Manufacturing Technology Lecture 3 PDF

EIM 1101 Manufacturing Technology Lecture 3. Mechanical Properties of Materials & Heat Treatment of Steels Department of Industrial and Management Engineering Slides have voice over Deformation, Stress and Strain Engineers are primarily concerned with the development and design of machines,...

EIM 1101 Manufacturing Technology Lecture 3. Mechanical Properties of Materials & Heat Treatment of Steels Department of Industrial and Management Engineering Slides have voice over Deformation, Stress and Strain Engineers are primarily concerned with the development and design of machines, structures, etc. These products are often subjected to forces and deformations resulting in stresses and strains. The response of a material to applied forces depends on the type and nature of the bond and the structural arrangements of atoms, molecules, and ions. 2/17 Types of Deformation Basic deformation types for load- carrying materials are: 1. Elastic deformation (deformations are instantaneously recoverable). 2. Plastic deformation (deformations are non- recoverable). 3/17 Elastic Deformation The ability of an object or material to resume its normal shape after being stretched or compressed. Elastic means reversible 4/17 Plastic Deformation Material does not return to the original shape when the applied load is removed. Plastic deformation means permanent change in an object’s shape and size, which cannot be reversed. 5/17 Mechanical Properties of Materials The behavior of engineering materials under applied forces is called “Mechanical Properties”. Mechanical properties of a material could be determined from the stress-strain relationship under an applied tensile load. Tensile Testing Machine 6/17 Tensile Test 7/17  Tensile Test Load: Applied force on the specimen in (N). Extension: The increase in the length of the specimen due to the applied load in (mm). Stress: The ratio of the tensile load applied F on the specimen to its original cross- s = MPa A0 sectional area in (MPa). Strain: The ratio of the increase of specimen e= l - l0 mm / mm length to its original length. l0 8/17 Stress-Strain Diagram Stress-Strain Diagram is determined by tensile test. It expresses a relationship between a load applied to a material and the material deformation. Necking begins 9/17 Stress-Strain Relationships E is a constant, known as Young’s Modulus or Modulus of Elasticity. The value of Young’s Modulus is determined mainly by the nature of the material. (Stress) (Strain) The uniform strain (uniform deformation) is the strain up to necking or ultimate tensile stress (UTS) level 10/17 Mechanical Properties of Metals 1. Elasticity is the ability of material to deform under load and restore its shape or volume after load release 2. Plasticity is the ability of the material to deform under load and maintain its shape or volume after load release 3. Stiffness is the resistance of the material to any elastic deformation (tensile loading or deflection) 4. Ductility ability of material to deform by elongation without failure measured by maximum achieved strain up to fracture. 11/17 Mechanical Properties of Metals 5. Brittleness is a characteristic of the material to break without noticeable plastic deformation 6. Strength is the measure of the ability of material to resist stresses until failure. 7. Toughness is the energy absorbed by the material before it fails under loading and it is a measure of resistance to dynamic loads. 8. Hardness is the resistance of the material to scratch and penetration by another body. Hardness can be determined using special hardness tests. 12/17 Heat Treatment of Metals & Alloys Definition It is a technological procedure, including controlled heating (NOT melting) and cooling operations. Purpose To change the microstructure of the alloy to achieve required properties. Microstructure: is the structure of the surface of material revealed by a microscope. Microstructure 13/17 Heat Treatment of Metals & Alloys Most common Heat treatment Processes for Steel 1. Annealing 2. Normalizing 3. Hardening then Tempering Most of the heat treatment processes are performed by heating the steel alloy to a temperature of about (750°C - 950°C). 14/17 Annealing Material is exposed to an elevated temperature for an extended time period and then slowly cooled (usually in a furnace). Objectives of Annealing Treatment Improve ductility and toughness Improves Machinability. The microstructural product of this anneal is coarse 15/17 Normalizing It is an annealing heat treatment that is used to develop a uniform small average grain size. Fine-grained structures are tougher than coarse-grained ones. Normalizing is accomplished by heating the steel, holding for relatively short time and then air cooling to room temperature. Objectives Small grain structure Produce harder and stronger steels compared to annealed steel 16/17 Hardening Heating the alloy, and then cooling at a high rate (quenching) in water or oil, which results in hard structure. Increases hardness, strength, and brittleness. After hardening, steels must be tempered to improve ductility and toughness. 17/17 Tempering Heating the hardened steel, holding for a specific time before cooling in air. Objectives Improve ductility and toughness Decrease brittleness while keeping acceptable hardness. 18/17 Thanks