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Viscous forces
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The proportionality factor is the dynamic viscosity of the fluid, often simply referred to as the viscosity. It is denoted by the Greek letter mu (μ). The dynamic viscosity has the dimensions ( m a s s / l e n g t h ) / t i m e {\displaystyle \mathrm {(mass/length)/time} } , therefore resulting in the SI units and the derived units: = k g m ⋅ s = N m 2 ⋅ s = P a ⋅ s = {\displaystyle ={\frac {\rm {kg}}{\rm {m{\cdot }s}}}={\frac {\rm {N}}{\rm {m^{2}}}}{\cdot }{\rm {s}}={\rm {Pa{\cdot }s}}=} pressure multiplied by time.The aforementioned ratio u / y {\displaystyle u/y} is called the rate of shear deformation or shear velocity, and is the derivative of the fluid speed in the direction perpendicular to the normal vector of the plates (see illustrations to the right).
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Viscous forces
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If the velocity does not vary linearly with y {\displaystyle y} , then the appropriate generalization is: τ = μ ∂ u ∂ y , {\displaystyle \tau =\mu {\frac {\partial u}{\partial y}},} where τ = F / A {\displaystyle \tau =F/A} , and ∂ u / ∂ y {\displaystyle \partial u/\partial y} is the local shear velocity. This expression is referred to as Newton's law of viscosity.
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Yield (engineering)
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In materials science and engineering, the yield point is the point on a stress-strain curve that indicates the limit of elastic behavior and the beginning of plastic behavior. Below the yield point, a material will deform elastically and will return to its original shape when the applied stress is removed. Once the yield point is passed, some fraction of the deformation will be permanent and non-reversible and is known as plastic deformation. The yield strength or yield stress is a material property and is the stress corresponding to the yield point at which the material begins to deform plastically.
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Yield (engineering)
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The yield strength is often used to determine the maximum allowable load in a mechanical component, since it represents the upper limit to forces that can be applied without producing permanent deformation. In some materials, such as aluminium, there is a gradual onset of non-linear behavior, and no precise yield point. In such a case, the offset yield point (or proof stress) is taken as the stress at which 0.2% plastic deformation occurs.
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Yield (engineering)
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Yielding is a gradual failure mode which is normally not catastrophic, unlike ultimate failure. In solid mechanics, the yield point can be specified in terms of the three-dimensional principal stresses ( σ 1 , σ 2 , σ 3 {\displaystyle \sigma _{1},\sigma _{2},\sigma _{3}} ) with a yield surface or a yield criterion. A variety of yield criteria have been developed for different materials.
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Uranium metallurgy
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In materials science and materials engineering, uranium metallurgy is the study of the physical and chemical behavior of uranium and its alloys.Commercial-grade uranium can be produced through the reduction of uranium halides with alkali or alkaline earth metals. Uranium metal can also be made through electrolysis of KUF5 or UF4, dissolved in a molten CaCl2 and NaCl. Very pure uranium can be produced through the thermal decomposition of uranium halides on a hot filament.
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Functionally graded element
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In materials science and mathematics, functionally graded elements are elements used in finite element analysis. They can be used to describe a functionally graded material.
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Toughness
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In materials science and metallurgy, toughness is the ability of a material to absorb energy and plastically deform without fracturing. Toughness is the strength with which the material opposes rupture. One definition of material toughness is the amount of energy per unit volume that a material can absorb before rupturing. This measure of toughness is different from that used for fracture toughness, which describes the capacity of materials to resist fracture. Toughness requires a balance of strength and ductility.
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Thermostability
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In materials science and molecular biology, thermostability is the ability of a substance to resist irreversible change in its chemical or physical structure, often by resisting decomposition or polymerization, at a high relative temperature. Thermostable materials may be used industrially as fire retardants. A thermostable plastic, an uncommon and unconventional term, is likely to refer to a thermosetting plastic that cannot be reshaped when heated, than to a thermoplastic that can be remelted and recast. Thermostability is also a property of some proteins. To be a thermostable protein means to be resistant to changes in protein structure due to applied heat.
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Slip line field
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In materials science and soil mechanics, a slip line field or slip line field theory is a technique often used to analyze the stresses and forces involved in the major deformation of metals or soils. In essence, in some problems including plane strain and plane stress elastic-plastic problems, elastic part of the material prevent unrestrained plastic flow but in many metal-forming processes, such as rolling, drawing, gorging, etc., large unrestricted plastic flows occur except for many small elastic zones. In effect we are concerned with a rigid-plastic material under condition of plane strain. it turns out that the simplest way of solving stress equations is to express them in terms of a coordinate system that is along potential slip (or failure) surfaces. It is for this reason that this type of analysis is termed slip line analysis or the theory of slip line fields in the literature.
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Poisson's Ratio
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In materials science and solid mechanics, Poisson's ratio ν {\displaystyle \nu } (nu) is a measure of the Poisson effect, the deformation (expansion or contraction) of a material in directions perpendicular to the specific direction of loading. The value of Poisson's ratio is the negative of the ratio of transverse strain to axial strain. For small values of these changes, ν {\displaystyle \nu } is the amount of transversal elongation divided by the amount of axial compression. Most materials have Poisson's ratio values ranging between 0.0 and 0.5.
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Poisson's Ratio
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For soft materials, such as rubber, where the bulk modulus is much higher than the shear modulus, Poisson's ratio is near 0.5. For open-cell polymer foams, Poisson's ratio is near zero, since the cells tend to collapse in compression. Many typical solids have Poisson's ratios in the range of 0.2–0.3. The ratio is named after the French mathematician and physicist Siméon Poisson.
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Biaxial tensile testing
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In materials science and solid mechanics, biaxial tensile testing is a versatile technique to address the mechanical characterization of planar materials. It is a generalized form of tensile testing in which the material sample is simultaneously stressed along two perpendicular axes. Typical materials tested in biaxial configuration include metal sheets,silicone elastomers,composites,thin films,textiles and biological soft tissues.
