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Improving ductility and strength of high-entropy alloy [formula omitted] via multi-directional forging and annealing

A dual-phase high-entropy alloy Fe50Mn30Co10Cr10 is treated via multi-directional forging (MDF) and subsequent annealing at 600°C–1000°C. Different microstructures with totally different grain sizes and phase ratios are obtained. The MDF increases yield strength and ultimate tensile strength at the expense of ductility. Via annealing the MDF-processed alloy at 1000°C, the full recrystallized sample yields a excellent combination of high strength and good ductility due to the grain boundary strengthening, transformation-induced plasticity and twinning-induced plasticity. The yield strength, ultimate tensile strength and elongation at failure are 16.2%, 14.2% and 35.3% than those of the as-cast sample. The postmortem characterizations of this annealed sample show strong 〈111〉 texture in the austenite phase along the loading direction and intense martensite transformation with the gradually disappearance of the annealing twins.

Material properties and finite element analysis of adhesive cements used for zirconia crowns on dental implants

This study aimed to evaluate the material properties of four dental cements, analyze the stress distribution on the cement layer under various loading conditions, and perform failure analysis on the fractured specimens retrieved from mechanical tests. Microhardness indentation testing is used to measure material hardness microscopically with a diamond indenter. The hardness and elastic moduli of three self-adhesive resin cements (SARC), namely, DEN CEM (DENTEX, Changchun, China), Denali (Glidewell Laboratories, CA, USA), and Glidewell Experimental SARC (GES—Glidewell Laboratories, CA, USA), and a resin-modified glass ionomer (RMGI—Glidewell Laboratories, CA, USA) cement, were measured using microhardness indentation. These values were used in the subsequent Finite Element Analysis (FEA) to analyze the von Mises stress distribution on the cement layer of a 3D implant model constructed in SOLIDWORKS under different mechanical forces. Failure analysis was performed on the fractured specimens retrieved from prior mechanical tests. All the cements, except Denali, had elastic moduli comparable to dentin (8–15 GPa). RMGI with primer and GES cements exhibited the lowest von Mises stresses under tensile and compressive loads. Stress distribution under tensile and compressive loads correlated well with experimental tests, unlike oblique loads. Failure analysis revealed that damages on the abutment and screw vary significantly with loading direction. GES and RMGI cement with primer (Glidewell Laboratories, CA, USA) may be suitable options for cement-retained zirconia crowns on titanium abutments. Adding fillets to the screw thread crests can potentially reduce the extent of the damage under load.

Computer Simulation of Deformation characteristics of Hybrid Orthotropic Composite Sandwich Beams Under Bending and Axial Loading

This study focuses on the deformation characteristics of hybrid orthotropic composite sandwich beams under axial and bending loading. The homogeneous cores of the hybrid orthotropic sandwich beams affect different parameters on structures. We followed by analytically determining effective material properties to study response of the hybrid sandwich beam under axial and bending loading. Ensuing, we programmed all steps and procedures of solution algorithm into commercially available MATLABTM 2020 code to simulate practical scenarios. Subsequently, we collected and processed data in tabular and graphical forms to facilitate analyses. We compared simulation generated results to the data results available in the literature and found to be within the acceptable range of (±6%) deviations. We observed that the hybrid structure beams had undergone less deformation that confirmed that the hybrid structure beams have comprehensive mechanical advantages as well as has high strength and specific energy absorption capabilities. Based on comparison of the results, the hybrid beams are more damage resistant and tolerant than beams made of the other type of materials. Since hybrid sandwich beams are relatively light, economical, and perform better under axial and bending deformations. Therefore, this study could also be extended to investigate performance of the orthotropic sandwich beam structures under multiple loading directions as well as proposes that the usage of the hybrid sandwich beam components will be useful in global structures.

