Mechanical properties of metals Stress and Strain in metals Engineering Materials Mechanical properties of metals Stress and Strain in metals Engineering Stress-Strain Diagram Experimental plot of engineering stress (σ) Versus Engineering strain (ε); σ is normally plotted as the y axis and ε as the x axis.

Mechanical properties of metals Engineering Materials Mechanical properties of metals Mechanical property data obtained from Tensile test and the Engineering Stress-Strain Diagram The mechanical properties of metals and alloys that are of engineering importance for structural design and can be obtained from the engineering tensile test are: Modulus of Elasticity (E) Yield Strength Ultimate Tensile strength (UTS) Percent Elongation Percent reduction in area

Mechanical properties of metals Engineering Materials Mechanical properties of metals Mechanical property data obtained from Tensile test and the Engineering Stress-Strain Diagram 1. Modulus of Elasticity (E) The linear elastic region (OP): linear means that the relationship between stress and strain obeys the uniaxial Hook’s law. σ=E ε E (modulus of elasticity) can be determine by measuring the slope of the curve in this region. E= σ/ε Units of psi or Pa

Mechanical properties of metals Engineering Materials Mechanical properties of metals Mechanical property data obtained from Tensile test and the Engineering Stress-Strain Diagram 2. The Elastic Limit (E) Upon continued loading past point P, a transition to a new region takes place. In this region (PE), the relationship between stress and strain is no longer linear but the behavior is still elastic. Point E called the elastic limit. Up to point E, if one removes the load, the specimen will regain its original shape and dimensions.

Mechanical properties of metals Engineering Materials Mechanical properties of metals Mechanical property data obtained from Tensile test and the Engineering Stress-Strain Diagram 3. Yield Strength (point) (Y) With additional loading applied to the specimen, past point E, the material reaches the yield point (Y). The deformation experienced by the material past point Y is permanent and is called plastic deformation.

Mechanical properties of metals Engineering Materials Mechanical properties of metals Mechanical property data obtained from Tensile test and the Engineering Stress-Strain Diagram 3. Yield Strength (point) (Y) The stress at which yield occurs, is called the yield strength of the material. In order to have a unified standard, the 0.2 % offset yield strength is used. Engineers often design various components to protect against yield. Calculation method of the yield strength

Mechanical properties of metals Engineering Materials Mechanical properties of metals Mechanical property data obtained from Tensile test and the Engineering Stress-Strain Diagram 4. Ultimate Tensile strength (UTS) With continued loading past the yield point (Y), the specimen undergoes sever plastic deformation. Although the specimen becomes longer and thinner in this region, it retains its cylindrical shape up to point U. The stress corresponding to point U is called ultimate strength of the metal. It represents the largest stress or the peak point in the stress-strain diagram.

Mechanical properties of metals Engineering Materials Mechanical properties of metals Mechanical property data obtained from Tensile test and the Engineering Stress-Strain Diagram 4. Ultimate Tensile strength (UTS) With continued loading past the yield point (Y), the specimen undergoes sever plastic deformation. Although the specimen becomes longer and thinner in this region, it retains its cylindrical shape up to point U. The stress corresponding to point U is called ultimate strength of the metal. It represents the largest stress or the peak point in the stress-strain diagram. In region YU, as the metal plastically deforms, it becomes stronger, i.e, one needs to apply larger loads to cause the same level of deformation. This phenomenon is called strain hardening).

Mechanical properties of metals Engineering Materials Mechanical properties of metals Mechanical property data obtained from Tensile test and the Engineering Stress-Strain Diagram 4. Ultimate Tensile strength (UTS) With continued loading past the yield point (Y), the specimen undergoes sever plastic deformation. Although the specimen becomes longer and thinner in this region, it retains its cylindrical shape up to point U. The stress corresponding to point U is called ultimate strength of the metal. It represents the largest stress or the peak point in the stress-strain diagram. In region YU, as the metal plastically deforms, it becomes stronger, i.e, one needs to apply larger loads to cause the same level of deformation. This phenomenon is called strain hardening). Also in this region (YU), as the length increases, the cross-sectional area of the specimen becomes smaller. This is called Poissons effect.

Mechanical properties of metals Engineering Materials Mechanical properties of metals Mechanical property data obtained from Tensile test and the Engineering Stress-Strain Diagram Necking This is the point at which the specimen undergoes extensive necking; where the diameter drops sharply in an unstable manner. Necking occurs at point U.

Mechanical properties of metals Engineering Materials Mechanical properties of metals Mechanical property data obtained from Tensile test and the Engineering Stress-Strain Diagram The fracture strength and ductility Upon loading past point (U), rate of increase in stress due to reduction in area becomes significantly larger than the rate of strain hardening. Thus the curve starts to dip very quickly. That is way the fracture strength is smaller than the ultimate strength.

Mechanical properties of metals Engineering Materials Mechanical properties of metals Mechanical property data obtained from Tensile test and the Engineering Stress-Strain Diagram 4. Percent Elongation The amount of elongation that a tensile specimen undergoes during testing provides a value for the ductility of a metal. Ductility of metals is most commonly expressed as percent elongation. Percent elongation is a measure of the ductility of the metal and is also an index of quality of the metal.

Mechanical properties of metals Engineering Materials Mechanical properties of metals Mechanical property data obtained from Tensile test and the Engineering Stress-Strain Diagram 5. Percent reduction in area The ductility of a metal or alloy can also be expressed in terms of the percent reduction in area. Percent reduction in area is a measure of the ductility of the metal and is also an index of quality.

Mechanical properties of metals Stress and Strain in metals Engineering Materials Mechanical properties of metals Stress and Strain in metals

Mechanical properties of metals Stress and Strain in metals Engineering Materials Mechanical properties of metals Stress and Strain in metals HW 2 A tensile specimen of cartridge brass sheet has a cross section of 0.32 in. X 0.12 in. And a gage length of 2.00 in. Calculate the engineering strain that occurred during a test if the distance between gage markings is 2.35 in. after the test. 2. A 0.5 in. diameter round sample of a 1030 carbon steel is pulled to failure in a tensile testing machine. The diameter of the sample was 0.343 in. at the fracture surface. Calculate the percent reduction in area of the sample.