Plastic Strain Research Articles

Finite Element Analysis of the Mechanical Response for Cylindrical Lithium-Ion Batteries with the Double-Layer Windings

The plastic properties for the jellyroll of lithium-ion batteries showed different behavior in tension and compression, showing the yield strength in compression being several times higher than in tension. The crushable foam models were widely used to predict the mechanical responses to compressive loadings. However, since the compressive characteristic is dominant in this model, it is difficult to identify distributions of the yield strength in tension. In this study, a simplified jellyroll model consisting of double-layer windings was devised to reflect different plastic characteristics of a jellyroll, and the proposed model was applied to an 18650 cylindrical battery under compressive loading conditions. One winding adopted the crushable foam model for representing the compressive plastic behavior, and the other winding adopted the elastoplastic models for tracking the tensile plastic behavior. The material parameters in the crushable foam model were calibrated by comparing the simulated force–displacement curve with the experimental one for the case where the cell was crushed between two plates when the punch was displaced by 7 mm. A specific cut-off value (10 MPa) was assigned to a yield stress limit in the elastoplastic model. Further, the computational model was validated with two more loading cases, a cylindrical rod indentation and a spherical punch indentation, as the punch was displaced by 6.3 mm and 6.5 mm, respectively. For three loading cases, deformed configurations and plastic strain distributions were investigated by finite element analysis. It was found that the proposed model clearly provides the plastic behavior both in compression and tension. For the crush simulation, the maximum compressive stress approached 222 MPa in the middle of the jellyroll, and the maximum effective plastic strain approached 60% in the middle of the layered roll. For indentation with the cylindrical and the spherical punch, the maximum effective plastic strain approached 52% and 277% in the layered roll, respectively. The local crack or location of a short circuit could be predicted from the maximum effective plastic strain.

An Optimized Approach to Multistage Permanent Deformation Testing of Granular Materials.

Accurately characterizing permanent deformation in granular materials subjected to cyclic loading is crucial for pavement design. This paper introduces an alternative approach to characterizing permanent deformation in a framework that reduces the number of load cycle repetitions by applying an alternative analytical strategy based on plastic strain rate variation over time. The methodology uses a cycle-hardening approach to establish correlations between short-term (post-compaction) and long-term (shakedown state) plastic strain accumulation. This alternative approach provides an efficient means to accelerate the characterization of permanent deformation, ensuring the integrity and validity of the assessment in a more time-efficient and resource-optimized way.

Embrittlement of notched duplex stainless steel: Role of hydrogen-assisted void growth and cleavage

The micro-degradation processes related to the ductile-brittle transition are crucial for revealing hydrogen embrittlement mechanisms. This study investigates the evolution and transition of hydrogen-assisted damages in notched duplex stainless steel using a combination of microstructural characterization, numerical simulations, and mechanistic models. The results show that the brittle area of the fracture surface increases rapidly with decreasing cathodic potential, accompanied by the fractography transition in a sequence of voids, voids mixed with quasi-cleavage, and quasi-cleavage. While hydrogen-assisted dislocation emission from the void surface and stress concentration at the phase boundary promote nanovoid growth, hydrogen-enhanced plasticity facilitates preferential void growth along the ferrite block. At higher hydrogen concentrations, ferrite cleavage cracking may originate from prolate voids and hydrogen-augmented Cottrell dislocation reactions, reducing plastic strain near the crack tip and hence diminishing the formation of vacancies as void nuclei. Previous studies have focused on the statistics of hydrogen's effect on void size. This work demonstrates the dislocation mechanism of hydrogen-assisted void growth and provides new insights into the development of micro-mechanism-based models to predict hydrogen embrittlement.

Dynamic Response of Ti-6Al-2Zr-1Mo-1V Alloy Manufactured by Laser Powder-Bed Fusion.

