Quantitative characterization of irradiation embrittlement effect is important to ensure the service safety of ceramic materials in irradiation environments. Based on the Li's Principle of Energy Equivalence, taking into account the equivalent relationship between the irradiation energy absorbed by the material and the strain energy, theoretical models for irradiation embrittlement dependent fracture strength and mode I fracture toughness of ceramics have been developed, respectively. These models reveal a quantitative relationship between irradiation fluence and fracture strength/mode I fracture toughness, enabling the prediction of irradiation data over a wide range based on limited irradiation experimental data. The predicted results of both models are well validated by all available experimental data, including two groups of fracture strength data and four groups of mode I fracture toughness data. These models offer an effective theoretical approach for the convenient prediction of the mechanical properties of ceramic materials under wide irradiation fluence ranges. This effectively reduces reliance on difficult irradiation experiments, while providing a theoretical basis for the structural design and reliability assessment of reactor ceramics, as well as for regulatory and cost optimization aspects.

As the core components of equipment designed for detecting extreme environments, semiconductor materials typically encounter the dual challenges of extreme pressure and temperature during the service life. Bandgap energy, a crucial physical parameter of semiconductor materials, is particularly sensitive to pressure and temperature variations. Therefore, it is of significant importance to quantitatively characterize the influences of pressure and temperature on the bandgap energy. In this paper, a non-fitting theoretical model for the pressure-temperature-dependent bandgap energy of semiconductor materials is developed based on the force-heat equivalence energy density principle (Li's principle of energy equivalence). This model characterizes the quantitative relationship among pressure, temperature, and bandgap energy through considering the equivalent contributions of external pressure work, thermal energy, and bandgap energy to electronic transitions. Furthermore, this model requires only three experimentally available bandgap values to predict bandgap energies at different pressure and temperature. The model's predictions have achieved good agreement with 16 sets of all the available experimental data. This work provides a theoretical foundation for the performance evaluation and material design of semiconductors under varying pressure and temperature conditions, which is beneficial for expanding the application of semiconductor materials in extreme environments.

The competition between surficial and volumetric diffusion during the sintering process for ceramic polymorphism at different sintering temperatures is worth deeply exploring. In the current work, various sintering cases of mixed TiO2 nanoparticles with rutile and anatase types were investigated and the effects of crystalline phase, sintering temperature, and particle size on the sintering process were systematically investigated. The difference in thermodynamic stability and surficial activity of the crystalline phase could promote the decomposition and densification of the nanoparticles. Comparing the mixed-phase sintering process at different sintering temperatures, the results showed that the particle binding process at low temperature relied mainly on surficial diffusion, however, volumetric diffusion played a crucial role at high temperature. The internal occurrence of volumetric diffusion inhibited the surficial diffusion, resulting in a smaller diameter of the sintering neck and a different sintering rate. In the case of sintering three nanoparticles with rutile and anatase types, it could be found that the decomposition of nanoparticles is more uniform in mixed-phase sintering at high temperatures and the sintering rate is not significantly influenced by the sintering temperature. This work demonstrates the advantage of a mixed-phase sintering strategy for TiO2 nanoparticles, which could provide insight into ceramic materials with polymorphism.

Especially, the quantitative relationship between the thickness and volume fraction of graphene and the grain size of graphene nanoplatelets reinforced metal matrix composites was revealed, based on which the influence of grain refinement, load transfer and dislocation strengthening on the yield strength of composites and their evolution with temperature was quantitatively characterized. Furthermore, by introducing the weakening effect of graphene agglomeration on associated control mechanism of yield strength, a prediction model of temperature dependent yield strength of graphene nanoplatelets reinforced metal matrix composites was established. The proposed prediction approach is verified by comparing the predictions with the experimental data in other literature. Moreover, using the established model, the quantitative effects of length and thickness of nanoplatelets on the yield strength of composites and their evolution with temperature were carried out. This research also provides an effective method for investigating the optimal volume fraction and failure volume fraction of added graphene.

