Plastic Yield Research Articles

Nonlinear Finite Element Simulation and Analysis of Steel Frame Structures Considering Nonlinear Behavior

This paper focuses on investigating the nonlinear behavior of steel frame structures in practical engineering applications. Utilizing finite element analysis, the study simulates the response of structures under extreme loads such as strong earthquakes. By incorporating nonlinear material properties and contact effects, the numerical simulation and analysis explore phenomena such as plastic deformation, yield, and instability in frame structures. The research outcomes contribute to a deeper understanding of the energy dissipation and safety performance of these structures.

Stress relaxation aging of 7050 aluminum alloy under elastic and plastic loadings: A perspective from the geometrically necessary dislocations

Aerospace integral panels with large curvature often experience not only elastic loading but also plastic loading during creep age forming. However, the stress relaxation aging behaviors and mechanisms under loading stresses ranging from elastic to plastic regions, especially from the perspective of geometrically necessary dislocations (GNDs), have not been fully explored. The stress relaxation aging (SRA) behavior of 7050 aluminum alloy under elastic (200/250/300 MPa) and plastic loadings (350/400 MPa) are studied by uniaxial SRA, hardness and tensile tests, and corresponding mechanisms are clarified by Electron Back Scatter Diffraction (EBSD) tests and transmission electron microscopy (TEM) observations. Regardless of the loading stress, the stress relaxation of 7050 alloy shows a typical two-stage behavior (rapid stress reduction and stable stress relaxation rate). The second stage of stress relaxation under elastic loading shows an abnormal stress rebound, while the stress continuously decreases under plastic loading, and hardness and yield strength at 350 MPa are lower than that at 200 MPa during SRA. These results are attributed to strong dislocation pinning from small and dense precipitates at elastic loading and dislocations shearing large and sparse precipitates at plastic loading, respectively. Furthermore, both the stress reduction and its ratio increase with the increase of initial stress. GNDs contribute to the formation of low-angle grain boundaries (LAGBs) and accumulate at the LAGBs intersection to coordinate grain orientation for creep deformation. Compared to elastic loading, plastic loading promotes global growth of intragranular precipitates by elastic stress field and local heterogeneous nucleation and coarsening of precipitates at subgrain boundaries by more GNDs.

Study on plastic yield surfaces of pyramidal lattice materials with circular and rectangular cross-sections

The yield surfaces and the evolution of yield surfaces of a bending-dominated pyramidal lattice material under complex stress states considering the coupling effect of axial force and bending moment of a strut are studied theoretically. The two-dimensional primary yield surfaces, secondary yield surfaces, and complete yield surfaces of pyramidal lattice materials of two kinds of cross-section struts are obtained, and the analytical expressions of yield surfaces are established. The effects of the inclination angle and diameter-to-length ratio of the struts on the yield surfaces of pyramidal lattice materials with circular cross-sections are discussed. The results provide a basis for analyzing homogenized plastic properties of complex lattice material structures.

Design of lattice metamaterials under the equal strength concept and research on the mechanical properties of their sandwich structures

This study proposes a novel lattice metamaterial with equal strength struts based on the concept of equal strength of beams, which has been designated the strut-enhanced body-centered cubic lattice structure (EBCC). The structure is capable of effectively reducing the stress concentration of the lattice structure at the nodes and increasing the structural energy absorption. The effective elastic properties of EBCC unit cells are investigated in detail under periodic boundary conditions (PBC), and the results show that the deformation response of the unit cell under compressive loading is dominated by bending. A novel sandwich structure, designated S-EBCC, was developed utilizing EBCC as the core material. The effects of geometrical parameters and relative density on the deformation mechanism and mechanical properties of the sandwich structure were analyzed through experiments, numerical simulations and theoretical predictions. The results show that under compressive loading, the stress concentration at the nodes of the EBCC structure is effectively improved and the peak stress is reduced while the energy absorption is increased compared with the traditional S-BCC structure. Under three-point bending load, the larger the strut angle of the S-EBCC structure, the higher the load capacity. Comparison of experimental and theoretical results shows that the failure modes of the S-EBCC structure under both compressive and three-point bending loads are plastic yield.

