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Testing Method

Tensile Test

A tensile test is a basic testing method to measure the yield point, the tensile strength and the elongation of a steel sheet. In case of a usual tensile test, some load is increased until the test piece is broken while some load is added to a fixed test piece.

Test Piece

The kind and sizes, etc. of test pieces are specified in all of the specifications, such as KS, JIS and ASTM, etc. in order for you to prepare for test a tensile test. In case of a cold-rolled steel sheet, a way of selecting a test piece, which is specified in KS B 0801 No.5, is generally used.

Results from a Tensile Test

The results from a tensile test are used as the most basic standards to judge the workability and formability.

  • Elongation (El)
    The higher the elongation is, the better the formability is.
  • Yield Point (YP)
    The lower the yield point is, the better the shape of a final product is.
  • Yield Ratio (Yield Point/Tensile Strength, YR)
    The lower the yield ratio is, the wider the gap between the yield point and the tensile strength is, and the wider the gap is, the better the shape reezing property of a steel sheet is when it is processed at the same strength level.
  • Elastic Modulus (E)
    An elastic modulus is inversely proportional to the inverse elasticity of a steel sheet. The lower the inverse elasticity is, the better the shape of a final product is.
  • Working Hardening Exponent (n)
    When some stress is put onto materials, a deformed part becomes hard in order for it to be constrained not to be deformed more and the force of deformation is spread to the other un-deformed parts in order for the whole parts of a material to be deformed evenly. Since the bigger the work hardening exponent is, the quicker and the evener the spread of deformation becomes, such kind of material is considered as the one with a good formability.

Rockwell Hardness Test

In this test, a hard steel ball is forced into surface of the test specimen, first under a fixed minor load and than under a major load. On remove the major load, the permanent depth of impression is measure, and a number derived form the net increase in the depth of impression in the two operations is read directly on the Rockwell hardness B- scale and Rockwell superficial hardness 30T-scale. The B-scale is based on a steel ball 1/16 in. [1.558 mm] in diameter and a 100kg test-load. The 30T-scale consists of a 30kg test load and a steel ball of the same diameter. The B-scale is highly dependable when the test specimen is 0.762mm [0.030in] or thicker. For thicknesses less than 0.762mm, therefore, use of the 30T-scale is recommended.