Evolution Of Modulus Research Articles

Presenting in-situ AFM investigations for the evolution of micro-surface topography and elastic modulus of rock under variable loads

Understanding the micro and nano-scale surface deformation and mechanical properties of rock under load possess enormous significance for underground engineering research and provides strong basis for comprehending rock failure as well. According to the documented research, the in-situ observation of micro-surface under dynamic load has not been yet reported. With this motive, a novel approach is presented in this work that takes advantages of combined Atomic Force Microscope (AFM) and customized micro-loading device for in-situ characterization of the the micro-surface topography and elastic modulus of rocks under different load strength. The in-situ comparison of micro-surface properties is carried out using interactive tools of AFM image post-processing software including crop and split, and section analysis. Taking the typical observation results of igneous rock and shale as an example, the results show that the micro-surface topography undulations of rock can reach up to tens of nanometers. Although no apparent fracture occurred, the local fluctuation of the rock samples’ micro-surface changed with the increasing load strength at nanometer level, and in the measurement area of 5 × 5 μm2, the topographies of different pixel points are various, showing significant local difference. With the increasing load strength, the elastic modulus distribution of the rock’s micro-surface shows heterogenity, and the local elastic modulus also increases or decreases, while the variation difference at different pixel points reaches hundreds of MPa. Additionally, the macroscopic fracture characteristics of rock under load, especially the non-uniform crack propagation and its mechanism are discussed. The analysis indicates that the heterogeneous distribution of the rock’s micro-surface elastic modulus and its local complex change with load are accounting for the complexity of the macroscopic crack path and the numerous crack branches. This study provides a novel insight into micro-surface behavior in rock and presents a new method for the investigation of the fracture mechanism of rock.

The impact of sulfate- and sulfide-bearing sand on delayed ettringite formation

With the increase of aggregate quarrying to meet the growing need for concrete construction comes a risk associated with new aggregate sources, which may not have uniform compositions and contain potentially harmful substances, such as sulfate and sulfide. To provide insights into the impact of sulfate- and sulfide-bearing sand on susceptibility to delayed ettringite formation (DEF), this study measures the evolution of expansion, acoustic nonlinearity (representing microscale damage), and dynamic elastic modulus of mortars prepared with varying cement compositions and exposed to an early-age high-temperature curing cycle. Samples containing sulfate- and sulfide-bearing sand show substantially higher initial levels of damage, with expansion starting at earlier ages than control samples. Damage in mortars using this sand can be attributed to accelerated decomposition of alkali-feldspar, microcracking due to relative thermal deformation between phases, early release of alkali that increases the amount of sulfate in the pore solution, and release of sulfate ions from aggregates.

Using the Instrumented Indentation Technique to Determine Damage in Sintered Metal Matrix Composites after High-Temperature Deformation

The paper shows the applicability of data on the evolution of the elastic modulus measured by the instrumented microindentation technique to the determination of accumulated damage in metal matrix composites (MMCs) under high temperature deformation. A composite with a V95 aluminum alloy matrix (the Russian equivalent of the 7075 alloy) and SiC reinforcing particles is used as the research material. The metal matrix composite was produced by powder technology. The obtained results show that, under macroscopic compression at temperatures ranging between 300 and 500 °C, the V95\10% SiC MMC has the best plasticity at 300 °C. At a deformation temperature of 500 °C, the plastic properties are significantly lower than those at 300 and 400 °C.

Extraction of microstructural parameters from sculptured thin films nanoindentation

