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International Journal of Impact Engineering

International Journal of Impact Engineering

Archives Papers: 880
Elsevier
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Numerical study on the structural response of blast-loaded thin aluminium and steel plates
V. Aune; G. Valsamos; F. Casadei; M. Larcher; M. Langseth; T. Børvik;
Keywords:Airblast loading;Reversed snap buckling;Negative phase;Ductile failure;EUROPLEXUS;
Abstracts:The inelastic response of thin aluminium and steel plates subjected to airblast loading is studied numerically and validated against experimental data. Special focus is placed on the influence of elastic effects and negative phase on the structural response. The blast loading was varied by detonating spherical charges of plastic explosives at various stand-off distances relative to the centre point of the plates. The numerical results obtained with the finite element code EUROPLEXUS were in good agreement with the experiments and predicted the entire range of structural response from complete tearing at the supports to a more counter-intuitive behaviour (CIB) where the final configuration of the plate was in the opposite direction to the incident blast wave due to reversed snap buckling (RSB). RSB attracted special attention since this is an unstable configuration sensitive to small changes in the loading and in structural characteristics. The negative phase of the blast pressure is usually neglected in blast-resistant design. However, the numerical simulations showed that the negative overpressure dominated the structural response and led to RSB at some loading and structural conditions. Two distinctive types of CIB were identified and both were found to depend on the timing and magnitude of the peak negative overpressure relative to the dynamic response of the plates. The study also revealed that CIB may occur in thin plates when the negative impulse is of the same order of magnitude as the positive impulse. The partial and complete failure along the boundaries observed in some of the tests was also successfully recreated in the simulations by using an energy-based failure criterion and element erosion.
Dynamic material parameters of closed-cell foams under high-velocity impact
Shilong Wang; Yuanyuan Ding; Changfeng Wang; Zhijun Zheng; Jilin Yu;
Keywords:Closed-cell foam;Finite element analysis;Velocity field;Shock wave;Dimensional analysis;
Abstracts:Cellular materials under high-velocity impact have highly localized deformation with the cells layer-wise collapse, which is usually characterized by the propagation of shock wave. Researches have shown that the shock wave speed is strongly dependent on the impact velocity, but the effect of the meso-structural and base-material parameters is unclear. In this study, the dynamic material parameters of closed-cell foams are investigated with cell-based finite element models. The one-dimensional velocity distribution along the loading direction is used to capture the propagation of shock front. The shock wave speed is thus determined and it exhibits a linear relationship with impact velocity when the impact velocity is high enough. The difference between the shock wave speed and the impact velocity is a dynamic material parameter of cellular material and the effect of meso-structural and base-material parameters on this dynamic material parameter is investigated with dimensional analysis. An expression of the dynamic material parameter with respect to the relative density and the base-material parameters is obtained. It shows that the dynamic material parameter intensively relies on the relative density and increases linearly with the relative density. The investigation of dynamic stresses with the aid of a shock model shows that the initial crushing stress increases in a power-law tendency with the increase of relative density. As a result, a stress–strain relation involving the relative density of material cellular and the yield stress and density of base material is obtained for the closed-cell foams considered. The effects of hardening behaviors of cell-wall material and gas trapped within cells are also considered. It is found that the dynamic material parameter exhibits nearly linear increase with the increase of hardening parameters of base material and initial gas pressure, while the dynamic initial crushing stress is independent of the strain-hardening parameter and the entrapped gas pressure but increases with the strain-rate hardening parameter linearly. These findings may be helpful for guiding the crashworthiness design of cellular materials and structures.
Hugoniot data of Seeberger sandstone up to 7 GPa
Tobias Hoerth; Frank Bagusat; Stefan Hiermaier;
Keywords:Sandstone;Shock equation of state;Planar plate test;VISAR interferometer;Pore collapse;
Abstracts:Planar-plate impact tests were carried out for the measurement of Hugoniot data of dry Seeberger sandstone in the pressure range of up to 7 GPa. A special inverse testing method suitable for rock targets was applied together with a laser interferometer for the measurement of the free-surface velocity of the target plate required for the calculation of the particle velocity (up ) and the shock wave velocity (US ) in the sandstone specimen. In our measurement range (impact velocity between about 50m/s and about 1300 m/s), the US up data show significant scattering. The travel times of the impact-induced shock waves indicate that pore crushing occurs. A strong dependance of the US up data on the test batch selected for the impact experiments and, thus, on the mining location was observed. This dependance is greater than the scattering of the individual data sets.
