Impact Hammer Test Research Articles

Analysis of moose motion trajectory after bullet train-moose collisions

Collisions between trains and moose that cross a track are common occurrences according to rail accident statistics. A moose lying on a track after a crash may increase the risk of train derailment. In addition, a moose thrown into the air during a collision may also hit and damage the pantograph, which prevents a train from running. This paper developed a finite element (FE) model of moose and is aimed at investigating the train crash safety and moose motion trajectory in train-moose collisions for different moose crossing scenarios using the FE method. Material biomechanics tests were conducted to obtain the mechanical property parameters of moose. Drop hammer impact tests were performed to validate the constitutive models of different moose segments. The whole moose FE model was verified against previous vehicle-moose crash tests. The numerical impact scenes of moose crossing the rail at different collision positions were established in LS-DYNA. The results showed that the impact force depends on the contact area between the train and the moose. A larger contact area corresponded to a larger impact force. The moose would be pushed away by the V-shaped locomotive and would not cause a derailment, and the height of the moose thrown into the air cannot reach the height of the pantograph, which would prevent damage to the pantograph of a bullet train.

Study on ballistic mechanism of B4C/Al gradient armor

AbstractIn order to improve the anti‐penetration performance of gradient armor, the constitutive models of B4C/Al composites with different compositions were determined according to the bending curves. The anti‐bullet simulation of B4C/Al gradient armor was carried out by ANSYS‐DYNA finite element software, and the stress state of B4C/Al gradient material under 7.62‐mm bullet penetration was analyzed. Meanwhile, the propagation law of stress wave in armor was studied by Hopkinson bar simulation and the improved internal stress wave model, which further revealed the ballistic mechanism of B4C/Al gradient armor. The simulation results showed that, compared with the traditional laminated armor, the toughness of B4C/Al gradient armor material increased with the change of layer thickness, resulting in the fact that the whole armor could withstand greater stress without breaking, and the anti‐penetration time was prolonged. In addition, the performance difference between the layers of the gradient armor was slight, and the spallation phenomenon of the relative double‐layer armor decreases, which enhanced the multiple hit performance of the armor and the absorption capacity of the stress wave. The performance of B4C/Al gradient armor specimens and double‐layer specimens were tested by drop hammer impact test. The test results were consistent with the simulation results.

Dynamic response of bidirectional bonded prestressed concrete slabs subject to low velocity impact: Impact energy and prestress degree

Bidirectional bonded prestressed concrete (PS) structures have been widely used in energy engineering. However, the systematic studies on the failure mechanism and dynamic response of this structure suffering from impact load are still inadequate. This paper has carried out nine drop hammer impact tests and corresponding numerical models. The results reveal that overall flexure and local punching co-occur in the bidirectional PS slabs under the impact, with the local punching failure as the failure mode. The dynamic response of the slab includes: inertia loading stage, load holding stage and rebound unloading stage. Due to the influence of the membrane force enhancing effect and specimen damage weakening effect, the impact force in the load holding stage may present three conditions. The compressive prestress applied to concrete can provide in-plane constraint and limit the appearance and development of cracks, resulting in decreasing the plastic damage of the specimen and the drop hammer displacement, while improving the bearing capacity and stiffness of the specimen. For impact energy of 5.48 kJ, when the prestress degree increase from 0% to 11.6%, the equivalent impact force increases 95%, the peak drop hammer displacement, equivalent spalling and scabbing diameter decrease 40%, 22.6% and 8.6%, respectively.

Structural damage severity classification from time-frequency acceleration data using convolutional neural networks

