Flashcards
Materials and Structures
Cards in this deck (62)
- 1SealantsUsed to seal gaps or joints between materials to prevent ingress of water
- 2AdhesivesFasten materials or components together to make larger unit
- 3Relative MovementGaps open and close. Movement caused by:
Temperature changes
Humidity (moisture) changes
Stress - 4Relative Movement: Temperature ChangesExpand and contract depending on the coefficient of thermal expansion (CTE).
Metals have highest CTE
Concrete low CTE
Train tracks buckling - solution, expansion gaps. - 5Relative Movement: Humidity ChangesPorous materials (bricks etc.)
Material equilibrates with surrounding air.
Expands / Shrinks accordingly. - 6Relative Movement: Stress"Time dependant permanent deformation under continuous applied load which is deemed 'safe' load.
Generally occurs at high temp (thermal creep), but at room temp for concrete, lead, glass etc. - 7Bonding / AdhesionBest bond when surfaces are rough
Mechanisms of Adhesion:
Mechanical Keying
Molecular Entanglement (polymers)
Direct Chemical Bonding - 8Sealing / Jointing Materials AvailableBrittle materials - (e.g. cement based mortars). Used when there is zero movement.
Putties - Glazing purposes - oils and powdered chalk
Mastics - non hardening, viscous and ductile
Elastomeric sealants - more resilient than mastics, withstand greater joint movements - 9Strength of Adhesive JointsDesigned so that adhesives are subjected to SHEAR not tensile stress
If 2 elements are used - design should be a Lap Joint - 10Shear StressAct parallel to a surface.
Shear stress = Force / Area - 11GlassMade from Silicon (Si) and Oxgen (O2)
Is a ceramic. Also INORGANIC POLYMER
Si forms 4 bonds with O = SiO4 - 12GlassmakingRequirs: Sand, Soda Ash, Limestone, Dolomite, Feldspar, Sodium sulphate, Cullet
- 13Borosilicate Glass (PYREX)81% SiO4
2& Al2O3
4% Na2O (Sodium Oxide)
* 12% B2O3 (Boron Oxide) *
Low thermal expansion, low ion exchange - 14Flat Glass (FLOAT)73% SiO4
9% CaO
* 14% Na2O *
4% MgO
High Durability - 15Glass Manufacturing - FLAT GLASSHeated (doesn't melt) - SUPERCOOLED LIQUID
Pilkington Glass - 1959
Hot glass floats on tin and becomes flat
Carried out in inert atmosphere to prevent oxidation of tin
GLASS TANK / FURNACE > FLOAT BATH > ANNEALING LEHR > CUTTING - 16Glass DurabilityHighly resistant to water corrosion and atmospheric agencies
Readily dissolved by Hydrofluoric Acid
Good resistance to attack by most acids
Can be affected by alkaline solutions
Attack by lime and cementitious water - 17Problems with Glass & GlazingLow fracture toughness (cracks propagate easily)
Thermal problems - high U value, solar gain
Sound or acoustic problems
Fire and impact problems - vulnerable to thermal shock (Cracks then shatters) - 18Toughened Glassx5 stronger than glass
subjecting final size panes of glass to a heating and cooling treatment.
When broken - shatters into blunt edged fragments
Applications - stair ballustrading, curtain walling, structural glazing - 19Laminated GlassConsists of two sheets of glass with a special film between them (polyvinyl butyl PVB).
Applications - cars, houses, buildings - 20CompositesMade because no single material will give us the combination of properties we require
A mixture of materials to give us 'best of both worlds'
"A materials system composed of two or more physically distinct phases whose combination produces aggregate properties that are different from those of its constituents" - 21Composites +vesGood strength-to-weight and stiffness-to-weight rations - Strong and stiff, yet light in weight
Low levels of fatigue
High toughness
Can be low corrosion - 22Composites -ves / limitationsAnisotropic - properties differ depending on direction in which they are measured
Polymer based composites prone to attack by chemicals / solvents
Generally expensive
Manufacturing methods for shaping can be slow and costly - 23Types of Composites (TRADITIONAL COMPOSITES)Composite materials that occur in nature or have been produced by civilisations for many years.
E.g. wood, concrete (& steel reinforced), asphalt - 24Types of Composites (SYNTHETIC)Modern material systems - components are first produced separately then combined in a controlled way to achieve the desired structure, properties and geometry.
