材料物理Material physics.docx

1、材料物理Material physics材料物理2（Material physics 2）Fill in the. Noun interpretation1. phonon: energy quantum of independent harmonic oscillator in lattice vibration.Wave characteristics: the propagation medium is not connected with the medium. It is the crystal lattice of the yard, ion, etc. The lattice v

2、ibration mode (wave is on the lattice thermal vibration of atoms can be described as similar to the mechanical results of wave propagation, the wave is called latticewave)Griffith crack theory: Griffith that many tiny cracks or defects exists in actual material, under the action of external force, a

3、nd these cracks around the defect will produce stress concentration phenomenon, when the stress reaches a certain level, the crack began to rupture propagation. This is the famous theory of Griffith microcracks.The mechanism of particle reinforced material is that particles can prevent dislocation m

4、ovement in the matrix or absorb part of the energy through plastic deformation of particles, thus strengthening the purpose.The reason of thermal expansion hysteresis in complex is that the expansion coefficient varies greatly in different directions between different phases or grains, resulting in

5、great internal stress, resulting in microcracks.There are several types of crack propagation: fracture type (the main cause of low stress fracture) (Zhang Kaihang, I type), stagger type (sliding type, II type), tearing type (III type)The nature of thermal breakdown: a medium in an electric field tha

6、t is heated due to dielectric loss and may be charged from a heat balance state of heat dissipation and heating when the applied voltage is high enough. If the energy emitted is greater than that, the temperature of the medium will become higher and higher until permanent damage occurs.The carriers

7、in conducting materials: any substance, as long as the existence of free particle charge, which can be produced in the electric field to store the current carrier metal conductor is the free electron, inorganic materials (electronic negative electron, ion (hole) ions or voids) as carrier ion conduct

8、ance said as a carrier for ionic conductance, the electron conductance called electronic conductivityThe form of force and deformation of inorganic materials; elastic deformation; plastic deformation; viscous flow; high temperature creepThe factors causing phonon scattering, phonon frequency and dop

9、ing point defectsAt the Curie point in dielectric polarization mechanism; electron polarization, ion displacement polarization and ionic relaxation polarization, spontaneous polarization (some dielectric at a certain temperature, when the external electric field after the withdrawal is still a certa

10、in polarization)The main structure of ferrite in structure: the spinel garnet type 3 magnetoplumbite type 4 5 6 perovskite type ilmenite type tungsten bronze typeThe particle diffusion mechanism includes: sublattice gap diffusion; vacancy diffusion; interstitial diffusion mechanismDielectric breakdo

11、wn type: thermal breakdown, electric breakdown, partial discharge breakdownFracture energy: the action of an external force on an object per unit volume until an object is broken by an external forceSurface discharge; surface discharge of solid medium belongs to gas discharge; solid medium is often

12、in the surrounding gas and coal; sometimes the medium itself does not break through, but sparks blow over its surface, which is surface discharge.The intrinsic conductivity and impurity conductivity; basic ion source in the crystal lattice of the movement known as the intrinsic conductance (intrinsi

13、c ion conductance) caused by the movement of the fixed ion is weak, is the main impurity ions, called impurity conductivity.Space charge polarization: under the action of electric field, the positive and negative interstitial ions in inhomogeneous media move towards negative and positive poles respe

14、ctively. The change in the density of the ions in the ceramic body results in an electric dipole moment, which is called space charge polarization.Equilibrium carriers and nonequilibrium carriers: at certain temperatures, carriers due to thermal excitation in semiconductors are called equilibrium ca

15、rriers. Due to external conditions (plus voltage). Guang Zhao) a carrier with a large number of carriers is called a non-equilibrium carrierPressure sensitive effect refers to the effect of nonlinear resistor sensitive to voltage changes, which is in a critical voltage condition, the resistance valu

16、e is very high, almost no current through, exceeds the critical voltage (voltage sensitive resistor) value decreased quickly, so that the current through the.Dielectric strength: when the electric field strength exceeds a critical value. The phenomenon that a dielectric changes from a dielectric sta