Titanium parts fabricated by additive manufacturing, i.e., laser or electron beam-powder bed fusion (L- or EB-PBF), usually exhibit columnar grain structures along the build direction, resulting in both microstructural and mechanical anisotropy. Post-heat treatments are usually used to reduce or eliminate such anisotropy. In this work, Ti-6Al-2Zr-1Mo-1V (TA15) alloy samples were fabricated by L-PBF to investigate the effect of post-heat treatment and load direction on the dynamic response of the samples. Post-heat treatments included single-step annealing at 800 °C (HT) and a hot isotropic press (HIP). The as-built and heat-treated samples were dynamically compressed using a split Hopkinson pressure bar at a strain rate of 3000 s-1 along the horizontal and vertical directions paralleled to the load direction. The microstructural observation revealed that the as-built TA15 sample exhibited columnar grains with fine martensite inside. The HT sample exhibited a fine lamellar structure, whereas the HIP sample exhibited a coarse lamellar structure. The dynamic compression results showed that post-heat treatment at 800 °C led to reduced flow stress but enhanced uniform plastic strain and damage absorption work. However, the HIP samples exhibited both higher stress, uniform plastic strain, and damage absorption work owing to the microstructure coarsening. Additionally, the load direction had a subtle influence on the flow stress, indicating the negligible anisotropy of flow stress in the samples. However, there was more significant anisotropy of the uniform plastic strain and damage absorption. The samples had a higher load-bearing capacity when dynamically compressed perpendicular to the build direction.

Numerical study of low‐rise composite steel frame responses to blast loading using direct simulation method

AbstractThis paper investigated the blast behavior of a low‐rise composite steel structure of three stories subjected to internal and external explosions for the same explosive charge of 250 kg TNT. A comparison of three various blast scenarios is aimed at better understanding how blast waves propagate in confined risk zones and their damage effects on far and exposed elements to an explosive charge. Evaluation of the damage level and the overall response of the proposed numerical model is done by estimating the adequacy of structural members subjected to blast loading using general limits in attempting to check the structure's strength and regularity. The analysis was based on load combinations and damage criteria according to the Unified Facilities Criteria which are general design approaches suitable for civil design applications in forecasting blast loads and structural system responses. The overall behavior of this structure was simulated based on a dynamic analysis by the direct simulation approach, which was chosen for modeling blast loads using the Friedlander blast load equation, and the simpler, less expensive, more accurate, and realistic A.T.‐BLAST model to deduce the simplified blast‐wave overpressure profile. The material nonlinearity at a high strain rate using the Johnson‐Cook strength and concrete plasticity damage model is studied dynamically using ABAQUS finite element code to simulate the explicit dynamic nonlinear analysis. The overall response of the proposed numerical model was evaluated by estimating the adequacy of structural members, considering the blast load as the initial cause of failure, such as axial plastic strain, internal forces limits, maximum deformation, support rotation, demand‐capacity‐ratio (DCRshear/moment), drift index and material damage model. The position of the explosive charge played an important role in determining the rate at which the structural element begins to plastic strains, displacements, moments, or rotations beyond the limits, and then key elements should be considered in structural design against progressive collapse. Results showed that steel members exhibit early indicators of failure, such as buckling necking, shear tearing, or plastic hinges, whereas concrete slabs break up immediately due to brittleness. DCRmoment values successfully showed the columns in which the first plastic joint can occur, whereas DCRshear values signaled the onset of shear failure at connections. Besides, plastic hinges played an important role in dissipating energy and preventing total structural collapse via the Strong Column‐Weak Beam design concept, which appears repeatedly in this study. The structure is a well‐designed and ductile building capable of supporting higher loads and is considered to be repairable and intact.

Quantifying damage zones width in strike-slip faults: Insights from a two-dimensional finite-element modeling approach

