Search

Hypersonic non-equilibrium air flows over a laminar double-cone configuration are numerically investigated. In this paper, the effects of thermochemical non-equilibrium gas, chemical non-equilibrium gas, and thermally perfect gas models on the prediction of the wall-surface heat transfer and pressure are investigated. Comparing to the high-enthalpy experimental data, the results of simulations indicate that all models have a similar tendency, and underpredict the length of the separation region, while the heat transfer peaks are overpredicted. The experimental data for surface pressure and heat transfer is insensitive to the choice of the thermally perfect gas model and non-equilibrium thermochemistry models. Quantitatively, the thermochemical non-equilibrium gas and thermally perfect gas models predict the same separation and reattachment locations within the uncertainty in the simulation, but the chemical non-equilibrium gas model predicts a smaller separation region.

In order to evaluate the performance of the slip critical bolted connection of HSS members, 30 specimens fabricated from high strength steel (HSS) (Q550, Q690 and Q890), are tested to investigate the slip factors of shot-blasted surface and rusted surface after blasting. For comparison, a group of specimens fabricated from mild steel Q345 are tested as well. In order to investigate the effect of the steel strength grade on slip factor, the values of hardness, roughness and capacity of plastic deformation of steels with different strength grades are also tested and analyzed. Based on experimental results and friction theory, it is found that with the same blasting treatment, the surface roughness tends to decrease with the increase of steel hardness, which induces the decreasing of the slip factor. Based on the friction mechanism, the slip factor is not only decided by surface roughness, but also can be affected by the capacity of plastic deformation of the contacting materials. With the increasing of plastic deformation capacity of the steel, the slip factor tends to be higher. According to the test results, the suggested slip factor of HSS specimens with blasted surfaces is 0.40. Moreover, for the specimens with rusted surface after blasting, there may be an increment in the slip factor owing to the increased surface roughness by rusting. However, the positive influence of rusting on the slip factor is not recommended to be considered in the connection design due to its instability. Therefore, the recommended slip factor of the specimen with rusted surface after blasting takes the value of 0.40 as well.

This chapter is devoted to mechanical properties under monotonic action, including the 1D and 3D stress–strain constitutive relations and the statistic for resistance partial coefficients of high-strength steel.

As one of the indispensable components in lithium–sulfur batteries, the binders greatly impact battery performance. Herein, we report a new multifunctional supramolecular eutectic liquid (SEL) binder, consisting of diphenylamine (DP) and benzophenone (BP), which enables a strongly improved conductive network and anchored polysulfides for high-performance lithium–sulfur batteries. Compared with the traditional polyvinylidene fluoride (PVDF) binder, the SEL binder demonstrates remarkable improvement in both the mechanical performance and the capacity retention (83% over 200 cycles at 1C).

In this work, Au nanoparticles (AuNPs) network structures were fabricated by the self-assembly method at air-water interface, and the continuous AuNPs network thin films with higher stability can be obtained by further growth at room temperature. The proposed approach does not require any inducer to assist the assembly of AuNPs. The formation mechanism of AuNPs network films was studied by changing the relative amount of HAuCl4 and AgNO3 and aging time, and it was found that the amount of AgNO3 was very important to the formation of AuNPs network structures. AgNO3 can promote the fusion of AuNPs and the formation of nano-chain, and could further evolve into a nano-chain network structure. A large area and good stability of Au nanoparticles network films were fabricated after further growth of gold nanoparticles by ascorbic acid reduction. Furthermore, the surface enhanced Raman scattering (SERS) activity of the as-prepared AuNPs network films was investigated by using 4-aminothiophenol (4-ATP) as the SERS probe molecule. Compared with unassembled AuNPs, the AuNPs network films showed enhanced SERS performance for 4-ATP.

