【作者】 李伟；

【导师】 王启智；

【作者基本信息】 四川大学 ， 固体力学， 2005， 硕士

【摘要】 根据国际岩石力学学会(ISRM)于1978年颁布的利用巴西圆盘(Brazilian disc-BD)测试岩石拉伸强度的试验方法,对试样的形状进行了改进。为避免在加载位置附近的高度应力集中,在巴西圆盘试样上加工了两个平行平面作为加载面,试样变为平台巴西圆盘试样(flattened Brazilian disc-FBD)。制备的试样具有不同直径和不同厚度,其中FBD试样的加载平台角均为20°。同时还按照ISRM于1995年颁布的测试岩石断裂韧度的建议方法加工了人字型切槽巴西圆盘试样(cracked chevron notched Brazilian disc-CCNBD),同样为便于加载,在该试样上也加工两个平行平面作为加载面。 更重要的是,本文将上述的两个静态试验方法都推广到动态。本次实验利用直径为100mm的Hopkinson压杆和薄圆形铝片作为波形整形器以不同弹速径向冲击BD试样和FBD试样。首先利用有限元软件ANSYS对这两种试样在炮弹冲击下的动态应力分布进行了数值模拟,按照完整动态劈裂拉伸实验所应具备的条件,分析了实验的有效性,并对这两种试样在动态冲击下的优劣性进行了对比。然后验证了实验结果的一致性并考虑了试样两个平台附近应力的时间不均匀性与空间不均匀性在动态劈裂拉伸实验中的影响,分析了试样的应变率,破坏时间,破坏模式,以及破坏过程中的应力应变关系,得到了大理岩在高应变率下的弹性模量,拉伸强度的一些变化规律及其对应变率的敏感程度,最后讨论了试样几何尺寸及应变率对结果的影响。 此外,利用该装置径向冲击CCNBD试样,对试样的起裂时间进行了初步的研究,以便今后对动态断裂韧度进行进一步的测试。更多还原

【Abstract】 Brazilian disc (BD) specimens were prepared according to the test method for split tensile strength which was suggested by International Society for Rock Mechanics (ISRM) in 1978. Furthermore, two parallel flat ends were introduced in the original Brazilian disc in order to avoid the high stress concentration near the loading area, thus the specimen becomes flattened Brazilian disc (FBD). The specimens have different diameter and thickness, the loading angle of all the FBD specimens is 20°. In addition, cracked chevron notched Brazilian discs (CCNBD) were made according to the new type of rock fracture toughness specimen proposed by ISRM in 1995. For the same reason, two parallel flat ends were made in the specimen for the benefit of loading.More importantly, these two ISRM suggested methods used in static testing were extended to dynamic situation. The BD and FBD specimens were subjected to diametral impact by the projectile with different speed using the split Hopkinson pressure bar (SHPB) of 100mm diameter with a thin aluminum circular plate as pulse shaper. First, the dynamic stress distribution in the BD and FBD specimens was obtained by using the finite element software ANSYS, and the validity of the tests was affirmed according to the qualifications which a complete dynamic split tension test should have. The performance of BD and FBD specimens under the dynamic impact was compared, then the repetitive of tests was validated and the influence of stress nonuniformness near two flattened ends of specimen to the results was taken into account. The strain rate, failure time, failure pattern and the relationship betweenstress and strain during the failure process were analyzed to get some conclusions about the elastic modulus, tensile strength and its sensitivity of marble at high strain rate. Finally, the influence of the geometry and strain rate to the results of the test was also analyzed.Finally, using the same equipment, the cracked chevron notched Brazilian disc specimens were subjected to diametral impact, the fracture initiation time for the specimen was studied, which laid a foundation for dynamic fracture toughness test in the future.更多还原