High Strength Ratio Research Articles

Research on the effect of manufacturing processes on the fatigue life of TC4 fasteners

Abstract TC4 fasteners have the characteristics of high specific strength and yield ratio, excellent high and low temperature performance, corrosion resistance, etc., and are widely used in many fastener fields, including aerospace. In long-term use, fatigue fracture has become the main failure mode of TC4 bolt fasteners. The common manufacturing processes of TC4 fasteners include shot peening, bottom corner rolling pressure, anodizing and molybdenum disulphide coating, etc. At present, few researchers have studied the effect of the stress level of the manufacturing process on the fatigue life of TC4 fasteners. Therefore, this paper designs the process and parameter influence test from the perspective of different manufacturing processes, and analyses the fatigue test results to reveal the influence mechanism of different processes on the fatigue life of TC4 fasteners. The research results show that the increase of residual compressive stress greatly improves the fatigue strength of fasteners, the shot peening process improves the fatigue life of TC4 fasteners by increasing the residual stress of fasteners, and rolling pressure also increases the surface residual compressive stress. However, it is necessary to find suitable rolling parameter values, and anodizing reduces the residual compressive stress of fasteners. The coating of molybdenum disulfide also reduces the residual stress value of the fastener surface and leads to a decrease in fatigue life. Therefore, in order to control the fatigue life of TC4 fasteners, it is necessary to carry out the shot peening process, and control the rolling pressure, anodizing time and the coating thickness of molybdenum disulfide. The research in this paper provides a reference for the subsequent research on fastener fatigue strength control.

Evolution of microstructure and mechanical properties along the thickness direction of 500 MPa HSLA steel heavy plates

High strength heavy plates with large thickness are demanded for the construction of large-span bridge projects. However, there is a lack of understanding on the microstructure evolution and mechanical properties through the entire thickness of heavy plates with yield strength over 500 MPa, especially manufactured by the thermo-mechanical control processing (TMCP) and tempering (T) process. In this research, the microstructure and mechanical property evolution through the thickness was investigated for the 85 mm thick, 500 MPa grade heavy steel plate manufactured by TMCP + T. The results show that the microstructure throughout the thickness predominantly consists of granular bainite (GB) and polygonal ferrite (PF). The yield strength and tensile strength at 1/8t, 1/4t, 3/8t and 1/2t (t, the thickness) are 659.4 MPa, 520.6 MPa, 500.3 MPa and 494.0Mpa, and 739.2 MPa, 642.9 MPa, 627.8 MPa and 625.2 MPa, respectively. Yield and tensile strength both significantly decline from 1/8t to 1/2t. The strengthening mechanisms at different thickness were analyzed, and grain refinement has the most significant contribution. In addition, the mechanical properties of ferrite/bainite heterostructure were analyzed by Cyclic load-unload-reload (LUR) tests. The hetero-deformation induced (HDI) stress increases from 1/8t to 1/2t. At 1/8t, HDI hardening is higher but occurs over a narrower strain range compared to that at 1/2t. The impact energy at −40 °C for 1/8t, 1/4t, 3/8t and 1/2t are 182.7 J, 213.0 J, 242.2 J and 253.7 J, respectively. It was discerned that PF undergoes plastic deformation and absorbs a large amount of energy, constituting the primary rationale for the enhanced impact toughness at 1/2t compared to 1/8t. Through this research, not only the microstructure and mechanical property evolution through the thickness was revealed, but also the ferrite/bainite microstructure was found a promising heterostructure to obtain high strength, high toughness and low yield ratio for heavy plates.

Effects of Mean Normal Stress and Microstructural Properties on Deformation Properties of Ultrahigh-Strength TRIP-Aided Steels with Bainitic Ferrite and/or Martensite Matrix Structure.

The effects of mean normal stress on the deformation properties such as the strain-hardening, strain-induced martensite transformation, and micro-void initiation behaviors of low-carbon ultrahigh-strength TRIP-aided bainitic ferrite (TBF), bainitic ferrite/martensite (TBM), and martensite (TM) steels were investigated to evaluate the various cold formabilities. In addition, the deformation properties were related to the microstructural properties such as the matrix structure, retained austenite characteristics, and second-phase properties. Positive mean normal stress considerably promoted strain-induced martensite transformation and micro-void initiation, with an increased strain-hardening rate in an early strain range in all steels. In TM steel, the primary martensite matrix structure suppressed the micro-void initiation through high uniformity of a primary martensite matrix structure and a low strength ratio, although the strain-induced transformation was promoted, and a large amount of martensite/austenite constituent or phase was contained. A mixed matrix structure of bainitic ferrite/primary martensite in TBM steel also suppressed the micro-void initiation because of the refined microstructure and relatively stable retained austenite. Promoted micro-void initiation of TBF steel was mainly promoted by a high strength ratio.

