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Context: The electronic properties and optical properties of Cr-doped monolayer WS2 under uniaxial compressive deformation have been investigated based on density functional theory. In terms of electronic structure properties, both intrinsic and doped system bandgaps decrease with the increase of compression deformation, and the values of the bandgap under the same compression deformation after Cr doping are reduced compared with the corresponding intrinsic states. When the compressive deformation reaches 10%, both the intrinsic and doped system band gaps are close to zero. New electronic states and impurity energy levels appear in the WS2 system when doped with Cr atoms. For the optical properties, the calculation and analysis of the dielectric function under each deformation regime of monolayer WS2 show that the compression deformation affects the dielectric function, and when the compression deformation is 10%, the un-doped and Cr-doped regimes show a decrease in ε1(ω) compared to the compression deformation of 8%. For each deformation system, the peak reflections occur in the ultraviolet region. Near the position where the second peak of the absorption spectrum appears, it can be seen that the ability of each system to absorb light gradually decreases with the increase of the amount of deformation and appears to be red-shifted to varying degrees. Methods: This study follows the initial principles of the density functional theory framework and is based on the CASTEP module of Materials-Studio software GGA and PBE generalizations are used to perform computations such as geometry optimization of the model. We have calculated the energy band structure of monolayer WS2 with intrinsic and compressive deformations of 2% and 4% using PBE and HSE06, respectively. The band gap values calculated using PBE are 1.802 eV, 1.663 eV, and 1.353 eV, respectively, and the band gap values calculated with HSE06 are 2.267 eV, 2.034 eV, 1.751 eV. The results show that the bandgap values calculated by HSE06 are significantly higher than those calculated by PBE, but the bandgap variations calculated by the two methods have the same trend, and the shape characteristics of the energy band structure are also the same. However, it is worth noting that the computation time required for the HSE06 calculation is much longer than that of the PBE, which is far beyond the capability of our computer hardware, and the purpose of this paper is to investigate the change rule of the effect of deformation on the bandgap value, so to save the computational resources, the next calculations are all calculated using the PBE. The Monkhorst–Pack special K-point sampling method is used in the calculations. The cutoff energy for the plane wave expansion is 400 eV, and the K-point grid is assumed to be 5 × 5 × 1. Following geometric optimization, the iterative precision converges to a value of less than 0.03 eV/Å for all atomic forces and at least 1 × 10−5 eV/atom for the total energy of each atom. The vacuum layer's thickness was selected at 20 Å to mitigate the impact of the interlayer contact force. [ABSTRACT FROM AUTHOR]

Context: The electronic properties and optical properties of Cr-doped monolayer WS2 under uniaxial compressive deformation have been investigated based on density functional theory. In terms of electronic structure properties, both intrinsic and doped system bandgaps decrease with the increase of compression deformation, and the values of the bandgap under the same compression deformation after Cr doping are reduced compared with the corresponding intrinsic states. When the compressive deformation reaches 10%, both the intrinsic and doped system band gaps are close to zero. New electronic states and impurity energy levels appear in the WS2 system when doped with Cr atoms. For the optical properties, the calculation and analysis of the dielectric function under each deformation regime of monolayer WS2 show that the compression deformation affects the dielectric function, and when the compression deformation is 10%, the un-doped and Cr-doped regimes show a decrease in ε1(ω) compared to the compression deformation of 8%. For each deformation system, the peak reflections occur in the ultraviolet region. Near the position where the second peak of the absorption spectrum appears, it can be seen that the ability of each system to absorb light gradually decreases with the increase of the amount of deformation and appears to be red-shifted to varying degrees. Methods: This study follows the initial principles of the density functional theory framework and is based on the CASTEP module of Materials-Studio software GGA and PBE generalizations are used to perform computations such as geometry optimization of the model. We have calculated the energy band structure of monolayer WS2 with intrinsic and compressive deformations of 2% and 4% using PBE and HSE06, respectively. The band gap values calculated using PBE are 1.802 eV, 1.663 eV, and 1.353 eV, respectively, and the band gap values calculated with HSE06 are 2.267 eV, 2.034 eV, 1.751 eV. The results show that the bandgap values calculated by HSE06 are significantly higher than those calculated by PBE, but the bandgap variations calculated by the two methods have the same trend, and the shape characteristics of the energy band structure are also the same. However, it is worth noting that the computation time required for the HSE06 calculation is much longer than that of the PBE, which is far beyond the capability of our computer hardware, and the purpose of this paper is to investigate the change rule of the effect of deformation on the bandgap value, so to save the computational resources, the next calculations are all calculated using the PBE. The Monkhorst–Pack special K-point sampling method is used in the calculations. The cutoff energy for the plane wave expansion is 400 eV, and the K-point grid is assumed to be 5 × 5 × 1. Following geometric optimization, the iterative precision converges to a value of less than 0.03 eV/Å for all atomic forces and at least 1 × 10−5 eV/atom for the total energy of each atom. The vacuum layer's thickness was selected at 20 Å to mitigate the impact of the interlayer contact force. [ABSTRACT FROM AUTHOR]