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Residual stress
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In materials science and solid mechanics, residual stresses are stresses that remain in a solid material after the original cause of the stresses has been removed. Residual stress may be desirable or undesirable. For example, laser peening imparts deep beneficial compressive residual stresses into metal components such as turbine engine fan blades, and it is used in toughened glass to allow for large, thin, crack- and scratch-resistant glass displays on smartphones. However, unintended residual stress in a designed structure may cause it to fail prematurely.
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Residual stress
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Residual stresses can result from a variety of mechanisms including inelastic (plastic) deformations, temperature gradients (during thermal cycle) or structural changes (phase transformation). Heat from welding may cause localized expansion, which is taken up during welding by either the molten metal or the placement of parts being welded. When the finished weldment cools, some areas cool and contract more than others, leaving residual stresses. Another example occurs during semiconductor fabrication and microsystem fabrication when thin film materials with different thermal and crystalline properties are deposited sequentially under different process conditions. The stress variation through a stack of thin film materials can be very complex and can vary between compressive and tensile stresses from layer to layer.
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Work hardened
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In materials science parlance, dislocations are defined as line defects in a material's crystal structure. The bonds surrounding the dislocation are already elastically strained by the defect compared to the bonds between the constituents of the regular crystal lattice. Therefore, these bonds break at relatively lower stresses, leading to plastic deformation. The strained bonds around a dislocation are characterized by lattice strain fields.
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Work hardened
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For example, there are compressively strained bonds directly next to an edge dislocation and tensilely strained bonds beyond the end of an edge dislocation. These form compressive strain fields and tensile strain fields, respectively. Strain fields are analogous to electric fields in certain ways.
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Work hardened
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Specifically, the strain fields of dislocations obey similar laws of attraction and repulsion; in order to reduce overall strain, compressive strains are attracted to tensile strains, and vice versa. The visible (macroscopic) results of plastic deformation are the result of microscopic dislocation motion. For example, the stretching of a steel rod in a tensile tester is accommodated through dislocation motion on the atomic scale.
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Flow stress
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In materials science the flow stress, typically denoted as Yf (or σ f {\displaystyle \sigma _{\text{f}}} ), is defined as the instantaneous value of stress required to continue plastically deforming a material - to keep it flowing. It is most commonly, though not exclusively, used in reference to metals. On a stress-strain curve, the flow stress can be found anywhere within the plastic regime; more explicitly, a flow stress can be found for any value of strain between and including yield point ( σ y {\displaystyle \sigma _{\text{y}}} ) and excluding fracture ( σ F {\displaystyle \sigma _{\text{F}}} ): σ y ≤ Y f < σ F {\displaystyle \sigma _{\text{y}}\leq Y_{\text{f}}<\sigma _{\text{F}}} . The flow stress changes as deformation proceeds and usually increases as strain accumulates due to work hardening, although the flow stress could decrease due to any recovery process.
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Flow stress
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In continuum mechanics, the flow stress for a given material will vary with changes in temperature, T {\displaystyle T} , strain, ε {\displaystyle \varepsilon } , and strain-rate, ε ˙ {\displaystyle {\dot {\varepsilon }}} ; therefore it can be written as some function of those properties: Y f = f ( ε , ε ˙ , T ) {\displaystyle Y_{\text{f}}=f(\varepsilon ,{\dot {\varepsilon }},T)} The exact equation to represent flow stress depends on the particular material and plasticity model being used. Hollomon's equation is commonly used to represent the behavior seen in a stress-strain plot during work hardening: Y f = K ε p n {\displaystyle Y_{\text{f}}=K\varepsilon _{\text{p}}^{\text{n}}} Where Y f {\displaystyle Y_{\text{f}}} is flow stress, K {\displaystyle K} is a strength coefficient, ε p {\displaystyle \varepsilon _{\text{p}}} is the plastic strain, and n {\displaystyle n} is the strain hardening exponent. Note that this is an empirical relation and does not model the relation at other temperatures or strain-rates (though the behavior may be similar).
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Flow stress
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Generally, raising the temperature of an alloy above 0.5 Tm results in the plastic deformation mechanisms being controlled by strain-rate sensitivity, whereas at room temperature metals are generally strain-dependent. Other models may also include the effects of strain gradients. Independent of test conditions, the flow stress is also affected by: chemical composition, purity, crystal structure, phase constitution, microstructure, grain size, and prior strain.The flow stress is an important parameter in the fatigue failure of ductile materials.
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Flow stress
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Fatigue failure is caused by crack propagation in materials under a varying load, typically a cyclically varying load. The rate of crack propagation is inversely proportional to the flow stress of the material. == References ==
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MXenes
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In materials science, MXenes are a class of two-dimensional inorganic compounds , that consist of atomically thin layers of transition metal carbides, nitrides, or carbonitrides. MXenes accept a variety of hydrophilic terminations. MXenes were first reported in 2012.
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Ostwald's step rule
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In materials science, Ostwald's rule or Ostwald's step rule, conceived by Wilhelm Ostwald, describes the formation of polymorphs. The rule states that usually the less stable polymorph crystallizes first. Ostwald's rule is not a universal law but a common tendency observed in nature.This can be explained on the basis of irreversible thermodynamics, structural relationships, or a combined consideration of statistical thermodynamics and structural variation with temperature.
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Ostwald's step rule
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A dramatic example is phosphorus, which upon sublimation first forms the less stable white phosphorus, which only slowly polymerizes to the red allotrope. This is notably the case for the anatase polymorph of titanium dioxide, which having a lower surface energy is commonly the first phase to form by crystallisation from amorphous precursors or solutions despite being metastable, with rutile being the equilibrium phase at all temperatures and pressures. == References ==
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Schmid's law
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In materials science, Schmid's law (also Schmid factor) describes the slip plane and the slip direction of a stressed material, which can resolve the most shear stress. Schmid's Law states that the critically resolved shear stress (τ) is equal to the stress applied to the material (σ) multiplied by the cosine of the angle with the vector normal to the glide plane (φ) and the cosine of the angle with the glide direction (λ). Which can be expressed as: τ = m σ {\displaystyle \tau =m\sigma } where m is known as the Schmid factor m = cos ( ϕ ) cos ( λ ) {\displaystyle m=\cos(\phi )\cos(\lambda )} Both factors τ and σ are measured in stress units, which is calculated the same way as pressure (force divided by area). φ and λ are angles. The factor is named after Erich Schmid who coauthored a book with Walter Boas introducing the concept in 1935.
