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- Date Submitted: 09/25/2013 6:35 AM
- Category: Technology
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R&DE (Engineers), DRDO

Theories of Failure

rd_mech@yahoo.co.in

Ramadas Chennamsetti

Summary

R&DE (Engineers), DRDO

Maximum principal stress theory Maximum principal strain theory Maximum strain energy theory Distortion energy theory Maximum shear stress theory Octahedral stress theory

rd_mech@yahoo.co.in

Ramadas Chennamsetti

2

Introduction

R&DE (Engineers), DRDO

Ramadas Chennamsetti

3

rd_mech@yahoo.co.in

Failure occurs when material starts exhibiting inelastic behavior Brittle and ductile materials – different modes of failures – mode of failure – depends on loading Ductile materials – exhibit yielding – plastic deformation before failure Yield stress – material property Brittle materials – no yielding – sudden failure Factor of safety (FS)

Introduction

R&DE (Engineers), DRDO

Ductile and brittle materials

σ σY

σF

σY

σ

σF

εe

εp

Ductile material

ε

0.2% ε Brittle material

ε

rd_mech@yahoo.co.in

Well – defined yield point in ductile materials – FS on yielding No yield point in brittle materials sudden failure – FS on failure load 4

Ramadas Chennamsetti

Introduction

R&DE (Engineers), DRDO

Stress developed in the material < yield stress Simple axial load

σx σx

If σx = σY => yielding starts – failure Yielding is governed by single stress component, σx Similarly in pure shear – only shear stress. If τmax = τY => Yielding in shear Multi-axial stress state ??

5

σx

σx

rd_mech@yahoo.co.in

Ramadas Chennamsetti

Introduction

R&DE (Engineers), DRDO

Various types of loads acting at the same time

T N Axial, moment and torque M

Internal pressure and external UDL

Ramadas Chennamsetti

6

rd_mech@yahoo.co.in

p

Introduction

R&DE (Engineers), DRDO

Ramadas Chennamsetti

7

rd_mech@yahoo.co.in

Multiaxial stress state – six stress components – one representative value Define effective / equivalent stress – combination of components of multiaxial stress...

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