Materials Science MDPG121 Introduction PDF

Materials Science MDPG121 Introduction Cairo University – Faculty of Engineering Fall-2024  Mechanical properties Before discussing the classification of engineering materials, we need to be familiar with the main mechanical properties and how to evaluate them. Te...

Materials Science MDPG121 Introduction Cairo University – Faculty of Engineering Fall-2024  Mechanical properties Before discussing the classification of engineering materials, we need to be familiar with the main mechanical properties and how to evaluate them. Tensile test is usually used to evaluate many of the mechanical properties. A test sample having an original cross-section area A0 and an original length L0 is pulled. The force needed to extend the sample is recorded versus the displacement (sample elongation) Tensile test In order to normalize the results with respect to the sample dimensions: We divide the force by the sample original cross-section area to get the stress. We divide the elongation by the original length to get the strain 𝐹 ∆𝐿 𝜎= 𝜀= 𝐴0 𝐿𝑜 (MPa) The stress-strain curve is divided into two regions: The elastic region: when the load is Engineering stre removed, the sample retracts to its original dimensions. The plastic region: the sample shape/dimensions change permanently. Engineering strain 𝜖 Mechanical properties Yield strength 𝜎𝑦 : the maximum stress that can be applied to the sample without causing permanent deformation. Ultimate tensile strength 𝜎𝑇𝑆 : the maximum stress that can be applied to the sample without fracture Ductility: the maximum (MPa) strain calculated at fracture point Engineering strain Engineering strain 𝜖 Mechanical properties The opposite of ductile is brittle. Materials that fracture after small elongation are called brittle. Impact Toughness: is the material resistance to impact (sudden) loads. For example, the toughness of steel is much higher than the toughness of glass. Hardness: is the material resistance to penetration. High hardness is usually an indication of high strength, and vice versa. Alloying elements: elements intentionally added to improve certain properties. e.g. Chromium is added to steel to improve corrosion resistance ( stainless steel). Tungsten, cobalt and Vanadium are added to steel to improve high temperature mechanical properties. (those elements form carbides that stabilize the mechanical properties at high temperatures.) Impurities: elements that may have harmful effects such as Sulphur and phosphorous in steel alloys. The polymerization process depend on creating reaction sites on this chemically stable form, by subjecting the ethylene to the appropriate pressure, temperature, and adding a catalyst R Packaging Industry  Addition (Chain) Polymerization – Initiation – Propagation – Termination 12 12 Types of Polymers: 1. Thermoplastic polymers:  Relatively soft and ductile.  Recyclable.  The chains are packed by secondary bonding. 2. Thermo-set polymers:  Hard and brittle.  Non-recyclable.  Cross links between chains 3. Elastomers:  Very high elastic deformation.  Lightly cross linked.  Mechanical Properties Stress-strain behavior of polymers brittle polymer FS of polymer ca. 10% that of metals plastic elastomer elastic modulus – less than metal Adapted from Fig. 15.1, Strains – deformations > 1000% possible Callister 7e. (for metals, maximum strain ca. 10% or less) 14 14 Composites: Made from two or more materials to achieve certain properties. Strength To achieve new materials with high strength to weight ratio  Weight Example: Machining tools like Cermets which require: strength, hardness, temperature resistance, toughness, thermal conductivity. You can achieve these properties by combining metals with ceramics. Cermets: WC/TiC particles embedded in a metallic matrix (Ni, Co) Electrical Conductivity (1/ohm-meters)  Advanced Materials These advanced materials are typically traditional materials whose properties have been enhanced, and, also newly developed, high-performance materials. Furthermore, they may be of all material types (e.g., metals, ceramics, polymers), and are normally expensive.  Biomaterials Biomaterials are employed in components implanted into the human body for replacement of diseased or damaged body parts. These materials must not produce toxic substances and must be compatible with body tissues (i.e., must not cause adverse biological reactions). Example – Hip Implant With age or certain illnesses joints deteriorate. Particularly those with large loads (such as hip). Adapted from Fig. 22.25, Callister 7e. 23 Example – Hip Implant Requirements Mechanical strength (many cycles) Good lubricity. Biocompatibility. Adapted from Fig. 22.24, Callister 7e. 24 Example – Hip Implant Adapted from Fig. 22.26, Callister 7e. 25 Hip Implant Key problems to overcome Ball Fixation agent to hold acetabular cup Cup lubrication material Femoral stem – fixing agent Acetabular must avoid any debris in cup Cup and Liner Femoral Stem Adapted from chapter-opening