Bolt pre-tension is regularly used in the practical case of bearing-type connection. Due to confinement of lap plates, complicate triaxial stress field can be observed near bolt hole, which may affect bearing behavior of the whole connection. Currently, investigations on the related issues are limited. To fill this research gap, this paper presents a combined experimental and numerical study on high strength steel single-bolt connections with bolt pre-tension. Results reveal several meaningful recognitions on the bearing behavior of connection with bolt pre-tension. Firstly, the effect of bolt pre-tension on the final tearout failure mode is negligible. Secondly, distribution of triaxial stress field initiates with a circular pattern and gradually shrinks to a localized pattern between shear fracture lines at ultimate resistance of the connection. Thirdly, out-plane confinement will limit the piling-up of plate material in front of bolt, which will reduce the related bearing resistance. However, increasing bolt grade is still beneficial to the whole connection due to a trade-off between ultimate resistance of the connection and related bearing resistance. Comparison with current code is further conducted. It is found that current Eurocode3 has adequate design safety for connection with bolt pre-tension while extra safety is needed for current AISC 360-16.

High Strength Structural (HSS) steels, with nominal yield strength greater than 450 MPa exhibit phenomena including Lode angle dependence of yield, and accelerated cyclic softening at large strains that cannot be conveniently simulated by existing constitutive models that are developed primarily for conventional strength structural steels. This paper presents an experimental study consisting of 25 coupon scale tests (monotonic and cyclic) as well as 2 large scale cantilever column tests. According to experimental results, a classical combined isotropic and kinematic hardening constitutive model, the Armstrong and Frederick (A-F) model is identified by using the particle swarm optimization (PSO) algorithm. However, the yield plateau region and full-range softening behavior of HSSs under cyclic loading are difficult to be captured by the A-F model. A new constitutive model, termed the HSS-TD model with consideration of the yield plateau and three-stage strength softening, is formulated to simulate the response of HSS steels. The HSS-TD model shows significantly lower errors relative to the conventional A-F model, when assessed relative to test data. Moreover, the limitations of the HSS-TD model including influence of strain history and nonproportional loading are discussed.

Recently structural members fabricated of high strength constructional steels in civil and building engineering has been widely explored. However, their usage in earthquake zones is still restricted by seismic standards worldwide due to its poor ductility. In order to attain potential seismic application, this paper conducted five cyclic lateral loading experiments on H-shaped beam-columns fabricated of Q690D high strength structural steel. The tested members were cyclically bent about the weak axis. It was recognized that the low-fatigue fracture of edge fiber around bottom cross-section was the main failure mode. Besides, the hysteretic curves, cyclic backbones and energy dissipation characteristics were thoroughly discussed. The ultimate inter-storey drift was greater than the limitation of 1/50. All tested beam-columns exhibit favorable cyclic deformability and energy dissipated ability. To further study the influence of several factors, a series of FEA simulations were performed through verified numerical models. Ductile damage behaviors and advanced cyclic constitutive relationships were considered to improve the simulation performance. The influences of plate component slenderness and axial load ratio on seismic performance of steel beam-columns were thoroughly discussed. It is concluded that there exist interdependence characteristics between different influential factors on seismic performance.

Chaboche model has gained prominent utilization in numerical simulation on cyclic behaviors of metal structure. However, the calibration of its material parameter may produce considerable cost. A simplified calibration way is of great importance to ease its application. To this end, a re-evaluation on chaboche model material parameters and simulated elastic-plastic laws was conducted regarding various steel grades. Futhermore, the characterisitcs of isotropic softening was coupled with the present model hardening rule. The kinematic rule was correlated with cumulative plastic strain. The modified model was then calibrated and validated base upon the coupon test result on 41 batches of steels, whose yield stress ranges from 100 MPa to 890 MPa. The calibrated material parameter were then correlated with corresponding monotonic mechanical properties. Accordingly, a simplified calibration procedure, based upon which the material parameters of modifed Chaboche model can be fastly estimated by yield strength and yield ratio, was constructed. As for low yield point steels, mild steels and high strength steels, this calibration method can ease the calibration of modified Chaboche model considerably.

