1 / 15

DOKUZ EYLÜL UNIVERSITY MECHANICAL ENGINEERING DEPARTMENT

DOKUZ EYLÜL UNIVERSITY MECHANICAL ENGINEERING DEPARTMENT. INTRODUCTION TO FRACTURE MECHANICS Prof. Dr. M. Evren Toygar. FRACTURE MECHANICS. REFERENCES: 1. Anderson, “Fracture Mechanics Fundamentals and Applications.”

benjaminlouis
Download Presentation

DOKUZ EYLÜL UNIVERSITY MECHANICAL ENGINEERING DEPARTMENT

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. DOKUZ EYLÜL UNIVERSITYMECHANICAL ENGINEERING DEPARTMENT INTRODUCTION TO FRACTURE MECHANICS Prof. Dr. M. Evren Toygar

  2. FRACTURE MECHANICS • REFERENCES: • 1. Anderson, “Fracture Mechanics Fundamentals and Applications.” • 2. Richard W.Hertzberg, “Deformation and Fracture Mechanics Of Engineering Materials.” • 3. Dowling, "Mechanical Behavior of Materials" • 4. Broek, “Elementary Engineering Fracture Mechanics” • 5. Ağah Uğuz, “Kırılma Mekaniğine Giriş “

  3. FRACTURE When material damage like micro-cracks andvoidsgrow in size and become localized, theaveragingprocedure can no longer be applied and discontinuities must be taken into account.This localization results in a macroscopic crack, whichmay grow very fast, resulting in globalfailure.

  4. Fracture Mechanics Definition: It is thefield of mechanicsconcernedwiththestudy of propagation of cracks in materails. Itusesmethods of analyticalsolidmechanicstocalculatethedrivingforce on a crackandthose of experimentalsolidmechanicstocharacterizethematerial’sresistancetofracture.

  5. Fracture Mechanics • In modern materials science, fracture mechanics is an important tool in improving the mechanical performance of mechanical components. • It applies the physics of stress and strain, in particular the theories of elasticity and plasticity, to the microscopic defects found in real materials in order to predict the macroscopic mechanical failure of bodies.

  6. Fracture Mechanics In fracture mechanics attention is basically focused on a single crack. Theoretical conceptsand experimental techniques have been and are being developed, which allow answers toquestions like: • Will a crack grow under the given load ? • When a crack grows, what is its speed and direction ?

  7. Fracture Mechanics • Will crack growth stop ? • What is the residual strength of a construction (part) as a function of the (initial) crack • What is the length and the load ? • What is the proper inspection frequency ? • When must the part be repaired or replaced ?

  8. Fracture mechanics Fracture mechanics is a failure theory that • determines material failure by energy criteria, possibly in conjunction withstrength (or yield) criteria • considers failure to be propagating throughout the structure rather thansimultaneous throughout the entire failure zone or surface.

  9. Linear elastic fracture mechanics (LEFM) A large field of fracture mechanics uses concepts and theories in which linear elastic materialbehavior is an essential assumption. This is the case for Linear Elastic Fracture Mechanics(LEFM). • is the basic theory of fracture, that deals with sharp cracks in elastic bodies. • It is applicable to any materials as long as the material is elastic except in a vanishingly • small region at the crack tip (assumption of small scale yielding), • brittle or quasibrittle fracture, stable or unstable crack growth

  10. Elastic-plastic fracture mechanics • is the theory of ductile fracture, usually characterized by stable crack growth • (ductile metals) the fracture process is accompanied by formation of large • plastic zone at the crack tip

  11. Why structures Fail • Negligenceduringdesign, constuction, oroperation of structure. • Application of a newdesignormaterial, whichproduces an unexpectedresult.

  12. Historical Perspective • Experimentsperformedby Leonardo da Vinci severalcenturiesearlierprovidedsomeclues as totherootcause of fracture. He measuredthestrength of ironwiresandfoundthatthestrengthvariedinverslywithwirelength. • A quantitativeconnectionbetweenfracturestressandflaw size camefromthework of Griffth 1920. He applied a stressanalysis of an elliptical hole totheunstablepropagation of crack. Griffthinvokedthefirstlaw of thermodynamicstoformulate a fracturetheorybased on a simpleenergybalance.

  13. Figure 1 Galileo’ s tension bar Figure 2 Da Vinci’s cable

  14. Figure 3 schematic representation of ancient Rome bridge

  15. During Design someimportanttitlesare: • DeformationandFracture • ExceedtheElasticDeformation • Buckling (Burkulma) • PlasticDeformation • Fracture (Kırılma) • Fatique (Yorulma) • Creep (Sünme ) • StressCorrosionCracking (Gerilme Korozyon Çatlağı )

More Related