Information on the most widely used ASTM standards within the materials testing industry
ISO 11491: Implants for surgery -- Determination of impact resistance of ceramic femoral heads for hip joint prostheses. It defines two standardized impact test methods to evaluate the ability of ceramic femoral heads to resist fracture under impact loading.
Hip prostheses are a common medical device used to treat hip diseases and injuries. Ceramic femoral head is an important component in hip prostheses, which has excellent biocompatibility and mechanical properties, so it is widely used in clinical practice.
However, due to its brittleness and fragility, ceramic femoral heads are prone to cracking and breaking during use, affecting the lifespan and safety of the prosthesis. Therefore, it is necessary to evaluate and test the impact resistance of ceramic femoral heads.
The ISO 11491 standard specifies a test method for determining the impact resistance of ceramic femoral heads. This test method is based on impact testing, which evaluates the impact resistance of ceramic femoral heads by measuring the failure of them at a certain impact energy.
ISO 11491 Test Principle:
Impact resistance (cyclic strength) is determined by applying impacts of increasing energy to the head/taper construct and identifying the maximum energy that does not result in fracture.
Alternatively, the impact load (cyclic strength) may be determined by quasi-static load-release cycles identifying the maximum load that does not result in fracture.
Test methods specified:
ISO 11491 provides two alternative test methods for impact resistance:
Method A: Drop-weight impact test (falling weight onto a mounted ceramic head assembly);

Method B: Cyclic load-release burst test. 5 kN incremental cyclic loading (starting at 20 kN), hold time ≥ 1 s, unloading interval 5 min.
ISO 11491 Test equipment used:
| Method A: Falling Hammer Impact Tester | Adjustable drop height, calibrated impact mass, guided drop system, safety enclosure.
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| Method B: Universal Testing Machine | Force upto of 50 kN (±0,1 kN) and can apply constanct loading rate of (0,5 ± 0,1) kN/s.
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Test Procedure of ISO 11491 Impact Resistance of Ceramic Femoral Heads for hip joint prostheses:
1, Preparation of the test specimen.
Copper ring shall be cleaned with organic solvent and neutral detergent in order to remove oil, fat and contaminants.
Use a new ceramic femoral head and a new neck unit both cleaned according to the requirements of ISO 7206-10, for each test.
Use a new copper ring load distributing device for each test. A single copper ring shall be used for each test specimen (femoral head) until the test has been completed.
Mount the ceramic femoral head onto the neck unit. Care should be taken to maintain the alignment of the neck unit and ceramic femoral head.
2.1, Test method for impact resistance (cyclic strength):
Apply an initial impact energy of 20J to the sample by employing the appropriate falling weight mass (M) and falling height (H) of 1m. This ensures proper seating of the femoral head on the neck unit and deforms the shape of the copper ring to match the shape of the femoral head and holding block.
Apply progressive energy impact steps with increasing energy starting at a level that does not cause fracture. Increase the energy impact in 10J steps, increasing the falling mass.
Inspect and correct the alignment of the copper ring and the loading axis of the test specimen between impacts. Wait at least 1 h between impacts. Continue testing steps until the femoral head cracks or fractures.
If a shorter interval time between impacts is used, a rational should be provided as part of the test report.
The interval of at least 1h between impacts is required because a delayed fracture can occur after a certain period of time in spite of not observing a failure immediately after applying an impact.
Load cell data sampling: The maximum force value (peak force) recorded by the data recorder from the load cell shall be recorded as impact load. Produce a plot of impact load versus time.
2.2, Test method for the cyclic load-release burst test:
Apply a compressive force up to an initial force of 20 kN (±0,1 kN) at a loading rate of (0,5 ± 0,1) kN/s, taking a record of the force-time behaviour. Keep the load for at least 1s, then apply subsequent load-
release cycles as described in the following.
a) Release the initial force (maximum force) at an unloading rate equal to the loading rate until 0,2 kN ± 0,1 kN (unloaded state).
b) Keep the unloaded state for Δt = 5 min ± 5 s.
c) Increase the force again up to the previous maximum force plus 5 kN ± 0,1 kN with a loading rate of 0,5 kN/±0,1 kN/s (new maximum force). Keep the force for at least 1s.
d) Go back to a).
Termination of the load-release cycles:
Continue with the load-release cycles and record the number of cycles achieved until one of the following occurs:
a) the occurrence of cracks or fracture of the head;
b) fracture or permanent deformation of the neck.
Examination of the specimen:
Examine the conical loading bore after each test, and discard it if damaged. If a copper ring is used for the contact, replace it for each test.
(FROM ISO 11491) .
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Related Standard
ISO 7206-10: Implants for surgery --Partial and total hip joint prostheses -- Part 10: Determination of resistance to static load of modular femoral heads.
It specifies a method for determining the static load resistance of the connection between a modular femoral head and a tapered cone of a femoral stem (the "head/cone junction") in hip joint prostheses. Include static compression (fracture) and tensile (disassembly) tests to quantify the load capacity of modular femoral heads with conical taper (Morse taper) connections.
ISO 7206‑4 and ISO 7206‑6 are key international standards defining fatigue endurance tests for stemmed femoral components of partial and total hip joint prostheses. ISO 7206‑4 evaluates the femoral stem under simulated proximal loosening; ISO 7206‑6 evaluates the femoral neck under well‑fixed, normal in‑vivo loading.
ISO 7206-8: Implants for surgery -- Partial and total hip joint prostheses -- Part 8: Endurance performance of stemmed femoral components with application of torsion.
ISO 7206-8 standard as a series of test methods capable of effectively evaluating the endurance performance of stemmed femoral components designed for total and partial hip joint prosthesis. The standard allows experts to subject test specimens to loading conditions that mirror those seen in real conditions when patients use their hip joint prosthesis. The standard’s objective is to determine if hip implants perform as expected, ensuring their functionality and safety will be reliable for the patients who depend on them.
ASTM F2068: Standard Specification for Femoral Prostheses – Metallic Implants
ASTM F2068 covers metallic stemmed femoral prostheses used to replace the natural hip joint by means of hemi-arthroplasty or total hip surgical procedures. Prostheses for hemi-arthroplasty are intended to articulate with the natural acetabulum of the patient. Prostheses for total hip replacement are intended to articulate with prosthetic acetabular cups. Prostheses may have integral femoral heads or cones designed to accept modular heads.
The mechanical strength (fatigue test ISO 7206-4, ISO 7206-6, shear strength test ASTM F1044, tensile test ASTM F1147, abrasion resistance test ASTM F1978), corrosion resistance, and biocompatibility of the head portions of one-piece integral implants are covered by this specification.
ASTM F2996 Standard Practice for Finite Element Analysis (FEA) of Non-Modular Metallic Orthopaedic Hip Femoral Stems
ASTM F2996 standard establishes requirements and considerations for developing Finite Element models to evaluate static implant stresses and strains of non-modular metallic orthopaedic hip stem designs. It can be used for worst-case assessment within a family of implant sizes to reduce the need for physical testing. The boundary conditions are set-up according to ISO 7206-4.
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