Micromechanical Behavior Research Articles

High-throughput screening of the potential alloying elements for high-strength Mg alloys based on solid-solution strengthening

Abstract 49 types of alloy atomic dopants and their effects on the doping stability and micro-mechanical behaviour of magnesium matrix were investigated using density functional theory and high throughput first-principles calculations. Geometry optimization was performed for each doping system, and the ability of atom doping into the magnesium matrix was assessed based on the doping energy and atomic radius. Results show that the transition metal elements have negative or near negative doping energy, especially for the elements with a radius that similar to Mg. The micro-mechanical properties of the doping system were evaluated by computing the fracture energy and theoretical tensile stress. Through a screening on the doping stability and strengthening effect of 49 types of alloy atoms, a set of elements (Re, Os, Ir, Tc and W, etc.) are screened out that could strengthen the magnesium matrix with a good doping stability. The high throughput screen results serve as a theoretical guide for the selection of appropriate alloy elements for designing the high-strength magnesium alloys in the regime of solid solution strengthening effects.

Quasi-static/dynamic energy absorption characteristics and micromechanical behavior of Al/Ep cast metal braided tubular structures

As a low-density, high-strength material with high energy release potential, Al/Ep cast metal braided tubes have a wide range of application prospects in the combatant shell, which is one of the most important means to realize the integrated destructive effect of kill and blast. In this paper, Al/Ep composites with mass ratios of 3:7, 4:6 and 5:5 were prepared, and the intrinsic model of Al/Ep was established by studying its quasi-static and dynamic mechanical properties. The Al/Ep cast three-dimensional braided metal skeletons were used to obtain the required cast braided tubes with different mass ratios, and the destruction behaviors of the tubes under axial and radial compressive loads were analyzed by a combination of experimental and numerical simulations. The results show that the addition of Al particles can significantly improve the elastic-plastic properties of Al/Ep composites, and the energy storage and absorption capacities are positively correlated with the ratio of the relative contents of Al powder. When the mass ratio of Al powder to epoxy resin is 5:5, the energy absorption of Al/Ep composites is 23.16 MJ/m3, which is optimal among similar specimens and much higher than that of pure epoxy resin materials (the energy absorption of epoxy resin is 9.63 MJ/m3). The strength of binary resin matrix composites is improved, and the intrinsic models of three kinds of different mass ratios of Al/Ep composites are obtained. The intrinsic models of various Al/Ep cast braided tubes with crushing force efficiency CFE, energy absorption capacity, and specific energy absorption SEA decreased with the ratio of mass occupied by the braided filaments.

Molecular dynamics study on the deformation mechanism of Cu–Zr/Al laminated composites

In this paper, molecular dynamics simulation was used to investigate the micromechanical behavior of the Cu–Zr/Al composite interface after rapid solidification. The effects of different Zr contents and different strain rates on the tensile strength of the Cu–Zr/Al composite interface were investigated. The results show that the tensile strength of the composite plate increased and then decreased with the increase of Zr content, and the tensile strength is the highest when the Zr content is 0.33 wt%. It was found that the plastic deformation process of the composite model at different strain rates is similar, which is divided into three stages: the expansion of stacking faults in the Cu–Zr/Al solid solution, the expansion of stacking faults successively in the Al and Cu–Zr alloy layers, and the spreading of cross - stacking faults. But the greater the strain rate is, the slower the stacking faults fracture is. So the composite model with different strain rates had different fracture modes during the tensile fracture process. When the strain rate is 0.01 ps−1 and 0.001 ps−1, it is a ductile fracture, while when the strain rate is 0.0001 ps−1, it is a brittle fracture.