We use a two-dimensional finite-element modeling approach to investigate the structural evolution of strike-slip faults under five different confining pressures and determine how their damage zone widths vary depending on the kinematic. Three representative fault segments are modeled, accounting for movement obliquity forming in pure strike-slip, oblique convergence and oblique divergence scenarios. The elastoplastic constitutive model (Drucker-Prager) was employed to couple an associated flow rule into the initial stress state of a geostatic stage. We applied two empirical methods for determining the width of the damage zone from progressive model response. The first method involves using the plastic strain distribution curve's inflection points, to mathematically fixate the width. The second method uses the standard deviation obtained from a trend Gaussian/Normal probability distribution, with over 98% fit to the plastic strain curve data, simplifying the inference of the strain propagation along the model. The simulation results indicate inverse proportional relationships between confining pressure and both porosity and plastic strain intensity, while showing a direct proportional relationship with the damage zone width. For fault zone width quantification, results show convergence between the methods, revealing widths of 2.46–2.65 m for oblique divergence (displacement of 0.20 m), 2.65–3.55 m for pure strike-slip (displacement of 0.20 m), and 4.36–4.46 m for oblique convergence zones (displacement of 0.70 m). The pure strike-slip and the oblique convergence damage zone width results align well with outcrop observations of faults with similar kinematics from the literature, underscoring the significance of numerical modeling as a valuable tool for measure and study the mechanics of characterizing the nucleation of fault zones and quantifying the width of the damage zone.

A strain components-based Mohr–Coulomb fracture criterion for proportional loading

Ductile fracture criteria are crucial in the application of elastoplastic materials like advanced high-strength steels, particularly due to their tendency to fail without significant localized necking. It is aimed to figure out the unified mechanism for ductile fracture and accurately describe it with phenomenological criteria. In this study, the effect of the stress triaxiality and the Lode parameter is analyzed mathematically. The maximum shear strain and the normal strain to fracture are emphasized in the proposed strain components-based Mohr–Coulomb fracture criterion particularly designed for plane stress states, and it is assumed that fracture occurs when the combination of the maximum shear strain and the normal strain reaches the critical value. It is then extended to describe fracture with the equivalent plastic strain and the normal strain to fracture. The experimental fracture data of AA 2024-T351 and the additively manufactured Ti-6Al-4V titanium alloy are used to verify the proposed models. A fracture forming limit diagram comprising forming limit curves calibrated from stress states under different stress triaxialities is proposed based on the proposed fracture criteria for plane stress states. This study shows that a strong correlation between the maximum shear strain and the normal strain to fracture has been observed, and it can be described piecewise-linearly. Besides, the orientation of the fracture surface under both tension (including plane strain tension) and compression (including plane strain compression) can be qualitatively explained by the Mohr’s strain circles. The results provide a new insight into the intrinsic deformation and fracture mechanism of materials that fail without severe localized necking.

Effects of Static Strain Aging on Mechanical Performance of Ductile Cast Iron

EN-GJS-400-15U nodular cast iron intended to be used as load-bearing element in long-term geological disposal canisters containing spent nuclear fuel in Finland and Sweden was studied for static strain aging (SSA). Tensile test specimens manufactured from the nodular cast iron were pre-strained to 1%, 2% and 3% nominal plastic strains. The pre-strained specimens were aged at different temperatures ranging from room temperature to 400 °C for varying times. The aged specimens were tested with conventional tensile testing using constant cross-head speed of 0.016 mm/s. Additionally, four specimens were studied with digital image correlation (DIC) during the tensile testing to obtain full-field strain measurements. SSA resulted in elevated pronounced yield point in all the conditions, while the as-received material showed continuous yielding behavior. SSA reduced the elongation to fracture. DIC tests showed more localized yielding behavior in the SSA specimens. Over-aging effect was observed at 400 °C where increasing pre-strain did not increase the yield stress more. For 1-day aging time, the highest yield stress increment was found after aging at 200°C. The yield stress of the material was almost identical after aging in 100°C and 200°C.

Prediction of martensitic transformation start temperature of steel using thermodynamic model, empirical formulas, and machine learning models

Three methods are used to predict the martensitic transformation start temperature (Ms ) of steel. Based on the database containing 832 compositions and corresponding Ms data, prediction models are built, modified, and trained. Firstly, Ms was re-calculated by establishing a thermodynamic model to link the martensitic transformation driving force (Gibbs free energy difference of martensite and austenite) with resistance (elastic strain energy, plastic strain energy, interface energy, and shearing energy). Secondly, the existing Ms data is cleaned and re-predicted using traditional empirical formulas within different composition application ranges. Thirdly, four different algorithms in machine learning including random forest, k nearest neighbor, linear regression, and decision tree are trained to predict 832 new Ms values. By comparing the Ms results re-predicted by the mentioned three methods with the original Ms values, the accuracy is evaluated to identify the optimal prediction model.

