《专业英语（材料科学）》材料物理班20111110学习内容

Unit 4

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19. This constant is equal to approximately 1.257×10-6 Henry per meter (H/m) in free space (a

(Unit 4, P32, Para 6, Line 3) vacuum). 20. Materials that cause the lines of flux to move farther apart, resulting in a decrease in

magnetic flux density compared with a vacuum, are called diamagnetic. (Unit 4, P32, Para 7, Line 1) 21. Materials that concentrate magnetic flux by a factor of more than one but less than or equal

to ten are called paramagnetic; materials that concentrate the flux by a factor of more than

(Unit 4, P32, Para 7, Line 2) ten are called ferromagnetic. 22. For non-ferrous metals such as copper, brass, aluminum etc., the permeability is the same

as that of “free space”, i.e. the relative permeability is one. For ferrous metals however the

(Unit 4, P33, Para 2, Line 1) value of μr may be several hundred. 23. This effect is useful in the design of transformers and eddy current probes. (Unit 4, P33, Para

3, Line 2)

Reading Material

1. The electrons carry a negative electrostatic charge and under certain conditions can move

from atom to atom. (Unit 4, P35, Para 1, Line 1) 2. The directional movement of electrons due to an electromotive force is what is known as electricity. (Unit 4, P36, Para 1, Line 3) 3. It is the ratio of the current density to the electric field strength. (Unit 4, P36, Para 2, Line 2) 4. Its SI derived unit is the Siemens per meter, but conductivity values are often reported as percent IACS. (Unit 4, P36, Para 2, Line 2) 5. IACS is an acronym for International Annealed Copper Standard or the material that was used to make traditional copper-wire. (Unit 4, P36, Para 2, Line 4) 6. Conductivity values in Siemens/meter can be converted to % IACS by multiplying the conductivity value by 1.724×10-6. (Unit 4, P36, Para 3, Line 1) 7. Electricity conductivity is a very useful property since values are affected by such things as a substance chemical composition and the stress state of crystalline structures. (Unit 4, P36, Para 4, Line 1)

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《专业英语（材料科学）》材料物理班20111110学习内容

8. Electrical resistivity is the reciprocal of conductivity. 9. The SI unit for electrical resistivity is the ohm meter.

(Unit 4, P36, Para 5, Line 1) (Unit 4, P36, Para 6, Line 1)

10. Resistivity values in microhm centimeters units can be converted to % IACS conductivity

values with the following formula: 172.41 / resistivity = % IACS. (Unit 4, P36, Para 6, Line 5) 11. Thermal conductivity (λ) is the intrinsic property of a material which relates its ability to

conduct heat. (Unit 4, P36, Para 7, Line 1) 12. Conduction takes place when a temperature gradient exists in a solid (or stationary fluid) medium. (Unit 4, P36, Para 7, Line 3) 13. Thermal conductivity is defined as the quantity of heat (Q) transmitted through a unit thickness (L) in a direction normal to a surface of unit area (A) due to a unit temperature gradient (ΔT) under steady state conditions and when the heat transfer is dependent only on

(Unit 4, P37, Para 2, Line 1) the temperature gradient. 14. When heat is added to most materials, the average amplitude of the atoms’ vibrating within

the material increases. (Unit 4, P37, Para 3, Line 1) 15. As shown in the following equation, α is the ratio of change in length (Δl) to the total starting length (li) and change in temperature (ΔT). (Unit 4, P37, Para 3, Line 6) 16. By rearranging this equation, it can be seen that if the linear coefficient of thermal expansion is known, the change in components length can be calculated for each degree of

(Unit 4, P37, Para 4, Line 1) temperature change. 17. That is to say, if energy is removed from a material then the object’s temperature will

decrease causing the object to contract. (Unit 4, P37, Para 4, Line 3) 18. Thermal expansion (and contraction) must be taken into account when designing products with close tolerance fits as these tolerances will change as temperature changes if the materials used in the design have different coefficients of thermal expansion. (Unit 4, P37, Para 5, Line 1) 19. For example, thermostats and other heat-sensitive sensors make use of the property of

(Unit 4, P37, Para 5, Line 7) linear expansion.

