Fatigue refers to the gradual failure of a material due to repeated or cyclic loading. Even if the stresses are below the material’s ultimate strength, this repeated stress causes microscopic cracks to form and grow, eventually leading to failure.
Which of the following is a primary factor in causing creep in materials?
A Low pressure
B High strain
C High temperature
D Low temperature
Creep is the slow, permanent deformation of materials under constant stress, particularly at high temperatures. It is most noticeable in materials used in power plants and engines where they are subjected to both high stress and temperature.
What property of a material is most influenced by fracture toughness?
A Electrical conductivity
B Resistance to crack propagation
C Resistance to wear
D Resistance to deformation
Fracture toughness is a material property that measures its ability to resist crack propagation under stress. A material with high fracture toughness is less likely to fail suddenly due to crack growth under loading conditions.
Which of the following is a common cause of material fatigue failure?
A Constant load
B High temperature
C Sudden impact
D Cyclic loading
Fatigue failure occurs when a material is subjected to repeated or cyclic loading. Even if the load is below the material’s yield strength, the repeated stress causes microscopic cracks that lead to material failure over time.
What is the most important factor in the creep behavior of materials?
A Grain size
B Composition
C Temperature
D Stress duration
The most critical factor in creep behavior is temperature. At high temperatures, materials can undergo creep, which is the slow deformation under constant stress, commonly occurring in materials used for high-temperature applications.
What type of material is most commonly tested for fracture toughness?
A Ductile metals
B Brittle ceramics
C Polymers
D Composites
Fracture toughness testing is especially important for brittle materials, such as ceramics, which tend to fracture suddenly and without significant plastic deformation. High fracture toughness in these materials can prevent catastrophic failure.
Which of the following materials is most resistant to fatigue?
A Steel
B Cast iron
C Aluminum
D Brass
Steel, especially high-carbon and alloy steels, has excellent fatigue resistance due to its strength and toughness. It is widely used in structural components subjected to cyclic loading, such as bridges and vehicle parts.
What is a major factor contributing to creep deformation in metals?
A Magnetic field exposure
B Temperature and stress
C Grain boundary sliding
D Chemical composition
Creep deformation is mainly influenced by high temperature and applied stress. At elevated temperatures, atoms in the material can move more easily, leading to slow, permanent deformation over time under constant stress.
Which of the following testing methods is used to measure fracture toughness?
A Tensile test
B Charpy impact test
C KIc test
D Rockwell hardness test
The KIc test is specifically used to measure fracture toughness, which is a material’s ability to resist crack propagation. It involves testing a material under stress to determine the critical stress intensity factor.
Which property is typically enhanced by alloying metals?
A Thermal conductivity
B Ductility
C Strength
D Electrical conductivity
Alloying metals enhances properties like strength and hardness. For example, adding carbon to iron creates steel, which is stronger and more durable than pure iron, making it suitable for structural applications.
What is the primary cause of material failure in fatigue testing?
A Cyclic stresses
B Excessive humidity
C High tensile strength
D Sudden temperature changes
Fatigue failure occurs due to cyclic stresses, where a material is subjected to repeated loading and unloading. This leads to the formation of micro-cracks that gradually grow and ultimately cause failure even under relatively low stress levels.
Which of the following materials is commonly used for making turbine blades due to its high creep resistance?
A Copper
B Steel
C Aluminum
D Nickel alloys
Nickel alloys are often used for turbine blades in engines due to their excellent creep resistance at high temperatures, along with good strength and oxidation resistance, making them ideal for high-stress, high-temperature environments.
What is the effect of grain size on the creep behavior of materials?
A Larger grains reduce creep
B Smaller grains increase creep
C Smaller grains reduce creep
D Grain size has no effect
Smaller grains tend to enhance the creep resistance of materials. This is because the grain boundaries act as barriers to dislocation movement, reducing the material’s tendency to deform under high temperatures and stress.
What is the typical result of high-temperature creep in metals?
A Increased ductility
B Deformation and failure
C Increased hardness
D Increased strength
High-temperature creep leads to gradual deformation in metals under sustained stress. Over time, this can result in the material losing its structural integrity, leading to failure, especially in high-temperature applications such as turbine engines.
Which of the following materials exhibits the most resistance to fracture under impact loading?
A Glass
B Ductile steel
C Cast iron
D Aluminum
Ductile steel exhibits the most resistance to fracture under impact loading. Its ability to undergo significant plastic deformation before fracturing makes it much more resilient to impact compared to brittle materials like cast iron or glass.