不均匀脆性材料动强度提高机理及破坏形态研究

Mechanism for enhancement of dynamic strength and failure model of nonuniform brittle materials

论文通过理论分析指出,材料的动强度较静强度是否有提高,提高幅度有多大,以及静动强度差异的根源与材料的类型、加载速率以及不均匀程度有关,不能撇开具体情况来讨论材料的静动强度的关系。重点研究了岩石、混凝土类不均匀脆性材料的静动强度差异及机理,指出其动强度较静强度有一定的提高,静、动强度的差异与其破坏时裂纹的发展路径有关。静态破坏时裂纹沿着材料的薄弱面向前发展,即静态裂纹开裂遵循最小耗能原理;而动态破坏时,材料内部的应变能需要在瞬间得到释放,裂纹沿着能量释放最短路径向前发展,这时的裂纹穿过了材料的部分高强度区,使得材料的动强度高于静强度,即动态裂纹开裂遵循能量释放率相关原理。动强度提高的根源是由于材料的不均匀性和惯性力造成的。对于岩石、混凝土类不均匀脆性材料而言,其动强度也不是一个定值,而是随加载速率而变化。加载速率越大,裂纹穿过高强度区的能力越强,材料的强度越高。加载速率较低时动强度提高幅值主要受裂纹穿越材料高强度区的面积影响;加载速率超过某个临界值时,动强度提高幅值就只受到惯性项的影响。论文给出了岩石、混凝土类不均匀脆性材料动强度的具体表达式。并通过特殊设计的不均匀脆性材料的数值试验和物理试验验证了以上理论研究的正确性。

Based on the theory analysis, this paper points out that whether dynamic strength of materials is in-creased, the increased range of dynamic strength and the source of the differences between static and dynamic strength are related to material types, loading rates and inhomogeneous degree, the relationship between static and dynamic strength should be discussed according to the specific conditions. The author mainly studies on the differences between static and dynamic strength of rock-concrete-like brittle material and its mechanism ; show clearly the dynamic strength higher than static strength, the differences are related to the fracture courses of cracks. The cracks propagate on the weak interface of material at static failure, in which the least energy consumption principle is followed at static crack opening, while the strain energy in the material releases instantly at dynamic fracture, the cracks propagate along the path in which the energy release is the fastest, cracks go through partial high strength re-gions in the material make the static strength higher than the dynamic strength of material, in which the energy release rate dependent principle is followed at dynamic crack opening. The increase of dynamic strength can be caused by inhomogeneity of material and the inertia force. The dynamic strength changes with loading rates rather than being a fixed value for rock-concrete-like inhomogeneous brittle materials. The faster the loading rate is, the greater the ability that cracks can go through high strength regions is, the higher the strength of material is. The amplitude of dynamic strength increase is decided on the areas of high strength regions in which the cracks go through at lower loading rates; it is merely decided by the inertia force when loading rate exceeds some critical value. In this paper, the concrete expression of dynamic strength for rock-concrete-like inhomogeneous brittle materials is given. The validity of the above mentioned theory is confirmed through numerical and physical experiments of nonuniform brittle materials which are specially designed.