Structural damage identification involves interpretation of vibration measurements to identify patterns that are indicative of changes in structural characteristics. Identification of such patterns using machine learning (ML) algorithms is a primary task in data-driven structural health monitoring. However, providing ML algorithms with features that are sensitive to damage has always been a challenge for accurate damage detection. In recent years, deep Convolutional Neural Networks (CNNs) proved to be versatile and powerful tools to identify the underlying patterns directly from low-level raw data. This study explores the applicability of CNNs to damage severity classification. A new format of input data for CNN damage identifiers is proposed based on time–frequency representations of acceleration data from multiple sensors. First, Continuous Wavelet Transformation (CWT) of acceleration response is employed to derive the time–frequency data, then, the results of transformations from multiple accelerometers are stored in separate channels creating a three-dimensional block of data. Such input data provide a CNN with structural information that expands into time, frequency, and spatial domains. To evaluate the accuracy of such a CNN-based classifier, a dataset comprised of free vibration response of a concrete beam under impact hammer tests is utilized. It is shown that a CNN trained with CWT data can successfully classify various severity of the damage, from minor to severe, with 100% accuracy. Also, this study examines the sensitivity of the CNN classifier to the number of training samples. It is demonstrated that the accuracy of such a network has a relatively lower sensitivity to the number of training samples and/or the number of measurement points to the degree that it maintains an F1-score above 0.813 when trained with data from one impact point and one sensor. On the other hand, for the case of a CNN classifier trained directly with time-series acceleration data the value of the F1-score drops to 0.590. Moreover, when compared with a multilayer perceptron trained with the extracted modal properties, it is illustrated that CNN classifiers have a better capability in capturing key features from the measurement, and thus produce more accurate predictions. Therefore, the combination of CNN classifiers with time–frequency data from multiple sensors results in damage identifiers that are less sensitive to sample size and more robust to changes in excitations and measurement points.

Experimental and numerical simulation study on failure mode transformation law of reinforced concrete beam under impact load

Changes in the primary influencing factors, such as structural configuration and impact energy, have an influence on the impact dynamic response and failure modes of reinforced concrete beams. In this paper, drop hammer impact tests with different reinforced concrete beam configurations and various impact conditions were conducted. Additionally, parameters of impact force, support force, reinforcement strain, concrete strain, impact local deformation and overall structural deformation were obtained by comprehensive measurements. On the dynamic response and failure modes of reinforced concrete beams, the effects of various concrete strengths, longitudinal/stirrup configurations, hammerhead shapes, and impact velocities were examined. LS-DYNA was applied to perform numerical simulations of reinforced concrete beams with various impact velocities, tensile longitudinal reinforcement ratios, and stirrup ratios. The result of the experiment proved that the peak displacement and residual displacement of reinforced concrete beams under low velocity impact increased with the improvement of impact velocity. Besides, the peak displacement and residual displacement were approximately linearly related to the ratio of impact kinetic energy to ultimate static bearing capacity. The higher the concrete strength and the greater the longitudinal reinforcement ratio were, the larger the peak impact force on the beam was under the equal impact conditions, whereas the smaller the overall displacement response was. The support force, midspan deflection, and residual deflection were less impacted by the form of the hammer head. However, the peak impact force was significantly influenced. Four failure modes of a beam under impact are assessed in accordance with the failure limit state of the structure: bending failure, bending-shear failure, shear failure, and punching failure. According to the test findings, with the improvement of impact velocity, the reinforced concrete beam went from bending failure to bending shear failure, shear failure, and punching failure under the same structural arrangement. By raising the concrete strength and stirrup ratio or lowering the longitudinal reinforcement ratio, the failure mode of the beam progressively changed from punching failure to bending failure while the impact velocity was the same. Through numerical simulation, it was found that the impact velocity of the falling hammer had the greatest influence on the failure mode of the reinforced concrete beam, followed by the ratio of the tensile longitudinal reinforcement, and the smallest was the stirrup ratio.

Investigation on lateral impact resistant performance of aluminum foam-filled 6082-T6 aluminum alloy circular tubes: Experimental and numerical study

Nowadays, the aluminum alloy building structure is at risk of the accidental impact loadings, which seriously threatens the personal security and the safety of the property. However, the existing research on the local lateral impact performance of the aluminum foam-filled tube applied to building structures is limited. In this study, impact tests on 9 aluminum foam-filled tubes with fixed boundaries were conducted by using a drop hammer impact test device to investigate the dynamic performance of the foam-filled tube under local lateral low-velocity impact loadings. The failure modes, impact force histories, displacement histories, and permanent deformation of the foam-filled tubes were obtained and compared with those of the empty tubes under the same impact loading. The finite element (FE) model was also established via the software ANSYS/LS-dyna and the accuracy of the FE method was verified against impact test results. Based on the experimental and numerical results, the aluminum foam-filled aluminum tube shows better lateral impact resistant performance than the empty tube due to the support effect of the aluminum foam on the tube wall by good energy absorption and deformation characteristics. Especially, filling the aluminum foam prevents the generation of cracks for the composite tube near the impact position when the impact energy is high. The influence law of the aluminum foam filler and its density, shape of hammer head on the lateral impact resistant performance of the aluminum foam-filled composite tube was then investigated based on the experimental and numerical results by consideration of the damage level, energy absorption, impact force–lateral displacement relationship, and permanent deformation. By filling the aluminum foam into the empty tube, the energy absorption is improved by up to 67.2% and 44.9%, respectively, when the hammer displacement reaches 20 mm and 40 mm within the impact load condition conducted in this study.

