Mechanism and Method of Testing Fracture Toughness and Impact Absorbed Energy of Ductile Metals by Spherical Indentation Tests

To address the problem of conventional approaches for mechanical property determination requiring destructive sampling, which may be unsuitable for in-service structures, the authors proposed a method for determining the quasi-static fracture toughness and impact absorbed energy of ductile metals from spherical indentation tests (SITs). The stress status and damage mechanism of SIT, mode I fracture, Charpy impact tests, and related tests were frst investigated through fnite element (FE) calculations and scanning electron microscopy (SEM) observations, respectively. It was found that the damage mechanism of SITs is diferent from that of mode I fractures, while mode I fractures and Charpy impact tests share the same damage mechanism. Considering the diference between SIT and mode I fractures, uniaxial tension and pure shear were introduced to correlate SIT with mode I fractures. Based on this, the widely used critical indentation energy (CIE) model for fracture toughness determination using SITs was modifed. The quasi-static fracture toughness determined from the modifed CIE model was used to evaluate the impact absorbed energy using the dynamic fracture toughness and energy for crack initiation. The efectiveness of the newly proposed method was verifed through experiments on four types of steels: Q345R, SA508-3, 18MnMoNbR, and S30408.

Influence of unsupported sleepers on the dynamic stability of ballasted bed based on wheelset impact tests

The unsupported sleeper can change the load characteristics of ballast particles and thus affect the dynamic stability of a ballasted bed.In this work,a laboratory test was constructed on a ballasted track containing unsupported sleepers.The ballasted track was excited by a wheelset,and the influence of unsupported sleepers on the dynamic stability of a ballasted bed was studied.The results show that the main frequency of the sleeper vibration appeared at 670 Hz,and the first-order rigid vibration mode at the frequency of 101 Hz had a significant effect on the condition without the unsupported sleeper.When the sleepers were continuously unsupported,the vibration damping effect of ballasted bed within the frequency range of 0–450 Hz was better than that at higher frequencies.Within the frequency range of 70–250 Hz,the vibration damping effect of the ballasted bed with unsupported sleepers was better than that without the unsupported sleeper.Owing to the excitation from the wheelset impact,the lateral resistance of the ballasted bed with unsupported sleepers whose hanging heights were 30,60,and 90 mm increased by 37.43%,12.25%,and 18.23%,respectively,while the lateral resistance of the ballasted bed without the unsupported sleeper remained basically unchanged.The unsupported sleeper could increase the difference in the quality of the ballasted bed between two adjacent sleepers.In addition,test results show that the hanging height of the unsupported sleeper had little effect on the lateral resistance of a ballasted bed without external excitation,but had an obvious effect on the rate of change of the lateral resistance of a ballasted bed and the acceleration amplitude of the sleeper vibration under the wheelset impact.

Instrumented oscillographic study on impact toughness of an axle steel DZ2 with different tempering temperatures

Compared with the conventional Charpy impact test method,the oscillographic impact test can help in the behavioral analysis of materials during the fracture process.In this study,the trade-off relationship between the strength and toughness of a DZ2 axle steel at various tempering temperatures and the cause of the improvement in impact toughness was evaluated.The tempering process dramatically influenced carbide precipitation behavior,which resulted in different aspect ratios of carbides.Impact toughness improved along with the rise in tempering temperature mainly due to the increase in energy required in impact crack propagation.The characteristics of the impact crack propagation process were studied through a comprehensive analysis of stress distribution,oscilloscopic impact statistics,fracture morphology,and carbide morphology.The poor impact toughness of low-tempering-temperature specimens was attributed to the increased number of stress concentration points caused by carbide morphology in the small plastic zone during the propagation process,which resulted in a mixed distribution of brittle and ductile fractures on the fracture surface.

