Crease Trough Depth
0.0 µm
Residual plastic deflection
Optical Distortion Angle
0.00°
Max surface specular slope
Peak Bending Strain ($\varepsilon$)
0.47%
UTG tensile threshold: ~1.8%
Crease Visibility Index
Imperceptible
Diffuse ambient condition
Specular Glare & Reflection Distortion Field
Interactive Optical Ray-Tracing View
Hinge Zone: ±12.0 mm Specular Ray Deviation: 0.0 mrad Surface Gloss: 99.4%
Crease Surface Topography Profile ($x$ vs $y$)
W: 18.4 mm · Max: 0.0 µm
Layer Strain & Neutral Axis Distribution
UTG Strain: 0.47%
The Science of the Foldable Display Crease: Why First Impressions Fade

1. Initial Elastic Flatness vs. Viscoelastic Plastic Fatigue

When unboxing a state-of-the-art foldable device like the iPhone Duo or flagship waterdrop-hinge foldables, the screen appears remarkably flat. This is because modern Ultra-Thin Glass (UTG, 30–50 µm) operates well below its elastic limit during single folds. However, displays are composite multi-layer laminates comprising hard protective coatings, UTG/CPI, touch sensors, OLED encapsulation, and Optically Clear Adhesives (OCA). Over tens of thousands of cycles, OCA experiences shear strain hysteresis, adhesive cavitation, and polymer micro-yielding, preventing complete elastic recovery.

2. Hinge Kinematics & Specular Reflection Distortion

Human eyes rarely detect display creases from emissive light (RGB subpixels emitting straight out); instead, creases become glaringly visible through specular reflection of ambient light bars, overhead fixtures, and straight lines. Even a minuscule 15-micrometer trough with a 1.2-degree slope change dramatically bends reflected light rays by over 40 milliradians, breaking specular coherence and creating the characteristic twin-reflection highlight that makes foldables look creased over time.

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