Drop Hammer Test Research Articles

Investigation on the dynamic failure characteristics of concrete slab based on mesoscopic simulation and energy conversion analysis

In this study, Continuous Discontinuous Element Method (CDEM) was employed to analyze the failure of concrete slab under drop-hammer impact at the mesoscopic level. Initially, simulation models of the impact system were established, and concrete slab models, including three-dimensional random aggregates, were generated. Mesoscopic simulations of concrete failure were then conducted by considering different variables, such as impact energy, slab size and the number of hammerheads. Corresponding drop hammer tests were used to validate the simulation results. Furthermore, an energy conversion formula for the dynamic failure of concrete slabs was derived, and the energy conversion process within the impact system was analyzed. The study also revealed the dynamic failure mechanisms of concrete slabs under various impact conditions. The research demonstrates that the simulation results are generally consistent with the impact tests. CDEM effectively investigates the impact characteristic and the energy conversion process of concrete slab failure. Under varying impact energies, slab sizes and hammerhead numbers, distinct differences in the failure characteristics of concrete-slab structure were observed. Increased impact energy accelerates the failure of concrete slabs, whereas larger concrete slab sizes inhibit crack propagation. The number of impact heads determines the initial crack position and its propagation path within the concrete slab. Moreover, the energy conversion process of the impact system significantly influences the failure behavior of the concrete slab. The effect of slab size on the energy utilization rate is greater than those of hammerhead number and impact speed.

Super anti‐impact silicone elastomer with shell‐less shear thickening fluid droplets in matrix

AbstractA soft and stretchable safeguarding silicone rubber is obtained by embedding large amount of shell‐less shear thickening fluid (STF) droplets into polydimethylsiloxane (PDMS) matrix through the synergistic process of emulsification and polymerization. Feeding time and temperature are optimized to generate the efficient STFs with 72.2 wt% SiO2 and high thickening viscosity of 6340 Pa·s. The embedding process and the evolution of the shell‐less STF droplets in PDMS matrix are explored by both optical and scanning electronic microscopes. The influence of the STF content on the mechanical and anti‐impact performance of the composites is explored through tensile tests and drop hammer tests. The STF content could be as much as 75 wt%, which enhances not only the softness and stretchability (elongation at break >200%) but also the impact‐protective performance of the silicone rubber. The STF/PDMS composites covering on planar and nonplanar glass substrates demonstrate self‐adaptive protection effect by reducing the force impact peak by 35%, due to the shear thickening and energy absorption of STF in the composites. This study develops a facile and scalable method for the implantation of the STF into polymer matrix, extending the applications of STF/PDMS composites in varied fields.

Investigation of high-performance alkali-activated slag concrete-filled steel tubular members under lateral impact

This paper studied the behaviour of High-performance Alkali-activated slag Concrete-Filled Steel Tubular members under transverse impact along with axial compression. Combining alkali-activated slag concrete with concrete-filled steel tubes provides a novel composite material incorporating the benefits of alkali-activated slag concrete and steel tubes. Alkali-activated slag concrete, known for its environmentally beneficial traits compared to traditional concrete, improves sustainability, while concrete-filled steel tube increases structural stability. Seven specimens composed of one hollow tube and six high-performance alkali-activated slag concrete-filled steel tubular specimens were tested using a drop hammer test setup to enhance our understanding of the structural performance of high-performance alkali-activated slag concrete-filled steel tubular members. A finite element analysis model was then established to broadly compare the impact resistance of circular high-performance alkali-activated slag concrete-filled steel tubular members. The mid-span displacement and impact test durations of specimens subjected to lateral impact and axial compression were assessed using a high-speed video camera called Phantom V411. This analysis includes the examination of maximum impact load, impact plateau value, maximum displacement, residual displacement, indentation, impact duration and strain responses, and an investigation into the failure modes of the specimens. The obtained results closely align with the experimental outcomes, indicating the effectiveness of the FEA model in predicting the behaviour of circular high-performance alkali-activated slag concrete-filled steel tubular members.

