High-speed Impact Tests Research Articles

Numerical study of the influences of pressure confinement on high-speed impact tests of dynamic material properties of concrete

Although tests of Modified Split-Hopkinson Pressure Bar (MSHPB) system with a pressure vessel filled with pressurized fluid or air give concrete material properties under multi-axial stress states, as will be demonstrated in this study, they do not lead to accurate results because the confining pressure under impact tests changes when specimen deforms. Unfortunately there is no reliable apparatus yet to perform impact tests on specimens with a controllable confining pressure. In this study, a mesoscale concrete model with consideration of randomly distributed aggregates is developed to study the strain rate effect on concrete under confining pressures. The results show that the strain rate sensitivity of concrete decreases with the increment of the confining pressure, indicating the strain rate effect of concrete under multi-axial stress states is less prominent as compared to that under uniaxial stress state. Using the uniaxial impact testing data overestimates the strain rate effect of concrete material under multi-axial stress states. An empirical relation is proposed in this study to model the concrete Dynamic Increase Factor (DIF) for the case with pressure confinement, which can be used to more accurately represent the DIF of concrete material under multi-axial stress states.

High speed impact test on rock specimens with a compressive stress pulse

In exploration for a methodology to analyze fast deformation of a thick specimen where a state of equilibrium cannot be assumed, high-speed impact tests on pumice-stone and granite sample specimens are conducted with Hopkinson bar test apparatus. A compressive stress pulse from the input bar is applied to the specimens ranging from 8 mm to 30 mm in thickness. The stresses on the front (input-bar) side and the rear (output-bar) side of the specimen are evaluated separately based on the strain gauge signals from the input and output bars. Optical emission from the specimen is captured with a photomultiplier. Analyses on the time variation of the strain gauge and photomultiplier signals lead to the following observations. (a) The front-side stress plays an important role in the deformation and fracture, (b) the transition from the elastic to plastic regime can be estimated from oscillatory features observed in the front-side stress and other quantities derived from the strain gauge signals, (c) the optical emission is highly correlated with the front side stress and step-wise energy loss in the specimen, and (d) the main frequency components of the stress wave associated with the energy-loss are found in the same frequency band as conventional acoustic emissions observed in rock fractures. A question remains, and provides an interesting subject for future study, regarding the step-wise energy loss observed in the strain gauge signal unaccompanied by the optical emission. In view of a recent fracture mechanical theory that states the evolution of fracture is accompanied by a reduction in frequency on the emission spectrum, it is possible that these energy loss is associated with emission in frequency ranges outside the sensitivity of the photomultiplier.

Multi-Scale Modeling of Composites with Surrogate and Uncertainty in Residual Velocity for High-Speed Impacts

The bullet impact onto a composite plate has been investigated both numerically and experimentally. The main purpose is to numerically identify the range of uncertainty shown in the residual velocities from the high-speed impact test data. The simulation is based on the multi-scale modeling for composites. The experimental results presented here include the tensile tests of composite specimen to identify the range of failure strains and mainly the ballistic shot test onto a laminated plate to measure the residual velocities with especial interests in the range of uncertainty. All test data have been compared with numerical predictions and the scattered test data are reasonably well captured with simulations.

Penetration resistance of ultra-high-strength concrete protected with layers of high-toughness and lightweight energy absorption materials

Aluminium foam has advantages of excellent shock absorption, cyclic utilization, and lightweight. Ultra-high-molecular-weight polyethylene (UHMWPE) fibre has a low density, a high specific strength, a high modulus and a great capability in energy absorption. Steel wire mesh has high toughness and elongation properties and a good effect on energy absorption. In the present study, UHMWPE fibre, steel wire mesh and aluminium foam were used to protect ultra-high-strength concrete (UHSC) targets to resist DT300 high-strength alloy-steel projectile penetration with striking velocities from 550 m/s to 800 m/s. High-speed impact tests on normal-strength concrete (NSC) targets were also conducted for comparison. Testing results including the failure mode, depth of penetration (DOP), crater dimensions and damage area of protected concrete targets, indicate that the new composite material protective cover has an outstanding performance in the shock wave absorption, especially in reducing the crack propagation and debris spatter of protected UHSC targets, as well as increasing the deviation angles of projectile terminal ballistic trajectories. It is a successful demonstration of anti-penetration properties research for new concrete composite structures.

