Velocity Of Hammer Research Articles

Numerical analysis of dynamic collapse response of beam–column substructures under impact loads

To investigate the collapse resistance performance of steel-frame structures at varying scale ratios, numerical simulations were performed to scrutinize the influence of different scale ratios on the dynamic response of beam–column substructures subjected to impact loads. In this study, two drop-hammer impact tests were modeled and simulated, their results were compared, and the accuracy of the finite element modeling method was verified. Concurrently, a detailed model of a double half-span beam–column substructure was established to examine the effect of impact energy variations (altering the mass and velocity of the drop hammer) on the structural impact force and vertical displacement. This study analyzed variations in the impact force, impact time history, vertical displacement, internal forces, and energy absorption for models with different scale ratios when altering the impact energy. Finite element analysis results indicated that the impact velocity of the drop hammer affected the peak impact force of the substructure, whereas the drop-hammer mass influenced the force plateau and impact duration. Both the impact duration and maximum vertical displacement were positively correlated with the impact of the drop hammer and were approximately linearly positively correlated with the impact kinetic energy, resulting in the establishment of a linear fitting model between the maximum vertical displacement and the impact energy. For scaled-down substructures, variations in the impact energy could be achieved by adjusting the drop-hammer impact velocity (drop height). A proposed scale ratio for the substructure drop-hammer impact anti-collapse test is provided.

Study on dynamic response and loading mitigation characteristics of liquid-filled cell under drop-weight impact

In order to explore the anti-impact properties of the liquid-filled structure, concave and cuboid cell structures are selected for drop weight impact tests and finite element numerical analysis with and without liquid filled in the structures. Dynamic deformations were observed using high-velocity photography, and dynamic strains at typical positions were tested. The final failure modes of the cells were obtained using the 3D scanner. Then the deformation/failure processes and modes of the structures, the variation of the energy absorption ratio of each wall and the mitigation characteristics of the cell to the impact load were analyzed, and the influence of impact velocity of the drop hammer and cell wall thickness were discussed. The results showed that water medium reduced the risk of the overall instability of the cell structure; the water pressure changed the cell wall deformation from instability-bending to instability-bulging; the cell structure with concave configuration has better cushioning effect than that with cuboid configuration.

RESISTANCE OF THICK-WALLED BARRIER IN PENETRATION OF A SOLID BODY

The authors discuss bursting of barriers by solid bodies. The resistance function changes along a single-arc sinusoid. The equation of motion of a solid body is solved. The velocity of the drift hammer to reach the back of the barrier is determined. The alternative initial velocities such that the solid body is jammed in the barrier or is shot outside the barrier are examined. Determination of the barrier resistance force versus the shoot-out velocity of the drift hammer is discussed.

Three-Dimensional Numerical Simulation of Energy Transfer Efficiency and Rock Damage in Percussive Drilling With Multiple-Button Bit

Abstract Percussive drilling is suitable for the fragmentation of rocks and other similar materials with hard and brittle properties. Research on energy transfer efficiency is of great significance to improving the rock-breaking efficiency of percussive drilling. This paper numerically studied energy transfer efficiency and rock damage in percussive drilling with a multiple-button bit. In this study, the finite element method was used, and the concrete was selected as the research object. Moreover, the damage-plasticity model for concrete and the explicit dynamics solver in abaqus were adopted. Based on the above model, we analyzed the effects of different parameters on the energy transfer efficiency and the concrete damage. Results show that the degree of concrete damage is positively correlated with the output energy, referring to the energy actually absorbed by the concrete, of the percussive system. Under the condition of the same input energy, the energy transfer efficiency decreases as the number of buttons increases. With the increase of impact velocity of the impact hammer, the energy transfer efficiency augments. Multiple repeated impacts will cause the repeated damaging of the concrete, which reduces the energy transfer efficiency.

Numerical Simulation of Low Impact Velocity Behaviour of Polymeric Syntactic Foam

In this study a FE model is prepared for drop weight impact hammer testing of polymeric syntactic foam. The foam is modelled using crushable foam material and hammer is modelled using bilinear material model of LS-DYNA®. A series of simulation is performed by varying density of foam and impact velocity of hammer. Based on the prepared FE model and the force-displacement relation, energy absorption of the foam is computed and compared for three densities and three velocities. A comparative study is presented based on the displacement, reaction force-time history, and forcedisplacement behaviour.