Maximum displacement prediction model for steel beams with hexagonal web openings under impact loading based on artificial neural networks

The estimation of the maximum displacement of steel beams with hexagonal web openings under impact loads is crucial for the anti-impact design of structures. The dynamic characteristics are complex, and the maximum displacement can be obtained experimentally, although the time cost, and expense of such experiments are high. In this context, a 6-5-1 artificial neural network model based on the Levenberg-Marquardt backpropagation algorithm was developed, incorporating 5-fold cross-validation techniques. Due to limited experimental data, 324 high-precision finite element models were created in bulk using Python-based ABAQUS software scripts to provide additional numerical data, and 26 specimens were designed for drop hammer tests to validate the finite element models. The artificial neural network model on the test data yielded a mean squared error of 0.0268, a mean absolute error of 0.0014, and a coefficient of determination value of 0.9806, with samples having an error of less than 10% comprising 77.16% of the total samples. Using Garson’s algorithm, the contribution of input features was estimated, and a full parameter analysis of the proposed model was conducted. The results indicate that the most significant factor is the impact mass, which accounts for 37.58%. When the impact mass increased from 530 kg to 630 kg, the maximum displacement of Q235 surged by 93.75%. The factor with the least impact is the opening spacing, accounting for 2%, with an average increase in maximum displacement of only 3.45%. Finally, ANN-based equations that can be used as design tools are established.

Experimental and numerical study of drop hammer test on honeycomb sandwich panel resistant to rock burst in coal mine roadway

This study addresses the ubiquitous issue of effective support resistant to the rock bursts within coal mine roadways and introduces an innovative solution in the form of a steel honeycomb sandwich panel (HSP). It is designed for installation on traditional metal supports in coal mine roadways, serves as an integral element of an energy-absorption support system tailored to withstand rock burst impacts. The investigation incorporates drop hammer impact tests conducted on eight HSP specimens, varying in cell wall thickness and core height. A comprehensive three-dimensional finite element model, inclusive of mesh considerations, was constructed and subsequently validated. Combining experimental and numerical approaches, the drop hammer impact response and energy absorption characteristics of HSP structures were analyzed. The findings reveal good energy absorption capabilities, with HSPs dissipating over 90 % of impact energy, over 85 % attributed to the core layer. Thinner core cell walls reduce peak impact loads, mitigating structural impact effects. In the experimental parameters delineated in the present study, it is observed that core layers with thicknesses of 1.0 mm and 1.5 mm demonstrate enhanced energy absorption capabilities. Variations in core height minimally affect peak impact forces, with only a 7.41 % distinction between 60 mm and 140 mm core layers. However, it is worth noting that higher core layers can achieve an enhanced energy absorption capacity. Thinner facesheets enhance energy absorption, and alterations in impactor mass have minimal effects under constant impact energy conditions. Additionally, a predictive equation for estimating indentation depth was proposed, closely aligned with finite element results. This equation holds potential for informing future HSP designs, offering valuable insights for diverse engineering applications.

Infrared temperature evolution law and thermal effect mechanism of concrete impact failure

Concrete impact failure can occur quickly and cause severe failure, which is of great significance for effective monitoring of concrete impact failure. Infrared thermal imaging technology possesses the merits of high sensitivity, noncontact, and nondestructive monitoring, rendering it extensively employed in monitoring the stability of concrete structures. However, the infrared radiation temperature (IRT) evolution law and thermal effect mechanism of concrete impact failure are not clear at present. In this study, infrared monitoring experiments were conducted on concrete impact failure and static load failure using drop hammer (DH) testing machines, pressure testing machines, and infrared thermal imagers. The infrared thermal images and the IRT change law of concrete subjected to DH impact failure were analysed. The infrared thermal effect difference and mechanism between DH impact and static load failure were compared. The results indicate that there is an infrared high-temperature point at the impact location of concrete DH impact failure, and both average infrared radiation temperature (AIRT) and maximum infrared radiation temperature (MIRT) increase suddenly. The increase in the MIRT is tens of times that of the AIRT. Compared with that of static load failure, the infrared high-temperature area of concrete DH impact failure is concentrated, while the IRT of static load failure increases overall, and the heating area is large. Moreover, the change in the IRT under DH impact failure is much greater than that under static load failure. The infrared thermal effect of concrete under DH impact failure was mainly composed of the thermoelastic effect, frictional thermal effect and tensile failure endothermic effect. The infrared data obtained for concrete impact failure should focus on the highest and lowest IRT change indicators. The highest IRT corresponds to the impact failure point, and the lowest IRT corresponds to the tensile failure position. The research results provide a new infrared thermal effect approach for monitoring the stability of concrete under impact failure.