Impact pressure of waves generated by landslides on bank slopes

Impulse waves that are generated by landslides in narrow reservoir areas threaten the stability of buildings and bank slopes.To discuss the action process and evolution law of the wave pressure on bank slopes,a three-dimensional physical model test that considers impulse waves generated by landslides was performed,and factors including landslide width,thickness,slope angles of the sliding surface,and bank slope angle were considered.Based on wave forms on the bank slopes,wave pressure curve characteristics,and peak value,the action process of wave pressure could be divided into the following stages:maximum pulsating pressure stage,wave impact stage(when waves break),and stationary pulsation stage.It was found that wave breaking is dependent on the value of the surf similarity parameterξ.The distribution pattern of impact pressure decays linearly on both sides of the maximum impact pressure point,and the attenuation degree decreases when it attains 40%of the maximum value.Thus,it is proposed that the prediction formula for the maximum effective impact pressure of the bank slope be related to the reciprocal of wave steepness,relative water depth,and slope rate.The prediction formula provides strong theoretical support for early safety warning and for predicting the bank slope under impulse waves generated by landslides.

Enhanced air-coupled impact echo technique by phase analysis of signals from multiple sensors

This paper presents an air-coupled impact echo(IE)technique that relies on the phase spectrum of the collected data to find the frequencies corresponding to the reflections from delaminations.The proposed technique takes advantage of the fact that the IE compression wave is not a propagating wave,but it is the 1st order symmetrical(S1)mode Lamb wave at zero group velocity(S1-ZGV).Therefore,it searches the phase spectra of the data collected by multiple sensors to locate the frequency corresponding to the lowest phase difference.As a result,the technique reduces the effect of propagating waves,including the direct acoustic wave and ambient noise.It is named the Constant Phase IE(CPIE).The performance of the CPIE is experimentally compared with the regular amplitude spectrum-based IE technique and two other multisensor IE techniques.The CPIE shows a performance advantage,especially in a noisy environment.

Entangled relationship:Chinese parents’involvement in young learners’English tests

Young learners’English(YLE)tests have become increasingly prevalent among and important to Chinese English learners and their parents.In China,parents are actively involved in their children’s education and test-taking decisions,and their participation has given rise to a series of social impacts.Although parent involvement has received increasing public and academic attention in newspaper and scholarly articles,there exists no thorough analysis of current research on parents’roles in young learners’test-taking.To address this gap,we systemically analyzed Chinese newspaper articles and academic articles between 2011 and 2021 to elicit Chinese parents’roles in YLE test-taking.Our thematic analysis of the literature identifies the ways in which parents influence their children’s test-taking experiences,and how the tests affect this influence.Specifically,our results elicit 1)parents’engagement in YLE testing;2)parents’understanding of the intended uses of YLE tests;3)parents’perception and consequences of their involvement in YLE testing;and 4)parents’backgrounds.This analysis reveals the popularity of YLE tests among young learners and their parents in China and public concern over test-related issues.It also broadens our understanding of YLE testing impact and suggests future potential research directions.

Dynamic fracture toughness of TA15ELI alloy studied by instrumented impact test

The dynamic fracture toughness of TA15ELI alloy with two types of microstructures was studied by instrumented impact test.Charpy specimens with both the 0.2 mm U-notch and the a/W = 0.2 pre-crack were adopted to compare notch sensitivity in the two microstructures.The result shows that the specimen with Widmanst？tten microstructure exhibits a better dynamic fracture toughness and lower notch sensitivity than that with lath-like microstructure.Fracture surfaces in the case of the two microstructures are analyzed to have a ductile and brittle mixed feature under dynamic loading.The fracture surface of lath-like microstructure is composed of dimples and tear ridges,while that of Widmanst？tten microstructure is covered with rough block-like facets and dimples and tear ridges.The α phase boundaries and α/β interfaces act as locations for void nucleation and crack arrest and deviation.The decrease in width of α phase lamellae leads to the increase in the amount of boundaries and interfaces,which causes the increase in the consumption of impact energy and results in the improvement in dynamic fracture toughness.

