Dynamic Plastic Behavior Research Articles

Analysis of Saturated Impulse for Square Plates under Flat Slamming Impact: Experimental and Numerical Investigation

The saturated impulse is a special phenomenon in the dynamic plastic behavior of engineering structures under intensive pulse loading, such as slamming loading. In this study, slamming experiments were performed on steel plates to investigate their slamming pressure and dynamic plastic responses, as well as the saturation phenomenon, and elucidate the effect of the plate thickness and material properties on the dimensionless saturated deflection and saturated impulse in combination with the published test data. The results show that the dimensionless saturated deflection and saturated impulse of the test plates gradually increased as the dimensionless stiffness decreased. After being validated against the experimental results, a numerical method that considered the fluid–structure interaction (FSI) effect was then employed to provide comprehensive insight into the transient plastic responses and saturated impulse of the flat plates under slamming impact. Numerical simulations revealed that the compressed air layer always existed during the effective process of the flat slamming impact. Through the numerical prediction of the dynamic plastic deflection and slamming pulse loading, it was observed that the saturated impulse phenomenon always took place after the time instant of the peak value of the pressure pulse. Furthermore, the analysis of the saturated impulse based on the numerical simulations indicated that the saturation phenomenon was more likely to be achieved as the water impact velocity increased.

Extraction of the dynamic plastic behavior of AlON single crystals by nanoimpact

Extraction of the dynamic plastic behavior of AlON single crystals by nanoimpact

Effect of underwater friction stir welding parameters on AA5754 alloy joints: experimental studies

The water as a welding environment may generate serious technological and metallurgical problems but in certain cases, the physicochemical properties of water can be used effectively, e.g., to impart the specific properties of welded materials. The purpose of the work was verification of effectiveness of the water cooling of aluminium alloy AA5754 for various sets of technological parameters of underwater friction stir welding (UFSW). For the joints performed with the range of parameters of rotational speed: 475–925 rpm and welding speed: 47.5–95 mm/min, the following examinations were carried out: visual tests, radiographic tests, static tensile test, fractography (SEM, scanning electron microscope) analysis, and surface texture analysis performed with 3D measurement system. All of the joints were characterized with some amount of flash. Besides, depending on the values of selected parameters, the defects arising from inadequate stirring were found—tunnel defects and melting. The best appearance of the joint was obtained for the set of parameters of 925 rpm and 47.5 mm/min. The samples of the same joint were found to be of the highest mechanical properties—ultimate tensile strength (UTS) of 194 MPa and elongation (A) of 9.2%. The results were confirmed by the fractography analysis, which in this case indicated the ductile fracture mode. Dynamic plastic behaviour strongly depends on the process parameter values, which was reflected in the results of surface texture analysis. The parameter selection resulted in significant changes in the roughness results (from 8 to 14.2 µm depending on the sample) as well as the flow ring distance of the weld (from 20 to 50 µm depending on the sample).

Dynamic yielding and plastic flow behavior of Ti-6Al-4V under complex loading

The mechanical properties of metallic materials under complex loading at high strain rates are very important for material processing and engineering design. In this paper, a newly developed electromagnetic Hopkinson bar system is used to conduct dynamic experiments on Ti-6Al-4V titanium alloy under tension/compression-torsion loading conditions. The dynamic plastic behavior of the alloy, subject to complex stress states, was investigated at different loading rates under tension–torsion and compression-torsion conditions. A dynamic asymmetry yield criterion (DAYC) and loading surface (DALS) with different loading paths were proposed. The coupling effects of strain rate and stress state were considered in the yield and hardening functions. The results reveal non-uniformity in the initial yield surface and the expansion of loading surfaces at different stress states under high strain rates. Through comparison with experimental results, the reliability and accuracy of the proposed yield criterion and loading surface were validated. At last, a study on the direction of plastic flow was conducted, which demonstrated that the associated flow rule was basically satisfied.

