ASTM D3410 - Measuring the Compressive Strength of Polymer Matrix Composites

ASTM D3410 is a testing standard that determines the in-plane compressive properties of polymer matrix composite materials reinforced by high-modulus fibers. This test method is designed to produce compressive property data on CFRP’s (Carbon Fiber Reinforced Polymers) mainly used by the Aerospace industry for material specifications, research and development, quality assurance, and structural design and analysis. Carbon fiber reinforced polymers are a preferred material whenever high strength-to-weight ratio and stiffness (rigidity) is required, such as when building aircraft, ships, and automotives, as well as in civil engineering. CFRPs are also being used in an increasing number of consumer and technical applications, such as in sporting equipment.

The compressive force is being introduced by shear loading with wedge grip faces inside a loading fixture. Important results obtained during this test are the ultimate compressive strength, compressive and ultimate compressive strain, the compressive Chord modulus of elasticity, compressive Poisson’s ratio by chord modulus and the transition strain.

Test Fixture

ASTM D3410 testing requires an S4690A IITRI Compression Fixture, which is placed between two platens - a spherical platen on top, and a rigid one on the bottom. Through the wedge action of the test fixture, the compressive force is initiated through shear onto the specimen, (different than the end loading in ASTM D695, for example).

Materials Testing System

This test is best performed on a high force universal testing system such as Instron's 6800 Series along with an AlignPRO fixture. Though a 250 kN capacity system is usually sufficient for composites, a higher capacity system may be preferred for labs who perform a wide variety of high force testing.

Testing Tips and Tricks

• Compression modulus, and especially ultimate compressive stress, are sensitive to poor material fabrication practices, damage induced by improper specimen machining, and lack of control of fiber alignment.

• The data resulting from ASTM D3410 has been shown to be sensitive to the flatness and parallelism of the specimen tabs, so care should be taken to ensure that the specimen tolerance requirements are met. This usually requires precision grinding of the tab surfaces after bonding them to the specimen.

• The surface finish of the mating surface of the wedge grip assembly can have a significant effect on test results. Since these surfaces undergo sliding contact, they must be polished, lubricated, and nick-free.