High Plastic Strain Research Articles

Multi-scale ceramic TiC solves the strength-plasticity equilibrium problem of high entropy alloy

High entropy alloys (HEAs) with single FCC structure exhibits unique structure and properties. However, lack of strength hinds the engineering application ability seriously. Therefore, it is urgent to propose effective methods and theories to enhance the strength while maintaining favorable plasticity. Introducing reinforced phases is one crucial research approach for improving the mechanical properties of HEAs. However, the resulting reduction in ductility has been neglected. In this work, we propose a novel multi-scale TiC coupling reinforced alloy which preserves the high plasticity while increasing the strength. The results demonstrate that TiC (μm) hinders the dislocations movement and improves strength through the second phase strengthening mechanism. Apart from acting as barriers to dislocation motion, the TiC (nm) also provides more dislocation sources in the distortion area at the junction with the matrix, which increasing the number of movable dislocations and enhancing the plastic strain capacity. Compared with the Al0.4 alloy, the tensile yield strength of the Al0.4-TiC (μm + nm) alloy is increased by 145 %, the ultimate tensile strength is up to 574 MPa, while maintaining a high plastic strain by 30.1 %. The addition of multi-scale ceramic phase TiC provides a novel approach to obtain high strength and high plasticity HEAs.

Stress and Strain Characterization for Evaluating Mechanical Safety of Lithium-Ion Pouch Batteries under Static and Dynamic Loadings

The crashworthiness of electric vehicles depends on the response of lithium-ion cells to significant deformation and high strain rates. This study thoroughly explores the mechanical behavior due to damage of lithium-ion battery (LIB) cells, focusing on Lithium Nickel Manganese Cobalt Oxide (NMC) and Lithium Iron Phosphate (LFP) types during both quasi-static indentation and dynamic high-velocity penetration tests. Employing a novel approach, a hemispherical indenter addresses gaps in stress–strain data for pouch cells, considering crucial factors like strain rate/load rate and battery cell type. In the finite element method (FEM) analysis, the mechanical response is investigated in two stages. First, a viscoplastic model is developed in Abaqus/Standard to predict the indentation test. Subsequently, a thermomechanical model is formulated to predict the high-speed-impact penetration test. Considering the high plastic strain rate of the LIB cell, adiabatic heating effects are incorporated into this model, eliminating heat conduction between elements. Addressing a notable discrepancy from prior research, this work explores the substantial reduction in force observed when transitioning from a single cell to a stack of two cells. The study aims to unveil the underlying reasons and provide insights into the mechanical behavior of stacked cells.

The liquid metal embrittlement of a reactive system at room temperature: α-brasses in contact with the liquid eutectic Ga-In

We studied the liquid metal embrittlement (LME) at room temperature of α-brasses by the liquid eutectic Ga-In (EGaIn). The EGaIn partially wets the α-brasses and forms the CuGa2 intermetallic. 3-point bending tests, Finite Element Analysis, and in situ testing were conducted. When LME occurs, there is a ductile fracture followed by an intergranular brittle fracture that propagates through the zones with the highest plastic strain. The LME sensitivity increases with higher strain rates, higher Zn content, and higher work hardening rates, suggesting a significant role of dislocation mobility in LME and a lack of influence from the CuGa2 intermetallic.

Pressure effect on the structural, electronic, mechanical, optical and thermal properties of Ga2TiX6 (X = Cl, Br): A DFT simulation

