Taylor Impact Research Articles

A method to represent the strain hardening effect in the hyper-elastic model within a fully Eulerian framework

We propose a method to treat the strain hardening effect in the hyperelastic model. Coupled with the level set interface capturing method and a real ghost fluid method, it is formulated in a fully Eulerian framework. The HLLD approximate Riemann solver is used to obtain the interface state. We use the elastic inverse deformation gradient tensor to track the material deformation state. Once the solid starts to yield, along the normal direction in stress space, an iterative algorithm is used to relax the elastic inverse deformation gradient tensor to target value where the equivalent stress meets the requirement of consistency condition in plasticity. This approach is intuitive and can avoid the use of the physical delay time, which is difficult to calibrate from experiments. We use the Wilkins flying plate impact, cylindrical shell collapse, Taylor impact and the conical-nosed projectile penetration test cases to validate the method. The results show good agreement with the theoretical analysis and experiments. This approach can also apply without further extension when thermal softening effect or damage models are considered.

A high-order, localized-artificial-diffusivity method for Eulerian simulation of multi-material elastic-plastic deformation with strain hardening

A high-order method for Eulerian simulation of material undergoing large elastic–plastic deformation is developed. Thermodynamically consistent hyperelastic constitutive relations are assumed, facilitating the treatment of solids, liquids, and gases in a unified manner. The method enables the simulation of multi-material interactions using a diffuse interface approach. Numerical capturing of material interfaces, shock waves, contact surfaces, and elastic-plastic strain discontinuities using high-order compact-difference schemes is assisted by Localized Artificial Diffusivity (LAD). In the new setting involving elastic–plastic deformation, the previously established terms for the artificial properties are verified to effectively regularize normal shocks. Additional LAD terms are introduced to the elastic and plastic kinematic equations to regularize shear shocks and other strain discontinuities, improving solution stability. Other important features of the method that improve robustness include the numerical treatment of compatibility terms in the kinematic equations, and the treatment of rotation. Particular emphasis is focused toward new advancements of the methods for plastic-deformation integration and the associated strain hardening of the material, including rate-dependent plasticity. The method is demonstrated on a variety of test problems, including 1-D impacts, a variant of the Shu-Osher problem, a Taylor impact, and a Richtmyer-Meshkov instability between two elastic–plastic solids with strain hardening.

Calibration and validation of the foundation for a multiphase strength model for tin

In this work, the Common Model of Multi-phase Strength and Equation of State (CMMP) model was applied to tin. Specifically, calibrations of the strength-specific elements of the CMMP foundation were developed with a combination of experiments and theory, and then the model was validated experimentally. The first element of the foundation is a multi-phase analytic treatment of the melt temperature and the shear modulus for the solid phases. These models were parameterized for each phase based on ab initio calculations using the software VASP (Vienna Ab initio Simulations Package) based on density functional theory. The shear modulus model for the ambient β phase was validated with ultrasonic sound speed measurements as a function of pressure and temperature. The second element of the foundation is a viscoplastic strength model for the β phase, upon which strength for inaccessible higher-pressure phases can be scaled as necessary. The stress–strain response of tin was measured at strain rates of 10−3 to 3×103s−1 and temperatures ranging from 87 to 373 K. The Preston–Tonks–Wallace (PTW) strength model was fit to that data using Bayesian model calibration. For validation, six forward and two reverse Taylor impact experiments were performed at different velocities to measure large plastic deformation of tin at strain rates up to 105s−1. The PTW model accurately predicted the deformed shapes of the cylinders, with modest discrepancies attributed to the inability of PTW to capture the effects of twinning and dynamic recrystallization. Some material in the simulations of higher velocity Taylor cylinders reached the melting temperature, thus testing the multiphase model because of the presence of a second phase, the liquid. In simulations using a traditional modeling approach, the abrupt reduction of strength upon melt resulted in poor predictions of the deformed shape and non-physical temperatures. With CMMP, the most deformed material points evolved gradually to a mixed solid–liquid but never a fully liquid state, never fully lost strength, stayed at the melt temperature as the latent heat of fusion was absorbed, and predicted the deformed shape well.

