The Four Transverse Effects and Their Relations in Certain Metals

Thermoelectric effect

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The first equation formulates Faraday's Law of Electromagnetic Induction, which states that changing magnetic fields generate electrical fields, producing electrical current.

The second equation is called the Ampere-Maxwell Law. It adds to Ampere's Law, which states an electric current flowing over a wire produces a magnetic field around itself, and another law that says a changing magnetic field also gives rise to a property similar to an electric current a displacement current , and this too creates a magnetic field around itself. The term displacement current actually is a crucial point.

The third equation is the law stating there is an electric charge at the source of an electric field. The fourth equation is Gauss's Law of magnetic field, stating a magnetic field has no source magnetic monopole equivalent to that of an electric charge. If you take two parallel metal plates electrodes and connect one to the positive pole and the other to the negative pole of a battery, you will create a capacitor. Direct-current DC electricity will simply collect between the two metal plates, and no current will flow between them.

However, if you connect alternating current AC that changes drastically, electric current will start to flow along the two electrodes. Electric current is a flow of electrons, but between these two electrodes there is nothing but space, and thus electrons do not flow. Maxell wondered what this could mean. Then it came to him that applying an AC voltage to the electrodes generates a changing electric field in the space between them, and this changing electric field acts as a changing electric current. This electric current is what we mean when we use the term displacement current.

A most unexpected conclusion can be drawn from the idea of a displacement current. In short, electromagnetic waves can exist. This also led to the discovery that in space there are not only objects that we can see with our eyes, but also intangible fields that we cannot see. The existence of fields was revealed for the first time. Solving Maxwell's equations reveals the wave equation, and the solution for that equation results in a wave system in which electric fields and magnetic fields give rise to each other while traveling through space. The form of electromagnetic waves was expressed in a mathematical formula.

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Magnetic fields and electric fields are inextricably linked, and there is also an entity called an electromagnetic field that is solely responsible for bringing them into existence. Now let's take a look at a capacitor. Applying AC voltage between two metal electrodes produces a changing electric field in space, and this electric field in turn creates a displacement current, causing an electric current to flow between the electrodes. At the same time, the displacement current produces a changing magnetic field around itself according to the second of Maxwell's equations Ampere-Maxwell Law.

The resulting magnetic field creates an electric field around itself according to the first of Maxwell's equations Faraday's Law of Electromagnetic Induction. Based on the fact that a changing electric field creates a magnetic field in this manner, electromagnetic waves-in which an electric field and magnetic field alternately appear-are created in the space between the two electrodes and travel into their surroundings. Antennas that emit electromagnetic waves are created by harnessing this principle.

Maxwell calculated the speed of travel for the waves, i.

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He said speed was simply one over the square root of the electric permittivity in vacuum times the magnetic permeability in vacuum. This exactly matched the previously discovered speed of light. This led Maxwell to confidently state that light is a type of electromagnetic wave. The theory of light being a particle completely vanished until the end of the 19th century when Albert Einstein revived it.

Now that the dual nature of light as "both a particle and a wave" has been proved, its essential theory was further evolved from electromagnetics into quantum mechanics.

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Einstein believed light is a particle photon and the flow of photons is a wave. The main point of Einstein's light quantum theory is that light's energy is related to its oscillation frequency. He maintained that photons have energy equal to "Planck's constant times oscillation frequency," and this photon energy is the height of the oscillation frequency while the intensity of light is the quantity of photons. The various properties of light, which is a type of electromagnetic wave, are due to the behavior of extremely small particles called photons that are invisible to the naked eye.

The German physicist Albert Einstein to , famous for his theories of relativity, conducted research on the photoelectric effect, in which electrons fly out of a metal surface exposed to light. The strange thing about the photoelectric effect is the energy of the electrons photoelectrons that fly out of the metal does not change whether the light is weak or strong. If light were a wave, strong light should cause photoelectrons to fly out with great power.

Another puzzling matter is how photoelectrons multiply when strong light is applied. Einstein explained the photoelectric effect by saying that "light itself is a particle," and for this he received the Nobel Prize in Physics. The light particle conceived by Einstein is called a photon.

The main point of his light quantum theory is the idea that light's energy is related to its oscillation frequency known as frequency in the case of radio waves. Oscillation frequency is equal to the speed of light divided by its wavelength. Photons have energy equal to their oscillation frequency times Planck's constant.

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Einstein speculated that when electrons within matter collide with photons, the former takes the latter's energy and flies out, and that the higher the oscillation frequency of the photons that strike, the greater the electron energy that will come flying out. In short, he was saying that light is a flow of photons, the energy of these photons is the height of their oscillation frequency, and the intensity of the light is the quantity of its photons. Einstein proved his theory by proving that the Planck's constant he derived based on his experiments on the photoelectric effect exactly matched the constant 6.

This too pointed to an intimate relationship between the properties and oscillation frequency of light as a wave and the properties and momentum energy of light as a particle, or in other words, the dual nature of light as both a particle and a wave.