The relationship between von Mises equivalent stress σ ¯ and equivalent plastic strain e ¯ (PEEQ), termed as von Mises stress-strain, plays an important role in numerical simulations for ductile fracture of structural metallic materials with large plastic strain. The standard uniaxial tensile test on cylindrical specimens is the most straightforward method to derive the ( σ ¯ − e ¯ ) data. However, the distribution of the stress and strain along the necking section of the tensile specimen is no longer uniform in the post-necking process, which induces difficulty in acquiring the ( σ ¯ − e ¯ ) data. The existing correction methods to identify von Mises stress-strain in the post-necking regime need instantaneous geometry of the notched region and ignore influence of the initial geometry of the specimen, which induces these methods are inconvenient for application and inapplicable for circumferentially notched tensile specimens to determine ( σ ¯ − e ¯ ) of each individual material zone in a hybrid coupon (e.g. weldment). In the present study, influences of initial geometry of the specimen and plastic hardening property of material on necking process are investigated firstly. It is found that the shrinking behavior of the minimum cross-section of the specimen is determined by the geometric parameter of specimen and plastic hardening exponent of materials. Based on an extensive parametric study a modified power law function to characterize the von Mises stress-strain curve from tensile tests on circumferentially notched specimens without measuring instantaneous geometry of cross-section is proposed.

Loading of Au nanoparticles (AuNPs) onto environmentally sensitive polymer microgels is increasingly used to regulate their optical properties and catalytic activities. Herein, we synthesized composite polymer microgels composed of poly(N-isopropylacrylamide-co-3-methacryloxypropyltrimethoxysilane)/poly(acrylic acid) with a core–shell structure, and AuNPs were controllably loaded onto/into the network chains of the polymer microgels using seed-mediated growth. The prepared AuNPs composite materials possessed good pH sensitivity; the electromagnetic coupling between the AuNPs could thus be tuned via the swelling/deswelling of the polymer microgels under various acidic/alkaline conditions. More importantly, the coordination interaction between the carboxyl groups in the PAA chains and Cu2+ ions changed by varying the copper ion content under various pH conditions, thus enabling regulation of the localized surface plasmon resonance of the AuNPs. These structural features of the prepared composite microgels enabled to tailor the optical performance of the AuNPs by varying the pH of the surrounding medium.

A new uniform shallow trenches termination (ST 2 ) with field plate for high-voltage VDMOS transistor is proposed in this Letter. In ST 2 structure, the electric field near the source is decreased and the depletion region is extended by the field plate, besides, many electric field peaks are introduced in shallow trenches under the field plate and the average electric field strength is increased, both improve the characteristic of the breakdown voltage (BV). Simulation results show the BV of ST 2 VDMOS is 706 V with a termination length L d = 132 μm, which reaches 97% of that of the parallel-plane junction, and the influence of the edge curvature effect is almost entirely eliminated. The ST 2 structure is compatible with conventional CMOS process with only one additional mask and its fabrication is low-cost.

Herein, we present a universal bottom-up interface self-assembly of hairy nanoparticle strategy for 2D monolayered composite and functional nanosheets, including polymeric composite nanosheets and functional porous polymer and carbon nanosheets. By using diverse hairy nanoparticles as building blocks, a series of 2D monolayered polymeric composite nanosheets was prepared, demonstrating the universality of our strategy. Furthermore, the 2D polymeric composites could be easily transformed into 2D monolayered functional porous polymer and carbon nanosheets. We hope that this strategy will open a new door for the design and fabrication of advanced 2D composite and functional nanosheets and thus provide new opportunities for different fields including the environment, energy, catalysis and medicine.