Experimental Study on the Impact Resistance of Steel Fiber Reinforced All-Lightweight Concrete Beams under Single and Hybrid Mixing Conditions

An impact action can cause local, or even overall, damage to structural components. This paper investigates the effect of flat and wavy steel fibers on the mechanical impact resistance of all-lightweight concrete beams under single and mixed conditions. Four all-lightweight concrete beams were subjected to drop hammer impact tests. From the failure mode, local shear-type damage occurred at the midspan of the all-lightweight concrete beams, with mainly shear cracks. The steel fiber has an inhibitory effect on the generation and development of cracks and improves the phenomenon of concrete crushing and spalling after the impact of the beam. Different mixing methods will have different effects on the crack-inhibition effect of steel fiber. The mixed addition of steel fiber has a more prominent effect on crack-development inhibition, making the cracks finer. Under the conditions of adding the flat steel fibers alone, the wavy steel fibers alone, and the mixed addition of steel fibers, the peak displacement at the midspan was reduced by 14.29%, 22.86%, and 37.14%, respectively; in comparison, residual displacement was reduced by 18.18%, 50.91%, and 54.55%, and the peak impact force was increased by 6.98%, −2.62%, and 1.89%. In addition, the stiffness loss of the steel fiber-added specimens is slight, which can have a higher impact response when the drop hammer falls. The results show that the addition methods of the steel fibers have different effects on the improvement of the impact resistance of the all-lightweight concrete beams, and the mixed addition has a better effect than the single addition.

Dynamic compressive and splitting tensile characteristics of rubber-modified non-autoclaved concrete pipe piles

Non-autoclaved concrete pipe piles are gaining attention as an environmentally friendly alternative to autoclaved concrete pipe piles. The purpose of this study was to investigate the changes in the impact resistance of a non-autoclaved concrete pipe pile with the addition of rubber. To this end, various volume fractions of rubber particles were used to replace the fine sand in the non-autoclaved pipe pile concrete (0%, 5%, 10%, 15% and 20%). The dynamic and static mechanical responses of rubber-modified non-autoclaved pipe pile concrete were explored through quasi-static and dynamic compression and splitting tensile tests. The results showed that (1) The tensile-compression ratio of the rubber-modified non-autoclaved pipe pile concrete increased with the rubber content, and the brittleness of non-autoclaved concrete was improved by adding rubber. (2) When subjected to impact load, rubber particles could absorb some of the impact energy, reduce the impact load on the aggregate, and prevented the aggregate from being crushed. (3) The impact toughness index and energy consumption ratio of non-autoclaved pipe pile concrete increased with the increase of rubber content. When the rubber content was 10%, the impact toughness index and energy consumption ratio of non-autoclaved pipe pile concrete were 52.2% and 51.2% higher than those of non-autoclaved pipe pile concrete without rubber particles, respectively, and its impact resistance was the best. The impact resistance of rubber-modified non-autoclaved pipe pile concrete was better than that of traditional autoclaved pipe pile concrete, and met the mechanical performance requirements of prestressed high-strength concrete pipe pile. It could be used as a new prestressed high-strength concrete pile material, which helped to reduce energy consumption in the production process of piles. The study provided parameter basis for the subsequent drop hammer impact test and numerical simulation of pipe piles.