The tensile deformation is the most common forming principle in the sheet forming process, but there is a new tube forming process—tube hydro-forging has been developed based on the principle of compression deformation. In addition to the instability problem, a new surface defect—thickness distortion—was found in the compression deformation. In this paper, the wall thickness distortion is analyzed from the point of view of mechanics and deformation. It is revealed that in the low pressure tube hydroforming process, a bending moment exists and leads to some small wrinkles in the straight wall. In the tube hydro-forging, the small wrinkles would develop to the thickness distortion with the increase of compressive deformation. The wall thickness and compressive strain are two major effect factors. It is verified by experiments and simulation. This study helps to recognize the new surface phenomenon in compressive deformation. [ABSTRACT FROM AUTHOR]

In today's manufacturing industries, hard competition between rival firms makes it compulsory for researchers to design lighter and cheaper machine components due to the megatrends of cost-effectiveness and anti-pollution. At this point, aluminum syntactic foams (ASFs) are new-generation engineering composites and come into the upfront as a problem-solver. Owing to their features like low density, sufficient elongation, and perfect energy absorption ability, these advanced foams have been considerably seductive for many industrial sectors nowadays. In this study, an industrial-oriented automatic die casting technology was used for the first time to manufacture the combination of AA7075/porous expanded clay (PEC). Micro evaluations (optical and FESEM) reveal that there is a homogenous particle distribution in the foam samples, and inspections are compatible with the other ASF studies. Additionally, T6 aging heat treatment was operated on one half of the produced foams to explore the probable impact of aging on the compressive responses. Attained results show that PEC particles can be an alternative to expensive hollow spheres used in the previous works. Besides, a favorable relationship is ascertained between the aging treatment and mechanical properties such as compression strength and plateau strength. [ABSTRACT FROM AUTHOR]

Nickel-based superalloys have become essential materials due to their excellent comprehensive properties as the miniaturization of products in the aerospace and energy fields develops. The complex microstructure and various strengthening mechanisms of nickel-based superalloys make the plastic deformation behavior extremely complicated at the mesoscopic scale. In this paper, compression experiments of nickel-based superalloy samples with different feature sizes (i.e. the sample diameter to grain size ratio, D/d) and different aging times at the mesoscopic scale were carried out. The coupling effect of feature size and δ phase on the compressive deformation behavior was studied. The results show that the δ phase plays a role in precipitation strengthening during compressive deformation at the mesoscopic scale. When D/d is in the range of 9.7–10.9, the flow stress decreases significantly with the increase of grain size, and a “smaller is weaker” size effect appears. When D/d is less than 9.7, the flow stress increases with the grain size, and a “smaller is stronger” size effect appears. Considering grain boundary strengthening, solid solution strengthening, and precipitation strengthening, a size effect model of flow stress was established. The calculated values were in good agreement with the experimental values. The inhomogeneity of the end surface and side surface increases with the decrease of feature size and the decrease of aging time. The presence of the δ phase reduces the inhomogeneous deformation of nickel-based superalloys during compressive deformation at the mesoscopic scale.

