Rate Sensitive Material Research Articles

Effect of loading velocity on the seismic behavior of RC joints

The strain rate of reinforced concrete (RC) structures stimulated by earthquake action has been generally recognized as in the range from 10-4/s to 10-1/s. Because both concrete and steel reinforcement are rate-sensitive materials, the RC beam-column joints are bound to behave differently under different strain rates. This paper describes an investigation of seismic behavior of RC beam-column joints which are subjected to large cyclic displacements on the beam ends with three loading velocities, i.e., 0.4 mm/s, 4 mm/s and 40 mm/s respectively. The levels of strain rate on the joint core region are correspondingly estimated to be 10-5/s, 10-4/s, and 10-2/s. It is aimed to better understand the effect of strain rates on seismic behavior of beam-column joints, such as the carrying capacity and failure modes as well as the energy dissipation. From the experiments, it is observed that with the increase of loading velocity or strain rate, damage in the joint core region decreases but damage in the plastic hinge regions of adjacent beams increases. The energy absorbed in the hysteresis loops under higher loading velocity is larger than that under quasi-static loading. It is also found that the yielding load of the joint is almost independent of the loading velocity, and there is a marginal increase of the ultimate carrying capacity when the loading velocity is increased for the ranges studied in this work. However, under higher loading velocity the residual carrying capacity after peak load drops more rapidly. Additionally, the axial compression ratio has little effect on the shear carrying capacity of the beam-column joints, but with the increase of loading velocity, the crack width of concrete in the joint zone becomes narrower. The shear carrying capacity of the joint at higher loading velocity is higher than that calculated with the quasi-static method proposed by the design code. When the dynamic strengths of materials, i.e., concrete and reinforcement, are directly substituted into the design model of current code, it tends to be insufficiently safe.

Investigation on activation volume and strain-rate sensitivity in ultrafine-grained tantalum

The activation volume and strain-rate sensitivity (SRS) of a plastic deformation process and their relationship are investigated in the present work. Through theoretical modeling based on the movement of both isolated kinks and kink pairs in a dislocation line, a new form of theoretical relationship between the strain-rate sensitivity and activation volume was developed, which reduces to the conventional and frequently used form of the same relationship when SRS is approaching zero. The strain rate jump test during the necking stage of tensile testing process is validated through combined theoretical analytical approaches, for obtaining strain rate sensitivity of materials with short uniform tensile stage, such as UFG metals. To validate the theoretical approaches and modeling presented in this work, strain-rate jump tests and repeated stress relaxation experiments were conducted, to measure the SRS and activation volume of commercial pure ultrafine-grained tantalum prepared by equal channel angular pressing. The experimental relationship between the strain-rate sensitivity and the activation volume of these tantalum samples fits well with the new form of theoretical relationship developed in this investigation. Experimental data from literature on nickel confirms the new form as well. The new form of theoretical relationship between strain-rate sensitivity and activation volume can be applied for both bcc and fcc metals as long as the major plastic deformation mechanism is dislocation gliding.

The influence of strain-rate on the perforation resistance of fiber metal laminates

The rate-sensitivity of a range of fiber metal laminates (FMLs) has been investigated though split Hopkinson bar, quasi-static perforation and low velocity impact tests. Initial attention focused on assessing the rate-sensitivity of the constituent materials, that is the glass fiber reinforced epoxy and the three aluminum alloys. This was followed by a series of perforation tests on multilayer configurations.It has been shown that both the composite and the aluminum substrates exhibit a low degree of rate-sensitivity, with both the tensile strength and the perforation energy increasing slightly in passing from quasi-static to dynamic rates of loading. Similarly, FMLs based on combinations of the composite and metal constituents exhibit a low degree of rate-sensitivity, with the impact perforation energy and the maximum impact force being only ten to fifteen percent higher than their quasi-static values. An examination of the cross-sections of the failed laminates indicated that the failure processes were similar at both quasi-static and dynamic rates of strain. Also, similar levels of plastic deformation, fiber fracture and delamination were observed at both rates. Finally, it has been shown that the energy to perforate the various FMLs is directly related to the aggregated perforation energies of their constituent parts.