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Bingham fluid
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In materials science, a Bingham plastic is a viscoplastic material that behaves as a rigid body at low stresses but flows as a viscous fluid at high stress. It is named after Eugene C. Bingham who proposed its mathematical form.It is used as a common mathematical model of mud flow in drilling engineering, and in the handling of slurries. A common example is toothpaste, which will not be extruded until a certain pressure is applied to the tube. It is then pushed out as a relatively coherent plug.
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Frank-Read source
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In materials science, a Frank–Read source is a mechanism explaining the generation of multiple dislocations in specific well-spaced slip planes in crystals when they are deformed. When a crystal is deformed, in order for slip to occur, dislocations must be generated in the material. This implies that, during deformation, dislocations must be primarily generated in these planes.
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Lomer–Cottrell junction
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In materials science, a Lomer–Cottrell junction is a particular configuration of dislocations. When two perfect dislocations encounter along a slip plane, each perfect dislocation can split into two Shockley partial dislocations: a leading dislocation and a trailing dislocation. When the two leading Shockley partials combine, they form a separate dislocation with a burgers vector that is not in the slip plane. This is the Lomer–Cottrell dislocation.
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Lomer–Cottrell junction
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It is sessile and immobile in the slip plane, acting as a barrier against other dislocations in the plane. The trailing dislocations pile up behind the Lomer–Cottrell dislocation, and an ever greater force is required to push additional dislocations into the pile-up. ex. FCC lattice along {111} slip planes |leading| |trailing| a 2 → a 6 + a 6 {\displaystyle {\frac {a}{2}}\rightarrow {\frac {a}{6}}+{\frac {a}{6}}} a 2 → a 6 + a 6 {\displaystyle {\frac {a}{2}}\rightarrow {\frac {a}{6}}+{\frac {a}{6}}} Combination of leading dislocations: a 6 + a 6 → a 3 {\displaystyle {\frac {a}{6}}+{\frac {a}{6}}\rightarrow {\frac {a}{3}}} The resulting dislocation is along the crystal face, which is not a slip plane in FCC at room temperature. Lomer–Cottrell dislocation == References ==
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Composite laminate
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In materials science, a composite laminate is an assembly of layers of fibrous composite materials which can be joined to provide required engineering properties, including in-plane stiffness, bending stiffness, strength, and coefficient of thermal expansion. The individual layers consist of high-modulus, high-strength fibers in a polymeric, metallic, or ceramic matrix material. Typical fibers used include cellulose, graphite, glass, boron, and silicon carbide, and some matrix materials are epoxies, polyimides, aluminium, titanium, and alumina.
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Composite laminate
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Layers of different materials may be used, resulting in a hybrid laminate. The individual layers generally are orthotropic (that is, with principal properties in orthogonal directions) or transversely isotropic (with isotropic properties in the transverse plane) with the laminate then exhibiting anisotropic (with variable direction of principal properties), orthotropic, or quasi-isotropic properties. Quasi-isotropic laminates exhibit isotropic (that is, independent of direction) inplane response but are not restricted to isotropic out-of-plane (bending) response. Depending upon the stacking sequence of the individual layers, the laminate may exhibit coupling between inplane and out-of-plane response. An example of bending-stretching coupling is the presence of curvature developing as a result of in-plane loading.
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Dislocation
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In materials science, a dislocation or Taylor's dislocation is a linear crystallographic defect or irregularity within a crystal structure that contains an abrupt change in the arrangement of atoms. The movement of dislocations allow atoms to slide over each other at low stress levels and is known as glide or slip. The crystalline order is restored on either side of a glide dislocation but the atoms on one side have moved by one position. The crystalline order is not fully restored with a partial dislocation.
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Dislocation
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A dislocation defines the boundary between slipped and unslipped regions of material and as a result, must either form a complete loop, intersect other dislocations or defects, or extend to the edges of the crystal. A dislocation can be characterised by the distance and direction of movement it causes to atoms which is defined by the Burgers vector. Plastic deformation of a material occurs by the creation and movement of many dislocations.
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Rule of mixtures
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In materials science, a general rule of mixtures is a weighted mean used to predict various properties of a composite material . It provides a theoretical upper- and lower-bound on properties such as the elastic modulus, ultimate tensile strength, thermal conductivity, and electrical conductivity. In general there are two models, one for axial loading (Voigt model), and one for transverse loading (Reuss model).In general, for some material property E {\displaystyle E} (often the elastic modulus), the rule of mixtures states that the overall property in the direction parallel to the fibers may be as high as E c = f E f + ( 1 − f ) E m {\displaystyle E_{c}=fE_{f}+\left(1-f\right)E_{m}} where f = V f V f + V m {\displaystyle f={\frac {V_{f}}{V_{f}+V_{m}}}} is the volume fraction of the fibers E f {\displaystyle E_{f}} is the material property of the fibers E m {\displaystyle E_{m}} is the material property of the matrixIt is a common mistake to believe that this is the upper-bound modulus for Young's modulus.
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Rule of mixtures
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The real upper-bound Young's modulus is larger than E c {\displaystyle E_{c}} given by this formula. Even if both constituents are isotropic, the real upper bound is E c {\displaystyle E_{c}} plus a term in the order of square of the difference of the Poisson's ratios of the two constituents.The inverse rule of mixtures states that in the direction perpendicular to the fibers, the elastic modulus of a composite can be as low as E c = ( f E f + 1 − f E m ) − 1 . {\displaystyle E_{c}=\left({\frac {f}{E_{f}}}+{\frac {1-f}{E_{m}}}\right)^{-1}.} If the property under study is the elastic modulus, this quantity is called the lower-bound modulus, and corresponds to a transverse loading.
