Dynamic Behavior Of Materials Research Articles

The effect of plastic fines on the shear modulus and damping ratio of silty sands

The dynamic behavior of soil material is of importance in construction and geotechnical engineering. This study focuses on the dynamic properties of silty sands, particularly on the effect of plastic fines content (FC) on the shear modulus and damping ratio. Natural sand (Taiyuan sand) and fines (Taiyuan loess) were collected from an engineering site in China. Fujian standard sand, kaolin, and stone powder were also used for comparison. Fines plasticity, FC, effective confining pressure, and relative density were considered. A series of tests were conducted using a Stokoe-type resonant column apparatus manufactured by GDS Instruments, UK. The small strain shear modulus (Gmax) of the samples were investigated under various test conditions. Hardin’s function was used to fit the experimental data. The results indicate that the shear modulus changes non-linearly with increasing FC. The shear modulus of various mixtures initially decreases and then increases. The threshold FC (FCth) of Taiyuan and Fujian sand mixtures is 30% and 20%, respectively, which indicates that the FCth is related to the host sand. The addition of plastic fines will decrease the shear modulus. The effect of non-plastic fines on the shear modulus of sand–fines mixtures is dependent on FC. The damping ratio of various mixtures initially increases and then decreases with increasing FC. The addition of fines will increase the damping ratio. Moreover, the damping ratio of plastic fines mixtures is higher than that of non-plastic fines mixtures. The values of the fitting constant, namely, A, n, and d, are related to fines plasticity. The findings of this study can provide a reference for engineering designers.

Dynamic behaviour of bio-based and recycled materials for indoor environmental comfort

Abstract UK construction industry contributes 120 Mt of waste every year. Bio-based building materials may be a solution for this problem, as they combine re-use and recycling abilities together with hygroscopic characteristics, leading to buildings energy savings. For the first time, the dynamic response to hygrothermal changes of bio-based materials is examined in terms of Moisture Buffering Value (MBV), dry/wet thermal conductivity, microstructure, density and latent heat through daily cycles. It is shown that MBV is a useful tool for characterisation but needs to be combined with the shape of the change in mass of the final hygrothermal cycle. Mastering this is required to obtain significant improved indoor environment quality in buildings. Ten samples of bio-based insulation materials and one thermoplastic recycled polymer were analysed (wool, hemp, saw mill residue, wood, straw, cork and polyethylene terephthalate). Saw and wool are the most promising, as materials exhibit dynamic response to hygrothermal changes. Only half the amount of samples revealed equivalent efficient moisture transfer to be able to desorb the adsorbed quantity of water. Latent heat of vaporisation and condensation tests led to the conclusion that samples of wool and saw mill residue can qualify as bio-based materials for ‘green’ panels.

On the Development of Material Constitutive Model for 45CrNiMoVA Ultra-High-Strength Steel

For the implementation of simulations for large plastic deformation processes such as cutting and impact, the development of the constitutive models for describing accurately the dynamic plasticity and damage behaviors of materials plays a crucial role in the improvement of simulation accuracy. This paper focuses on the dynamic behaviors of 45CrNiMoVA ultra-high-strength torsion bar steel. According to investigation of the Split-Hopkinson pressure bar (SHPB) and Split-Hopkinson tensile bar (SHTB) tests at different strain rate and different temperatures, 45CrNiMoVA ultra-high-strength steel is characterized by strain hardening, strain-rate hardening and thermal softening effects. Based on the analysis on the mechanism of the experimental results and the limitation of classic Johnson-Cook (J-C) constitutive model, a modified J-C model by considering the phase transition at high temperature is established. The multi-objective optimization fitting method was used for fitting model parameters. Compared with the classic J-C constitutive model, the fitting accuracy of the modified J-C model significantly improved. In addition, finite element simulations for SHPB and SHTB based on the modified J-C model are conducted. The SHPB stress-strain curves and the fracture morphology of SHTB samples from simulations are in good agreement with those from tests.

