Instrumented tensile-impact tests of bone

An instrumented pendulum-type impact tester was used to obtain tensile-impact properties for compact bone. Load-time histories throughout impact were recorded. Impact tests on 50 longitudinally oriented fresh-beef-bone samples yielded a proportional limit of 9.6±4.1 ksi (66.2±28.2 MPa), an ultimate stress of 17.6±5.3 ksi (121.3±36.5 MPa) and an energy-absorption capacity of 142±85 in. Ib/in.² (24900±14900 J/m²). A static tensile strength of 14.7±2.8 ksi (101±19 MPa) was obtained from static testing of 24 additional specimens. The tensile-impact strength was 20 percent higher than the static strength. Statistically significant correlations between elastic properties, impact strength and impact energy were found. Bone microstructure and fracture-surface topography were also examined.     

Pressure due to high-velocity impact of a water jet

A pressure-transducer technique was developed for determining the transient distribution of pressure on a surface caused by the impact of a high-velocity jet. Jet parameters known to be effective in producing ring craters were selected for the study. The average jet velocity was 2100 ft/s (640 m/s) and its approximate diameter was 0.26 in. (0.66 cm). A hardened, small-diameter (0.039 in., 0.099 cm) ‘pressure pin’ was used to transmit the pressure from the impact surface to the pressure transducer. The average pressure was thus found over an area of 0.001192 in.² (0.007690 cm²) at several locations within the impact area. Results show the greatest pressure to occur at the center of the impact area. These results refute the idea that ring craters are produced by the existence of higher pressures near the jet edge.     

Optimizing material strength constants numerically extracted from taylor impact data

Advanced design requirements have dictated a need for the mechanical properties of materials at high strain rates. Mechanical testing for these data poses a significant problem for experimentalists. High-speed testing machines have a limited capability at rates approaching 10²/s. The split Hopkinson pressure bar is the most reliable alternative for rates approaching 10⁴/s. Plate impact experiments are capable of generating strain rates of 10⁸/s and higher. The Taylor impact test occupies a place of particular importance by providing data at strain rates on the order of 10⁴/s–10⁵/s. The issue at present is extracting the data. This paper provides a method for obtaining dynamic strength model material constants from a single Taylor impact test. A polynomial response surface is used to describe the volume difference (error) between the deformed specimen from the Taylor test and the results of a computer simulation. The volume difference can be minimized using an optimizer, with the result being an optimum set of material constants. This method was applied to the modified Johnson-Cook model for OFHC copper. Starting from a nominal set of material constants, the iterative process improved the relative volume difference from 23.1 percent to 4.5 percent. Other starting points were used that yielded similar results. The material constants were validated by comparing numerical results with Taylor tests of cylinders having varying aspect ratios, calibers and impact velocities.     

炸药参数对高锰钢爆炸硬化性能的影响

为了研究炸药参数对高锰钢爆炸硬化效果的影响,对两种不同密度的炸药进行爆速测试,并利用该炸药分别对高锰钢试样进行爆炸硬化实验,测试了从硬化表面向材料内部的硬度、抗拉强度和冲击韧性随深度的变化。测试结果表明:高锰钢试样在相同深度下,经过密度1.38 g/cm3炸药3次爆炸硬化得到的硬度大于密度1.48 g/cm3炸药2次爆炸硬化后的硬度,而冲击韧性小于密度1.48 g/cm3炸药作用后的冲击韧性;从爆炸硬化表面向下15 mm内,经过密度1.38 g/cm3炸药3次爆炸硬化得到的抗拉强度大于密度1.48 g/cm3炸药2次爆炸硬化后的抗拉强度,但深度大于15 mm时,经过密度1.38 g/cm3炸药3次爆炸硬化得到的抗拉强度小于密度1.48 g/cm3炸药2次爆炸硬化后的抗拉强度。从硬化后试件的硬度、抗拉强度以及冲击韧性这3方面考虑,使用单次爆炸冲量较小的炸药进行多次爆炸硬化效果较好。     

Dynamical calculation and analysis on penetration of target plates by truncated conical projectiles

In this paper, dynamical calculation and analysis are made on penetration of thin plates by truncated conical projectiles in terms of the needs of fuze designing. The impact velocity ranges from 200w/s ts to 1000m/s (including both low and high velocities). The target plates include the thin aluminium plate (metal) and the plywood (non-metal).Because a strength effect of target plates is considered in the establishment of dynamical models, we solved the problem that some previous models were not suitable to lowvelocity impact, for example, M. Zaid and B. Paul’s models [1][2][3] Bv comparison of menial effect with strength effect, we theoretically proved Zaid and Paul’s experimental conclusion131: "Only when the impact velocity is more that 500m/s can the strength effect be neglected. Otherwise this effect can not be neglected".     

