Drop Hammer Research Articles

Tensile and Flexural Behavior of Ultra-High Performance Concrete (UHPC) under Impact Loading

The rate-sensitive properties of ultra-high performance concrete (UHPC) subjected to flexural and direct tensile loads were investigated. Dynamic flexural tests were performed by means of a drop hammer impact machine, whereas a servo-hydraulic system was utilized to conduct direct tension tests. The absorbed energy of the UHPC specimens under flexure increased from 0.74 to 4.49 J as the input energy varied from 6.7 to 67 J. The load-bearing capacity and maximum flexural deformation exhibited identical trends as the input energy increased. The high-speed tensile properties, including strength, ductility, and energy dissipation capacity, improved upon increasing the strain rate up to 100 s-1. A nonuniform distribution of the deformation of UHPC specimens under high-speed tension was observed by identifying the zones of strain localization (near crack), uniform strain (far field), and shear lag (transition zone in between) using digital image correlation. The full-field data of displacement, strain, and strain rates were obtained and quantitatively evaluated. The results indicated that multiple mechanisms were involved in the rate-dependent behavior of the UHPC specimens.

Adiabatic shear bands formation in polycrystalline aluminium

The microstructure and texture evolutions during dynamic (or high strain rate) deformation of commercially pure AA1050 alloy have been studied to elucidate the mechanisms of shear band (SB) formation and its propagation across the flattened grains arranged in layers with special attention to texture evolution. The hat-shaped samples were compressed using drop hammer at a strain rate of 5.3 × 102 s−1. Detailed microstructure and texture characterizations were carried out using SEM equipped with EBSD facility. The shear displacement moves the upper part of the hat-shaped sample towards the bottom one leading to a strain localization in the form of SB. It was found that the strain localization occurs via deflection of flattened grains within narrow areas leading to kink-type bands that are considered to be the precursors of SB. The strain-induced crystal lattice rotation led to the formation of new texture components, different from those identified inside the undeformed matrix. It also facilitates slip propagation across the grain boundaries. The mechanism of macro-SB formation is essentially crystallographic in nature since in all grains of the sheared zone, the crystal lattice rotated in such a way that one of the {111} slip planes became nearly parallel to the shear plane and the <011> direction became parallel to the direction of maximum shear.

Research on the Drop Hammer Impact Test System

The drop hammer impact test system adopts the multi-purpose and modular design to solve the four problems of the airbag door of automobile test instrument panel: the test conditions are generally inconsistent with the actual conditions; The secondary impact problem exists in the collision test. The experiment does not have the experimental data, cannot provide the technical question for the enterprise; There are some problems in the equipment construction mode, such as universality, repeatability and low utilization rate. The improvement of mechanical structure and control system makes the device simple in structure, powerful in function, able to obtain accurate experimental data, and able to realize the instrument panel airbag door detection of different vehicle models.

Shear Thicking and Impact Resistance Properties of STG in Flexible Protection Application

The rheological properties of shear thickening gel(STG) and its application as protective composite were studied in the paper. Upon applying a shear stress with excitation frequency from 1 Hz to 100 Hz, the storage modulus (G’) of the STG increases from 101 Pa to 105 Pa, demonstrating an excellent shear thickening effect. The reduction of temperature increases the G’min of STG, but when the temperature reaches at 50°C, the G’ curve shows a moderate slope and a gradual transition to the constant plateau value. By introducing STG into polyurethane foam and kevlar fiber with dip and dry method, successfully fabricate a nove safeguarding polymer composite. The protective performance of composite protective materials was studied by static compression experiment and drop hammer impact experiment. The addition of STG increases the impact resistance and puncture resistance of PU and kevlar by at least two times. The materials shows excellent shear stiffening effect, creep resisting and impact resistant propertie.

