Where is the yield point

Typical Stress-Strain Curve Plastics. Alternate values are sometimes used instead of yield strength. Several of these are briefly described below. The yield point , determined by the divider method, involves an observer with a pair of dividers watching for visible elongation between two gage marks on the specimen.

When visible stretch occurs, the load at that instant is recorded, and the stress corresponding to that load is calculated. Soft steel, when tested in tension, frequently displays a peculiar characteristic, known as a yield point.

If the stress-strain curve is plotted, a drop in the load or sometimes a constant load is observed although the strain continues to increase. Eventually, the metal is strengthened by the deformation, and the load increases with further straining.

The high point on the S-shaped portion of the curve, where yielding began, is known as the upper yield point, and the minimum point is the lower yield point. This phenomenon is very troublesome in certain deep drawing operations of sheet steel. The steel continues to elongate and to become thinner at local areas where the plastic strain initiates, leaving unsightly depressions called stretcher strains or "worms. The proportional limit is defined as the stress at which the stress-strain curve first deviates from a straight line.

Below this limiting value of stress, the ratio of stress to strain is constant, and the material is said to obey Hooke's Law stress is proportional to strain. The proportional limit usually is not used in specifications because the deviation begins so gradually that controversies are sure to arise as to the exact stress at which the line begins to curve. The elastic limit has previously been defined as the stress at which plastic deformation begins. This limit cannot be determined from the stress-strain curve.

The method of determining the limit would have to include a succession of slightly increasing loads with intervening complete unloading for the detection of the first plastic deformation or "permanent set. Elastic limit is used, however, as a descriptive, qualitative term.

The yield point indicates the end of the elastic behavior of the material and the start of the plastic behavior. This means that if the yield point is exceeded, the material is irreversibly, or in other words permanently, plastically deformed.

As a rule, components and constructions can no longer be used safely if the yield point is exceeded even locally or partially. The offset yield R p0. Cold-rolled or cold formed materials do not have a pronounced yield point. Generally for these materials an offset yield of 0. This 0. The 0. Tensile strength. The tensile strength is determined in the tensile test as the maximum mechanical tensile stress.

Tensile Test. The tensile test is used to characterize the strength and deformation behavior under tensile load. Tensile test ISO Test load 0. Type of test Tensile test Compression test Flexure test. Applications Universal testing applications in a small force range. ProLine for standardized tests Industries Universal. Test load 5 kN - kN. Applications Simple test applications. AllroundLine Individual and versatile Industries Universal.

Test load 5kN - kN. Applications Universal testing applications in a medium force range. Test load - 2, kN.