Aircraft Laminated Glazing Composite Interlayer Impact Resistance
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Solution Overview
Problem
Aircraft windshields face challenges in withstanding hail and small bird impacts due to the thickness constraints of glass, which affects mass and resistance, leading to frequent ruptures.
Innovation Solution
A laminated glazing design featuring a structural transparent substrate bonded with an adhesive interlayer comprising a combination of flexible and stiff polymer materials, where the interlayer includes a flexible first polymer material with a relaxation modulus of up to 2 GPa and a stiff second polymer material with a modulus of at least 4 GPa, allowing for a thinner glass sheet while enhancing impact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the thickness of the outer glass is reduced to decrease mass, then the mass of the glazing is reduced, but the resistance to hail impact is intrinsically lower
Solution Approach 1:
The patent applies composite materials by combining two polymer materials with different mechanical properties (a flexible first polymer material and a stiff second polymer material) in the interlayer. This composite structure allows the interlayer to provide both flexibility for stress relief and stiffness for impact resistance, enabling the use of thinner glass while maintaining hail resistance.
Solution Approach 2:
The patent applies local quality by creating an interlayer with spatially varying properties - the first polymer material provides flexibility in certain regions while the second polymer material provides stiffness in other regions. This localized differentiation of material properties allows the system to simultaneously address both weight reduction and impact resistance requirements.
2Weight of moving object
If the thickness of the outer glass is reduced, then the mass of the glazing is reduced, but the glass is more prone to rupture under hail or small bird impact
Solution Approach 1:
The composite interlayer structure combines flexible and stiff polymer materials to provide both weight reduction and enhanced reliability. The stiff second polymer material specifically contributes to rupture resistance under discrete impacts while the flexible first polymer material manages thermomechanical stresses.
Solution Approach 2:
The patent applies beforehand cushioning by designing an interlayer with predetermined mechanical properties that cushion and absorb impact energy before it reaches the glass. The interlayer acts as a pre-positioned protective element that mitigates the effects of hail or bird impacts on the thinner glass sheet.
3Shape
If a thick mat of interlayer adhesive is used to maintain aerodynamic continuity, then aerodynamic continuity is maintained, but the glass bends excessively under hail impact possibly until rupture
Solution Approach 1:
The patent resolves this contradiction by using composite materials in the interlayer - the stiff second polymer material provides resistance to bending under impact while the flexible first polymer material maintains aerodynamic continuity. This composite approach allows the interlayer to simultaneously provide structural support and aerodynamic smoothness.
Solution Approach 2:
The patent applies parameter changes by modifying the mechanical properties of the interlayer through material composition rather than thickness alone. By changing the relaxation modulus parameters of the polymer materials (with the stiff material having E≥4 GPa and flexible material having E≤2 GPa), the system achieves both aerodynamic continuity and impact resistance without excessive glass bending.
4Strength
If a stiff polymer material is used in the interlayer to increase impact resistance, then resistance to hail impact is improved, but thermomechanical stresses in the glazing increase
Solution Approach 1:
The patent applies local quality by positioning the stiff second polymer material specifically in regions where impact resistance is needed, while the flexible first polymer material is positioned to manage thermomechanical stresses. This spatial differentiation allows each material to perform its optimal function without the downsides of the other.
Solution Approach 2:
The composite interlayer structure combines materials with complementary properties - the stiff second polymer material (E≥4 GPa) provides hail impact resistance while the flexible first polymer material (E≤2 GPa) accommodates thermomechanical stresses, allowing both requirements to be satisfied simultaneously.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution increases the stiffness of the adhesive interlayer, limiting glass deformations and impact velocity, enabling the use of thinner glass sheets that reduce mass while maintaining or improving resistance to hail and small bird impacts, thus reducing the likelihood of breakage.
Implementation Method 1
a flexible first polymer material having a relaxation modulus at most equal to 2 GPa for relaxation times at least equal to 10 min
Implementation Method 2
a stiff second polymer material having a relaxation modulus at least equal to 4 GPa, for time constants at most equal to 0.1 millisecond
Implementation Method 3
bonded to a glass sheet with a thickness of between 0.5 and 4 mm, intended to constitute an outer surface of the laminated glazing, by means of an adhesive interlayer
Data Source
AI summary
A laminated glazing includes a structural transparent substrate bonded to a glass sheet of 0.5 to 4 mm, intended to constitute an outer surface of the laminated glazing, by an adhesive interlayer of 4 to 10 mm, which successively includes 0.25 to 2.5 mm of a flexible first polymer material having a relaxation modulus at most equal to 2 GPa for relaxation times at least equal to 10 min, at temperatures at least equal to −40° C., in contact with the glass sheet, then a stiff second polymer material having a relaxation modulus at least equal to 4 GPa, for time constants at most equal to 0.1 millisecond and temperatures at most equal to 40° C.