3D finite element simulations of high velocity projectile impact

An explicit three-dimensional (3D) finite element (FE) code is developed for the simulation of high velocity impact and fragmentation events. The rate sensitive microplane material model, which accounts for large deformations and rate effects, is used as a constitutive law. In the code large deformation frictional contact is treated by forward incremental Lagrange multiplier method. To handle highly distorted and damaged elements the approach based on the element deletion is employed. The code is then used in 3D FE simulations of high velocity projectile impact. The results of the numerical simulations are evaluated and compared with experimental results. It is shown that it realistically predicts failure mode and exit velocities for different geometries of plain concrete slab. Moreover, the importance of some relevant parameters, such as contact friction, rate sensitivity, bulk viscosity and deletion criteria are addressed.

An Effective Computational Approach for the Numerical Simulation of Elasto-/Viscoplastic Solid Materials

The effects of different loading programs on the elasto-/viscoplastic behavior of rate-sensitive materials are analyzed with specific numerical examples. An appropriate solution scheme and a consistent tangent operator are applied which are capable of being adopted for general computational procedures. Numerical computations and results are reported which illustrate the rate-dependence of the elasto-/viscoplastic constitutive model in use. In the numerical analysis the loading is applied by increasing the pressure and accordingly a nondimensional loading program parameter is introduced. In the numerical results the significance of the loading program is thus emphasized with reference to the nonlinear response of the elasto-/viscoplastic material behavior of solids.

Hot Deformation Behavior and Processing Map of SiCp/2024Al Composite

Abstract The hot deformation behavior of 30%SiCp/2024 aluminum alloy composites was studied by hot compression tests using Gleeble-1500D thermo-mechanical simulator at the temperatures ranging from 350∼500 °C under strain rates of 0.01∼10 s −1 . The true stress-true strain curves were obtained in the tests. Constitutive equation and processing map were established. The results show that the flow stress decreases with the increase of deformation temperature at a constant strain rate, and increases with the increase of strain rate at constant temperature, indicating that composite is a positive strain rate sensitive material. The flow stress behavior of composite during hot compression deformation can be represented by a Zener-Hollomon parameter in the hyperbolic sine form. Its activation energy for hot deformation Q is 153.251 kJ/mol. To demonstrate the potential workability, the stable zones and the instability zones in processing map were identified and verified through micrographs. Considering processing map and microstructure, the hot deformation should be carried out at the temperature of 450 °C and the strain rate of 1 s −1 .

Hot Deformation Behaviors of SiCp/Al Composites

The hot deformation behaviors of 30%SiCp/2024 aluminum alloy composites was studied by hot compression tests using Gleeble-1500 thermomechanical simulator at temperatures ranging from 350-500°C under strain rates of 0.01-10 s-1. The true stress-true strain curves were obtained in the tests. Constitutive equation and processing map were established. The results show that the flow stress decreases with the increase of deformation temperature at a constant strain rate, and increases with the increase of strain rate at constant temperature, indicating that composite is a positive strain rate sensitive material. The flow stress behavior of composite during hot compression deformation can be represented by a Zener-Hollomon parameter in the hyperbolic sine form. Its activation energy for hot deformation Q is 183.251 kJ/mol. The optimum hot working conditions for this material are suggested.

Evaluation of Ductile-to-Brittle Transition Temperature by Reference Temperature (T) Approach at Higher Loading Rates for a Mod.9Cr-1Mo Steel

Abstract To evaluate the ductile-to-brittle transition temperature of ferritic–martensitic steels, the ASTM E1921-based reference temperature (T0) approach has now been widely recognized; however, until now, the standard restricts itself to static/quasi-static loading rates. It is well recognized that the flow stress of rate-sensitive material increases with the strain rate, and thus it is imperative that the increase in loading rate would lead to limited plasticity-induced brittleness, reflected in higher T0. There have been efforts in the literature for developing empirical correlations to derive T0 at higher loading rates from T0 at quasi-static loading rates or vice versa. However, there is a need to experimentally evaluate the T0 at higher loading rates, especially for the 9Cr-1Mo family of steels, proposed to be used as wrapper material in the upcoming commercial liquid-sodium-cooled fast breeder reactors in India. The present study is directed toward determining T0 for Mod.9Cr-1Mo steel at loading rates of 1.12, 3, and 5 m/s.

