Chevron notch specimen

In addition, it has been shown (Boccaccini etal., 2001 Chlup etal., 2001) that the chevron-notched specimen flexural technique (the CN-technique) can be a reliable method of assessing fracture properties (fracture toughness, work of fracture) in thermally shocked brittle matrix composites reinforced by brittle fibres. 

L. Chuck, E. R. Fuller, and S. W. Freiman, Chevron-Notch Bend Testing in Glass Some Experimental Problems, in Chevron-Notched Specimens Testing and Stress Analysis, eds. J. H. Underwood, S. W. Freiman, and F. R. Baratta, ASTM STP 855, ASTM, Philadelphia, PA, 1984, pp. 167-175. 

Figure 11.6 (a) Schematic of single-edge notched beam specimen (b) Chevron notch specimen. 

In this configuration, shown schematically in Fig. 11.6/), the chevron notch specimen looks quite similar to the SENB except for the vital difference that the shape of the initial crack is not flat but chevron-shaped, as shown by the shaded area. The constant widening of the crack front as it advances causes... 

Munz, D.M., Shannon, J.L., and Bubsey, R.T. (1980) Fracture-toughness calculation from maximum load in 4 point bend tests of chevron notch specimens, Int. J. Fracture 16, R137. The straight-through crack assumption approach to determination of Y. the geometric constant in Ki, measurements (cf. Blum et al.). 

D.G. Munz, J.L. Shaimon, and R.T. Bubsey, Fracture Toughness Calculations from Maximum Load in Four Point Bend Tests of Chevron Notch Specimens, Int J. of Fracture 16R137-R141 (1980). 

Specimens were 3x4y30mm in thickness, height and span. The SERB specimens were tested at a stroke rate of 0.5mm/min. Chevron-notch specimens were tested at 0.005mm/min. The low stroke rate used for chevron-notch testing was required to insure stable crack extension. 

Fracture toughness results are summarized in Table 2. The chevron-notch specimens exhibited nonlinear load-displacement behavior, indicating stable crack extension. Fracture toughness, calculated from maximum load and minimum stress intensity coefficient, decreased with temperature up to... 

Because of the multiple variables associated with the chevron notch specimens, a second study has been planned. Standard GAPD flexure bars (1/8 x 1/4 x 2 inch) will be used. Both Vicker s and spherical indentors at various loads will be used to generate cracking. Several tests per bar will be accomplished to generate multiple AE events per bar. This will reduce the error caused by setup variability equipment parameters and machine noise will also be evaluated. After indenting the bars, the crack size will be determined destructively. The AE data will be evaluated as a function of load and crack size. 

The fracture toughness values determined by the chevron notched specimen technique are strongly dependent on the ageing condition, as shown in Figure 3. In the figure, also data of the as received material are shown. 

J.A. Salem, J.L. Shannon, Jr., and M.G. Jenkins, Some Observations in Fracture Toughness Testing with Chevron Notched Specimens, in Chevron Notch Fracture Test Experience Metals and Non Metals, ASTM STP 1172, edited by K.R. Brown and F.I. Baratta (American Society for Testing and Materials, West Conshohocken, PA, 1992) pp. 9 25. 

R. Kolhe, C.Y. Hui, A.T Zehnder, Effects of Finite Notch Width on the Fracture of Chevron Notched Specimens, International Journal of Fracture, 94 (2) 189 198 (1998). 

Figure 8. Chevron notch specimen, configuration A , (a) shows matching halves, (b) shows a close up of one tip with the piece tilted to show how well the two sides of the chevron meet.

R. T. Bubsey, J. L. Shannon, Jr. and D. Munz, Development of Plane Strain Fracture Toughness Test for Ceramics Using Chevron Notched Specimens, in Ceramics for High Performance Applica tions HI. Reliability, (Plenum, NY, 1983), pp. 753 771. 

The second common test uses a chevron notch specimen. In this specimen, the initial crack is chevron-shaped. As the crack grows by the increasing load, the crack front constantly widens. This causes the crack growth to be stable prior to fracture. Because the crack grows with the increasing load, the growth is the result of the atomically sharp crack formation. Thus, there is no need to precrack the specimen. The fracture toughness [5] is obtained from ... 

Munz, D. G., Shannon, J. L., Bubsey, R. T. Jr. (1980). Fracture Toughness Calculation fromMaximumLoadinFourPointBendTests of Chevron-Notch Specimens. International Journal of Fracture, 16(3), R137-R141. doi 10.1007/BF00013393. 

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