What is the minimum allowable radius of the test cap used in SFRM bond strength testing?

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Multiple Choice

What is the minimum allowable radius of the test cap used in SFRM bond strength testing?

Explanation:
In SFRM bond strength testing, the test cap defines the footprint over which the pull force is applied, so its size directly affects how the load is distributed and how the failure mode is interpreted. The radius sets the contact area; using too small a cap concentrates stress and makes the test sensitive to edge effects, usually inflating apparent strength or causing premature coating failure at the cap edge rather than true adhesion failure. A cap with a radius of one inch provides a reasonable, standardized contact area (about 3.14 square inches) that distributes the load more evenly and yields more repeatable, comparable results. Larger caps are allowable, but the question asks for the minimum, so one inch is the correct lower limit.

In SFRM bond strength testing, the test cap defines the footprint over which the pull force is applied, so its size directly affects how the load is distributed and how the failure mode is interpreted. The radius sets the contact area; using too small a cap concentrates stress and makes the test sensitive to edge effects, usually inflating apparent strength or causing premature coating failure at the cap edge rather than true adhesion failure. A cap with a radius of one inch provides a reasonable, standardized contact area (about 3.14 square inches) that distributes the load more evenly and yields more repeatable, comparable results. Larger caps are allowable, but the question asks for the minimum, so one inch is the correct lower limit.

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