Definitions

Question 1

Define normal stress

Answer 1

A normal stress acts perpendicularly to the face of a specimen or element of material.

Question 2

Define shear stress

Answer 2

Shear stress acts parallel to the face of an element of material or specimen.

Question 3

Define yield strength

Answer 3

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.

Question 4

Define specific strength

Answer 4

Strength per unit mass

Question 5

Define ductility

Answer 5

The amount of plastic strain a material undergoes prior to failure.

Question 6

What are the three types of toughness?

Answer 6

Fracture, impact, and tensile

Question 7

Define tensile toughness

Answer 7

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

Question 8

Define fracture toughness

Answer 8

The ability of a material to withstand the presence of cracks.

Question 9

Define impact toughness

Answer 9

The work per unit volume required for an instantaneously applied load to take a material from an unstressed state to a failed state.

Question 10

Define ultimate tensile strength

Answer 10

The maximum engineering stress a material can bear over the course of its deformation.

Question 11

Define viscoelasticity

Answer 11

A material property that indicates a material’s deformation has a temporal dependency.

Question 12

Define amorphous

Answer 12

No long-range periodicity at the atomic level.

Question 13

Define crystalline

Answer 13

Has long-range periodicity at the atomic level and is highly symmetrical.

Question 14

What is a hybrid material?

Answer 14

The combination of two or more materials with different properties to form another material with properties distinct from its constituents.

Question 15

What is a composite material?

Answer 15

A material consisting of two or more chemically and/or physically distinct phases arranged in a specific manner.

Question 16

What is a ceramic?

Answer 16

An inorganic, non-metallic material made from compounds of a metal and a non-metal.

Question 17

What is a metal?

Answer 17

A metalically-bonded material that consists of only metal atoms.

Question 18

What is a polymer?

Answer 18

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.

Question 19

Define linear density

Answer 19

The number of atoms per unit length in a given crystal direction.

Question 20

Define critical shear stress

Answer 20

The minimum shear stress required to initiate slip in a given slip system.

Question 21

What is the glass transition temperature of a polymer?

Answer 21

The temperature at which it transforms from a hard, brittle substance into a ductile, rubbery one.

Question 22

In the Ashby method, what is a constraint?

Answer 22

A non-negotiable condition that must be met.

Question 23

In the Ashby method, what is a free variable?

Answer 23

Some attribute that can be altered by the designer without limit.

Question 24

What are the three possible ways of defining the yield strength of a material?

Answer 24

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