Select face sheet and core material combinations to instantly calculate bending stiffness, maximum deflection, face sheet stress, core shear stress, face wrinkling load, and safety factors.
What exactly is a "sandwich panel" and why is it so special in engineering?
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Basically, it's a lightweight structure with two strong, thin face sheets bonded to a thick, lightweight core. It's like an I-beam in panel form! The faces carry bending stress, while the core keeps them apart to maximize stiffness. In practice, this gives you incredible strength-to-weight ratio. Try moving the "Face Thickness" slider in the simulator above—you'll see how a tiny increase dramatically reduces deflection.
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Wait, really? So the core material doesn't matter much for bending? Why can't I just use a solid piece of the face material?
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The core is crucial! It provides shear resistance to keep the faces from sliding past each other. A solid piece would be incredibly heavy and wasteful. For instance, in an aircraft floor panel, a solid aluminum sheet would be too heavy, but an aluminum skin with a honeycomb core is both light and stiff. Change the "Core Material" in the simulator from foam to a stiffer option and watch the "Shear Deflection" component drop—that's the core's job.
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The results show a "Wrinkling" stress limit. What is that, and when does it become a problem?
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Great question! Wrinkling is a local buckling failure where the thin face sheet crumples into the soft core, like pushing on a soda can. It's a common failure mode when you use very thin, stiff faces with a soft core. A common case is in composite boat hulls under high point loads. In the simulator, if you select a very stiff carbon fiber face and a soft foam core, then crank up the load, you'll likely hit the wrinkling limit before the bending stress limit.
Physical Model & Key Equations
The bending stiffness (D) of a sandwich panel determines how much it resists bending under load. It depends heavily on the face material stiffness and the distance between the faces, which is why a thicker core is so effective.
$$D = \frac{E_f t_f (t_c+t_f)^2}{2}$$
Where $E_f$ is the Young's modulus of the face material, $t_f$ is the face thickness, and $t_c$ is the core thickness. The term $(t_c+t_f)^2$ shows why separating the faces is key—stiffness increases with the square of that distance.
The total deflection under a uniformly distributed load (UDL) has two parts: bending deflection (from face stretching/compressing) and shear deflection (from core deformation). For short spans or soft cores, shear deflection dominates.
Here, $q$ is the load intensity, $L$ is the span, $D$ is the bending stiffness, $A_g$ is the shear area (≈ panel width × core thickness), and $G_c$ is the core's shear modulus. The first term is classic beam bending; the second is the critical sandwich panel addition.
Frequently Asked Questions
If the material data is not in the list, users cannot add arbitrary materials. Please select and substitute an existing material with similar physical properties. Since significant differences in Young's modulus or shear modulus can affect calculation accuracy, it is recommended to choose a material with close physical properties.
For materials with low core shear stiffness (such as foam or honeycomb), ignoring shear deformation will underestimate the actual deflection. Errors become particularly large for short-span, thick panels. Therefore, the calculation formulas in this tool must always include shear deformation for evaluation.
If the safety factor is below 1, first increase the face sheet thickness or switch to a higher-strength face sheet material (e.g., CFRP). Next, increasing the core thickness improves bending stiffness and is effective in reducing stress. If the core material's shear strength is insufficient, consider switching to a higher-density core.
Yes, the physical model of this tool is based on general bending and shear theory for sandwich panels, so it is also applicable to building floor panels and wall materials. However, since construction involves additional requirements such as creep under long-term loads and fire resistance, please use the results as reference values for structural design.
Real-World Applications
Aerospace Structures: Aircraft floors, wing panels, and satellite doors use aluminum or carbon fiber faces with aluminum honeycomb or foam cores. The simulator's load type "UDL" mimics the pressure on an aircraft floor from passengers and cargo, where minimizing weight is absolutely critical for fuel efficiency.
Wind Turbine Blades: Modern blades are massive sandwich structures with composite faces (fiberglass/carbon) over balsa wood or PVC foam cores. Engineers use analysis like this to optimize the core thickness along the blade's length, balancing stiffness against weight and material cost.
Marine & Transportation: High-speed boat hulls, train interior panels, and truck trailers use sandwich panels for a stiff, lightweight body. The "Wrinkling" calculation is vital here—slamming into waves or cargo impact can create local stresses that cause face wrinkling if the panel isn't designed correctly.
Building Facades & Architecture: Curved architectural cladding and insulated building panels often have metal faces over a rigid insulating foam core. The analysis helps determine the maximum panel span between supports to avoid excessive sagging or visible deflection, which you can explore by changing the "Span L" parameter.
Common Misconceptions and Points to Note
First, there is a misconception that "increasing stiffness solves everything". While increasing the core thickness (tc) dramatically raises the bending stiffness D, it also increases weight. For instance, in aircraft interiors, even if stiffness is doubled, a 30% weight increase would make the design unacceptable. The essence of design is optimizing the trade-offs between stiffness, strength, and cost within given weight targets.
Next, blindly trusting material data "nominal values". The elastic modulus and shear modulus you input into the tool are often catalog values from material manufacturers. However, in actual products, these values can vary by 10-20% due to manufacturing processes (e.g., ply angles or resin content in CFRP) or environmental conditions (temperature, humidity). A practical approach is to run simulations using a reduced value, applying a factor of 0.8 to 0.9 to the nominal value for a safety margin.
Finally, assuming "buckling only means global buckling". The "face wrinkling" calculated by this tool is a local phenomenon, but there are various other buckling modes such as "global bending buckling" and "core shear buckling". Especially for panels with a long span (L) and a soft core, global buckling may occur first. Don't rely on a single metric; you need to consider multiple limit states.
Enter face sheet thickness (tf) in millimeters—typical glass-fiber composite faces range 3–6 mm
Input core thickness (tc)—polyurethane or PVC foam cores typically 25–100 mm depending on load class
Specify panel length (L) and width (b) in millimeters for your application geometry
Select material properties from dropdown menus: E-modulus for face sheets (epoxy-glass ~35 GPa, carbon ~150 GPa) and core shear modulus (polyurethane ~15 MPa, PVC ~5 MPa)
Click Calculate to generate bending stress, shear stress, and deflection results instantly
Worked Example
A marine deck sandwich panel with glass-fiber faces (E=35 GPa, tf=4 mm each side), PVC foam core (Gc=5 MPa, tc=60 mm), length L=2400 mm, width b=1200 mm, and distributed load q=2.5 kN/m². Calculation yields midspan deflection δ=12.3 mm, face sheet stress σf=145 MPa (below 250 MPa allowable for epoxy-glass), and core shear stress τc=0.8 MPa. Panel passes design criteria with 1.7 safety margin against face failure.
Practical Notes
Core thickness dominates bending stiffness—doubling tc from 50 to 100 mm reduces deflection by ~75% while adding minimal weight for aerospace or wind turbine applications
Asymmetric face sheets (e.g., 2 mm carbon + 5 mm glass) require separate E-values; input weighted average or use advanced solver
Verify core shear strength against calculated τc; PVC foams fail abruptly at 2–3 MPa, unlike gradual face sheet yielding
Temperature effects: polyurethane core Gc drops 40% at +60°C; adjust input for hot-climate marine or automotive uses