Notch Fracture Toughness Evaluation for a Brittle Graphite Material

Abstract

First, several disc-type test samples weakened by a central bean-shaped slit with two U-shaped ends, called U-notched Brazilian disc (UNBD) specimens, made of commercial graphite, were prepared. Four notch tip radii were considered in the tests. Then, a monotonic compressive load was diametrally applied to each sample along the slit, resulting in pure mode I loading. After sudden fracture, the fracture loads were recorded and converted into the corresponding values of the notch fracture toughness (NFT) K Iq,c . The main advantage of the UNBD specimen is that the NTF test can be easily conducted without using complicated fixtures. The well-established brittle fracture model, namely the strain energy density (SED) over a specified control volume, which embraces the notch edge, was employed to estimate the fracture loads theoretically. A good agreement was found between experimental and theoretical results. Under Mode I loading, the SED and the NFT are linked by a simple relationship providing a powerful tool for the fracture assessment of different specimens and structural components weakened by notches.

Theoretical and experimental investigation of brittle fracture in V-notched PMMA specimens under compressive loading

“…An example of the coupled equations for the notch angle of 60°and the two arbitrary notch radii of 1 and 2 mm is provided in Eq. (14). The parameters r 0 ; k 1 ; l 1 and n hh ð0Þ in Eq.…”

“…The parameters r 0 ; k 1 ; l 1 and n hh ð0Þ in Eq. (14) vary with the notch geometry, but r c and r c remain constant since they are assumed to be the material properties. In general, there are two approaches to solve the system of Eq.…”

“…In general, there are two approaches to solve the system of Eq. (14) for r c and r c . The first and certainly more accurate approach is to solve Eq.…”

“…For example, the following publications can be quoted under (i) pure mode I loading [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]; (ii) mixed mode I/II loading ; (iii) pure mode II loading [39][40][41]; and (iv) mode III and mixed mode I/III loadings [42][43][44]. Most of the investigations carried out in the context of brittle fracture of notched components have been quoted in two valuable review papers [45,46].…”

Combined tension–shear fracture analysis of V-notches with end holes

“…As the most recent works on mode I brittle fracture of notched components, one can refer to Refs. [36,37].…”