The Effect of Al on the Mechanical Properties and Microstructure of Copper-based Metallic Glass

An investigation was carried out into the effect of different amounts of Al on the mechanical properties, and glass-forming ability, of a three component alloy (Cu–Zr–Al). The mechanical properties were studied using a universal materials tester and a Split-Hopkinson bar tester. A series of amorphous alloys with different Al content were subjected to static compression and dynamic high-speed impact tests at 10−1 s−1, 10−2 s−1, and 10−3 s−1 for the static condition and 2000 s−1, 3000 s−1, and 4000 s−1 for the dynamic condition. Experiment showed that the flow stress value and the strain rate sensitivity coefficient of the copper-based amorphous alloys varied with changes of strain and strain rate. An increase in the rate of strain caused the flow stress value and the sensitivity coefficient of the strain rate to rise. When the Al content in an amorphous alloy Cu47.5Zr45.5Al7 was 7%, both the flow stress value and the strain were improved and effectively upgraded the mechanical properties of the material.

Failure Localization and Correlation of High-Speed Tension and Impact Tests of Strain-Hardening Cement-Based Composites

AbstractMechanical properties of strain-hardening cement-based composites (SHCC) subjected to impact and high-speed tensile loading were studied. The impact test setup was based on a free-fall drop...

A preliminary study on the local impact behavior of Steel-plate Concrete walls

International regulations for nuclear power plants strictly prescribe the design requirements for local impact loads, such as aircraft engine impact, and internal and external missile impact. However, the local impact characteristics of Steel-plate Concrete (SC) walls are not easy to evaluate precisely because the dynamic impact behavior of SC walls which include external steel plate, internal concrete, tie-bars, and studs, is so complex.In this study, dynamic impact characteristics of SC walls subjected to local missile impact load are investigated via actual high-speed impact test and numerical simulation. Three velocity checkout tests and four SC wall tests were performed at the Energetic Materials Research and Testing Center (EMRTC) site in the USA. Initial and residual velocity of the missile, strain and acceleration of the back plate, local failure mode (penetration, bulging, splitting and perforation) and deformation size, etc. were measured to study the local behavior of the specimen using high speed cameras and various other instrumentation devices. In addition, a more advanced and applicable numerical simulation method using the finite element (FE) method is proposed and verified by the experimental results.Finally, the experimental results are compared with the local failure evaluation formula for SC walls recently proposed, and future research directions for the development of a refined design method for SC walls are reviewed.

Multiscale Analysis of Open-Cell Aluminum Foam for Impact Energy Absorption

The energy-absorbing characteristics of crash members in automotive collision play an important role in controlling the amount of damage to the passenger compartment. Aluminum foams have high strength-to-weight ratio and high deformability, thus good crashworthiness is expected while maintaining or even saving weights when foams are implemented in crash members. In order to investigate the effect of the open-cell aluminum foam fillers on impact performance and weight saving, a multiscale framework for evaluating the crashworthiness of aluminum foam-filled members is used. To circumvent the difficulties of mechanical tests on foams, a micromechanical model of the aluminum foam is constructed using the x-ray micro tomography and virtual tests are conducted for the micromechanical model to characterize the behavior of the foam. In the macroscale, the aluminum foam is represented by the crushable foam constitutive model, which is then incorporated into the impact test simulation of the foam-filled crash member. The multiscale foam-filled crash member model was validated for the high-speed impact test, which confirms that the material model characterized by the micromechanical approach represents the behavior of the open-cell foam under impact loading well. Finally, the crash member design for maximizing the energy absorption is discussed by investigating various designs from the foam-only structure to the hollow tube structure. It was found that the foam structure absorbs more energy than the hollow tube or foam-filled structure with the same weight.

