SCHOOL OF MECHANICAL ENGINEERING SEMINAR
Wednesday November 24, 2021 at 14:00
Wolfson Building of Mechanical Engineering, Room 206

Failure Criteria for Quasi-Brittle Materials at V-Notch Tips

Vered Mendelovich

MSc zohar yosibash

Many structures made of metals that contain V-notches may fracture at the V-notch tip. Failure criteria for brittle materials with V-notches have been proposed to predict such fractures where mode I loading is considered. Since metals are not brittle, a small plastic zone near the notch tip may evolve.

Herein, we investigated by experiments and finite element analyses whether the finite fracture mechanics coupled criterion (FFM CC) for brittle material is valid for metals, depending on the plastic zone size. Experiments were performed on AISI 4340 specimens which contain four different V-notch opening angles and three different tempering temperatures. We used finite element analysis for the computation of the parameters that are required by the criterion. Finally, we compared the predicted fracture load and the experimental fracture load for the different V-notch opening angles and tempering temperatures.

Comparing predicted and computed fracture force, we expected a good agreement for the smallest angle due to the small plastic zone. However, predicted fracture load is lower by about 70% than the experimental load, which may occur due to underestimation of  in our experiments.

Recomputing the fracture force using lowest value of  in literature (same Young’s modulus as our specimens), the criterion prediction of fracture force is at most within 20% difference for 30° V-notch angle (where the plastic zone is small), 29% difference for 60° V-notch angle, and 51% difference for 90° V-notch angle. As the notch angle increases the difference between the experimental and computed load increases due to the plastic zone area size, which increases as the notch angle increases.

Further study is warrant to determine the proper  to be used for current metallic material, and to enhance the FFM CC to better predict fracture in metals involving small scale yielding.

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