Journal of Central South University最新文献

The creep strain of conventionally treated 2195 alloy is very low, increasing the difficulty of manufacturing Al-Cu-Li alloy sheet parts by creep age forming. Therefore, finding a solution to improve the creep formability of Al-Cu-Li alloy is vital. A thorough comparison of the effects of cryo-deformation and ambient temperature large pre-deformation (LPD) on the creep ageing response in the 2195 alloy sheet at 160 °C with different stresses has been made. The evolution of dislocations and precipitates during creep ageing of LPD alloys are revealed by X-ray diffraction and transmission electron microscopy. High-quality 2195 alloy sheet largely pre-deformed by 80% without edge-cracking is obtained by cryo-rolling at liquid nitrogen temperature, while severe edge-cracking occurs during room temperature rolling. The creep formability and strength of the 2195 alloy are both enhanced by introducing pre-existing dislocations with a density over 1.4×10¹⁵ m⁻². At 160 °C and 150 MPa, creep strain and creep-aged strength generally increases by 4–6 times and 30–50 MPa in the LPD sample, respectively, compared to conventional T3 alloy counterpart. The elongation of creep-aged LPD sample is low but remains relevant for application. The high-density dislocations, though existing in the form of dislocation tangles, promote the formation of refined T₁ precipitates with a uniform dispersion.

Due to the long-term plate tectonic movements in southwestern China, the in-situ stress field in deep formations is complex. When passing through deep soft-rock mass under non-hydrostatic high in-situ stress field, tunnels will suffer serious asymmetric deformation. There is no available support design method for tunnels under such a situation in existing studies to clarify the support time and support stiffness. This study first analyzed the mechanical behavior of tunnels in non-hydrostatic in-situ stress field and derived the theoretical equations of the ground squeezing curve (GSC) and ground loosening curve (GLC). Then, based on the convergence confinement theory, the support design method of deep soft-rock tunnels under non-hydrostatic high in-situ stress field was established considering both squeezing and loosening pressures. In addition, this method can provide the clear support time and support stiffness of the second layer of initial support. The proposed design method was applied to the Wanhe tunnel of the China-Laos railway in China. Monitoring data indicated that the optimal support scheme had a good effect on controlling the tunnel deformation in non-hydrostatic high in-situ stress field. Field applications showed that the secondary lining could be constructed properly.

The problems associated with vibrations of viaducts and low-frequency structural noise radiation caused by train excitation continue to increase in importance. A new floating-slab track vibration isolator-non-obstructive particle damping-phononic crystal vibration isolator is proposed herein, which uses the particle damping vibration absorption technology and bandgap vibration control theory. The vibration reduction performance of the NOPD-PCVI was analyzed from the perspective of vibration control. The paper explores the structure-borne noise reduction performance of the NOPD-PCVIs installed on different bridge structures under varying service conditions encountered in practical engineering applications. The load transferred to the bridge is obtained from a coupled train-FST-bridge analytical model considering the different structural parameters of bridges. The vibration responses are obtained using the finite element method, while the structural noise radiation is simulated using the frequency-domain boundary element method. Using the particle swarm optimization algorithm, the parameters of the NOPD-PCVI are optimized so that its frequency bandgap matches the dominant bridge structural noise frequency range. The noise reduction performance of the NOPD-PCVIs is compared to the steel-spring isolation under different service conditions.

Wire-arc additive manufacture (WAAM) has great potential for manufacturing of Al-Cu components. However, inferior mechanical properties of WAAM deposited material restrict its industrial application. Inter-layer cold rolling and thermo-mechanical heat treatment (T8) with pre-stretching deformation between solution and aging treatment were adopted in this study. Their effects on hardness, mechanical properties and microstructure were analyzed and compared to the conventional heat treatment (T6). The results show that cold rolling increases the hardness and strengths, which further increase with T8 treatment. The ultimate tensile strength (UTS) of 513 MPa and yield stress (YS) of 413 MPa can be obtained in the inter-layer cold-rolled sample with T8 treatment, which is much higher than that in the as-deposited samples. The cold-rolled samples show higher elongation than that of as-deposited ones due to significant elimination of porosity in cold rolling; while both the T6 and T8 treatments decrease the elongation. The cold rolling and pre-stretching deformation both contribute to the formation of dense and dispersive precipitated θ′ phases, which inhibits the dislocation movement and enhances the strengths; as a result, T8 treatment shows better strengthening effect than the T6 treatment. The strengthening mechanism was analyzed and it was mainly related to work hardening and precipitation strengthening.

One of the challenges for bimetal manufacturing is the joining process. Hence, transient liquid phase (TLP) bonding was performed between 304L stainless steel and Cp-Ti using an Ag-Cu interlayer with a thickness of 75 µm for bonding time of 20, 40, 60, and 90 min. The bonding temperature of 860 °C was considered, which is under the β transus temperature of Cp-Ti. During TLP bonding, various intermetallic compounds (IMCs), including Ti₅Cr₇Fe₁₇, (Cr, Fe)₂Ti, Ti(Cu, Fe), Ti₂(Cu, Ag), and Ti₂Cu from 304L toward Cp-Ti formed in the joint. Also, on the one side, with the increase in time, further diffusion of elements decreases the blocky IMCs such as Ti₅Cr₇Fe₁₇, (Cr, Fe)₂Ti, Ti(Cu, Fe) in the 304L diffusion-affected zone (DAZ) and reaction zone, and on the other side, Ti₂(Cu, Ag) IMC transformed into fine morphology toward Cp-Ti DAZ. The microhardness test also demonstrated that the (Cr, Fe)₂Ti + Ti₅Cr₇Fe₁₇ IMCs in the DAZ on the side of 304L have a hardness value of HV 564, making it the hardest phase. The maximum and minimum shear strength values are equal to 78.84 and 29.0 MPa, respectively. The cleavage pattern dominated fracture surfaces due to the formation of brittle phases in dissimilar joints.