Structural state awareness through integration of global dynamic and local material behavior

Structural health monitoring and nondestructive inspection techniques typically assess the lifecycle and reliability of high-value aerospace, mechanical, and civil systems. Maintenance and inspection intervals are typically time-based and dependent on the structural health monitoring/nondestructive inspection technique to detect macroscale damage resulting from fatigue or environmental damage. The current work proposes an integrated materials-structures-dynamics approach for providing state awareness of structural health. The proposed approach shifts the conventional structural health monitoring/nondestructive inspection focus of searching for cracks to a health state awareness based on tracking changes in the energetics of the materials-structures-dynamics states. Energy variations are tracked in a cantilevered structure exposed to nonlinear harmonic oscillation, where the strain energy of the beam was derived and used to determine a health state index. Nanoindentation was used to probe the near-surface mechanical properties of the beam to characterize local material variations as a function of fatigue cycles. A nonlinear ultrasonic approach was considered in order to connect the local material behavior changes to the variations in the dynamic performance of the beam. The intent of the investigation was to connect the traditionally detached materials, structural, and dynamics approaches to structural health monitoring/nondestructive inspection, while providing a framework for enabling damage precursor detection.

Micromechanical modeling of the effects of adiabatic heating on the high strain rate deformation of polymer matrix composites

Fiber reinforced polymer matrix composites are increasingly being used to fabricate energy-absorbing aerospace structural components susceptible to impact loading, such as jet engine containment structures subjected to blade-out events. The development and certification of such structures necessitates a detailed understanding of the dynamic behavior of the constituent materials, particularly the strain rate, temperature, and pressure dependent polymer matrix, and their complex interaction. As the rate of deformation increases, the thermodynamic condition transitions from isothermal to adiabatic. The conversion of plastic work to heat causes local adiabatic heating in the polymer matrix, but the rapid nature of impact events does not allow sufficient time for heat to dissipate; ballistic impact events can therefore be regarded as fully adiabatic. Local adiabatic heating can significantly affect the high rate deformation response if thermal softening effects outweigh strain and strain rate hardening effects and therefore, must be explicitly modeled at the appropriate length scale. In this paper, an existing isothermal viscoplastic strain rate and pressure-dependent polymer constitutive formulation is extended to nonisothermal conditions by modifying the inelastic strain rate tensor components to explicitly depend on temperature based on the Arrhenius equation for nonisothermal processes. A methodology based on shifting neat resin dynamic mechanical analysis data is utilized to determine the polymer elastic properties over a range of strain rates and temperatures. Temperature rises due to the conversion of plastic work to heat are computed, assuming adiabatic conditions. It is demonstrated that the modified polymer constitutive model is capable of capturing strain rate and temperature dependent yield as well as thermal softening associated with the conversion of plastic work to heat at high rates of strain. The nonisothermal polymer constitutive model is then embedded within the Generalized Method of Cells micromechanics framework to investigate the manifestation of matrix thermal softening, due to the conversion of plastic work to heat, on the high strain rate response of a T700/Epon 862 unidirectional composite. Adiabatic model predictions for high strain rate composite longitudinal tensile, transverse tensile, and in-plane shear loading are presented. Results show a substantial deviation from isothermal conditions; significant thermal softening is observed for matrix dominated deformation modes (transverse tension and in-plane shear), highlighting the importance of accounting for local adiabatic heating in the polymer matrix in the high strain rate analysis of polymer matrix composite structures.

Semi-analytical solution of nonlinear dynamic behaviour for fully saturated porous media

In this study, a semi-analytical solution of the constitutive nonlinear differential equations of fully saturated porous media is presented. Also, the nonlinear dynamic behaviour of material and geometry is considered. The u–w–p formulation of fully coupled dynamic field is used to simulate the pore fluid and soil skeleton responses with the change of pore pressure. The governing equations with the corresponding boundary conditions were solved analytically using regular perturbation technique. The parametric study was utilized to investigate the effect of nonlinearity of material and geometry on the pore pressure, total stress, solid and fluid displacements. Results are illustrated graphically for the presented semi-analytical model. It was found that the values of frequencies of applied load and level of permeability had a great effect on the total stress distribution, pore pressure, solid displacement and fluid displacement.

DNA-Inspired Strand-Exchange for Switchable PMMA-Based Supramolecular Morphologies.

Inspired by nanotechnologies based on DNA strand displacement, herein we demonstrate that synthetic helical strand exchange can be achieved through tuning of poly(methyl methacrylate) (PMMA) triple-helix stereocomplexes. To evaluate the utility and robustness of helical strand exchange, stereoregular PMMA/polyethylene glycol (PEG) block copolymers capable of undergoing crystallization driven self-assembly via stereocomplex formation were prepared. Micelles with spherical or wormlike morphologies were formed by varying the molecular weight composition of the assembling components. Significantly, PMMA strand exchange was demonstrated and utilized to reversibly switch the micellesbetween different morphologies. This concept of strand exchange with PMMA-based triple-helix stereocomplexes offers new opportunities to program dynamic behaviors of polymeric materials, leading to scalable synthesis of "smart" nanosystems.