Shock Absorbers Damping Characteristics by Lightweight Drop Hammer Test for Naval Machines

The technical requirements for naval ships machine foundations are far more strict in comparison to merchant’s vessels. These requirements are confirmed in the military standardization of many countries. Underwater Explosion (UNDEX phenomena) detonation pulses, force naval engineers to design and implement different shock absorbers made from a wide variety of materials. This study presents the tests results of typical shock absorber designs made of various types of rubber and elastomers. The initial objective of the study was to determine the energy absorption of shock impacts, the choice of materials capable of operating within the temperature range of 0 °C to 70 °C, resistance to contact with oils and marine fuel, performance at frequencies ranging from 5 to 30,000 Hz, and absorption no less than 40% of harmonic vibration energy. Initial studies conducted on tensile testing machine were used to determine the static and dynamic stiffness of a shock absorbers. Considerations of stiffness coefficient for the linear and nonlinear range is typical for shock pulses. Further tests were carried out on a lightweight drop hammer to determine the characteristics of the damping coefficient for high-speed wave interactions—Shock Response Spectrum (SRS). The final aim of the study was to assess the repeatability of the shock absorbers response to multiple impact loads. Mechanical properties describing possibilities of tested dampers materials to absorb energy of UNDEX were also presented.

Selection of optimal parting line for forging in various equipments using numerical analysis

While designing of dies for forging, one of the most important criteria which has to be considered is the selection of parting line/plane. Selection and location of the parting line greatly affect the grain flow direction in the component, load which is coming on the dies and it also determines the location of the burr which is formed in the component after trimming. The main objective of this paper is to select a suitable parting line/plane, for hot forging a circular component in mechanical press and drop hammer. For studying the effect of parting line, four dies are designed with different parting lines (top parting line, bottom parting line, central parting and inverted dies) location for hot forging of an automotive component coupling flange. Two commonly used equipments (mechanical press and drop hammer) are considered for determining the effect of parting line location on load requirement which finally decides the die wear and die life. Numerical analysis is carried out with these dies using a finite element based software DEFORM-3D. Top parting line gave best results with minimum load, minimum effective-stress and favourable grain flow in mechanical press. Whereas, in case of hammer, inverted dies yielded in minimum load, minimum effective stress and favourable grain flow.

Comprehensive study on quasi-static and dynamic mechanical properties and wear behavior of Mg—B4C composite compacted at several loading rates through powder metallurgy

The present study aims to fabricate and evaluate the mechanical properties and wear behavior of Mg metal matrix composite, reinforced by 0, 1.5, 3, 5 and 10 vol.% B 4 C microparticles. Mg—B 4 C samples were fabricated at 450 °C and under different loading rates by using split Hopkinson bar (SHB), drop hammer (DH) and Instron (QS) at strain rates of 1600, 800 and 0.008 s −1 , respectively. The mechanical properties including microhardness, quasi-static and dynamic compressive strengths and wear behavior of samples were experimentally investigated. The results show that, the hardness of SHB and DH samples is obtained to be 20.2% and 5.7% higher than that of the QS sample, respectively. The wear rate and wear mass loss of Mg−10.0%B 4 C samples fabricated by SHB were determined lower than those of the QS sample by nearly 33% and 39%, respectively. The quasi-static compressive strengths of Mg−5.0%B 4 C are improved by 39%, 30% and 29% for the SHB, DH and QS samples, respectively, in comparison with the case of pure Mg. Furthermore, it is discovered that the dynamic compressive strength of samples is 51%–110% higher than their quasi-static value with respect to the B 4 C content.

The effects of particle breakage and shape on the strength parameters of sandy soil

Many laboratory and full-scale studies found that pile foundation is a reliable structure that has a long-term durability. This aspect makes it favourable when construction is in an area like the coastal where granular materials are normally in great scale. Generally, method used for the installation of pilling such as the drop hammer method will involve high energy to drive a single pile into the ground. Hence, the soil particles may undergo serious physical changes that will affect the engineering properties of soil used in the design work. The main aim of this research is to know the impact of pile installation work on sand particles. To understand the impact of sand particle breakage to the soil strength, an actual soil breaking mechanism simulated in the laboratory by using an automated soil compactor where the sand samples were crushed using 500 and 1000 times of blows respectively. The behaviour of sand were then analysed using a series of test which are; sieve analysis, specific gravity, relative density and the shear box test in order to measure the engineering properties of the sand. Mackintosh probe test was conducted in-situ to identify the undrained shear strength of sand and to correlate the cohesion of the sand with laboratory testing. This research confirmed that particle breakage has a significant influence with sand shape and therefore its strength changes with crushing impact.

