Lecture 1: Material Classifications - EME 205

Properties and Testing of Electromechanical Materials EME 205 Lecture 1 Materials Classification Dr. Mohamed M. Abdelkader Hassan 1  Course Contents: 1. Engineering Material Classifications 2. Atomic Structure and Interatomic Bond...

Properties and Testing of Electromechanical Materials EME 205 Lecture 1 Materials Classification Dr. Mohamed M. Abdelkader Hassan 1  Course Contents: 1. Engineering Material Classifications 2. Atomic Structure and Interatomic Bonding 3. Mechanical Properties. 4. Hardness 5. Diffusion 6. Phase-Diagram 7. Heat Treatment 8. Polymers Structure 9. Composite Materials References Materials Science and Engineering: An Introduction, 8th Edition by William D. Callister Jr. , David G. Rethwisch 2  Materials Over 70,000 different kinds and grades of engineering materials This number grows daily 1,000 different materials make up an automobile 3  The Three Basics Materials Metals Polymers Ceramics There are three other groups of important engineering materials: Composites Semiconductors Biomaterials 4 Smart materials 5  The Basic Materials Classifications 1- Metals INTRODUCTION Metals are composed of one or more metallic elements (e.g., iron, aluminum, copper, titanium, gold, nickel), and often also nonmetallic elements (e.g., carbon, nitrogen, oxygen) in relatively small amounts. Atoms in metals and their alloys are arranged in a very orderly manner and are relatively dense in comparison to the ceramics and polymers (Figure 1). 6 FIG. (1)Bar chart of room temperature density values for various metals, ceramics, polymers, and composite materials 7  With regard to mechanical characteristics, these materials are relatively stiff (Figure 2) FIG.(2) Bar chart of room temperature stiffness (i.e., elastic modulus) values for various metals, ceramics, polymers, and composite materials. 8 and strong (Figure 3), yet are ductile (i.e., capable of large amounts of deformation without fracture), FIG.(3) Bar chart of room temperature strength (i.e., tensile strength) values for various metals, ceramics, polymers, and composite materials. 9 and are resistant to fracture (Figure 4), which accounts for their widespread use in structural applications. FIG.(4) Bar chart of room-temperature resistance to fracture (i.e., fracture toughness) for various metals, ceramics, polymers, and composite materials. 10  Many properties of metals are directly attributable to its electrons. For example, metals are extremely good conductors of electricity (Figure 5) and heat, and are not transparent to visible light. FIG.(5) Bar chart of room temperature Electrical conductivity ranges for metals, ceramics, polymers, and Semiconducting materials. 11 (Figure 6) shows several common and familiar objects that are made of metallic materials. FIG.(6) Familiar objects made of metals and metal alloys. 12 Metal alloys 13  POLYMER 14  POLYMER The word polymer means Poly means many and meros means units, parts. Polymer means many parts or many units. 15  CERAMICS 16  CERAMICS Applications 17  The Engineering Materials Classifications 1- Composite Composite materials are materials which are a combination of two or more distinct individual materials. This is called the principle of combined action. One example of this principle is the use of composites for aircraft structures. These composites are designed to be lighter weight with comparable strength to metal structural elements that they are replacing. Typically, a composite is formed with a continuous phase called the matrix. As shown in the figure below, the matrix phase surrounds another phase which is discontinuous and referred to as the dispersed phase. 18 Example: Material used in the Boeing 787 Composites are typically classified by the type of dispersive phase used: particle reinforced, fiber reinforced, or structural. 19 The dispersed phase (reinforcement) typically depends on which material type it is composed of: Metal dispersive phases are typically used to increase yield strength, tensile strength, and/or provide stability over the life of the product. Ceramic dispersive phases are typically used to produce materials which resist fracture. Polymer dispersive phases are typically used to increase the modulus of elasticity, yield strength, tensile strength, and/or provide stability over the life of the product. 20 2- Smart Materials  Have properties that react to changes in their environment.  Their properties can be changed by an external condition, such as: temperature, light, pressure, voltage, or chemical compounds.  This change is reversible and can be repeated many times. 21 22 i- Piezoelectric Materials generate an electric charge across its surface when it undergoes mechanical stress, due to the asymmetry of its crystalline structure. The effect is reversible, so an electrical charge will cause the material to change shape. The most well-known piezoelectric material is Quartz. Piezoelectric materials are used as electromechanical transducers - actuators and sensors. 23 24  ii – Magneto-strictive materials Are routinely employed as actuator and sensor elements in a wide variety of noise and vibration control problems. In infrastructural applications, other technologies such as hydraulic actuation, piezoelectric materials and more recently, magnetorheological fluids, are being favored for actuation and sensing purposes. Application: MR damper MRF = Magneto-rheological fluid Magneto-rheological fluids are fluids that exhibit a change in rheological properties when a magnetic field is induced through the fluid (Apparent Viscosity). 25 MR Fluid Operations No Field Applied Filed 26 iii – Thermoelectric Materials Thermoelectric materials are the materials which can transfer heat energy and electrical energy to each other. HISTORY – In 1821 Thomas Johann Seebeck discovered that if you place a hot metal next to a dissimilar cold metal the electrons would transfer from one to the other producing an electro motive force causing a current, this is called the Seebeck effect. In 1834 Physicist Joan Peltier found that you can have a converse effect whereby passing a current through two dissimilar metals one goes hot and the other cold, this is called the Peltier effect. 27 (a) thermoelectric generation (Seebeck effect) (b)Thermoelectric cooling (Peltier effect). 28 iv – Shape Memory Alloy Shape memory alloys are metals that change their shape in response to a change in temperature. Although, these metals don’t just change their shape randomly when there is a change in temperature, they retain the first shape they were originally molded into. 29 Application 30