Proposed Test Method Research Articles

A simple estimation method of grid‐forming inverter inertia based on rate of change of frequency

AbstractInertia is the core index of the estimation of power system frequency stability; a simple estimation method of grid‐forming inverter inertia based on the rate of change of frequency (RoCoF) is proposed in this paper. The method records and fits the active power curve by applying RoCoF to obtain the value of the grid‐forming inverter inertia, and it is simpler and higher accuracy compared to existing methods. In addition, the inertia and damping are analysed to support the system, and the relationship equation between the grid frequency slope change and the output active power is derived. Considering the theoretical analyses and influencing factors, the inertia and damping are obtained by using the method of function fitting. The test steps show the simplicity of the proposed test method. Finally, the effectiveness of the proposed method is verified in MATLAB/Simulation and two 1.575‐MW parallel grid‐forming electrochemical energy storage power plants.

Fast Power Coefficient vs. Tip–Speed Ratio Curves for Small Wind Turbines with Single-Variable Measurements following a Single Test Run

Small wind turbines (SWTs) face tremendous challenges in being developed into a more reliable and widespread energy solution, with a number of efficiency, reliability, and cost issues that are yet to be resolved. As part of the development stages of an SWT, testing the resulting efficiency and determining appropriate working ranges are of high importance. In this paper, a methodology is presented for testing SWTs to obtain characteristic performance curves such as Cp (power coefficient) vs. TSR (tip–speed ratio), and torque vs. ω, in a simpler and faster yet accurate manner as an alternative energy solution when a wind tunnel is not available. The performance curves are obtained with the SWT mounted on a platform moving along a runway, requiring only a few minutes of data acquisition. Furthermore, it is only required to measure a single variable, i.e., the generator output voltage. A suitable physics-based mathematical model for the system allows for deriving the desired performance curves from this set of minimal data. The methodology was demonstrated by testing a prototype SWT developed by the authors. The tested prototype had a permanent magnet synchronous generator, but the methodology can be applied to any type of generator with a suitable mathematical model. Given its level of simplicity, accuracy, low cost, and ease of implementation, the proposed testing method has advantages that are helpful in the development process of SWTs, especially if access to a proper wind tunnel is prevented for any reason. To validate the methodology, Cp vs. TSR curves were obtained for an SWT prototype tested under different test conditions, arriving always at the same curve as would be expected. In this case, the test prototype reached a maximum power coefficient (Cp) of 0.35 for wind velocities from 20 to 50 km/h for a TSR of 5.5.

Small-scale laboratory tests for quantifying aggregate interlocking in short-panelled concrete pavements

In the present study, a simple and reliabe small-scale laboratory test to assess the performance of aggregate interlocked joints in short-panelled concrete pavements in terms of LTE is proposed. In the proposed test method, conventional standard flexural strength test beam specimens (100×100× 500mm) are used for understanding the performance of aggregate interlocking of PQC mix specimens prepared using coarse aggregates of different NMAS and with addition of both micro and macro fibers. The test setup is also modelled in ANSYS FE software. The experimentally obtained LTE is compared with the LTE obtained from the FE model. The field FWD test is conducted for validation. The relative movement is determined from FWD test, and corresponding LTE is determined using the LTE and RM relationship obtained from experimental results using the proposed test apparatus. There exists good linear fit between the LTE determined using proposed test and field FWD test results.

