Impact Loading Experiments Research Articles

Non-contact impact load identification based on intelligent visual sensing technology

Accurate identification of impact loads is vital for structural assessment and design. Traditional methods rely on complex equipment, such as accelerometers or strain gauge, which can be expensive and prone to failure. This study introduces a non-contact intelligent identification approach incorporating visual sensing technology, providing a convenient means to identify impact loads. Numerical simulations explore the differences in identifying impact forces through acceleration and displacement responses, particularly by considering such variables as measurement noise and number of measurement points. A meticulously designed experiment verified the feasibility of the proposed method for measuring the displacement and velocity of rapidly moving targets, and evaluated its performance in terms of accuracy. A series of impact loading experiments were conducted on a simply supported girder bridge model to validate the effectiveness of the proposed impact force identification method. Results indicate strong agreement between displacement response measurements and percentile meters. The proposed non-contact method accurately identifies single or continuous impact loads, with a minimum peak relative error of 0.2%. This study represents a pioneering application of intelligent visual sensing technology in the field of impact load identification. Moreover, the current research introduces a novel approach to address the challenges faced by conventional methods in identifying impact loads. Future research can leverage the groundwork laid by this study to further optimize and expand the proposed method, enhancing its capabilities and fully harnessing its potential to offer advanced solutions in structural health monitoring.

Influence of dynamic load and water on energy accumulation and dissipation in sandstone

In various engineering projects such as mineral extraction, hydropower resource utilization, railway construction, and geological hazard mitigation, rock engineering is often encountered. Furthermore, dynamic loads and moisture content exert notable influence on the energy transformation processes within rocks. Yet, the specific interplay of dynamic loading and water's impact on the energy conversion mechanism within the sandstone remains unexplored. To address this gap, this study conducted impact loading experiments on sandstone, elucidating the rock’s mechanical response under these conditions and unraveling the underlying energy conversion mechanisms. It was observed that the strength of sandstone exhibits a direct correlation with impact velocity. Moreover, employing energy calculation principles, we established a connection between moisture content and the sandstone’s internal energy conversion properties. The study also delved into the microscopic fracture mechanisms within the sandstone, ultimately concluding that both water content and dynamic loading have a significant impact on these microscopic fracture mechanisms.

Failure characteristics and conditions of rock-coal combination structure with weak layer under dynamic and static stresses

To comprehensively understand the mechanical response of a rock-coal combination structure containing a weak layer, a series of laboratory static loading and impact loading experiments were conducted. The results showed that under static load, the sliding process of the rock coal structure was relatively slow, and fragments can be observed. Under the action of horizontal impact loading, the whole coal stratum slipped out rapidly, and the process lasted only 0.05 s. Under the horizontal and axial impact loads, the coal stratum remained stable first, and then it slipped out as a whole under the action of static load. Additionally, a sliding instability criterion of a rock coal structure containing a weak layer was established based on theoretical analysis. The key parameter P value was checked through a numerical simulation experiment. It was found that the value was linearly related to the mechanical properties of the weak layer and overburden stress, and the experimental results coincided with the theoretical results. Finally, the relationship between sliding rockburst and strain rockburst was discussed, and these results can provide an important scientific basis for the prevention and control of dynamic disasters in deep mining.

Impact mechanical properties of frozen soil after experiencing freeze–thaw cycles: Experimental and numerical study

When frozen soil serves as the foundation of engineering facilities in cold regions, it often suffers from the combined action of freeze–thaw cycles (FTC) and impact loading, which changes its stability and reliability. This study analyzed frozen soil by conducting FTC experiments with varying FTC numbers and impact loading experiments under varying strain rates. The experimental results revealed that frozen soil exhibited FTC and strain rate effects. The peak stress of frozen soil gradually weakened with a decrease in the strain rate and an increase in the FTC number. The expansion stress caused by the water–ice phase transition during an FTC was investigated, assuming that the expansion stress was comparable to the cyclic load, and the deterioration mechanism of frozen soil under the FTC action was discussed. An expression of FTC damage was derived using thermodynamic and continuous damage mechanical principles. A finite element model of frozen soil, derived from the cohesive zone model, was established by inserting cohesive elements into the common surfaces between solid soil elements. A traditional traction–separation (T–S) model for cohesive elements was improved by considering the influence of the strain rate using the overstress model. An elastic–plastic model was used to model the solid elements. The improved T–S model and elastic–plastic constitutive law were used to implement a numerical simulation via a user subroutine VUMAT integrated in ABAQUS/Explicit. When the FTC damage was considered, the microcrack evolution and impact mechanical behavior of frozen soil under impact loading after experiencing FTC action were observed. Having compared the numerical results with the experimental data, it is concluded that a good experimental–numerical correlation was obtained.

