Temperature-controlled triaxial compression/creep test device for thermodynamic properties of soft sedimentary rock and corresponding theoretical prediction

In deep geological disposal of high-level nuclear waste,one of the most important subjects is to estimate long-term stability and strength of host rock under high temperature conditions caused by radioactive decay of the waste.In this paper,some experimental researches on the thermo-mechanical characteristics of soft sedimentary rock have been presented.For this reason,a new temperature-controlled triaxial compression and creep test device,operated automatically by a computer-controlled system,whose control software has been developed by the authors,was developed to conduct the thermo-mechanical tests in different thermal loading paths,including an isothermal path.The new device is proved to be able to conduct typical thermo-mechanical element tests for soft rock.The test device and the related testing method were introduced in detail.Finally,some test results have been simulated with a thermo-elasto-viscoplastic model that was also developed by the authors.

Dynamic recrystallization behavior and coincidence site lattice evolution in thermal deformation of 316H stainless steel used in nuclear systems

The hot deformation behavior of 316H stainless steel used in the 4th-generation nuclear systems was investigated by thermal compression tests at 1000–1150 C and 0.01–10 s^(-1).It was found that true stress firstly increased and then decreased with the increasing strain rate with a threshold of 1 s^(-1).Electron backscatter diffraction was used to analyze the microstructure evolution.Discontinuous dynamic recrystallization(DDRX)was the dominant dynamic recrystallization(DRX)mechanism,while continuous dynamic recrystallization(CDRX)was the supplementary one.DDRX happened before CDRX and provided additional nucleation sites for the latter.Twin grain boundaries(R3)appeared in DRX grains due to growth accidents.As the length fraction of R3 increased,the coincidence site lattice(CSL)boundary transition began to occur,forming R9 and R27.After the occurrence of full DRX,the growth and annexation of DRX grains were easy to be promoted,in which progress both equiaxed grains and CSL boundaries disappeared.The ideal deformation microstructure with fine and uniform DRX grains,which was accompanied by a high length fraction of CSL boundaries,appeared at 1000℃–0.01 s^(-1),1050℃–0.01–0.1 s^(-1),1100℃–0.1–1 s^(-1) and 1150℃–1–10 s^(-1).That is,the deformation conditions mentioned above were the preferable thermal forming parameters for 316H stainless steel in actual productions.

挤压型盆地构造热演化模拟研究综述

挤压过程对地质构造和沉积盆地的形成演化具有重要的作用.研究挤压型盆地的构造热演化模拟对认识岩石圈内部应力分布、力学属性和流变结构具有重要意义.本文介绍了挤压型盆地构造模拟的弹性模型、粘弹性模型和深度控制的弹塑性模型,对比了这几种模型的优缺点和适用范围.简单介绍了前人在研究地壳隆升时用到的几种热演化模拟方法.虽然挤压过程的构造模拟已经取得了很大进展,挤压型盆地的热演化模拟则具有很大的发展空间,这应是进一步研究的重点.

Geotechnical characterization of peat-based landfill cover materials

Natural methane （CH4） oxidation that is carried out through the use of landfill covers （biocovers） is a promising method for reducing CH4 emissions from landfills. Previous studies on peat-based landfill covers have mainly focused on their biochemical properties （e.g. CH4 oxidation capacity）. However, the utilization of peat as a cover material also requires a solid understanding of its geotechnical properties （thermal, hydraulic, and mechanical）, which are critical to the performance of any biocover. Therefore, the objective of this context is to investigate and assess the geotechnical properties of peat-based cover materials （peat, peat–sand mixture）, including compaction, consolidation, and hydraulic and thermal conductivities. The studied materials show high compressibility to the increase of vertical stress, with compression index （Cc） values ranging from 0.16 to 0.358. The compressibility is a function of sand content such that the peat–sand mixture （1：3） has the lowest Cc value. Both the thermal and hydraulic conductivities are functions of moisture content, dry density, and sand content. The hydraulic conductivity varies from 1.74 × 10^-9 m/s to 7.35 × 10^-9 m/s, and increases with the increase in sand content. The thermal conductivity of the studied samples varies between 0.54 W/（m K） and 1.41 W/（m K） and it increases with the increases in moisture and sand contents. Increases in sand content generally increase the mechanical behavior of peat-based covers; however, they also cause relatively high hydraulic and thermal conductivities which are not favored properties for biocovers.

