Deformation Behavior Research Articles

Microscopic Characterization of Deformation Behavior during Kerogen Evolution: Effects of Maturity and Skeleton Moisture Content.

The CH4 storage and seepage capacity of shale kerogen are the main controlling factors of the natural gas production rate, and the porosity and permeability of kerogen are greatly affected by kerogen deformation. Therefore, the study of the deformation rule and CH4 adsorption characteristics of kerogen at different maturities and skeleton moisture contents has an important impact on the proper understanding of the development potential of shale gas reservoirs. In this paper, kerogen maturity (II-A, II-B, II-C, and II-D) and skeleton moisture content (0.0, 0.6, 1.2, 1.8, and 2.4 wt %) were considered. The deformation of kerogen, the adsorption of CH4 after deformation, and the quadratic deformation induced by CH4 were studied by using Grand Canonical Monte Carlo (GCMC) and molecular dynamics (MD). The results show that the kerogen volume strain increases with increasing skeleton moisture content, following the order II-A < II-B < II-C < II-D for the same moisture content. The density of the kerogen matrix decreases, and porosity increases with rising moisture content. The void fraction of immature kerogen decreases with increasing water content, while the opposite is true for postmature kerogen. The presence of skeleton moisture decreases the CH4 adsorption capacity of immature kerogen and increases the CH4 adsorption capacity of postmature kerogen. The chemical structure of immature kerogen is relatively soft, making its volume more affected by CH4 adsorption compared with postmature kerogen. In the same water environment, postmature kerogen has greater CH4 storage, diffusion, and seepage capacity compared to those of immature kerogen, suggesting that reservoirs with high organic matter maturity should be prioritized for development.

Mechanical properties and deformation behavior of a high entropy alloy with precipitate under cycle loading

Mechanical properties and deformation behavior of a high entropy alloy with precipitate under cycle loading

Flow Behavior and Microstructure of Hot‐Worked TiNbTaVW Refractory High‐Entropy Alloy

The high‐temperature deformation behavior of an equiatomic TiNbTaVW refractory high entropy alloy (RHEA) was studied at temperatures of 950, 1000, and 1050 °C and a strain rate of 10−3 s−1. The flow stress, high‐temperature strength, and softening mechanisms were analyzed and compared with the IN718 nickel‐based superalloy. The results indicate that the flow stress of both TiNbTaVW and IN718 is sensitive to deformation temperature, with high temperatures resulting in reduced flow stress. Globular grains and elongated grains were observed at 950 and 1000 °C for TiNbTaVW, signifying both dynamic recovery and dynamic globularization as the softening mechanisms. Globular grains were only observed at 1050 °C for TiNbTaVW, signifying dynamic globularization as the softening mechanism. The TiNbTaVW RHEA has a higher temperature strength of 910, 870, and 658 MPa compared to the IN718 alloy with 72, 87, and 61 MPa at 950–1000 °C/10−3 s−1. By demonstrating comparable or superior performance in specific aspects, RHEAs can be considered in the near future for potential applications traditionally dominated by nickel‐based superalloys.

Hot deformation behavior and physical-based constitutive modelling under plane-stress state for nickel-based superalloy sheets

Forming limit curves (FLC) at high temperatures under plane-stress states are beneficial for guiding the process parameter design of hot forming superalloy sheets. Constrained by the high deformation temperatures, the establishment of FLCs of superalloy sheets at high temperatures is extremely difficult. This paper conducts an experimental and modelling research to establish the physical-based model with the accurate prediction of hot flow behavior as well as micro grain sizes, using which, the forming limit curves can be predicted. First, the uniaxial tensile tests under different temperatures and strain rates and electron backscattered scattering detection (EBSD) observations of typical conditions were conducted to obtain the hot flow behavior and grain evolution. Second, the dome test at room temperature was performed, and the corresponding simulation was further carried out to obtain the forming limit at room temperature under plane-stress states. Using the above results, a plane-stress constitutive model for GH3128 superalloy was established enabling plane-stress test results under typical hot conditions to be accurately predicted. The prediction accuracies of hot uniaxial and biaxial stretching results are 94.2% and 95.4%, respectively.

A methodology for direct parameter identification for experimental results using machine learning — Real world application to the highly non-linear deformation behavior of FRP

In this work, we demonstrate how Machine learning (ML) techniques can be employed to externalize the knowledge and time intensive process of material parameter identification. This is done on the example of a recent data driven material model for the non-linear shear behavior of glass fiber reinforced polypropylene (GF/PP) (Gerritzen, 2022). A convolutional neural network (CNN) based model architecture is trained to predict material modeling parameters based on the input of stress–strain-curves. The optimal model architecture and training setup are determined by hyperparameter optimization (HPO). Solely virtual data, generated using the target material model, is used throughout the training and HPO. The final CNN is capable of calculating model parameter combinations from experimental stress–strain-curves which lead to excellent agreement between experimental and associated model curve.

