Area of contact between two surfaces in relative motion
Coefficient of Friction
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
Ratio of frictional force and the normal compressive force necessary to initiate sliding motion
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:
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
Study of forces & moments acting on a body in motion
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
Kinetic E=½mv²
Agular motion KE=½I.w²
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
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
Boundary lubrication
Hydrodynamic lubrication
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
Force x perpendicular distance from turning point
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
Thermoplastics
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.
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
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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