical bone structures under compression and three-point bending loads. MethodsThree-point bending and compression experiments and the corresponding fracture simulations were performed on the rat femoral cortical bone structures. Different values of energy release rate were repeatedly assigned to the finite element models to perform fracture simulations, and then the load–displacement curves predicted in each simulation were compared with the experimental data to back-calculate the critical energy release rate. ResultsThe predicted data were similar to the experimental results when the calibrated energy release rate was suitable. The results showed that the cortical bone structure occurred shear open failure under compression load, and the predicted critical energy release rate was 0.12 N/mm. The same cortical bone structure occurred tensile open failure under three-point bending load, and the predicted critical energy release rate was 0.16 N/mm. ConclusionsThe critical energy release rates were different under various failure conditions in one cortical bone structure. A comprehensive analysis from the perspectives of material mechanical properties, failure mode, and damage fracture mechanism was conducted to reveal the reasons for the differences in the critical energy release rate in the cortical bone structure, which provided a theoretical basis for the measurement of the critical energy release rate and the accurate fracture simulation.

A SENSOR FAULT-TOLERANT CONTROL SOLUTION BASED ON CURRENT OBSERVERS APPLIED TO THREE PHASE INDUCTION MOTOR DRIVE

This paper presents a fault-tolerant control (FTC) solution to enhance the reliability and sustainability of a three-phase induction motor drive (IMD) against open circuit sensor failures (or total sensor faults). The motor speed control in the investigated drive will operate based on a field-oriented control (FOC) strategy. A typical FTC function consists of two main processes: fault detection of feedback signals from the sensors and reconfiguration of the control methods. This paper proposes using two-phase current observers to diagnose various sensor failures, and then the corresponding sensorless methods are applied to the control reconfiguration. Using MATLAB/SIMULINK software, the IMD-integrated FTC function was operated and tested under different fault conditions. Simulation results have proved that the IMD-integrated FTC function has worked stably and sustainably even in sensor failure conditions.

Improved Outcomes in Distal Tibial Non-Union: A Retrospective Study of 8 Patients Treated with Distal Tibial Nail and Screw Fixation.

BACKGROUND Non-union of distal tibia fractures is a challenge in orthopedic surgery and can be due to open fractures, osteopenia, infection, or failure of surgical devices. This retrospective study aimed to describe 8 patients with non-union of distal tibial fractures treated with distal tibial nail and screw fixation. MATERIAL AND METHODS According to the Gustilo-Anderson classification, 3 patients had type 2 open fractures, 1 had a type 3 open fracture, 1 had a type 1 open fracture, and 3 had closed fractures. The Association of Osteosynthesis AO classified 4 patients as A2, 2 as B2, and 2 as C2. Seven patients received distal supporting bolt-locking-screw nails (DSBLS) and 1 received DSBLS nail and plate in their most recent operation. Clinical outcomes were evaluated with American Orthopaedic Foot and Ankle Society (AOFAS) and Olerud-Molander scores. RESULTS All 8 patients were male, with a mean age of 35.5±14.6 years. Six patients had atrophic non-union, 1 had hypertrophic non-union, and 1 had infected non-union. Union was achieved in all patients. The average union time was 25.1 (range, 12-60) months, and the follow-up duration was 3.6 (range, 2-6) years. The mean Olerud-Molander score was 92.5 (range 85-100), and the mean AOFAS score was 91.2 (range, 85-100). There was no evidence of rotational deformity or shortening. CONCLUSIONS Distal tibial non-unions benefit from nails with DSBLS system due to their excellent biomechanical properties. These nails facilitate union and allow patients to bear weight early in the postoperative period, enabling a quicker return to normal activities.

Selective Laser Trabeculoplasty-What Do We Know So Far? Review

Abstract Selective laser trabeculoplasty (SLT) has been used for lowering intraocular pressure (IOP) in patients with different types of glaucoma. It is a safe and effective procedure as initial or additional therapy when target IOP could not be achieved with medical therapy. SLT could specifically target pigmented cells in trabecular meshwork (TM) leaving nonpigmented cells unaffected, which may allow repeat treatments and thus has lower complication rate. It can be successfully used for IOP reduction in primary open angle glaucoma (POAG), normotensive glaucoma (NTG), pigmentary glaucoma (PG), pseudoexfoliation glaucoma (PXFG), primary angle closure glaucoma (PACG), silicone-oil-induced glaucoma, and high IOP after failed trabeculectomy. SLT could also be used in all stages of open agle glaucoma but failure of SLT in advanced glaucoma patients should go to immediate filtering surgery to avoid postoperative fibrosis. SLT reduces IOP fluctuation. IOP-lowering effect of SLT diminishes over time, but it can be repeated in order to achieve additional or recurrent IOP reduction. Higher baseline IOP up to a certain level is the strongest predictor of success after SLT.

