Experimental Test Results Research Articles

Numerical investigation of shear behavior of steel fiber reinforced concrete beams without stirrups subjected to an asymmetric point load

Steel fibers have been shown in numerous studies to enhance the shear performance of steel fiber reinforced concrete (SFRC) beams effectively, and to evaluate the shear behavior of these beams, a nonlinear finite element (NLFE) analysis is required. In the present study, from recent experimental results of asymmetrical loading tests on SFRC beams without stirrups, three NLFE models have been validated and further developed to evaluate the impact that the ratio of shear span-to-depth (a/d) and the compressive strength of steel fiber concrete (SFC) have on the shear behavior and shear strength of SFRC beams without stirrups. The validation shows a good agreement between the chosen NLFE model and the reported experimental results. Applying the NLFE model to five different values of the a/d ratio (e.g., 1.0, 1.5, 2.0, 2.54, and 3.1) reveals a gradual decline in shear strength, while the ductility of the beam increases with the increase in ratio. Meanwhile, with increasing SFC compressive strength, the shear strength and ductility of SFRC beams without stirrups significantly increase for the same ratio of shear span-to-depth. Moreover, the failure mode of SFRC beams without stirrups dominantly depends on the a/d ratio.

Ability of pre-cast strain-hardening cementitious composite plates to enhance the shear performance of RC haunched beams

The purpose of this paper is to test ten identical reinforced concrete haunched beams (RCHBs) to determine the effectiveness of pre-cast strain-hardening cementitious composite (PSHCC) plates for shear strengthening. For this purpose, the PSHCC plates have been manufactured in accordance with the test parameters, let to cure for roughly 30 days, and then dipped into the strengthened RCHBs' concrete cover at the critical shear span. The used PSHCC plates are rectangular in shape with a 20 mm thickness and a 100 mm width, and they are reinforced with a single layer of steel wire mesh. The considered key parameters were the effect of shear reinforcement in the test region, the PSHCC plate orientation angle (450, 600, or 900), and the spacing between PSHCC plates (200, 250, or 300 mm). In addition, it was interesting to observe how the strengthening plates, if they exist, are positioned in relation to the inner stirrups (aligned, un-aligned, or inclined). The application of PSHCC substantially enhanced the ultimate shear capacity of the strengthened beams, according to the results of experimental tests. Moreover, the inclined configuration of the PSHCC demonstrated higher shear performance than the vertical configuration, both in terms of the shear cracks characteristics and ultimate capacity. As well, the ductility and serviceability characteristics of the strengthened RCHBs were obviously affected by the application of PSHCC plates. Finally, a proposed analytical model was developed to estimate the shear capacity of the strengthened RCHBs using PSHCC plates.

FPGA-Based VFF-RLS Algorithm for Battery Insulation Detection in Electric Vehicles

As the adoption of electric vehicles (EVs) continues to rise, attention has switched to ensuring the safety of EV operations. The exponential growth in battery technology over the past several years has changed the face of energy storage and sparked a revolution in several industries. The degradation of battery insulation during regular use is a significant concern. The high voltage (HV) and current levels in HV electric vehicles pose a significant electrical threat.The advancement of electric vehicle technology has led to an increasing presence of HV electric equipment throughout the vehicle. The insulation strength and early health status detection of the batteries are essential in ensuring safety in EVs. This paper studies the different insulation detection techniques and the development of adaptive filter (AF) algorithms based on field-programmable gate arrays (FPGAs) for insulation detection. FPGAs are amongst the most accurate and fast detection techniques among all the insulation detection techniques used so far in electric vehicles. This study proposes an FPGA-based VFF-RLS algorithm for effectively implementing insulation detection in EVs. The experimental test results using FPGAs demonstrate that the proposed method can rapidly monitor changes in insulation resistance (IR). The VFFRLS-based FPGA technique works sufficiently well to reduce errors when dealing with variations in voltage and resistance conditions at the battery terminals.

