PPT: Design for Strength | Design of Machine Elements - Mechanical Engineering PDF Download

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 Page 1


overview
I. Fatigue
II. How fatigue occurs
III. How  start  fatigue
IV. Fatigue life estimation
V. What is S-N curve
VI. Failure of a material due to fatigue
VII. Mechanism of Fatigue Crack Initiation
VIII.Avoidance of fatigue damage
Page 2


overview
I. Fatigue
II. How fatigue occurs
III. How  start  fatigue
IV. Fatigue life estimation
V. What is S-N curve
VI. Failure of a material due to fatigue
VII. Mechanism of Fatigue Crack Initiation
VIII.Avoidance of fatigue damage
fatigue
? in materials science, when materials fails at stresses below the yield point, 
fatigue is structural damage that occurs when a material is subjected to cyclic 
loading. 
Fatigue failure of a crankshaft
Page 3


overview
I. Fatigue
II. How fatigue occurs
III. How  start  fatigue
IV. Fatigue life estimation
V. What is S-N curve
VI. Failure of a material due to fatigue
VII. Mechanism of Fatigue Crack Initiation
VIII.Avoidance of fatigue damage
fatigue
? in materials science, when materials fails at stresses below the yield point, 
fatigue is structural damage that occurs when a material is subjected to cyclic 
loading. 
Fatigue failure of a crankshaft
How fatigue occurs
? Fatigue occurs when a material is subjected to repeated loading and 
unloading. If the loads are above a certain threshold, microscopic cracks 
will begin to form at the surface. when a crack will reach a critical size, 
and the structure will suddenly fracture. The shape of the structure will 
significantly affect the fatigue life; square holes or sharp corners will lead 
to elevated local stresses where fatigue cracks can initiate. 
Page 4


overview
I. Fatigue
II. How fatigue occurs
III. How  start  fatigue
IV. Fatigue life estimation
V. What is S-N curve
VI. Failure of a material due to fatigue
VII. Mechanism of Fatigue Crack Initiation
VIII.Avoidance of fatigue damage
fatigue
? in materials science, when materials fails at stresses below the yield point, 
fatigue is structural damage that occurs when a material is subjected to cyclic 
loading. 
Fatigue failure of a crankshaft
How fatigue occurs
? Fatigue occurs when a material is subjected to repeated loading and 
unloading. If the loads are above a certain threshold, microscopic cracks 
will begin to form at the surface. when a crack will reach a critical size, 
and the structure will suddenly fracture. The shape of the structure will 
significantly affect the fatigue life; square holes or sharp corners will lead 
to elevated local stresses where fatigue cracks can initiate. 
How  start  fatigue
? In metals and alloys, the process starts with dislocation movements, 
eventually  continuing slip bands that nucleate short cracks.
? Fatigue is a  often showing considerable scatter even in controlled 
environments.
? Damage is cumulative  Materials do not recover when rested.
Page 5


overview
I. Fatigue
II. How fatigue occurs
III. How  start  fatigue
IV. Fatigue life estimation
V. What is S-N curve
VI. Failure of a material due to fatigue
VII. Mechanism of Fatigue Crack Initiation
VIII.Avoidance of fatigue damage
fatigue
? in materials science, when materials fails at stresses below the yield point, 
fatigue is structural damage that occurs when a material is subjected to cyclic 
loading. 
Fatigue failure of a crankshaft
How fatigue occurs
? Fatigue occurs when a material is subjected to repeated loading and 
unloading. If the loads are above a certain threshold, microscopic cracks 
will begin to form at the surface. when a crack will reach a critical size, 
and the structure will suddenly fracture. The shape of the structure will 
significantly affect the fatigue life; square holes or sharp corners will lead 
to elevated local stresses where fatigue cracks can initiate. 
How  start  fatigue
? In metals and alloys, the process starts with dislocation movements, 
eventually  continuing slip bands that nucleate short cracks.
? Fatigue is a  often showing considerable scatter even in controlled 
environments.
? Damage is cumulative  Materials do not recover when rested.
Characteristics of fatigue
? Fatigue life is influenced by a variety of factors, such as temperature, 
surface finish, microstructure, presence of oxidizing or inert chemicals, 
residual stresses, etc.
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FAQs on PPT: Design for Strength - Design of Machine Elements - Mechanical Engineering

1. What is the importance of design for strength in mechanical engineering?
Ans. Design for strength is crucial in mechanical engineering as it ensures that the designed structures or components can withstand the applied loads without failure. It involves selecting appropriate materials, dimensions, and configurations to optimize the strength and durability of the system.
2. How do mechanical engineers determine the strength of a design?
Ans. Mechanical engineers determine the strength of a design through various methods such as analytical calculations, simulation using finite element analysis (FEA), and physical testing. These approaches help in evaluating stress levels, identifying potential failure points, and ensuring the design meets safety requirements.
3. What are some common factors considered in design for strength?
Ans. Some common factors considered in design for strength include the material properties, load conditions, safety factors, fatigue life, and structural integrity. Additionally, factors like manufacturing constraints, cost-effectiveness, and weight optimization are also taken into account for practical design solutions.
4. How can design for strength contribute to reducing product failures?
Ans. Design for strength plays a significant role in reducing product failures by ensuring that the designed components can handle the expected operating conditions and loads. By considering factors like material selection, stress analysis, and appropriate safety margins, engineers can minimize the risk of failure, enhancing the reliability and longevity of the product.
5. Are there any design guidelines or standards available for design for strength in mechanical engineering?
Ans. Yes, several design guidelines and standards exist for design for strength in mechanical engineering. Organizations like the American Society of Mechanical Engineers (ASME) and the International Organization for Standardization (ISO) provide codes and standards that outline best practices, design methodologies, and safety factors to be considered for designing mechanically strong systems. These guidelines serve as valuable references for engineers to ensure robust and reliable designs.
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