Mestrado em Design e Desenvolvimento do Produto 2011/12
Resistência dos Materiais
R2
0
Análise dos materiais e processos de fabrico do banco “taburet C” desenhado por Jorgen Moller e produzido pela Askman
R5
Trabalho realizado por: Artur Branco Emanuel Vinhas Guilherme Nunes
7950 8176 8179
Índice Pág.1
Índice
Pág.2
Sumário
Pág.3
Jorgen Moller
Pág.4
Taburet C
Pág.6
Análise da adequabilidade dos materiais originais
Pág.19
Sugestão para alteração dos materiais e processos de fabrico
Pág.28
Conclusões
Pág.29
Bibliografia
Sumário: Análise do banco “Taburet C” desenhado por Jorgen Moller e produzido e comercializado pela Askman. Análise da adequação dos materiais e processos de produção prováveis do objecto em estudo. Proposta de melhoria tanto a nível de materiais como de processos de fabrico.
Jorgen Moller, 1930 Jorgen Moller segue as pisadas do seu mestre Arne Jacobsen produzindo peças muito típicas do design escandinavo apelando à sobriedade formal e escolha por materiais naturais sem nenhuma ornamentação. Abriu o seu próprio escritório em 1967 tendo já sido alvo de várias publicações internacionalmente conhecidas tais como: “Living Architecture”,”Graphics”, entre outras. É conhecido por ter em exposição o banco em forma de W e produzido em contraplacado “Taburet M” no MoMA de Nova York. A atenção aos detalhes e a capacidade de síntese formal são as principais características desde arquitecto tornado designer, produzindo peças de alto valor comercial que só uma pessoa de créditos provados pode produzir.
Taburet C
Material: Produzido em contraplacado de bétula com diversos acabamentos Parafusos em aço inoxidável Dimensões: H 40 x Ø 38 cm Preço: €110 Designer: Jorgen Moller Produção/Comercialização: Askman
Esta simples mas requintada peça é objecto de estudo por vários arquitectos e designers sendo muitas vezes considerada um dos ícones do design escandinavo e mundial. Possui uma das estruturas mais simples e com pequenas alterações foi redesenhada de forma a se adequar a diferentes tempo e utilizações mas sempre com a mesma essência e funcionalidade.
Processo de fabrico: Tampo . Corte mecânico · Lixagem · Envernizamento · Furação Pernas · Dobragem a vapor · Corte mecânico · Lixagem · Envernizamento · Furação
Anรกlise da adequabilidade dos materiais originais:
R2 0
380
360
400
R5
80
40
15
120째
A
2
40
25
DETAIL A SCALE 1 : 5 UNLESS OTHERWISE SPECIFIED: DIMENSIONS ARE IN MILLIMETERS SURFACE FINISH: TOLERANCES: LINEAR: ANGULAR: NAME
DEBUR AND BREAK SHARP EDGES
FINISH:
SIGNATURE
DATE
DO NOT SCALE DRAWING
TITLE:
DRAWN
REVISION
taburet C by Jorgen Moller
CHK'D APPV'D MFG Q.A
MATERIAL:
WEIGHT:
DWG NO.
SCALE:1:10
taburet C SHEET 1 OF 1
A4
LCA Calculator PDF report on 'Taburet C', produced for Artur Branco
Overview of 'Taburet C' Manufacture 371000000 g
Total product impact during lifetime
Transport 37100000 g
408,000,000 g CO2
Use 0g Disposal 39200 g
Manufacture and disposal Assembly name: Taburet C Part name
Material
Part mass
Qty
CO2
perna
Plywood, indoor
275 g
30000
107000000 g
Material:
Plywood, indoor
107000000 g
Process:
Cutting
5260g
Disposal method:
75% recycled, 25% landfilled
11300g
assento
Plywood, indoor
Material:
Plywood, indoor
264000000 g
Process:
Cutting
1750g
Disposal method:
75% recycled, 25% landfilled
27900g
Totals:
Page 1 of 3
2030 g
28500000 g
10000
Graph
264000000 g
371000000 g
Š IDC 2012
LCA Calculator PDF report on 'Taburet C', produced for Artur Branco
Transport Transport name
Assembly transported
Mode
Distance
CO2
entrega
Taburet C
Truck
10000 km
37100000 g
Totals:
Page 2 of 3
37100000 g
Š IDC 2012
LCA Calculator PDF report on 'Taburet C', produced for Artur Branco
Product use Electricity use This product has no electrical usage.
