Engineering Material

Engineering Material

Ir.Soeweify, M.Eng Head of Strength and Structure Groups Department of Shipbuilding Engineering Surabaya Institute of Technology Welding Engineer 1980 Hiroshima University Welding Inspector 1984 Hamburg University Fracture Mechanic 1990 Bandung Institute of Technology

Engineering Materials • Metals • Polimers • Ceramics • Glasses • Elastomers • Composite

Metal • High moduli Elastisity • Can be made strong by alloying,

mechanical process, and heat treatment, but they remain ductile. • Least resistance to corrosion • High strength still use, even the ductility decrease more than 2 % • Easy to machining and joining.

Ceramic and glases • High moduli • But unlike metal they are brittle • The tension strength is the fracture

strength, in compression is brittle crushing strength which is about 15 time larger. • Low tolerance of stress concentration ( hole, crack ) and high contact stress ( Clamp ) • Stiff and hard abrasion resistance so used in bearing and cutting tools. • Retain their strength to high temperatur and low corrosion well

Polimer and Elastomer • The moduli from low to high • Elastic deflection can be large • Creep in the room temperature • No have useful strength above 200º C • Easy to shape, complicated part can be moulded. • Making assembly fast and cheap • Corrosion resistance, low coef friction, • Good design exploits these properties

Composite • Combine the attractive properties of other

classes of material while avoiding some of drawbacks ( demerit ) • They are light,stiff and strong,and can be tought. • Most of composite available to the engineering reinforce by fibre glas, carbon or kevlar. • Cannot be use more than 250º C because polimer matrix will soften.

Material Properties • Phisically properties – Melting temperatur – Conductifity – Density etc

• Processable properties – Machinability – Castability – Weldability etc

• Mechanical properties – Strength – Fracture toughness – Hardness etc

Definition of material properties • Density ρ units Kg/m3 • Elastic modulus GN/m2 or GPa The

slope of the linear elastic part of the stress strain curve Young Modulus E for the tension and compression, Shear Modulus G for shear loading.Bulk Modulus K for hydrostatic pressure • Poison’s ratio ν it is negative ratio of the lateral strain ε2 / ε1 in axial

Steel selection for Boiler and Pressure vessel

• Strength and ductility – Mechanical Properties • Tensile strength • Yield Strength • Elongation • Reduction 0f Area

• Fracture Strength

– Fracture Toughness • K Parameter – Noch toughness • Impact value • Transition brittle to ductile .

Steel selection for Boiler and Pressure vessel • Fatigue Strength – Fatigue limit • S-N Diagram – Crack grow rate • dA/dN

• Corrosion Resistance – Rate of corrosion – Stress corrosion cracking

Stress Strain Diagram • Mechanical Properties

Stress strain diagram

Mechanical properties

•σ, ultimate

= P ultimate / Ao

[ N/mm2 ]

•σ, Yield = P yield /Ao [ N/mm2 ] •ε, Elongation = ( Li – Lo ) / Lo [ % ] • Ra, Reduc.of Area = ( Ao – Ai ) /Ao [%]

• E,modulus Elastisity σ / ε [ N/mm2] • R, Resilience = ½ σ ε [ J/mm3 ]

Stress strain for britlle material

Stress Strain curve • For ceramic

Stress Strain Diagram • Polimer • Glasses

Operation Load • Static Load

– Tension σ, tensile – Bending σ, bending – Shear G shear stength – Torsion • Dynamic Load – Impact load Impact value – Fatigue Load Fatigue strength • Combine load – Static load, tension and bending – Dynamic load, fatigue in tension and bending

Impact value • Dynamic test ( load ) • Impact value [ Joule ] ( 3 specimens )

– Parameter for fatigue strength – Parameter for ductile material

• Transition temp ( 10 specimens ) – – –

50 % Brittle, 50 % Ductile Low temp to high temperature More higher transition temp more better

Standard Charpy Impact Specimen

Placement of charpy specimen

Impact testing machine

Transition temperature

Ductile and brittle fracture

Ductile and Brittle charactristic • Brittle material – – – – –

Fracture by cleveage Fracture surface Perpendiculair to the force No deformation High hardness High crack growth rate

– – – – –

Fracture by micro voit coalesence Fracture surface 45 degree to the force Some deformation Lower hardness Lower crack growth rate

• Ductile material

Fracture Toughness Test • Centre crack specimen

Specimen for fracture test

Specimens extracted from plate

Specimens extracted from disk

Hardness brinell test

Hardness brinell used steel ball HB Hardness Vickers use diamont HV Hardness Rockwell used ball and diamont HRB,HRC

Parameters of fatigue strength

• S-N Diagram – – – – –

Fatigue strength Final fracture Unfracture Some amount specimens No calculation just plotted

• dA/dN versus Stress intensity ( Δ K ) – – – – –

Crack growth rate Crack propagation A certain cyrcle Only one specimen Need some calculation to the final diagram

Fatigue Crack Growth Under CA Loading

N.E.Dowling, Mechanical Behaviour of Materials, F-11.7,P-465

Modulus of Rupture • Tri point bending test

Loss coeffisient in Stress Strain cycle

Thermal conductivity • Flux heat

Thermal expansion Coef • Heating the sample

Creep rupture • Statically and constant loading

Wearing test • Archard wear contant

Corrosion test • Surface corrosion

Heat treatment terms • Annealing

– A generik term denoting the threatment, consisting of heating to and holding at suitable temperature followed by cooling at suitable rate, used primary to soften metalic material but also to simultanuously produce desire change in other properties or in microstructure to improve of machineability,cold work, mechanical or electrical or increase in stability of dimension

• Annealing time

– Time elapsing while holding a piece at annealing temperatur

Several heat treatment of steel • Quenching

– Rapid cooling after heating to harden the steel

• Tempering

– Reheating a quench hardened or normalized ferro alloy to e temperature bellow the transformation rangeand than cooling at any desired rate.

• Normalizing

– Heating a ferrous alloy to suaitable temp above the transformation temp range and than cooling in air to a temperature substantially bellow the temp trans temp range

• Annealing

– Heating to and holding at a suitable temp followed by cooling to soften material or to change the other properties