Ⅱ型能量尺寸效应与应变率效应关联研究

发布时间：2018-06-13 04:09

  本文选题：断裂过程区 + 尺寸效应　； 参考：《北京建筑大学》2017年硕士论文

【摘要】：准脆性材料(岩石,混凝土等材料)所具有的强度等物理特性与构件的空间尺寸以及结构构件所受荷载的加载率有关,而不是简单的经典弹塑性力学假设的理想值的大小。准脆性材料表现出来的材料强度与材料内部的结构构造特性相关,而且与施加在构件上的荷载加载率,以及与结构试件的尺寸大小也是有关系的。在时间和空间维度上,材料的物理特性都会存在一定的影响因素。然而,关于岩石,混凝土的结构尺寸与动力荷载之间联系的分析理论相对较少,两者的关联性没有充分的研究,造成了很多实际的问题。例如,对于结构发生破坏的进程没有被充分的认识,以导致无法进一步使工程结构的设计更加安全可靠。戚承志教授,成功分析出了在I型尺寸效应下,结构的强度与应变率以及构件大小的内在联系,并且证明应变率变化过程中存在临界应变率,另外求解出了结构应变率和破碎的岩石的块体大小的关系式,证明了准脆性材料的I型尺寸效应与应变率效应是统一的。本文主要是结合岩石类的结构层次,考虑裂纹尖端存在的断裂过程区,进而参考戚承志教授对Ⅰ型(无裂纹试样)尺寸效应和应变率关联的研究,应用Hu,Duan的边界效应公式,对有Ⅱ型尺寸效应和应变率效应进行研究,主要研究成果包括:(1)依据动态裂纹尖端应力场和摩尔强度准则,求解出了裂纹的断裂过程区尺寸。基于Freund求解出的变速动态裂纹尖端的应力场,结合摩尔强度准则,求解出来裂纹尖端断裂过程区的形状和大小。得出结论:在裂纹起裂过程中,裂纹尖端的断裂过程区随着应变率的增大而增大;在裂纹传播过程中,裂纹尖端的断裂过程区面积随着裂纹传播速度的增大而增大;裂纹传播相比裂纹起裂过程,断裂过程区增大的幅度更大。(2)结合Hu,Duan的边界效应公式,理论推导出了带裂纹体的起裂韧度与加载率的关系,传播韧度与裂纹速度的关系,实现了Ⅱ型尺寸效应和应变率效应关联研究。得出结论:含有裂纹的准脆性材料试件,试件的起裂韧度随着应变率的提高而增大,在裂纹传播过程中,试件的传播断裂韧度随着裂纹速度的提高而增大,试件的传播韧度要大于起裂韧度。所得到的理论结果与实验结果相符。(3)结合动态裂纹尖端的能量释放率,推导出了裂纹尖端断裂过程区尺寸与裂纹速度的关系,带入边界效应公式,计算出了试件的断裂韧度与裂纹速度的关系,从能量的角度,验证了前面的理论结果。即随着裂纹的速度的增加,裂纹长度的增加,裂纹尖端的能量释放率不断增大,可以发现裂纹尖端的断裂过程区的面积随裂纹速度增加而增大,进而材料抵抗裂纹扩展的阻力增大,表现出了试件的断裂韧度随着裂纹速度增大而增大。
[Abstract]:The physical properties of quasi-brittle materials (such as rock, concrete, etc.) are related to the spatial size of the members and the loading rate of the structural members, rather than the ideal values of simple classical elastoplastic mechanics assumptions. The strength of the quasi-brittle material is related to the structural characteristics of the material, the loading rate applied on the members, and the size of the structural specimen. In the dimension of time and space, there are some influence factors on the physical properties of materials. However, there are relatively few theories about the relationship between the structure size and the dynamic load of concrete, and the correlation between them is not fully studied, which has caused many practical problems. For example, the process of structural failure is not fully understood, resulting in a failure to further make the design of engineering structures more secure and reliable. Professor Qi Chengzhi has successfully analyzed the intrinsic relationship between the strength of the structure and the strain rate and the size of the member under the model I size effect, and has proved that the critical strain rate exists in the process of strain rate variation. In addition, the relationship between the strain rate of structure and the block size of broken rock is obtained. It is proved that the I size effect and strain rate effect of quasi-brittle materials are unified. In this paper, considering the fracture process zone at the crack tip, and referring to Professor Qi Chengzhi's research on the correlation between the size effect and strain rate of model 鈪，

本文编号：2012661