Drop-weight Test Research Articles

A method of reverse and revision of material mechanics performance parameters for vehicle collision simulation

In the process of vehicle collision, the steel material will be deformed by the impact speed. The stress under the same strain will be affected by the change of strain rate. The accuracy of the strain rate curve directly determines the accuracy of the model simulation. This article studies the optimization of material mechanical performance parameters and the correction reprocessing methods of the stress that cannot be obtained by the test in the strain interval. This paper proposes the principle of the modified constitutive equations and the corresponding formula. Based on the approximate model of thin-walled beam under the dynamic impact, the correction coefficient is obtained reversely. While ensuring the accuracy between fitting curve based on the material constitutive equation and the experimental data, the modified constitutive model solves the effect of the non-convergence of stress in a large strain region on the accuracy of the collision simulation model. The dynamic drop weight test results of thin-walled beams show that the modified constitutive equation has great significance for improving the accuracy of simulation models under high-speed impact conditions.

Microstructure and Thickness Effects on Impact Behavior and Separation Formation in X70 Pipeline Steel.

In an effort to optimize the transportation of oil and gas, the pipeline industry is developing large-diameter, thick-walled pipelines that can withstand low temperatures and high pressures. In this study, three X70 steel plates of similar chemistry, ranging in thickness from 13.5 mm to 22 mm, were subjected to drop-weight tear and Charpy V-notch tests to determine the effects of plate thickness and microstructure on the formation of separations and impact behavior. Constraint induced by specimen thickness appears to dictate the location of separations, the three microstructures exhibited different separation behaviors, and microstructural banding was not found to promote separation formation. Separations were most frequent when the primary fracture plane was parallel to the rolling direction. This study also found that standardized empirical relationships between Charpy V-notch and drop-weight tear tests do not estimate to the advanced high-strength and -toughness steels investigated.

Advanced Joining Processes Unit

The Advanced Joining Processes (AJP) is an autonomous research unit at the Institute of Science and Innovation in Mechanical and Industrial Engineering (INEGI) that works closely with the Faculty of Mechanical Engineering of the University of Porto (FEUP). This unit is staffed by professors, post-doctoral researchers, PhD students, MSc students and research fellows. The AJP unit has four key competences, established to support all aspects related to the study of advanced joining processes: testing, simulation, production and machine design. The AJP unit has robust and fully independent competences in the manufacture of experimental specimens and components. The unit operates a fully equipped laboratory with all facilities necessary to manufacture specimens, moulds, test fixtures and testing equipment. The unit has extensive experience in testing complex specimens’ geometry under a wide range of conditions. Research is carried out to determine the performance of structural joints under quasi-static loads, high strain rates, fatigue and creep conditions, among many others. Complementarily, the unit also has a strong machine design capability, being experienced in the development and manufacture of custom designed testing equipment (such as creep testing machines, drop-weight testing machines, torsion testing machines, split Hopkinson pressure bars and devices for glass transition temperature measurement). These experimental capabilities are complemented with robust numerical simulation competencies, which allow to streamline the design process by creating powerful models that can accurately predict the mechanical behaviour of advanced structural joints. These capabilities enable the AJP unit to undertake new and challenging research projects, reacting quickly to current industrial demands and scientific trends, due to its autonomy. This work methodology allows the AJP unit to simultaneously operate in two main fronts. One is fundamental academic research, resulting in MSc and PhD thesis and scientific publication, and the other is comprised of knowledge-transfer activities with industrial partners, which generate funding that can be used to support additional fundamental research. By combining these two approaches, the AJP unit proves that sound technological based educational processes can be achieved while undertaking cutting edge research with practical and industrial value.

