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The shear fracture toughness, KIIc, of graphite.

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Bibliographic Details
Title:	The shear fracture toughness, KIIc, of graphite.
Authors:	Burchell, Timothy D.¹ burchelltd@ornl.gov, Erdman, Don¹
Source:	Carbon. Mar2016, Vol. 98, p267-279. 13p.
Subjects:	Fracture toughness, Shearing force, Graphite, Acoustic emission, Mechanical loads
Abstract:	The critical shear stress intensity factor, K IIc , here-in referred to as the shear fracture toughness, K IIc (MPa√m), of two grades of graphite are reported. The range of specimen volumes was selected to elucidate any specimen size effect, but smaller volume specimen tests were largely unsuccessful, shear failure did not occur between the notches as expected. This was probably due to the specimen geometry causing the shear fracture stress to exceed the compressive failure stress. In subsequent testing the specimen geometry was altered to reduce the compressive footprint and the notches (slits) made deeper to reduce the specimen's ligament length. Additionally, we added the collection of Acoustic Emission (AE) during testing to assist with the identification of the shear fracture load. The means of K IIc from large specimens for PCEA and NBG-18 are 2.26 MPa√m with an SD of 0.37 MPa√m and 2.20 MPa√m with an SD of 0.53 MPa√m, respectively. The value of K IIc for both graphite grades was similar, although the scatter was large. In this work we found the ratio of K IIc /K Ic ≈ 1.6. [ABSTRACT FROM AUTHOR]
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Database:	Engineering Source

Description
Abstract:	The critical shear stress intensity factor, K IIc , here-in referred to as the shear fracture toughness, K IIc (MPa√m), of two grades of graphite are reported. The range of specimen volumes was selected to elucidate any specimen size effect, but smaller volume specimen tests were largely unsuccessful, shear failure did not occur between the notches as expected. This was probably due to the specimen geometry causing the shear fracture stress to exceed the compressive failure stress. In subsequent testing the specimen geometry was altered to reduce the compressive footprint and the notches (slits) made deeper to reduce the specimen's ligament length. Additionally, we added the collection of Acoustic Emission (AE) during testing to assist with the identification of the shear fracture load. The means of K IIc from large specimens for PCEA and NBG-18 are 2.26 MPa√m with an SD of 0.37 MPa√m and 2.20 MPa√m with an SD of 0.53 MPa√m, respectively. The value of K IIc for both graphite grades was similar, although the scatter was large. In this work we found the ratio of K IIc /K Ic ≈ 1.6. [ABSTRACT FROM AUTHOR]
ISSN:	00086223
DOI:	10.1016/j.carbon.2015.10.084