Role of prior austenite grain boundary and retained austenite in strain localization of medium-carbon high-strength steels

Exploring the micromechanical behavior of lath-martensitic quenching and tempering (Q&T), as well as quenching and partitioning (Q&P) steels presents a significant challenge due to their complex multi-phase constituents and hierarchical structures. This study conducts a comprehensive comparative analysis using medium-carbon Q&T and Q&P steels with identical chemical compositions. Atom probe tomography (APT) was used to investigate the distribution of chemical elements, while high-resolution digital image correlation (HR-DIC) provided insights into nanoscopic strain localization and partitioning. Both Q&T and Q&P steels exhibit significant strain localization at prior austenite grain boundaries (PAGBs) due to substantial carbon segregation. Strain localization in Q&T steel at PAGBs and packet boundaries strongly depends on preferred geometric orientations, with boundaries inclined 45° to the loading direction experiencing severe deformation. Conversely, in Q&P steel, PAGBs adjacent to large clusters of fine lath martensite, lacking a packet with a longitudinal direction parallel to boundaries and a feasible in-lath slip system, primarily undergo deformation. Carbon partitioning from martensite to retained austenite (RA), along with coexisting carbon and manganese segregation at phase interfaces, stabilizes the RA, resulting in a neighborhood-dependent deformation behavior of RA. The existence of RA not only absorbs carbon, maintaining low strength and high deformability, but also uniformly distributes and induces stable interfaces to hinder the formation of large packets with easily activated in-lath slip transmission.

Optimizing heterostructure parameters towards enhanced toughening in micro/nano-reinforced bimodal-grained Al alloy composites

We manipulated soft coarse-grained (CG) domains to design optimized and toughened B4Cp/6061Al composites, featuring bimodal domains with in-situ MgO nanoparticles (n-MgO) and ex-situ carbon nanotubes (CNTs). Manipulating CG fractions influenced heterostructure parameters such as CG band width and domain distribution. A systematic optimization strategy integrating intrinsic/extrinsic toughening and strengthening mechanisms identified optimal conditions for maximizing strength-ductility-toughness. The optimal 20:80 CG-to-ultrafine-grain (UFG) weight ratio offered an ultimate strength of 550 MPa and ∼7 % elongation. Intrinsic toughening mechanisms enhanced UFG domain dislocation storage capacity. Multiscale analysis of crack behavior revealed pronounced crack-blunting in well-dispersed CG domains. Extrinsic toughening mechanisms included nanobridge formation, crack-deflection, micro-crack proliferation, and crack-branching. Micromechanical behavior was examined using the strain gradient model. Designing strong and ductile micro/nano-reinforced bimodal grained composites requires selecting a smaller amount of CG domains, a CG band width larger than double the interface affected zone (IAZ), and larger grain sizes in the CG domains.

Quantitative analysis of the micromechanical behavior and work hardening in Fe-0.1C–10Mn steel via in-situ high-energy X-ray diffraction

In the current work, the micromechanical behavior and work hardening behavior of Fe-0.1C–10Mn (in wt.%) steel deformed at 100, 63, 25 and −50 °C were investigated via in-situ high-energy X-ray diffraction (HE-XRD) technique. As the deformation temperature decreased, the yield strength (YS) and ultimate tensile strength (UTS) increased, while the total elongation (TE) reached a maximum value at 25 °C. The transformation kinetics of retained austenite (RA) was fitted by the Olson and Cohen (OC) model. The phase stress and flow stress contributed by the constituent phases were obtained based on the lattice strain and the volume fraction of the corresponding phase. The work hardening rate was decomposed into four contributors related to the TRIP effect and load partitioning, ie., the austenite phase stress, load partitioning between austenite and martensite, martensitic formation rate and load partitioning between ferrite and austenite. The influence of each contributor on the work hardening behavior was quantitatively evaluated and stacked, the stacked results agreed reasonably well with the experimental work hardening rate obtained from the true stress-strain curve. Finally, the volume fraction of austenite to martensite transformation promoted by the Lüders band (LB) and the stacking fault energy (SFE) of RA were found to be highly temperature-dependent. A linear relationship was revealed between the volume fraction of austenite to martensite transformation during the LB propagation and the SFE of RA. These findings offer insights into the TRIP effect and the LB propagation in medium-Mn steels.

Microstructural evolution and mechanical behaviors of rock salt in energy storage: A molecular dynamics approach

The microstructure of rock salt significantly influences its macroscopic mechanical behaviors and deformation phenomena. Understanding the deformation and failure characteristics of rock salt at multiple scales is crucial for the secure and efficient functioning of energy storage in salt caverns. Although the macroscopic behaviors of rock salt are well understood, the microstructural changes occurring under uniaxial compression have not been thoroughly investigated. This study aims to investigate the evolving laws of rock salt microstructure and mechanical properties during the damage process, thereby providing a fundamental understanding of the underlying mechanism. To achieve this, a series of characterization tests on rock salt were conducted to study its microstructure and defects. Building on this, molecular dynamics simulations were utilized in rock mechanics to elucidate the mechanical behaviors, structural evolutions, and dislocation motions of rock salt during the damage process. The rock salt obtained from Qianjiang, China, is a polycrystalline material with an average subgrain size of 46 nm and an average dislocation density of 4.76 × 10−6 1/Å2. Uniaxial compression of single crystal NaCl exhibits three stages: elastic compression, rapid dislocation multiplication, and forest hardening. Scattered dislocations and isolated dislocation tangles trigger further plastic slippage, leading to decreased strength. Later, the formation of a dislocation cell network hinders further slip and reinforces the strength of rock salt. Plastic deformation is found to be a dominant factor in grain refinement and the formation of polycrystalline structures. Intergranular cracking results from cross-patterned dislocation lines on grain boundaries, which become vulnerable areas of the structure. This study describes the evolutionary process of rock salt microstructures and mechanical properties, identifies the micro-destruction mechanisms during the damage process at the ionic level, and provides insights into the micro-mechanical behavior of rock salt and for the design and stability assessment of underground energy storage facilities.

Macro- and micromechanical behavior of oil palm wood (Elaeis guineensis Jacq.): tensile, compression and bending properties

Macro- and micromechanical behavior of oil palm wood (Elaeis guineensis Jacq.): tensile, compression and bending properties

Investigating grain-resolved evolution of lattice strains during plasticity and creep using 3DXRD and crystal plasticity modelling

Microstructure-informed crystal plasticity finite element models have shown great promise in predicting plastic and creep deformation in polycrystalline materials. These models can provide substantial insight into the design, fabrication and lifetime assessment of critical metallic components during operation, for instance, in thermal power plants. However, to correctly incorporate damage prediction into models, the microstructural strain simulated at the grain level must be accurately predicted with suitable validation. For this reason, a 3D X-ray Diffraction (3DXRD) experiment was carried out on 316H stainless steel, a material commonly used in thermal power plants, to obtain the per-grain strain response during plastic and creep deformation at 550°C. Several hundred grains within a probed X-ray volume were tracked and measured whilst loading in-situ, obtaining per-grain centre-of-mass positions, crystallographic orientations, and average lattice strain over individual grains. These data were used to calibrate a crystal plasticity model to study the plastic and creep deformation using macroscopic stress-strain and stress-relaxation data. Subsequently, the model was used to predict the average elastic strain in different grains during the cyclic creep experiment, which was validated by 3DXRD datasets. The model results reveal that {100} or {311} grain families are strongly sensitive to microstructure, thereby a polycrystal model that describes specific orientation and neighbourhood characteristics is essential to predict the local response of these grain families. Whereas, self-consistent models are suitable for {110} and {111} grain families. This study shows that only with a suitable calibration of subsurface grain behaviour, crystal plasticity models reveal grain characteristic-dependent micromechanical behaviour.

Effect of wire diameter compression ratio on drawing deformation of micro copper wire

A crystal plasticity finite element model was developed for the drawing deformation of pure copper micro wire, based on rate-dependent crystal plasticity theory. The impact of wire diameter compression ratio on the micro-mechanical deformation behavior during the wire drawing process was investigated. Results indicate that the internal deformation and slip of the drawn wire are unevenly distributed, forming distinct slip and non-slip zones. Additionally, horizontal strain concentration bands develop within the drawn wire. As the wire diameter compression ratio increases, the strength of the slip systems and the extent of slip zones inside the deformation zone also increase. However, the fluctuating stress state, induced by contact pressure and frictional stress, results in a rough and uneven wire surface and diminishes the stability of the drawing process.

