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• Compressive properties of 3D graphene are studied by theory and MD simulations. • The unified constitutive relations of three kinds of 3D graphene are derived. • Compressive deformation mechanisms of three kinds of 3D graphene are discussed. • The configuration-property relationships of 3D graphene are elucidated. • Energy absorption capacities of three kinds of 3D graphene are analyzed. Combining molecular dynamics (MD) simulations and continuum modeling, the uniaxial in-plane compressive properties of honeycomb three-dimensional (h3D), triangle-like 3D (t3D) and non-equilateral hexagon 3D (nh3D) graphene are investigated to elucidate configuration-property relationships, and the constitutive relations of three kinds of 3D graphene are derived to evaluate the compressive mechanical properties. Based on theoretical and MD simulation results, it is found that the compressive stress-strain responses of 3D graphene can be divided into five stages. The compressive mechanical properties and deformation mechanisms of each stage are different. When 3D graphene is compressed, graphene sidewalls undergo rotations, bending and buckling deformations, collapses. Because graphene sidewalls of h3D graphene are prone to undergo buckling deformations, there is large locking strain in h3D graphene. For t3D and nh3D graphene, their high plateau stress is attributed to unique configurations. Moreover, we also find that with increasing graphene sidewall width, Young's modulus and plateau stress of 3D graphene gradually decrease. In addition to the above investigations, the energy absorption mechanisms and compression-unloading stress-strain curves of 3D graphene are also studied. It is found that there are extraordinary compression-recovery properties and energy absorption capacities in 3D graphene. Finally, the selection criteria of 3D graphene are proposed. [Display omitted] [ABSTRACT FROM AUTHOR]

Background: Image-based computational models are widely used to determine atherosclerotic plaque stress/strain conditions and investigate their association with plaque progression and rupture. However, patient-specific vessel material properties are in general lacking in those models, limiting the accuracy of their stress/strain measurements. A noninvasive approach of combining in vivo 3D multi-contrast and Cine magnetic resonance imaging (MRI) and computational modeling was introduced to quantify patient-specific carotid plaque material properties for potential plaque model improvements. Vessel material property variation in patients, along vessel segment, and between baseline and follow up were investigated. Methods: In vivo 3D multi-contrast and Cine MRI carotid plaque data were acquired from 8 patients with follow-up (18 months) with written informed consent obtained. 3D thin-layer models and an established iterative procedure were used to determine parameter values of the Mooney-Rivlin models for the 81slices from 16 plaque samples. Effective Young’s Modulus (YM) values were calculated for comparison and analysis. Results: Average Effective Young’s Modulus (YM) and circumferential shrinkage rate (C-Shrink) value of the 81 slices was 411kPa and 5.62%, respectively. Slice YM value varied from 70 kPa (softest) to 1284 kPa (stiffest), a 1734% difference. Average slice YM values by vessel varied from 109 kPa (softest) to 922 kPa (stiffest), a 746% difference. Location-wise, the maximum slice YM variation rate within a vessel was 311% (149 kPa vs. 613 kPa). The average slice YM variation rate for the 16 vessels was 134%. The average variation of YM values for all patients from baseline to follow up was 61.0%. The range of the variation of YM values was [-28.4%, 215%]. For plaque progression study, YM at follow-up showed negative correlation with plaque progression measured by wall thickness increase (WTI) (r = -0.7764, p = 0.0235). Wall thickness at baseline correlated with WTI negatively, with r = -0.5253 (p = 0.1813). Plaque burden at baseline correlated with YM change between baseline and follow-up, with r = 0.5939 (p = 0.1205). Conclusion: In vivo carotid vessel material properties have large variations from patient to patient, along the diseased segment within a patient, and with time. The use of patient-specific, location specific and time-specific material properties in plaque models could potentially improve the accuracy of model stress/strain calculations. [ABSTRACT FROM AUTHOR]