This work deals with the indentation analysis of nanocolumnar thin films and the difficulties encountered to deduce relevant mechanical parameters by this methodology. SiO 2 thin films prepared by physical vapour oblique angle deposition with different nanocolumnar microstructures have been subjected to indentation analysis. Despite the fact that the films had been made of the same material, deposited on the same substrate and had similar thickness, their indentation responses were different and depended on their particular microstructure. It has been also reali s ed that the measured hardness and elastic modulus variation with the indentation depth were length scale dependent and that there is not a unique analytical thin-film nanoindentation model to extract the mechanical properties from the experimental nanoindentation curves. To overcome these limitations a numerical finite element model (FEM) of the nanocolumnar coatings has been built to figure out the contributions of the different physical phenomena intervening in the indentation process. This FEM simulation relies on a description of the elasto-plastic microstructural units of the coatings and the contact friction interactions between them. Based on this simulation a parametrical representation, incorporating two length scales and the contributions of densification and/or the buckling of nanocolumnar units, has been developed to account for the evolution of the apparent elastic modulus deduced from numerical indentation tests . A Hall-Petch modification of this description considering two length scales instead of the common approximation considering a single length scale has rendered the best agreement with the elastic values determined experimentally. Although, at the present stage, the particular microstructure of the films can not be deduced from the evolution of their elastic moduli with the indentation depth, the obtained results and their interpretation constitute a first though essential step for the elaboration of an inverse analysis methodology capable of correlating microstructure and elastic response of nanocolumnar coatings. • The indentation response of multi-layered PVOAD columnar coatings greatly depends on their microstructure. • Buckling but also densification drive the evolution of indentation elastic modulus and hardness with indentation depth. • FEM of a columnar structure under indentation allow s to reproduce the experimental response of multi-layered PVOAD coatings. • Size dependent model allows to extract length scale parameters from elastic response of PVOAD coatings.

Effectiveness of common water-reducing admixtures in alkali-activated slag pastes with different types of activator

Rheology of alkali-activated slag (AAS) is a very complex issue, where the activator nature as well as its dose play an important role. Moreover, the use of water-reducing admixtures in these systems is an issue, as they often do not work properly. This could be attributed to the high pH as well as to the surface chemistry of AAS. Therefore, lignosulfonate-, polynaphthalene- and polycarboxylate-based superplasticizers were used to modify AAS pastes with sodium waterglass, hydroxide and carbonate activator. These pastes were tested using a rotational rheometer in an oscillatory shear mode of increasing shear strain to observe the evolution of viscoelastic moduli and to determine the oscillatory stress corresponding to the linear viscoelastic region limit (“yield point”) and to the crossover point, where the storage modulus equals the loss modulus (“flow point”). In most cases, the used plasticizers did not improve the rheological properties; the only exception was the lignosulfonate one in sodium hydroxide-activated slag.

Epoxy coating as effective anti-corrosive polymeric material for aluminum alloys: Formulation, electrochemical and computational approaches

In this work, a formulation based on epoxy coating composed of DGEBA cured with polyaminoamide has been used as anti-corrosive material for aluminum alloys (2024-T3, 5086 and 7075-T6) substrates for accelerated corrosion assays. The epoxy coating on aluminum alloys samples was tested in 3.0 wt% NaCl solution using salt spray test chamber. The anticorrosive behavior of the aluminum alloys samples under these conditions was monitored by impedance diagrams Bode and Nyquist plots and theoretical studies by DFT, MC and MD. The results showed that the evolution of the impedance modulus plots |Z|0.01 Hz values of the epoxy coating applied on AA2024-T3, AA5086 and 7075-T6 samples began from 2.63, 1.46 and 0.43 MΩ.cm2 after 1 h of immersion and finally reached 0.27, 0.26 and 0.24 MΩ.cm2 after 4392 h of immersion, respectively. The lessening of impedance with submersion time means that the electrolyte scatters into the epoxy coating and diminishes the boundary properties of the film. DFT calculations were used to determine the coatings adsorption centers. Additionally, the Monte Carlo and Molecular Dynamics calculations support the coatings strong adsorption interaction with the metal surface, providing molecular evidence for the epoxy molecule's adsorption behavior (geometry) and adsorption energy on the aluminum surface. Theoretical results (DFT, MC, and MD) corroborate the experimental results.