Development and validation of a set-up to measure the transferred multi-axial impact momentum of a bird strike on a booster vane
Frederik Allaeys; Geert Luyckx; Wim Van Paepegem; Joris Degrieck;
Keywords:Force measurements;Impact;Bird strike;Numerical simulation;
Abstracts:Reaction force has always been one of the main characterization parameters for impact events. Today, a set of force transducers are a common and valuable tool to measure reaction forces. But the force signals are often influenced by vibrations of the supporting structures. Many other attempts were already taken in the past to use other methods to measure force, such as ballistic pendulums, Hopkinson bars, etc., all having their advantages and disadvantages. In this work, a multi-axial force measurement tool is developed to serve in a test campaign of bird strike experiments on booster vanes. The idea is to give some well-chosen mass three rotational degrees of freedom and acquire the transferred rotational momentum from an optical measurement, which is a direct measure for the impact force. The tool is validated experimentally and numerically using a simplified steel vane.
Modeling dynamic fragmentation of heterogeneous brittle materials
David Cereceda; Lori Graham-Brady; Nitin Daphalapurkar;
Keywords:Dynamic fragmentation;Heterogeneous;Extreme loading rates;Fragmentation statistics;Brittle;Glass;Concrete;Masonry;
Abstracts:Extreme high-rate loading of structural materials triggers a complex process of fragmentation involving probabilistic, energetic and mechanical aspects. One-dimensional modeling approaches based on elastodynamics have been successfully used to predict strain-rate dependence of average fragment-size. However, the ability of such approaches to correctly predict the statistical distribution of fragment-size has not been quantitatively compared with experiments. In this work, we use a one-dimensional approach based on the model suggested by Zhou et al. [1] to assess dynamic fragmentation in glass, concrete and masonry. The model considers a one-dimensional bar under a uniform initial tensile strain rate, with spatially varying strength to represent variations in the materials microstructure. The results include fragment-size, fragment-mass and time of formation distributions for strain rates between 103 and 105 s - 1 . Results show that the generalized gamma distribution is highly suitable for describing the fragment-size statistics. Given uncertainty in the standard deviation of the strength, a parametric study was performed to assess the effects of these variations on the fragmentation statistics. The trend in the rate-dependence of average fragment-size shows good agreement with measurements from shock tube experiments for all the materials studied. However, the estimated parameters of the fragment-size distribution from the 1D modeling approach do not compare well with the measurements from shock tube experiments for three common brittle materials studied in this work. Particularly, the predicted distribution of fragment-size extracted for a single value of strain rate exhibits a smaller variance than that observed in the experiments. A formulation that includes the heterogeneity of strain rates in the shock tube tests is proposed towards the development of quantitatively validated fragmentation models.
Damage evolution of hot-pressed boron carbide under confined dynamic compression
L. Farbaniec; J.D. Hogan; K.Y. Xie; M. Shaeffer; K.J. Hemker; K.T. Ramesh;
Keywords:Boron carbide;Kolsky bar technique;Confined compression;Brittle failure;
Abstracts:The dynamic response of hot-pressed boron carbide was studied under uniaxial and confined loading conditions using a modified compression Kolsky bar setup at strain rates of 102 – 103 s–1. The progression of damage in the prismatic specimens was captured using a high-speed camera. This experimental approach was reproduced in a quasi-static regime (10–4 – 10–3 s–1) to study the rate dependance of the strengths and damage modes. The results showed that the compressive strength of boron carbide was both stress state and strain rate dependent. A real-time visualization showed a change in the crack path under confined compression loading. Our observations revealed the formation of column-like fragments and slabs in the uniaxial and confined compression, respectively. Collected fragments of the specimens were used to investigate failure mechanisms by SEM and TEM. Both observations showed transgranular fracture. It was found that microcracks originate at large carbon inclusions and have tensile character. TEM examinations also point to the absence of stress-induced damage at grain boundaries and inside boron carbide grains. The formation of microcracks was responsible for experimentally observed inelastic response under dynamic loading conditions.