Research on dynamic responses of multi-float systems during wet towing

Very large floating structures (VLFS) are substantial in scale, typically comprising dozens to hundreds of interconnected modules. This paper utilizes a multi-float towing approach to enhance transport efficiency. A numerical model of multi-float system, based on potential flow theory and multi-body hydrodynamic interaction, is developed and validated. The dynamic responses for six towing configurations under various wave periods and environmental load directions are investigated by using this model. In addition, a selection method is proposed to determine the optimal towing configuration that meets the towing stability criteria while maximizing efficiency, cost-effectiveness, and minimizing environmental impact. Results indicate that during towing multi-float systems, the rear module's vertical motion caused by the combination of heave and pitch is significantly greater than that of the front module, especially in long wave periods. When the number of longitudinal tandem modules reaches four, the low-frequency motion modes with sway and yaw as the main motions are excited, leading to a significant lateral displacement and horizontal rotation of the multi-float system. This also results in uneven tensions of the symmetrical cables. Additionally, the dynamic behaviors of the towing configurations are more pronounced in oblique or lateral waves than in forward waves. As the current direction shifts from forward to lateral, the sway amplitude of the system with four longitudinal tandem modules decreases. Furthermore, an optimal towing configuration is determined by the selection method, which has good stability in moderate sea conditions. The findings of this paper provide valuable insights for towing multi-float systems and have implications for future VLFS construction.

Equiaxed microstructure design enables strength-ductility synergy in the eutectic high-entropy alloy

Eutectic high-entropy alloys (EHEAs) represent attractive candidate materials for overcoming the strength-ductility trade-off, which can be enhanced through the directional alignment of the lamellar structure along the loading direction. Here, we put forward a new route to optimize the strength-ductility synergy without orientation dependence. Through a combination of severe plastic deformation and annealing, we convert the initially lamellar structure into a dual-phase structure comprised of ultrafine equiaxed grains. The significant grain refinement improves the yield strength from 703 MPa to 1199 MPa without sacrificing any ductility. During deformation, the localized softening resistance of the achieved dual-phase microstructure avoids necking, and the intrinsic microcrack-arresting mechanism effectively improves the fracture resistance. Grain boundaries and phase boundaries provide nucleation sites for dislocations and restrict dislocation transfer while the strain incompatibility is accommodated by geometrically necessary dislocations. This work demonstrates that dual-phase alloys comprised of ultrafine equiaxed grains provide a pathway for strengthening without loss of ductility.

Nonlinear friction dynamics of water-lubricated bearings under transient shocks considering cavitation and turbulence effects

This study proposes a transient elastohydrodynamic mixed lubrication (EHML) model for water-lubricated bearings (WLBs) that incorporates cavitation and turbulence effects to evaluate the nonlinear friction dynamic performance under transient shock loads. The generalized average Reynolds equation is discretized using the control volume technique (CVM), and the constrained system is solved using the Fischer-Burmeister-Newton-Schur (FBNS) method. The validity of the model is verified by a comparison of experimental data from published literature. On this basis, the effects of cavitation, turbulence, shock load amplitude, direction, time, and rotational speed on WLB nonlinear friction dynamics characteristics are investigated. The results show that cavitation induces hydrodynamic loss under transient shock conditions, significantly increases contact time and load, and exacerbates the hydrodynamic instability phenomenon. In contrast, the turbulence effect effectively reduces frictional contact. The stability of WLBs under transient shock conditions is closely related to the load offset angle. Reducing the load offset angle improves the anti-shock stability of the bearings. Nevertheless, an increase in the amplitude and duration of the shock load may result in a deterioration of the frictional contact behavior. Increasing the rotational speed appropriately favors accelerating the lubrication regime transition and improving WLB’s anti-shock stability. This study provides a reference for enhancing WLB anti-shock performance and optimizing structural design.

Study of Impact Load Directions on Tunnel Stability in a Cracked Rock Mass

Study of Impact Load Directions on Tunnel Stability in a Cracked Rock Mass

Bidirectionally graded honeycombs under quasi-static loading: Experimental and numerical study

Density-graded cellular solids possess tailorable mechanical properties through variable localized densities, made possible with design freedom offered by additive manufacturing. In this paper, a novel design strategy is proposed to generate bidirectionally graded honeycombs where the gradient direction is both parallel and perpendicular to the loading direction. A gradient function is developed to design three density gradient honeycombs having three different thickness gradients. The graded honeycombs along with their uniform density regular honeycomb counterparts of similar relative density are manufactured using material extrusion process. In-plane compression tests are carried out to perform a comparative study of the honeycombs. Unlike the regular honeycombs, graded honeycombs show layer-by-layer deformation, in addition to cell-wise collapse in lateral direction. Graded honeycombs show better energy absorption characteristics in low and high energy compressions, and high strain regime. Also, graded honeycombs have similar or higher specific energy absorption, densification strain, mean crushing force, and peak crushing force. The compressive responses of the honeycombs are simulated with finite element analysis and the simulation results agree well with the experimental results. The results substantiate the significance of thickness gradient in controlling the density gradation, and effectively tailoring the load-bearing capacity, deformation behavior, and energy absorption characteristics of cellular structures.