Mechanical and wear behaviors of 316L stainless steel after ball burnishing treatment

The performance and durability of orthopedic implants are mainly determined by their surface integrity. Ball burnishing (BB) is a kind of finishing treatment which improves the surface dependant mechanical properties of metallic biomaterials. In this work, this process was applied on the flat surface of 316L stainless steel to enhance its microhardness and wear resistance. The mathematical modeling of microhardness Vickers was performed by the response surface method (RSM) based on Box–Behnken plans, and the optimum regime was applied under several passes to investigate the effect of number of passes (i) on the surface properties. The evolution of microhardness, nano-hardness and elastic modulus was then examined. Wear resistance, in terms of variation of Coefficient of friction and wear loss, was also investigated. Finally, XRD analysis was performed to evaluate any change in structure produced by BB. The results show that burnishing treatment permits to raise the microhardness by up to 38.3% and to reduce the wear loss by up to 65.2%. Nano-hardness and elastic modulus were also increased after application of the process. XRD patterns indicate that grain refinement was induced with no change in phases composition. The number of passes is proved effective in increasing the depth of the hardened layer, which influences subsequently on the frictional behavior of 316L stainless steel.

Phase diagram, structure and rheology of boehmite dispersions: role of electrostatic interactions

Improving industrial processes such as filtration of colloidal suspensions requires an in depth understanding of colloidal stability that is linked to interparticle interactions. One way of investigating such phenomena is to determine colloidal phase diagrams and to characterize structure and rheology in various regions of the phase diagrams. Such a strategy was applied in the present paper to the case of boehmite dispersions. The phase diagram of this material, obtained from osmotic stress experiments shows a non trivial behavior, as the sol/gel transition line of boehmite displays a positive slope at low ionic strength and a negative one at higher ionic strength. Combining structural (SAXS) and rheological measurements, it appears that such a behavior can be linked to the ratio between particle anisotropy and Debye length. Such an interpretation is confirmed by modeling the evolution of elastic moduli in various regions of the phase diagram. The model developed takes into account the anisometric nature of particles and provides reasonably accurate predictions of the electrostatic interaction potential in the system.

Young’s modulus evolution during sintering and thermal cycling of pure tin oxide ceramics

Pure tin oxide (SnO2) ceramics is well known for its bad sinterability, more precisely for the difficulty to densify without additives by conventional pressureless sintering. This is related to the fact that the sintering mechanisms in pure tin oxide ceramics are non-densifying (surface diffusion at low temperature and evaporation-condensation at high temperature). On the other hand, for the same reason, pure tin oxide ceramics is a very unusual model system that can be used to demonstrate the effects of microstructural changes on effective properties without the otherwise dominating effect of changes in porosity. In this paper we show that pure tin oxide ceramics uniaxially pressed at 50 MPa, pre-sintered at 500 °C and re-sintered at 1000, 1200 and 1400 °C exhibit relative Young’s modulus increases of 30, 70 and 120 % while the porosity remains essentially constant at a value of 51.6 ± 0.7 %.

Modulation of soft glassy dynamics in aqueous suspensions of an anisotropic charged swelling clay through pH adjustment

HypothesisSodium-montmorillonite (Na-Mt) particles are geometrically anisometric that carry a pH dependent anisotropic surface charge. Therefore, it should be possible to manipulate the particle–particle interaction of colloidal range Na-Mt suspensions through pH changes which in turn should alter the soft glassy dynamics of Na-Mt suspensions. ExperimentsRheological experiments were used to probe the impact of pH mediated colloidal particle–particle interaction on the physical aging, linear viscoelastic response, and yield stress behavior of Na-Mt suspension. FindingsThe temporal evolution of the storage modulus (G') was stronger in the acid regime (pH < 9.5) than the base (pH ≥ 9.5) pH regime. Horizontal shifting of the aging curves in the acid and base regimes led to aging time–H+ concentration and aging time–OH– concentration superposition. An aging time–Na-Mt concentration superposition was also observed in both pH regimes. The critical stress associated with the viscosity bifurcation behavior increased linearly with G' but with different slopes for acid and base regime. We propose that positively charged patches on the Na-Mt particle edge merge with the characteristic surface as a function of H+ ions in the system. This leads to a strongly associated microstructure at low pH and a relatively weak but associated microstructure at natural pH, hence confirming the hypothesis.