Effects of fiber and rubber materials on the dynamic mechanical behaviors and damage evolution of shotcrete under cyclic impact load

Dynamic loads in underground construction environments can significantly damage supporting structures. The mechanical behavior of shotcrete under high strain rate impact has received significant attention. However, few researchers have investigated the performance degradation law, damage evolution process, and failure mode of shotcrete under cyclic impact load. This study utilized the split Hopkinson pressure bar (SHPB) to conduct cyclic impact loading experiments on shotcrete reinforced with copper-plated steel fiber (CSF), basalt fiber (BF), polypropylene fiber (PF), and rubber particles (RP). The addition of reinforcing materials significantly improved the dynamic mechanical properties of shotcrete. Under cyclic impact, the stress-strain curves of reinforced shotcrete basically coincided in the elastic deformation stage. As the content of the reinforcing materials increased, the dynamic mechanical properties of the shotcrete improved. The performance of fiber-reinforced shotcrete improved under the compaction effect caused by the first impact. Only rubber shotcrete sustained 6 impacts under cyclic constant impact pressure. Based on the ultrasonic velocity obtained by non-destructive testing, a cumulative damage evolution model during cyclic impact was established. The incorporation of RP effectively slowed down the damage evolution rate and increased the shotcrete's bearing capacity for cumulative damage. This paper conducted a comprehensive comparative analysis and concluded that the addition of rubber particles at a content level of 5% was the most cost-effective option to enhance the dynamic mechanical properties of shotcrete. The findings provide a theoretical reference for underground engineering supporting structures subject to long-term cyclic dynamic loading.

Dynamic impact constitutive relation of 6008-T6 aluminum alloy based on dislocation density and second-phase particle strengthening effects

To investigate the mechanical properties and constitutive relationship of 6008-T6 aluminum alloy under dynamic impact loading, dynamic impact and microscopic experiments were conducted on 6008-T6 aluminum alloy. The results demonstrated that 6008-T6 aluminum alloy exhibits strain hardening effects. As the loading strain rates increased, the grains became more refined, whereas the dislocation density and number of second-phase particles (mainly Mg2Si) increased. Several dislocations interacted with each other, thereby preventing further dislocation movement and improving the material's strength. The precipitation of second-phase particles impeded the motion of dislocations and increased the flow stress of the material. A constitutive model of dynamic impacts was developed based on the evolution of dislocation density and reinforcing effects of second-phase particles. Furthermore, based on the isotropic assumption, the damage evolution equation of 6008-T6 aluminum alloy was obtained by introducing the energy release rate. By combining the dynamic constitutive model of materials under dynamic impact compression conditions, the dynamic constitutive model of materials was obtained under dynamic impact tensile conditions. Moreover, the rationality of the model was confirmed by comparing the model's data with experimental data. In this study, we examined the macro mechanical response, microstructure, and dynamic mechanical behavior of the 6008-T6 aluminum alloy under dynamic impact conditions, which can serve as a theoretical basis and analytical tool for the structural design and safety evaluation of high-speed trains.

Dynamic Mechanical Behaviors of Rock's Joints Quantified by Repeated Impact Loading Experiments with Digital Imagery

Dynamic Mechanical Behaviors of Rock's Joints Quantified by Repeated Impact Loading Experiments with Digital Imagery

Dynamic Deformation and Perforation of Ellipsoidal Thin Shell Impacted by Flat-Nose Projectile.