Analysis of tensile failure mechanism in intact, foliated, and cracked rocks using distinct element method: Influence of anisotropy

A thorough numerical analysis was conducted to understand the failure mechanisms and behaviour in intact rocks, foliated rocks and rocks with pre-existing cracks using the Brazilian tensile strength tests. The dominant anisotropy in rocks, especially foliated rocks like phyllites, slates and schists, as well as sedimentary rocks like sandstone, limestones and shale, leads to complex failure mechanism. The presence of cracks leads to anisotropy causing different mechanisms of failure and variation in tensile strengths of rock mass. Numerical simulations were conducted based on experimental studies of foliated phyllite and dolomitic limestone from the Tejam Group, Lesser Himalaya. The variations in failure behaviour and strength of foliated rocks were studied for samples at different foliation angle using the particle distinct element model. The simulation results show that with increase in foliation angle to the loading direction (from 0° to 90°), the peak tensile strength of rocks remains almost same for specimens with θ = 0° to 30° and then increases linearly till 90°. The influence of cracks as anisotropy was also studied by changing crack length (from 5 mm to 30 mm) and angle (from 0° to 90°). The development of failure patterns in rocks with pre-existing cracks leads to a better understanding of the failure modes and makes it possible to interpret failure behavior, pattern, and strength parameters. With increase in crack length, the tensile strength of rocks decreases. Overall, this study depicts the influence of anisotropy and microparameters on failure modes and behavior in Brazilian tensile strength tests on foliated and pre-cracked rocks.

The texture evolution near the shear band and corresponding impact on the microvoid nucleation and crack propagation of Ti6242s alloys under high strain rates

This study investigates the texture evolution near the adiabatic shear bands (ASBs) and its impact of on the adiabatic shear failure mechanism, focusing on microvoid nucleation and crack propagation in Ti6242s alloy with an equiaxed α microstructure under high strain rates, using a split Hopkinson pressure bar (SHPB) for the experiments. To achieve this, the initial microstructure was used to enable the texture with the c-axis perpendicular to the loading direction. After compression, the initial texture transformed into two main texture components through different mechanisms. One texture component, aligned parallel to the loading direction, is strongly associated with the {10 1‾ 2} tensile twins, which were widely distributed near the ASBs with their c-axis are 85° to the parent grains in the initial microstructure. The other texture component, with its c-axis perpendicular to the ASB, is formed by the basal slip activation during adiabatic shear deformation. Besides, it should be noted that twinning resulted in the formation of hard grains (with the c-axis of α-grains parallel to the loading direction), increasing the number of hard-soft grain boundaries. A key finding of this paper is the presence of numerous microvoids near the ASB mainly initiated at soft-hard grain boundaries (approximately 65 %), attributed to stress concentration at the boundaries of soft-hard grains, making these boundaries potential nucleation sites for microvoids. Additionally, basal slip bands in the equiaxed α grains provide rapid channels, accelerating the crack propagation rate. This study provides new insights into refining the adiabatic shear failure mechanism under dynamic loading.

Design of improved multi-cell L-shaped CFST columns under compression and bending

