Drop Hammer Research Articles

Experimental study on particle size distribution of impact crushed coal containing gas

Coal and gas outburst is a coal-rock dynamic disaster caused by the combined action of multiple factors, accompanying by the impact crushing on coal particles containing gas. Therefore, the study of coal impact crushing is of great significance to reveal the mechanism of coal and gas outbursts. In this study, a self-designed experimental system was used to investigate the characteristics of the coal particles under impact crushing. The coal samples from Xiaoqing Coal Mine 7# coal seam in Liaoning (XQ) and Zouzhuang Coal Mine 32# coal seam in Anhui (ZZ) were selected, and tested for drop hammer experiments under different gas pressures. The particle size distribution model and parameters such as surface area distribution ratio and average particle size were analyzed. The results show that GGS model and RR model can well fit the particle size distribution of coal samples after impact. The test results of coal samples with different gas pressures show that gas weakens the strength of coal significantly. A specific functional relationship was established between particle size distribution and specific crushing work and Protodyakonov coefficient, which is expected to be applied in coal mining enterprises.

Study of SPRC Impact Resistance Based on the Weibull Distribution and the Response Surface Method.

Silica-fume–polyvinyl-alcohol-fiber-reinforced concrete (SPRC) is a green and environmentally friendly composite material incorporating silica fume and polyvinyl alcohol fiber into concrete. To study the impact resistance of SPRC, compressive-strength and drop hammer impact tests were conducted on SPRC with different silica-fume and polyvinyl-alcohol-fiber contents. The mechanical and impact resistance properties of the SPRC were comprehensively analyzed in terms of the compressive strength, ductility ratio and impact-energy-dissipation variation. Based on the impact resistance of the SPRC, the impact life of SPRC with different failure probabilities was predicted by incorporating the Weibull distribution model, and an impact damage evolution equation for SPRC was established. The impact life of SPRC under the action of silica-fume content, polyvinyl-alcohol-fiber content and failure probability was analyzed in depth by the response surface method (RSM). The research results show that, when the content of silica fume is 10% and the content of polyvinyl alcohol fiber is 1%, the compressive strength and impact resistance of SPRC are the best. The RSM response model can effectively predict and describe the impact life of SPRC specimens under the action of three factors.

Impact-resistant design of RC slabs in nuclear power plant buildings

The concrete structures related to nuclear safety are threatened by accidental impact loadings, mainly including the low-velocity drop-weight impact (e.g., spent fuel cask and assembly, etc. with the velocity less than 20 m/s) and high-speed projectile impact (e.g., steel pipe, valve, turbine bucket, etc. with the velocity higher than 20 m/s), while the existing studies are still limited in the impact resistant design of nuclear power plant (NPP), especially the primary RC slab. This paper aims to propose the numerical simulation and theoretical approaches to assist the impact-resistant design of RC slab in NPP. Firstly, the continuous surface cap (CSC) model parameters for concrete with the compressive strength of 20–70 MPa are fully calibrated and verified, and the refined numerical simulation approach is proposed. Secondly, the two-degree freedom (TDOF) model with considering the mutual effect of flexural and shear resistance of RC slab are developed. Furthermore, based on the low-velocity drop hammer tests and high-speed soft/hard projectile impact tests on RC slabs, the adopted numerical simulation and TDOF model approaches are fully validated by the flexural and punching shear damage, deflection, and impact force time-histories of RC slabs. Finally, as for the two low-velocity impact scenarios, the design procedure of RC slab based on TDOF model is validated and recommended. Meanwhile, as for the four actual high-speed impact scenarios, the impact-resistant design specification in Chinese code NB/T 20012-2019 is evaluated, the over conservation of which is found, and the proposed numerical approach is recommended. The present work could beneficially guide the impact-resistant design and safety assessment of NPPs against the accidental impact loadings.

Study on the impact performance of RC fences strengthened with high strength strain-hardening cementitious composites

This paper presents a numerical study on the impact performance of reinforced concrete (RC) fences strengthened with high-strength strain-hardening cementitious composite (HS-SHCC) through finite element (FE) modeling. To accurately simulate the peculiar material characteristics of HS-SHCC, the MAT_72R3 material model was calibrated and verified against experimental data. A comparison study for RC and HS-SHCC panels subjected to drop hammer impact was conducted to observe the impact performance of HS-SHCC. Results showed that the impact resistance and energy dissipation capacity of HS-SHCC are significantly higher due to its high strength and high ductility. A full-scale study of pick-up truck collisions was then conducted to investigate the response, failure, and best strengthening configuration of conventional RC fences strengthened with HS-SHCC layers. Results showed that both strengthened configurations under moderate impact energy could significantly improve the impact resistance and reduce the residual deflection. While in the case of large impact energy, the back-strengthened RC fence gave notably better performance and higher impact resistance due to the composite effects between RC and HS-SHCC layers. Based on the analysis of the failure modes and energy dissipation, the mechanism of such composite effects was summarized.

