Location

La Jolla, CA

Start Date

1-1-1991 12:00 AM

Description

Strong nonlinear responses originating mainly from sliding on microfractures and open grain boundaries occur when rocks are strained above a threshold near 10−6 (1). We report here that introducing artificial tensile fractures in a brittle rock such as granite produces even stronger nonlinearities. By applying sufficient normal stress perpendicular to the fracture, the nonlinear response can be reduced to that typical of the intact rock. Our measurements are made by driving the sample in torsion at low frequency near 1 Hz. The nonlinear effects we observe are analogous to those caused by partially open fatigue cracks in metals, which generate harmonics when insonified at ultrasonic frequencies (2).

Book Title

Review of Progress in Quantitative Nondestructive Evaluation

Volume

10B

Chapter

Chapter 7: Characterization of Materials

Section

Non-Linear Acoustic Properties

Pages

1861-1867

DOI

10.1007/978-1-4615-3742-7_94

Language

en

File Format

application/pdf

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Jan 1st, 12:00 AM

Acoustic Nonlinearities Produced by a Single Macroscopic Fracture in Granite

La Jolla, CA

Strong nonlinear responses originating mainly from sliding on microfractures and open grain boundaries occur when rocks are strained above a threshold near 10−6 (1). We report here that introducing artificial tensile fractures in a brittle rock such as granite produces even stronger nonlinearities. By applying sufficient normal stress perpendicular to the fracture, the nonlinear response can be reduced to that typical of the intact rock. Our measurements are made by driving the sample in torsion at low frequency near 1 Hz. The nonlinear effects we observe are analogous to those caused by partially open fatigue cracks in metals, which generate harmonics when insonified at ultrasonic frequencies (2).