Dynamic Compression Experiments Research Articles

Integrated experimental and computational studies of deformation of single crystal copper at high strain rates

Quasi-static (0.0033 s−1) and dynamic (103 s−1) compression experiments were performed on single crystal copper along ⟨100⟩ and ⟨110⟩ directions and best-fit parameters for the Johnson-Cook (JC) material model, which is an important input to hydrodynamic simulations for shock induced fracture, have been obtained. The deformation of single crystal copper along the ⟨110⟩ direction showed high yield strength, more strain hardening, and less strain rate sensitivity as compared to the ⟨100⟩ direction. Although the JC model at the macro-scale is easy to apply and describes a general response of material deformation, it lacks physical mechanisms that describe the influence of texture and initial orientation on the material response. Hence, a crystal plasticity model based on the theory of thermally activated motion of dislocations was used at the meso-scale, in which the evolution equations permit one to study and quantify the influence of initial orientation on the material response. Hardening parameters of the crystal plasticity model show less strain rate sensitivity along the ⟨110⟩ orientation as compared to the ⟨100⟩ orientation, as also shown by the JC model. Since the deformation process is inherently multiscale in nature, the shape changes observed in the experiments due to loading along ⟨100⟩ and ⟨110⟩ directions are also validated by molecular dynamics simulations at the nano-scale.

Effects of Micronized Fibers on the Cushion Properties of Foam Buffer Package Materials

Foam buffer package materials composed of plant fibers have been a focus of research in recent years because of their environmentally beneficial ability to become fully disintegrated. In this study, bleached bagasse pulp was micronized using a PFI mill, and foam buffer materials were prepared using the micronized fiber. The effects of the beating degree of micronized fibers on the dimensional stability, moisture absorption, static compression, and dynamic compression characteristics were discussed. Results showed that, in both the static and the dynamic compression experiments, the buffer properties improved with an increasing beating degree. The buffer materials made of highly micronized fiber were stronger under pressure and impact. Specifically, the highly micronized fiber’s ability to absorb energy curing impact was improved, demonstrating that it can support a higher compression and impacting load in a certain deformation scope. However, during the drying process, the dimensional stability of the samples also declined with an increasing beating degree. The moisture absorption of the samples improved when the beating degree was increased.

Thermal transport in shock wave-compressed solids using pulsed laser heating.

A pulsed laser heating method was developed for determining thermal transport properties of solids under shock-wave compression. While the solid is compressed, a laser deposits a known amount of heat onto the sample surface, which is held in the shocked state by a transparent window. The heat from the laser briefly elevates the surface temperature and then diffuses into the interior via one-dimensional heat conduction. The thermal effusivity is determined from the time history of the resulting surface temperature pulse, which is recorded with optical pyrometry. Thermal effusivity is the square root of the product of thermal conductivity and volumetric heat capacity and is the key thermal transport parameter for relating the surface temperature to the interior temperature of the sample in a dynamic compression experiment. Therefore, this method provides information that is needed to determine the thermodynamic state of the interior of a compressed metal sample from a temperature measurement at the surface. The laser heat method was successfully demonstrated on tin that was shock compressed with explosives to a stress and temperature of ~25 GPa and ~1300 K. In this state, tin was observed to have a thermal effusivity of close to twice its ambient value. The implications on determining the interior shock wave temperature of tin are discussed.

Influence of Braiding Parameters on the Dynamic Compressive Properties and Failure Mechanism of 3D Braided Composites

The dynamic compressive experiments were performed on 3D braided composites with different braiding parameters using the Split-Hopkinson-Pressure-Bar (SHPB) technique. The dynamic stress versus strain curves and the important mechanical properties were determined. The influence of braiding parameters on the dynamic properties and failure mechanism of composites are analyzed in detail. The results show that the smaller braiding angle and higher fiber volume fraction will contribute to better longitudinal dynamic compression properties. The damage drastically increases with the braiding angle. Moreover, the composites with a higher fiber volume fraction bear a more severe destruction and become more brittle in failure.

Prediction of Debye-Scherrer diffraction patterns in arbitrarily strained samples

The prediction of Debye-Scherrer diffraction patterns from strained samples is typically conducted in the small strain limit. Although valid for small deviations from the hydrostat (such as the conditions of finite strength typically observed in diamond anvil cells) this assertion is likely to fail for the large strain anisotropies (often of order 10% in normal strain) found in uniaxially loaded dynamic compression experiments. In this paper, we derive a general form for the (θB,ϕ) dependence of the diffraction for an arbitrarily deformed polycrystalline sample in any geometry, and of any crystal symmetry. We show that this formula is consistent with ray traced diffraction for highly strained computationally generated polycrystals, and that the formula shows deviations from the widely used small strain solutions previously reported.

