Improving the Fatigue of Newly Designed Mechanical System Subjected to Repeated Impact Loading

Seongwoo Woo; Dennis L. O’Neal; Dereje Engida Woldemichael; Samson Mekbib Atnaw; Muluneh Mekonnen Tulu

doi:10.3390/met11010139

Metals (Jan 2021)

Improving the Fatigue of Newly Designed Mechanical System Subjected to Repeated Impact Loading

Seongwoo Woo,
Dennis L. O’Neal,
Dereje Engida Woldemichael,
Samson Mekbib Atnaw,
Muluneh Mekonnen Tulu

Affiliations

Seongwoo Woo: Department of Mechanical Engineering, College of Electrical and Mechanical Engineering, Addis Ababa Science & Technology University, PO Box 16417 Addis Ababa, Ethiopia
Dennis L. O’Neal: Department of Mechanical Engineering, Dean of Engineering and Computer Science, Baylor University, Waco, TX 76798-7356, USA
Dereje Engida Woldemichael: Department of Mechanical Engineering, College of Electrical and Mechanical Engineering, Addis Ababa Science & Technology University, PO Box 16417 Addis Ababa, Ethiopia
Samson Mekbib Atnaw: Department of Mechanical Engineering, College of Electrical and Mechanical Engineering, Addis Ababa Science & Technology University, PO Box 16417 Addis Ababa, Ethiopia
Muluneh Mekonnen Tulu: Department of Mechanical Engineering, College of Electrical and Mechanical Engineering, Addis Ababa Science & Technology University, PO Box 16417 Addis Ababa, Ethiopia

DOI: https://doi.org/10.3390/met11010139
Journal volume & issue: Vol. 11, no. 1
p. 139

Abstract

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This paper develops parametric accelerated life testing (ALT) as a systematic reliability method to produce the reliability quantitative (RQ) specifications—mission cycle—for recognizing missing design defects in mechanical products as applying the accelerated load, expressed as the inverse of stress ratio, R. Parametric ALT is a way to enhance the prediction of fatigue failure for mechanical systems subjected to repeated impact loading. It incorporates: (1) A parametric ALT plan formed on the system BX lifetime, (2) a fatigue failure and design, (3) customized ALTs with design alternatives, and (4) an assessment of whether the last design(s) of the system fulfills the objective BX lifetime. A BX life concept with a generalized life-stress model and a sample size equation are suggested. A domestic refrigerator hinge kit system (HKS), which was a newly designed mechanical product, was used to illustrate the methodology. The HKS was subjected to repeated impact loading resulting in failure of the HKS in the field. To conduct ALTs, a force and momentum balance was utilized on the HKS. A straightforward impact loading of the HKS in closing the refrigerator door was examined. At the first ALT, the housing of the HKS failed. As an action plan, the hinge kit housing was modified by attaching inside supporting ribs to the HKS to provide sufficient mechanical strength against its loading. At the second ALT, the torsional shaft in the HKS made with austenitic ductile iron (18 wt% Ni) failed. The cracked torsional shaft for the 2nd ALTs came from its insufficient rounding, which failed due to repeated stress. As an action plan, to have sufficient material strength for the repetitive impact loads, the torsional shaft was reshaped to give it more rounding from R0.5 mm to R2.0 mm. After these modifications, there were no problems at the third ALT. The lifetime of the HKS in the domestic refrigerator was assured to be B1 life 10 years.

Published in Metals

ISSN: 2075-4701 (Online)
Publisher: MDPI AG
Country of publisher: Switzerland
LCC subjects: Technology: Mining engineering. Metallurgy
Website: http://www.mdpi.com/journal/metals

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