Static Cyclic Tests Research Articles

Nonlinear finite element analysis of shear defective reinforced concrete beam to column connections strengthened with three practical techniques

Extensive research efforts over the last decades have focused on the rehabilitation of vulnerable reinforced concrete (RC) beam to column moment resisting connections. Shear failure in the panel zone of the beam to column connections (BCCs) under the lateral seismic loads stands out as one of the main reasons of the vulnerability of moment resisting frames (MRFs), potentially resulting in severe consequences for the entire structure. The main aim of this study is to fairly investigate the effectiveness of three practical retrofitting methods to eliminate the joint shear failure in the RC beam to column connections which suffer from this undesirable brittle failure mode. To achieve this, a comprehensive review categorizing available retrofit techniques for shear-defective joints is first provided, outlining their advantages and limitations. The study then presents findings from a nonlinear three-dimensional (3D) finite element (FE) study on the performance of (RC) connections, characterized by predominant joint shear mode of failure and retrofitted using the three practical techniques. In this context, the FE model is validated through the monotonic simulation of quasi static cyclic tests conducted on connections strengthened by the three practical retrofitting methods from the literature. The selected methods were diagonal steel haunch method, RC planar joint expansion, and pre-tensioning of the joint core. The models, encompassing their precise geometric details, are applied to a full-scale exterior connection experiencing shear deficiencies to evaluate their effectiveness in real-world scenarios Additionally, a parametric study is conducted to assess the effects of various influential design variables on the effectiveness of these selected strengthening methods. These findings provide insights into the efficiency of retrofit techniques, thereby informing more robust design practices aimed at enhancing the performance and resilience of vulnerable shear defective RC BCCs retrofitted using the aforementioned strengthening techniques. The study has identified key design parameters crucial for the effectiveness of retrofit techniques in practical applications. These included haunch dimensions (thickness and length) for the haunch retrofit technique, additionally, the size of the added RC blocks for planar joint expansion technique and finally the enlargement size and the amount of applied prestressing bolt loads for pre-tensioning of the joint core retrofit technique.

Design and development of model for proton exchange membrane fuel cell

Fuel prices are rising, and fossil fuel resources are depleting. This fuel is consumed by conventional fuel vehicles, which contributes to increased greenhouse gas emissions and air pollution. Various vehicle technologies have been introduced in modern times. Among these innovations, fuel cell vehicle technology stands out due to its ease of use, robustness, and simplicity. The primary energy source for this system is hydrogen. Fuel cells use hydrogen to generate electricity through a chemical process that does not involve combustion. The purpose of this paper is to describe the design and development of a simulation model for a fuel cell (proton exchange membrane type) vehicle using mathematical equations and the MATLAB/Simulink R2020a software, taking into account all voltage losses and temperature variations of the proton exchange membrane (PEM) type fuel cell. The designed model is validated in two ways: first by generating V-I characteristics for the designed PEM-type fuel cell, and then by performing a performance test in Simulink using the driving cycle on one of the fuel cell vehicles. The obtained simulated results are nearly identical to the expected results, and the designed PEM-type fuel cell performed well in all real-time driving cycle test conditions.

Performance optimization and scheme evaluation of liquid cooling battery thermal management systems based on the entropy weight method

Liquid cooling battery thermal management system (BTMS) is widely used in electric vehicles (EVs). A suitable liquid cooling BTMS scheme needs to be selected based on the magnitude of the weights for system performance. In this paper, thirty-six liquid cooling BTMS schemes involving the variables of cooling plate material types, flow channel layouts and inlet flow velocities are evaluated by using the entropy weight method (EWM) based on information theory. The weights and information entropies of the cooling performance, energy consumption performance and material cost of the system have been calculated and analyzed. The optimal scheme is selected considering global optimization based on the evaluation indicators. In addition, the cooling performance of the optimal scheme is examined under cyclic testing conditions (WLTC and US06). It is found that the flow channel layouts of the liquid cooling plate have a greater influence on the temperature control capability and temperature uniformity capability of the system. The liquid cooling system with a serpentine flow channel at an inlet flow velocity of 0.5 m·s−1, and aluminum as the cooling plate material exhibits the best cooling performance, energy consumption performance, and lowest material cost. The weights of material cost are 0.44, 0.32, and 0.34 under 1C discharge rate and cycle tests (WLTC and US06), respectively, which are the largest weight among the evaluation indicators. Material cost has the greatest degree of information dispersion because of the minimum information entropy, which plays a significant role in multi-attribute decision-making process. The temperature rise variation of the maximum temperature of the battery module under cyclic testing conditions is more reliable and dynamic compared with constant discharge rate conditions.

