Abstract
In this study, the effect of baking heat treatment on fatigue strength and fatigue life was evaluated by performing baking heat treatment after shot peening treatment on 4340M steel for landing gear. An ultrasonic fatigue test was performed to obtain the S–N curve, and the fatigue strength and fatigue life were compared. The micro hardness of shot peening showed a maximum at a hardened depth of about 50 μm and was almost uniform when it arrived at the hardened depth of about 400 μm. The overall average tensile strength after the baking heat treatment was lowered by about 80–111 MPa, but the yield strength was improved by about 206–262 MPa. The five cases of specimens showed similar fatigue strength and fatigue life in high cycle fatigue (HCF) regime. However, the fatigue limit of the baking heat treated specimens showed an increasing tendency rather than that of shot peening specimens when the fatigue life was extended to the very high cycle fatigue (VHCF) regime. The effect of baking heat treatment was identified from improved fatigue limit when baking heat was used to treat the specimen treated by shot peening containing inclusions. The optimum temperature range for the better baking heat treatment effect could be constrained not to exceed maximum 246 °C.
Highlights
Demands on the long life reliability and endurance evaluation of aircraft component materials are rapidly increasing
AISI 4340 [4], 4340M [5] and 300M [6] steels are used in aircraft landing gear components
These materials are super high-strength materials with tensile strength above 2000 MPa, and high strength and toughness are very important in aircraft landing gear materials [6]
Summary
Demands on the long life reliability and endurance evaluation of aircraft component materials are rapidly increasing. Poisson’s ratio and fatigue characteristics are among the most important and basic properties, but they have disadvantages of difficulty and long period in precise testing. The simple and accurate measurement technique of dynamic elastic modulus and Poisson’s ratio using a characteristic frequency of acoustic resonance evaluation technique of fatigue test using ultrasonic elastic resonance in a short period of time were world-widely applied in many component materials [1,2,3]. AISI 4340 [4], 4340M [5] and 300M [6] steels are used in aircraft landing gear components These materials are super high-strength materials with tensile strength above 2000 MPa, and high strength and toughness are very important in aircraft landing gear materials [6]. Aircraft landing gear needs to resist impact energy when landing on and high specific strength is required in order to obtain anti-fatigue and weight lightening during when
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