The Application of Impact Echo Scanning on Nondestructive Test of Pavement

A new nondestructive test method-Impact Echo Scanning was introduced. Application of this method on pavement structure test was discussed. A method to increase the measurement accuracy of the test on multi-layers was proposed, and was verified by field test. The test results show that the basic structural information can obtained rapidly and accurately by 3-D scanning of the impact echo system.

Assessment of rapid impact compaction in ground improvement from in-situ testing

Ground improvement has been used on many construction sites to densify granular materials,in other word,to improve soil properties and reduce potential settlement.This work presents a case study of ground improvement using rapid impact compaction(RIC).The research site comprises the construction of workshop and depots as part of railway development project at Batu Gajah-Ipoh,Malaysia.In-situ testing results show that the subsurface soil comprises mainly of sand and silty sand through the investigated depth extended to 10m.Groundwater is approximately 0.5m below the ground surface.Evaluation of improvement was based on the results of pre-and post-improvement cone penetration test(CPT).Interpretation software has been used to infer soil properties.Load test was conducted to estimate soil settlement.It is found that the technique succeeds in improving soil properties namely the relative density increases from 45% to 70%,the friction angle of soil is increased by an average of 3o,and the soil settlement is reduced by 50%.The technique succeeds in improving soil properties to approximately 5.0m in depth depending on soil uniformity with depth.

State of the art of impact testers for spot welds

Impact testing is a primary method to evaluate the impact property of resistance spot welding,which is an important quality index in automotive industry.For testing impact properties of spot welds,many customized testers have been developed.This paper summarized some of the impact testers reported in open literatures and the emphasis was placed on the equipment structures,functions,technical parameters,advantages and disadvantage,etc.Some key issues about the development of the testers such as kinematic energy input mode,fixture design,combined load testing,sensor and data acquisition were discussed.Finally,the problems and prospects in the research and development of impact testers for spot welds were pointed out.

Optimal design and dynamic impact tests of removable bollards

Anti-ram bollard systems, which are installed around buildings and infrastructure, can prevent unauthorized vehicles from entering, maintain distance from vehicle-borne improvised explosive devices （VBIED） and reduce the corresponding damage. Compared with a fixed bollard system, a removable bollard system provides more flexibility as it can be removed when needed. This paper first proposes a new type of K4-rated removable anti-ram bollard system. To simulate the collision of a vehicle hitting the bollard system, a finite element model was then built and verified through comparison of numerical simulation results and existing experimental results. Based on the orthogonal design method, the factors influencing the safety and economy of this proposed system were examined and sorted according to their importance. An optimal design scheme was then produced. Finally, to validate the effectiveness of the proposed design scheme, four dynamic impact tests, including two front impact tests and two side impact tests, have been conducted according to BSI Specifications. The residual rotation angles of the specimen are smaller than 30~ and satisfy the requirements of the BSI Specification.

Performance of identical rockbolts tested on four dynamic testing rigs employing the direct impact method

Impact drop tests are routinely used to examine the dynamic performance of rockbolts.Numerous impact tests have been carried out in the past decades on independently designed,constructed and operated testing rigs.Each laboratory has developed testing procedures;thus,the results are often reported in different ways by various laboratories.The inconsistency in testing procedures and reporting formats presents a challenge when comparing results from different laboratories.A series of impact tests of identical rockbolts was carried out using the direct impact method(i.e.the mass free-fall method)on the rigs in four laboratories in different countries.The purpose of these tests was to investigate the level of consistency in the results from the four rigs.Each rig demonstrated a high level of repeatability,but differences existed between the various rigs.The differences would suggest that there is noticeable equipment-dependent bias when test results obtained from different laboratories are compared.It was also observed that the energy dissipated for the plastic displacement of the bolt was smaller than the impact energy in the tests.The average impact load(AIL)and the ultimate plastic displacement(D)of the bolt describe the ultimate dynamic performance of the bolt.In the case where the bolt does not rupture,the specific plastic energy(SPE)is an appropriate parameter in describing the impact performance of the bolt.Two other relevant parameters are the first peak load(FPL)and the initial stiffness(K)of the bolt sample.The information from this test series will guide the formulation of standardised testing procedures for dynamic impact tests of rockbolts.