A new method for determination of segregation stability of pumped ready‐mixed concrete: Rapid wet‐sieved test

AbstractIn the process of pumping, the segregation of concrete mixture will lead to the difficulty of construction, and even the possibility of pipe blocking. There is a lack of a quickly evaluation for on‐site construction. In order to solve this problem, a rapid wet‐sieved test was proposed in this study and then its feasibility was evaluated based on concrete mixes with different water–cement ratios. Subsequently, the influence of sand ratio on the segregation degree of concrete was investigated. The test results show that a combination of 2.36 mm screen size and 20 s vibrating time did the best. The wet‐sieved mortar content and stratification degree were increased by 4.6%–25.2% and 0.3%–17.9% by pumping, respectively. With the sand ratio increasing from 0.40 to 0.60, the pumping pressure decreased by 51.9%. The linear fitting correlation between pumping pressure and wet‐sieved mortar content (0.96) is better than that between pumping pressure and stratification degree (0.85), which indicates that the proposed test method can reliably characterize the degree of segregation during the pumping of ready‐mixed concrete.

Analysis of the Effect of an Open Hole on the Buckling of a Compressed Composite Plate.

This paper investigates the effect of an open hole on the stability of a compressed laminated composite plate. The study was carried out in two ways: using experimental tests and numerical analysis. As a result of the experiment, the buckling form and path of the plate were recorded. The form of buckling was determined using the ARAMIS non-contact measurement system. The critical load value was determined from the working path using the approximation method. The experimental results were verified by numerical analysis based on the finite element method. FEM investigations were carried out in terms of a linear eigenproblem analysis. This allowed the bifurcation load and the corresponding buckling form of the numerical model of the plate to be determined. Investigating the effect of the hole in the compressed plate at a critical state showed high agreement between the proposed test methods. No clear effect of the hole size on the buckling of the plate was observed. In contrast, a clear effect of the hole on the critical load value was determined. The maximum decrease in the critical load value was 14%. The same decrease was observed for the stiffness of the post-critical characteristics. It was shown that the [45|-45|90|0]s composite plate had more than three times lower strength compared to [0|-45|45|90]s and [0|90|0|90]s. The novelty of this article is the development of a research methodology based on new interdisciplinary research methods for describing the influence of the central hole on the stability of compressed composite plates. The ABAQUS system was used for the numerical analysis.

A stress-controlled soil column test equipment for investigating water seepage-consolidation characteristics of the compacted soil

For deep-filled building site, it is not acceptable to neglect water seepage and land settlement caused by the coupling effect of wetting and loading. However, previous soil column tests employed in investigating the water seepage always failed to consider the vertical stress. In this article, a stress-controlled soil column test was conducted to investigate the effect of vertical stress on water seepage and deformation of the compacted soil. The soil column was equipped with a vertical loading device and a water-recharge device to control the boundary conditions and water sensors, tensiometers, dial indicators and a data collector to monitor the displacement and water movement. The soil column test was utilised to perform seepage tests on compacted loess with vertical stresses of 0 and 400 kPa. The time-history data of wetting front depth, volumetric water content (VWC), suction and vertical displacement have been monitored directly. The VWC and suction profiles, soil–water characteristic curves and hydraulic conductivity curves were then obtained with the monitored data. The test results demonstrated that the vertical stress affected the water seepage and consolidation of the compacted soil, but this effect gradually decreased as the depth of the soil column increased. Moreover, the reliability of the proposed test method was verified by the comparison of some available test results. The findings of this study contribute to a better understanding of water seepage and consolidation characteristics of the compacted soil subjected to vertical stress.

Enhanced Soft Error Rate Estimation Technique for Aerospace Electronics Safety Design via Emulation Fault Injection