Dynamic responses of concrete-filled steel tubes impacted horizontally by a rigid vehicle: Experimental study and numerical modelling

Concrete-filled steel tubes (CFSTs), composed of an outer tube made of steel as the confining material and an inner concrete core, have been popularly utilised as high-rise building columns and urban bridge piers owing to their superior structural behaviour. Since the invention of CFSTs, their mechanical performance under static and seismic loading conditions have been extensively studied, while the investigation on their dynamic behaviour under impact loading is relatively limited. Of these limited studies about CFSTs under impact loading conditions, most experiments were completed using a drop-hammer testing facility or a pendulum-hammer testing device. Against this background, this study investigated six large CFSTs being impacted horizontally by a rigid vehicle to analysis their dynamic response. All specimens were vertically placed with the bottom pedestal fixed on the lab floor and the top end free. The main parameters of these CFSTs included the impact velocity (i.e., vi = 3.16–7.18 m/s), the CFST section size (i.e., D = 180–300 mm), as well as the CFST column height (i.e., hc = 1500–2100 mm). Test results revealed that, (1) all CFSTs experienced a bending-dominant failure when impacted horizontally by a rigid vehicle; (2) the impact velocity had a positive correlative trend with the peak impact force Fpeak and the peak lateral displacement δpeak of the CFST column; (3) a larger section size of the CFST column resulted in a higher flexural stiffness and a larger flexural capacity, thus leading to a higher Fpeak, a smaller time duration T and a smaller δpeak; (4) the column height would affect the inertial response of the CFST column; a larger column height led to a larger Fpeak caused by the larger inertia effect of the CFST segment above the impact point. Finite-element model was established on the platform of LS-DYNA to simulate these CFSTs under horizontal impact loading, which was able to predict both impact force–time history curves and lateral displacement–time history curves with reasonably accuracy.

Evaluation of measurement uncertainty of drop hammer impact test for composite materials

Future aircraft structures are usually dominated by composites, and one of the key defects and forms of damage to composite structures is the impact damage caused by low-energy (especially low-speed) foreign matter. This kind of low-energy impact test is usually completed by the drop hammer testing machine, so accurately assessing the impact test of the falling hammer completed in accordance with the standard test method, and the reliability of the permissible value of the impact performance of the objective reaction composite is of great significance to the future aircraft structure design. Taking a standard composite test piece as an example, considering the key factors in the whole process of impact test, a mathematical model is constructed, and the measurement uncertainty of different configuration composite test pieces of different configurations is calculated according to the test data, which provides a basis for aircraft structural design.

Low-velocity impact failure of foam-filled GFRP trapezoidal corrugated sandwich structures

In this paper, a new lightweight sandwich structure with polyurethane foam filled glass fiber reinforced polymer (GFRP) trapezoidal corrugated sandwich structure is fabricated. Based on the low-velocity impact tests, the impact failure performance and energy absorption efficiency of polyurethane foam filled sandwich structures are investigated. Low-velocity impact tests were carried out on the node and base positions of the foam filled trapezoidal corrugated sandwich structure by using a drop hammer test machine, and the set impact energy range was 25 J – 150 J. Experimental results show that when the impact energy is the same, the maximum impact load and maximum energy absorption generated by the node impact are greater than the base impact, which proves that the node position has better impact resistance and energy absorption effect than the base position. In addition, by comparing the displacement-time curves of foam filled and unfilled sandwich structures, it is found that when the impact energy is the same, the slope of the displacement-time curve of unfilled specimen is greater than that of foam filled specimen. Therefore, within the same time, the deformation of unfilled specimen is larger than foam filled specimen during the impact process, which demonstrates the effectiveness of polyurethane foam filling on the gain of sandwich structure.

