Define hardness | Dictionary and Thesaurus

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Brinellhardness test (HB);Janka Wood Hardness Rating;Knoophardness test (HK) or microhardness test, for measurement oversmall areas;Meyerhardness test;Rockwellhardness test (HR), principally used in the USA;Shoredurometer hardness, used for polymers;Vickershardness test (HV), has one of the widest scales;Barcolhardness test, for composite materials, scale from 0 toThere is, in general, no simple relationshipbetween the results of different hardness tests. Though there arepracticalconversion tables for hard steels, for example, some materialsshow qualitatively different behaviours under the variousmeasurement methods. The Vickers and Brinell hardness scalescorrelate well over a wide range, however, with Brinell onlyproducing overestimated values at high loads.Hardness increases with decreasing particlesize. This is known as the Hall-Petcheffect. However, below a critical grain-size, hardnessdecreases with decreasing grain size. This is known as the inverseHall-Petch effect.For measuring hardness of nanograined materials,nanoindentationis used.In the December 4,2005 issue ofTheJerusalem Post, Professors Eli Altus, Harold Basch andShmaryahu Hoz, with doctoral student Lior Itzhaki reported the discovery of a polyyne that is 40 times harderthan diamond. It is a "superhard" molecular rod, comprised ofacetylene units.It is important to note that hardness of amaterial to deformation is dependent to its microdurability orsmall-scale shearmodulus in any direction, not to any rigidity or stiffness properties such asits bulkmodulus or Young'smodulus. Scientists and journalists often confuse stiffness forhardness, and spuriously report materials that are not actuallyharder than diamond because the anisotropy of their solidcells compromise hardness in other dimensions, resulting in amaterial prone to spallingand flaking in squamose or acicular habits in that dimension. E.g.,osmium is stiffer thandiamond but is as hard as quartz. In other words, a claimedhard material should have similar hardness characteristics at anylocation on its surface.Rebound hardnessAlso known as dynamic hardness, reboundhardness measures the height of the "bounce" of a diamond-tippedhammer dropped from a fixed height onto a material. The device usedto take this measurement is known as a scleroscope.One scale that measures rebound hardness is theBennettHardness Scale.PhysicsIn solidmechanics, solids generally have three responses to force, depending on the amount offorce and the type of material:They exhibit elasticity—theability to temporarily change shape, but return to the originalshape when the pressure is removed. "Hardness" in the elasticrange—a small temporary change in shape for a given force—is knownas stiffness in thecase of a given object, or a high elasticmodulus in the case of a material.They exhibit plasticity—theability to permanently change shape in response to the force, butremain in one piece. The yieldstrength is the point at which elastic deformation gives way toplastic deformation. Deformation in the plastic range isnon-linear, and is described by the stress-straincurve. This response produces the observed properties ofscratch and indentation hardness, as described and measured inmaterials science. Some materials exhibit both elasticityand viscosity whenundergoing plastic deformation; this is called viscoelasticity.They fracture—splitinto two or more pieces. The "ultimate strength" or toughness of an object is thepoint at which fracture occurs.Strengthis a measure of the extent of a material's elastic range, orelastic and plastic ranges together. This is quantified as compressivestrength, shearstrength, tensilestrength depending on the direction of the forces involved.Ultimatestrength is measure of the maximum straina material can withstand.Brittleness, intechnical usage, is the tendency of a material to fracture withvery little or no detectable deformation beforehand. Thus intechnical terms, a material can be both brittle and strong. Ineveryday usage "brittleness" usually refers to the tendency tofracture under a small amount of force, which exhibits