S1-1 PAT318, Section 1, March 2005 SECTION 1 OVERVIEW OF DURABILITY AND FATIGUE LIFE ANALYSIS. - презентация

1 S1-1 PAT318, Section 1, March 2005 SECTION 1 OVERVIEW OF DURABILITY AND FATIGUE LIFE ANALYSIS

2 S1-2 PAT318, Section 1, March 2005

3 S1-3 PAT318, Section 1, March 2005 COMPANY OVERVIEW n The MSC.Software corporation (formerly MacNeal-Schwendler Corporation) has been supplying sophisticated computer-aided engineering (CAE) tools since 1963 n MSC.Software is the developer, distributor, and supporter of the most complete and widely-used structural analysis program in the world, MSC.Nastran as well as the first commercial nonlinear analysis program in the world, MSC.Marc, and the world leader suite of Multi-Body Dynamics analysis program MSC.ADAMS. u MSC.Nastran u MSC.Marc u MSC.Patran u MSC.Dytran u MSC.ADAMS MSC.MVision MSC.Fatigue MSC.Laminate Modeler MSC.Autoforge MSC.Superform … and more

4 S1-4 PAT318, Section 1, March 2005 COMPANY OVERVIEW

5 S1-5 PAT318, Section 1, March 2005 SimOffice Over 150 VPD Applications Included MSC.SOFY MSC.Patran MSC.Nastran MSC.Marc MSC.Dytran MSC.Fatigue MSC.ADAMS

6 S1-6 PAT318, Section 1, March 2005 SimDesigner for CATIA V5 Analysis and Simulation MSC.Nastran MSC.Marc STEP-AP209 ANSYS ABAQUS Gateway Products LS-DYNA ESTGASFMSFMDGDY CATIA V5 Products Vertical Apps AutoOtherAero Suspension Motion Generative Products Linear ASPThermal Nonlinear Fatigue Composites Flex Materials Robust Design Controls Crash

7 S1-7 PAT318, Section 1, March 2005 MSC.SimManager

8 S1-8 PAT318, Section 1, March 2005 COMPANY OVERVIEW (CONT.) n MSC.Software Milestones u 1963Company founded by Dr. Richard MacNeal and Mr. Robert Schwendler. Developed first program called SADSAM for Structural Analysis by Digital Simulation of Analog Methods. This was the forerunner of MSCs flagship program, MSC.Nastran. u 1965MSC participates in NASA-sponsored project to develop a unified approach to computerized structural analysis. The program became known as NASTRAN (NASA Structural Analysis Program)

9 S1-9 PAT318, Section 1, March 2005 COMPANY OVERVIEW (CONT.) u 1965A team of researchers at Brown University initiated the development of the technology leading to the MARC program. u 1971The MARC Analysis Research Corporation was founded. u 1972MSC releases proprietary version of NASTRAN, called MSC.Nastran. u 1972MAR Corporation releases the first proprietary version of MARC, the first commercial Nonlinear Finite Element program. u 1990PDA Engineering releases P/Fatigue (precursor to MSC.Fatigue)

10 S1-10 PAT318, Section 1, March 2005 COMPANY OVERVIEW (CONT.) u 1994MSC merged with PDA Engineering (Developer of PATRAN) to become the largest single provider of finite element analysis (FEA) software to the CAE market. u 1999MSC.Software merged with MARC Analysis Research to lead both the linear and the nonlinear analysis worldwide CAE market. u 2001MSC.Software partners with Dassault system to work on a suite of product that enables the depth and strength of MSC solution within the Catia V5 environment. u 2002MSC.Software acquires MDI, world leader in Multi Body Dynamics with the suite of Adams solutions, consolidating its position of world leader of CAE solution.

11 S1-11 PAT318, Section 1, March 2005 n With corporate headquarters in Santa Ana, California, MSC.Software maintains regional sales and support offices worldwide. u MSC Technical Support Hotline (USA/Canada). (Check with your local MSC offices in your country/region) u support (USA/Canada) at u Support (USA/Canada) Fax u Internet support (knowledge base and more) u Sign up to our MSC.Forums and become a member of our talented community at MSC CLIENT SUPPORT

12 S1-12 PAT318, Section 1, March 2005 OVERVIEW OF DURABILITY AND FATIGUE LIFE ANALYSIS

13 S1-13 PAT318, Section 1, March 2005 WHAT IS DURABILITY? n Durability is… u the ability to do what its supposed to u for as long as its supposed to do it! n Reliability is… u having half a chance of doing what its supposed to for as long as its supposed to do it!

