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Introduction to Materials and Properties. Dr. Elena Gordo elena.gordo@uc3m.es. Department of Materials Science and Engineering and Chemical Engineering. Talk layout. Materials selection Materials selection in transportation industry Engineering materials Materials properties
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Introduction to Materials and Properties Dr. Elena Gordo elena.gordo@uc3m.es Department of Materials Science and Engineering and Chemical Engineering
Talklayout • Materialsselection • Materialsselection in transportationindustry • Engineeringmaterials • Materialsproperties • Comparison of materials • Materialscharacterisation
Materialsselection At eachstage, decisionsneedto madeaboutwhatto make it out of (materials) and howtomakeit (processingand shape) TREND in transportation industry creation of products that incorporate advanced structural materials and benefit from new manufacturing technologies.
Materialsselection in transportationindustry Objective of transportation industry: To create value by - Improving materials performance • Reducing costs • Extending system life • Reducing environmental impact • Higher structural efficiency • Reduced product weight • Materials capabilities • + • Design methodology • + • Improved reliability Ej. Honeycombconstruction
Materialsselection in transportationindustry • Large range of materials is available • Complex system engineering • Increased number of design constraints • Growing number of product requirements • Availability of materials in appropriate form • Casting, forgings, rolled products, extrusions • Amenable to net shape forming • Superplastic forming • Stretch/thermal aging • Welding, brazing • Other manufacturing methods • Designer faced with complex choices for selection to meet system requirements • It is no longer appropriate to treat processing as a separate consideration from materials selection
Lightweight structures • First order importance • Necessary, but not sufficient • Requires new design methods • Requires improved properties • Requires improved processing methods • Requires improved manufacturing technologies • Structural materials to satisfy a variety of properties • Improved performance achieved through: • Better understanding of relationships among composition, processing, microstructure, and properties
Goal: fly faster High specific strength High temperature capability (skin) Skin materials evolution: Wood Fabric Aluminum Titanium Composites SR71: all Ti alloy skin: M3.6 Concorde: Al skin: M1.8 Practical limitations for commercial supersonic flight: temperature economics Role of materials http://www.concordesst.com/
Safe Life Design Requirements • Since beginning of flight: • Static strength is first order consideration • Withstand maximum operating load plus safety factor of 1.5 • Since 1930s: • Design to consider fatigue as constraint • Safe life • No fatigue failure in 4 lifetimes • Detailed knowledge of service experience • Rigorous product testing • Since 1950s • Fail safe • Redundant systems • Incorporate redundant crack pathways in design • Periodic inspections to detect cracks • Rigorous maintenance
Component material property requirements • Fuselage • Semi-monocoque structure • Skin: carry cabin pressure (tension) and shear loads • Circumferential frames: maintain fuselage shape and redistribute loads into skin • Bulkheads: carry concentrated loads • Wing • Beam loaded in bending • Supports static weight of aircraft • Supports loads due to maneuvering and turbulence • Additional loads: • landing gear during taxi, take-off, and landing • Leading and trailing edge flaps • Upper wing surface: • Compression during flight • Tension during taxiing • Lower wing surface • Tension during flight • Compression during taxiing • Tail • Like wing • Upper and lower side of tail wing critical in compression loading due to bending: important property is modulus of elasticity in compression
Weight reduction for fuel efficiency Designer considers how a certain property impacts weight savings: trade-off studies $ of materials for weight reduction should not exceed $ saved from reduced fuel consumption and maintenance Improved performance through material choice • Cost-benefit analysis required for new material candidates • Acquisition • Operation • Support • Non-recurring development costs
Important mechanical properties • Strength and strain • Young’s modulus • Alternating loads during flight: Compressive yield strength and modulus of elasticity in compression must be included in design considerations • Fatigue crack initiation resistance • Fatigue crack growth rate • Fracture toughness (limiting design consideration!) • Corrosion resistance
Materials vs. Structures • Structures are made out of materials but the design parameters are not identical forthetwo: • MaterialsMaterial Properties – Failure Stress, Young’s Modulus, Density • StructuresStructuralProperties – MaximumForce, Stiffness, Weight
MaterialsProperties: General Properties • Cost per unit Material ($/Kg) • Deal with in a simple manner - complex function of the marketplace • Depends on the components that make up the material (e.g. alloying additions)
MaterialsProperties: General Properties • Density (Kg/m3) • NormalizedMass
Compressive Both the resistance to elastic buckling and plastic collapse must be considered in components such as floor beams and support struts. Strength and Stiffness. • Tensile • Many components are designed for maximum load (strength) or minimum deflection (stiffness). • For optimum efficiency in these applications, materials are selected on a basis of specific strength or specific stiffness.
Fabrication processes are more difficult for low ductility materials. Ductility • Ductility important for both formability and toughness. • Metals generally have high ductility and composite materials and ceramics have low ductility. Stretch-Formed Component
Ductility • Ductility important for both formability and toughness. • Ductility allows the relaxation of stress concentrations. Stress Concentration at a hole
Toughness • Toughness is the resistance of a material to the unstable propagation of cracks. • A material must have sufficient toughness to allow stable cracks to be detected. Ductile failure
Fatigue • Fatigue is the nucleation and growth of cracks due to cyclic loading. Test: rotating bending Aloha Flight 423, 1988
Fatigue Stress • The fatigue test gives an S-N curve • An infinite life fatigue limit or finite life fatigue endurance limit can be defined • The endurance limit is sometimes called the Fatigue Strength Fatigue Limit Fatigue Endurance Limit 106 cycles Log Cycles to Failure, N
Temperature Effects • Most aircraft components operate in the range -50º to +90ºC, with the exception of engine components, high speed flight and space applications. The thermal envelopes for aircraft.
Temperature Effects • Low temperatures reduce ductility and toughness and can cause embrittlement in steels. Brittle Failure Ductile Failure
Wear • Wear is the damage caused by sliding contact between two moving surfaces. • Coping with wear requires careful matching of materials and lubricants. Rolling Contact Wear
Corrosion • Corrosion is a major cause of component failure and replacement. Sn-Au Galvanic Corrosion inF16 Fuel Shut-off Valve(www.corrosion-doctors.org) Stress Corrosion Cracking in Aluminium Alloy(www.corrosion-doctors.org)
Cost • Cost is important - even in military aerospace engineering. It is necessary to consider whether the use of a new material is justified by the design benefits it creates. Costs include raw materials and processing and maintenance
