Hollow Spring Inner Surface Compression for Fatigue Life
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Solution Overview
Problem
Existing methods for applying compressive residual stress to the inner surfaces of hollow springs, such as those used in vehicle stabilizers, require complex equipment and can damage the inner surfaces during processing, especially for complex shapes or smaller diameters, and are not effective in reducing tensile stress in bending portions.
Innovation Solution
A method involving a steel tube where compressive residual stress is applied to the inner surface by pressing a die with a circumferentially extending pressing surface onto the outer surface, reducing tensile stress and enhancing fatigue life without the need for complex equipment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If shot peening is applied to the outer surface to impart compressive residual stress, then the stress on the outer surface is relieved, but the stress difference between outer and inner surfaces is reduced and breakage may occur from the inner surface
Solution Approach 1:
Instead of applying compressive residual stress to the outer surface through shot peening, the invention inverts the approach by applying compressive residual stress to the inner surface through a die pressing the outer surface. This internal compression counteracts the tensile stress that causes fatigue failure from the inside, thereby improving overall reliability and fatigue life.
2Weight of moving object
If the thickness of the hollow spring is reduced to reduce weight, then weight reduction is achieved, but the stress difference between outer and inner surfaces becomes more remarkable and inner surface breakage may occur
Solution Approach 1:
The invention applies compressive residual stress to the inner surface in advance through die pressing before the hollow spring undergoes service loading. This preliminary compression counteracts the tensile stress that would otherwise cause fatigue failure, allowing the use of thinner walls for weight reduction while maintaining or improving fatigue life and reliability.
3Reliability
If reflection member and guide member are used to apply compressive residual stress to inner surface, then fatigue life can be prolonged, but equipment complexity increases and inner surface may be scratched
Solution Approach 1:
The invention extracts and eliminates the complex equipment components (reflection members, guide members, wires, dust collectors) from the shot peening system. Instead, it uses a simple die that presses the outer surface to generate internal compressive residual stress, thereby prolonging fatigue life while dramatically reducing equipment complexity and eliminating the risk of inner surface scratches from sliding guide members.
4Reliability
If reflection member is moved by wire through the hole, then compressive residual stress can be applied to inner surface, but the guide member scratches the inner surface at bending portions
Solution Approach 1:
The invention uses the outer surface as an intermediary medium. By pressing the outer surface with a die, compressive residual stress is transmitted through the tube wall to the inner surface without any physical contact with the inner surface itself. This eliminates the harmful scratching effect while still achieving the desired compressive stress state for improved fatigue life.
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 effectively prolongs the fatigue life of hollow springs by applying compressive residual stress to the inner surfaces, particularly in bending portions, without causing damage and is applicable to both straight and bending parts of the spring.
Implementation Method 1
applying the compressive force to at least a portion of an outer surface of the steel tube from a circumferential direction to apply the compressive residual stress to at least a portion of an inner surface of the steel tube
Data Source
AI summary
A method includes, providing a tubular member (10) used for a hollow spring, and applying the compressive residual stress to at least a portion of an inner surface of the steel tube by applying the compressive force to at least a portion of an outer surface of the tubular member (10) from a circumferential direction, and a fatigue life of the tubular member (10) is prolonged by applying the compressive residual stress to the inner surface of the tubular member (10). Applying the force to the outer surface of the tubular member (10) includes pressing the tubular member (10) with a die (1). The die (1) has a pressing surface (1a) shaped such that the compressive force can be applied to at least the portion of the outer surface of the tubular member (10) from the circumferential direction.