ASTM F1264 Annex 3 is a test method for bending fatigue testing of intramedullary fixation devices (IMFD). This cyclic 4 point bend test determines the fatigue life at a specified bending moment or estimates the fatigue strength for a specified number of cycles.

1.) The four point bend fixture should be attached to a Universal Testing System and adjusted as follows;

  • The suggested Short and Long Spans in A1.8.1 should be used whenever possible. The two spans listed below are common.

s=c=38mm (1.5in.) L=114mm(4.5in.)

s=c=76mm (3.0in.) L=228mm(9.0in.)

  • Guides could be added to the outside edges of the bend fixture to prevent the IMFD from shifting position during testing. The guides must not interfere with load application or specimen deformation.
  • If the IMFD is a unique shape or curved be careful to secure the specimen as directed in the full description of this specification.

bone fixation  bone plate assortment  4 point bend

IMFD   Bone Plates            4-pt. bend fixture

2.) Before starting the multicycle test the load and the #of cycles the test will run, runout, must be determined. There are a few methods to use;

  • Test IMFD at different load levels to failure and plot failure loads vs. number of cycles.
  • Determine nominal stress through moment analysis using analytical or experimental methods.
  • Fatigue Strength Determination- 1 million cycle test to determine maximum moment applied to the IMFD to cause failure.
 Using MTESTQuattro, our PC based control system, it is easy to create a variety of testing profiles. This profile is a compression test repeating for multiple cycles.
ASTM F1264-A3 requires you to;
  • create a sinusoid cyclic curve at a rate of <=5Hz.
  • Record number of cycles as the test is progressing.
  • Set limits that will tell the testing system to stop the test when the specimen fails or deviates from intended load.
Recommended system
ADMET eXpert 7603, single column testing system or ADMET eXpert 2610, dual column testing system both equipped with MTESTQuattro data acquisition, analysis, and control system and with a 4-point bend fixture. This system can be equipped with a Torque Actuator to create a biaxial testing system capable of servo control of load, position, torque and angle.
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