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Grain boundary
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In materials science, a grain boundary is the interface between two grains, or crystallites, in a polycrystalline material. Grain boundaries are two-dimensional defects in the crystal structure, and tend to decrease the electrical and thermal conductivity of the material. Most grain boundaries are preferred sites for the onset of corrosion and for the precipitation of new phases from the solid. They are also important to many of the mechanisms of creep. On the other hand, grain boundaries disrupt the motion of dislocations through a material, so reducing crystallite size is a common way to improve mechanical strength, as described by the Hall–Petch relationship.
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Matrix (composite)
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In materials science, a matrix is a constituent of a composite material.
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Sponge metal
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In materials science, a metal foam is a material or structure consisting of a solid metal (frequently aluminium) with gas-filled pores comprising a large portion of the volume. The pores can be sealed (closed-cell foam) or interconnected (open-cell foam). The defining characteristic of metal foams is a high porosity: typically only 5–25% of the volume is the base metal. The strength of the material is due to the square–cube law.
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Sponge metal
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Metal foams typically retain some physical properties of their base material. Foam made from non-flammable metal remains non-flammable and can generally be recycled as the base material. Its coefficient of thermal expansion is similar while thermal conductivity is likely reduced.
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Metal matrix composite
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In materials science, a metal matrix composite (MMC) is a composite material with fibers or particles dispersed in a metallic matrix, such as copper, aluminum, or steel. The secondary phase is typically a ceramic (such as alumina or silicon carbide) or another metal (such as steel). They are typically classified according to the type of reinforcement: short discontinuous fibers (whiskers), continuous fibers, or particulates.
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Metal matrix composite
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There is some overlap between MMCs and cermets, with the latter typically consisting of less than 20% metal by volume. When at least three materials are present, it is called a hybrid composite. MMCs can have much higher strength-to-weight ratios, stiffness, and ductility than traditional materials, so they are often used in demanding applications. MMCs typically have lower thermal and electrical conductivity and poor resistance to radiation, limiting their use in the very harshest environments.
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Partial dislocation
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In materials science, a partial dislocation is a decomposed form of dislocation that occurs within a crystalline material. An extended dislocation is a dislocation that has dissociated into a pair of partial dislocations. The vector sum of the Burgers vectors of the partial dislocations is the Burgers vector of the extended dislocation.
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Polymer blend
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In materials science, a polymer blend, or polymer mixture, is a member of a class of materials analogous to metal alloys, in which at least two polymers are blended together to create a new material with different physical properties.
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Polymer matrix composite
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In materials science, a polymer matrix composite (PMC) is a composite material composed of a variety of short or continuous fibers bound together by a matrix of organic polymers. PMCs are designed to transfer loads between fibers of a matrix. Some of the advantages with PMCs include their light weight, high resistance to abrasion and corrosion, and high stiffness and strength along the direction of their reinforcements.
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Porous media
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In materials science, a porous medium or a porous material is a material containing pores (voids). The skeletal portion of the material is often called the "matrix" or "frame". The pores are typically filled with a fluid (liquid or gas). The skeletal material is usually a solid, but structures like foams are often also usefully analyzed using concept of porous media.
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Porous media
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A porous medium is most often characterised by its porosity. Other properties of the medium (e.g. permeability, tensile strength, electrical conductivity, tortuosity) can sometimes be derived from the respective properties of its constituents (solid matrix and fluid) and the media porosity and pores structure, but such a derivation is usually complex. Even the concept of porosity is only straightforward for a poroelastic medium.
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Porous media
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Often both the solid matrix and the pore network (also known as the pore space) are continuous, so as to form two interpenetrating continua such as in a sponge. However, there is also a concept of closed porosity and effective porosity, i.e. the pore space accessible to flow. Many natural substances such as rocks and soil (e.g. aquifers, petroleum reservoirs), zeolites, biological tissues (e.g. bones, wood, cork), and man made materials such as cements and ceramics can be considered as porous media.
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Porous media
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Many of their important properties can only be rationalized by considering them to be porous media. The concept of porous media is used in many areas of applied science and engineering: filtration, mechanics (acoustics, geomechanics, soil mechanics, rock mechanics), engineering (petroleum engineering, bioremediation, construction engineering), geosciences (hydrogeology, petroleum geology, geophysics), biology and biophysics, material science. Two important current fields of application for porous materials are energy conversion and energy storage, where porous materials are essential for superpacitors, (photo-)catalysis, fuel cells, and batteries.
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Precipitate-free zone
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In materials science, a precipitate-free zone (PFZ) refers to microscopic localized regions around grain boundaries that are free of precipitates (solid impurities forced outwards from the grain during crystallization). It is a common phenomenon that arises in polycrystalline materials (crystalline materials with stochastically-oriented grains) where heterogeneous nucleation of precipitates is the dominant nucleation mechanism. This is because grain boundaries are high-energy surfaces that act as sinks for vacancies, causing regions adjacent to a grain boundary to be devoid of vacancies. As it is energetically favorable for heterogeneous nucleation to occur preferentially around defect-rich sites such as vacancies, nucleation of precipitates is impeded in the vacancy-free regions immediately adjacent to grain boundaries
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Refractory lining
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In materials science, a refractory (or refractory material) is a material that is resistant to decomposition by heat, pressure, or chemical attack, and retains strength and form at high temperatures. Refractories are polycrystalline, polyphase, inorganic, non-metallic, porous, and heterogeneous. They are typically composed of oxides or carbides, nitrides etc. of the following elements: silicon, aluminium, magnesium, calcium, boron, chromium and zirconium.ASTM C71 defines refractories as "non-metallic materials having those chemical and physical properties that make them applicable for structures, or as components of systems, that are exposed to environments above 1,000 °F (811 K; 538 °C)".Refractory materials are used in furnaces, kilns, incinerators, and reactors. Refractories are also used to make crucibles and moulds for casting glass and metals and for surfacing flame deflector systems for rocket launch structures. Today, the iron and steel industry and metal casting sectors use approximately 70% of all refractories produced.
