Optimization of chevron-notched short bar specimen configuration for determination of the fracture toughness and crack growth rate of aluminum alloys

The goal of the study is optimization of the fracture toughness determination procedure on the samples with a chevron notch. Well-known principles of fracture mechanics are used to determine the geometry of a specimen with a chevron notch, which ensures the independence of the stress intensity factor from the crack length in the range sufficient for its practical application. A requirement to the shape of the dependence «compliance – crack length» is formulated for a chevron-notched specimen. The choice of the cross-sectional shape of the specimen with a chevron notch, the geometric dimensions of the specimen, and the drawing of the gripping device are justified. The formula for calculation of the fracture toughness from the maximum test load and thickness of the specimen is derived and experimentally validated. The results of the fracture toughness tests of the samples with a chevron notch and standard samples are compared for a number of aluminum alloys. The data on the scale factor in the range of a sample thicknesses of 12.5, 25, and 50 mm and variation coefficient obtained upon the fracture toughness determination revealed the absence of the significant effect of the scale factor, 6% variation under the normal law of the fracture toughness distribution in the tests of chevron-notched specimens. The results on the fracture toughness distribution in the height of the thick plates of alloys 1163T1 and V95pchT2 are presented. The temperature dependence of the fracture toughness of the plate (alloy 1201T1) are constructed for chevron-notched specimens within a temperature range of –196 – +200°C. The features of using chevron-notched specimens for determination of the crack growth rate attributed to independence of the stress intensity factor at the crack tip on crack length are considered in a rather wide range. The method of the crack growth rate determination is described and the results of assessing da/dN – ΔK for an aluminum alloy plate 1163T are presented. The simplicity and reliability of the methods for determination of the fracture toughness and fracture growth rate (fatigue, creep, corrosion) on chevron-notched specimen of the proposed geometry allow us to recommend them for control tests and research in various test conditions.

chevron-notched specimen, compliance, fracture toughness, crack growth rate, aluminum alloys

1. Munz D. G. Compliance and stress intensity coefficients for short bar specimens with chevron notches/ Int. J. Fract. 1980. Vol. 16. N 4. P. 359 – 374.

2. Grant T. J., Weber L., Mortensen A. Plasticity in Chevron-notch fracture toughness testing / Eng. Fract. Mech. 2000. Vol. 67. P. 263 – 276.

3. Bartisch M., Zang Z. F., Scheu C., Rühle M., and Messerschmidt U. Fracture parameters of chevron-notched Al2O3/Nb sandwich specimens / Z. Metallkd. 2004. Vol. 95. P. 779 – 784.

4. Rakhimkulov R. R. Comparison of the values of the fracture toughness K1c obtained on samples with Chevron slotting and the standard method for steel St3sp / Neftegazovoe delo. 2010. N 2. P. 59 – 60 [in Russian].

5. Dai F., Chen R., Xia K. A Dynamic CCNBD Method for Measuring Dynamic Fracture Parameters. Dynamic Behavior of Materials / Proceedings of the 2010 Annual Conference on Experimental and Applied Mechanics. P. 42 – 48.

6. Deryugin E. E., Panin V. U., Suvorov B. I., Kibitkin V. V. Engineering method for determining the crack resistance of materials according to the test data of samples with Chevron notch. International conference «Perspective materials with hierarchical structure for new technologies and reliable constructions», Tomsk, 2015, Abstracts. P. 299 [in Russian].

7. Zagar G., Singh A., Pejchal V., Mueller M., Mortensen A. On measuring fracture toughness under load control in the presence of slow crack growth / J. Eur. Ceram. Soc. 2015. Vol. 35. P. 3155 – 3166.

8. Berdigulov L. R., Schipachev A. M. Investigation of fracture toughness of metals / Juvenis scientia. 2016. N 2. P. 28 – 32.

9. Deryugin E. E., Lepov V. V. Determination of fracture toughness of materials when testing small-sized samples with Chevron incision / Zavod. Lab. Diagn. Mater. Vol. 82. N 1. P. 64 – 68 [in Russian].

10. Deryugin E. E. Determination of crack resistance of materials according to test data of samples with Chevron incision / LVII international conference «Actual problems of strength», Sevastopol, 2016, Collection of abstracts. P. 59.

11. Deryugin Y., Narkevich N., Antipina N. New Method of Determininig Fracture Toughness Characteristics of Small-Size Chevron-Notched Specimens / Int. J. Innovative Res. Eng. Manag. 2016. Vol. 3, July. P. 339 – 348.

12. Bogdanov A. A. Analytical calculation of fracture toughness of materials on tests of small-sized samples with a chevron notch. XV international conference «Prospects of development of fundamental works», Tomsk, 2018. Vol. 1. P. 72 – 74.

13. Erarslan N. The importance of testing method to evaluate the most representative mode I fracture toughness value of brittle rocks / MOJ Civil Eng. 2018. Vol. 4(5). P. 437 – 441.

14. Seitl S., Ruziska V., Miarka P., Sobek J. Analysis of various chevron notch types and its influence on the ligament area / Transactions of the VSB-Technical University of Ostrava, Civil Engineering Series. 2019. Vol. 19. N 1. P. 28 – 34.

15. Irwin G. R., Kies J. A. Critical Energy Rate Analysis of Fracture Strength / Weld J. 1954. Vol. 33. P. 193 – 198.