Finite Element Analysis of Polymeric Matrix Composites with Sisal Fiber Reinforcement

Recently, there has been a growing interest in investigating the mechanical properties of plant fibers, particularly in developing nations. This surge is primarily fueled by the escalating environmental concerns, which are becoming more evident and alarming. Against this backdrop, various sectors of materials engineering are actively seeking alternatives to mitigate the environmental impact across the entire lifecycle of products - from production to use and disposal. This study aims to conduct a computational analysis to examine the influence of fiber quantity on the tensile strength of composites containing sisal fibers. It compares the findings with existing experimental test results and demonstrates the outcomes using the finite element method. The research reveals that greater tensile strength in the composites is achieved with higher volumetric fractions of sisal fiber, as observed in both experimental and computational analyses. These results underscore a strong correlation between finite element analysis and experimental tests documented in the literature.

Development of Second Order High Frequency Filter for Partial Discharge Measurement

Partial discharge (PD) can occur on any high-voltage equipment. This study is particularly concerned with the PD that occurs on underground cables. Researchers frequently struggle to isolate interference noise from the PD signal when doing PD measurements. Therefore, to reduce the interference noise during PD measurements, Sallen-Key high-pass filters with a 500 kHz, or a little bit higher cut-off frequency are designed. This filter is designed with a designated cut-off frequency value because the frequency range of the PD signal is between 1 MHz to 1 GHz. Based on the results of experimental testing for actual filters, the designed filter is a high-pass filter with a cut-off frequency of 500KHz. When the generator function's input frequency values are set between 500 kHz and 2.4 MHz, the signal will pass the filter and provide output values for both frequencies and amplitude. However, at frequencies lower than 500 kHz, the signal is beginning to be filtered and the output signal's amplitude is getting close to zero. Based on the PD testing results, there is interference on the PD signal shown on the oscilloscope when a 1kV supply is applied to an underground cable without using a filter. But, when the proposed filter is used in PD testing, the ripple voltage is reduced from 123 mV to 67 mV. This proves that when the designed filter is used in PD testing, it can reduce interference noise on the PD signal.

Особенности расчета температуры резания при высокоскоростном фрезеровании алюминиевых сплавов без применения СОЖ

Introduction. The calculation of temperature during high-speed milling of aluminum alloys is of interest, since temperature can act as one of the main limiting factors in choosing rational milling modes. This is especially important when milling thin-walled products used in aircraft construction, since its high values can lead to local warping of the structure. It is not possible to control the temperature factor in production conditions, which makes it necessary to develop a mathematical model for calculating temperature. The purpose of the work is to develop a methodology for predicting the cutting temperature during high-speed milling of aluminum alloy workpieces for cutting conditions, in which it is not possible to use cutting fluid. Methods. This paper presents experimental studies of the cutting temperature during high-speed milling of aluminum alloy workpieces without the use of cutting fluid using non-contact temperature measurement methods. The results obtained were used to determine the coefficients substituted into formulas for calculating temperatures on the front and back surfaces of the cutting blade. Results and discussions. Based on the results of experimental tests and theoretical modeling, a temperature graph is drawn up. A comparison of experimental studies of milling of aluminum alloy D16T, with changing cutting conditions (the cutting speed changed) with theoretical data, gave a satisfactory result. The average relative error when comparing experimental data with theoretical one is 6.05 %. Based on experimental data, it can be concluded that the comparison of experimental data for measuring cutting temperatures is in satisfactory agreement with the proposed method of theoretical calculation of temperatures. The advantage of this technique is that it allows, without time-consuming and costly experimental studies, theoretically calculate (forecast) the temperatures on the front and back surfaces of the cutting blade, as well as the cutting temperature, for those narrow milling conditions, where effective heat removal from the cutting zone is impossible. It can also be used for milling aluminum alloys, the mechanical and thermophysical properties of which differ.

Assessment of Cementitious Composites for High-Temperature Geothermal Wells.

