Study on Reliability Design of Mechanical Systems Such as Compressor Subjected to Repetitive Stresses

This study demonstrates the use of parametric accelerated life testing (ALT) to detect design flaws in mechanical products when developing a reliable quantitative (RQ) specification. It includes: (1) a system BX lifetime for which X of a product population fails, developed using the parametric ALT scheme, (2) fatigue and redesign, (3) adapted ALTs with design alternations, and (4) an assessment of whether the system design(s) achieve the objective BX lifetime. As a result, a life-stress model and a sample size formulation are proposed. To analyze the pressure loading of the compressor and carry out parametric ALT, a mass/energy balance on the vapor-compression cycle was examined. At the first ALT, the compressor failed due to a cracked or fractured suction reed valve made of Sandvik 20C carbon steel (1 wt% C, 0.25 wt% Si, 0.45 wt% Mn). The suction reed valves were fatigued due to an overlap between the suction reed valve and the valve plate, as well as frequent pressure loading. The valve plate's trespan dimensions, tumble process, ball peening, and brushing process were used to change the problematic design. The compressor locked at the second ALT owing to interference between the crankshaft and thrust washer. The corrective action plan specified to perform the heat treatment to the exterior of the crankshaft made of cast iron (0.45 wt% C, 0.25 wt% Si, 0.8 wt% Mn, 0.03 wt% P). There were no issues during the third ALT after these design changes.