Microbiological quality and efficacy of preservatives in marigold-based skin care products

<p>The microbiological stability of cosmetic products is crucial, especially in products with high water content, such as creams. Therefore, preservatives are used in order to protect consumers from harmful pathogens that would otherwise invade the cosmetics. Despite their function, the addition of preservatives can be considered controversial in the cosmetics industry. Parabens are frequently used synthetic preservatives in various industries. According to regulatory directives concerning cosmetics (Cosmetic Directive by the European Commission) usage of some parabens (methylparaben, propylparaben, butylparaben, and ethylparaben) is safe and permitted in allowed concentrations. On the other hand, the European Commission prohibited the use of isopropylparaben, isobutylparaben, phenylparaben, benzylparaben and pentylparaben. Therefore, a comprehensive stability study was conducted to evaluate the influence of paraben-based preservative (Gujsol-1<sup>®</sup>, INCI name: Phenoxyethanol, Methylparaben, Ethylparaben, Propylparaben, Butylparaben) and potassium sorbate in order to preserve plant extracts-based skin-care products, Day and Night creams with marigold extract. Previously, mentioned skin-care products were preserved with the preservative Dekaben C<sup>®</sup>, which contained paraben mixture with banned isobutylparaben. All tested formulations showed favorable texture and sensory characteristics, desirable mild acidic pH values, satisfactory physical stability and appropriate microbiological quality at the initial point, as well as after storage at elevated temperature or at cyclic stress test conditions and at room temperature during two years. In addition, both preservatives significantly reduced the number of inoculated microorganisms during the challenge test. It can be concluded that potassium sorbate in plant-based creams could be an efficient alternative to paraben-based preservatives.</p>

AC Power Cycling Test Setup and Condition Monitoring Tools for SiC-Based Traction Inverters

AC power cycling tests allow the most realistic reliability assessment by applying close to real stress to the device or module under test to meet functional safety standards, which is highly critical for traction applications. This paper presents a comprehensive guideline and shares critical know-how to develop a 120 KVA AC power cycling test setup for high-power Silicon Carbide (SiC) modules. As of today, traction applications can not generate an early warning signal for drivers to replace critical components on time. For this purpose, the suitable precursors for all dominant failure mechanisms are discussed, and the corresponding condition monitoring tools are proposed to monitor the device aging on power converters. These condition monitoring tools are integrated into the built-in desaturation protection circuit of the electric vehicle (EV) gate driver for low-cost, practical implementation. The on-resistance of all twelve switches is monitored online as a temperature-sensitive electrical parameter (TSEP) to measure the junction temperature of the devices. To avoid heavy processing load in the microcontroller, the out-of-order equivalent time sampling technique is developed for data sampling, which leads to a measurement error of less than 1.5%. In addition, the design considerations regarding common mode noise and aging effect on DESAT protection are investigated, and experimental findings are presented.

An efficient state-of-health estimation method for lithium-ion batteries based on feature-importance ranking strategy and PSO-GRNN algorithm

As a critical index in ensuring the safe and reliable deployment of lithium-ion batteries (LIBs), the estimation performance of state-of-health (SOH) seriously affects the popularization of electric vehicles (EVs). However, for the existing SOH estimation methods based on machine learning algorithms, the health features are manually extracted mainly based on personal experience, without algorithm-based automatic preferential selection. Thus, this study proposes a battery SOH estimation method based on the feature-importance ranking strategy and generalized regression neural network optimized by particle swarm optimization (PSO-GRNN). Firstly, 19 vital features were extracted from charging voltage, charging current, temperature, and incremental capacity (IC) curves. Secondly, the importance indexes for these features were calculated and optimally ranked by fusing the machine learning algorithm (random forest) and statistical analysis (Pearson correlation coefficient). Accordingly, different combinations of high-ranking features were compared to determine the best number of the final feature set. Thirdly, the SOH estimation model is built by the PSO-GRNN algorithm with optimal 7 high-ranking features. Based on the publicly available NASA datasets, the proposed SOH estimation model was validated on the data from a single-cell battery. Furthermore, the datasets from three cells with different cycling test conditions were utilized, where the data from two cells and the other cell were alternately selected as the training and test sets, respectively. The SOH estimation errors (squared absolute error and mean squared error) for single-cell and multi-cell experiments were less than 1 % and 3 %, respectively. Experimental results show that the proposed method is robust and can achieve accurate and lightweight SOH estimation.