Experimental and theoretical studies were carried out on the dynamic deformation and penetration response characteristics of metal ellipsoidal thin curved shells under impact loads. The deformation characteristics of the impacted ellipsoid shell was investigated via the use of a light gas gun to carry out impact loading experiments at different speeds. Ten cases of experiments were conducted with the impact velocities distributed between 25.69 m/s and 118.97 m/s. Stereo digital image correlation (3D-DIC) technology was applied to capture the dynamic deformation and penetration process of the impacted shell. The recovered shells were measured, and the deformation characteristics were analyzed, along with the dynamic evolution, as observed through 3D-DIC analysis. Based on the experimental results, the displacement mode was summarized and the displacement distribution of the locally impacted ellipsoid shell was proposed. The governing equations were derived for the dynamic deformation and penetration of the impacted ellipsoid shell by means of the Lagrange equation. The proposed theoretical model was verified based on the experimental results. Finally, the influence of the curvature distribution on the impact resistance of ellipsoidal shells is discussed. The results indicated that the proposed theoretical model was effective in analyzing the large deformation and the penetration speed. Stretching the axial length of the ellipsoid shell in the impact direction improved its resistance to penetration. Stretching the axial length of the ellipsoid shell perpendicular to the impact direction improved its resistance to deformation, but reduced its resistance to penetration. Maintaining the triaxial ratio and appropriately reducing the size of the ellipsoidal shell improved its resistance to both deformation and penetration. The above research provides a reference for the analysis of the impact resistance of thin-walled curved shell structures in engineering.

On Numerical Modeling of Fiber Deformation and Destruction under Impact Load

The motion, deformation, and destruction of a thin fiber under the action of a transverse shock load are numerically simulated. The fiber is described by the equations of Rakhmatulin’s theory. The system of dynamic equations is solved using the finite-difference method. The parameters for the model can be obtained directly from impact loading experiments, so the dependence of the material properties on the strain rate can be taken into account. Numerical results for aramid fibers under impact load are presented. Loading modes with and without fiber breakage are considered. A direct comparison of the numerical and experimental data is presented. A good agreement between them is demonstrated. The resulting validated numerical model of a single fiber can further be used to describe a fabric material as a system of interacting fibers.

Non-contact monitoring and evaluation of subsurface white etching area (WEA) formation in bearing steel using Rayleigh surface waves

The extreme dynamic loading on bearings during transient operating conditions in wind turbine gearbox instigates white etching area (WEA) formation and abrupt premature cracking. Thus there is much interest in developing an appropriate condition monitoring system to predict premature bearing failures instead of destructive microstructure analysis. Recently, guided ultrasonic waves have been extensively used for health monitoring of engineering components. This feasibility study aims to detect subsurface WEA formation using ultrasonic surface (Rayleigh) waves. WEA is replicated from impact loading experiments at 2 GPa contact pressure, with loading frequency 4.5 Hz on AISI 52100 bearing steel balls by varying test durations. Rayleigh wave signatures of the ball were analysed before and after experiments to recognize microstructural changes and confirmed using destructive microstructural analyses.

Effects of frost-damaged reinforced concrete beams on their impact resistance behavior

Impact loading experiments were conducted to clarify the impact resistance behavior of frost-damaged reinforced concrete (RC) beams. The load-bearing performance and their response deflections were evaluated based on the energy conservation concept. The experimental results indicated that 1) when frost deterioration occurred on the top face, the compressive failure of the top concrete was significant; and the response deflection increased, and 2) when frost deterioration occurred at the bottom face, the response waveform was almost identical to that generated when no deterioration occurred; however, the bottom cover concrete peeled off during elastic stress wave propagation.

On the effect of aluminum and chromium on the deformation twinning of body-centered cubic iron

This paper reports on investigations on the effect of aluminum and chromium on the formation of deformation twins in body-centered cubic iron. For this purpose, impact loading experiments (ε = 104 s−1) were carried out at room temperature on samples of iron and the alloys Fe-10at.-% Al and Fe-10at.-% Cr. Furthermore, the grain size was varied in order to consider the effect of the alloying elements for both fine-grained and coarse-grained microstructures. The investigations on twin formation were carried out by electron backscatter diffraction (EBSD) and by quantitative image processing using optical microscopy. The observations show a comparable twin portion in iron and Fe 10at.-% Cr after impact loading for both grain sizes. In the alloy Fe-10at.-% Al the portion of twins is significantly increased for fine-grain and coarse-grain state. In order to clarify the possible reason, X-ray diffraction analyses (XRD) were additionally carried out. These show a shift in the reflexes which can be attributed to an elastic distortion of the lattice. This lattice distortion due to the formation of solid solution correlates very well with the determined twin fractions.