Safety risk assessment of aircraft EWIS based on the improved combined weight and cloud model

Purpose This study aims to conduct the aircraft electrical wiring interconnection system (EWIS) safety risk assessment process abundantly and hierarchically and establish the assessment index system considering the weights and interrelationships of different levels of indices. Design/methodology/approach Due to the failure of EWIS being multifactorial, hidden and diverse, this paper divides the factors influencing the failure of EWIS into 3 primary indices, 13 secondary indices and 38 tertiary indices. Taking open circuit failure (OCF) and short circuit failure (SCF) as examples, calculate the weights of assessment indices based on the triangular fuzzy number analytic hierarchy process (TFNAHP) and triangular fuzzy number decision-making trial and evaluation laboratory (TFNDEMATEL). The cloud model (CM) divides the risk levels and obtains the safety risk assessment results. The comparative analyses of different weight calculation methods, different failure modes and different aircraft EWIS zones verify the effectiveness and practicability of the proposed method. Findings The results show that the proposed method aligns more with the actual situation than other methods. Also, the results identify key focus objects in EWIS safety risk assessment, such as the surrounding environmental factors among the primary indices having the most significant influence on OCF and SCF, the risk level of SCF being higher than that of OCF, etc. Originality/value This paper proposes a safety risk assessment index system for aircraft EWIS based on the cable parameters, surrounding environmental factors, installation and protection methods. The weight assignment is added to the assessment index system, and the safety risk assessment model is constructed by combining TFNAHP, TFNDEMATEL and CM.

Comparative analysis of ischemic and non-ischemic etiology of acute heart failure - analysis from the "OP-AHF" registry

Abstract Funding Acknowledgements Type of funding sources: Public Institution(s). Main funding source(s): This work was supported by a grant from the Institute of Medical Sciences, University of Opole, Poland. ROCHE Diagnostics Poland. Introduction Current guidelines of the European Society of Cardiology define acute heart failure as the rapid onset of symptoms and/or signs of heart failure, severe enough for the patient to seek urgent medical attention, leading to an unplanned hospital admission or an emergency department visit. Purpose The aim of this study was to compare clinical characteristics, treatment, and 12-month outcomes of patients with ischemic(I-AHF) and non-ischemic acute heart failure(NI-AHF). Materials and Methods As a part of the open prospective Acute Heart Failure Registry (OP-AHF),data 122 patients hospitalized in the Intensive Cardiac Care Unit were collected in the period from June 2019. The inclusion criteria were hospitalization for acute heart failure and the need to use at least one of: intravenous diuretics, catecholamines or mechanical circulatory support. The project was approved by the Bioethical Committee. Results Patients with ischemic etiology of acute heart failure (I-AHF) constituted 43% of the study group (53 of 122 patients). Compared to patients with non-ischemic etiology of acute heart failure (NI-AHF), patients with I-AHF were older (69 vs. 64 years, p = 0.04) and slightly more frequently male (79% vs. 67%, p=0.12). BMI was similar in both groups (29 vs. 30, p=0.21). On admission, they reported more frequently chest pain (49% vs. 33%, p = 0.08), and less frequently than NI-AHF patients, edema (40% vs. 54%, p = 0.12) and dyspnoea (91% vs. 97%, p =0.25). History of diabetes (60% vs. 20%, p<0.01) and chronic kidney disease (38% vs. 20%, p =0.03) were predominant in I-AHF patients,but atrial fibrillation (36% vs 57%, p=0.02) was less common than in NI-AHF patients. Laboratory results on admission showed significantly higher NT-proBNP levels in the I-AHF patients (11078 vs 7785 pg/ml, p < 0.004). Left ventricle ejection fraction (LVEF) was lower on admission (29% vs 35%, p= 0.02) and at discharge (34% vs 39%, p = 0.19) in I-AHF patients. At 12-month follow-up, there was no improvement of LVEF in I-AHF patients in contrast to NI-AHF patients (34% vs 47%, p <0.001). Death during hospitalization occurred more frequently in the I-AHF patients group (15% vs 3%, p=0.01). The rates of cardiovascular rehospitalisations within 12 months was 23% in patients with I-AHF patients compared to 32% in NI-AHF patients, p=0.3;HR=0.70 (95% CI = 0.35-1.38). The risk of death from any cause within 12 months was lower in patients with I-AHF (17% vs. 32%, p=0.056; HR = 0.49 (95% CI = 0.23-1.02)), nevertheless, after adjustment for age, sex, LVEF and NT-proBNP, mortality was essentially identical in both groups, 24% inI-AHF and 23% in NI-AHF, p=0.99; HR=1.00 (0.45-2.24). Conclusions Despite a worse in-hospital outcomes, ischemic etiology of acute heart failure was not associated with a higher risk of cardiovascular rehospitalization and death at 12-month follow-up than non-ischemic etiology.