Using non-destructive testing to assess static elastic modulus of a limestone exposed to high temperatures

The determination of static elastic modulus in the laboratory requires rock core extraction and the subsequent testing of the samples by means of standardised uniaxial compressive strength tests. However, this destructive procedure is not always suitable – as in the case of protected historic buildings. In these cases, the static elastic modulus can be obtained from the dynamic elastic modulus, in turn derived from the velocity of ultrasonic waves (a non-invasive and non-destructive test). The relationship between both the dynamic and static moduli of rocks has been extensively addressed in the scientific literature. Furthermore, several researchers have separately studied the evolution of static or dynamic elastic moduli of rocks exposed to high temperatures – although few studies have compared both values. It is well known that the dynamic modulus is generally higher than the static modulus, and the values diverge especially in rocks with a low modulus of elasticity. These differences can be mainly explained by the effect of porosity and the size of cracks in the determination of both parameters. In this research, the relationship between static and dynamic moduli for ‘Borriol’ limestone is studied for samples previously subjected to 200, 400, 600 and 800 °C and then cooled slowly (in air) or quickly (immersed in water). The results show that the static modulus of samples heated up to 600 °C decreased 80.9 and 79.1 % and dynamic modulus decreased 62.5 and 64.8 % for slow and quick cooling samples, respectively. For samples heated to 600 and 800 °C, the static and dynamic moduli are similar. In general, no significant differences between both cooling methods are observed, even though static modulus shows more loss than dynamic modulus. Finally, linear models were used to correlate static and dynamic moduli, providing coefficients of determination of 0.99 and 0.97, for slow and quick cooling, respectively. It is also remarkable that the Edyn/Est rate was smaller than 1 for elastic moduli over 30 GPa (i.e., 105, 200 and 400 °C) and greater than 1 for lower moduli (i.e., 600 and 800 °C). The results obtained can be used to calculate the static elastic modulus of ‘Borriol’ limestone from dynamic modulus determined by non-destructive techniques.

Evolution of complex modulus and higher harmonics of stress response of asphalt concrete in strain-controlled four-point beam fatigue tests

ABSTRACT The modulus of asphalt concrete that is conventionally obtained from large amplitude oscillations (LAOs) in fatigue tests cannot be considered a material property since the response changes from cycle to cycle. It is necessary to determine how viscoelastic properties vary with the extent of damage, and they cannot be obtained from LAOs without making specific constitutive assumptions. Moreover, the higher harmonics of the stress response can be used to quantify the distortion of the stress waveform and, therefore, the point of failure in fatigue tests. This should also be explored further. With these as the objectives, strain-controlled four-point bending (4PB) tests were conducted in this study with the LAOs regularly interrupted to apply a few cycles of small amplitude oscillations (SAOs). The stress response from both SAOs and LAOs were subjected to Fourier analysis. The fundamental harmonic was used to define the apparent storage and loss moduli, and the moduli from the SAOs and LAOs were compared with each other. The ratio of the amplitude of the third harmonic to the first harmonic was found to sharply increase after a certain point in the test. This was used to define a new failure criterion for 4PB fatigue tests.

Evolution of the electrical resistivity at rest and during oscillatory shearing of co‐continuous morphology (PP/PMMA)/MWCNT systems

AbstractIn this work, a modified parallel‐disks configuration on a strain‐controlled ARES rheometer (TA Instrument) was used to study the evolution of the electrical resistivity at rest and during oscillatory shearing of a co‐continuous immiscible polymer blend morphology based on polypropylene and /polymethyl(methacrylate) (PP/PMMA) in which various amounts (0–3 wt%) of multiwall carbon nanotubes (MWCNT) were added. The co‐continuity of both PP and PMMA phases allowed the buildup of a conductive network due to the preferential localization of the conductive MWCNT at the interface between PP and PMMA. Under a stepwise increase of the oscillatory strain amplitude below a critical value (γc = 6.3%), a significant decrease in the electrical resistivity was observed for MWCNT concentrations above the percolation threshold (0.3 wt%) due to the conductive paths induced by both thermal (Brownian) motion and oscillatory shearing. However, for deformation amplitudes higher than γc, the resistivity increased due to the destruction of the MWCNT paths induced by the large deformation imposed on the PP/PMMA interface. These observations were also confirmed by the evolution of the storage modulus (G′) which remained constant for γc &lt; 6.3% (linear viscoelastic regime), while the values decreased above γc due to the destruction of the system's morphology.