Impact response of lightweight steel foam concrete composite slabs: Experimental, numerical and analytical studies.

This paper presents a study on the low-velocity impact response of lightweight steel foam concrete (LSFC) composite slabs. The LSFC composite slab consisted of a W-shaped steel plate, foam concrete and oriented strand board (OSB). Low-velocity impact tests on the LSFC composite slabs were conducted by employing an ultra-high heavy-duty drop hammer testing machine. The tests revealed the failure mode, impact force and displacement response of LSFC composite slabs. The effects of density and thickness of foam concrete and drop height on the peak impact force and energy absorption ratio were investigated. A finite element (FE) model was set up to predict the impact resistance of the LSFC composite slabs, and a good agreement between simulation and test results was achieved. In addition, an equivalent-single-degree-of-freedom (ESDOF) model was set up to predict the displacement response of the LSFC composite slabs under impact loading.

Failure mechanism and impact resistance of a novel all-composite double-corrugated sandwich plate under low-velocity impact

A novel composite double trapezoidal corrugated sandwich plate (CDTCSP) was prepared by mold hot pressing and secondary bonding of carbon fiber reinforced polymer (CFRP) prepregs. The DIT302E drop hammer testing machine with a hammerhead of 5.5 kg was selected to realize the impact test of the new corrugated sandwich structure and the all-composite trapezoidal corrugated sandwich plate (CTCSP) with three different energies of 10 J,30 J, and 50 J by changing the height. The failure modes of the two samples were further studied by experimental investigation along with the finite element model established in Abaqus/Explicit. Based on the verified numerical model, the failure process of CDTCSP under 30 J and 50 J impact energy is analyzed. At the same time, the effects of different impact positions and layup angles on the impact resistance of CDTCSP at 10 J energy were evaluated. It can be observed that as the impact energy increases, the peak load of the composite corrugated sandwich plate decreases. Compared with the traditional ones, the impact position has no noticeable effect on the overall impact resistance of CDTCSP. Based on the analysis of CDTCSP with five different layup parameters, it is found that the matrix compression failure extends along the fiber direction, and the peak load of the sample with all the surfacing layup of ± 45° is 17% larger than that of the sample with 0°.

Dynamic properties of micro-NPR material and its controlling effect on surrounding rock mass with impact disturbances

A novel meta steel with negative Poisson’s ratio effect (termed as micro-NPR steel) is developed for rock support in deep underground engineering. It possesses high strength, high ductility, and high energy absorption characteristics. In this paper, static tension and modified dynamic drop hammer tests are performed on this novel material to investigate its mechanical properties first. Then based on this material, a new generation of micro-NPR anchor cable is developed and applied in field tests subjected to blasting dynamic loads. The results of laboratory tests reveal that the ultimate elongation of micro-NPR steel under dynamic impacts is more than 30% and it is over 1.5 times that of Q235; the plastic and total energy absorption of micro-NPR are both significantly higher than that of Q235. Field test indicates the fine controlling effect of micro-NPR anchor cable on surrounding rock mass under dynamic loads. Axial force confirms that micro-NPR cables can distribute and absorb the dynamic energy uniformly around the supported rock when subjected to dynamic disturbance, avoiding local failure induced by excessive stress concentration. The excavation compensation principle and energy-absorbing characteristics are used to explain the support mechanisms. Thus, micro-NPR material and anchor cable can control and prevent dynamic disasters in deep underground engineering effectively.

Experimental and numerical studies on UHPC-filled Q690 high-strength steel tubular members subjected to axial impact

With the advances in high-performance materials and structures, the impact behavior of ultra-high-performance concrete (UHPC) filled Q690 high-strength steel tubular columns was systematically investigated in this study. A total of 19 axial impact tests on UHPC-filled steel tubular columns were conducted by a drop hammer test apparatus, experimentally obtaining the failure model, impact force and displacement time histories, and energy absorption. The main parameters, including steel strength, steel ratio, impact energy, and specimen length, were considered. The results showed that UHPC-filled Q690 high-strength steel tubular members exhibited excellent impact resistance and could withstand higher energy impacts. As the impact energy increased, the impact force also increased owing to the strain-rate effect, and the deformation was significantly enlarged. Increasing the steel ratio significantly enhanced the impact resistance and energy absorption efficiency of components; the use of high-strength steel and UHPC also improved the impact resistance and energy absorption; the effect of specimen length on the axial impact behavior was limited. Additionally, a finite element model considering the strain-rate effects of high-strength steel and UHPC was established and benchmarked with the test results from the present study and literature. The simulated results were in good agreement with the experimental results, which contributed to the relevant research on UHPC-filled steel tubular components subjected to axial impact.

