Curved Sandwich Shear Test Fixture
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Solution Overview
Problem
Traditional methods for testing sandwich structures with curved shapes, such as those with honeycomb cores, often result in inaccurate mechanical property characterization due to the reliance on data from flat panel tests, leading to unconservative design configurations.
Innovation Solution
A test fixture and method for determining circumferential shear properties of arcuate test specimens, which includes a test frame with an outer and inner fixture, load plates, and displacement measurement devices, allowing for the application of a circumferential shear load that is substantially pure and minimizes out-of-plane loading, enabling accurate characterization of curved sandwich structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional flat panel test data is used to characterize curved sandwich structures, then the testing process is simple and familiar, but the mechanical property characterization becomes inaccurate leading to unconservative design
Solution Approach 1:
The test fixture employs curved pressing surfaces (socket and shaft) that match the arcuate geometry of the test specimen. The socket and shaft are formed with radii of curvature that correspond to the specimen's geometry, allowing the specimen to be properly supported and loaded in its curved configuration. This curvature matching enables accurate measurement of shear properties specific to curved sandwich structures rather than forcing flat panel test methods onto curved geometries.
Solution Approach 2:
The test fixture incorporates rotational movement where the shaft rotates relative to the socket around a rotation axis. This dynamic rotation allows shear force to be applied and measured along different axes between the first and second axes in a single test procedure, capturing the full shear behavior of the curved specimen under varying load orientations.
2Productivity
If a single test procedure is used to measure shear properties under different normal loads, then testing efficiency improves, but the test fixture design becomes more complex
Solution Approach 1:
The test fixture combines multiple testing capabilities into a single integrated system. The socket and shaft assembly can apply both normal loads (through radial compression) and shear loads (through rotation) simultaneously. This allows shear properties to be measured under different normal load conditions within one continuous test procedure rather than requiring separate tests for each normal load level, thereby improving productivity while maintaining manageable complexity through unified design.
Solution Approach 2:
The test fixture is designed to perform multiple functions: it can apply radial compressive forces to create different normal load conditions, rotate to apply shear forces in various directions, and measure shear properties across multiple axes. This multi-functionality allows a single fixture to replace what would otherwise require multiple specialized test setups, achieving high productivity without proportionally increasing complexity.
Data Source
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AI summary
A test fixture (198) for determining circumferential shear properties of an arcuate test specimen (100) may include an outer fixture (220) and an inner fixture (200). The outer fixture (220) may be coupled to an outer side (106) of the test specimen (100), and may be rotatably mounted on a central pin (240) and may include a rocker arm (228). The inner fixture (200) may be coupled to an inner side (104) of the test specimen (100), and may be rotatably mounted on the central pin (240) and may include a load arm (204) extending in a direction opposite the rocker arm (228). The inner fixture (200) and the outer fixture (220) may be configured such that application of a test load (280) to the rocker arm (228) and the load arm (204) causes rotation thereof about the central pin (240) producing circumferential movement of the inner side (104) relative to the outer side (106) and inducing a circumferential shear load (150) in the test specimen (100).