Impact Hammer Test Research Articles

Smart Graphene Nanoplatelet Strain Sensor for Natural Frequency Sensing of Stainless Steel (SS304) and Human Health Monitoring

The main purpose of this article is to monitor the natural frequency of stainless steel (SS304) with and without defect by spray-coated smart graphene nanoplatelet (GNPs)-doped poly (methyl methacrylate) (PMMA) nanocomposite strain sensor and human health by smart Lycra denim textile sensor. Methods such as impact hammer test and NI-daq, finite element method (FEM) simulation by Abaqus 6.12, and fast Fourier transform (FFT) study were applied for frequency monitoring of SS304. For human health monitoring, edema disease inspection, cough, and biceps locomotion were studied by graphene sol–gel textile sensor. We report eight sensors fabricated by scotch tape exfoliation method and their sensitivity was checked in terms of gauge factor (GF). The highest and lowest GF-based sensors were checked for sensitivity in the defect (hole) specimen. These sensors were used to sense the natural frequency of SS304 at three different positions in the cantilever beam. The same quantity of GNPs was used for making Lycra denim textile sensors for human health monitoring. The Lycra denim textile sensor showed a 216% change in resistance in the left calf muscle, which is less than right leg flexibility, indicating good sensitivity. In addition, the textile sensor helped in sensing coughing and biceps monitoring. The ease in fabrication and high sensitivity demonstrate the potential ability of GNPs for futuristic smart material for structural and human health monitoring.

Enhancement of vibration attenuation and shock absorption in composite sandwich structures with porous foams and surface patterns

In the present study, composite sandwich structures were investigated to evaluate the effects of porous foams and surface patterns on structural stability and mass reduction of the composite sandwich structures. The composite structures used in the experiments consisted of three layers; the top and bottom polycarbonate (PC) layers and the core porous foam layers. Copper, nickel, and polypropylene (PP) foams were considered in the modeling of composite structures. Laser cutting technology was applied to the top PC layers of the composite structures to realize the surface patterns. Impact hammer and mass drop tests were performed on the composite structures to investigate their vibration attenuation and shock absorption performances. Numerous combinations of composite structures were considered by varying the foam materials and layer thicknesses to determine the best configuration. Finite element method (FEM)-based simulations were conducted to verify the experimental results. The results of this study support the implementation of porous foams and surface patterns for the increase in vibration attenuation and shock absorption performance, while achieving mass reduction for various applications in the engineering field.

Research on Impact Resistance of Reinforced Concrete Beams Strengthened with Carbon Fiber Reinforced Polymer Grid and Engineered Cementitious Composites.

When reinforced concrete structures are subjected to impact loads, they may suddenly yield or fail, or even collapse as a whole. In this paper, the impact resistance of reinforced concrete (RC) beams strengthened with carbon fiber reinforced polymer (CFRP) grid and engineered cementitious composites (ECC) was studied. Drop hammer impact tests were conducted on eight beams, then the finite element model was used to simulate the impact test, finally a simplified two-degree-of-freedom (TDOF) model was proposed for CFRP grid reinforced ECC layer strengthened RC beams under impact loading. The results showed that CFRP grid reinforced ECC layer significantly improved the impact resistance of RC beams. When the ECC and CFRP grid were used, the crack development was inhibited after the concrete cracked in the tensile area, avoiding the brittle damage of concrete beams with one crack to the end. Compared with the control beam, the reaction force of RC beams strengthened with CFRP grid and ECC under impact load increased by 16.2%~34.5%, the maximum mid-span displacement decreased by 16.3%~31.6% and the mid-span residual displacement decreased by 36.02%~49.53%. The finite element model and the proposed TDOF mode were demonstrated to effectively simulate the strengthened beam under impact loading.

Dynamic crushing of uniform and functionally graded origami-inspired cellular structure fabricated by SLM

This paper investigated the dynamic crushing of a novel periodic origami-inspired cellular structure. The large-scale multi-layer metallic specimens considered geometry, anisotropy and gradient design were fabricated by an SLM system. Mechanical properties and energy absorption characteristics under dynamic load were investigated through drop hammer impact test. The results show that this novel structure has obvious negative Poisson's ratio (NPR) effect and relatively balanced mechanical properties in the three orientations under impact load. Among them, the z-axis orientation was the best bearing orientation. Three gradient modes of this structure were designed and tested for the first time. Results showed the gradient design effectively improved the energy absorption performance of this structure. Besides, high-speed tensile tests on the additively manufactured metallic coupons showed the strain rate effect and anisotropy of AM stainless steel 304L were significant. Corresponding Cowper-Symonds models were fitted. The numerical simulation reproduction based on LS-DYNA was validated to be well-matched with the test results. Parametric analysis showed that the initial folding angle was the crucial factor for the initial peak force, and the gradient growth rate can significantly affect the energy absorption of the structure.