マグネシウム合金製円管の衝撃エネルギー吸収特性

Weight reduction is effective for improving fuel efficiency of automobiles. Although magnesium is widely recognized as the lightest structural metal, applications for the automobile are limited because of the relatively low ductility, toughness, impact resistance and fatigue resistance. The aim of this research was to evaluate the impact energy absorption capability of a magnesium alloy pipe by a numerical simulation. First of all, finite element (FE) analysis of impact compression of magnesium alloy pipes was performed to design the shape of anvils for a dynamic compression experiment. The compression tests were conducted at a high strain rate on two Mg alloys, AZ31 and Mg-0.6Y, to examine the deformation response. The load-displacement data obtained were compared with the results of FE analysis to validate the simulation. The FE analysis revealed that the AZ31 pipe fractured at an early stage of deformation, while the Mg-0.6Y pipe fractured at about 90% compressed. As a result, Mg-0.6Y pipe exhibited lower yield strength, but a higher absorption energy capability than AZ31 pipe due to a weakened basal texture.

Introducing objective power law rate dependence into a visco-elastic material model of bovine cortical bone

The strain rate dependent behaviour of some visco-elastic materials can be modelled accurately in 1-D by including a stress contribution which depends non-linearly on strain rate. A visco-elastic model by Shim et al. (2005) [3] comprises a Voigt and Maxwell element in parallel and provides an effective representation of cancellous bone from the human cervical spine. The present study demonstrates that the model by Shim et al. is also suitable for modelling the strain rate dependent compression of cortical bone from bovine femurs. Shim et al. found that the model requires a Voigt dash-pot contribution which is proportional to ε˙1/2 in order to model specimen response accurately over a large range of strain rates. Shim et al. proposed an expansion of the 1-D formulation to 3-D where the 1-D strain rate is replaced with a function of the strain rate tensor. This paper provides a frame invariant version of the model by Shim et al. which allows general power law rate dependence for the 3-D case. The response of the model is investigated under a load condition which comprises of an axial deformation and a shear twist. The model is implemented in a commercial finite element package and is used to simulate quasi-static and dynamic bovine bone compression experiments.

Effects of strain rate and temperature on compressive strength and fragment size of ZrB2–SiC–graphite composites

The quasi-static (strain rate of 10−4s−1) and dynamic compression experiments (strain rate of 200–1500s−1) of ZrB2–SiC–graphite composites are conducted at 293K and 1073K. The initial compressive strength and Weibull modulus are calculated to handle the discrete quasi-static experimental data. Considering effects of strain rate and temperature, the compressions of ZrB2–SiC–graphite composites are investigated. The results show that both compressive strength and fragment size are higher at 1073K than those at room temperature. The compressive strengths increase with increasing strain rate at room temperature and 1073K, whereas fragment sizes decrease. Moreover, a micromechanical model is utilized to characterize the effect of strain rate on the compressive strength. The predictions of this micromechanical model are good agreement with the experimental results. Meanwhile, the fragment sizes of dynamic compressive specimens are analyzed through analytical approaches.

Compression Tests of Polycarbonate under Quasi-Static and Dynamic Loading

Strain rate response of polycarbonate was investigated under uniaxial compression at different rates of strain ranging from 0.0001/sec to about 8200/sec and different temperature ranging from 145k to about 423k. A split Hopkinson pressure bar was used to determine the dynamic compressive responses. A pulse-shaping technique was employed in dynamic compression experiment to ensure that valid experimental conditions were satisfied. Results show that, compared with quasi-static behavior, dynamic compression results in significantly higher compressive strengths for polycarbonate materials.

Establishment and comparison of four constitutive models of 5A02 aluminium alloy in high-velocity forming process

In high-velocity forming process, material constitutive relationships are remarkably changed, which has a significant effect on forming process and deformation behaviors. Based on the quasi-static tensile experiments and compression experiments at different temperatures, and dynamic tensile experiments and compression experiments at room temperature, the constitutive behaviors of 5A02 aluminium alloy and the mechanism of high strain rate influencing material dynamic responses are investigated in this paper. According to the above experimental results, Johnson–Cook model (J–C model), modified Cowper–Symonds model (C–S model), modified Rusinek–Klepaczko model (R–K model) and artificial neural network model (ANN model) have been proposed to describe the stress–strain relationship of 5A02 aluminium alloy in high-velocity forming process, and their predictability are compared by employing several statistical evaluation measures. The results show that the prediction precision of J–C model is limited, for the calculated coefficient of strain rate is too little to reflect the increasing trend of stress as strain rate is elevated; modified C–S model takes into consideration the effect of strain in the description of strain rate effect, thus it has a more precise correlation between predicted stress and measured stress; based on the influences of strain and strain rate on the dislocation evolution mechanism, the prediction precision of modified R–K model is higher when the strain rate is in the range of 10−3–3000s−1, while the precision decreases as the strain rate exceeds 3000s−1 due to the changed micromechanism of dislocation evolution; ANN model exhibits most powerful predictability due to its self-organizing ability, self-learning ability and high capacity of error tolerance.