In this paper, we propose Automatic Configuration Memory Fault Injection (ACMFI), a tool that calculates the architectural vulnerability factor (AVF) and soft error rate (SER) using the emulation fault injection technique. SER, which is essential for the safety design of aerospace electronics, can be obtained by experiments (beam tests) performed in a beam facility equipped with high-energy radiation facilities. However, SER calculation using beam tests has the disadvantage of a high cost and a long waiting time, making it difficult to use in the conceptual design stage, which is the aerospace system development stage and the initial HW/SW development stage. Using the emulation fault injection method, it is possible to estimate the SER, which can be used in the system safety design phase. This paper describes the ACMFI tool, which automatically performs emulation fault injection in SRAM-based FPGAs, which are widely used in aerospace electronic hardware. Unlike the existing methods, the proposed method has the advantage of minimizing the side effects by injecting faults into a dedicated SRAM area. In other words, the SER obtained by the proposed method can be estimated more accurately than the SER result obtained by the existing method. To prove the accuracy of the proposed test method, the SER calculated by performing an emulation fault injection test on the same FPGA was compared with the SER results tested at the beam facility. The method of obtaining SER using the proposed ACMFI gave results that were closer to the SER obtained by testing at the beam facility than the method of obtaining SER using the existing EMFI. The proposed method is used to calculate the failure rate, which is a key variable in determining the development assurance level when performing safety design tests in aerospace system development, enabling the development of safer systems and lower cost/higher quality aerospace electronic equipment than before.

Large-scale combined torsional and axial loading system (TorAx) – A new perspective on multiaxial testing of fracture and stress transfer in plain and reinforced concrete

Civil engineering structures are exposed to complex loading scenarios leading to multiaxial fracture and activation of stress transfer mechanisms along cracks controlled by combined deformations in two independent spatial directions (crack opening and crack sliding). Such multi-degree of freedom conditions cannot be properly investigated by state-of-the-art testing procedures. That is why – based on a thorough review of existing experimental procedures – this paper presents a novel testing methodology that applies shear via torsional loading and can simultaneously load specimens in axial direction (TorAx) to explore the material behavior before, during, and after macro-cracking. Independent control of both degrees of freedom allows the generation of arbitrary biaxial load or deformation paths. To prove the technical feasibility of the proposed testing method, several tests on thin-walled concrete tubes have been conducted. The obtained results proved uniformity of strain distribution along the tested ligament which guarantees several advantages (e.g., elimination of size/boundary effects and reduced scatter) over existing testing methods. With low costs (material/time) TorAx will serve as a benchmark for future studies under monotonic, cyclic, and fatigue loading. By experimentally quantifying all stress transfer mechanisms in one unifying test setup, an unbiased comparison of the individual mechanisms is possible, which is the first necessary step towards accelerated yet economical and reliable mechanical and numerical models.

A Universal Test on Spikes in a High-Dimensional Generalized Spiked Model and Its Applications

This paper aims to test the number of spikes in a generalized spiked covariance matrix, the spiked eigenvalues of which may be extremely larger or smaller than the non-spiked ones. For a high-dimensional problem, we first propose a general test statistic and derive its central limit theorem by random matrix theory without a Gaussian population constraint. We then apply the result to estimate the noise variance and test the equality of the smallest roots in generalized spiked models. Simulation studies showed that the proposed test method was correctly sized, and the power outcomes showed the robustness of our statistic to deviations from a Gaussian population. Moreover, our estimator of the noise variance resulted in much smaller mean absolute errors and mean squared errors than existing methods. In contrast to previously developed methods, we eliminated the strict conditions of diagonal or block-wise diagonal form of the population covariance matrix and extend the work to a wider range without the assumption of normality. Thus, the proposed method is more suitable for real problems.

Biodegradation of plastics in the pelagic environment of the coastal zone – Proposed test method under controlled laboratory conditions