Understanding dislocation plasticity of single crystalline Ta micropillars under dynamic loading

Recent experimental findings have shown that tantalum single crystals display strong anisotropy during Taylor impact testing in stark contrast to isotropic deformation in polycrystalline counterparts. In this study, a coupled dislocation dynamics and finite element model was developed to simulate the complex stress field under dynamic loading of a Taylor impact test and track the intricate evolution of the dislocation microstructure. Our model allowed us to investigate detailed motion of dislocations and their mutual interactions and the effect of varying simulation parameters, such as sample size, initial dislocation density, crystallographic orientation, and temperature. Simulation results show good agreement with experimental observations and shed light on the mechanical response at small-scale under extreme loading conditions. In addition, resolved shear stress analysis incorporating the effect of shear stress from impact was performed to quantitatively support and provide a means to understand the model predictions of the impact foot shape.

Modeling of strain hardening behaviors of 6061 aluminum alloy considering strain rate and temperature effects

This paper focuses on the plastic strain hardening behaviors of 6061 aluminum alloy (AA6061), considering its dependence on strain rate and temperature. Quasi-static tensile tests were conducted over a wide temperature range (20 °C-300 °C), and the digital image correlation technique was used to capture the deformation process of specimens. Additionally, the uniaxial compressive mechanical response of AA6061 was tested utilizing quasi-static compression and split Hopkinson pressure bar experiments over a wide range of strain rates (0.001 s−1–6000 s−1). Experimental results showed that the flow stress decreased and increased nonlinearly with temperature and strain rate, respectively. A modified Johnson–Cook (MJC) model was developed by incorporating a temperature-dependent strain softening term, along with corrections to the temperature and strain rate product terms, to reproduce the nonlinear dependence. Furthermore, the MJC model was proven to be able to accurately reproduce the deformation of the specimens tested in Taylor impact experiments (strain rates up to 105 s−1), suggesting its effectiveness for interpolating and extrapolating stress-strain relationships. This model provides applicable modeling for materials with nonlinear rate sensitivity and temperature sensitivity, and it is expected to be applied in engineering problems involving ultra-high strain rates.

Numerical and Experimental Investigation on Aluminium 6061 Solid Cylindrical Bar Subjected to Close-in Blast Loading

Compaction force generated by blasting load requires strong material such as steel to act as a plunger to spread the force evenly. The problem with this method is retaining the plunger's original dimension from intolerable deformation. This paper uses ABAQUS software to study the ability to predict the response of solid cylindrical aluminium bars (6061) subjected to different close-in blast loads. The solid cylindrical aluminium bars treated as a plunger were evaluated numerically using a combination of the finite element method (FEM) and smoothed particle hydrodynamic (SPH) methods. The plunger was simulated using the Johnson-Cook (J.C.) model, and Jones-Wilkins-Lee (JWL) equation parameters modelled the explosive. Field tests were conducted by detonating explosives of two different weights, which are 100g and 250g, in the designated blast area. Both data and observation were compared and analysed regarding deformation behaviour in term of dimension difference and fracture. Based on the graph of the deformation dimension versus the plunger length, the deformation trend shows a very close relation between numerical and experimental data with a percentage error of less than 4%. The fracture mode generated using FEM is comparable to the actual specimen. This fracture mode can be described as similar to the behaviour of the specimen obtained using the Taylor impact test. Thus, it can be concluded that the numerical analysis performed for this study is consistent with the actual results.

