Investigation of creep behaviours of gypsum specimens with flaws under different uniaxial loads

The aim of this study is to identify the influence of the dip angle of a pre-existing macrocrack on the lifetime and ultimate deformation of rock-like material. Prediction of lifetime has been studied for three groups of specimens under axial static compressive load levels. The specimens were investigated from 65% to 85% of UCS(uniaxial compressive strength) at an interval of 10% of UCS for the groups of specimens with a single modelled open flaw with a dip angle to the loading direction of 30°(first group), at an interval of 5% of UCS increment for the groups of specimens with single(second group), and double sequential open flaws with a dip angle to the loading direction of 60°(third group). This study shows that crack propagation in specimens with a single flaw follows the same sequences. At first, wing cracks appear, and then shear crack develops from the existing wing cracks. Shear cracking is responsible for specimen failure in all three groups. A slip is expected in specimens from the third group which connects two individual modelled open flaws. The moment of the slip is noticed as a characteristic rise in the axial deformation at a constant load level. It is also observed that axial deformation versus time follows the same pattern, irrespective of local geometry. Specimens from the first group exhibit higher axial deformation under different load levels in comparison with the specimens from the second and third groups.     

冲击荷载作用下的I/II复合型裂纹扩展规律研究

 为了研究纯I和I/II复合型裂纹在冲击荷载作用下的动态断裂行为,基于提出的单裂纹半孔板(SCSC)构型和大直径分离式霍普金森压杆设备,使用2种石材进行岩石的纯I和I/II复合型的动态断裂实验;同时,实验中使用新装置(裂纹扩展计和高速摄影系统)来监测裂纹的扩展速度。为了检验实验结论,基于Drucker-Prager强度模型和累积损伤失效准则,建立针对纯I和I/II复合型裂纹的数值模型,并使用AUTODYN软件来模拟裂纹的扩展行为。总体上,由数值模拟得到的裂纹扩展路径和实验结果十分吻合。研究结果表明,在裂纹扩展的过程中,其扩展速度是一个变化量,甚至有可能停滞,也就是说可能出现止裂现象;同时,CPG和高速摄影系统都可以很好的反映出此现象,并且高速摄影系统更加直观,说明在动态断裂研究中是适用的,同时给出纯I型动态断裂实验裂纹扩展速度特征,供工程参考。     

三类钢板剪力墙结构试验研究

防屈曲钢板剪力墙已被试验证明是优秀的抗侧耗能构件,但墙板嵌入受弯框架时,二者之间的相互作用尚需进一步研究。为此进行了两层单跨钢框架内嵌防屈曲钢板剪力墙的试验研究,作为比较同时进行了两层单跨钢框架内嵌非加劲钢板剪力墙与两层单跨钢框架内嵌组合钢板剪力墙结构的试验研究。在试验的基础上,对试件进行有限元分析,比较了三类钢板剪力墙之间的性能差异。研究表明,防屈曲钢板剪力墙能够消除无加劲钢板剪力墙在水平荷载下产生的巨大屈曲噪声,具有较大的初始刚度与承载力,拥有良好的延性与滞回耗能性能,而且由于其屈服先于屈曲发生,对周边框架产生的附加弯矩很小;组合钢板剪力墙的性能与防屈曲钢板剪力墙相似,但由于后期外包的混凝土发生脱离,内嵌钢板剪力墙会产生拉力带,不仅对框架产生不利影响,而且自身承载力、刚度与耗能能力均有不同程度的退化。图32表1参12