Chapter 3 - Properties of Engineering Materials Flashcards
What is the dilemma between design and manufacturing in terms of mechanical properties?
To achieve design function and quality, the material must be strong; for ease of manufacturing, the material should not be strong.
What are the three types of static stresses to which materials are subjected?
Tensile, compressive and shear.
What is the difference between engineering stress and true stress in a tensile test?
Engineering stress divides the load on the test specimen by the original area, while true stress divides the load by the instantaneous area which decreases as the specimen stretches.
Define tensile strength.
The max load experienced divided by the original area.
Define yield strength.
Stress at which the material begins to plastically deform. It is usually measured as the 0.2% offset value.
Why cannot a direct conversion be made between the ductility measures of elongation and reduction in area using the assumption of constant volume?
Because of necking that occurs in the test specimen.
What is work hardening?
Increase in strength that occurs in metals when they are strained.
In what case does the strength coefficient have the same value as the yield strength?
When the material is perfectly plastic and does not strain harden.
How does the change in cross sectional area of a test specimen in a compression test differ from its counterpart in a tensile test specimen?
In a compression test, the specimen area increases as the test progresses; while in a tensile test, the area decreases.
What is the complicating factor that occurs in a compression test?
Barreling of the test specimen due to friction at the interfaces with the testing machine platens.
What is the test commonly used to determine the strength of ceramics?
A three point bending test provides a measure called the transverse rupture strength for these materials.
How does G relate to E?
G = 0.4E
How is shear strength (S) related to tensile strength (TS)?
S = 0.7TS
What is hardness and how is it generally tested?
Hardness is defined as the resistance to indentation of a material. It is tested by pressing a hard object into the test material and measuring the size of the indentation.
Why are different hardness tests and scales required?
Because different materials possess widely differing hardnesses. A test whose measuring range is suited to very hard materials is not sensitive for testing very soft materials.
