ASTM D5379

ASTM D5379 is the standard test method used to determine the in-plane shear properties of fiber-reinforced composite materials using a specialized V-notched beam fixture. This method is commonly referred to as the Iosipescu shear test and is widely used in aerospace, automotive, and defense industries for characterizing composite laminates.

This guide explains the scope of ASTM D5379, its unique test setup and procedure, the required testing equipment, and how it compares to other shear testing standards.

What is ASTM D5379?

ASTM D5379 – Standard Test Method for Shear Properties of Composite Materials by the V-Notched Beam Method describes a procedure for measuring shear modulus, shear stress-strain response, and ultimate shear strength of composite laminates in a controlled, repeatable way.

The key feature of this method is the V-notched specimen geometry, which allows shear stresses to be concentrated in a defined region at the center of the sample. By minimizing bending and axial loads, the method ensures accurate and isolated shear property measurements.

Scope and Applications

ASTM D5379 is specifically designed for:

• Unidirectional and multidirectional composite laminates

• Thermoset and thermoplastic matrix composites

• Carbon fiber, glass fiber, aramid fiber composites

It is commonly used for:

• Material selection and qualification

• Quality control during manufacturing

• Design validation in high-performance applications

Shear strength is critical for load transfer between layers in laminated composites, making this test essential for structural safety and performance.

Specimen Design

Geometry

The specimen is a rectangular beam with a V-notch on each side, located symmetrically about the midline. These notches define the test region and promote uniform shear stress distribution.

Typical dimensions:

• Length: ~76 mm (3 in)

• Width: ~20 mm (0.75 in)

• Thickness: ~3 mm (0.125 in)

Notch Angle and Radius

• 90° notch angle

• Small notch root radius (typically 0.5 mm) to localize shear zone

• Notches must be precisely machined to avoid stress concentration anomalies

Testing Equipment Required

1. Universal Testing Machine (UTM)

• Capable of applying uniaxial compressive load through the V-notched shear fixture

• Test loads typically range from 5 kN to 100 kN, depending on the material

2. Iosipescu Shear Fixture

• Specialized fixture applies opposing forces above and below the notched region

• Maintains fixed spacing and alignment of upper and lower loading arms

• Often includes spherical seatings to reduce unintended bending

3. Strain Measurement Device

• Biaxial strain gage (45° orientation to fiber direction) mounted on the specimen to capture in-plane shear strain

• Alternatively, a video extensometer or digital image correlation (DIC) system can be used for non-contact strain measurements

4. Test Software

• Controls loading rate and records force and strain

• Calculates shear modulus, stress-strain curve, and ultimate shear strength

Test Procedure

1. Prepare the Specimen
   Machine and notch the composite sample with tight tolerances. Attach strain gages or prepare for video extensometer measurement. Inspect for surface damage or fiber breakout.

2. Mount in Fixture
   Secure the specimen in the V-notched shear fixture. Align the notched region precisely within the loading zone.

3. Apply Load
   Load the specimen at a constant crosshead speed, typically 0.5–2 mm/min, until failure. The test is conducted in compression mode, applying opposing shear forces through the fixture.

4. Record Data
   Collect force and strain data throughout the test. Observe the location and mode of failure.

5. Post-Test Analysis
   Calculate:

   • Shear Stress = Force / Area between notches

   • Shear Strain = Based on strain gage or extensometer data

   • Shear Modulus = Slope of the initial linear portion of the stress-strain curve

   • Ultimate Shear Strength = Peak stress before failure

Advantages of ASTM D5379

• Isolates pure shear stress with minimal bending

• Ideal for small or thin composite samples

• Provides reliable shear modulus and strength values

• Well-suited for research and development of advanced materials

Similar and Related Standards

Several other standards exist for measuring the shear properties of composites, each with different geometries and test methods:

• ASTM D7078 – V-notched rail shear test for larger specimens and more uniform stress field

• ASTM D2344 – Short-beam shear test, a quicker alternative often used for quality control

• ASTM D3518 – In-plane shear response of polymer matrix composites using tensile loading of ±45° laminates

• ISO 14129 – International standard for in-plane shear testing using ±45° tensile method

ASTM D5379 offers greater precision and better isolation of the shear zone compared to these alternatives, making it the preferred method in many design and R&D settings.

Conclusion

ASTM D5379 is a critical shear testing method for composite materials, offering reliable, repeatable data for engineering design, material development, and quality control. Using a universal testing machine equipped with the correct Iosipescu shear fixture, strain measurement system, and control software, you can accurately characterize in-plane shear properties.

Whether you're a manufacturer of aerospace structures or an R&D lab testing advanced composites, ASTM D5379 ensures your data meets the rigorous demands of modern material science.

Need Equipment for ASTM D5379 Testing?
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