Showing papers on "Strain rate published in 2023"

A rate-dependent constitutive model for saturated frozen soil considering local breakage mechanism

Abstract: A rate-dependent constitutive model for saturated frozen soil is vital in frozen soil mechanics, especially when simultaneously describing the nonlinearity, dilatancy and strain-softening characteristics. The distribution of the non-uniform strain rate of saturated frozen soil at the meso-scale due to the local ice-cementation breakage is described by a newly binary-medium-based homogenization equation. Based on the field-equation-based approach of the meso-mechanics theory, the interaction expression of the strain rate at macro- and meso-scale is derived, which can give the strain rate concentration tensor at different crushed degrees. With the thermodynamics and empirical assumption, a breakage ratio in the rate-dependent form is determined. This overcomes the limitations of the existing binary-medium-based models that are difficult to simulate rate-dependent mechanical response. Based on these assumptions, a newly binary-medium-based rate-dependent model is proposed considering both the ice bond breakage and material composition characteristics of saturated frozen soil. The proposed constitutive model has been validated by the test results on frozen soils with different temperatures and strain rates.

Strain Engineering to Boost Piezocatalytic Activity of BaTiO3

Abstract: Piezoelectric materials are sensitive to lattice strain, which is always related with their macroscopic properties. Therefore, it is of scientific significance to improve piezocatalytic performance by strain engineering and clarify the underlying mechanism. Herein, BaTiO3 (BTO) powder is fabricated by a solid‐state reaction and ball‐milling is employed to induce lattice strain in BTO. By prolonging ball‐milling time, the lattice strain increases, leading to an enhancement of tetragonality and piezocatalytic performance of BTO. The strain‐engineered BTO exhibited an excellent piezocatalytic activity, with a degradation rate constant k of ∼0.03 min−1 and a H2 evolution rate of 0.899 mmol g−1 h−1, which are 3 and 3.52 times those of the strain‐free one, respectively. The enhanced piezocatalytic performance can be ascribed to the improved piezoelectricity, piezoelectric polarization and adsorption activities for O2, OH and H of the strain‐engineered BTO. This work not only provides a simple and general method to improve piezocatalytic performance by strain engineering, but also unveils the enhancement mechanism.

Prediction of True Stress at Hot Deformation of High Manganese Steel by Artificial Neural Network Modeling

Abstract: The development of new lightweight materials is required for the automotive industry to reduce the impact of carbon dioxide emissions on the environment. The lightweight, high-manganese steels are the prospective alloys for this purpose. Hot deformation is one of the stages of the production of steel. Hot deformation behavior is mainly determined by chemical composition and thermomechanical parameters. In the paper, an artificial neural network (ANN) model with high accuracy was constructed to describe the high Mn steel deformation behavior in dependence on the concentration of the alloying elements (C, Mn, Si, and Al), the deformation temperature, the strain rate, and the strain. The approval compression tests of the Fe–28Mn–8Al–1C were made at temperatures of 900–1150 °C and strain rates of 0.1–10 s−1 with an application of the Gleeble 3800 thermomechanical simulator. The ANN-based model showed high accuracy, and the low average relative error of calculation for both training (5.4%) and verification (7.5%) datasets supports the high accuracy of the built model. The hot deformation effective activation energy values for predicted (401 ± 5 kJ/mol) and experimental data (385 ± 22 kJ/mol) are in satisfactory accordance, which allows applying the model for the hot deformation analysis of the high-Mn steels with different concentrations of the main alloying elements.

Effects of nanoparticles on the tensile behavior of ultra-high-performance fiber-reinforced concrete at high strain rates

