Flexure method, surface crack

FN ISO (2003) 18756. Fine ceramics (Advanced Ceramics, Advanced Tedmical Ceramics) - Determination of Fracture Foulness of Monolithic Ceramics at Room Temperature by the Surface Crack in Flexure (SCF) Method, International Organization for Standardization. 

R. Moon, K. Bowman, K. Trumble, J. Roedel, Comparison of R curves from single edge V notch beam (SEAfB) and surface crack in flexure(SCF) fracture toughness test methods on multilayered alumina zirconia composites, J. Am. Ceram. Soc. 83 [2] 445 47 (2000)... 

G. D. Quinn and J. A. Salem, Effect of Lateral Cracks Upon Fracture Toughness Determined by the Surface Crack in Flexure Method, J. Am. Ceram. Soc., 85 (4) 873 80 (2002). 

K. Yasuda, T. Taguchi, J. Tatami, and Y. Matsuo, Estimation of Short Crack R Curves of Polycrystalline Ceramics by Surface Crack in Flexure Method, pp. 115 120 in Improved Ceramics Through New Measurements, Processing and Staruiards, Ceramic Transactions, vol. 133, (2002). 

G.D. Quinn, R.J. Gettings, and J.J. Kubler, Fractography and the Surface Crack in Flexure (SCF) Method for Evaluating Fracture Toughness of Ceramics, Fractography of Glasses and Ceramics, Ceramic Transactions, Vol. 64, American Ceramic Society, Westerville, OH, 1996, pp. 107 144. G.D. Quinn and J.A. Salem, Effect of Lateral Cracks on Fracture Toughness Determined by the Surface Crack in Flexure Method, J. Am. Ceram. Soc., 85 [4] 873 880 (2002). 

ASTM C 1421 for advanced ceramics includes three related test method procedures as illustrated in Figure 2. The three methods are the surface crack in flexure (SCF), precracked beam (PB) [also known as single-edge precracked beam (SEPB)], and chevron notch in bending (CNB) methods. The content and development of C 1421 and its precursor, ASTM PS 070-97 are documented elsewhere [2,3,4,5]. The SRM may also be used with three ISO standard test methods that are under development in Technical Committee TC 206, based on the SEPB, SCF, and CNB methods. It may also be used with a draft CEN standard that features SCF, CNB, SEPB, and single edge-V-notched beam methods, as well as JIS R 1607 which has the SEPB method. "... 

Technical Working Area 3, Structural Ceramics, has conducted thirteen major round robins over the course of 13 years, including five round robins and 4,500 experiments on fracture toughness alone.The 1993 to 1994 round robin featured the surface crack in flexure (SCF) method. Twenty laboratories around the world obtained very consistent results on test specimens from a single billet (designated E ) of the NC... 

One of the advantages of the three methods in C 1421 is that they all use a simple bend bar. Each 3 mm x 4 mm x 45 mm to 47 mm bar test specimen was prepared in accordance with the generic ( standard ) preparation procedure specified in the flexural strength standards MIL STD 1942 MR," ASTM C 1161," and ISO 14704. ° One 4 mm wide face was finished with a 900 grit wheel (finer than is normally required) to produce a flat and smooth surface for the Knoop indentation in the SCF test method. The four long edges of the test specimens were chamfered in accordance with requirements for the surface crack in flexure (SCF) and precracked beam (SEPB) test methods. 

G. D. Quinn, VAMAS After Twelve, Bulletin of the American Ceramic Society, 78 (7) 78 83 (1999). G. D. Quinn, J. J. Kiibler, and R. J. Gettings, Fracture Toughness of Advanced Ceramics by the Surface Crack in Flexure (SCF) Method A VAMAS Round Robin, VAMAS Technical Report 17, National Institute of Standards and Technology, Gaithersburg, MD 20899, June, 1994. 

ISO 4600 details a ball or pin impression method for determining the ESCR. In this procedure, a hole of specified diameter is drilled in the plastic. An oversized ball or pin is inserted into the hole, and the polymer is exposed to a stress cracking agent. The applied deformation, given by the diameter of the ball or pin, is constant. The test is multiaxial, relatively easy to perform, and with not very well-defined specimens, and the influence of the surface is limited. Drawbacks are the small testing surface and the undefined stress state. After exposure, tensile or flexural tests may be performed on the specimens. This leads to the determination of either the residual tensile strength or the residual deformation at break. 

The indentation strength (IS) method induces Vickers indentations into flexure strength bars with smooth surfaces. The critical stress intensity at fracture is measured, and calculated. It is not necessary to measure crack lengths, but results are dependent on the indenter load. 

The deterioration of mechanical properties is normally assessed by measurements of fracture resistance by pendulum impact test methods or slow speed flexural strength measurements and by ensuring that the surface of the specimens subjected to tensile stresses corresponds to the face exposed to the UV (or weathering) source. These tests are generally more meaningful than nondestructive tests, such as modulus measurements, since the chemical changes and the creation of fine cracks (often invisible to the naked eye) may involve only a very fine layer on the surface of the exposed samples. 

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