Mechanics of materials lecture 01, Engr. Abdullah Khan
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This document provides information about a Mechanics of Materials course, including: - The instructor's contact information and the course grading criteria. - An outline of the course content which will cover topics like stresses, strains, bending of beams, torsion, and failure theories. - Recommended study sources and learning objectives/outcomes which aim to equip students to analyze and design agricultural machinery and structures. - An introduction to mechanics of materials and definitions of important material properties like strength, hardness, ductility, and elasticity that engineers must understand when designing with different materials.
Mechanics of materials lecture 01, Engr. Abdullah Khan
- 1. MECHANICS OF MATERIALS (AE-106) LECTURE: 01 Engr. Abdullah Khan Visiting Lecturer, Department of Agricultural Engineering.
- 2. CLASS INFORMATION • COURSE NAME AND CODE: MECHANICS OF MATERIALS (AE-106) • CREDIT HOURS: 2 • INSTRUCTOR: ENGR. ABDULLAH KHAN, DEPARTMENT OFAGRICULTURAL ENGINEERING. • CONTACT NO.: 0315-9608632 • EMAIL: abdullahkhansaddiqui48@gmail.com • ADDRESS: STATION KOROONA POST OFFICE SARDHERI TEHSILAND DISTRICT CHARSADDA. • GRADING CRITERIA: MID TERM = 30% FINAL TERM = 40% ASSIGNMENTS = 05% QUIZZES = 10% ATTENDANCE = 15%
- 3. COURSE CONTENT 1. Introduction, types of stresses and strains, elastic limit, modulus of elasticity, yield point. 2. Factor of safety, mechanical properties of materials, stresses due to change of temperature. 3. Poisson’s ratio, elastic constant: young’s modulus, shear modulus, bulk modulus, and relation between elastic constants. 4. Methods for the determination of stresses on oblique sections. 5. Use of Mohr’s circle to stress problems. 6. Bending moments and shear forces in beams for cantilever beam. 7. Bending moments and shear forces in beams for simply supported beam and over hanging beam. 8. Bending stresses in beams, theory of simple bending, derivation of flexure formula. Mid Term
- 4. COURSE CONTENT 9. Center of gravity, moment of inertia, and radius of gyration. 10. Section modulus 11. Deflection of beams; area moment method and mohr’s theorem. 12. Castigliano’s theorem. 13. Failure theories 14. Stresses in thin cylinders and spherical shells. 15. Stresses in composite bars and riveted joints. 16. Torsion theory for shafts of circular section, power transmitted by shaft, torsion combined with bending. 17. Open and closely coiled helical springs subjected to axial loading . Final term
- 5. RECOMMENDED STUDY SOURCES 1. Dr. R.K. Bansal (2009). A text book of Strength of Materials. Fourth edition. Laxmi Publication Private Ltd, New Delhi. 2. Strength of Material by Professional Staff of Benette College. 3. Shigley, J.E. and C. R. Mischhe, (2000). Mechanical engineering Design. Tenth edition. McGraw Hill publications Inc. USA. 4. Muvdi, B.B. And W. McNabb. (1984). Engineering Mechanics of Materials. McMillan Publishing CO., New York. 5. Provided lecture notes.
- 6. LEARNING OBJECTIVES To equip the students with 1. The basic understanding of • Force vectors and their operations, force equilibrium, • Stresses and strains of a body when the body is subjected to external loads. 2. Provide essential technical basis for the • Analysis and • Design of agricultural machinery and civil structures.
- 7. LEARNING OUTCOMES Upon the completion of the course, the student should be able 1. To use vectors to represent the force acting on a system and correctly plot free body diagram and check the equilibrium of a rigid body 2. Know the types of internal loadings, the relationships between stress and strain and the basic mechanical properties of materials 3. Compute the stress of a beam section due to tension, compression, torsion, bending, shear and combined loading 4. Transform stress (strain) components from one orientation to another learn the concepts for the design of beams
- 8. WHAT IS MECHANICS OF MATERIALS? • Three fundamentals areas of engineering mechanics are 1. Statistics 2. Dynamics 3. Strength of Materials. Study of the external effects of forces on rigid bodies, that is, bodies for which the change in shape (deformation) can be neglected. In contrast, Strength of Materials deals with the relation between externally applied loads and their internal effects on bodies. The bodies are no longer assumed to the rigid: the deformations, however small, are of major interest.
