Chapter 3 Flashcards
What is the dilemma between design and manufacturing in terms of mechanical properties
A design should have strong material, but in order to manufacture it, said material should not be strong
What are the three types of static stresses
Shear, tensile, and compression
State Hooke’s law
Hooke’s Law defines the stress-strain relationship for an elastic material: σ = Eε, where E = the modulus of elasticity.
What is the difference between engineering stress and true stran
Engineering stress divides the load on the test specimen by the original area, while true stress idvides the load by the instantaneous area
Define tensile stress of a material
Maximum load experienced during the tensile test divided by the original area
Define yield strength of a mateila
Stress at which the material begins to plastically deform.
Why can’t a direct conversion be made between the ductility measure of elongation and reduction in area using the assumption of constant volume
Because of necking
What is work hardening (strain hardening)
Increase in strength that occurs when metals are strained
In what case does 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 compression test differ from its counterpart in a tensile test specimen?
In compression, the cross-sectional area increases while in the tenisle test, the cross-sectional area decreases
What is the complicating factor that occurs in a compression test
Tha barreling (diameter go big) of the test specimen, causes more friction between the machine and the material, meaning that it requires extra force to compress
Tensile testing ins not appropriate for hard brittle materials such as ceramics. What is the test commonly used oto determine the strength properties of such materials
A three point bending test is commonly used to test the strength og brittle materials. The test provides a measure called the transverse rupture strength for these materiañsH
How is the shear modulus of elasticity G related to the tensile modulus of elasticoty E on average
G = 0.4E, on average
How is shear strength S related to tensile strenght TS, on average
S = 0.7 TS, on average
What is hardness and how is it generally testedh
Hardness is defined as teh resisitance to indentation of a material. It is tested by pressing hard objects into the test and measuring the size (deph, area) of the indentation
Why are different hardness tests and scales required?
Because different material possess widely differing hardnesses A test whose measuring range is suited for very hard materials is not good for testing bery soft material
Define the rectystallization temperature for a metal
The recrystallization temperature is the temperature at whcih a metal recrystallizes rather than work hardens when deformed
Define viscocity of a fluiD
Vsicocity is the resistance to flow of a fluid of a nateral. The thicker teh fluid teh grater the material
What is the definind characteer of a newtonian fluid
One for which viscocity is constant at a fiven temperature
Strain hardening?
since the lattice structure starts ahanging after entering the plastic region, the defects start moving, when they meet, they can no longer go forward, so they make the material harder
Types of materials that are perfectly elastic
brittle (ceramics works)
Materials that are elastic and perfectly plastic
Melted metals. When they yield, but don’t break
Materials taht are elastic and strain hardening
Ductile metals
Can compresison tenst be used in brittle materials
No, they go boom.
When does strain hardening not occur
hot
Recrystalization of a meral
half its melting point (aprox)
What is viscoelasticity as a materia property?
Refers to the property of plymers that defines the strain of the martial as a function of stress and temperature over time. viscosity + elasticity.
Which of the follwing are three basic types of static stresses? a) compression, (b) hardness, (c) reduction in area, (d) shear, (e) tensile, (f)
true stress, and (f) yield?
a, d, e
Which one of the following is the correct definition of ultimate tensile strength, as derived from the
results of a tensile test on a metal specimen: (a) the stress encountered when the stress-strain curve
transforms from elastic to plastic behavior, (b) the maximum load divided by the final area of the
specimen, (c) the maximum load divided by the original area of the specimen, or (d) the stress
observed when the specimen finally fails?
c
If stress values were measured during a tensile test, which of the following would have the higher
value: (a) engineering stress or (b) true stress?
b
If strain measurements were made during a tensile test, which of the following would have the higher
value: (a) engineering strain, or (b) true strain?
a
The plastic region of the stress-strain curve for a metal is characterized by a proportional relationship
between stress and strain: (a) true or (b) false?
b The plastic region is characterized by a power function of stress and strain
Which one of the following types of stress strain relationship best describes the behavior of brittle
materials such as ceramics and thermosetting plastics: (a) elastic and perfectly plastic, (b) elastic and
strain hardening, (c) perfectly elastic, or (d) none of the above?
c
Which one of the following types of stress strain relationship best describes the behavior of most
metals at room temperature: (a) elastic and perfectly plastic, (b) elastic and strain hardening, (c)
perfectly elastic, or (d) none of the above?
b
Which one of the following types of stress strain relationship best describes the behavior of metals at
temperatures above their respective recrystallization points: (a) elastic and perfectly plastic, (b) elastic
and strain hardening, (c) perfectly elastic, or (d) none of the above?
a
Which one of the following materials has the highest modulus of elasticity: (a) aluminum, (b)
diamond, (c) steel, (d) titanium, or (e) tungsten?
b
The shear strength of a metal is usually (a) greater than or (b) less than its tensile strength?
b
Most hardness tests involve pressing a hard object into the surface of a test specimen and measuring
the indentation (or its effect) that results: (a) true or (b) false?
a
Which one of the following materials has the highest hardness: (a) alumina ceramic, (b) gray cast
iron, (c) hardened tool steel, (d) high carbon steel, or (e) polystyrene?
a
Viscosity can be defined as the ease with which a fluid flows: (a) true or (b) false?
b: it is the resistance to flow
