Through-Thickness Reinforcement of Laminated Composites
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Solution Overview
Problem
Laminated composite materials exhibit poor inter-laminar mechanical properties due to challenges in inserting through-thickness reinforcing fibers, such as fiber deflection, splitting, and deformation during conventional stitching or z-pinning processes, which can reduce the effectiveness of reinforcement and in-plane material properties.
Innovation Solution
A method involving heating the composite material to a specific temperature to reduce matrix viscosity, forming holes with a conically tipped needle, and inserting reinforcing fibers through these holes to minimize damage and ensure accurate alignment, with optional ultrasonic energy and surface coatings to facilitate easier insertion and reduce processing time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional stitching or z-pinning is used to insert through-thickness reinforcing fibres, then inter-laminar strength is improved, but fibre deflection, splitting and deformation occur which reduce the effectiveness of reinforcement and in-plane material properties
Solution Approach 1:
The patent applies parameter changes by heating the matrix material to a temperature above its glass transition temperature (Tg), which fundamentally changes the rheological properties of the matrix from a rigid state to a softened, more compliant state. This temperature parameter change allows the reinforcing fibres to be inserted without causing fibre deflection, splitting, or deformation, while still achieving improved inter-laminar strength. The matrix softening reduces resistance to fibre insertion and prevents damage to both the inserted fibres and the existing laminate fibres.
Solution Approach 2:
The patent employs preliminary action by pre-heating the matrix material to a softened state before inserting the through-thickness reinforcing fibres. This preliminary thermal treatment creates optimal conditions for fibre insertion by reducing matrix viscosity and increasing matrix compliance, thereby preventing fibre damage during the subsequent insertion process. The pre-heating step ensures that fibres can be inserted cleanly without causing splitting or deflection, maintaining both fibre integrity and alignment.
2Length of moving object
If a needle with large diameter is used for stitching, then through-thickness reinforcement is achieved, but significant cutting and deformation of laminate fibres occurs reducing in-plane properties by more than 20%
Solution Approach 1:
The patent uses parameter changes by heating the matrix material to a temperature above its glass transition temperature, which transforms the matrix from a rigid state to a softened, compliant state. This parameter change allows the use of larger diameter needles for through-thickness reinforcement without causing significant cutting or deformation of laminate fibres. The softened matrix accommodates the needle passage more easily, preserving in-plane material properties while still achieving effective through-thickness reinforcement.
3Ease of manufacture
If conventional z-pinning is used with chamfered fibres, then insertion is facilitated, but fibres are deflected from desired trajectory by interaction with densely packed fibres reducing through-thickness reinforcing properties
Solution Approach 1:
The patent applies parameter changes by heating the matrix material to a temperature above its glass transition temperature, which softens the matrix and reduces its resistance to fibre insertion. This thermal parameter change allows chamfered fibres to be inserted more easily while maintaining accurate trajectory and alignment. The softened matrix reduces the deflection effect caused by densely packed fibres, enabling both easy insertion and precise fibre positioning for optimal through-thickness reinforcing properties.
4Strength
If conventional z-pinning is used, then through-thickness reinforcement is provided, but fibrous reinforcing pins split or fracture during insertion reducing effectiveness
Solution Approach 1:
The patent uses parameter changes by heating the matrix material to a temperature above its glass transition temperature, which fundamentally changes the matrix rheology from rigid to softened. This thermal parameter change prevents fibrous reinforcing pins from splitting or fracturing during insertion, as the softened matrix offers reduced resistance and allows smooth fibre passage. The matrix softening ensures pin integrity is maintained while still achieving effective through-thickness reinforcement.
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
This method enhances through-thickness reinforcement by reducing fiber deflection and splitting, maintaining in-plane material properties while improving inter-laminar strength and fracture toughness, making the process more efficient and cost-effective.
Implementation Method 1
heating the uncured composite laminated material to a first pre-determined temperature, the first pre-determined temperature being defined as the temperature at which there exists a first pre-determined time interval until the gel point is reached
Implementation Method 2
allows the fibres of the laminate to be deflected by the needle during its passage through the material which minimises the possibility of the needle damaging the laminate fibres
Implementation Method 3
ultrasonic energy is applied to the or each needle as it is inserted into the laminated material. The application of ultrasonic energy to the needle as it is inserted into the material causes localised heating of the laminate in contact with the needle which results in localised softening
Data Source
AI summary
A laminated composite material (100) comprising a polymeric matrix material (130) and plurality of fibre layers (110) is heated to a first pre-determined temperature which is defined as the temperature at which there is a first pre-determined time interval until the matrix material reaches its gel point. The first pre-determined time interval being defined as the time required to insert the required quantity of through-thickness reinforcement fibres into the laminated material. A plurality of holes (180) is formed in the laminated material; each hole being formed by inserting a needle (160) having a conical tip (170), into the laminated material. A reinforcing element (190) is then inserted into each of a respective one of the plurality of holes.