MECH 5312 Solid Mechanics II. Dr. Calvin M. Stewart Department of Mechanical Engineering The University of Texas at El Paso

Transcription

1 MECH 5312 Solid Mechanics II Dr. Calvin M. Stewart Department of Mechanical Engineering The University of Texas at El Paso

2 Outline Founders of Fracture Mechanics Disastrous and Examples of Fracture Recent Advances in Fracture Standards, Journals, and More Questions YouTube Videos

3 Contributors to Fracture Rankine (1842) Inglis (1913) Griffith (1920s) Irwin (1950s) Paris (1961) Wells (1961) Rice (1960s) Landes & Bagley and Nikbin et al., (1976) Saxena (1990)

4 Industrial Revolution Enormous increase in the use of irons and steels for structural applications Failures in railway equipment, boilers due to poor design and existing defects

5 William John Macquorn Rankine Worked with railroad axles and other stress concentrations Participated in studies following the Versailles accident Recognized the distinctions between fatigue cracks from other cracks Recognized the importance of stress concentrations in his investigation of railroad axle failures MAX SCF NOM W. J. M. Rankine ( )

6 ASTM formed In 1898, Charles Benjamin Dudley investigated problems with the chemistry of materials used by the Pennsylvania Railroad He later went on to found the ASTM, a committee based organization focused on industrial progress Committee on fracture was formed in the 1950 s

7 Sir Charles Edward (C.E.) Inglis In, 1913, considered the fracture behavior of thin glass plates with elliptical holes Determined that the ratio of a to b plays a great role in determining the stress at A 2a C.E. Inglis ( )

8 Alan Arnold Griffith In 1920s, he extended the work of Inglis He believed that the value of the stress at the crack tip reached a theoretical maximum Used strain energy concepts to predict when a crack was able to propagate The Energy of Fracture, G f Linear-Elastic (Brittle Fracture) A. A. Griffith ( )

9 Liberty Ships of WWII

10 Liberty Ships of WWII Early ships suffered hull and deck cracks Number of ships that broke in half: 19 Failure mechanism due to brittle crack growth at stress concentration Temperature of the Steel submerged in water fell below the Brittle to Ductile Transition Temperature

11 George Rankin Irwin In 1950 s, Irwin extended the work of Griffith by extending theories to ductile materials Conducted research at the US Naval Research Lab Irwin ( )

12 De Havilland Comet Three plane crashes caused by repeated pressurization of the metallic fuselage skin at sharp corners near windows Fatigue crack growth at Stress Concentration

13 De Havilland Comet

14 Paul C. Paris In, 1961, Paris discovered that the increment of fatigue crack growth is related to the stress intensity factor range Proposed method for predicting the rate of growth of individual fatigue cracks Investigated the De Havilland Comet Failures K K K MAX MIN da C K dn m

15 James Robert Rice In 1968, J. R. Rice developed the Path Independent Integral for the approximate analysis of strain concentration by notches and cracks. Encompasses both elastic and plastic energy of material. Large Plastic Zones (Ductile Fracture) J. R. Rice ( ) du i J Wdy Ti ds dx

16 Conference on Fracture International Conference on Fracture (ICF) started in 1965 European Conference on Fracture (ECF) started in 1976

17 Landes & Bagley and Nikbin et al., (1976) Two groups of researchers independently developed the time-dependent analogy of the J- integral, called the C*-integral for TDFM Landes JD, Begley JA. A fracture mechanics approach to creep crack growth. In: Mechanics of Crack Growth. ASTM STP 590. Philadelphia, p Nikbin KM, Webster GA, Turner CE. Relevance of nonlinear fracture mechanics to creep cracking. In: Crack and Fracture. ASTM STP 601. Philadelphia, p Kamran Nikbin

18 Ashok Saxena Saxena developed the Ct-parameter to characterize creep crack growth under conditions from small-scale creep to extensive creep. Ashok Saxena

19 High Temperature Fracture 5 Airfoil LCF Crack Solidification Direction [100] Root Primary Stress Axis

20 High Temperature Fracture Blade/Bucket Failure can lead to catastrophic failure of gas turbine system. Turbomachinery Industrial Gas Turbine Aero Gar Turbine Marine Gas Turbine Etc.

21 Stress Corrosion Cracking CC Continuous Cycling HC Hold Compressive HT Hold Tensile Stress Axis T 871 C, 0.8%, CC, N 3699 m i T 871 C, 0.8%, HC, N 678 m i T 871 C, 0.8%, HT, N 248 m i

22 Stress Corrosion Cracking Pressure Vessels and Piping Industry Primary Water Pipes Heat Exchanges Turbine Susceptible to high fluency radiation damage to microstructure

23 On-going Challenges in Fracture Multiscale Modeling - correlating local and global fracture behavior of materials Chemical Interaction - characterizing crack growth in the presence of chemical reactions (i.e., corrosion, oxidation, high fluence radiation) Variable Amplitude Loading - development of models appropriate for variable amplitude fatigue crack growth

24 Perspectives of Fracture

25 Connotation of Fracture Society s perspective of fracture is that the cracked object(s) is preventable but irreparable

26 Fracture Journals International Journal of Fracture Engineering Fracture Mechanics Fatigue and Fracture of Engineering Materials & Structures Engineering Failure Analysis Materials Science and Engineering

27 Fracture Texts

28 Fracture Mechanics Fracture mechanics can be used to determine each of the following: Allowable load to avoid failure Crack growth that can be expected during fatigue cycling Design microstructures for optimum fracture strength Condition of material in vicinity of crack front And more

29 Contact Information Calvin M. Stewart Assistant Professor Department of Mechanical Engineering The University of Texas at El Paso 500 W. University Blvd. Suite A126 El Paso, Texas URL: Phone: Fax: