Biomechanics

Question 1

Tension / tensile loading

Answer 1

Equal and opposite loads are outward from the surface of the structure, and tensile stress result inside the structure. Tensile stress many small forces directed away from surface of structure. Structure lengthens and arrows.

Question 2

Compression / compressive loading

Answer 2

Equal and opposite loads applied toward the surface of structure and compressive stress and strain result inside structure. Many small forces directed away into the surface of structure - which shortens and widens.

Eg vertebrae

Question 3

Shear loading

Answer 3

Load is applied parallel to the surface of the structure, and shear stress and strain result inside the structure. Many small forces acting on surface on a plane parallel to the applied load - deforms internally in an angular manner - right angles within plane surface become acute = shear stress causing angular deformation.

Question 4

Torsion

Answer 4

Causes a twist about an axis and a torque (moment) is production within structure. Shear stresses are distributed over entire structure. Shear stresses act on planes parallel and perpendicular to neutral axis.

Question 5

Isotropy

Answer 5

Uniformity in all orientations. Same mechanical behaviour regardless of direction.

Question 6

Anisotropy

Answer 6

The alteration in mechanical properties when bone is loaded along different axes - occurs as result of dissimilar longitudinal and transverse crystalline microstructure of bone.

Question 7

Stress

Answer 7

Force/area

A physical quantity that expresses the internal forces that neighbouring particles exert on each other.

Question 8

Bending

Answer 8

A load applied to a structure causing it to bend on the axis - one side is compressed while another side has tensile forces.

Question 9

Strain

Answer 9

Is a measure of deformation of the material. Strain takes into account ratio of change in deformation from original position. Units are a percentage.

Question 10

Modulus of elasticity

Answer 10

Relationship between stress and strain - value for stiffness obtained by dividing the stress at a point in the elastic portion of the curve by the strain at that point.

Relative stiffness.

Same as strain unit.

Pascals = newtons per m^2. Same as stress.

Question 11

Stiffness

Answer 11

The extent to which a structure resists deformation in response to an applied force. Lack of compliance.

Unit = distance/force

Question 12

Compliance

Answer 12

Opposite of stiffness. Is a property - the ability of something to deform with an intrinsic of extrinsic factor. Can also be compression.

Unit = distance / force

Question 13

Elasticity

Answer 13

Ability of material to resume its original size and shape on removal of applied loads. ‘Solid material property’

Question 14

Elastic deformation

Answer 14

On removal of applied load, the structure will recover the elastic deformation following unloading path.

Question 15

Viscoelasticity

Answer 15

Viscosity (thickness of fluid) - fluid resistance to flow.

Viscoelasticity is the time it takes for elastic material to return back to unloaded/unstressed/unrestrained position.

Question 16

Mechanotransduction

Answer 16

Mechanotransduction is any of various mechanisms by which cells convert mechanical stimulus into electrochemical activity.

Question 17

Plastic behaviour

Answer 17

Plastic implies permanent deformation. Unable to change dimensions. Something can be elastic, go too far, and become plastic.

Question 18

How is stress different to load?

Answer 18

Stress is different to load as it considers distribution of load across a cross-sectional area.

Question 19

Creep

Answer 19

YT: Creep is a time dependant deformation that occurs in response to a constant load. There will be elastic recoil with permanent damage (if plastic, no recoil)

Creep is when viscoelastic solid is subjected to the action of constant load. Rapid initial deformation followed by a slow (time-dependent), progressively increasing deformation - until equilibrium state is reached.

Question 20

Relaxtion

Answer 20

Characteristic of viscoelastic materials where the loading curve does not match the unloading curve. The strain energy is lost due to the internal friction between loading and unloading material being lost as heat.

Question 21

Hysteresis

Answer 21

The original Greek definition was defined as deficiency or lagging behind. All viscoelastic structures exhibit hysteresis, a phenomenon in which there is a loss of energy when a structure is sub- ject to repetitive loading and unloading cycles.