AS3020: Aerospace Structures
Jul-Nov, 2025
Table of Contents
Introduction
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Figure 1: Course Textbook: "Aircraft Structures for Engineering Students", T.H.G. Megson
Instructor, TA, and the basics
- Dr. Nidish Narayanaa Balaji
- nidish@iitm.ac.in, Room 139 AE building
- TA: TBD
- Textbook Reference: "Aircraft Structures for Engineering Students", T.H.G. Megson
Some Planning
The lectures will be split into seven modules:
SNo. Topic Lectures Assignments 1 Design of Aircrafts 3 1 2 Aircraft Materials 3 1 3 Elasticity 6 1 4 Bending of Beams 6 1 5 Torsion of Beams 5 1 6 Variational Mechanics 5 1 7 Structural Stability 4 1 Total 32 7
- We have a total of 53 working days ahead of us. The weekly splitup is:
- 3 Lectures: ~39 in total
- 1 Tutorial With Faculty: ~13 in total
- 1 Extended Tutorial With TA: ~13 in total
Evaluation Rubrics
- One assignment will be given for each module due in one week from
the date of posting.
- Each assignment will include 2 numerical/analytical exercises and one reading exercise.
Two Quizzes and an End Sem occupy the examination portion.
Evaluation Assignments Quizzes End-Sem Weightage 30% 30% 40%
Policies
Honor Code Policy
You are required to sign an honor code for each submission, failing
which evaluation will not be done.
Honor Code
Upon my honor I state that I have received no unauthorized support and can attest that the submission reflects my understanding of the subject matter.
- Attendance Policy
- We will enforce the institute's 75% attendance policy.
- No one will be turned away from class, but the time of entry will be logged in the attendance application.
- Attendance will be computed based on total minutes spent in class divided by 50 minutes.
- Late Submission Policy
- No late submissions will be encouraged. If you miss the deadline, you miss the submission.
- Exceptions will be considered only if I receive written communication through Moodle before the submission date.
- Communication Medium
- Moodle will be used as the primary mode of communication for the class. You can also write emails, but I prefer moodle.
Module 1: Design of Aircrafts
Figure 2: Reference textbook for aircraft design overview
Overview
Figure 3: A400m structure
Figure 4: Fan from my home
- Fuselage construction
- Stressed skin design
- monocoque, semi-monocoque, etc.
- Pressurized vs un pressurized design
- Stringers and stiffeners.
- Wing construction
- Shape requirements: lift generation from airfoil.
- Wing ribs, spars, etc.
- Loads on the different members.
- Load distribution. Discuss loads for different maneuvers.
- Load envelopes (V-n diagrams).
- Relate global loads to local loads on members.
- Airworthiness.
- Joining Processes
- Screwing, Bolting, Riveting, Welding.
- Rivets over bolts: blind riveting, resistance to vibration, "permanence", etc.
- Riveting process.
- Bolt-load distribution calculations.
- Other joining methods.
Note: The following objects have the same drag (according to laminar simulation)!
Useful Links
Fastening
Practice Problems
- Chapter 12 Problems in Megson.
- Aircraft FBD from Chapter 14 in Megson.
Module 2: Aircraft Materials
Overview
- Understanding the stress-strain curve.
- Elastic regime, plastic yield, proof load, failure, elongation at failure, toughness, etc.
- Strain hardening.
- The need for alloys.
- Show dramatic difference between raw Al and Al-alloy. Raw Fe & steels.
- Outline basic considerations.
- Examples of some common alloys with historical context.
- Aluminum Alloys
- Aluminum-Copper (Al-Cu) (High strength-to-weight ratio)
- Aluminum-Magnesium (Al-Mg) (Good corrosion resistance but cracks)
- Aluminum-Silicon (Al-Si) (Machinability)
- Titanium Alloys
- Titanium-Aluminum (Ti-Al) (High specific properties)
- Nickel-based Superalloys (High temperature components)
- Nickel-Chromium, Nickel-Aluminum
- Fatigue
- Failure at stress levels way below yield through repeated application.
- Show S-n curves. Contrast behavior of Steel and Al-alloys.
