Similarity Relations for the Impact Penetration of an Elastic Rod into a Brittle Target

Similarity factors for the kinetic parameters of the rod (impact velocity or energy) in case of geometric and energy similarities of target fracture patterns are determined from the analysis of the penetration equation and experimental results. The geometric and energy similarities of the target fracture upon the rod penetration over the investigated range of impact velocities (up to 10 m/s) and penetration depths (h >> d) are shown to be attained on linear variations of longitudinal and transverse rod dimensions, with impact velocities remaining unchanged.     

Penetration dynamics of rods from direct ballistic tests of advanced armor components at 2–3 km/s

The penetration of semi-infinite steel and spaced-plate armors by continuous and segmented rods has been analyzed and measured by direct ballistic tests, hydrocode calculations, and hydrodynamic models at velocities from 2 to 4 km/s. An empirical equation of rod penetration in semi-infinite steel was formulated from hydrodynamic models of rod impact. Penetrations predicted by the equation agreed well with measured values. Increasing the spacing between segments from one to two diameters increased the penetration significantly (20%). Structures to support and align the segments can either increase or decrease the penetration, depending on their design. The relative penetrations of continuous and segmented rods depend on the parameters selected for the comparison: the segmented rod having greater penetration for equal mass and diameter and vice versa for equal mass and length. Tests of segmented rods penetrating spaced-plate armor showed that the armor is defeated by the front segment (or segments) punching a hole in the front plate (or plates) that allows the remaining segmented rod through intact to attack the main armor.     

Penetration of semi-infinite AD995 alumina targets by tungsten long rod penetrators from 1.5 to 3.5 km/s

The performance of confined AD995 Alumina against L/D 20 tungsten long rod penetrators was characterized through reverse ballistic testing. The semi-infinite ceramic target was cylindrical with a diameter approximately 30 times the rod diameter. The target configuration included a titanium confinement tube and a thick, aluminum coverplate. The impact conditions ranged from 1.5 to 3.5 km/s with three or four tests performed at each of six nominal impact velocities. Multiple radiographs obtained during the penetration process allowed measurement of the penetration velocity into the ceramic and the consumption velocity, or erosion rate, of the penetrator. The final depth of penetration was also measured.

Primary penetration approaches 75% of the hydrodynamic limit. Secondary penetration is very small, even at 3.5 km/s. The effective R_t value decreased from 90 kbar to 70 kbar with increasing impact velocity over the range of velocities tested.

In tests in which the ratio of target diameter to penetrator diameter was reduced to 15, R_t, dropped by 30% to 50%. When a steel coverplate was used, total interface defeat occurred at 1.5 km/s.     

Ultra-high velocity impacts: cratering studies of microscopic impacts from 3 km/s to 30 km/s

Cratering experiments performed under carefully controlled conditions at impact velocities ranging from 3 km/s to 30 km/s into a wide variety of target materials are presented. These impact experiments use the 6 MV vertical Van de Graaff accelerator of the Ion Beam Facility at the Los Alamos National Laboratory to electrostatically accelerate highly charged iron micro-spheres. The sub-micron spheres, from a random size distribution, are shocklessly accelerated along an 8 m flight path. Ultra-sensitive charge detectors monitor the passage of the projectiles at a rate of up to 100 projectiles/second. An online computer records and displays in real time the charge, velocity and mass of the projectiles and provides cross correlation between the events observed by the several in-flight charge detectors and impact detectors. Real-time logic controls an electrostatic kicker which deflects projectiles of selected charge and velocity onto the target. Thus each experiment consists of an ensemble of 10 to 40 impacts onto a single target within a narrow window of the projectile parameter space, providing excellent statistical resolution of each data point.

The target materials used include single crystal copper and single crystal aluminum, gold, and quartz as well as pyrolytic graphic and anoxy used in composite materials of interest to space applications. We also conducted impact experiments onto thin Mylar and nickel foils. This paper presents these experiments and summarizes the cratering characterization performed to date. Emphasis is placed on cratering results in several materials over a range of impact velocities.     