Model analysis of gas residence time in an ironmaking blast furnace

Gas residence time distribution (RTD) is an effective and convenient indicator for evaluating the performance of complex multiphase chemical reactors including ironmaking blast furnaces (BFs). However, in the open literature, there lacks the systematic RTD research for BFs. In this study, an integrated mathematical model is developed for describing the gas RTD of a BF. The model combines a steady multi-fluid model for describing the in-furnace state of flow and thermo-chemical behavior of gas-solid-liquid phases and a transient model for describing the dynamic behavior of tracer materials. The results show that the gas flow field inside the BF is quite complex, resulting from many factors such as furnace geometry and coupled thermo-chemical behaviors of other phases. The tail of gas RTD curve resulted from the lagging phenomenon of tracer flow inside BFs, is captured. The gas RTD is discussed by using mean residence time, dispersion of molecules distribution, cumulative distribution function and residence time intensity function. Under the given BF conditions, mean residence time and space time of gas fluids are predicted as 13.5 s and 16.3 s, respectively. The existence of stagnant flow in the BF can be both derived and directly identified. Moreover, it is indicated the gas flow patterns in the BF are composed of piston-type flow, stagnant flow and limited mixing flow. This study provides a cost-effective tool for better understanding BF gas flow dynamics and optimizing BF operations.

Numerical Investigation on the Necessity of a Constant Strain Rate Condition According to Material’s Dynamic Response Behavior in the SHPB Test

The split Hopkinson pressure bar (SHPB) apparatus is frequently used to investigate the dynamic compression properties of various materials at strain rates from 102 to 104 s−1. Keeping the strain rate constant during loading is an important condition for obtaining accurate experimental results. However, we do not always need to take additional measures to control the constant strain rate loading conditions for materials with different dynamic response behaviors. To investigate the necessity of a constant strain rate condition in the SHPB test according to the different dynamic mechanical response behaviors of materials, a comprehensive numerical analysis scheme combined with the Cowper-Symonds plastic kinematic model was designed to perform the simulation tests. There are two factors primarily resulting in the errors in the calculated stress-strain response for the representative material model. One of them is the dynamic scale factor, which represents the strain rate sensitivity and controls the variation amplitude of flow stress with the change in strain rate. The other factor is the work-hardening rate, which affects the results by expanding the decrease in strain rate. This paper quantitatively describes the effects of strain rate sensitivity and the strain-hardening modulus on the accuracy of the reconstructed stress-strain behavior of a sample under a constant incident pulse. The conclusion presents several reference guides for the necessity of a constant strain rate condition for different dynamic response behaviors of materials based on the representative constitutive model.

Investigation and Analysis of Static and Dynamic Behaviour of a New Natural Composite Material of a Wind Turbine Blade Using the Finite Element Method

A wind turbine blades modeling study is so critical because of their design, as we all know, domestic wind turbine blades are usually designed using aluminum alloy and glass fiber. In this paper we are going to study the resistance of a new natural composite material based on hemp fiber and an Epoxy matrix, for that we had conceived a three-dimensional model of the blade using aerodynamic profile parameters and geometric parameters on SolidWorks modeling software. Then, the model was imported into the ANSYS Workbench to perform a static, modal and harmonic analysis using FEM. The results were compared between the three materials; this comparative study shows that there is a good agreement between the three materials under stress. And for natural frequencies, the hemp fiber composite blade has higher natural frequencies than the aluminum alloy blade and the glass composite blade with a large standard deviation. For harmonic response, results show that the blade operates stably under resonance conditions, resonance does not occur and the composite hemp fiber blade functions safely

A fractional approach to the time-temperature dependence of dynamic viscoelastic behavior

Fractional derivative and WLF equation are effective in describing the dynamic behavior and time-temperature effect of viscoelastic damping materials, respectively. These approaches have essentially evolved from the viscoelastic constitutive behavior. Based on such intrinsic relation, a fractional time-temperature superposition principle model (FTTSPM) that integrates the fractional constitutive relation and WLF equation was proposed. The parameters of this model were determined by performing tensile and DMA tests, and the master curves at 5 °C constructed by FTTSPM and WLF equation were compared. The theoretical prediction over the extended frequency span as the master curves was made by using the fractional standard linear solid model (FSLSM) to validate FTTSPM. The numerical results show that FTTSPM conforms to the time-temperature superposition principle. The parameters α and B′ in this model denote the impact of the material and environment on the shifted factor, respectively. For the storage and loss modulus, the extended frequency obtained by FTTSPM is broader than that obtained by the WLF equation. Moreover, the evaluation of the storage and loss modulus by FTTSPM is much closer to the theoretical prediction compared with that by the WLF equation. Therefore, FTTSPM is a concise and experiment-based approach with a higher precision and greater frequency-extended capacity compared with the WLF equation. However, FTTSPM inevitably faces a vertical shift when non-thermo-rheologically simple materials are considered. The physical mechanism and practical application of FTTSPM will be examined in further research.

