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To study influence of thermal-mechanical action on creep for the geothermal wellbore, Dalian limestone was taken as the research object, and triaxial creep tests were carried out on samples under different temperatures and the effects of different temperatures on the creep deformation, creep rate and long-term strength of limestone are discussed. The test results show that the creep process of limestone under thermal-mechanical action shows three distinct phases. As the temperature increases, the creep time and long-term strength gradually decrease. The macroscopic failure modes of limestone under different temperatures are shear failure and the fracture surface is more obvious. Meanwhile, based on the principle of statistical damage and fractional calculus, the damage body under high temperature is proposed, and a fractional creep damage model that can characterize the triaxial creep mechanical behavior of limestone under different temperatures is constructed. The reasonableness of the model is proved by comparing. The parameters analysis shows that the fractional order δ mainly affects the creep rate, which is expressed in the stable and accelerated phases. The aging damage parameter λ is related to the time coordinate scale. The research results in this paper can provide a certain guiding significance for the long-term stability evaluation of the surrounding rock of the geothermal wellbore. [ABSTRACT FROM AUTHOR]

Although cylindrical and prismatic specimens are often used in laboratory tests, the differences between their deformation and failure characteristics remain unclear. Cylindrical and prismatic specimens of two rocks (marble and granite) were analyzed under various conventional triaxial conditions. The failed prismatic specimens exhibit multiple fractures intersecting in the cross section. With increasing confining pressure, the failure mode of the prismatic specimen changes from tensile failure to shear failure. In the progressive failure process of prismatic specimens, the two lateral strains ε 2 and ε 3 are the same before the peak, but some differences arise after some degree of post-peak failure, where the acoustic emission (AE) activity clearly increases. The mechanical parameters (peak strength, internal friction angle, cohesion, Young's modulus, and Poisson's ratio) determined for the cylindrical and prismatic specimens are consistent. However, a significant difference in the fracture morphology exists among them, even with similar change trends in the tensile-shear failure mode with confining pressure. [ABSTRACT FROM AUTHOR]

The short beam shear performance of GLARE 3A-3/2 laminates with adhesive layers was investigated by combining the short beam test and the digital image correlation technique. The failure behavior was further analyzed based on finite element simulation and micro failure morphology. The results show an 8% and 58% difference in the short beam strength and bending displacement at failure of laminates along two orthogonal directions; The damage behavior of laminates is determined by the bottom unidirectional glass fiber reinforced plastic (GFRP) layers. The two typical failure modes are matrix and fiber fracture in the GFRP layer caused by local bending deformation, and interlaminar delamination between GFRP layers; The distribution of surface strain ε y indicates the damage initiation and evolution process. The simulation result of the finite element model established in ABAQUS/Explicit shows consistency with digital image correlation analysis, which provides an effective method to predict the damage behavior of specimens with different ply structures. [ABSTRACT FROM AUTHOR]

The coal seam and the roof of the roadway bear loads together in the underground engineering of coal mine. Especially for the roadway driven along the roof, its deformation is completely different from that arranged in the complete rock stratum. Accurately knowing the mechanical mechanism of coal-rock combined body can help understand the deformation and failure modes of such roadways. This article started with tests of coal-rock combined samples with different height ratios, based on the test results, a strain softening damage constitutive model of coal-rock combined body and a method for solving the parameters of the model were proposed, and the influence of the model parameters was discussed. The test results show that the stress peak value and residual strength of the coal-rock combined samples are negatively correlated with the proportion of coal in the coal-rock combined samples, and have a positive correlation with the confining pressure. The damage constitutive model fitted the test curve well. The model can accurately describe the stress-strain curve of coal-rock combined samples, and can reflect the influence of different height ratios of coal and rock samples and confining pressures. The effects of model parameters were discussed based on the damage constitutive model, which are expected to be widely used in underground engineering. [ABSTRACT FROM AUTHOR]

Stress-induced instability is associated with rock damage. Here, the progressive brittle fracturing process in Jinping marble is studied by introducing two types of true triaxial pre-peak unloading tests, namely, the incrementally cyclic loading-unloading minimum principal stress test (ICM test) and the incrementally cyclic loading-unloading maximum and minimum principal stress test (ICMM test). By comprehensively analysing the irreversible strains, dissipated energy, acoustic emission (AE) characteristics and scanning electron microscopy (SEM) results, the rock damage evolution can be quantified and divided into two distinctive damage stages. At the boundary point, the irreversible strain increments reach their minimum values. In the gentle damage stage, the normalized irreversible strains increase linearly, and this process is associated with a small number of AE hits with low amplitude. The rapid damage stage is characterized by a nonlinear increase in the normalized irreversible strains, and this process is associated with a large number of AE hits with high amplitude. The dissipated energy mainly increases in the rapid damage stage. In addition, the rapid damage stage in the ICMM test mainly occurs in the last five cycles, due to the differences in the deviatoric stresses in each cycle. In both of these tests, the failure mode is principally characterized by tensile failure. Moreover, the precursory signals of rock fracturing and the influence of the loading paths on the strength are discussed. [ABSTRACT FROM AUTHOR]