Collapse Pattern in Gypseous Soil using Particle Image Velocimetry

Abstract Gypseous soil is prevalent in arid and semi-arid areas, is from collapsible soil, which contains the mineral gypsum, and has variable properties, including moisture-induced volume changes and solubility. Construction on these soils necessitates meticulous assessment and unique designs due to the possibility of foundation damage from soil collapse. The stability and durability of structures situated on gypseous soils necessitate close collaboration with specialists and careful, methodical preparation. It had not been done to find the pattern of failure in the micromechanical behavior of gypseous sandy soil through particle image velocity (PIV) analysis. This adopted recently in geotechnical engineering to track the motion of soil grains and using tracer particles by applying digital particle image analysis. It has also been used to study the displacement distribution in some cases of granular materials. Therefore, the goal of this study is to find out how gypseous sand medium moves when in contact with a rigid strip foundation that is under static stress and plane strain conditions. The experimental model would focus on two common types of wetting, namely water table rise and dry conditions. The PIV showed that the collapse pattern under the footing is of the type of punching shear failure. The predominant mechanism of soil deformation was the vertical compression of the gypseous granular soil. The results showed that understanding gypseous sandy grain displacement and failure patterns at the local scale is crucial for enhancing the design of foundations under static stress conditions.

Long-term aging behavior and mechanism of CMSX-4 nickel-based single crystal superalloy at 950 ℃ and 1050 ℃

Nickel-based single crystal superalloys CMSX-4 have been widely used to manufacture aeroengine turbine blades because of their excellent high-temperature comprehensive properties. The microstructure evolution behavior, mechanism, and influence on micromechanical behavior of the second-generation nickel-based single crystal superalloy during long-term aging at 950°C and 1050°C for 10–2000 h were investigated. The results show that, with the extension of aging time, the average size of γ' phase increased, whose morphology changed from square block to strip and L shape and rafting phenomenon was observed. The coarsening of γ' conforms to Lifshitz–Slyozov–Wagner (LSW) theory and the coarsening rates are 4.241×10−5 and 9.954×10−5μm3/h at 950°C and 1050°C, respectively. After aging at 950°C and 1050°C for 1000 h, segregation of refractory elements was formed in the samples. There are hard topological close-packed (TCP) phases surrounded by γ' envelope precipitates, which destroyed the continuous structure of γ'. The precipitation of TCP caused the depletion of refractory element Re in the γ' envelope phases, resulting in softening effect. It was also found that high temperature can not only accelerate the coarsening of γ' phase but also promote the precipitation and growth of TCP phases.

Effects of methanol and ethylene glycol on the interactions between methane hydrate particles and water droplets

Hydrate particle agglomeration is one of the main causes of hydrate blockage in pipelines. Although methanol (MeOH) and ethylene glycol (MeG) are the most used thermodynamic hydrate inhibitors, their effects on the micromechanics behavior of natural gas hydrate particle agglomeration are not clear. In this study, the effects of MeOH and MeG on the interaction force between methane hydrate particles and droplets were investigated using a self-built high-pressure hydrate microforce measuring device. The results suggest that, with the concentration increase from 1% to 7%, for the system with MeOH, the adhesion force reduced by 11% to 33%, while for MeG, the adhesion force reduced by 15% to 43%. On the one hand, the addition of inhibitors reduces the phase equilibrium temperature, which decreases the solidification rate of water in liquid bridge, and on the other hand, they reduce the interfacial tension. both reductions lead to lower adhesion force. Furthermore, in comparison with MeG, the MeOH solutions present a lower contact angle, resulting in a larger hydrate particle-droplet contact area and thus relatively higher adhesion force. The measurement and observation in the present work provide new insight into the mechanism of methanol and ethylene glycol on inhibiting hydrate agglomeration, which is important in advancing the management of hydrate formation in pipelines.

Effect of Microstructure on Oxidation and Micro-mechanical Behavior of Arc Consolidated Mo-Ti-Si-(B) Alloys