The percussive process and energy transfer efficiency of percussive drilling with consideration of rock damage

Considering the strong nonlinearity of the percussive process, this paper used the finite element method to establish a three-dimensional percussive system model to study the energy transfer efficiency of percussive drilling. The model consists of 12-button bit model, damage-plasticity model for the rock, bit-rock interaction model, etc. The explicit dynamics solver in ABAQUS was adopted to solve the above model. In order to study different impactors, the percussive system was loaded by the prescribed pulse load that can be generated by ultrasonic impactor or electro-magnetic impactor, and by impact hammer with initial velocity that can be driven by high-pressure fluid or compressed gas, respectively. The simulation results are as follows. Increasing load duration and dynamic amplitude of the pulse load can improve the input energy, output energy and energy transfer efficiency. With the increase of the load duration or dynamic amplitude, the energy transfer efficiency first increases rapidly in the low input energy phase and then increases slowly in the high input energy phase. For the three pulse shapes--sine, triangle, square in this paper, the input energy, output energy and energy transfer efficiency under the condition of square pulse are the largest when the load duration and dynamic amplitude of the pulse force are fixed. While, the energy transfer efficiency under the condition of square pulse are the smallest and that of sinusoidal pulse are the largest when the input energy of the pulse force is fixed. Both the output energy and the energy transfer efficiency under dynamic loading increase first and then decrease with the static load. For the impact hammer, the energy transfer efficiency increases with the impact velocity of impact hammer.

A novel energy absorber based on magnetorheological gel

In this work, a novel magnetorheological energy absorber (MREA) was designed by using magnetorheological gel (MRG) as the damping medium. The proposed MREA had tunable piston gap distances and variable inner magnetic flux density distribution. The piston gap distance could be varied from 7–2 mm and the magnetic flux density at the gap increased from 120–860 mT, respectively. Under both low velocity compression and high speed impact, the damping could be divided into three parts. In the impact test, the velocity of a drop hammer could be reduced from to 3.4–0 m s−1 within a very short time (13 ms) and distance (17 mm). The maximum damping force of the MREA reached to as high as 8 kN. The damping force could also be adjusted by changing the current input. Under a 2 A current, the energy absorption ratio increased about 23% (from 4.13–5.07 J mm−1).

Pile-sinking force modeling and analysis of anti-pull impact pile driver

A "Rigid body - spring - rigid body - elastic rod - rigid body - spring - elastic rod" impact system dynamics model for an anti-pull impact pile driver is established based on the Newton mechanics and stress wave theory. In the developed model, the force, velocity, and stress curves are acquired by solving the dynamic equations. Influences of system dynamics parameters on the maximum pile-sinking force are discussed. Results show that mass and velocity of the impact hammer, stiffness of buffer spring and pile cap have significant impacts on maximum pile-sinking force, while mass of transmission box and platen have less effects. In engineering applications, maximum pile-sinking force can be controlled by rational allocation and design of pile cap and platen’s stiffness. This work can provide some guidelines for the future product optimization design. As a result, impact performance pile drivers with much better can be designed.

Investigation on the Energy Efficiency of Innovative Hybrid Impact Hydroforming

The innovative hybrid impact hydroforming (IHF) technology use high energy forming complex parts in very short time which can improving forming quality of hardforming materials like Aluminum alloy widely used in automotive and aircraft industries. The impact hydroforming technology means the most features are formed by hydroforming and the small features are rapidly reshaped by high intensity impact energy in a very short time after the traditional hydroforming. Thus, the impact energy is the most important parameter of Innovative Hybrid Impact Hydroforming. Using numerical simulation software MSC.PATRAN/DYTRAN, the whole system of hybrid impact hydroforming apparatus was analyzed. The initial gas pressure and the mass of hammer directly affect the energy efficiency. The results show greater initial gas pressure will linear increase the energy output. Moreover, the bigger mass of hammer will reduce the velocity of hammer, but it still increase the energy output. Therefore, the research is very useful for improving energy efficiency of IHFand widing its application.

Parametric Analysis of the Dynamic Response of Hot-Rolled H-Shaped Steel Beam under Lateral Impact Load

The analysis on the basic mechanical properties of hot-rolled H-shaped steel beam under lateral impact load was done by use of ABAQUS. The reliability of the FEA model was verified through comparing with the existing experiment of H-shaped steel beam subjected to lateral impact. And then, this FEA model was used to research the dynamic response of the H-shaped steel beam subjected to lateral impact. The main parameters include the impact energy, mass and impact velocity of the impact hammer. The results indicate that the finite element analysis model built in this paper could accurately simulate the process of hot-rolled H-shaped steel beam under lateral impact load and the impact energy, mass and impact velocity have different influences on the dynamic response of H-shaped steel beam.

Water hammer simulation in spiral wound reverse osmosis membranes

The purpose of this work is the development of a mathematical model for the formation and the propagation velocity of water hammer in spiral wound reverse osmosis (RO) membranes. Unexpected shutdowns of the RO plants and failure of the check valves can cause water hammer formation and its propagation as a pressure wave inside the membrane envelope resulting in membrane destruction. The model is based on energy and mass balances at flow conditions inside the membrane envelope. The mathematical analysis results in explicit equations for the local permeate pressure in steady state conditions and the increase of pressure in unsteady situations. During the water hammer formation the permeate pressure may increase so as to cause damaging results to the RO membranes.

