Acrylic and plastic deflection calculator
Use our engineering plastics deflection calculator (acrylic / PMMA, solid polycarbonate, Dibond, rigid PVC). The tool calculates the actual deflection of a beam/sheet in millimetres based on span length, material thickness and applied point or line load, and checks the structural safety factor.
Kalkulator ugięcia tworzyw Plexi / PMMA
Wartości E orientacyjne (typowe zakresy literaturowe dla tworzyw handlowych). Dibond to płyta kompozytowa (aluminium + rdzeń PE) — jej rzeczywista sztywność różni się od jednorodnego materiału, wynik dla Dibond ma charakter poglądowy. Przy dużych obciążeniach skonsultuj kartę techniczną produktu.
Mechanical properties and Young’s modulus (E) of plastics
The modulus of elasticity (Young’s modulus E) and density are the key parameters determining the stiffness of a plastic sheet under wind, snow, self-weight or point loads:
| Material | Young’s modulus (E) | Density (g/cm³) | Structural application |
|---|---|---|---|
| Acrylic (PMMA) | 3,100 – 3,300 MPa | 1.19 g/cm³ | Display shelves, display cases, machine guards, illuminated signs |
| Solid polycarbonate (PC) | 2,300 – 2,400 MPa | 1.20 g/cm³ | Safety glazing, roof glazing, anti-vandal protection (20x the impact strength of PMMA) |
| Dibond / composite panel | 70,000 MPa (Al layer) | 3.8 kg/m² (3mm thick) | Advertising light boxes, facades, large-format pylons (high stiffness at low weight) |
| Rigid PVC (U-PVC) | 3,000 MPa | 1.42 g/cm³ | Industrial panels, chemical tanks, technical structures |
| PET-G (copolyester) | 2,100 MPa | 1.27 g/cm³ | Thermoforming, clear covers with food-contact certification (FDA) |
| Foamed PVC | 900 – 1,200 MPa | 0.55 – 0.70 g/cm³ | Advertising boards, trade-fair stand construction, lightweight graphics |
When is deflection safe? (Thickness selection criteria)
- SAFE status (deflection < 1.5% of span length): The deflection is not visible to the eye or does not affect aesthetics and mounting stability. Recommended for shop shelves, display cases and canopies.
- ACCEPTABLE status (deflection 1.5% – 3.0% of span): Visible elastic deflection under full load, returning to its original shape once unloaded. Adding a centre support or increasing thickness by 1–2 mm is advisable.
- UNSAFE status (deflection > 3.0% of span): Risk of the sheet coming out of its frame, permanent plastic deformation or cracking under dynamic stress. Requires a thicker sheet or a material change (e.g. from PMMA to Dibond, or added stiffening profiles).
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