Development of high performance polyether-ether-ketone (PEEK)) composites is of great significance for aerospace engineering application. The fused filament fabrication (FFF)-based 3D printing process is promising for manufacturing high performance short carbon fiber (SCF) reinforced PEEK composites. However, a comprehensive investigation of the combined effects of SCF content and annealing condition has not been conducted on the mechanical performances of SCF/PEEK composites; also, elevated temperature mechanical properties that are required for aerospace engineering have not been reported for 3D printed SCF/PEEK composites. This work develops a creative strategy that combines the optimal short carbon fiber (SCF) content with annealing treatment to achieve significant improvements in the mechanical properties both at room and elevated temperatures of FFF-3D printed SCF/PEEK composites. First, the influences of SCF content on the mechanical performances of 3D printed SCF/PEEK composites are studied to determine the optimal fiber content (5 wt%) for the best mechanical performances of non-annealed PEEK composites. Then, the effects of SCF content and annealing on room temperature and elevated temperature mechanical performances are examined for both PEEK and the 5 wt% SCF/ PEEK composite. It is elucidated that the increase of interface strength and crystalline region as well as the reduction of residual stress by annealing are all responsible for the observed improvements in mechanical performances. This work presents a comprehensive study of 3D printed short fiber reinforced thermoplastics and serves as a valuable reference for the 3D printing of high-performance thermoplastic composites.

A physics-based temperature-dependent yield strength model without fitting parameters was developed for single-phase FCC high-entropy alloys. The model considered the temperature dependence of lattice friction stress, solid solution strengthening, grain boundary strengthening, dislocation strengthening, and their evolution with temperature to the overall yield strength. The results show that a quantitative relationship between temperature, material parameters, and yield strength was successfully captured by the model. This model can predict the yield strength at different temperatures only by using the easily available material parameters at room temperature. The accuracy of model was well verified by 17 sets of available experimental data over a wide temperature range (4.2-1273 K). Moreover, the contribution of different strengthening mechanisms to the yield strength was quantitatively analyzed and discussed from 4.2 to 1273 K, and some suggestions for improving the temperature-dependent yield strength were put forward.

Metal/ceramics interfaces, ubiquitous in functional materials, alloys, and coatings/films systems, provide excellent mechanical and chemical properties, mainly originating from atomic structures and charge distribution at the hetero-interfaces. In the present work, the alpha-Fe/TMN (TM = Ti/Zr/Hf/V/Nb/Ta) interfaces were chosen as the typical metal/ceramic candidates to explore the atomic structures and electronic properties at such types of heterostructures. After full optimization, the relaxed models kept the stacking sequence OT (on top) of FeN, producing a slight difference in interfacial distance (Delta z). Furthermore, a significant charge transfer emerged in interfacial Fe and N atoms, indicative of the stronger bond strength across the interfaces obtained from the analysis of plane-average charge density difference, PDOS, charge density and difference, partial charge density and ELF. Moreover, the increasing gain of interfacial N1 atoms and enhanced overlap of Fe and TM1 atoms could account for the higher adhesion strength of Fe/TMN. Finally, the amount of charge transfer for interfacial Fe1 was tiny compared to that of inner Fe4 atoms based on the Bader charge analysis, indicative of insignificant variation of interfacial ionicity. However, the magnetic moment (in mu B) of interfacial Fe1 changed significantly compared to Fe4 atoms, indicating the charge redistribution, which enhanced the hybridization of N1 -p and TM1-d states. One can conclude that the enhanced interfacial bonding strength could be ascribed to the strengthened hybridization of interfacial Fe1-d and N1 -p covalence. These findings are relevant for a better comprehension of these specific configurations and improving technological modification of such kind of metal/ ceramic system.

Molecular dynamics (MD) simulations were performed to study the effects of the interface imperfections and modulation periods (lambda) on deformation mechanisms of Cu/Ta nanoscale metallic multilayers (NMMs) under uniaxial tension. We found that the Cu(1 1 1)/Ta (1 1 0) interface can serves as the source for dislocation nucleation and the barrier impeding the motion of dislocations. The yield stress of Cu/Ta NMMs depends only on the material properties instead of the lambda. With the increase of lambda,more dislocations would store in the incoherent interface, resulting in larger local residual stress, and thus dislocations would be easier nucleate from the interface in Ta layer, so the maximum stress decreases with the increase of lambda. There is a critical lambda (about 11.18 nm), in which flow strength of the NMMs is maximized. In this stage, dislocations absorption in Ta layers and dislocations nucleation in Cu layers dominates the plastic deformation in the material, jointly. (C) 2017 Elsevier B.V. All rights reserved.