Stability Analysis of Borehole Walls When Drilling with Normal-Temperature Drilling Fluids in Permafrost Strata

Permafrost is a temperature-sensitive geological formation characterized by low elasticity and high plasticity. Inappropriate engineering design during borehole drilling in permafrost can result in the collapse of surrounding strata. To evaluate the stability of borehole walls, a finite element model was developed based on the inherent physical properties of permafrost. This model was utilized to investigate the thermal, stress, and plastic yield zone evolution around the borehole during drilling with normal-temperature fluids. The borehole expansion rate was employed as a quantitative measure to assess wall stability. The analysis reveals that the strata adjacent to the borehole, when drilled with normal-temperature fluids, experience thawing and yielding, with secondary stress concentrations in unthawed strata driving the progressive expansion of the plastic zone. The degree of plastic deformation diminishes with increasing distance from the borehole. Consequently, the borehole expansion rate was utilized to evaluate collapse risk under varying conditions, including permafrost thickness, depth, plastic strain thresholds, and drilling fluid densities. The findings suggest that normal-temperature drilling fluids are appropriate for thin permafrost layers, whereas for thicker permafrost, adjustments in drilling fluid density are required to ensure the stability of borehole walls due to the elevated temperatures and geostress at greater depths.

High-temperature dependence of yield strength and microstructure in Ni54Fe19Ga27 and (Ni54Fe19Ga27)99.7B0.3 alloys

The deformation behavior, yield strength temperature dependence, and plasticity of the high-temperature L21(B2)-phase during compression in the temperature range 773–1173 K for Ni54Fe19Ga27 and (Ni54Fe19Ga27)99.7B0.3 shape memory alloys was determined for the first time. The studied alloys were characterized by high plasticity (over 70 %) and minimum yield strength level (13–65 MPa) at temperatures from 973 to 1173 K. Possible mechanisms of yield strength decrease, plasticity increase, and microstructure formation during the deformation process depending on test temperature and chemical composition are discussed. The possibility of hot rolling of Ni54Fe19Ga27 alloys at elevated temperatures was demonstrated.

The influence of mineral inclusion on the effective strength of rock-like geomaterials

The influences of microstructure on the macroscopic mechanical behavior of a composite with a porous matrix reinforced by mineral inclusions are investigated in the present work by both numerical and theoretical methods. The mineral inclusions are embedded at the mesoscopic scale and much bigger than the pores which are located at the microscopic scale. In order to consider the properties of the studied rock-like geomaterials, such as the dissymmetry between tension and compression, the solid phase at the microscopic scale is assumed to obey to a Drucker–Prager criterion. Based on the studied microstructure, the Fast Fourier Transform (FFT) based numerical method is firstly adopted to investigate the macroscopic plastic yield stress of the studied composite. Different microstructure having different volume fraction of inclusion, micro-porosity and frictional coefficient of the solid phase are considered. Based on these numerical results, the existing theoretical yield criterion is estimated. One finds that it should be improved for the case of a microstructure having a high inclusion content. Then, a new macroscopic yield criterion is constructed in the present work by using the modified secant method. This criterion ameliorates fundamentally the one proposed in Shen et al. (2013), specially for the case of a deviatoric loading. It is then estimated and validated by comparing with the FFT based numerical results which were carried out in this work with different volume fractions of heterogeneous phase.