Unit 5

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《专业英语（材料科学）》材料物理班20111110学习内容

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1. The most common properties considered are strength, ductility, hardness, impact resistance,

(Unit 5, P39, Para 1, Line 4) and fracture toughness. 2. Most structural materials are anisotropic, which means that their material properties vary (Unit 5, P39, Para 2, Line 1) with orientation. 3. The variation in properties can be due to directionality in the microstructure (texture) from

forming or cold working operation, the controlled alignment of fiber reinforcement and a

(Unit 5, P39, Para 2, Line 2) variety of other causes. 4. In products such as sheet and plate, the rolling direction is called the longitudinal direction,

the width of the product is called the transverse direction, and the thickness is called the

(Unit 5, P39, Para 2, Line 6) short transverse direction. 5. The mechanical properties of a material are not constant and often change as a function of (Unit 5, P39, Para 3, Line 1) temperature, rate of loading, and other conditions. 6. For example, temperatures below room temperature generally cause an increase in strength

properties of metallic alloys; while ductility, fracture toughness, and elongation usually

(Unit 5, P39, Para 3, Line 2) decrease. 7. There are five fundamental loading conditions: tension, compression, bending, shear, and (Unit 5, P40, Para 2, Line 3) torsion. 8. If a material is subjected to a constant force, it is called static loading. If the loading of the

material is not constant but instead fluctuates, it is called dynamic or cyclic loading. (Unit 5, P40, Para 3, Line 1) 9. The term stress (S) is used to express the loading in terms of force applied to a certain

(Unit 5, P40, Para 4, Line 1) cross-sectional area of an object. 10. However, a bar loaded in bending will have a stress distribution that changes with distance (Unit 5, P40, Para 4, Line 7) perpendicular to the normal axis. 11. Engineering strain is defined as the amount of deformation in the direction of the applied (Unit 5, P40, Para 5, Line 2) force divided by the initial length of the material. 12. For example, the strain in a bar that is being stretched in tension is the amount of elongation

or change in length divided by its original length. (Unit 5, P40, Para 5, Line 5) 13. If the stress is small, the material may only strain a small amount and the material will return to its original size after the stress is released. This is called elastic deformation, because of

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《专业英语（材料科学）》材料物理班20111110学习内容

liking elastic, it returns to its unstressed state. (Unit 5, P40, Para 6, Line 1)

14. If a material is loaded beyond it elastic limit, the material will remain in a deformed

condition after the load is removed. This is called plastic deformation. (Unit 5, P40, Para 6, Line 4) 15. Tensile properties indicate how the material will react to forces being applied in tension.

(Unit 5, P40, Para 7, Line 1) 16. Hardness measurements are widely used for the quality control of materials because they are

quick and considered to be nondestructive tests when the marks or indentations produced by

(Unit 5, P41, Para 2, Line 7) the test are in low stress areas.

Unit 7

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1. Metals are sometimes described as a lattice of positive ions surrounded by a cloud of (Unit 7, P58, Para 2, Line 7) delocalized electrons. 2. Metals are one of the three groups of elements as distinguished by their ionization and (Unit 7, P58, Para 2, Line 8) bonding properties, along with the metalloids and nonmetals. 3. On the periodic table, a diagonal line drawn from boron (B) to polonium (Po) separates the

metals from the nonmetals. (Unit 7, P58, Para 2, Line 9) 4. Most elements on this line are metalloids, sometimes called semi-metals; elements to the lower left are metals; elements to the upper right are nonmetals. (Unit 7, P58, Para 2, Line 11) 5. An alternative definition of metals is that they have overlapping conduction bands and