An incremental form of constitutive model is proposed for shape memory alloys using the modified strain based on experimental results and the finite element analysis, taking into account of the laminar microstructure, the thickness of martensite phase lamina and the interaction between the two phases. The pseudoelastisity of NiTi shape memory alloy micro-tube subjected to pure tension and pure torsion are analyzed and compared with the experimental results respectively. It can be seen that the pseudoelastic behavior, especially the stress drop during tension processes, can be well described with the proposed model.

On the one hand, fractal is character of damage mechanics and fractal dimension can fully be used to describe macro-behaviors in strata in mine. On the other hand, fractal dimension is the measurement of periodical pressure of working face in mine. Based on the study of damage and fractal dimension of periodical pressure in roof rock-mass at working face, new methods to predict periodical pressure are applied. Meanwhile, the relationship between damage and fractal is obtained, which it is important to guide safety in mining activities at working face.

Two models for the constitutive behavior of polycrystalline shape memory alloys (SMAs) are presented. One is a two-phase mixture model, and the other is a microstructure-based two-phase model, accounting for the typical constitutive behavior of Ni-Ti SMAs under different stress states. In both models, it is assumed that in the interested ranges of stress and temperature, the austenite phase is linearly elastic while the martensite phase is elastoplastic.In the first model, an SMA is considered to be composed of austenite and martensite phases, and its constitutive behavior is the combination of the individual behavior of each of the two phases. Making use of the simple Tanaka's phase-transformation rule, the main features of SMAs, such as shape memory effect and pseudoelasticity, can be successfully described. The constitutive behavior of SMA Au-47.5 at.% Cd subjected to uniaxial tension/compression and the pseudoelasticity of a polycrystalline Cu-Al-Zn-Mn SMA subjected to proportional and nonproportional complex stress/strain histories were simulated and compared with experimental results.Experiments showed that the pseudoelastic behavior of NiTi SMAs under pure tension and that under pure torsion were distinctly different, due to the different deformation-induced-transformation microstructures. SEM observation showed parallel texture on the surface of the NiTi SMA microtubes subjected to pure torsion, indicating alternatively arranged parallel fine lamellas of austenite and martensite phases. During pure tension, it was observed that martensite initiated from the parent phase and grew to macroscopic bands, and, correspondingly, a typical stress drop or macroscopic instability was observed in the tensile stress strain curve. FE analyses based on these microstructures replicated the experimental results under pure tension and under pure torsion, respectively, indicating the important role of the microstructure in the macroscopic constitutive response.A microstructure-based two-phase model was developed for the pseudoelastic behavior of NiTi SMAs, which includes three stages: elastoplastic model for the martensite phase and the linearly elastic model for the austenite phase; the model for a representative volume element (RVE) of a cell composed of alternatively arranged parallel austenite and martensite lamellas; and the model for an NiTi SMA by considering the material as an aggregate of numerous cells and making use of the Hill's self-consistent scheme. The model could satisfactorily describe the main characteristics of the pseudoelastic behavior of the NiTi SMA under pure tension and pure torsion. The pseudoelastic behavior of the NiTi SMA under biaxial tension-torsion were also analyzed and compared with experimental results.

On the basis of test results of micro-fracturing process and evolution of micro-cracks of rock in uniaxial compression, the theory of bifurcation, chaos and self organization in the nonlinear dynamics are applied in this research. The results show that, the evolution of micro-cracks could be described by the Logistic equation, so that the evolution of micro-cracks of rock has the characteristics of bifurcation and chaos. Meanwhile, the relationship between length and number of micro-cracks at each stress level has been studied. The results show that the process and evolution of micro-cracks are satisfied with power law, the system of micro-cracks in rock has the feature of self organization.