Reliability Evaluation of Board-Level Flip-Chip Package under Coupled Mechanical Compression and Thermal Cycling Test Conditions.

Flip Chip Ball Grid Array (FCBGA) packages, together with many other heterogeneous integration packages, are widely used in high I/O (Input/Output) density and high-performance computing applications. The thermal dissipation efficiency of such packages is often improved through the use of an external heat sink. However, the heat sink increases the solder joint inelastic strain energy density, and thus reduces the board-level thermal cycling test reliability. The present study constructs a three-dimensional (3D) numerical model to investigate the solder joint reliability of a lidless on-board FCBGA package with heat sink effects under thermal cycling testing, in accordance with JEDEC standard test condition G (a thermal range of -40 to 125 °C and a dwell/ramp time of 15/15 min). The validity of the numerical model is confirmed by comparing the predicted warpage of the FCBGA package with the experimental measurements obtained using a shadow moiré system. The effects of the heat sink and loading distance on the solder joint reliability performance are then examined. It is shown that the addition of the heat sink and a longer loading distance increase the solder ball creep strain energy density (CSED) and degrade the package reliability performance accordingly.

A novel method of prediction for capacity and remaining useful life of lithium-ion battery based on multi-time scale Weibull accelerated failure time regression

Lithium-ion batteries are essential energy storage components for electrical grid, and the health diagnosis determines the safety of the battery during usage and the rational classify of echelon utilization. In this article, a multi-timescale capacity and lifespan prediction method is proposed where capacity prediction and remaining useful life prediction are divided into the short-time scale and the long-time scale. For capacity prediction, the long short term memory neural network with five significant features is applied according to its accuracy performance in time series prediction. As for remaining useful life, the Weibull accelerated failure time regression is proposed to improve the prediction efficiency of a large amount of data. Finally, the predictive capability, robustness and effectiveness of proposed methods are verified using two datasets with different cycling test conditions within an error of 3.9 % in long-time scale and 2.7 % in short-time scale. The proposed method has great potential for targeted and accurate health state forecasting and long-term end of life prediction.

Physicochemical Analysis of Particle Matter from a Gasoline Direct Injection Engine Based on the China Light-Duty Vehicle Test Cycle

This paper investigated the physical and chemical properties of gasoline direct injection (GDI) engine particulate matter (PM). The physical properties mainly included the particulate aggregate morphology, primary particle size, and internal nanostructure. High-resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM) were used to obtain particle morphology information and to conduct image processing and analysis. The chemical characterization tests included X-ray photoelectron spectroscopy (XPS), energy dispersive scanning (EDS), Raman spectroscopy, Fourier-transform infrared spectroscopy (FTIR), and thermal gravimetric analysis (TGA). XPS can be used to observe the content of carbon and oxygen components and the surface carbon chemistry status, EDS can be used to obtain the elemental composition of particles, and TGA is used to analyze the oxidative kinetics of particles. Samples were collected from the exhaust emissions of a passenger vehicle compliant with China’s VI emission standards under China Light-Duty Vehicle Test Cycle (CLTC) test conditions. The study found that the particle morphology mainly comprised primary particles stacked on top of each other to form agglomerate structures, and the primary particles exhibited a core–shell structure. Analysis showed that carbon and oxygen were the predominant components of the particles, with other metallic elements also present. The XPS observations agreed with the FTIR results, indicating a small amount of oxygen was present on the particle surface and that the carbon components consisted mainly of sp2 hybridized graphite and sp3 hybridized organic carbon. The TGA results indicated high characteristic temperatures and low oxidation activity.