bothbrittleness and a lack of strength (in the technical sense). Forbrittle materials, yield strength and ultimate strength are thesame, because they do not experience detectable plasticdeformation. The opposite of brittleness is ductility.The toughness of a material is themaximum amount of energyit can absorb before fracturing, which is different than the amountof force that can beapplied. Toughness tends to be small for brittle materials, becauseit is elastic and plastic deformations that allow materials toabsorb large amounts of energy.Materials whose properties are different indifferent directions (because of an asymmetrical crystal structure) are referredto as anisotropic.Examples of hard matterCeramicsCompositesMetalsSemiconductorsMechanisms for Strength HardeningIt is no surprise that materials can bemanipulated so that they may exhibit properties such as higheryield strength. Some mechanisms that can be used are WorkHardening, solid solution strengthening, precipitationhardening, and grain boundary strengthening.For more information, check out this link.http://www.virginia.edu/bohr/mse209/chapter7.htmReferencesMaterials science:External linksAnintroduction to materials hardnessHardness of ceramicshardness in Arabic: صلادةhardness in Catalan: Duresahardness in Czech: Tvrdost kovůhardness in Danish: Hårdhedhardness in German: Härtehardness in Estonian: Kõvadushardness in Spanish: Durezahardness in Esperanto: Durecohardness in French: Dureté (matériau)hardness in Galician: Durezahardness in Croatian: Tvrdoćahardness in Italian: Durezzahardness in Hebrew: קשיותhardness in Latvian: Cietībahardness in Lithuanian: Kietis (medžiaga)hardness in Dutch: Hardheidhardness in Japanese: 硬さhardness in Polish: Twardośćhardness in Portuguese: Durezahardness in Romanian: Duritatehardness in Russian: Твёрдостьhardness in Slovak: Materiálová tvrdosťhardness in Slovenian: Trdotahardness in Serbian: Тврдинаhardness in Finnish: Kovuushardness in Swedish: Hårdhethardness in Ukrainian: Твердістьhardness in Yiddish: הארטקייטhardness in Chinese: 硬度Synonyms, Antonyms and RelatedWordsPhilistinism, abstruseness, arduousness, armor, asperity, astringency, austerity, bothersomeness, burdensomeness, callosity, callousness, callus, closeness, cohesiveness, coldbloodedness,coldheartedness,coldness, compactness, complexity, complication, congestedness, congestion, consistence, consistency, crabbedness, crampedness, crowdedness, cruelty, deepness, denseness, density, difficultness, difficulty, durability, esoterica, firmness, flintiness, formidabledefenses, fundamentalism, gluiness, grimness, hairiness, hard heart, hardshell, hardenedness, hardheartedness,hardiness, hardness ofheart, hardship,harshness, heart ofstone, heartlessness, impenetrability,impenitence,impenitentness,impermeability,imperviousness,impliability,imporosity, inclemency, incompressibility,induration, inexorability, inexorableness, inflexibility, infrangibility, insensitiveness,insensitivity,insolence, intricacy, inuredness, irrepentance, jammedness, knottiness, laboriousness, lastingness, leatherlikeness,mercilessness,nonrepentance,obduracy, obdurateness, obstinacy, onerousness, oppressiveness, orthodoxy, pitilessness, precisianism, profoundness, profundity, purism, puritanism, reconditeness, relativedensity, relentlessness, remorselessness,resistance,rhinoceros hide, rigidity, rigidness, rigor, rigorousness, ropiness, roughness, ruggedness, ruthlessness, searedconscience, severity,short shrift, solidity,solidness, soundness, specific gravity,spissitude, stability, stamina, staunchness, sternness, stiffness, stoniness, stoutness, strength, strenuousness, stringency, stringiness, stubbornness, sturdiness, temper, tenacity, tender mercies, thickskin, thickness,toilsomeness,toughness, troublesomeness,unabjectness,unbendingness,unbreakability,unbreakableness,uncompassionateness,uncompromisingness,uncontriteness,unfeeling, unfeelingness, unforgivingness,ungentleness,unmercifulness,unnaturalness,unrelentingness,unremorsefulness,unresponsiveness,unsympatheticness,unyieldingness,vicissitude,vigor, viscidity, viscosity, viscousness, vitality

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