Plastic Phase Research Articles

A comprehensive molecular dynamics simulation of plastic and liquid succinonitrile: Structural, dynamic, and dielectric properties.

Molecular dynamics simulations at constant temperature and pressure were carried out to investigate the structural, dynamical, and dielectric properties of succinonitrile in its plastic and liquid phases at several thermodynamic states. A six-site united atom model was employed with a force field incorporating an intramolecular torsional term that accurately describes gauche and trans conformers. Analysis of the radial distribution function showed that succinonitrile adopts a body-centered cubic arrangement below its melting point, transitioning to a less ordered state in the liquid phase. In addition, examination of alignments between methylene bonds and the diagonals of the simulating cubic box revealed pronounced directional preferences in the plastic phase. The study of conformational states suggested that succinonitrile molecules predominantly adopt gauche conformations, which exhibit longer lifetimes than trans conformers. Spectral density analysis highlighted distinct peaks for different molecular sites, revealing significant differences between gauche and trans conformers. The correlation functions of bending and torsional angles, as well as vectors joining different atoms, illustrated a sensitivity to internal motions, which were notably faster for trans conformers. Differences in decay rates between trans and gauche conformers underscored the influence of gauche-trans transitions. The static dielectric constant, which has been derived from the total dipole moment, was primarily influenced by the contribution of the gauche conformers. In addition, the distance-dependent Kirkwood factor was computed, revealing antiparallel alignment at short distances. Finally, the dielectric relaxation time and the static dielectric constant values were compared with experimental data.

Assessing the effectiveness of bio-based oil in rejuvenating aged asphalt: a comprehensive physical, rheological, chemical, and mechanical examination

The utilization of reclaimed asphalt pavement (RAP) in flexible pavement construction and rehabilitation has gained significant traction, driven by the need to conserve limited natural resources. This study explores the effectiveness of bio-based oils derived from harvested crops as rejuvenators in asphalt mixtures containing 50% RAP. Comprehensive assessments were conducted, including penetration, softening point, viscosity and ductility tests, to determine the optimal rejuvenator dosage. Additionally, evaluations of rolling thin film oven (RTFO) aging, retained penetration and ductility, equivalent softening and breaking points, plasticity temperature range, stiffness modulus, complex modulus, and phase angle were performed. Fourier-transform infrared (FTIR) spectroscopy, Marshall immersion, and moisture susceptibility tests further validated the rejuvenator's efficacy in improving asphalt properties. The incorporation of 1.8% bio-oil significantly reduced the viscosity of the mixtures, enhancing workability. The rejuvenator effectively compensated for the loss of light components in aged binders, restoring the maximum and minimum temperature performance to levels comparable to virgin asphalt (VA). Mechanical testing revealed that bio-oil mitigated the aging effects of RAP asphalt, and the rejuvenated mixtures showed considerable improvements over both VA and non-rejuvenated RAP mixtures, where the rejuvenated specimens achieved 90.8 and 89.4% of retained strength index (RSI) values for 24- and 48-h immersion periods, respectively comparing with 88.9 and 86% post-immersion of VA for similar durations. These findings underscore the potential of bio-oil as a sustainable and eco-friendly solution for rejuvenating aged asphalts, paving the way for more sustainable asphalt production practices.

Plastic evolution and phase transition mechanisms in γ-TiAl nano polycrystal by a molecular dynamics simulation

γ-TiAl based alloys are widely regarded as one important high-temperature structural material, however the deformation behaviors are still not clearly clarified. The microscopic plastic deformation and phase transition of γ-TiAl nano polycrystals under compression are investigated by molecular dynamics simulations. The results show that the initial plasticity is dominated by slip of partial dislocations whose continuous formation and secondary slip on the same slip plane result in the generation and disappearance of intrinsic stacking faults (ISFs). At the strain of about 0.2, a continuous structure transformation of “ISF → ESF → TB” is observed, during which the interaction between different ISFs causes the atomic misalignment corresponding to the change in atomic stacking order near ISF. As the compressive strain exceeds 0.2, the FCC-to-BCC phase transition occurs within polycrystals due to the high Mises stress, the high stress level within grains facilitates the expansion of BCC phase from initial FCC phase, and the newly formed BCC phase maintains the atomic-arrangement orderliness of original phase. The interface between FCC and BCC phases obeys the low-energy Kurdjumov-Sachs orientation relationship. This work is helpful for better understanding the atomic-scale deformation behaviors and provides a theoretical guidance for designing high-performance alloy materials.