Hybrid Finite-Discrete Element Modeling of the Mode I Tensile Response of an Alumina Ceramic

We have developed a three-dimensional hybrid finite-discrete element model to investigate the mode I tensile opening failure of alumina ceramic. This model implicitly considers the flaw system in the material and explicitly shows the macroscopic failure patterns. A single main crack perpendicular to the loading direction is observed during the tensile loading simulation. Some fragments appear near the crack surfaces due to crack branching. The tensile strength obtained by our model is consistent with the experimental results from the literature. Once validated with the literature, the influences of the distribution of the flaw system on the tensile strength and elastic modulus are explored. The simulation results show that the material with more uniform flaw sizes and fewer big flaws has stronger tensile strength and higher elastic modulus.

Analytical Method for the Optimization of the Open-Hole and Filled-Hole Laminates at the Preliminary Design Stage

In recent years, there has been an increasing interest in open-hole and filled-hole laminate failure analysis. The open and filled-hole laminate failure analysis is used in several important areas, especially in designing mechanically fastened composite joints. Various analytical, empirical, and numerical methods are available for the design of mechanically fastened composite joints. The large number of material and geometrical design variables at the preliminary design stage makes the empirical and numerical methods effortful, expensive, and time-consuming. Therefore, analytical methods are recommended over numerical and empirical methods at the preliminary design stage merely because of their simplification in calculations, making them computationally efficient. Taking this into consideration, current research presents an improvement to the analysis capabilities of the previously introduced analytical method, i.e., the coupled approach of Classical laminate theory (CLT) and Lekhnitskii solutions. These improvements include the development of failure envelops for the open-hole and filled-hole laminates, estimation of optimized filling material for attaining maximum load-bearing capacity of filled-hole laminates, and optimization of stacking sequence for maximum load-bearing capacity of open-hole and filled-hole laminates. From the failure envelop results, it was found that failure envelopes of filled-hole laminates are bigger than open-hole laminates. Furthermore, it was found that the stiffness of the filling material should be equal to the stiffness of the laminate to achieve maximum bearing strength of the filled-hole laminate. It was also demonstrated that the coupled approach of CLT and Lekhnitskii solutions may provide carpet plots that can be utilized to optimize the stacking sequence for open-hole and filled-hole laminates.

Analysis of a database of open pit mine slope failures to predict travel distance, setback distance, and geometric properties

In mining, open pits have slopes cut as steep as possible to ensure efficient mining yet not too steep to jeopardize safety. Building on existing contributions, the Texas A&M University Mine Slope database (TAMU-MineSlope) was created to provide global-scale insights into the runout mechanics of open pit slope failures and offer the database to engineers for further study. The database includes 134 cases of open pit slope failures that occurred at 76 mines worldwide. Based on energy principles and an analysis of the TAMU-MineSlope data, an equation to predict the travel distance of the slope failure mass is presented in this paper. Furthermore, based on the case histories analysis, an equation to predict the setback distance is proposed. Finally, the TAMU-MineSlope database shows that the average width to height ratio of the failing slope mass is 2.7 and that, for this ratio, the 3D factor of safety (FS) can reach a value 15% higher than the 2D FS. The database has been released in the public domain.

A lifetime prediction approach for LED packages in paralleled under thermal-electronic coupling effects

For LED packages in parallel, the driving current depends on the catastrophic failure history, so LEDs break down faster than that with the constant current hypothesis. This work proposes a hybrid reliability assessment approach that is based on the combination of the symbol sequence with Physics of Failure (PoF) modelling for parallel LEDs. A symbol sequence is proposed to abstract lumen maintenance curves into several failure modes. According to the monotonicity of the proposed symbol sequence, the boundary lifetime and probability is required to obtain the reliability of the light source in terms of mean time to failure (MTTF). The PoF simulations are utilized to calculate lifetime, temperature and thus probability of each failure mode with consideration of interaction between the lumen decay and open circuit. A temperature- and time-dependent model is applied to describe the LED lumen depreciation. LED's open circuit probability is considered as functions of temperature. The parameters of the proposed methodology are extracted by experiments which select a commercial type of LED. With the combined effect of the lumen depreciation and open circuit failuires, the time of open circuit failure determines the failure mode of the light source. By finding 3 boundary points among failure modes, the proposed approach obtains accurate survival rates as function of lifetime and MTTF of LED packages in parallel than conventional approaches.