T Classical and new concepts of fracture mechanics are combined into a proposed method for the study of compressive fracture induced failure of rock structures. The strain energy release concept and a critical strain energy density fracture theory are applied to mixed mode fracture in simple structures. The theory is implemented through a finite element code which incorporates accurate crack tip singularity elements and which allows efficient fracture propagation through the mesh. The validity of the proposed method is studied in an experimental program using structural models in two types of rock.
In 1913, Inglis (8) presented the first solution for the stress field corresponding to the problem shown in Figure 1. Since then, his solution to this problem has served as a well-spring for various theories of fracture and failure. However, it is now recognized that the problem of predicting e due to brittle fracture generated by elliptical flaws under n has never been solved. No theory has claimed to completely predict the behavior shown in Figure 2. Complete solution of this problem necessitates predictions of:
Fracture initiation load
Point of initiation on the flaw
Incremental fracture loads and path of propagation
Effects of interactions between flaws or between flaws and boundaries
In this paper, classical and new concepts of fracture mechanics are combined into a proposed method for the study of compressive fracture-induced failure of rock structures. Both the finite element method and analytical techniques are used to implement the method on the structural configuration shown in Figures 1 and 2. The validity of the proposed method is studied in an experimental program using two types of rock.
Many rock ( 3, 7) and fracture (4) mechanicians have documented experimentally the initially stable nature of fracture under compression. That is, fracture initiation and rupture are not synonymous under compression. Structural failure requires the propagation of fractures from initial flaws. Consequently, the fracture initiation load is only the first item of interest in a complete solution. For example, the sequence of photographs in Figure 2 depicts the increasing load necessary to propagate
( Figure available in fullpaper)
fractures under compression. Here, rupture was due to fracture/fracture and fracture/ boundary interaction. Failure occurred at a maximum load equal to 2.7 times the fracture initiation load. The basic, unanswered question arising from the behavior shown in Figure 2 is: A t each increment of load, which field variables govern the onset, direction, and length of the corresponding fracture increment?
Theoretical concepts from classical rock mechanics and fracture mechanics will now be surveyed for potential contributions to the answer to this question.