Consumables use This product has no consumables.
Page 3 of 3
Š IDC 2012
Stage 1 - E e RRR
Polyurethane
Rigid Polymer Foam (LD) Rigid Polymer Foam (HD)
Polyoxymethylene (Acetal, POM)
Recycle
True
Tungsten alloys Polychloroprene (Neoprene, CR)
Leather False
Bamboo
1e-3
0.01
0.1
1
Young's Modulus (GPa)
No warranty is given for the accuracy of this data. Values marked * are estimates.
10
100
Stage 2 - â‚Ź e RRR
Cast iron, grey Low alloyPolyethylene steel (PE) Polyvinylchloride (tpPVC) EVA Copper alloys
True
Polycarbonate (PC)
Recycle
Stainless steel Rigid Polymer Foam (HD) Rigid Polymer Foam (LD) Concrete
Rigid Polymer Foam (LD)
Stone
False
Cork Leather
0.1
1
Price (EUR/kg)
No warranty is given for the accuracy of this data. Values marked * are estimates.
10
100
Page 1 of 3
Plywood Description The Material Plywood is laminated wood, the layers glued together such that the grain in successive layers are at right angles, giving stiffness and strength in both directions. The number of layers varies, but is always odd (3, 5, 7…) to give symmetry about the core ply - if it is unsymmetric it warps when wet or hot. Those with few plies (3,5) are significantly stronger and stiffer in the direction of the outermost layers; with increasing number of plies the properties become more uniform. High quality plywood is bonded with synthetic resin. The data listed below describe the in-plane properties of a typical 5-ply. Composition Cellulose/Hemicellulose/Lignin/12%H2O/Adhesive Image
Caption Plywood dominates the market for both wood and steel stud construction. It is widely used, too, for furniture and fittings, boat building and packaging.
General properties Density Price
700 0.4342
-
800 0.7237
kg/m^3 EUR/kg
-
13 2 2.5 0.3 9 30 44 25 3 16 1.8 0.11
GPa GPa GPa
Mechanical properties Young's Modulus Shear Modulus Bulk modulus Poisson's Ratio Hardness - Vickers Elastic Limit Tensile Strength Compressive Strength Elongation Endurance Limit Fracture Toughness Loss Coefficient
6.9 * 0.5 * 1.6 0.22 3 *9 10 8 2.4 *7 *1 * 8e-3
HV MPa MPa MPa % MPa MPa.m^1/2
Thermal properties Thermal conductor or insulator? Thermal Conductivity Thermal Expansion Specific Heat Glass Temperature
Good insulator 0.3 - 0.5 6 - 8 1660 - 1710 120 - 140
No warranty is given for the accuracy of this data. Values marked * are estimates.
W/m.K µstrain/°C J/kg.K °C
Page 2 of 3
Plywood Maximum Service Temperature Minimum Service Temperature
* 100 * -100
-
130 -70
°C °C
Electrical properties Electrical conductor or insulator? Resistivity Dielectric Constant Power Factor Breakdown Potential
Poor insulator 6e13 - 2e14 6 - 8 * 0.08 - 0.11 * 0.4 - 0.6
µohm.cm
1000000*V/m
Optical properties Transparency
Opaque
Eco properties Production Energy CO2 creation Recycle Downcycle Biodegrade Incinerate Landfill A renewable resource? Impact on the environment
25 -0.9
-
29 -0.7
MJ/kg kg/kg
Wood is a renewable resource, absorbing CO2 as it grows. Present day consumption for engineering purposes can readily be met by controlled planting and harvesting, making wood a truly sustainable material.