Damage evaluation and protection method of resin pipe for gas conduit subjected to impact load

Medium-density polyethylene pipe has been widely introduced to low-pressure gas pipes because of its high flexibility and corrosion resistance. However, many third-party damages due to the impact of heavy equipment have been reported during the construction every year, thus, to prevent the third-party damage, materials such as high-density polyethylene and polyamide have been considered as the new gas pipe candidates. However, their impact resistance capacity under the third-party attack has not been clarified. In this study, static and impact loading experiments were conducted to compare load resistance capacities. As a result, it was revealed that the high-density polyethylene pipe and the polyamide pipe had higher static load capacity and impact resistance than the medium-density polyethylene pipe. By comparing the absorbed energy of the static test and the impact test and calculating the pseudo absorbed energy of the impact test, the evaluation formula judging the safer side of whether the penetration occurred was proposed. Furthermore, as one of the methods to protect the gas pipe, the protective effect of winding a sheet made of reinforced fiber and non-woven fabric was clarified.

Effect of thermal treatment on energy dissipation of granite under cyclic impact loading

Abstract High temperature treatment causes thermal damage to rocks in deep mining. To study the thermal effect on the energy dissipation of rocks during the dynamic cyclic loading, cyclic impact loading experiments of heat-treated rocks were carried out using the splitting Hopkinson pressure bar (SHPB) experimental system. The correlations among the energy dissipation, energy dissipation rate, impact times, accumulated absorbed energy per volume, failure mode and temperature were analyzed. The results show that the reflected energy under the first impact increases and finally exceeds the absorbed energy when the temperature increases; however, the total reflected energy decreases above 200 °C. The absorbed energy under the first impact and the total absorbed energy all decrease as the temperature increases, the rates of which decrease accordingly. And the same phenomenon appears for the transmitted energy and the rate of the transmitted energy. On the contrary, the rate of the reflected energy increases with the rising temperature. When the temperature increases, the fewer impact times are needed to destroy the sample. In addition, the failure modes are different when the rock is treated at different temperatures; that is, when the temperature is high, even though the absorbed energy is low, the sample breaks into powder after several impacts.

Dynamic Weakening of Sandstone Subjected to Repetitive Impact Loading

Dynamic weakening is commonly observed when stone is subjected to a single or repetitive impact loading. In a series of impact loading experiments conducted using the split Hopkinson pressure bar system with external confinement pressure, we observe evident nonlinear dynamic response for each impact loading, an accompanying dynamic weakening effect, and significant plastic deformation of the specimen. The dynamic response can be predicted accurately by the nonlinear granular model (Johnson and Jia in Nature 437:871–874, 2005). In the framework of statistics, an analytical model for dynamic weakening is proposed and it suggests that the weakening effect is induced by the increasing number of broken inter-particle bonds after impact. This is related to a decrease in the dynamic modulus that can be described by introducing a confinement pressure-dependent energy portion parameter $$\mu$$ . A further nonlinear analysis of the experimental data provides detailed insights into the nonlinear dynamic response. The proposed weakening mechanism is based on inter-particle statistics and it comprises a wealth of dynamic regimes, including modulus softening and damage evolution, which can be extended to other granular materials but not limited to rocks.

NMR Pore Structure and Dynamic Characteristics of Sandstone Caused by Ambient Freeze-Thaw Action

For a deeper understanding of the freeze-thaw weathering effects on the microstructure evolution and deterioration of dynamic mechanical properties of rock, the present paper conducted the nuclear magnetic resonance (NMR) tests and impact loading experiments on sandstone under different freeze-thaw cycles. The results of NMR test show that, with the increase of freeze-thaw cycles, the pores expand and pores size tends to be uniform. The experimental results show that the stress-strain curves all go through four stages, namely, densification, elasticity, yielding, and failure. The densification curve is shorter, and the slope of elasticity curve decreases as the freeze-thaw cycles increase. With increasing freeze-thaw cycles, the dynamic peak stress decreases and energy absorption of sandstone increases. The dynamic failure form is an axial splitting failure, and the fragments increase and the size diminishes with increasing freeze-thaw cycles. The higher the porosity is, the more severe the degradation of dynamic characteristics is. An increase model for the relationships between the porosity or energy absorption and freeze-thaw cycles number was built to reveal the increasing trend with the freeze-thaw cycles increase; meanwhile, a decay model was built to predict the dynamic compressive strength degradation of rock after repeated freeze-thaw cycles.

