Studies on Improving the Reliability of Mechanical Components that have Failed in the Field Due to Repetitive Stress

To improve the reliability of mechanical parts that have failed in the field, a reliability methodology for
parametric accelerated life testing (ALT) is proposed. It consists of: (1) a parametric ALT plan, (2) a
load analysis, (3) a tailored series of parametric ALTs with action plans, and (4) an evaluation of the
final designs to ensure the design requirements are satisfied. This parametric ALT should help an
engineer reproduce the fractured or failed parts in a product subjected to repetitive loading and
correct the faulty designs. As a test case, the helix upper dispenser of a refrigerator icemaker
fractured in field was studied. Using a load analysis, we discerned that the helix upper dispenser
fracture was due to repetitive loads and a faulty design with a 2 mm gap between the blade dispenser
and the helix upper dispenser. To improve the reliability of a mechanical part that fails in the field, we
have suggested a reliability methodology that includes: (1) a parametric ALT plan, (2) a load analysis,
(3) a tailored series of parametric ALTs with action plans, and (4) an evaluation of the final design
requirements of the mechanical part to ensure the requirements were satisfied. During the first and
second ALTs, the fracture in the helix upper dispenser was reproduced. The failure modes and
mechanisms found were similar to those of the failed sample in field. As an action plan, the design of
the helix upper dispenser was modified by eliminating the 2 mm gap and adding enforced ribs. In the
third ALT there were no problems. After three rounds of parametric ALTs, the reliability of the helix
upper dispenser was guaranteed as a 10-year life with an accumulated failure rate of 1%. This
reliability design methodology should be applicable to other mechanical systems such as automobiles,
airplanes, construction equipment, washing machines, vacuum cleaners, and civil structures like
bridges.