Effect of wet grinding carbonation of sintering red mud on the performance of carbon sequestered mortar

The use of alkaline solid waste to CO2 capture is a potential way to upgrade the recycling of solid waste and reduce CO2 emission. In previous work, we proposed a novel wet grinding carbonation technique to achieve rapid carbonation of sintering red mud (SRM). Herein, the effect of wet grinding carbonation of SRM (WGCS) replacement rate (0 %, 5 %, 10 %, 15 %, 20 % and 25 %) on the hydration and hardening of Portland cement was further explored, such as rheology, compressive strength, hydration products and water transfer properties. The plastic viscosity and yield stress of carbon sequestered paste rose together with the WGCS replacement rate, which was due to the decreased D50 of SRM after wet grinding carbonation. When the WGCS replacement rate was 15 %, the 56 d compressive strength of carbon sequestered mortar was increased by 14.1 %. The microscopic characterization showed that the nucleation of calcite crystals and the pozzolanic reaction of silica-rich gels clearly improved the microstructure compactness. The electric flux and porosity of cement mortar was decreased by 25.7 % and 11.4 %, respectively. In terms of environmental and economic benefits, the CO2 sequestration of carbon sequestered mortar reached as high as 24.7 kg/m3 and the CO2 emission was reduced by 30.9 %.

Active and passive salt diapirs: a numerical study

Summary Salt diapirs dominate the structure in many sedimentary basins and control the preservation and migration of hydrocarbon. The formation of salt diapirs generally falls into two endmember models: active (up-building) and passive (down-building) diapirism. In the active model, salt diapirs rise from salt buoyancy to pierce through the sedimentary overburden, whereas in the passive model, salt diapirs result from differential loading of sediments during deposition. These endmember models are mostly conceptual or kinematic, the mechanics of active and passive diapirism, and their relative roles and interactions in the formation of salt diapirs, remain uncertain. Here, we use two-dimensional high-resolution numerical models to investigate the primary factors and critical conditions for active and passive diapirism. Our results indicate that it is improper to use driving mechanisms to classify salt diapirs, because the buoyancy-driven active salt diapirism involves differential loading, while the passive diapirism requires salt buoyancy. The rise of salt diapirs is more sensitive to the effective viscosity of the overburden than to the salt viscosity. Stiff overburdens could prevent the rise of salt diapirs, but they could be pierced by salt diapirs if plastic yield of the overburden is allowed. During deposition, the coupled salt-sediment deformation, driven by both salt buoyancy and differential loading of sediments, can lead to various diapiric salt structures and minibasins. Regional tectonic stress generally promotes salt diapirism by enhancing strain weakening of salts and overburdens. We suggest that the classification of active and passive salt diapirism is an oversimplification in most cases. We propose a general model of the formation of salt diapirs that usually begins with dome initiation driven by salt buoyancy, followed by syndepositional down-building controlled by sedimentation and differential loading, and ends with canopy formation when sedimentation stops.

Enhancement of Rheological Properties of Nano-Fe2O3-Modified Drilling Fluids

Summary In this study, we explore the potential of using nanoparticles (NPs) to enhance the properties of water-based drilling fluids (WBDFs). Specifically, we investigate the effects of nano-Fe2O3 on the rheological behavior of drilling fluid muds under high-temperature and high-pressure (HTHP) conditions to determine the optimal concentration of Fe2O3 NPs to maintain consistent rheology and improve drilling fluid systems. Results show that as temperature increases, the rheological properties of water-based muds (WBMs) decrease, leading to compromised structural integrity. To address this issue, nano-Fe2O3 is introduced into the system. We prepared and evaluated six WBM formulations with varying weight percentages of Fe2O3 NPs, and found that an optimal NP concentration of 2.5 g wt% resulted in a 13.8% reduction in American Petroleum Institute (API) filtrate volume and a 40% reduction in filter-cake thickness. Under conditions of 300°F temperature and 10,000 psi pressure, consistent reductions were observed in the rheological properties of plastic viscosity (PV), yield point (YP), and gel strength with the addition of Fe2O3 NPs. The YP-PV span was measured at 2.7, and the yield strength was determined to be 11 lb/100 ft2. Regarding fluid loss, Drilling Mudcake A containing 0.5 wt% NPs experienced a loss of 6 mL of fluid after 30 minutes, whereas Mudcake E containing 3 wt% NPs exhibited a fluid loss of 5.1 mL in the API filter press test. According to the Bingham plastic model, Muds E and F, containing 2.5 wt% and 3 wt% NPs, respectively, displayed the maximum shear stress vs. shear rate. This highlights the efficacy of nano-Fe2O3 in adjusting the properties of drilling fluids, presenting opportunities for enhanced performance and efficiency in drilling operations.

