ASTM F1044-05 Standard Test Method for Shear Testing of Calcium Phosphate Coatings and Metallic Coatings

The standard "ASTM F1044-05 Standard test method for shear testing of calcium phosphate coatings and metallic coatings" developed by the American Society for Testing and Materials (ASTM) describes the shear test method for continuous calcium phosphate coatings and metallic coatings bonded to dense metal substrates at ambient temperatures. This test method evaluates the degree of adhesion of coatings to substrates or the internal cohesion of a coating in shear parallel to the surface plane.

• For calcium phosphate or metallic coatings, the shearing method consists of subjecting a sample assembly consisting of one coated and one uncoated component to a shear load. The components to be tested may be bonded directly by thermomechanical means, for example, by sintering or diffusion bonding, or they may be bonded together using a polymeric adhesive. The adhesive may be in film form or in bulk form, but shall have a bulk shear strength of at least 34,5 MPa or the minimum required adhesion or cohesion strength of the coating, whichever is greater. The shear load is applied parallel to the plane of the coating using a tensile machine capable of determining the maximum strength of the coating to substrate interface bond.
• For metallic coatings only, the shear method (lap shear method) consists of subjecting a porous coated area to a single shear loading, usually using a suitable polymeric adhesive or bone cement adhesive and a test fixture in a tensile machine, and determining the maximum shear stress required to achieve separation, i.e. the shear strength of the coating or substrate bond or the shear strength of the coating.

The shear test method is recommended for shear testing of calcium phosphate and metallic/substrate combinations and can provide information on the adhesive or cohesive strength of coatings under uniaxial shear stress.

This test method can be useful for comparative evaluation of the adhesive or cohesive strength of various types of coatings. Information developed using this test method can be useful for certain quality control and design purposes.

The test method should not be considered to provide intrinsic values ​​for direct use in making calculations such as determining the ability of a coating to withstand specified environmental stresses.

Processing variables such as substrate preparation prior to coating, surface texture, coating technique variables, or post-coating heat treatment or heat can have a significant impact on the results of the shear test. The sample evaluated should be representative of the actual end-use coating.

The machines used for testing shall comply with the requirements of the standard “ASTM E4-13 Standard Practices for Strength Verification of Testing Machines”. The loads used to determine shear strength and yield strength shall be within the loading range of the testing machine as defined in this standard.

Various types of couplings can be used to transmit the load applied to the specimens by the testing machine. To provide axial shear stress, it is important that the specimen axis coincides with the centre line of the testing machine heads and that the coating test plane is parallel to the axial load. Any deviation from this requirement (i.e. any eccentric loading) will result in bending stresses that are not included in the usual stress calculation (force/sectional area).

In the aligned interface method for calcium phosphate or metallic coatings, drawings of a typical holding device for the test fixture, an adapter for connecting the cutting apparatus to the tensile machine and a schematic of the test fixture are shown in the figures within the standard.

For the lap shear method for metallic coatings only, the lap shear test clamping fixture and the lap shear test loading fasteners are shown in the figures in the standard.

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