Definitions Flashcards
Define normal stress
A normal stress acts perpendicularly to the face of a specimen or element of material.
Define shear stress
Shear stress acts parallel to the face of an element of material or specimen.
Define yield strength
Yield strength is the stress at the point of transition between elastic and plastic deformation. It also a measure of a material’s ability to resist plastic deformation.
Define specific strength
Strength per unit mass
Define ductility
The amount of plastic strain a material undergoes prior to failure.
What are the three types of toughness?
Fracture, impact, and tensile
Define tensile toughness
The work per unit volume required to take a material from an unstressed condition to a failed condition –> u = failure strain*(yield strength + ultimate tensile strength)/2
Define fracture toughness
The ability of a material to withstand the presence of cracks.
Define impact toughness
The work per unit volume required for an instantaneously applied load to take a material from an unstressed state to a failed state.
Define ultimate tensile strength
The maximum engineering stress a material can bear over the course of its deformation.
Define viscoelasticity
A material property that indicates a material’s deformation has a temporal dependency.
Define amorphous
No long-range periodicity at the atomic level.
Define crystalline
Has long-range periodicity at the atomic level and is highly symmetrical.
What is a hybrid material?
The combination of two or more materials with different properties to form another material with properties distinct from its constituents.
What is a composite material?
A material consisting of two or more chemically and/or physically distinct phases arranged in a specific manner.
What is a ceramic?
An inorganic, non-metallic material made from compounds of a metal and a non-metal.
What is a metal?
A metalically-bonded material that consists of only metal atoms.
What is a polymer?
A polymer is made up of polymer chains, which consist of repeating chemical units and are entangled with one another and may form cross-links.
Define linear density
The number of atoms per unit length in a given crystal direction.
Define critical shear stress
The minimum shear stress required to initiate slip in a given slip system.
What is the glass transition temperature of a polymer?
The temperature at which it transforms from a hard, brittle substance into a ductile, rubbery one.
In the Ashby method, what is a constraint?
A non-negotiable condition that must be met.
In the Ashby method, what is a free variable?
Some attribute that can be altered by the designer without limit.
What are the three possible ways of defining the yield strength of a material?
The elastic limit - the stress at which it is possible to detect some small amount of plastic strain
The offset yield stress - the stress required for a 0.2% strain (draw line parallel to elastic region)
The proportional limit - where stress !\prop strain