Ultra-high strength concrete (UHSC) and Ultra-high performance concrete (UHPC) with high compressive strength and good durability have been increasingly used in engineering structures. In the present study, uniaxial and triaxial compression tests on UHSC and UHPC are carried out by using servo-hydraulic actuators to investigate the mechanical properties of UHSC and UHPC under various stress states. In triaxial compression tests, the confining pressure ranging from 0 to 50 MPa is applied on UHSC and UHPC specimens. The mechanical responses of UHSC and UHPC specimens under various confining pressures, including peak strength, axial and circumferential strain are recorded in the loading process. According to the elastoplastic behavior of UHSC and UHPC specimens in tests, the influence of confining pressure on the compressive strength and plastic deformation performances of UHSC and UHPC are studied. It is found that the compressive strength and plastic deformation capacity of UHSC and UHPC tend to be higher with the increasing of confining pressure. The enhancement of compressive strength of UHPC is slightly lower than that of UHSC However, due to the lateral restraint effect of the confining pressure and the tensile action of the steel fibers inside the UHPC specimen, failure of the cylindrical specimen are delayed more significantly with increasing of confining pressure. Failure surfaces based on Ottosen’s criterion for UHSC and UHPC are identified accroding to test data. By comparing and analyzing the tests results on UHSC, UHPC and previously tested C200, it is concluded the effect of confining pressure on the enhancement of compressive strength of concretes has a negative relationship with the uniaxial compressive strength of concretes.

The high strength steel (HSS) with a nominal yield stress not less than 460 N/mm2 has been increasingly used in engineering structures. Compared with mild steels, HSSs have higher strength but lower ductility. This paper is concerned with the ductile fracture prediction of the HSS in a wide range of stress triaxiality and Lode angle. Experimental investigation is conducted to study the influence of stress triaxiality and Lode angle on fracture ductility of three different HSSs (Q550, Q690 and Q890). The experimental results are used to calibrate three typical fracture criteria: Void Growth Model (VGM), Combined Fracture Model (CFM) and Bai-Wierzbicki Model (BWM). It is found that without of consideration of Lode angle, the VGM fails to give an accurate prediction of fracture responses of all types of experiments. Compared with VGM, the CFM gives better fitting results. However, because the stress triaxiality dependence and Lode angle dependence are separated in CFM, there still exists discrepancy between prediction and real responses. The BWM gives the most accurate fitting results and prediction for all tests on three different HSSs. Moreover, it is found that elongation at fracture fails to describe the fracture ductility of HSS in a wide range of stress states. Based on parametric study results, it is found that with increasing Lode angle dependence of plasticity, the Lode angle dependence of fracture ductility of HSSs tend to decrease.

In order to evaluate the slip performance of hybrid connections between high strength steel and mild steel, 30 hybrid connection specimens between high strength steel (Q550, Q690 and Q890) and mild steel (Q235 and Q345) with shot-blasted surface are designed to measure slip factors. The test results are compared with the slip factors measured from the connections with the same grade of high strength steel. According to the test results, the slip factors of hybrid connections are lower than the slip factor of 0.5 for mild steel specified in existing design code. Furthermore, the influence of steel strength grade on slip factor is investigated based on friction mechanism. It can be concluded that with the increase of steel grade, the slip factor of hybrid connection tends to decrease due to the reduction of surface roughness and the reduced potential increase in contact surface by plastic deformation. The slip factor of 0.45 is recommended for hybrid connections between Q550 or Q690 and Q235 mild steel. The slip factor of 0.40 is recommended for hybrid connections between Q550 or Q690 and Q345 mild steel. For hybrid connections between Q890 and mild steel Q235 or Q345, slip factor of 0.40 is recommended.

