ASTM E855 Bend Testing of  Flat Metals for Spring Applications Involving Static Loading

Test specimens should be rectangular. It should not be twisted or wavy. No attempt should be made to flatten or straighten specimens before testing. All burrs should be removed before testing. The microstructure of the specimen should not be altered during the preparation of the specimen. The specimen size depends on the testing machine capacity. The recommended minimum specimen thickness is 0.015 inches (0.38 mm). Specimens having thickness variations over 2 % of the average (of these five measured thicknesses) is not acceptable. 

The ratio of the specimen span to thickness should be greater than 15. Since the span is 2.0 inches (50.8 mm), the specimen thickness cannot exceed 0.13 in. (3.30 mm). The width to thickness ratio should be greater than 10. Specimens having width variations greater than 0.5 % of the average width will not be tested. The minimum specimen width is 0.5 inches (12.7 mm). 

Test Method B (three-point loaded bend test) and Test Method C (four-point loaded bend test):  

At least six specimens are required, half of which will be tested with the concave surface facing upwards and half with the convex surface facing upwards. Test specimens should be rectangular. They should not be twisted or wavy. No attempt should be made to flatten or straighten specimens before testing. During specimen preparation, the microstructure of the specimen should not be altered. All burrs should be removed before testing. 

The minimum specimen thickness is 0.010 inches (0.25 mm). Specimens having measured thickness variations over 2 % of the average (of these five measured thicknesses) will not be tested. The span length should be 150 times the nominal thickness in the range 0.010 inches to 0.020 inches (0.25 to 0.51 mm), inclusive, and 100 times the nominal thickness in the range exceeding 0.020 inches (0.51 mm). 

Specimen width should be 0.150 inches (3.81 mm) in the thickness range 0.010 to 0.020 inches, inclusive, and 0.500 inches (12.7 mm) in the thickness range exceeding 0.020 inches. Specimens having width variations greater than 0.2 % of the average width will not be accepted. The total specimen length should be 250 times the nominal thickness in the range of 0.010 to 0.020 inches and 165 times the nominal thickness in the range exceeding 0.020 inches. 

Test Method A (Cantilever Beam Test): 

A cantilevered beam is fixed at one end, and the other end is free. In cantilever beam tests, a load is applied to the free end of the beam until failure occurs. If the load is known at failure, the stress in the top of the beam can be calculated. The top of the beam is in tension, and the bottom of the beam is in compression. 

Test Method B (three-point loaded bend test) and Test Method C (four-point loaded bend test):  

The three-point bend test consists of placing the sample horizontally on two points and applying force to the top of the sample through a single point so the sample bends into a “V” shape. 

A four-point bend test is roughly the same except that instead of the force applied through a single point on top, it is applied through two points so that the sample experiences contact at four different points and is bent more in the shape of a “U”. 

The three-point flexure test is ideal for testing a specific location on the sample, whereas the four-point flexure test is better suited for testing a larger section of the sample and highlights defects more effectively than a 3-point bending test.

• Type of test
• Modulus of elasticity in bending
• The bending proof strength, and 
• The offset yield strength.