Numerical study of convective heat transfer in static arrangements of particles with arbitrary shapes:A monolithic hybrid lattice Boltzmann-finite difference-phase field solver

A compressible lattice Boltzmann-finite difference method is extended by the phase-field approach into a monolithic scheme to study fluid flow and heat transfer through regular arrangements of solid bodies of circular,elliptical and irregular shapes.The advantage of using the phase-field method is demon-strated both in its simplicity of accounting for flow and thermal boundary conditions at solid surfaces with irregular shapes and in the capability of generating such complex-shaped objects.For an array of discs,numerical results for the overall solid-to-gas heat transfer rate are validated via experiments on flow through arrays of hot cylinders.The thus validated compressible LB-FD-PF hybrid scheme is used to study the dependence of heat transfer on flow and thermal boundary conditions(Reynolds number,temperature difference between the hot solid bodies and the inlet gas),porosity as well as on the shape of solid objects.Results are rationalized in terms of the residence time of the gas close to the solid body and downstream variations of gas velocity and temperature.Perspective for further applications of the proposed methodology are also discussed.

Thermal forming properties of a Cr-Mn-Si-Ni alloyed naval steel under different forming conditions by different constitutive models

A series of thermal compression tests on a CrMn-Si-Ni alloyed naval steel were carried out at different strain rates(0.0005-0.0100 s^(-1)) at different temperatures(1023-1173 K).Based on the friction-corrected data obtained from the compression tests,strain-compensated Arrhenius-type constitutive(SCAC) and backpropagation artificial neural network(BP-ANN) models with the optimized structure of the Cr-Mn-Si-Ni alloyed naval steel were established.The optimized BP-ANN model,where the operation time and overfitting of BP-ANN were shortened and avoided,respectively,exhibited improved predictive performance.The two models were assessed further in terms of the correlation coefficient(R),average absolute relative error,and root mean square error.The results validated that the optimized BP-ANN model predicted the flow behavior of the Cr-Mn-Si-Ni alloyed naval steel better than the SC AC model.The effect of the forming temperature and strain rate on the microstructural evolution behavior of the naval steel during thermoplastic deformation was investigated through the electron backscatter diffraction analysis of the compressed samples.It was observed that the dynamic recrystallization of the naval steel was promoted by an increase in the forming temperature and a decrease in the strain rate during thermoplastic deformation.

Thermal and Mechanical Properties of Graphene-Titanium Composites Synthesized by Microwave Sintering

The x wt%graphene-Ti composites（x = 0,0.2,0.3 and 0.4） were obtained using the powder metallurgy method.The X-ray diffraction results demonstrated that the peak intensity of graphene increased monotonically with increasing graphene content.Furthermore,the number of grain boundary and interface between graphene and matrix increased as graphene increased,which led to a sharp rise of thermal resistances.The thermal conductivity and specific heat capacity of composites initially decreased drastically with addition of graphene,but then increased with increasing graphene content from 0.2 to 0.4 wt%.This phenomenon was connected with the graphene content and the characteristics of Ti matrix（pores,grain boundary and interface between graphene and matrix）.The variation of the compressive strength of composites was attributed to the interaction effects of the average grain size of the Ti matrix（d_m） and the volume fraction（V_f） and aspect ratio（A） of graphene.

Static recrystallization behavior of SA508Gr.4N reactor pressure vessel steel during hot compressive deformation

The two-pass isothermal hot compression method was used to study the effect of different thermal deformation conditions on static recrystallization behavior in Ni-Cr-Mo series SA508Gr.4N low alloy steel with interval holding time ranging from 1 to 300 s,temperature ranging from 950 to 1150℃,strain rate ranging from 0.01 to 1 s^(-1),true strains ranging from 0.1 to 0.2,and initial austenite grain size ranging from 175 to 552μm.It can be concluded that the static recrystallization volume fraction gradually increases with the increase in the deformation temperature,strain rate,strain and pass interval,and the decrease in the initial grain size,which is mainly due to the increase in the deformation energy storage and dislocations.Moreover,strain-induced grain boundary migration is the nucleation mechanism for static recrystallization of SA508Gr.4N low alloy steel.Based on the stress-strain curve,the predicted value obtained from the established static recrystallization kinetics model is in good consistence with the experimental value,and the static recrystallization thermal activation energy of SA508Gr.4N steel was calculated as 264,225.99 J/mol.