- 25Theory of Composites - Components in composite materialsTWO PHASES ;
PRIMARY PHASE - forms the matriculates within which the secondary phase is imbedded
SECONDARY PHASE - imbedded phase sometimes referred to as a reinforcing agent - usually serves to strengthen the composite - may be FIBRES / PARTICLES - 26Classification scheme for synthetic composites: MMC - metal matrix compositeMixtures of ceramics and metals such as cemented carbines
- 27Classification scheme for synthetic composites: CMCs - Ceramix matrix compositeAl2O3 and SiC imbedded fibres to improve properties, especially in high temperature applications.
LEAST COMMON COMPOSITE MATRIX - 28Classification scheme for synthetic composites: PMCs - Polymer matrix compositeThermosetting resins are widely used in PMCs
examples - epoxy and polyester with fibre reinforcement, and phenolic with powders - 29PRIMARY PHASE - Matrix materialProvides the bulk form of the part or produce made of the composite material
Holds the imbedded phase in place
When a load is applied, the matrix shares the load with the secondary phase, in some cases deforming so that the stress is essentially born by the reinforcing agent - 30SECONDARY PHASE - reinforcing phaseReinforces the primary phase.
Imbedded phase is most likely;
Fibres
Particles
Flakes
Bars (reinforced concrete) - 31Reinforcing - FibresContinuous fibres - long, continuous path through the composite by which a load can be carried
Discontinuous - chopped sections of continuous fibres - whiskers, hair like single crystals. - 32Reinforcing - Fibres OrientationOne dimension (longitudinal) - strength and stiffness in the direction of fibre
Planar reinforcement - two dimensional woven fabric
Random / three dimensional - 33COMPOSITE CALCULATIONS YOUNGS MODULS:(uni directional) VOIGT EQUATION:
Ecomp = Ef.Vf + Em.Vm
(transverse) REUSS EQUATION:
Ecomp = Em.Ef / (Ef.Vm + Em.Vf) - 34COMPOSITE CALCULATIONS: DENSITYDENSITY
Pcomp - Pf.Vf + Pm.Vm
kg/m3 - 35COMPOSITE CALCULATIONS INSULATIONRESISTANCE = 1/K m2K/W
TOTAL THERMAL RESISTANCE OF COMPOSITE
Rcomp = Ra + Rb - 36COMPOSITE APPLICATIONSGLARE - Glass reinforced aluminium laminate - aeroplanes = very strong, light weight (30% lighter than aluminium), good fatigue properties
REINFROCED CONCRETE
concrete - compression, steel = tension
Concrete protects against corrosion & fire
FIBRE REINFORCED CONCRETE (FRC)
Steel fibres added to concrete. Polypropylene fibres used to improve crack resistance.
Fibres 50mm long.
Results in x10 increase in tensile strength = parity between tensile and compressive strength - 37COMPOSITE SUMMARYReasons for use in structures = ARCHITECTURAL - longer spans, thinner slabs, slender columns, more design opportunities
ECONOMICAL - reduction of height = less cladding, longer spans = less columns, quicker time of erection
FUNCTIONALITY - Fire - fire protection
ASSEMBLY - positives of multiple materials - concrete gives freedom of form and shapes, easy to handle, thermal resistance. Steel brings high accuracy, able to be prefab, high ratio between bearing capacity and weight - 38PolymersPOLY = "many"
MER = "Building blocks"
Plastics or Rubbers
Compound of carbon & hydrogen
Low density (< 1000kg/m3)
non load bearing
Corrosion resistant
Degrades under UV radiation
Low melting points (between 150 deg C and 300 deg C)
20% of polymers made are used in construction
Poor fire resistance - acts as fuel - 39PoymerisationBuilding block heated to high temp + catalyst = polymer chain
e.g. polyethylene (PE). Made from ethylene (C2H4) - typically 30,000 chain repeats
LDPE = low density PE - bags
HDPE = high density PE - more than 20,000 and as many as 50,000 chain repeats - 40Polymer Structure & Usage PVCPolyvinylchloride
CH2=CHCl
Carbon, Hydrogen and Chlorine
windows and doors - 41Polymer Structure & Usage PTFEPolytetrafluoroethylene
C2F4