Spalling strength of rock under different static pre-confining pressures
Xibing Li; Ming Tao; Chengqing Wu; Kun Du; Qiuhong Wu;
Keywords:Hopkinson bar;Spalling strength;Confining pressure;Laser detector system;
Abstracts:A testing method of spalling strength at different static pre-confining pressure is proposed in this paper. Using a modified split Hopkinson bar facility, a static pre-confining pressure was loaded before dynamic loading. The pull-back method is used to calculate the spalling strength and the free surface velocities of the specimen were measured by a laser detector system. The experimental results indicate that the spalling strength is related to the static pre-confining pressures. When the impact loading and rate effect are almost the same, the results demonstrated that the spalling strength decreases with an increase in the confining pressure.
Effect of composite covering on ballistic fracture damage development in ceramic plates
Dennis B. Rahbek; Jeffrey W. Simons; Bernt B. Johnsen; Takao Kobayashi; Donald A. Shockey;
Keywords:Ballistic;Ceramic armor;Cracking;Composite;Modeling;
Abstracts:This paper describes the damage development in ceramics with and without composite cover during ballistic impact. This is relevant for ceramic inserts in body armor that are often covered with a composite material. To study the effect of the cover on the damage development in the ceramic, projectile impact experiments were performed at sub-muzzle velocities on bare alumina tiles and plates covered with a fiberglass composite. In addition to the experiments, finite element simulations were performed. An atypical formulation was used; Arbitrary Lagrangian–Eulerian (ALE) for the projectile and Lagrangian for the ceramic target. For the ceramic target, an unconventional material model was chosen; the pseudo-geological model 72_R3 in LS-DYNA.
Radial distribution of fragment velocity of asymmetrically initiated warhead
Yuan Li; Yan-hua Li; Yu-quan Wen;
Keywords:Fragment velocity;Asymmetric initiation;Gurney formula;Aimable warhead;
Abstracts:Cylinder casing filled with explosive under asymmetric initiation is an easy way to increase the warhead efficiency. The radial distribution of fragment velocity is an important design parameter for the asymmetrically initiated warhead. Available formulas either can only apply to calculating fragment velocity of certain radial direction, or their applications need experiments to determine unknown parameters. Establishment of a new math model to calculate velocity distribution was presented in this paper. Firstly, in the central section of warhead cylinder (treated as 2D problem), a stationary point was proposed existing between the asymmetric initiation point and the warhead center. From this stationary point the warhead can be radially cut into many segments of explosive and fragments. Then the ratios of charge mass to casing mass of those segments were computed, corrected and used to obtain fragments velocities by Gurney formula. Most importantly, the position of the stationary point was theoretically determined by the one-dimensional detonation pushing piston theory (Zhang et al., 2001) [14]. The math model established in the present work was finally validated with the numerical modeling and the experiment results. The results indicate that the model can accurately compute the radial distribution of fragment velocity of asymmetrically initiated warhead and is completely theoretically enclosed, needing no experiments to determine unknown parameters. In addition, the fragment velocity distribution gotten from experiments was found to be different with the theoretical velocity distribution near the initiation side because of influence of the initiator volume.
Investigation of toughness of ultra high performance fibre reinforced concrete (UHPFRC) beam under impact loading
L. Mao; S.J. Barnett;
Keywords:UHPFRC;Toughness;Impact load;Numerical simulation;Strain rate;
Abstracts:This paper provides a systematic study about toughness of ultra high performance fibre reinforced concrete (UHPFRC) in order to better understand the UHPFRC resistance under impact loading condition. UHPFRC beams containing various fibre volumes are tested under impact load at different strain rate. From the test results, the relationship between UHPFRC toughness and strain rate can be determined. Moreover, a numerical model of UHPFRC beam under impact load is developed and its performance is verified using test data. With developed UHPFRC model, the evolution of UHPFRC toughness can be better investigated.
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