Materials - Stress, strain and Young’s modulus, Graphs, Ductile, Brittle and Polymeric

tensile stress

the force per unit cross-section area, measured in Pa (Nm⁻²)

stress equation

σ = F/A

tensile strain

the extension per unit length, a dimensionless quantity

strain equation

ε = x/L

Young’s Modulus Equation(s)

E - σ/ε

E= FL/Ax

What does a large Young’s Modulus/steep gradient on a σ-ε graph represent?

a stiff material

yield point

a point on a stress-strain graph beyond which the deformation is no longer entirely elastic (between two yield points strain increases largely with a small applied stress)

UTS (Ultimate tensile strength)

the maximum stress that a material can withstand before it breaks

beyond the UTS, material becomes thinner+longer (necking)

Breaking strength

the stress value at the point of snapping (value of stress)

σ-ε graph for a ductile material (and labels)

ductile

property of a material that has a large plastic region in a σ-ε graph, so can be drawn into wires

σ-ε graph for brittle materials (and properties)

brittle

property of a material that does not show plastic deformation and deforms very little (if at all) under high stress

σ-ε graph for polymeric materials (and properties)

polymeric

description of a material comprising of long-chain molecules, such as rubber, which may show large strains