Chapter 6 Mechanical Properties Flashcards
elasticity
is the ability of a body to resist a distorting influence and to return to its original size and shape when that influence or force is removed.
elastic deformation
the temporary change in length, volume, or shape produced in an elastic substance by a stress that is less than the elastic limit of the substance.
plastic deformation in metals
is the permanent distortion that occurs when a material is subjected to tensile, compressive, bending, or torsion stresses that exceed its yield strength and cause it to elongate, compress, buckle, bend, or twist.
* plastic deformation continued *
plastic means perminent
engineering stress
is the applied load divided by the original cross-sectional area of a material. Also known as nominal stress.
tensile stress
Tensile stress (σ) is the resistance of an object to a force that could tear it apart.
shear stress
often denoted by τ, is the component of stress coplanar with a material cross-section. It arises from the shear force, the component of the force vector parallel to the material cross-section.
engineering stress example
simple tension and torsion
tension = is a reaction force applied by a stretched string (rope or a similar object) on the objects which stretch it.
torsion = the twisting or wrenching of a body by the exertion of forces tending to turn one end or part about a longitudinal axis while the other is held fast or turned in the opposite direction
states of stress example
3 other common stress states
compression
bi axial
hyrdostatic
strain
number that describes relative deformation or change in shape and size of elastic, plastic, and fluid materials under applied forces
tensile strain
the deformation or elongation of a solid body due to the application of a tensile force or stress. In other words, tensile strain is produced when a body increases in length as applied forces try to “stretch” it.
lateral strain
the ratio of the change in diameter of a circular bar of a material to its diameter due to deformation in the longitudinal direction
shear strain
amount of contortion caused by the sliding of plane layers over each other within a deformity
engineering strain equations
stress-strain testing example
hooke’s law
a law stating that the strain in a solid is proportional to the applied stress within the elastic limit of that solid.
Poisson’s ration
the ratio of the proportional decrease in a lateral measurement to the proportional increase in length in a sample of material that is elastically stretched.
other elastic properties
useful linear elastic relationships
linear elastiscity is a mathematical model of how solid objects deform and become internally stressed due to prescribed loading conditions.
yield strength
is the maximum stress that can be applied before it begins to change shape permanently
tensile strength
the resistance of a material to breaking under tension.
necking
describe the localized reduction of cross-sectional area of a specimen under tensile load
ductility
the ability of a material to be drawn or plastically deformed without fracture. ( copper wire)
toughness
is the ability of a material to absorb energy and plastically deform without fracturing.
resilience
the ability of a material to absorb energy when it is deformed elastically, and release that energy upon unloading.
hardness
is a measure of the resistance to localized plastic deformation induced by either mechanical indentation or abrasion.
4 different types of hardness testing
Rockwell Hardness
Brinell Hardness
Knoop Hardness
Vickers Hardness
hardness testing techniques
true stress and strain equations
hardening
The metalworking process used to increase the hardness of a metal. The hardness of a metal is directly proportional to the uniaxial yield stress at the location of the imposed strain. A harder metal will have a higher resistance to plastic deformation than a less hard metal.
design or safety factors example
Summary of this chapter