Wave propagation in transversely impacted composite laminates

An experimental investigation was conducted to determine wave-propagation characteristics, transient-strain distributions and residual properties for unidirectional and angle-ply boron/epoxy and graphite/epoxy laminates impacted with silicon-rubber projectiles at velocities up to 250 ms^?1 (820 ft/s). Tests were conducted at normal and 45-deg oblique impact. Strain signals obtained from surface and embedded strain gages were recorded and analyzed to determine the types of waves, propagation velocities, peak strains, strain rates and attenuation characteristics. The predominant wave is a flexural on propagating at different velocities in different directions. The flexural wave velocity is higher in the higher-modulus direction. In general, measured wave velocities were higher than theoretically predicted. The amplitude of the in-plane wave is less than ten percent of that of the flexural wave. Peak strains and strain rates in the transverse to the (outer) fiber direction are much higher than those in the direction of the fibers. Strain rates up to 640 s^?1 were measured. Under oblique 45-deg impact, the flexural wave is still the predominant one. Peak strains under this oblique impact range between 36 and 56 percent of those under normal impact of the same velocity. Residual elastic properties and strength were measured around the point of impact. The most significant result was a reduction in the transverse strength of the unidirectional laminates. The dynamics of impact were also studied with high-speed photography. The projectile is completely flattened within 50–70 μs and the total contact time is of the order of 300 μs.     

Influence of Mass Ratio on Forward and Reverse Ballistic Impact Equivalence: Experiments,Simulations, and Mechanism Analysis

Reverse ballistic impact tests are widely used for studying dynamic responses because they provide more comprehensive and quantitative projectile/rod response results than forward impact tests. To examine equivalent forward and reverse conditions, a series of 8-cm length oxygen-free copper rods with varying length–diameter ratios was used in forward and reverse ballistic Taylor impact experiments with velocities and strain ratios of 104–215 m/s and 1.25?×?10³–2.5?×?10³ s^-1, respectively. Digital image correlation (DIC) and traditional optical measurements were used to determine instantaneous responses at the μs level. Based on DIC, transient structural deformation, and plastic wave propagation, the forward and reverse length difference at similar velocities ranges from 2 to 6.95 %. Rules governing deformation from the perspective of energy, along with rules for changes in energy and plastic wave propagation were determined. The relative deformation energy error was below 5 % for target projectile mass ratios above 20.     

大长细比结构弹体侵彻2024-O铝靶的弹塑性动力响应

为研究大长细比结构弹体在撞击典型硬目标早期的结构动力学响应,利用57轻气炮进行了直径1.4 cm、量纲一壁厚0.1和0.15、长细比8和12、头部系数3和4.5的卵形空心弹体对2024-O铝靶的侵彻实验研究,利用高速摄影系统记录了弹体撞靶过程,观察到大长细比弹体垂直撞击硬目标过程中的局部墩粗、塑性屈曲2种结构破坏模式,以及斜侵彻过程中的整体塑性弯曲、弯曲与墩粗耦合、弯曲与屈曲耦合3种结构破坏模式和实时动力学响应过程。基于对指数硬化材料的空腔膨胀理论建立了弹体垂直侵彻模型,给出了在轴向及横向载荷交互作用下计算刚塑性自由梁危险截面屈服函数的控制方程,计算值与实验结果吻合较好。     

A bar impact tester for dynamic fracture testing of ceramics and ceramic composites

A bar impact test was developed to study the dynamic fracture responses of precracked ceramic bars, Al₂O₃ and 15/29-percent volume SiC_w/Al₂O₃. Crack-opening displacement was measured with a laser-interferometric displacement gage and was used to determine the crack velocity and the dynamic stress-intensity factorK _I ^dyn . The crack velocity andK _I ^dyn increased with increasing impact velocity while the dynamic-initiation fracture toughness,K _Id, did not vary consistently with increasing impact velocities.Paper was presented at the 1992 SEM Spring Conference on Experimental Mechanics held in Las Vegas on June 8–11.     

