Mechanical Properties of Materials PDF Fall 2021/2022

Dr./ Ahmed Yassin..... Physics 11/26/2021 Physics by Dr. Ahmed Yassin Fall 2021/2022...

Dr./ Ahmed Yassin..... Physics 11/26/2021 Physics by Dr. Ahmed Yassin Fall 2021/2022 Objectives Introduction. Ductility. Stress and its types. Malleability. Strain and its types. Difference between Brittle Elastic moduli. material and Ductile material. Elasticity Wear. (Elastic Deformation). Fatigue. Plasticity (Plastic Deformation). Dr. Ahmed Yassin >>> Physics Dr./ Ahmed Yassin.. Faculty of Applied Health Science Technology 1 Dr./ Ahmed Yassin..... Physics 11/26/2021 Introduction  The properties of materials that determine its behavior under applied external forces (loads) are called mechanical properties.  They are usually related to the elastic and plastic behavior of the material.  The International System of Units of force is the Newton (N). Dr. Ahmed Yassin >>> Physics  Quantities of force, stress, strain, strength, toughness, hardness, friction, and wear can help to: 1- identify the properties of a material (polymer, ceramic, and metal). Dr. Ahmed Yassin >>> Physics 2- understand reasons of failure. 3- select and design of dental restorations and appliances. Dr./ Ahmed Yassin.. Faculty of Applied Health Science Technology 2 Dr./ Ahmed Yassin..... Physics 11/26/2021 Stress  is defined as a force applied (F) per unit area (A). Or  is an internal resistance developed per unit area opposing the external deforming force.  It is given by the following formula: 𝑭 𝝈 𝑨  Its unit is N/m2. Dr. Ahmed Yassin >>> Physics Types of Stress Dr. Ahmed Yassin >>> Physics  Its types depend on the applied force and are: 1- Compressive, 2- Tensile, and 3- Shear. Dr./ Ahmed Yassin.. Faculty of Applied Health Science Technology 3 Dr./ Ahmed Yassin..... Physics 11/26/2021 1- Compressive Stress  is a stress occurs when equal and opposite forces are directed toward each other. Dr. Ahmed Yassin >>> Physics  Force : Compression. 2- Tensile Stress  is a stress occurs when equal and opposite forces are directed away from each other. Dr. Ahmed Yassin >>> Physics  Force : Tension. Dr./ Ahmed Yassin.. Faculty of Applied Health Science Technology 4 Dr./ Ahmed Yassin..... Physics 11/26/2021 3- Shear Stress  A shearing force F causes the body to deform.  Force : Tangent. Dr. Ahmed Yassin >>> Physics TYPES OF PURE FORCES Dr. Ahmed Yassin >>> Physics  Compressive: a force that results in a decrease in length along the direction of the force.  Tensile: a force that results in an increase in length along the direction of the force.  Shear: a force that causes a sliding displacement of one side of a structure relative to another side. Dr./ Ahmed Yassin.. Faculty of Applied Health Science Technology 5 Dr./ Ahmed Yassin..... Physics 11/26/2021 Dr. Ahmed Yassin >>> Physics Strain  is the change in length per unit length that a material undergoes when a force is applied to it. or  Change of length /original length. ∆𝒍 𝑺𝒕𝒓𝒂𝒊𝒏 𝒍𝒐  No unit. Dr. Ahmed Yassin >>> Physics Dr./ Ahmed Yassin.. Faculty of Applied Health Science Technology 6 Dr./ Ahmed Yassin..... Physics 11/26/2021 Types of Strain Dr. Ahmed Yassin >>> Physics 1- Elastic Strain is a strain that totally disappears once the external load, that caused it, is removed. 2- Plastic Strain is a strain that permanently remains once the external load, that caused it, is removed. Example 1 A 10 m steel wire stretches 3.08 mm due to the 200 N load. What is the longitudinal strain? Given: L = 10 m; L = 3.08 mm 𝜟𝑳 𝟎. 𝟎𝟎𝟑𝟎𝟖 m L 𝑺𝒓𝒂𝒊𝒏 𝑳 10 m Longitudinal Strain = 3.08 x 10-4 L Dr. Ahmed Yassin >>> Physics Dr./ Ahmed Yassin.. Faculty of Applied Health Science Technology 7 Dr./ Ahmed Yassin..... Physics 11/26/2021 Elastic Moduli Elastic modulus represents the degree of resistance of the material to a deforming force. 𝒔𝒕𝒓𝒆𝒔𝒔 𝑬𝒍𝒂𝒔𝒕𝒊𝒄 𝒎𝒐𝒅𝒖𝒍𝒖𝒔 𝒔𝒕𝒓𝒂𝒊𝒏 Strain is called fractional change in dimension or volume. Dr. Ahmed Yassin >>> Physics Elastic Moduli 1- Young’s modulus 2- Bulk modulus 3- Shear modulus Dr. Ahmed Yassin >>> Physics Dr./ Ahmed Yassin.. Faculty of Applied Health Science Technology 8 Dr./ Ahmed Yassin..... Physics 11/26/2021 Dr. Ahmed Yassin >>> Physics Young's Modulus L0 A Fn Fn Fn Fn A force applied normal to the end face of a rod causes a change in length. Shear Modulus x A Ft h fixed Dr. Ahmed Yassin >>> Physics The shear force is applied tangentially to the surface. Dr./ Ahmed Yassin.. Faculty of Applied Health Science Technology 9 Dr./ Ahmed Yassin..... Physics 11/26/2021 Bulk Modulus The bulk modulus of a solid or a fluid indicates its resistance to a change in volume. Volume stress Volume stress Bulk modulus Volume strain Dr. Ahmed Yassin >>> Physics 𝐹 𝐹. 