Fracture assessment of polymethyl methacrylate using sharp notched disc bend specimens under mixed mode I + III loading

The cracked chevron notched Brazilian disc (CCNBD) specimen, suggested by the International Society for Rock Mechanics for testing mode I fracture toughness of rocks, usually yields rather conservative toughness measurements, and the reasons have not been fully explored. In this study, the CCNBD method is compared with the cracked chevron notched semicircular bending (CCNSCB) method in the fracture process zone (FPZ) and its influence on the fracture toughness measurement. Theoretical analysis reveals that the FPZ is longer in the CCNBD specimen than in the CCNSCB specimen using a relatively large support span, the toughness measurement using the former is affected more seriously by the presence of FPZ, and thus the CCNBD method is usually, more or less, conservative compared with the CCNSCB method. These inferences are further validated by experimental results, which indicate that the CCNBD test indeed produces much lower fracture toughness values and even the results of 75‐mm radius CCNBD specimens are still lower than those of 25‐mm radius CCNSCB specimens. Consequently, due to smaller FPZ, the CCNSCB specimen with a relatively large span is more likely to produce comparably accurate or representative toughness value, and it may be more suitable than the CCNBD specimen for the engineering applications that require more representative or less conservative fracture toughness.

Section: Discussionmentioning

confidence: 99%

An experimental and theoretical comparison of CCNBD and CCNSCB specimens for determining mode I fracture toughness of rocks

Wei

Dai

Liu

et al. 2017

“…However, corner and edge effects (s = 0) on the obtained fracture mechanics parameters are not considered. At the same time, the analysis of these effects on the stress intensity factor and the T‐stress can be found in previous studies …”

Section: Model Of Fatigue Crack Propagation In the Presence Of Residumentioning

confidence: 77%

Fatigue surface crack propagation and intersecting cracks in connection with welding residual stresses

Chernyatin

Matvienko

Razumovsky

2018

The effect of welding residual stress on surface fatigue crack propagation and fracture mechanics parameters of intersecting orthogonal cracks is discussed. The effect of welding residual stresses on fatigue propagation of the internal surface crack is analysed in the case of welded joint of the pipeline. To predict fatigue crack propagation, the modified Forman law taking into account the nonsingular T‐stress as the crack‐tip constraint has been employed. It is shown by means of numerical simulation (the software ANSYS and MATLAB) that welding residual stress and crack‐tip constraint effects lead to the semielliptical form of final configuration of the surface fatigue crack. Fracture mechanics parameters for intersecting surface cracks, namely, circular and semielliptical cracks in welded joint of the pipeline are also analysed by numerical simulation. It was concluded that welding residual stress intensifies the effect of intersecting orthogonal surface cracks on fracture mechanics parameters including the crack‐tip constraint.

“…The possible reason is because of difference in the type of stress field singularity at those locations which in general is different from definitions that are widely accepted for the crack tip stress/strain field and classical stress intensity factors. This issue is more crucial for those cases in which the length of crack front is relatively large in which the stress gradient between the free surfaces and the midpoints can be noticeable . However, because of very small width of INBB specimen (ie, small length of crack front), the influence of out‐of‐plane sliding component (ie, K III ) is neglected in fracture process of investigated bitumen material, and thus, it is assumed that a combine mode I + II fracture problem dominantly controls the cracking response of INBB specimen in which the nominal K I and K II value was adopted at the midplane of the crack front.…”

Section: Specimen Manufacturing and Testingmentioning

confidence: 99%

Aging effect on combined mode fracture resistance of bitumen

Shaker

Aliha

Keymanesh

2019

Crack growth behaviour of aged and unaged 30/40 asphalt binder at subzero temperature was studied both experimentally and theoretically using a test sample called inclined notched bend beam specimen. A series of fracture tests were conducted on this specimen at two subzero temperatures and different combinations of modes I and II. The fracture toughness of tested asphalt binder was significantly dependent on the aging condition such that the load‐carrying capacity of aged bitumen was up to 60% less than the corresponding fracture resistance of unaged bitumen. Moreover, the effective fracture resistance value of tested binder was reduced by increasing the contribution of mode II and also decreasing the test temperature. The obtained experimental results for both binder types were also evaluated theoretically using a stress base crack growth theory.