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Research Papers

Design of Threaded Fatigue Test Specimen for Machining

[+] Author and Article Information
Hamza K. Akyildiz

Department of Mechanical Engineering,
Bozok University,
TR-66200 Yozgat, Turkey
e-mail: hkemal.akyildiz@bozok.edu.tr

Haydar Livatyali

Department of Mechanical Engineering,
Istanbul Technical University,
Gumussuyu, Istanbul TR-34437, Turkey
e-mail: Haydar.Livatyali@mam.gov.tr

1Corresponding author.

Contributed by the Manufacturing Engineering Division of ASME for publication in the Journal of Manufacturing Science and Engineering. Manuscript received July 1, 2011; final manuscript received June 7, 2013; published online July 17, 2013. Assoc. Editor: Patrick Kwon.

J. Manuf. Sci. Eng 135(4), 041004 (Jul 17, 2013) (6 pages) Paper No: MANU-11-1236; doi: 10.1115/1.4024813 History: Received July 01, 2011; Revised June 07, 2013; Accepted June 11, 2013

Design and machining of the fatigue test specimens have significant effects on the duration and reliability of fatigue test. Fatigue test specimens essentially consist of three parts: the center or critical test section, which is the region where required conditions are simulated as closely as possible, and the two ends, which serve to transfer the load from the grips to the center section. When high strength materials are used for a complex geometry, such as a thread need to be tested, design and manufacturing of the specimens become more influential on the reliability and duration of the tests. Threaded fatigue test specimens were designed, machined, and tested in a four-point rotary bending fatigue testing machine. An innovative threaded fatigue test specimen that consistently fails at the critical test section was designed, machined, and tested successfully to give the required fatigue notch factor. Because of full scale fatigue testing with threaded parts is very expensive and sometimes dangerous, evaluated threaded fatigue specimen can be used in fatigue testing and it reduces duration of the experiment more than 60% for machined threaded specimens.

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Figures

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Fig. 1

Schematic of the Moore type four-point rotary bending fatigue testing machine: 1, specimen; 2, gripping part; 3, gripping part; 4, load arm; 5, loads; 6, fixed joint; 7, bearing; 8, bearing; 9, electric motor; 10, flexible coupling

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Fig. 5

Machined threaded specimens in the CNC lathe.

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Fig. 4

Final design threaded fatigue test specimen for machining

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Fig. 3

Modified threaded fatigue test specimen for machining

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Fig. 2

Initial design of threaded fatigue test specimen

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Fig. 8

Final design threaded fatigue test specimens, all of the specimens are fractured from the full developed screw threads in the critical test section, third (a), second (b), and first whole developed thread teeth

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Fig. 6

Test results of the initial designed threaded fatigue test specimens. Specimens fractured in the outer of the critical test sections: (a) grip ends are grinded and Cu coated (b) screw threads are machined through the length of the specimen and Cu coated (c) limited threaded section and the length of grip ends are increased and ground (d) length of grip ends is shortened (e) length of the threaded section is increased and grip ends are Cu coated (f) length of the threaded section is increased and threads are machined throughout the length of the specimen (g) increased length of the threaded section and grip ends are Sn coated.

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Fig. 7

Test results of modified fatigue test specimens broken from undeveloped thread (a) and broken from fully developed thread (b)

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