Impact damage of laminated composite with energy dissipation: Part II — Damage evolution

Having developed the methodology for analyzing the failure of a ceramic/rubber/steel composite laminate impacted by a tungsten rod in Part I, Part II of the work is concerned with the progressive damage process where material continuity would be interrupted at different locations and time intervals. Depending on the time rate dependent threshold values of the surface and volume energy density, the degree and extent of damage by fragmentation, mass loss, etc. are determined by finite element calculations for time steps of 0.15, 5.0, 7.5, 10, 20, 21 and 21.5 μs. Stresses and strains possess an oscillatory character in time; they alternate in sign as the impact waves bounce back and forth in the three-layered dissimilar materials.Local strain rates of approximately 10⁵, 10³ and 10⁴ s⁻¹ are formed in the ceramic, rubber and steel layer respectively at locations underneath the tungsten rod after 16 μs of impact. A more wide range of strain ratio would have prevailed for a homogeneous layer of the same thickness. The tungsten rod is now badly fragmented while cracking near the surface of the ceramic is also predicted. Local temperature and dissipation energy density rise rapidly as time approached 20 μs. The maximum surface and volume.energy density in the ceramic near the impact region reached 260 MPa · m and 6.39 MPa, respectively. Complete disintegration of the tungsten rods occurred at 21.5 μs. At this time, the ceramic layer is perforated and the rubber layer is partially cracked. The back-up steel plate, however, remained in tack. These predictions agree qualitatively with past observations.     

Physical relations for problems of impact loading and unsteady deformation of composite structures

A problem of determining elastic and viscous characteristics of composite materials, necessary and sufficient for choosing physical relations in solving problems of impact loading with low impact velocities (up to 200 m/sec) and unsteady deformation in the range of strain rates within 10 ² sec⁻¹ for multilayer beams, plates, and shells, is considered. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 1, pp. 187–196, January–February, 2009.     

Measurement and simulations of hollow atom X-ray spectra of solid-density relativistic plasma created by high-contrast PW optical laser pulses

K-shell spectra of solid Al excited by petawatt picosecond laser pulses have been investigated at the Vulcan PW facility. Laser pulses of ultrahigh contrast with an energy of 160 J on the target allow studies of interactions between the laser field and solid state matter at 10²⁰ W/cm². Intense X-ray emission of KK hollow atoms (atoms without n = 1 electrons) from thin aluminum foils is observed from optical laser plasma for the first time. Specifically for 1.5 μm thin foil targets the hollow atom yield dominates the resonance line emission. It is suggested that the hollow atoms are predominantly excited by the impact of X-ray photons generated by radiation friction to fast electron currents in solid-density plasma due to Thomson scattering and bremsstrahlung in the transverse plasma fields. Numerical simulations of Al hollow atom spectra using the ATOMIC code confirm that the impact of keV photons dominates the atom ionization. Our estimates demonstrate that solid-density plasma generated by relativistic optical laser pulses provide the source of a polychromatic keV range X-ray field of 10¹⁸ W/cm² intensity, and allows the study of excited matter in the radiation-dominated regime. High-resolution X-ray spectroscopy of hollow atom radiation is found to be a powerful tool to study the properties of high-energy density plasma created by intense X-ray radiation.     