The shape effect and mechanism of particle‐reinforced shear‐thickening gel composites

AbstractIn order to meet the requirements of practical applications, the shape effect of particles and their shear‐thickening mechanism is very crucial to the shear thickening gels (STG). In this work, three kinds of STG/particle composites were successfully prepared by blending nanoscale SiO2, microscale MWCNTs, and millimeter‐scale carbon fiber in STG. The Rheological Property, compression, and impact resistance of STG/particle composites were tested and analyzed. The results showed that the enhancement of the shear‐thickening properties of STG by nanoparticles was more pronounced than that of micrometer and millimeter‐sized particles. Nanoscale SiO2 significantly improved the storage modulus of STG, the G'max of STG/6%SiO2 increased by 124.63% compared with pure STG. Nanoscale SiO2 also had a great enhancement effect on the compression resistance of STG, the bearing capacity of STG/6%SiO2 and STG increased by 7.7 and 4.5 times. Furthermore, the energy absorption of STG/6%SiO2 and STG increased by 545% and 282% respectively. The drop hammer impact test also showed that STG/6%SiO2 had the best impact resistance. In addition, a possible mechanism of shear‐thickening properties of particle‐enhanced STG was proposed.

Run-Time Cutting Force Estimation Based on Learned Nonlinear Frequency Response Function

Abstract The frequency response function (FRF) provides an input–output model that describes the system dynamics. Learning the FRF of a mechanical system can facilitate system identification, adaptive control, and condition-based health monitoring. Traditionally, FRFs can be measured by off-line experimental testing, such as impulse response measurements via impact hammer testing. In this paper, we investigate learning FRFs from operational data with a nonlinear regression approach. A regression model with a learned nonlinear basis is proposed for FRF learning for run-time systems under dynamic steady state. Compared with a classic FRF, the data-driven model accounts for both transient and steady-state responses. With a nonlinear function basis, the FRF model naturally handles nonlinear frequency response analysis. The proposed method is tested and validated for dynamic cutting force estimation of machining spindles under various operating conditions. As shown in the results, instead of being a constant linear ratio, the learned FRF can represent different mapping relationships under different spindle speeds and force levels, which accounts for the nonlinear behavior of the systems. It is shown that the proposed method can predict dynamic cutting forces with high accuracy using measured vibration signals. We also demonstrate that the learned data-driven FRF can be easily applied with the few-shot learning scheme to machine tool spindles with different frequency responses when limited training samples are available.

Vibration control of laminated composite cantilever beam operating in elevated thermal environments using fuzzy logic controller

In the present study, vibration control of laminated composite cantilever beam operating in the elevated thermal environment is achieved using combined experimental and numerical techniques. The impact hammer test is performed on the glass-epoxy cantilever beam at different temperatures. Experimentally recorded impact hammer force signals and piezoelectric accelerometer time-domain signals are processed through a system identification toolbox in MATLAB to obtain transfer functions of the plant models. A robust fuzzy logic controller is developed to accomplish the effective vibration control of a cantilever composite beam operating at different temperatures. The fuzzy logic controller with two inputs and one output is designed using the 20 if-then rules. The results are presented in both frequency and time domain, keeping the vibration attenuation of the fundamental frequency as the point of interest. The results indicate the proposed fuzzy logic control strategy can attenuate the vibrations of a cantilever composite beam for a wide temperature range.

Dynamic properties of impact hammer operator and their influence on dynamics of lightweight structures

This paper considers the dynamics of a human in a crouching posture (assumed during manual impact hammer tests) and their influence on system dynamics. Intra-subject and inter-subject statistics for the dynamics of crouching humans are determined for three and nine test subjects, respectively. The average hammer operator's undamped natural frequency was 3.49 Hz with a damping ratio of 13.7%. Knowledge of the hammer operator dynamics is then utilised to identify the dynamic properties of the supporting structure in an unoccupied state. The results are verified on two fibre-reinforced polymer composite footbridges. Criteria for identifiability of the hammer operator-structure interaction are presented and used to identify bridge properties for which the hammer operator's influence on the structure can be compensated for.