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Sandwich structured composite
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In materials science, a sandwich-structured composite is a special class of composite materials that is fabricated by attaching two thin-but-stiff skins to a lightweight but thick core. The core material is normally low strength, but its higher thickness provides the sandwich composite with high bending stiffness with overall low density. Open- and closed-cell-structured foams like polyethersulfone, polyvinylchloride, polyurethane, polyethylene or polystyrene foams, balsa wood, syntactic foams, and honeycombs are commonly used core materials.
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Sandwich structured composite
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Sometimes, the honeycomb structure is filled with other foams for added strength. Open- and closed-cell metal foam can also be used as core materials. Laminates of glass or carbon fiber-reinforced thermoplastics or mainly thermoset polymers (unsaturated polyesters, epoxies...) are widely used as skin materials. Sheet metal is also used as skin material in some cases. The core is bonded to the skins with an adhesive or with metal components by brazing together.
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Mono-crystalline silicon
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In materials science, a single crystal (or single-crystal solid or monocrystalline solid) is a material in which the crystal lattice of the entire sample is continuous and unbroken to the edges of the sample, with no grain boundaries. The absence of the defects associated with grain boundaries can give monocrystals unique properties, particularly mechanical, optical and electrical, which can also be anisotropic, depending on the type of crystallographic structure. These properties, in addition to making some gems precious, are industrially used in technological applications, especially in optics and electronics.Because entropic effects favor the presence of some imperfections in the microstructure of solids, such as impurities, inhomogeneous strain and crystallographic defects such as dislocations, perfect single crystals of meaningful size are exceedingly rare in nature. The necessary laboratory conditions often add to the cost of production.
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Thermosetting polymer
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In materials science, a thermosetting polymer, often called a thermoset, is a polymer that is obtained by irreversibly hardening ("curing") a soft solid or viscous liquid prepolymer (resin). Curing is induced by heat or suitable radiation and may be promoted by high pressure, or mixing with a catalyst. Heat is not necessarily applied externally, but is often generated by the reaction of the resin with a curing agent (catalyst, hardener). Curing results in chemical reactions that create extensive cross-linking between polymer chains to produce an infusible and insoluble polymer network.
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Advanced composite materials (engineering)
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In materials science, advanced composite materials (ACMs) are materials that are generally characterized by unusually high strength fibres with unusually high stiffness, or modulus of elasticity characteristics, compared to other materials, while bound together by weaker matrices. These are termed "advanced composite materials" in comparison to the composite materials commonly in use such as reinforced concrete, or even concrete itself. The high strength fibers are also low density while occupying a large fraction of the volume.
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Advanced composite materials (engineering)
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Advanced composites exhibit desirable physical and chemical properties that include light weight coupled with high stiffness (elasticity), and strength along the direction of the reinforcing fiber, dimensional stability, temperature and chemical resistance, flex performance, and relatively easy processing. Advanced composites are replacing metal components in many uses, particularly in the aerospace industry. Composites are classified according to their matrix phase.
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Advanced composite materials (engineering)
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These classifications are polymer matrix composites (PMCs), ceramic matrix composites (CMCs), and metal matrix composites (MMCs). Also, materials within these categories are often called "advanced" if they combine the properties of high (axial, longitudinal) strength values and high (axial, longitudinal) stiffness values, with low weight, corrosion resistance, and in some cases special electrical properties. Advanced composite materials have broad, proven applications, in the aircraft, aerospace, and sports equipment sectors.
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Interstitial defect
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In materials science, an interstitial defect is a type of point crystallographic defect where an atom of the same or of a different type, occupies an interstitial site in the crystal structure. When the atom is of the same type as those already present they are known as a self-interstitial defect. Alternatively, small atoms in some crystals may occupy interstitial sites, such as hydrogen in palladium. Interstitials can be produced by bombarding a crystal with elementary particles having energy above the displacement threshold for that crystal, but they may also exist in small concentrations in thermodynamic equilibrium. The presence of interstitial defects can modify the physical and chemical properties of a material.
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Intrinsic properties
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In materials science, an intrinsic property is independent of how much of a material is present and is independent of the form of the material, e.g., one large piece or a collection of small particles. Intrinsic properties are dependent mainly on the fundamental chemical composition and structure of the material. Extrinsic properties are differentiated as being dependent on the presence of avoidable chemical contaminants or structural defects.In biology, intrinsic effects originate from inside an organism or cell, such as an autoimmune disease or intrinsic immunity. In electronics and optics, intrinsic properties of devices (or systems of devices) are generally those that are free from the influence of various types of non-essential defects. Such defects may arise as a consequence of design imperfections, manufacturing errors, or operational extremes and can produce distinctive and often undesirable extrinsic properties. The identification, optimization, and control of both intrinsic and extrinsic properties are among the engineering tasks necessary to achieve the high performance and reliability of modern electrical and optical systems.
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Torsion tensor
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In materials science, and especially elasticity theory, ideas of torsion also play an important role. One problem models the growth of vines, focusing on the question of how vines manage to twist around objects. The vine itself is modeled as a pair of elastic filaments twisted around one another. In its energy-minimizing state, the vine naturally grows in the shape of a helix. But the vine may also be stretched out to maximize its extent (or length). In this case, the torsion of the vine is related to the torsion of the pair of filaments (or equivalently the surface torsion of the ribbon connecting the filaments), and it reflects the difference between the length-maximizing (geodesic) configuration of the vine and its energy-minimizing configuration.
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Asperity (material science)
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In materials science, asperity, defined as "unevenness of surface, roughness, ruggedness" (from the Latin asper—"rough"), has implications (for example) in physics and seismology. Smooth surfaces, even those polished to a mirror finish, are not truly smooth on a microscopic scale. They are rough, with sharp, rough or rugged projections, termed "asperities". Surface asperities exist across multiple scales, often in a self affine or fractal geometry.
