Test Method For Resistance Research Articles

An Alternative Junction-to-Case Thermal Resistance Test Method for High Power Press-Pack IGBTs

An Alternative Junction-to-Case Thermal Resistance Test Method for High Power Press-Pack IGBTs

Simulation and Experimental Study on Indentation Rolling Resistance of a Belt Conveyor

In this paper, in order to reduce the indentation rolling resistance of a belt conveyor and improve its operation efficiency, the indentation rolling resistance of a belt conveyor is studied. Firstly, the theoretical calculation of the indentation rolling resistance caused by the contact between a conveyor belt and an idler is studied. Additionally, the expression of the indentation rolling resistance including the multi-element Maxwell relaxation modulus is simplified and deduced using the assumption of small deformation, and the steps of iterative calculation of the indentation rolling resistance through setting the initial values are designed. Then, the multi-component Maxwell relaxation modulus function of the conveyor belt tested in the previous work of the authors is substituted into COMSOL 5.6 finite element software, and the stress distribution caused by the contact between the conveyor belt and the idler under different working conditions is analyzed. Also, a series of measures to reduce the indentation rolling resistance are found through the laws presented by the simulation results. Finally, the experimental study of the indentation rolling resistance is carried out using the indentation rolling resistance testing device from our research group. By comparing the experimental results for the indentation rolling resistance under different working conditions with the theoretical calculation results for the indentation rolling resistance, it was found that the relative error was less than 13%, which proved the feasibility of the indentation rolling resistance and relaxation modulus testing method, as well as the theoretical calculation method for indentation rolling resistance.

Evaluation of Flexible Pavement Friction Coefficients: A Case Study of East-West Highway Near Mahendranagar City, Nepal

Friction is a crucial factor in highway engineering, as it affects the traction between a vehicle's wheels and the road surface. This traction significantly influences the movement, speed, and efficiency of vehicles on highways. The coefficient of friction depends on various factors, such as pavement materials, traffic volume, road age, temperature, and weather conditions. The Skid Resistance Test Method is adopted for the study, which involves using a Portable Skid Resistance Tester to measure the British Pendulum Number (BPN) and then calculating the coefficient of friction by dividing the BPN by 10. An evaluation of a 5 km stretch of the East-West highway near Mahendranagar Bazaar revealed a longitudinal coefficient of friction of 0.354 and a lateral coefficient of friction of 0.184 under both dry and wet conditions. These findings were relevant for design speeds ranging from 60 to 80 km/h and considered an Annual Average Daily Traffic (AADT) of 10,321 Passenger Car Units (PCU) during the year 2023/2024. The assessment also indicated a variance of 0.19% and a poor International Roughness Index (IRI) value of 2.05. These aggregates had specific gravities ranging from 2.6 to 2.67 and were sized at 13.2 mm. The application rate for the aggregates ranged from 12 to 15 kg per square meter. It is important to note that a higher coefficient of friction leads to reduced vehicle efficiency. Thus, it is crucial to carefully consider the coefficient of friction values and detailed specifications to ensure traffic safety and road integrity.

Performance of an in-house multiplex PCR assay for HIV-1 drug resistance testing – A cheaper alternative

BackgroundCurrently, most HIV drug resistance PCR assays amplify the protease-reverse transcriptase (PR-RT) fragment separately from the integrase (IN) fragment. The aim of this study was to develop a multiplex PCR assay that simultaneously amplifies PR-RT and IN fragments for HIV-1 drug-resistance testing. MethodsThe in-house multiplex PCR assay was evaluated on extracted total nucleic acids obtained from the National Health Laboratory Service (NHLS) and Lancet laboratories. Sanger sequencing was performed on amplicons, and HIV-1 drug-resistance mutations (DRMs) were assessed using HIV Stanford drug resistance database. ResultsThis study tested 59 patient samples with known HIV-1 viral load and DRM results; 41 from Lancet and 18 from NHLS. In-house multiplex PCR assay detected one or both fragments in most samples but had higher sensitivity for detection of IN fragment (93.2 %) compared to PR-RT fragment (83.1 %). There was 100 % concordance between Lancet assay versus in-house assay sequence data for IN DRMs, but lower concordance with PR-RT (87.0 %). The in-house multiplex PCR assay’s precision and reproducibility analysis showed ≥99.9 % sequence similarity and yielded similar DRM results for both PR-RT and IN fragments. ConclusionsThe in-house multiplex PCR assay demonstrated satisfactory performance and higher sensitivity for IN fragment amplification. This could be a cost-effective method for HIV-1 drug resistance testing as both PR-RT and IN fragments are successfully amplified in one reaction in most samples.

Evaluating the accuracy of the MBT Lipid Xtract Kit for assessing colistin resistance in comparison to broth microdilution.

Colistin resistance testing methods such as broth microdilution (BMD) are time-consuming and labour intensive for clinical laboratories. MBT Lipid Xtract Kit on MALDI Biotyper Sirius System (Bruker, Billerica, MA, USA) utilizes lipidomic analysis to identify specific cell wall modifications associated with colistin resistance. We compared MBT to BMD (ComASP Colistin, Liofilchem) across 36 Gram-negative isolates (non-resistant MIC ≤2 µg ml-1, resistant MIC ≥4 µg ml-1). All samples were tested twice on MBT with discrepant results repeated before assessing categorical agreement between MBT and BMD. 44.4% (16/36) of isolates were colistin resistant via BMD. MBT Lipid Xtract had 80.6% agreement (29/36) with BMD, with 5/7 discrepancies corrected to match upon repeat testing. There was 100% agreement for Escherichia coli isolates (n=16). The whole-genome sequencing was completed on the two discrepant Klebsiella pneumoniae isolates, with variants within colistin resistance-associated loci identified (MIC 0.5 µg ml-1: arnC S30T, pmrB T246A, lapB N212T, lpxM S253G, crrB Q287K and MIC >16 µg ml-1: arnC S30T, pmrB R90insRN, pmrB T246A, pmrA E57G, lpxM S253G). Further evaluation, particularly for non-E. coli, of MBT is required prior to implementation in clinical laboratories.

Rapid inference of antibiotic resistance and susceptibility for Klebsiella pneumoniae by clinical shotgun metagenomic sequencing

ObjectivesThe study aimed to develop a genotypic antimicrobial resistance testing method for Klebsiella pneumoniae using metagenomic sequencing data. MethodsWe utilized Lasso regression on assembled genomes to identify genetic resistance determinants for six antibiotics (Gentamicin, Tobramycin, Imipenem, Meropenem, Ceftazidime, Trimethoprim/Sulfamethoxazole). The genetic features were weighted, grouped into clusters to establish classifier models. Origin species of detected antibiotic resistant gene (ARG) was determined by novel strategy integrating “possible species,” “gene copy number calculation” and “species-specific kmers.” The performance of the method was evaluated on retrospective case studies. ResultsOur study employed machine learning on 3928 K. pneumoniae isolates, yielding stable models with AUCs > 0.9 for various antibiotics. GenseqAMR, a read-based software, exhibited high accuracy (AUC 0.926–0.956) for short-read datasets. The integration of a species-specific kmer strategy significantly improved ARG-species attribution to an average accuracy of 96.67%. In a retrospective study of 191 K. pneumoniae-positive clinical specimens (0.68–93.39% genome coverage), GenseqAMR predicted 84.23% of AST results on average. It demonstrated 88.76–96.26% accuracy for resistance prediction, offering genotypic AST results with a shorter turnaround time (mean ± SD: 18.34 ± 0.87 hours) than traditional culture-based AST (60.15 ± 21.58 hours). Furthermore, a retrospective clinical case study involving 63 cases showed that GenseqAMR could lead to changes in clinical treatment for 24 (38.10%) cases, with 95.83% (23/24) of these changes deemed beneficial. ConclusionsIn conclusion, GenseqAMR is a promising tool for quick and accurate AMR prediction in Klebsiella pneumoniae, with the potential to improve patient outcomes through timely adjustments in antibiotic treatment.

Transient temperature measurement of silicon carbide Schottky barrier diode based on thermal reflection.

In this article, we present a transient temperature detection device for silicon carbide (SiC) Schottky barrier diodes (SBDs) based on thermal reflection theory. We constructed a thermal reflection temperature measurement device based on a 530-nm green laser. This device is more suitable for transient temperature measurement of SiC SBDs than previous thermal reflection equipment. The accuracy of temperature measurement by our device was confirmed by comparison with the results of infrared thermal imaging. The high temporal resolution characteristics of the thermal reflection technology allowed the detection of millisecond-level transient temperature changes in SiC SBDs. In addition, we investigated the complementarity of transient temperature change curves during heating and cooling processes, as well as the reasons for the differences between these curves. Finally, we used the structural function method combined with the Bayesian deconvolution algorithm to obtain the thermal resistance along the heat flow path of the device and validated the results using an established thermal resistance testing method.

