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22-Mec-B9 Advanced Engineering Structures: December 2018

Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)

  1. Question 1 Thermal stress in a two-segment rod between rigid supports
  2. Question 2 Yield prediction under a three-dimensional stress state
  3. Question 3 Unsymmetrical bending of a thin-walled channel
  4. Question 4 Shear centre and shear flow in an idealised nose box
  5. Question 5 Torsion of a three-cell thin-walled wing box
  6. Question 6 Sizing a square bar under combined axial force and torque
  7. Question 7 Inspection interval from fatigue crack growth
  8. Question 8 Stresses in a unidirectional composite skin panel

Start with Question 1 →

Paper format. National Exams, December 2018 — 16-Mec-B9 Advanced Engineering Structures. Three hours, open book, any non-communicating calculator permitted. Eight questions are printed and the rubric states that any five constitute a complete exam paper, with all problems of equal total value (20 marks each). All eight are worked here. Marks for the individual parts are those printed inside each problem.

Reference texts. T. H. G. Megson, Aircraft Structures for Engineering Students, 6th ed. (thin-walled open and closed sections, shear flow, shear centre, multi-cell torsion, crack growth, laminated plates); A. P. Boresi and R. J. Schmidt, Advanced Mechanics of Materials, 6th ed. (yield criteria, unsymmetrical bending, torsion of non-circular sections); N. E. Dowling, Mechanical Behavior of Materials, 4th ed. (Paris law, linear elastic fracture mechanics); R. C. Hibbeler, Mechanics of Materials, 10th ed. (statically indeterminate axial members, thermal stress).

Check: the direction of the 500 N load in Question 3. On the isometric view the 500 N arrow lies antiparallel to the direction in which both flanges project (both make the same 28° angle with the horizontal on the drawing, in opposite senses). The solution therefore takes the 500 N as acting away from the flange tips, so that its bending contribution puts the lower-flange tip A into tension and adds to the contribution of the 900 N load. Had the arrow been read the other way, the stress at A would be 122.5 MPa compressive instead of 155.3 MPa tensile; every section property and both moment components are unchanged, so only the sign of the 500 N load’s contribution (138.9 MPa of the 155.3) moves.

Check: two rubric details not printed on the paper. (i) Question 8 gives no mark split for its parts (a) and (b); an even 10 + 10 is assumed, consistent with every other two-part question on this sitting. (ii) In Question 4(b) “120 mm to the left of the shear center” is taken as 120 mm further forward, i.e. towards the semicircular nose, which is what “left” means on the printed figure. Moving the load the other way would simply reverse the sign of the superposed torsional flow.