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.

Forming of Multiple Straight Convex Shapes on Aluminum Sheet Using Impulsive Water Pressure

Several types of multiple straight convex shapes were formed on a thin aluminum sheet with a grooved die using impulsive water pressure. The maximum pressure was 160 MPa in the high-speed forming, wherein a drop hammer testing machine was used, whereas it was 100 MPa in the low-speed forming because of the limitations of the press machine. The effects of the forming speed, cross-sectional shape, and pitch of the grooves on the deformation behavior were investigated. The increase in the impulsive water pressure was found to be affected significantly by the compressibility of water. The symmetricity of the convex shape in the cross-section decreased at both ends for a smaller pitch because of the imbalance of the material flow at both peripheries of the groove. The concave surface profile of the pressure side was more rounded in the high-speed forming than that in the low-speed forming when semicircular and rectangular grooved dies were used. This may be attributed to the fact that the plastic deformation becomes more uniform owing to the positive strain rate sensitivity of the test material. In the forming with rectangular grooves, fracture occurred under the low- and high-speed conditions, wherein the maximum pressure was set to 100 MPa. However, the material did not fracture during high-speed forming with a pressure of 160 MPa, where the convex shape was higher and the material contacted the bottom of the groove. This behavior may be because the dislocation density of the material did not increase rapidly owing to the strain rate being maintained high until the material suddenly stopped deforming in the latter condition. In forming with a trapezoidal grooved die, the formed profiles were considerably similar under all conditions because the strain was considerably smaller than that with the other grooves.

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.

Dynamic mechanical characteristics and application of constant resistance energy-absorbing supporting material

In deep underground engineering, rock burst and other dynamic disasters are prone to occur due to stress concentration and energy accumulation in surrounding rock. The control of dynamic disasters requires bolts and cables with high strength, high elongation, and high energy-absorbing capacity. Therefore, a constant resistance energy-absorbing (CREA) material is developed. In this study, the dynamic characteristics of the new material are obtained via the drop hammer tests and the Split Hopkinson Pressure Bar (SHPB) tests of the new material and two common bolt (CB) materials widely used in the field. The test results of drop hammer test and SHPB test show that the percentage elongation of CREA material is more than 2.64 and 3.22 times those of the CB material, and the total impact energy acting on CREA material is more than 18.50 and 21.84 times, respectively, indicating that the new material has high elongation and high energy-absorbing capacity. Subsequently, the CREA bolts and cables using the new material are developed, which are applied in roadways with high stress and strong dynamic disturbance. The field monitoring results show that CREA bolts and cables can effectively control the surrounding rock deformation and ensure engineering safety.

A study on damage evolution in Cu–TiO2 composite fabricated using powder metallurgy followed by hot extrusion

In this paper, damage evolution of Copper/Titanium Dioxide, fabricated by powder metallurgy, based on Young modulus reduction is investigated. The Cu matrix is reinforced by different volume fraction of TiO2 nano and micro particles using mechanical milling, cold pressing at different loading rates (Quasi-Static, Drop Hammer, Split Hopkinson Bar), and hot extrusion process. The composite tensile test specimens were produced using powder metallurgy (cold pressing) followed by hot extrusion. The effects of the strain rate and the reinforcing particles size on damage evolution of Cu reinforced by 0, 2.5 and 5% volume fractions of nano- and micro-sized TiO2 were investigated. The results showed that the Quasi-Static method was more efficient than the other two methods. In addition, the experimental results showed that strain rate, plastic strain, fracture strain, volume fraction of reinforcement particles and particles aspect ratio were effective on damage evolution. Finally, these effective parameters were incorporated into a new model proposed to predict the damage evolution of Metal Matrix Composite (MMC). The model was validated by experimental results.

