Hardness Wikipedia. This article is about mechanical properties of materials. For other uses, see hard. Hardness is a measure of how resistant solidmatter is to various kinds of permanent shape change when a compressive force is applied. Some materials e. Macroscopic hardness is generally characterized by strong intermolecular bonds, but the behavior of solid materials under force is complex therefore, there are different measurements of hardness scratch hardness, indentation hardness, and rebound hardness. Hardness is dependent on ductility, elasticstiffness, plasticity, strain, strength, toughness, viscoelasticity, and viscosity. Common examples of hard matter are ceramics, concrete, certain metals, and superhard materials, which can be contrasted with soft matter. Measuring hardnessedit. A Vickers hardness tester. There are three main types of hardness measurements scratch, indentation, and rebound. Within each of these classes of measurement there are individual measurement scales. For practical reasons conversion tables are used to convert between one scale and another. Scratch hardnesseditScratch hardness is the measure of how resistant a sample is to fracture or permanent plastic deformation due to friction from a sharp object. The principle is that an object made of a harder material will scratch an object made of a softer material. When testing coatings, scratch hardness refers to the force necessary to cut through the film to the substrate. The most common test is Mohs scale, which is used in mineralogy. One tool to make this measurement is the sclerometer. Rockwell_Type.png' alt='Rockwell Hardness Test Manual Pdf' title='Rockwell Hardness Test Manual Pdf' />Another tool used to make these tests is the pocket hardness tester. This tool consists of a scale arm with graduated markings attached to a four wheeled carriage. A scratch tool with a sharp rim is mounted at a predetermined angle to the testing surface. Rockwell Hardness Test Manual Pdf' title='Rockwell Hardness Test Manual Pdf' />In order to use it a weight of known mass is added to the scale arm at one of the graduated markings, the tool is then drawn across the test surface. The use of the weight and markings allows a known pressure to be applied without the need for complicated machinery. Indentation hardnesseditIndentation hardness measures the resistance of a sample to material deformation due to a constant compression load from a sharp object they are primarily used in engineering and metallurgy fields. The tests work on the basic premise of measuring the critical dimensions of an indentation left by a specifically dimensioned and loaded indenter. Common indentation hardness scales are Rockwell, Vickers, Shore, and Brinell. Rebound hardnesseditRebound hardness, also known as dynamic hardness, measures the height of the bounce of a diamond tipped hammer dropped from a fixed height onto a material. This type of hardness is related to elasticity. The device used to take this measurement is known as a scleroscope. Two scales that measures rebound hardness are the Leeb rebound hardness test and Bennett hardness scale. HardeningeditThere are five hardening processes Hall Petch strengthening, work hardening, solid solution strengthening, precipitation hardening, and martensitic transformation. PhysicseditIn solid mechanics, solids generally have three responses to force, depending on the amount of force and the type of material They exhibit elasticitythe ability to temporarily change shape, but return to the original shape when the pressure is removed. Hardness in the elastic rangea small temporary change in shape for a given forceis known as stiffness in the case of a given object, or a high elastic modulus in the case of a material. They exhibit plasticitythe ability to permanently change shape in response to the force, but remain in one piece. Java Programming Tutorials For Beginners Pdf here. The yield strength is the point at which elastic deformation gives way to plastic deformation. Deformation in the plastic range is non linear, and is described by the stress strain curve. This response produces the observed properties of scratch and indentation hardness, as described and measured in materials science. INSTRUCTION MANUAL 3601 E. St. Tucson, AZ 85713 USA Tel. Product Information MICRODUR MIC 10 Portable hardness tester UCI PI 453 2. Range of application Rapid hardness tests, simple handling and a high degree. Wheel and differential axles b Single purchase crab c Double purchase crab d System of pulleys Mechanics of deformable body 8. Mouse Robot Serial here. Determination of hardness of. This manual discusses the properties of clay masonry units including definitions, physical properties such as strength, durability, dimensions, tolerances and. N. V Diwakar et al International Journal of Current Engineering and Technology, Special Issue2 Feb 2014. Navdesk Software on this page. Bulletin no. 20253 rockwell hardness testing machines test equipment hr300400500 series and seismometers. Rockwell_hardness_tester_001.jpg/440px-Rockwell_hardness_tester_001.jpg' alt='Rockwell Hardness Test Manual Pdf' title='Rockwell Hardness Test Manual Pdf' />Some materials exhibit both elasticity and viscosity when undergoing plastic deformation this is called viscoelasticity. They fracturesplit into two or more pieces. Strength is a measure of the extent of a materials elastic range, or elastic and plastic ranges together. This is quantified as compressive strength, shear strength, tensile strength depending on the direction of the forces involved. Ultimate strength is an engineering measure of the maximum load a part of a specific material and geometry can withstand. Brittleness, in technical usage, is the tendency of a material to fracture with very little or no detectable plastic deformation beforehand. Thus in technical terms, a material can be both brittle and strong. In everyday usage brittleness usually refers to the tendency to fracture under a small amount of force, which exhibits both brittleness and a lack of strength in the technical sense. For perfectly brittle materials, yield strength and ultimate strength are the same, because they do not experience detectable plastic deformation. The opposite of brittleness is ductility. The toughness of a material is the maximum amount of energy it can absorb before fracturing, which is different from the amount of force that can be applied. Toughness tends to be small for brittle materials, because elastic and plastic deformations allow materials to absorb large amounts of energy. Hardness increases with decreasing particle size. This is known as the Hall Petch relationship. However, below a critical grain size, hardness decreases with decreasing grain size. This is known as the inverse Hall Petch effect. Hardness of a material to deformation is dependent on its microdurability or small scale shear modulus in any direction, not to any rigidity or stiffness properties such as its bulk modulus or Youngs modulus. Stiffness is often confused for hardness. Some materials are stiffer than diamond e. Mechanisms and theoryedit. A representation of the crystal lattice showing the planes of atoms. The key to understanding the mechanism behind hardness is understanding the metallic microstructure, or the structure and arrangement of the atoms at the atomic level. In fact, most important metallic properties critical to the manufacturing of todays goods are determined by the microstructure of a material. At the atomic level, the atoms in a metal are arranged in an orderly three dimensional array called a crystal lattice. In reality, however, a given specimen of a metal likely never contains a consistent single crystal lattice. A given sample of metal will contain many grains, with each grain having a fairly consistent array pattern. At an even smaller scale, each grain contains irregularities. There are two types of irregularities at the grain level of the microstructure that are responsible for the hardness of the material. These irregularities are point defects and line defects. A point defect is an irregularity located at a single lattice site inside of the overall three dimensional lattice of the grain. There are three main point defects. If there is an atom missing from the array, a vacancy defect is formed. If there is a different type of atom at the lattice site that should normally be occupied by a metal atom, a substitutional defect is formed. If there exists an atom in a site where there should normally not be, an interstitial defect is formed. This is possible because space exists between atoms in a crystal lattice.