FRP Drive Shaft Joint Structure for Torsion and Fatigue Strength
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Solution Overview
Problem
Existing methods for joining metal and fiber reinforced plastic (FRP) members in rotational driving force transmission mechanisms face challenges in achieving sufficient torsional and fatigue strength while reducing weight, as mechanical joining damages fibers and adhesive joining lacks bonding strength.
Innovation Solution
A rotational driving force transmission mechanism using a metallic intervening member with a shaft portion inserted into the FRP shaft and a tubular portion fitted over it, allowing the constant velocity joint to be externally attached, providing enhanced bonding strength without damaging fibers or increasing weight.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If mechanical joining (riveting) is used to join metal member and FRP member, then firm joining is achieved, but reinforcing fibers in FRP member are damaged and severed, reducing strength
Solution Approach 1:
A metal tube serving as an intermediary component is introduced between the metal member and FRP member. The metal tube receives the rivet and transmits the joining force to both members without requiring direct piercing of the FRP member, thereby preventing fiber damage while achieving firm joining.
Solution Approach 2:
The joining system is segmented into distinct functional components: the metal member, the metal tube (intermediary), and the FRP member. This segmentation allows the metal tube to bear the mechanical stress of rivet insertion while the FRP member remains intact, avoiding fiber severance.
2Object-affected harmful factors
If adhesive joining is used to join metal member and FRP member, then fiber damage is avoided, but bonding strength is insufficient for adequate torsional strength and fatigue strength
Solution Approach 1:
The invention merges two joining approaches: adhesive bonding (which protects fibers) and mechanical fastening via the metal tube (which provides strength). The adhesive bonds the metal tube to both members without piercing FRP, while the rivet through the metal tube provides mechanical reinforcement, achieving both fiber protection and adequate strength.
3Strength
If rivets are inserted to join metal member and FRP member, then firm joining is achieved, but the thickness of metal member or FRP member must be increased to enable rivet insertion, increasing weight
Solution Approach 1:
The metal tube acts as an intermediary that concentrates the mechanical joining function in a localized, thin-walled structure. This allows the rivet to be inserted through the metal tube without requiring increased thickness of the FRP member or metal member, thereby maintaining weight efficiency while achieving firm joining.
4Weight of moving object
If shaft is made from FRP material to reduce weight, then weight reduction is achieved, but machining accuracy at end portions cannot be obtained for constant velocity joint attachment
Solution Approach 1:
The shaft is designed with different material properties at different locations: the central portion is made of lightweight FRP material, while the end portions are equipped with metal members or metal tubes that provide the necessary machining accuracy and strength for constant velocity joint attachment. This local differentiation allows weight reduction in the main shaft body while maintaining precision where required.
Solution Approach 2:
The shaft employs a composite construction combining FRP material for the central portion with metal components at the ends. This composite approach leverages the weight advantage of FRP and the machinability and strength of metal, achieving both weight reduction and manufacturing precision.
Data Source
AI summary
A rotational driving force transmission mechanism includes a cylindrical shaft made of fiber reinforced plastic, and a first constant velocity joint. The shaft is joined to the first constant velocity joint via a metallic intervening member which is attached to one end of the shaft in the axial direction. The intervening member includes a shaft portion and a main body portion. The shaft portion is inserted into the one end of the shaft from a distal end side thereof. The main body portion is of a bottomed tubular shape made up from a bottom part joined to a proximal end side of the shaft portion, and a tubular portion fitted over the one end of the shaft. The first constant velocity joint includes an inner ring fitted externally over the tubular portion of the intervening member.