Effects of recycled tyre rubber and steel fibre on the impact resistance of slag-based self-compacting alkali-activated concrete

Accumulation of waste tyres causes an environmental disaster because of the rapid rise in transport vehicle demand resulting from modern developments, Covid-19 and similar pandemics. Thus, recycling waste tyres in the form of aggregates as a sustainable construction material can be a solution to reduce the environmental problems. Current research focuses on the impact resistance and mechanical properties of the crumb rubber self-compacting alkali-activated concrete reinforced with 1% steel fibres (SFs) where fine and coarse crumb rubbers (CR) are partially replaced with 10% and 15% replacement ratios. The compressive, flexural, splitting tensile strengths and modulus of elasticity were investigated; impact resistance was found using a drop hammer impact test. The incorporation of CR reduced the mechanical properties, and the reduction was found more with increased rubber contents, whereas the incorporation of SF compensated for the strength loss. The impact performance was enhanced with the CR and SF incorporations. The 15% CR incorporation improved the impact energy up to three times, whereas both 1% SF and 15% CR incorporations significantly enhanced the impact energy up to 30 times. Similar mechanical strengths were obtained for the different sizes of CR. However, impact performance was significantly influenced by the sizes of CR.

Experimental and numerical investigation on transverse impact resistance behaviour of pipe-in-pipe submarine pipelines after service time

The transverse impact resistance behaviour of pipe-in-pipe submarine pipelines after 15 years of service is studied experimentally and numerically. From drop hammer impact tests of 4 full-scale specimens, the influence of specimens’ span, corrosion and dent defect on the transverse impact resistance is studied in terms of failure mode, impact force-time history curves, displacement-time history curves, strain-time history curves and impact force-displacement curves. The experimental results indicate that the dynamic failure process consists of four stages, including primary vibration stage, secondary vibration stage, stable stage and unloading stage. As the suspension span of the specimen increases, the primary failure mode changes from local indentation to global bending deformation. The corrosion and the dent defect impair the impact resistance. Finite element (FE) models are then established and verified through comparison with experimental results. Numerical analyses indicate that the total impact energy is mainly dissipated by the outer pipe and the inner pipe according to the energy dissipation analysis for each component of the pipe-in-pipe specimens under transverse impact load. Parametric study is implemented finally to disclose the influence of the dimensions of pre-existing corrosion and dent defect on the transverse impact behavior of pipe-in-pipe submarine pipelines.

Nonlinear visco-hyperelastic tensile constitutive model of spray polyurea within wide strain-rate range

Spray polyurea (SPUA) is widely used as a protective coating material for structures subjected to the intensive impulsive loadings, attributed to its prominent large tensile deformation capacity and strain-rate hardening effect. This paper aims to study the tensile properties of SPUA within a wide strain-rate range both experimentally and theoretically. Firstly, by reasonably designing the geometry and dimension of specimens, a series of quasi-static and dynamic uniaxial tensile tests were carried out, and the nonlinear stress-strain curves corresponding to the strain-rates ranging from 10−3 s−1 to 103 s−1 were obtained. It showed that the mechanical properties of SPUA are sensitive to the strain-rate, i.e., the elastic modulus and tensile stress increase with the rising of the strain-rate, while the fracture strain is linearly negatively correlated with the logarithm of strain-rate. Then, a nonlinear visco-hyperelastic (NVHE) constitutive model composed of a 3rd-order polynomial hyperelastic model and seven Prony series terms describing the viscoelastic properties were established, and the corresponding twenty-three model parameters were calibrated through a multi-objective optimization based on genetic algorithm. Furthermore, based on the finite element program ABAQUS/Explicit, the validations of the proposed NVHE model and the parameters determination approach are verified by the present tensile test and existing drop hammer impact test. This work could provide a helpful reference for the retrofitting design of the protective structures.

Mechanical Property Test and Damage Evaluation Analysis of Steel Fiber Stainless-Steel Reinforced Concrete Beams (SFSRCBs) under Impact Load

In this paper, the ultra-high drop hammer impact test system is adopted for the vertical impact experiment on six SFSRCBs with steel fiber volume fraction of 2.0% and build the relevant numerical model. The research variables mainly include impact energy, impact mass and cumulative impact mode. The results show that, under a single equal energy impact, with the increase of the impact speed, the crack distribution of the specimen gradually tends to the mid-span local position. Compared with the impact mass, the impact speed has a greater effect on the failure mode, deformation resistance and deformation recovery ability of SFSRCBs. When the total cumulative impact energy is the same as the single impact energy, then the overall damage of the specimen caused by high-mass low-velocity cumulative impact is less significant than that caused by low-mass high-velocity cumulative impact. Combined with the finite element analysis, the calculation formula of the maximum deflection of SFSRCB under impact load is obtained. Finally, the calculation method of the impact damage evaluation factor of SFSRCBs is proposed.

