MEMS 1 Lesson 2 - Materials Testing PDF

COLLEGE OF ENVIRONMENTAL DESIGN AND ENGINEERING Second Trimester A.Y. 2024-2025 MEMS 1: Materials Science and Engineering FIVE MAJOR CATEGORIES OF MATERIALS...

COLLEGE OF ENVIRONMENTAL DESIGN AND ENGINEERING Second Trimester A.Y. 2024-2025 MEMS 1: Materials Science and Engineering FIVE MAJOR CATEGORIES OF MATERIALS TESTING 1. Mechanical Testing 2. Thermal Properties Testing 3. Electrical Properties Testing 4. Resistance to Corrosion, Radiation, and TOPICS: Biological Deterioration Testing 1. Materials Testings 5. Nondestructive Testing 2. Five Major Categories of Materials Testing a. Mechanical Testing MECHANICAL TESTING b. Thermal Properties Testing c. Electrical Properties Testing Structures and machines can fail due to d. Resistance to Corrosion, Radiation, and fractures or excessive deformation. To Biological Deterioration prevent such failures, designers assess the e. Nondestructive Testing expected stress—essentially the load per unit area—that the structure will face and MATERIALS TESTING select materials capable of handling that stress. Measurement of the characteristics and To identify potential weak points, a stress behavior of substances such as metals, analysis is conducted, either through ceramics, or plastics under various experiments or mathematical modeling, conditions. The obtained data can be which reveals areas that may experience used in specifying the suitability of high stress during operation. materials for various applications—e.g., building or aircraft construction, KINDS OF MECHANICAL TESTING machinery, or packaging. A full- or small-scale model of a proposed 1. Static Tension and Compression Tests machine or structure may be tested. When a material is pulled or stretched, Alternatively, investigators may construct it elongates and will eventually break mathematical models that utilize known under tension. material characteristics and behavior to A basic static tension test measures predict capabilities of the structure. both the breaking point and the Standard test methods have been elongation of the material, known as established by such national and strain. international bodies as the International Static compression tests assess how a Organization for Standardization (ISO), material reacts to crushing forces, with headquarters in Geneva, Switzerland which is important for understanding and the American Society for Testing and how materials support loads, such as Materials (ASTM) in Philadelphia, USA. those experienced by beams in a house.  5. Impact Test Materials that are sensitive to flaws, 2. Static Shear and Bending Tests cracks, and notches can fail rapidly Shear tests measure how a material when subjected to impact. The most deforms when forces are applied common tests for measuring impact tangentially, and they are mainly used resistance are the Charpy and Izod for thin sheet materials like metals and tests, which use a swinging pendulum composites, such as fiberglass- to strike a notched bar. By comparing reinforced plastic. However, these tests the height of the pendulum before and offer only limited insights. after the impact, these tests calculate For brittle materials like glass and the energy needed to fracture the bar, ceramics, where direct tensile testing is providing a measure of its impact challenging, a bend test can be used strength. to determine their tensile strength In the Charpy test, the specimen is instead. positioned horizontally between two vertical supports, while in the Izod test, 3. Measures of Ductility the specimen is held upright. Ductility refers to a material's ability to undergo permanent deformation 6. Fracture Toughness Tests when subjected to stress. A prime Fracture toughness tests measure a example is steel, which is highly ductile material's ability to resist crack and can handle localized stress propagation and eventual fracture, concentrations without breaking. In making it a key property for contrast, brittle materials like glass lack understanding material performance. ductility, making them unable to In these tests, a steadily increasing load absorb stress effectively, leading to is applied to the material until it fails, easy fracture under pressure. allowing researchers to determine how much energy the material can absorb 4. Hardness Testing before breaking. Knowing a material's Hardness tests measure a material's fracture toughness is crucial, as all resistance to deformation by pressing a materials are likely to develop flaws hardened steel ball (in the Brinell test) during manufacturing or use that can or a steel or diamond cone (in the lead to cracking. Rockwell test) into its surface. Similar indentation tests can also be 7. Creep Test conducted on wood. However, Creep refers to the gradual hardness tests for materials like rubber deformation of a material over time or plastic differ in significance when subjected to prolonged stress, a compared to those for metals. behavior commonly observed in many Additionally, some tests, especially metals. In a creep test, loads that are those assessing wear or abrasion lower than those required for resistance, involve dynamic methods immediate fracture are applied to the where a weight drops from a specific material, and the resulting height, or a hammer is used to create deformation, known as creep strain, is an indentation. measured over time while the load remains constant.  