Processability (Scale 1 = impractical to 5 = excellent) Mouldability Machinability
3 5
-
4
Durability Flammability Fresh Water Sea Water Weak Acid Strong Acid Weak Alkalis Strong Alkalis Organic Solvents UV Oxidation at 500C
Poor Average Average Average Very Poor Good Poor Good Good Very Poor
Supporting information Design guidelines Plywoods offers high strength at low weight. Those for general construction are made from softwood plys, but the way in which plywood is made allows for great flexibility. For aesthetic purposes, hardwoods can be used for the outermost plys, giving "paneling plywoods" faced with walnut, mahogany or other expensive woods on a core of softwood. Those for ultra-light design have hardwood outer plys on a core of balsa. Metal-faced plywoods can be riveted. Curved moldings for furniture such as chairs are made by laying-up the unbonded plys in a shaped mould and curing the adhesive under pressure using an airbag or matching mould. Singly curved shapes are straightforward; double curvatures should be minimized or avoided. Technical notes Low cost plywoods are bonded with starch or animal glues and are not water resistant -- they are used for boxes and internal construction. Waterproof and marine plywoods are bonded with synthetic resin -- they are used for external paneling and general construction. Typical uses
No warranty is given for the accuracy of this data. Values marked * are estimates.
Plywood Furniture, building and construction, marine and boat building, packaging, transport and vehicles, musical instruments, aircraft, modeling.
Links Reference ProcessUniverse Producers
No warranty is given for the accuracy of this data. Values marked * are estimates.
Page 3 of 3
Organic solvent-based painting Description The process In ORGANIC-SOLVENT BASED PAINTING, the coloring materials (pigments) are suspended, together with the binding agents (resins), in a volatile organic solvent (VOC). When spread thin over a surface, the solvent evaporates; the resins hold the pigments in place to form a decorative and protective coating. Some few paints are not much more than this today. Watching paint dry is a synonym for boredom. But modern paints are far from boring. New developments now give formulations that dry in seconds, have fade-resistant colors, soft textures, visual effects, powerful protective qualities, and much more. But there is a problem. Solvent-based paints are environmentally bad, so bad that their very future is under threat. Process Schematic
Figure caption Organic solvent-based painting
Physical Attributes Surface roughness (A=v. smooth) Curved surface coverage Coating thickness Surface hardness Component size Processing temperature
A Good 15 - 500 10 - 16 non-restricted 9.85 - 99.85
Process Characteristics Discrete Continuous
Economic Attributes Relative tooling cost Relative equipment cost Labor intensity
low medium medium
Function of Treatment Corrosion Protection (aqueous) Corrosion Protection (gases) Corrosion Protection (organics) Electrical Insulation No warranty is given for the accuracy of this data. Values marked * are estimates.
¾m Vickers °C
Page 1 of 2
Organic solvent-based painting Aesthetics Colour Reflectivity
Supporting Information Design guidelines Solvent-based paints give the smoothest, most uniform coating and the greatest control of color the automobile industry and most product designers insists on them. Metallic paints mix flake aluminum powder in the coating; the trick is to have the coating thin enough that the metal flakes lie in a plane so that the color does not 'flip' when viewed from different angles. But there is a taste, too, for 'traveling colors'. Color is determined by the differential absorption and reflection of the various wavelengths of light; the color seen is that at the least absorbed wavelength form the angle of view. Traveling colors use additives to change the absorption-reflection characteristics from various angles. Technical notes Paints are applied by brushing, dipping or spraying, and can be applied to virtually any surface provided it is sufficiently clean. Examples of uses
Typical uses About half of all paints are used for decorating and protecting buildings, the other half for manufactured products, most particularly cars and domestic appliances; marine applications create important market for high-performance corrosion and anti-fouling formulations; 'printers inks' are paints that play a central role in publishing and packaging. The economics Painting is cost effective. The equipment costs are low for non-automated painting, but can be high if the equipment is automated. Paints are a $75 billion per year industry. The environment Emissions from the evaporating solvents from solvent-based paints (VOCs) are toxic, react in sunlight to form smog and are generally hostile to the environment. Auto manufacturers and others are under increasing pressure to meet demanding environmental standards. The solvents must now be recaptured, burnt or recycled. There is growing incentive to replace them by water-based paints (but they dry slowly) or dry polymer coatings (but they cannot yet offer the same surface quality).
Links Reference MaterialUniverse
No warranty is given for the accuracy of this data. Values marked * are estimates.
Page 2 of 2
Page 1 of 2
Threaded fasteners Description The process When we get "down to the nuts and bolts" we are getting down to basics. Screws are as old as engineering - the olive press of roman times relied on a gigantic wooden screw. THREADED FASTENERS are the most versatile of mechanical fasteners, with all the advantages they offer: they do not involve heat, they can join dissimilar materials of very different thickness and they can be disassembled. Ordinary screws require a pre-threaded hole or a nut; self-tapping screws cut their own thread.
