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Why Things Break (and how we try to make sure they don’t!)

Why Things Break (and how we try to make sure they don’t!)

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Why Things Break (and how we try to make sure they don’t!)

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  1. Why Things Break (and how we try to make sure they don’t!) Robert Love, Venkat Jayaraman July 10, 2008 SSTP Seminar – Lecture 6

  2. Overview • Presentation • Analysis • Statics • Mechanics of Materials • Finite Element Analysis (Method) • Testing Methods • Production • Industrial Quality Practice • Failure Mode and Effect Analysis (FEMA) • Statistical Process Control (SPC) • Six Sigma • Post-Mortem • Failure Analysis • Discussion • Activity UF Flight Controls Lab

  3. Statics • Net force = 0 • Free Body Diagrams • External Forces • Basic Structure • Trusses, Members • Constraints • Common: Fixed, Pin, Roller UF Flight Controls Lab

  4. Loading and BC’s UF Flight Controls Lab

  5. Mechanics of Materials • External Loading Determines Internal Loading • Shear and Moment Diagrams • Cross Section Characteristics • Centroid vs. Center of Mass • Moment of Inertia • MUST be given about an axis! UF Flight Controls Lab

  6. Mechanics of Materials • Internal Stresses • Shear vs. Axial Stress • Bending vs. Torsion • Represented by Stress Tensor UF Flight Controls Lab

  7. Testing • Destructive (see below) vs. Non-Destructive (ex: dye penetrant) • Tensile Strength: Tensile Tester (also for fatigue) • Impact Strength: Charpy/Izod Testing (temp. variations) • Hardness: Vickers/Rockwell/Brinell Scale w/Indenter • Creep: Creep Test Rig • Fatigue: Fatigue Tester UF Flight Controls Lab

  8. Finite Element Analysis • Types of Elements • 1D: Bar, Beam • 2D: Quadrilateral, Triangle • 3D: Tetrahedral, Hexahedral • May use multiple Nodes • Static or Dynamic Analysis • Static Load or Modal Analysis • Common FEA Programs • Patran/Nastran, Abaqus, Pro-E Mechanica, Ansys UF Flight Controls Lab

  9. Quality assurance is the set of planned and systematic actions necessary to provide appropriate confidence that a product or service will satisfy the requirements for quality. Quality assurance activities Failure testing Operation of a product until it fails Exposes many unanticipated weakness in the product Statistical Process Control Effective method of monitoring a process through the use of tools like control charts Industrial Quality Practices

  10. FMEA – A tool used to comprehensively analyze and fix a failure of a product or process. Definitions Failure mode - The way the failure occurs Failure Effect – The immediate consequence of the failure mode Severity(1-10) – Degree of worst potential consequence Occurrence(1-10) – Estimate of number of chances a failure mode can occur Detection(1-10) – Degree of ease of detection of the failure mode Risk Priority Number – Product of Severity, Occurrence and Detection Failure Mode and Effect Analysis (FMEA)

  11. Failure Mode and Effect Analysis (FMEA) FMEA Flow Chart Sample FMEA Worksheet

  12. SPC - involves using statistical techniques to measure and analyze the variation in processes. Statistical Process Control(SPC) Control Chart

  13. Process Capability The shaded areas represent the percentage of off-spec production This curve is the distribution of data from the process Voice of Customer Voice of Process Ideally, you want to reduce the variability in the product until NO off-spec product is made.

  14. Six Sigma process is one that produces 3.4 defective parts per million opportunities Basic Methodology Define Process Improvement Measure key aspects Analyze cause-effect relationships Optimize the process Control the process Implementation key roles Executive leadership Champions Master black belts Black belts Green belts Yellow belts Six Sigma Traditional After Six Sigma

  15. Failure Analysis • What was the “failure mode”? • Hint: Look at the surface (even under a microscope)! • Visualize how the material broke • Use your knowledge of material bonding and possible loading conditions to understand • Look for evidence of other effects • Know so that can prevent recurrence • Engineers as expert witnesses Ex: Impact UF Flight Controls Lab

  16. Failure Analysis • Some types of failures • Fracture (brittle or ductile) • Impact • Buckling • Fatigue • Corrosion • High Temperature • Bending • Torsion • Shear • Vibration • Resonance/Flutter • Creep • Delamination • Weak Bonding/Joint/Weld UF Flight Controls Lab

  17. Activity • Finite Element Analysis Procedure • Define CAD Model • Define Boundary Conditions • Define Loading Conditions • Define Material Properties • Discretize model (make a mesh of finite elements) • Run Analysis • Visualize Analysis UF Flight Controls Lab

  18. Activity • 14.1GPa=Young’s Modulus,E (tensile) • 0.25=Poisson’s Ratio, nu • 1900kg/m3=density UF Flight Controls Lab