Dynamic Behavior and Energy Absorption of Typical Porous Materials under Impacts.

Porous materials are known for their excellent energy absorption capability and, thus, are widely used in anti-impact applications. However, how the pore shape and size impact the failure mechanism and overall behavior of the porous materials under impact loading is still unclear or limitedly touched. Instead of using homogeneous solids for the porous material model, pores with various shapes and sizes were implanted in a solid to establish the porous materials that have true porous structures, which permits exploration of the local failure mechanism. The results revealed that differently shaped holes have two different dominant deformation modes. And due to their different local stress distributions, they enter the plastic phase earlier and, thus, have higher specific energy absorption. Meanwhile, the model changes from hardening to a quasi-zero stiffness model as the hole size increases. The application of this work can be extended into the field of impact resistance.

Designing Isocyanate‐Containing Elastomeric Electrolytes for Antioxidative Interphases in 4.7 V Solid‐State Lithium Metal Batteries

AbstractTo facilitate the use of solid polymer electrolytes (SPEs) with high‐nickel (Ni) cathodes in high‐voltage lithium (Li) metal batteries (LMBs), it is crucial to address the challenges of low oxidative stability and the formation of vulnerable interphases. In this study, isocyanate groups (−N═C═O) are incorporated to develop an SPE with a bi‐continuous structure, consisting of elastomeric and plastic crystal phases. This rationally designed SPE exhibits high ionic conductivity (0.9 × 10−3 S cm−1 at 25 °C), excellent elasticity (elongation at break of 330%), and enhanced oxidative stability (over 4.8 V vs. Li/Li⁺). A full cell, incorporating this SPE with a thin Li foil of 40 µm, and a high‐Ni LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode operating at 4.7 V vs. Li/Li⁺, demonstrates excellent cyclability, retaining 70% of its initial capacity after 200 cycles under a high C‐rate of 1C at 25 °C. The extended cycling of isocyanate‐containing SPE at 4.7 V vs. Li/Li⁺ is attributed to robust and compact inorganic‐rich interphases enabled by antioxidative −N−C═O components, as well as uniform Li deposition attributed to the bi‐continuous structured SPE. This study suggests that the isocyanate‐containing SPE system is a promising candidate for high‐voltage solid‐state LMBs by constructing stable interphases.

PECULIARITIES OF CRACK FORMATION IN HETEROPHASE INCLUSIONS OF THE “EUTECTICS OF INCLUSION − MATRIX” TYPE

Purpose. The goal of the work was to study the peculiarities of crack nucleation in heterophase inclusions of the “eutectic inclusion − matrix” type during steel deformation. Methods. The research was carried out after deformation of samples from steels 08Yu, 12GS, 08kp, 09G2S, NB-57, 08GSYUTF in the temperature range of 20…1 200 °C with the speed of movement of grips 1 680 mm/min. The research methods were used − petrography, micro-X-ray spectral analysis (Cameca MS-4, Nanolab-7), optical microscopy (Neophot-21). Results. It is established that the variety of phases that make up heterophase inclusions of the type “eutectic of inclusion − matrix” leads to their different behavior under conditions of plastic deformation. It is shown that the nucleation of brittle or viscous microcracks occurs along the internal interfacial boundaries between the metal matrix and the second phase of the eutectic. It is determined that the nature of cracks is determined by the level of plasticity of the inclusion phases and the deformation temperature. It is shown that the critical degrees of deformation of the samples, at the achievement of which there were noticeable microcracks along the internal interfacial boundaries, depend on the temperature and nature of the phases of inclusions “eutectic of inclusion − matrix”. It is established that the values of critical degrees of deformation determine the level of cohesive strength of the internal interfacial boundaries in heterophase inclusions “inclusion − matrix eutectic”. Scientific novelty. Peculiarities of microcracking nucleation in heterophase inclusions of the “inclusion − matrix eutectic” type have been established. It is shown that the nature of microcracks formed along the interfacial boundaries depends on the temperature, level of plasticity and conditions of combination of brittle and plastic phases in inclusions of the “eutectic of inclusion − matrix” type, as well as on the deformation temperature. It is shown that the critical degrees of deformation of steels, when microcracks occurred along the inner interfacial boundaries, determine the cohesive strength of these boundaries and depend on the temperature and nature of the phases of inclusions such as “inclusion − matrix eutectic”. Practical significance. The use of the results obtained will make it possible to develop technologies for producing steels with regulated types of heterophase nonmetallic inclusions, which will significantly increase their technological and operational characteristics, as well as prevent the formation of various kinds of defects during the processing of steels by pressure and the operation of products.