Process Schematic
Physical Attributes Section thickness Unequal thicknesses Component size Dissimilar materials Need for surface preparation Processing temperature
1
-
1000
mm
non-restricted
16.85
-
36.85
째C
Process Characteristics Discrete
Function Electrically conductive Thermally conductive Watertight/airtight Demountable Service temperature regime
Limited by material of joint
Economic Attributes Relative tooling cost Relative equipment cost Labor intensity
low low medium
Materials to be joined Metals Polymers Composites Glasses Natural materials
Joint Geometry Lap Butt Sleeve Scarf No warranty is given for the accuracy of this data. Values marked * are estimates.
Threaded fasteners Tee
Recommended Loading Tension Compression Shear Bending Torsion
Shape Circular Prismatic Non-circular Prismatic Dished Sheet
Supporting Information Design guidelines Mechanical fasteners allow great freedom of design, while allowing replacement of components or access to components because of the ease of which they can be disassembled. They can be used up to high temperatures (700 C) and - with proper location - allow high precision assembly. Technical notes Threaded fasteners are commonly made of carbon steel, stainless steel, nylon or other rigid polymers. Stainless steel and nickel alloy screws can be used at high temperatures and in corrosive environments. Tightening is critical: too little, and the fastener will loosen; too much, and both the fastener and the components it fastens may be damaged - torque wrenches overcome the problem. Locking washers or adhesives are used to prevent loosening. Typical uses Threaded fasteners are universal in engineering design. But increasingly their use is becoming limited to products in which disassembly (or the ability to have access) is essential because other joining methods are cheaper, less likely to loosen, lighter and easier to automate. The economics Threaded fasteners are cheap, as is the equipment to insert them when this is done by hand. But the insertion is difficult to automate, making other methods (welding, riveting, adhesives) more attractive for a permanent bond. The environment Threaded fasteners have impeccable environmental credentials.
Links Reference MaterialUniverse
No warranty is given for the accuracy of this data. Values marked * are estimates.
Page 2 of 2
Sugestão para alteração dos materiais e processos de fabrico
Verificação de materiais: Depois de uma sessão de brainstorming verificou-se que apesar do custo excessivo do banco a possibilidade de ter uma peça que é mais do que um simples objecto do dia-a-dia, se justifica mesmo com o elevadíssimo preço final. Visto isto decidimos ir numa direcção completamente diferente e aliar o que aprendemos com o trabalho anterior com a selecção de materiais e processos. Com a utilização do modelo de SolidWorks e o CES edupack podemos fazer uma extensa pesquisa e partir para a selecção de materiais duma forma mais esclarecida tirado pleno uso das ferramentas ao nosso dispor. Os dados acerca do contraplacado de bétula já tinham sido verificados e discutidos no último trabalho facilitando por isso a selecção dos materiais.
Vamos portanto primeiro definir os materiais do redesenho: Para as pernas há as seguintes possibilidades: .tubular metálico .bambo Para o assento as possibilidades são maiores visto não estar sujeito a tanto esforço: .bambo laminado .formica .polipropileno Os processos são alterados consoante os materiais: .bambo (dobrado a vapor) .tubular metálico (extrudido, dobrado e soldado) .polipropileno (moldagem por injecção)
Stage 1 - E e RRR
Polyurethane
Rigid Polymer Foam (LD) Rigid Polymer Foam (HD)
Polyoxymethylene (Acetal, POM)
Recycle
True
Tungsten alloys Polychloroprene (Neoprene, CR)
Leather False
Bamboo
1e-3
0.01
0.1
1
Young's Modulus (GPa)
No warranty is given for the accuracy of this data. Values marked * are estimates.
10
100
Stage 2 - â‚Ź e RRR
Cast iron, grey Low alloyPolyethylene steel (PE) Polyvinylchloride (tpPVC) EVA Copper alloys
True
Polycarbonate (PC)
Recycle
Stainless steel Rigid Polymer Foam (HD) Rigid Polymer Foam (LD) Concrete
Rigid Polymer Foam (LD)
Stone
False
Cork Leather
0.1
1
Price (EUR/kg)
No warranty is given for the accuracy of this data. Values marked * are estimates.