Dynamic Yielding and Plastic Flow Behavior of Ti-6al-4v Under Complex Loading

Dynamic Yielding and Plastic Flow Behavior of Ti-6al-4v Under Complex Loading

Dynamic plastic behavior of single and nested rings under lateral impact

This paper aims to investigate the dynamic plastic behavior of single and nested circular rings traditionally used as energy absorbers. The response characteristics of these structures are experimentally and numerically determined when they are subjected to high rate lateral impacts. It should be emphasized that a gas gun is employed in order to conduct experimental tests in which a load cell is utilized to measure the force-time response at the distal end. Furthermore, the finite element software LS-Dyna is employed to obtain numerical results in which the Johnson-Cook constitutive equation is used to take into account the strain rate and hardening effects. It is revealed that employed single rings as energy absorbers are absorbing input energies while transmitting small amounts of forces particularly peak loads to protected specimens or occupants. Moreover, it is determined that circular rings having smaller thicknesses and greater inner diameters are much more efficient energy absorbers. However, it is found that single rings have low energy absorption capacity leading to high peak loads for high input energies. It is shown in the presented paper that nested rings can be used as suitablealternatives since they can absorb much more energy and transmit much fewer forces compared to single rings.

Dynamic plastic impact behavior of CNTs/fiber/polymer multiscale laminated composite doubly curved shells

In the present paper, the dynamic elastoplastic response of carbon nanotube (CNT) fiber/polymer multiscale laminated composite (CNTFPC) doubly curved shell subjected to low-velocity impact of the projectile is investigated. For this purpose, the effective material properties of the multiphase composite are calculated by combining the Halpin-Tsai model and a micromechanical approach that strengths are estimated by an empirical equation and modified through a mixture rule. The elastoplastic constitutive equations are obtained incrementally using Hoffman’s criterion and isotropic hardening model. Also, the Green-Lagrange type of nonlinear kinematics is extracted in terms of displacement terms based on Reddy’s higher-order shear deformation theory for the CNTFPC shell. All incremental relations are regulated in the framework of the updated Lagrangian formulations to solve by an iterative finite element procedure through conforming isoparametric quadrilateral elements. Moreover, an elastoplastic Brake’s contact model is developed to determine truly the contact force between the CNTFPC plate and impactor. Temporal discretization is done by the Newmark’s average acceleration scheme. The results are validated with the data available in the literature to demonstrate the accuracy of the model. A parametric study was carried out to analysis stress and investigate the yield conditions and the effects of plastic deformation, weight percentage of CNTs, fiber volume fraction and curvature radius on the contact force history, indentation, permanent indentation depth, central deflection. Numerical results show that in the low velocity impact analysis, the stresses occurring in the shell for the areas further away from the contact area are also yielded.

Influence of laser peening on the high-temperature fatigue life and fracture of Inconel 718 nickel-based alloy

High-temperature fatigue test was performed to study the effects of laser peening (LP) on the fatigue behavior of Inconel 718 nickel-based alloy at high temperature. Compressive residual stress (CRS) induced by LP was investigated at both room and high temperature. Microstructural evolution was also studied before and after LP process. The macro- and micro-fracture morphologies in fatigue crack initiation (FCI) region, fatigue crack growth (FCG) region and finial rupture (FR) region of LPed samples with different laser power densities at different temperatures were systematically analyzed. The results showed that LP process can enhance the fatigue life of IN718 nickel-based alloy at both room and high temperature. Excessively high temperature (e.g. 800 °C) may result in a sudden decrease in the fatigue life of LPed samples due to the weakening of grain boundaries and oxidation damage. The losing of coherent strengthen between γ″ phase and matrix was another reason for the rapid reducing of fatigue life. Compared to the untreated samples, the crack source transferred from the surface to deeper layer indicated that LP can retard the crack initiation on the metal surface, which is conducive to enhance the final fatigue life. Some direct evidence, such as the decreased distance between the parallel fatigue striations, the tortuous crack growth path in the LPed specimen confirmed the retarding effects of LP on the FCG. The mechanism of microcracking and the dynamic plastic behavior of LPed specimens during high-temperature fatigue test of IN718 nickel-based alloy were also discussed.