Experimental and numerical study of X-type energy dissipation device under impact loads

To obtain the optimal size and shape of X-type energy dissipation device, 20 specimens were tested using a drop hammer impact test machine, then the finite element model was established by using the software LS-DYNA. The dynamic responses of X-type energy dissipation device including failure mode, impact force, displacement and energy absorption were obtained and analyzed with emphasis on the effect of the height reduction parameter a, length reduction coefficient b and high span ratio c. The effectiveness of the finite element model is verified by comparing the simulation results with the experimental results. The finite element model is then used to optimize the X-type energy dissipation device. The height reduction parameter a and high span ratio c were taken as the optimization parameters, and the strain uniformity was taken as the target for improvement. Through regression analysis, the formulas of height reduction parameter a, height span ratio c and strain uniformity degree are derived. After four levels of optimizations, the optimized shape of the X-type energy dissipation device is obtained, and its energy dissipation performance is significantly improved compared with that of the traditional X-type energy dissipation device.

Crack Detection in an Aluminium Oxide Grinding Wheel by Impact Hammer Tests

Grinding is widely used as the last step of the manufacturing process when a good surface finish and precise dimensional tolerances are required. However, if the grinding wheels have cracks, they may lead to a hazardous working environment and produce poor tolerance in machined products. Therefore, grinding wheels should be inspected for cracks before being mounted onto the machine. In this study, a novel method of finding possible internal cracks in the aluminium oxide grinding wheel will be explored by examining the natural frequency and displacement of wheels using an impact hammer testing method. Grinding wheels were cracked into two segments using a three-point bend fixture and then bonded intentionally to simulate cracks. The impact hammer test indicated that cracks in the grinding wheels caused a drop in natural vibration frequency and an increase in the maximum displacement of the accelerometer sensors.

Vibration analysis of electric motors considering rotating rotor structure using flexible multibody dynamics-electromagnetic-structural vibration coupled analysis

AbstractIn this study, we develop flexible multibody dynamic-electromagnetic-structural vibration coupled analysis method to accurately predict motor vibration by considering the electromagnetic force characteristics, rotating characteristics of rotating motor motors, and their interactions at the no-load rated speed and operating speed range. The structural characteristics are accurately reflected by developing a three-dimensional (3D) finite element model considering the entire components of the motor. The reliability of the 3D finite element model of the motor is verified using the impact hammer test. In addition, to consider the rotational characteristics of the rotor structure, we develop a flexible multibody dynamics model that connects the flexible rotor and the bearing with revolute joint. The vibration of the motor at the no-load rated speed is analyzed using flexible multibody dynamics-electromagnetic-structural vibration coupled analysis. Comparing the vibration test results, it is confirmed that the flexible multibody dynamics-electromagnetic-structural vibration coupled analysis result predicts the actual motor vibration more accurately than the conventional finite element analysis-based electromagnetic-structural vibration coupled analysis result. By using flexible multibody dynamics-electromagnetic-structural vibration coupled analysis in the operating speed range, it is confirmed that not only electromagnetic force harmonics but also sideband harmonics caused by rotor eccentricity-induced large vibrations, and also confirmed that it accurately predicts the vibration characteristics of actual motors with rotating rotors.

Impact toughness and fractography of diverse microstructure in Al-Cu alloy fabricated by arc-directed energy deposition

To investigate the effects of heterogeneous microstructure, precipitates, and pore defects on dynamic impact toughness of Al-Cu alloy fabricated by arc-directed energy deposition (Arc-DED). Samples with diverse microstructures were prepared by adjusting the forming parameters, namely air cooling (AC), water cooling (WC), and the post-treatment, hot isostatic pressing (HIP), and heat treatment (T6) samples. The impact fracture behavior of samples with Charpy V-notched was studied by an instrumented drop hammer impact testing machine which can provide a load-displacement curve. The important load parameters and the absorbed energy at different stages can be determined by the load-displacement curve. The results show that the impact absorbed energy of the AC/WC/HIP/T6 sample was 1.33 ± 0.20, 1.96 ± 0.26, 1.91 ± 0.18, and 2.54 ± 0.21 J, respectively. The impact fracture mechanism was discussed as the corresponding fractographic observations. Brittle fractures with inhomogeneous dimples were observed in all the samples. The key determinant of the impact toughness was the block-shaped brittle θ phase that precipitated along the grain boundaries and pore defects. The equiaxed/columnar heterogeneous microstructure affects not only the coordinated deformation ability of grains but also the distribution of brittle θ phases. Therefore, compared with the AC sample, the impact toughness of the WC sample with a low-volume fraction θ phase, the HIP sample with low porosity, and the T6 sample with a large amount of ductile θ″/θ' phases was significantly improved. This study provides valuable insights for improving the dynamic impact resistance of Arc-DED fabricated Al-Cu alloy.

