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Paul Banaszkiewicz | Section Editor, Segment Author |

- The stress which results in a 0.1% plastic strain. For materials in which the yield stress is not easily identified, e.g. aluminium. Proof stress not usually quoted for polymers.

- A substance containing two or more metals mixed in the liquid phase.
- The alloying metal is introduced to improve either the mechanical properties or corrosion resistance

- Different properties in different directions.

- Process involving heating to and holding at a temperature high enough for recrystallisation to occur and then cooling slowly.
- This removes dislocation and therefore strain from the lattice making the metal more ductile.

- % Elongation.= {[a x sq.rt.(csa)/gauge length] + b} x100
- Takes into consideration the effect of CSA on percentage elongation in tensile testing

Area of contact between two surfaces in relative motion

**Coefficient of Friction**

- metal-ceramic= v. high
- metal-bone= 0.1-0.2
- metal-UHMWPE= 0.02
- metal-on-metal= 0.008
- ceramic-UHMWPE= v. low
- ceramic-ceramic= v. low
- Normal joints= 0.002-0.004

Bone fails in TENSION. Shear failure is a tension failure, but crack propagates in spiral because of the ANISOTROPY of bone. Haversian canals help to prevent crack propagation.

A fracture occurring with little or no prior plastic deformation. Once a crack has initiated no increase in stress is required to propagate the crack.

A substance comprised of metallic and non-metal elements usually produced at high temperatures. Can be either ionic or covalent.

Examples

- Zirconium dioxide (ZiO2)
- Aluminum oxide (Al2O3)
- Titanium oxide (TiO2)

Ratio of frictional force and the normal compressive force necessary to initiate sliding motion

- Proportional to load
- Independent of sliding speed
- Independent of contact area

F=µN

F= Frictional force

N= Normal reaction force

µ= co efficient of friction

A multiphase material. The constituents must be chemically dissimilar & separated by a distinct interface. It should provide distinctive properties that cannot be obtained by the individual components alone. High strength to weight ratio.

Breakdown of a material by electrochemical action:

- Pitting
- Crevice
- Galvanic
- Intergranular
- Stress
- Fatigue
- Fretting

Any situation where and anode and cathode are set up due to an electrochemical gradient. This can happen when metals have difference reactivities or even the same metal in different conditions e.g. areas of low oxygen concentration under screw heads.

Magnitude of kinetic friction is independent of the sliding speed between two dry solid surfaces. Part of the 3 laws that make up Coulombs model of friction

This is deformation under load that is well below the yield point of the material. It is stress, time and temp dependent.

The area of a plane cut through an object usually at 90° to the axis

Materials which develop significant permanent deformation before they break.

**Measures of Ductility**

Percentage Elongation =[final-initial length]/[initial length] x 100

- Ductile material (mild steel)= >20%;
- Brittle material (cast iron)= <1%

Study of forces & moments acting on a body in motion

- v=u+at
- v²=u²+2as
- s=ut+0.5at²
- s=0.5(u+v)/t
- s=vt-0.5at²

v=final velocity

u=initial velocity

s=distance

a=acceleration

t=time

The point beyond which stress and strain are no longer proportional

Potential E=mgh

- energy a body possesses)

Kinetic E=½mv²

- energy a body has due to motion

Agular motion KE=½I.w²

- I=mass moment of inertia, w=angular velocity

Pcrit = C.(E.I/L²)

Pcrit is the critical load

C is the end conditions

E is the modulus of elasticity

I is the cross sectional moment of inertia

L is the column length.

Describe the pathway through which a joint segment moves from one position to another in terms of three independent rotations.

These angles describe the attitude/ orientation of the second position w/ respect to the first.

When a material loses its ability to satisfy the original design function.

The reduction of strength by the application of cyclic loads below the tensile strength of the material.

Failure at stresses well below the ultimate tensile strength of a material usually at low temperatures relative to the melting point in response to cyclical loading

Estimates the fatigue life of a component

The ability to model structures of complex geometry as an assemblage of simple elements.

Ability to resist crack propagation.

The segment of the body of interest. The segment is assumed to be in equilibrium.

The resistance to movement between two surfaces

- Increases in direct proportion to load on the two surfaces
- Independent of the size of the contact distances
- Does not depend on sliding speed

Measure of a materials resistance to abrasion or indentation.

Force is directly proportional to displacement.

