An investigation on the impact fatigue characteristics of valve leaves for small hermetic reciprocating compressors in a new automated test system

Abstract

This paper presents an investigation on the impact fatigue characteristics of valve leaves that are prevalently used in hermetic reciprocating compressors especially for the household type refrigerators. A unique automated impact fatigue test system has been designed and produced, which enables to carry out impact fatigue tests of the compressor valve leaves under the desired impact velocities. The test system incorporates a noncontact actuation, a data acquisition system and an acoustic-based damage detection technique, which continuously monitors the health of the structure. The damage detection system allows parametrical investigation on the impact fatigue life by detecting any possible damage and automatically terminating the test. The investigation relates the impact fatigue lifetime of the valve leaves with the impact velocity, asymmetrical impact, operation temperature, material type (carbon strip steel, stainless strip steel and new stainless strip steel grade) and tumbling operation duration. The observations show that the cracks have initiated from the edges of the valve leaf where is in contact with the valve plate. Subsequently, the cracks initially have propagated in the radial direction inwards the center of the impact area. Various failure cases have been resulted in by either a single crack or inter-related multiple cracks. Microscopic and metallographic observations have been performed on the specimens to enhance the understanding of the damage mechanisms. The investigation and introduced test system guide the design optimization of the valve leaves in terms of compressor performance due to the energy consumption and lifetime of the valve leaf.