Combined effects of temperature and axial pressure on dynamic mechanical properties of granite

In order to get the dynamic mechanical properties of deep rock mass suffered both high temperature and high pressure, impact loading experiments on granite subjected to temperature and axial pressure were carried out. Furthermore, the internal structure characteristics of granite under different temperatures were observed by scanning electron microscopy (SEM). The results show that the longitudinal wave velocity assumes a downward trend which shows a rapid drop before falling slowly as the temperature increases. The uniaxial compressive strength of the specimen decreases significantly at temperatures of 25–100 °C compared to that at temperatures of 100–300 °C. The peak strain rises rapidly before the dividing point of 100 °C, but increases slowly after the dividing point. The internal structure of the rock changes substantially as the temperature increases, such as the extension and transfixion of primary and newborn cracks. In addition, the thermal damage under axial pressure is greater than that described by the longitudinal wave velocity and the phenomenon shows obviously when the temperature increases.

Fractal particle size distribution of pulverized fault rocks as a function of distance from the fault core

AbstractThe size distributions of particle in pulverized rocks from the San Andreas fault and the Arima‐Takatsuki Tectonic Line were measured. The rocks are characterized by the development of opening mode fractures with an apparent lack of shear. Fragments in the rocks in both fault zones show a fractal size distribution down to the micron scale. Fractal dimensions, dependent on mineral type, decrease from 2.92 to 1.97 with increasing distance normal to the fault core. The fractal dimensions of the rocks are higher than those of both natural and experimentally created fault gouges measured in previous studies. Moreover, the dimensions are higher than the theoretically estimated upper fractal limit under confined comminution. Dimensions close to 3.0 have been reported in impact loading experiments. The observed characteristics indicate that pulverization is likely to have occurred by a dynamic stress pulse with instantaneous volumetric expansion, possibly during seismic rupture propagation similar to impact loading.

A novel predictive model for mechanical behavior of single-lap GFRP composite bolted joint under static and dynamic loading

Mechanical connection of composite is critical due to its complicated meso-structure and failure mode, which has become a bottleneck on reliability of composite material and structure. Although many researches on composite bolted joints have been carried out, the theory and experiment on mechanical behavior of such a joint structure under dynamic loading were rarely reported. Here, we propose a novel predictive model for quasi-static and dynamic stiffness of composite bolted joint by introducing the strain rate dependent elastic modulus into the mass spring model. Combined with the composite laminate theory and Tsai-Hill theory, the present model was capable of predicting the strain rate dependent stiffness and strength of the composite bolted joint. Quasi-static and impact loading experiments were carried out by Zwick universal hydraulic testing machine and split Hopkinson tension bar, respectively. The stiffness and strength predicted by our model showed good accordance with the experiment data with errors below 12% under quasi-static loading and below 30% under impact loading. The results indicated that under impact loading, stiffness and strength of the composite bolted joint were significantly higher than their quasi-static counterparts, while the failure mode of the joint structure trended towards localization which was mainly bearing failure. Among various lay-up ratios studied, the optimal lay-up ratio for quasi-static and dynamic stiffness was 0:±45:90 = 3:1:1.

The blast and impact loading of aluminium foam

This paper reports results from impact and blast loading experiments on aluminium foam. The impact tests covered the velocity range required to induce non-uniform strain, and the propagation of a densification front through the specimen (often referred to as ‘shock’). In the direct impact tests, the velocity and test direction influenced the material response, with the stress tending to increase with velocity in the reverse direction. No significant increase in the stress was exhibited during the forward direction tests. This is in accordance with shock theory. Taylor test results confirmed the presence of shock in the foam specimens at impacts in excess of 60m/s. For the blast tests, the impulse range produced by detonating plastic explosive did not result in shock loading of foam core cladding specimens. As strength enhancement due to shock may be undesirable in cladding structures due to the increased stress transfer to the protected structure, the cladding was considered acceptable.