The Hysteresis Behavior of Steel Beam–Column Joint with the Load Bearing-Energy Dissipation Connection for Converter Station Building

Prefabricated converter station building has been gradually applied in the field of power engineering construction due to the advantages of standardized design, high construction efficiency, and quality control. The beam–column joint is the essential constitutive part to ensure structural integrity and reliable force transmission for the prefabricated structure. In this paper, a novel load bearing-energy dissipation connection is proposed and applied to the beam–column joint to improve seismic performance and seismic resilience. Pseudo-static tests were conducted on the beam–column joint with the load bearing-energy dissipation connection, and the test results demonstrated that the tested beam–column joints developed with similar failure modes, and the damage was concentrated in the load bearing-energy dissipation connection while the beam and column remained elastic. The beam–column joint with the load bearing-energy dissipation connection had stable hysteresis behavior, with favorable bearing capacity and energy dissipation behavior. A shorter slip length and a larger bolt distance could lead to better stress development and enhance the bearing capacity, while the slip length barely affected the ductile behavior. Moreover, a finite element model was established and validated to extend the parametric study to provide a preliminary understanding of the mechanical mechanism of the proposed beam–column joint with the load bearing-energy dissipation connection. It was confirmed that the load–-deformation behavior was greatly affected by the slip length, but the slip length barely affected the initial stiffness. The width of the sliding steel fuse influenced the bearing capacity and the degradation behavior. A wider width could lead to a higher bearing capacity and improve the degradation behavior. Based on the analysis of the stress development and stress distribution corresponding to different feature points, it was concluded that the use of bearing-energy dissipation improved the stress development in the framing components and achieved damage concentration.

Behaviour of steel-fibre-reinforced geopolymer concrete-filled square steel tubular stub column under axial compression

Resource utilisation of industrial waste has become a crucial issue in construction aiming for sustainable development. Research on geopolymer concrete-filled square steel tubular (GCFST) structures is limited. Moreover, methods for calculating the bearing capacity of steel-fibre-reinforced GCFST (SFRGCFST) structures require further investigation. This study presents an experimental and analytical investigation of the axial compression performance of SFRGCFST stub columns. Twenty-four specimens were tested to assess the effect of steel tube thickness, steel fibre (SF) volume fraction, SF aspect ratio, and concrete strength grade on failure modes, load–deformation behaviour, load–strain response, ultimate resistance, and ductility of SFRGCFST columns. The results indicated that the failure modes of SFRGCFST columns are influenced by the coefficient index, which varies with the test parameters. When the coefficient index exceeded 0.88, the failure mode of the specimens transitioned from shearing failure to waist-drum-shaped failure. The average ultimate bearing capacity of the SFRGCFST columns increased by 35.13 % compared with that of the plain concrete-filled steel tubes (CFSTs). When the SF volume fraction reached 0.9 %, the ultimate bearing capacity of the SFRGCFST columns increased by 21.85 % compared with that of steel-fibre-reinforced concrete-filled steel tube (SFRCFST) columns. The incorporation of SF significantly improved the deformation capacity and ductility of the SFRGCFST columns and moderated the slope of the post-peak load–displacement and load–strain curves, slowing the descent of the curve. Utilising the multi-axial strength criterion and mechanical equilibrium equation for square CFSTs, a formula for calculating the ultimate bearing capacity of SFRGCFST stub columns was developed. This formula enables accurate prediction of the axial compressive load capacity of SFRGCFST stub columns and provides a basis for revising relevant standards.

Mechanical properties and deformation behavior of Zr-based bulk metallic glass composites reinforced with tungsten fibers or tungsten powders

Mechanical properties and deformation behavior of Zr-based bulk metallic glass composites reinforced with tungsten fibers or tungsten powders

Effect of deformation temperature on the dynamic recrystallization mechanism and dynamic precipitation behavior of Mg-Gd-Nd-Zr alloy