Dynamic plastic behaviour of strain rate sensitive tubes under axial impact

In this paper, the axisymmetric buckling of circular strain rate sensitive tubes subjected to axial impact is investigated theoretically and experimentally. The nonlinear governing equations are first derived in an incremental form. Then, the finite difference method is employed to solve the obtained equations implicitly for the case when a stationary tube is impacted by a striking mass. Experimental tests are performed by using a gas gun. The effect of linear and multi-linear approximation for strain hardening and strain rate on the shortening, buckling shape and axial force of steel tubes are investigated in which the strain rate is considered as a function of time. By applying the strain rate effect and using the multi-linear approximation for strain hardening, we showed there is a significant association between theoretical and experimental results of steel tubes. Also, using the nonlinear dynamic equations and newly developed inexact finite similitude theory it is revealed that the response characteristics of full-scale strain rate sensitive tubes can be predicted using small-scale strain rate insensitive tubes.

Closed-form analytical analysis on the effect of coupled membrane and bending strains on the dynamic plastic behaviour of fully clamped thin quadrangular plates due to uniform and localized impulsive loading

The problem of studying plastic response of structures loaded dynamically has been extensively investigated over many years. A survey of literature on dynamic plastic behaviour of plates subjected to impulsive loading reveals that most analytical studies on fully clamped thin quadrangular plates consider bending moments and membrane forces separately and the coupled yielding analysis is ignored. Therefore, this paper investigates large plastic deformation of thin quadrangular plates due to both uniform and localized loading when the coupled interaction between membrane and bending strains has been incorporated into the closed-form analytical analysis. The present closed-form analytical analysis is developed by pursuing the energy approach based on upper bound solution in which the Cowper-Symonds constitutive equation is employed to take into account strain-rate effects. The material coefficients in Cowper-Symonds equation have been considered as functions of plate thickness based on Jones' experiments on steel materials. The analytical predictions are compared with different set of experiments in terms of maximum permanent transverse deflections, in addition to Jones' theoretical model and our previous analytical model. It is found that incorporating the coupled yielding into the analysis leads to reduce the error value in predicting the maximum permanent transverse deflections.

A study of dynamic plasticity in austenite stainless steels with a gradient distribution of nanoscale twins

The dynamic plastic behavior related to the gradient distribution of twin spacing in 304 stainless steel thin wires is investigated experimentally with the strain rate varying from 1×10−3/s to 1.5×104/s. Such gradient-nanotwinned structures are prepared by surface mechanical attrition treatment. A mechanism-based dynamic plastic model is developed to describe the strain-rate dependent stress-strain response in gradient-nanotwinned austenite stainless steels. A good agreement between experimental data and simulations was achieved, and further theoretical predictions demonstrated that the dynamic plastic behavior is sensitive to the twin spacing and volume fraction of gradient-nanotwinned region in austenite stainless steel wires.

Theoretical analysis on the effect of uniform and localized impulsive loading on the dynamic plastic behaviour of fully clamped thin quadrangular plates

This paper presents an approximate theoretical analysis of inelastic behaviour of fully clamped thin quadrangular plates subjected to two different distributions of impulsive loading. The presented analysis has been developed based on plastic work of plate and kinetic energy in which it assumes that the plate behaves rigid perfectly plastic. The rigid plastic analysis uses an interaction yield surface based on reasonable assumption that only membrane force considers for plastic flow and employs the Cowper-Symonds equation to cater for material strain rate effect. In this study, the applied load is estimated by assuming the initial velocity field of flat plate based on the boundary conditions of plate and geometry of explosive charge setup. Obtained models predict final deflection of the quadrangular plate loaded by uniformly and localized loading. The proposed solution permits consideration of characteristic influence of the load and material on the response of plate. It is observed that the present theoretical models are in good agreements with experimental results and also in comparison with other approximate solution, the present models are found to be simpler and in better agreements with experimental values.