10
100
Page 1 of 2
Bamboo Description The Material Bamboo is nature's gift to the construction industry. Think of it: a hollow tube, exceptionally strong and light, growing so fast that it can be harvested after a year, and - given a little longer reaching a diameter of 0.3 meters and a height of 15 meters. This and its hard surface and ease of working makes it the most versatile of materials. Bamboo is used for building and scaffolding, for roofs and flooring, for pipes, buckets, baskets, walking sticks, fishing poles, window blinds, mats, arrows and furniture. Tonkin bamboo is strong and flexible (fishing poles); Tali bamboo is used for structural applications (houses or furniture); Eeta bamboo is the fastest growing and is used as a source of cellulose for the production of cellulose or Rayon. Composition Cellulose/Hemicellulose/Lignin/12% H2O Image
Caption Bamboo is exceptionally light, and stiff and strong in bending. It is widely used for construction (like this bridge), even today.
General properties Density Price
600 1.447
-
800 2.171
kg/m^3 EUR/kg
-
20 44 45 5.5 12 35 7
GPa MPa MPa % HV MPa MPa.m^1/2
Mechanical properties Young's Modulus Elastic Limit Tensile Strength Elongation Hardness - Vickers Endurance Limit Fracture Toughness
15 35 36 2.88 2 * 25 5
Thermal properties Thermal conductor or insulator? Thermal Conductivity Thermal Expansion Specific Heat Maximum Service Temperature
Good insulator 0.1 - 0.18 2.6 - 10 1660 - 1710 116.9 - 136.9
Electrical properties Electrical conductor or insulator?
Poor insulator
Optical properties Transparency
Opaque
No warranty is given for the accuracy of this data. Values marked * are estimates.
W/m.K µstrain/°C J/kg.K °C
Page 2 of 2
Bamboo Eco properties Production Energy CO2 creation Recycle
14.4 * -1.16
-
15.9 -1.05
MJ/kg kg/kg
Supporting information Typical uses Building & construction; scaffolding; furniture; pulp & paper making; ropes; reinforcement for concrete; frames for early aircraft, pipes, baskets, walking sticks, fishing poles, window blinds, mats, arrows and furniture.
Links Reference ProcessUniverse Producers
No warranty is given for the accuracy of this data. Values marked * are estimates.
Page 1 of 3
Stainless steel Description The Material Stainless steels are alloys of iron with chromium, nickel, and - often - four of five other elements. The alloying transmutes plain carbon steel that rusts and is prone to brittleness below room temperature into a material that does neither. Indeed, most stainless steels resist corrosion in most normal environments, and they remain ductile to the lowest of temperatures. Composition Fe/<0.25C/16 - 30Cr/3.5 - 37Ni/<10Mn + Si,P,S (+N for 200 series) Image
Caption One the left: Siemens toaster in brushed austenitic stainless steel (by Porsche Design). On the right, scissors in ferritic stainless steel; it is magnetic, austenitic stainless is not.
General properties Density Price
7600 2.171
-
8100 8.684
kg/m^3 EUR/kg
189 74 134 0.265 130 170 480 170 5 * 175 62 * 2.9e-4
-
210 84 151 0.275 570 1000 2240 1000 70 753 150 1.48e-3
GPa GPa GPa
Mechanical properties Young's Modulus Shear Modulus Bulk modulus Poisson's Ratio Hardness - Vickers Elastic Limit Tensile Strength Compressive Strength Elongation Endurance Limit Fracture Toughness Loss Coefficient
HV MPa MPa MPa % MPa MPa.m^1/2
Thermal properties Thermal conductor or insulator? Thermal Conductivity Thermal Expansion Specific Heat Melting Point Maximum Service Temperature Minimum Service Temperature
Poor conductor 12 - 24 13 - 20 450 - 530 1375 - 1450 650 - 900 -272.2 - -271.2
W/m.K µstrain/°C J/kg.K °C °C °C
Good conductor 64 - 107
µohm.cm
Electrical properties Electrical conductor or insulator? Resistivity
No warranty is given for the accuracy of this data. Values marked * are estimates.
Page 2 of 3
Stainless steel Optical properties Transparency
Opaque
Eco properties Production Energy CO2 creation Recycle Downcycle Biodegrade Incinerate Landfill A renewable resource? Impact on the environment
* 77.2 * 4.86
-
85.3 5.37
MJ/kg kg/kg
Stainless steels are FDA approved -- indeed, they are so inert that they can be implanted in the body, and are widely used in food processing equipment. All can be recycled.