In recent years, there has been a notable surge in proposals for various forms of special-shaped concrete-filled steel tubular (CFST) columns. Despite various methods developed by researchers for determining the bearing capacity of multi-cell special-shaped CFST columns under different loading conditions, these methods remain lack unified. In this study, FE models were developed to simulate performances of improved multi-cell L-shaped CFST (ML-CFST) column under compression and bending. Parametric analyses have been performed to evaluate impact of various factors, including steel yield strength fy, compressive strength of concrete fcu, steel thickness t, loading direction θ, web height c, and axial load ratio n, on performances of ML-CFST columns. The findings of study indicate that the unidirectional flexural capacity of ML-CFST member exhibits a nearly linear relationship with the variables of t, fy, and c, with a minimal impact observed from fcu on flexural capacity. The width of extended section b, fcu, fy, and t have a certain effect on flexural capacity at any angle, particularly fy, t, and b. While fcu, fy, and t exert some influence on N/Nu-M/Mu correlation curves, their influences are marginal compared to the loading direction, which is the predominant influencing factor. Additionally, Mx0/Mπ/4-My0/M3π/4 curves gradually protrude outward with the increase in n. The effects of t, fy, and fcu on the shape of Mx0/Mπ/4-My0/M3π/4 curve were relatively insignificant. Simplified unidirectional flexural capacity calculation models were proposed based on stress analysis of cross-section under ultimate states. Given that flexural capacities estimated by simplified calculation model are slightly conservative, it is recommended to increase the flexural capacities by 10 %. Furthermore, an elliptical equation was formulated to predict the flexural capacity at any angle, with the predictions being slightly conservative. Based on ultimate equilibrium theory, a simplified calculation method was presented to predict unidirectional eccentric bearing capacities of ML-CFST columns. Through regression analysis, a simplified calculation method expressed as polar coordinate form for biaxial eccentric bearing capacity was established, with calculated values aligning well with FE results.

Influence of texture on anomalous yielding behavior of thermomechanically processed nickel-based superalloy 720Li

Precipitation-strengthened Ni-base superalloys are extensively used for high-temperature load-bearing applications due to their unique combination of yield stress anomaly (YSA), excellent creep, fatigue, and corrosion resistance. However, in line with the previous reported results, it is shown in the present study that 720Li alloy does not exhibit YSA during uniaxial deformation. The investigation explores the role of anti-phase boundary (APB) energy, Zener ratio and break away stress of Kear-Wilsdrof (KW) lock on YSA behavior. It is shown that in spite of meeting all the energetic requirements necessary for YSA (viz. energy for octahedral to cubic cross slip along with high break away shear stress, i.e. ∼ 80 MPa); the thermo-mechanically processed 720Li alloy does not exhibit YSA. In support of the observed absence of YSA, a plausible mechanism is provided for the first time through this work. This unusual absence of YSA has been attributed to the crystallographic texture of the alloy (specifically, the loading direction (LD) being parallel to [11¯1]), which prevents the formation of KW-locks in the first place. The [11¯1] texturing has been shown to rather lead to direct cubic plane slip i.e. {001} <110>, thereby paving way for suppression of KW-locks (and hence YSA). In order to validate this postulate, the study also examines a vacuum induction melt and cast Ni75(Al11, Ti14), L12 compound. The presence of YSA in the L12 compound under conditions of LD not being parallel to [11¯1], confirms that texturing impacts the occurrence of YSA.

A flexible yield criterion for strength modeling from biaxial compression to biaxial tension

Accurate strength modeling from equi-biaxial tension (EBT) to equi-biaxial compression (EBC) is critical for the plastic behavior prediction covering the wide-range of stress triaxiality encountered in sheet metal forming. To date, however, few yield criteria are available that can precisely model the initial yield and hardening behavior under six typical stress states between EBC and EBT, simultaneously. Furthermore, there is still a lack of a unified yield criterion for accurate strength modeling across various stress state ranges. To address the issues, a theoretical framework for constructing yield criteria dependent on stress states is provided and a new analytically described isotropic yield criterion is presented in this study. The flexibility in terms of the yield locus and application range is thoroughly explored to make the new yield criterion general. Subsequently, the isotropic yield criterion is extended into an analytically described anisotropic-asymmetric yield criterion. Furthermore, the extended yield criterion is applied to capture the initial yield behavior of DP980, AA5754-O, and AZ31 sheets, and the strain hardening behavior of QP1180 sheets at various stress states ranging from EBC to EBT along different loading directions. The predicted results from the extended criterion agree well with the corresponding experimental findings. The applications demonstrate that the proposed anisotropic-asymmetric yield criterion can effectively model the initial yield and hardening behavior of HCP, BCC, and FCC metal sheets under EBT, EBC, uniaxial tension (UT), plane strain tension (PST), shear (SH), and uniaxial compression (UC) in an analytical way.

