mom notes 1 vtu mechanical engin vtu eeering

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1. B.N.M. Institute of Technology Department of Mechanical Engineering

2. Semester : 3rd Course Name : Mechanics of materials Course Code : 18ME32 Module No: 1 Strive for Excellence

3. COURSE LEARNING OBJECTIVES To know the different types of stresses and strains developed in the member subjected to axial, bending, shear, torsional & thermal loads. To know behaviour & properties of engineering materials To understand the stresses developed in bars, compounds bars, beams, shafts, and cylinders. To understand the concepts of calculation of shear force and bending moment for beams with different supports. To expose the students to concepts of Buckling of columns and strain energy. Slide #1 Department of Mechanical Engineering Strive for Excellence

4. MODULE-1 Slide #2 Department of Mechanical Engineering Strive for Excellence Stresses and Strains: Introduction, Properties of materials, Stress, Strain and Hooke’s law, Stress strain diagram for brittle and ductile materials, True stress and strain, Calculation of stresses in straight, Stepped and tapered sections, Composite sections, Stresses due to temperature change, Shear stress and strain, Lateral strain and Poisson’s ratio, Elastic constants and relations between them.

5. INTRODUCTION Mechanics of Materials or Strenght of Materials deals with the study of mechanism or behaviour of materials under the action of external loads within elastic limit. Here external loads refers to forces, Slide #3 Department of Mechanical Engineering Strive for Excellence

6. MECHANICAL PROPERTIES OF MATERIALS Slide #4 Department of Mechanical Engineering Strive for Excellence Some of the Important Mechanical properties are: Elasticity: It is the ability of the material to regain it’s original shape and size after the removal of external load. This property is desirable for materials used in machines and machine tools. Steel is perfectly elastic up to certain limit and more elastic in nature than rubber. Plasticity: It is the ability of the material to retain deformation produced due to external load on a permanent basis. This property is useful in case of forging, stamping on coins and in ornamental work

7. MECHANICAL PROPERTIES OF MATERIALS Slide #5 Department of Mechanical Engineering Strive for Excellence Ductility: It is the ability of a material to deform to greater extent before indication of crack when subjected to tensile load. This is usually expressed in terms of percentage elongation or percentage reduction in cross sectional area. This property is utilized in wire drawing. Mild Steel, aluminium, copper, tin and lead are some of the ductile materials. Brittleness: It is the property of a material which shows negligible plastic deformation before the occurrence of fracture. Cast iron, high carbon steel, concrete, stone, glass, ceramic materials, etc.

8. MECHANICAL PROPERTIES OF MATERIALS Slide #6 Department of Mechanical Engineering Strive for Excellence Strength: It is the ability of the material to resist the external forces causing various types of stresses without breakage or rupture. Stiffness: Stiffness or Rigidity is the ability of the material to resist deformation under the action of external load. Modulus of Elasticity is the measure of Stiffness . Resilience: It is the ability of the material to absorb energy when deformed elastically and release the same when unloaded.

9. MECHANICAL PROPERTIES OF MATERIALS Slide #7 Department of Mechanical Engineering Strive for Excellence Toughness: It is the ability of the material to absorb energy before the occurrence of fracture. Malleability: It is the ability of material to deform to a greater extent before the occurrence of crack, when it is subjected to compressive force. This property is utilized in forging, hot rolling, drop stamping etc. Hardness: It is the resistance of the material to the penetration or permanent deformation or indentation. Indentation test involves pressing a body of standard shape against the surface of test specimen. Ex: Brinell , Rockwell and Vicker’s test.

10. MECHANICAL PROPERTIES OF MATERIALS Slide #8 Department of Mechanical Engineering Strive for Excellence CREEP: Whenever a member or part of a machine is subjected to a constant stress at high temperature for a longer period of time, it will undergo a slow and permanent deformation known as CREEP. This is considered in designing IC engines, boilers and turbines.

11. STRESS ( σ ) Slide #9 Department of Mechanical Engineering Strive for Excellence It is defined as the resistance offered for the deformation per unit area due to applied external load. It is usually denoted by the symbol ‘ σ ‘. ie . σ = F/A Where F is the external load or force and A is the cross sectional area. The unit commonly used is Mega Pascal (MN/m 2 ) or 10 6 N/m 2 which is numerically equal to N/mm 2 . 1 Pascal = 1N/m 2 1 Kpa (Kilo Pascal) = 1000 N/m 2 1 Bar = 100 Kpa =10 5 N/m 2 1MPa (Mega Pascal) = 10 6 N/m 2 =1 N/mm 2 1GPa (Giga Pascal) = 10 9 N/m 2 =10 3 N/mm 2

12. Slide #10 Department of Mechanical Engineering Strive for Excellence Stress induced on a plane perpendicular to the direction of the load applied is known as Direct Stress or Normal Stress and perpendicular to the direction of the load applied is known as Tangential or Shear Stress. When the load tends to pull apart the particles of the material causing extension in the direction of the load applied then the load applied is known as tensile load and the corresponding stress is Tensile Stress. On similar lines Push causes contraction and the corresponding stress is Compressive Stress.

13. Summary Slide # 11 Department of Mechanical Engineering Strive for Excellence Importance of the course Mechanics of Materials. 2. Topics to be discussed in Module1. 3. Important Mechanical Properties of Materials in use. 4. Engineering Applications of the Materials.

14. Slide #12 NEXT VIDEO Department of Mechanical Engineering Strive for Excellence TO BE CONTINUED WITH.. Strain, Hooke’s law, Stress strain diagram for brittle and ductile materials, True stress and True strain Title of the next video here