Bolted Joint Pre-Tension Control Near Yield Strength
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Solution Overview
Problem
Conventional methods for establishing bolted joints do not fully utilize the mechanical potential of the joints due to excessive safety margins, leading to increased material usage and weight, and often require specialized materials, which is inefficient and costly.
Innovation Solution
A method that sets target pre-tension levels closer to the maximum yield strength of the bolted joint, measuring actual pre-tension levels during tightening, and using a bolt elongation measuring device to ensure accurate force application, thereby reducing material consumption and allowing the use of standard components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional planning procedures with significant safety margins are used, then the reliability of the bolted joint is improved, but the amount of material required increases and the weight increases
Solution Approach 1:
The patent changes the pre-tension parameter from conventional values (70% of yield strength) to higher values (90-95% of yield strength). This parameter change allows reducing the safety margin while maintaining reliability through direct measurement, thereby reducing material requirements and weight.
Solution Approach 2:
The patent implements feedback by directly measuring the actual pre-tension level during tightening and comparing it to the target pre-tension level. This closed-loop control ensures the joint reaches the optimal pre-tension state, eliminating the need for excessive safety margins and reducing material usage.
2Reliability
If conventional planning procedures with significant safety margins are used, then the reliability of the bolted joint is improved, but the amount of material required increases
Solution Approach 1:
The patent changes the pre-tension parameter from conventional values (70% of yield strength) to higher values (90-95% of yield strength). This parameter change allows reducing the safety margin while maintaining reliability through direct measurement, thereby reducing material requirements.
Solution Approach 2:
The patent implements feedback by directly measuring the actual pre-tension level during tightening and comparing it to the target pre-tension level. This closed-loop control ensures the joint reaches the optimal pre-tension state, eliminating the need for excessive safety margins and reducing material usage.
3Quantity of substance
If target pre-tension levels closer to maximum yield strength are used, then the use of material is optimized and standard components can be used, but the risk of exceeding maximum pre-tension level increases
Solution Approach 1:
The patent implements real-time feedback by measuring the actual pre-tension level during tightening and comparing it to the target pre-tension level. This closed-loop control allows using higher target pre-tension levels (90-95% of yield) while preventing exceeding the maximum yield strength, thus optimizing material usage without compromising reliability.
Solution Approach 2:
The patent performs preliminary measurement of the bolt's unloaded length before tightening and measures the loaded length after tightening. This preliminary action enables accurate calculation of elongation and pre-tension level, allowing safe operation near the yield point.
4Manufacturing precision
If direct measurement of pre-tension level is implemented, then the manufacturing precision is improved, but the device complexity increases
Solution Approach 1:
The patent replaces complex direct force measurement systems with a simpler mechanical measurement approach based on Hooke's Law. By measuring bolt elongation (change in length) and calculating pre-tension from the known stiffness, the system achieves high measurement precision without requiring complex sensors or measurement devices.
Solution Approach 2:
The patent uses bolt elongation as an intermediary parameter to indirectly measure pre-tension level. Instead of directly measuring the complex internal stress state, the method measures the simple geometric parameter (length change) and calculates the force, simplifying the measurement system while maintaining precision.
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 optimizes the use of bolted joints by minimizing material requirements and enabling the use of conventional materials, while ensuring the joints operate within their mechanical potential, reducing errors and costs.
Implementation Method 1
measuring an unloaded length of a bolt in the bolt joint, prior to the tightening process; measuring a loaded length of the bolt, after the tightening process; determining the actual pre-tension level based on a difference between the unloaded and the loaded length of the bolt
Data Source
AI summary
The present invention relates to a method of establishing a bolted joint, the method comprising the following steps: selecting a type of bolted joint; determining a target pre-tension level for the selected bolted joint, wherein the target pre-tension level is less than 10% lower than a maximum pre-tension level of the bolted joint, the maximum pre-tension level relating to a pre-tension level that must not be exceeded without compromising the bolted joint; installing the bolted joint, wherein an actual pre-tension level of the bolted joint is measured during the tightening process.