Abstract: This study investigated the effects of nanoparticles (NPs) on the tensile resistance of ultra-high-performance fiber-reinforced concrete (UHPFRC), containing 1.5 vol% smooth steel fibers, at both static (0.000167 s−1) and high strain rates (61.86–162.00 s−1). Three types of NPs, namely nano-CaCO3 (3 wt%), nano-SiO2 (1 wt%), and nano-carbon nanotube (CNT) (1 wt%) were considered. All the UHPFRCs containing NPs generated higher rate-sensitive tensile resistance than the UHPFRCs without NPs. For instance, the dynamic increase factor (DIF) for the post-cracking strengths of the UHPFRCs containing nano-CaCO3, nano-SiO2, or nano-CNT was 2.94, 2.79, and 2.69, respectively, while that of the UHPFRCs without NPs was 2.65. The DIFs for tensile parameters of UHPFRCs were dependent upon the types of NPs: nano-CaCO3 produced the highest DIFs for first- and post-cracking strengths, and the number of microcracks, whereas nano-CNT generated the highest DIFs for strain capacities and peak toughness. Besides, the sources of the rate sensitivity of tensile resistances of UHPFRCs containing NPs are closely related to the interfacial bond strengths and compressive strength of matrices.

On the nanomechanical properties and local strain rate sensitivity of selected Aluminium-based composites reinforced with metallic and ceramic particles

Abstract: Nanoindentation derived mechanical properties and strain rate sensitivity assessment of a set of stir cast metallic reinforced Aluminium-based composites, with an antecedence of anomalous stress oscillations and strain rate insensitivity during hot compression, was investigated in this study. For the evaluation, Al6063 based composites reinforced with 6 wt% CuZnAl, steel, nickel, and SiC particles were subjected to nanoindentation, and their strain rate sensitivity was assessed using strain rate jump test. The results show that the AMCs reinforced with the metallic particles, presented better mechanical properties than those reinforced with SiC. The CuZnAl reinforced AMC had the best hardness (1.25 ± 0.25 GPa) and elastic modulus (∼83GPa), which is opined to be on account of thermoelastic contributions to the basic strengthening mechanisms. The large scatter observed in the mechanical response of the AMCs is largely due to the inhomogeneous particle distribution. The higher indentation resistance with an increase in strain rate, coupled with the absence of displacement bursts, indicated that the composites largely exhibit positive strain rate sensitivity.

Dependence of mechanical and thermal deformation behaviors on crystal size and direction of Cu3Sn intermetallic: A molecular dynamics study

Abstract: The implementation of environment friendly technologies in microelectronic packaging industry has widened the essentialities of lead-free solder alloys. The Cu3Sn intermetallic compound is blameworthy for the adverse influences of the mechanical and thermal properties of the lead-free solder alloys. This study explored the effects of crystal size and direction on mechanical and thermal deformation behavior of Cu3Sn using the modified embedded atom method (MEAM) parameter in molecular dynamics simulation. The stress–strain characteristics were tracked down at 25 °C temperature and 1010 s−1 strain rate, and the thermal deformation manner was observed from −100 °C to 200 °C temperature, which came up with the thermal expansion coefficient (CTE). Investigations show that the tensile properties differ 43–63 % owing to anisotropy, whereas the CTE varies only less than 1 %. Meanwhile, the tensile properties and CTE plummet topmost 25 % and 58 % consecutively throughout the crystal size. However, the thermal expansion proclivity in different crystal size was quite indistinguishable at higher temperature.

Fiber Orientation and Strain Rate-Dependent Tensile and Compressive Behavior of Injection Molded Polyamide-6 Reinforced with 20% Short Carbon Fiber

Abstract: As the interest in short-fiber reinforced polymer (SFRP) composites manufactured by injection molding increases, predicting the failure of SFRP structures becomes important. This study aims to systemize the prediction of failure of SFRP through mechanical property evaluation considering the anisotropy and strain rate dependency. To characterize the mechanical properties of polyamide-6 reinforced with carbon fiber of a weight fraction of 20% (PA6-20CF), tensile and compressive experiments were conducted with different load-applying directions and strain rates. Additionally, the results were discussed in detail by SEM image analysis of the fracture faces of the specimen. FE simulations based on the experimental condition were constructed, and the numerical model coefficients were derived through comparison with experimental results. The coefficients obtained were verified by bending tests of the specimens manufactured from composite cross members fabricated by injection molding. Predicting under static and high strain rate conditions, small errors of about 9.6% and 9.3% were shown, respectively. As a result, it proves that explained procedures allow for better failure prediction and for contribution to the systematization of structural design.