14 S1-14 PAT318, Section 1, March 2005 n From a practical point of view fatigue is: u a process where repeated variations in loading cause failure even when the nominal stresses are below the material yield strength; n and is… u made up of crack initiation and subsequent crack growth as a result of cyclic, plastic deformation. According to BS 7608 FATIGUE is: the damage of a structural part by the initiation and gradual propagation of a crack or cracks caused by repeated applications of stress DEFINITION OF FATIGUE

15 S1-15 PAT318, Section 1, March 2005 THE PHYSICAL BASIS OF FATIGUE n Fatigue failures typically start at the surface of a specimen or component n Fatigue failures start at small microscopic cracks and accordingly are very sensitive to even minute stress raisers n The process of Fatigue encompasses the entire range from the formation of a microcrack in a persistent slip band to the propagation of a long crack in an elastic-plastic continuum.

16 S1-16 PAT318, Section 1, March 2005 n There are many ways of starting a small crack: u cracking or debonding of second phase particles, u natural scratches and machining marks on the surface u corrosion pits or intergranular attack u porosity from casting u laps from forging and forming u brittle surface layers THE PHYSICAL BASIS OF FATIGUE INITIATION AND PROPAGATION

17 S1-17 PAT318, Section 1, March 2005 THE PHYSICAL BASIS OF FATIGUE INITIATION AND PROPAGATION

18 S1-18 PAT318, Section 1, March 2005 Persistent Slip band formation Stage I Crack Growth Stage II Crack Growth ~1mm THE PHYSICAL BASIS OF FATIGUE CRACK INITIATION AND GROWTH : STAGE I AND II

19 S1-19 PAT318, Section 1, March 2005 A SHORT HISTORY OF FATIGUE

20 S1-20 PAT318, Section 1, March 2005 Product life used to be a hit and miss affair Over design 42 Under design 7 HISTORY OF FATIGUE – EARLY DAYS

21 S1-21 PAT318, Section 1, March 2005 A SHORT HISTORY OF FATIGUE ALBERT tests mine hoist chains under cyclic loading 1839 PONCELET designs mill wheels with cast iron axles. First uses the term Fatigue in a book on mechanics 1849 IMechE debate the "CRYSTALLIZATION" theory 1850 on WÖHLER conducts first systematic Fatigue investigations on axles. Develops the ROTATING-BENDING Fatigue test, S-N curves and the concept of Fatigue LIMIT Starts the development of design strategies for Fatigue. Identifies importance of cyclic and mean stresses

22 S1-22 PAT318, Section 1, March 2005 Wohlers Railway Component Test Rig

23 S1-23 PAT318, Section 1, March 2005 StressAmplitude NotchedShaft UnnotchedShaft Log (Fatigue life) Some of Wohlers data for rotating bending tests

24 S1-24 PAT318, Section 1, March 2005 A SHORT HISTORY OF FATIGUE FAIRBAIRN experiments with repeated loads 1886 BAUSCHINGER first documents Stress-Strain HYSTERESIS 1903 EWING & HUMPHREY disprove the Crystallisation theory and show that Fatigue is due to SLIP 1910 BAIRSTOW investigates stress-strain response during cycling - develops concepts of cyclic HARDENING and SOFTENING 1920 GRIFFITH investigates cracks in glass - the birth of FRACTURE MECHANICS

25 S1-25 PAT318, Section 1, March 2005 A SHORT HISTORY OF FATIGUE MANSON and COFFIN investigate Fatigue under STRAIN conditions - thermal cycling - low cycle & plastic strain considerations 1959 PARIS and ERDOGAN present first systematic method for handling CRACK PROPAGATION using fracture mechanics 1961FORSYTH identified stage I and stage II crack propagation NEUBER proposed a method for estimating elastic-plastic stresses and strains at stress concentrations MATSUISHI and ENDO present the rainflow method for cycle counting

26 S1-26 PAT318, Section 1, March Between % of all structural failures occur through a fatigue mechanism…...The estimated annual cost of fracture and fatigue to the US was 4.4% of GDP…and could be reduced by 29% by application of current technology… Battelle Study 1982

