Value of Charpy impact test results with sub-and half-size specimens extracted from overage steel bridge members

For the maintenance of steel bridges,the mechanical properties of steel used in the bridges must be elucidated.When enough dimensions of specimens cannot be extracted from the actual members,miniaturized specimens are used for evaluation.In the case of the Charpy impact test,sub-and half-size specimens are specified instead of full-size specimens of which the thickness is 10 mm.The value of absorbed energy and energy transient temperature obtained by Charpy impact tests with sub-size and half-size specimens were investigated from the viewpoint of maintenance of bridges in this study.The absorbed energy was not in proportion to the thickness of specimens of steel used in the actual overage bridges.The tendency of energy transient temperature obtained by thin specimens of the overage steel differed from that of the present steel.A method for evaluating the performance against brittle fracture occurrence based on the WES3003 criterion was examined.The results show the significance of evaluation based on the energy transient temperature for reasonable maintenance of bridges.

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.

Dynamic fracture of Ti-6Al-4V alloy in Taylor impact test

The dynamic fracture behaviors of Ti-6Al-4V alloy at high strain rate loading were investigated systemically through Taylor impact test, over the range of impact velocities from 145 m/s to 306 m/s. The critical impact velocity of fracture ranges from 217 m/s to 236 m/s. Smooth surfaces and ductile dimple areas were observed on the fracture surfaces. As the impact velocity reached 260 m/s, the serious melting regions were also observed on the fracture surfaces. Self-organization of cracks emerges when the impact velocity reaches 260 m/s, while some special cracks whose ＂tips＂ are not sharp but arc and smooth, and without any evidence of deformation or adiabatic shear band were also observed on the impact end surfaces. Examination of the sections of these special cracks reveals that the cracks expand along the two maximum shear stress directions respectively, and finally intersect as a tridimensional ＂stagger ridge＂ structure.

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.

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.

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.

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.

Numerical modeling and analysis of the mechanism of a novel shock wave regulator for impact test

Based on the concept of hydraulic dissipation of kinetic energy, a novel shock wave regulator, which is composed of a damper and an extemally triggered valve, is presented with thorough analyses on its working mechanism. By establishing motion equations of each component of the regulator and simulating the dynamic behavior of the whole system, the shock wave regulator is demonstrated numerically to be able to change the width and amplitude of shock pulses. Prompt and easy adjustment can be achieved by changing the equivalent flow area of damping orifices and consequently the closing velocity of the flow area of a valve, which makes it applicable to different impact testing.

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.

Quantitative analysis of the protective performance of bicycle helmet with multidirection impact protection system in oblique impact tests

Purpose:The current study aimed to assess the protective performance of helmets equipped with multidirectional impact protection system(MIPS)under various oblique impact loads.Methods:Initially,a finite element model of a bicycle helmet with MIPS was developed based on thescanned geometric parameters of an actual bicycle helmet.Subsequently,the validity of model wasconfirmed using the KASK WG11 oblique impact test method.Three different impact angles(30°,45°,and 60°)and 2 varying impact speeds(5 m/s and 8 m/s)were employed in oblique tests to evaluateprotective performance of MIPS in helmets,focusing on injury assessment parameters such as peaklinear acceleration(PLA)and peak angular acceleration(PAA)of the head.Results:The results demonstrated that in all impact simulations,both assessment parameters werelower during impact for helmets equipped with MIPS compared to those without.The PAA wasconsistently lower in the MIPS helmet group,whereas the difference in PLA was not significant in the noMIPS helmet group.For instance,at an impact velocity of 8 m/s and a 30°inclined anvil,the MIPS helmetgroup exhibited a PAA of 3225 rad/s^(2) and a PLA of 281 g.In contrast,the no-MIPS helmet group displayeda PAA of 8243 rad/s^(2) and a PLA of 292 g.Generally,both PAA and PLA parameters decreased with theincrease of anvil angles.At a 60°anvil angles,PAA and PLA values were 664 rad/s^(2) and 20.7 g,respectively,reaching their minimum.Conclusion:The findings indicated that helmets incorporating MIPS offer enhanced protection againstvarious oblique impact loads.When assessing helmets for oblique impacts,the utilization of larger angleanvils and rear impacts might not adequately evaluate protective performance during an impact event.These findings will guide advancements in helmet design and the refinement of oblique impact testprotocols.

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.

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.

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.

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.

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.

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.

Micro-impact testing: A novel nano-/micro-tribological tool for assessing the performance of wear-resistant coatings under impact/fatigue conditions

A novel repetitive contact technique, micro-impact testing, has been developed forcoating evaluation. Impact test results have proved a more consistent measure of coating per-formance under impact/fatigue conditions than traditional tribological methods such as scratch orpin-on-disk testing. The operating principles of the technique are described with some illustrativeresults on hard and soft coatings. The technique can provide information on impact wear resis-tance, susceptibility to brittle fracture, and strength of interfacial adhesion to substrate.

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.

基于落石模型试验的棚洞垫层力学响应及优化设计

结合边坡落石灾害现状,基于落石模型试验,系统分析落石质量、下落高度、垫层厚度、加筋位置、加筋材料等因素对落石冲击力及其动态演化的影响,揭示落石冲击棚洞的动力响应规律,结合垫层自重与落石冲击作用双因素影响确定垫层最优厚度,并对垫层设计提出优化建议。结果表明:随着垫层厚度增加,棚洞所受落石冲击力呈非线性减小,减小幅度先大后小而后趋于稳定;在同一垫层厚度下,棚洞所受落石冲击力随落石高度和落石质量近似呈线性增大;当复合垫层设计为“5 cm河砂+聚苯乙烯泡沫(EPS)+10 cm河砂”时,落石中心处土压力峰值相较于纯河砂垫层降低约60%,缓冲耗能效果最佳;通过多元回归分析得到了落石冲击力计算公式,且计算结果与实验数据吻合良好。