Investigation of meso-mechanical properties of Jinping dolomitic marble based on flat-joint model

Brittle rock has the mechanical characteristics of a high ratio of uniaxial compressive strength to tensile strength, brittle-ductile transition, and so on. The mineral meso-structure of brittle rock shows the interlocking behavior and there are some microcracks between the mineral grains, so it is difficult to analyze the mechanical characteristics accurately with a regular constitutive model. The previous numerical models have some limitations when applied to brittle rock, that they cannot provide sufficient internal interlocking and are incapable of considering the microcracks. These limitations are addressed by using the updated flat-joint contact model to join notional polygonal particles with an initial gap and increasing the particle coordination number by adding flat-joint contacts to more particles that are within some non-zero distance of one another via the range coefficient contact identification method. A comparison of experimental and numerical results confirms that the updated flat-jointed model provides a good match with the mechanical properties of brittle rock. In this paper, we investigate the influence of mineral meso-structure (micro-cracks, range coefficient, and radius multiplier) on the meso-mechanical properties of Jinping dolomitic marble via the updated flat-joint contact model under direct-tension tests and compression tests. It is found that the updated model can reproduce the microstructure effect of brittle rock and can better simulate the mechanical characteristics of the brittle rock than conventional models, such as high strength ratio, brittle-ductile transition, initial nonlinearity, and different modulus in compression and tension.

Dynamic behaviors of nickel coated carbon nanotubes reinforced ultra-high performance cementitious composites under high strain rate impact loading

Understanding the dynamic mechanical behaviors of materials is a prerequisite for reliably analyzing and predicting the dynamic response of structures, which is of great significance for transportation infrastructure and military engineering subjected to extreme loads, particularly dynamic loads at high strain rates. Nickel coated multi-walled carbon nanotubes (Ni-MWCNTs) show promise as a reinforcement to modify the dynamic mechanical behaviors of ultra-high performance cementitious composites (UHPCC). Because Ni-MWCNTs combine the high tensile strength and large aspect ratio characteristics of fibers with the nano effect of nanomaterials, as well as have excellent dispersibility due to the nickel plating on the CNTs’ surface, they effectively improve the dynamic mechanical properties of UHPCC under impact loading at high strain rates of about 100 s−1/300 s−1/500 s−1 and reduce the brittle damage degree of composites. The maximal increase in dynamic compressive strength and energy absorption capacity of UHPCC reaches 47.9% and 68.2%, respectively. This enhancement effect arises from that Ni-MWCNTs improve the microstructure and form multiple fine cracks, resulting in an increased energy consumption required for crack formation, propagation and coalescence. Additionally, the dynamic mechanical properties of Ni-MWCNTs reinforced UHPCC exhibit noticeable strain rate effects. Consequently, a strain rate-dependent logarithmic functional dynamic increase factor model and dynamic constitutive model of UHPCC filled with Ni-MWCNTs are modified herein for predicting and modeling the dynamic mechanical behaviors of composites.

Methods to Increase Fatigue Life at Rib to Deck Connection in Orthotropic Steel Bridge Decks

Orthotropic steel bridge decks (OSDs) are very popular all over the world because of the low dead load, high stiffness in the longitudinal direction, high strength ratio to weight, and can be used in various types of bridges. The life of these bridges is affected by fatigue cracks in different portions. One of major areas where the fatigue cracks appear in these bridges is rib-to-deck connection. In this research finite element analysis is carried out by using ABAQUS/CAE 2022 software to determine the ways to increase the fatigue life at rib to deck connection in OSDs. In the first part, smaller models are simulated; stress concentration is analyzed and hot spot stress (HSS) is calculated according to International Institute of Welding (IIW) and Det Norske Veritas (DNV) recommendations. In the second part, a parametric analysis is carried out to analyze the effect of weld penetration, thickness of deck, thickness of rib and rib to deck connection type. In the third part, simulation of models similar to the real field is carried out to determine whether the double welded connections are better than single welded connections. Different models are analyzed for different load cases like single wheel load, double wheel load and also the position of the wheels is changed. The boundary conditions are changed to analyze whether the boundary condition has any significant effect on the result obtained. It is found that thicker decks, thinner ribs, and low penetrated welded connections reduce the stress concentrations at rib to deck connections which ultimately increase fatigue life. Among the parameters examined, deck thickness is the most important parameter. It is found that the percentage of stress increase with percentage decrease in deck thickness follows a power relation. The overall fatigue life of double welded connection is excepted to be lower since the stress concentration is maximum at the weld toe at deck on the outer side of the closed stiffener; however, if the cracks initiate on the inner side of closed stiffener, the cracks at the weld root of single welded connection can propagate much rapidly than the cracks initiating on the inner side of the closed stiffener at the weld toe, thereby reducing the fatigue life of the single-welded specimen significantly.