The impact of wood fiber surface modification on physical properties of wood-polymer composites

In this paper, the impact of wood fiber surface modification on mechanical properties of poly-(methyl methacrylate)(PMMA)-wood composite was examined. FTIR analysis has shown that the wood fiber surface modification was accomplished and that the matrix-fiber bond was established. The SEM image of the breakage surface has affirmed the improved adhesion between the fibers and the polymer in the specimen with modified wood fibers. The bond improvement between the wood fibers and the matrix results in increased hardness and a better distribution of strain within the composite. High speed impact testing results have shown that the specimen with the bonding agent can increase the absorbed energy six times when compared to the pure PMMA specimen.

FEM analysis on the deformation and failure of fiber reinforced metallic glass matrix composite

In the present manuscript the finite element method (FEM) simulations on the deformation and failure of composite are conducted systemically by integrating with the related quasi-static, dynamic and high-speed impact tests. The corresponding deformation and failure characteristics are discussed in detail, especially the shear banding behaviors, including the initiation and propagation of shear band, and the shear banding-induced failure, are emphasized. Furthermore, the influences of various internal and external factors on the mechanical behaviors of composite are analyzed. Related analysis shows that the reinforced fibers could improve effectively the plasticity of composite. Moreover, several factors, e.g., the volume fraction of fiber and the mechanical property of fiber material, have significant influence on the mechanical behavior of composite, and the strain rate also plays an important role for the deformation mode. The corresponding deformation and failure characteristics depend firmly on the impact of shear band from the MG matrix onto the reinforced fibers.

Hard projectile impact on layered SFRHSC composite target

A series of hard projectile high-speed (500–700 m/s) impact tests on the steel fiber reinforced high strength concrete (SFRHSC) panel with rear steel liner and (or) backfilled sandy soil were conducted. The impact resistance of the above layered composite target as well as the parametric influences were assessed experimentally. It indicates that, within the discussed parameters variation ranges: (i) the rear sandy soil layer enhance the impact resistance of the SFRHSC/steel composite target; (ii) the steel liner also enhance the impact resistance of SFRHSC/sandy layer composite target; (iii) the strengthening effect of the rear sandy soil layer on the impact resistance of bare SFRHSC panel is more influential than the rear steel liner; (iv) Reinforcing steel bars of the concrete panel has no obvious effect on the impact resistance of SFRHSC/steel/sandy soil composite target; (v) Mixing steel fibers can efficiently reduce the damages of the concrete target. An approach for predicting the ballistic limits of SFRHSC/steel and SFRHSC/steel/sandy soil composite targets were proposed and compared with the present test data.

High and Low Speed Impact Characteristics of Nanocomposites

Nanocomposites attracted the attention of scientists due to their superior mechanical, thermal, chemical and electrical properties. This research studied the impact of adding carbon nanotubes (CNTs) to the woven Kevlar laminated composites on the high and low speed impact characteristics. Different percentages of CNTs were added to the woven Kevlar-Vinylester composite materials. An in-house developed drop weight testing apparatus was utilized for the low speed impact testing. Two different concentrations of the CNTs were added to a 15-layer woven Kevlar laminates, 0.32 wt% and 0.8 wt%. The results showed that: The 0.32 wt % CNT sample enhanced the interlaminar strength of the composite without enhancing the energy absorption capacity whereas, the 0.8 wt % CNT sample did not improve the impact resistance of the Kevlar composite.For the high speed impact tests, a bulletproof vest was prepared using woven Kevlar, resin, and CNTs at 1.5 w% percentage. The ballistic shooting was carried out by a professional shooter using a 30 caliber and 9 mm bullets for the tests. The CNT bulletproof sample bounced back the 30 caliber copper alloy bullet with no penetration.