8. Fatigue Materials that can withstand a single application of stress often fail when 3. Thermal Expansion subjected to repeated stress, a The general increase in the volume of phenomenon known as fatigue. This is a material as its temperature is assessed through mechanical tests that increased. It is usually expressed as a apply varying stresses in a regular fractional change in length or volume cycle, ranging from maximum to per unit temperature change; a linear minimum values. Many fatigue-testing expansion coefficient is usually machines use a rotating eccentric employed in describing the expansion weight to create these cyclic loads. A of a solid, while a volume expansion material is typically classified as coefficient is more useful for a liquid or experiencing low-cycle fatigue if it fails a gas. after 10,000 cycles or fewer. ELECTRICAL PROPERTIES TESTING THERMAL PROPERTIES TESTING To understand electrical properties and Thermal properties testing is a scientific testing methods, it's helpful to start with the method that measures how materials, free electron gas theory of electrical substances, or components react to conduction. While this theory is somewhat temperature and behave in harsh simplistic compared to modern solid-state environments. It can be used for quality physics, it serves as a useful foundation. assurance, product analysis, and testing. Electrical conductivity refers to the flow of free electrons within a solid. Metals are KINDS OF THERMAL PROPERTIES TESTING typically good conductors because they have free or valence electrons that form 1. Thermal Conductivity an electron "cloud" around the atoms, Thermal conductivity refers to the allowing them to move rapidly throughout ability of a given material to the material. In contrast, materials like conduct/transfer heat. It is generally plastics restrict the movement of their denoted by the symbol ‘k’ but can also valence electrons, preventing the be denoted by ‘λ’ and ‘κ’. The formation of a free-electron cloud and reciprocal of this quantity is known as making them effective insulators. thermal resistivity. Materials with high To measure a material's conductivity, a thermal conductivity are used in heat known current is passed through it at a sinks whereas materials with low values constant voltage, and its resistance is of λ are used as thermal insulators. calculated in ohms. Some materials, such as silicon, germanium, and carbon, are 2. Specific Heat classified as semiconductors because they Specific heat, the quantity of heat experience a significant increase in free required to raise the temperature of electrons when heated. one gram of a substance by one Celsius degree.  Testing methods may include total RESISTANCE TO CORROSION, RADIATION, AND immersion in environments like BIOLOGICAL DETERIORATION TESTING seawater or exposure to salt fog, which can occur in chemical processing In recent years, there has been a operations or near coastal areas significant increase in testing materials for where seawater is present in fog. breakdown or deterioration when In corrosion testing, materials are exposed to specific environments. typically immersed in a 5% or 20% Mechanical, thermal, and electrical solution of sodium chloride or calcium property tests are often conducted chloride mixed with water. before, during, and after exposure to Alternatively, the solution can be controlled conditions. The changes in sprayed into a chamber where the material properties are then recorded specimens are suspended freely. over time. These environments can include heat, 2. Radiation moisture, chemicals, radiation, electricity, Materials can be tested for their biological agents, or combinations of responses to various forms of these factors. For instance, a material's electromagnetic radiation, including X- tensile strength may decrease after being rays, gamma rays, radio-frequency exposed to heat, moisture, or salt spray, waves, and atomic radiation like while it might actually improve with neutrons from radioactive substances. exposure to radiation or electrical current. Polymers, such as plastics and synthetic Additionally, organic materials can suffer rubber, are particularly affected by reduced strength due to certain types of these types of radiation due to their fungi and mold. long chains of repeating chemical units. 