A microstrucure-based constitutive description for pearlitic steel is proposed by three stages: (1) Formulating the constitutive model for the ferrite and cementite phase, respectively; (2) Deriving the model for a colony composed of parallel lamellas of the ferrite and cementite; and (3) Obtaining the description of pearlitic steels with the Hill's self-consistent scheme and general anisotropic eshelby tensor. With the proposed model, the experimental results of pearlitic steel can be well replicated. Compared with the results using isotropic eshelby tensor, it shows that the isotropic approximation can provide acceptable overall elastoplastic responses.

Monitoring and measuring of new Austrian tunnelling method(NATM) was conducted with a Leica TCA2003 Total Station and an XP99 Cymometer in a shallowly-buried long-span tunnel.The deformation and movement of country rock in tunnel were obtained to guide tunnel construction.Based on the country rock deformation,the optimum time for primary and permanent support was applied.Optimum timing successfully can avert accidents in construction and enhance construction quality.Numerical simulation indicates that tunnel excavation may have great influence on surrounding rock stability.It is important to reinforce monitoring to relevant locations during the construction process,to have timely feedback to guide construction,to adopt corresponding shoring measures,and to ensure construction safety.

A pearlitic steel is composed of numerous pearlitic colonies with random orientations, and each colony consists of many parallel lamellas of ferrite and cementite. The constitutive behavior of this kind of materials may involve both inherent anisotropy and plastic deformation induced anisotropy. A description of the cyclic plasticity for this kind of dual-phase materials is proposed by use of a microstructure-based constitutive model for a pearlitic colony, and the Hill’s self-consistent scheme incorporating anisotropic Eshelby tensor for ellipsoidal inclusions. The corresponding numerical algorithm is developed. The responses of pearlitic steel BS11 and single-phase hard-drawn copper subjected to asymmetrically cyclic loading are analyzed. The analytical results agree very well with experimental ones. Compared with the results using isotropic Eshelby tensor, it is shown that the isotropic approximation can provide acceptable overall responses in a much simpler way.

Based on the laminar microstructure formed by ferrite and cementite with very fine interlamellar spacing, and the morphology of microdefects in the ferrite, cementite and interface, a unified damage evolution is proposed by making use of the work dissipated on damage. It is then embedded in the constitutive model of each phase and a damage elastoplastic constitutive model is obtained for a single pearlitic colony. The damage constitutive description for pearlitic materials is formulated using the Hill's self-consistent scheme by assuming that a pearlitic material element is an aggregate of numerous cells of pearlitic colonies with randomly distributed orientations. It is significant that the obtained constitutive description contains explicitly the interlamellar spacing as a microstructure parameter, which easily accounts for the better comprehensive mechanical properties of the pearlitic materials with smaller interlamellar spacing. The constitutive behavior of pearlitic steel is simulated, and compared with the experimental results.

Based on the CT real-time testing of coal microscopic damage propagation, the comparison of damage variable between CT scanning and Bellonoi equation, Lemaitre equation in the process of uniaxial damage spread was obtained which solves successfully damage discriminating 'scale' problem, and the results is more reasonable than Bellonoi equation and Lemaitre equation. In order to describe logically its behaviors and evolution, its constitutive model and evolvement function under uniaxial compression were carried through separately in pre-linearity phase, start and development. phase, speedup phase, which it is important to guide engineering.

A microstructure-based constitutive model is proposed for the NiTi SMAs by three stages: 1) the constitutive relationships for the martensite phase and austenite phase, respectively; 2) the model for a cell composed of alternatively arranged parallel lamellas of austenite and martensite; and 3) the description for the NiTi SMAs by considering the materials as aggregates of numerous cells with different orientations and making use of Hill's self-consistent scheme. The proposed model can satisfactorily describe the main characteristics of the pseudoelastic behavior of NiTi shape memory alloys under pure tension and pure torsion. The capability for the model to be applied to the pseudoelastic responses of NiTi SMAs under complex triaxial deformation is also discussed.

It is important that monitor measuring was applied in tunnel in regard to NATM. In this paper, the monitor measuring of NATM was studied in one tunnel in express. Based on the regularity and conditions of the surrounding rock deformation of monitor measuring in site, the Grey model is successful used to forecast the tunnel deformation. The optimum time for primary and permanent supports are obtained which averting successfully accidents in construction, which indicated that the forecast results are in good accord with monitor data. This measure insured to enhance the construction qualities and guide to Highway tunnel construction in Karst areas.