MECHANICS OF MATERIALS 17ME34
Module 5: Theories of Failure
Objectives:
Various types of theories of failure and its importance
Learning Structure
• 5.0 Introduction
• 5.1 Stress-Strain relationships
• 5.2 Types of Failure
• 5.3 Use of factor of safety in design
• 5.4 Theories of Failure
• 5.5 Problems
• Outcomes
• Further reading
DEPARTMENT OF MECHANICAL ENGINEERING, ATMECE, MYSURU 80
, MECHANICS OF MATERIALS 17ME34
5. 0 Introduction:
Failure indicate either fracture or permanent deformation beyond the
operational range due to yielding of a member. In the process of designing a
machine element or a structural member, precautions has to be taken to avoid
failure under service conditions.
When a member of a structure or a machine element is subjected to a system of
complex stress system, prediction of mode of failure is necessary to involve in
appropriate design methodology. Theories of failure or also known as failure
criteria are developed to aid design.
5.1 Stress-Strain relationships:
Following Figure-1 represents stress-strain relationship for different type of
materials.
Ductile material e.g. low carbon steel Low ductility
Brittle material Elastic – perfectly plastic material
Figure-: Stress-Strain Relationship
Bars of ductile materials subjected to tension show a linear range within which the materials
exhibit elastic behaviour whereas for brittle materials yield zone cannot be identified. In general,
various materials under similar test conditions reveal different behaviour. The cause of failure of a
ductile material need not be same as that of the brittle material.
DEPARTMENT OF MECHANICAL ENGINEERING, ATMECE, MYSURU 81
Module 5: Theories of Failure
Objectives:
Various types of theories of failure and its importance
Learning Structure
• 5.0 Introduction
• 5.1 Stress-Strain relationships
• 5.2 Types of Failure
• 5.3 Use of factor of safety in design
• 5.4 Theories of Failure
• 5.5 Problems
• Outcomes
• Further reading
DEPARTMENT OF MECHANICAL ENGINEERING, ATMECE, MYSURU 80
, MECHANICS OF MATERIALS 17ME34
5. 0 Introduction:
Failure indicate either fracture or permanent deformation beyond the
operational range due to yielding of a member. In the process of designing a
machine element or a structural member, precautions has to be taken to avoid
failure under service conditions.
When a member of a structure or a machine element is subjected to a system of
complex stress system, prediction of mode of failure is necessary to involve in
appropriate design methodology. Theories of failure or also known as failure
criteria are developed to aid design.
5.1 Stress-Strain relationships:
Following Figure-1 represents stress-strain relationship for different type of
materials.
Ductile material e.g. low carbon steel Low ductility
Brittle material Elastic – perfectly plastic material
Figure-: Stress-Strain Relationship
Bars of ductile materials subjected to tension show a linear range within which the materials
exhibit elastic behaviour whereas for brittle materials yield zone cannot be identified. In general,
various materials under similar test conditions reveal different behaviour. The cause of failure of a
ductile material need not be same as that of the brittle material.
DEPARTMENT OF MECHANICAL ENGINEERING, ATMECE, MYSURU 81