Penetration of HSLA-100 steel with tungsten carbide spheres at striking velocities between 0.8 and 2.5 km/s

A 51 mm thick plate of high-strength low-alloy (HSLA-100) steel was impacted by 6.4 mm diameter tungsten carbide spheres traveling at velocities ranging from 0.8–2.5 km/s. The width and depth of the crater for each impact event are provided in tabulated form and graphed as a function of velocity. The impacts were simulated using an explicit Lagrangian finite element model. A residual stress map over a cross-section through the crater was also measured by the Contour Method for the 2.2 km/s impact. The predominant feature of the stress map was a peak compressive stress of 1100 MPa, which is 1.6 times the yield strength, centered approximately one crater diameter below the crater floor. Residual stresses in the as-received HSLA-100 plate were also measured and were used to evaluate the effect of initial stresses on the model prediction. Good agreement is shown between the numerical simulation of the impact event and the experimental data.     

Hypervelocity penetration of gold rods into SiC-N for impact velocities from 2.0 to 6.2 km/s

This paper presents the experimental design and results of an advanced set of reverse ballistic experiments with long gold rods, impacting SiC-N ceramics at impact velocities from 2.0 to 6.2 km/s. Important issues for these experiments were the high accuracy and position requirements necessary to detect a possible failure wave or failure kinetics in SiC-ceramics as might be evidenced by a change in the slope of the penetration velocity–impact velocity curve. New and sophisticated evaluation methods were developed for this purpose and produced very reliable results. Analyses of the experimental results show clearly that there is no change in the slope of the penetration velocity–impact velocity curve, contrary to that inferred from previous data and analysis.     

Impact of thin aluminum sheets with aluminum spheres up to 9 km/s

The results of further development of the University of Dayton Research Institute (UDRI), three-stage, light-gas gun and impact test data are presented. We have successfully launched 2.38-mm-diameter aluminum spheres to velocities in excess of 9 km/s with no damage to the launcher components. The results of several tests in which 2.38-mm-diameter aluminum spheres impacted thin aluminum sheets at velocities up to 9.10 km/s are presented. Quantitative data obtained from these tests were used to extend previously established relationships to velocities which are typical of the collisions of orbital debris with spacecraft. These test results include: bumper-sheet hole diameter as a function of impact velocity; determination of the fragmentation-initiation-threshold velocity for spheres impacting very thin sheets; and continued demonstration of the “scalability” of the test results using the bumper-thickness-to-projectile-diameter ratio (t/D) as the scaling factor.     

A Model of the Process of Penetration of a Compound Elongated Projectile into a Shielded Target

We present the results of theoretical investigation of the mechanism of deformation and fracture of compound elongated projectiles penetrating into a shielded target. The process of penetration is analyzed by taking into account the thermal and mechanical characteristics of the materials, the thickness of the shield, the geometric parameters of the (leading and head) components, and the conditions of collision with the target. The numerical simulation is carried out by using the LasTan 2D-Impact software package based on the finite-element method. The proposed model of penetration enables us to study the distinctive features of deformation and fracture of compound elongated projectiles in the process of their interaction with shielded targets. The analysis of the accumulated results shows that the maximum degree of damage to compound elongated projectiles is attained in their leading part and caused by shear and tensile strains.     

Hugoniot measurement by hyper-velocity impact at velocities up to 9 km/s using a two-stage light-gas gun under optimized shot conditions

The optimization for acceleration of a projectile was performed by varying piston mass in consideration with the correlation with projectile mass and the engineering limits of the two-stage light-gas gun, and the projectile velocity has been achieved 9.2 km/s using the optimum acceleration conditions. Moreover, the Hugoniot measurements of oxygen-free copper were performed using the line reflection method at pressures up to 380 GPa by symmetric impact. The tilt and curvature of shock front were investigated according to the impact velocity, and it is proved to be important that the continuous spatial profile of shock front would be recorded.     

Ultra-high-speed deformation by impact of a projectile flying at speeds on the order of km s

An apparatus was developed to facilitate application of an electro-thermo-chemical accelerator to high-speed deformation experiments. The apparatus is designed on the principle of sequential collision of elastic bodies. Speeds ranging from 600 to 780 m s⁻¹ were achieved, and estimated strain rate of deformation is 10⁷ s⁻¹. The newly developed apparatus can be applied to various types of accelerators for attaining deformation speeds as high as several km s⁻¹. Transmission electron microscopy of aluminum deformed at high speed by use of the apparatus revealed the formation of very small stacking fault tetrahedra (SFTs). This observation is quite new for aluminum; previously, SFTs had not been observed in aluminum, although deformation had been carried out at strain rates lower than 10⁶ s⁻¹. Use of the apparatus promises to provide new insight into high-speed deformation.     