Alüminyum Alaşımlarının Ahtapot Akışkanlık Testi ile Karakterizasyonu

Aluminium and its alloys are the most commonly used alloys in the transportation sector due to their high lightness and strength ratio. The higher corrosion resistance increases the reason why this alloy is preferred. In order to increase the strength values to the desired levels, aluminium alloys are subjected to grain refining with Ti, solution hardening with Mg and Cu and microstructural modifications with Sr. In this study, the relationship between Ag addition to Al-Cu alloy, mould filling ability with Sr addition to Al-Si alloys were investigated. In addition to the traditional spiral tests, newly developed 8-spoke, which is named as octopus design, was used to characterise the fluidity. Ag addition in the Al-Cu alloy (201) has no effect on fluidity particularly in spiral test but it has been observed to increase the strength by 50-80 MPa. On the other hand, high fluidity and strengths up to 350 MPa were achieved by A380 alloy.

α″ martensite engineering: A strategy to achieve high yield strength and low yield ratio synergy for dual-phase titanium alloy

To breakthrough the long-term contradictory issue of high yield strength and low yield ratio for titanium alloys, and achieving the superior balance between these two key mechanical parameters. We have proposed an efficient “Quenching → Cold deformation → Recrystallization annealing” (QCR) strategy, which realizes the high yield strength (900 MPa) and low yield ratio (0.74) synergy for a model Ti6Al4V5.5Cu (wt.%) alloy which characterized with the unique multi-scale heterogeneous structure. The developed QCR processing route is based on the subtle utilization of orthorhombic α″ martensite, which plays the various roles in each processing step. By elaborately manipulating the recrystallization degree, chemical stability, effective domain of β phase and αt nano-precipitates in β phase, the stress-induced α″ martensite transformation (SIM α″) can be controlled effectively and even postponed until after yielding induced by dislocation mechanisms, thus leading to substantially improvement of yield strength. After yielding, abundant proliferation of SIM α″which assisted by multi-scale α phases and their interactions are the fundamental reasons for achieving higher work-hardening ability, tensile strength (1215 MPa) and uniform elongation (11%). Thus, the core strategy to realize the excellent combination of high yield strength and low yield ratio is manipulating the activation sequence of the plastic deformation carriers.

Properties of Heat-Treated Wood Fiber-Polylactic Acid Composite Filaments and 3D-Printed Parts Using Fused Filament Fabrication.

Wood fibers (WFs) were treated at a fixed heat temperature (180 °C) for 2-6 h and added to a polylactic acid (PLA) matrix to produce wood-PLA composite (WPC) filaments. Additionally, the effects of the heat-treated WFs on the physicomechanical properties and impact strength of the WPC filaments and 3D-printed WPC parts using fused filament fabrication (FFF) were examined. The results revealed that heat-treated WFs caused an increase in crystallinity and a significant reduction in the number of pores on the failure cross section of the WPC filament, resulting in a higher tensile modulus and lower elongation at break. Additionally, the printed WPC parts with heat-treated WFs had higher tensile strength and lower water absorption compared to untreated WPC parts. However, most of the mechanical properties and impact strength of 3D-printed WPC parts were not significantly influenced by adding heat-treated WFs. As described above, at the fixed fiber addition amount, adding heat-treated WFs improved the dimensional stability of the WPC parts and it enabled a high retention ratio of mechanical properties and impact strength of the WPC parts.