The pressure effect on the physical properties of Ga2TiX6(X = Cl, Br) has been carried out through density function theory (DFT) accomplished via CASTEP guidelines. At ambient condition the structural aspects of Ga2TiX6(X = Cl, Br) show well accord with the previous theoretical data. A dramatically decrease of lattice constants, cell volumes and bond length with pressure is perceived. The negative enthalpy energy ensured the chemical formation of Ga2TiX6(X = Cl, Br). The positive stiffness constants (Cij) ensure the mechanical stability of Ga2TiX6(X = Cl, Br) at ambient and hydrostatic pressure. Moreover, the fundamental polycrystalline factors of phases Ga2TiX6(X = Cl, Br) such as bulk, shear and Young’s moduli, Poisson’s and Pugh’s fraction, machinability index as well as hardness of these materials have been calculated and discussed at ambient and hydrostatic pressure. Having very low values of bulk modulus (<100 GPa) they can be considered as soft materials. The increase of machinable index with pressure ensure the high lubricating properties, low friction, and high plastic strain of Ga2TiX6(X = Cl, Br) and also ensure their possible industrial applications. Band structure analysis ensure the semiconducting nature of Ga2TiX6(X = Cl, Br) at ambient condition but the semiconducting nature shift to metallic manner at 55 GPa and 65 Gpa respectively. The decrease of total density of states is observed at high pressure. The creation of new bond at high pressure is also observed in materials Ga2TiX6(X = Cl, Br). The investigated optical features ensured that the studied phases can be used in UV photodiodes, and UV light emitters since they revel intense peaks at UV region. Very low Debye temperature, melting temperature and thermal conductivity are observed at ambient condition which ensures that the compounds Ga2TiX6(X = Cl, Br) can be used as thermal barrier coating materials (TBC).

Effects of Hard-to-Measure Material Parameters on Clinching Joint Geometries Using Combined Finite Element Method and Machine Learning

&lt;div&gt;In this article, we investigated the effects of material parameters on the clinching joint geometry using finite element model (FEM) simulation and machine learning-based metamodels. The FEM described in this study was first developed to reproduce the shape of clinching joints between two AA5052 aluminum alloy sheets. Neural network metamodels were then used to investigate the relation between material parameters and joint geometry as predicted by FEM. By interpreting the data-driven metamodels using explainable machine learning techniques, the effects of the hard-to-measure material parameters during the clinching are studied. It is demonstrated that the friction between the two metal sheets and the flow stress of the material at high (up to 100%) plastic strain are the most influential factors on the interlock and the neck thickness of the clinching joints. However, their dependence on the material parameters is found to be opposite. First, while the friction between the two metal sheets promotes the formation of the interlock, it reduces the neck thickness and thus increases the risk of breaking in this region. Second, it is easier to form the interlock if the deformed material exhibits small flow stress at high plastic strain, but the neck thickness tends to be thinner in this case. The identified material parameters help to significantly reduce the relative error between the simulated results and the experimental results, not only in the configurations from which they are identified but also in a new configuration. This methodology shows its potential in the cases where material parameters are not available or difficult to measure.&lt;/div&gt;

Interfacial crack-tip fields in beaded fiber composites

Beaded fiber composites represent ingenious design strategies capable of resolving the conflicts between strength and toughness in most engineering materials. Although intermittent beading holds great potential for improving mechanical properties, the underlying mechanisms responsible for strengthening and toughening of beaded fiber composites are largely unknown. In this study, we explore near-tip fields of an interface crack between the fiber and the polymeric bead, which is associated with fiber-bead debonding in the course of fiber pullout. The post-yield strain softening followed by strain hardening of polymer matrix, and friction between the bead and matrix are accounted for in the numerical analyses. It is found that pullout of fibers leads to development of multiple shear bands near the tip of the interface crack between the fiber and bead, and coalescence of shear bands gives rise to a zone of high plastic strain. Compared with the low level of friction between the bead and matrix, the bead-matrix interface with high friction coefficient can generate a larger zone of high plastic strain, increasing the propensity of interfacial debonding between the fiber and bead. Furthermore, we have revealed the role of thin coating of carbon nanotubes (CNT). Adding a CNT coating on the fiber enables the emergence of a small zone of high plastic strain near the interface crack tip and reduces the shear stress levels, thereby delaying bead debonding. Additionally, the introduction of CNT coating facilitates stress transfer from the bead to fiber, leading to high pullout force. The findings of this study provide important mechanistic insight into the design principles of beaded fiber composites.