AbstractThe present study deals with the development and characterization of Mo-35Ti-10Si and Mo-35Ti-10Si-2B (wt.%) alloy for ultra-high temperature applications beyond the temperature limit of existing super alloys. The microstructural characterization using scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), electron back scattered diffraction (EBSD), x-ray diffraction (XRD) revealed that the Mo-35Ti-10Si-2B alloy was consisted of three phases, namely, (Mo, Ti)ss, (Mo, Ti)5SiB2 and (Ti, Mo)5Si3; whereas, Mo-35Ti-10Si alloy was found to be consisting of (Mo, Ti)ss, and (Mo,Ti)3Si phases. Since quantification of boron is difficult by EDS, Particle Induced Gamma-ray Emission (PIGE), a nuclear reaction analysis technique was used for chemical composition analysis of boron. The oxidation behavior of the Mo-35Ti-10Si-2B alloy in the temperature regime of 825-1250 °C was studied in detail and compared with boron-free Mo-35Ti-10Si alloy. Mo-35Ti-10Si-2B alloy exhibited superior oxidation behavior at intermediate temperatures of 825 °C, and excellent oxidation resistance at higher temperatures between 1000 and 1250 °C due to the formation of the protective borosilica and double oxide layers (TiO2 and duplex borosilica-TiO2), respectively. High-temperature oxidation mechanisms were discussed using detailed microstructural cross section analysis of the oxidized alloy samples. The micro-mechanical behavior of constitutive phases of the Mo-35Ti-10Si-2B alloy were studied by microhardness, nano-indentation and micropillar compression testing. The micropillar compression of (Mo, Ti)ss phase showed fairly ductile behavior with the evidence of activation of dislocation in the form of slip lines revealed through the post-deformation fractography. Deformation studies of (Mo, Ti)5SiB2 and (Ti, Mo)5Si3 phases were also carried out which showed large strain bursts indicating possibility of activation of dislocation activities even at room temperatures imparting low level of ductility.

Relationship between electrical resistance and single CNT fiber displacement relative to cement matrix – new insights on the electric polarization and spreading at debonded/slipped interface

New relationships between electrical resistance (r) at the CNT fiber-to-cement matrix interface and fiber-to-matrix displacement (u) are established, enhancing the accuracy of self-sensing technology for post-cracking concrete. In the experiment, micromechanical behavior and electrical response (steady and sweeping direct current, DC) were simultaneously monitored through a single-fiber pullout test. It revealed that significant polarization exists at the interface, leading to incorrect resistance measurement. The polarization is eliminated by adding carbon fibers to percolation; after that, an exponential increase of r with u was then observed in both fiber debonding and slippage stages, while r dropped right after full debonding. In the simulation, the spreading of electric current from a partially debonded/slipped interface to distant matrix bulk was computed with a multi-physics FEM model, to correlate resistance change with the interfacial damage level – debonding crack length and fiber slippage. The model-based parametric study showed that the r-u relationship is more sensitive to fiber conductivity than fiber dimensions or matrix conductivity.

Experimental and numerical studies of breakage and fractal characteristics of silica sands in high-pressure triaxial tests

Triaxial compression tests were performed on silica sands with confining pressure ranging from 0.5 to 60 MPa. A multigenerational DEM model was employed parallelly to investigate how micromechanical behaviors evolve with particle breakage. Prediction of the relative breakage considering the influence of axial strain and confining pressure is proposed. A strong correlation between the relative breakage and the input work is proposed regardless of the shear path. A nonlinear relationship is proposed to correlate the relative breakage and the volumetric strain. As the input work goes to infinity, the fractal dimension has an ultimate value approaching 2.66, which is greater than the values from previous theoretical and experimental studies. The mean coordination number in an uncrushable sample is higher than the crushable one during whole shearing. The normal contact force distribution is sensitive to the shear path, and particle breakage makes the contact force more inhomogeneous.

The Influence of the Interface on the Micromechanical Behavior of Unidirectional Fiber-Reinforced Ceramic Matrix Composites: An Analysis Based on the Periodic Symmetric Boundary Conditions