Carbon and Fluorine
Teflon, non stick etc. - 42Polymer Structure & Usage PPPolypropylene
C3H6
Carbon and Hydrogen
Used to increase elasticity, Tupperware - 43Polymer Structure & Usage PSPolystyrene
C8H8
Carbon & Hydrogen
Insulation, packaging - 44Polymer Structure & Usage AcrylicPoly methyl methacrylate
C5O2H8
Carbon, Oxygen and Hydrogen
Perspex - 45Polymer TypesTHERMOPLASTICS (recyclable)
THERMOSETS (non-recyclable)
ELASTOMERS (non-recyclable) - 46THERMOPLASTICSSoften when heated & stiffen when cooled
Spaghetti like in structure - no cross links
Very ductile and workable
Easy to recycle
Examples - DPC, vapour barriers, uPVC windows, nylon
Easily mouldable - 47THERMOSETSDo not soften when heated
Non-Reversible process
Structure is heavily cross linked
Is rigid & hard - brittle
Wear resistant
No plastic deformation - it will break
Examples - melamine work surfaces, urea formaldehyde - electrical socket outlets etc. - 48ELASTOMERSCompletely elastic, no plastic deformation
Structure consist of long and helically wound carbon chains
Can extend elastically over 300%
Not ductile - yield point = break point - 49Polymers Stress v Strain
- 50OTHER POLYMERS PMMAPolymethylmathacrylate
PERSPEX
ORGANIC - based on hydrogen and carbon
Robust - can withstand cracks without losing stability - 51OTHER POLYMERS PCPolycarbonate Glass
BULLETPROOF
Layers of organic and inorganic glass - energy absorbed by organic glass layer (PC) - 52OTHER POLYMERS KEVLARVery strong polymer
TENSILE STRENGTH = 3600 MPa (Steel is ~450-1000MPa)
Used in air crafts (cockpit door) and trains - 53OTHER POLYMERS PSPolystyrene
EPS insulation - 54Manufacturing of POLYMERSThermoplastics - shaped through extrusion to make long lengths, moulding for individual items. Pellets fed into mould under heat and pressure.
Thermosets - Shaped and polymerised in one operation - compression moulded. Granules are placed in a die and heated & compressed.
Elastomers - Can be moulded to form sealing rings etc. - 55Degradation of POLYMERSExcellent corrosion resistance
Highly susceptible to degradation from UV radiation - subsequently loses strength
UV breaks C-C bond - called SCISSION
Protection against UV - mixing UV absorbing materials into polymer during manufacture - Powders used are Carbon Black (C) or Titanium Dioxide (TiO2) - 56AIRCETECement and/or PFA (fly ash) + lime + sand + water + aluminium oxide powder
Produced through AUTOCLAVING - heat and pressure.
Porous material - up to 80% porosity for Low Density = 80% air pockets
Density 350kg/m3 to 800kg/m3
Compressive strength:
Low - 2-3.5 N/mm2
Medium 4-4.5 N/mm2
High - 7.0-8.5 N/mm2
(compared to concrete = 30-80 N/mm2) - 57production of AIRCRETE
- 58AIRCRETE BENEFITS* FIRE PROTECTION *
* THERMAL EFFICIENCY *
SOUND ABSORPTION
RESISTANT TO MOISTURE
FASTER BUILD TIME
FROST RESISTANT - 59AIRCRETE - FIRENon combustible - Euroclass A1, Building Regs "class 0"
100mm aircrete = 4 hours fire protection (non load bearing), 2 hours fire protection (load bearing)
Does not emit smoke or gases - 60AIRCRETE - environmental +vesThermal efficiency
Use of PFA fly ash (industrial by product)
Low density material - cheaper to transport
Air pockets / high porosity = 1m3 of raw material produce 4m3 of construction material - 61LOW DENSITY AIRCRETE LDA80% porosity
Density < 450kg/m3
Compressive strength <3 N/mm2
(two storey dwelling) - 62THIN JOINT MASONRYPremixed cement based product that only requires addition of water to make mortar
Depth of mortar reduced from 10mm to 3mm = u value reduction of up to 10%
Stronger bond than mortar = stronger wall (twice as strong)
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- Flashcards on Materials and Structures, created by Mathew Morgan on 08/12/2018.
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- Mathew Morgan
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