Strain rate sensitivity of Al-based composites reinforced with MnO2 additions

Fine-grained Al-based composites reinforced with MnO2 particles were manufactured by means of powder metallurgy (PM) and mechanical alloying (MA) methods. It was found that the applied powder consolidation methods, including KOBO extrusion, did not induce any chemical reaction between thermodynamically unstable components. However, it was shown that addition of magnesium to the Al-matrix initiated a reaction in the vicinity of MnO2 particles that resulted in the nucleation and growth of nano-sized aluminum–magnesium oxides. This led to a local refining of structural components. The most intense refining of structural components was observed for the MA Al–MnO2 composite. Strain rate sensitivity (SRS) of as-extruded materials was tested in compression in the range 293–773K. SRS was determined by making a rapid change in the basic true strain rate from ε̇=1.2·10-3 to ε̇=1.2·10-2. It is found that SRS did not practically depend on strain. The highest value of SRS was observed for the PM Al–MnO2–Mg composite. SRS of PM materials evidently increases with deformation temperature; however, it becomes smaller above a temperature of ∼600K. For the MA Al–MnO2 composite, tested at high temperatures, primary mechanical alloying resulted in relatively low increase of SRS with temperature that also becomes smaller above ∼600K. Suppression of the increase in SRS at high temperatures can be attributed to the specific features of grain boundaries created by the adhesive bonding between powder particles. This could hinder grain boundary sliding mechanisms and micro-cracks development at the compound interfaces.

Effect of Surface Modification on Strain Rate Sensitivity of Polypropylene/Muscovite Layered Silicate Composites

Surface modification is one of the treatment methods that can be implemented to improve the strain rate sensitivity of composite materials. In this study, both untreated and treated polypropylene/muscovite layered silicate composites were tested under static and dynamic loading up to 1100 s-1 using the universal testing machine and the split Hopkinson pressure bar apparatus, respectively. Muscovite particles were treated with lithium nitrate and cetyltrimethylammonium bromide as a surfactant through ion exchange treatment. Results show that the treated polypropylene/muscovite specimens with fine state of dispersion level shows better rate of sensitivity as compared to untreated polypropylene/muscovite specimens under a wide range of strain rate investigated. Apart from that, the rate of sensitivity of both tested polypropylene/muscovite layered silicate composites also show great dependency on the strain rate sensitivity was steadily increased with increasing strain rate. Unfortunately, the thermal activation values show contrary trend. Key words: Ion exchange treatment; Strain rate sensitivity; Muscovite particles; Split Hopkinson pressure bar apparatus; Strain rates

Hot deformation behaviors of 35%SiCp/2024Al metal matrix composites

The hot deformation behaviors of 35%SiCp/2024 aluminum alloy composites were studied by hot compression tests using Gleeble–1500D thermo-mechanical simulator at temperatures ranging from 350 to 500 °C under strain rates of 0.01–10 s−1. The true stress–true strain curves were obtained in the tests. Constitutive equation and processing map were established. The results show that the flow stress decreases with the increase of deformation temperature at a constant strain rate, and increases with the increase of strain rate at constant temperature, indicating that composite is a positive strain rate sensitive material. The flow stress behavior of composite during hot compression deformation can be represented by a Zener–Hollomon parameter in the hyperbolic sine form. Its activation energy for hot deformation Q is 225.4 kJ/mol. To demonstrate the potential workability, the stable zones and the instability zones in the processing map were identified and verified through micrographs. Considering processing map and microstructure, the hot deformation should be carried out at the temperature of 500 °C and the strain rate of 0.1–1 s−1.

Stress analysis of a complete maxillary denture under various drop impact conditions: a 3D finite element study

Complete maxillary dentures are one of the most economic and easy ways of treatment for edentulous patients and are still widely used. However, their survival rate is slightly above three years. It is presumed that the failure reasons are not only due to normal fatigue but also emerge from damage based on unavoidable improper usage. Failure types other than long-term fatigue, such as over-deforming, also influence the effective life span of dentures. A hypothesis is presumed, stating that the premature/unexpected failures may be initiated by impact on dentures, which can be related to dropping them on the ground or other effects such as biting crispy food. Thus, the behavior of a complete maxillary denture under impact loading due to drop on a rigid surface was investigated using the finite element method utilizing explicit time integration and a rate-sensitive elastoplastic material model of polymethylmethacrylate (PMMA). Local permanent deformations have been observed along with an emphasis on frenulum region of the denture, regardless of the point of impact. Contact stresses at the tooth–denture base were also investigated. The spread of energy within the structure via wave propagation is seen to play a critical role in this fact. Stress-wave propagation is also seen to be an important factor that decreases the denture's fatigue life.