Influence of guideway friction on the cutting point receptance in machine tools

Motivated by the fact that the tool cutting point (TCP) receptance demonstrates significant variation between the idle and in-motion conditions of a machine tool, this paper studies the relationship between guideway friction and TCP dynamics. The fundamental effect is modelled and demonstrated on a laboratory testbench considering structural mechanics, servo dynamics, and guideway friction. The findings are then extended to an industrial-scale machine, for which improved measurement of the TCP receptance is obtained using a dedicated inertial linear actuator. Finally, practical in-motion impact hammer testing guidelines are proposed for more accurate characterization of the TCP receptance and chatter stability predictions.

Frequency response function simulation and evaluating in boring

Finite element method of simulating frequency response function (FRF) for boring tool in LS-Dyna solver is investigated in this work. Nowadays, computer numerical simulation allows to obtain FRF using different materials model with high precision compared to real experiments with sensors like impact hammer testing. This function is used in construction of stability lobe diagrams that allows operator of machining center to avoid chatter self-excited vibrations. Such vibration is led to decreasing of productivity and quality in cutting of metals and other materials. Amplitude and phase angle for the model is obtained from LS-Dyna result interpreter, that reads binary files, created during simulation by the program. Amplitude and phase angle of frequency response function are depending on dynamic stiffness of machining system. Real and imaginary part of frequency response function have been obtained during simulation. With luck of dynamic stiffness amplitudes of response increases. 

Dynamic response and failure mode of steel-concrete composite panels under low-velocity impact

There are two types of failure modes when a steel-concrete composite panel (SC panel) is subjected to low-velocity impact, local punching failure mode and overall flexure failure mode. Current studies have mainly focused on the former. To analyze the dynamic response process and mechanism of local punching failure, drop hammer impact test of seven SC panels, and static loading test of one SC panel have been completed. With increasing in impact energy, five types of damage patterns under the local punching failure mode appeared in turn. Comparing the residual deformation and the peak value of the membrane force, it could be concluded that reducing the spacing of tie bars improved the impact resistance of SC panels. The impact force-displacement curve of the drop hammer could be divided into five stages. Based on the dynamic response characterized curve and static loading test, a five-segment resistance function model for the entire process of impact response was proposed. The difference between the two failure modes of an SC panel under low-velocity impact reflected the different abilities to resist overall flexure failure and local punching failure. It also reflected the different method of energy dissipation. The criterion and formulas for distinguishing failure modes were proposed in this paper, and the calculation results were in good agreement with tests.

Experimental and Numerical Study of RC Square Members Under Unequal Lateral Impact Load

Reinforced concrete members under impact loading stress may be destroyed in a split period. Because of the need to investigate the impact resistance of reinforced concrete members, this issue remains a much-debated topic. This study investigates the response of reinforced concrete (RC) square members under an unequal lateral impact force. The performance of RC members under the effect of impact load is examined using a drop hammer impact test system. The importance of unequal lateral impact load is highlighted and addressed by examining RC members’ failure mode and dynamic response characteristics. Four types of RC members are experimentally investigated in detail. A finite element method (FEM) modeling is proposed to predict the impact responses of the RC members. Moreover, the effects of the impact position, height, and hammer mass on the dynamic response characteristics under an impact force are evaluated. The predictions of the proposed numerical model are validated against experimental results, emphasizing impact force history, deflection time history, and failure modes. Results indicate the viability of the FEM model. The findings from the experimental and numerical studies can improve the impact-resistant performance of reinforced concrete members.

Magnetorheological Elastomer based torsional vibration isolator for application in a prototype drilling shaft

Smart materials properties are altered using external stimuli such as temperature, pressure and magnetic field. Magnetorheological Elastomer (MRE) is a type of smart composite material consisting of a polymer matrix embedded with ferromagnetic particles. In the presence of an external magnetic field, its mechanical properties, such as stiffness, change due to the interaction between the magnetic particles, which have applications in vibration isolation. Unwanted vibration in machines can cause severe damage and machine breakdown. In this work, a semi-active vibration isolator using MRE is proposed for a potential application in a drilling system to isolate the torsional vibration. The MRE was fabricated with a 35% mass fraction (MF) consisted of silicon rubber and iron particles. It was fitted with aluminium couplers and attached to the shaft (drill string) to study its efficiency in vibration isolation under a magnetic field. Two tests were conducted on the drilling prototype setup used in this work; the first test was a hammer impact test. The torsional transfer function TTF analysis showed that the system’s natural frequency has shifted from 13.9 Hz to 17.5 Hz by the influence of increasing magnetic field around the MRE. The results showed that the continuous rotational vibration amplitude of the prototype is attenuated by more than 40%.

