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Standard Test Method For Pull-Off Strength Of Coatings Using Portable Adhesion Testers Part 2
- Nov 22, 2017 -

1. Test Procedure

1.1 Select an adhesion-tester with a detaching assembly having a force calibration spanning the range of expected values along with its compatible loading fixture. Mid-range measurements are usually the best, but read the manufacturer’s operating instructions before proceeding.

1.2 If a bearing ring or comparable device is to be used, place it concentrically around the loading fixture on the coating surface. If shims are required when a bearing ring is employed, place them between the tester base and bearing ring rather than on the coating surface.

1.3 Carefully connect the central grip of the detaching assembly to the loading fixture without bumping, bending, or otherwise prestressing the sample and connect the detaching assembly to its control mechanism, if necessary. For nonhorizontal surfaces, support the detaching assembly so that its weight does not contribute to the force exerted in the test.

1.4 Align the device according to the manufacturer’s instructions and set the force indicator to zero.

NOTE 6—Proper alignment is critical. If alignment is required, use the procedure recommended by the manufacturer of the adhesion tester and report the procedure used.

1.5 Increase the load to the fixture in as smooth and continuous a manner as possible, at a rate of 1 MPa/s (150psi/s) or less for a 20 mm loading fixture so that the test is completed in about 100 s or less.

1.6 Record the force attained at failure or the maximum force applied.

1.7 If a plug of material is detached, label and store the

fixture for qualification of the failed surface in accordance with

1.8 Report any departures from the procedure such as possible misalignment, hesitations in the force application, etc.

1.9 Calculation and Interpretation of Results

1.10 If instructed by the manufacturer, use the instrument calibration factors to convert the indicated force for each test into the actual force applied.

1.11 Either use the calibration chart supplied by the manufacturer or compute the relative stress applied to each coating

sample as follows:

D4541 – 09

3

X 5 4F/pd2 (1)

where:

X = greatest mean pull-off stress applied during a pass/fail

test, or the pull-off strength achieved at failure. Both

have units of MPa (psi),

F = actual force applied to the test surface as determined in

8.1, and

d = equivalent diameter of the original surface area

stressed having units of inches (or millimetres). This is

usually equal to the diameter of the loading fixture.

1.12 For all tests to failure, estimate the percent of adhesive and cohesive failures in accordance to their respective areas and location within the test system comprised of coating and adhesive layers. A convenient scheme that describes the total test system is outlined.(See ISO 4624.)

NOTE 7—A laboratory tensile testing machine is used in ISO 4624.


1.13.1 Describe the specimen as substrate A, upon which successive coating layers B, C, D, etc., have been applied, including the adhesive, Y, that secures the fixture, Z, to the top coat.

1.13.2 Designate cohesive failures by the layers within which they occur as A, B, C, etc., and the percent of each.

1.13.3 Designate adhesive failures by the interfaces at which they occur as A/B, B/C, C/D, etc., and the percent of each.

1.13.4 A result that is very different from most of the results may be caused by a mistake in recording or calculating. If either of these is not the cause, then examine the experimental

circumstances surrounding this run. If an irregular result can be attributed to an experimental cause, drop this result from the analysis. However, do not discard a result unless there are valid

nonstatistical reasons for doing so or unless the result is a statistical outlier. Valid nonstatistical reasons for dropping results include alignment of the apparatus that is not normal to

the surface, poor definition of the area stressed due to improper application of the adhesive, poorly defined glue lines and boundaries, holidays in the adhesive caused by voids or inclusions, improperly prepared surfaces, and sliding or twisting the fixture during the initial cure. Scratched or scored

samples may contain stress concentrations leading to premature fractures. Dixon’s test, as described in Practice D3980,may be used to detect outliers.

1.13.5 Disregard any test where glue failure represents more than 50 % of the area. If a pass/fail criterium is being used and a glue failure occurs at a pull-off strength greater than the criterium, report the result as “pass with a pull-off strength >{value obtained}...”

1.13.6 Further information relative to the interpretation of the test results is given in Appendix X1.


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2. Report

2.1 Report the following information:

2.1.1 Brief description of the general nature of the test, such as, field or laboratory testing, generic type of coating, etc.

2.1.2 Temperature and relative humidity and any other pertinent environmental conditions during the test period.

2.1.3 Description of the apparatus used, including: apparatus manufacturer and model number, loading fixture type and dimensions, and bearing ring type and dimensions.

2.1.4 Description of the test system, if possible, by the indexing scheme outlined in 8.3 including: product identity and generic type for each coat and any other information supplied,the substrate identity (thickness, type, orientation, etc.), and the adhesive used.

2.1.5 Test results.

2.1.5.1 Date, test location, testing agent.

2.1.5.2 For pass/fail tests, stress applied along with the result, for example, pass or fail and note the plane of any failure (see 8.3 and ANSI N512).

2.1.5.3 For tests to failure, report all values computed in 8.2 along with the nature and location of the failures as specified, or, if only the average strength is required, report the average strength along with the statistics.

2.1.5.4 If corrections of the results have been made, or if certain values have been omitted such as the lowest or highest values or others, reasons for the adjustments and criteria used.

2.1.5.5 For any test where scoring was employed, indicate it by placing a footnote superscript beside each data pointaffected and a footnote to that effect at the bottom of each page on which such data appears. Note any other deviations from the procedure.


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