Course Description
Course Objectives:
This course is specifically focused on aircraft structural materials with the objective to
- Impart knowledge about important materials used in airframe: their nomenclature, their constitution and treatments and the underlying scientific concepts, properties and usage as well as some of the processes commonly used in their treatments or for making airframe parts.
- Develop understanding of relationship of materials and processes with structural performance.
Note : Focus on Airframe, not Engine. However, an overview of engine materials is included.
Course Plan : The course is planned in 6 modules to be covered in about 40 standard lecture-hours, as given below in the Course Content. It will cover metallic materials such as Al-alloys, Ti-alloys and aircraft steels as well as composite materials, especially laminated carbon-epoxy composites. Some other miscellaneous materials will also be covered. 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.
Course Content
Module 1: Introduction and Overview : Aircraft Materials and Processes (3)
- 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; 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 aircraft structural materials (7)
- 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: Metallic Materials - Science behind Alloying (6)
- 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)
- 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)
- Introduction to Composites: A brief overview of composites - Polymer matrix, Metal-matrix Ceramic-Matrix; Fibres and Resins; Laminated composites; Sandwich composites, Fiber-metal laminates.
- Raw materials: Fibers - Carbon, Glass, Aramid, 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)
- Transparencies: glass, acrylic, polycarbonate, laminated Sandwich Materials;
- Joining- Fasteners and adhesives (materials);
- Corrosion and Stress Corrosion;
- Coatings: Corrosion protection, thermal barrier, Stealth, Paints;
- Future directions
Course Audience
Post-graduate (Masters, Doctoral) students with background and interest in aircraft.
Final year B Tech students with solid background of aircraft structures.
Outcomes of this Course
Equip the students with awareness and basic knowledge of
- aircraft structural materials, both metallic and composites, their treatments and usage
- relationship of materials with aircraft structural performance and issues involved in choice of materials
- unresolved issues and research areas