The deformation temperature is an important factor influencing the thermal deformation behavior of alloys. In this paper, thermal compression tests of Mg-Gd-Nd-Zr alloy were carried out at 350 ∼ 500 °C using the Gleeble-3800 thermal simulator, and the dynamic recrystallization (DRX) mechanism and microstructure evolution of the alloy were investigated by electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The results show that the basal slip a and pyramidal slip a+c were consistently high activity at the test temperatures. As the temperature increased, the pyramidal slip a was gradually activated. At 350 °C, monolayer necklace-like dynamic recrystallized (DRXed) grains were formed around the initial grains via discontinuous dynamic recrystallization (DDRX). At 400 ∼ 450 °C, the monolayer DRXed grains expanded into the initial grain via continuous dynamic recrystallization (CDRX) to form multilayer necklace-like DRXed grains. However, at 500 °C, no necklace-like structure was formed around the initial grains. The initial grains were split into subgrains by low angle grain boundaries (LAGBs), which continuously absorbed dislocations and rotated for DRX. In addition, at 350 ∼ 400 °C, the alloy produced significant precipitation bands (mainly β phase). Above 450 °C, the dynamic precipitation was significantly attenuated. Precipitates greater than 200 nm could well impede dislocation movement and induce DRX nucleation. Nevertheless, the precipitates at the grain boundaries of the DRXed grains in turn pined the grain boundaries, refining the DRXed grains.

Mechanical Properties and Martensitic Transformation Behavior of 316LN Stainless Steel Under Cryogenic Deformation

Digital image correlation (DIC) technology can capture strain anomalies and predict crack initiation providing early warning of material failure. Herein, DIC technique is used to calculate the full‐field strain by analyzing the grayscale patterns of speckle images during the tensile process. This allowed for an analysis of the microstructure evolution of the 316LN austenitic stainless steel (SS) at cryogenic temperatures. Deformation behavior of the 316LN SS at cryogenic temperatures is further analyzed using electron backscatter diffraction technology and transmission electron microscopy. Based on the strain field obtained by the DIC technique, a comprehensive analysis of the martensite volume fraction at different strains can be conducted. The results show that the strain localization under cryogenic deformation is related to martensitic transformation, while the random distribution of slip bands aligns with local strain peak values. Notably, fracture under cryogenic deformation occurs in regions where the strain field reaches its peak, rather than at locations with the maximum strain value.

Continuous Dynamic Recrystallization and Deformation Behavior of an AA1050 Aluminum Alloy during High-Temperature Compression

Continuous dynamic recrystallization (CDRX) forms a new recrystallized microstructure through the progressive increase in low-angle boundary misorientations (LAGBs) during the hot forming of metallic materials with high stacking fault energy (SFE), such as aluminum alloys. The present work investigates the effect of deformation parameters on the evolution of the dynamic recrystallization microstructures of an AA1050 aluminum alloy during compression at elevated temperatures. The alloy microstructure is investigated at deformation temperatures and strain rates in the range of 300 °C to 500 °C and 0.001 to 0.8 s−1. A well-defined substructure and subsequent DRX grains provide indication that recrystallization can proceed with continued strain under high-temperature compression. At a strain rate of 0.1 s−1, the DRX fraction is observed to be 0.25 at a temperature of 300 °C. This fraction increases to 0.32 as the temperature rises to 400 °C. The recrystallization mechanism is identified by analyzing the flow stress, the evolution of the subgrain misorientation angle, and the distribution of recrystallized grains. The observations of discontinuous dynamic recrystallization (DDRX) and CDRX under various deformation parameters are discussed. Moreover, the main substructure evolution laws observed from the high-temperature compression of an AA1050 Al alloy are summarized.

Superelastic electromechanical behaviors in ferroelectric PbTiO[formula omitted] ceramics under coupled mechanical-electric fields: Higher-order piezoelectric constitutive equations from first-principles

With the recent discovery of superelastic behaviors of ferroelectric (piezoelectric) ceramics, understanding their non-linear mechanical and electromechanical responses under high stress and electric field conditions is crucial for engineering and designing advanced piezoelectric devices, such as ultrasmall actuator systems. In this study, we carry out first-principles finite electric field calculations to clarify the mechanical and electromechanical properties under the electric field for typical ferroelectric ceramics of PbTiO3. Superelastic-like non-linear deformation behavior is enhanced or suppressed depending on the electric field direction, suggesting the possible design of superelasticity. We clarified that positive and negative electric fields to spontaneous polarization promote and inhibit deformation due to strain loading, thereby providing tunable superelasticity. We also investigate the mechanical loading and electric field dependence of the piezoelectric coefficient of PbTiO3. The tunable piezoelectric response can be provided with a coupling of mechanical loading and electric field. Finally, we present higher-order piezoelectric constitutive equations applicable for superelastic-like non-linear deformations under an electric field. The present results will open promising paradigms for functional piezoelectric devices, and the proposed piezoelectric constitutive equations broaden the design scope through finite element method analysis.

