Papers by Keyword: Electrical Resistance

Abstract: An interfacial resistance measuring method was proposed to evaluate the quality of diffusion bonded joints. To study the feasibility of the method, a finite element (FE) model with periodically distributed interfacial microdefects was presented. The influences of bonded area fraction, width and length of microdefects on increments of resistance were analyzed by applying the electromagnetic module in ANSYS software. Results indicated that the evolution of resistance increment along with the interfacial bonded area fraction could be described by a hyperbolic function. Based on the FE results, a modified theoretical solution was developed referred to Lodge’s work to accommodate the size effects of interfacial microdefect and thus could lead to a more precise quality evaluation for diffusion bonded joints.

Abstract: The method of generating the most practicable shape recovery force in smart composite materials which embedded shape-memory alloy (SMA) fiber under the resin matrix is electric heating. However, because the calorie for the heating of the resin matrix increases in the low temperature environment, it is necessary to control the electric heating corresponding to an ambient temperature to obtaining a steady shape recovery force. Then, the method of self-detecting the temperature without using a special temperature sensor by measuring the electrical resistance of the SMA fiber in the composite material was examined.

Abstract: This paper describes the piezoresistance behavior in CFRP cross-ply laminates with transverse cracking loaded in tension. The resistance change due to transverse cracking and the gage factor (the rate of resistance change per mechanical strain) for each transverse crack density were experimentally measured during loading/unloading cycles. The resistance change-strain curves in the unloading/ reloading processes show the bilinear behavior where two gage factors are defined as the slopes of the bilinear curve. The residual resistance change after full unloading increases almost linearly with the mechanical strain while the gage factors do not always increase with the strain. The residual resistance change and gage factors are associated with transverse crack density on the basis of an equivalent resistance circuit.

Abstract: Carbon nanotubes have received considerable attention because of their excellent electrical and mechanical properties. In this study, carbon nanotube - copper nanocomposites with homogeneously dispersed nanotubes within the copper matrix have been fabricated by two different methods; a mechanical mixing process and a molecular-level mixing process, which consists of mixing copper ions with functionalized nanotubes in a solvent. Small punch creep tests showed significantly improved mechanical properties of the nanocomposites. The electrical resistance of the nanocomposites also decreased.

Abstract: For a cryogenic fuel tank of a next generation rocket, a Carbon Fiber Reinforced Plastic (CFRP) laminated composite tank is one of the key technologies. For the fuel tank made from the laminated composites, matrix cracks are significant problems that cause leak of the fuel. In the present paper, electrical resistance change method is adopted to monitor the matrix cracking of the CFRP laminate. Previous studies show that tension load in fiber direction causes electrical resistance increase due to the piezoresistivity of the carbon fibers, and fiber breakages also cause the electrical resistance increase of the CFRP laminates. In order to distinguish the electrical resistance changes due to matrix cracking from those due to the piezoresistivity and the fiber breakages, residual electrical resistance change under the complete unloading condition is employed in the present study. Experimental investigations were performed using cross-ply laminates in cryogenic temperature. As a result, it can be revealed that the residual electrical resistance change is a useful indicator for matrix crack monitoring of the cross-ply CFRP laminates.

Abstract: The magnetic and magnetoresistive properties of nanostructured Fe/Cr multilayers with ultra-thin Fe layers (the nominal Fe thickness tFe is down to 0.3 Å) have been investigated at low temperatures (down to 2 K) in magnetic fields up to 90 kOe. Nanostructures were MBE grown in ultrahigh vacuum on single crystal MgO substrates. It is shown that Fe layers in nanostructures with tFe < 2 Å are not continuous but consist of separate ferromagnetic clusters. Such cluster-layered nanostructures exhibit superparamagnetic properties and the Kondo-like behavior of resistivity.

Abstract: In this study, we propose a new process to fabricate electrically conductive alumina by gelcasting and reduction sintering. The process used the conventional gelcasting method except for varying amounts of monomer at 2.8, 5.5, and 8.0 wt.% relative to the weight of the slurry. In the plastic mould, the slurry was under in situ solidification for 3 hrs at 25oC to achieve gelation. The freshly gelled bodies were demolded, carefully dried, and then sintered at 1100oC, 1300oC, and 1550oC in nitrogen atmosphere. The holding times at 1100oC and 1300oC was 2 hours, while at 1550oC were 2, 4, and 6 hrs. The sintered alumina body was characterized by electrical property, X-ray diffraction, and scanning electron microscopy. Results showed that monomer additions and sintering schedule significantly affect in lowering electrical resistance. The low value was 3.6×106 +cm at 8.0wt.% monomer addition and sintering at 1550oC for 2 hrs. The effect of physical properties on electrical conductivity and the corresponding reaction mechanism were discussed in details.

Abstract: The aging of Al-Zn alloys has been vastly studied for decades. In the previous paper, 0hta et al. studied carefully the hardness of the alloy during aging and revealed the existence of softer regions near the surface and the grain boundary than the interior of the specimen even after aging for a long time. Electrical resistivity measurement and X-ray small angle scattering experiment together with hardness test suggested that in these regions vacancy decay to the surface and grain boundaries was severe, thus the growth of GP zones were suppressed and therefore age hardening was retarded. Also, it is well-known that an addition of a small amount of Ag raised solvus temperature of GP zones. In this paper, soft surface layer formed in an Al-12mass%Zn alloy is studied by adding small amount of Ag by means of hardness test and resistometry. Addition of Ag more than 0.1% decreases the thickness of soft surface layer as well as accelerates age hardening rate and suppresses the formation of soft region near the grain boundaries. Higher quenching temperature also reduces the thickness of soft surface layer. Together with the behavior of aging curves of the specimen with various thicknesses, the origin of the soft surface layer is confirmed to be the effective role of surface as sinks for vacancies.

Abstract: Nanocrystalline indium tin oxide (ITO) thin films were deposited on Si/SiO2 substrates by laser ablation from a ceramic target with a composition of 0.9 In2O3 . 0.1 SnO2. Samples were prepared in the pressure range from 10-1 to 5mbar, either in-situ at 500°C or at room temperature and heat-treated in air at 500°C. X-ray diffraction results show that the films are not oriented, except the ones made at high temperature which exhibit strong (400) orientation. AFM pictures show that the grains are round shaped and the sizes are in the range between 50 and 200nm, except for films made in-situ at 10-1mbar which are elongated and faceted. For higher pressures the grains tend to be small and to form agglomerates. The porosity of the films increases with the deposition pressure and the thicknesses reach a maximum of 2.8µm at 1mbar for the films made at room temperature and of 1.2µm at 2mbar for the ones made in-situ; for higher pressures the growth rate drop drastically, as revealed from SEM observations of cross-sections. The electrical resistance increases with the deposition pressure due to the increase in porosity, changing from 3.3k to 38.9M for films deposited at room temperature and from 20 to 265k for the ones made in-situ.

Abstract: This work demonstrated an in-situ pyrolysis of gelcast alumina under reduction sintering to make alumina and carbon composite in providing semi-electrical conductivity. To increase the carbon content, the monomer was varied in the premix solution with reduction sintering in nitrogen gas. Two-probe method was used to measure electrical resistance of the sintered samples. The results revealed that the increase of monomer addition and sintering treatment were effective in reducing electrical resistance. The lowest value was 3.6×106
-cm, which is a potential candidate for electrostatic shielding application. The reduction-sintered sample was re-sintered in an air in order to gain insight on the conductive path due to carbon network. Further tests such as XRD, TGA/DTA, and scanning electron microscopy
were used to explain the semi-conductive property of the material.