1. Lecture # 7 Mechanical Properties(Cont) Intended learning Outcomes: After the end of this lecture the student should be able to: 1- Evaluate and measure Ductility. 2- Different methods for measuring Hardness. 3-Define Toughness. 4- Failure and its types. 5-Fatigue and its meaning.

2. Another ductility measure: DUCTILITY, %EL

4.  Hardness : is a measure of material's resistance to localized plastic deformation (small scratch ) by indentor(indentation).which is related to hardness number.  The soft material,larger deeper the indentation,lower hardness index number.  Tests for hardening : Rock well Hardness Tests. Brinell Hardness Tests. Knoop and vickers. Hardness Conversion Correlation between hardness and tensile strength Correlation Between Hardness and Tensile Strength

6. FUNDAMENTALS OF FRACTURE:  Simple fracture is the separation of a body into two or more pieces in response to an imposed stress that is static (i.e., constant or slowly changing with time) and at temperatures that are low relative to the melting temperature of the material.  Two fracture modes are possible: ductile and brittle.  Compare between ductile and brittle fracture.

7. Fracture involves two steps:  Crack formation  Propagation Compare in shape between fracture of highly ductile,moderately ductile,and brittle ductile fracture.

8. DUCTILE FRACTURE In this type of fractured specimen (Figure 9.3a), the central interior region of the surface has an irregular and fibrous appearance, which is indicative of plastic deformation Cup and cone fracture

10. BRITTLE FRACTURE V –Shape or chevron

11. Fatigue : is a form of failure that occurs in a structure subjected to dynamic and fluctuating stresses. Ex:bridges,aircracft,and machine components. Rotating bending test