Composite Hip Stem Pseudo-Isotropy and Void Reduction
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Solution Overview
Problem
Current methods for manufacturing composite hip prostheses using FRP materials face challenges in achieving pseudo-isotropy and minimizing air voids, leading to issues with strength, rigidity, and accuracy in shape, which are critical for withstanding complex loads and ensuring a proper fit for individual patients.
Innovation Solution
The method involves evenly stacking prepreg sheets with carbon fibers arranged at ±45 degrees and 0/90 degrees, integrated with a thermoplastic resin, and applying heat and pressure to form a stem with overlapping sections that reduce shearing loads and air voids, resulting in a structurally sound and accurately shaped FRP prosthesis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If FRP materials are stacked to form a composite stem, then the stem becomes lighter and has higher longitudinal elastic modulus and fatigue strength, but the stem exhibits anisotropy due to woven cloth structure
Solution Approach 1:
The patent uses composite materials consisting of carbon fiber reinforcement and resin matrix to create a stem that is both lightweight and mechanically strong. The composite structure combines different materials to achieve superior longitudinal elastic modulus and fatigue strength compared to metallic materials.
Solution Approach 2:
The patent introduces a new dimension to solving the anisotropy problem by curving the stacked sheets in three-dimensional space. Instead of simply alternating fiber directions in flat layers, the sheets are curved to follow the stem's geometry, creating pseudo-isotropy through spatial arrangement rather than just material orientation.
2Shape
If sheets are curvedly stacked to fit the stem contour, then the stem obtains the correct outer shape, but air voids are frequently produced between the sheets
Solution Approach 1:
The patent applies curvature to the stacked sheets to match the contour of the stem. Each sheet is curved to follow the three-dimensional geometry of the stem, allowing the flat sheets to conform to the curved surface and achieve the correct outer shape while maintaining sheet integrity.
Solution Approach 2:
The patent converts the potential harm of air voids into a benefit by designing the stacking sequence and curvature to systematically manage air evacuation. The curved stacking pattern creates pathways for air to escape during curing, transforming the air void problem into an opportunity for improved consolidation.
3Stability of the object's composition
If sheets are alternately stacked at 0/90 degrees and ±45 degrees to obtain pseudo-isotropy, then the anisotropy is reduced, but the adherence of curvedly stacked sheets declines
Solution Approach 1:
The patent uses composite materials with alternating fiber orientations (0/90 degrees and ±45 degrees) to achieve pseudo-isotropy. This multi-directional fiber arrangement distributes mechanical properties more uniformly in all directions, reducing the anisotropic behavior inherent in unidirectional composites.
Solution Approach 2:
The patent applies curvature to the stacked sheets to match the contour of the stem. Each sheet is curved to follow the three-dimensional geometry of the stem, allowing the flat sheets to conform to the curved surface and achieve the correct outer shape while maintaining sheet integrity.
4Manufacturing precision
If the stem is custom-made for individual patients, then the fit within the medullary cavity is precise, but the manufacturing complexity increases
Solution Approach 1:
The patent divides the stem manufacturing process into discrete stacking steps where individual sheets are prepared and stacked in a controlled sequence. This segmentation allows for custom design while maintaining manufacturing control, as each layer can be tailored to the patient's anatomy through the stacking pattern rather than requiring complete custom tooling.
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 approach enhances the strength, proof stress, and rigidity of the prosthetic stem, reduces air voids, and ensures a precise fit within the medullary cavity, mimicking the mechanical properties of metallic stems while allowing for custom-made shapes.
Implementation Method 1
applying heat and pressure to the structural elements to melt resins impregnated in each of the elements
Implementation Method 2
applying heat and pressure to the structural elements to melt resins impregnated in each of the elements
Implementation Method 3
applying heat and pressure to form a stem with overlapping sections that reduce shearing loads and air voids
Data Source
AI summary
A stem 8 has the following elements made from FRP: an upper outer shell 4U, a main structure upper half 3U, a main structure lower half 3L, and a lower outer shell 4L when the stem is placed in a flat state. The elements are integrated into one piece by stacking the elements and applying heat and pressure to melt resins impregnated in the FRP structural elements. Each outer shell is a curved prepreg sheet formed by impregnating carbon fibers arranged at angle of ±45 degrees with a thermoplastic resin, and each upper and lower halve is an evenly stacked part in which prepreg sheets are stacked. Overlapping section 5 of the upper and lower outer shells are formed such that the left and right portions of a main structure 3 formed by integrating the upper and lower halves 3U, 3L does not have a stepped outer surface.