27 S1-27 PAT318, Section 1, March 2005 "Despite 150 years of Fatigue research, unintended Fatigue failures still occur. More research will NOT reduce the incidence of Fatigue failure - more education will!" -Quote by Prof. D. Socie University of IIIinois,1990 FATIGUE FAILURE AND TRAINING

28 S1-28 PAT318, Section 1, March 2005 A SHORT HISTORY OF FATIGUE MSC.Fatigue launched by PDA Engineering

29 S1-29 PAT318, Section 1, March 2005 A partnership for excellence in durability technology

30 S1-30 PAT318, Section 1, March 2005 USE OF FATIGUE TECHNOLOGY

31 S1-31 PAT318, Section 1, March 2005 USE OF FATIGUE TECHNOLOGY n Fatigue Technology is not new ( years old); n A collection of empirical rules to fit observed behaviour; n Does not require the engineer exploiting it to understand all the finer points; n Can be used (with training and experience) to achieve Integrated Durability Management (IDM) goals.

32 S1-32 PAT318, Section 1, March 2005 FATIGUE CALCULATIONS IN…? n Concept design phase: u Analytical loads, previous design loads, estimated u properties, early design optimization n Verification phase: u Measured loads, real properties, design u refinement and optimization n Production phase: u Continued development, new markets, firefighting

33 S1-33 PAT318, Section 1, March 2005 WHO DOES WHAT FATIGUE CALCULATIONS? n Design analyst: u Design optimization for durability on the virtual u component n Development engineer u Measures data on the real component, tells the u design analyst where its wrong and how to fix it. n Test rig engineer u Pre-predicts rig tests and edits out non damaging u parts to speed them up. n Production engineer u Investigates service failures, monitors production, u feeds back improvement ideas.

34 S1-34 PAT318, Section 1, March 2005 DESIGNING AGAINST FATIGUE n Requirements: u Higher Performance u Lower Weight u Longer Life u Reasonable Cost u As Soon As Possible

35 S1-35 PAT318, Section 1, March 2005 DESIGNING AGAINST FATIGUE n Constraints: u Life calculations are much less precise than strength calculations u Fatigue properties can not be inferred from static mechanical properties u Laboratory tests often exhibit scatter and are difficult to translate to full size components u Full scale prototype testing is often required to confirm an acceptable life u Designs should be defect tolerant - stressing and materials selection to ensure slow crack growth and detectability before failure u Designs should be Fail Safe, where possible

36 S1-36 PAT318, Section 1, March 2005 DESIGN APPROACHES* n SAFE LIFE u Evaluate expected life, use a margin of safety, design to survive expected service life, then retire. n FAIL SAFE u Provides redundant load paths, design to fail into a safe condition and survive until repair. n DEFECT TOLERANCE u Assumes flaws do exist, design to live with some crack growth below critical size, requires regular inspections. *source BS 7608

37 S1-37 PAT318, Section 1, March 2005 WHAT DRIVES DURABILITY MANAGEMENT?

38 S1-38 PAT318, Section 1, March 2005 GOALS, DRIVERS AND REALITIES n Competition requires FASTER concept-to-customer. n Costs/profits require CHEAPER products, materials and manufacturing processes. n Functionality requires BETTER products with hi-tech features and performance. n Legislation requires products with LONGER, more reliable durability and inspection periods. n The customer requires the last mile/flight/hour to be the same as the first.

39 S1-39 PAT318, Section 1, March 2005 Production Pilot Engineering Prototype Engineering Prototype Traditional Design Development VPD Design Objectives FIX TEST Mechanical Prototype Mechanical Prototype Concept Development Time Cumulative Cost DESIGN VPD (CAE) for Durability PRODUCT DEVELOPMENT LIFE CYCLE COSTS

40 S1-40 PAT318, Section 1, March 2005 Build it Test it Begin Production OK? Out of time? NO YES Generate idea Fix it TRADITIONAL APPROACH WITHOUT CAE: BUILD IT, TEST IT, FIX IT

41 S1-41 PAT318, Section 1, March 2005 Generate idea Analyse Optimize Previous experience Build it Test it OK? Begin Production Measure Correlate test & analysis NOYES NO ADD CAE: ANALYSE AND OPTIMIZE