The increasing quantities of plastic litter accumulated in the oceans, including microplastics, represent a serious environmental threat. Despite the recent legislative actions, the plastic littering problem will not disappear in a short time. It may, however be ameliorated by replacing conventional non-degradable plastics with bio-based materials biodegradable in marine environment (targeting the non-recycled or mismanaged plastic waste). Although priority is set to prevention of plastic litter by means of the circular economy principles, biodegradability is a means of controlling unintentional plastic pollution. In this effort, the development of reliable test methods that would be used along with standard specifications for determining the biodegradability of novel polymeric materials or plastics in marine environments, is a necessary complementary component of the whole strategy to control the marine plastic litter and micro-, nano-plastics threat. The present work focuses on identifying gaps and improving available laboratory test methods for measuring the aerobic biodegradation of plastics in the seawater column within the coastal zone (pelagic environment). The research work followed a methodology that is based on recommendations of ASTM D6691:2017 concerning biodegradation of plastics in the seawater and the similar ISO 23977-1:2020. Three different implementation schemes of the test method were applied using different experimental setups and measuring techniques for monitoring the evolved CO2. The effect of critical parameters affecting nutrient adequacy (concentration in inoculum) and oxygen adequacy (bioreactor size, sample size, frequency of aeration) on the biodegradation of four tested materials was explored, and optimal values are proposed. The results allowed for the refinement of the proposed test method to improve reliability and reproducibility.

ML-Enabled Piezoelectric-Driven Internal Defect Assessment in Metal Structures

With the growth of 3D printing in the production space, it is inevitable that quality assurance will be needed to keep final products within the constraints of requirements. Also, the variety of materials that can be used with 3D printing has increased over the years. Testing also must consider the process of manufacturing. This paper focuses its efforts on the finished product and not the process of manufacturing. Ultrasonic testing is a type of nondestructive testing. The experiments performed in this study aim to explore the usefulness of ultrasonic testing in materials that are 3D printed. The two materials used in this study are steel alloy metals and aluminum blocks of the same dimensions—120 mm × 40 mm × 15 mm. These materials represent common choices in additive manufacturing processes. The chosen alloys, such as Aluminum (6063T6) and grade-304 stainless steel, possess distinct properties crucial for validating the proposed testing method. Metal 3D-printed materials play a pivotal role in diverse industries, since ensuring their structural integrity is imperative for reliability and safety. Testing is crucial to identify and mitigate defects that could compromise the functionality and longevity of the final products, especially in applications with demanding performance requirements. An ultrasonic transducer is used to scan for subsurface defects within the samples and an oscilloscope is used to analyze the signals. Furthermore, several Machine Learning (ML) techniques are used to estimate the severity of the defects. The application of Machine Learning methods in the manufacturing industry has proven advantageous in terms of detecting defects due to its practicality and wide application. Due to their distinct benefits in processing image information, convolutional neural networks (CNNs) are the preferred method when working with picture data. In order to perform binary and multi-class classification, support vector machines that employ the alternative kernel function are a viable option for processing sensor signals and picture data. The study reveals that ultrasonic tests are viable for metallic materials. The primary objective of this work is to evaluate and validate the application of ultrasonic testing for the inspection of 3D-printed steel alloy metals and aluminum blocks. The novelty lies in the integration of Machine Learning techniques to estimate defect severity, offering a comprehensive and non-invasive approach to quality assessment in 3D-printed materials. The proposed method can successfully detect the presence of internal defects in objects, as well as estimate the location and severity of the defects.

Testing powers of the ratio of variances of two normal populations with a common mean

This article addresses the problem of hypothesis testing about the powers of the ratio of variances of two normal populations with a common mean. Different test procedures are proposed, such as the likelihood ratio test, the standardized likelihood ratio test, the parametric bootstrap likelihood ratio test, the computational approach test and its modification. Further, several generalized p-value approach test procedures are derived using some of the existing common mean estimators. The performances of all the suggested test methods are compared numerically in terms of their size values and power functions. In light of our simulation findings, we provide a few suggestions for utilizing the proposed test methods. Finally, we analyse real-life data to show the potential application of the proposed model.

Bond Wire Fatigue of Au, Cu, and PCC in Power LED Packages.