Dynamic Failure Characteristics and Behavior of Rock Materials

Dynamic Failure Characteristics and Behavior of Rock Materials

Time-Resolved Mechanical Spectroscopy of Soft Materials via Optimally Windowed Chirps

The ability to measure the bulk dynamic behavior of soft materials with combined time- and frequency-resolution is instrumental for improving our fundamental understanding of connections between the microstructural dynamics and the macroscopic mechanical response. Current state-of-the-art techniques are often limited by a compromise between resolution in the time and frequency domain, mainly due to the use of elementary input signals that have not been designed for fast time-evolving systems such as materials undergoing gelation, curing or self-healing. In this work, we develop an optimized and robust excitation signal for time-resolved mechanical spectroscopy through the introduction of joint frequency- and amplitude-modulated exponential chirps. Inspired by the biosonar signals of bats and dolphins, we optimize the signal profile to maximize the signal-to-noise ratio while minimizing spectral leakage with a carefully-designed modulation of the envelope of the chirp. A combined experimental and numerical investigation reveals that there exists an optimal range of window profiles that minimizes the error with respect to standard single frequency sweep methods. The minimum error is set by the noise floor of the instrument, suggesting that the accuracy of an optimally windowed chirp signal is directly comparable to that achievable with a standard frequency sweep, while the acquisition time can be reduced by up to two orders of magnitude, for comparable spectral content. Finally, we demonstrate the ability of this optimized signal to provide time- and frequency-resolved rheometric data by studying the fast gelation process of an acid-induced protein gel. The use of optimally windowed chirps enables a robust rheological characterization of a wide range of soft materials undergoing rapid mutation and has the potential to become an invaluable tool for researchers across different disciplines.

The model of dynamic mechanical behaviour of brittle solids based on kinetic theory of strength

The paper presents the kinetic theory-based model of dynamic mechanical behavior of brittle solids. The model adopts the ideas of the kinetic theory of strength which postulate the finite time of nucleation of discontinuities and relaxation of local stresses in the material. The model is a generalization of the formalism of classical “quasi-static” Nikolaevsky’s plasticity model (non-associated plastic flow rule with the plasticity criterion in the form of Mises-Schleicher) and the Drucker-Prager model of failure to describe the material behavior at strain rates corresponding to dynamic loading. Three new dynamic (time) parameters are used to describe the dynamic mechanical behavior of brittle material. The dynamic model developed in the paper can be implemented within the framework of various Lagrangian numerical methods using an explicit integration scheme (including finite and discrete element methods).

Nonlinear dynamic behavior of cemented granular materials under impact loading

Nonlinear sound propagation in stressed cemented granular materials is investigated using the split Hopkinson pressure bar (SHPB) system, via frequency spectra analysis. The sandstone is selected for performing the experimental investigation. The sound velocity is deduced from experimental measurement of amplitude ratio of incident to transmitted waves, showing a power (1/6) law scaling with confining pressure, confirming the applicability of Hertzian nonlinear elasticity on cemented granular materials. Analysis on the measured magnitude of second-harmonic gives the coefficient of nonlinearity whose order of magnitude is consistent with that deduced from acoustoelastic method with a relationship βAE ≈ (1.5 ∼ 4.5)βWM. The transmitted wave amplitude is also analyzed by applying repetitive impact load, demonstrating that relatively high intensity incident wave as well as lower confining pressure induces intensive weakening of the rocks.

Comprehensive study of projectile impact on lightweight adobe masonry

We conduct a comprehensive experimental and numerical study of the impact response of lightweight adobe masonry with a density of 1.2 g/cm3. Based on two independent test cases, a simulation model for lightweight adobe is validated and applied. First, we investigate the impact of a spherical projectile on finite and semi-infinite targets. Then, the penetration behavior of a generic hollow projectile is studied. In each case, the data from the ballistic experiments is compared to the results of corresponding numerical simulations. The employed numerical model utilizes a p-α-equation of state, recently derived from planar plate impact experiments on the same lightweight adobe material [Sauer et al., Journal of Dynamic Behavior of Materials 4 (2018) 231–243]. Strength and failure modeling are based on a validated numerical description of another adobe material that has a density of 1.8 g/cm3. The simulation model for lightweight adobe is capable of simultaneously reproducing all experimental results in a quantitatively appropriate way. This reveals that, although the phenomenology and quantitative properties differ significantly, lightweight adobe (1.2 g/cm3) and adobe (1.8 g/cm3) can be described by the same approach. Hence, this work suggests that the utilized model is applicable for analyses of impact loading of the entire class of adobe materials.