Role of Prior Cyclic Oxidation on Tensile Deformation Behaviour of IN 713 C Alloy

Role of Prior Cyclic Oxidation on Tensile Deformation Behaviour of IN 713 C Alloy

In-situ neutron diffraction study of the strengthening mechanism and deformation behavior of cellular structure in high-entropy alloys by additive manufacturing

Additively manufacturing alloys by a selective laser melting (SLM) usually generates large temperature gradients and rapidly cooling, which enables a refined microstructure, an elemental segregation and high-density dislocations network to achieve an excellent strength-ductility synergy. In this study, the SLM fabricates FeCoNiAlTi high-entropy alloys (HEAs) with a cellular structure composed of high-density dislocations network and elemental segregation, which results in a noteworthy combination of a yield strength and a significant uniform plastic elongation. Strengthening mechanism and deformation behavior of SLM-prepared FeCoNiAlTi HEAs are investigated by a transmission electron microscopy in combination with an in-situ neutron diffraction technique. The results demonstrate that the high strength is mainly derived from cellular structure strengthening, which accounted for over 64 % of the yield strength. The cellular structure's capability to alleviate severe stress concentrations can facilitate deformation homogenization, and break a strength-ductility trade-off. This study provides essential insights into the underlying mechanisms governing the strength and ductility of additively manufactured HEAs.

A model for capturing the rate-dependent mechanical behaviour of liquid crystal elastomers

A modelling framework is adopted and adapted here to model the rate-dependent deformation behaviour of liquid crystal elastomers (LCEs). On using an isotropic hyperelastic strain energy function WI1,I2 of binomial form, previously employed for capturing the (quasi-static) deformation of polydomain LCEs, an extension is presented for application to the rate-dependent behaviour of LCEs by incorporating the deformation rate into the model parameters. That is, the model parameters of the core hyperelastic strain energy function W are considered to evolve with, i.e., be a function of, the deformation rate. A specific measure of deformation rate ɛ̇ is utilised, and a particular functional dependency of the hyperelastic model parameters on ɛ̇, of a skewed exponential form, is devised and presented. The ensuing rate-dependent model Wr is then applied to a range of extant experimental datasets, encompassing various LCE specimens and across different deformation rates, under uniaxial loading and including both tension and compression deformations. The model is shown to capture and predict the data favourably. Given the simplic of devising and implementing the presented modelling framework, the flexibility it provides for incorporating different choices of strain energy W function as well as the functional form(s) of the dependency of the model parameters on the deformation rate, and the accuracy of the modelling results, the application of this modelling approach to capturing the rate-dependent deformation behaviour of LCEs is hereby presented.

Unraveling the plastic deformation, recrystallization, and oxidation behavior of Waspaloy during thermal fatigue crack propagation

Thermal fatigue is one typical failure mode for engine components involving cyclic thermal stresses/strains. However, the microstructure evolution and its microscopic interaction with thermal fatigue cracking in Ni-based superalloys featuring intragranular γ′ and intergranular carbides have yet to be clarified. In this study, cyclic temperature variations ranging from 25 °C to 700 °C were conducted on Waspaloy to unravel the synergistic damage mechanisms including stress distribution, plastic deformation, recrystallization, oxidation, and crack propagation. The thermal fatigue cracks are found to predominantly propagate along grain boundaries with a gradually descending rate from 3.5 μm/cycle to 1.5 μm/cycle. Compared with the macroscopic thermal stress up to ∼800 MPa, the local thermal stress induced by different sizes of M23C6 carbides marginally affects the crack propagation. Intensive slip bands and sparse deformation twins in the deformed matrix are observed, indicating the plastic deformation is mainly achieved by dislocation slipping and supplemented by twinning. Trans-granular cracks parallel to {111} planes form occasionally when the propagation directions of intergranular cracks are almost parallel to the {111} slip bands. Besides, dislocations promote the oxidation damage of the crack surface through pipe diffusion of solutes, and the γ′-precipitate free zones (PFZs) and recrystallized areas are produced accordingly. The quantitation analysis of the PFZ thickness provides a reference for predicting crack initiation time during thermal fatigue.

