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What is the term used to describe the maximum allowable flaw size in a material?
What is the term used to describe the maximum allowable flaw size in a material?
What type of failure occurs when a material is subjected to cyclic stresses and chemical attack?
What type of failure occurs when a material is subjected to cyclic stresses and chemical attack?
What is the term used to describe the minimum stress level required to cause failure in a material?
What is the term used to describe the minimum stress level required to cause failure in a material?
What is the primary mechanism of fatigue failure in materials?
What is the primary mechanism of fatigue failure in materials?
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What is the term used to describe the stress levels that occur in a material when it is subjected to dynamic and fluctuating stresses?
What is the term used to describe the stress levels that occur in a material when it is subjected to dynamic and fluctuating stresses?
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What is the term used to describe the failure of a material that occurs at a stress level lower than its tensile or yield strength?
What is the term used to describe the failure of a material that occurs at a stress level lower than its tensile or yield strength?
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What is the primary factor that affects the fatigue life of a material?
What is the primary factor that affects the fatigue life of a material?
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What is the term used to describe the curve that relates the number of stress cycles to the stress level required to cause failure?
What is the term used to describe the curve that relates the number of stress cycles to the stress level required to cause failure?
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What is the term used to describe the failure of a material that occurs due to the simultaneous action of a cyclic stress and thermal stress?
What is the term used to describe the failure of a material that occurs due to the simultaneous action of a cyclic stress and thermal stress?
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What is the primary reason why fatigue failure is brittle-like in nature?
What is the primary reason why fatigue failure is brittle-like in nature?
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Study Notes
Failure of Engineering Materials
- Failure of engineering materials is an undesirable event due to human lives being put in jeopardy, economic losses, and interference with product availability.
- Causes of failure include improper materials selection and processing, inadequate design, and misuse of components.
- It is the engineer's responsibility to anticipate and plan for possible failure, assess its cause, and take preventive measures.
Fracture
- Simple fracture is the separation of a body into two or more pieces in response to an imposed static stress at low temperatures relative to the material's melting temperature.
- Two fracture modes are possible: ductile and brittle, classified based on the material's ability to experience plastic deformation.
Principles of Fracture Mechanics
- This subject allows quantification of relationships between material properties, stress level, crack-producing flaws, and crack propagation mechanisms.
- Design engineers can anticipate and prevent structural failures using fracture mechanics.
Stress Concentration
- Measured fracture strengths for brittle materials are lower than predicted by theoretical calculations due to microscopic flaws or cracks at the surface and interior of the material.
- Stress concentration occurs around internal cracks, with the magnitude of localized stress decreasing with distance away from the crack tip.
Fracture Toughness
- The critical stress required for crack propagation in a brittle material is described by the expression σc = Kc / √(πa), where Y is a dimensionless parameter.
- The Kc value for a thick-specimen situation is known as the plane strain fracture toughness.
Design Using Fracture Mechanics
- The design (or critical) stress must be less than the material's fracture toughness to prevent failure.
- The maximum allowable flaw size ac is determined by the design stress and fracture toughness.
Impact Fracture Testing
- Impact testing is a technique used to determine the fracture toughness of a material.
Fatigue
- Fatigue is a form of failure that occurs in structures subjected to dynamic and fluctuating stresses.
- Failure can occur at a stress level lower than the tensile or yield strength for a static load.
- Fatigue failure is brittle-like in nature, with little to no gross plastic deformation.
Cyclic Stresses
- Failure occurs by the initiation and propagation of cracks, with the fracture surface perpendicular to the applied tensile stress.
S-N Curve
- The S-N curve is a graph that shows the relationship between the number of stress cycles and the stress magnitude.
Factors that Affect Fatigue Life
- Mean stress and surface effects can affect fatigue life.
- Environmental effects, such as thermal fatigue and corrosion fatigue, can also contribute to fatigue failure.
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Description
This quiz covers the importance of preventing failure in engineering materials, the causes of failure, and the consequences of material failure on human lives, economy, and services.