Low velocity impact performance of fiber-reinforced polymer impregnated with shear thickening fluid

In this study, the mechanical performance of fiber-reinforced polymer (FRP) impregnated with shear thickening fluid (STF) under low-velocity impact was investigated. Three types of FRPs, with basalt (BFRP), carbon (CFRP), and glass (GFRP) fibers were prepared and 20 wt% STF was impregnated into these FRPs to develop FRP composite materials. The resistive force and energy dissipation of STF-impregnated FRP (FRP-STF) specimens and corresponding neat FRP specimens were evaluated using a drop hammer test. The test results demonstrate that the impregnation of the STF can effectively enhance the impact resistance performance of the three FRPs. Nevertheless, the enhancing effect and mechanism are different for different FRP types. For the BFRP and CFRP, the STF only improves their mechanical performance, while for the GFRP, the STF changes its mechanical mechanism. In terms of maximum enhancement resistive force, the STF has a significant effect on the CFRP, with a 78.0% increase compared to neat CFRP. In addition, the GFRP-STF shows excellent energy dissipation performance; the energy absorbability is increased to 90.7%, an increase of 119% compared to neat GFRP.

A smart passive MR damper with a hybrid powering system for impact mitigation: An experimental study

This paper presents a smart passive MR damper with fast-responsive characteristics for impact mitigation. The hybrid powering system of the MR damper, composed of batteries and self-powering component, enables the damping of the MR damper to be negatively proportional to the impact velocity, which is called rate-dependent softening effect. This effect can keep the damping force as the maximum allowable constant force under different impact speed and thus improve the efficiency of the shock energy mitigation. The structure, prototype and working principle of the new MR damper are presented firstly. Then a vibration platform was used to characterize the dynamic property and the self-powering capability of the new MR damper. The impact mitigation performance of the new MR damper was evaluated using a drop hammer and compared with a passive damper. The comparison results demonstrate that the damping force generated by the new MR damper can be constant over a large range of impact velocity while the passive damper cannot. The special characteristics of the new MR damper can improve its energy dissipation efficiency over a wide range of impact speed and keep occupants and mechanical structures safe.

Experiment and Simulation of Impact Response of Woven CFRP Laminates with Different Stacking Angles

The effects of different laying angles on impact resistance and damage types of woven carbon fibre-reinforced polymer (CFRP) laminates were studied. The drop hammer impact test and simulation analysis of woven CFRP laminates at four different velocities were carried out by means of the combination of experiment and explicit finite element analysis. The effect of impact velocity on damage pattern and fracture of woven CFRP laminates with eight layers and four laying angles (0°, 15°, 30°, and 45°) was studied by drop weight impact test, and the damage area of woven CFRP laminates with different laying angles was measured by ultrasonic nondestructive testing method. A user-defined material model was developed based on LS-DYNA to simulate the impact behavior of woven CFRP laminates. A finite element simulation model was established to effectively predict the complex damage evolution of woven CFRP laminates under low-speed impact loading. Its effectiveness was verified by impact response and damage crack pattern. The energy absorption and impact force of the laminated plate increase gradually from 0° to 45° in the laying angle of woven fabric. With the increase of laying angle from 0° to 45°, the length of fracture crack and the damage area increase. The developed model can accurately predict the impact properties of the composites.

Dynamic responses of reinforced ultra-high performance concrete members under low-velocity lateral impact

This paper presents a combined experimental and numerical study on the low-velocity lateral impact behavior of reinforced ultra-high performance concrete (UHPC) members. Firstly, a total of eleven steel bar reinforced UHPC and two reinforced normal strength concrete (NSC) control specimens with the identical dimensions (300 mm × 300 mm × 2200 mm) were prepared and tested under drop hammer impact. By examining the influences of impact energy (16.66–33.32 kJ) and the axial force (140–1400 kN) on the dynamic damage and responses of specimens, the outstanding impact resistance of UHPC members is validated and assessed quantitatively. Besides, the presence of axial force can effectively improve the lateral impact resistance of the UHPC members, particularly the recovery of deformation. Secondly, based on the commercial finite element (FE) program LS-DYNA, a FE model was established to predict the impact behavior of UHPC members. The Continuous Surface Cap (CSC) model for NSC was adopted, and the corresponding model parameters for UHPC were calibrated based on a series of test data, i.e., static compressive and direct tensile tests, dynamic compressive and tensile tests, triaxial compressive tests, and hydrostatic tests. Furthermore, the generation method of CSC model parameters for UHPC was proposed, which was fully validated by comparing with the present and existing low-velocity impact test data on reinforced UHPC and UHPC filled steel tube (UHPC-FST) members.

