Numerical study and experimental validation of the size effect of smooth and mode I cracked semi-circular bend specimens
Scientific Reports 13, Article number: 7570 (2023)
Abstract
The edge-cracked semi-circular bend (SCB) specimen subjected to three-point bending loading is used in many applications to measure the fracture behavior of quasi-brittle materials. The main objective of the present work was to study the effect of the crack length to SCB specimen radius ratio (a/R), span to specimen diameter ratio (S/D), and specimen size on its flexural and mode I crack growth behavior. The contour integral method was implemented using the 3-D finite element method to determine the mode I stress intensity factor. In addition, high-strength concrete specimens were experimentally studied to validate the numerical results. The results show that the maximum compression stress is not sensitive to the S/D value, while the tensile stress is very sensitive. The value of S/D is the main parameter controlling the crack driving force (i.e., the crack mouth opening displacement (CMOD) and the normalized stress intensity factor, YI). For the same S/D, the SCB specimen diameter value change has a marginal effect on CMOD and YI. The specimen with S/D = 0.8 showed that it is the most compatible specimen with three-point bending test conditions, regardless of the SCB specimen size. A good agreement between the numerical and experimental results was achieved.
Introduction
The edge-cracked semi-circular bend (SCB) specimen under three-point bending loading is used to measure the material fracture behavior of rock materials, concrete, asphalt mixtures, and biomaterials1,2,3,4,5. The main advantage of using the SCB specimen is that it can easily be taken from the cores of any material6. Furthermore, it has a simple geometry and test procedure for calculating mixed mode I–II fracture toughness7,8,9. Arsalan et al.10 recently improved the SCB specimen to obtain a ductile adhesive’s mixed-mode fracture behavior with a considerable fracture process zone ahead of the crack tip. The mixed-mode SIF is a function of the crack length ratio a/R. Its orientation concerns the loading direction and the distance between the supports11,12, as shown in Fig. 1. Crack length appears to be a more significant factor than the specimen thickness on the SIF13. Furthermore, the SIFs become very sensitive at the large crack length to SCB specimen radius ratio (a/R) values8.
Geometry and loading conditions of SCB specimens.
https://www.nature.com/articles/s41598-023-34201-z
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