Predicting the structural behaviour and failure mechanism of hybrid steel-grout connectors for cross-laminated timber panels using high-fidelity finite-elements modelling

In this paper, a symbiotic experimental and numerical approach is used to determine the structural performance parameters and analyse the failure behaviour of a novel high-performance hybrid steel-grout connector for cross-laminated timber (CLT) panels. The connector is composed of a steel rod, which is embedded into a 3-ply CLT panel with the aid of a thick layer of epoxy-based grout. Material tests on wood from the two lumber grades present in the CLT panels, and on the epoxy-based grout were conducted to provide an insight into their mechanical behaviour. Forty-two monotonic push-out shear tests were conducted on connectors, varying the grout layer diameter thrice and the loading direction twice. A finite-elements (F.E.) model for the connector was developed in the F.E. software ANSYS and calibrated based on experimental observations on materials and connectors. The tested connectors proved to be strong and stiff in both loading directions, with a maximum slip modulus of 111 kN/mm, yield resistance of 177 kN, and maximum resistance of 192 kN. The diameter of the grout was found to significantly influence all three performance parameters, and much so when the connector was loaded in the direction perpendicular to the CLT face layers. The developed F.E model was able to capture the slip modulus, yield resistance, and maximum resistance with an accuracy above 95 %. The F.E. model also sheds light on the structural performance, yield mechanism, and failure propagation for connectors.

Development of improved finite element formulations for pile group behavior analysis under cyclic loading

AbstractThe effect of cyclic loading is an essential factor leading to progressive soil strength degradation. Therefore, a comprehensive analysis of the pile‐soil system behavior under cyclic loading is required to ensure the stability of pile group. There is room for improvement in the inherent constraint of the conventional numerical model in terms of approximating the soil resistance distribution along the pile by point loads at element nodes, necessitating a specific element that integrates considerations of pile group effect and cyclic loading within a unified framework. This study aims to develop a newly specific type of element for efficiently predicting nonlinear behavior within the pile‐soil system, addressing simulations involving nonlinear pile‐soil interaction, pile group effect, and cyclic loading. Modified element formulations based on soil stiffness matrices and soil resistance vectors specifically address pile group effect and consider parameters that influence pile behavior under cyclic lateral loading. The numerical solution procedure with Newton‐Raphson iteration allows the calculation of pile responses in geometric and material nonlinear analyses. The validation of the proposed method includes several examples, comparing it with existing numerical solutions and experimental tests of single piles and pile groups under cyclic loading. These comparisons further support the consistency of the proposed method with measured data and validate its accuracy in considering group effect and cyclic loading. The parametric study illustrates the ability of the proposed method to capture cyclic loading parameters while considering the influence of the number and magnitude of load cycles, the cyclic load direction, and the installation methods.

Internal Short Circuit and Dynamic Response of Large-Format Prismatic Lithium-Ion Battery Under Mechanical Abuse

Abstract Prismatic lithium-ion batteries (LIBs) are becoming the most prevalent battery type in electric vehicles, and their mechanical safety is garnering increased attention. Understanding the mechanical response and internal short circuit (ISC) of prismatic LIBs during dynamic impact is important for enhancing the safety and reliability of electric vehicles. Thanks to the pioneer's works on the cylindrical and pouch LIB, prismatic LIB can draw on relevant experimental and numerical modeling methods. However, there is still a lack of research on the dynamic effects of prismatic LIB in various loading directions. To address this disparity, the current research utilizes quasi-static and dynamic impact experiments on prismatic LIBs as a foundation. First, the mechanical response of a sizable prismatic LIB under quasi-static conditions and the dynamic effects are examined when subjected to mechanical abuse from various loading directions. Second, an anisotropic finite element model that considers dynamic strain rates are developed, enabling it to accurately represent the mechanical response to both quasi-static and dynamic impact loads. At last, we performed an analysis of ISC occurring under dynamic loading conditions combining the experimental and simulated results. The experimental results as well as the established model can provide reference for the safe design, application, and analysis of prismatic LIBs.

Fabrication and in-plane compressive collapse of CFRP honeycomb metamaterials

A pin-slot positioning method was proposed to fabricate carbon fiber reinforced polymer (CFRP) metamaterials of hexagonal and zero Poisson’s ratio semi-re-entrant honeycombs with the same mass of monolayer continuous twill-woven carbon fiber/epoxy prepregs. The in-plane compressive collapse of CFRP honeycombs was explored through experiments and finite element (FE) simulations. Furthermore, analytical models were developed to predict the modulus and initial collapse stress of the hexagonal and semi-re-entrant honeycombs. Good agreement is achieved between analytical predictions, FE simulations and experimental results. It is shown that the initial collapse of CFRP honeycombs is by the bending of cell walls. Once initial collapse has been attained, both hexagonal and semi-re-entrant honeycombs have a stress softening. The collapse and failure modes of CFRP honeycombs strongly depend on cellular configurations and loading directions.

