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.
If you plan on conducting ASTM D7774 we recommend acquiring the test standard from ASTM. There are many important details regarding this test method that are provided which are key to achieving successful results. Every standard provides important environmental conditions, test sample preparation and conditioning requirements, sample dimensions and test reporting expectations. It’s critical that you fully understand the standard so that you can set up the test, run the procedure, and report the results requirements.
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.
What Other Standards Focus On Flexural Fatigue of Plastics?
- ISO 13003 covers flexural fatigue testing of fiber reinforced plastic composites
- ASTM D3479 covers tension-tension fatigue testing of polymer matrix composites
- ASTM D790, ASTM D6272 and ISO 178 focus on three and four point static tests of plastics
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.
ASTM D7774 Test Systems→
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ASTM D7774 Testers
800 Series All-Electric Dynamic & Fatigue Test Machines
These all-electric test systems are optimized for both dynamic and static testing and is the ideal solution for mid force fatigue testing.
ASTM D7774 Test Grips
ASTM D7774 Strain Measurement
E3540 Deflectometer
E3540 deflectometers are the most common solution to measuring deflection values which are important to generating modulus and yield data.
ASTM D7774 Test Machine Software
ASTM D7774 Test Machine Controller Software | ND7774
Application specific module features preset settings, test calculations, and graphical test report contents.
ASTM D7774 Digital Micrometer | TestGage
TestGage is used with a digital micrometer or caliper to measure sample thickness (depth) and width. After the user makes measurements, data is transferred to the control software.
Video Recording and Playback Software Module | TestVideo
High resolution video capture of the test. Playback is time synchronized with load data.