Synthesis and compression study of orthorhombic Fe7(C, Si)3: a possible constituent of the Earth’s core

ABSTRACT The orthorhombic phase of Si-doped Fe carbide is synthesized at high-pressures and temperatures using laser-heated diamond anvil cell (LHDAC), followed by its characterization using X-ray diffraction (XRD), Transmission Electron Microscopy (TEM) and Raman spectroscopy. Room-temperature high-pressure XRD measurements are carried out up to about 104 GPa for the determination of the equation of state parameters. No evidence of structural transition is observed. Pressure evolution of isothermal bulk modulus shows elastic stiffening around 28 GPa followed by softening around 78 GPa, which are possibly related to magnetic transitions driven by pressure-induced anisotropic strain in the unit cell. Extrapolation of the density profile of our study to the inner core conditions agrees very well with PREM data with an uncertainty of about 3–4%. Our estimated bulk modulus value at core pressures seems to be 8-9% less than that of PREM data and is best matched in comparison to other reported values.

Resistive-IR Hybrid Heating in FDM Printing

FDM printing is based on resistance to heat of the polymer filament, which starts in a viscous state and is extruded from nozzle to the printing area. The printing area is hot around 70°C for a better adherence of the deposited polymer and for slow cooling of it. The later deposited layers will experience faster cooling and the characteristics of the polymer will suffer light changes. The paper aims to present the results of a preliminary research regarding the double source successive heating and double source hybrid heating of the extruded polymer in FDM process. There were used two distinct heat sources, the resistive source mounted in the extrusion nozzle and IR lamp heat source placed in the printing chamber. The first heating, which acts during the extrusion process, is a hybrid heating and it is developed inside the extrusion nozzle (hot-end); it is given by the resistive heat source by the IR lamp. After the extrusion, during the deposition process and after the deposition process, the heating of the polymer continues due to the IR lamp. The difference between the printing with IR heating and without IR heating was monitored. A decreasing of about 5-8% of the material stiffness was noticed when the IR lamp was introduced. The material became more viscous and the bonding of the successive layers was improved. DSC analysis has been performed in both cases: with and without IR heat source. The evolution of the elastic modulus proved a decreasing of the plasticity during the simple printing process. The decreasing was less (at least by about 25%) when used IR heat source. The elongation viscosity was analysed and its values were decreasing while the temperature was increasing that took place. The decreasing was produced by the reduction of the elasticity, when the chain branches were decreasing their length. The decreasing is more pronounced while the increasing of the temperature. A low difference (of about 2-5%) was observed to the mechanical characteristics after tensile tests.

Energy and Fatigue Damage Evolution of Sandstone under Different Cyclic Loading Frequencies

To study the energy dissipation characteristics and damage evolution law of sandstone under cyclic loading, uniaxial cyclic loading tests are conducted on sandstone specimens under different frequencies with an MTS-815 rock testing machine. Furthermore, the characteristics of elastic modulus and energy evolution law during cyclic loading and unloading are explored. The results show that the loading and unloading moduli increase with the loading frequency. Under higher frequencies, the deformation resistance of the specimen is stronger, the elastic energy stored in a single cycle of loading is larger, the released energy is less, and it is less likely for the specimen to be damaged. At the beginning of loading, the energy dissipation ratio K decreases slowly with increasing loading cycles, and it then remains stable. When the specimen is close to failure, an inflection point of K appears, and K increases rapidly. Furthermore, the evolution equation of the damage variable is derived according to the strength characteristics and energy evolution law in the process of cyclic loading, and the reasons for the failure of sandstone specimens are explained from the perspectives of energy and fatigue damage.