Mechanical properties and JC constitutive modification of tungsten alloys under high strain rates and high/low temperatures

The original Johnson-Cook model's poor prediction of W90 alloy stress at high strain rate and high and low temperatures restricts research and utilization of this alloy. This study used a Split Hopkinson Pressure Bar (SHPB) device to conduct dynamic compression tests on W90 alloy over a temperature range of [-90℃,700℃] and analyze its mechanical behavior. We examined the material's different plastic phase characteristics at high and low temperatures and conducted microstructure research on impact test specimens. Then, we analyzed the stress-strain data from SHPB experiments and quasi-static compression tests on the classical Johnson-Cook model. The original Johnson-Cook model was calibrated using the stress-strain data from SHPB and quasi-static compression tests, and the modified Johnson-Cook model was established and verified. The results show that: low temperature significantly strengthens the material's stress, while increasing temperature thermal softening reduces stress; increasing strain rate increases the strain generated by the workpiece, causing faster strain hardening and thermal softening effects, resulting in higher and more stable stress; low temperature makes thicker grain boundaries, increasing plastic stress, and increasing strain rate also increases plastic stress, as well as making the material's grain boundaries thicker. The increase of strain rate makes the grain more dense, which will also show up in the increase of stress on the macroscopic level; the modified Johnson-Cook model in this paper has high agreement with experimental data, with a mean value of MAPE of only 1.85 %,which is 90.20 % lower than the traditional model, and the average value of the RMSE is 85.56 % lower than the traditional model. The modified model significantly outperforms the traditional model in predicting stress and better describes stress changes in W90 at different temperatures.

Assessing Aquatic Baseline Toxicity of Plastic-Associated Chemicals: Development and Validation of the Target Plastic Model.

We developed a Target Plastic Model (TPM) to estimate the critical plastic burden of organic toxicants in five types of plastics, namely, polydimethylsiloxane (PDMS), polyoxymethylene (POM), polyacrylate (PA), low-density polyethylene (LDPE), and polyurethane ester (PU), following the Target Lipid Model (TLM) framework. By substituting the lipid-water partition coefficient in the TLM with plastic-water partition coefficients to create TPM, we demonstrated that the biomimetic nature of these plastic phases allows for the calculation of critical plastic burdens of toxicants, similar to the notion of critical lipid burdens in TLM. Following this approach, the critical plastic burdens of baseline (n = 115), less-inert (n = 73), and reactive (n = 75) toxicants ranged from 0.17 to 51.33, 0.04 to 26.62, and 1.00 × 10-6 to 6.78 × 10-4 mmol/kg of plastic, respectively. Our study showed that PDMS, PA, POM, PE, and PU are similar to biomembranes in mimicking the passive exchange of chemicals with the water phase. Using the TPM, median lethal concentration (LC50) values for fish exposed to baseline toxicants were predicted, and the results agreed with experimental values, with RMSE ranging from 0.311 to 0.538 log unit. Similarly, for the same data set of baseline toxicants, other widely used models, including the TLM (RMSE: 0.32-0.34), ECOSAR (RMSE: 0.35), and the Abraham Solvation Model (ASM; RMSE: 0.31), demonstrated comparable agreement between experimental and predicted values. For less inert chemicals, predictions were within a factor of 5 of experimental values. Comparatively, ASM and ECOSAR showed predictions within a factor of 2 and 3, respectively. The TLM based on phospholipid had predictions within a factor of 3 and octanol within a factor of 4, indicating that the TPM's performance for less inert chemicals is comparable to these established models. Unlike these methods, the TPM requires only the knowledge of plastic bound concentration for a given plastic phase to calculate baseline toxic units, bypassing the need for extensive LC50 and plastic-water partition coefficient data, which are often limited for emerging chemicals. Taken together, the TPM can provide valuable insights into the toxicities of chemicals associated with environmental plastic phases, assisting in selecting the best polymeric phase for passive sampling and designing better passive dosing techniques for toxicity experiments.