Finite Element Analysis of Geogrid-Incorporated Flexible Pavement with Soft Subgrade

Improving the durability of flexible pavements and constructing new roads on weak soil foundations present significant challenges, prompting designers to explore alternative methods to prolong pavement lifespan. Geosynthetics have emerged as a promising solution for soil stabilization, with various materials developed for this purpose. The current study concentrates on using the finite element (FE) method to examine the effectiveness of geogrid-incorporated flexible pavements on soft soil substrates. A three-dimensional layered pavement is constructed with an FE model, incorporating subgrade layers of varying strengths based on their California bearing ratio (CBR) values, with a geogrid layer implemented to enhance subgrade stability. Additionally, attention is also given to investigating the effect of base course thickness. The findings reveal that the geogrid layer primarily influences the formation of plastic strains in the subgrade rather than resilient strains, effectively reducing vertical compressive strain by approximately 40%. With increasing CBR values, there is a reduction in vertical strain, although the influence zone extends up to a depth of 300 mm within the subgrade. At the surface of the subgrade, vertical strain decreases by around 17%, 39%, and 49% as the CBR values increase from 1% to 3%, 5%, and 8%, respectively.

A novel slit damper configuration to enhance ductility and seismic behavior of concentrically braced frames

Steel slit dampers are the specific type of metallic yielding dampers used for the structural passive control. They are constructed by introducing a series of openings or slits in a steel plate to control the seismic behavior of structures. These dampers absorb energy through shear yielding, flexural yielding, or a combination of both. In this paper, a new form of steel slit damper is introduced and examined. The novel damper, called the Zipper-shaped Slit Damper (ZSD), is composed of two nested boxes connected through high-strength bolts. There are several steel strips in an external box and L-shaped profiles to prevent out-of-plane buckling, maximize flexural capacity, and ensure optimal lateral force distribution. Additionally, L-shaped profiles are welded to the ends of the steel strips. To assess the structural capacity and seismic behavior, ZSD is modeled in three dimensions using ABAQUS finite element software. The model is first validated against experimental results and then subjected to cyclic nonlinear static analysis, comprising 15 models with different width-to-thickness and height-to-width ratios of steel strips. The failure index (FI), based on equivalent plastic strain, is employed to predict the moment of failure. The results obtained from the FI were analyzed, and the analysis was limited until the moment of the first failure. On average, the novel damper demonstrated improved durability with an increase in the height-to-width ratio, resulting in enhanced ductility up to 8.75. Additionally, within each width -to-thickness ratio group, a 0.5 unit increase in this ratio corresponded to a reduction of approximately 10 % in energy dissipation efficiency. The equivalent viscous damping in the models averaged 42 %. The analysis indicated that all models exhibited stable hysteresis cycles and had high ductility and energy dissipation. Also, considering the obtained results, it can be concluded that the ZSD, due to its replaceable components, ease of construction, and easy installation, can be utilized in concentrically braced frames. Mechanical models, as well as stiffness and force relationships for design and implementation in braced frames, are presented. The findings provide valuable insights for the utilization of this innovative damper in seismic-resistant structural systems.

Lagrangian Finite Element Model Formulation and Experimental Validation of the Laser Impact Weld Process for Ti/Brass Joining

Information on the flyer deformation during laser impact welding (LIW) is an important aspect to consider when high reliability of the welded components is required. For this reason, accurate numerical models simulating thermal and mechanical aspects are needed. In the present work, the cross-section morphology during LIW of Ti/Brass joints at varying laser pulse energies is modeled by a 2D finite element (FE) model. A hydrodynamic plasma pressure model able to describe the evolution of the pressure load step by step, taking into account the progressive deformation of the flyer, was implemented. Hence, this paper proposes an alternative method to the conventional node concentrated forces or predefined velocity as flyer boundary conditions. The levels of the equivalent plastic strain (PEEQ), shear stress, and critical flyer velocity at the collision point were used as reference parameters to predict the success of the welding bond, distinguishing the welded area from the unwelded area. The model was validated by comparison with the experimental data, which showed the effectiveness of the proposed FE code in predicting the cross-section morphology of the welded materials. Moreover, practical industrial information such as variation in the flyer impact velocity, collision angle, and process temperatures was predicted by varying the process laser pulse energy according to the basic principle of the process.

