Chapter 2: Deformation of Solids

the amount of stress a material can resist before fracture (permanently deformed)

what is strength

σ = force/instantaneous area

what is the equation for true stress

σ = force/original area

what is the equation for engineering stress

ε = change in length/original length

what is the equation for engineering strain

draw a stress-strain curve

recoverable

elastic deformation is what type of strain

straight line

what part of the stress-strain curve represents elastic deformation

permanent

what type of strain is plastic deformation

the maximum point

what point on the stress-strain curve represents the Ultimate Tensile Strength (UTS)

the local reduction in area of a material which occurs when stress is greater than the UTS

what is the process of necking

E = stress/strain

what is the equation for Young’s Modulus

ratio of how thin a material needs to be when stretched by a certain amount

what is Poisson’s ratio

v = - ε_x/ε_z

what is the equation for Poisson’s ratio

geometric tool used to find the yield point when its not very obvious

→ measure 0.2% of the total strain and draw a straight line going upwards

what is the 0.2% proof stress tool

pretend that:

• material is weaker than it actually is

• applied force is bigger than it actually is

what are the safety factors used by engineers when designing materials

elastic region where σ < σ_y

in what region of the stress-strain curve do engineers operate in

how much plastic deformation a material can withstand before fracture

what is ductility

• % elongation: % EL = ∆L/∆L₀ × 100%

• % reduction in area: % RA = ∆A/∆A₀ × 100%

what are the two equations that describe ductility

the energy required to fracture a material

what is toughness

area under the stress-strain curve

how is toughness calculated

draw the stress strain-curve for ceramics and glass, steel (Fe-C alloys), metals and ductile materials, and polymers