Torsional properties of spiral carbon nanocones

Carbon nanostructure plays a unique role in advanced nanodevices. This work investigated the torsional properties and underlying mechanisms of spiral carbon nanocones (SCN) via atomistic simulations. The SCN exhibits four deformation stages, including linear elastic, nonlinear elastic, plastic and failure. The elastic phase is characterized by compressive stress at the inner covalent bond and tensile stress at the outer edge. The plastic transition is initiated at the innermost region, accompanied by in-plane folding. The interlayer interactions of the SCN facilitate its capacity to elicit an axial response during torsion. The resulting axial forces are governed by the layer number, cone angle, and the dimensions of both inner and outer radii. Outer radius exerts the most significant influence on SCN via the interlayer contact area. Furthermore, the inner radius and cone angle are intrinsically linked to the structural stiffness of the inner bore, which affects the axial mechanical response of the SCN during the nonlinear elastic and plastic phases. The Pearson correlation coefficient analysis has validated that these two parameters are the most crucial for SCN torsional performance. This work elucidates the prospective utility of SCN as a novel twist-to-push actuator for advanced nanodevices.

The influence of menstrual phase on synaptic plasticity induced via intermittent theta-burst stimulation

BackgroundOvarian hormones influence the propensity for short-term plasticity induced by repetitive transcranial magnetic stimulation (rTMS). Estradiol appears to enhance the propensity for neural plasticity. It is currently unknown how progesterone influences short-term plasticity induced by rTMS. ObjectiveThe present research investigates whether the luteal versus follicular phase of the menstrual cycle influence short-term plasticity induced by intermittent theta-burst stimulation (iTBS). We tested the hypothesis that iTBS would increase motor evoked potentials (MEPs) during the follicular phase. Further, we explored the effects of the luteal phase on iTBS-induced neural plasticity. MethodTwenty-nine adult females participated in a placebo-controlled study that delivered real and sham iTBS to the left primary motor cortex in separate sessions corresponding to the follicular phase (real iTBS), luteal phase (real iTBS), and a randomly selected day (sham iTBS). Outcomes included corticospinal excitability as measured by the amplitude of MEPs and short-interval intracortical inhibition (SICI) recorded from the right first dorsal interosseous muscle before and following iTBS (612 pulses). ResultsMEP amplitude was increased following real iTBS during the follicular condition. No significant changes in MEP amplitude were observed during the luteal or sham visits. SICI was unchanged by iTBS irrespective of menstrual phase. ConclusionThese findings suggest women experience a variable propensity for iTBS-induced short-term plasticity across the menstrual cycle. This information is important for designing studies aiming to induce plasticity via rTMS in women.

Polar groups promoting in-situ polymerization phase separation for solid electrolytes enabling solid-state lithium batteries

Plastic-crystal-embedded elastomer electrolytes (PCEEs), produced through polymerization-induced phase separation (PIPS), are gaining popularity as solid polymer electrolytes (SPEs). However, it remains to be investigated whether all monomer molecules can achieve polymerization-induced phase separation and the corresponding differences in lithium metal battery performance. Herein, we prepared PCEEs with different functional groups (OH, CN, F) through in situ polymerization. Research findings show that PCEE containing – CN or – F achieves the separation of the plastic crystalline phase and succinonitrile (SN) phase, whereas PCEE containing OH cannot due to hydrogen bonding with the SN phase. Notably, the PCEE synthesized with the F monomer (FBA-PCEE) exhibited exceptional interfacial stability with lithium metal anodes and lithium iron phosphate (LFP) cathodes, due to its unique coordination mechanism with lithium ions. The FBA-PCEE demonstrated a high ionic conductivity (2.02 × 10−3 S cm−1) and lithium-ion migration number (tLi+ = 0.75). Moreover, lithium symmetric cells incorporating FBA-PCEE demonstrated stable cycling performance for more than 1000 h at a current density of 0.1 mA cm−2, resulting in the development of a solid electrolyte interphase (SEI) rich in LiF, Li3N, and Li2CO3 over time. Additionally, incorporating FBA-PCEE facilitated the stable cycling of LPF over 1000 cycles at 0.5C, maintaining a capacity retention of 77.38 % after 500 cycles. When coupled with high-voltage Nickel Cobalt Manganese Oxide (NCM-622) cathodes and lithium metal anodes, a discharge capacity of 119.70 mAh g−1 at 0.1C was sustained after 100 cycles, exhibiting a capacity retention of 78.95 %. This study elucidates the critical role of monomer design in achieving PIPS, offering valuable insights into developing high-performance polymer composite electrolytes for advanced lithium metal batteries.