𝑉 Δ𝑃 𝐵 𝐴 ∆𝑉 𝐴. ∆𝑉 Δ𝑉/𝑉 The bulk modulus is negative 𝑉 because of decrease in V. Stress-Strain Behavior 1.Elastic deformation Reversible: when the stress is removed, the material returns to the dimension it had before the loading. Dr. Ahmed Yassin >>> Physics Elastic means reversible. Dr./ Ahmed Yassin.. Faculty of Applied Health Science Technology 10 Dr./ Ahmed Yassin..... Physics 11/26/2021 2. Plastic deformation Irreversible: when the stress is removed, the material does not return to its previous dimension.  Stress and strain are not proportional. Plastic means permanent. Dr. Ahmed Yassin >>> Physics Stress – Strain Curve Dr. Ahmed Yassin >>> Physics Dr./ Ahmed Yassin.. Faculty of Applied Health Science Technology 11 Dr./ Ahmed Yassin..... Physics 11/26/2021 Stress – Strain Curve Dr. Ahmed Yassin >>> Physics Proportional Limit: Limit till which increase in Stress causes proportional increase in Strain. A high value of the proportional limit shows a material can withstand greater stress without permanent deformation. is represented on the stress-strain diagram as the point where the plotting converts from a straight line to a curve. Below the proportional limit, stress is proportional to strain. Dr. Ahmed Yassin >>> Physics A high proportional limit is desirable for a restorative material. Dr./ Ahmed Yassin.. Faculty of Applied Health Science Technology 12 Dr./ Ahmed Yassin..... Physics 11/26/2021 Yield Stress It is the stress at which materials start to show permanent deformation. Dr. Ahmed Yassin >>> Physics Disadvantage: Any dental restoration that is permanently deformed through the forces of mastication is usually a functional failure to some degree. Advantage: Permanent deformation and stresses in excess of the elastic limit are desirable when shaping an orthodontic arch wire. (Ultimate) Tensile Strength: Maximum stress that the material can withstand without fracture. The material could not withstand any more stresses, as it will fracture.  Imp. Note: The yield strength is often of greater importance than ultimate strength in design and material selection because it is an estimate of when a material will start to deform permanently. Dr. Ahmed Yassin >>> Physics Dr./ Ahmed Yassin.. Faculty of Applied Health Science Technology 13 Dr./ Ahmed Yassin..... Physics 11/26/2021 Fracture strength: It is the strength at which the material fractures. Flexibility Dr. Ahmed Yassin >>> Physics is defined as the strain occurring when the material is stressed to its proportional unit. DUCTILITY is the ability of a material to undergo permanent tensile deformation without fracture or rupture. An increase in temperature decreases ductility because a material's strength generally decreases with an increase in temperature.  The ductility of a material represents its ability to be drawn and shaped into wire by means of tension. When tensile forces are applied, the wire is formed by permanent deformation. Dr. Ahmed Yassin >>> Physics Dr./ Ahmed Yassin.. Faculty of Applied Health Science Technology 14 Dr./ Ahmed Yassin..... Physics 11/26/2021 Malleability is the ability of a material to undergo permanent compressive deformation without fracture. An increase in temperature generally results in an increase in malleability because malleability is dependent upon dislocation ‫ﺍﻧﺨ ﻼﻉ‬/‫ ﻏﻴ ﺎﺏ‬movement, and dislocations generally move more easily at higher temperature. Dr. Ahmed Yassin >>> Physics  The malleability of a substance represents its ability to be hammered or rolled into thin sheets without fracturing. Malleability dislocation movement. Dr. Ahmed Yassin >>> Physics Dr./ Ahmed Yassin.. Faculty of Applied Health Science Technology 15 Dr./ Ahmed Yassin..... Physics 11/26/2021 Brittleness is the material behavior where a material undergoes fracture or rupture with little or no prior permanent deformation.  have a very ordered atomic Structure which does not permit the easy movement of dislocations.  An example: ceramics. Dr. Ahmed Yassin >>> Physics Brittle and ductile materials Dr. Ahmed Yassin >>> Physics Dr./ Ahmed Yassin.. Faculty of Applied Health Science Technology 16 Dr./ Ahmed Yassin..... Physics 11/26/2021 Fatigue refers to the fact that under cyclic loading (type of repetitive loading) a material will undergo failure at a lower applied stress than it normally would if it were not under cyclic loading. Wear is the loss of material from one or both of two contacting surfaces because of the mechanical activity between them. Dr. Ahmed Yassin >>> Physics Dr. Ahmed Yassin >>> Physics Dr./ Ahmed Yassin.. Faculty of Applied Health Science Technology 17