The loading resistance of slip critical steel connection is determined by the slip factor between faying surfaces and pretension force in bolts. The shot-blasting treatment is a commonly used and simple type of surface treatments. In order to avoid the risk of rusting of shot-blasted surfaces which threatens the structure safety, shot-blasted surfaces are generally coated with aluminum or zinc-based product. In this study, the slip factors of high strength steels (Q550, Q690 and Q890) with inorganic zinc-rich coating are investigated. Two values of coating thickness (60 μ m and 80 μ m ) are selected and the influence of thickness of coating on slip factor is studied. Based on classical friction mechanism theory, compared with slip factor of shot-blasted surface, the decreasing of slip factor of surface with inorganic zinc-rich coating is analyzed. Moreover, the coating thickness effect on slip factor is also investigated. Because the difference between the measured slip displacement at 5 min (short-term tests) and 3 h (long-term tests) exceed 2 μ m , corresponding creep tests are carried out to evaluate long-term effects. Based on tests results, the recommended values of slip factor of high strength steel surface with inorganic zinc-rich coating is 0.30.

The high strength steel (HSS) with a nominal yield stress not less than 460 N/mm2 has been increasingly used in engineering structures. An accurate yield criterion which describes the elastoplastic behavior of high strength steels under complex stress states, is significant for the analysis and design of high strength steel structures. For ductile metal materials, the most generally used the von Mises yield criterion neglects the effects of stress triaxiality and Lode angle on the metal plasticity. However, due to the reduce ductility with the increase in strength, such yield criterion may not applicable to HSSs. In the present paper, the tests of six types of specimens are carried out to evaluate effects of stress triaxiality and Lode angle on the plastic behavior of HSSs (Q550, Q690 and Q890). The applicability of von Mises yield criterion is examined firstly using experimental results and finite element analyses. It demonstrates that an appropriate yield function of HSSs should consider effects of the Lode angle while the influence of stress triaxiality is negligible. Based on the experimental and numerical results, a yield function for HSSs is proposed, to essentially simulate the elastoplastic behavior of high strength steel under complex stress states.

The penetration paths of chloride ions in recycled aggregate concrete (RAC) are of significant interest and have not been well studied previously. This study used X-ray computed tomography (X-CT) as a novel approach to investigate chloride ion penetration paths in RAC. The results indicate that X-CT can be used for the constant monitoring of chloride ion penetration paths in RAC, and the influence of mix proportions on the chloride ion penetration can be understood through the X-CT visualization.

A stacked lateral double-diffused metal–oxide–semiconductor field-effect transistor (LDMOS) with enhanced depletion effect by surface substrate is proposed (ST-LDMOS), which is compatible with the traditional CMOS processes. The new stacked structure is characterized by double substrates and surface dielectric trenches (SDT). The drift region is separated by the P-buried layer to form two vertically parallel devices. The doping concentration of the drift region is increased benefiting from the enhanced auxiliary depletion effect of the double substrates, leading to a lower specific on-resistance (R on,sp). Multiple electric field peaks appear at the corners of the SDT, which improves the lateral electric field distribution and the breakdown voltage (BV). Compared to a conventional LDMOS (C-LDMOS), the BV in the ST-LDMOS increases from 259 V to 459 V, an improvement of 77.22%. The R on,sp decreases from 39.62 mΩcm2 to 23.24 mΩcm2 and the Baliga's figure of merit (FOM) of is 9.07 MW/cm2.

Bi2 (Mg1/3Nb2/3-xSnx)2O7(BMNS)(x=0.1,x=0.15,x=0.2,x=0.25 mol) ceramics was prepared by traditional solid-state reaction method and the influence of tin ion doped amount on the dielectric properties and structure of BMNS ceramics were investigated. The results show that all of the doped samples keep a single monoclinic pyrochlore phase and there is no second phase observed. The grain size of ceramics gradually increases, the dielectric constant decreases first and then increases, the dielectric loss increases first and then decreases and the density reduces with the increase of tin ion doped amount. The density of ceramics increases first then decreases with the increase of sintering temperature. The BMNS ceramics sintered at 980 °C with 0.25 mol tin ion doping amount has a biggest density and the best properties,whose εr is 155(1MHz),tanδ is 0.0011(1MHz), the bulk density is 7.62 g/cm3.