Effect of strain rate on the tension–compression asymmetric responses of Ti–6.6Al–3.3Mo–1.8Zr–0.29Si

An experimental investigation is performed to explore the tension–compression asymmetry of Ti–6.6Al–3.3Mo–1.8Zr–0.29Si alloy over a wide range of strain rates. A split Hopkinson bar technique is used to obtain the dynamic stress–strain responses under uniaxial tension and compression loading conditions. Experimental results indicate that the alloy is a rate sensitive material. Both tension yield strength and compression yield strength increase with increasing strain rate. The mechanical responses of the alloy have the tension–compression asymmetry. The values of yield strength and subsequent flow stress in compression are much higher than that in tension. The yield strength is more sensitive to change with strain rate in tension than compression. The difference of the yield strength between tension and compression increases with the increase of strain rate. The tensile specimen is broken in a manner of ductile fracture presenting characteristic dimples, while the compressive specimen fails in a manner of localized shearing failure.

Rate-dependent hardening model for polymer-bonded explosives with an HTPB polymer matrix considering a wide range of strain rates

This article is concerned with the effect of the strain rate on the strain hardening behavior of polymer-bonded explosives at a wide range of strain rates ranging from 0.0001 s–1 to 3870 s−1. Inert polymer-bonded explosive simulants are prepared as specialized particulate composites to acquire analogous mechanical characteristics to polymer-bonded explosives for safety reasons. Uniaxial compressive tests were conducted from quasi-static states to intermediate strain rates ranging from 0.0001 s−1 to 100 s−1 with cylindrical specimens using a dynamic material testing machine (INSTRON 8801) and a high-speed material testing machine. An experimental method was developed for uniaxial compressive tests at intermediate strain rates ranging from 10 s−1 to 100 s−1. Split Hopkinson pressure bar tests were performed at high strain rates ranging from 1250 s−1 to 3870 s−1. Deformation behavior was investigated using captured images from a high-speed camera. The strain hardening behavior of polymer-bonded explosive simulants was formulated as a function of the strain rate with the proposed rate-dependent hardening model based on the DSGZ model. The model is capable of representing the complicated strain rate effects on the strain hardening behavior for rate-sensitive materials with a second-order exponentially-increasing function of the strain rate sensitivity. The rate-dependent hardening model of polymer-bonded explosives can be readily applied to prediction of deformation modes of polymer-bonded explosives in a warhead that undergoes severe dynamic loads.

AN IMPROVED ANALYTICAL METHOD FOR RESTRAINED RC STRUCTURES SUBJECTED TO STATIC AND DYNAMIC LOADS

Once a RC structure is laterally restrained, both the static and dynamic load resistances will be enhanced due to the membrane action. Despite this known advantage, the apparent lack of systemic and efficient methods of analysis poses a drawback in the design and assessment of blast-resistant RC structures. First, a simplified membrane action theory was presented by modifying the maximum membrane force design method (MMFM) for predicting the total static resistance-deflection curves of restrained beam-slab RC structures. Second, a series of constrained beams were tested to validate the new theory, for which better agreement was observed between the test data, the results predicted by the proposed theory and those by MMFM. The results show that the static load carrying capacity and membrane force increase with increasing restraint stiffness, and the smaller the reinforcement ratio is, the larger the load carrying capacity increases. Third, based on the improved compressive static membrane action theory, a new analytical method was developed to investigate the dynamic responses of restrained RC structures subjected to blast loads, using an equivalent single degree of freedom system that combines the three-parameter elasto-viscoplastic rate-sensitive material model with the proposed static theory. Good agreement is observed between the test data and the analytical results. Finally, it is demonstrated that the dynamic resistance capacity increases with increasing load rate and restraint stiffness and with decreasing tensile reinforcement ratio, but the larger the dynamic resistance is, the larger the plastic deformation of the structure.