The mechanical properties of bicrystalline graphene nanoribbons with various tilt grain boundaries (GBs) which typically consist of repeating pentagon–heptagon ring defects are investigated based on the method of molecular structural mechanics. The GB models are constructed via the theory of disclinations in crystals, and the elastic properties and ultimate strength of bicrystalline graphene nanoribbons are calculated under uniaxial tensile loads in perpendicular and parallel directions to grain boundaries. The dependence of mechanical properties is analyzed on the chirality and misorientation angles of graphene nanoribbons, and the experimental phenomena that Young's modulus and ultimate strength of bicrystalline graphene nanoribbons can either increase or decrease with the grain boundary angles are further verified and discussed. In addition, the influence of GB on the size effects of graphene Young's modulus is also analyzed. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) graphene possesses a variety of excellent properties. It is worth using 2D graphene as building block to construct novel three-dimensional (3D) graphene which "inherits" superb performance of 2D graphene. Combining theoretical calculations and finite element method (FEM) based on molecular structural mechanics, the effects of graphene sidewall width, junction structure, in-plane domain size and in-plane overall shape on the elastic properties of zigzag honeycomb 3D graphene and three types of triangle-like 3D graphene are investigated, and the analytical expressions for Young's modulus of triangle-like 3D graphene are derived. The results of FEM are consistent with those of theoretical method. It is found that as graphene sidewall width increases, in-plane/out-of-plane Young's moduli of the above-mentioned 3D graphene first decrease and then tend to stabilize. For the armchair and zigzag triangle-like 3D graphene (sidewall width remains unchanged) with rectangular in-plane overall shape, the Young's modulus will vary with in-plane domain size. These results show that the elastic properties of 3D graphene are strongly dependent on structural size. In addition, junction structure has little influence on the elastic properties of 3D graphene. • A novel triangle-like 3D graphene containing sp3-sp3 carbon bond is constructed. • The size-dependent Young's modulus of triangle-like 3D graphene is investigated. • Analytical expressions of Young's modulus of triangle-like 3D graphene are derived. • The influencing factors for elastic properties of 3D graphene are studied by FEM. [ABSTRACT FROM AUTHOR]

X-ray diffraction (XRD) analysis showed that metal oxide peaks appear at 2θ = 47.7°, 54.5°, and 56.3°, corresponding to Yb2O3 (440), Co2O3 (422), and Co2O3 (511). It was found that oxide formation plays an important role in magnetic, electrical, and surface energy. For magnetic and electrical measurements, the highest alternating current magnetic susceptibility (χac) and the lowest resistivity (×10−2 Ω·cm) were 0.213 and 0.42, respectively, and at 50 nm, it annealed at 300 °C due to weak oxide formation. For mechanical measurement, the highest value of hardness was 15.93 GPa at 200 °C in a 50 nm thick film. When the thickness increased from 10 to 50 nm, the hardness and Young's modulus of the Co60Fe20Yb20 film also showed a saturation trend. After annealing at 300 °C, Co60Fe20Yb20 films of 40 nm thickness showed the highest surface energy. Higher surface energy indicated stronger adhesion, allowing for the formation of multilayer thin films. The optimal condition was found to be 50 nm with annealing at 300 °C due to high χac, strong adhesion, high nano-mechanical properties, and low resistivity. [ABSTRACT FROM AUTHOR]

The hydraulic fracture aperture packed by proppants determines the fracture conductivity and is pivotal to oil and gas production. After hydraulic fracturing, the fracture width decreases owing to proppant embedment, deformation, and crushing. However, the analysis of fracture width reduction based on the mechanical properties of the proppant pack is limited. In this study, an experiment is designed to obtain the apparent Young's modulus, which represents the rigidity of the entire pack, and steel sheets are used to replace rock samples to eliminate heterogeneity and weaken the effect of proppant embedment. Subsequently, the effects of proppant type, concentration, and size on the apparent Young's modulus are discussed. Finally, the controlling factors and mechanisms of fracture width reduction are determined. The results indicate that the fracture width decreases linearly with increasing closure pressure for the ceramsite pack, and that the apparent Young's modulus is associated with the fracture aperture variation, which is governed by proppant embedment and deformation. The apparent Young's modulus increases as the proppant concentration increases or the proppant size decreases, whereas the proppant size imposes a more prominent effect. However, the mixed-size ceramsite pack shows only slight improvements in terms of propping ability. This study provides new insights into factors governing proppant pack deformation. • The apparent Young's modulus is defined through experimental results to quantitatively characterize mechanical properties of the whole proppant pack. • The proppant pack will experience at least 1 rigid-to-plastic deformation cycle under closure pressure. • The apparent Young's modulus for ceramiste can be inserted into fracture width calculation correlation, of which the fracture width decrease is mainly dominant by proppant embedment and deformation. • Proppant concentration and size both have influence on apparent Young's modulus, but the latter is more profound. The finer the particles are, the higher the modulus of the proppant pack is. [ABSTRACT FROM AUTHOR]