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Asperity (material science)
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The fractal dimension of these structures has been correlated with the contact mechanics exhibited at an interface in terms of friction and contact stiffness. When two macroscopically smooth surfaces come into contact, initially they only touch at a few of these asperity points. These cover only a very small portion of the surface area.
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Asperity (material science)
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Friction and wear originate at these points, and thus understanding their behavior becomes important when studying materials in contact. When the surfaces are subjected to a compressive load, the asperities deform through elastic and plastic modes, increasing the contact area between the two surfaces until the contact area is sufficient to support the load. The relationship between frictional interactions and asperity geometry is complex and poorly understood. It has been reported that an increased roughness may under certain circumstances result in weaker frictional interactions while smoother surfaces may in fact exhibit high levels of friction owing to high levels of true contact.The Archard equation provides a simplified model of asperity deformation when materials in contact are subject to a force. Due to the ubiquitous presence of deformable asperities in self affine hierarchical structures, the true contact area at an interface exhibits a linear relationship with the applied normal load.
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Bulk density
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In materials science, bulk density, also called apparent density or volumetric density, is a property of powders, granules, and other "divided" solids, especially used in reference to mineral components (soil, gravel), chemical substances, pharmaceutical ingredients, foodstuff, or any other masses of corpuscular or particulate matter (particles). Bulk density is defined as the mass of the many particles of the material divided by the total volume they occupy. The total volume includes particle volume, inter-particle void volume, and internal pore volume.Bulk density is not an intrinsic property of a material; it can change depending on how the material is handled. For example, a powder poured into a cylinder will have a particular bulk density; if the cylinder is disturbed, the powder particles will move and usually settle closer together, resulting in a higher bulk density. For this reason, the bulk density of powders is usually reported both as "freely settled" (or "poured" density) and "tapped" density (where the tapped density refers to the bulk density of the powder after a specified compaction process, usually involving vibration of the container.) In contrast, particle density is an intrinsic property of the solid and does not include the volume for voids between particles.
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Ceramic Matrix Composite
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In materials science, ceramic matrix composites (CMCs) are a subgroup of composite materials and a subgroup of ceramics. They consist of ceramic fibers embedded in a ceramic matrix. The fibers and the matrix both can consist of any ceramic material, whereby carbon and carbon fibers can also be regarded as a ceramic material.
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Friction force microscopy
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In materials science, chemical force microscopy (CFM) is a variation of atomic force microscopy (AFM) which has become a versatile tool for characterization of materials surfaces. With AFM, structural morphology is probed using simple tapping or contact modes that utilize van der Waals interactions between tip and sample to maintain a constant probe deflection amplitude (constant force mode) or maintain height while measuring tip deflection (constant height mode). CFM, on the other hand, uses chemical interactions between functionalized probe tip and sample. Choice chemistry is typically gold-coated tip and surface with R−SH thiols attached, R being the functional groups of interest.
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Friction force microscopy
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CFM enables the ability to determine the chemical nature of surfaces, irrespective of their specific morphology, and facilitates studies of basic chemical bonding enthalpy and surface energy. Typically, CFM is limited by thermal vibrations within the cantilever holding the probe. This limits force measurement resolution to ~1 pN which is still very suitable considering weak COOH/CH3 interactions are ~20 pN per pair. Hydrophobicity is used as the primary example throughout this consideration of CFM, but certainly any type of bonding can be probed with this method.
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Creep (deformation)
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In materials science, creep (sometimes called cold flow) is the tendency of a solid material to undergo slow deformation while subject to persistent mechanical stresses. It can occur as a result of long-term exposure to high levels of stress that are still below the yield strength of the material. Creep is more severe in materials that are subjected to heat for long periods and generally increase as they near their melting point. The rate of deformation is a function of the material's properties, exposure time, exposure temperature and the applied structural load.
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Creep (deformation)
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Depending on the magnitude of the applied stress and its duration, the deformation may become so large that a component can no longer perform its function – for example creep of a turbine blade could cause the blade to contact the casing, resulting in the failure of the blade. Creep is usually of concern to engineers and metallurgists when evaluating components that operate under high stresses or high temperatures. Creep is a deformation mechanism that may or may not constitute a failure mode.
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Creep (deformation)
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For example, moderate creep in concrete is sometimes welcomed because it relieves tensile stresses that might otherwise lead to cracking. Unlike brittle fracture, creep deformation does not occur suddenly upon the application of stress. Instead, strain accumulates as a result of long-term stress. Therefore, creep is a "time-dependent" deformation.
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Critical resolved shear stress
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In materials science, critical resolved shear stress (CRSS) is the component of shear stress, resolved in the direction of slip, necessary to initiate slip in a grain. Resolved shear stress (RSS) is the shear component of an applied tensile or compressive stress resolved along a slip plane that is other than perpendicular or parallel to the stress axis. The RSS is related to the applied stress by a geometrical factor, m, typically the Schmid factor: τ RSS = σ app m = σ app ( cos ϕ cos λ ) {\displaystyle \tau _{\text{RSS}}=\sigma _{\text{app}}m=\sigma _{\text{app}}(\cos \phi \cos \lambda )} where σapp is the magnitude of the applied tensile stress, Φ is the angle between the normal of the slip plane and the direction of the applied force, and λ is the angle between the slip direction and the direction of the applied force. The Schmid factor is most applicable to FCC single-crystal metals, but for polycrystal metals the Taylor factor has been shown to be more accurate.
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Critical resolved shear stress
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The CRSS is the value of resolved shear stress at which yielding of the grain occurs, marking the onset of plastic deformation. CRSS, therefore, is a material property and is not dependent on the applied load or grain orientation. The CRSS is related to the observed yield strength of the material by the maximum value of the Schmid factor: σ y = τ CRSS m max {\displaystyle \sigma _{y}={\frac {\tau _{\text{CRSS}}}{m_{\text{max}}}}} CRSS is a constant for crystal families. Hexagonal close-packed crystals, for example, have three main families - basal, prismatic, and pyramidal - with different values for the critical resolved shear stress.
