Quiz 3 Flashcards
Brittleness
Tendency to fracture when even a small load/deformation is applied. Ex: glass
Ductile
How much a material can deform without sustaining internal damage. Ex: Gummy bear or rubber
Elasticity
Ability to return to the original shape after deforming/loading the material. Ex: rubber elastic
Plasticity
Ability of a material to stay deformed after external force is removed. Ex: blacksmith, I beams
Fatigue
Weakening pf a material due to repeated loading. Ex: Barbecue propane tanks
Hardness
The ability to resist permanent change in shape due to external loads. Ex: diamonds
Resilience
The ability to absorb energy and resist impact. Ex shock absorption or blast materials
Stiffness
Ability of a metal to resist additional deformation when loading continues.
Toughness
Ability of a metal to resist fractures. Ex: superheros
ASTM
The standard to quantify parameters and enable comparison of material properties
Engineering Stress
O= F/Ao
F -force
Ao- original area of the sample cross section
Engineering Strain
E = li-lo/lo or deltal/lo
li- instantaneous length
lo - original length
Creep
Deformation at elevated temperature (over a period of time)
Shear
t = F/Ao
y = alpha + beta given alpha and beta are in radians
Torsion
If we are not deforming by parallel plates, but by twisting the material.
Poissons ratio
For elastic behaving materials the tensile force in the z direction creates z strain -> Ez. This causes a contraction in the x and y directions. If the material is isotropic the. Ex and Ey are the same:
V = -Ex/Ez = -Ey/Ez
Relationship between shear and tension in elastic behavior
E = 2G(1+V)
E- elastic modulus
G- shear modulus
V- poissons ratio
Common poisson ratio for most material
0.3
Hookes Law
During the initial stage if loading a material the stress is proportional to the strain:
o = Ee
Stress = Elastic modulus x strain
Youngs modulus
E, the slop of the initial stress strain linear relationship. As temp increases the value if E decreases! We call this, that the material became less stiff. E is a measure of stiffness of the material
Relationship can be fir torsion and shear
Torsion = G shear (t =Gy)
Stress = E shear (o= Ee)
Plastic deformation
Many materials exhibit elastic behavior up to 0.005 strain or 0.5%. Above this strain the materials crystal bonds begin to fracture -> plastic deformation. The permanent change in material is possible by the movement of dislocations.
Yielding
The transition from E -> P regimen. In many many cases we do not wish to approach this load, but is is sometimes difficult to estimate when the transition from E to P happens. We can approximate by drawing a straight line starting at 0.002 strain. This line is parallel to the initial stress strain curve. Another common value is 0.005
Ultimate Tensile Strength
As the load continues to increase past yield, the dislocations move faster and start to combine. The dislocations form voids which form micro cracks which form cracks.