Impact Hammer Research Articles

On dynamic response and damage evaluation of bridge piers under far-field explosion loads

This paper aims to investigate of the dynamic response and damage mechanism of typical bridge piers under far-field explosions numerically and develop a feasible scheme for rapid damage evaluation of bridge piers. An ANSYS-AUTODYN-based explicit finite element formulation is introduced in which the dynamic input method of blast waves is developed using subroutines. The tests of drop hammer impact and far-field explosion are referenced to verify the reliability of the formulation and the mesh scale applicable to beam-column members is determined. Based on the validated formulation, the refined fluid–solid coupling models of typical single-column and double-column piers are established to explore their far-field blast responses. The effects of input parameters (i.e., the strength and angle of the blast wave,) on the pier response are analyzed. It is demonstrated that bending damage occurs in bridge piers is similar to that of cantilever beam under different strength loads, while the damage of double-column pier members under the constant displacement increases with the increase of the blast wave angle. By incorporating the crack distribution, quantitative assessing criterion and P-I diagram, a damage evaluating scheme is proposed and the damage regularities of piers under far-field blast loads are acquired. The present work can serve as a valuable reference for blast-resistant design and damage assessment of bridge piers under far-field blast loads.

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.

Piezo sensor based multiple damage detection under output only structural identification using strain modal flexibility

Strain, being superiorly sensitive towards damage, has been widely explored in modal testing based damage monitoring. Piezo sensors have been successfully evaluated for their sensitivity toward incipient damage detection in experimental modal analysis under forced excitations based experimental modal analysis. However, the efficacy of piezo sensors for damage monitoring under operational/ambient conditions is yet to be investigated in depth. This study addresses this gap by evaluating a scaled-down bridge model under pedestrian motions for damage monitoring by piezo sensors under operational modal analysis (OMA). Artificial damage is created by introducing a vertical cut at four locations with two different intensities. Displacement and strain responses are measured using accelerometers and piezo sensors, respectively, and corresponding displacement and strain based modal parameters are extracted using impact hammer and under operational pedestrian motions. Modal flexibility based curvature and coordinated modal assurance criteria (CoMAC) are employed for damage monitoring. Variation in modal flexibility based curvature is adopted as damage sensitive feature (DSF). rComac is defined as the difference of CoMAC from unity and is also adopted as DSF. Mahalanobis distance based outlier analysis proves the strain-based DSF’s superiority to the displacement-based DSFs for damage monitoring, especially for the incipient damage states. CoMAC is observed to possess higher sensitivity than the curvature for incipient damage. Neighbouring sensor locations exhibit potential damage in higher damage states with Mahalanobis distances higher than the critical value. It is found that the CoMAC-based damage strategy is better approach toward damage monitoring combined with curvature as DSF. In overall, the piezo sensors are successfully established as effective strain sensors for damage monitoring in OMA under output-only identifications.

COMPARISON OF THE COMPRESSION TEST AND THE REBOUND TEST FOR EVALUATING THE BRAND OF CONCRETE IN PRECAST REINFORCED CONCRETE ELEMENTS

This paper will provide information about the concrete brand produced in the factory for the prefabricated elements and the comparison of the results given by the test of resistance to compression and the results of the test of the hammer impact of the sclerometer. The idea and the need to conduct this study arose for 2 main reasons: first, from the poor results often obtained from sclerometer impact to the elements in the field, despite the compression resistance test with cubic samples taken in the concrete cast and the carrot test directly on the element assembled in the building provides good results. Secondly, to have a connection between the values ​​of the concrete brand resulting from the pressure resistance test with a press performed in the laboratory and the impact test with the sclerometer hammer which is often performed in the field under different conditions. The sclerometer impact tests will be performed on each cube sample before it is broken, in the press, and the sclerometer impact tests will be performed on the concrete elements from which the cube sample was taken on the day that this sample will be destroyed. The predicted results are relatively close values ​related to the age between 14th day and the 28th day of the concrete maturity, as determined by the manual of the sclerometer that the study is going to use, and other close values ​​for the other days (1, 3,7,14,28). But in fact, just like in the field tests done before, it is noticed that the results obtained from the blows with the sclerometer hammer are weak. The aim of the paper is finding a logical connection between the results of these 2 types of tests. This study will contain information on the composition of the concrete produced in the IXHEM SHPK factory (ltd) located in Durres - Albania, the brands of concrete on different days for different elements, and the comparison of the results between the 2 methods mentioned above.

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.

