Engineering Design, Mechanical Failure, Theory of Failures

1. INTRODUCTION TO ADVANCED
MACHINE DESIGN
Dr. RUDRESH M
ASSISTANT PROFESSOR
DEPARTMENT OF AERONAUTICAL ENGINEEIRNG
DAYANANDA SAGAR COLLEGE OF ENGINEERING

2. ENGINEERING DESIGN
• It is an iterative decision making process that has its objective of creation and
optimization of a new or improved engineering system or device for the
fulfillment of a human need or desire, with due regard for conservation of
resources and environment impact.
RUDRESH.M, DEPT. OF MECHANICAL ENGINEERING, EWIT

3. DESIGN CONSIDERATIONS
• All machine parts must be capable of transmitting the necessary forces and
performing the necessary motions efficiently and economically.
• Failure should not occur in any part before a predetermined span of operating life.
• It must be possible to inspect all the potential critical point in the assembly so that
any failure initiation event may be detected and corrected before it becomes
dangerous.
• Each machine part must perform its function without interfering with any other part
of the machine.
• The weight, space and cost of the finished product must be consistent with the
application.
• It must be possible to service and maintain all parts requiring service during the
design life.
RUDRESH.M, DEPT. OF MECHANICAL ENGINEERING, EWIT

4. MECHANICAL FAILURE
• It is defined as any change in the size, shape or material properties of a structure,
machine or machine part that renders it in capable of satisfactorily performing its
intended function.
Modes of mechanical failure
 Manifestation of failure – elastic, plastic
deformation, fracture and material change.
 Failure inducing agents – force, time,
temperature and reactive environment.
 Location of failures – body, surface.
RUDRESH.M, DEPT. OF MECHANICAL ENGINEERING, EWIT

5. FAILURE MODES OBSERVED
IN PRACTICE
• Force and/or temperature
induced elastic deformation
• Yielding
• Brinelling
• Ductile rupture
• Brittle fracture
• Fatigue failure
• Corrosion failure
• Thermal relaxation or stress
relaxation failure
• Impact failure
• Fretting
• Creep
• Thermal shock failure
• Galling failure
• Radiation damage
• Spalling failure
• Buckling failure
• Stress rupture
• wear
RUDRESH.M, DEPT. OF MECHANICAL ENGINEERING, EWIT

6. RUDRESH.M, DEPT. OF MECHANICAL ENGINEERING, EWIT

7. THEORIES OF FAILURE
RUDRESH.M, DEPT. OF MECHANICAL ENGINEERING, EWIT

8. THEORIES OF FAILURE
RUDRESH.M, DEPT. OF MECHANICAL ENGINEERING, EWIT

9. THEORIES OF FAILURE
• DUCTILE MATERIALS
(YIELD CRITERIA)
 MAXIMUM SHEAR
STRESS THEORY(MSS)
 DISTORTION
ENERGY(DE)
DUCTILE COLUMB
MOHR (DCM)
• BRITTLE MATERIAL
(FRACTURE CRITERIA)
 MAXIMUM NORMAL
STRESS(MNS)
 BRITTLE COLUMB
MOHR(BCM)
 MODIFIED
MOHR(MM)
RUDRESH.M, DEPT. OF MECHANICAL ENGINEERING, EWIT

10. THANK YOU