Use of dynamic compression to probe semiconductor response at large strains

AbstractLarge strains in semiconductors are expected to be more common in future electronic devices utilizing nanostructure components. Hydrostatic pressure (HP) and uniaxial stress (US) loading have inherent limitations for probing the desired strain conditions. Uniaxial strain loading, achieved in dynamic compression experiments, is particularly attractive for attaining well‐defined, large strains and to complement HP and US loading. Recent dynamic compression studies on III–V semiconductors (GaN, GaP, and GaAs) are summarized to review notable findings ranging from improved deformation potentials to free carrier properties. These findings demonstrate the benefits of dynamic compression experiments for semiconductor research.

Dynamic compression failure mechanisms and dynamic effects of integrated woven sandwich composites

Low-velocity dynamic compression tests were performed to reveal the failure mechanism and the energy absorption capacity of the integrated woven sandwich composite. Shear deformations were induced by the tilting of fiber piles in the core of the integrated woven sandwich composite. Ductile load–displacement curves are featured by a long deformation plateau originated from rotations of the core piles. Densification is apparent in the later stage of compression. Stout piles in the core also lead to plastic compression failure mode accompanying with much smaller rotations of core piles. Controlled by the latter failure mode, the dynamic strength and the energy absorption of the panel are stronger. In dynamic compression experiments, the integrated woven sandwich composite panels exhibit similar failure modes with those observed in quasi-static compression tests. The dynamic strength is much greater and the corresponding deformation plateau is much more stable, which leads to greater energy absorption. The dynamic effects of the strength and the energy absorption were explained by the dynamic buckling of the woven struts in the core. The tests suggest that the integrated woven sandwich composite is ideal to serve as a lightweight anti-impact material in engineering structures.

Impact system for ultrafast synchrotron experiments

The impact system for ultrafast synchrotron experiments, or IMPULSE, is a 12.6-mm bore light-gas gun (<1 km/s projectile velocity) designed specifically for performing dynamic compression experiments using the advanced imaging and X-ray diffraction methods available at synchrotron sources. The gun system, capable of reaching projectile velocities up to 1 km/s, was designed to be portable for quick insertion/removal in the experimental hutch at Sector 32 ID-B of the Advanced Photon Source (Argonne, IL) while allowing the target chamber to rotate for sample alignment with the beam. A key challenge in using the gun system to acquire dynamic data on the nanosecond time scale was synchronization (or bracketing) of the impact event with the incident X-ray pulses (80 ps width). A description of the basic gun system used in previous work is provided along with details of an improved launch initiation system designed to significantly reduce the total system time from launch initiation to impact. Experiments were performed to directly measure the gun system time and to determine the gun performance curve for projectile velocities ranging from 0.3 to 0.9 km/s. All results show an average system time of 21.6 ± 4.5 ms, making it possible to better synchronize the gun system and detectors to the X-ray beam.

Implementation of Tillotson Equation of State for Hypervelocity Impact of Metals, Geologic Materials, and Liquids

The Tillotson equation of state (EOS), which was originally developed for the hypervelocity impact of metals, was augmented with an additional region in expansion to provide full coverage of the density-energy space and a new cavitation model for liquids. This EOS was implemented into CTH, Sandia National Laboratories Eulerian, finite-volume, shock physics code, for the general purpose of simulating hypervelocity impacts of metals, geologic materials, and liquids; however, the salient features of this EOS in both compression and expansion are evaluated for water given the ubiquity of available data. Addition of a cavitation model allows for treatment of liquid spall when the local pressure drops below the vapor pressure in events such as underwater blasts and high speed projectiles or fragments in liquids. The EOS is evaluated by comparing the response to previously published dynamic compression experiments. Additionally, the model results are compared against the Mie-Gruneisen and SESAME equations of state already in the CTH database.

Prospects for achieving high dynamic compression with low energy

Laser driven dynamic compression experiments may, in materials with picosecond equilibration times, be possible with orders of magnitude less drive energy than currently used. As we show, the compression energy for geometrically similar experiments varies as the third power of the time scale of compression. For materials which equilibrate and can be characterized on picosecond time scales, the compression energy can be orders of magnitude smaller than the 1–100 ns scale time scale of many current experiments. The use of substantially lower compression energy is a great practical advantage in such experiments, potentially enabling the observation of extreme states of matter with table top scale laser systems.

