What does 'creep' refer to in materials science?
A
Sudden fracture under impact
B
Permanent deformation under constant stress over time
C
Elastic recovery after unloading
D
Reversible deformation due to temperature change
Analysis & Theory
Creep is the **gradual, permanent deformation** of a material under constant load at elevated temperatures.
Creep typically occurs at what type of temperature conditions?
C
High temperatures (typically > 0.4 Tm)
D
Low humidity environments
Analysis & Theory
Creep becomes significant at **high temperatures**, usually above **0.4 times the melting point** (Tm) of the material in Kelvin.
Which of the following is **not** a stage of the creep curve?
Analysis & Theory
The **three stages** of creep are **primary, secondary, and tertiary**. 'Quaternary creep' does not exist.
During the secondary stage of creep:
D
Material fractures suddenly
Analysis & Theory
**Secondary creep** is characterized by a **steady-state (constant) creep rate**.
The time to rupture during creep testing is called:
Analysis & Theory
**Creep life** is the total time before the material ruptures under constant stress and temperature.
Which material property is most affected by creep?
Analysis & Theory
**Dimensional stability** is impacted as the material deforms permanently under sustained stress.
Which of the following materials is most likely to exhibit significant creep?
A
Glass at room temperature
B
Steel at cryogenic temperatures
C
Lead at room temperature
Analysis & Theory
**Lead** has a low melting point and shows **creep** even at **room temperature**.
Creep testing is usually conducted under:
C
Constant load and temperature
Analysis & Theory
Creep testing is typically done under **constant load and constant elevated temperature**.
What is the unit of creep strain rate?
Analysis & Theory
Creep strain rate is the **rate of deformation** per unit time, so its unit is **1/s**.
What is the main cause of tertiary creep?
C
Microstructural damage and necking
Analysis & Theory
**Tertiary creep** occurs due to **microstructural degradation** like void formation and necking, leading to rupture.