A DIC-based Taylor impact test by measuring inertia force from acceleration distribution to obtain uniaxial stress–strain behavior of pure aluminum

The digital image correlation (DIC) technique is widely used to capture several kinematical quantities fields including displacement, velocity, strain, strain rate and acceleration in various kinds of the mechanical tests with the deformation of specimen. Considering the nature of nonuniform deformation in Taylor impact test, except the mentioned fields, the axial stress distribution is also required to evaluate the deformation behavior of materials. Recently, a measurement method for axial stress distribution is proposed based on an assumption of bilinear internal force distribution in specimen. However, the measured result only gives an approximate result. Besides, because the satisfaction of the assumption limits to several conditions, only the result obtained at a particular moment and position region is reliable. On the other hand, it is possible to calculate the axial stress distribution from the momentum balance law to avoid the mentioned assumption if the axial acceleration distribution is captured by the DIC technique. Unfortunately, the feasibility and accuracy for the method has not been discussed yet, even though some challenges on introducing DIC technique to Taylor impact test has already been done. Here, a method based on momentum balance law and axial acceleration distribution is newly proposed to obtain the axial stress distribution. The stress–strain curve in Taylor impact test is obtained by a simultaneously spatial combination between the stress and strain distributions. Then, the feasibility of the proposed method is discussed computationally and experimentally.

A Study of the Dynamic Mechanical Properties of Q460D Steel

The dynamic mechanical properties of Q460D steel were studied to facilitate an assessment of the impact resistance of building structures. In the present work, material performance tests of Q460D steel at different temperatures, strain rates, and stress states were conducted. Using a hybrid experimental–numerical approach, a modified Johnson–Cook (JC) constitutive relation, a modified Johnson–Cook (JC) fracture criterion, and a lode-dependent fracture criterion were calibrated. To validate the calibration, Taylor impact tests of Q460D steel rods onto rigid target plates were carried out in a one-stage light-gas gun system. Mushrooming, tensile splitting, and petalling failure modes were obtained as the impact velocity was increased from 191.6 to 422.1 m/s. A three-dimensional finite element model was built for the Taylor impact tests, and FE simulations were run using the material models calibrated. It was found that the FE simulations using the lode-dependent fracture criterion were reasonable in terms of the failure modes of the Taylor rods. In contrast, the fracture behavior of the Taylor rods was significantly underestimated using the lode-independent JC fracture criterion. Finally, the effect of anisotropy, strain rate sensitivity and yield plateau on the Taylor impact FE predictions were explored and discussed.

Design of a low-velocity impact framework for evaluating space-grade materials

Material deformation and failure under impact loading is a subject of active investigation in space science and often requires very specialized equipment for testing. In this work, we present the design, operational analysis and application of a low-velocity (∼100m/s) projectile impact framework for evaluating the deformation and failure of space-grade materials. The system is designed to be modular and easily adaptable to various test geometries, while enabling accurate quantitative evaluation of plastic flow. Using coupled numerical methods and experimental techniques, we first establish an operating procedure for the system. Following this, its performance in two complementary impact configurations is demonstrated using numerical and experimental analysis. In the first, a Taylor impact test is performed for predicting the deformed shape of a cylindrical projectile impinging on a rigid substrate. In the second, deformation of a plate struck by a rigid projectile is evaluated. In both cases, physics-based models are used to interpret the resulting fields. We present a discussion of how the system may be used both for material property estimation (e.g., dynamic yield strength) as well as for failure evaluation (e.g., perforation and fracture) in the same projectile impact configuration.

Modified Taylor Impact Tests with Profiled Copper Cylinders: Experiment and Optimization of Dislocation Plasticity Model.

Current progress in numerical simulations and machine learning allows one to apply complex loading conditions for the identification of parameters in plasticity models. This possibility expands the spectrum of examined deformed states and makes the identified model more consistent with engineering practice. A combined experimental-numerical approach to identify the model parameters and study the dynamic plasticity of metals is developed and applied to the case of cold-rolled OFHC copper. In the experimental part, profiled projectiles (reduced cylinders or cones in the head part) are proposed for the Taylor impact problem for the first time for material characterization. These projectiles allow us to reach large plastic deformations with true strains up to 1.3 at strain rates up to 105 s-1 at impact velocities below 130 m/s. The experimental results are used for the optimization of parameters of the dislocation plasticity model implemented in 3D with the numerical scheme of smoothed particle hydrodynamics (SPH). A Bayesian statistical method in combination with a trained artificial neural network as an SPH emulator is applied to optimize the parameters of the dislocation plasticity model. It is shown that classical Taylor cylinders are not enough for a univocal selection of the model parameters, while the profiled cylinders provide better optimization even if used separately. The combination of different shapes and an increase in the number of experiments increase the quality of optimization. The optimized numerical model is successfully validated by the experimental data about the shock wave profiles in flyer plate experiments from the literature. In total, a cheap, simple, but efficient route for optimizing a dynamic plasticity model is proposed. The dislocation plasticity model is extended to estimate grain refinement and volume fractions of weakened areas in comparison with experimental observations.