Modal testing with a pedestrian as a vibration exciter

A novel approach, for identification of modal properties using a dynamic excitation induced by a human walker, has previously been proposed to identify natural frequencies, damping ratios and modal masses. The developed approach is now expanded to also estimate vibration mode shapes, thus fully characterising the dynamic behaviour of a structure in a simple and affordable way. Additionally, the reliability of the method is parametrically analysed and validated against simulated and real world data of a footbridge. Results indicate that, given a reasonable initial estimate of the target modal properties values and with careful consideration of the number and location of measured responses, it is possible to estimate all modal properties of a structure in a reliable and simpler way than conventional modal testing methods: handheld impact hammer, electrodynamic shaker or ambient vibration tests.

Influence of Bonding Area on Dynamic Failure Behavior of Notched Reinforced Concrete Beams.

To study the effect of the bonding area on the dynamic failure process of a reinforced concrete beam with the same reinforcement ratio, the experimental and numerical researches on the impact response of notched reinforced concrete beams in the low-velocity regime (≤2.5 m/s) are presented. The tests are carried out with a drop hammer impact testing machine and then the structural responses under different impact velocities are analyzed. Additionally, the dynamic three-point bending simulation for specimens with different bonding areas, but the same reinforcement ratio is conducted. In this numerical model, the parameters of a cohesive model verified from a steel bar pullout test are applied to the bonding layer to simulate the bond-slip behavior of steel bars. Then, the energy dissipation for each component (e.g., concrete, a steel bar, and the bonding layer) are compared and discussed. The dynamic experimental results suggest that the energy absorbed during the impact process increases with the growth of the impact velocity, while the effect of the impact velocity on the reaction force can be ignored. The numerical results indicate that the failure pattern changes from a bending failure to shear failure with the increase in the bonding area and impact velocity. With the growth of the bonding area, the steel bars reach the plastic stage easily and the internal energy dissipation of the bonding layer decreases, which protects the bonding effect between the steel bar and concrete effectively.

Operational Modal Analysis of Offshore Wind Turbine Tower under Ambient Excitation

The condition of an offshore wind turbine (OWT) should be monitored to assure its reliability against various environmental loads and affections. The modal parameters of the OWT can be used as an indicator of its condition. This paper combines the Kalman filter, the random decrement technique (RDT), and the stochastic subspace identification (SSI) methods and proposes an RDT-SSI method to estimate the operational frequency of an OWT subjected to ambient excitation. This method imposes no requirement on the input/loads; therefore, it is relatively easy for field application. An experimental study with a small-scale OWT was conducted to verify the accuracy of the proposed RDT-SSI method. The test results implied that the frequency estimated by the RDT-SSI method is close to that estimated by an impact hammer test. Moreover, the small-scale OWT was buried at different embedment depths to simulate the influence of the scouring phenomenon, and the frequency of the OWT decreased with decreasing embedment depth. Additionally, the bolts at the root of the turbine blades were also loosened to investigate their influence on the frequency. As more blades were loosened, the identified frequency of the OWT also decreased, indicating that the proposed RDT-SSI method can be employed for the health monitoring of an OWT.

Study on impact resistance of precast light-weight concrete sandwich panels

To investigate the dynamic impact resistance of precast lightweight sandwich panels (PLCSP) composed of non-sintered coal ash ceramsite concrete and self-developed thermal blocking shear connectors, drop hammer impact tests with different impact energy were carried out in the central area of the exterior wythe. The dynamic response of PLCSP under different steel fibers content, wythe thickness, and the different number of shear connectors was compared and analyzed. The numerical simulation was carried out by LS-DYNA. The results show that 2% volume fraction of steel fibers enhance the stiffness of the panel by improving the overall impact toughness, while the increase in wythe thickness slows down the panel amplitude to enhance the stiffness. The exterior wythe of the PLCSP has penetrated failure, and the failure mode of the interior wythe changes from bending failure to collapse failure with the increase of the number of shear connectors. Therefore, the arrangement spacing of shear connectors can be appropriately reduced to reduce the risk of collapse failure. The ratio of maximum displacement and residual displacement of the panel under different impact energies ranged from 3.37 to 5.94, and the maximum erosion depth of the hammer was twice the displacement of the bottom of the panel, indicating that the unique sandwich structure and material of the PLCSP have good impact resistance. The research results can provide reference for the design and application of PLCSP.