42 S1-42 PAT318, Section 1, March 2005 Customer Usage Product Life Build it and Use It Check Life Based on Customer Usage PREDICTING PRODUCT LIFE 1 - BUILD AND USE

43 S1-43 PAT318, Section 1, March 2005 Customer Usage Accelerated Sign-off Test Product Life Re-Design PREDICTING PRODUCT LIFE 2 - ADD SIGN-OFF TESTING

44 S1-44 PAT318, Section 1, March 2005 Customer Usage Accelerated Sign-off Test Product Life Re-Design Simulated Component Test Measured Service Loading PREDICTING PRODUCT LIFE 3 - ADD SIMULATION TESTING

45 S1-45 PAT318, Section 1, March 2005 Re-Design Optimize Simulated Component Test Computer-based Fatigue Life Simulation Customer Usage Measured Service Loading Stress Analysis Material Properties Product Life Correlation Product Life Accelerated Sign-off Test PREDICTING PRODUCT LIFE 4 - ADD CAE

46 S1-46 PAT318, Section 1, March 2005 OVERVIEW OF FATIGUE LIFE CALCULATION METHODS

47 S1-47 PAT318, Section 1, March 2005 FATIGUE LIFE CALCULATION METHODS n S-N (Total Life Method) u Relates nominal or local elastic stress to total life n E-N (Crack Initiation Method) u Relates local strain to crack initiation life n LEFM (Crack Propagation Method) u Relates stress intensity to crack propagation rate n All methods rely on SIMILITUDE

48 S1-48 PAT318, Section 1, March 2005 n Also known as Stress Life and Total Life Method n Estimates the total fatigue life to catastrophic failure n Fatigue life computed from the log stress vs. log cycles (S-N) curve. n Method is appropriate for long life fatigue problems where there is little plasticity since the method is based on nominal elastic stress n Fatigue life estimates are associated with a probability of failure due to the large amount of scatter in the S-N curve. S-N METHOD

49 S1-49 PAT318, Section 1, March 2005 The life of this is the same as the life of this..... if both are subject to the same nominal stress nom nom NotchedShaft UnnotchedShaft Stress Amplitude Life in Cycles S-N METHOD - SIMILITUDE

50 S1-50 PAT318, Section 1, March 2005 n E-N method u It is also called the local strain approach, the crack initiation method, and the strain-life approach u Strain-life method is one of the most common life prediction methods used in the automotive industry u Practically, crack initiation means that a crack of around 1-2 mm has developed. This is often a high proportion of the component life. u Many automotive components are designed to survive some significant plastic strains in use (especially on the test track!). The E-N method will handle these better than the S- N method which basically ignores plasticity. E-N METHOD (Crack Initiation)

51 S1-51 PAT318, Section 1, March 2005 The crack initiation life here..... is the same as it is here..... if both experience the same local strains e E-N METHOD - SIMILITUDE

52 S1-52 PAT318, Section 1, March 2005 Also known as Low Cycle Fatigue or Local Strain Approach Local strains can be elastic or plastic hence its suitability for Low Cycle fatigue E-N METHOD – STRAIN LIFE CURVE

53 S1-53 PAT318, Section 1, March 2005 Total Life = Crack Initiation + Crack Growth S-N Local Strain LEFM N f = N i + N p S-N AND E-N METHODS

54 S1-54 PAT318, Section 1, March 2005 /S N 1000 Cycles Low Cycle Region (EN Method) High Cycle Region (SN or EN Method) 'Infinite Life' 10 7 Cycles E-N Life Curve S-N Life Curve S-N & E-N curves coincide in high cycle region because nominal stresses will be linear elastic E-N can also be used in low cycle region. S-N cannot, because linear stress-strain relationship is invalid S-N and E-N FATIGUE CURVES COMPARED

55 S1-55 PAT318, Section 1, March 2005 FATIGUE CRACK PROPAGATION (LEFM) METHOD n What remnant life is there after initiation? n What is the safe life or inspection schedule for a component that is or may be cracked? n The crack growth method is based on the principles of Linear Elastic Fracture Mechanics (LEFM) n It relates stress intensity factors to crack growth rates n It uses cycle-by-cycle calculations to predict lifetimes n It is frequently used in Aerospace, Offshore, and Power Generation industries

56 S1-56 PAT318, Section 1, March 2005 This crack grows at the same rate as this one if both experience the same stress intensity factors CRACK PROPAGATION METHOD

