01 / Explore composites
Stiff fibers carry load. A surrounding matrix holds them together and transfers load between them. Changing the ingredients and their arrangement gives engineers another way to design.
From aircraft to bicycles, composites help designers balance stiffness and mass. The exercises do not reproduce a manufacturer’s proprietary design or certify its performance. No manufacturer endorsement is implied.
Joby identifies its airframe as carbon-fiber composite. Manufacturer background ↗
Ask: How does stiffness per unit mass influence a weight-sensitive structure?
Explore fiber content →U.S. Air Force / Harlan Huntington · public domain in the United States. Photo source
Boeing reports that composites make up approximately 50% of the 787 airframe by weight. Manufacturer background ↗
Ask: What happens when a laminated cylinder carries pressure in two directions?
Explore a published cylinder study →Melvin Loi · CC BY-SA 2.0. Display cropped; image adaptations share the same license. Photo source · License
Carbon fibers, resin and layer placement let bicycle designers tailor composite parts. Trek describes this construction for frames, wheels and handlebars; the pictured frame is Edelsten, not Trek. Manufacturer background ↗
Ask: How does changing ply direction change the response to different loads?
Explore the laminate layup →Markus Spiske · CC0 1.0. Photo source · License
Try it yourself: build a light, stiff strip ↓
Pick any block to jump back and forth. Your design stays with you. Try one change, see what happens, then choose your next move.
Your challenge: make a 120 × 25 mm strip—about the length of a small ruler. Hold one end still and push down on the other with 0.5 N (about the weight of 50 g). Can you keep the bend below 2 mm and the strip’s mass below 7 g? The strip’s length, width and push stay the same.
Current design: Glass fiber / resin · 60% fiber → 8 plies · 1.00 mm → bending study. Changes upstream automatically update the later stages.
Start with glass fibers held together by resin. One thin layer of this mixture is called a lamina. A stack of bonded layers is a laminate.
Resin: 40% · Voids: 0%
A bigger stiffness number means the material stretches less under the same pull. Lower density means an equal-sized piece has less mass.
This score compares stiffness with density. Higher means more stiffness for the same mass in a straight bar pulled along its length.
At equal axial stiffness and length, this ideal composite bar needs 115% of the aluminum bar’s mass, if its cross-sectional area can change freely.
This is not a wing, bicycle or aircraft prediction. Strength, buckling, joints and minimum thickness may govern a real design.
Axial modulus = fiber fraction × fiber modulus + resin fraction × resin modulus. Density follows the same volume-weighted rule. Specific modulus = modulus ÷ density.
For a bar, axial stiffness = EA/L. At equal length and axial stiffness, mass ratio = (composite density / composite modulus) ÷ (metal density / metal modulus).
Illustrative values, not manufacturer specifications: Glass fiber 73 GPa, 2550 kg/m³; resin 3.5 GPa, 1200 kg/m³; Aluminum 70 GPa, 2700 kg/m³.
Perfect bonding, aligned continuous fibers, uniform strain, linear elasticity, no voids and room-temperature behavior. This rule does not predict transverse stiffness, failure, fatigue or process effects. More fiber is not automatically manufacturable or better.
∑ Micromechanics theory · MIT OpenCourseWare: Introduction to CompositesNext challenge: why do fibers in several directions change the behavior? Explore the layup exercise →
Website teaching study only. Workbench links open the existing exercises; they do not transfer or save this trial into the master database. This page’s trials reset when you reload.
High stiffness relative to density can help in mass-sensitive structures. The benefit depends on the load, shape and fiber direction.
Try stiffness-to-weight ↑Trade-off: a stiff material is not necessarily strong, damage tolerant or stable against buckling.
Fiber orientation lets a laminate favor axial, transverse or shear response. Combining orientations makes this a structural design decision.
Change the layup →Trade-off: off-axis loading, free edges and interfaces can become critical. Delamination and impact damage need attention.
Fiber architecture and resin choice open different ways to form a component. Thermal history and moisture exposure can change its response.
Explore a thermal cycle →Trade-off: production cost, inspection, joining, repair and end-of-life recovery belong in the comparison.
Read further: US Department of Energy: lightweight materials and manufacturing challenges · ∑ Laminate assumptions and limitations.
The website builds intuition. Workbench is where you choose traceable material records, define geometry and loads, run the full available models and examine their limits. These links use the existing shared curriculum—not a separate set of exercise databases.
Workbench availability: released models, inputs and compatible study paths. The wider theory library includes reference formulations not available in every Workbench solve.
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