Experimental and numerical studies on square steel-reinforced concrete-filled steel tubular (SRCFST) members subjected to lateral impact

Steel-reinforced concrete-filled steel tubular (SRCFST) structures were proposed in recent years and have been employed in engineering practices. To date, the existing studies mainly focused on the behaviours of SRCFST structural members under static or seismic load. Only very limited studies of the SRCFST structural members subjected to impact load, which might cause severe damage and even structural collapse, can be found in literature. In this study, experimental and numerical studies on square SRCFST specimens under lateral impact load are conducted. A total of eighteen square SRCFST specimens are fabricated and tested via a drop hammer impact device. Various parameters (i.e. impact velocity, boundary condition, impact direction, cross-section of steel profile and axial load level) are considered to evaluate their effects on impact responses of square SRCFST members. The damage modes, impact forces, mid-span displacement responses and energy absorption capacities of the tested specimens are extracted from testing data and analysed. Furthermore, by using the software ABAQUS, numerical model is established and validated with the testing results. With the validated numerical models, the damage evolution, sectional stress and energy distribution of the structure with different parameters and impacting scenarios are evaluated. The impact behaviours of square SRCFST and concrete-filled steel tubular (CFST) members are also compared and discussed.

Determining the weight of the hammer based on expert experience for estimating load-carrying capacity

Inexperience geotechnical engineer has difficulty in specifying the best type of weight of the hammer. Here, this study aims to help inexperience geotechnical engineers to decide the optimum weight of the hammer on the pile driving machine. The Bayes method is applied to decide between drop hammer and diesel hammer pile driving machines. Furthermore, we interviewed the expert by several questions about the criteria of the best pile driving machine using a Likert scale. The result suggests that the best type of pile driving is Drop Hammer. The weight of the hammer required to carry out the piling process is 0.9 ton. Recommendations for allowable bearing use the Meyerhof 1976 method. This condition meets the workload that more 141.14 tons at a depth of 26 m when using a square pile dimension of 35 x 35 and 40 x 40 cm. The dimensions are 45 x 45 cm, the recommended depth of piles is 26 m. the allowable bearing carrying when compared with the dynamic capacity using the Hilley, ENR, and WIKA methods meet the requirement. This is given the result of the allowable load-carrying capacity of 170 tons that less than 280 tons until 390 tons at dynamic capacity.

Elucidation of Mechanism Underlying Workpiece Jump in Hammer Forging

During the process of drop hammer forging, workpieces sometimes jump after strikes. The present research investigates the mechanism of the workpiece jump by means of experiments and numerical simulations. In the experiments, workpieces were struck by vertical symmetrical flat dies or vertical asymmetrical dies. A high-speed camera was used to measure the workpiece deformation, the position of workpieces during jumping and the position of the dies. Strain of lower dies and structures of the hammer were measured by strain gauges. Vibration of the antirattler under the hammer, elastic vibration of lower dies and structures of the hammer, and contact area between workpieces and dies were analyzed by numerical simulations. The results indicate that workpieces jump by adhesive force between workpieces and dies, and by elastic vibration of lower dies and structures of the hammer.

Experimental Study on the Impact Resistance of Closed‐Cell Aluminum Foam Protective Materials to RC Piers under Lateral Impact

In this study, the lateral impact tests of six RC piers which were protected by closed‐cell aluminum foam (CCAF) were carried out by making use of an ultrahigh drop hammer horizontal impact test system. The protective effects of CCAF with different densities on the piers were then analyzed. The data regarding the piers’ impact force, displacement, reinforcement strain, and crack and damage development were mainly collected during the experimental testing processes. The results indicated that, when the impact energy was less than 7258 J and the density of the CCAF was 0.45 g/cm3, the cumulative impact force and displacements of the piers decreased by 67% and 35%, respectively. Therefore, it was considered that the CCAF with a density of 0.45 g/cm3 had displayed the best protective effects at that stage. It was also observed that when the impact energy was greater than 7258 J and the density of the CCAF was 0.55 g/cm3, the cumulative impact force and displacements of the piers decreased by 25% and 18%, respectively. Therefore, the CCAF with a density of 0.55 g/cm3 had displayed the best protective effects at that stage. Furthermore, under the conditions of constant accumulative impact energy, the protective effects of CCAF on the piers were observed to be weakened if it entered the densification stage too early and high‐yield platforms were formed due to the density levels becoming too high. However, it was found that reasonable density and thickness increases could effectively delay the entry of CCAF into the densification stage, which effectively reduced the shearing effects which occurred when the impact speeds were too high, thereby preventing the shear failure of the piers.