High-temperature (HT) geothermal wells can provide green power 24 hours a day, 7 days a week. Under harsh environmental and operational conditions, the long-term durability requirements of such wells require special cementitious composites for well construction. This paper reports a comprehensive assessment of geothermal cement composites in cyclic pressure function laboratory tests and field exposures in an HT geothermal well (300-350 °C), as well as a numerical model to complement the experimental results. Performances of calcium-aluminate cement (CAC)-based composites and calcium-free cement were compared against the reference ordinary Portland cement (OPC)/silica blend. The stability and degradation of the tested materials were characterized by crystalline composition, thermo-gravimetric and elemental analyses, morphological studies, water-fillable porosity, and mechanical property measurements. All CAC-based formulations outperformed the reference blend both in the function and exposure tests. The reference OPC/silica lost its mechanical properties during the 9-month well exposure through extensive HT carbonation, while the properties of the CAC-based blends improved over that period. The Modified Cam-Clay (MCC) plasticity parameters of several HT cement formulations were extracted from triaxial and Brazilian tests and verified against the experimental results of function cyclic tests. These parameters can be used in well integrity models to predict the field-scale behavior of the cement sheath under geothermal well conditions.

Fatigue crack growth and microstructural analysis of rail steel specimens under periodic overloads

The present paper aims to study the effects of periodic overloads on the fatigue crack growth and microstructure of railway rail specimens. Numerical analysis and experimental tests were exploited to examine the crack path in specimens. A three-dimensional nonlinear boundary element model was used to predict the crack path in specimens. The effect of several parameters on the fatigue life of the rail steel specimens were evaluated using numerical model and experimental tests. The numerical and experimental test results revealed that the fatigue life curve had an optimal overload ratio at which the fatigue life was maximized. The number of fixed cycles was kept fixed between the overloads, measuring the effect of the overload ratio on the fatigue crack growth. Also, the fractographic analysis showed that by increasing the stretching speed of the rail steel specimens, the amount of plastic deformation is reduced and the brittleness of the material is increased.

Investigation on the elastic flexural stiffness of dot-by-dot wire-and-arc additively manufactured stainless steel bars

Among different metal additive manufacturing (AM) technologies, arc-based Directed Energy Deposition, also known as Wire-and-Arc Additive Manufacturing (WAAM), is considered the most suitable for large-scale structural components production. In particular, the WAAM printing strategy referred to as “dot-by-dot” allows the realization of complex 3D lattice forms at the scale of structural steel parts, composed of unitary cells made of slender bars. Nonetheless, the outcomes of this process are still to be properly investigated in terms of their mechanical behavior under various loading conditions. To assess the buckling behavior of WAAM-produced slender bars, extensive effort is requested to properly characterize the main driving aspects, namely the flexural stiffness possibly influenced by mechanical anisotropy induced by the printing process and the influence of the geometrical imperfections. The present work reports the first results of experimental bending tests conducted on vertically printed (i.e. with a fixed build angle equal to 0°) straight dot-by-dot WAAM stainless steel bars, as an initial investigation towards a more comprehensive analysis of the buckling behavior of WAAM slender elements. The results are then interpreted by introducing three approaches of increasing complexity, including two analytical approaches based on a simplified idealization of the real geometry of the bar, and a third approach based on the reconstruction of the real geometry of the bar using advanced numerical simulations and 3D scanning. The three approaches lead to a different appraisal of the influence of the geometrical irregularities on the flexural stiffness of the specimens. The main results of the present study could be utilized to interpret the results of future experimental compressive tests on WAAM slender elements and to develop ad-hoc buckling curves for structural design purposes.

Uncertainty Constraint on Headphone Secondary Path Function for Designing Cascade Biquad Feedback Controller with Improved Noise Reduction Performance

The uncertainty in the secondary path of active noise control (ANC) headphones affects the waterbed effect and stability of the feedback system. This study focuses on the uncertainty of the secondary path when real users wear headphones and proposes a new uncertainty constraint based on the measured results of the secondary path transfer function under different wearing conditions of a dummy head and limited subjects. This constraint and a cascaded second-order infinite impulse response filter with fixed coefficients are used to formulate a control strategic function, which is optimized using the Improved Grey Wolf Optimizer (IGWO) algorithm to obtain the optimal controller with better noise reduction performance. The proposed method and simulation model are validated based on the experimental test results. The results demonstrate that the safety factor and waterbed suppressing factor contained in the proposed uncertainty constraint ensure more stable noise reduction and effective suppression of the waterbed effect for new subjects without a priori data.

