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Ductility is defined as the amount of plastic deformation that metal undergoes in resisting the fracture under stress. This is a structure sensitive property and is affected by the chemical composition.

From the above Figure 2.1 we see that the material shows some level of ductility, the stress range between the limit of proportionality and ultimate tensile strength (UTS) defines the metals ductility. This varies from metal to metal. The amount of plastic deformation that the metal or the weld undergoes all through the fracture as shows in the stress and strain diagram above is the measure of metal or weld metals ductility. The Stress and strain plot do not actual characteristics of ductility but shows a relative value as a comparative number for the metal in identical condition. The plasticity of the metal is the deformation during the yielding process, as shown in the Figure 2.1.

Ductility is a structure sensitive property; hence it is affected by the test conditions, that may include any or a combination of several of the following.

 • Test temperature,

 • Shape and size of the test specimen,

 • Rate of straining,

 • Metallurgical structure of the metal,

 • The surface condition of the specimen.

The ductility values obtained through the testing is used only as an indicator of materials ductility. For design purpose the precise values obtained through the testing is seldom used. Most structures are designed to operate much below the yield strength of the material; thus, the metal is rarely tested (in real operation) for its ductility. Often metals are tested to determine some degree of ductility and Toughness through Impact testing at given temperature. The subject of impact testing spans through the low temperature ductility of metals , this is discussed in much detail further in the chapter, however this is the place to discuss various approaches to impact test a metal.