Temporal dynamics of white and gray matter plasticity during motor skill acquisition: a comparative diffusion tensor imaging and multiparametric mapping analysis.

Learning new motor skills relies on neural plasticity within motor and limbic systems. This study uniquely combined diffusion tensor imaging and multiparametric mapping MRI to detail these neuroplasticity processes. We recruited 18 healthy male participants who underwent 960min of training on a computer-based motion game, while 14 were scanned without training. Diffusion tensor imaging, which quantifies tissue microstructure by measuring the capacity for, and directionality of, water diffusion, revealed mostly linear changes in white matter across the corticospinal-cerebellar-thalamo-hippocampal circuit. These changes related to performance and reflected different responses to upper- and lower-limb training in brain areas with known somatotopic representations. Conversely, quantitative MRI metrics, sensitive to myelination and iron content, demonstrated mostly quadratic changes in gray matter related to performance and reflecting somatotopic representations within the same brain areas. Furthermore, while myelin and iron-sensitive multiparametric mapping MRI was able to describe time lags between different cortical brain systems, diffusion tensor imaging detected time lags within the white matter of the motor systems. These findings suggest that motor skill learning involves distinct phases of white and gray matter plasticity across the sensorimotor network, with the unique combination of diffusion tensor imaging and multiparametric mapping MRI providing complementary insights into the underlying neuroplastic responses.

Explanation for the linear solid/liquid interface recoil observed during directional solidification of a TRIS-NPG alloy under microgravity conditions

During the initial transient stage of a directional alloy solidification experiment, a solid/liquid interface asymptotically recoils from a position that is given by the liquidus temperature to a position given by the solidus temperature. Recent observations onboard the International Space Station revealed that for the organic compound TRIS-NPG, the recoil appears much larger and varies linearly with time. In addition, such conditions were found that the high-temperature non-facetted plastic phase gradually dissolves and, although it seems contradictory to the interpretation of the thermodynamics of the binary system, the low-temperature facetted phase comes into direct contact with the liquid. Both unexpected observations can be understood by assuming that the TRIS-NPG alloy gradually decomposes at the hot side of the furnace. The decomposition products are then transported to the solid/liquid interface by diffusion and the sample motion. The presence of decomposition products changes the binary alloy into a TRIS-NPG-X ternary alloy, with a liquidus temperature that decreases with an increasing amount of decomposed substances.

Seismic Response and Collapse Analysis of a Transmission Tower Structure: Assessing the Impact of the Damage Accumulation Effect

This paper delves into the impact of the damage accumulation effect, which leads to the degradation of material strength and stiffness, on the seismic resistance of transmission towers. Building upon the elastic–plastic finite element theory, a mixed hardening constitutive model is derived for circular steel tubes, standard elements in transmission towers, incorporating the damage accumulation effect. A user material subroutine, UMAT, is created within the LS–DYNA framework. The program’s validity and reliability are established through axial constant–amplitude loading tests on single steel tubes. The subroutine is employed to conduct the incremental dynamic analysis (IDA) of an individual transmission tower and to contrast it with the structure utilizing the Plastic Kinematic material model, assessing the discrepancies in tower top displacements and segment damage indices (SDIs) at both macroscopic and microscopic scales. The results shows that the Plastic Kinematic model inflates the seismic performance of the transmission tower. When considering the damage accumulation effect in structural failure, the damage index of the members increases, leading to a reduction in both the structural strength and stiffness. The dynamic response in the plastic phase becomes more pronounced, and the onset of structural failure is accelerated. Consequently, structural analysis under seismic conditions should account for the damage accumulation process. Through the delineation of member and segment damage, the extent of damage to transmission tower segments can be quantitatively assessed. Subsequently, the ultimate load–bearing capacity and the most vulnerable location of the transmission tower can be ascertained. Finally, this paper provides a detailed analysis of the transmission tower collapse process under seismic action and summarizes the mechanism of collapse for the structure.