In situ approach to characterize effects of pile-driving on black sea bass behavior, Centroprisits striata

With the threat of climate change and global energy demands rapidly growing, offshore wind farms are quickly becoming a contender in renewable energy strategies in countries around the world, including the United States. In the US, numerous offshore wind turbines are in the planning process for coastal Mid-Atlantic waters, spurring investigation into potential effects of the high-intensity construction noise on local species. Black sea bass, Centropristis striata, is a commercially important mid-water fish that inhabits these same waters and are reported to experience behavioral changes in response to pile-driving, although only demonstrated in the lab. Verification and expansion on these results requires an in situ approach to minimize tank effects on sound propagation and animal behavior. This study, conducted in coastal waters of Woods Hole, MA, used video observation to characterize behavior of 40 caged black sea bass before and during 15-min bouts of actual impact and vibratory hammer pile driving, repeated 5 times per day. Pressure and particle motion were measured. We examined immediate reactions to the onset of noise, prolonged behavioral changes, and habituation. Initial results show increased hiding or sheltering behaviors, as well as bursts of escape-motivated movements in response to the noise. While preliminary, the results suggest that pile driving can induce a range of behavioral impacts on this important fisheries species, and some concern is warranted with respect to offshore wind development.

Measured changes in the bridge mobility and radiativity of violins due to material creep following tensioning of strings

Violins have been observed to undergo a small, but measurable, deformation of the corpus after being brought into tune following a prolonged period without string tension. This behavior, which is analagous to the flexing of a bow, can be attributed to the viscoelastic properties of wood. Because of the relatively long time scale of deformation, the process is sometimes referred to as material “creep.” To assess the impact of creep on the sound of a violin, we measured the vibrational and acoustic response of multiple violins during this period of deformation. The measurement process involves tapping the bridge with a small modal impact hammer and recording the velocity response of the top plate using a laser Doppler vibrometer, as well as the far-field acoustic response in an anechoic chamber. Results show modest changes in the amplitude of the main body modes, most notably the CBR and B1- modes, and a consistent shift in the peak frequency of higher modes, over a two-day period after the strings were tuned.

Vibro-acoustic characterization of the bone-implant system during insertion

The femoral stem primary stability achieved by the impaction of a beam called “ancillary” attached to the implant during its insertion is an important factor of success in cementless surgery. However, surgeons rely on their proprioception, making the process subjective. The use of experimental modal analysis (EMA) without sensor nor probe fixation on the implant or on the bone is a promising non-destructive approach to determine implant stability. This study investigates whether EMA performed directly on a beam, which is temporary fixed to the implant during its insertion, could provide information on the boundary condition, which corresponds to the implant stability. A cementless femoral stem was inserted into 10 bone phantoms of human femurs and EMA was carried out on the ancillary using a dedicated impact hammer for each insertion step. Two bending modes were identified in the frequency range 400–8000 Hz for which the resonance frequency was shown to be sensitive to the insertion step and to the bone-implant interface properties. A significant correlation was obtained between the two modal frequencies and the implant insertion depth (R² = 0.95 ±0.04 and R² = 0.94 ±0.06). This study opens new paths towards the development of noninvasive vibration-based evaluation methods to monitor cementless implant insertion.

Experimental Study on the Vibration Transfer Function of a Small Autonomous Underwater Vehicle

This paper presents the experimental results about vibration characteristics of a small autonomous underwater vehicle (AUV) named OKPO 300. The autonomy of AUVs leads to the increased use of AUVs in scientific, military, and commercial areas because their autonomy makes it possible for AUVs to be utilized instead of humans in hazardous missions such as mine countermeasure missions (MCMs). It is impossible to use devices with electro-magnetic waves for gathering information in an underwater environment. Only sonar systems that use sound waves can be utilized underwater, and the performance of sonar can strongly affect the autonomy of AUVs. Since a thruster system that combines a motor and propeller in a single structure is widely used as the propulsion system of an AUV and is mounted on the outside of the AUV’s stern, the vibration generated by the thruster system can be transferred throughout the shell of the AUV from the stern to the bow. The transferred vibration can affect the performance of various sonar systems that are installed in the AUV such as side-scan sonar or forward-looking sonar. Therefore, it is necessary to identify the effect of the transferred vibration of the AUV on the sonar systems. Even if various numerical methods were used to analyze the vibration problem of surface ships, it would be hard to apply numerical methods of the surface ships to identify the vibration phenomena of an AUV because of the underwater environment. In this work, an experimental study with OKPO 300 and an impact hammer was carried out to analyze vibration features of an actual small AUV in the air. Based on the experimental results, the frequency response function of vibration is presented. Based on the experimental results of this study, the natural frequency of OKPO 300 was confirmed, and the possibility of estimating the vibration characteristics of AUV using the transfer function method was shown.

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.