This work aims to experimentally and theoretically study the effects of ethylene–propylene copolymers as compatibilizer on the phase morphologies, interfacial properties, rheological behaviors and mechanical properties of ultrahigh molecular weight polyethylene/homopolymerized polypropylene (UHMWPE/HPP) blends. The results indicate that the addition of ethylene–propylene block copolymer EPS30R or random copolymer DP3000 ranging within 1–3 parts per hundred parts (phr) of UHMWPE/HPP blends can remarkably reduce the sizes of the UHMWPE particles and significantly improve the mechanical property such as tensile strength and elongation at break. Moreover, the ternary blends still show two-phase morphologies, and the favorable melt flowability of the UHMWPE/HPP blends can be basically maintained. Besides, dissipative particle dynamics simulations on the ternary UHMWPE/HPP/ethylene–propylene copolymer blends indicate that with fixed mole number of the block copolymer, longer block chains have higher efficiency on reducing the interfacial tension than the shorter ones. But for the block copolymers with fixed volume fraction, interfacial tensions firstly decrease and then increase with increasing the chain length of block copolymer.

In this work, montmorillonite (Mt) was modified by octadecyl amine ethoxylate ether (A) which has two poly(ethylene oxide) segments. Montmorillonite/polypropylene (Mt/PP) nanocomposites were prepared by a melt blending technique using different contents of modified Mt with and without maleic anhydride grafted polypropylene (PPg). The intercalated and exfoliated structures of Mt/PP nanocomposites were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Because of the typical intercalated and exfoliated structures, the mechanical properties of Mt/PP nanocomposites were improved significantly. The modified Mt in a PP matrix led to a significant reduction of melt viscosity and enhancement in Izod-notched impact strength and elongation at break. The Izod-notched impact strength and elongation at break of Mt/PP nanocomposites were 1.95 and 2.77 times as high as those of pure PP. The tensile strength of Mt/PP nanocomposites was also improved in the presence of PPg.

The charge islands SOI LDMOS with Back-side Etching technology structure is proposed. The new structure features the equally spaced charge islands of the upper LDMOS and a back-side etched structure of the lower LDMOS. A series of equidistant high concentration N+ regions are formed at the upper SOI LDMOS by the ion implanting method. The breakdown voltage of the device is improved due to dielectric field enhancement and the interaction of charges. The results show that the breakdown voltage is increased from 210V to 615V (192.8% enhanced), compared to the conventional LDMOS. The on-resistance of the as-studied stacked SOI LDMOS reduces from 48.2 Ω⋅mm2 to 37.23 Ω⋅mm2 comparing with conventional charge islands device, leading to a reduction ratio of 22.7%.

Numerous studies suggest that two-phase morphology and thick interface are separately beneficial to the viscosity reduction and mechanical property maintainence of the matrix when normal molecular weight polymer (NMWP) is used for modification of ultrahigh molecular weight polyethylene (UHMWPE). Nevertheless, it is very difficult to obtain a UHMWPE/NMWP blend which may demonstrate both two-phase morphology and thick interface. In this work, dissipative particle dynamics simulations and Flory-Huggins theory are applied in predicting the optimum NMWP and the corresponding conditions, wherein the melt flowability of UHMWPE can be improved while its mechanical properties can also be retained. As is indicated by dissipative particle dynamics simulations and phase diagram calculated from Flory-Huggins theory, too small Flory-Huggins interaction parameter (χ) and molecular chain length of NMWP (N NMWP) may lead to the formation of a homogeneous phase, whereas very large interfacial tension and thin interfaces might also appear when parameters N NMWP and χ are too large. When these parameters are located in the metastable region of the phase diagram, however, two-phase morphology occurs and interfaces of the blends are extremely thick. Therefore, metastable state is found to be advisable for both the viscosity reduction and mechanical property improvement of the UHMWPE/NMWP blends.