1. Corrosion Testing Radiation tests involve exposing Corrosion testing is conducted to materials to a known radiation source assess how materials perform in for a set duration. This exposure can be specific environments and to explore controlled using robotic systems in methods for protecting them from remote chambers with nuclear fuels, environmental damage. Corrosion is a after which conventional methods are chemical reaction that leads to the loss used to assess any changes in the of metallic electrons from metals, material's properties over time. In resulting in the formation of more practical applications, paint samples stable compounds, such as iron oxide may be subjected to sunlight for (rust), which typically contain fewer extended periods to evaluate fading free electrons. or cracking. While exposure to These tests evaluate the performance radiation often negatively impacts of metals and other materials when material strength, this is not always the exposed to various electrolytes. case.  A similar method for nonmetals uses an 3. Biological Deterioration electrically charged liquid applied to Materials such as paints, wrappers, and the surface. After removing the excess coatings on buried pipelines, liquid, a dry powder with an opposite structures, and storage tanks are charge is sprayed on, which adheres commonly susceptible to biological to the cracks. However, neither of deterioration. When the biological these techniques can identify internal makeup of the soil in a specific area is flaws in the materials. not well understood samples of its fungi, bacteria, or algae are collected 2. Radiation and incubated using standard X-ray and gamma-ray techniques can laboratory techniques to identify the detect both internal and external flaws various microbial colonies present. The in materials by passing radiation isolated microbial cultures are used to through the material and onto evaluate materials for biological photographic film. In certain cases, the degradation and to test the X-rays can be focused on a specific effectiveness of fungicides or plane within the material, allowing for bactericides. a three-dimensional representation of the flaw's geometry and location. NONDESTRUCTIVE TESTING 3. Sound The tensile-strength test is inherently Ultrasonic inspection involves destructive; in the process of gathering transmitting sound waves above the data, the sample is destroyed. Though this human hearing range through a is acceptable when a plentiful supply of material to detect flaws. the material exists, nondestructive tests are In the reflection technique, a sound desirable for materials that are costly or wave is sent from one side of the difficult to fabricate or that have been sample, reflects off the far side, and formed into finished or semifinished returns to a receiver at the starting products. point. If the wave encounters a flaw or crack, the signal is reflected back with TECHNIQUES OF NONDESTRUCTIVE TESTING altered travel time, which helps determine the flaw's location and 1. Liquids geometry, allowing for a detailed map A common nondestructive testing of the material. technique for detecting surface cracks In the through-transmission method, and flaws in metals involves using a the transmitter and receiver are brightly dyed or fluorescent positioned on opposite sides of the penetrating liquid. This liquid is applied material. Interruptions in the sound to the material's surface, allowed to wave's passage indicate the presence seep into tiny cracks, and then wiped and size of flaws. This method typically off, making the cracks visible. uses a water medium to immerse the transmitter, sample, and receiver. 4. Magnetism Where the adhesive bonds are intact, As the magnetic characteristics of a the core acts as a heat sink, resulting in material are strongly influenced by its consistent temperature across the overall structure, magnetic techniques bond lines. Conversely, if a bond is can be used to characterize the inadequate or faulty, the temperature location and relative size of voids and will not drop uniformly. Infrared cracks. photography can then reveal the In magnetic testing, a device features location and shape of any defective a large primary coil carrying a steady adhesive. Another variation of this alternating current, with a smaller technique uses thermal coatings that secondary coil inside it connected to a change color when they reach a measuring instrument. The primary coil certain temperature. induces a current in the secondary coil. When an iron bar is placed in the secondary coil, any sharp changes in current can indicate defects in the bar. However, this method primarily detects variations along the bar's length and struggles to identify long or continuous defects. An alternative technique uses eddy currents generated by the primary coil to find flaws and cracks. In this approach, a steady current is induced in the test material, and flaws that disrupt this current will change the material's resistance, which can be measured with appropriate equipment. 5. Infrared Infrared techniques are used to assess material continuity in complex structures, such as testing the quality of adhesive bonds in sandwich construction materials like plywood. In this method, heat is applied to the surface of the sandwich skin.