Effect of partial substitution of Cr with Co on the properties of Fe35Ni20Cr20-xCoxMo5P12C4B4 high-entropy bulk metallic glasses

Novel Fe35Ni20Cr20-xCoxMo5P12C4B4 (x = 0, 4,8, 12, 16 in at.%, denoted as Cr20-xCoxMo5) high-entropy bulk metallic glasses (HE-BMGs) with excellent comprehensive performance were successfully fabricated using Fluxing and J-quenching methods. The focus was on studying the influences of different Co content on the glass-forming ability (GFA), mechanical performances, magnetic properties, and anti-corrosion performance. It was found that adding an appropriate amount of Co to replace Cr in Cr20-xCoxMo5 alloys can improve GFA. The Cr12Co8Mo5 specimen displays the maximum critical diameter of 3.5 mm and maximum super-cooled liquid phase of 51 K. The compression tests show that the plasticity was enhanced from 0.2 % for the Co-free alloy to 2.5 % for the 12 at.% Co-added alloy. The saturation magnetization (Js) of Cr20-xCoxMo5 alloys gradually increased from 0.04 to 0.68 T with the increase of Co. Electrochemical tests indicate that in 3.5 wt.% NaCl solution at room-temperature (RT), the anti-corrosion performance of Cr20-xCoxMo5 alloys expresses a trend of first increasing and then decreasing with the increase of Co, and all samples show a remarkably higher anti-corrosion performance than 316 L and 304 L stainless steel. The Cr16Co4Mo5 sample exhibits the highest anti-corrosion performance with the self-corrosion current density (Icorr) and the self-corrosion potential (Ecorr) are 9.5 × 10−9 A/cm2 and -0.270 V, respectively. The X-ray photoelectron spectroscopy (XPS) analysis of the Cr16Co4Mo5 shows that there is a higher content of metal kation oxides of Fe2+, Cr3+ and Mo4+ in the passive films compared to Cr20Mo5 and Cr4Co16Mo5. It is indicated that the Cr16Co4Mo5 specimen has the optimal corrosion resistance in this current research. The present HE-BMGs have high GFA, high plastic strain,and excellent anti-corrosion performance, which have potential application value in the engineering field.

Thermomechanical Performance Assessment of U-Mo Monolithic Fuel Plates With Zircaloy Cladding

Abstract Performance of two distinct fuel systems, U-7Mo fuel in Zircaloy (Zry-4) cladding and U-10Mo fuel in aluminum (Al6061-O) cladding was studied. First, a mini plate with Zry-4 cladding from a previous irradiation experiment was evaluated via finite element analysis (FEA). By using the same plate geometry and irradiation conditions, another plate consisting of U-10Mo fuel and Al6061-O cladding was simulated. The results were then comparatively evaluated to explore the feasibility of employing Zry-4 as an alternative cladding. Simulations indicated the Zircaloy cladding plate would operate roughly 50 °C hotter as compared with the Al alloy cladding plate. Larger deformations in the thickness direction for the plate with Zry cladding were noted. It was observed that the postfabrication stresses in the fuel would be relieved quickly in the reactor, regardless of cladding type. Although the fuel stresses would still develop at reactor shutdown, the fuel would be stress-free during the entire irradiation period for both cladding types. At shutdown, the plate with Zry cladding would have higher stresses due to higher operating temperatures. Similarly, the stresses after shutdown are higher in the foil core for the plates with Zry cladding. The Al cladding plate would have higher plastic strains as compared with the Zry cladding plate. The Zry cladding plate is significantly stiffer, causing higher stresses in the fuel zone and at the interface. Overall, employing Zry as an alternate cladding is not expected to produce a more favorable thermomechanical performance as compared to the performance of an Al alloy cladding plate.