DSM design of cold-formed steel fixed-ended lipped channel columns undergoing distortional-global interaction

This work reports a numerical investigation dealing with the post-buckling behaviour, strength, and Direct Strength Method (DSM) design of cold-formed steel fixed-ended lipped channel columns experiencing coupling between distortional and global (flexural-torsional) buckling − distortional-global (D–G) interaction. Various cross-section dimensions and lengths are considered, to ensure that the columns selected undergo different levels and types (“true”, “secondary-bifurcation distortional” or “secondary-bifurcation global”) of D–G interaction. The results presented and discussed, determined by means of Abaqus shell finite element geometrically and materially non-linear analyses, consist of elastic and elastic-plastic post-buckling equilibrium paths, failure loads and collapse modes. The steel material behaviour is deemed elastic-perfectly plastic and several yield stresses are considered, thus making it possible to cover a wide column D–G slenderness range. Particular attention is devoted to identifying the most detrimental initial geometrical imperfection shapes, in the sense that they lead to the lowest column failure loads. The numerical failure load data gathered are subsequently used to assess the merits of the available DSM-based design approaches developed to handle cold-formed steel columns undergoing D–G interaction. Since these design approaches are shown to be either inefficient and/or improvable, the above failure load data are also used to propose modifications/improvements aimed at achieving an efficient failure load prediction in the specific context of fixed-ended lipped channel columns. The success of this endeavour provides encouragement to the authors in their search for a safe, accurate and reliable DSM-based design approach capable of handling cold-formed steel columns with arbitrary cross-section shapes and/or end support conditions that fail in D–G interactive modes.

Forecasting the rheological state properties of self-compacting concrete mixes using the response surface methodology technique for sustainable structural concreting.

It is structurally pertinent to understudy the important roles the self-compacting concrete (SCC) yield stress and plastic viscosity play in maintaining the rheological state of the concrete to flow. It is also important to understand that different concrete mixes with varying proportions of fine to coarse aggregate ratio and their nominal sizes produce different and corresponding flow- and fill-abilities, which are functions of the yield stress/plastic viscosity state conditions of the studied concrete. These factors have necessitated the development of regression models, which propose optimal rheological state behavior of SCC to ensure a more sustainable concreting. In this research paper on forecasting the rheological state properties of self-compacting concrete (SCC) mixes by using the response surface methodology (RSM) technique, the influence of nominal sizes of the coarse aggregate has been studied in the concrete mixes, which produced experimental mix entries. A total of eighty-four (84) concrete mixes were collected, sorted and split into training and validation sets to model the plastic viscosity and the yield stress of the SCC. In the field applications, the influence of the sampling sizes on the rheological properties of the concrete cannot be overstretched due to the importance of flow consistency in SCC in order to achieve effective workability. The RSM is a symbolic regression analysis which has proven to exercise the capacity to propose highly performable engineering relationships. At the end of the model exercise, it was found that the RSM proposed a closed-form parametric relationship between the outputs (plastic viscosity and yield stress) and the studied independent variables (the concrete components). This expression can be applied in the design and production of SCC with performance accuracies of above 95% and 90%, respectively. Also, the RSM produced graphical prediction of the plastic viscosity and yield stress at the optimized state conditions with respect to the measured variables, which could be useful in monitoring the performance of the concrete in practice and its overtime assessment. Generally, the production of SCC for field applications are justified by the components in this study and experimental entries beyond which the parametric relations and their accuracies are to be reverified.

