The ASTM F1541 standard is the standard mechanical testing methodology for external skeletal fixation devices (ESFD). The test is used to measure the mechanical characteristics of external skeletal fixation devices (ESFD) and how they attach and fixate to the bone. The series of tests involved with ASTM F1541 further identify performance criteria and the development of test methods.
For the determination of ESFD’s in-plane compressive properties of ring segment bridge elements or circular rings, compressive quasistatic loading is applied at 180 degrees until failure. Plot load versus displacement, compressive yield, compressive stiffness, in-plane compressive strength is designated at an offset yield.
For external skeletal fixator joints, testing is a bit more complicated, involving the testing of part dynamics, stiffness, and the connector’s durability. Elastic flexure in the loading input element of the device should be minimized.
Fixator pins are tested by running static four-point bend assessments on pin samples to obtain a flexural deformation curve and a bending moment. Measurements calculated include the designated percentage of flexural strain, bending stiffness, and strength. These results determine bending rigidity. A static torsion test is performed involving both ends of a fixator pin. One end remains stationary while the other is gripped as the torsional load is applied. This allows for torque vs. angle plotting and calculations of rigidity, strength, and stiffness.
Individual bridge and connector elements differ in size, pattern, and material. These tests include axial, anterior-posterior shear, lateral shear force loadings, torsion, anterior-posterior bending, and medial-lateral moment loadings. When assessed, the top grip is at the loading end, while the subassemblies’ bottom grip holds it in a rigid position. Chord stiffness, ultimate strength, and yield strength of the subassembly are calculated.
To establish the design’s performance characteristics, angular and linear load conditions are conducted with static tests to determine strength and stiffness. Multi-cycle dynamic fatigue tests are performed to test it for repeated loading conditions.