Uji Kerentanan Aedes aegypti terhadap Malation, Permetrin, dan Bendiokarb di Kelurahan Tangkerang Timur Kecamatan Tenayan Raya, Pekanbaru

Insecticide resistant of Aedes aegypti populations is one of the main problems in controlling dengue hemorrhagic fever vectors because it will produce resistant offspring. This study aimed to determine the insecticide susceptibilty status of Ae. aegypti to 5% malathion, 0,75% permethrin, and 0,1% bendiocarb in Tangkerang Timur Village, Tenayan Raya District, Pekanbaru. This study is a descriptive observational study with a cross-sectional design. The resistance test method in this study was the World Health Organization (WHO) susceptibility test method with impregnated paper (5% malation, 0,75% permethrin, and 0,1% bendiocarb). The larval that were reared into adult mosquitoes were collected from 100 houses in Tangkerang Timur Village. Total adult mosquitoes aged 3-5 days tested in this study were 100 mosquitoes. The test mosquitoes were exposed to impregnated paper for 1 hour and the number of knock down mosquitoes was counted. Mosquito mortality was counted after 24 hours. The results of the susceptibility test in this study showed the mortality of Ae. aegypti to 5% malathion, 0,75% permethrin, and 0,1% bendiocarb were 100%, 85%, and 3.75%. The results of this study indicated that Ae. Aegypti has been resistant to 0,75% permethrin and 0,1% bendiocarb and susceptible to 5% malathion.

Development of test methods for fire-retardant coatings of steel engineering structures during operation

Introduction. Prediction of the durability of flame-retardant coatings of steel engineering structures and preservation of their performance during operation remain important research directions. There is a lack of normative documents in the field of fire protection, regulating the process of testing of flame-retardant coatings during operation, as well as determination of their durability (service life).Aim. To develop test methods for determining the resistance of flame-retardant coatings of steel engineering structures exposed to climatic factors, preservation of their fireproof and anti-corrosion properties during operation.Materials and methods. Test specimens included 600 x 600 x 5 mm plates made of 08kp and 08ps sheet steel according to State Standard 16523-97 and State Standard 9045-93 with a flame-retardant agent applied on the front side.Results. Methods for testing thin-layer intumescent and structural flame-retardant coatings during operation are proposed. The methodology of accelerated climatic testing of specimens coated with thin-layer intumescent flame-retardant coatings (flame-retardant paints) corresponds to State Standard 9.401-2018. These coatings are inherently high-solid paint materials. A new methodology, sequence, and modes of testing are developed for structural flame-retardant coatings. The subsequent assessment of fireproof properties of coatings and their preservation is carried out by the methods of fire protection efficiency according to State Standard R 53295-99 and the methods of thermal analysis. These methods imply comparison of the characteristics of the initial flame-retardant coating and those obtained after sample aging. The preservation of fireproof properties by thin-layer intumescent and structural coatings is additionally evaluated by the intumescence coefficient and the change in thermal conductivity, respectively.Conclusions. Test methods for flame-retardant coatings of steel engineering structures during operation are developed. Threshold levels of changes in their properties are established. After accelerated climatic tests, fire protection efficiency should not decrease by no more than 20 %. For structural fire protection, an increase in thermal conductivity by no more than 5 % is permitted. For thin-layer coatings, the arithmetic mean value of the intumescence coefficient should not decrease by no more than 30 % of the initial value.Implications. The developed methods were used in the preparation of a draft national standard of the Russian Federation “Steel engineering structures with fireproof coatings. Test methods for anticorrosion properties and resistance to climatic factors during operation” to ensure regulatory fire safety requirements for these structures.

A One Health perspective on the use of genotypic methods for antimicrobial resistance prediction.