The Effect of Phase Transformations on the Interaction of Aluminum Alloys at Speeds above 9 km/s

Technical Physics Letters - The penetration of an aluminum jet into an aluminum alloy target with a speed of 8–11 km/s is investigated. An analysis of the kinetics and parameters of...     

A Numerical/Experimental Study on the Impact and CAI Behaviour of Glass Reinforced Compsite Plates

This paper focuses on the development of an advance numerical model specifically for simulating low velocity impact events and related stiffness reduction on composite structures. The model is suitable for low cost thick composite structures like wind turbine blade and maritime vessels. The model consist of a combination of inter and intra laminar models. The intra-laminar model present a combination of Puck and Hashin failure theories for the evaluation of the fibre and matrix failure. The inter-laminar damage is instead simulated by Cohesive Zone Method based on energy approach. Basic material properties, easily measurable according to standardized tests, are required. The model has been used to simulate impact and compression after impact tests. Experimental tests have been carried out on thick E-Glass/Epoxy composite commonly used in the wind turbine industry. The clustering effect as well as the consequence of the impact energy have been experimentally tested. The accuracy of numerical model has been verified against experimental data showing a very good accuracy of the model.     

Equation of state measurements of materials using a three-stage gun to impact velocities of 11 km/s

Results of an experimental series performed utilizing a three-stage gun to obtain precise material property equation of state (EOS) data for a titanium alloy (Ti6-Al-4V) at extreme pressure states that are not currently attainable using conventional two-stage light-gas gun technology is reported herein. What is new is the technique being implemented for use at engagement velocities exceeding 11 km/s. Shock-velocity in the target is being determined using 100 μm diameter fiber-optic pins and measuring shock transit times over a known distance between two parallel planes. These fiber-optic pins also indicate that the flyer-plate bow and tilt is comparable to two-stage light-gas gun technology. The thermodynamic state of the flyer plate prior to impact has also been determined both experimentally and calculationally. In particular, the temperature, and hence the density of the flyer-plate is also well known prior to impact. Results of these studies indicate that accurate Hugoniot information can be obtained using the three-stage light gas gun. This new test-methodology has extended the EOS of Ti6-Al-4V titanium alloy to stresses up to approximately 250 GPa.     

Procedure of Experimental Investigation into the Cyclic Crack Growth Resistance of Materials under Nonisothermal Conditions

A procedure has been developed for cyclic crack growth resistance tests of material samples under nonisothermal conditions with a controlled phase shift between cyclic heating and mechanical low-cycle loading. The efficiency of the procedure has been verified by the results obtained.__________Translated from Problemy Prochnosti, No. 2, pp. 151 – 158, March – April, 2005.     

Safety effects of reducing the speed limit from 90 km/h to 70 km/h

Speed is one of the main risk factors in traffic safety, as it increases both the chances and the severity of a crash. In order to achieve improved traffic safety by influencing the speed of travel, road authorities may decide to lower the legally imposed speed limits. In 2001 the Flemish government decided to lower speed limits from 90 km/h to 70 km/h on a considerable number of highways. The present study examines the effectiveness of this measure using a comparison group before- and after study to account for general trend effects in road safety. Sixty-one road sections with a total length of 116 km were included. The speed limits for those locations were restricted in 2001 and 2002. The comparison group consisted of 19 road sections with a total length of 53 km and an unchanged speed limit of 90 km/h throughout the research period. Taking trend into account, the analyses showed a 5% decrease [0.88; 1.03] in the crash rates after the speed limit restriction. A greater effect was identified in the case of crashes involving serious injuries and fatalities, which showed a decrease of 33% [0.57; 0.79]. Separate analyses between crashes at intersections and at road sections showed a higher effectiveness at road sections. It can be concluded from this study that speed limit restrictions do have a favorable effect on traffic safety, especially on severe crashes. Future research should examine the cause for the difference in the effect between road sections and intersections that was identified, taking vehicle speeds into account.