Residual load-carrying performance of CFRP strengthened RC beam after drop hammer impact

Carbon fiber reinforced polymer (CFRP) external bonding is a common approach to strengthen the bearing capacity of the reinforced concrete (RC) members. In this study, two types of RC beams, i.e., CFRP strengthened beam and conventional RC beam, were tested under drop hammer impact and subsequent quasi-static loading. The strengthening effect of the CFRP on the dynamic responses, failure modes and residual load-carrying performance of the RC beams were fully investigated. Then, a high-resolution explicit numerical simulation was conducted to further investigate the residual load-carrying mechanism of the CFRP strengthened beam. The experimental results demonstrate that even though the CFRP sheet peels off from the soffit of the investigated beam instantaneously upon impact, which provides a little contribution to the impact damage elimination in the mid-span of the beam, the oblique cracks within the flexure-shear zone were reduced moderately. Further, the bonded CFRP sheet can effectively reduce the maximum and residual displacement of the beam and improve the recovery performance of deformation. In addition, the residual resistance, residual stiffness and post-impact energy absorption capacity of the beams with CFRP are shown to be higher than those of the unstrengthened ones. The experimental and numerical results both show that the effective anchoring approach has an important effect on the residual loading performance enhancement. Larger impact energy and more significant impact dynamic effect tend to degrade the bearing performance of the beam more.

A simplified non-axisymmetric pile-soil interaction model for pile integrity testing analysis

A simplified model of non-axisymmetric pile-soil interaction (NPSI) that considers both vertical and radial motions of the pile body is developed and applied to the investigation of pile integrity test (PIT) with eccentric hammer impact. The pile is treated as a simplified three-dimensional (3D) continuum and the soil along the pile shaft is simulated as a series of independent thin soil layers, while the soil under the pile base is defined by the fictitious soil-pile model. Theoretical solution of the velocity-time history of each point on the pile top section is deduced by integral transformation technique. Based on the NPSI model, characteristics of test signals of PIT for large-diameter piles under non-axisymmetric condition are analyzed. The optimal testing position for acquiring signals, which minimizes the influence of high frequency (HF) interference resulting from the pile body 3D effect, is identified. Findings from this study provide the basis for accurate interpretation of the PIT of large-diameter piles with eccentric hammer impact.

Comparative study on the low-velocity impact properties of unidirectional flax and carbon fiber reinforced epoxy plates

Flax and carbon fibers reinforced polymer composites have high potentials to be used as sustainable building materials. To understand the impact resistance of these fiber composites, the present article studied the impact resistance of unidirectional flax fiber and carbon fiber reinforced polymer (FFRP and CFRP) composite plates. The impact response, damage resistance, and impact tolerance were investigated using drop hammer impact and compression after impact (CAI) tests. The internal damage of FFRP and CFRP due to impact loads was studied using acoustic emission technology. In addition, the development process of impact damage was analyzed. CFRP plates show a higher specific energy absorption rate than that of FFRP, because of the more serious internal damage and brittle fracture tendencies. Matrix cracking was the primary damage in FFRP and CFRP under impact load. Compared with CFRP, FFRP possesses a higher CAI due to less damage. Further expansion of the matrix crack caused by the original impact occurs in the impacted fiber-reinforced polymer composites (FRP) under a compressive load.

Protective Behaviors of Bio-Inspired Honeycomb Column Thin-Walled Structure against RC Slab under Impact Loading.

In order to protect the reinforced concrete (RC) slab structure from damage under some accidental conditions, such as impacting and explosion, we used bio-inspired honeycomb column thin-walled structure (BHTS) to serve as a buffer interlayer for the concrete structure inspired by the biological structure of beetle's elytra. The mechanical properties of AlSi10Mg used to fabricate the BHTS buffer interlayer were determined by low- and medium-speed uniaxial compression tests and numerical simulations. Subsequently, based on the drop weight impact test models, the effect of the buffer interlayer on the response of the RC slab under the drop weight tests with different energy input was compared by the impact force and duration, maximum displacement and residual displacement, energy absorption (EA), energy proportion, and other indicators. The results show that the proposed BHTS buffer interlayer has a very significant protection effect on the RC slab under the impact of the drop hammer. Due to its superior performance, the proposed BHTS buffer interlayer provides a promising solution for EA of augmented cellular structures widely used in defensive structural components, such as floor slabs, building walls, etc.