A Laboratory-Scale Instrumented Forging Hammer as an Intermediate Strain Rate Testing Device

Mechanical characterisation of metallic materials at intermediate strain rates is essential to calibrate and validate computational models for industrial applications such as high-speed forming processes i.e. hammer forging, blanking, forming, etc. The most common devices that perform medium to high loading rate experiments are the servo-hydraulic universal testing machines and Split Hopkinson bar systems. Here we analyse the possibility of employing an in-house designed and constructed DirectImpact Drop Hammer (DIDH) for material mechanical characterisation at medium strain rates, ranging from 100 to 300 s-1. To show the suitability of the DIDH for mechanical characterisation, uniaxial compression experiments on S235JR structural steel are conducted and compared with finite element (FE) simulations performed with an elasticthermoviscoplastic material model previously calibrated with Split Hopkinson Pressure Bar (SHPB) tests.

Study and selection of hot forging die materials and hardness

This review discusses in detail the process of hot forging and the types of machines involved and explains the die materials used for hot forging of the respective types of machines, such as vertical forging presses (friction presses), drop hammer forging presses and horizontal forging machines. Forging requires forging the metal using compressive forces. It investigates the chemical properties of die materials used in hot forging. The article covers the materials, the properties of the forging die inserts and the master die inserts. The hardness of the materials has been defined on the basis of the chemical composition and the heat treatment process, the heat treatment is widely used for tungsten-based and chromium-based hot work tool steel to achieve microstructure. This article ends with the required die content and uses it on the basis of the hardness of the billet utilized.

Experimental study of RC columns and composite columns under low-velocity impact

In this study, thirty specimens were tested using a drop hammer impact test machine, comprising six reinforced concrete columns and twenty-four specimens of the composite columns. The composite columns include steel tubular-encased reinforced concrete (R-ST) columns, steel-reinforced concrete-filled steel tubular (S-ST) columns, hollow concrete-filled double steel tubular (H-DS) columns, and solid concrete-filled double steel tubular (S-DS) columns. The influences of different axial load levels and different column sections on the responses, such as impact force, the impact duration, the deflection, and the longitudinal strain, are investigated and discussed in detail. The results indicate that compared with the brittle failure of RC columns, all R-ST columns and composite columns behaved in a ductile manner. Moreover, the steel tube can effectively enhance the impact resistance of RC columns. The variation of axial load level has an important influence on the axial load attenuation, deflection, the impact duration, and the plateau value of the impact force. Under the same test conditions, S-DS columns have the best impact resistance with the lowest mid-span displacement, followed by H-DS columns, whereas the impact resistance of S-ST columns is slightly inferior with the highest mid-span displacement among the composite columns.

Performance of concrete-encased CFST subjected to low-velocity impact: shear resistance analysis

The performance of concrete-encased concrete-filled steel tube (concrete-encased CFST) subjected to low-velocity impact is investigated through experimental and numerical studies in this paper. A total of 40 concrete-encased CFST specimens, 20 square and 20 circular ones, are tested under a drop hammer apparatus. It shows that while the outer RC components have a shear-dominated failure mode, the core CFST deforms in a flexural pattern. The influence of tested parameters on the impact force and midspan deflection of the specimens is summarized. A finite element analysis (FEA) model is then established to investigate the shear mechanism of concrete-encased CFST under impact. A comparative study between a concrete-encased CFST member and an RC member shows that the core CFST component could effectively mitigate the shear failure of the outer RC section under impact due to its high shear resistance; meanwhile, the outer RC component could well protect the core CFST and reduce its flexural deformation. Such composite effects make the concrete-encased CFST a desirable impact-resisting structure. Subsequently, a parametric study on the impact velocity shows that the debonding between outer RC and core concrete can be more prominent for the impact with a relatively higher velocity, and the use of shear studs is suggested for members under such circumstances.