Laminate Splice Strap Stiffness for Fatigue Life
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Solution Overview
Problem
Laminates of bonded adhesive layers and metal sheets suffer from internal stresses during manufacturing, which negatively impact their strength and fatigue life, particularly at low temperatures and with thick or stiff metal layers, limiting their performance in structural applications like aircraft.
Innovation Solution
A laminate design featuring a splice strap with a lower bending stiffness than the spliced metal sheets, connected across the splicing region, which improves fatigue life by reducing stress concentrations and enhancing the laminate's structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If thick and/or stiff metal layers are used, then structural strength is improved, but internal stresses increase and fatigue life decreases
Solution Approach 1:
The invention changes the stiffness parameter of the splice strap relative to the metal sheets by controlling the thickness ratio. The splice strap has a reduced stiffness parameter (Es*t3)strap layer compared to the spliced metal sheets, which reduces stress concentrations and internal stresses while maintaining structural strength. This parameter optimization allows thick metal layers to be used without compromising fatigue life.
Solution Approach 2:
The invention uses a composite structure combining metal sheets with a splice strap made of fiber-reinforced adhesive or metal. This composite approach allows the splice strap to have different mechanical properties than the metal sheets, specifically lower bending stiffness, which helps mitigate internal stresses and improve fatigue life while maintaining overall structural strength.
2Adaptability or versatility
If low temperature operation is considered, then environmental adaptability is improved, but internal stresses increase and strength decreases
Solution Approach 1:
The invention optimizes the stiffness parameter of the splice strap to be lower than that of the metal sheets, which reduces thermal stress concentrations. This parameter change allows the laminate to better accommodate temperature variations and maintain strength under low temperature conditions while preserving environmental adaptability.
3Strength
If splice strap with high bending stiffness is used, then structural strength is improved, but stress concentrations increase and fatigue life decreases
Solution Approach 1:
The invention inverts the conventional approach by reducing the bending stiffness of the splice strap relative to the metal sheets. The reduced stiffness parameter (Es*t3)strap layer < (Es*t3)spliced layer minimizes stress concentrations at the splice region while maintaining adequate structural strength, thereby improving fatigue life.
Solution Approach 2:
The invention applies different stiffness characteristics to different parts of the laminate structure. The splice strap has locally reduced bending stiffness compared to the metal sheets, which optimizes stress distribution in the splice region and improves overall fatigue performance while maintaining structural integrity.
Data Source
AI summary
Described is a laminate, including a stack of mutually bonded adhesive layers and metal sheets. The laminate includes abutting and/or overlapping metal sheet edges that extend along a length direction within a splicing region. A splice strap is connected to the laminate at an outer surface of the laminate across said splicing region. The splice strap includes one layer of fiber-reinforced adhesive or of metal sheet, or stacked layers of fiber-reinforced adhesive and/or metal sheets. A widest splice strap layer is connected to the laminate over a transverse distance of at least 5 times the widest strap layer thickness, and the widest strap layer has a lower bending stiffness than the bending stiffness of one of the spliced metal sheets.