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Cross Slip
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In materials science, cross slip is the process by which a screw dislocation moves from one slip plane to another due to local stresses. It allows non-planar movement of screw dislocations. Non-planar movement of edge dislocations is achieved through climb. Since the Burgers vector of a perfect screw dislocation is parallel to the dislocation line, it has an infinite number of possible slip planes (planes containing the dislocation line and the Burgers vector), unlike an edge or mixed dislocation, which has a unique slip plane.
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Cross Slip
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Therefore, a screw dislocation can glide or slip along any plane that contains its Burgers vector. During cross slip, the screw dislocation switches from gliding along one slip plane to gliding along a different slip plane, called the cross-slip plane. The cross slip of moving dislocations can be seen by transmission electron microscopy.
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Euler angle
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In materials science, crystallographic texture (or preferred orientation) can be described using Euler angles. In texture analysis, the Euler angles provide a mathematical depiction of the orientation of individual crystallites within a polycrystalline material, allowing for the quantitative description of the macroscopic material. The most common definition of the angles is due to Bunge and corresponds to the ZXZ convention. It is important to note, however, that the application generally involves axis transformations of tensor quantities, i.e. passive rotations. Thus the matrix that corresponds to the Bunge Euler angles is the transpose of that shown in the table above.
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Direct laser interference patterning
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In materials science, direct laser interference patterning (DLIP) is a laser-based technology that uses the physical principle of interference of high-intensity coherent laser beams to produce functional periodic microstructures. In order to obtain interference, the beam is divided by a beam splitter, special prisms, or other elements. The beams are then folded together to form an interference pattern.
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Direct laser interference patterning
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Sufficiently high power of the laser beam can thus result in the removal of material at the interference maximums thanks to ablation phenomenon, leaving the material intact at the minimums. In this way, a repeatable pattern can be permanently fixed on the surface of a given material. DLIP can be applied to almost any material and can change the properties of surfaces in many technological areas with regard to electrical and optical properties, tribology (friction and wear), light absorption and wettability (e.g., which can be related to hygienic properties).
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Disappearing polymorphs
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In materials science, disappearing polymorphs (or perverse polymorphism) describes a phenomenon in which a seemingly stable crystal structure is suddenly unable to be produced, instead transforming into a polymorph, or differing crystal structure with the same chemical composition, during nucleation. Sometimes the resulting transformation is extremely hard or impractical to reverse, because the new polymorph may be more stable. It is hypothesized that contact with a single microscopic seed crystal of the new polymorph can be enough to start a chain reaction causing the transformation of a much larger mass of material. Widespread contamination with such microscopic seed crystals may lead to the impression that the original polymorph has "disappeared."
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Dispersion (materials science)
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In materials science, dispersion is the fraction of atoms of a material exposed to the surface. In general, D = NS/N, where D is the dispersion, NS is the number of surface atoms and NT is the total number of atoms of the material. It is an important concept in heterogeneous catalysis, since only atoms exposed to the surface can affect catalytic surface reactions. Dispersion increases with decreasing crystallite size and approaches unity at a crystallite diameter of about 0.1 nm.
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Effective medium
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In materials science, effective medium approximations (EMA) or effective medium theory (EMT) pertain to analytical or theoretical modeling that describes the macroscopic properties of composite materials. EMAs or EMTs are developed from averaging the multiple values of the constituents that directly make up the composite material. At the constituent level, the values of the materials vary and are inhomogeneous. Precise calculation of the many constituent values is nearly impossible.
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Effective medium
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They both were derived in quasi-static approximation when the electric field inside a mixture particle may be considered as homogeneous. So, these formulae can not describe the particle size effect. Many attempts were undertaken to improve these formulae.
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Environmental stress fracture
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In materials science, environmental stress fracture or environment assisted fracture is the generic name given to premature failure under the influence of tensile stresses and harmful environments of materials such as metals and alloys, composites, plastics and ceramics. Metals and alloys exhibit phenomena such as stress corrosion cracking, hydrogen embrittlement, liquid metal embrittlement and corrosion fatigue all coming under this category. Environments such as moist air, sea water and corrosive liquids and gases cause environmental stress fracture. Metal matrix composites are also susceptible to many of these processes.
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Environmental stress fracture
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Plastics and plastic-based composites may suffer swelling, debonding and loss of strength when exposed to organic fluids and other corrosive environments, such as acids and alkalies. Under the influence of stress and environment, many structural materials, particularly the high-specific strength ones become brittle and lose their resistance to fracture.
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Environmental stress fracture
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While their fracture toughness remains unaltered, their threshold stress intensity factor for crack propagation may be considerably lowered. Consequently, they become prone to premature fracture because of sub-critical crack growth. This article aims to give a brief overview of the various degradation processes mentioned above.
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Fast ion conductor
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In materials science, fast ion conductors are solid conductors with highly mobile ions. These materials are important in the area of solid state ionics, and are also known as solid electrolytes and superionic conductors. These materials are useful in batteries and various sensors.
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Material fatigue
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In materials science, fatigue is the initiation and propagation of cracks in a material due to cyclic loading. Once a fatigue crack has initiated, it grows a small amount with each loading cycle, typically producing striations on some parts of the fracture surface. The crack will continue to grow until it reaches a critical size, which occurs when the stress intensity factor of the crack exceeds the fracture toughness of the material, producing rapid propagation and typically complete fracture of the structure. Fatigue has traditionally been associated with the failure of metal components which led to the term metal fatigue.
