Leaf Spring Tempering for Fatigue Strength and Toughness Balance
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Solution Overview
Problem
Increasing the hardness and fatigue strength of steel plates for leaf spring devices to reduce vehicle weight leads to a decrease in toughness, particularly in the connecting sections, making them prone to fatigue and delayed fractures.
Innovation Solution
Tempering the connecting sections of leaf spring devices at a higher temperature than the elastic sections to enhance toughness while maintaining high fatigue strength in the elastic sections, thereby balancing both properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the steel plate is heat-treated to increase hardness and fatigue strength, then the fatigue strength is improved, but the toughness decreases
Solution Approach 1:
The patent applies different tempering temperatures to different sections of the leaf spring. The elastic section is tempered at a first temperature to achieve high fatigue strength (Brinell hardness > 461 HBW), while the connecting section is tempered at a higher second temperature to achieve high toughness (Brinell hardness ≤ 461 HBW). This local differentiation of material properties resolves the contradiction between fatigue strength and toughness.
Solution Approach 2:
The leaf spring is divided into distinct functional sections (elastic section and connecting section) with different tempering requirements. The elastic section requires higher hardness for fatigue resistance, while the connecting section requires lower hardness for toughness. By segmenting the heat treatment process into separate temperature zones, both requirements are satisfied simultaneously.
2Strength
If the connecting section is hardened to increase fatigue strength, then the fatigue strength is improved, but the susceptibility to fatigue fracture and delayed fracture increases
Solution Approach 1:
The connecting section is specifically tempered at a higher temperature than the elastic section, creating a local quality difference. This higher temperature tempering reduces the Brinell hardness to 461 HBW or less, which increases toughness and reduces susceptibility to fatigue fracture and delayed fracture, while the elastic section maintains higher hardness for fatigue strength.
3Reliability
If the entire leaf spring is tempered at high temperature to increase toughness, then the toughness is improved, but the fatigue strength decreases
Solution Approach 1:
Instead of uniform high-temperature tempering, the patent applies selective tempering where only the connecting section receives high-temperature treatment. The elastic section is tempered at a lower first temperature to maintain Brinell hardness above 461 HBW, preserving fatigue strength, while the connecting section is tempered at a higher second temperature to improve toughness.
Solution Approach 2:
The heat treatment process is segmented into at least two separate tempering operations with different temperature profiles. The first tempering at a lower temperature preserves fatigue strength in the elastic section, while the second tempering at a higher temperature improves toughness in the connecting section, avoiding the pitfall of uniform high-temperature tempering.
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 method results in leaf spring devices with improved fatigue strength and increased toughness in the connecting sections, reducing the likelihood of fatigue and delayed fractures, while maintaining the required fatigue strength in the elastic sections.
Implementation Method 1
the connecting section of the leaf spring device is tempered at the higher temperature than the elastic section
Implementation Method 2
the elastic section is tempered at a lower temperature, fatigue strength of the elastic section is increased
Data Source
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AI summary
A leaf spring device (1) includes a main leaf (20) made of a steel plate including an elastic section (20b) configured to generate elastic force when bent; and an eye section (20a) formed in an end portion of the elastic section (20b), the elastic section (20b) and the eye section (20a) being tempered. There is also provided a method for manufacturing the leaf spring device (1). The eye section (20a) is formed by rolling the end of the elastic section (20b) into a circular form. The eye section (20a) is tempered at a higher temperature than the elastic section (20b).