Cylindrical Fatigue Specimen With Concentric Hole
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Solution Overview
Problem
Conventional fatigue and crack growth testing methods face limitations in achieving high-frequency testing due to design constraints, leading to non-uniform stress intensity and irregular crack shapes, which impairs data correlation and reproducibility.
Innovation Solution
A novel specimen configuration utilizing a circular cylindrical sample with a substantially circular hole, designed to reduce stress intensity as the crack grows, combined with a stiff load train and solid-state actuators for high-frequency cyclic loading, enabling axial and torsional loading modes while maintaining conventional low-frequency testing capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional fatigue test samples are used with standard testing machines, then testing can be performed with existing equipment, but the testing frequency is limited to below 100 Hz due to design limitations
Solution Approach 1:
The patent changes the geometric parameters of the test sample, specifically using a circular cylindrical sample with a hole whose diameter is 0.4 to 0.6 times the outer diameter. This parameter change enables the sample to maintain uniform stress intensity distribution during crack growth, allowing it to be used with high-frequency testing equipment operating at frequencies up to 2000 Hz, thereby resolving the frequency limitation of conventional samples
2Manufacturing precision
If conventional compact tension specimens are used, then crack growth testing can be performed, but the stress intensity is non-uniform across the crack front resulting in irregular crack shapes
Solution Approach 1:
The patent introduces asymmetry in the loading configuration by applying load through an internal load frame extension that interfaces with the hole in the sample. This asymmetric loading arrangement, combined with the specific hole-to-outer-diameter ratio, creates a stress intensity distribution that promotes uniform crack growth across the crack front, producing stable concentric crack shapes rather than irregular patterns
Solution Approach 2:
The patent employs a circular cylindrical sample geometry with a circular hole, utilizing curved surfaces rather than flat or angular shapes. This spheroidal geometry ensures uniform stress distribution around the crack front during loading, preventing stress concentration at corners or edges and thereby maintaining consistent crack propagation rates across the entire crack front
3Productivity
If high-frequency cyclic loading is applied to achieve faster testing, then test duration is reduced, but maintaining closed-loop control and arbitrary waveform capability becomes difficult
Solution Approach 1:
The patent replaces conventional mechanical testing machine systems with a high-frequency actuator system capable of operating at frequencies up to 2000 Hz. This substitution enables the maintenance of closed-loop control and arbitrary waveform capability at high frequencies, as the new actuation system is specifically designed to provide the necessary bandwidth and control precision that traditional mechanical systems cannot achieve
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 configuration allows for stable, concentric crack growth and uniform plasticity-induced closure, enhancing the reproducibility and accuracy of fatigue and crack growth tests, particularly at higher frequencies up to 2000 Hz.
Implementation Method 1
The cyclic loading device includes an actuator including a solid state material system which undergoes deformations in response to the application of energy
Data Source
AI summary
A sample for fatigue and/or crack growth testing, including an axisymmetric or cylindrical gage section with a concentric hole running from a first end, and terminating within the gage section, with one mode of loading introduced at the terminus of the hole, and reacted at the end where the hole originates. A second mode of loading is optionally introduced at a second end of the specimen. Use of the specimen is described in both in the context of an apparatus for fatigue/crack growth testing described in the referenced parent application, as well as with conventional test machines.