Making security glazing from modified TEMPO oxidized nanofibers and poly vinylbutyral

Safety glazing is a type of laminated glazing that holds together when shattered, due to the presence of an interlayer usually made of polyvinyl butyral (PVB). It is widely used in industrial application where the glazing could fall, or become a projectile to avoid serious injuries to humans after an impact with a foreign object. To replace the PVB, we have developed a modified cellulose nanofibers (NFC) by grafting poly(glycidyl methacrylate) with glycerol addition. This modification has improved the NFC pure performance as well as their compatibility with polar polymers. Therefore, this study reports the preparation and characterization of laminated glazing with composites of PVB reinforced with 40, 50 and 70% by weight of modified NFC. Composites interlayers are very transparent (up to 93% light transmission) with an interesting light character (up to 18.72% weight loss) in comparison to a PVB interlayer only. The chosen laminated glazing have been characterized by quasi-static (three-point bending) and dynamic impact loading (drop weight test). The quasi-static show the force–displacement curves of glazing while the dynamic testing give the energy absorption capability and maximum impact force. In our testing, the glazing with modified NFC have shown increased mechanical properties. Moreover, the laminated glazing made with an interlayer reinforced with 40% NFC exhibits the highest impact properties with a maximum force at break of 36,270 N and 24.81 J of absorbed energy. This study has shown that the modified NFC is indeed a lighter and environment-friendlier alternative for laminated glazing.

Eksperimentalno i numeričko istraživanje čeličnih profila pri udarnom opterećenju

Experimental and numerical behaviour of steel test specimens with various types of joints is investigated in this study. A drop weight test setup with necessary test equipment is used for this purpose. The mass and drop height of the hammer is taken to be constant so that the same impact energy can be applied on test specimens. The acceleration, displacement, impact load, drop numbers and drop durations, are obtained through experimental study. In addition, development of damage to test specimens is observed during tests. Numerical analyses of behaviour of test specimens under impact load are also conducted to verify test results using the Abaqus software, and a comparison of results is made.

Study on mechanical properties at different test temperatures of SA-738 Gr.B plate in two states

This paper describes the study on mechanical properties at different test temperatures of SA-738 Gr.B plate in both delivery state and simulated post-welding heat treatment state. And the properties of the plate were characterized by tensile tests, Charpy impact tests and drop weight tests. We found that as temperature increasing, the strength of the SA-738 Gr.B plate decreased when temperature was below 200°C. While as temperature decreasing, the Charpy impact absorb energies decreased, that is, toughness of the plates became worse gradually. Through drop weight tests, we obtained the nil-ductility transition temperature for the plate. The tests data indicated the SA-738 Gr.B plate possessed good strength and toughness, which can meet the design requirements for the containment vessel and some other components of nuclear plant. The tests data also showed that post-welding heat treatment may influence both strength and toughness, so attention should be paid to simulated post-weld heat treatment when purchasing materials for plant construction. By optical microscope and scanning electron microscope, microscopic pictures have been obtained for the plate to help analyze the properties of this material, and the microstructure was the ensurance of the strength and toughness.

Axial impact behavior of confined concrete filled square steel tubes using fiber reinforced polymer

Existing research on confined concrete filled steel tubular (CCFT) columns has been mainly focused on static or cyclic loading. In this paper, square section CCFT and CFT columns were tested under both static and impact loading, using a 10,000 kN capacity compression test machine and a drop weight testing equipment. Research parameters included bonded and unbonded fiber reinforced polymer (FRP) wraps, with carbon, basalt and glass FRPs (or CFRP, BFRP, and GFRP), respectively. Time history curves for impact force and steel strain observed are discussed in detail. Experimental results show that the failure modes of specimens under impact testing were characterized by local buckling of the steel tube and cracking at the corners, for both CCFT and CFT columns, similar to those under static loading. For both static and impact loading, the FRP wraps could improve the behavior and increase the loading capacity. To analyze the dynamic behavior of the composite columns, a finite element, FE, model was established in LS-DYNA. A simplified method that is compared favorably with test results is also proposed to predict the impact load capacity of square CCFT columns.

Mechanical response of shear thickening fluid filled composite subjected to different strain rates

Shear thickening fluid (STF) has been used in many areas due to its unique rheological property. In this study, the dynamic mechanical properties of STF-filled composite structures were investigated by in-house fabricated drop weight testing apparatuses. Results indicated that the strength and modulus increase with strain rate for all tube structures. Liquid-filled tubes possess similar strength and modulus, which are larger than air-filled tube at all strain rates. However, STF-filled tube absorbs 5 and 4 times more impact energy than air- and silicone oil-filled tubes, respectively. The energy absorption capacity of STF-filled tube increases with input impact energy. Meanwhile, the shear thickening effect of STF is more sensitive to the loading rate than the input energy, which is an important reference for the designing of STF integrated composite. The STF-filled silicone gel achieves repeatable test due to good protection of the encapsulation, which absorbs 4 times more energy than neat silicone gel during impact. Longitudinal symmetrical profile can be achieved for silicone gel encapsulated STF during impact due to the hardening of the STF which leads to a quick balance state. Moreover, the mechanical response of STF is found to correspond with the rheological performance of the STF.