Antimicrobial resistance is a global One Health concern with critical implications for the health of humans, animals, and the environment. Phenotypic methods of bacterial culture and antimicrobial susceptibility testing remain the gold standards for the detection of antimicrobial resistance and appropriate patient care; however, genotypic-based methods, such as PCR, whole genome sequencing, and metagenomic sequencing, for detection of genes conferring antimicrobial resistance are increasingly available without inclusion of appropriate standards for quality or interpretation. Misleading test results may lead to inappropriate antimicrobial treatment and, in turn, poor patient outcomes and the potential for increased incidence of antimicrobial resistance. This article explores the current landscape of clinical and methodological aspects of antimicrobial susceptibility testing and genotypic antimicrobial resistance test methods. Additionally, it describes the limitations associated with employing genotypic-based test methods in the management of veterinary patients from a One Health perspective. The companion Currents in One Health by Maddock et al, AJVR, March 2024, addresses current and future needs for veterinary antimicrobial resistance research.

Belgian pre-normative research project SuChar-BiLan on surface monitoring of bicycle lanes

Recently the need for more and better cycling infrastructure is soaring. The diversity of the means of transport other than ordinary bikes is increasing rapidly. Consequently, the users’ expectations change. In their endeavor to deliver, road authorities managing cycle paths will benefit from new condition assessment and efficient asset management. In the two-year project “Surface Characteristics of Bicycle Lanes” (SuChar-BiLan), started on 1 November 2022, the Belgian Road Research Centre (BRRC) collects knowledge, information and practical experiences about measurement techniques and management allowing the assessment of the condition of bicycle infrastructure: evenness, skid resistance, texture and rolling resistance. The aim of the project is to help with developing European standards and with expanding the use of such techniques – to a better quality of the cycling experience. This contribution presents results of a literature review, mentions the development of surveys addressed to different stakeholders (users, road authorities, technology providers), describes how technology and service providers, and research organisations will be invited to demonstrate their solutions on bicycle lanes in Belgium, hints on future design by BRRC of laboratory test methods for skid and rolling resistance, and explains the importance of the expected outcomes and of the aimed development of European standards.

Validation of an HIV whole genome sequencing method for HIV drug resistance testing in an Australian clinical microbiology laboratory.

Detection of HIV drug resistance (HIVDR) is vital to successful anti-retroviral therapy (ART). HIVDR testing to determine drug-resistance mutations is routinely performed in Australia to guide ART choice in newly diagnosed people living with HIV or in cases of treatment failure. In 2022, our clinical microbiology laboratory sought to validate a next-generation sequencing (NGS)-based HIVDR assay to replace the previous Sanger-sequencing (SS)-based ViroSeq. NGS solutions for HIVDR offer higher throughput, lower costs and higher sensitivity for variant detection. We sought to validate the previously described low-cost probe-based NGS method (veSEQ-HIV) for whole-genome recovery and HIVDR-testing in a diagnostic setting. veSEQ-HIV displayed 100% and 98% accuracy in major and minor mutation detection, respectively, and 100% accuracy of subtyping (provided > 1000 mapped reads were obtained). Pairwise comparison exhibited low inter-and intrarun variability across the whole-genome (Jaccard index [J] = 0.993; J = 0.972) and the Pol gene (J = 0.999; J = 0.999), respectively. veSEQ-HIV met all our pre-set criteria based on WHO recommendations and successfully replaced ViroSeq in our laboratory. Scaling-down veSEQ-HIV to a limited batch size and sequencing on Illumina iSeq. 100, allowed easy implementation of the assay into the workflow of a small sequencing laboratory with minimal staff and equipment and the ability to meet clinically relevant test turn-around times. As HIVDR-testing moves from SS- to NGS-based methods and new ART drugs come to market (particularly those with targets outside the Pol region), whole-genome recovery using veSEQ-HIV provides a robust, cost-effective and "future-proof" NGS method for HIVDR-testing.

Comparative Analysis of the Metabolic Profiles of Strains of Tribolium castaneum (Herbst) Adults with Different Levels of Phosphine Resistance Based on Direct Immersion Solid-Phase Microextraction and Gas Chromatography-Mass Spectrometry