Implementation of Finite Strain-Based Constitutive Formulation in LLLNL-DYNA3D to Predict Shockwave Propagation in Commercial Aluminum Alloys AA7010

The constitutive models adopted to represent dynamic plastic behaviour are of great importance in the current design and analysis of forming processes. Many have studied this topic, leading to results in various technologies involving analytical, experimental and computational methods. Despite of this current status, it is generally agreed that there is still a need for improved constitutive models. There are still many issues relating to algorithm implementation of the proposed constitutive model in the selected code to represent the proposed formulation. Using this motivation, the implementation of a new constitutive model into the LLNL-DYNA3D code to predict the deformation behaviour of commercial aluminium alloys is discussed concisely in this paper. The paper initially explains the background and the basic structure of the LLNL-DYNA3D code. This is followed by a discussion on the constitutive models that have been chosen as the starting point for this work. The initial stage of this implementation work is then discussed in order to allow all the required material data and the deformation gradient tensor F to be read and initialised for the main analysis. Later, the key section of this implementation is discussed, which mainly relates to subroutine f3dm93 including equation of state (EOS) implementation. The implementation of the elastic-plastic part with isotropic plastic hardening, which establishes the relationship between stress and strain with respect to the isoclinic configuration Ω̄i in the new deviatoric plane, is then presented before the implemented algorithm is validated against Plate Impact test data of the Aluminium Alloy 7010. A good agreement is obtained in each test.

Experimental and numerical investigation of dynamic plastic behavior of tube with different thickness distribution under axial impact

In this study, the dynamic behavior of uniform thickness, stepped thickness and functionally graded thickness tubes under axial impact are investigated experimentally and numerically. A striking mass has been used to impact tubes. Experimental tests are performed by using gas gun and numerical results are obtained by FE simulation. The effect of thickness distribution on shortening, energy absorption, axial force and buckling shape of tubes are investigated. It is found that a change in thickness distribution of tube can convert the buckling shape from buckling with mild folds to progressive buckling and vice versa. In addition, it is found that stepped thickness tube can be an approximate of functionally graded thickness tube which in this case almost, their behavior is identical. This study reveals that stepped thickness and functionally graded thickness tubes in comparison with uniform thickness tube absorb the same energy with more shortening and less peak load or less mean load; thus, they are better energy absorption specimens. With comparing experimental and numerical results, it is found that there is a good agreement between them.

Experimental Techniques and Measurements in Impact Engineering Using Hopkinson Bar Technique

In the paper, experimental analysis of dynamic plastic behaviour of different structural materials at high and very high strain rates up to 105 s-1 in various modes at lowered, room and elevated temperatures, is presented. The paper describes laboratory set ups for testing material specimens, based on various modifications of the Hopkinson bar technique. The paper focuses the attention on experimental tests and their interpretation. The results reported here will be useful for the designers working on the dynamic behaviour of building and mechanical protective structures made of different materials such as steels, aluminium alloys, ceramic and sand bricks, mortars, woods (pine, birch and aspen), ceramics and concrete fireproof and soils (sand, clay and sandy soil clay).

Self-Similar Random Process and Chaotic Behavior In Serrated Flow of High Entropy Alloys.

The statistical and dynamic analyses of the serrated-flow behavior in the nanoindentation of a high-entropy alloy, Al0.5CoCrCuFeNi, at various holding times and temperatures, are performed to reveal the hidden order associated with the seemingly-irregular intermittent flow. Two distinct types of dynamics are identified in the high-entropy alloy, which are based on the chaotic time-series, approximate entropy, fractal dimension, and Hurst exponent. The dynamic plastic behavior at both room temperature and 200 °C exhibits a positive Lyapunov exponent, suggesting that the underlying dynamics is chaotic. The fractal dimension of the indentation depth increases with the increase of temperature, and there is an inflection at the holding time of 10 s at the same temperature. A large fractal dimension suggests the concurrent nucleation of a large number of slip bands. In particular, for the indentation with the holding time of 10 s at room temperature, the slip process evolves as a self-similar random process with a weak negative correlation similar to a random walk.