Integrated Durability of Automobile Alternator Test System Design Based on LabVIEW

New standards in the automotive industry highlighted the situation of the actual operation of the alternator and a variety of harsh environment simulation limit test. Using new standards in the automotive industry as a guide, this article presents a virtual instrument based on the durability of automobile generator integrated test system. The design adopt virtual instrument technology in designing the system, Graphic language, LabVIEW is applied in writing measure-control program. The system uses a lot of features on LABVIEW, including Data acquisition, control of serials port, etc. Test implementation uses the host computer via RS232 and RS485 communication port and the data acquisition card, NI PCI- 6221, to control the frequency hybrid motor, temperature control box, electronic loads and other intelligent devices, and to simulate a variety of automotive alternator working conditions and real-time monitoring to monitor the status of generators. Using this system, two separate automobile alternators can be tested in terms of high-speed vehicle impact and high temperature durability test and electrical performance test and other tests at the same time. As a result, the generator speed measurement error is within 1%, the control error is within 2%, voltage and current measurement errors were within 0.5% and 0.4%, which meets the requirements.

Interfacial reaction and mechanical evaluation in multi-level assembly joints with ENEPIG under bump metallization via drop and high speed impact test

The criteria of mechanical reliability in solder joints can be identified and described by comparative evaluation via drop test and high speed pendulum impact test. Systematic samples of assembly and attachment joints with various Pd additions were employed and investigated in this study. The statistical values of mechanical performances were calculated and compared. Better high speed impact performance of SAC305/ENEPIG attachment joints with 0.06μm Pd layers was confirmed owing to the single Cu6Sn5 phase growth. However, the comparative measurement of the better performance on drop testing exhibited in ENEPIG/SAC305/immersion Sn assembly joints with 0.1μm Pd layers deposit resulted from the thinner and layer-type IMC growth. The correlation between the cracks propagation and Pd addition was established on the basis of the elemental X-ray color mapping via Field-Emission Electron Probe Microanalyzer (FE-EPMA). It is expected that through comparison between impact and drop test in mechanical reliability, a criterion of joints reliability can be established. Besides, the optimal Pd layer deposit for the ENEPIG surface finish in the attachment and assembly solder joints was demonstrated and confirmed.

Improving the shear strength of Sn–Ag–Cu–Ni/Cu–Zn solder joints via modifying the microstructure and phase stability of Cu–Sn intermetallic compounds

This study focuses on the correlation between high-speed impact tests and the interfacial reaction in Sn-3.0Ag-0.5Cu-0.1Ni/Cu (wt%) and Sn-3.0Ag-0.5Cu-0.1Ni/Cu-15Zn solder joints. Adding Ni into the Sn–Ag–Cu solder alters the interfacial morphology from scallop type to layer type and exhibits high shear strength after reflow in both solder joints. However, the shear strength of Sn-3.0Ag-0.5Cu-0.1Ni/Cu solder joints degrades significantly after thermal aging at 150 °C for 500 h. It is notable that Sn-3.0Ag-0.5Cu-0.1Ni/Cu-15Zn solder joints still present higher shear strength after aging at 150 °C. The weakened shear strength in Sn-3.0Ag-0.5Cu-0.1Ni/Cu solder joints is due to stress accumulation in the interfacial (Cu,Ni)6Sn5 compound induced by the phase transformation from a high-temperature hexagonal structure (η-Cu6Sn5) to a low-temperature monoclinic structure (η'-Cu6Sn5). However, doping small amounts of Zn into (Cu,Ni)6(Sn,Zn)5 can inhibit the phase transformation during thermal aging and maintain strong shear strength. These experiments demonstrate that Sn-3.0Ag-0.5Cu-0.1Ni/Cu-15Zn solder joints can act as a stable connection in the micro-electronic packaging of most electronic products at their average working temperatures.

Influence of the concrete DIF model on the numerical predictions of RC wall responses to blast loadings