The management of phosphine (PH3) resistance in stored grain pests is an essential component of implementing timely and effective pest control strategies. The prevailing standard method for PH3 resistance testing involves the exposure of adult insects to a specific concentration over a fixed period. Although it is widely adopted, this method necessitates an extensive period for assay preparation and diagnosis. To address this issue, this study employed Direct Immersion Solid-Phase Microextraction (DI-SPME) coupled with Gas Chromatography-Mass Spectrometry (GC-MS) to compare and analyze the metabolic profiles of PH3-sensitive (TC-S), PH3 weak-resistant (TC-W), and PH3 strong-resistant (TC-SR) Tribolium castaneum (Herbst) adults. A total of 36 metabolites were identified from 3 different PH3-resistant strains of T. castaneum; 29 metabolites were found to present significant differences (p < 0.05) across these groups, with hydrocarbon and aromatic compounds being particularly prevalent. Seven metabolites showed no significant variations among the strains, consisting of four hydrocarbon compounds, two iodo-hydrocarbon compounds, and one alcohol compound. Further multivariate statistical analysis revealed a total of three, two, and nine differentially regulated metabolites between the TC-S versus TC-W, TC-S versus TC-SR, and TC-W versus TC-SR groups, respectively. Primarily, these metabolites comprised hydrocarbons and iodo-hydrocarbons, with the majority being associated with insect cuticle metabolism. This study demonstrates that DI-SPME technology is an effective method for studying differentially expressed metabolites in T. castaneum with different levels of PH3 resistance. This approach may help to provide a better understanding of the development of insect PH3 resistance and act as a valuable reference for the establishment of rapid diagnostic techniques for insect PH3 resistance.

Analysis of test methods for frost resistance of concrete

Introduction. Frost resistance of concrete is one of the most challenging problems in concrete studies. Particularly important is the issue of methods of testing concrete for frost resistance. The existing standard methods require more detailed regulation of the test process in order to improve the reliability of the results.Aim. To analyze the regulatory procedures of testing concrete for frost resistance with a view to make suggestions for improving standards.Materials and methods. The analysis involved Russian and foreign standards and publications on methods of testing concrete for frost resistance.Results. The authors analyzed the methods of testing concrete for frost resistance, included in Russian and some foreign standards. The quality of determining the frost resistance of concrete can be improved by controlling the temperature while freezing and thawing, in particular, by assessing the temperature in the concrete of the test samples. Controlling the air temperature in the freezer should be recognized as insufficient. The criteria for the state of concrete samples during and after cyclic freezing and thawing should be further verified. It is necessary to continue full-scale testing of concrete under severe climatic conditions, taking into account the real conditions of freezing and thawing of concrete in structures, and comparing the results of laboratory and full-scale tests, including satellite samples.Conclusion. The analysis revealed the necessity to continue the research on clarifying the test methodology and criteria for assessing the state of concrete samples after freezing and thawing cycles. It is advisable to recreate devices for determining the dynamic modulus of elasticity of samples in freeze-thaw testing, to resume long-term full-scale tests of concrete under severe climatic conditions, and to develop a manual for creating frost-resistant concrete, taking into account the current level of concrete technology. Elimination of the existing drawbacks of the methodology will improve the reliability of test results.

Development of cementitious capillary crystalline waterproofing agents and durability study of concrete in the presence of chloride with sulfate in aqueous environment

In this study, the chemical composition of cementitious capillary crystalline waterproofing agents (CCCW) was developed by using the water penetration resistance test method. Response to impermeability by first permeability and self-healing properties by second permeability, five effective single components were obtained: Ethylene diamine tetraacetic acid (EDTA), l-aspartic acid, sodium sulfate, sodium silicate and nano-silica. With the help of chloride ion diffusion coefficient measurement and sulfate attack resistance test, it investigates the effect of five components on the durability of the concrete matrix. According to the differential thermogravimetric analysis (TG), X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis methods, the waterproof mechanism of each component acting in the matrix was proposed. Finally, also combined with the results of macroscopic performance and microscopic analysis designed orthogonal experiments, the results show that the optimal blending of five waterproofing agent components up to 300% increase in substrate impermeability. The optimal amount of each component is 0.5% EDTA, 2% l-aspartic acid, 3% sodium sulfate, 2% sodium silicate, and 2% nano-silica.

Improvement of the Standard Test Method for Effective Series Resistance (ESR) and Capacitance of Ultra High-Q Capacitors at High Frequencies

Improvement of the Standard Test Method for Effective Series Resistance (ESR) and Capacitance of Ultra High-Q Capacitors at High Frequencies

