TASK 70-71-02-700-003
1 . General.
This procedure describes the method, test specimens and materials required for determining the bond lap-shear strength of thermal spray coatings. Use this testing procedure when specified in the applicable thermal spray coating procedure.
2 . Equipment.
Subtask 70-71-02-700-031
A.Testing machine per requirements of ASTM Specification E4.
B.Test specimen per Figure 1.
Figure 1   Lap-Shear Test Specimen
3 . Materials.
Subtask 70-71-02-700-032
 
Material
Solution/Product Number
 
A. Adhesive Film or Liquid

 
(1) FM-1000
C01-103  
 
(2) EC2186 or EC2086
C01-105  
 
(3) 2214
C01-146  
4 . Preparation of Test Specimen.
Subtask 70-71-02-700-033
C.Make test panels of the same type of material and hardness as production parts. The test panels must be prepared for coating in the same manner as the production part and must be coated identically with the part which they represent. See Figure 1.
(1)Specimen Blanks.
(a)Edges of panels adjacent to the bonded joint shall be machined at right angles to the faces, and shall be without bevels or burrs. Dimensions are shown in Figure 1.
(2)Surface Preparation.
(a)Before applying the thermal spray coating, mask the specimen so that the coating is applied only to the region shown in Figure 1.
1After application of the thermal spray coating, the thickness of the coating must be uniform within 0.0005 inch (0.013 mm), and burrs at the coating-mask interface must be removed before bonding.
2Degrease the center panel, and roughen both surfaces to 100-150 microinches (rms), minimum, by grit blasting. The roughened area must be larger than the area required for bonding.
(b)Bonding the Specimen.
1All surfaces to be bonded must be degreased before bonding.
2Adhesive for bonding should be C01-103  , C01-105   or C01-146  . Cut the adhesive film to the size and shape of the bonding area before bonding.
3Assemble the test panels and adhesive film strip as shown in Figure 1; then apply contact pressure of 25 psi (172.4 kPa) for one hour at a temperature of 300°F(149°C) or as recommended by the adhesive manufacturer to bond the panels together. When shims are required, use C01-105   adhesive and bond at 375°F (191°C).
4When the assembled test specimen has cooled to room temperature after bonding, remove all excess adhesive from the sides by carefully scraping and sanding.
5 . Testing.
Subtask 70-71-02-700-034
D.Mount the test specimen in a testing machine that conforms to the requirements of ASTM Specification E4. Clamp as follows:
(1)Use shims of sufficient thickness to fill the space between the ends of the outer panels so that they will not be bent or sprung by the clamps of the machine when tightened for testing.
(2)Align the test specimen in the testing machine so that the jaws and the centerline of the specimen are in a straight line, jaws directly opposite each other, with the imaginary extension of the centerline passing through the points of suspension. The jaws should be no closer than 2 inches (51 mm) to the edge of the lap joint, and must grip tightly and uniformly.
(3)The test specimen shall be at room temperature when the test is made.
(4)Apply load at a constant rate between 940-1100 lbs/min (4.18-4.89 KN/min) or a headspeed travel rate of 0.05 inch/min(1.3 mm/min) until the test specimen shears. ASTM C-633 is an acceptable test method.
6 . Test Results.
Subtask 70-71-02-700-035
E.Record the following information derived from the test.
(1)Maximum applied load at failure.
(2)Length and width of shear area(s), measured to nearest 0.010 inch (0.25 mm) to calculate surface area of bonded joint.
(3)Shear strength is expressed by the following formula:
Shear strength, psi (MPa) =
Applied Load, lb (N) divided by Surface area of bonded joint, sq. in. (sq mm)
(4)Nature or location of failure, such as:
(a)Cohesive failure of thermal spray coating.
(b)Cohesive failure of adhesive.
(c)Failure of adhesion between thermal spray coating and substrate metal.
(d)Failure of bond between adhesive and thermal spray coating.
(e)Failure of bond between adhesive and center panel.
NOTE:
If the test fails in the adhesive below specified values, it indicates a bad test specimen and the test should be repeated.