Influence of Taper surface topographies on contact deformation and stresses

The role of bore and trunnion surface topography on the failure rate of total hip joint replacements due to trunnionosis is not clear despite significant variations in the design of taper components between manufacturers. Taper surface topography, along with other taper design parameters such as clearance, diameter, and assembly force, determine the initial interlock of the contacting surfaces after assembly; this has been related to relative motions that can cause fretting and corrosion at the taper interface. However, in most in-silico parametrical taper studies associated with taper micromotions, the bore and trunnion surfaces have been simplified using a flat surface and/or sinusoidal functions to mimic the surface roughness. The current study tests the hypothesis that the use of simple geometrical functions for the taper surface topography can predict the surface mechanics developed in assembled tapers. Measured and simulated surfaces of bores and trunnions were characterised using common roughness parameters and spectral density estimations. Using the same characterised surface profiles, 2D Finite Element (FE) models of CoCr alloy femoral heads and Ti alloy trunnions were developed. Models simulated assembly conditions at different resultant forces ranging from 0.5 to 4.0 kN, contact conditions were determined and associated with their topographical characteristics. Measured surfaces of bore and trunnion components comprise up to seven dominant spatial frequencies. Flattening of the trunnion microgrooved peaks was observed during the assembly of the taper. When the femoral head bore and trunnion topography were both considered a reduced number of microgrooved peaks were in contact, from 51 in an idealised taper surfaces to 35 in measured surfaces using an assembly reaction force of 4 kN. The contact points in the models developed high plastic strains, which were greater than that associated with failure of the material. Results showed that line and sine wave functions over estimate contact points at the taper interface compared to those surfaces that consider roughness and peak variation. These findings highlight the important role of modelling the full surface topography on the taper contact mechanics, as surface variations in the roughness and waviness change the performance of tapers.

In-situ investigation of dynamic precipitation in pre-aged Al-Zn-Mg-Cu alloy AA7075

High strength Al-Zn-Mg-Cu alloys rely for their properties on nano-scaled precipitates formed during artificial ageing. Deformation profoundly affects the evolution of these precipitates. This study investigates the effect of warm deformation on precipitation in a pre-aged AA7075 aluminium alloy. Warm deformation was performed using an electro-thermomechanical testing machine for rapid resistance heating. Transmission electron microscopy showed slightly larger, yet evenly distributed, precipitates in the warm deformed sample compared to the thermally treated condition without deformation. Synchrotron small angle X-ray scattering revealed accelerated growth rates of precipitates due to deformation. At low plastic strains, the growth rate increased linearly with applied strain, while at high plastic strains, a slight deviation from linear behaviour was observed. Temperature and strain rate effects were also examined, with a stronger enhancement effect at low temperature and fast strain rate for a given strain. The deformation enhancement effect disappeared rapidly upon finishing plastic deformation (within 400 s for the studied condition). The enhanced growth rate during and after deformation can be reasonably explained by the excess vacancy concentration, indicating the influence of strain-induced excess vacancies. However, the simple excess vacancy model used fails to explain the observed strain rate effect, and possible explanations for this discrepancy are discussed.

Atomic insights on nanoindentation-induced plastic-deformation behavior of tetrahedral amorphous carbon film

The nanoindentation-induced deformation behavior of the Cr-doped diamond-like carbon (DLC) films was clarified with Cr concentration varying from 0 to 16.5 at.% by experiment and molecular dynamics simulation. The Cr-DLC films were fabricated by a direct cathode vacuum arc technique and Cr dopants existed in the form of stripes owing to the deposition features. Results showed the addition of Cr facilitated the transformation of sp3-C bonds to sp2-C bonds, resulting in a decrease of the hardness and elastic modulus. Especially, the sp2 nano-crystallites with the lamellar structure were found in the Cr (16.5 at.%)-DLC film. During nanoindentation, the ring-like cracking on the surface and lateral crack at the interface are exhibited in the Cr-free DLC film, while the introduction of Cr makes the DLC film alleviate the cracking trend. According to the atomic-scale analysis, Cr can significantly improve the plasticity of the DLC film because the Cr-rich cluster with a high free volume can facilitate the shear transformation zones percolation and the shear bands (SBs) nucleation by collective coordinated vortex-like movements of atoms. The Cr-free DLC film can hardly accommodate high plastic strain with very few fine SBs and blockage of the SBs.