- Creep
- Gradual increase in strain for fixed load
- Fundamentally a high-temperature phenomenon
- Phase Diagrams
- Binary
- Cu-Ni
- Eutectic
- Pb-Sn
- The Iron-Carbon System
- Equilibrium phases: $α$-Ferrite, $γ$-Austenite, $δ$-ferrite, Cementite (Fe$_3$C)
- Non-equilibrium phases: Bainite, Martensite
- Binary
Useful Links
Practice Problems
- Only concepts. Chapters 11, 15 in Megson.
- Fe-C phase diagram.
Module 3: Elasticity
Overview
- Fundamentals
- Use the stress-strain curve and go into elasticity.
- Strain
- Introduce strain. Constitutive relationship.
- Strain compatibility.
- Stress
- Derive stress-balance => governing equations.
- Stress Mohr's circle.
- Constitutive Relationships
- Thermo-elasticity outline.
- Introduction to 2D Problems. Will revisit in Module 6.
Practice Problems
- Chapter 1 problems in Megson.
- Chapter 1-3 problems from Sadd.
Module 4: Bending of Beams
Figure 5: An I-section beam subjected to 3-point bending
Figure 6: sigma12 section strains for an I section under bending
Figure 7: sigma13 section strains for an I section under bending
Figure 8: Analytical shear flow predictions for an I section beam
Figure 9: Shear flow and Shear Centre calculation for a C-sectino
Overview
- Motivate by applications (wings, wing spars, etc.).
- Beam theory assumptions and justifications (stringer-stiffeners, shape-preservation).
- Unsymmetrical bending of solid beams (wings).
- Shear of thin-walled beams (wing sections).
- Open sections, closed sections.
- Multi-cell closed/open combination sections.
Useful Links
- Course Notes by Prof. Massoud Rais-Rohani
- Code_Aster
- files/mod4/Isection.hdf: Salome_Meca file for 3-point bending analysis of an I-Section built using solid brick elements (to visualize shear flow).
- files/mod4/ShearLag1.hdf: Salome_Meca file for the shear lag examples with and without cutout.
- files/mod4/TSection.hdf: Salome_Meca file for a canilevered T-section beam built using plane stress elements (to visualize effects of tip point loads applied at shear center and at centroid).
Practice Problems
- Chapter 16, 17, 20 problems in Megson.
- Chapter 5 problems from CT Sun.
Module 5: Torsion of Beams
Overview
- Solid section torsion.
- Prandtl stress function.
- Warping of section.
- Discussion of physicality.
- Mention St. Venant's principle, will revisit in Module 6.
- Thin-walled torsion.
- Closed section, open section.
Useful Links
- FreeFem++ Scripts numerically solving the Poisson problem for both
stress function and warping for different solid sections.
- a_ellipse.edp: Ellipse section
- b_rectangle.edp: Rectangle section
- c_triangle.edp: Triangle section
- g_thinwalledrect.edp: (Closed) Thin-walled rectangular section
- h_csect.edp: (Open) C section
- Code_Aster Tutorial for Solid Section Torsion
- ellbeam.hdf : HDF file for running the FEA
- Wxmaxima sheet for two cell section
- Advanced Solid Mechanics Notes from Prof. U. Saravanan
- Structural Mechanics Notes, MIT AeroAstro
- Steel Construction Notes
Practice Problems
- Chapter 18, 19 problems from Megson.
- Chapter 4 problems from CT Sun.
Module 6: Variational Mechanics
Overview
- Principle of Virtual Work
- Primer on Calculus of Variations
Class Slides
Practice Problems
- Chapter 4, 5 problems in Megson (only straight beam type).
Module 7: Structural Stability
Figure 10: Animation of post-buckling of pinned-pinned/roller supported beam.
Overview
- Column buckling.
- Derive governing equation for column-buckling.
- Sturm-Liouville ODE.
- Euler buckling analysis.
- Plate buckling.
- Write down governing equation (derivation left for self study).
- Show examples from aircrafts.
- Possibility and avenue for thermal buckling from governing equations.
Class Slides
Useful Links
Practice Problems
- Chapter 7, 8, 9 problems from Megson (only whatever was covered in class).
- Class notes/assignment type problems.