Machine learning-accelerated inverse design of programmable bi-functional metamaterials

Bi-functional metamaterials with programmable coefficients of thermal expansion (CTEs) and Poisson’s ratios (PRs) have garnered significant attention among researchers due to the ability to manifest desired deformations under thermal and mechanical loads. Nevertheless, a current challenge lies in efficiently achieving the inverse design of these metamaterials to meet diverse application requirements. This paper presents a machine learning (ML) model that can establish a logical mapping relationship between geometric/material parameters and mechanical properties, and it is applied to the inverse design of bi-functional metamaterials with desired CTEs and PRs. Furthermore, the inverse design capability of the ML model was validated by the finite element analysis and experimental test. The results demonstrate that the geometric models obtained from the inverse prediction can effectively exhibit the desired deformation behavior under thermal and mechanical loads. And the ML model proves to be a valuable tool, offering effective guidance for the design of bi-functional metamaterials with specific CTEs and PRs.

Stochastic nature of incipient plasticity in a body-centered cubic medium-entropy alloy

The stochastic nature of the small-scale incipient plasticity (i.e., “pop-in” behavior manifested as a sudden displacement excursion in the load-displacement curves) in a single grain of the body-centered cubic NbTiZr medium-entropy alloy is explored through a series of nanoindentation tests with three spherical tips having different radii (1.8, 3.4, and 8.2 μm). The maximum shear stress underneath the indenter shows distinct distributions depending on the tip radius, wherein both a narrow high-stress regime and a broad low-stress regime are observed. By recourse to deconvolution of the data and detailed statistical analysis, the two regimes were found to be dominated by homogeneous and heterogeneous yielding mechanisms, respectively. Upon hydrogen charging, the tip radius dependence is sustained, but the fraction of heterogeneous yielding is enhanced, which is due to the hydrogen's effect in assisting defect formation. The suggested scenarios for how the mechanisms are affected by the stressed volume (or tip radius) and hydrogen-induced structural changes were confirmed by direct observations of the deformation behavior underneath the indenter with cross-sectional transmission electron microscopy made on post-pop-in samples.

Atomistic insight of deformation mechanisms and mechanical characteristics of nano-scale silver (100) using nanoindentation

This work aims to utilize the widely adopted nanoindentation technique to explore the deformation behavior and mechanical characteristics of nanocrystalline silver (Ag) materials. Molecular Dynamics simulations were conducted to understand the material behavior at the nanometer scale. In this simulation, the effect of indentation velocity and indentation depth on defect formation and hardness during nanoindentation of Ag specimens was analyzed and discussed in detail. The results show that the deformation behavior of the Ag specimen was affected by different indentation velocities. These phenomena were confirmed by analyzing the load-displacement curve, which indicates elastic deformation by the appearance of a linear load-displacement at low indentation velocities. In contrast, plastic deformation was found by the presence of intensified serration in the load-displacement relationship at higher indentation velocities. In these cases, the hardness showed little variation when the indenter velocity was increased from 5 m/s to 10 m/s, whereas a significant increase in hardness was observed when the indentation velocity was further increased to 20 m/s. Importantly, the progression of load-displacement curves during nanoindentation demonstrates the occurrence of minor and major load drops, corresponding to an increase in indentation depth from 0.5 nm to 2 nm respectively. These findings were elucidated through dislocation extraction analysis (DXA), which revealed that a minor load drop at low indentation depths is attributed to the nucleation of an amorphous structure, while a major load drop at higher indentation depths is associated with the expansion of dislocation nucleation. Consequently, the hardness increased significantly as the indentation depth increased. This research, provides insight into atomistic investigation and offers guidelines for designing materials with excellent mechanical properties using nanoindentation.

Hot deformation and constitutive modeling of a Ti-Al-Sn-Zr-Mo-Cr-Nb alloy

Titanium alloys are the ideal structural materials for automotive and aerospace industries, and hot deformation is widely used to modify the microstructure of the alloy. In this work, a Ti-Al-Sn-Zr-Mo-Cr-Nb alloy was hot deformed at various strain rates and temperatures. The deformation behavior, microstructure, processing maps, and constitutive modeling are investigated. The results show that the hot deformation behavior of the studied alloy is sensitive to the processing parameters, the revised Johnson-Cook model with an average relative error of 1.463 %, and a correlation coefficient of 0.991 can accurately describe the hot deformation behavior of the alloy. Based on the established processing maps, the safe processing areas are 1133–1213 K, 0.004–0.1 s−1 and 1093–1213 K, 0.001–0.004 s−1. With the increased deformation temperature, both the fraction and size of the equiaxed α and lamellar α phases are gradually decreased, and the spheroidization degree of the lamellar α phase gradually decreases too. The strain rates have different influences on the evolution of α and β phases. With the increased strain rates, the fraction of recrystallized and deformed β phase is remarkably decreased, the fraction of sub-structured microstructures of β phase is obviously increased, while the fraction of deformed structures of the α phase is less affected.