Landslide generated impulse waves. 2. Hydrodynamic impact craters

Landslide generated impulse waves were investigated in a two-dimensional physical laboratory model based on the generalized Froude similarity. Digital particle image velocimetry (PIV) was applied to the landslide impact and wave generation. Areas of interest up to 0.8 m by 0.8 m were investigated. PIV provided instantaneous velocity vector fields in a large area of interest and gave insight into the kinematics of the wave generation process. Differential estimates such as vorticity, divergence, and elongational and shear strain were extracted from the velocity vector fields. At high impact velocities flow separation occurred on the slide shoulder resulting in a hydrodynamic impact crater, whereas at low impact velocities no flow detachment was observed. The hydrodynamic impact craters may be distinguished into outward and backward collapsing impact craters. The maximum crater volume, which corresponds to the water displacement volume, exceeded the landslide volume by up to an order of magnitude. The water displacement caused by the landslide generated the first wave crest and the collapse of the air cavity followed by a run-up along the slide ramp issued the second wave crest. The extracted water displacement curves may replace the complex wave generation process in numerical models. The water displacement and displacement rate were described by multiple regressions of the following three dimensionless quantities: the slide Froude number, the relative slide volume, and the relative slide thickness. The slide Froude number was identified as the dominant parameter.List of symbols a wave amplitude (L) - b slide width (L) - c wave celerity (LT^–1) - d _g granulate grain diameter (L) - d _p seeding particle diameter (L) - F slide Froude number - g gravitational acceleration (LT^–2) - h stillwater depth (L) - H wave height (L) - l _s slide length (L) - L wave length (L) - M magnification - m _s slide mass (M) - n _por slide porosity - Q _d water displacement rate (L³) - Q _D maximum water displacement rate (L³) - Q _s maximum slide displacement rate - s slide thickness (L) - S relative slide thickness - t time after impact (T) - t _D time of maximum water displacement volume (L³) - t _qD time of maximum water displacement rate (L³) - t _si slide impact duration (T) - t _sd duration of subaqueous slide motion (T) - T wave period (T) - v velocity (LT^–1) - v _p particle velocity (LT^–1) - v _px streamwise horizontal component of particle velocity (LT^–1) - v _pz vertical component of particle velocity (LT^–1) - v _s slide centroid velocity at impact (LT^–1) - V dimensionless slide volume - V _d water displacement volume (L³) - V _D maximum water displacement volume (L³) - V _s slide volume (L³) - x streamwise coordinate (L) - z vertical coordinate (L) - slide impact angle (°) - bed friction angle (°) - x mean particle image x-displacement in interrogation window (L) - _x random displacement x error (L) - _tot total random velocity v error (LT^–1) - _xx streamwise horizontal elongational strain component (1/T) - _xz shear strain component (1/T) - _zx shear strain component (1/T) - _zz vertical elongational strain component (1/T) - water surface displacement (L) - density (ML^–3) - _g granulate density (ML^–3) - _p particle density (ML^–3) - _s mean slide density (ML^–3) - _w water density (ML^–3) - granulate internal friction angle (°) - _y vorticity vector component (out-of-plane) (1/T)     

Mechanics of Taylor impact testing of polycarbonate

The deformation of polymers under high-rate loading conditions is a governing factor in their use in impact-resistant applications, such as protective shields, safety glass windows and transparent armor. In this paper, Taylor impact experiments were conducted to examine the mechanical behavior of polycarbonate (PC), under conditions of high strain rate (∼10⁵ s⁻¹) and inhomogeneous deformation. High-speed photography was used to monitor the progression of deformation within the sample. A recently developed three-dimensional large strain rate-dependent elastic–viscoplastic constitutive model which describes the high-rate behavior of glassy polymers was used together with the ABAQUS/Explicit finite-element code to simulate several Taylor impact conditions. The simulation results are compared directly with experimental images for a range in initial rod dimensions and velocities. Final deformed shapes are found to correspond with those obtained experimentally, demonstrating the ability to predict complex inhomogeneous deformation events during very high-rate impact loading scenarios. The dependence of the observed behaviors on the various features of the polymer stress–strain behavior are presented in detail revealing the roles of strain softening and strain hardening in governing the manner in which deformation progresses in a polymer during dynamic inhomogeneous loading events.     

Shock response of the commercial high explosive Detasheet

The mechanical and chemical response of the flexible commercial high explosive Detasheet^R is studied under controlled impact and plane-wave, high explosive loading. Results on nonreactive material behavior, sound speed, shock-initiation sensitivity and detonation pressure are presented. The material is found to respond in a viscous manner reminiscent of viscoelastic response of polymeric materials. Time-resolved pressure and pressure-rate measurements with PVDF piezoelectric polymer gauges are presented along with Manganin pressure and plate-dent test measurements of detonation pressure. Detonation pressures of 18GPa are indicated. Pressure measurements show initiation of reaction between 3 and 8 mm for an impact stress of 3.1 GPa. Plane wave loading wedge tests show run distances to detonation consistent with the pressure measurements, and with behavior like that of XTX8003 (80 % PETN/20 % Sylgard 182^R).This article was processed using Springer-Verlag T_EX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society.     