17、te into a conductive state is called a breakdown in dielectric strength. The corresponding critical field strength is called dielectric strength.What is the essence of absorption of light by a medium?As an energy flow, light passes through the medium, causing the valence electron transition of the m

18、edium, or the atomic vibration, to consume energy. In addition, the valence electrons in the medium absorb the photon energy and excite it. Yet when a photon deexcitation, collisions with other molecules in motion, i.e. thermal energy transformation kinetic energy electrons into molecules, which con

19、stitute the light attenuation, even in the transparent medium is not light scattering of light, there will be loss of energy, light absorption.4., why do most ceramic materials do not produce plastic deformation at normal temperature, but brittle fracture?Ceramic multi crystal plastic deformation de

20、pends not only on the material constituting the crystal itself, but also to a great extent on the grain boundary control material, so the polycrystalline plastic deformation including the following, the dislocations caused by plastic deformation, the relative sliding between the grain and grain boun

21、dary, vacancy diffusion, viscous flow, at room temperature due to the structure characteristics of non metallic crystal and grain boundary, the plastic deformation is difficult to achieve, because the micro cracks often exist in the material, when the external stress is not enough to make the plasti

22、c deformation velocity, the critical stress of the stress may have been more than micro crack propagation required, eventually lead to brittle materials.5. what is the rule of lattice sliding?The slip distance must be integer times of lattice constant; crystal slip in the middle always occurs in the

23、 main crystal surface and main crystal orientation; slip occurred in the shear stress under the action of the sliding surface only when the shear stress exceeds the critical shear stress, can slip along the crystal surface.6. what are the causes of crack initiation and rapid propagation in ceramic m

24、aterials? What are the measures to prevent crack propagation?Production: the development of micro defects into the crystal crack; surface mechanical strength and chemical corrosion damage formation of surface cracks caused by thermal stress; crack; crack gas formation; crystal growth or amorphous to

25、 crystal transition of crack formation. Because dynamic crack propagation, when C increases, G increases, and #=4r is a constant, therefore, once they reach a critical size and initial fracture initiation and propagation of failure process is a critical stage, because of brittle material basically d

26、id not absorb large amounts of energy of plastic deformation measures: the use of stress does not exceed # device settings in energy absorption; materials; artificially caused a lot of very fine is smaller than the critical size crack in the material7. what are the factors that affect thermal conduc

27、tivity?Influence of temperature; the influence of microstructure; the influence of chemical composition; the influence of porosity; the thermal conductivity of multiphase ceramics8 glass is a disorder network structure, it is impossible to have a slip system is brittle, but at high temperatures can

28、deformation? Why?Answer: it is because of the non long-range order, many atoms are not in the potential curve trough; some bond is weak, only small stress can make the bond breaking of these atoms; the gap position near the atomic transition, caused by atomic migration and rearrangement, without the

29、 initial yield stress to deformation of viscous flow.9, the reason of ferromagnetic domain formation is explained from the viewpoint of energyAnswer: according to the laws of thermodynamics, the steady-state magnetic state must be corresponding to the total free ferromagnetic material within the ene

30、rgy minimum state, formation and stability of structure of a domain is corresponding to the total free energy to meet the minimum conditions. For ferromagnetic materials, the energy is reduced before splitting into domains. Therefore, when the ferromagnetic material is magnetized spontaneously, it w

31、ill inevitably be divided into magnetic domains in the small region, which makes the total free energy the lowest and satisfies the minimum energy principle. It can be seen that the demagnetizing field is the reason for the formation of magnetic domains.Analysis questionsThe causes of cracks and the

32、ir fracture mechanisms are briefly described. How can crack propagation be prevented?Answer: cause: because of the defects in the crystal microstructure, when subjected to external force, these defects caused by stress concentration, resulting in crack nucleation of a grains with different orientati

33、ons B Journal of atomic stress concentration C thermal defectsMechanical damage and chemical corrosion on the surface of the material form surface cracksCracks formed due to thermal stressThe mechanism of crack or defect: Griffith believed that many of the small total actual material, under the action of