Study on vertical vibration and transmission characteristics of railway ballast using impact hammer test

The vertical vibration and transmission characteristics of ballast are key factors that affect the dynamic stability of railway track structures and control the settlement of ballasted beds. Therefore, the following study was conducted to explore this topic. Firstly, through an impact hammer test on a ballast sensor with embedding chip, the vertical vibration data of the ballast was accurately measured. Therefore, the vertical vibration characteristics of a single ballast can be studied. Then, the vertical vibration characteristics at different positions in the stack were obtained by embedding ballast sensors into a ballasted stack. Finally, combined with field tests, a discrete element numerical model was established, then the vibration transmission speed and diffusion angle in a ballasted stack were calculated. The results of this study show that the damping ratio of ballast particles is less than 0.1, and the natural frequency is above 1000 Hz. The damping ratio and natural frequency of ballasts are greatly affected by their shape. The damping ratio of a ballasted stack is greater than that of ballast particles, and its natural frequency is lower. This indicates that the ballasted stack has the attributes of a soft material. The vertical acceleration transmission rate of ballasts is lower at frequencies below 257.94 Hz. This shows that the vibration suppression ability of the ballasted bed is better in the lower frequency range. As the depth increases, the vertical vibration transmission speed of the ballast gradually decreases, as does the accumulated external force. In the impact hammer test of a ballasted box, the average vertical vibration transmission speed was calculated to be 0.88 mm/μs, and the ballast vibration was transmitted downward at a diffusion angle of 35.32°–54.51° from the direction of gravity.

Experiment and Simulation Study on the Dynamic Response of RC Slab under Impact Loading

Reinforced concrete (RC) slab is an important component in civil construction and protection engineering, and its dynamic response under impact loading is a complex mechanical problem, especially for two or multiple continuous impact loads. In this paper, a series of drop hammer impact tests were carried out to investigate the dynamic response of RC slabs with two successive impacts. The time history of impact force and the failure characteristic of the slab surface were recorded. Moreover, four influence factors, including slab thickness, reinforcement ratio, impact location, and drop hammer height have been discussed. Besides, a 3D numerical model based on the finite element method (FEM) was established to expand the research of constrained force, deflection, and vertical stress of an RC slab. The results show that increasing the slab thickness and reinforcement ratio can improve the impact resistance of an RC slab. The impact point location and drop hammer height have a great influence on the dynamic response of the RC slab. In addition, the RC slab will have more obvious damage under the second impact, but the dynamic response becomes weaker. It may be because of the local damage in the concrete caused by the first impact that would weaken the propagation of vibration.

Experimental study of the effect of GO/WMCNTs on the mechanical properties and impact response of magnesium‐based fiber metal laminates

AbstractIn order to investigate the effect of graphene oxide (GO)/multi wall carbon nanotubes (WMCNTs) on the mechanical properties and low‐velocity impact response of magnesium‐based fiber metal laminates (FMLs), the FMLs specimens reinforced with GO, WMCNTs or their mixture were prepared, and quasi‐static tensile and low‐velocity drop hammer impact tests were performed. The tensile test results showed that the mechanical performance of FMLs could be improved by adding a certain concentration of nanoparticles. The tensile strength increased by 14.9% and 26.6% when the concentration of GO or WMCNTs is 0.6 wt%, respectively. Due to the agglomeration phenomenon, there are the opposite effect for the tensile strength of FMLs when the particle concentration is excessive. After the mixture of GO and WMCNTs was added to the epoxy matrix, the tensile strength of FMLs could still be increased by 12.8% at the GO to WMCNTs ratio of 0.6:0.9 (the overall concentration of particle is 1.5 wt%). And the elastic modulus is also significantly increased, but it has a negative effect on the ductility. The low‐velocity impact test results showed that the FMLs reinforced a mixture of GO and WMCNTs have greater peak impact load due to the lager stiffness. The FMLs reinforced with WMCNTs have better energy absorption capacity under impact load due to lager damage area.