Transition-Thread Bolt Structure for Fatigue Load Distribution
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Solution Overview
Problem
Conventional bolts experience uneven force distribution and high fatigue fracture rates due to stress concentration on the first few threads, leading to connection failures under fluctuating loads, which existing solutions fail to adequately address.
Innovation Solution
A bolt design featuring a screw cap, a bolt bar with a positioning bar, a flexible bar, and a threaded portion that includes standard and transition threads with a truncated crest and varying thread height, along with an anti-shearing stand, optimized for force distribution and stress reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional standard threads are used on all bolts, then the manufacturing process is simple, but the force distribution is uneven and stress concentration occurs on the first few threads leading to fatigue fracture
Solution Approach 1:
The thread structure is divided into multiple segments: standard threads at the beginning for easy engagement, and transition threads with gradually decreasing height toward the end. This segmentation allows different portions of the thread to serve different functions - the standard threads provide reliable initial engagement while the transition threads distribute stress more evenly, preventing fatigue fracture at the thread roots.
Solution Approach 2:
Different thread heights are applied to different locations along the bolt. The first few threads have standard height for reliable engagement, while subsequent transition threads have progressively smaller heights. This local variation in thread quality optimizes the force distribution at each location, reducing stress concentration at critical points where fatigue fractures typically occur.
2Strength
If high-strength materials are used to manufacture flexible bolts, then tensile strength is improved, but anti-fatigue performance under fluctuating loads remains insufficient
Solution Approach 1:
The thread height parameter is changed along the length of the bolt, creating a gradient structure. Instead of uniform thread height, the transition threads have progressively smaller heights, which changes the stress distribution pattern. This parameter variation allows the bolt to maintain high tensile strength while significantly improving anti-fatigue performance by eliminating stress concentration points that cause fatigue failures under fluctuating loads.
3Stress or pressure
If the thread height is reduced on transition threads, then stress concentration is reduced and force distribution is improved, but the load-bearing capacity of individual threads decreases
Solution Approach 1:
The transition threads create a continuous gradient of thread heights rather than abrupt changes. This continuity ensures that the load is gradually transferred from higher threads to lower threads along the engagement length. The continuous variation in thread height maintains stress distribution uniformity while preserving overall load-bearing capacity through the cumulative effect of multiple threads working together with optimized stress distribution.
Data Source
AI summary
A bolt and a method for manufacturing the bolt are provided. The bolt includes a screw cap and a bolt bar, the bolt bar includes a positioning bar, a flexible bar and a threaded portion, the positioning bar is connected to one end of the screw cap, and the flexible bar is connected to the positioning bar and the threaded portion respectively. Wherein, an anti-shearing stand is formed on the flexible bar. The threaded portion includes standard threads and transition threads, the transition threads are formed between the flexible bar and the standard threads, and a thread height of the transition threads is smaller than a thread height of the standard threads, wherein the thread height of the standard threads keeps constant. The force distribution of the threads can be optimized, and the threads can effectively cooperate with the threads of the nut.