Tests to evaluate the ecological impact of treated ballast water on three Chinese marine species

Ballast water has been a topic of concern for some time because of its potential to introduce invasive species to new habitats. To comply with the International Convention for the Control and Management of Ships' Ballast Water and Sediments, members of the International Maritime Organization(IMO) must equip their ships with on-board treatment systems to eliminate organism release with ballast water. There are many challenges associated with the implementation of this IMO guideline, one of which is the selection of species for testing the ecological impacts of the treated ballast water. In the United States, ballast water toxicity test methods have been defined by the United States Environmental Protection Agency. However, the test methods had not been finalized in China until the toxicity test methods for ballast water were established in 2008. The Chinese methods have been based on species from three trophic levels: Skeletonema costatum, Neomysis awatschensis, and Ctenogobius gymnauchen. All three species live in broad estuarine and open sea areas of China; they are sensitive to reference toxicants and acclimatize easily to different conditions. In this paper, the biological characteristics, test processes and statistical analysis methods are presented for the three species. Results indicate that the methods for evaluating these three organisms can be included in the ecological toxicity tests for treated ballast water in China.

Dynamic Fracture of Ti-5553 Alloy in Taylor Impact Test

The dynamic fracture behavior of a new near-beta Ti-5Al-5Mo-5V-3Cr-1Fe（Ti-5553）alloy under a high strain rate loading was investigated systemically using the Taylor impact test,over the impact velocity ranging from156 ms-1 to 256 ms-1.An optical microscope（OM）and a scanning electron microscope（SEM）were used to characterize the microstructure evolution.The experimental results have demonstrated that the velocity from deformation to fracture is 256 ms-1 for the alloy with anα＋βduplex microstructure including more primaryαphase,while the velocity is 234 ms-1 for the alloy with a duplex microstructure including less primaryα phase.From the impact fracture morphologies,smooth and smeared surfaces and ductile dimple areas can be observed.The failure mode of the titanium alloy with both microstructures is adiabatic shear banding.According to the fracture analysis,the ductile fracture area with the dimple area in the alloy with much more primaryαphase were more than that with less primaryαphase.Compared to the duplex microstructure with less primaryα phase,Ti-5553 alloy with more primaryαphase exhibited a better capability to resist an adiabatic shear damage.

Determination of failure degree of 1.2 kV SiC MOSFETs after short-circuit test using an improved test setup

Analysis of the short-circuit characteristics of SiC metal-oxide-semiconductor field-effect transistors(MOSFETs)is very important for their practical application.This paper studies the SiC MOSFET short-circuit characteristics with an improved test setup under different conditions.A high-current Si insulated gate bipolar transistor is used as a circuit breaker in the test circuit rather than the usual short-circuit test conducted without a circuit breaker.The test platform with a circuit breaker does not influence the calculation results regarding the shortcircuitwithstand time and energy,but the SiCMOSFETwill switch off after failure in a very short time.In addition,the degree of failure will be limited and confined to a small area,such that the damage to the chip will be clearly observable,which is significant for short-circuit failure analysis.

Deformation mechanism at impact test of Al-11% Si alloy processed by equal-channel angular pressing with rotary die

Al-11%Si(mass fraction)alloy was transformed into a ductile material by equal-channel angular pressing(ECAP)with a rotary die.Two mechanisms at impact test,slip deformation by dislocation motion and grain boundary sliding,were discussed.The ultrafine grains with modified grain boundaries and the high content of fine particles(<1μm)were necessary for attaining high absorbed energy.The results contradict the condition of slip deformation by dislocation motion and coincide with that of grain boundary sliding.Many fine zigzag lines like a mosaic were observed on the side surface of the tested specimens.These observed lines may show grain boundaries appeared by the sliding of grains.