Energy Absorption Characteristics of Closed-cell AZ91 Magnesium Alloy Foam

Abstract The energy absorption characteristics of foam materials can be represented by specific energy absorption W, energy absorption efficiency E and ideal energy absorption efficiency I. The influences of strain rate, cell size, relative density and the content of SiC on energy absorption characteristics of magnesium alloy foam were investigated by dynamic compression experiments. The experimental results showed that the cell size of magnesium alloy foam had significant effect on energy absorption characteristics and the strain rate effect of closed-cell AZ91 magnesium with larger cell size was more sensitive, and the strain rate effect was more sensitive to the closed-cell AZ91 magnesium with larger cell size. The energy absorption characteristics could be optimized by adjusting the cell size. Moreover, the influence of relative density on energy absorption characteristics was not significant and high content of SiC particle had unfavorable effect on energy absorption properties of magnesium foam.

Mechanisms of dynamic deformation and dynamic failure in aluminum nitride

Uniaxial quasi-static, uniaxial dynamic and confined dynamic compression experiments have been performed to characterize the failure and deformation mechanisms of a sintered polycrystalline aluminum nitride using a servohydraulic machine and a modified Kolsky bar. Scanning electron microscopy and transmission electron microscopy (TEM) are used to identify the fracture and deformation mechanisms under high rate and high pressure loading conditions. These results show that the fracture mechanisms are strong functions of confining stress and strain rate, with transgranular fracture becoming more common at high strain rates. Dynamic fracture mechanics and micromechanical models are used to analyze the observed fracture mechanisms. TEM characterization of fragments from the confined dynamic experiments shows that at higher pressures dislocation motion becomes a common dominant deformation mechanism in AlN. Prismatic slip is dominant, and pronounced microcrack–dislocation interactions are observed, suggesting that the dislocation plasticity affects the macroscopic fracture behavior in this material under high confining stresses.

Sensitivity and dynamic electrical response of CNT-reinforced nanocomposites

A series of dynamic compressive experiments were performed to experimentally investigate the electrical response of multi-wall carbon nanotube (CNT)-reinforced epoxy nanocomposites subjected to split Hopkinson pressure bar (SHPB) loading. Low-resistance CNT/epoxy specimens were fabricated using a combination of shear mixing and ultrasonication. Utilizing the CNT network within, the electrical resistance of the nanocomposite was monitored using a high-resolution four-point probe method during each compressive loading event. In addition, real-time deformation images were captured using high-speed photography. The percent change in resistance was correlated to both strain and real-time damage. The results were then compared to previous work conducted by the authors (quasi-static and drop weight impact) in order to elucidate the strain rate sensitivity on the electrical behavior of the material. Furthermore, the percent change in conductivity was determined using a Taylor expansion model to investigate the electrical response based on both dimensional change as well as resistivity change during mechanical loading within the elastic regime. Experimental findings indicate that the electrical resistance is a function of both the strain and deformation mechanisms induced by the loading. The bulk electrical resistance of the nanocomposites exhibited an overall decrease of 40–65% and 115–120% during quasi-static/drop weight and SHPB experiments, respectively.

A unified approach for extracting strength information from nonsimple compression waves. Part I: Thermodynamics and numerical implementation

We describe a comprehensive method of extracting estimates of the complete plastic deformation behavior, including full deviatoric-stress/plastic-strain (τ − ψ) curves, from one-dimensional dynamic compression experiments at moderate pressures (up to ∼50 GPa). The method combines and extends selected aspects of previous approaches and features a second-order velocity interpolation function designed to accommodate highly rate-dependent phenomena. Assumptions, and the expected limitations thereof, are made explicit and kept to a minimum. In particular, we do not assume any particular plasticity model, nor do we assume that the wave propagation is either simple or steady. Instead, we allow the data themselves to constrain any such behavior. We develop generalizations of standard equation-of-state analyses that account for the effects of rate-dependent relaxation on wave speeds and paths through thermodynamic space and show the potential to extract a great deal of strength information from the details of wave propagation.

The dynamic strength of an ordinary chondrite

Abstract– Dynamic and quasistatic unconfined compression experiments were performed on samples of the L5 ordinary chondrite MacAlpine Hills (MAC) 88118. The dynamic compressive strength measurements are the first of its kind for a stony meteorite, and indicate that the material tested here exhibits significant increase in compressive strength with increasing strain rate. This increase in compressive strength is larger than the increases typically observed in terrestrial rock specimens compressed over a similar range of strain rates. The details of the failure process are investigated by recording images of the experiments in real time. Specifically, the crack growth speeds in the dynamic compression experiments are measured from ultrahigh‐speed images. These speeds are significantly lower than the speeds observed in terrestrial analogs that are typically used in numerical investigations of large‐scale impacts. The implications of these measurements of strength and failure process are explored in the contexts of atmospheric disruption of meteors and impact cratering/disruption of asteroids.