The long-term periodicity and uncontrollable interface properties during the preparation process for silicon carbide fiber reinforced silicon carbide-based composites (SiCf/SiC CMC) make it difficult to thoroughly investigate their mechanical damage behavior under complex loading conditions. To delve deeper into the influence of the interface strength and toughness on the mechanical response of microscopic representative volume element (RVE) models under complex loading conditions, in this work, based on numerical simulation methods, a microscale representative volume element (RVE) with periodic symmetric boundary conditions for the material is constructed. The phase-field fracture theory and cohesive zone model are coupled to capture the brittle cracking of the matrix and the debonding behavior at the fiber/matrix interface. Simulation analysis is conducted for tensile, compressive, and shear loading as well as combined loading, and the validity of the model is verified based on the Chamis theory. Further investigation is conducted into the mechanical response behavior of the microscale RVE model under complex loading conditions in relation to the interface strength and interface toughness. The results indicate that under uniaxial loading, increasing the interface strength leads to a tighter bond between the fiber and matrix, suppressing crack initiation and propagation, and significantly increasing the material’s fracture strength. However, compared to the transverse compressive strength, increasing the interface strength does not continuously enhance the strength under other loading conditions. Meanwhile, under the condition of strong interface strength of 400 MPa, an increase in the interface toughness significantly increases the transverse compressive strength of the material. When it increases from 2 J/m2 to 20 J/m2, the transverse compressive strength increases by 28.49%. Under biaxial combined loading, increasing the interface strength significantly widens the failure envelope space under σ2-τ23 combined loading; with the transition from transverse compressive stress to tensile stress, the transverse shear strength shows a trend of first increasing and then decreasing, and when the ratio of transverse shear displacement to transverse tensile/compressive displacement is −1, it reaches the maximum. This study provides strong numerical support for the investigation of the interface properties and mechanical behavior of SiCf/SiC composites under complex loading conditions, offering important references for engineering design and material performance optimization.

Microstructures and micromechanical behaviors of high-entropy alloys investigated by synchrotron X-ray and neutron diffraction techniques: A review

Microstructures and micromechanical behaviors of high-entropy alloys investigated by synchrotron X-ray and neutron diffraction techniques: A review

Macro-micro mechanical behavior of saturated cemented sands during drained triaxial shearing

To enhance the understanding of the macro-micro mechanical behavior of cemented sands, a series of drained triaxial shearing tests were conducted on saturated cemented sands with varying cement contents and confining stresses. These tests incorporated high-performance acoustic emission (AE) monitoring and an environmental scanning electron microscope (ESEM) technique. The results yielded quantitative interpretations of macro-mechanical response, microstructural variation, and AE behaviors. Specifically, increasing cement content led to an exponential reduction in porosity (or pore area ratio) and a power increase in pore number, possibly due to the production of hydration products that segment large pores. Relationships were established among peak strength (or AE hits), cement content, and confining stress. However, AE trends diverged from those observed in peak strength due to microstructural modifications under different cement contents and their resulting differences in micromechanical behavior during shearing. General relationships between AE rate and mechanical parameters were established during the initial shearing stage, regardless of cement content and confining stress. Moreover, AE evolution efficiently characterized subtle variations in failure patterns due to its high sensitivity to failure-induced structural modifications. These contributions have the potential to establish a non-destructive field evaluation framework and provide guidelines for the efficient utilization of cemented soils in geological and geotechnical engineering applications.

Microstructure-Based Modeling of Deformation and Damage Behavior of Extruded and Additively Manufactured 316L Stainless Steels.

In this study, we investigated the micromechanical deformation and damage behavior of commercially extruded and additively manufactured 316L stainless steels (AMed SS316L) by combining experimental examinations and crystal plasticity modeling. The AMed alloy was fabricated using the laser powder bed fusion (LPBF) technique with an orthogonal scanning strategy to control the directionality of the as-fabricated material. Optical microscopy and electron backscatter diffraction measurements revealed distinct grain morphologies and crystallographic textures in the two alloys. Uniaxial tensile test results suggested that the LPBFed alloy exhibited an increased yield strength, reduced elongation, and comparable ultimate tensile strength in comparison to those of the extruded alloy. A microstructure-based crystal plasticity model was developed to simulate the micromechanical deformation behavior of the alloys using representative volume elements based on realistic microstructures. A ductile fracture criterion based on the microscopically dissipated plastic energy on a slip system was adopted to predict the microscopic damage accumulation of the alloys during plastic deformation. The developed model could accurately predict the stress-strain behavior and evolution of the crystallographic textures in both the alloys. We reveal that the increased yield strength in the LPBFed alloy, compared to that in the extruded alloy, is attributed to the higher as-manufactured dislocation density and the cellular subgrain structure, resulting in a reduced elongation. The presence of annealing twins and favorable texture in the extruded alloy contributed to its excellent elongation, along with a higher hardening rate owing to twin-dislocation interactions during plastic deformation. Moreover, the grain morphology and defect state (e.g., dislocations and twins) in the initial state can significantly affect strain localization and damage accumulation in alloys.