Unified two-way shear model for steel and FRP-RC slabs: Evaluation and reliability calibration

This study introduces a unified two-way (punching) shear design model for concrete reinforced with slabs steel- and FRP bars. The unified model modifies the ACI 318-19 punching shear model to account for the axial stiffness of the tension reinforcement by providing a new modification term (ρ Ereft./Ec)0.26, representing the reinforcing ratio multiplied by the elastic modular ratio of longitudinal bars to concrete. The unified punching shear model has been evaluated over two experimental datasets: FRP-RC slabs (145 specimens) and steel-RC slabs (390 specimens). A comparative assessment between the ACI 440.11-22, CSA S806, JSCE, and the proposed models to test their generalization abilities for slabs reinforced with both types of reinforcement. The assessment indicated a similar performance of the proposed model to the CSA S806 and the JSCE models in terms of statistical measures. The ACI 440.11–22 showed a high average strength ratio (Vexp./Vpred.) of 1.83. However, the ACI and the CSA models showed reduction in the conservatism at high reinforcement axial stiffness. In addition, reliability analysis using Monte Carlo simulation indicated that the unified punching shear model provides a satisfactory safety level with a reliability index between 3.5 and 4.0 for both steel and FRP-RC slabs.

Effect of CNT film interleaves on the flexural properties and strength after impact of CFRP composites

Abstract Carbon nanotubes (CNTs), with their high strength, modulus, and large aspect ratio, have emerged as a frontrunner in nano-reinforcements. In this study, CNT films (CNTFs) were inserted between carbon fiber-reinforced polymer (CFRP) prepregs and were cured together to form interleaved composite laminates. The influence of CNTF interleaves on the flexural and interlaminar properties of fiber-reinforced polymer (FRP) laminates is investigated. Three different types of FRP specimens were tested, namely, 0CNTs-CFRP, 2CNTs-CFRP, and 4CNTs-CFRP. The surface and internal damage characteristics and mechanism of CNTF were analyzed using scanning electron microscopy and computed tomography testing methods. The results showed that the flexural strength of 0° CNTs-CFRP beams increased by 3.79 and 14.34% for 2CNTs-CFRP and 4CNTs-CFRP, respectively, while the flexural modulus increased by 7.33 and 13.76%, respectively. It was also found that the damage area and overall deformation after impact with the energy of 5 J was reduced in the CNTF interleaved composite beams. This work has confirmed that the mechanical properties of FRP laminates can be improved by conveniently inserting CNTF during stacking prepregs in the manufacturing process. However, there is a reduction in the flexure after impact properties of the CNTF-CFRP composites, suggesting that the interface between CNTF and FRP layers should be optimized for high residual strength.

An overview of hydrogen production from Al-based materials

Abstract A profound overview of the recent development for on-time, on-demand hydrogen production from light metal-based hydrolysis is presented. Hydrogen energy is one of the clean and renewable energy sources which has been recognized as an alternative to fossil fuels. In addition, aluminum is the most suitable light activity metal for hydrolysis materials attributed to its safety, environmental friendliness, high-energy density, inexpensive, and low density with high strength ratio. In general, dense oxide films formed act as a barrier on aluminum surfaces. Accordingly, effective removal of the oxide film is a key measure in solving the Al–water reaction. In this review, recent advances in addressing the main drawbacks including high-purity aluminum with acid–alkali solutions, nano-powders of aluminum or composite with acid–base solutions, ball-milled nano-powders, alloying blocks, and gas atomization powders are summarized. The characteristics of these three technologies and the current research progress are summarized in depth. Moreover, it is essential to promote low-cost aluminum-based materials based on effective hydrogen production efficiency and explore ways for practical large-scale applications.

Test and Numerical Simulation of the Axial Compressive Capacity of Concrete Columns Reinforced by Duplex Stainless Steel Bars

Stainless steel has the characteristics of oxidation resistance, high temperature resistance, corrosion resistance, high strength, and high yield ratio. The use of stainless steel bars can extend the life of a structure, reduce later maintenance costs, and reduce the whole life cycle cost of the structure. In this paper, nine concrete columns reinforced with duplex stainless steel (S2205) (DSSRC) and nine ordinary reinforced concrete columns (ORC) were poured with the diameter of steel bars as the parameter, and axial compression tests were carried out on these eighteen concrete columns. The failure mode of the concrete columns is analyzed, and the compressive performance indexes of the two kinds of concrete columns are compared. The results show that, compared with the ORC, the cracking load of DSSRC is increased by 33%, the ultimate load is increased by 30.7%, and the deformation performance of the DSSRC is also improved significantly. On the basis of the test, the finite element model of DSSRC was established with the help of ABAQUS software, and the obtained failure law was consistent with the test; the experimental value, the calculated value, and the numerical simulation value of the axial compression capacity were in good agreement, which verified the feasibility of the test and provided a theoretical basis for practical engineering applications.