Dismantling of Reinforced Concrete Using Steam Pressure Cracking System: Drilling and Crack Propagation

This study investigated a new dismantling system for concrete structures using a steam pressure cracking agent. We improved the mechanical systems such that it can drill through reinforcing steel bars. Therefore, the control method of the system and shape of the drill tip were improved. When the drill tip is stuck with chips and stopped, it is automatically pulled out and reinserted to recover the rotation. By changing the tip angle of the drill bit from 75° to 90°, it became possible to cut reinforcing bars, which were difficult to cut previously. In addition, we designed a crawler-type mechanical system and improved it such that it can be moved to the appropriate position and operated at any angle. This study revealed that the energy required for the drilling process accounts for more than 90% of the total dismantling energy. Through experiments using an impact hammer drill and observations of fracture surfaces using a three-dimensional scanner, we analysed the characteristics of reinforced concrete. In addition, the feasibility of the design for dismantling reinforced concrete was confirmed based on the determined energy associated with crack propagation.

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.

Learning to Break Rocks With Deep Reinforcement Learning

This work proposes a scheme for learning how to break rocks with an impact hammer. The problem is formulated as a Partially Observable Markov's Decision Process, and then solved through deep reinforcement learning. We propose a simple formulation, requiring only a basic sensorization of the hammer's manipulator, and involving just two discrete actions. We use Dueling Double Deep-Q Networks to parameterize the policy, and wield it with an auxiliary output. The proposed auxiliary task is also trained in simulation, and allows deciding when to stop the operation by detecting the absence of a rock from the observed joints' movement. The resulting policy is tested in a real world experimental environment, using a Bobcat E10 mini-excavator, and various rock types. The results show that a good performance can be obtained in a safe, and robust manner. A video showing some of the obtained results is available in <uri xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">https://youtu.be/tMqDJjK6zPo</uri> .

Numerical and experimental investigation of the narrow-band impact sound insulation of layered floors

Measurement results of the impact sound insulation of (floating) floors are generally limited to one-third octave bands. As a consequence, detailed information on modal behavior and on the influence of the impact source, are largely lost due to band-integration. To this end, narrow-band measurements are performed on five different layered floors. Various tapping machine locations are considered and the results are averaged over several receiver positions for each tapping machine location in order to reduce the influence of the spatial distribution of the sound pressure in the receiver room. A new prediction model for impact sound transmission, termed the modal TMM, or mTMM, is used to interpret and investigate the measurement results. This prediction method includes a detailed source model and accounts for the finite dimensions of the layered floors. The measurement results of the layered floors clearly indicate the importance of considering all five impact hammer locations of the tapping machine to achieve a high prediction accuracy, especially at low frequencies. The influence of the impact source and the modal behavior of the floor can lead to high peaks in the radiated sound power level.

Transient longitudinal waves on impact excited viscoelastic rods with lateral inertia.

An analytical and numerical Fourier transform based approach is presented to investigate the space-time dependence for the longitudinal velocity resulting from the longitudinal impact force excitation of viscoelastic rods with lateral inertia. A one-dimensional dissipative Rayleigh-Love wave equation including material memory, dissipation, and/or transverse effects due to Poisson coupling is developed from a generic model of the time dependent stress strain relationship for the rod material. A Gaussian signal with a suitable time scale is used to represent the hammer impact forces. Fourier transform, standing wave, and modal methods are utilized to develop analytical solutions for the longitudinal velocity resulting from the impact excitation of semi-infinite and finite length free-free elastic rods with no transverse effects to provide a baseline and segue to analogous results for viscoelastic rods with transverse effects. Numerical results from an FFT approach are presented to illustrate the effects of material losses and transverse effects on attenuation and dispersion in viscoelastic rods using the Kelvin-Voigt model for the constitutive equation of the rods.

Measured effect of resilient edge joints on airborne sound insulation of heavyweight wall

It is common assumption that resilient joints around a heavyweight construction improve sound insulation between adjacent rooms. Effect of resilient joints on sound insulation has not been studied sufficiently. This study investigated how the joint resiliency around a heavyweight wall affected sound reduction index (SRI) measured directly through the construction. A calcium silicate block wall was built three times in a laboratory using three different joint types A−C between the wall and the building frame: A) all four edge joints rigid, B) three resilient and one rigid joint, C) all four joints resilient. SRI was determined for A−C. Total loss factor (TLF) was determined for A−C by measuring structural reverberation time using hammer impact stimulus. SRI reduced, remarkably, with increasing level of joint resiliency. For joint type A Rw was 50 dB while it was 45 dB for B and 43 dB for C. Correspondingly, TLF reduced with increasing level of resiliency. The effect of joint type was evident above the critical coincidence frequency 185 Hz of the wall. Resilient joints prevented the sound transmission to the building frame, which increased sound radiation to the receiving room. Therefore, heavyweight wall should be mounted to surrounding heavy constructions using rigid joints.