Quasi-static and high-rate mechanical behavior of aluminum-based MMC reinforced with boron carbide of various length scales

We report on an investigation of the quasi-static and dynamic mechanical behavior of an ultrafine-grained (UFG) aluminum composite reinforced with nanoscale boron carbide under uniaxial compression. Aluminum composites reinforced with either nanometric or half-micron sized B4C exhibit high strength ~900MPa and considerable strain-to-failure under compression (>15pct.) at quasi-static (10−3s−1) and dynamic (103s−1) strain rates. Microstructural analyses of the composites and unreinforced aluminum alloy were performed to determine the strengthening mechanisms and plastic behavior that govern the structure–property relationships for this class of materials. Our results reveal that the flow stress of the composites does not depend strongly on strain rate if high rate data are included, while strain rate jump tests via instrumented nanoindentation indicate that the strain rate sensitivity exhibits similar behavior as the unreinforced matrix. The unreinforced alloy undergoes strain hardening at both quasi-static and dynamic strain rates, while the composites show strain softening at dynamic strain rates and elastic nearly-perfectly plastic behavior at quasi-static rates. Adiabatic shear band formation was evident in the composite samples during dynamic loading, whereas no shear banding was observed in the unreinforced alloy for the strain rates studied herein. The notion of adiabatic shear band toughness was adopted to identify the increased propensity to shear localization in the composites vis-a-vis the unreinforced material. An attempt is made to account for the effect of the boron carbide reinforcement size on the strengthening mechanism and overall plastic response for these metal matrix composites.

On the importance of recrystallization to reproduce the Taylor impact specimen shape of a pure nickel

Taylor tests are a mean to investigate the dynamic plastic and failure behaviour of metals under compression. By taking in account the strengthening occurring at high strain rates, the Taylor final diameter of a pure nickel impacted at 453 m/s have been numerically reproduced by 13%. Through post-mortem observations of the specimen impacted at 453 m/s, a recrystallization process has been found to occur resulting in a softening of the pure nickel. Subsequent numerical simulations taking in account this softening have been found to reduce the difference between experimental and numerical diameter by 10%.

Dynamic Viscoplastic Response of a Circular Plate Subjected to Underwater Shock

A structure subjected to underwater shock exhibits surprising dynamic behavior, different from the permanent plastic deformation of a structure subjected to air blast, due to the presence of complicated fluid-structure interaction (FSI) effect. Previous studies of a circular plate subjected to underwater shock indicate that there exist large discrepancies between theoretical and experimental results of plastic deformations. Herein we thus propose a new double-scale and double-phase (DSDP) FSI model for correct prediction of the dynamic plastic behavior of a circular plate subjected to underwater shock. Results obtained from this DSDP model are compared with several experimental tests, with excellent agreement observed. This model is believed useful for further implementation in those software programs that handle underwater explosion and its effects on marine structures.

Influence of the Heat Treatment Condition upon the High-Speed Cutting Mechanism of Aluminum Alloy A2017

This paper discusses the influence of heat treatment condition of aluminum alloy upon cutting mechanism. The orthogonal cutting experiments of A2017-T3 and A2017-O with a cutting speed of from 0.5 m/s to 160 m/s are conducted. The experiments obtain the following results: A2017-T3 forms discontinuous and serrated chip, while A2017-O forms continuous flow-type chip, regardless of cutting speed. The tendencies of the changes in shear angle, cutting forces, friction angle and the shear stress on the shear plane with the cutting speed are the same between A2017-T3 and A2017-O, when the cutting speed is less than 80 m/s. The significant dissimilarities in the cutting mechanism, however, between A2017-T3 and A2017-O come to appear gradually, when the cutting speed exceeds 80 m/s. For A2017-T3, the shear stress on the shear plane is steady, and the friction angle at the tool-chip interface increases slightly in such a high-speed cutting condition. In contrast, for A2017-O, the shear stress on the shear plane rises gradually, while the friction angle keeps decreasing with the cutting speed. An analysis based on the simple shear model shows that the shear strain rate at the shear zone reaches up to 107 1/s when the cutting speed is beyond 80 m/s. The appearance of these dissimilarities in the cutting mechanism due to the difference in the heat treatment conditions will depend on the characteristics of dynamic plastic behavior and dynamic friction property of aluminum alloy appearing at high-strain-rate fields.