Hypergravity prompt thermal crack in 1060 aluminium slat

Abstract

High-speed rotation instruments that apply gradient hypergravities can induce local variations in structure and thus induce cracking. Rotation-induced hypergravity is a kind of gradient force, and it has a gradient value that depends on distance and local weight. Conventional mechanical testing applies a constant force or periodic force instead of true gradient hypergravity to rotating components. In this study, a dedicated instrument was designed and assembled, and a special sample of 1060 aluminium slats with multiple thinned necks was used to reveal the difference between gradient hypergravity and conventional constant forces. Hypergravity caused more significant damage to the aluminium slat, and the ultimate crack strength was approximately 10% of the strength observed under the constant force applied at the same temperature. All the samples cracked on the inner neck which bears the highest hypergravity. Two types of cracks were categorized based on the relative extension: type Ⅰ mode cracks occurred in the centre of the neck with long extension before cracking under hypergravity more than 3.5 MPa, while type Ⅱ cracks occurred in the root of the neck without long extension before cracking under hypergravity less than 3.5 MPa. Combination of hypergravity and torsional force in high-speed rotation system prompt cracking and exhibit similar microstructure with that under high constant force. Typical cracking and its microstructure under the effects of hypergravity and temperature provided a convenient and practicable method for evaluating service safety of commercial rotating machines for industrial applications and raw alloys.