Dynamic Testing of Materials with the Rotating Disk Indirect Bar-Bar Tensile Impact Apparatus

Abstract An experimental method is proposed to investigate the tensile behavior of materials at high strain rates by using a developed split Hopkinson tension bar, rotating disk indirect bar-bar tensile impact apparatus. The mechanically-filtered input tensile pulse is generated by incorporating a prefixed metal bar connected between the impact block and the input bar. The pulse amplitude is controlled by the diameter of the prefixed metal bar. The pulse duration is determined by the length of the prefixed metal bar and the velocity of the impact hammer. Dynamic properties of metallic and nonmetallic materials are presented as examples by using this developed rotating disk indirect bar-bar tensile impact apparatus.

Numerical and physical experiments on hammer and piano strings

Numerical experiments have been made on the piano string with a discrete model using a finite difference calculation procedure. The string model was previously applied to the guitar [A. Chaigne, J. Acoust. Soc. Am. Suppl. 1 88, S188 (1990)] and is now tested with experimentally obtained data for the piano. The numerical experiments include systematic variations of parameters such as hammer velocity and nonlinearity of the felt hammer and their influence on generated waveforms and spectra. Earlier physical experiments on pianos have provided data on the velocity of the hammer and the string. In addition, the hammerstring interaction force has been estimated by measuring the compression of the hammer felt during string contact. Recorded string tones and measured waveforms will be presented and compared with typical examples of those calculated.

初期たわみを有する弾塑性棒の縦衝撃による残留変形

Behavior of a slightly curved bar under longitudinal impact with a heavy rigid hammer at a low velocity was analyzed numerically, and the residual deformation of the bar was investigated. Dynamic elasto-plastic deformation was discussed for the bar subjected to the plastic strain of the same order as the elastic one. Because of difficulty in obtaining a closed form of solution for this problem due to geometric and material nonlinearity, the solid bar was replaced by a lumped-parameter model, and the equations of motion were integrated numerically.The stress at each point on the cross section was evaluated by taking account of a detailed deformation history of that point. The bending moment was calculated by integrating these stresses. This method has been confirmed to give more accurate results than using the conventional method for analyzing the behavior of bars of small slenderness ratios, in which the stress distribution over the cross section is highly nonlinear.The residual deformation of the bar was evaluated by the residual axial displacement of the struck end. The effects of the following two factors on the residual axial displacement were investigated; the ratio of the mass of the rigid hammer to that of the bar, and the impact velocity of the rigid hammer. As the result, it was shown that the residual axial displacement was expressed by the product of the power function of the mass ratio and that of the impact velocity.

Water hammer and propagation of perturbations in elastic fluid-filled pipes

A Korteweg—de Vries (KV) approximation is constructed in this paper for the perturbations being propagated in elastic pipes filled with fluid. On the basis of the approximation constructed and the equation obtained for the perturbations of a finite-amplitude velocity, the water-hammer phenomenon is analyzed in the Zhukovskii formulation, and the water hammer in systems with preliminary longitudinal tension is considered separately. Special attention in the study of the perturbations is paid to the signal structure and evolution in the hydraulic line. Taking account of the inertial properties of the pipe in the approximation mentioned permitted the indication of new effects, in principle, which are essential for applied problems of the propagation of perturbations in elastic hydraulic lines. In particular, it is shown that the initial signal can be doubled in such lines by redistributing its intensity over the frequencies. It is established that the origination of an oscillating forerunner is possible in hydraulic lines with preliminary tension. Starting with [1], the water-hammer phenomenon was investigated in many papers, in [2], for example. The main attention in these papers was paid to the propagation velocity of the water hammer and its intensity. After simplification, the initial system of Zhukovskii equations contains no mechanism hindering the twisting of the wave profile, and, therefore, there is no possibility of stationary shock formation within the framework of this theory. Moreover, the Zhukovskii theory of the water hammer and of propagation of perturbations in elastic pipes results in the conclusion that the wave structure, velocity, and amplitude depend essentially on the characteristics of the initial perturbation and can differ significantly from the water hammer predicted by theories for powerful signals in sufficiently long pipes.

Instrumentation for the Study of Impact Sound

Instrumentation will be described for the measurement of the relation between the total acoustic energy emitted by a floor when subjected to a mechanical impact and the striking velocity of the impact hammer. In addition, the mechanical force generated during the impact is measured. Some experimental results on a wooden floor and steel plate will be described. The relation between these measurements and the problem of standardizing routine impact sound measurements on floors will be discussed.