等幅循环荷载下钾长花岗岩疲劳损伤力学特性试验

Fatigue Damage Mechanics of Potassic Granite Under Constant Amplitude Cyclic Loading

摘要:

为研究上限应力比对钾长花岗岩疲劳损伤力学特性的影响，开展了单轴压缩试验和4组不同上限应力比（0.75、0.80、0.85、0.90）下的等幅循环加卸载试验。基于试验数据，总结分析了钾长花岗岩应力?应变曲线、疲劳寿命、疲劳极限应变比及宏微观破坏特征演变规律。基于循环加卸载过程中的滞回曲线，计算了动模量、阻尼比、动泊松比及累积残余应变等重要参数。进一步地提出了平均残余应变法计算钾长花岗岩变形破坏过程中的损伤值。结果表明，试样存在一个扩容应力比，当上限应力比高于此值时，试样发生疲劳破坏。疲劳寿命随上限应力比增大而减小，且疲劳破坏时的轴向变形受到单轴静力应力?应变曲线演化的控制。试样宏观破坏程度随上限应力比增大而加剧，断口微观形貌随上限应力比增大而趋于复杂。疲劳破坏时的试样动模量和动泊松比呈现两阶段变化趋势，而阻尼比和残余应变呈现三阶段变化特征。通过平均残余应变法计算得到的试样疲劳损伤值与循环次数呈三阶段的“反S”型演化规律。最后，引入了低周疲劳损伤模型描述疲劳损伤规律，与试验结果对比表明，模型预测效果良好。

Abstract:

To investigate the effects of the upper limit stress ratio on the fatigue damage mechanics of potassic granite， uniaxial compression tests and constant amplitude cyclic loading tests with four upper limit stress ratios （0.75， 0.80， 0.85， 0.90） were conducted. Based on the experimental data， the stress-strain curves， fatigue life， fatigue limit strain ratio， as well as the macroscopic and microscopic evolution pattern of granite failure characteristics were summarized and analyzed. Based on the hysteresis curves during cyclic loading， key parameters such as dynamic modulus， damping ratio， dynamic Poisson’s ratio， and cumulative residual strain were calculated. Additionally， a damage value computation method based on average residual strain was proposed to describe the deformation and failure process of the rock sample. The results indicate the presence of a dilatancy stress ratio. When the upper limit stress ratio exceeds this threshold， the samples undergo fatigue failure， and the fatigue life decreases as the upper limit stress ratio increases. The axial deformation during fatigue failure is governed by the evolution of the uniaxial static stress-strain curve. Macroscopically， the extent of damage in the samples increases with the upper limit stress ratio， while microscopically， the complexity of fracture morphology also intensifies. The dynamic elastic modulus and Poisson’s ratio during fatigue failure exhibit a two-stage variation trend， while the damping ratio and residual strain show a three-stage varying feature. The fatigue damage values， calculated using the average residual strain method， exhibit a three-stage “inverse ‘S-shaped’” evolution pattern as the number of cycles increases. Finally， a low-cycle fatigue damage model was introduced to describe the fatigue damage pattern， whose predictive performance was satisfactory according to the comparison with experimental data.