Hot Deformation Behaviors of SiCp/2024 Aluminum Composites

The hot deformation behaviors of 30%SiCp/2024 aluminum alloy composites was studied by hot compression tests using Gleeble-1500 thermomechanical simulator at temperatures ranging from 350-500 °C under strain rates of 0.01-10 s-1. The true stress-true strain curves were obtained in the tests. Constitutive equation and processing map were established. The results show that the flow stress decreases with the increase of deformation temperature at a constant strain rate, and increases with the increase of strain rate at constant temperature, indicating that composite is a positive strain rate sensitive material. The flow stress behavior of composite during hot compression deformation can be represented by a Zener-Hollomon parameter in the hyperbolic sine form. Its activation energy for hot deformation Q is 153.251 kJ/mol. The optimum hot working conditions for this material are suggested.

Microstructure Evolution of Hypereutectic Al-Si Alloy in Semi-Solid Compression Deformation

The semi-solid microstructure evolution of hypereutectic Al-20Si-3Fe-1Mn-4Cu-1Mg alloy was studied by unidirectional compression deformation experiment, at a range of deformation temperature of 833K~873K and a range of strain rate of 0.1s-1~0.001s-1. The results showed that the microstructure of the reheating alloy was more spherical and fine than the microstructure of as-cast, the alloy was a positive strain rate sensitive material that the flow stress was decreased with increasing in deformation temperature and it was increased with increasing in strain rate. The mechanical properties of the alloy were hardly improved when the deformation temperature was too high to fracture the thick phase of the alloy.The lower strain rate was not only reducing the productivity but also reducing the plastic deformation. The microstructure of the alloy which the thick phase was broken fundamentally and the grain became further refinement can be obtained at 833K~853K, and at 0.1s-1~0.01s-1.It can be done that reducing the plastic deformation resistance and strengthening the fabrication procedure of the alloy.

Cyclic strain rate effects in fatigued face-centred and body-centred cubic metals

The present work deals mainly with the effect and the use of strain rate and temperature changes during cyclic deformation as a means to obtain valuable information on the thermally activated dislocation glide processes, based on the assessment of reversible changes of the thermal effective stress and of transient changes of the athermal stress. The importance of closed-loop testing in true plastic strain control with constant cyclic plastic strain rate throughout the cycle is explained and emphasized, especially with respect to the case of strain rate sensitive materials. Stress responses of face-centred cubic and body-centred cubic (bcc) metals to cyclic strain rate changes are presented to illustrate that the deformation modes of these two classes of materials differ characteristically at temperatures below that the so-called knee temperature of bcc metals. When such tests are performed in cyclic saturation, the temperature and strain rate dependence of bcc metals can be measured very accurately on one and the same specimen, permitting a thorough analysis of thermal activation.

Enhanced Formability in Sheet Metals Produced by Cladding a High Strain-Rate Sensitive Layer

The necking behavior of cladding sheets with a rate-sensitive layer cladding on a rate-insensitive core material has been studied. A nonlinear long-wavelength analysis, similar to the one proposed by Hutchinson and Neale (1977, “Influence of Strain-Rate Sensitivity on Necking Under Uniaxial Tension,” Acta Metal., 25, pp. 839–846) for monolithic rate-sensitive materials, is developed to identify the onset of necking in a rate-sensitive clad sheet. This relatively simple analysis is validated by comparing its numerical results with those based on more complicated finite element analysis. It is demonstrated that for monolithic rate-sensitive materials the proposed nonlinear analysis reduces to the one developed by Hutchinson and Neale (1977). For cladding sheets, it is found that the necking strain increases monotonically by increasing the strain-rate sensitivity of the clad layer if the volume fraction of cladding is fixed. It is also revealed that, for fixed strain-rate sensitivity of the clad layer, necking localization is retarded by increasing the volume fraction of the cladding layer.

Applying Research on Creep Constitutive Model of No.35 Steel Based on BC-BPNN

The inelastic response constitutive description of metal material under different stress and wide temperature range is very important in many practical engineering. It can accurately reflect the level of material rate sensitivity and set up a simple and practical strengthening evolution rate. Take No.35 steel as an example; because of the action of load, temperature, time and other factors in its forming process, the creep relation is very important and complex. In view of this situation, the BC-BPNN (Based on Back propagation Neural Network), owing high precision nonlinear fitting ability has and good generalization ability, is applied to the research on creep constitutive relationship of 35 steel. At first, the creep relationship is numerically fitted using testing data of 35 steel; then, the fitting results is compared with the creep testing data. The results show that the applying of BC-BPNN to research on metal creep relationship has a strong practical value.