Simulic
English

Stresses and stiffening of structures

Design & TechnologyEngineering Drawing & DesignAges 15–16Virtual lab

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Use with my class

Load a rod, post, shelf, shaft or pin in tension, compression, bending, torsion or shear, made of steel, aluminium alloy, pine, acrylic or concrete, and raise the load until it fails: see the stress, the deformation, and where and how it fails (yielding, snapping, buckling, cracking, shearing). Then shape the same strip of sheet as flat, folded, corrugated, ribbed, laminated or webbed and compare its stiffness under the same load through the second moment of area. A lab screen measures the depression of a metre scale clamped at one end or supported at both ends, against load, length and thickness, to find Young's modulus.

Lesson: Forces and stresses in structures; reinforcing and stiffening

What it shows

Structures carry loads through five kinds of stress: tension stretches, compression squashes, bending stretches one face and squashes the other, torsion twists, and shear makes layers slide. Stress is force per area (σ = F/A), and a member fails when the stress reaches the material's strength for that kind of loading; long, thin members in compression buckle earlier. Stiffness depends on shape as well as material: folding, corrugating, ribbing, laminating or adding a web moves material away from the neutral axis and raises the second moment of area I. Values are typical, members ideal, and deflections assume small, elastic bending.

How to use

In Five kinds of stress, choose a kind of stress and a material, set the load, length and size, and press Load until it fails; each failure goes into the table. In Stiffening a sheet, choose a shape and its depth and press Test this shape to compare deflections. In Metre-scale lab, choose the setup and scale, add masses with Hanger mass, press Record reading and use the slope of the graph to find Y.

Parameters you can change

  • Screen Five kinds of stress, Stiffening a sheet, Metre-scale lab
  • Kind of stress (Five kinds of stress) Tension, Compression, Bending, Torsion, Shear
  • Material (Five kinds of stress) Mild steel, Aluminium alloy, Pine (softwood), Acrylic, Concrete (unreinforced)
  • Load F (Five kinds of stress) 1–100000 N
  • Length or span (Five kinds of stress) 0.2–2 m
  • Rod diameter or shelf thickness (Five kinds of stress) 4–40 mm
  • Sheet material (Stiffening a sheet) Aluminium, Steel, Polypropylene, Card
  • Sheet thickness (Stiffening a sheet) 0.5–3 mm
  • Shape (Stiffening a sheet) Flat, Folded, Corrugated, Ribbed, Laminated, Webbed (I-section)
  • Depth of fold, wave, rib or web (Stiffening a sheet) 5–40 mm
  • Layers (Stiffening a sheet) 2–6
  • Layers glued together (Stiffening a sheet)
  • Load at mid-span (Stiffening a sheet) 1–500 N
  • Setup (Metre-scale lab) Cantilever (clamped at one end), Both ends supported, load in the middle
  • Metre scale (Metre-scale lab) Scale A, Scale B, Scale C
  • Length L (Metre-scale lab) 30–90 cm
  • Scale thickness d (Metre-scale lab) 4–8 mm
  • Hanger mass (Metre-scale lab) 0–500 g

Questions to explore

  1. Why does a long thin rod fail at a much smaller load in compression than in tension?
  2. Why does corrugated card bend much less than flat card made from the same sheet?
  3. How does the depression of a cantilever change when its length is doubled?

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