On multiaxial failure behavior of closed-cell aluminum foams under medium strain rates

Metal foams are commonly used to withstand impact loading from different directions in real life applications attributable to their superior performance of energy absorption to weight. It has been of special interest to explore the complex yield/failure behavior of metal foams under dynamic impact recently. However, existing studies have mainly focused on crushing behavior under simple quasi-static loading conditions. Hence, this study aims to explore the multiaxial dynamic failure behavior of closed-cell aluminium foams. First, the uniaxial failure behavior of foams with three different apparent densities is experimentally investigated at varying strain rates (10−3-150 s−1) through quasi-static compression and drop weight tests, respectively. It is found that the initial failure strength exhibits evident strain-rate dependency. An empirical relation is established to associate the initial failure strength with relative density and nominal strain rate. Second, the multi-axial failure behavior is characterized based upon the developed microscopic computed tomography (micro-CT) image foam models. It is revealed that at low and medium strain rates, the hardening of the uniaxial failure strength is rate-dependent on the foam cell-wall base material. Under compression-shear and triaxial compression loadings, the initial failure surface in the von Mises - mean stress plane significantly expands with increasing strain rates. After normalized by the uniaxial failure strength at the corresponding strain rates, the failure surface is almost independent of loading or strain rates. The normalized failure surface can be well depicted by an elliptic or a parabolic function. Moreover, with use of suitable plastic Poisson's ratio, the normalized failure surface could be well characterized by Deshpande and Fleck (D&F) model and Miller model. The modified rate-dependent constitutive models are suggested for foam materials subject to quasi-static and dynamic loadings.

РАСЧЕТНО-ЭКСПЕРИМЕНТАЛЬНОЕ ИССЛЕДОВАНИЕ ИСПЫТАНИЯ ПАДАЮЩИМ ГРУЗОМ ВЫСОКОПРОЧНОЙ ТРУБНОЙ СТАЛИ Х100 (К80)

The behavior of samples of the promising pipe steel X100 under dynamic three-point bending is studied. This steel is compared with steel X80 currently used in the gas transmission pipeline engineering. Experimental and calculated mechanical characteristics were obtained for pipe steel X100 produced by JSC “VMZ” using data of the standard tests for laboratory samples and drop-weight tests (DWT). Steel X100 demonstrates higher strength indexes in comparison with steel X80, however, it has lower indexes of plasticity and ductile fracture resistance. High-speed video-recording of the crack propagation in a sample of steel X100 was performed in the drop-weight test. In combination with the sample resistance force dependence on the drop-weight movement distance, such testing provided much more information for studying the metal resistance to ductile fracture and allowed revealing the crack propagation law, estimating the specific dissipation energy during the crack propagation, and verifying the computational model used in DWT. Parameters of the X100 steel strain and fracture model were calibrated. The numerical simulation of the behavior of the X100 steel samples in tests at room temperature was performed. Simulation results satisfactorily agree with data of the tests with regard to such parameters as: the sample resistance force dependence as a function of the drop-weight movement distance; the striker work; strained foils, and macrogeometry of fractures in the tested sample. This results may be used for the development of requirements and conditions of using equipped DWT, as well as for the numerical simulation of full-scale tests of pipes made of steel X100 to predict the pipeline resistance to a propagating ductile crack.

Experimental Study on Impact Resistance of Concrete Containing Steel Fibers

This study is an experimental study aims to examine the effect of utilization of straight, and low cost steel fibers on the impact resistance of concrete. The impact resistance of steel fiber reinforced concrete (SFRC) was assessed using drop weight test as per ACI committee 544. The steel fibers were randomly dispersed in concrete during mixing. Five mixes made with steel fibers dosages of 0% (control mix), 0.5%, 1%, 1.25% and 1.5% by volume of concrete were examined in the study. The results show that mixes containing steel fibers show better impact resistance than plain concrete (control Mix). The results also indicate that increasing the dosage of fiber increases the impact resistance of concrete but up to a certain content of fibers. The maximum increase was recorded at steel fiber dosage of 1.25% by volume of concrete. Also the patterns of failure of the concrete specimens show that fibers are very effective in increasing the concrete toughness which enhance the ductility of concrete and delays the crack initiation.

