Volume 20, Issue 5 (September 1992)
Fracture Toughness Determination Related to Indentation Problems Avoidance in Three-Point Bend Specimens
In elastic-plastic fracture toughness of the three-point bend specimens (3P-SENB) test, fracture toughness is obtained as a function of the energy put into the specimen, and it is measured from the area under the load versus load-line displacement record. A fraction of this energy is not developed as a work in the crack tip, but it is expended in plastic deformation near the loading points. There also exists an overestimation of this energy because of spurious displacements involved between measurement points when a remote transducer is used to measure the load-line displacement. Actual standards provide some techniques to discriminate this spurious energy from the total measured energy.
By checking the experimental setup performance, some differences are evident between the proposed corrections and the real phenomenon during the test. In this paper a simple method for measuring the load-line displacement is proposed, which is able to avoid automatically the spurious energy.
The energy developed by the load components on the outer loading points and its contribution on J is also discussed, and equations to take into account this energy are proposed.