Lateral impact test and inertial force of concrete-filled steel tube column

The mechanical behavior of concrete-filled steel tube (CFST) subjected to lateral impact was studied by drop hammer test and finite element method (FEM). Lateral deformation occurred when the midspan of CFST was impacted by a drop weight. Two plastic hinges were formed in the mid-span and near the fixed support, respectively. The numerical and experimental results were compared to ensure that the numerical model was reasonable for investigating the stress development, damage, and inertial force of the CFST column. The effects of the impact velocity, impact mass, cross-sectional steel ratio, and boundary conditions on the inertial force of the CFST column were analyzed. During the impact process, the maximum stress was at the steel tube part of the impact location and the fixed support, while the other parts were still in the elastic or elastoplastic stages. The region under restraint at the fixed end of the CFST column exhibited the first signs of concrete core damage under tension, followed by the region near the location of the impact at midspan. At the peak impact force (Fp), the impact velocity had a considerable influence on the distribution of inertial force of CFST, while the impact mass and cross-sectional steel ratio had no discernible impact on the inertial force at the Fp, and boundary conditions had little impact on the distribution of inertial force. Based on a research of the inertial force at the Fp, a simple mechanical model of the inertial force was built.

Dynamic response of concrete-filled square steel tubular columns under lateral impact load at flat or corner zone

The dynamic response of columns under lateral impact is of great significance for guiding structural design under accidental loads. The present study aims to investigate the effect of different impact directions on the dynamic response of square concrete-filled steel tubular (CFST) columns by conducting drop hammer tests at flat or corner zones. The main experimental parameters included hammer mass, drop height, indenter radius, built-in steel bars, shear span ratio, width-thickness ratio, and column sizes. The experimental results showed that the impact zone has a significant effect on the dynamic response of CFST specimens. Under higher impact energies, specimens impacted at corner zones were more likely to fracture on the tensile side of the steel tube than specimens impacted at flat zones. And the specimens impacted at the corner zone were more sensitive to the change of indenter radius. Smaller shear span ratios, built-in steel bar, and larger column sizes improved the impact resistance of tested specimens. The 3D finite element models were developed and analyzed by ABAQUS/Explicit to explore dynamic behavior further.

Performance of stringer sheet parts under static and dynamic load

The stringer sheet forming process chain enables the cost-effective production of components with significantly increased stiffness for mass markets such as the automotive sector. In the first process step, a stringer is added to a conventional sheet by laser welding. In the subsequent process step, the stringer sheet parts are formed by a deep drawing operation. Previous investigations of component performance focused in particular on the static stiffness of the stringer sheets. The behavior under dynamic load, such as in crash events, has not been systematically investigated to date. Static testing focused on the stringer height as the only influence on part performance. This study characterizes the crash performance of stringer sheet components by means of a drop hammer test. The energy absorption of the components is evaluated in the experiment based on the rebound height of the drop hammer, whereas the structural integrity is characterized based on the maximum dynamic as well as permanent deformation. Furthermore, a quasi-static compression test is carried out to obtain the static stiffness of the parts. In these tests, the geometric design of the stringer sheets as well as two forming process parameters are varied individually. The influence of these parameters on the static stiffness, energy absorption and structural integrity is assessed and discussed on their own and with regard to their influence on the part weight.