• Bearing capacity and energy absorption characteristics of the optimized AlSi10Mg structure are significantly enhanced. • Finite element calculation model used in this paper accurately describes the mechanical behavior of AlSi10Mg structure. • Fracture features of AlSi10Mg porous structure indicate a ductile as well as a brittle failure under compressive load. • Normalized energy absorption helps designers select the one structure most suitable for a given application. In order to correctly understand the mechanical behavior, damage mode and damage mechanism of AlSi10Mg optimized structure under compressive load, a series of experimental and simulation studies were carried out. The stress-strain response, bearing capacity, energy absorption characteristics, damage mode and mechanism of the structure are analyzed and discussed. The results show that AlSi10Mg porous structure has obvious strain hardening effect, but no obvious strain rate effect. The volume fraction of AlSi10Mg porous structure increased from 9.43% to 22.15%, and its bearing strength increased from 22.34 MPa to 50.98 MPa. The optimized design structure is complex in this paper, which eliminates undesirable failure modes, and the benefit of high specific energy absorption is retained. The experimental and simulation results show that shear failure is the main cause of structural damage, and the normal of the failure section and the load action direction are roughly inclined at an angle of 45° ∼ 55°. The research results can provide an important reference for the optimal design of porous metal structure. [ABSTRACT FROM AUTHOR]

For engineering materials, it is important to search for strategies to enhance certain combinations of mechanical properties, because many performances, such as strength and toughness, are mutually exclusive. Effective strategies have evolved in the biological tissues of many plants and animals to construct composite materials with unique combinations of mechanical properties. One impressive example is found in the hammer-like appendages of mantis shrimp, which are exceptionally resistant to crushing because they must withstand the reaction forces created when attacking prey. In this paper, quasi-static compression tests, advanced microscopic observation, and spectroscopic analysis were employed to identify a series of characteristic changes, including changes in mineral composition and arrangement of chitin fibers, and the resulting toughening mechanisms are also examined. The combination of experiments and finite element analysis revealed that by combining different fiber arrangements and components in adjacent macroscopic layers, longitudinal stress could be shifted to the lateral direction, hence efficiently enhancing longitudinal compression resistance while avoiding catastrophic failure. Overall, these findings further the understanding of the fiber structure and toughening mechanism of appendages, which may serve as a foundation for the development of tough bioinspired composites.

Electromagnetic interference (EMI) cause the equipments used in electronics and avionics industries to either deteriorate or malfunction. Therefore, EMI shielding is essential to ensure electronics equipment safety. The present investigation explores the EMI shielding effectiveness of micro-size cenosphere (2 wt.%, 4 wt.%, and 6 wt.%) filled aluminum matrix syntactic foams. The aluminum matrix syntactic foams were fabricated using stir-casting. The prepared samples were studied for their EMI shielding, microstructural characterization, compressive deformation behavior, and hardness. The cenosphere-filled aluminum syntactic foam exhibited better EMI shielding effectiveness, varied from −41.38 dB to −56.68 dB measured in the frequency range 8 to 12 GHz. This is due to microwave absorption and the dielectric nature of porous cenosphere fillers in the syntactic foam. The highest plateau strength 316.48 MPa and compressive yield strength of 289.53 MPa was achieved in 6 wt% cenosphere-filled syntactic foam. The microstructural study showed the presence of cenospheres in spherical form with homogeneous distribution. The observation shows good bonding between the matrix and cenosphere filler element. The micro-hardness measurement varied from 114 HV to 125.6 HV for the cenosphere filled syntactic foam (up to 4 wt %); further increasing the cenosphere wt% reduced the hardness. The XRD analysis showed the presence of reaction compounds AlSiO2, and Al2SiO5 which enhanced the brittleness in the syntactic foams. [ABSTRACT FROM AUTHOR]