57 S1-57 PAT318, Section 1, March 2005 INTEGRATED DURABILITY MANAGEMENT

58 S1-58 PAT318, Section 1, March 2005 DESIGN ANALYSIS Structural Integrity Optimization DEVELOPMENT ANALYSIS Characterisation Correlation with FEA Assess Modifications SIMULATION TEST Verification Monitoring Correlation MEASURED STRAINS & LOADS Measurement Validation Correction Analytical Loads Kinematic Modelling DATA DATA & CORRELATION Modern Integrated Approach INTEGRATED DURABILITY MANAGEMENT ACTIVITIES

59 S1-59 PAT318, Section 1, March 2005 INTEGRATED APPROACH TO DURABILITY n Facts: u Testing is not a good way to optimize designs, but is always required for sign-off. u Useful Fatigue analysis requires verification and good test-based information. u Neither Testing nor Analysis have exclusively the right Fatigue answer; therefore its not an argument between rivals. u Best results are obtained when an integrated approach is adopted incorporating analysis and testing.

60 S1-60 PAT318, Section 1, March 2005 HOW TESTING SUPPORTS ANALYSIS n Provision of load data n Provision of material Fatigue properties n Verification of stress/strain analysis results n Correlation of life predictions n Final sign-off

61 S1-61 PAT318, Section 1, March 2005 HOW ANALYSIS SUPPORTS TESTING n Eliminating unnecessary tests n Test acceleration n Gauge type selection and positioning n Test design

62 S1-62 PAT318, Section 1, March 2005 AN OVERVIEW OF VIRTUAL DURABILITY AND VPD

63 S1-63 PAT318, Section 1, March 2005 Production Pilot Engineering Prototype Engineering Prototype Traditional Design Development VPD Design Objectives FIX TEST Mechanical Prototype Mechanical Prototype Concept Development Time Cumulative Cost DESIGN VPD (CAE) for Durability PRODUCT DEVELOPMENT LIFE CYCLE COSTS

64 S1-64 PAT318, Section 1, March 2005 VIRTUAL DURABILITY ANALYSIS FOR VPD n FE Stress Analysis is a pre-processing activity for durability analysis n The essential requirement is for good local stress information in the critical areas n Loading information can be: u Assumed (idealized loading), u Experimentally acquired u Semi-analytical loads u Computed (full analytical loads)

65 S1-65 PAT318, Section 1, March 2005 Achieving Faster, Cheaper, Better Integrated Durability Management requires: u Integrated multi-disciplinary teams. u Integrated software tools common to all departments. u Integrated data exchange within company structure. u Integrated data exchange between the company and its suppliers and service providers. VIRTUAL DURABILITY ANALYSIS FOR VPD allows for close cooperation

66 S1-66 PAT318, Section 1, March 2005 Geometry Loading Material AnalysisResults Optimization u Geometry. Stresses are dependent on geometry. u Loading. Loads from physical tests or from simulation. u Material. Select material from database. Stress-cycles curves etc. u Analysis. Fatigue analysis is performed with geometry, loading and material data as input. u Results. Post-processing of results. VIRTUAL DURABILITY ANALYSIS: 5 box trick

67 S1-67 PAT318, Section 1, March 2005 Geometry & FEA Results Test (Lab) Results Materials and Loading Information Damage Distributions Analysis Options Stress (total) Life Strain (initiation) Life Crack Propagation Vibration Fatigue Multi-axial Fatigue Spot/Seam Weld Analyzer Software Strain Gauge Utilities Fatigue Life Contours Sensitivity Analysis and Optimization Strain (uE) Time (seconds) DISPLAY OF SIGNAL: TEST101. DAC 1E31E41E51E Cross Plot of Data : S61STRAIN1KT Life(Miles) Kt( ) VIRTUAL DURABILITY ANALYSIS FOR VPD MSC.Fatigue

68 S1-68 PAT318, Section 1, March 2005 n Contour plots: damage, repeats, factor-of-safety and much more Fatigue Contours Results from 4-poster simulation MSC.Fatigue RESULTS

69 S1-69 PAT318, Section 1, March 2005 Engineering is the art of being approximately right rather than exactly wrong -Quote by Prof. Rod Smith University of Sheffield,1990

70 S1-70 PAT318, Section 1, March 2005