Investigating the Impact of Superabsorbent Polymer Sizes on Absorption and Cement Paste Rheology.

This study aims to understand the water retention capabilities of Superabsorbent Polymers (SAPs) in different alkaline environments for internal curing and to assess their impact on the rheological properties of cement paste. Therefore, the focus of this paper is on the absorption capacities of two different sizes of polyacrylic-based Superabsorbent Polymers : SAP A, with an average size of 28 µm, and SAP B, with an average size of 80 µm, in various solutions, such as pH 7, pH 11, pH 13, and cement filtrate solution (pH 13.73). Additionally, the study investigates the rheological properties of SAP-modified cement pastes, considering three different water-to-cement (w/c) ratios (0.4, 0.5, and 0.6) and four different dosages of SAPs (0.2%, 0.3%, 0.4%, and 0.5% by weight of cement). The results showed that the absorption capacity of SAP A was higher in all solutions compared to SAP B. However, both SAPs exhibited lower absorption capacity and early desorption in the cement filtrate solution. In contrast to the absorption results in pH 13 and cement filtrate solutions, the rheological properties, including plastic viscosity and yield stress, of the cement paste with a w/c ratio of 0.4 and 0.5, as well as both dry and wet (presoaked) SAPs, were higher than those of the cement paste without SAP, indicating continuous absorption by SAP. The viscosity and yield stress increased over time with increasing SAP dosage. However, in the mixes with a w/c ratio of 0.6, the values of plastic viscosity and yield stress were initially lower for the mixes with dry SAPs compared to the reference mix. Additionally, cement pastes containing wet SAP showed higher viscosity and yield stress compared to the pastes containing dry SAP.

NUMERICAL SIMULATIONS OF ELASTIC-PLASTIC CONTACT CONSIDERING FRICTION

The solution of the elastic-plastic contact is of major importance in contact mechanics because contact damage and wear are responsible for the failure of many machine elements subjected to contact load. In many situations including gears and bearings, the load is transmitted through a small contact region, i.e. a concentrated contact, and the resulting high gradients of stress often exceed the plastic yield limit of the softer material. Plastic flow is initiated at a certain depth, resulting in modification of contact geometry and of the stress state that can lead to crack inception and propagation. Understanding the contact behaviour in the presence of plastic strains is fundamental for predicting the contact resistance. Considering the mathematical model complexity for the contact between bodies of arbitrary boundary, as well as the dissipative nature of plasticity, an analytical solution for the elastic plastic contact problem is hard to accomplish. Alongside finite element analysis, semi-analytical methods are the only existing simulation tools for the elastic-plastic contact problems. This paper extends a previously reported elastic-plastic contact solver developed by the same author, by considering friction. In the previous solver iteration, residual displacements were calculated only in the normal contact direction, thus assuming that the shear displacements are small enough to be neglected, in other words, the contact was assumed frictionless. By considering friction, a slip-stick contact process is introduced, adding a new iterative loop in which the contact pressure and shear stresses are iterated until convergence is reached. The new computer simulation tool is expected to give more realistic predictions for the elastic-plastic contact between materials with dissimilar elastic properties, in which case the shear tractions disturb the stress and displacements fields calculated for the frictionless contact case. The results are expected to contribute to a better understanding of the contact processes in the presence of both plastic strains and friction.

Effects of the Space Holder Shape on the Pore Structure and Mechanical Properties of Porous Cu with a Wide Porosity Range.

Porous copper (Cu), with varying porosities, has been made using carbamide as a space holder through the powder metallurgy route. Two shapes of carbamide particles were used, (i) needlelike and (ii) spherical, in order to investigate the effect of the space holder shape on the pore structure and mechanical properties of porous Cu. The compressive deformation behavior of porous Cu was studied under a compression test. The pores' structural characteristics and mechanical properties of the porous Cu varied significantly with the shape of the space holder. Although the effect of the space holder shape on the porosity was not regular, the effect on the mechanical properties was regular. The stress increased monotonically with the increase in the strain, and strain hardening occurred at the plastic yield stage. The elastic modulus and yield strength followed the power law, with the relative density irrespective of the space holder shape. The empirical constants associated with different empirically developed power law relations were different, according to the shape of space holder. A quantitative relationship between the elastic modulus and yield strength and the spacer content was obtained to control the mechanical properties of the present porous Cu or other porous metals and metal foams using the well-known space holder method.