photograph, Chapter 22, Callister 7e. (Photograph courtesy of Zimmer, Inc., Warsaw, IN, USA.) 26  Smart Materials The adjective “smart” implies that these materials are able to sense changes in their environments and then respond to these changes in predetermined manners Shape memory alloys are metals that, after having been deformed, revert back to their original shapes when temperature is changed Piezoelectric ceramics expand and contract in response to an applied electric field (or voltage); conversely, they also generate an electric field when their dimensions are altered Magnetostrictive materials is analogous to that of the piezoelectrics, except that they are responsive to magnetic fields  Nano-engineered Materials the “nano” prefix denotes that the dimensions of these structural entities are on the order of a nanometer (10-9 m)—as a rule, less than 100 nanometers (equivalent to approximately 500 atom diameters) it has become possible to manipulate and move atoms and molecules to form new structures and, thus, design new materials that are built from simple atomic-level constituents (i.e., “materials by design”). This ability to carefully arrange atoms provides opportunities to develop mechanical, electrical, magnetic, and other properties that are not otherwise possible. We call this the “bottom-up” approach. The ‘‘top-down’’ approach is different because it is dependent upon taking a bulk solid with a relatively coarse grain size (crystal size) and processing the solid to produce ultrafine grain (UFG) and Nano structured microstructure through heavy straining. This approach avoids the small product sizes and the contamination which are inherent features of materials produced using the‘‘bottom-up’’. Nano-engineered Materials  Performance Materials Engineering Designing the structure to achieve specific properties of materials. Structure Processing Properties Materials Science Investigating the relationship between structure and properties of materials. The Materials Selection Process 1. Pick Application Determine required Properties Properties: mechanical, electrical, thermal, magnetic, optical, deteriorative. 2. Properties Identify candidate Material(s) Material: structure, composition. 3. Material Identify required Processing Processing: changes structure and overall shape ex: casting, sintering, vapor deposition, doping forming, joining, annealing. 32 Structure, Processing, & Properties Properties depend on structure ex: hardness vs structure of steel (d) 600 Hardness (BHN) 30 μm 500 (c) Data obtained from Figs. 12.31(a) and 12.32 with 4 wt% C composition, and from 400 (b) Fig. 17.8, Callister & Rethwisch 9e. (a) Micrographs adapted from (a) Fig. 12.19; 4 μm 300 (b) Fig. 11.29; (c) Fig. 12.33; and (d) Fig. 12.21, Callister & Rethwisch 9e. (Figures 30 μm 12.19, 12.21, & 12.33 copyright 1971 by United 200 30 μm States Steel Corporation. Figure 9.30 courtesy of Republic Steel Corporation.) 100 0.01 0.1 1 10 100 1000 Cooling Rate (ºC/s) Processing can change structure ex: structure vs cooling rate of steel 33 Units of Length 1 cm*  10–2 m  0.01 m 1 mm  10–3 m  0.001 m 1 micron (m)  10–6 m  0.000001 m 1 nanometer (nm)  10–9 m  0.000000001 m 1 Angstrom (Å)  10–10 m  0.0000000001 m *nota bene: cm are not typically used. Multiple Length Scales Critical in Engineering 1000 m 500 m 0.05 m In Askeland and Phule’s book, from J. Allison and W. Donlon (Ford Motor Company) ELECTRICAL Electrical Resistivity of Copper: 6 Fig. 19.8, Callister & Rethwisch 9e. [Adapted from: J.O. Linde, Ann Physik 5, 219 (1932); and C.A. Wert and R.M. Thomson, 5 Physics of Solids, 2nd edition, McGraw-Hill Company, New York, 1970.] Resistivity, ρ (10-8 Ohm-m) 4 3 2 1 0 -200 -100 0 T (°C) Adding “impurity” atoms to Cu increases resistivity. Deforming Cu increases resistivity. 36  OPTICAL Transmittance: -- Aluminum oxide may be transparent, translucent, or opaque depending on the material’s structure (i.e., single crystal vs. polycrystal, and degree of porosity). polycrystal: polycrystal: single crystal no porosity some porosity Fig. 1.2, Callister & Rethwisch 9e. (Specimen preparation, P.A. Lessing) 37 Week Lecture Tutorial 1 Introduction - Interatomic Bonding-1 Grades distribution: 2 Interatomic Bonding-2 - Interatomic Bonding (Tut) 40% Final exam Crystal Structures-1 25% Midterm exam (week 8) 3 Crystal Structures-2 Crystal Structures-1(Tut) 15% Quizzes (during 4 Imperfections in Solids Crystal Structures-2(Tut) lecture/tutorial time) 5 Mechanical Properties-1 Imperfections in Solids (Tut) 20% lab 6 Mechanical Properties-2 Mechanical Tension test (Lab) reports/assignments Properties-1 (Tut) 7 Diffusion Mechanical Tension test (Lab) Properties-2 (Tut) 8 Midterm Exam 9 Strengthening Mechanisms-1 Diffusion (Tut) Google 10 Strengthening Mechanisms-2 Compression/hardness test (Lab) classroom code: 11 Phase Diagrams Strengthening (Tut) h5ogc3j 12 Iron-Carbon Diagram Phase Diagrams-1(Tut) 13 Classification of Ferrous alloys Phase Diagrams-2 Microstructure (Tut) (Lab) 14 Revision Revision