ASTM D7774 Flexural Fatigue Testing of Plastics

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ASTM D7774 Flexural Fatigue Testing of Plastics

ASTM D7774 describes how to measure the full reversed fatigue properties of plastics in flexure, and applies to both rigid and semi-rigid plastics. Stress and strain levels are below the proportional limit of the plastic where the strains and stresses are relatively elastic. Both three and four point bend fixtures are used for the tests.

What Is ASTM D7774?

ASTM D7774 describes how to measure the full reversed fatigue properties of plastics in flexure, and applies to both rigid and semi-rigid plastics. Stress and strain levels are below the proportional limit of the plastic where the strains and stresses are relatively elastic. Both three and four point bend fixtures are used for the tests.

Why Perform Fatigue Tests on Plastics?

These tests help determine the effect of processing, surface condition, stress, and other factors, on the fatigue resistance of plastic material. The results help guide the selection of plastic materials for service under conditions of repeated flexural stress.

Important Considerations When Testing per ASTM D7774

Testing is needed because material response in fatigue is not identical for all plastics. If a plastic does not exhibit an elastic region, where strain is reversible, plastic deformation will occur during fatigue testing, causing the amplitude of the programmed load or deformation to change during testing. Caution shall be taken when using the results for design as they are generally not indicative of the true fatigue properties of the material.

The results of tests are suitable for application in design only when the specimen test conditions realistically simulate the actual service conditions.

ASTM D7774 Test Methods

Procedure A Three Point Flexural Fatigue Test — Specimen dimensions, shape, surfaces, and limitations are in compliance with Test Method ASTM D790.

Procedure B Four Point Flexural Fatigue Test — Specimen dimensions, shape, surfaces, and limitations are in compliance with Test Method ASTM D6272. The test method only covers specimens with 1:2 or 1:3 load span-to-support span ratios.

Specimens are cyclically loaded equally in the positive and negative directions to specific stress or strain level at a uniform frequency until the specimen ruptures or yields.

Dynamic Test Machines for ASTM D7774

Our 800 series fatigue test machines serve both static and fatigue testing applications. The 800 series is capable of performing plastics fatigue tests at speeds up to 15 hz with load capacities up to 50 kN (11,250 lbf). They feature all electric dynamic actuators. All of our fatigue testers are capable of load, strain and position control.