An approach for identifying the deformation-induced strain from tensile tests and x-ray diffraction measurements

ABSTRACT Non-uniform plastic deformation and phase transformation introduce residual stress (RS) in a material. The present study focuses on the influence of tensile strain on RS development in 304L austenitic stainless steel, wherein strain-induced martensite (SIM) transformation influences deformation behaviour. Room temperature tensile tests were interrupted at various tensile strains between the material yield and ultimate tensile strength at 5.21 × 10−4 and 1.3 × 10−2 s−1 strain rates. Microstructural characterisation of as-received and deformed samples by electron backscatter diffraction provides evidence of SIM formation and shear bands. Analysis of tensile flow and work hardening behaviour is discussed in correlation to the microstructural and dislocation density variations. In addition, RS in the austenite and martensite phases was measured using the x-ray diffraction method, and the RS balance that occurs between the longitudinal and transverse components and the two phases after tensile deformation is presented. It is shown that a combined analysis of RS and x-ray diffraction peak width could be utilised to find the deformation level in tensile fractured, press brake bent, and roll bent samples.

Biodegradable Ferroelectric Molecular Plastic Crystal HOCH2(CF2)7CH2OH Structurally Inspired by Polyvinylidene Fluoride.

Ferroelectric materials, traditionally comprising inorganic ceramics and polymers, are commonly used in medical implantable devices. However, their nondegradable nature often necessitates secondary surgeries for removal. In contrast, ferroelectric molecular crystals have the advantages of easy solution processing, lightweight, and good biocompatibility, which are promising candidates for transient (short-term) implantable devices. Despite these benefits, the discovered biodegradable ferroelectric materials remain limited due to the absence of efficient design strategies. Here, inspired by the polar structure of polyvinylidene fluoride (PVDF), a ferroelectric molecular crystal 1H,1H,9H,9H-perfluoro-1,9-nonanediol (PFND), which undergoes a cubic-to-monoclinic ferroelectric plastic phase transition at 339 K, is discovered. This transition is facilitated by a 2D hydrogen bond network formed through O-H···O interactions among the oriented PFND molecules, which is crucial for the manifestation of ferroelectric properties. In this sense, by reducing the number of -CF2- groups from ≈5000 in PVDF to seven in PFND, it is demonstrated that this ferroelectric compound only needs simple solution processing while maintaining excellent biosafety, biocompatibility, and biodegradability. This work illuminates the path toward the development of new biodegradable ferroelectric molecular crystals, offering promising avenues for biomedical applications.

A new insight to investigate the strain distribution, evolution, and crack development of cement-stabilized coral aggregate

Cement-stabilized coral aggregate (CSCA) can be used as a base material for roads and airports in island engineering. In this study, four-point bending (FPB) tests were conducted on CSCA with different prefabricated crack depths, and distributed fiber optic sensor (DFOS) was used. The testing process of the CSCA beams was simulated using an improved bond-based peridynamic (BBPD) model that combines the bilinear damage principle and fracture parameters random field. The results indicate that DFOS has the potential to monitor strain evolution and detect crack in CSCA. The strain distribution in the spanwise direction of the beam during the plastic phase presents a single peak, which can be described by a Pearson-VII function. The fracture location can be predicted from the positions of the tensile strain peaks. The neutral axis begins to move gradually toward the compressed part of the specimen after the external load greater than 0.6 Pmax. The compression modulus of the CSCA material peaks is 4500 MPa, that is three times larger than its tensile modulus and can satisfy the requirement of semi-rigid base layer construction of island roads. The improved BBPD model is able to effectively simulate the strain-softening behavior of CSCA materials with consideration of the effect of material inhomogeneity on the actual fracture path. The peak load prediction error was less than 7 %. The R2 between the numerically predicted load-displacement curves and the test results were bigger than 0.95. The improved BBPD method can predict the actual fracture location of the specimen with a horizontal position deviation of less than 2 cm. The bending fracture process of CSCA are further explored from both experimental and numerical simulations by this study.