Cobalt remobilization during tectonic–hydrothermal overprinting: A case from the Tuolugou Co(–Au) deposit in East Kunlun Orogenic Belt, China

Stratiform Cu-Co deposits hosted in (meta-) sedimentary and volcaniclastic rocks contribute two-thirds of the global Co supply. However, the mechanisms driving Co remobilization during tectonic-hydrothermal overprinting events remain poorly understood. As a dominant Co repository, pyrite can provide valuable insights into mineralization history due to its refractory nature. Here, we present the first micro-analytical investigation of pyrite from the Tuolugou Co(–Au) deposit in East Kunlun Orogenic Belt. Ore textures indicate that Co mineralization is attributed to two distinct stages: primary enrichment and subsequent overprinting processes. The former is characterized by pyrite (PyI with up to 3.92 wt% Co) remnants exhibiting oscillatory zones, while the latter is marked by deformation of pyrite (PyII) ores. Three overprinting episodes, namely Da, Db, and Dc, are further distinguished according to varying extents of deformation and mineral assemblages. The Da is characterized by synkinematic PyIIa (up to 4.18 wt% Co) augens, which were most likely formed via pressure–solution mechanism. The Db is represented by polygonal PyIIb (up to 4.75 wt% Co) and siegenite with 120° triple–point junctions. The random orientation and rare intragrain misorientation of cobaltiferous sulfides at Db suggest their formation by recrystallization without plastic strains. The Dc resulted in the formation of Co ± As–rich PyIIc (up to 5.36 wt% Co) along with minor occurrence of cobaltite–gersdorffite, pyrrhotite (up to 1.25 wt% Co), and marcasite (up to 1.28 wt% Co). The PyIIc replacing PyI underscores the role of fluid-coupled dissolution and precipitation during fluid–rock interactions in the formation of these cobaltiferous sulfide assemblages at Dc. The presence of PyIIc infilling within the PyI fissures, in conjunction with the transition from siegenite to cobaltite–gersdorffite, suggests a shift towards low fO2 and low temperature conditions under relatively brittle setting. There is a discernible disparity in sulfur isotope compositions between the two mineralization stages. The PyI exhibits a narrow range of δ34SV–CDT values from –2.14 to 1.35 ‰, indicating a magmatic sulfur origin. In contrast, PyII displays a wide δ34SV–CDT range of –5.22 to 6.16 ‰, suggesting an involvement of strata sulfur during the overprinting stage. Monazite U-Pb dating has effectively constrained two mineralization events. The ca. 453 Ma age implies a potential correlation of the primary Co mineralization with the Late Ordovician to Early Silurian exhalative-syngenetic processes in a Proto–Tethyan-related post–collisional extension setting. Conversely, the ca. 190 Ma age indicates that Co remobilization was instigated by the early Mesozoic ductile–brittle deformation associated with the Paleo-Tethyan orogenesis. Finally, geochemical modeling was performed by simulating the interaction of a Co-rich acidic, reducing fluid with typical quartz-albitite rocks. The simulations demonstrate the appearance of independent Co minerals such as Co-pentlandite during the reaction progression, greatly supporting ore upgrading via tectonic-hydrothermal overprinting.

Unraveling the complexity of Fe-based bulk metallic glasses: Insights into dynamic mechanical relaxation in atomic-scale

