Mechanical properties Flashcards
It is necessary to know the characteristics of materials for design purposes so that … will not be excessive and … will not occur.
deformation, fracture
Factors considered when testing a material:
nature of applied load and its magnitude, environment
When a force is applied to a material, it will change its shape and size, this is called…
deformation
A tensile load produces an…
A compressive load produces a …
elongation, contraction
… of a material depends on its ability to sustain a load without undue deformation or failure. This is determined experimentally using the … test.
Strength, tension
… machines are designed to read the load required to maintain specimen streching
Tensile
Shapes of the cross-sections of specimens for testing are usually … and …
Circular , rectangular
… configuration was chosen so that during testing, deformation is confined to the narrow centre region and reduce likelihood of fractures at the end.
Dogbone
Output of a tensile test is recorded as … vs …
load, elongation
Load and deformation characteristics depend on specimen …
size
Engineering stress is obtained by…. Expressed with formula…
Dividing applied load F by Specimen’s original cross-sectional area A0, N/m^2=Pa
Strain is obtained by….
It has no units.
Dividing the change in the specimens gauge length by original gauge length.
Stress-strain diagram is … of the specimen geometry
independent
For yielding, there is a slight increase in … above … limit which will cause material to deform permanently. Hence plastic deformation occurs.
stress, elastic
After yielding, an increase in load is supported by the specimen until it reaches the ultimate tensile stress. What is this stage called?
Strain hardening
At ultimate stress, cross-sectional area begins to decrease in a localised region of the specimen. The specimen breaks at the fracture stress, what is this stage called?
Necking
Linear relationship between stress and strain within elastic region is defined by …
Hookes law
When can E / Modulus of elasticity / Young’s modulus be used?
Only if material has linear-elastic behaviour
Young’s modulus is a … property
material
1 GPa = … Pa
… MPa
10^9
10^3
The modulii of elasticity are smaller for …
polymers (0.2 and 5 Gpa)
Deformation in which stress and strain are proportional is called …
elastic deformation
Young’s modulus is a measure of … , or a material’s resistance to elastic deformation.
stiffness
The … the modulus, the stiffer the material, or the … the elastic strain that results from the application of a given stress.
greater, smaller
There are some materials for which the elastic portion of the stress-strain curve is not linear, hence not possible to determine the modulus of elasticity. Such as…
gray cast iron, concrete, and many polymers
Elastic means …
reversible
On the atomic scale, macroscopic elastic strain is manifested as small changes in the … spacing and the stretching of … bonds
both interatomic
Magnitude of modulus of elasticity is a measure of the … to … of adjacent atoms, that is, the interatomic bonding forces.
resistance, seperation
Differences in E values among metals, ceramics, and polymers are a direct consequence of … that exist for the three material types.
different types of atomic bonding
When deformation exceeds the elastic region , … deformation occurs
plastic
Transition from elastic to plastic is gradual for most metals, some curvature results at the onset of plastic deformation, which … more rapidly with rising stress.
increases
Plastic deformation is accomplished by means of …; motion of dislocations.
slip
For metals, point of yielding may be determined as the initial departure from linearity of the stress-strain curve, called the…
proportional limit
Proportional limit is difficult to measure, by convention, a straight line is constructed parallel to the elastic portion of the stress strain curve at some specified strain offset, usually 0.002, the stress corresponding to the intersection of this line is the …
yield strength
When a material is loaded into the plastic region and then unloaded, … …. is recovered.
elastic strain
When a material is loaded into the plastic region and then unloaded, … … remains and material is subjected to a … …
plastic strain, permanent set
When a material is loaded into the plastic region and then unloaded, if load is re-applied, there will be a higher … … because of strain hardening but less ductility.
yield stress
Maximum stress on the the stress-strain curve is … …
Tensile strength
A measure of the degree of plastic deformation that has been sustained at fracture is…
ductility
Ductility can be measured by percent … and percent …
elongation, reduction in area
A material that experiences very little or no plastic deformation upon fracture is termed …, they are considered to be those having a fracture strain less than 5%
brittle
Ceramic materials are … brittle than metals.
more
What is the mechanism of deformation of crystalline?
dislocation motion
what is the mechanism of deformation in highly ionic compounds?
slip systems and resistance to motion of ions of like charge past one another.
… is the capacity of a material to absorb energy when it is deformed elastically and upon unloading have this energy recovered
resilience
… is the strain energy per unit volume required to stress a material from an unloaded state up to the point of yielding.
Modulus of resilience. Ur
… is indicative of a materials ability to absorb energy up to fracture.
Toughness
… represents entire area under stress-strain curve.
Toughness
… materials must display both strength and ductility
Tough
A … body both elongates and contracts laterally under an axial tensile load
deformable
Measure of a material’s resistance to localised plastic deformation is …
Hardness
For hardness, the … the material, the larger and deeper is the indentation, and the lower is the hardness index number.
softer
Large hardness refers that the material is:
resistant to plastic deformation, resistance to cracking in compression, has good wear properties.
Both … and … are indicators of a metal’s resistance to plastic deformation.
tensile strength, hardness
