摘要
对Ⅰ-Ⅱ型复合型断裂的力学特征进行研究,选用石膏岩制作单裂纹直切槽巴西圆盘作为室内试验的研究对象。采用位移伺服方式对巴西圆盘进行加载,并对荷载和位移进行监测。根据室内试验得出的峰值应力和复合型断裂力学相关理论,计算出对应的断裂韧度值。选用能模拟裂隙演化的离散元软件PFC3D对室内试验进行模拟,在加载方式上选用更为合理的点墙加载方式,以代替传统的墙体加载方式。根据不同加载角β直切槽巴西圆盘室内试验结果,对数值模拟试验的试件细观参数进行标定,分别从宏观和细观上分析直切槽巴西圆盘的力学特性,PFC3D数值试验破坏过程中展现出与巴西圆盘试验一致的细观特征。研究结果表明:当0°β75°时,断裂韧度差值K_Ⅰ-K_Ⅱ与加载角β呈线性关系;根据试验结果建立荷载峰值与加载角β的关系表达式,可预测不同加载角β下的荷载峰值;3维数值模拟分析结果显示裂隙尖端拉压临界角大于2维经典理论结果,误差范围在4%~7%之间,且拉压临界角具有显著的空间特征,由圆盘边面到跨中截面逐渐增加,增加幅度为0.7°;随着加载角β的增加,直切槽周围最大张拉应力点由尖端向圆盘中心偏移,且偏移量单调增加,全截面由受压逐渐转变为受拉;不同断裂形式的空间效应存在差异,Ⅱ型断裂的空间效应最小,巴西劈裂最显著。
Focusing on the mixed mode fracture(Ⅰ-Ⅱ),the cracked straight through Brazilian disc(CSTBD) of gypsum was chosen for investigating the mechanical characteristics of mixed mode fracture.Adopting the displacement servo,the applied load and the displacement were monitored.Based on the peak loading and classical theory of mixed mode fracture,the mixed mode fracture toughness of rocks were calculated.The PFC3D code was chosen to simulate the evolution of cracks and adopt the point loading to replace the traditional loading manner.On the basis of the experimental results of cracked straight through Brazilian disk test under different angle β,by testing whether it was consistent for the outcomes of laboratory experiments and numerical simulations,microcosmic parameters were calibrated.By analyzing the mixed-mode Brazilian disk under microcosmic and macrocosmic perspectives,the microcosmic characteristics of simulations were coincident with the Brazilian disk destructive processes.The results showed that when the value of β was between 0 and 75°,there was a linear relation between K_Ⅰ-K_Ⅱ and β;according to the experimental results,a fitting equation between peak load values and β could be established to predict the peak load values with different β;according to three-dimensional simulations,the critical values of tensile and press transition angle on crack tips were greater in the three dimensional space than that in the two dimensional space,the error range was between 4% and 7%,in addition that the critical angle had significant spatial effect and gradually increases from surface to mid-span section.As β augments,the maximum tensile stress point moved from the crack tip towards the center of Brazilian disk and the rate monotonously increased with the increase of the loading angle.The three-dimensional analytical results denotes that the spatial effect of three fracture modes were different,the mode was minimal,and yet the Brazilian split was maximal.
出处
《四川大学学报（工程科学版）》
CSCD
北大核心
2017年第S1期132-138,共7页
Journal of Sichuan University (Engineering Science Edition)
基金
国家重点基础研究发展计划资助项目(2015CB057903)
国家自然科学基金资助项目(51079092)