The webs such as paper, plastic film and thin metal are produced by Roll-to Roll manufacturing system, and are wound into a roll in the final process of this system. However, if the winding conditions of the web are inappropriate, the defects such as gage band, wrinkle and slippage will occur in wound roll, and then quality of products is significantly reduced. In previous studies, some analysis models of in-roll stress considering various factors, have been established to predict the defects. However, as far as authors know, there is few research regarding the gage band. In particular, the plastic films used for high functional flexible devices are being thinner, the defects can occur easily. In this paper, the in-roll stress analysis considering the web thickness variation in width direction and compressive deformation of web in the radial direction using the Hertz contact theory is presented. Moreover, optimization of winding conditions is conducted to prevent simultaneously the gage band, wrinkle and slippage. As a result, it was confirmed that the presented analysis can estimate the radial stress distribution of wound roll in the width direction. And, the effectiveness of optimized wind-up tension is verified theoretically and experimentally.

The compressive deformation of backfill materials is large due to the large mining depth of coal seams and high mining-induced stress during the deep backfill mining. Therefore, the controlling effect on strata movement significantly differs from that in shallow coal seams. The research aims to explore the influences of the compressive deformation of backfill materials on the strata movement and stress evolution in deep backfill mining. For this purpose, the backfill panel in Xinjulong Coal Mine, Shandong Province, China was taken as an engineering case study; the changes in displacement, structural evolution, and stress distribution of overlying strata in the panel under compression ratios of backfill materials of 70%, 40%, and 20% were investigated. In addition, the influences of different compressive deformations of the backfill materials on the controlling effect on overlying strata were compared and investigated. The results showed that the displacement of overlying strata in the backfill panel decreases with the decreasing compression ratio: the maximum displacement of overlying strata decreases from 24.32 to 13.74 and 6.83 mm as the compression ratio is reduced from 70 to 40%, and 20%, respectively. Relative to the overlying strata at a compression ratio of 70%, the vertical displacements at compression ratios of 40 and 20% separately decrease by 43.5 and 71.9%. The lower the compression ratio of backfill materials, the better the control of overlying strata. The results provide theoretical support for optimizing the performance of backfill materials in deep backfill mines and controlling the ground pressure in the stope. [ABSTRACT FROM AUTHOR]

In this study, the compressive deformation of crushed sandstone was tested using a crushed rock deformation-seepage test system, and the effects of various factors, including crushed rock grade, grade combination, water saturation status, and stress loading method (i.e., continuous loading or cyclic loading and unloading), on the compressive deformation of crushed sandstone was analyzed from four perspectives including stress-strain, bulking coefficient, deformation mechanism and energy dissipation. The results indicate that the stress-strain relations of crushed sandstone are closely associated with all factors considered, and are well represented by exponential functions. The strain observed for a given applied stress increased with increasing crushed rock grade throughout the loading period. Crushed sandstone grades were combined according to a grading index (n), where the proportion of large-grade rocks in the sample increased with increasing n. The bearing capacity of a water-saturated crushed sandstone sample with n = 0.2 was less than that of an equivalent dry sample for a given applied stress. The stress-strain curve of a water-saturated crushed sandstone sample with n = 0.2 under cyclic loading and unloading was similar to that obtained under continuous loading. Observation and discovery, the deformation mechanism of crushed sandstone was mainly divided into four stages, including crushing, rupture, corner detachment and corner wear. And 20% of the work done by testing machine is used for friction between the crushed sandstone with the inner wall of the test chamber, and 80% is used for the closing of the void between the crushed sandstone, friction sliding, crushing damage. [ABSTRACT FROM AUTHOR]