Investigation of mechanical behavior, constitutive modeling, and fracture criteria for as-cast Al0.3CoCrFeNi high entropy alloy

High entropy alloys (HEAs) have garnered significant attention in recent years, primarily focusing on alloying design and thermal processing. The objective of this study was to investigate the mechanical response of Al0.3CoCrFeNi, a representative HEA, under various stress states, temperatures, and strain rates, aiming to establish its constitutive equation and fracture criteria. Employing a hybrid FEM/EX approach, the constitutive behaviour of the alloy was characterized using the modified Johnson-Cook (MJC) model, while the fracture properties were assessed using the Hosford-Coulomb (HC) equation. Experimental findings highlighted the remarkable tensile strength (578.1 MPa) and ductility (69%) of the as-cast Al0.3CoCrFeNi at room temperature. However, at elevated temperatures ranging from 400 °C to 650 °C, a reduction in ductility was observed, accompanied by serration behaviour. Notably, precipitation hardening was detected at 800 °C, indicative of strengthening through precipitate formation. Additionally, Al0.3CoCrFeNi exhibited significant strain rate sensitivity and a positive strain rate effect, emphasizing its dynamic response under different loading conditions. The accuracy of the constitutive model and fracture criteria was validated through the examination of deformation and fracture modes in Taylor impact tests. The MJC model demonstrated predictions within a 10% deviation from experimental data, while the HC fracture criterion, accounting for stress triaxiality and Lode parameters, effectively predicted shear fracture in the projectiles. Crack formation in the projectiles resulted from a combination of tension and shear, followed by propagation at a 45° angle under combined compression and shear loading. This comprehensive study enhances understanding of the mechanical properties of Al0.3CoCrFeNi, providing valuable insights for its application in engineering, particularly in impact protection.

Dynamic response characteristics of grooved cylindrical shells in Taylor impact experiments

Buffer energy absorbing structures have very high use value in daily life, industrial production, aerospace and other fields. Cylindrical shells are used as a highly efficient buffer and energy absorbing structure due to their own structure and good mechanical properties. Taylor impact experiments were conducted on three types of structural cylindrical shells (non grooved, inner grooved, and outer grooved) and numerical model was also established to study and analyze the dynamic response characteristics of the three types of structural cylindrical shells. Finally, the deformation mechanism of the cylindrical shell was analyzed theoretically to explore the impact of grooving treatment on the deformation of the cylindrical shell. The results show that with the increase of impact velocity, the length of the cylindrical shells of the three structures decreased, and the diameter of the impact end and the maximum diameter increased. Each of the three specimens had a convergence velocity(convergence velocity: The impact end diameter of cylindrical shell is the initial impact velocity at the maximum diameter), that is, when the impact velocity was greater than or equal to the convergence velocity, its maximum diameter was equal to the diameter of the impact end. When the impact velocity exceeded a certain value, the deformation modes of the three types of cylindrical shells changed. The comparison of experimental and simulation results proved the effectiveness of the numerical model. The maximum stress was always above the impact end face. It was concluded from the theoretical analysis Due to the stress concentration at the groove, the stress distribution and internal stress distribution of the cylindrical shell were affected, which in turn affected the deformation and energy absorption capacity of the cylindrical shell. At the same impact velocity, the outer grooved cylindrical shell has the shortest buffer time and the BW specimen had the most gentle buffer curve before 35μs .