Lateral-torsional buckling resistance of non-prismatic and prismatic mono-symmetric I-section steel beams based on stress utilization

The lateral-torsional resistance of prismatic double-symmetric I-section beams is accurately predicted using a mechanically consistent Ayrton-Perry approach, combined with a calibrated generalized imperfection. The corresponding design formulation was recently adopted in the revised version of Eurocode 3. However, for prismatic mono-symmetric I-section beams, the General Case shall be used while for non-prismatic beams only the General Method is available. Both methods present a very large scatter and highly underestimate the lateral-torsional buckling resistance. This paper proposes an extension to the General Formulation for non-prismatic beams with arbitrary boundary conditions, partial lateral restraints, and arbitrary loading for mono-symmetric I-sections. Using an advanced numerical model calibrated with experimental test results, a large parametric study is undertaken, and its results are used to assess the available design methodologies and the proposed method. It is concluded that the General Formulation provides excellent safe-sided estimates of the LTB resistance, and it is confirmed the very poor performance of the General Case and the General Method.

Diagnosis and Treatment of Oil Film Whirl Fault in the Bearing of Large Synchronous Condenser

The oil film vortex of a synchronous condenser rotor can cause an increase in bearing vibration. When the vibration amplitude exceeds the threshold value, it can cause the condenser to trip. The oil film vortex is related to many factors and often occurs during the start-up and acceleration process of the unit, as well as during the loading process of the unit. This article elaborates on the low-frequency oscillation accident of the bearing system caused by the oil film vortex fault of the rotor of a large synchronous condenser and its handling methods. This article presents a sudden low-frequency vibration of a large synchronous condenser. Based on the data collected on site and experimental test results, this condenser analyzes and diagnoses the low-frequency vibration incident, and ultimately determines it as an oil film vortex fault in the bearing system. The article combines the operation and maintenance plan of the synchronous condenser and conducts on-site dynamic balance tests on the synchronous condenser. After the dynamic balance test, the low-frequency vibration of the bearing system disappears and the fault is eliminated.

Environmental causality calibration: Advancing WLAN RF fingerprinting for precise indoor localization.

In recent years, considerable and valuable research progress has been made in indoor positioning technologies based on WLAN Radio Frequency (RF) fingerprinting, identifying it as one of the most promising positioning technologies with substantial potential for wider adoption. However, indoor environmental factors significantly influence the propagation of wireless RF signals, resulting in a considerable decrease in positioning accuracy as the indoor environmental conditions vary. Thus, effectively mitigating the impact of indoor environmental factors on WLAN RF fingerprinting-based positioning systems has become a crucial research problem. Currently, there is a dearth of comprehensive research on the influence of indoor climatic factors, particularly the variations in relative humidity, on the propagation of WLAN RF signals within indoor spaces and its consequential impact on positioning accuracy. To address the aforementioned issues, this paper proposes an Adaptive expansion fingerprint database (AeFd) model based on a regression learning algorithm. The AeFd, through the design of a relationship model describing the interaction between fingerprint databases under varying relative humidity, allows the fingerprint database expanded by AeFd to dynamically adapt to the changes in indoor relative humidity. Our experiments show that using the AeFd model with the KNN algorithm, a 5% performance improvement was observed over 10 days and an 8% improvement over 10 months. According to experimental test results, the fingerprint database expansion model AeFd proposed in this paper can effectively expand the fingerprint database under different relative humidity levels, thereby significantly enhancing the positioning performance of the system and improving its stability.

Experimental and analytical investigations on backbone curve models for RC shear keys under sequential seismic-tsunamic impacts

Reinforced concrete (RC) sacrificial shear keys play a crucial role in enhancing the structure resilience of coastal bridge against lateral impacts induced by seismic-tsunami scenarios. Existing researches have primarily focused on their performance under cyclic effects to simulate seismic impacts during earthquakes. However, their ability to withstand enduring forces under tsunami wave has been rarely studied yet. In this research, an experimental test was carried out to investigate the failure mechanism of RC shear keys under sequential cyclic-persistent effects, in which three typical failure modes of shear keys were considered. Various damage states were introduced to account for the possible damage levels after sustaining seismic impacts. The test results were analyzed by focusing on damage pattern, hysteretic behavior, peak capacity, and strain development, showing great distinctions with respect to different failure modes and corresponding damage stages. Furthermore, the analytical backbone curve models were developed based on the experimental test results. The presented models were validated using the typical strain-stress curve of reinforcement, and exhibited better applicability in characterizing the performance of shear keys under either cyclic or cyclic-persistent sequential effects, comparing to the other approaches that emphasizes on their seismic properties.

