| A | B |
|---|
| loads can cause material to... | stress, shear, compress, bend |
| when in equilibrium, materials will resist any loading on them with... | equal magnitude but opposite direction |
| strain (ε) | change in length over actual length ε=ΔL/L |
| stress | δ=F/A, force applied divided by cross sectional area by which froce is applied |
| modulus of elasticity | E=δ/ε, the stress divided by the strain. aka stiffness. if material is very stiff will not have a lot of strain. if compliant will have a lot of strain |
| area under stress strain curve | represents the energy strored per unit volume of material (in elastic region). energy stored as we strech it |
| brittle material | can be stressed to high level, but cant deform it very much bc will brake (e.g. glass). least stored energy |
| stiff material | can take some level of stress, but will deform more than brittle |
| compliant material | can take less force, but deforms more. most stored energy |
| linearly elastic material | oscillating loading and unloading occur in phase, when deformed, material stores strain energy. strain energy returned completely during unload |
| linearly viscoelastic materials | show time-dependent properties. the magnitude of stress developed depends on the stress rate (i.e. rate of loading). energy is dissapted within the material when it is stressed. loading and unloading curves dont overlap |
| linearly viscoelastic stress strain graph | difference between loading and unloading curve is called hysteresis. the area below each curve represents the strain energy stored during loading and then recovered during unloading. the area between the curves represents the energy dissipated dut to viscous flow within material. |
| total energy stores in viscoelastic materials | hysteresis + energy recovered |
| toe region of stress strain curve for living materials | un-crimping of collagen fibrils, low stiffness area |
| linear region of stress strain curve for living materials | majority of fibrils uncrimped, actual collagen strained, stiffness increases |
| yield region of stress strain curve for living materials | collagen begins to fail |
