Comparison of mode I and mode II elastic-plastic fracture toughness for two low alloyed high strength steels

Abstract

In the present work, mode I and mode II tests were carried out on two low alloyed high strength steels. An asymmetrical four point bend specimen and Jn-integral vs. crack growth resistance curve technique were used for determining the mode II elastic-plastic fracture toughness, Ji~ • Jn-integral expression of the specimen was calibrated by finite element method. The results indicate that the present procedure for determining the Jn, values is easy to use. Moreover, the mode I fracture toughness Jt, is very sensitive to the rolling direction of the test steels, but the mode H fracture toughness Ji~ is completely insensitive to the rolling direction of the steels, and the Ja~/Ji, ratio is not a constant for the two steels, including the same steel with different orientations. Finally, the difference of the fracture toughness between the mode I and mode II is discussed with consideration of the different fracture mechanisms.

Food mechanical properties and dietary ecology

“…Because some materials differ in their ability to resist tensile and shear loads, results from Mode I, II, and III fracture tests are not comparable. In addition, as the ratio of a materials ability to resist Mode I and II or III fracture is not constant, no correction factor can be used to compare results across fracture modes (Hussain et al, ; Shi et al, ; Amstutz et al, ; Darvell et al, ; Dunn et al, ; Sui et al, ; Lucas et al, ). Direct comparison among modes of fracture is done in feeding biomechanics studies, where results from scissors, wedge, and punch tests are directly compared (Agrawal et al, ; Sanson et al, ; Agarwal and Lucas, ; Agrawal and Lucas, ; Sui et al, ; Vogel et al, ; Ang et al, ; Dominy et al, ; Wich, ; Kitajima and Poorter, ; Lucas et al, ; Venkataraman et al, ).…”

“…, Table (Sui et al, ; Freeman and Lemen, ; Lucas et al, )]. Furthermore, the ratio of results between modes of fracture (e.g., Mode I/Mode II) are not comparable, as materials differ in their ability to resist tensile and shear stresses (Shi et al, ; Dunn et al, ). For example (assuming the same amount of plastic deformation is occurring in the scissors and the wedge test, which may or may not be true), it appears that fibrous foods are more efficient at resisting fracture through tensile forces than shear ones (see ginger and rhubarb in Fig.…”

“…And when they do not, mechanical properties are no longer being measured. In addition, energy release rates obtained from different modes of fracture (e.g., wedge test [mode I] vs. scissors test [mode III]) are not comparable to one another (Hussain et al, ; Shi et al, ; Amstutz et al, ; Dunn et al, ). Thus, violating the assumptions of these equations and tests can lead to inaccurate experimental results.…”

On the use of an anti-symmetric four-point bend specimen for mode II fracture experiments

“…Therefore, different test specimens have been used in the past by researchers for investigating pure mode II fracture. The Y-shape specimen containing two edge cracks, 1,2 the angled centre-crack specimen under biaxial loading, 3 the centre-crack specimen subjected to two skew-symmetric point loads applied at holes located near the crack edges, 4 the end notched flexure specimen (often used for composite materials), 5-7 the punch-through shear test, [8][9][10] the shear-box test configuration, [11][12][13][14][15] the compact tension-shear specimen, [16][17][18] the S-shape crack specimen, 19 the disc-type specimens such as the Brazilian disc [20][21][22][23][24][25] and semi-circular bend [26][27][28] specimens and the edge-cracked anti-symmetric four-point bend (ASFPB) specimen [29][30][31][32][33][34][35][36][37][38] are to name a few. In any of the mentioned specimens, pure mode II condition is achieved by appropriately setting the crack location or the crack orientation with respect to the applied load.…”

“…In any of the mentioned specimens, pure mode II condition is achieved by appropriately setting the crack location or the crack orientation with respect to the applied load. The ASFPB configuration has been frequently used in the past for pure mode II fracture toughness testing and obtaining the K IIc value in ceramics, 30,33,38 metals, 31,34 rocks and soils, 35,36 concretes 37 and polymers. 29,32 Hence, there are extensive numerical, experimental and theoretical research studies conducted on this test configuration.…”