Microstructure and indentation hardness study of CAE-PVD (Cr,Ti,Al)N solid solution coatings deposited using a combinatorial multitarget approach

In this study we have analysed the indentation hardness and modulus of cathodic arc deposited CrTiAlN coatings as a function of the stoichiometric variables Ti/Cr, Al content and cation mix. The coatings have been prepared using a combinatorial cathode composition approach, leading up to 14 different stoichiometries produced in 5 batches. The coatings have been inspected by glow discharge optical emission spectroscopy, scanning electron microscopy, X-ray diffraction and nanoindentation techniques. The coatings develop crystalline structures compatible with solid solutions of face–centered cubic unit cells for all the compositions produced. Such unit cells exhibited a downwards lattice parameter dependency on the aluminum concentration of the coatings (from 0.417 nm down to 0.413 nm). The indentation hardness as a function of the Ti/Cr is compatible with other previous studies reported. The films hardnesses and moduli also increase as the aluminum concentration increases (21 GPa up to 34 GPa). Both indentation responses upon Ti/Cr and Al are attributed to solid solution strengthening. However in order to prove this statement, the indentation hardness and modulus were studied as a function of the mixing term of the cations, as this term is well representative of the solid solution compositional map. The observed results unambiguously evidence that the solid solution strengthening effect is confirmed on the basis of the dependency between the indentation hardness and the so called degree of mixing. • CrTiAlN arc coatings deposited using a multi-cathode combinational approach. • CrTiAlN coatings form solid solutions of decreasing lattice parameter as the Al content increases. • The absolute aluminum concentration increases the hardness and modulus of the quaternary solid solution. • Solid solution strengthening constituted the as main mechanism of the coating indentation hardness and modulus evolution.

Development of a Magneto-Mechanical Bench and Experimental Characterization of Magneto-Rheological Elastomers

Magneto-rheological elastomers (MREs) belong to the class of smart materials whose mechanical properties can be controlled by an external magnetic field. These materials can be integrated into mechatronic systems and submitted to multiple loadings such as temperature, mechanical stress, and magnetic field. Thus, this work is dedicated to the development of a magneto-mechanical bench and on first experimental characterizations of hard MREs taking multiphysics coupling into account. Regarding the mechanical loading, the experimental setup is able to create a uniaxial tensile stress in case of low strain (< 1%) without friction effect. In regards to the magnetic loading, a magnetic circuit made of a strong permanent magnet has been designed to impose a variable and a homogeneous magnetic field strength up to 41 kA/m. Experimental analysis has been performed on silicone rubber filled with 36%vol. of NdFeB particles. The purpose was first to investigate the evolution of the Young modulus with or without magnetic field. Results obtained from measurements show that the developed test bench is able to depict the mechanical behavior and phenomena linked to rubber-like material.

Permanent Deformation and Stiffness Degradation of Open Hole Glass/PA6 UD Thermoplastic Composite in Tension and Compression.

UD glass/PA6 coupons with an open hole are subjected to tensile and compressive loading. Three layups: [0/90]5s, [+45/−45]5s and [+45/0/−45/90]3s with a shape based on ASTM D5766 were tested. Both monotonic loading as well as loading–unloading–reloading tests were executed. The strain field on the sample surface was measured with digital image correlation. This allowed identifying the distribution of the strain field during loading, permanent deformation and the evolution of the sample elastic modulus. This information is not frequently measured. Yet, it is vital for the development and validation of advanced failure models. The results indicate that the thermoplastic matrix allows large plastic deformation under tensile loading for the specimens with layup [+45/−45]5s. In addition, the specimen elastic modulus reduces by about 70%. The other layups show minor permanent deformation, while the elastic modulus reduces by up to 15%. Furthermore, the quasi-isotropic laminate shows a significant post-failure load-bearing capacity under compression loading. The results are complemented with post-mortem damage and fracture observations using optical microscopy and ultrasound inspection.

Nano-indentation nanohardness and elastic modulus evolution of molybdenum processed by high-pressure torsion

In this paper, high-pressure torsion (HPT) was conducted on pure molybdenum (Mo) (99.9 wt.%) under the 6 GPa pressure at room temperature with an angular velocity of 1 rev min−1. The samples processed by 1, 2, 5 turns of HPT were obtained. After 5 revolutions of HPT, the grains were significantly refined to 0.77 ± 0.17 µm and the main textures are {012}<121> and {001}<110>. The dislocation density of the sample after 2 turns of HPT deformation reaches to the maximum value. The elastic modulus of pure molybdenum after 5 turns of HPT has a great decrease. It is found that texture structures, dislocations and non-equilibrium grain boundaries can influence the elastic modulus evolution, and the latter two are the main factors.