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Material fatigue
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However, there are also a number of special cases that need to be considered where the rate of crack growth is significantly different compared to that obtained from constant amplitude testing. Such as the reduced rate of growth that occurs for small loads near the threshold or after the application of an overload; and the increased rate of crack growth associated with short cracks or after the application of an underload.If the loads are above a certain threshold, microscopic cracks will begin to initiate at stress concentrations such as holes, persistent slip bands (PSBs), composite interfaces or grain boundaries in metals. The stress values that cause fatigue damage are typically much less than the yield strength of the material.
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Fracture toughening mechanisms
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In materials science, fracture toughness is the critical stress intensity factor of a sharp crack where propagation of the crack suddenly becomes rapid and unlimited. A component's thickness affects the constraint conditions at the tip of a crack with thin components having plane stress conditions and thick components having plane strain conditions. Plane strain conditions give the lowest fracture toughness value which is a material property. The critical value of stress intensity factor in mode I loading measured under plane strain conditions is known as the plane strain fracture toughness, denoted K Ic {\displaystyle K_{\text{Ic}}} .
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Fracture toughening mechanisms
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When a test fails to meet the thickness and other test requirements that are in place to ensure plane strain conditions, the fracture toughness value produced is given the designation K c {\displaystyle K_{\text{c}}} . Fracture toughness is a quantitative way of expressing a material's resistance to crack propagation and standard values for a given material are generally available. Slow self-sustaining crack propagation known as stress corrosion cracking, can occur in a corrosive environment above the threshold K Iscc {\displaystyle K_{\text{Iscc}}} and below K Ic {\displaystyle K_{\text{Ic}}} . Small increments of crack extension can also occur during fatigue crack growth, which after repeated loading cycles, can gradually grow a crack until final failure occurs by exceeding the fracture toughness.
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Fragile matter
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In materials science, fragile matter is a granular material that is jammed solid. Everyday examples include beans getting stuck in a hopper in a whole food shop, or milk powder getting jammed in an upside-down bottle. The term was coined by physicist Michael Cates, who asserts that such circumstances warrant a new class of materials.
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Fragile matter
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The jamming thus described can be unjammed by mechanical means, such as tapping or shaking the container, or poking it with a stick. Cates proposed that such jammed systems differ from ordinary solids in that if the direction of the applied stress changes, the jam will break up. Sometimes the change of direction required is very small.
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Fragile matter
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Perhaps the simplest example is a pile of sand, which is solid in the sense that the pile sustains its shape despite the force of gravity. Slight tilting or vibration is enough to enable the grains to shift, collapsing the pile. Not all jammed systems are fragile, i.e. foam.
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Fragile matter
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Shaving foam is jammed because the bubbles are tightly packed together under the isotropic stress imposed by atmospheric pressure. If it were a fragile solid, it would respond plastically to shear stress, however small. But because bubbles deform, foam actually responds elastically provided that the stress is below a threshold value. Fragile matter is also not to be confused with cases in which the particles have adhered to one another ("caking").
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Friability
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In materials science, friability ( FRY-ə-BIL-ə-tee), the condition of being friable, describes the tendency of a solid substance to break into smaller pieces under duress or contact, especially by rubbing. The opposite of friable is indurate. Substances that are designated hazardous, such as asbestos or crystalline silica, are often said to be friable if small particles are easily dislodged and become airborne, and hence respirable (able to enter human lungs), thereby posing a health hazard. Tougher substances, such as concrete, may also be mechanically ground down and reduced to finely divided mineral dust.
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Galfenol
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In materials science, galfenol is the general term for an alloy of iron and gallium. The name was first given to iron-gallium alloys by United States Navy researchers in 1998 when they discovered that adding gallium to iron could amplify iron's magnetostrictive effect up to tenfold. Galfenol is of interest to sonar researchers because magnetostrictor materials are used to detect sound, and amplifying the magnetostrictive effect could lead to better sensitivity of sonar detectors. Galfenol is also proposed for vibrational energy harvesting, actuators for precision machine tools, active anti-vibration systems, and anti-clogging devices for sifting screens and spray nozzles.
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Grain growth
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In materials science, grain growth is the increase in size of grains (crystallites) in a material at high temperature. This occurs when recovery and recrystallisation are complete and further reduction in the internal energy can only be achieved by reducing the total area of grain boundary. The term is commonly used in metallurgy but is also used in reference to ceramics and minerals. The behaviors of grain growth is analogous to the coarsening behaviors of grains, which implied that both of grain growth and coarsening may be dominated by the same physical mechanism.
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Grain refining
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In materials science, grain-boundary strengthening (or Hall–Petch strengthening) is a method of strengthening materials by changing their average crystallite (grain) size. It is based on the observation that grain boundaries are insurmountable borders for dislocations and that the number of dislocations within a grain has an effect on how stress builds up in the adjacent grain, which will eventually activate dislocation sources and thus enabling deformation in the neighbouring grain as well. By changing grain size, one can influence the number of dislocations piled up at the grain boundary and yield strength. For example, heat treatment after plastic deformation and changing the rate of solidification are ways to alter grain size.
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https://www.kaggle.com/datasets/conjuring92/wiki-stem-corpus
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wiki_198_chunk_0
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Hardness tester
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In materials science, hardness (antonym: softness) is a measure of the resistance to localized plastic deformation induced by either mechanical indentation or abrasion. In general, different materials differ in their hardness; for example hard metals such as titanium and beryllium are harder than soft metals such as sodium and metallic tin, or wood and common plastics. Macroscopic hardness is generally characterized by strong intermolecular bonds, but the behavior of solid materials under force is complex; therefore, hardness can be measured in different ways, such as scratch hardness, indentation hardness, and rebound hardness. Hardness is dependent on ductility, elastic stiffness, 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.
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https://www.kaggle.com/datasets/conjuring92/wiki-stem-corpus
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wiki_199_chunk_0
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Intergranular corrosion
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In materials science, intergranular corrosion (IGC), also known as intergranular attack (IGA), is a form of corrosion where the boundaries of crystallites of the material are more susceptible to corrosion than their insides. (Cf. transgranular corrosion.)
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https://www.kaggle.com/datasets/conjuring92/wiki-stem-corpus
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