Comparative analysis by simulating and testing pole impact for hot stamping front crossbeam of automobile

Hot stamping 22MnB5 steel plate with ultra-high strength has been widely used for body structural members in consideration of automobile safety and lightweight.This paper presents a verification program of simulating and testing pole impact in order to verify if the front crossbeam reinforcement assembly can meet the design requirements,reduce the overall vehicle simulation and test cost and shorten the operation period.In the same condition,the simulation proved conforming to the design requirements;however,the bumper cracked at the impacting point in the course of pole impact test.The analysis of the crack by optical microscope,Vickers and scanning electron microscope indicates that mixture of ferrite,bainite and martensite was produced in the weld heat-affected zone of the 340/590DP tow hook holder and the 22MnB5 front crossbeam;therefore,their hardness and mechanical property were reduced obviously,so that they fractured when impacted.No welding process with continuous weld but spot welding or other bonding method may be employed for the reason that the capacity of the 22MnB5 steel plate in the weld heat-affected zone was reduced obviously.

Dimensional analysis of the impact toughness test for synthetic diamond grits

The method,in which a few carats of diamond grits are placed inside a capsule together with a steel ball,shaken for a number of times,and the unbroken ratio of the grits is then used to evaluate the quality of the diamond,has been well established for many years.However,the unbroken percentage,in an equivalent view,represents the impact toughness of the grits and cannot reflect the value of the crushing energy.Most of the previous empirical formulas obtained from experiments by scholars cannot be applied to practical tests.In this paper,a dimensional analysis was applied to investigate the impact toughness experiment,and the dimensionless relationship has been built among those variables such as the toughness index,the impact time,the impact frequency and the crushing energy per unit area.According to the results of a large number of experiments with synthetic diamond grits of mesh size 45/50,the percentage of the broken grits H is proportional to the impact time T^（1.14） when the impact frequency is 2400 r/min,and the impact frequency f^（2.576） when the number of impacts is 2000.

Impacts of Recent Infection Testing Integration into HIV Surveillance in Ekiti State, South West Nigeria: A Retrospective Cross Sectional Study

Background: Timely detection of recent HIV infections is critical in achieving the HIV epidemic. The aim of this study was to evaluate the effects of integrating the Recent Infection Testing Algorithm in HIV surveillance in Ekiti State, South West Nigeria. Method: Data from the Nigeria Medical Records System (NMRS)/National Data Repository (NDR) and Index Testing (IT) Services data capturing tools were abstracted for a retrospective cross-sectional study of 719 newly diagnosed HIV-positive cases who were screened for HIV incident infection using Asante rapid recency test kits between August 2020 and June 2022 at 5 selected recency testing health facilities. The venous blood (10 ml) of all the rapid Asante tested recent patients were collected into an EDTA tube and processed for viral load testing. The plasma level of HIV-1 RNA was quantified using the CAP/CTM and cobas 4800 platform at Obafemi Awolowo University Teaching Hospital PCR Laboratory Ife. Chi-square was used to characterize the recency status of the patients. A measure of the association was done using Chi-square, while the p-value of 0.05 was considered statistically significant. Results: The median age of the participants was 39 years. The result from the study showed that of the total number of 719 new cases of diagnosed HIV-positive, 626 of them were screened for rapid Test for Recency infection (RTRI) (87%). Overall, we found that 1.8% (11/626) of clients were classified as recent. The investigation also showed that from the index cases of the 11 confirmed recent infections, a total number of 125 additional positive cases were found. Conclusion: This result indicated a rise in the number of cases discovered in the State. Therefore, incorporating recency testing within regular HIV testing programs becomes essential in order to prioritize clients for index testing and provide useful information on transmission clusters.

The Impact of Language Testing on Language Teaching

Language testing is of great value in language teaching. This paper is intended to deal with its washback effects in the following aspects. On one hand, it explores the impacts of language testing on objects invovled. On the other hand, it directs at the positive and negative washback effects of testing on language teaching.