Modeling multi-source plastic pollution yield and transport driven by catchment hydrometeorological processes

Plastic pollution has emerged as a global environmental concern, impacting both terrestrial and marine ecosystems. However, understanding of plastic sources and transport mechanism at the catchment scale remains limited. This study introduces a multi-source plastic yield and transport model, which integrates catchment economic activities, climate data, and hydrological processes. Model parameters were calibrated using a combination of field observations, existing literature, and statistical random sampling techniques. The model demonstrated robust performance in simulating both plastic yield and transport from 2010 to 2020 in the upper and middle Mulan River Catchment, located in southeast China. The annual average yield coefficients were found to closely align with existing estimations, and the riverine outflow exhibited a high correlation coefficient of 0.97, with biases ranging from -63.0 % to -21.4 % across all monitoring stations. The analysis reveals that, on average, 12.5 ± 2.5 % of the total plastic yield is transported to rivers annually, with solid waste identified as the primary source, accounting for 37.8 ± 20.7 % of the total load to rivers, followed by agricultural film (26.4 ± 9.8 %), impermeable surfaces (21.5 ± 10.3 %), urban and rural sewage (10.4 ± 5.0 % and 3.0 ± 1.5 %, respectively), and industrial wastewater (0.9 ± 0.7 %). The annual average outflow was estimated to between 9.3 and 43.0 ton/year (median: 23.1) at a 95 % confidence level. This study not only provides insights into the primary sources and transport pathways of plastic pollution at the catchment scale, but also offers a valuable tool for informing effective plastic pollution mitigation strategies.

Utilizing integrated neutron diffraction and elastoplastic self-consistent crystal plasticity model to quantitatively assess the strengthening mechanism in Al–12.5Ce and Al–12.5Ce–0.4Mg alloys

An integrated in-situ neutron diffraction and elastic plastic self-consistent crystal plasticity (EPSC-CP) modeling scheme is performed on a binary Al–12Ce alloy and a ternary Al–12Ce–0.4Mg alloys. Using this scheme, the constitutive parameters, i.e. elastic constants and slip system parameters of individual phases can be calibrated which can be used in microstructure-based CP models to predict materials performance. From this study, it is shown that the elastic constants of Al11Ce3 intermetallics calculated from density function theory calculation in the literature are rather accurate. When applied to the EPSC-CP model, the lattice strains of both the binary and ternary alloys are correctly predicted as compared with experiments, and large lattice strain differences between Al (100) plane and Al11Ce3 (010) plane are demonstrated. The slip system parameters calibrated by the scheme shows that the addition of 0.4 wt% Mg in the alloy has little influence on the critical resolved shear stress of initial dislocation glide in the Al matrix which caused plastic yield in the material. This can be explained by the very dilute Mg solute content in the Al solid solution, causing large spacing of Al–Mg lattice misfit sites and little impact on resistance of dislocation glide at initial yield. The 0.4 wt% Mg addition, on the other hand, has a large influence on the hardening term in the slip system parameters, indicating those Al–Mg misfit sites do help dislocation accumulation during the deformation. The impact of dilute Mg addition on the Al slip system parameters is also reflected in the flow behavior of the ternary alloy: little impact on the yield stress, but a large impact on working hardening and tensile strength of the materials which is consistent with the literature.

