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通过MTS 815试验机研究了煤岩组合体分级加卸载试验。分级加卸载下煤岩组合体破坏以脆性破坏机制为主,与单轴作用相比,分级加卸载作用下煤岩组合体的破坏更为破碎,且破坏强度有所提高,但轴向和环向应变却有所降低。同一循环中的加载与卸载曲线基本不重合,且多数情况不形成闭合环路;卸载曲线与下一个循环的加载曲线通常也不重合,但会形成闭合环路。第1循环结束时残余变形较大,加卸载曲线形成了类似“牛角”状的曲线;随着循环加卸载地进行,与残余变形相比第1循环有所降低,加载和卸载曲线在逐渐靠近,并且加卸载曲线类似“竹叶”状。获得了残余变形和加卸载弹性模量随循环加卸载的变化关系,并且实验表明卸载到1 MPa附近时,卸载线是曲折波动的;但在再次加载初期,加载线几乎是直线,且随着荷载的继续增加,加载线和上一个循环的卸载线逐渐分离。循环加卸载后应变相位逐渐滞后于应力相位,内因可能是因为岩石矿物颗粒间的黏滞性以及煤岩组合体界面之间的摩擦引起的,而外因可能是循环加卸载导致了煤岩体内部损伤,并由此诱发不可恢复的残余变形。
Through the MTS 815 testing machine, the coal-rock combination grade loading-unloading test was studied. Under the action of graded loading and unloading, the failure of coal and rock composite is mainly caused by the brittle failure mechanism. Compared with the uniaxial action, the failure of the coal and rock composite under the action of graded loading and unloading is more broken and the breaking strength is improved, but the axial and ring Decreased to the strain. The loading and unloading curves in the same cycle basically do not coincide, and most cases do not form a closed loop; the unloading curve usually does not coincide with the loading curve of the next cycle, but forms a closed loop. The residual deformation is larger at the end of the first cycle, and the loading-unloading curves form a curve similar to the “horn” shape. With the cycle loading and unloading, the first cycle is reduced compared with the residual deformation. The loading and unloading curves Gradually close, and loading and unloading curve similar to “bamboo” shape. The relationship between residual deformation and loading and unloading elastic modulus was obtained with cyclic loading and unloading, and experiments show that the unloading line is tortuous when unloading to around 1 MPa; however, loading line is almost straight line at the beginning of reloading, The loading continues to increase, with the loading line gradually decoupled from the previous unloading line. The phase of strain gradually lags behind the stress phase after cyclic loading and unloading, and the internal cause may be due to the viscosity of the rock mineral particles and the friction between the interface of the coal and rock assembly. The external cause may be that the cyclic loading and unloading lead to the interior of the coal and rock mass Damage, and thus induce irreversible residual deformation.