AX61 magnesium alloy was reinforced with short Saffil fibres using squeeze cast technology. Samples were cut from the casting in two directions: parallel and perpendicular to the fibre plane. Samples were deformed in compression at various temperatures from room temperature to 300 °C. Various strengthening mechanisms such as load transfer, increased dislocation density, Orowan and Hall–Petch strengthening were analysed. During deformation, the stress relaxation tests were subsequently performed. The relaxation curves were evaluated with respect to Li and Feltham equations with the aim to find stress components in matrix and parameters of the thermally activated process(es). [ABSTRACT FROM AUTHOR]

The 6xxx aluminum alloy is the first choice for automotive lightweight forgings due to its excellent performance, high strength and low weight. The production time of current aluminum alloy forging generally exceeds 10 h. To reduce the production time of traditional aluminum alloy forgings, 6082-T6 aluminum alloy is used in the forming process. The effects of different heating temperatures (200 °C, 300 °C, and 400 °C) and deformation degrees (30%, 50%, and 70%) on the deformability and properties of 6082-T6 billets have been investigated. The results show that when the heating temperature is higher than 300 °C, the compressive deformation resistance obviously decreases with increasing strength. With compression at 200 °C and 70% deformation with short heating time, the strength of the sample is close to the T6 (solution treatment and artificial aging) state. A large number of dislocations and subgrains were introduced due to the compression deformation, and their amounts decreased as the heating temperature increased. The size of the precipitated phase β′′ slightly grows under a heating temperature of 200 °C. However, when the heating temperature is higher than 300 °C, the precipitated phase gradually changes from β′′, which is optimal for the strengthening effect, to β′ and β, which offer weaker strengthening. Therefore, under a lower heating temperature of 200 °C for 5 min, a large number of dislocations are introduced with the β′′ precipitated phase, leading to higher strength with less heat treatment time. [ABSTRACT FROM AUTHOR]

Under compressive testing at 400 °C and a strain rate range of 0.05–5 s−1, the hot deformation behavior and microstructure evolution of an as-cast (AC), as-extruded (with a bimodal grain structure (named as Ex-1) or a relatively uniform fine grain structure (Ex-2)) WE43 alloy have been investigated and compared. The results indicate that the AC sample exhibits the highest peak stress, while the Ex-2 sample has the lowest value. Within the AC material, fine grains were firstly formed along the pancake-like deformed grains (as a necklace structure). The necklace structure was also formed within the Ex-1 and Ex-2 materials at high strain rates of 0.5 and 5 s−1. However, a lamellar structure that the coarse elongated grains divided by parallel boundaries was formed within the Ex-1 material. A relatively more homogeneous fine grain structure is achieved after a true strain of 1.0 within the Ex-2 material at a low strain rate of 0.05 s−1. In addition, a discontinuous dynamic recrystallization mechanism by grain boundary bulging is found to occur. After a true strain of 1.2, a (0001) fiber texture, a typical rare earth (RE) texture, and a relatively random texture are formed within the AC, Ex-1, and Ex-2 WE43 alloy material, respectively. [ABSTRACT FROM AUTHOR]

We present the polarization-dependent highly absorptive in Ka-band composition of conventional polyurethane foam filled with in situ synthesized aerogel coated by reduced graphene oxide (rGO). The rGO-based aerogel was in situ prepared into the open-cell polyurethane foam (PUF) skeleton through a bidirectional freeze-drying process. The aerogel is composed of the flat lamellas stacks, possessing the anisotropic structure and unique electromagnetic properties. Further improvement of the electromagnetic shielding ability was possible by the rGO coating introduction as a coupling layer between PUF and rGO-based aerogel. This enhances the overall conductivity of the resulting composites: 1.41 + 3.33i S/m vs. 0.9 + 2.45i S/m for PUF loaded with in situ synthesized aerogel without rGO coating.With this mechanically robust plane easy to process coating one could achieve −20 dB by power with the record light structure (0.0462 g/cm2). That could compete in view of the weight per cm2 even with graphene-based absorbers comprising either dielectric matching elements or back metal reflectors, or both. [ABSTRACT FROM AUTHOR]