Concrete Screw Rounded Transition Reduces Hydrogen Embrittlement
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Solution Overview
Problem
Concrete screws are prone to hydrogen embrittlement, leading to delayed brittle fracture under load, particularly in high-strength applications above 1000 N/mm^2, due to hydrogen diffusion during surface treatments, which can result in failure during oblique pull tests.
Innovation Solution
A concrete screw design featuring a constant mean core diameter thread over half its length, a transition area with increasing core diameter from the thread to the shank section, a rounded thread root and flank, and a smooth transition from the threaded section to the shank section to reduce stress peaks and inhomogeneous structures, along with a thread pitch to outer diameter ratio greater than 0.5 for improved torque and holding values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a stepped transition from core diameter to shank diameter is used, then manufacturing is simpler, but hydrogen-induced brittle fracture tendency increases
Solution Approach 1:
The patent applies curvature by implementing a rounded transition area between the threaded section and shank section, replacing the conventional stepped (angular) transition. This curved geometry eliminates sharp corners and stress concentration points, thereby reducing the tendency for hydrogen-induced brittle fracture while maintaining manufacturing feasibility through standard rolling or forging processes.
2Strength
If high tensile strength above 1000 N/mm² is achieved, then fastening capacity is improved, but susceptibility to hydrogen embrittlement increases
Solution Approach 1:
The patent applies local quality by creating a transition area with differentiated properties between the threaded section and shank section. This transition zone has a gradual diameter change and rounded geometry that reduces stress concentration, thereby locally mitigating hydrogen embrittlement susceptibility in the most vulnerable region while maintaining high overall tensile strength of the screw.
3Ease of manufacture
If surface treatments such as pickling are applied, then coating adhesion is improved, but hydrogen diffusion into the surface layer increases
Solution Approach 1:
The patent applies preliminary anti-action by designing a rounded transition area that preemptively reduces stress concentration before hydrogen can accumulate and cause embrittlement. This geometric feature acts as a preventive measure against hydrogen-induced failure, countering the harmful effect of hydrogen diffusion that occurs during surface treatments like pickling.
Data Source
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AI summary
The invention relates to a concrete screw (1). In order to reduce the tendency toward hydrogen-induced brittle fracture, the minor diameter dK according to the invention rises to the body diameter ds in a transition region (14) and, at the same time, the major diameter da of the thread (10) falls to the body diameter ds. In addition, according to the invention, the flank crest (15) and the flank root (16) are rounded off. As a result, the microstructure becomes more homogeneous and stress peaks are avoided.