- 9. PROPERTIES OF MATERIALS Different materials possess different properties in varying degree and therefore behave in different ways under given conditions. Thesepropertiesinclude Mechanical Electrical Thermal Chemical Magnetic Physical A design engineer is interested in the behavior of materials under load which is mechanical in nature, for the design of machines & structures. Any material subjected to a load either deforms, yield, or break, depending upon the magnitude of the load. We are basically interested in knowing as to how a particular material will behave under applied load i.e. In knowing the mechanical properties.
- 10. WHY TO STUDY TO MECHANICAL PROPERTIES OF MATERIALS? An elementary knowledge of the properties of the various materials enables the designer to decide which particular material is the best to use for any particular purpose. An elementary knowledge of the principal processes by which iron and steel are produced is also essential to every engineer, As in specifications of engineering designs and structures it is frequently stated by which particular process the material to be employed is to be made. Certain terms relating to the properties of materials are constantly being used by engineers. The exact meaning of these terms must therefore be explained at this stage.
- 11. 1. Tenacity / Strength It is the resistance offered by a material when subjected to external loading. So, stronger the material the greater the load it can withstand. Depending upon the type of load applied the strength can be Tensile Compressive Shear Torsion 2. Hardness It is the ability of a material to resist scratching, abrasion, indentation. Thus machine cutting tools are made hard To prevent them from being blunted By contact with the materials they are intended to cut. Softness is the converse of Hardness.
- 12. 3. Brittleness The property of material to break readily without much permanent distortion, subjected to shocks. Usually the tensile strength of brittle materials is only a fraction of their compressive strength. Therefore, a non-ductile material is said to be a brittle material. Brittle Material Should not be considered as lacking strength. It only shows the lack of plasticity. Do not have Yield Point on Stress-Strain Diagram + Low Value of E Glass Cast Iron Examples 4. Ductility The property possessed by certain bodies that they may be drawn out in the direction of their length. The elongations are permanent. It enables the material to draw out into thin wire on application of the load. Possess the properties both of tenacity and softness. The ductility decreases with increase of temperature. Mild steel, gold, silver, copper, aluminum, etc. Examples
- 13. 5. Malleability Malleability of a material is its ability to be flattened into thin sheets without cracking by hot or cold working. A body is said to be malleable when it can be beaten out and extended in all directions. Ductility is a tensile property, whereas malleability is a compressive property Malleability increases with increase of temperature. Aluminum, copper, tin, lead, steel, etc. are malleable metals. 6. Welding Power Separate pieces of certain metals, when heated to a high temperature, may be joined together by hammering so as to form one piece. Such metals are said to be weld able. 7. Elasticity Elasticity of a material is its power of coming back to its original position after deformation when the stress or load is removed. Elasticity is a tensile property. The greatest stress that a material can endure without taking up some permanent set is called elastic limit.
- 14. 8. Stiffness (Rigidity) The resistance of a material to deflection is called stiffness or rigidity. Stiffness is measured by young’s modulus E. The higher the value of the young’s modulus, the stiffer the material. 9. Plasticity The plasticity of a material is its ability to undergo some degree of permanent deformation without failure. Due to this properties various metal can be transformed into different products of required shape and size. Plasticity is an important property and widely used in several mechanical processes like forming, shaping, extruding and many other hot and cold working processes. In general, plasticity increases with increasing temperature This conversion into desired shape and size is effected either by the application of pressure, heat or both.
- 15. 10. Toughness 11. Hardenability The toughness of a material is its ability to withstand both plastic and elastic deformations. Toughness is a measure of the amount of energy a material can absorb before actual fracture or failure takes place. “The work or energy a material absorbs is called modulus of toughness”. For e.g., If a load is suddenly applied to a piece of mild steel and then to a piece of glass the mild steel will absorb much more energy before failure occurs. Thus, mild steel is said to be much tougher than a glass. wrought iron, mild steels It is a highly desirable quality for structural and machine parts to withstand shock and vibration. Hardenability is the degree of hardness that can be imparted to metal by process of hardening. The material is heated above a certain temperature and then suddenly quenched in a cold oil or water bath. Hardness does not directly relate to the hardenability. Hardenability is indicative of the degree of hardness that the metal can acquire through the hardening process. i.e., Heating or quenching.
- 16. 12. Impact Strength 13. Resilience It can be defined as the resistance of the material to fracture under impact loading. i.e., Under quickly applied dynamic loads. Two standard tests are normally used to determine this property. The IZOD impact test. The CHARPY test. Resilience is the capacity of material to absorb energy elastically. On removal of the load, the energy stored is released as in a spring. The quantity gives capacity of the material to bear shocks and vibrations. The maximum energy which can be stored in a body up to elastic limit is called the proof resilience.