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French theoretical physicist Louis de Broglie to furthered such research on the wave nature of particles by proving that there are particles electrons, protons and neutrons besides photons that have the properties of a wave. According to de Broglie, all particles traveling at speeds near that of light adopt the properties and wavelength of a wave in addition to the properties and momentum of a particle.

From another perspective, one could say that the essence of the dual nature of light as both a particle and a wave could already be found in Planck's constant. The evolution of this idea is contributing to diverse scientific and technological advances, including the development of electron microscopes. Chapter 1: The Mysteries of Light. Furthermore, the entire process will be strongly influenced both by material types and structural lay-up.

For elevated-temperature applications such as the HSCT, the effects of various environmental factors must also be accounted for in addition to the mechanical degradation modes. Continuing damage accumulation is induced and driven by combined cyclic loads, high-temperature exposure, oxidative attack, solvent infusion, moisture, and other factors.

The coupling process linking the growth of various damage modes and the external environmental drivers will undoubtedly prove complex. Damage mechanisms to consider for elevated-temperature composite applications include thermal oxidation, hygrothermal combined moisture and temperature effects, matrix cracking, and microstructural changes. The evaluation of the degradation of polymer-matrix composites is complex, requiring not only an integration of many contributing factors, but also an assessment of poorly understood synergistic accelerations in damage accumulation as driven by external factors.

Moisture absorption, high-temperature exposure, heating and cooling rates, and loading rates represent a number of those factors that affect basic composite properties such as toughness, glass transition temperature, and strength. The combined influence of such factors on the failure mechanism may be pivotal in deriving any reliable modeling process.

High-temperature thermosetting polymers such as bismaleimides commonly incorporate discrete toughening phases, typically 25—weight percent of a soluble thermoplastic polyimide in granular or particulate form, to improve impact resistance.

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Using a common optical microscope, distinct color differences can be seen between the two phases, with both phases showing considerable darkening as exposure time increases. This phase separation progresses from the surface to the interior and is assumed to be driven by differences in oxidation rates of both the bismaleimide and the added toughening agent. Phase separation has a deleterious effect not only on matrix toughness, but can also lead to matrix cracking since phase boundaries represent discontinuities with associated stress concentrations.

This combined degradation phenomenon can be seen generally after 5, hours of exposure and represents a valid concern for long-term HSCT applications. Perhaps the most critical damage mechanism operating in high-temperature polymeric composites is the formation of transverse ply cracks shown schematically in Figure and in-plane microcracks in matrix polymers of multiaxial composites.

Matrix cracking can result from initial laminate processing, mechanical static, and fatigue loading Reifsnider and Giacco, , residual stresses resulting from hygrothermal exposures, thermal cycling, and combined effects of mechanical and environmental cycles Sensmeier, As the cycles mechanical or thermal advance, matrix cracks become more pronounced and increase in density until a saturation level is reached NRC, Fiber anisotropy 1 and differences between thermal expansion coefficients of the matrix and fiber can result in residual thermal stresses during processing or exposure to temperature.

These stresses can cause fiber-matrix interfacial failure or radial cracking in the matrix radiating from fiber surfaces. Hygrothermal combined moisture and temperature cycling of composite laminates can produce transverse matrix cracks that initiate in surface plies and progress deeper into the laminate with accumulating cycles. The rate and severity of transverse matrix cracking is dependent on several conditions, including matrix properties, fiber properties especially thermal expansion and stiffness , processing conditions, service conditions including temperature cycle and humidity , ply thickness, and ply stacking sequence.

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Composite strength, stiffness, and thermal properties as well as failure modes can be affected by transverse matrix cracking. In addition to damage-induced reduction of matrix-dominated mechanical properties, the advancing microcracking promoted higher uptake of moisture deeper in the laminate Carey, ; Anderson and Healey, ; Epstein and Bandaruk, Exposure to high temperatures can cause chemical degradation of composite-matrix polymers. Thermal degradation usually implies chemical reactions associated with polymer chain scission as a result of temperature or diffusion of small molecules e.

Degradation of composite-matrix polymers will more likely be due to thermal instability and the accelerating effects of oxidative attack. Polymer degradation in an inert atmosphere is the result of the breaking of covalent bonds in the polymer network. The result is a reduction in molecular weight and eventually volatilization of low-molecular-weight fragments void growth.

This process is important and is used positively in the production of polymer-precursor carbon and ceramic materials. The susceptibility of a polymer to thermal degradation is a function of the bond strength Rodriguez, The thermal stability of high-performance polymers in an inert atmosphere are generally very good due to their highly crosslinked and aromatic nature. Unfortunately, most high-temperature aircraft applications involve exposure in oxidizing environments e. While both carbon fibers and matrix polymers are susceptible to oxidative degradation, the degradation of the fibers is negligible at the service temperatures envisioned for application of polymeric composites Magendie et al.

However, oxidation of high-temperature matrix.

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