This research conducts a thorough investigation into the structural and mechanical evolution of Fe74B20Nb2Hf2Si2 bulk metallic glass (BMG) subjected to thermal aging. Utilizing X-ray diffraction (XRD) and selected area electron diffraction (SAED), the study verifies the amorphous structure of the as-cast BMG, highlighting evidence of short-range ordering (SRO). Thermal aging conducted between 342 and 570 K induces substantial changes, notably the formation of Fe23B6 and α-Fe phases and reduced defect concentrations. During dynamic mechanical analysis, a significant shift was observed, which is characterized by a decrease in the intensity of β-relaxation and an increase in β-activation energy from 333.3±2.1 kJ/mol (for the sample aged at 342 K) to 384.6±5.6 kJ/mol (for the sample aged at 570 K). Nanoindentation evaluations reveal an increase in hardness from 11.85±0.22 GPa (for the as-cast BMG) to 14.65±0.41 GPa (for the sample aged at 570 K), accompanied by an increase in Young’s modulus from 211.61±3.00–244.24±2.00 GPa. These changes imply tighter atomic packing and diminished free volume due to aging, suggesting an advanced stage of structural relaxation. Additionally, the material demonstrates a decrease in plastic strain from 0.0052 in its as-cast state to 0.0026 at 342 K, progressing to brittle behavior with further aging. This study shows the pivotal role of precise aging temperature control in optimizing BMGs for diverse applications, illustrating the intricate interplay between thermodynamics and kinetics in material science.

Elucidating the influence mechanisms of splat cooling on microstructure evolution in friction stir welding of 2195 Al–Li alloy by multi-scale simulation

Al–Li alloy has been widely used in the manufacture of aerospace aircraft structural parts due to its high specific strength and excellent comprehensive performance. Friction stir welding (FSW), as a solid-state joining technique, generates comparatively lower heat generation in contrast to fusion welding. However, even with this reduced heat input, the welded joints of 2195 Al–Li alloy still exhibit noticeable thermal softening. FSW is very sensitive to welding heat input, and the thermal cycle of high peak temperature coarsens the grain in the weld zone, thereby reducing joint properties. To overcome these problems, external cooling can be applied to reduce peak temperature and increase cooling speed, improving the performance of FSW joints. In order to study the mechanism of external cooling on the microstructure evolution of joints, this work established a multi-scale simulation of splat cooling assisted friction stir welding (SCaFSW) of 2195 Al–Li alloy. The temperature change and material deformation data in SCaFSW were calculated in the macroscopic finite element model and used for further Monte Carlo microstructure evolution simulation, and compared with the conventional FSW process. Results reveal that the splat cooling significantly reduces the area of the high temperature region of the workpiece, decreasing the temperature at the same location 10 mm behind the tool by approximately 50 °C compared to FSW. While the local temperature field around the tool pin is not affected by the splat cooling, which mainly accelerates the cooling rate of the welded joint and reduces the plastic strain. In addition, the dislocation density in the weld nugget zone (WNZ) of SCaFSW joint is higher than that in conventional FSW, which promotes the process of grain nucleation and finally refines the grain in the WNZ. The simulated average grain size and thermal cycling results are in good agreement with the experimental results.

Using the Poisson’s Ratio and Acoustic Anisotropy Parameter to Assess Damage and Accumulated Plastic Strain during Fatigue Failure of Austenitic Steels

Using the Poisson’s Ratio and Acoustic Anisotropy Parameter to Assess Damage and Accumulated Plastic Strain during Fatigue Failure of Austenitic Steels

Chromium gradient stainless steels with simultaneous high strength, ductility, and corrosion-resistant: In-depth study of continuous hardening mechanisms

Cr-rich stainless steel sheets exhibit superior corrosion resistance but low ductility, which presents a trade-off between fabrication complexity and performance of the materials in multiple industrial applications, such as marine equipment and microreactors. By transitioning the Cr-rich (30 wt.% Cr) stainless steel component to SS 316 L with a smooth composition gradient in the thickness direction, the intrinsic homogeneous elongation of the Cr-rich layer was increased by 260 % while maintaining the naturally high corrosion resistance (100 %) and retaining most of the strength (more than 80 %). By employing in-situ tensile testing and electron backscatter diffraction analysis, it was revealed that the Cr-rich layer in the gradient structure underwent a profound deformation mechanism, including significant heterogeneous deformation-induced hardening and grain reorientation induced by multiplication and accumulation of geometrically necessary dislocations, in such a way to enable a substantial plastic strain and thereby retarding the occurrence of fracture. The proportion of the Cr-rich layer makes a significant impact on the magnitude of the strain gradient in the gradient specimens, therefore affecting the increment of density of geometrically necessary dislocations. The critical proportion value of the Cr-rich layer is found to be around 22 %. Before and after the critical value the gradient specimens showed different sensitivities to the proportion. This discovery underlines the significance of intrinsic plasticity in low-ductility metals and the role of compositional gradient materials in enhancing strength and ductility.