Mechanical characterization and constitutive modeling of additively-manufactured polymeric materials and lattice structures

Additively manufactured polymeric lattice structures are being extensively studied, primarily because their mechanical properties can be tailored by controlling the unit cell geometry, giving them higher designability than stochastic materials. However, the inherent layer-wise additive manufacturing process affects the base material properties related to the printing direction, which in turn affects the macroscopic responses of the entire lattice materials. A robust understanding and modeling of lattice structures' elastic and plastic yield behavior in a homogenized approach are essential to enhance their design and analysis efficiency in engineering applications. In pursuit of this goal, a unified printing angle-dependent constitutive model of base materials is proposed in line with the tensile experimental data. The elastic material properties (elastic modulus, shear modulus, and Poisson's ratio), obtained through numerical simulations of one unit-cell with periodic boundary conditions, exhibit anisotropic properties, with the degree of anisotropy determined by the angle of the constituent members and base materials. Furthermore, both experimental and numerical results of lattices demonstrate anisotropic mechanical response under horizontal and vertical compression. Virtual multiaxial experiments are conducted through multi-cell numerical simulations, enabling the determination of initial yielding points of two different lattice structures (Kelvin and Simple cubic and body-centered cubic hybrid structures) under various loading conditions using a dissipation energy-based criterion. Overall, the multiaxial yield surface of the investigated lattices under various stress states, except for the isotropic principal stress plane, can be properly depicted by the Extended-Hill anisotropic yield criterion.

Quantized plastic deformation

In engineering crystal plasticity inelastic mechanisms correspond to tensorial zero-energy valleys in the space of macroscopic strains. The flat nature of such valleys is in contradiction with the fact that plastic slips, mimicking lattice-invariant shears, are inherently discrete. A reconciliation has recently been achieved in the mesoscopic tensorial model (MTM) of crystal plasticity, which introduces periodically modulated energy valleys while also capturing in a geometrically exact way the crystallographically-specific aspects of plastic slips. In this paper, we extend the MTM framework, which in its original form had the appearance of a discretized nonlinear elasticity theory, by explicitly introducing the concept of plastic deformation. The ensuing model contains a novel matrix-valued spin variable, representing the quantized plastic distortion, whose rate-independent evolution can be described by a discrete (quasi-)automaton. The proposed reformulation of the MTM leads to a considerable computational speedup associated with the use of a robust and efficient hybrid Gauss-Newton–Cauchy energy minimization algorithm. To illustrate the effectiveness of the new approach, we present a detailed case-study focusing on the aspects of crystal plasticity that are beyond reach for the classical continuum theory. Thus, we provide compelling evidence that the re-formulated MTM is fully adequate to deal with the intermittency of plastic response under quasi-static loading. In particular, our numerical experiments show that the statistics of dislocational avalanches, associated with plastic yield in 2D square crystals, exhibits a power-law tail with a critical exponent matching the value predicted by general theoretical considerations and also independently observed in discrete-dislocation-dynamics (DDD) simulations.

Rheological behavior of 3D printed concrete: Influential factors and printability prediction scheme

The rheological properties of cementitious materials play a crucial role in determining the printability for extrusion-based 3D concrete printing. This study develops data-driven machine learning (ML) models to predict two key rheological parameters - plastic viscosity (PV) and yield stress (YS) of 3D printable cementitious composites based on the mixture composition and time after water addition. A systematic experimental study is conducted by varying the contents of cement, fly ash, silica fume, sulfoaluminate cement, superplasticizer, and water-to-binder ratio, and time after water addition. The measured rheological data is used to construct a database for training predictive models including linear regression, support vector regression, random forest, extreme gradient boosting, and multi-layer perceptron neural network. The extreme gradient boosting model achieves the highest prediction accuracy with low root mean square error and all coefficients of determination exceeding 0.9 for both plastic viscosity and yield stress. Importance analysis identifies the most influential parameters affecting the rheological properties. A printability classification scheme is proposed using the model predictions by defining a printable zone of PV and YS. The data-driven framework is validated to effectively predict printability of new mixtures without trial-and-error. This study demonstrates the potential of ML models to accelerate the design and optimization of 3D printable cementitious materials.