Does Rotation and Anterior Translation Persist as Residual Instability in the Knee after Anterior Cruciate Ligament Reconstruction? (Evaluation of Coronal Lateral Collateral Ligament Sign, Tibial Rotation, and Translation Measurements in Postoperative MRI).

Purpose: The aim of this study was to evaluate the presence of residual instability in the knee after ACL reconstruction through the analysis of MRI findings. Methods: This study included patients who underwent isolated ACL reconstruction between December 2019 and December 2021, and had preoperative and postoperative MRI, clinical scores, and postoperative isokinetic measurements. The anterior tibial translation (ATT) distance, coronal lateral collateral ligament (LCL) sign, and femorotibial rotation (FTR) angle were compared preoperatively and postoperatively. The correlation between the changes in preoperative-postoperative measurements and postoperative measurements with clinical scores and isokinetic measurements was examined. The clinical outcomes were compared based on the presence of a postoperative coronal LCL sign. Inclusion criteria were set as follows: the time between the ACL rupture and surgery being 6 months, availability of preoperative and postoperative clinical scores, and objective determination of muscle strength using isokinetic dynamometer device measurements. Patients with a history of previous knee surgery, additional ligament injuries other than the ACL, evidence of osteoarthritis on direct radiographs, cartilage injuries lower limb deformities, and contralateral knee injuries were excluded from this study. Results: This study included 32 patients. After ACL reconstruction, there were no significant changes in the ATT distance (preoperatively: 6.5 ± 3.9 mm, postoperatively: 5.7 ± 3.2 mm) and FTR angle (preoperatively: 5.4° ± 2.9, postoperatively: 5.2° ± 3.5) compared to the preoperative measurements (p > 0.05). The clinical measurements were compared based on the presence of a postoperative coronal LCL sign (observed in 17 patients, not observed in 15 patients), and no significant differences were found for all parameters (p > 0.05). There were no observed correlations between postoperative FTR angle, postoperative ATT distance, FTR angle change, and ATT distance change values with postoperative clinical scores (p > 0.05). Significant correlations were observed between the high strength ratios generated at an angular velocity of 60° and a parameters FTR angle and ATT distance (p-values: 0.028, 0.019, and r-values: -0.389, -0.413, respectively). Conclusions: Despite undergoing ACL reconstruction, no significant changes were observed in the indirect MRI findings (ATT distance, coronal LCL sign, and FTR angle). These results suggest that postoperative residual tibiofemoral rotation and tibial anterior translation may persist; however, they do not seem to have a direct impact on clinical scores. Furthermore, the increase in tibial translation and rotation could potentially negatively affect the flexion torque compared to the extension torque in movements requiring high torque at low angular velocities.

A modified particle contact model for matching the ratios of uniaxial compressive to tensile strength of brittle rocks

The Hertz-Mindlin with bonding (HMB) contact model in the commercial discrete element method (DEM) software EDEM is widely used to simulate and analyze the mechanical behavior of rocks. However, it cannot match the high ratios of uniaxial compressive strength (UCS) to tensile strength (TS) observed in brittle rocks like basalt. In this study, a modified HMB contact model was developed by adequately considering the contribution of moment to stress and the influence of normal stress on shear strength. At the same time, a DEM parameters inversion method was proposed to achieve rapid and accurate calibration of various microscopic parameters. The results indicate that the moment-contribution factor and maximum tensile strength in the modified HMB contact model are two key parameters affecting the UCS/TS ratio. Specifically, the moment-contribution factor mainly affects UCS, while also jointly influencing TS together with the maximum tensile strength. The modified HMB contact model successfully achieves the high UCS/TS ratio that aligns with the test value and exhibits significant pressure-dependence. This model proves to be appropriate for accurately simulating the mechanical behavior of brittle rocks.