A unified experimental-theoretical approach to predict the critical stress characteristics of failure and yielding under quasi-static and dynamic loading

The results of experimental and theoretical studies on the dynamic response of brittle and ductile materials are presented. The work shows the possibility of predicting the critical stress of brittle materials or yield strength of ductile materials over a wide range of strain rates on the basis of a combination of a simple theoretical approach to dynamic strength and a set of experimental data obtained using a conventional technique. The studies were carried out using fine-grained concrete and ceramic brick as representatives of brittle materials, and copper and titanium as representatives of ductile materials. The traditional Kolsky method was used to determine the strength and ductility characteristics under dynamic loading conditions of the experimental samples. The sensitivity of the critical stress characteristics of failure and yielding of the studied materials to the strain rate is shown. The incubation time approach is used to interpret the effects of strain rate. The applicability of the incubation time criterion to prediction of the dynamic behaviour of both brittle and ductile materials is shown. The presented unified experimental-theoretical approach can be applied in engineering practice to model the dynamic response of structural materials.

Experimental and analytical investigation of the dynamic behavior of granular base course materials used for China's high-speed railways subjected to freeze-thaw cycles

With the rapid development of high-speed railways (HSRs) in seasonally frozen regions in China in recent years, there is an increasing need for better understanding of how the construction materials behave. In particular, the dynamic behavior of granular base course materials used for China's HSRs subjected to combined actions of cyclic loading and freeze-thaw (F-T) cycles has attracted much attention. In this study, a series of cyclic triaxial tests were performed to investigate the characteristics of granular base course materials. A number of factors including effect of F-T cycles were considered in these tests. As such, representative test results of dynamic shear stress amplitude (τ¯d), dynamic shear modulus (Gd), and damping ratio (λ) are presented and discussed. Based on the Hardin-Drnevich model, a fitting equation for determining maximum dynamic shear modulus (Gd,max) is proposed. Then, a unified normalized dynamic shear modulus (Gd/Gd,max) curve is drawn and well validated by the test results. Furthermore, equations for λ are expressed in terms of an exponential function of Gd/Gd,max. The test results show that the Gd/Gd,max curves are not completely consistent with previous studies. Overall, this study provides further insights into the dynamic behavior of granular base course materials subjected to F-T cycles.

Meshfree analysis on dynamic behavior of hard brittle material in abrasive flow machining

Erosion mechanism of hard brittle target subjected to abrasive particles has been investigated numerically in the present study. A coupled model based on smoothed particle hydrodynamics and finite elements was established. The large deformation and high strain rate of eroded material were concerned by using a strain rate-dependent constitutive model. Dynamic processes of material deformation and fracture growth were analyzed. The results indicated that the radial and lateral cracks were the main fracture modes of aluminum nitride target material. Moreover, the effects of different incident parameters such as impact angle and velocity on erosion mechanism were also investigated.

Explicit dynamic fracture simulation of two-phase materials using a novel meso-structure modelling approach

In order to reduce the experimental cost and enable the numerical modelling better approaches the actual meso-structures of two-phase materials, a novel meso-scale modelling approach, combining the image-based and the parameterized modelling approaches, has been presented. In this approach, only limited samples of the studied two-phase material need to be provided for establishing an aggregate library, through which finite element models with different spatial distributions and volume fractions of aggregate can be arbitrarily generated for the use of virtual test. In the present virtual test, fracture failures were simulated in the framework of explicit dynamics. A rate-dependent cohesive zone model (CZM) was implemented through the user subroutines in ABAQUS to characterize the dynamic damage and fracture of the meso-structures. At the same time, an algorithm of embedding cohesive elements automatically into the potential damage zones was put forward. Finally, two typical numerical examples were given to verify these proposed methods and models, meanwhile the influences of spatial distribution and volume fraction of aggregate on the mechanical performance of the meso-structure were investigated. It can be validated that the present developed methods and models can effectively and efficiently characterize the dynamic fracture behavior of two-phase materials.