Bond wire failure, primarily wire neck breakage, in power LED devices due to thermomechanical fatigue is one of the main reliability issues in power LED devices. Currently, the standard testing methods to evaluate the device's lifetime involve time-consuming thermal cycling or thermal shock tests. While numerical or simulation methods are used as convenient and quick alternatives, obtaining data from material lifetime models with accurate reliability and without experimental fatigue has proven challenging. To address this issue, a mechanical fatigue testing system was developed with the purpose of inducing mechanical stresses in the critical region of the bond wire connection above the ball bond. The aim was to accelerate fatigue cracks at this bottleneck, inducing a similar failure mode as observed during thermal tests. Experimental investigations were conducted on Au, Cu, and Pd-coated Cu bonding wires, each with a diameter of 25 µm, using both low- and high-frequency excitation. The lifetime of the wire bond obtained from these tests ranged from 100 to 1,000,000 cycles. This proposed testing method offers material lifetime data in a significantly shorter timeframe and requires minimal sample preparation. Additionally, finite element simulations were performed to quantify the stresses at the wire neck, facilitating comparisons to conventional testing methods, fatigue test results under various operating conditions, material models, and design evaluations of the fine wire bond reliability in LED and microelectronic packages.

Combined bearing/pull-through failure envelope of composite joints: Experimental setup and numerical validation

The failure envelope of composite fastened joints under combined bearing and pull-through loading conditions is obtained by developing, testing and validating a new experimental procedure. The new device proposed here is compatible with standard testing machines and captures the critical interactions between the two loading mechanisms for pull-through to bearing ratios ranging from 0.2 up to 0.8, allowing the characterization of the behaviour of composite joints under realistic loading scenarios. High-fidelity finite element simulations are used to support the validation of the test methodology: the ability of the fixture to maintain a constant mixed load ratio during the whole test was numerically confirmed and a detailed analysis of the failure modes provided further insights into the main degradation mechanisms occurring during the experiments. A very good agreement between the predicted and experimental failure load was obtained for the entire failure envelope, indicating the effectiveness of both the proposed test method and modelling strategy.

Calibration of a Test Method to Measure Mode I, Mode II and Mode III Fracture Toughness of Engineering Materials

A refined finite element model and a new post processing sub program to determine mixed mode stress intensity factors and their variation along a surface crack front in components and structures is presented. The proposed finite element model employs a fine mesh of singular isoparametric pentahedral solid element with user specified number and size from one crack face to another and a number of such segments along a surface crack front. A compatible mesh of regular elements namely hexahedral solid element and pentahedral solid element is used to discretize the rest of the domain under consideration. Consistent with the use of the singular element, formulae to compute the Mode I, Mode II and Mode III stress intensity factors using displacements only of flagged nodes on flagged singular elements are implemented in a special purpose post processing sub program named SIF 1-2-3. In the present work the finite element models developed using ANSYS, a commercial FEA program, and the stress intensity factors determined using SIF 1-2-3 are validated using benchmarks. This finite element model is then used to calibrate a proposed test method to measure Mode I, Mode II and Mode III fracture toughness of engineering materials.

A Unified Capacitor Stress Emulation Method for High-Power Converter Applications

This paper proposes a unified capacitors stress emulation method, which has two unique test capabilities: 1) concurrent electrical stress emulation to AC capacitors and DC capacitors; 2) different electrical stress levels (including different ripple current, ripple voltage, and DC voltage) can be individually controlled for the testing samples. It preserves the advantages of a recently reported method with a minimum required power supply and is robust to testing sample degradation. This method is suitable for application-oriented stress emulation testing with different types of DC / AC capacitors and multiple electrical stresses in high power converter systems. The circuit architecture and testing ability of this method are presented. Moreover, analytical models are derived to size the key components to realize various testing requirements. Proof-of-concept experimental results are presented to verify the feasibility of the proposed test method.