Study on milling flatness control method for TC4 titanium alloy thin-walled parts under ice fixation

Thin-walled parts are characterized by weak rigidity and are very prone to deformation during machining, which directly affects the machining accuracy and performance of the parts, so controlling the machining deformation of thin-walled parts is an urgent process problem to be solved. To address such problems, this paper proposes a flatness control machining method based on ice holding of workpieces. The method uses frozen suction cups to solidify liquid water to achieve stress-free clamping of workpieces. We conducted a low-temperature tensile test to investigate the low-temperature mechanical properties of the material. Comparative tests of ice-free and low-temperature ice-fixed milling were conducted to compare and analyze the changes of flatness and milling force in the two working conditions, to investigate the influence of machining parameters on the flatness of thin-walled parts, and to reveal the mechanism of low-temperature milling of ice-fixed workpieces. In addition, the low-temperature milling performance of titanium/aluminum alloy based on ice-fixation was compared. The results show that TC4 has good plasticity, high flexural strength ratio and strong resistance to deformation at low temperatures. Compared with no ice-holding, ice-holding machining effectively improves the flatness of the workpiece, and the order of the machining parameters affecting flatness is: feed rate > milling depth > spindle speed. The milling forces under ice-holding conditions were all greater than those without ice holding. The stiffness and hardness, resistance to damage and deformation of titanium alloy at low temperature are greater than those of aluminum alloy. This method provides a new method for high-precision machining of thin-walled parts.

Buckling Analysis of Cold-Form Steel Built-Up Column with Two Sections

Cold-formed steel has a high strength ratio, high corrosion resistance, and ease of fabrication. So, their range of applications has rapidly expanded as a primary structure for flexural and compression members due to their varieties of advantages. The increased load-carrying capacity and span length can be achieved by the build-up of the section connecting two or more individual sections by self-drilling screws or spot welds. This project deals with the buckling analysis of cold-form built-up sections using ANSYS software. The sections were made by connecting two sections using self-drilling screws. The sections used for the study were channel sections without lips. This project mainly aims to study the effect of buckling loads by changing the screw spacing. According to the findings, buckling load increases as screw spacing decreased. In contrast to open sections, closed sections display variable findings.

Buckling Analysis of Cold-Form Steel Built-Up Column with Two Sections

Cold-formed steel has a high strength ratio, high corrosion resistance, and ease of fabrication. So, their range of applications has rapidly expanded as a primary structure for flexural and compression members due to their varieties of advantages. The increased load-carrying capacity and span length can be achieved by the build-up of the section connecting two or more individual sections by self-drilling screws or spot welds. This project deals with the buckling analysis of cold-form built-up sections using ANSYS software. The sections were made by connecting two sections using self-drilling screws. The sections used for the study were channel sections without lips. This project mainly aims to study the effect of buckling loads by changing the screw spacing. According to the findings, buckling load increases as screw spacing decreased. In contrast to open sections, closed sections display variable findings.

Deformation Prediction Theory of Thermal Barrier Coatings near Cooling Holes under Thermal Cycling.

Thermal barrier coating (TBC) systems are widely adopted in gas turbine blades to improve the thermal efficiency of gas turbine engines. However, TBC failure will happen due to the thermal stress between the different layers of the TBC systems. The traditional two-layer theoretical model only considers TGO (thermally grown oxide) and a substrate in the inner cooling hole with the surface uncoated, which results in poor prediction of the deformations of the TBC systems. It should be mentioned that the effect of TBC is very important because the thickness of TBC is much larger than the TGO thickness. In this study, a new three-layer theoretical model was derived, which is composed of the cylindrical TGO and TBC mounted in the substrate with a circular hole, and the stress and strain of TGO near the cooling hole under the condition of the thermal cycles were calculated. The high temperature characteristics of TGO and the substrate including the high temperature strength and growth ratio were from the experiments. The results show that the strain of the developed three-layer model is irrelevant with increasing number of cycles, which indicates that TBC in the cooling hole significantly inhibits the deformation of TGO near the cooling hole. Therefore, aimed at confirming the feasibility of the three-layer theoretical model, the finite element analysis with coating in the cooling hole and on the surface was carried out with a three-layer axisymmetric model, which proves that the 3-layer theoretical model can predict the deformation trend near the cooling hole.

Single-Layer MoS2: A Two-Dimensional Material with Negative Poisson’s Ratio

Negative Poisson’s ratio (NPR) materials have broad applications such as heat dissipation, vibration damping, and energy absorption because of their designability, lightweight quality, and high strength ratio. Here, we use first-principles calculations to find a two-dimensional (2D) auxetic material (space group R3¯m), which exhibits a maximum in-plane NPR of −0.0846 and a relatively low Young’s modulus in the planar directions. Calculations show that the NPR is mainly related to its unique zigzag structure and the strong interaction between the 4d orbital of Mo and the 3p orbital of S. In addition, molecular dynamics (MD) simulations show that the structure of this material is thermodynamically stable. Our study reveals that this layered MoS2 can be a promising 2D NPR material for nanodevice applications.