Sinusoidal Web Bulb Stiffener Resists Shear Buckling
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Solution Overview
Problem
Bulb-shaped composite stringers are susceptible to shear buckling and failure under side loads, leading to increased production costs and weight due to the need for thicker webs to enhance resistance, which compromises their lightweight and cost-effective manufacturing advantages.
Innovation Solution
Incorporating a sinusoidal or non-linear web profile into the bulb stiffener design, which provides enhanced lateral stiffness and resistance to shear stresses without significantly increasing material thickness, thereby improving the stringer's ability to withstand abuse loads and side loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a thicker web is used to increase resistance to side loading, then the stringer's resistance to shear buckling improves, but the weight and production cost increase
Solution Approach 1:
The web is formed with a sinusoidal curvature profile instead of a straight linear profile. This curvature increases the moment of inertia and lateral stiffness of the web, providing enhanced resistance to shear buckling and side loads while maintaining a thin web thickness, thus avoiding the weight penalty associated with thicker straight webs
2Strength
If a thicker web is used to enhance resistance to side loading, then the stringer's lateral stiffness improves, but the production cost increases
Solution Approach 1:
The sinusoidal curvature of the web provides enhanced lateral stiffness and resistance to side loading without requiring increased web thickness. This allows the stringer to meet performance requirements while maintaining the cost advantages of thin-web construction and automated manufacturing processes
Solution Approach 2:
The web geometry is modified by changing its profile from linear to sinusoidal, altering the distribution of material along the web height. This parameter change increases the moment of inertia and lateral stiffness while keeping the web thickness constant, thereby improving performance without increasing material usage or production cost
3Reliability
If the web thickness is increased to withstand abuse loads, then the stringer's resistance to failure improves, but the lightweight advantage is compromised
Solution Approach 1:
The sinusoidal curvature profile of the web increases its bending stiffness and resistance to abuse loads through geometric reinforcement rather than material addition. This allows the thin web to withstand higher loads and abuse forces while maintaining the lightweight characteristics essential for aircraft applications
Data Source
AI summary
An improved composite stiffener and methods and tooling used to form the same. The stiffener includes one or more base flanges, a composite rod extending in an axial direction, a bulb cap surrounding the composite rod, and an upright web extending from the one or more base flanges to the base cap. The upright web includes a non-linear profile in the axial direction providing the improved lateral stiffness. The method includes providing tooling including a first compression tool extending in the axial direction and including a first web portion having a non-linear profile, and a second compression tool extending in the axial direction and including a second web portion having a non-linear profile. Plies are placed within the tooling and compressed such that at least a portion of plurality of plies are compressed in the web forming portion thereby forming a web of the bulb stiffener having a non-linear profile.