Fracture toughness crack opening displacement

The geometry-independent material characteristic Gic as a function of the initial crack opening displacement (ICOD) is introduced. Typical values of the delamination fracture toughness of 3D glass and carbon composites are presented. 

Fracture toughness, delamination, 3D composite, bridging law, crack opening displacement. 

Figure 4.11. Typical strain gage-based crack-opening displacement gage (left), and typical load-displacement traces observed during fracture toughness testing (right) [1].

Wells [11] first proposed the crack opening displacement as a measure of fracture toughness for tough metals such as the structural steels where LEFM is not valid. The concept became a standard in 1979 in the form of British Standard (BS) 5762 [12], which is now-superseded by BS 7448 Part 1. 1991. Method of determination of Afi. critical CTOD and critical J values of metallic materials [13], More recently. ASTM E1290-9,3, Crack-tip opening displacement (CTOD) fracture toughness measurement [14] was issued. It is stated that this method may be used to characterize the toughness of materials that arc (a) too ductile or fail the size conditions to be tested for or (b) likely to produce unstable crack extension that would invalidate Ji tests in accordance with the requirements of ASTM E81.3 [15]. 

Load-versus-crack opening displacements also were monitored during the fracture toughness tests using the cracked disk specimen. This specimen geometry was used tor the validation experiments. Also, it provided a means to evaluate whether the analytical model was able to predict load-displacement data under mixed-mode fracture conditions. It may be noted that in actual applications, loading is generally mixed mode in character. 

A craze at the crack tip in glassy polymer has a crack opening displacement of 4 /rm. Given that the fracture toughness is 1 MNm / and the plane strain modulus is 1.5 GPa, calculate the length of the craze and the craze stress. 

Fig. 5. Relationship between load and crack opening Fig. 6. Relationship between normalized crack displacement for mode I interlaminar fracture tough- length and compliance for DCB specimen in ness tests inT300/EpoxyH and Altex/EpoxyH lami- T300/EpoxyH laminates in TTK-LN -nates in 77K-LN,.

Fracture Toughness by Crack Tip Opening Displacement (CTOD)... 

ASTM El290. 1993. Crack-tip opening displacement (CTOD) fracture toughness measurement. 

VI.22] AMERICAN SOCIETY FOR TESTING AND MATERIALS, Standard Test Method for Crack Tip Opening Displacement (CTOD) Fracture Toughness Measurement, ASTM E1290-93, Annual Book of ASTM Standards, ASTM, PhUadelphia, PA (1993). 

The results show that fracture toughness K ic and critical strain energy release rate G are dependent on the dimensions specimens, but, critical crack tip opening displcement CTOD might be independent on the dimensions of specimens. Hence, the critival crack tip opening displacement CTODc could be taken as a material parameter to judge the fracture of concrete. 

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