(Unit 7, P58, Para 3, Line 1) valence bands in their electronic structure. 6. These synthetic materials often have the characteristic silvery-grey reflectiveness (luster) of

elemental metals. (Unit 7, P58, Para 3, Line 4) 7. Metals are usually inclined to form cations through electron loss, reacting with oxygen in the air to form oxides over changing timescales (iron rusts over years, while potassium burns in seconds). (Unit 7, P58, Para 4, Line 1) 8. The alkali metals are the most volatile, followed by the alkaline earth metals, found in the

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《专业英语（材料科学）》材料物理班20111110学习内容

leftmost two groups of the periodic table. (Unit 7, P58, Para 4, Line 3)

9. The transition metals (such as iron, copper, zinc, and nickel) take much longer to oxidize.

(Unit 7, P58, Para 5, Line 1) 10. Some metals form a barrier layer of oxide on their surface which cannot be penetrated by

further oxygen molecules and thus retain their shiny appearance and good conductivity for

(Unit 7, P58, Para 5, Line 3) many decades (like aluminium, some steels, and titanium). 11. The oxides of metals are basic (as opposed to those of nonmentals, which are acidic),

although this may be considered a rule of thumb, rather than a fact. (Unit 7, P58, Para 5, Line 5) 12. Painting, anodising or plating metals are good ways to prevent their corrosion. (Unit 7, P59,

Para 2, Line 1) 13. However, a more reactive metal in the electrochemical series must be chosen for coating,

(Unit 7, P59, Para 2, Line 1) especially when chipping of the coating is expected. 14. Water and the two metals form an electrochemical cell, and if the coating is less reactive

than the coatee, the coating actually promotes corrosion. (Unit 7, P59, Para 2, Line 3) 15. Metals in general have superior electric and thermal conductivity, high luster and density, and the ability to be deformed under stress without cleaving. (Unit 7, P59, Para 3, Line 1) 16. While there are several metals that have low density, hardness, and melting points, these (the alkali and alkaline earth metals) are extremely reactive, and are rarely encountered in their elemental, metallic form. (Unit 7, P59, Para 3, Line 2) 17. The high density of most metals is due to the tightly-packed crystal lattice of the metallic structure. (Unit 7, P59, Para 4, Line 4) 18. However, other factors (such as atomic radius, nuclear charge, number of bonding orbitals, overlap of orbital energies, and crystal form) are involved as well. (Unit 7, P59, Para 4, Line 7) 19. Planes of atoms in a metal are able to slide across one another under stress, accounting for

(Unit 7, P59, Para 5, Line 2) the ability of a crystal to deform without shattering. 20. The electrical and thermal conductivity of metals originate from the fact that in the metallic

bond, the outer electrons of the metal atoms form a gas of nearly free electrons, moving as an electron gas in a background of positive charge formed by the ion cores. (Unit 7, P59, Para 7, Line 1) 21. Good mathematical predictions for electrical conductivity, as well as the electrons’

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《专业英语（材料科学）》材料物理班20111110学习内容

contribution to the heat capacity and heat conductivity of metals can be calculated from the

free electron model, which does not take the detailed structure of the ion lattice into account. (Unit 7, P59, Para 7, Line 4) 22. When considering the exact band structure and binding energy of a metal, it is necessary to take into account the positive potential caused by the specific arrangement of the ion cores

(Unit 7, P59, Para 8, Line 1) which is periodic in crystals. 23. The most important consequence of the periodic potential is the formation of a small band

gap at the boundary of the brillouin zone. Mathematically, the potential of the ion cores is

(Unit 7, P59, Para 8, Line 3) treated in the nearly-free electron model. 24. An alloy is a mixture of two of more elements in solid solution in which the major

component is a metal. (Unit 7, P59, Para 9, Line 1) 25. Combining different ratios of metals as alloys modifies the properties of pure metals to produce desirable characteristics. (Unit 7, P60, Para 1, Line 2) 26. Examples of alloys are steel (iron and carbon), brass (copper and zinc), bronze (copper and tin), and duralumin (aluminium and copper). (Unit 7, P60, Para 1, Line 5)

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