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Losipescu Shear Test Fixture ASTM D5379

Losipescu Shear Test Fixture

ASTM D5379, ASTM D7078, ASTM D3518, ISO 14129

ASTM D5379 Iosipescu Fixture V-Notch Shear is used to determine the mechanical strength of composite material, is a four-point asymmetric flexure fixture which tests for shear properties by means of the V-notched beam method. Each half of the fixture contains a wedge-action grip which lightly clamps one half of the test specimen across the specimen width while simultaneously supporting the specimen on its back face. One of the grips, normally the lower half, is mounted on a base plate which also supports a linear bearing shaft, while the other grip, normally in the upper position, contains a linear bearing which mounts over the shaft on the base. Each element is attached to or supported by one of the testing machine heads. A specified gap is left unsupported between fixture halves. An alignment tool is provided to ensure that the specimen notch is aligned with the line of action of the loading fixture. Reference ASTM Standard D 5379 

General introduction

ASTM D5379 Iosipescu Shear Test Fixture – V-Notched Beam Method for Composite In-Plane Shear Testing | UnitedTest


ASTM D5379 Iosipescu Fixture V-Notch Shear is used to determine the mechanical strength of composite material, is a four-point asymmetric flexure fixture which tests for shear properties by means of the V-notched beam method. Each half of the fixture contains a wedge-action grip which lightly clamps one half of the test specimen across the specimen width while simultaneously supporting the specimen on its back face. One of the grips, normally the lower half, is mounted on a base plate which also supports a linear bearing shaft, while the other grip, normally in the upper position, contains a linear bearing which mounts over the shaft on the base. Each element is attached to or supported by one of the testing machine heads. A specified gap is left unsupported between fixture halves. An alignment tool is provided to ensure that the specimen notch is aligned with the line of action of the loading fixture. Reference ASTM Standard D5379 


Testing to ASTM D5379:

The Iosipescu shearing device is guided in the longitudinal direction. It is placed on a compression platen or the crosshead of the testing system.

A specimen notched on both sides is inserted in the shear test fixture. A zone of torque-free shear load emerges between the notches when a compression load is applied. The fibers must lie parallel or transverse in relation to the load direction. The shear strain is measured via two strain gauges that are applied at a 45° angle to the shear plane.

Characteristic values determined according to ASTM D5379:

Shear behavior

0.2% shear stress

Max. shear stress

Secant shear module


Losipescu Shear Test FixtureLosipescu Shear Test Fixture


Test Specimen: 

Length76 mm (3 in)
Width19 mm (0.75 in)
ThicknessUp to 12.7 mm (0.5 in); 3–4 mm recommended
Notch angle90°
Notch root radius≤ 1.27 mm (0.05 in)
Notch depth20–23% of specimen width


Key Features

  • Why the V-Notched Beam Method?
  • Key Features of UnitedTest Iosipescu Fixtures
  • Standard
  • How the Iosipescu Shear Fixture Works
  • Materials & Applications
  • ASTM D5379 vs. Other Composite Shear Test Methods
  • Keywords

Conventional four-point flexure produces bending stresses in the central section. The Iosipescu method uses an asymmetric four-point loading — achieved by rotating one pair of loading points by 180° — which converts bending into pure shear in the region between the notches.


The 90° V-notches machined into each side of the specimen:

Remove the low-stress outer regions of the beam

Create a surprisingly uniform shear stress state between the notch roots

Minimize stress concentrations when notch depth is 20–23% of specimen width.

Precision load-line alignment via retractable notch alignment pin

Cross-roller bearing system for frictionless, single-degree-of-freedom motion

Stainless steel construction for long-term stability and corrosion resistance

Adjustable tapered wedges to accommodate varying specimen widths

Customizable specimen dimensions — fixtures built to your exact specimen geometry

Compatibility with all UnitedTest UTM models, also customized adaptor to suitable for customer present other brand testing machine like MTS, Instron etc., 

Optional temperature chamber integration for elevated or sub-ambient testing

Competitive pricing, high quality, and fast delivery


ASTM D5379 Standard Test Method for Shear Properties of Composite Materials by the V-Notched Beam Method

ASTM D5379 / D5379M-19 is the Standard Test Method for Shear Properties of Composite Materials by the V-Notched Beam Method — widely known as the Iosipescu shear test. The method is designed to produce shear property data for material specifications, R&D, quality assurance, and structural design, and can evaluate either in-plane or interlaminar shear properties depending on specimen orientation. 