Tungsten alloy impact fracture for frangible armor piercing

This paper presents experimental and numerical studies of tungsten alloy fragmentation caused by impact loading. Impact loading is a complex mechanics including dynamic hardening and fracture coupled with a wide range of strain, strain rate, and temperature. In order to obtain the dynamic hardening behavior from low to high strain rates, compression tests have been conducted with the INTRON 5583 and the Split Hopkinson Pressure Bar testing machines. Taylor impact tests are also carried out at various impact velocities to evaluate the fragmentation. Considering the fragmentation tendency of tungsten alloy in this study, it could be utilized for the penetrator of FAP projectile. For the further investigation, finite element analysis is performed to predict the dynamic behaviors by using Lim–Huh hardening model and Mohr–Coulomb(MC) fracture model. In the MC fracture model, the mean stress concept is introduced. The fracture model parameters are calibrated using inverse engineering of the test results. The analysis successfully predicts the deformation and fragmentation according to the impact velocity. It is shown that the stress-based Mohr–Coulomb fracture model successfully predicts the direction of crack propagation and fragment size tendencies.

Numerical and experimental studies on specimens with integrated pulse-shaper used for the instrumented Taylor impact test to measure stress-strain curves at high rates of strain

In the previous studies, an instrumented Taylor impact test was established to measure the stress-strain curve at an ultrahigh strain rate. To calculate the axial stress distribution in the specimen, a bi-linearity of the internal force distribution in both the elasticity- and plasticity-dominant regions was assumed. However, the unavoidably generated excessive local deformation (ELD) near the impact surface results in early unloading and a strong nonlinear distribution of the internal force in the region near the impact surface. Consequently, the measurable stress-strain curve was limited to 0.1 of the axial strain. On the other hand, the pulse-shaping technique, which is widely used in split Hopkinson pressure bar tests, can be employed to increase the strain until the stress-strain curve is measurable through Taylor impact tests because the short rise time is considered to be a possible reason of ELD generation. For the first time, this study introduced the pulse-shaping technique to the instrumented Taylor impact test to expand the measurability of the stress-strain curve to a higher strain range. To suppress the ELD, the dimensions of the pulse shaper are determined through finite element analyses after a discussion of the mechanism to suppress ELD. Then, the proposed method with a newly designed specimen is validated conducting the real Taylor impact test.

Numerical Simulation of the Taylor Impact Test for Laser Powder Bed Fusion Parts Based on Microstructural Internal State Variables

The response of any engineering design components to stresses should be predictable, While the response of a material to complex loading, such as high strain rates experienced during service, is difficult to represent with simple tests, the Taylor impact test is one of a number of tests devised for high strain rate complex loading. To expedite the acceptance of LPBF Ti6Al4V (ELI) for use in demanding structural applications, there is a need to develop numerical models based on the internal microstructural state variables to predict the performance of the alloy over a wide range of high strain rates using such complex tests. This paper documents the numerical simulation of Taylor impact tests for direct metal laser-sintered and post-processed Ti6Al4V (ELI—Extra Low Interstitial) alloy. A microstructural variable-based constitutive model was used to predict the mechanical properties (stresses and evolution of plastic strains) of the material. The corresponding material parameters of the model were based on the specific microstructure obtained upon post-process heat treatment. The model was first implemented as a user material subroutine in the explicit finite element program ABAQUS using the VUHARD subroutine. Subsequently, the symmetrical Taylor impact tests of Laser Powder Bed Fusion (LPBF) Ti6Al4V (ELI) parts were numerically simulated using the VUHARD subroutine at different impact velocities. The equivalent von Mises stress and plastic strain obtained from numerical simulations were compared with the analytical solutions based on the strain rates obtained. It was shown that the instantaneous and average absolute errors between the numerical and analytical values of the model were generally less than 5%. The mushroom end, commonly observed in a Taylor test specimen, was also seen in the numerical model.

