Pentagon Mandrel Bend Test

There are two side plates, each of pentagon shape. Each of the five sides are 6.5 inches long, resulting in a 10.0 inch high assembly. One of the side plates is 1/8 inch thick and has one of the sides rounded to form a high-strength mandrel of this thickness. The other side plate is identical except it has a thickness of 1/4 inch and provides the 1/4 inch mandrel. The side plates are separated by five bars, each secured near the points of the side plates at center to center distance of 5.5 inches. The bars are each 5.5 inches long and have diameters of 3/8, 1/2, 5/8, 3/4 and 1 inch.

• The Pentagon Mandrel Bend Test Apparatus is constructed of black anodized aluminum.
• The Pentagon design provides a completely self-contained unit with no loose parts.
• Paramount importance in the design is the plate backing of the 1/8 and 1/4 inch mandrels which eliminate errors of mandrel flexing.
• The Pentagon Mandrel Apparatus is ruggedly and attractively constructed. It will accommodate essentially all standard test panels.
• Mandrel size is etched in the thicker side panel after anodizing for permanence and ease of identification.

1. The preparation of the test specimens must be made with considerable care if good comparative and reproducible results are to be obtained. Improper base cleaning, resulting in poor adhesion, will normally result in a lower tolerated elongation. Coating thickness and uniformity is of paramount importance, not only due to the usual relationship of thickness with most physical characteristics but also due to the direct effect in the mandrel bend test. The test panels should be prepared in a manner and with a coating thickness as near as possible to that which will be encountered by the base - coating system process. Compensate for the direct effect of coating thickness in the Pentagon Mandrel Bend Test by adding the appropriate correction factor for each mil of coating thickness to the base.
2. Place the test panel with the uncoated side over, and in contact with, the selected mandrel with a minimum of two inches overhang and insure that there is clearance for the other end of the panel to pass the adjacent mandrel.
3. Using a steady pressure of the fingers, bend the panel approximately 180 degrees around the mandrel in about one second. Remove the panel and examine immediately for cracking of the coating visible to the unaided eye.
4. If cracking has not occurred, repeat the procedure using successively smaller diameter mandrels until cracking of the coating occurs or until the smallest diameter mandrel has been used. Record the smallest mandrel accommodated by the base-coating system or the total elongation determined.

It is obvious from the following sketch that Base Length “LC” is greater than Base Length “L”, which is in contact with the Mandrel, and that this difference is a function of the Base Thickness.

It is also obvious that the Coating Length “C” is longer than its length at the interface with the base at “LC” and this difference is proportional to the Coating Thickness.