Microstructure and magnetic properties of SiO2/FeCoNiSi0.25 core-shell high-entropy alloys with nanotwinned structures

SiO2/FeCoNiSi0.25 core-shell high-entropy alloys (HEAs) containing nanotwinned structures combine good magnetic properties and bending ductility. This study successfully produced them by the combined mechanical alloying and spark plasma sintering method. The crystallization phase of the HEAs was a solid solution phase with a deformed twin face-centered cubic structure instead of a brittle intermetallic phase. In addition, the HEAs exhibited high yield strength (approximately 1365 MPa) and high plastic strain (about 22.5%). The magnetic intensity characteristics of the FeCoNiSi0.25 core-shell HEA significantly outperformed those of SiO2-shell-free HEAs. The improvement in mechanical properties and magnetic sensitivity can be attributed to the materials' strengthening and toughening by nanotwinned structures, while the excellent magnetic properties were due to the regulation of magnetic structure by grain boundaries and nanotwinned structures. These findings are instrumental in preparing HEAs with high magnetic sensitivity and an excellent combination of mechanical properties.

Effect of Inhomogeneous Mechanical Properties on the Stress-Strain Field at the Crack Tip and Crack Growth Direction in Dissimilar Metal Welded Joints

In the failure analysis and safety assessment of dissimilar metal welded joints, the mechanical heterogeneity of local regions is usually ignored and limited sampling locations are selected. The mechanical behavior of the crack tip region is the main variables affecting the environmentally assisted cracking behavior, and it is crucial for understanding the impact of mechanical heterogeneity on the local stress-strain state at the crack tip in welded joints. In this study, the effect of mechanical heterogeneity on the local mechanical behavior at the crack tip and on the stress-strain condition at the crack tip front for different crack sizes was investigated through finite-element simulations based on user-defined material subroutines. The local mechanical behavior of an interface region and crack propagation direction with mechanical heterogeneity and a series of initial crack locations were analyzed. The results show that mechanical heterogeneity has a significant effect on the mechanical condition and growth path of cracks at different sampling locations. The interaction between the mechanical heterogeneity around the crack and the crack depth determines the stress and plastic strain in front of the crack tip, which causes a substantial change in the crack growth path. The interface cracks have high stress and plastic strain; thus, the interface is often the weak position where damage occurs. To guarantee a reliable integrity assessment of cracks in mechanically heterogeneous interface regions, local mechanical properties related to crack locations should be determined and utilized.

Effect of through-thickness microstructure inhomogeneity on mechanical properties and strain hardening behavior in heavy-wall X70 pipeline steels

The ever-increasing demand for oil & gas exploration from land to subsea necessitates using higher-strength and high-ductility heavy-wall thickness pipes, which may increase the microstructural inhomogeneity along the steel plate sections, ultimately impacting the mechanical properties. In this work, the differences in microstructure and mechanical properties between the through-thickness layers of a heavy-wall ferrite/bainite (F/B) dual-phase (DP) X70 pipeline steel plate were studied. The results showed that the size of the ferrite grain and the volume fraction of bainite increased from the surface layer to the mid-thickness layer of the DP X70 pipeline steel plate. The surface and mid-thickness layers had a lower uniform elongation and higher strength and hardness. In comparison, the quarter layer had higher uniform elongation and lower strength and hardness. The refined grain size and the strong {001}<110> texture were responsible for enhanced in strength and hardness. The higher γ-fiber texture at the quarter layer favored the higher plasticity. The analysis results of strain-hardening behaviors based on the modified C-J model showed that the mid-thickness layer had a higher strain-hardening capacity at the beginning of the plastic strain, leading to deformation instability and reduced material plasticity. The surface layer maintained a high hardening exponent even at high plastic strains, which facilitated the deformation properties of the material. The results provide a basis for evaluating the influence of microstructural factors on the strength and plasticity of heavy-wall X70 pipeline steel and the coordination mechanism of micro deformation in DP steels.

