ASTM D7078
V-Notched
Rail Shear Fixture
ASTM D7078
V-notched Rail Shear Fixture
Standard Test Method for Shear Properties of Composite Materials by V-Notched Rail Shear Method - PDF
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Theory
ASTM D7078 defines a standardized shear testing method for composite materials using the rail shear technique. This method applies a uniform shear strain across the test specimen, leading to material failure at the notched region.
ASTM D7078 shares similarities with the ASTM D5379 Iosipescu shear test, as both rely on a comparable shearing mechanism. However, the two methods can produce slightly different results. ASTM D7078 is typically preferred for more flexible composites that are susceptible to edge crushing, whereas ASTM D5379 is better suited for rigid materials capable of withstanding compression forces at the edges.
Geometry
The test specimen resembles that of the Iosipescu shear test but has a more square-like shape. A 90-degree V-notch is machined into the center of both the top and bottom edges of the sample, ensuring consistent stress distribution during testing.
Testing Setup
This test requires a specialized Rail Shear Fixture designed specifically for ASTM D7078. The fixture includes metal gripping components along with plastic centering triangles to ensure precise specimen alignment. Various fixture designs are available, including models with additional tightening screws to accommodate higher load capacities.
Analysis
The primary performance metric in this test is maximum shear stress, calculated by dividing the applied force by the cross-sectional shear zone. Shear strain is concentrated at the notched region and can be accurately measured using a strain gauge or a laser extensometer, allowing for precise strain analysis.
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