Elliptical Shank Adapter Transition for Fatigue Resistance
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Solution Overview
Problem
Existing shank adapters in rock drilling suffer from high stress concentrations at the transition region between the threaded male spigot and the main length section, leading to fatigue and potential breakage, which limits their operational lifetime.
Innovation Solution
A shank adapter design featuring a transition section with an elliptical cross-sectional shape profile, defined by a semi-major axis (a) and semi-minor axis (b) ratio within the range 2b<a<8b, configured to minimize stress concentrations and enhance resilience to bending moments and tensile loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional single-radius curved transition profile is used at the spigot-shoulder interface, then the design is simple to manufacture, but high stress concentrations occur leading to fatigue and breakage
Solution Approach 1:
The transition section employs a double-curved profile with a first radius of curvature R1 and a second radius of curvature R2, where R1 ≠ R2. This double-curved geometry creates a more gradual and optimized stress distribution compared to conventional single-radius curves, reducing stress concentrations at the spigot-shoulder interface while maintaining manufacturability through standard machining operations.
Solution Approach 2:
The invention optimizes specific geometric parameters of the transition section, including the ratio of the first to second radii of curvature (R1/R2), the axial length of the transition section, and the angular orientation of the curved profile. These parameter adjustments create an optimized stress flow path that minimizes peak stresses while preserving the simplicity of the overall adapter design.
2Stress or pressure
If the transition region has a large radius curvature to reduce stress, then stress concentrations are minimized, but the space available for the threaded portion is reduced
Solution Approach 1:
The double-curved transition profile with optimized radii R1 and R2 creates a more efficient stress distribution that achieves low stress concentrations with a shorter axial transition length. This allows the threaded portion to maintain its required length and strength while the transition section provides adequate stress relief, resolving the spatial conflict between these two requirements.
Data Source
AI summary
A shank adapter, forming part of a drilling assembly, has a main body extending axially between a first end and a second end, an externally threaded male spigot portion provided at the second end, and a non-threaded shank positioned axially intermediate the main body and the threaded section. A radially projecting shoulder is positioned axially between the main body and the male spigot portion. The shank has a transition section positioned adjacent to the shoulder at the second end having an outside diameter that increases in a direction from the spigot portion to the shoulder. A cross-sectional shape profile of the outer surface of the transition section has a segment of an ellipse having a semi-major axis (a), a semi-minor axis (b) and an exponential factor (n) according to the equation:<semantics definitionURL="">❘<annotation encoding="Mathematica">"\[LeftBracketingBar]"</annotation></semantics>xa<semantics definitionURL="">❘<annotation encoding="Mathematica">"\[RightBracketingBar]"</annotation></semantics>n+<semantics definitionURL="">❘<annotation encoding="Mathematica">"\[LeftBracketingBar]"</annotation></semantics>yb<semantics definitionURL="">❘<annotation encoding="Mathematica">"\[RightBracketingBar]"</annotation></semantics>n=1A ratio of the semi-major to semi-minor axes (a:b) is within the range 2b<a<8b.