Functional Piezoresistive Polymer Composites Based on CO2 Laser-Irradiated Graphene Oxide-Loaded Polyurethane: Morphology, Structure, Electrical and Piezoresistive Properties

Nanocomposite materials have recently attracted great attention for their wide range of applications, such as in smart materials, flexible electronics, and deformation sensing applications. Such materials make it possible to combine a polymer with functional fillers. In this study, flexible artificial leathers, exhibiting insulating properties and containing 1.5 or 2wt.% of graphene oxide (GO) in the polyurethane (PU) layer, were electrically activated via CO2 laser irradiation to obtain conductive paths at the surface exposed to the laser beam. As the material retained its insulating properties out of the irradiation areas, the laser scribing method allowed, at least in principle, a printed circuit to be easily and quickly fabricated. Combining a variety of investigation methods, including scanning electron microscopy (SEM), optical profilometry, IR and Raman spectroscopies, and direct current (DC) and alternate current (AC) electrical measurements, the effects of the laser irradiation were investigated, and the so-obtained electrical properties of laser-activated GO/PU regions were elucidated to unveil their potential use in both static and dynamic mechanical conditions. In more detail, it was shown that under appropriate CO2 laser irradiation, GO sheets into the GO/PU layer were locally photoreduced to form reduced-GO (RGO) sheets. It was verified that the RGO sheets were entangled, forming an accumulation path on the surface directly exposed to the laser beam. As the laser process was performed along regular paths, these RGO sheets formed electrically conductive wires, which exhibited piezoresistive properties when exposed to mechanical deformations. It was also verified that such piezoresistive paths showed good reproducibility when subjected to small flexural stresses during cyclic testing conditions. In brief, laser-activated GO/PU artificial leathers may represent a new generation of metal-free materials for electrical transport applications of low-current signals and embedded deformation sensors.

Development and experimental verification of self-centering disc slit damper for buildings

The damage avoidance design (DAD) philosophy is oriented towards the low-damage design of building structures compared to the previous conventional ductile design. Low-damage structures with supplemental damping and self-centering ability are one of the main aspects of the DAD philosophy to decrease irreparable damage and enhance the seismic performance of structures. This research proposes an efficient, double-acting self-centering hysteretic damper by combining the widely used steel slit dampers and prestressed disc springs for building structures. The proposed seismic protection device is called Self-Centering Disc Slit Damper (SC-DSD), which consists of two square standard hollow steel sections, nested together with an assembly of prestressed disc springs within the steel sections. The performance of SC-DSD is assessed experimentally through a static cyclic loading test to evaluate the global system's dissipation capacity, self-centering ability, and hysteresis loop. A simplified numerical model is developed to predict the self-centering force-displacement relationship of the proposed device. Finally, the seismic force bearing capacity of the proposed damper is compared with the conventional slit damper.

Two-step parameter identification of multi-axial cyclic constitutive law of structural steels from cyclic structural responses

This paper presents a two-step Bayesian optimization (BO) method for identifying the elastoplastic material parameters of structural steels subjected to multi-axial cyclic loading. A series of simple elastic and elastoplastic shaking table tests is conducted for a structure that has a steel specimen experiencing elastoplastic response. An inverse problem is formulated to identify the multi-axial material parameters of the specimen from the structural responses obtained by the shaking table tests. This is notable because it is more difficult to carry out multi-axial static cyclic material tests than to conduct dynamic cyclic structural tests. The inverse problem minimizes the error between the measured structural responses and those simulated by finite element (FE) analysis. The two-step BO devised for solving the inverse problem successfully offers a global optimization framework while considerably reducing the number of costly simulations. It first seeks to infer Young’s modulus values from the cyclic elastic responses of the structure, thereby validating the FE model in its elastic state. It then finds the parameters for the nonlinear combined isotropic/kinematic hardening model of the specimen using the cyclic elastoplastic responses of the structure. Verification results show that the parameters identified by the proposed method well reproduce the cyclic responses of the structure under different cyclic loading conditions.