緩衝ゴムを設置した RC 梁の重錘落下衝撃荷重載荷実験

緩衝ゴムを設置した RC 梁の重錘落下衝撃荷重載荷実験

Experimental evaluation of impact energy on oobleck material (non-Newtonian fluid)

Non-Newtonian fluids especially shear thickening fluids like oobleck behave like a solid when subjected to impact loads and remains as a liquid when the loading is gradual and smooth. Shear thickening fluids are also known as dilatant fluids; they do not have linear shear stress versus shear rate relation. One of the examples of dilatant fluid is oobleck can be easily made by making a 2:1 mixture of corn flour and water. It is a liquid, but when stirred it becomes thicker and more difficult to stir. It has got good shock absorption capacity which could be used in many real-world applications such as inner shoe soles, body, and speed bumpers. An attempt is made to study the behaviour of oobleck under impact loading. By performing drop weight tests and depicting the trends of oobleck thickness versus impact energy and determining the fracture points of oobleck as well as materials wrapped inside it. In future directions, part of the report applications of oobleck is prescribed such as usage in packaging materials, fabrication in a safety gear like kneepad, forearm pad, etc.

The Influence of Rapid Prototyping Technology on Optimization of Automobile Energy-Absorbing Box

To optimize the structure of the automobile energy-absorbing box and obtain the energy-absorbing box structure with improved impact energy absorption property, and apply it to the structure of automobile energy absorption box, test piece of crystal lattice structure and polycrystalline structure of energy-absorbing box are designed via rapid prototyping technology in this study Four different crystal lattice structures of triangle, quadrangle, hexagon, and hollow lattice structure are designed respectively. And their mechanical properties, impact energy absorption properties, and impact properties are tested. The results show that the wall thickness of the four lattices differs greatly when the quality of all crystal lattice structures is 17.8g. The compressive strength and yield strength of the hollow crystal lattice structure test piece are the largest, reaching 51.1Mpa and 69.2Mpa respectively. The maximum compression modulus of the hexagonal lattice test piece is 1462.1, followed by the hollow crystal lattice structure test piece, whose compression modulus value is 1341. The minimum absorption energy of the hollow lattice structure energy-absorbing box test piece is 2847.99J. The minimum impact value of the hollow lattice structure energy-absorbing box test piece is 69.251KN, and the impact value of triangle structure energy-absorbing box test piece is 118.11 KN. The effective impact time of the drop weight test of the hollow lattice structure energy-absorbing box test piece is only 0.08s, the peak value of the impact acceleration is 28.96g, and the maximum load of the test piece is 26.95KN. According to the comprehensive indicators, the hollow lattice structure energy-absorbing box test piece designed based on rapid prototyping technology has improved the impact energy absorption property of the automobile energy-absorbing box.

Numerical investigation of dynamic response of honeycomb sandwich panels filled with circular tubes under low velocity impact in the in-plane direction

Honeycomb sandwich structures, composed of many regularly arranged hexagonal cores and two skins, show excellent impact performance due to strong energy absorption capability under impact loads. In this paper, a numerical study of low velocity impact on honeycomb sandwich panels filled with circular tubes in the in-plane direction was performed. To calibrate the numerical model, simulation results in the out-of-plane direction are compared with the experimental ones. The numerical modelling of the drop weight test was carried out using the nonlinear explicit finite element code Abaqus/Explicit. The impact responses are presented as the contact force between the impactor and the panel versus the time. It was concluded that the filled honeycomb panel absorbs the same amount of impact energy in a shorter time than an empty one. In addition, the deflections of the front and back face-sheets are investigated. The panel degradation and the stress distribution during the crushing are also discussed.