Soil Stabilization Using Precipitated Calcium Carbonate (PCC) Derived from Sugar Beet Waste

The objective of this research is to examine the use of precipitated calcium carbonate (PCC), obtained during the production of sugar from sugar beets, and to stabilize subgrades beneath highway pavements or to stabilize foundations built on loess (windblown silt). The research also aims to permanently capture the carbon from PCC in soil. The experimental process involved the collection of representative loess samples, the addition of variable percentages of PCC, and conducting laboratory experiments on compacted PCC soil mixes to evaluate the effect of PCC on subgrades beneath pavement and foundations beneath buildings. Samples of PCC were obtained from the Amalgamated Sugar Corporation, located 187 km away from Pocatello. In addition, soil was collected from local sources in which saturation collapse and damage have occurred in the past. Unconfined compressive strength tests, which index subgrade bearing failures, were performed on both untreated and PCC-treated soils to evaluate the effect of PCC in stabilizing pavement subgrades and foundations as well as sequestering carbon. The experimental test results revealed a significant average increase of 10% to 28% in the strength of loess samples stabilized with 5% PCC compared to the native soil. The chemical composition and microstructure of PCC were further analyzed through energy-dispersive X-ray spectroscopy (EDX) and scanning electron microscopy (SEM) tests. EDX analysis unveiled a carbon content of 9% by weight in PCC, which could contribute to the carbon footprint when it breaks down. Additionally, SEM images displayed an unsymmetrical and sub-rounded microstructure of PCC particles. Based on these findings, the study suggests that utilizing PCC could improve the resistance of loess to saturation collapse and potentially reduce carbon emissions associated with cement or lime production while offering an opportunity to use PCC in soil application.

Calibration of micromechanical fracture model parameters for Q355B steel and ER50–6 welds

To calibrate the micromechanical fracture model of Q355B steel and ER50–6 welds, 46 specimens of five types were subjected to monotonic tensile tests. The material constitutive model employed for finite element analysis (FEA) is determined by the Swift-Voce model, which leads to FEA results that closely align with the experimental test results. The parameters of the void growth model (VGM) and the stress-weighted damage model (SWDM) were calibrated, and the VUSDFLD user subroutine was written based on the two models to predict the fracture of each specimen. The prediction results show that the VGM model has good accuracy in the case of high-stress triaxiality. However, the prediction error of the VGM model is relatively large for shear specimens with low-stress triaxiality and significant changes in the Lode angle parameters. In contrast, the SWDM model with Lode angle parameters can predict the fracture of specimens under different stress states more accurately.

Installation and test procedure for frequency stability under cyclic loading of metals and alloys

Manufacture of parts operating under difficult conditions of cyclic loading, as well as products with stable dimensions necessitates the use of materials with minimal manifestations of inelastic properties. Study of these materials suggests conducting specialized narrowly focused tests using newly developed machines and installations with appropriate experimental techniques. We present the design, operation and control features of the original electromagnetic installation for testing fatigue and frequency stability and operating in a self- oscillating mode, which provides the equality of the frequency of cyclic loading and natural frequency of the sample. The system of the installation control contains two closed circuits: for excitation of self-oscillations and for stabilization of the oscillation amplitude. The sample is loaded by electromagnetic force, and unloading occurs due to the elastic forces of the material. The methodology and algorithms for calculating the stresses of samples of various geometric shapes for estimating changes in amplitude-frequency characteristics are presented. The calculated relationship between the force applied to the sample and its movement at the point of application of force is derived with subsequent determination of the stress by a known force. The results of calibration tests for the static mode of sample loading are presented and the forces acting on the sample (external, inertia, and elastic forces) are evaluated taking into account the maximum stress and maximum strain amplitude. Static and cyclic loading modes are compared. The frequency characteristics obtained during testing steel samples according to the proposed method are obtained. The experimental results of tests with interruptions in the process of cyclic loading and continuous testing are analyzed. It is shown that interruptions in cyclic tests lead to a jump-like increase in the frequency, whereas continuous tests revealed no jumps. At the same time, a comparative analysis with the results of continuous tests showed that the overall frequency deviation is approximately the same for the entire operating cycle in both cases. It is shown that an increase in the frequency after rest is random and does not depend on the number of operating cycles.