Effect of Nb Addition on Corrosion Resistance of U-6Zr Alloys

The fuel element plates in a research reactor can be exposed to an acidic, neutral, or alkaline environment based on its surroundings. This study aimed to investigate the effect of Nb addition on the corrosion properties of U-6Zr alloys in various environments. U-6Zr-xNb alloys (U-6Zr-2Nb, U-6Zr-5Nb, and U-6Zr-8Nb) with different Nb compositions of 2, 5, and 8 wt%, respectively, were prepared and cut into smaller pieces. The pieces were then mounted with chemical resin equipped with copper wire cables and metallography prepared by grinding using sandpaper with grit sizes ranging from 320 to 1200. The electrochemical corrosion tests used in this work were the polarization test and Tafel extrapolation method. In the first step of corrosion testing, the corrosion potential and polarization resistance were measured using standard settings from a voltage range of −0.02 to 0.02 V with a scanning rate of 0.05 mV/s. In the next step, a destructive method, called the Tafel extrapolation method, was used. Corrosion tests were carried out on U-6Zr-xNb alloys (x = 2, 5, 8) under various environmental conditions using electrochemical methods. Polarization resistance test and Tafel extrapolation methods revealed that the U-6Zr-2Nb alloy exhibited good corrosion resistance in an acidic HNO3 environment with a pH of 1.18. The best corrosion resistance of the U-6Zr-5Nb alloy was observed in demineralized water. Meanwhile, the U-6Zr-8Nb alloy showed the best corrosion resistance in an alkaline NaOH environment with a pH of 11.02. It can be concluded that the higher Nb composition added to U-6Zr alloys, the better their corrosion resistance in higher pH environments.

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.

Impact Resistance of CVD Multi-Coatings with Designed Layers

Coated cutting tools are widely used in the manufacturing industry due to their excellent properties of high heat resistance, high hardness, and low friction. However, the milling process is a dynamic process, so the coatings of milling tools suffer severe cyclic impact loads. Impact resistance is important for the life of milling tools. Multi-coatings with different layer thickness may influence their impact resistance, but few studies focus on this topic. In this study, CVD coating with a structure of TiN layer, Al2O3 layer, and TiCN layer was selected as the research objective. Four different CVD coatings with different layer thicknesses were designed and prepared. The impact resistance test method was proposed to simulate the impact due to cut-in during down the milling process. We obtained the load by setting an impact depth of 25/30/35 µm, recording the impact force during the impact process, and calculating the contact stress; it was found that, at the impact depth of 25/30/35 µm, the download loads were around 9/11/13 N, while the contact stresses were all around 1 GPa. The failure morphology of the coating surface was investigated after the impact process. By comparing the contact stress and the surface morphology of the designed coatings, the impact resistance of four kinds of designed CVD coatings were evaluated. Experiments have shown that an increase in coating thickness and total coating thickness reduces impact resistance by about 10%. The impact resistance of coating samples without a TiN surface layer also decreased by about 10%. When the surface layer of TiN was thinner than 1 µm, the surface layer of TiN was prone to chipping and peeling off. Decreasing the thickness of the middle layer of Al2O3 and increasing the thickness of the inner layer of TiCN obviously lowered the impact resistance.

Enhanced properties and homogeneity of Al-Zn-Mg-Cu alloy thick plate by non-isothermal aging

The desirable properties and homogeneity of Al-Zn-Mg-Cu alloy thick plate are urgent to acquire in the industrial field. An efficient method for determining the optimal non-isothermal aging (NIA) of Al-Zn-Mg-Cu alloy plates was proposed by employing an in-situ resistance testing method, and the microstructure, properties, and inhomogeneity of plates with 150 mm and 120 mm in thickness during NIA process were investigated. The in-situ resistance analysis suggested that the NIA process was divided into four stages, which were dominated by nucleation and atomic diffusion. The 190 °C (Peak temperature) and 30 °C/h (Temperature change rate) were the optimum parameters of the 150 mm plate, and the obtained ultimate tensile strength, elongation, and electrical conductivity were 569 MPa, 11%, and 40% IACS, respectively. The η' phases were the primary precipitates for strengthening after NIA. The excellent comprehensive properties of the non-isothermal aged alloy benefited from the secondary precipitation of fine precipitates in the cooling stage and the discontinuous distribution of grain boundary precipitates. The continuous temperature phase transition curves were conducted to formulate the optimal regime of 120 mm plate, which was optimized as 195 °C and 34 °C/h. The NIA treatment regulated the relative phase transformation variable of different positions of the thick plate to 42–46%, which verified the optimization of aging homogeneity along the thickness direction. Under the precondition of reducing the aging time by more than 76%, both plates after NIA maintained satisfactory strength and ductility and were characterized by an impressive corrosion resistance far beyond the two-step aging state.