Thermal management control strategy of liquid-cooled fuel cell vehicle

The thermal management of proton exchange membrane fuel cells is an essential guarantee for the smooth operation of fuel cell vehicles. Most typical fuel cell cooling systems are controlled by threshold control, resulting in a strong coupling relationship between the inlet temperature and the difference of temperature between import and export. To address this problem, this paper proposes a decoupled control strategy and establishes a pump flow controller and a Fuzzy-PID fan controller. According to the fuel cell parameters, a Simulink-GT fuel cell cooling system model is built to verify the optimization strategy in the New European Driving Cycle (NEDC) and compared with the traditional threshold control strategy. The results show that the decoupled control strategy works well under the NEDC cycle test conditions. The fuel cell temperature can be stabilized around the set target value at all times, keeping the fuel cell operating in the high-efficiency range.

DEVELOPMENT OF KNEE-BRACE FRICTION DAMPER FOR MID-RISE TIMBER FRAME BUILDING

This study aims to develop a knee-brace friction damper for mid-rise timber frame buildings. First, time history seismic response analysis was conducted to investigate the performance of the damper to improve the seismic performance of a four-story timber building. Then, static cyclic loading test on a beam-column joint with/without a prototype friction damper was carried out to verify the effectiveness of the damper. It is found that the damper mitigates slip behavior and increases equivalent viscous damping ratio and equivalent stiffness.

State of health estimation of lithium-ion batteries using Autoencoders and Ensemble Learning

This paper focuses on the state of health (SOH) estimation of lithium-ion batteries, which is critical for the reliable operation of electric vehicles. First, a convolutional autoencoder (AE) and a recurrent AE are designed to automatically extract health features (HFs), which are the low-dimensional mappings of the charging profiles at different aging stages. This feature extraction method with two AEs can avoid the artificial definition of HFs and the additional operation on the charging profiles. On this basis, an ensemble learning (EL) method is proposed to improve the SOH estimation accuracy, which consists of a series of sequentially trained gate recurrent unit (GRU) networks. This pattern of sequential training makes that the current GRU network can focus on the poor-performing samples of the previous trained network. Finally, four battery datasets under different cycling test conditions are used to verify the efficiency of the proposed SOH estimation method with the two AEs and the EL. The experimental results reveal that the proposed method can provide accurate battery SOH estimation, with the root mean square error and mean absolute error of Leave-One-Out cross validation (LOO) are 1.04% and 0.77%.

In vitro evaluation of cyclic fatigue resistance of thermally treated novel nickel-titanium rotary instruments

The objective of this study was to evaluate the cyclic fatigue resistance of novel NiTi files (subjected to heat treatment) using the in vitro model (artificial canal). Twelve ProDesign Logic instruments - PDL 25/.06 (Easy Equipamentos Odontológicos, Belo Horizonte, Brazil) and 12 Protaper Next X2 instruments - PTN (tip 25) were included in this research. The Static cyclic fatigue test was performed with a grooved stainless steel block simulating a canal of 1,5 mm diameters, a 60o angle of curvature and 5 mm radius. The files were positioned inside the artificial canal and rotated until the fracture occurred. Using the time until fracture (seconds) and the number of rotations per minute (RPM), the number of cycles until fracture (NCF) was calculated and the length of ruptured fragments was registered. Three samples from each group were analyzed in Scanning Electronic Microscopy (SEM) to characterize the metal rupture. Data were analyzed using the Mann-Whitney non-parametric test and the level of significance considered was p<0.05. PDL obtained a mean value of 956,0 NCF (352,0 - SD) and PTN achieved 391,0 NCF (36.7 - SD) with statistical significance between the groups (p < 0.001). There was no statistical difference on fragment length (p > 0.05). SEM analysis showed features compatible with ductile fracture. ProDesign LOGIC files showed higher NCF than Protaper Next X2. There was no difference between groups considering the length of the ruptured fragment.

