PSI - Issue 33

Jamaloddin Jamali et al. / Procedia Structural Integrity 33 (2021) 832–842 Author name / Structural Integrity Procedia 00 (2019) 000–000

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 Cracked specimen exhibits a linearly elastic behavior  Crack tip should have state of plane strain  Crack should be sharp enough to make certain that the smallest value of fracture toughness will be acquired

Fig. 1: Modes of fracture

The testing procedure for both tests requires a notched specimen cracked prior to the test using tension or 3 point bending. For the CT specimen, the width (w) and thickness (b) of the specimen are obliged to establish a ratio of 2 ≤ w/B < 4. This ratio will make certain that the specimen’s behavior is linear elastic as stated by the assumptions and conditions above. The length of the initial crack (a) should be approximately half the width or have a ratio of 0.45 ≤ a/w ≤ 0.55. Then, after gently hitting the notch with a sharp object, maximum and minimum loads which are equal in size but opposite in direction are applied in the circular holes of the CT specimen to propagate the crack. Fracture toughness results related to this kind of test is considered to be quite low compared to other specimens which is why the nuclear industry is mainly using CT to ensure safety with the lower bound results the CT results in. Fig. 2 below shows the CT specimen geometry and its fixture. SENB is also known as 3 point bending test. It is mostly used to test thermosets and not thermoplastics. According to ASTM D5045, the specimen’s thickness (B) is changeable and w = 2B, where w is the specimen’s width. The crack length should also follow this ratio 0.45 ≤ a/w ≤ 0.55. More details related to the steps of the tests can be found in the sections below. Fig. 3 shows the SENB specimen geometry and its fixture. After performing the fracture test study of the fracture morphology is helpful to investigate the process further Jamali et al.(2015) and Macek et al. (2021).

Fig.2: CT specimen (left) and fixture (right) Jamali (2014)

Fig. 3: SENB specimen ASTM (2014)