Simplification of the Testing and Analysis Procedure for the Two Parameter Fracture Model

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Title: Simplification of the Testing and Analysis Procedure for the Two Parameter Fracture Model

Author(s): D. C. Jansen, W. J. Weiss, and S. H. F. Schleuchardt

Publication: Special Publication

Volume: 201

Issue:

Appears on pages(s): 1-16

Keywords: compliance; concrete; cracking; effective crack; fracture mechanics; post-peak; test methods

Date: 7/1/2001

Abstract:
This work describes a modification to the two-parameter fracture method’s experimental procedure aimed at removing this operator/equipment dependence. With this method, three compliances are used to determine the focal point at which these compliances intersect. This focal point is then used to determine the slope of the unloading compliance that corresponds to the peak of the load vs. CMOD curve. The unloading compliance that corresponds to unloading at the peak load and initial compliance are then used to determine Ktc and CTODc as normally done with the Two Parameter Fracture Model. Use of this method makes it possible to remove operator and machine dependence, especially if the materials are extremely brittle, such as in pastes or high strength concrete, thereby permitting the loading and unloading to be programmed using testing software removing the need for manual operator loading changes. Tests on 15 mortar beams with 4 different notch lengths and initial unloading points ranging from 97% to 75% of maximum load are used to validate this approach. The experimental results are typically more consistent and better correlate to results from the peak load test method. These results indicate that utilizing the focal point correction typically reduces Ktc and CTODc by 12% and 38% respectively for the mortar tested thereby causing the TPFM and peak load method results to coincide even more closely.