Influence of fiber areal density on mechanical behavior of basalt fiber/epoxy composites under varying loading rates: An experimental and statistical approach

Abstract: The stress–strain characteristics and failure behavior of composites are strain rate dependent and affected by the fiber areal density. To elucidate the combined influence of areal density and strain rate on the strength of basalt fiber-reinforced polymer composites (BFRP), an experimental study was conducted on BFRP laminates of two different fiber areal densities, that is, 380 GSM and 200 GSM, having distinct stacking sequence under three different loading rates. Failure modes, failure strength, and Weibull parameters were used to characterize the experimental outcomes. The experiment was carried out to investigate the mechanical responses and associated failure modes at strain rates ranging from quasi-static 0.1 mm/min to a high strain rate of 10 mm/min. It has been demonstrated that there is a substantial correlation between the fiber areal density, loading rate, and stacking order of BFRP laminates and the increase in maximum flexural strength and interlaminar shear strength. For an increase in the fiber areal density from 200 GSM to 380 GSM flexural strength is increased by 18%–30%, while ILSS strength is increased by 30%–52%. Based on the finding, the asymmetric type-2 laminate exhibits better properties than the symmetric and asymmetric type-1 laminates due to the presence of more (0°/90°) laminae at the tensile side of the laminate. Inferring the mechanical characteristics of composite materials and their relationship to strain rate from experimental data required a statistical technique. The statistical analysis and experimental findings demonstrate that the shape parameter and linear coefficient are not reliant on the strain rate.

Promotion of thermomechanical processing of 2-GPa low-alloyed ultrahigh-strength steel and physically based modelling of the deformation behaviour

Abstract: A low-alloyed ultrahigh-strength steel comprising CrNiMoWMnV was designed based on thermodynamic calculations and by controlling the microalloying elements to promote various strengthening mechanisms upon processing. The hot deformation behaviour and mechanism were correlated with the processing parameters, that is, strain rate and temperature. The fine features of the deformed microstructures were analysed using electron backscatter diffraction (EBSD) and MATLAB software, combined with the MTEX texture and crystallographic analysis toolbox. The flow stress behaviour at high temperatures was modelled using the dislocation density-based Bergström's model, which could be applied up to the peak strain. However, the diffusional transformation (i.e. recrystallisation)-based Kolmogorov–Johnson–Mehl–Avrami model has been applied to fit the flow stress over a wide deformation strain. The effective grain size (EGS) of martensite and prior austenite grain size (PAGS) were correlated with the deformation temperature and strain rate. Because the PAGS was significantly refined from 16 μm in the initial microstructure to 6 μm after processing at 850 °C/0.01 s−1, the corresponding martensite EGSs were 1.38 and 1.01 μm, respectively. Therefore, these fine-controlled characteristics of the processed microstructures at high temperatures help to enhance the mechanical properties, such as the strength and toughness, of the designed ultrahigh-strength steel.

Understanding the transient large amplitude oscillatory shear behavior of yield stress fluids

Abstract: A full understanding of the sequence of processes exhibited by yield stress fluids under large amplitude oscillatory shearing is developed using multiple experimental and analytical approaches. A novel component rate Lissajous curve, where the rates at which strain is acquired unrecoverably and recoverably are plotted against each other, is introduced and its utility is demonstrated by application to the analytical responses of four simple viscoelastic models. Using the component rate space, yielding and unyielding are identified by changes in the way strain is acquired, from recoverably to unrecoverably and back again. The behaviors are investigated by comparing the experimental results with predictions from the elastic Bingham model that is constructed using the Oldroyd–Prager formalism and the recently proposed continuous model by Kamani, Donley, and Rogers in which yielding is enhanced by rapid acquisition of elastic strain. The physical interpretation gained from the transient large amplitude oscillatory shear (LAOS) data is compared to the results from the analytical sequence of physical processes framework and a novel time-resolved Pipkin space. The component rate figures, therefore, provide an independent test of the interpretations of the sequence of physical processes analysis that can also be applied to other LAOS analysis frameworks. Each of these methods, the component rates, the sequence of physical processes analysis, and the time-resolved Pipkin diagrams, unambigiously identifies the same material physics, showing that yield stress fluids go through a sequence of physical processes that includes elastic deformation, gradual yielding, plastic flow, and gradual unyielding.