This paper developed a statistical damage constitutive model for deep rock by considering the effects of external load and thermal treatment temperature based on the distortion energy. The model parameters were determined through the extremum features of stress – strain curve. Subsequently, the model predictions were compared with experimental results of marble samples. It is found that when the treatment temperature rises, the coupling damage evolution curve shows an S-shape and the slope of ascending branch gradually decreases during the coupling damage evolution process. At a constant temperature, confining pressure can suppress the expansion of micro-fractures. As the confining pressure increases the rock exhibits ductility characteristics, and the shape of coupling damage curve changes from an S-shape into a quasi-parabolic shape. This model can well characterize the influence of high temperature on the mechanical properties of deep rock and its brittleness-ductility transition characteristics under confining pressure. Also, it is suitable for sandstone and granite, especially in predicting the pre-peak stage and peak stress of stress – strain curve under the coupling action of confining pressure and high temperature. The relevant results can provide a reference for further research on the constitutive relationship of rock-like materials and their engineering applications.

The macroscopic mechanical properties of rocks are significantly influenced by their microstructure. As a material bonded by mineral grains, the grain morphology of crystalline rock is the primary factor influencing the strength. However, most strength criteria neglect the strength variations caused by different grain characteristics in rocks. Furthermore, the traditional linear criteria tend to overestimate tensile strength and exhibit apex singularity. To address these shortcomings, a piecewise strength criterion that considers the grain size effect has been proposed. A part of an ellipse was employed to construct the envelope of the tensive-shear region on the meridian plane, to accurately reproduce the low tensile-compressive strength ratio. Based on the analysis of experimental data, both linear and exponential modification functions that account for grain size effects were integrated into the proposed criterion. The corresponding finite element algorithm has been implemented. The accuracy and applicability of the proposed criterion were validated by comparing with the experimental data.

Landslide susceptibility mapping is a crucial tool for disaster prevention and management. The performance of conventional data-driven model is greatly influenced by the quality of the samples data. The random selection of negative samples results in the lack of interpretability throughout the assessment process. To address this limitation and construct a high-quality negative samples database, this study introduces a physics-informed machine learning approach, combining the random forest model with Scoops 3D, to optimize the negative samples selection strategy and assess the landslide susceptibility of the study area. The Scoops 3D is employed to determine the factor of safety value leveraging Bishop’s simplified method. Instead of conventional random selection, negative samples are extracted from the areas with a high factor of safety value. Subsequently, the results of conventional random forest model and physics-informed data-driven model are analyzed and discussed, focusing on model performance and prediction uncertainty. In comparison to conventional methods, the physics-informed model, set with a safety area threshold of 3, demonstrates a noteworthy improvement in the mean AUC value by 36.7%, coupled with a reduced prediction uncertainty. It is evident that the determination of the safety area threshold exerts an impact on both prediction uncertainty and model performance.

A study was conducted to analyze the deformation mechanism of strongly weathered quartz schist in the Daliangshan Tunnel, located in the western Transverse Mountain area. A large deformation problem was experienced during the tunnel construction. To mitigate this problem, a support system was designed incorporating negative Poisson ratio (NPR) anchor cables with negative Poisson ratio effect. Physical model experiments, field experiments, and numerical simulation experiments were conducted to investigate the compensation mechanical behavior of NPR anchor cables. The large deformations of soft rocks in the Daliangshan Tunnel are caused by a high ground stress, a high degree of joint fracture development, and a high degree of surrounding rock fragmentation. A compensation mechanics support system combining long and short NPR anchor cables was suggested to provide sufficient counter-support force (approximately 350 kN) for the surrounding rock inside the tunnel. Comparing the NPR anchor cable support system with the original support system used in the Daliangshan tunnel showed that an NPR anchor cable support system, combining cables of 6.3 m and 10.3 m in length, effectively prevented convergence of surrounding rock deformation, and the integrated settlement convergence value remained below 300 mm. This study provides an effective scientific basis for resolving large deformation problems in deeply buried soft rocks in western transverse mountain areas.

The effect of forging on the microstructure and texture evolution of a high Nb containing Ti-45Al-7Nb-0.3W (at.%) alloy was investigated by X-ray diffractometer (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results show that the as-cast alloy is mainly composed of α₂/γ lamellar colonies with a mean size of 70 µm, but the hot-forged pancake displays a near duplex microstructure (DP). Kinking and bending of lamellar colonies, deformation twinning and dynamic recrystallization (DRX) occur during hot forging. Meanwhile, dense dislocations in the β phase after forging suggest that the high-temperature β phase with a disordered structure is favorable for improving the hot-workability of the alloy. Unlike the common TiAl casting texture, the solidification process of the investigated as-cast alloy with high Nb content is completely via the β phase region, resulting in the formation of a <110>_γ fiber texture where the <110>_γ aligns parallel to the heat-flow direction. In comparison, the relatively strong <001> and weak <302> texture components in the as-forged alloy are attributed to the deformation twinning. After annealing, static recrystallization occurs at the twin boundary and intersections, which weakens the deformation texture.