Investigation on impact resistance of hierarchical lightweight lattice structure

Abstract This paper is majorly discussing the impact resistance of hierarchical lightweight lattice structure. Firstly, the unit cells of hierarchical pyramidal lattice structure and traditional single-stage hollow pyramidal lattice structure are designed. At the same time, the concept of relative density is introduced to better demonstrate the impact resistance of hierarchical structure. In this paper, ABAQUS/Explicit software is used to simulate the drop hammer impact simulation of hierarchical structure and hollow structure. The result shows that the impact resistance of hierarchical structure is better than hollow structure. Meanwhile, the samples are prepared by 3D printing, and then quasi-static compression experiment and drop hammer impact experiment are carried out. It is concluded that the bearing and impact resistance performance of the hierarchical structure has obvious improvement than the hollow structure under both quasi-static compression and low-speed drop hammer impact.

Electric Press Machine by Using Stepper Motor

Abstract: In ancient times material was shaped manually using hand hammers. Later on, big hammers were used to press large quantities of material at a time or to press a thick metal workpiece. Then after steam power and windmills were utilized to operate the large steam hammers. Prior to the invention of the machine press, workers were required to manually hammer metal by hand to change the shape of materials. After that, it cannot able used to change the shape of large or big size material, and itit’shysically ineffective. The steam hammer was developed around the mid – the 1800s and is also known as a drop hammer, the steam hammer or drop hammer was essentially an early version of the modern-day machine press. The only difference is that the steam hammer was powered by steam, whereas most modern-day machine presses are powered by hydraulics and electricity. Now day world, we are normally using a mechanical press machine and hydraulic press machine. In this paper, we are explaining about electric press machine by using stepper motor. Keywords: Arduino UNO R3, TB6600 4A Stepper Motor Driver, Permanent magnet Stepper Motor, SMPS (switched-mode power supply)

Impact behavior of hybrid-fiber reinforced concrete beams

The impact studies on concrete beams are primarily pertaining to the drop hammer impact, and studies involving projectile impacts on reinforced concrete beams are limited. In this research, the response of hybrid fiber reinforced concrete (HFRC) beams under quasi-static loading and the projectile impact was studied. The HFRC was produced using eight concrete mixes having different proportions and combinations of three fiber types (viz. polypropylene, steel, and Kevlar). The HFRC mixes had a total fiber volume fraction of 1.2% and 1.4%. In addition, plain concrete was used as a control. The beams were tested under the impact of hemispherical nose projectile at varying strike velocities. The projectile strike velocity was increased till the perforation of beams. The main flexural reinforcement in beams was provided on the back face. In order to assess the punching resistance of beams, the beams were tested under quasi-static punching load applied using the same projectile employed in impact tests. The use of hybrid fibers improved beams’ quasi-static punching resistance in terms of energy absorption and load–displacement behavior. The hybrid fibers also improved the impact response of beams by reducing damage levels, increasing perforation velocity, and reducing ejected mass. By modifying the earlier proposed model for slabs, the ballistic limit of HFRC beams is also predicted.

Numerical Simulation Study on the Strengthening Mechanism of Rock Materials under Impact Loads

Based on an analysis of real stress in rock specimens, the mechanisms of inertia and cracks on the dynamic properties of concrete material are discussed in this paper. A dynamic enhancement factor is introduced on the basis of static mesodamage constitutive theory, and a rate-dependent three-dimensional rock dynamic constitutive model is established. The orthogonal design and range method are used to analyze the sensitivity of the dynamic damage constitutive parameters, and a differential evolution algorithm is used to invert the relevant parameters of the constitutive model. Based on the drop hammer impact model established by the rock dynamic damage constitutive model, the AE distribution, crack propagation mode, and load-displacement curve of the rock sample are obtained. The numerical simulation results show that rock specimens under dynamic loading have different failure forms, mechanical response mechanisms, and energy evolution than those under static loading. Under dynamic loading, the rock specimen forms more cracks and releases more elastic energy. Furthermore, it shows greater strength characteristics. Inhomogeneities and inertial effects of rock materials are the fundamental reasons for the increase in the dynamic strength of rock materials. A reduction in inertial effects is the main reason for strength reduction in rock samples with hole defects.

Simulating failure behavior of reinforced concrete T-beam under impact loading by using peridynamics

Peridynamics has been proven to be a promising method for investigating the damage and failure behaviors of reinforced concrete structures due to its strong capacity in tackling discontinuous problems. To accurately describe the dynamic failure behavior and damage evolution of reinforced concrete structures under impact loading, the commonly used micropolar peridynamic model is improved. The improved micropolar peridynamic model considers the weak tensile strength and strong compressive strength of concrete materials, weakens the interactions between rebar and concrete in reinforced concrete structures, and optimizes the descending softening branch of the concrete constitutive model after tensile yielding. The present approach is demonstrated through a single bar pull-out test and a four-point-bending reinforced concrete beam test. Besides, by introducing the contact algorithm for rigid projectile impact and penetration to deformable targets, the peridynamic model and numerical solver are applied to simulate the failure behavior of the reinforced concrete T-beam under drop hammer impact. The peridynamic predictions agree well with available experimental observations, demonstrating the reliability and potentiality of the improved micropolar peridynamic model.