Studying the Characteristics of Explosives under Dynamic Load Using the Split Hopkinson Pressure Bar Technique

This paper presents the results of a study of the dynamic compression of plastic-bonded PETN using the split Hopkinson pressure bar (SHPB) technique. The test procedure and some aspects of this technique are described. The advantages of the SHPB technique over drop-weight tests of explosives are briefly discussed. In the experiments, the strain rates were 7500–12 000 s-1. Force–strain and force–displacement curves are obtained, and the amount of energy required to initiate explosive transformation is estimated. It is proposed to use this technique in addition to existing methods for studying the characteristics of explosives.

Development of structural testing equipment for impact and complex loading

ABSTRACT This paper summarizes the author’s work of developing various impact testing equipment and equipment for simulating complex earthquake loading for structural research. The equipment include large diameter split Hopkinson pressure bars (SHPB), large-scale drop-weight testing equipment, field-test facility of truck collisions and multi-axes seismic loading equipment. Several types of building and bridge components were tested under axial or lateral impact loads, simulating vehicular impact actions, sudden collapse and blasts. For vehicular impact action, a procedure of establishing simulative equivalent vehicular frame is proposed, making the vehicular loading tests much easier. Fundamental tests on concrete cylinders and confined concrete cylinders under high-strain rate impacts were also carried using the large-diameter equipment. Large to full-scale reinforced concrete or steel structures were also studied experimentally, using the developed equipment.

A comparative experimental study on the impact strength of standard and asymmetric involute spur gears

Gears are one of the main components of the power transmission systems and are used in various fields. Problems caused by sudden load changes in mobile systems are frequently encountered today. Gear dynamics have become more influential due to demands of high power transmission capability, long life, and low-cost. However, inertial forces caused by accelerated movements of gear can have unpredictable results. The impact loads must be calculated correctly. It is inconvenient to determine the impact strength of gear via standard drop-weight test rig due to inhomogeneity and complex geometries. This study investigates how the tooth profile affects the impact load on the involute spur gears. For this reason, a special test setup and experimental approach was proposed to examine the influence of the asymmetric profile on the impact strength. It was observed that the peak force values increased by approximately 15.3% when using 20°/30° asymmetric profile gears in comparison with the 20°/20° standard design. This improvement can reach up to 25.8% in terms of peak force energy. The results indicate that the proposed novel test setup and the experimental method can be used for measuring the impact strength of asymmetric involute gears.

DESIGN OF FORCE MEASURING SYSTEM ON MAIN LANDING GEAR WEIGHT DROP TESTING MACHINE FOR THE APPLICATION OF LSU SERIES

In this research, the design of the force measuring system on main landing gear weight drop test for the LSU series that developed by LAPAN was carried out. The principle of this machine is to apply the load according to the weight of the aircraft on the main landing gear and drop it at a certain height assisted by the guiding rail. At the bottom of this machine there is a impact platform where each angle is mounted with a load cell that functions to measure the reaction force due to the impact of the main landing gear. In addition, there is a data acquisition system whose function is to process the output signal from load cell and display measurement data. The data acquisition system used consists of DAQ measurement hardware made by national instruments and LabVIEW software installed on a PC. The design of this testing tools aims to carry out a dynamic impact test on the main landing gear structure of the UAV. In this study, static calibration has also been successfully performed on the impact platform and shows consistent results for various test masses.

Impact Strengthening of Laminated Kevlar/Epoxy Composites by Nanoparticle Reinforcement.

Herein, we report the fabrication and characterization of high-strength Kevlar epoxy composite sheets for structural application. This process includes optimization of the curing conditions of composite preparation, such as curing time and temperature, and the incorporation of nanofillers, such as aluminum oxide (Al2O3), silicon carbide (SiC), and multi-walled carbon nanotubes (MWCNT) in different weight percentages. Differential scanning calorimetry (DSC) was utilized to investigate the thermal stability and curing behavior of the epoxy, finding that a minimum of 5 min is required for complete curing under an optimized temperature of 170 °C. Moreover, mechanical characterization, including flexural and drop-weight tests, were performed and found to be in good agreement with the DSC results. Our results show that nanofiller incorporation improves the mechanical properties of Kevlar epoxy composites. Among the tested samples, 0.5% MWCNT incorporation obtained the highest mechanical strength.