Reliable prediction of structural responses to blast loadings requires an accurate dynamic material model. The dynamic strength of concrete material is normally higher than the static strength. Based on extensive experimental data, a number of empirical DIF (dynamic increase factor) relations have been proposed to model concrete material strength increment at high strain rates. Most of these empirical relations are obtained by fitting the scattered dynamic testing data. It is commonly acknowledged that the induced structural effects such as lateral inertia confinement effect are inevitable in high-speed impact tests. Therefore directly fitting the laboratory testing data may not necessarily obtain the true dynamic concrete material properties. Some recent studies investigated the contributions of lateral inertia and end friction confinement effects on DIF of concrete materials in laboratory tests, and proposed relations to remove these influences to obtain the true DIF for concrete materials. The present study carries out numerical simulations of a reinforced concrete wall under different blast loadings. Different DIF relations including CEB defined DIF, DIF proposed in previous studies after removing structural effect in laboratory tests, and NO DIF, i.e., neglecting dynamic strength increment, are considered in numerical simulations. Verification of the numerical model is made through the comparisons of the numerical simulation results with field test data. The results demonstrate that using the new DIF model yields the best prediction of the structural responses. The responses of a typical RC wall under blast loads with a 5m stand-off distance but different TNT explosive charge weights are also simulated using different DIF relations. The responses of RC wall obtained from numerical models with different DIF relations of concrete material are compared. From the numerical simulation results, the range of scaled distance that DIF relation has significant influences on the numerical simulation results is identified.

Effect of Textile Architecture on Energy Absorption of Woven Fabrics Subjected to Ballistic Impact

Woven fabrics are widely used in various protective applications. The effects of different woven architectures (such as plain, basket, twill and satin) on impact resistance performance have not been adequately studied. In this work, high-speed impact testing on single layer plain weave structures has been carried out using a gas gun experimental setup. Ballistic resistance performance of the woven fabric is evaluated based on the resultant velocity of the projectile, as well as the post-mortem failure analysis. Finite element computational models are presented in this research, thereby providing predictive capability for the manufacturer and designer in order to minimise field testing, as well as shedding light on to the damage mechanisms of composite fabrics subjected to ballistic impact. The numerical model is validated with the experimental results in terms of dissipated energy and resultant velocity. Numerical investigation is conducted on other woven structures of identical areal density for comparison, revealing the importance of fabric architecture. The influences of yarn-yarn and yarn-projectile friction properties on the ballistic performance of various textile structures are also presented.

Impact strength of Sn–3.0Ag–0.5Cu solder bumps during isothermal aging

In order to investigate the fracture behavior of Sn–3.0Ag–0.5Cu solder bump, solder balls with the diameter of 0.76mm were soldered on Cu pad in this study, then high speed impact test and static shear test of solder bumps were carried out to measure the joint strength of the soldering interface. The effect of isothermal aging on joint strength as well as fracture behavior of solder bumps was investigated, and the composition of the fracture surface was identified by means of EPMA. The results indicate that the fracture is inside the bulk solder in low speed shear test regardless of the aging effect, thus the maximum load reflects the solder strength rather than the interfacial strength. It is also found that under 1m/s impact loading, the crack initiation position is changed from solder/Cu6Sn5 interface to Cu3Sn/Cu interface after long time isothermal aging, and the fracture occurs inside the bulk solder accompanying with intermetallic compound in both of the as-soldered and aged joints. The thickened multiple IMC layers during isothermal aging account for the degraded impact resistance, and the change of the solder matrix is another factor for reduced impact resistance owing to Sn residue on the fracture surface.

Construction of Hammer for Sugarcane Shredder

Article deals with construction of hammer for cane shredder. Function of hammer in shredder consists in crushing sugarcane stalks for further processing in sugar production. Hammer loading and other calculations were made. Four weld deposit materials were suggested for protection of hammer against wear and dynamic loading. All samples with weld deposit were subjected to microstructure evaluation, chemical analysis, high speed impact testing and tribological PIN-on-DISC test for estimation of wear resistance. One weld deposit material was recommended as a result of these tests.

High-speed impact test using an inertial mass and an optical interferometer

A high-speed impact testing method for evaluating mechanical properties of materials is proposed using an inertial mass and a dual beat-frequencies laser Doppler interferometer (DB-LDI). In this method, an inertial mass levitated using an aerostatic linear bearing is made to collide with the material being tested at a high initial velocity. During the collision, the velocity of the mass, which is even higher than the critical velocity (±0.56 m/s) defined by the frequency difference of the Zeeman laser, is accurately measured using the DB-LDI. The position, acceleration, and impact force of the mass are calculated from the measured velocity. Using the proposed method, the mechanical properties of a visco-elastic material under a high-speed impact loading condition can be accurately evaluated.