GOST R 57968-2017 Polymer composites. Test method of samples for shearing

ISO 14129 Fibre-reinforced plastic composites - Determination of the in-plane shear stress/shear strain response, including the in-plane shear modulus and strength, by the ˝45° tension test method

ASTM D3518 Standard Test Method for In-Plane Shear Response of Polymer Matrix Composite Materials by Tensile Test of a ±45° Laminate

ASTM D7078 Standard Test Method for Shear Properties of Composite Materials by V-Notched Rail Shear Method

GB/T 28889 Test method for in-plane shear properties of composite materials

GOST R 57207 Polymer composites. Test method for shear properties of V-notched test samples

GB/T 30970 Test method for the shear properties of polymer matrix composite materials by V-notched beam method

GB/T 30969 Test method for short-beam shear strength of polymer matrix composite materials

ASTM D4255 Standard Test Method for In-Plane Shear Properties of Polymer Matrix Composite Materials by the Rail Shear Method


The core design challenge of any ASTM D5379 fixture is to ensure that the applied load line passes exactly through the root of the V-notch. Misalignment introduces off-axis forces and corrupts the pure shear state.

UnitedTest's ASTM D5379 Iosipescu shear fixture — and industry-leading designs from Wyoming Test Fixtures, Instron, and others — solve this through:


Notch Alignment Pin — A small pin is raised into the lower notch to center the specimen left-to-right during installation. The specimen is pushed against the flat back of the fixture for fore-and-aft locating.

Cross-Roller Bearing — A nearly frictionless bearing ensures movement is strictly vertical and only in the load direction, eliminating parasitic bending and out-of-plane rotation that plague older linear-bush designs.

Tapered Wedges — Provide light clamping to prevent specimen rotation during the test; they are not intended to act as heavy clamps.

Edge-Wise Loading — The fixture applies opposing compressive forces to the top and bottom edges of the specimen, generating shear in the notched section.


Strain Measurement:

A ±45° biaxial strain gage is mounted on the specimen surface in the notched region to directly measure shear strain. For 0° unidirectional specimens, specialized Iosipescu gages that span the full distance between notch tips are recommended to capture the true average shear strain — otherwise the modulus can read 5–10% high.


Alternative non-contact methods include video extensometers and Digital Image Correlation (DIC) systems.


ASTM D5379 is validated for a broad range of fiber-reinforced composites:


Unidirectional laminates with fibers at 0° or 90° to load axis

Cross-ply laminates with balanced 0°/90° ply countsWoven fabric laminates with warp direction at 0° or 90°

Short-fiber composites with randomly distributed fibers

Carbon fiber, glass fiber, and aramid fiber systems

Thermoset and thermoplastic matrix composites


Industries served:

Aerospace — laminate qualification, structural design

Automotive — lightweight composite component validation

Defense — ballistic and protective composite structures

Renewable energy — wind turbine blade materials

Research institutions — advanced materials R&D

StandardMethodSpecimen SizeBest For
ASTM D5379V-Notched Beam (Iosipescu)Small (76×19 mm)Pure shear, R&D, unidirectional & cross-ply
ASTM D7078V-Notched Rail ShearLarger (76×56 mm)High shear strength laminates, ±45° plies
ASTM D2344Short-Beam ShearSmallQuick QC screening
ASTM D3518±45° TensileStandard tensile couponIn-plane shear response


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Specification

Max. force capacity: 50 kN (11,250 lbf)

Opening: 24 mm

Standard adapter: M20 (Other adapters on request)

Weight: 10 kg

Material: Steel, nickel-plated

Temperature range: -10 … +80°C


Standard

ASTM D5379 Shear Test of Composite by the V-Notched Beam methods

ASTM D5379 Standard Test Method for Shear Properties of Composite Materials by the V-Notched Beam Method

ASTM D5379 used for characterizing the shear behavior of advanced fiber‑reinforced composites. Often referred to as the Iosipescu shear test. It quantifies both in-plane shear (1-2 plane) and interlaminar shear (1-3, 2-3 planes) of fiber-reinforced polymer composites, covering continuous unidirectional laminates, woven fabric laminates, balanced symmetric panels, and random short-fiber molded composites (SMC). This testing method measures shear stress/strain, ultimate strength and strain, as well as shear string elastic modulus. 

ASTM D7078 V-Notched Rail Shear Test for Composite Materials

ASTM D7078 V‑Notched Rail Shear Test for Composite Materials

ASTM D7078 determines shear properties of high‑modulus fibre‑reinforced composite materials by clamping a V‑notched specimen between two pairs of loading rails and pulling the rails in tension. The rails transmit shear forces through the faces of the specimen (face‑loading), which allows higher shear forces to be applied than in edge‑loaded methods.

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