Eco-friendly material extrusion 3D printing for fabricating W-Ni-Fe lattices with improved compressive resistance

Tungsten (W) and its alloys are prevalently utilized in many special fields, such as the military and nuclear industry, owing to their exceptional attributes, including superior hardness, high density, and remarkable resistance to high temperatures. However, there are still challenges to achieve easy preparation of porous W alloys and uncover the secrets of their mechanical behavior. In this work, a porous lattice made from W93Ni4.9Fe2.1 with uniform microstructure was designed using enhanced material extrusion (MEX) 3D printing technology, offering exceptional formability while ensuring safety and environmental friendliness. The W93Ni4.9Fe2.1 lattice, fabricated at an extrusion temperature of 150 °C and infill percentage of 60 % exhibits the optimal geometry and homogeneous sintering shrinkage. The W93Ni4.9Fe2.1 lattice, fabricated at an extrusion temperature of 170 °C and infill percentage of 60 % shows the best compressive properties with the ultimate compressive strength of 1442 MPa and plastic strain of 19.8 %. The study of rheological properties of designed slurry determines the viscous flow activation energy of 1.64 kJ·mol−1 for the smooth extrusion of slurry, which is crucial for the formability of W93Ni4.9Fe2.1 lattice 3D printing. The ball milling treatment significantly improves the sinterability of W93Ni4.9Fe2.1 powder, confirming the effectiveness of mechanical alloying. This work presents a novel approach for fabricating complex structured porous W alloy with high-performance in a low-cost and environmentally friendly manner.

Elastoplastic Mechanical Properties and Kinematic Hardening Model of 35CrNi3MoVR.

The existing tensile-compression elastoplastic models are not suitable for varies of materials. An accurate constitutive model of the elastoplastic mechanical properties more suitable for 35CrNi3MoVR was produced by optimizing the existing fitting equations based on uniaxial tensile-compression tests, which are able to describe the elastoplastic stress-strain relation and Bauschinger effect varying with the maximum tensile plastic strain. A UMAT subroutine of the constitutive model in ABAQUS was proposed and conducted for FEM calculation. Hydraulic autofrettage tests were carried out under different pressures on thick-walled 35CrNi3MoVR tubes, and the results were compared with those of FEM calculations to further validate the accuracy of the fitting model. The results show that the constructed power function kinematic hardening model can effectively describe the elastoplastic mechanical properties of 35CrNi3MoVR and can be applied to the autofrettage calculation of this material. The comparison among the calculation results of different models proved that the model proposed in this research has better performance compared to other existing models. Taking the Mises stress at the inner surface of the thick-walled tubes as the evaluation criterion, the error of the power function kinematic hardening model reaches less than 3%, decreasing the error by at least 50%.

Optimizing the compression resistance of low-nickel stainless steel coronary stents using finite element and response surface methodology

Considering the high strength and excellent biocompatibility of low-nickel stainless steel, this paper focused on optimizing the design of a vascular stent made from this material using finite element analysis (FEA) combined with the response surface methodology (RSM). The aim is to achieve the desired compressive resistance for the stent while maintaining a thin stent wall thickness. The parameters of the stent’s support unit width (H), strut width (W), and thickness (T) were selected as input parameters, while the output parameters obtained from FEA included the compressive load, the equivalent plastic strain (PEEQ), axial shortening rate, radial recoil rate, and metal coverage rate. The mathematical models of input parameters and output parameters were established by using the Box Behnken design (BBD) of RSM. The model equations were solved under constrained conditions, and the optimal structural parameters, namely H, W, and T, were finally determined as 0.770 mm, 0.100 mm, and 0.075 mm respectively. In this situation, the compression load of the stent reached the target value of 0.38 N/mm; the PEEQ resulting from the stent expansion was small; the axial shortening, radial recoil, and metal coverage index were all minimized within the required range.