NOVEL METHOD TO ASSESS THE DYNAMIC TENSILE PROPERTIES OF SPORTS MEDICINE SUTURE

Herein, a method was proposed for testing the dynamic tensile properties of a sports medicine suture and investigating the fatigue properties and elongation of the suture after a fatigue test. A test device was designed to test the dynamic tensile properties of sutures. The endurance limit of Nos. 1 and 4 sutures, which were used for laboratory comparisons, was [Formula: see text][Formula: see text]N and [Formula: see text][Formula: see text]N and the elongation rate was [Formula: see text], respectively. Furthermore, the Z-score, which is the offset divided by the standard deviation, was [Formula: see text]. The proposed test method is accurate and the repeatability is satisfied, making it suitable for determining the dynamic tensile properties of sutures. It is used as an industry standard to provide technical support for supervising sports medicine sutures.

Evaluation Method of Internal Resistance for Repurposing Using Middle and Large-Sized Batteries

The number of used batteries is expected to dramatically increase in the near future due to the expansion of the electric vehicle (EV) market globally. Accordingly, the Korean government has improved the supporting structures for the recycling system for used batteries, and in particular, in the field of repurposing, various studies are being conducted with a focus on effective evaluation methods that can secure the performance and safety of batteries after use. The repurposing of used batteries is mostly adapted in the field of energy storage systems for normally used EV batteries and a total inspection before repurposing is required due to battery characteristics that can vary depending on the operational environments of and accidents involving medium- and large-sized batteries for EVs and energy storage systems (ESSs) that have been occurring continuously for the past few years. Therefore, this paper investigates the operating mechanisms of the internal resistance test method and implements a test device for middle- and large-sized cells and packs. Based on the proposed test method, the internal resistance of nickel manganese cobalt (NMC)-type commercial large batteries is analyzed according to the SOC (state of charge), SOH (state of health), ambient temperature, and connection degradation of batteries. The distribution degrees of the alternative current (AC) internal resistance (IR) and direct current (DC) internal resistance (IR) measurement methods under state of health (SOH) test conditions are about 7% and 50%. It was found that the DC IR measurement method is more effective in diagnosing battery cell degradation. The distribution degree of DC IR measurements for the degraded connection condition shows an increase of less than 1% regardless of the state of charge (SOC), while the distribution degree of the AC IR measurements shows an increase of up to 319%, indicating that the AC IR method is more effective than the DC IR method in identifying connection degradation. It is confirmed that the proposed method is effective in internal resistance measurement and safety evaluations for the repurposing of batteries.

The Application of Tribological Tests to Study the Wear Behavior of Asphalt Cutter Teeth: An Experimental Investigation Using Baroid Tribometer

In this paper, the authors present the results obtained within a complex experimental program that focuses on determining the tribological characteristics of the active part (tungsten carbide tooth tip) of the cutter teeth of asphalt milling equipment. The experiments are performedunderdifferent testing conditions (in a dry environment and in water) to highlight the need to use water, when milling the asphalt coating, with the purpose to reduce the wear of milling teeth. The experimental results show that water contributes to the substantial reduction of wear rate (more than eight times) on the active area of the tooth. The proposed test method—testing with the Baroid tribometer—is intended to evaluate the tribological characteristics of the materials using parallelepiped-shaped samples. The authors of the work performed the tests on samples that represent the teeth of the milling cutter having the real shape (so not on samples). The obtained results demonstrate that the test method can be used with good results on real parts.

A New Analysis of Real-Time Fatality Rate in the Initial Stage of COVID-19.

Mortality is one of the most important epidemiological measures and a key indicator of the effectiveness of potential treatments or interventions. In this paper, a permutation test method of variance analysis is proposed to test the null hypothesis that the real-time fatality rates of multiple groups were equal during the epidemic period. In light of large-scale simulation studies, the proposed test method can accurately identify the differences between different groups and display satisfactory performance. We apply the proposed method to the real dataset of the COVID-19 epidemic in mainland China (excluding Hubei), Hubei Province (excluding Wuhan), and Wuhan from 31 January 2020 to 30 March 2020. By comparing the differences in the disease severity for differential cities, we show that the severity of the early disease of COVID-19 may be related to the effectiveness of interventions and the improvement in medical resources.