Comparison of junction temperature variations of IGBT modules under DC and PWM power cycling test conditions

Comparison of junction temperature variations of IGBT modules under DC and PWM power cycling test conditions

Degradation assessment of 1.2-kV SiC MOSFETs and comparative study with 1.2-kV Si IGBTs under power cycling

Although SiC MOSFETs has better performance than Si IGBTs, some obvious differences between SiC materials and devices and Si equivalents affect the robustness and reliability of SiC MOSFETs. In this paper, an in-depth comparison of degradation assessment of 1.2-kV SiC MOSFETs and 1.2-kV Si IGBTs under the same power cycling test condition is presented. The variations of electrical and thermal characteristics of the two kinds of devices are investigated comparatively. Both devices chip-related and package-related degradation analysis is provided to explain each parameter variation. And a detailed physical analysis is conducted to have a better understanding of the root cause of the aging. From test results, SiC MOSFETs with the same package process will fail earlier than Si IGBTs. After a long period of PCT, Si IGBTs are not observed other failure modes except for solder layer degradation, but SiC MOSFETs are successively observed three failure modes: solder layer crack and delamination, bond crack, threshold voltage shift. However, chip-level degradation failures are much later than package-level degradation failures for SiC MOSFETs. It is shown that although chips still have unresolved reliability problems for SiC MOSFETs, the package reliability is the shortcoming that limits their long-term service life.

Multifiber finite element model based on enhanced concrete constitutive law to account for the effects of early age damage on the seismic response of RC structures

RC structures get damaged over time due to several phenomenons such as shrinkage, thermal deformations, creep and corrosion. This damage starts at early age and continues during the lifetime of the structures. In order to account for the effects of early age damage on the seismic response of RC structures, a research project combining both an experimental and numerical part was conducted. In the experimental part, two types of portal frames that evolved either in endogenous conditions (by covering them using a plastic sheet to limit drying shrinkage) or in non-endogenous conditions (no imposed covering, thus similar conditions as in site constructions) during early age, were constructed and tested at the end of 28 days using static cyclic and pseudo-dynamic tests. Experimental tests performed and monitoring techniques used (ambient vibration, digital image correlation, optical fiber) showed that early age drying shrinkage can cause an increase of the seismic vulnerability of RC structures (50% decrease of the fundamental frequency, 33% lateral drift increase). This article presents the multifiber finite element model based on enhanced constitutive law which allows describing the early age damage due to shrinkage, creep, thermal and mechanical strains and to simulate the static and dynamic response of the portal frames. The resolution of a THC (Thermo-Hygro-Chemical) problem allows calculating shrinkage and temperature time evolutions. In the model, creep is calculated using three viscoelastic Kelvin Voigt models in series with the μ damage law for concrete (through the resolution of an internal equilibrium at the fiber level) whereas steel is accounted for using a Menegotto model. Results obtained using the numerical model were compared to experimental ones in order to validate the proposed model.

Enhancing the In-Plane Behavior of a Hybrid Timber Frame-Mud and Stone Infill Wall Using PP Band Mesh on One Side.

Traditional village dwellings in China consisting of timber frames with mud and stone infill walls represent an important part of cultural heritage and civilization. Due to the lack of an effective link between the wood frame and the infill and the poor cohesiveness of clay, the masonry infill can collapse during an earthquake, whereas the wood frame suffers minimal damage. In this study, current retrofitting techniques for village buildings were investigated and discussed. A method using polypropylene (PP) band mesh and cement mortar to retrofit the timber frame with a mud and stone infill was proposed and the connection construction details were designed. In-plane static cyclic tests were conducted on two full-scale wood–stone hybrid walls reinforced on one side with different grid sizes of the PP band mesh. The failure behaviors of the reinforced and non-reinforced sides of the specimens were compared, and the failure mechanics and seismic capacity of the two specimens, i.e., the strength, stiffness, ductility, and energy dissipation, were investigated. The results were also compared with those of a previous frame with stone infill without pebbles and no reinforcement. The study indicated that the retrofitting method strengthened the integrity and lateral resistance of the hybrid structure and prevented the collapse of the stone infill of the reinforced surface in a plane earthquake. The grid size of the PP band mesh substantially affected the lateral performance of the reinforced specimens. The hybrid wall with the narrow PP band mesh grid (150 mm × 150 mm) had a higher lateral stiffness (79%) and lateral capacity (50%) than the wall with the wide grid (250 mm × 250 mm). However, the narrow PP band mesh resulted in a lower ductility of the wall than the wide PP band mesh. The involvement of pebbles in the stone infill led to collapses sooner and a weaker lateral resistance than in the structure without pebble infill.