This course is intended for aircraft structural engineers to equip themselves with requisite familiarity with the materials for aircraft construction. The focus is thus on structural materials for airframe, covering their mechanical behaviour, major processes such heat-treatments of alloys and curing of composites, scientific principles behind alloying and their heat/mechanical treatments, relevance for aircraft structures and usage in aircraft. Major materials included are Al-alloys, Ti-Alloys, Aircraft steels and fiber composites. Study of other materials, such as transparent materials used in aircraft, coatings and adhesives, and also materials used in aero-engines is limited to only a brief overview.
The course is planned in 6 modules to be covered in 40 physical-lecture-hours, as given below. Changes may occur in the content or the duration or both, depending upon the progress shown by the students as well as other requirements that may arise during the conduct of the course.
Module 1: Introduction and Overview : Aircraft Materials and Processes (3 hrs)
Aircraft systems. Airframe structures. Various aircraft types and their structure. Structural requirements and material property requirements. What is special about Aircraft Materials? Demands on the airframe materials
Drivers for aircraft material development : Lightweight, Strength, Stiffness, Corrosion resistance…. Then Fatigue, Damage Tolerance; Also manufacturability.
Historical Evolution of Aircraft structures and materials: Early Requirements & Early materials (Wood, Fabric), Semi monocoque structures – Use of sheet metal work; Development of Al-alloys through several decades. Advent of Ti alloys; Use of Steels. Emergence of composites as major structural materials
Module 2: Performance parameters of structural materials (7 hrs)
Strength, Stiffness, Stress-strain curves. Various related terms and their significance. Tension, compression and shear loading. Buckling. Material Indices for choice of materials. Strength properties of commonly used materials.
Metal fatigue, fatigue performance and its characterization; Damage Tolerance, use of fracture mechanics and related material parameters fracture toughness, crack-growth resistance; crack growth in fatigue. Related material parameters.
Material characterization: Important properties and their assessment: strength, stiffness, hardness, fatigue, fracture
Variability and Scatter, Use of statistical parameters, Confidence Intervals, A and B basis values
Module 3: Science behind Alloying (6 hrs)
Elements of crystal structure; polycrystalline nature of metals, Important aspects: dislocations, slip. Yielding related to dislocation movement. Solid Solutions and alloying
Strengthening through solid solutions, dispersion and precipitation (age-) hardening, Grain Boundary strengthening, Strain hardening; Alloying for other properties, Fatigue and corrosion characteristics
Phase diagrams, TTT diagrams
Module 4: Metallic Materials and processes (8 hrs)
Al-alloys : Classification and Nomenclature; Cast and wrought, Heat-treatable and non-heat-treatable. Alloy and temper designations; Wrought Al-alloys Al-Cu, Al-Zn; Properties and treatments, usage; Other Al-Alloys
Ti-alloys : Classification; Nomenclature, properties and usage
Other miscellaneous alloys in airframe: Ferrous Alloys, Steels, Cast Iron, :Steels used in Aircraft; Mg Alloys, others
General overview of processes of fabrication
Engine materials: superalloys (an overview)
Module 5: Composite Materials and processes (11 hrs)
Introduction to Composites: Polymer matrix composites; a brief overview of Metal-matrix composites (MMC) and Ceramic-Matrix Composites (CMC); Laminated composites, Sandwich composites, Fiber-metal laminates, Carbon Fiber Composites, GRP.
Raw materials: Fibers: Carbon, Glass, Aramid; (Nomenclature, types, properties); Other miscellaneous. Matrix materials (polymeric), Thermosets vs thermoplastics, high temperature; Epoxies, various resins, Curing process of thermosets (mainly epoxy), role of various additives, cure cycles.
Processes: Autoclave and non-autoclave processes
Micromechanics: Composite properties relationship with constituent properties
Laminated Composites: Moduli and strengths, Characterization; Environmental Effects: Moisture absorption, hot-wet degradation; Essential aspects of laminate (carbon-epoxy) mechanical behavior; Carbon Fiber Composites: Implications for structural design;
Module 6: Miscellaneous Topics (5 hrs)
Transparencies: glass, acrylic, polycarbonate, laminated Sandwich Materials;
Joining- Fasteners and adhesives (materials);
Corrosion and Stress Corrosion;
Coatings: Corrosion protection, thermal barrier, Stealth, Paints;
Case study example of an aircraft structural component(s); Future directions
Post-graduate students in Aerospace Engineering specialising in structures stream and also those interested in lightweight structural materials from other allied branches of engineering.
Senior level B Tech students can also take this course if interested in lightweight materials, and if equipped with background of subjects such as strength of materials and /or solid mechanics.
Basic familiarity with common terms used in aircraft structures (such as wing, fuselage, frame, bulkhead, ribs, spars, aerofoil, etc) is expected of all students.
Outcomes of this Course
Will equip the students with essential knowledge of structural materials used in aircraft, implications of their use in structures and ability to make suitable choices for various parts of airframe or other lightweight structures.