Cyclic Loading and Fatiguemi@ser.e.cn
Cyclic Loading and Fatigue mi@seu.edu.cn
Contents·CyclicStressandFatigue（周变应力与疲劳）·CharacteristicsofFatigueFailure（疲劳失效特征）·TechniqueTermsInvolved inCyclic Loading（周变荷载指标）·ClassificationofCyclicLoading（周变荷载分类）·Stress-lifeDiagram（应力寿命图）·FactorsAffectFatigueStrength（疲劳强度的影响因素）·AllowableStress ScopeofEqualAmplitudeFatigue（常幅疲劳问题的许用应力范围）·FatigueStrengthCondition（疲劳强度条件）2
• Cyclic Stress and Fatigue（周变应力与疲劳） • Characteristics of Fatigue Failure（疲劳失效特征） • Technique Terms Involved in Cyclic Loading（周变荷载指标） • Classification of Cyclic Loading（周变荷载分类） • Stress-life Diagram（应力寿命图） • Factors Affect Fatigue Strength（疲劳强度的影响因素） • Allowable Stress Scope of Equal Amplitude Fatigue（常幅疲劳问 题的许用应力范围） • Fatigue Strength Condition（疲劳强度条件） 2 Contents
Cyclic Stress and Fatigue: Cyclic Stress: stresses varying periodically with time: Fatigue Failure: failure of structural members under theapplication of cyclic stresses typically with magnitude far less thanyield stress.: Examples: (a) coupling gears; (b) eccentric motors; (c) train wheelaxes.3
• Cyclic Stress: stresses varying periodically with time. Cyclic Stress and Fatigue • Fatigue Failure: failure of structural members under the application of cyclic stresses typically with magnitude far less than yield stress. • Examples: (a) coupling gears; (b) eccentric motors; (c) train wheel axes. 3
Characteristics of Fatigue Failure. Fatigue failure stress << ultimatestrength / yield stress: Fatigue failure typically occurs aftermany cycles of stress application: Fatigue failure experiences threestages: crack initiation & propagation.and eventual fracture: Fatigue failure happens in the form ofbrittle fractureRough zoneFatigue origin.Fracture surface is composed of aSmooth zonerough zone and a smooth zone2
Smooth zone Rough zone Characteristics of Fatigue Failure • Fatigue failure stress << ultimate strength / yield stress • Fatigue failure typically occurs after many cycles of stress application • Fatigue failure experiences three stages: crack initiation & propagation, and eventual fracture • Fatigue failure happens in the form of brittle fracture • Fracture surface is composed of a rough zone and a smooth zone Fatigue origin 4
Technique Terms Involved in Cyclic Loading. Maximum Stress: omaxT: Minimum Stress: 00minomar+0max0.min·Average Stress: ,20a0maxmin: Stress Amplitude: .2. Stress Scope: △o =0.Omaxmin0min· Cycle Characteristics:0max5
t σ o T m min a a max • Maximum Stress: • Stress Scope: max min • Minimum Stress: max min • Average Stress: min max 2 m • Stress Amplitude: max min 2 a Technique Terms Involved in Cyclic Loading • Cycle Characteristics: min max r 5