Axisymmetric model for Taylor impact test and estimation of metal plasticity using nonlinear deformation profile

Axisymmetric model for Taylor impact test and estimation of metal plasticity using nonlinear deformation profile

Experimental Study of the Microhardness and Microstructure of a Copper Specimen Using the Taylor Impact Test

One commonly used method for characterizing the dynamic characteristics of materials is the Taylor impact test. This method measures the dynamic yield strength of cylindrical specimens and determines material model constants required for the numerical simulation of the behavior of materials subjected to high-velocity deformation. The purpose of this work is to investigate the microhardness and microstructure of copper specimens at different impact velocities using the Taylor impact test. This paper describes experiments performed on copper specimens (OFHC 99.9%, M1) using a single-stage light-gas gun with impact velocities in the range of 150–450 m/s. After impact, the specimens were cut along the symmetry axis to measure the microhardness and the grain size of the microstructure. Microhardness in the entire area exceeded the initial value for all investigated velocities. The averaged microhardness curves were obtained for each specimen to identify four deformation zones and determine their dimensions depending on the impact velocity. The average grain size in the entire deformed specimen became smaller than in the starting specimen. The study of the microstructure of the specimens has shown that the grain size distribution corresponds to the four deformation zones in the copper specimens.

A unified elasto-viscoplastic peridynamics model for brittle and ductile fractures under high-velocity impact loading

Peridynamics (PD), as an alternative formulation of classical continuum mechanics, is a powerful method for predicting the spontaneous initiation and propagation of cracks. In this paper, a unified elasto-viscoplastic peridynamics model, named the Bodner-Partom theory-based Peridynamics (BPPD) model, is proposed to describe the whole deformation-damage-fracture process for both brittle and ductile materials under impact loadings. It defines the bond-wise elasto-viscoplastic deformation by incorporating the Bodner-Partom's (B-P) constitutive theory into the ordinary state-based PD framework. In BPPD model, the bond deterioration is introduced as an intrinsic variable coupled with the modified B-P theory and the bond fracture is realized by the critical bond stretch model. The proposed BPPD model permits the natural development of plastic deformation and material deterioration, which shares the same vision as PD theory. Equipped with the elastic short-range force contact model, the present study further investigates the modelling capacity of the BPPD model under various impact loadings. Simulations for brittle drop-ball test, Taylor impact test and ballistic penetration test show a good agreement between numerical results and experiment data. The proposed BPPD model can accurately capture the whole deformation processes of various impact fractures and thus contribute a new diversity to the development of PD theory and a new perspective to the understanding of material fracture mechanism.

Taylor impact of high-entropy alloy Al0.1CoCrFeNi: Dynamic severe plastic deformation and bulk gradient structure

Taylor impact experiments are conducted on a typical face-centered cubic single-phase high-entropy alloy (HEA) Al0.1CoCrFeNi, to investigate its dynamic severe plastic deformation and gradient structure. Parameters of the Johnson–Cook constitutive model are obtained, and finite element modeling based on this model is consistent with the experimental observations. A bulk gradient structure with deformation gradient is generated directly via the Taylor impact. The deformation mechanisms include the {111}〈112〉 deformation twins and kink bands with the 〈110〉 or 〈112〉 rotation axes, and vary considerably along the impact direction. Subsequent annealing at 800∘C and the impact-induced gradient in the degree of re-crystallization lead to a new bulk gradient structure with gradients in grain size and proportion of the non-recrystallized region, providing a novel approach to developing bulk gradient structured materials.

Assessing dynamic compression of AA2024-T351 with split Hopkinson pressure bar simulation

To understand the dynamic compressive behaviour of aluminium alloy AA2024-T351, which is commonly used in maritime and offshore structures, is vital. This is generally achieved using Taylor impact tests, projectile tests and split Hopkinson pressure bars (SHPBs). It can also be obtained in a less expensive way by using a finite-element simulation of an SHPB under different conditions. This paper numerically investigates the effects of striker velocity, striker shape and specimen shape on the dynamic compressive behaviour of AA2024-T351 using a simulated SHPB. The material behaviour was found to be sensitive to strain rates, striker shapes and specimen shapes under various situations.