Plastic deformation behavior of aluminum alloy fiber porous body and its filled tube under impact loading

The size of aluminum alloy fiber wire with a short side of 5mm, a long side of 10mm and an arc radius of 1mm were prepared from the raw material of 6061 aluminum alloy fiber with diameter of 0.15mm by Spring machine cutting, namely the structure size of 5×10mm bending aluminum alloy fiber. The aluminum alloy fiber porous body with different porosity were prepared by vacuum hot pressing sintering furnace, and it was sleeved with 6063 aluminum alloy round tube to prepare aluminum alloy fiber porous body filled tube. The impact test was carried out with drop hammer impact testing machine, The plastic deformation behavior of aluminum alloy fiber porous body and its filled tube under impact loading with different porosity was studied. The results show that the impact process of aluminum alloy fiber porous body can be divided into three stages: plastic platform stage, densification stage and unloading stage, the filled tube with aluminum alloy fiber porous body can be divided into four stages: elastic deformation stage, progressive buckling stage, densification stage and unloading stage. Low porosity will make more fibers, and more benefit the generation of the sintering necks, the plastic deformation strength increases with the porosity decrease. The coupling effect of the aluminum alloy tube and the aluminum alloy fiber porous body makes the filled tube absorb the same energy with shorter impact displacement, and has stronger impact resistance and better mechanical properties.

Artificial intelligence enhanced automatic identification for concrete cracks using acoustic impact hammer testing

Artificial intelligence enhanced automatic identification for concrete cracks using acoustic impact hammer testing

Dynamic Response and Numerical Simulation of Closed-Cell Al Foams.

The drop hammer impact test was carried out to investigate the dynamic response of closed-cell Al foams. A relatively reasonable method was also developed to evaluate the velocity sensitivity of cellular material. The typical impact load-displacement curve exhibited two stages containing the initial compression stage and the progressive crushing stage. Three compressive damage behaviors and four failure modes of closed-cell Al foams were revealed, while the effect of velocity on the impact properties and the energy absorption capacity of different specimens were investigated. The results showed that the specific energy absorption of the specimens increased with the increasing density of the specimen and the impact velocity. However, the specimens with higher specific energy absorption seemed not to indicate better cushioning performance due to the shorter crushing displacement. In addition, the uniaxial impact simulation of two-dimensional (2D) Voronoi-based foam specimens was conducted at higher impact velocities. The simulation results of impact properties and deformation behavior agreed reasonably well with the experimental results, exhibiting similar velocity insensitivity of peak loads and deformation morphologies during uniaxial impact.

Study on impact fatigue test and life prediction method of TC18 titanium alloy

To study the impact fatigue properties of TC18 titanium alloy and propose a new damage model for the impact fatigue life prediction of material, the impact fatigue test method and the impact response measurement scheme are designed. The impact fatigue tests are then implemented on a drop hammer impact test machine to obtain the fatigue lives and impact responses of the tested specimens under different impact conditions. A new impact damage model is proposed based on the theory of continuum damage mechanics considering the effect of strain rate. The calibration method of material parameters is presented, and the parameters of the impact damage model are obtained according to the test data of TC18. Afterward, the numerical implementation of impact damage calculation is established, and an ABAQUS user-defined subroutine is used to realize the finite element numerical simulation of impact fatigue damage accumulation. Finally, the damage evolution of TC18 under tensile impact fatigue loading is simulated and the corresponding fatigue life is predicted. The errors between the calculated impact fatigue lives and the experimental lives are less than 25%, which demonstrates the good validity and applicability of the proposed damage model and the numerical method.