Composite Joint Tapered Ends Stress Concentration Reduction
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Solution Overview
Problem
Existing composite joints in elongate composite components, such as wind turbine blades, face stress concentration issues at the thin ends due to resin starvation and brittle adhesive vulnerabilities, leading to potential failure and peeling problems.
Innovation Solution
Modifying the properties of the composite material and adhesive in the vicinity of the thin ends by adjusting fibre layer thickness, fibre/resin volume ratio, material type, and adhesive properties to reduce stress concentrations and prevent resin starvation, including the use of different materials and additives like elastomeric compounds for improved toughness and self-healing capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If a shallow scarf angle is used to reduce stress concentration, then stress distribution is improved, but the longitudinal extent of the joint becomes significant and it becomes vulnerable to failure at thin ends
Solution Approach 1:
The patent applies different material properties at different locations within the composite component. Specifically, the thin end region (within 5mm of the end) has modified properties including higher resin content (60-80% by volume) compared to the rest of the component, and the use of elastomeric compounds or self-healing capsules in this specific region to prevent and heal cracks, thereby locally addressing the stress concentration vulnerability without affecting the entire joint length
Solution Approach 2:
The patent changes the physical and chemical parameters of the composite material in the thin end region. This includes modifying the fibre/resin ratio to increase resin content, changing the mechanical properties through elastomeric compounds (increasing toughness and flexibility), and implementing self-healing mechanisms that activate when cracks form, thereby dynamically adjusting the material's stress-bearing capacity in the critical thin end region
2Reliability
If resin is used to impregnate fibres in the thin end region, then fibre wetting is improved, but resin may flow away during curing causing resin starvation
Solution Approach 1:
The patent incorporates elastomeric compounds and self-healing capsules into the resin matrix during the manufacturing process, before the component is put into service. This preliminary action ensures that the stress-absorbing and crack-healing mechanisms are already in place in the thin end region, preventing resin starvation and fibre debonding before they can occur during operation
Solution Approach 2:
The elastomeric compounds act as a cushioning mechanism that absorbs stress concentrations before they can cause fibre-matrix debonding or resin starvation. The self-healing capsules provide beforehand protection by automatically repairing cracks as they form, preventing the propagation of damage that would lead to resin starvation in the thin end region
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 effectively reduces stress concentrations and enhances joint integrity at the thin ends, improving the quality and reliability of the composite joint without significantly increasing costs, by distributing stress more evenly and preventing defects.
Implementation Method 1
the components being joined at their tapered ends by an adhesive
Data Source
Figure 1~3
Figure 4~5
Figure 6A~6C
AI summary
Composite member comprising first and second elongate composite elements (1,2). Each element (1,2) has a wedge shaped end (6) with a complimentary tapered end surface. At least one of the elements (1,2) is formed of a stack of fibre layers (7) impregnated in resin. The tapered end surface is formed by each fibre layer (7) extending longitudinally progressively further than the adjacent layer towards the thin end of the wedge at which the fibre layers (7) have the greatest longitudinal extent. The elements (1,2) are joined at their tapered ends (6) by an adhesive. The properties of the cured composite material of the at least one component (1,2) and/or the properties of the adhesive are different in the vicinity of the thin end of the wedge (6) as compared to the rest of the tapered surface in order to reduce the stress concentrations in this region.