Bonded Direct Fixation Fastener with Dual Durometer Elastomer
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Solution Overview
Problem
Bonded direct fixation fasteners (BDFFs) face challenges in achieving optimal noise and vibration mitigation while maintaining structural integrity under cyclic wheel loads, as softening the rubber for better noise reduction leads to premature failures due to increased lateral deflection.
Innovation Solution
A bonded direct fixation fastener design featuring a rail plate and bottom member made of cast steel or ductile iron, with an elastomeric portion of varying durometer hardness between 47 to 67, and angled attachments for rail and bed fixation, allowing for controlled vertical and lateral stiffness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the rubber element is softened to achieve better noise and vibration reduction, then noise and vibration mitigation performance is improved, but lateral stiffness decreases leading to premature failures under cyclic loading
Solution Approach 1:
The patent applies different durometer hardness values to different regions of the elastomeric portion. The first region (vertical cushioning zone) has a softer durometer (47-57) to maximize noise and vibration reduction, while the second region (lateral support zone) has a harder durometer (57-67) to maintain lateral stiffness and prevent premature failure. This local differentiation allows each region to optimize its function independently.
Solution Approach 2:
The elastomeric portion is constructed as a composite structure with two distinct rubber compounds of different durometer values bonded together. This composite approach enables the fastener to simultaneously exhibit soft vertical characteristics for noise reduction and stiff lateral characteristics for structural reliability, resolving the contradiction between these opposing requirements.
2Object-affected harmful factors
If the rubber element is softened to provide softer cushion under the rail, then noise and vibration reduction is improved, but lateral deflection of the rail head increases
Solution Approach 1:
The elastomeric portion is divided into regions with different durometer characteristics. The vertical cushioning region uses softer rubber (durometer 47-57) to reduce noise and vibration, while the lateral support region uses harder rubber (durometer 57-67) to resist lateral deflection. This spatial differentiation of material properties allows independent optimization of vertical and lateral performance.
3Adaptability or versatility
If the geometrical constraints are set by end user or track conditions, then adaptability to track conditions is improved, but design flexibility for optimizing noise reduction is reduced
Solution Approach 1:
The patent maintains the familiar geometric configuration of existing fasteners to satisfy user and track condition requirements, while introducing a new parameter - dual durometer elastomeric material - to achieve noise reduction optimization. This allows the fastener to meet geometric constraints while gaining enhanced performance through material property differentiation.
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 design enhances noise and vibration reduction while maintaining structural integrity by providing a controlled vertical spring-rate and preventing premature failures through balanced stiffness characteristics.
Implementation Method 1
Dynamic stiffness of the BDFFs dictates the noise and vibration mitigation performance of the BDFFs
Implementation Method 2
the vertical and lateral stiffness characteristics of BDFFs have been governed by a combination of the geometric details of the design and the properties of the rubber used in the BDFF
Data Source
AI summary
A bonded, direct fixation fastener as supportive structure for a rail on a railroad bed comprising: a substantially rectangular rail plate, wherein the rail plate has a generally horizontal center portion having a lower face and an upper face and wherein the rail plate defines an outer perimeter having a face defining a first angle to the railroad bed, the rail plate having attachment means to attach to the rail; a substantially rectangular bottom member defines an inner perimeter having a face defining a second angle to the railroad bed; and a substantially rectangular elastomeric portion disposed between, and bonded to each of, the outer perimeter and face of the rail plate and the inner perimeter and face of the bottom member.