Composite Washer for Precise Screw Tightening Force Control
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Solution Overview
Problem
Existing screw connection assemblies in mechanical parts face challenges in ensuring secure attachment under vibrating environmental conditions, particularly in space applications where intense vibrations can lead to loosening, and current methods like torque wrenches are inadequate for guaranteeing high forces due to dispersion and indirect force measurement.
Innovation Solution
A washer with two facing faces made of materials with differing stiffness, where one material deforms elastically and the other plastically, allowing for direct detection of the transition from elastic to plastic deformation through a break in slope, enabling precise control of tightening force without additional sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If torque wrench method is used to tighten screw or nut, then assembly can be tightened with predefined torque, but it does not guarantee very high forces due to significant dispersions and indirect force measurement
Solution Approach 1:
The patent introduces a washer as an intermediary element between the screw/nut and the mechanical part. This washer contains a material that undergoes plastic deformation at a predetermined load, serving as a mediator that transfers and indicates the tightening force. The plastic deformation of the washer material provides a direct visual indicator of the force applied, eliminating the need for indirect torque measurement and statistical calculations.
2Measurement precision
If force measurement sensor is inserted into the assembly, then tightening force can be directly measured, but it increases the cost of the assembly and requires additional implementation time
Solution Approach 1:
The washer is designed to automatically indicate the tightening force through its own plastic deformation. The material in the washer serves itself as both the force transmission element and the measurement indicator. When the predetermined force is applied, the material deforms plastically, providing a visible signal without requiring external sensors, electronics, or additional measurement equipment.
Solution Approach 2:
The washer acts as a disposable or single-use indicator element. After serving its purpose of indicating the tightening force through plastic deformation, it is replaced. This approach is more cost-effective than installing permanent force measurement sensors, as the washer is a simple mechanical component that can be easily manufactured and replaced without requiring complex measurement systems.
3Ease of operation
If single material washer is used, then assembly is simple, but it cannot provide both elastic deformation for force distribution and plastic deformation for force indication
Solution Approach 1:
The washer is constructed from composite materials with different mechanical properties. One material provides elastic deformation for even force distribution across the contact surface, while another material undergoes plastic deformation at a predetermined load to indicate the tightening force. This composite structure allows the single washer element to simultaneously perform multiple functions: force distribution, force indication, and vibration resistance.
Solution Approach 2:
Different regions of the washer have different material properties tailored to specific functions. The portion of the washer in contact with the mechanical part uses a material with appropriate elasticity for force distribution, while another portion contains a material designed to deform plastically at the target load for force indication. This local differentiation of material quality allows precise control of deformation characteristics in different areas of the same component.
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 solution ensures a reliable and consistent clamping force by allowing operators to manually or automatically detect the transition from elastic to plastic deformation, ensuring the assembly remains secure even in harsh environments.
Implementation Method 1
a first of the two materials has a lower stiffness than a second of the two materials, in that the stiffnesses of the two materials are defined so as to allow a deformation of the first material in its elastic domain
Implementation Method 2
the stiffnesses of the two materials are defined so as to allow a deformation of the first material in its elastic domain and of the second material in its plastic domain
Data Source
AI summary
The invention relates to a washer intended for use in a screwed assembly (10), the washer (18) comprising two opposing faces (21, 22), the washer (18) being intended to be compressed between its two faces (21, 22) in the assembly (10). According to the invention, the washer (18) comprises two materials (23, 24), both extending from one face (21, 22) to the other. One (23) of the two materials has a lower stiffness than the other (24) of the two materials. The stiffnesses of the two materials are defined such as to allow deformation of the first material (23) in its elastic range and of the second material (24) in its plastic range. The invention also relates to a method for assembling mechanical parts (11, 12) using the washer (18) of the invention.