Normal stress proportional to strain for elastic part of load-extension curve, up to the Limit of Proportionality

Elastic Modulus= Stress/Strain

This is the area at the center of the curve when force extension are plotted against each other. It represents the energy lost to internal fiction. It is more apparent at high strain rates.

Can either be solid or hollow, slotted or closed

The same properties in all directions

Analysis of motion w/out reference to forces

Analysis of motion under the action of given forces or moments

**Fluid-film lubrication**

- the bearing surfaces are completely separated by a film of fluid for most of their working life.;

**Boundary lubrication**

- the bearing surfaces come much closer together & the frictionless characteristics of the bearing are determined by the properties of the surface materials.

**Hydrodynamic lubrication**

- the action when the load carrying capacity of a fluid film bearing depends on motion of the bearing surfaces.;

** Elastohydrodynamic**

when the bearing materials deform elastically under hydrodynamic pressures.; 'Squeeze film action' occurs in hydrodynamically lubricated bearings.

Deformation where atoms in each successive plane within a block will move different distances, with the effect of altering the direction of the lattice so that each half of the crystal becomes a mirror image of the other half. As compared to 'slip' where all atoms in one block move the same distance.

Energy per unit volume that the material can absorb without yielding (= area under elastic portion of stress-strain curve).

High tensile strength and modulus of elasticity, medium hardness, can be ductile, poor resistance to corrosion, high electrical & thermal conductivity

Represents the resistance a structure has to angular acceleration

- Mass Moment of Inertia= resistance to angular acceleration
- Area Moment of Inertia= resistance to bending
- Polar Moment of Inertia= resistance to torsion

Force x perpendicular distance from turning point

- A body will remain at rest or continue moving with a constant velocity along a straight line, unless a resultant external force acts on it
- The acceleration of a body is proportional to the resultant force acting on it and is in the direction of this force. (F=ma)
- To every action there is an equal but opposite reaction

The properties in a given direction are the same throughout the material and the properties in all directions perpendicular to that direction are the same

Conditions existing on a metal surface because of the presence of a protective film that markedly lowers the rate of corrosion.

Rate of flow of fluid through a hollow tube is proportional to the fourth power of the radius, & inversely proportional to the length

The ratio of lateral to axial strains within the elastic limit of a material.

Measure of the Torsional Stiffness of a column/ shaft

Low modulus of elasticity; low hardness; medium tensile strengths; ductile; low densities; high corrosion resistance; low electrical & thermal conductivities; tend to creep; properties depend on temp. Can withstand high strains, not high stresses

Made up of long-chain molecules based on carbon & hydrogen. These materials are viscoelastic

**Thermosets**

- Decompose when heated. Bakelite

T**hermoplastics**

- Soften when heated

The rate of doing work.

P=W/t

P= power

W= work

T=time

A property which measures the distribution of the material around the cross section. The further the material is from the neutral axis, the stiffer the construct under a given

Plastic deformation in metals, one layer or plane of atoms gliding over another. Slip occurs step by step with the movement of dislocations within the crystal

Study of forces & moments acting on a body in equilibrium (at a constant speed)

ΔL / Lo

ΔL Change in length

Lo Original length

This is a ratio so unitless or given as a percentage

The increase in energy associated with the deformation of a structure, because of the application of a slowly increasing load. = Area under load-extension curve.

Energy associated with deformation of a structure, eliminating the effects of the structures size. =area under stress-strain curve

As the result of plastic deformation ductile metals become stronger. Can be expressed as a percentage cold working.

- Increases yield strength
- Unchanged Youngs modulus
- Decreased ductility and toughness

F/A= N/m²= Pa= the force pulling atoms at a point in a material apart. (measure of the intensity of a force on an object)

Decrease in stress under a constant strain

Max. Force/original csa= Strength of a material = the ability of a material to resist the application of forces without breaking.

Rotational Force

The ability of a material to resist breaking (i.e. absorb energy & deform plastically). Or how much energy a material can absorb before failure. This is equal to the area under the stress strain curve

Rate of change of the position of the body.

A vector has magnitude, direction & sense. Speed is scalar (only has direction).

Display the following properties

- Creep
- Stress relaxation
- Hysteresis
- Strain rate dependency

Removal of material from solid surfaces by mechanical action.

Work is done by a force when the point of application of the force moves in the line of action of that force

Stress at the elastic limit (yield point)

Measure of stiffness of a material. Measured in Pascals (Pa)

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