Assessment on concrete constitutive models for numerical simulations of vehicular collisions with RC bridge piers

Accident statistics showed that vehicular collision caused serious shear damage or failure of reinforced concrete (RC) bridge piers and even resulted in overall collapse of bridge structures. For the resistance evaluation of RC components under impact loads, numerical simulations have been performed by adopting different concrete constitutive models and obtained different results, e.g., Karagozian and Case Concrete (KCC) model and Continuous Surface Cap (CSC) model widely used, as well as Kong-Fang (KF) model recently proposed. This study mainly evaluates the accuracy of the above three concrete constitutive models in numerical analyses of vehicular collisions with RC bridge piers. Firstly, basic mechanical behaviors of these models are systematically compared based on single element simulations. Then, the scope of investigation is extended to component level by simulating a drop hammer test on RC beam and a lateral impact test on RC column, and the dynamic behaviors of impacted RC components are deeply compared. Finally, these models are further compared at structure level through performing the refined numerical simulation of a real truck colliding with a prototype bridge and evaluating its global structural behaviors and damage. The results show that, (i) KF model well reflects the post-peak softening behavior, stable strain-rate effect and independence of mesh size of concrete materials under uniaxial loading conditions at different loading rates; KCC and KF models both capture the brittle to ductile transition of concrete materials with increasing confinement pressure; (ii) KF model yields a better prediction in dynamic responses and damage characteristics of impacted RC beam and column, while KCC and CSC models both overestimate the damage degree; (iii) KF model better simulates the shear failure of RC pier in the real accident and provides the reasonable structural dynamic responses, but KCC and CSC models much underestimates the damage degree of impacted bridge pier and adjacent components.

Impact resistance of single-cell and multi-cell sandwich aluminum plates filled with aluminum foam

The aim of this paper is to investigate the impact resistance and energy dissipation capacity of a new type of multi-cell sandwich aluminum alloy plate filled with aluminum foam, in comparison to the single-cell structure. To achieve this goal, 30 sandwich aluminum alloy plates were tested using a drop hammer test machine, varying impact velocity, wall thickness, and the number of internal diaphragms. The results were analyzed and finite element analysis was conducted to explore the energy dissipation mechanisms and the effect of aluminum foam on multi-cell plates. The findings revealed three failure modes and three stages of the impact force time history curve. Multi-cell plate exhibited showed much better specific energy absorption compared with the single-cell plate. Taking an example displacement of 22.5 mm, which differentiates the specific energy absorption the most between the two types of structures, the multi-cell plate exhibited an average increase of 332% in specific energy absorption compared to the single-cell plate. The numerical simulations were consistent with experimental results and highlighted the contribution of different components to energy dissipation in both structures.

Sandstone Impact Damage Study

In order to study the impact of impact on sandstone, dynamic impact is conducted on sandstone through drop hammer test, wave velocity test is conducted on the impacted specimen by using wave velocity instrument, and the damage effect of impact on sandstone is analyzed by using wave velocity damage calculation formula. The results show that the greater the impact velocity, the smaller the measured wave velocity and the greater the damage to the sandstone.

Static and multi-impact performances of RC beams strengthened with large rupture-strain FRP composites

To solve the problem of inadequate plastic deformation capacity and energy dissipation of traditional fiber-reinforced polymer (FRP) strengthened structures under impact loading, this study proposes the use of novel large-rupture-strain fiber-reinforced polymer (LRS-FRP) materials combined with different strengthening schemes to improve the impact resistance of existing structures. This study conducted three-point bending and drop hammer tests to investigate the static and dynamic behaviors of flexure-dominated LRS-FRP-strengthened beams. Experiment results showed that the end-anchored FRP strengthening system at the beam soffit significantly improved the load capacity of beams under static loading and reduced the maximum mid-span deflection under impact loading, and the ductility factor of LRS-FRP strengthened beams under static loading was 2.7 times higher than that of the carbon-FRP (CFRP) counterpart. Specimens strengthened with a mid-span LRS-FRP wrapping scheme presented improved ductility and multi-impact performance. Specimens strengthened with a combined scheme enhanced the static load capacity and ductility of by 71.9 % and 159.7 %, respectively, compared to the unstrengthened beam, and exhibited the best energy dissipation capacity (23.8 kJ) under multiple impact loads. These findings from the test investigations can facilitate design guidance and evaluation methods for strengthening schemes for RC structures under impact loading.