Low-velocity impact response of sandwich composite panels with shear thickening gel filled honeycomb cores

Sandwich composite panels (SCPs) with carbon fiber reinforced plastic (CFRP) facings and honeycomb core are susceptible to impact damage. In this study, a method is proposed to improve the impact resistance and energy absorption capacity of SCPs by filling the honeycomb core with a shear-thickening gel (STG) mixed with silica particles. The low-velocity impact responses of the SCPs have been analyzed including the drop hammer ricochet from front facing, ricochet from back facing, and complete perforation. The load-displacement curves and damage patterns indicate that STG-filled honeycomb core could effectively decrease the penetration depth and reduce impact damage of the SCPs. Finite element simulations based on the Coupled Euler-Lagrangian (CEL) method were conducted to reveal the underlying mechanism for the enhanced anti-impact capacity of the SCP filled with STG.

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.

Numerical Investigation on the Dynamic Responses and Failure Criterion of RC Beam Under Impact

During the period of service, the infrastructure is subjected to various forms of impact. To investigate the impact responses of a reinforced concrete (RC) beam, a numerical model of the RC beam under impact was developed by the finite element package LS-DYNA in this study. The numerical model was verified by using the drop hammer test on the RC beam. Using the numerical model, the midspan displacement of the RC beam is analyzed under the interaction of impact mass and impact velocity. The results show that the response surface of midspan displacement can be fitted as a binary power function of impact mass and impact velocity. The midspan displacement under various impact conditions with equal impulse or equal impact energy is different. Within the scope of a low-speed impact, the midspan displacement decreases with an increase in the impact mass under the equal impulse, while it increases with an increase in the impact mass under the equal impact energy. In addition, the impact failure of the RC beam is judged by the deformation criterion. The threshold value of the ductility coefficient is recommended to be set as 15 in the impact-resistant design for RC beams in civil engineering structures within the scope of a low-speed impact.

The Use of Aluminium Alloy after High Plastic Deformation for Joining Riveted Structures.

This paper presents the results of a static and dynamic tensile test of an Al7.5Mg aluminium alloy taken from round bars made in the technology of hydrostatic extrusion. It is planned to use the Al7.5Mg aluminium alloy for joining riveted structures. Based on the obtained results, the nominal and true characteristics of the Al7.5Mg aluminium alloy, depending on the strain rate in the range from 0 to 2000 s−1, were developed. The failure criterion for tension was determined. The material characteristics were approximated by the Johnson–Cook equation, which can be used in CAE (computer-aided engineering) programs to simulate the impact processes. FEM (finite element method) simulation of the impact of the hammer on the part of the riveted aircraft structure was performed. The FEM simulation results were compared with the experimental results on a drop hammer to verify the material model. The following results were obtained: yield strength Re = 395.3 MPa; strength limit Rm = 523.1 MPa at deformation 0.067; Young’s modulus E = 7.9 × 104 MPa. The AL7.5Mg alloy after hydro-extrusion has favourable plastic and strength properties.

A high anti-impact STF/Ecoflex composite structure with a sensing capacity for wearable design

By encapsulating shear thickening fluid (STF) in Ecoflex-0030, a kind of composite structure with excellent anti-impact and high energy absorption properties was obtained. The drop hammer tests indicated that the increase of STF concentration could improve the anti-impact and energy absorption capacity of STF/Ecoflex. Furthermore, the loss rate of impact energy of STF/Ecoflex was 63.6% and 36.6% higher than that of aluminum alloy and Kevlar materials, respectively. Numerical simulation was used to explore the mechanism. It was found that the shear thickening effect of STF was enhanced with the increase of STF concentration, which could lead to the increase of the stress level of STF and the energy dissipated by friction and viscosity, thereby the anti-impact performance of the composite was improved. Then, the C-STF/Ecoflex was prepared by adding carbon nanotubes (CNTs) to STF, which had excellent impact sensing function and could be combined with Kevlar for multi-functional wearable devices with anti-impact properties.