EVALUATION OF WOOD DAMAGE AND FRACTURE BEHAVIOR BASED ON ENERGY ENTROPY OF ACOUSTIC EMISSION SIGNALS

In order to assess the damage and fracture behavior of wood under continuous loading, an energy entropy and b-value associated with the acoustic emission (AE) signal were defined to quantitatively describe the release of strain energy during loading. Firstly, the acoustic emission signals of the wood in the three-point bending test were collected. This paper presents the concept of energy entropy according to the definition of information entropy. In order to further evaluate the strain energy intensity released by the damage behavior of the wood specimen, the acoustic emission b-value was defined. Finally, by jointly analysing the dynamics of these two parameters, the test process can be divided into three phases. The results show that even in the elastic phase, micro-destructive behavior occur inside the wood specimen; in the plastic phase, the wood specimen is not only subjected to macroscopic damage, but also often accompanied by fine cracks inside.

Theoretical nonlinear force-displacement constitutive model of triangular-plate steel damper

Utilizing the inelastic deformation of a steel damper to dissipate seismic energy and control structural damage is a prevalent design strategy in a passive control field. Such a design strategy requires an explicit force-displacement constitutive model of the steel damper in both the elastic and plastic deformation phases. Currently, the nonlinear force-displacement relationship of the steel damper is mainly determined by quasi-static tests or numerical simulations which are generally time-consuming, and there is a lack of a theoretical and straightforward approach to determine the nonlinear force-displacement constitutive model of the steel damper. This study thus theoretically derives the nonlinear force-displacement constitutive model for a commonly used triangular-plate steel damper. The theoretical formula is derived based on the equal curvature assumption commonly applied to the triangular plate and is further modified based on the curvature shape function proposed in this study for the first time. After that, the force-displacement curves obtained from the theoretical formula are compared with those obtained from a large number of numerical simulations and several sets of quasi-static tests. The result shows that the theoretical formula derived based on the curvature shape function can better predict the nonlinear force-displacement curve of the triangular-plate steel damper, which significantly outperforms the theoretical formula derived based on the equal curvature assumption especially as the triangular-plate steel damper has a large plastic deformation. Furthermore, the influence factors of the strain-hardening phenomenon existing in the force-displacement curve of the triangular-plate steel damper are analyzed based on the modified theoretical formula. The result implies that the thickness-to-height ratio of the plate is the most significant factor for the strain-hardening behavior of the triangular-plate steel damper.

Numerical modeling of shear band effect on Goss grain recrystallization in electrical steels: Crystal plasticity finite element and phase field modeling

This study investigates the effect of shear band evolution on the nucleation of Goss {110}<001> texture during the primary recrystallization of 3.24 wt% Si grain-oriented electrical steel. Nucleation at the early stage of primary recrystallization of the steel is explored both experimentally and numerically. The experimental approach involves cold rolling the steel specimens to obtain a thickness reduction ratio of 76 % and then applying heat treatment to them at 600 °C for less than 1 min. The numerical simulation employes crystal plasticity (CP) finite element model (FEM) to simulate the plastic deformation induced by the dislocation slips on predefined slip systems and non-crystallographic shear bands during cold rolling. Based on the CPFEM results, the generalized strain energy release maximization (GSERM) model is used to predict the preferential orientation probability of recrystallized nuclei for the steel by considering shear band formation. Subsequently, the microstructure evolution during the early stage of primary recrystallization of the steel is simulated using the phase field model (PFM). The developed CP model successfully predicted shear band activation and evolution in the γ-fibers centered on the {111}<112> texture component. The model also demonstrated that shear bands would be the preferred nucleation sites at the early stage of primary recrystallization because of their high stored energy. Moreover, by coupling with the GSERM model, the PFM could reproduce the nucleation of Goss grains at the beginning of primary recrystallization in shear bands.