Experimental investigation of electromagnetic interference impact on phase change material coated solar photovoltaic panel

ABSTRACT High Voltage Transmission Line Electromagnetic Field’s (HVTL-EMF) impact on solar PV performance is analyzed in the proposed work. Depending on HV-EMF, the electrical characteristics and conversion process of PhotoVoltaic (PV) panels are analyzed. Electromagnetic (EM) field from HV lines has a partially positive and somewhat negative impact on solar PV. When absorption probability is low, one photon and one phonon are required. Phonons are vibrational energy units. A solar PV cell made of Silicon (Si) semiconductor material requires phonons to have high conversion efficiency and electric field from HV transmission line induces phonon. In addition, electric field from HV line increases the solar cell temperature (10 to 15°C) to the ambient temperature. Because of high solar PV cell temperature and high EM field, solar PV power generation is affected by increasing panel temperature. The proposed system uses unnatural Phase Change Material (PCM-Glauber salt (Na2SO4.10 H2O)) coated to the backside of solar PV to normalize the temperature. The impact of electromagnetic fields produced by HV lines on solar cells coated with PCM is validated with experimental testing results. The experiment considers a HVTL of 230kV and solar PV rating of 20 W. The experimental results are measured at various distance ranging from 12 to 22 meters between solar PV and HV transmission lines. Conversion efficiency of solar PV with PCM coating under the impact of HVTL- EMF has increased by 3%.

Effects of Lip Length and Inside Radius-to-Thickness Ratio on Buckling Behavior of Cold-Formed Steel C-Sections

Cold-formed steel (CFS) sections constructed with high-strength steel have gained prominence in construction owing to their advantages, including a high strength-to-weight ratio, shape flexibility, availability in long spans, portability, cost-effectiveness, and design versatility. However, the thin thickness of CFS members makes them susceptible to various forms of buckling. This study focuses on addressing and mitigating different types of buckling in columns and beams by manipulating the lip length (d) and the ratio of inside radius to thickness (Ri/t) in CFS C-sections. To achieve this objective, a comprehensive analysis involving 176 models was conducted through the Finite Element Method (FEM). The findings reveal that an increase in lip length leads to a corresponding increase in critical elastic buckling load and moment (Pcrl, Pcrd, Pcre, Mcrl, Mcrd, and Mcre). It is recommended to utilize a lip length greater than or equal to 15 mm for both columns and beams to mitigate various buckling types effectively. Conversely, an increase in the ratio of inside radius to thickness (Ri/t) results in an increase in critical elastic local buckling load (Pcrl) and moment (Mcrl). Thus, lip length (d) significantly influences column and beam buckling, whereas Ri/t exhibits a relatively impactful effect. Subsequently, the experimental test results were used to verify finite element models. These insights contribute significant knowledge for optimizing the design and performance of CFS C-sections in structural applications.

High Strain Rate Modeling of CFRP Composite Under Compressive Loading

An in-depth understanding of how carbon fiber-reinforced plastics (CFRP) respond to intense strain rates is essential, particularly in non-linear deformation and dynamic loading situations. The researchers undertook a computational study to examine the behavior of CFRP composites when exposed to high strain rates under compressive loading. Specifically, they employed Split Hopkinson Pressure Bar models for cohesive interfacial simulations, continuum shell analysis, and laminated composites oriented at 0° at a strain rate equivalent to 900 s-1. The Finite Element model utilized a custom Hashin damage model and a vectorized user material (VUMAT) sub-routine to identify degradation damage within the CFRP composite model. The quasi-isotropic composite demonstrated a significant enhancement in dynamic strength compared to static values, attributed to its intense sensitivity to strain. As confirmed by experimental test results, numerical simulations accurately predicted stress (σ)-strain (ε) and strain rate (ἐ) curves. Additionally, it was observed that the relationship between damage behavior varied depending on the element type used.