Systematic analysis of constitutive models of brain tissue materials based on compression tests

It's crucial to understand the biomechanical properties of brain tissue to comprehend the potential mechanisms of traumatic brain injury. This study, distinct from homogeneous models, integrates axonal coupling in both axial and transverse compressive experiments within a continuum mechanics framework to capture its intricate mechanical behaviors. Fresh porcine brains underwent unconfined compression at strain rates of 0.001/s and 0.1/s to 0.3 strain, allowing for a comprehensive statistical analysis of the directional, regional, and strain-rate-dependent mechanical properties of brain tissue. The established constitutive model, fitted to experimental data, delineates material parameters providing intuitive insights into the stiffness of gray/white matter isotropic matrices and neural fibers. Additionally, it predicts the mechanical performance of white matter matrix and axonal fibers under compressive loading. Results reveal that gray matter is insensitive to loading direction, exhibiting insignificant stiffness variations within regions. White matter, however, displays no significant differences in mechanical properties under axial and transverse loading, with an overall higher average stress than gray matter and a more pronounced strain-rate effect. Stress-strain curves indicate that, under axial compression, white matter axons primarily resist the load before transitioning to a matrix-dominated response. Under transverse loading, axonal fibers exhibit weaker resistance to lateral pressure. The mechanical behavior of brain tissue is highly dependent on loading rate, region, direction, and peak strain. This study, by combining experimentation with phenomenological modeling, elucidates certain phenomena, contributing valuable insights for the development of precise computational models.

True triaxial modeling test of high-sidewall underground caverns subjected to dynamic disturbances

Seismicity resulting from the near- or in-field fault activation significantly affects the stability of large-scale underground caverns that are operating under high-stress conditions. A comprehensive scientific assessment of the operational safety of such caverns requires an in-depth understanding of the response characteristics of the rock mass subjected to dynamic disturbances. To address this issue, we conducted true triaxial modeling tests and dynamic numerical simulations on large underground caverns to investigate the impact of static stress levels, dynamic load parameters, and input directions on the response characteristics of the surrounding rock mass. The findings reveal that: (1) When subjected to identical incident stress waves and static loads, the surrounding rock mass exhibits the greatest stress response during horizontal incidence. When the incident direction is fixed, the mechanical response is more pronounced at the cavern wall parallel to the direction of dynamic loading. (2) A high initial static stress level specifically enhances the impact of dynamic loading. (3) The response of the surrounding rock mass is directly linked to the amplitude of the incident stress wave. High amplitude results in tensile damage in regions experiencing tensile stress concentration under static loading and shear damage in regions experiencing compressive stress concentration. These results have significant implications for the evaluation and prevention of dynamic disasters in the surrounding rock of underground caverns experiencing dynamic disturbances.

A generalised framework for modelling anisotropic creep-ageing deformation and strength evolution of 2xxx aluminium alloys

The 2xxx aluminium alloys are extensively applied in the aerospace industry due to their lightweight and balanced performance characteristics. However, a comprehensive method for modelling both the anisotropic creep deformation and strengthening behaviour in creep age forming (CAF) for 2xxx aluminium alloys remains lacking. This paper presents a generalised framework for establishing constitutive models capable of describing the anisotropic creep deformation coupled with the microstructure and material strength evolutions during creep-ageing of both the original and the pre-deformed 2xxx series Al alloys. This framework extends the rolling direction-based material model to anisotropic scenarios at varying angles between the loading and rolling directions, by employing the non-uniform rational B-splines (NURBS). The details about the anisotropic model calibration and numerical simulation implementation are demonstrated. The feasibility of this method was verified by its application to various 2xxx series aluminium alloys with or without pre-deformation, through constitutive modelling and numerical simulation, with satisfactory agreements between prediction and experimental data. For the first time, the proposed framework provides a generalised routine for establishing anisotropic creep-ageing models for various 2xxx aluminium alloys.