Processability (Scale 1 = impractical to 5 = excellent) Castability Formability Machinability Weldability Solder/Brazability
3 2 2 5 5
-
4 3 3
Durability Flammability Fresh Water Sea Water Weak Acid Strong Acid Weak Alkalis Strong Alkalis Organic Solvents UV Oxidation at 500C
Very Good Very Good Very Good Very Good Good Very Good Very Good Very Good Very Good Very Good
Supporting information Design guidelines Stainless steel must be used efficiently to justify its higher costs, exploiting its high strength and corrosion resistance. Economic design uses thin, rolled gauge, simple sections, concealed welds to eliminate refinishing, and grades that are suitable to manufacturing (such as free machining grades when machining is necessary). Surface finish can be controlled by rolling, polishing or blasting. Stainless steels are selected, first, for their corrosion resistance, second, for their strength and third, for their ease of fabrication. Most stainless steels are difficult to bend, draw and cut, requiring slow cutting speeds and special tool geometry. They are available in sheet, strip, plate, bar, wire, tubing and pipe, and can be readily soldered and braised. Welding stainless steel is possible but the filler metal must be selected to ensure an equivalent composition to maintain corrosion resistance. The 300 series are the most weldable; the 400 series are less weldable. Technical notes
No warranty is given for the accuracy of this data. Values marked * are estimates.
Stainless steel Stainless steels are classified into four categories: the 200and 300 series austenitic (Fe-Cr-Ni-Mn) alloys, the 400 series ferritic (Fe-Cr) alloys, the martensitic (Fe-Cr-C) alloys that also form part of the 400 series, and precipitation hardening or PH (Fe-Cr-Ni-Cu-Nb) alloys with designations starting with S. Typical of the austenitic grades of stainless steel is the grade 304: 74% iron, 18% chromium and 8 % nickel. Here the chromium protects by creating a protective Cr2O3 film on all exposed surfaces, and the nickel stabilizes face-centered cubic austenite, giving ductility and strength both at high and low temperatures; they are non-magnetic (a way of identifying them). The combination of austenitic and ferritic structures (the duplex stainless steels) provide considerably slower growth of stress-induced cracks, they can be hot-rolled or cast and are often heat treated as well. Austenitic stainless steel with high molybdenum content and copper has excellent resistance to pitting and corrosion. High nitrogen content austenitic stainless steel gives higher strength. Superferrites (over 30% chromium) are very resistant to corrosion, even in water containing chlorine. More information on designations and equivalent grades can be found in the Users section of the Granta Design website, www.grantadesign.com Typical uses Railway cars, trucks, trailers, food-processing equipment, sinks, stoves, cooking utensils, cutlery, flatware, architectural metalwork, laundry equipment, chemical-processing equipment, jet-engine parts, surgical tools, furnace and boiler components, oil-burner parts, petroleum-processing equipment, dairy equipment, heat-treating equipment, automotive trim. Structural uses in corrosive environments, e.g. nuclear plants, ships, offshore oil installations, underwater cables and pipes.
Links Reference ProcessUniverse Producers
No warranty is given for the accuracy of this data. Values marked * are estimates.
Page 3 of 3
Conclusão: Neste trabalho tivemos a sorte de no sorteio dos números nos ter saído uma peça quase idêntica à do trabalho anterior o que facilitou em termos de compreensão da mecânica dos materiais. Já na compreensão da selecção de materiais tivemos algumas dificuldades pelo facto das aulas serem bastante espaçadas e não ter dado muito tempo para desenvolver trabalho tanto no SolidWorks como no CES edupack, mas o pouco que se investigou e tentou usar já foi suficiente para verificar a potencialidade dos softwares apresentados. Na aplicação dos materiais a maior dificuldade foi mesmo como modificar os materiais sem comprometer a forma e a estética dum ícone do design mas penso que isso foi ultrapassado com sucesso.
Bibliografia: http://grabcad.com/ http://www.lathamtimber.co.uk/ http://www.koskisen.com http://www.ikea.com http://www.theage.com.au http://www.youtube.com/watch?feature=player_embedded&v=nmvF2NWb6Gg http://www.askman.com CES edupack 2005
Trabalho realizado para a disciplina de Resistência dos Materiais leccionada no Instituto Politécnico do Cávado e Ave