Fatigue Analysis of a Simple Shaft under Combined Bending
Transcrição
Fatigue Analysis of a Simple Shaft under Combined Bending
Fatigue Analysis of a Simple Shaft under Combined Bending and Torsion Material baseado em exemplo da HBM-nCODE e Ansys PRESENTATION TOPICS • • • • • • • • Introduction SAE notched shaft Specimen Geometry and FEM model Boundary Conditions Linear Static Analysis Results Overview: Fatigue Life Estimation Conclusion References and Used Software Introduction Courtesy nCode Introduction Aloha Airlines Flight 243 (1988) Introduction • Fatigue life is estimated based on crack initiation method. • A notched shaft under combined bending and torsion loads is analised. • Two loading are combined , each load with its own loading history. • Linear stresses used for the calculation is obtained from bending and torsion loading independently. SAE notched shaft specimen • Standard SAE notched shaft [1] is modeled. • This kind of specimen was used [1] to produce experimental results for multiaxial fatigue ,and later, these results were compared to 5 different theories to estimate life to multiaxial fatigue (not the scope of this example). Geometry Finite Element Model: Mesh Boundary Condition: Fixed Support Boundary Condition: Force Boundary Condition: Moment Linear Static Structural Analysis • Two static analysis were performed – Bending due to unitary force – Torsion with a moment of 1000 N.mm – Following slides present stress distribution and dispacements Results: Applied load is unitary force Von Mises Equivalent Stress Displacements Maximum Principal Stress Results: Applied load is a Moment Von Mises Equivalent Stress Displacements Maximum Principal Stress Overview: Fatigue Life Estimation Select Method for Life Estimation: Crack Initiation • Crack Initiation(E-N) is the selected method 1. Stresses and strains calculated froma linear static analysis 2. Material Properties: E-N Curve and Cyclic Stress-Strain Curve 3. Variable Amplitude Loading: cycles counting performed through Rainflow counting method 4. Neuber Correction to consider local plastic strain 5. Mean Stress Correction performed using either Morrow or SmithWater-Thompson Methodologies 6. Damage Accumulation and Fatigue Life Calculation peformed using Palmgreen-Miner rule. Select Method for Life Estimation: Crack Initiation • Note: • Ansys Design Life is not limited to crack initiation. • One may perform: – S-N analysis – da/dN (Crack Propagation based of LEFM) – Vibration Fatigue (frequency domain fatigue life estimation) – Among other capabilities Material Properties Análise de Fadiga Material Properties: Carbon Steel SAE1045_390_QT Curva E-N Propriedades extraídas do banco de dados do Ansys Design Life Curva Tensão Deformação Cíclica nCode Material Propoerties Library Available Geometry for Life Estimation using FEM Geometry for Life Estimation using FEM Loading Análise de Fadiga LOADING : FORCE Loading History: Force x Time LOADING: MOMENT Loading History: Moment x Time Fatigue calculation in Ansys Design Life Fatigue calculation in Ansys Design Life “Gliphs” Ambiente de cálculo Results Análise de Fadiga Results Results: Life Results: Damage Results: Spreadsheet format New Calculation Cycle (optimization) Análise de Fadiga New Calculation Cycle (optimization) • One may change and try different values without running linear static analysis again: – – – – – Material Mean Stress Correction Loading Value, Scale and Offset Certainty of Survival Other parameters ... Conclusion • A typical example of Fatigue Life Estimation was presented • Finite Element Method (Ansys WB) and Ansys Design Life were used to perform the analysis • Selected Method for Fatigue Life Estimation: E-N • Remember: Good Estimation is expected if you have good imput data ( material properties, geometry and loading) • We expect to demonstrate the easy of useness and flexibility of these calculation tools. References • [1] Bannantine, J.A. Comer, J.J., Handcrock, J.L. Fundamentals of Metal Fatigue Analysis Prentice-Hall 1990 • [2] nCode - DesignLife Worked Examples: 3 AN-NC-DL-WE 14.50.083 © 2012 HBM UK Ltd. Used Software 1. Ansys Mechanical 14.5 2. Design Life - GlyphWorks V8.0 ISR3 Release Build 125 THANK YOU !! OBRIGADO!!