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2020: Volume 2, Issue 1

Reliability Design of Mechanical Systems Subjected to Repetitive Stresses

Seong-woo Woo1*, Dereje E. Woldemichael1, Samson M. Atnaw1, Muluneh Mekonnen Tulu1, Dennis L. O’Neal2

1Addis Ababa Science & Technology University, Ethiopia
2Dean of Engineering and Computer Science, Baylor University, Waco, TX 76798-7356

*Corresponding author: Seong-woo Woo, Addis Ababa Science & Technology University, Ethiopia, Tel: +251-90-047-6711; E-mail: [email protected].
Received: August 21, 2020
Published: November 27, 2020

ABSTRACT

To improve the lifetime of mechanical system, parametric Accelerated Life Testing (ALT) as new reliability methodology suggests to assess the design of mechanical systems subjected to repetitive stresses. It includes: (1) a parametric ALT plan based on product BX lifetime, (2) a load analysis for accelerated life time test, (3) a tailored sample of parametric ALTs with the design modifications, and (4) an evaluation of whether the final design(s) of the product achieves the target BX lifetime. We suggest a generalized life-stress failure model with a new effort concept, accelerated factor, and sample size equation with the acceleration factor. As a test case, based on field data and a tailored set of accelerated life tests, the redesign of hinge kit system (HKS) in a refrigerator was studied. To carry out parametric ALTs, using a force and moment balance analysis, the mechanical impact loads of HKS were calculated in closing the refrigerator door. At the first accelerated life testing (ALT), the HKS failure happened in the fracture of the kit housing, and oil damper leaked when the HKS broke.  The failure modes and mechanisms found in the 1st ALT were similar to those of the failed samples obtained in the field. The missing design parameters of the HKS included the stress raisers such as corner rounding and rib of the housing hinge kit, the oil seal in the oil damper, and the material of the cover housing. In the second ALT, the fracturing occurred in the cover housing. The missing design parameter of the cover housing in the HKS was the plastics material. As a corrective action plan, we modified the cover housing from plastic to aluminum. After two rounds of parametric ALTs with corrective action plans, the lifetime of the redesigned HKS was guaranteed to be a B1 life of over10 years with a yearly failure rate of 0.1%.

KEYWORDS: Lifetime Design; Hinge Kit System; Fracture; Parametric Accelerated Life Testing; Missing Design Parameter

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