Development of elastic and plastic strains in concrete damaged by alkali–silica reaction during various compression loading tests

In this study, the fracture process of concrete in the presence of alkali silica reaction (ASR) cracks under compressive stress was evaluated. Concrete specimens damaged by ASR expansion at various expansion levels were tested under monotonic, stepwise cyclic, and sustained compressive loadings to evaluate the change in mechanical properties. The evolution of expansion cracks under these loading conditions was assessed using digital image correlation (DIC). In stepwise cyclic and sustained loadings, the elastic and plastic strains generated under different stress levels were separately investigated to elucidate the stress resistance mechanism and the impact of expansion cracks on mechanical properties. An increase in the expansion level was found to remarkably decrease the elastic modulus of concrete but only slightly reduce the compressive strength. Using DIC, expansion cracks were observed with the accumulation of principal strain development even at low stress level. Elastic strains linearly developed in specimens with and without ASR damage, whereas plastic strains increased non-linearly with expansion. Despite the high plastic strains observed before reaching the peak load under stepwise cyclic and sustained loadings, the compressive strength and elastic modulus of concrete remained unchanged regardless of the loading pattern. Based on this evidence, the stress resistance mechanism in the cross-section of ASR-damaged concrete was explained.

Influence of Strain Rate on Plastic Deformation of the Flange in Steel Road Barrier.

This study investigates the influence of strain rate on plastic deformation developed in the flange of a steel road barrier. This effect can be investigated by the use of the uniaxial tensile test. It was found that the strain rate increases yield as well as ultimate strength and gently drops down the elongation at break. Moreover, the accelerated strain rate is connected with matrix heating and increasing the Taylor-Quinney coefficient. Despite the valuable matrix heating and the higher Taylor-Quinney coefficient at the higher strain rates, samples necking is initiated earlier and dislocation density is higher. Flange grains become preferentially aligned along the direction of uniaxial stress, especially at the higher plastic strains. Finally, surface Zn protective layer delamination is initiated quite early beyond the yielding. It is considered that the cracks are due to the different response of the Zn allayer and underlying steel matrix on the plastic straining. Increasing strain rate attenuates the degree of Zn layer delamination.

Study on the Dynamic Evolution Behavior and Failure Mechanism of Burn-Through Instability during In-Service Welding by Combining In-Situ Observation and Failure Analysis.

There remains a lack of systematic understanding of burn-through instability, which also restricts the development of evaluation criteria. Based on the designed test device, the dynamic evolution behavior and failure mechanism of burn-through instability were investigated by combining in-situ CCD observation and failure analysis. In the initial stage of burn-through instability, the penetrating defect initiated beneath the molten pool bulge and propagated toward the arc. Finally, the weld centerline cracks or pinholes contributed to the pipeline failure. Based on in-situ observation, the burn-through pinhole was found to be forming in the overheating zone. Cracks and pinholes were found simultaneously in the burn-through instability zone and played an essential role in the burn-through instability. It could be concluded that a major burn-through hole was mainly developed from the fusion line to the inner wall surface along the wall thickness. According to the failure behavior and phenomena, the in-service burn-through instability area was divided into four parts, which were the damage failure (DF) zone, burn-through instability (BTI) zone, propagation (P) zone, and secondary burn-through zone (BT2). The failure mechanisms of the damage failure (DF) zone and burn-through instability (BTI) zone were significantly affected by the high temperature and plastic strain. The failure behavior of the propagation (P) zone was influenced considerably by the DF and BTI zones. The secondary burn-through zone was mainly affected by the high temperature. The uneven distribution of chemical elements showed an important influence on defect initiation.

Numerical calculation of [formula omitted] to simulate fatigue crack growth under large scale viscoplastic deformations

Crack propagation under low cycle fatigue and thermomechanical fatigue is characterized by high plastic and creep strains that extend over large regions around the crack, so that concepts of linear-elastic fracture mechanics cannot be applied. In these cases, the cyclic crack tip opening displacement ΔCTOD is a promising loading parameter to quantify crack growth. In this work, suitable definitions and Finite Element techniques are investigated and compared for an accurate calculation of ΔCTOD under cyclic mechanical and/or thermal loading. A viscoplastic temperature dependent material model of Chaboche-type is used along with large strain settings, specified for the austenitic cast iron Ni-resist. Extensive two-dimensional analyses of Single Edge Notch Tension specimens revealed that collapsed special crack tip elements are superior compared with commonly used regular quadrilateral 8-node elements. At the same level of accuracy of ΔCTOD, they require an about ten times coarser mesh and show less sensitivity w.r.t. element size for both stationary and propagating cracks. In order to simulate fatigue crack growth, an efficient, fully automated FE-technique is developed for an incremental crack propagation by successive remeshing, whereby the deformations and internal state variables are mapped from the old mesh onto the new one. Recommendations are made regarding important numerical control parameters like optimal size of crack tip elements, length of crack growth increment in relation to plastic zone size and ΔCTOD value.

Biomechanical characteristics of self-expanding sinus stents during crimping and deployment_A comparison between different biomaterials

Self-expanding sinus stents are often used in functional endoscopic sinus surgery to treat inflamed sinuses. The PROPEL self-expanding sinus stent offers mechanical support to the sinus cavity to prevent restenosis. The stent is made of a bioabsorbable material (PLGA) that disappears after wound healing. However, complications such as foreign body sensation and severe stent migration/expulsion have been reported after implantation. Little is known about the contact characteristics of self-expanding sinus stents from when the stent is crimped into the insertion device through to deployment into the sinus cavity. This current study developed a test platform to analyze the biomechanical behavior of the stent during this process. Three common bioabsorbable materials, PLGA, PCL and Mg alloy, were evaluated to understand how the choice of material affects the biomechanical characteristics of self-expanding sinus stents. The results showed that the material can have a considerable influence on the contact characteristics during crimping and deployment. When crimped, the PLGA and Mg alloy stents showed much higher plastic strain and contact stress than the PCL stent. When deployed, the PCL stent had the largest contact area (4.3 mm2) and the lowest contact pressure (0.1 MPa) on the inner surface of the sinus canal. The results indicate that PCL could be a suitable choice for self-expanding sinus stents. This current study provides a method for observing the biomechanical characteristics of sinus stents during stent crimping and deployment.

Strain partition induced abnormal low-cycle fatigue behavior in single-phase heterostructured 316L stainless steels

The low-cycle fatigue (LCF) life of conventional materials is largely dependent on their ductility, i.e., the better the ductility, the longer the LCF life. In this work, 316L stainless steel (SS) was subjected to dynamic plastic deformation and subsequent annealing to obtain single-phase heterostructured samples consisting of recrystallized grains and remaining nanostructures. The tensile ductility of the heterostructured 316L SS increases monotonically with increasing volume fraction of recrystallized grains, while the strain-controlled LCF life first decreases and then increases, partially deviating from the monotonically increasing LCF-ductility relation. The reason is that the recrystallized grains with a low volume fraction (≤25 vol.%) in heterostructured 316L SS sustain high cumulative plastic strain due to plastic strain partitioning, leading to cracking in the recrystallized grains at the early stages of LCF and thus reducing the LCF life.