Seismic efficiency of a contact explosion and a high-velocity impact

The seismic energy transferred to an elastic half-space as a result of a contact explosion and a meteorite impact on a planet’s surface is estimated. The seismic efficiency of the explosion and impact are evaluated as the ratio of the energy of the generated seismic waves to the energy of explosion or the kinetic energy of the meteorite. In the case of contact explosions, this ratio is in the range of 10⁻⁴–10⁻³. In the case of wide-scale impact effects, where the crater in the planet’s crust is produced in the gravitational regime, a formula is derived that relates the seismic efficiency of an impact to its determining parameters. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 2, pp. 3–12, March–April, 2007.     

Design of an Impact Loading Machine Based on a Flywheel Device: Application to the Fatigue Resistance of the High Rate Pre-straining Sensitivity of Aluminium Alloys

This paper presents a device that has been designed for tensile loading at medium impact rates (up to 10³ s^–1) and for performing either interrupted or failure tests. This machine allows us to apply prescribed pre-straining to the specimen, and then apply subsequent loading histories such as impact fatigue. Two specimen loading systems are considered, which make it possible to carry out tests with various ranges of force and various durations of time. A multi-CCD camera system is triggered by a chosen threshold from the force signal. The system is dedicated to the displacement measurement and gives both qualitative and quantitative information about the stretching mechanism leading to fracture. To illustrate the performance of the device, experimental results concerning impact tensile tests at a strain rate of about 300 s^–1 are presented, as well as consecutive impact-fatigue tests on two aluminium alloys.     

Pressure-shear waves in 6061-T6 aluminum and alpha-titanium

Thepressure-shear plate impact technique is used to study material behavior at high rates of deformation. In this technique, plastic waves of combined pressure and shear stresses are produced by impact of parallel plates skewed relative to their direction of approach. Commercially pure alpha-titanium and 6061-T6 aluminum are tested under a variety of pressure and shear tractions by using different combinations of impact velocities and angles of inclination. A laser interferometer system is used to monitor simultaneously the normal and transverse components of motion of a point at the rear surface of the target plate. The experimental results are compared with numerical solutions based on an elastic/viscoplastic model of the material. Both isotropic and kinematic strain hardening models are used in the computations. The results indicate that unlike the normal velocity profiles, the transverse velocity profiles are sensitive to the dynamic plastic response and, thus, can be used to study material behavior at high strain rates. For the materials tested the results suggest that the flow stress required for plastic straining increases markedly with increasing strain rate at strain rates above 10⁴s^?1. Hydrostatic pressure of the order that exists in the tests (up to 2 GPa) does not affect the plastic flow in 6061-T6 aluminum and appears to have at most a minor effect on the deformation of the titanium.     

Nonequilibrium radiation of a strong shock wave

We examine the nonequilibrium radiation from the first negative band of the molecular nitrogen ion N ₂ ⁺ . The various N ₂ ⁺ ion excitation mechanisms are discussed. It is shown that for a shock wave velocity in air 8 km/sec the primary excitation mechanism is electronic impact.In conclusion the authors wish to thank V. K. Vertushkin and A. A. Gladkov for supplying the calculations on the structure of the normal compression shock and L. I. Ponomarev for helpful discussions.     

Perforation of 6082-T651 Aluminum Plates with 7.62 mm APM2 Bullets at Normal and Oblique Impacts

We conducted an experimental study to understand the mechanisms and dominant parameters for 7.62 mm APM2 bullets that perforate 6082-T651 aluminum armor plates at oblique impacts. The 7.62-mm-diameter, 10.7 g, APM2 bullet consists of a brass jacket, lead filler, and a 5.25 g, ogive-nose, hard steel core. The brass and lead were stripped from the APM2 bullets by the targets, so we conducted ballistic experiments with both the APM2 bullets and only the hard steel cores. These projectiles were fired from a rifle to striking velocities between 400 and 1,000 m/s into 20-mm-thick plates at normal impact (β?=?0^o) and at oblique angles of β?=?15^o, 30^o, and 45^o. Measured residual and ballistic-limit velocities for the full bullet and the hard core were within a few percent for normal impact and all oblique angles. Thus, we showed that the perforation process was dominated by the hard steel core of the bullet. In addition, we conducted large strain, compression tests on the 6082-T651 plate material for input to perforation equations derived from a cavity-expansion model for the steel core projectiles. Model predictions were shown to be in good agreement with measured ballistic-limit and residual velocity measurements for β?=?0^o, 15^o, and 30^o. We also presented a scaling law for the bullet that showed the ballistic-limit velocities were proportional to the square root of the product of plate thickness and a material strength term.