Key Engineering Materials Vols. 326-328

Abstract: This paper is focused on the capability of the Acousto-Ultrasonic (AU) technique and the non-contact technique to provide diagnostic information useful to detect defect in composite. An acousto-ultrasonics (AU) is to simulate stress wave that resemble acoustic emission waves but without disrupting the material. One launched inside the material sample, the wave are modified by stochastic processes like those that affect spontaneous acoustic emissions from internal sources during stressing, deformation, etc. Moreover, acousto-uloasonic waves are launched periodically at predetermined times and with predetermined reparation rates. A fiber reinforced composite materials should be inspected in fabrication process in order to enhance quality by prevent defects such as delamination and void. In conventional ultrasonic technique for the evaluation of FRP, the transducer should be contacted on FRP. Therefore, in this study, advanced conventional contacting method (AU) and non-contact technique using air-coupled transducer can make contact and noncontacting ultrasonic technique available in evaluation of FRP. This paper demonstrates first results using an acousto-ultrasonic technique.

Abstract: The cure kinetic properties of 191# resin was studied by means of the differential scanning calorimeter (DSC) data. Dynamic DSC scanning at four different heating rates (5, 10, 15 and 20
/min) are employed to investigate the cure kinetics. DSC curves show that there are two exothermal peaks. Kissinger’s method is applied to processing the data. The activation energy E and pre-exponential factor A were gained by linear regress and the cure kinetics model was developed. Based on T − β method, the temperatures of cure reaction beginning, maximum reaction rate and reaction ending were obtained. These will help to process designing of unsaturated polyester resin used in advanced composite materials.

Abstract: This study aims to find out cooling characteristics of TMA 25wt%-water clathrate compound with ethanol such as supercooling, phase change temperature and specific heat. For this purpose, ethanol is added as per weight concentration and cooling experiment is performed at -6
, -7
and -8
, cooling heat source temperature, and it leads the following result. (1) Phase change temperature is decreased due to freezing point depression phenomenon. Especially, it is minimized as 5.1
and 5.0, 3.8
according to cooling source temperature in case that 0.5wt% of ethanol is added. (2) If 0.5wt% of ethanol is added, average supercooling degree is 0.9
and minimum supercooling is 0.8, 0.7
according to cooling heat source temperature. The restraint effect of supercooling is shown. (3) Specific heat shows tendency to decrease if ethanol is added. It is 3.013~3.048 kJ/kgK according to cooling heat source temperature if 0.5wt% of ethanol is added. Phase change temperature higher than that of water and inhibitory effect against supercooling can be confirmed through experimental study on cooling characteristics of TMA 25wt%-water clathrate compound by adding additive, ethanol.

Abstract: This paper shows the performance analysis of a sealless cylinder with a conical type piston and one of three types of rod bearings. The piston without seal is composed of cylindrical and conical portions in the axial direction. The 2D Reynolds equation is solved with a finite difference method for the performance analysis. The relationship between self-centering force and leakage flow rate are investigated. The sealless cylinder fabricated with the proposed optimum design values was tested with three different types of rod bearings having four, five and six pockets respectively. Leakage flow rate tests were conducted to evaluate the performance of the proposed sealless cylinder.

Abstract: Eddy currents of electromagnetic field leads not only to the local heating of plate but also to the thermal-elasto-plastic deformation in the induction heating. It is necessary to have a simulation model to attract the possibility of induction heating equipment and to study the deformation behavior. The goal of present paper is to investigate the possibility of induction heating equipment for steel plate bending. The residual stress distribution of induction heating is investigated by an electromagnetic analysis in conjunction with thermal-mechanical analysis. A computational model based on FEA is used to study the electromagnetic field and thermalmechanical process. Comparison with the residual strain fields and deformation of both heating shows that the induction heating has good similarity with the gas heating.

Abstract: A finite element procedure to predict residual stresses on the multi-pass arc welding considering the multi-layered beads and solid–liquid phase transformation in the melted bead is implemented and experimentally validated. The nonlinearities of material properties are considered in the thermo-elasto-plastic distortion analysis. Element birth and death technique is used to simulate the weld metal added to base metal in both heat transfer and thermo-elasto-plastic analysis. Residual stresses and strains are computed for butt welding and T-joints fillet welding. The stress distributions calculated by proposed finite element analysis procedure are compared with the measured values of experiments and data available in the other studies. The efficiency of the proposed finite element analysis and experimental procedure is discussed and demonstrated.

Abstract: Warm-rolling can save the production cost and extend the production kind of hot-rolled IF steel strip, the precipitates strongly influence the annealing process and texture evolution so as to the final mechanical properties of the production, very few studies has relate to the precipitates of IF steels warm-rolled in ferrite region. In present work, two Ti- IF steels were warm-rolled in ferrite region under different rolling parameters and the precipitates were investigated. Transmission electron microscopy (TEM) and Energy dispersion Spectroscopy (EDS) microanalysis were carried out on carbon extraction replicas, the characteristics such as morphology, type, amount and size of precipitates were analyzed. The results show that different type of precipitates were appeared in two steels, TiN, TiS, Ti4C2S2 and TiC were found in common Ti-IF steel, but in high strength Ti-IF steel, the amount of TiS, Ti4C2S2 was very few and FeTiP precipitates appeared, the type and morphology of precipitates were not affected by rolling parameters, however, the number and size of precipitates were changed. Finally, the effect of different P content on the change of precipitates was analyzed, the precipitating mechanism was also discussed.

Abstract: The micro-encapsulated thermochromic liquid crystal has been used for the surface temperature measurement using its color change with heat. There are exciting new opportunities to apply this liquid crystal to the investigation of important and interesting heat transfer/fluid flow problems. The various techniques of using liquid crystal for the measurement of the local Nusselt numbers in very complex geometries are presented in this paper.

Abstract: In this experimental paper, the judder vibration of automotive disk brake was analyzed by the finite element method and compared with experimental results. The relationship between specific modes of disk and pad, and hot spot was investigated. Characteristics of the judder vibration were measured by using the chassis-dynamo and hot spots were photographed by highspeed infrared camera. Vibration modes of the brake disk and pad were measured and an specific relationship between mode shapes and hot spots was found. Results show that the judder vibration occurred due to the frequency modulation of the specific mode frequency of disk brake due to the non-linearity phenomenon. This relationship was examined by the frequency analysis of the judder vibration.

Abstract: The local heat transfer measurements in the cooling flow passage having both flat surface and semi-cylindrically grooved surface geometries inside the automobile disc brake were made. A uniform wall heat flux boundary condition on both surface geometries was created using gold film Intrex. Liquid crystal was used to measure the surface temperature. The experiments were made at Reynolds number (based on the hydraulic diameter of the rectangular duct) of Re=23,000, groove pitch-to-width (P/D) from 3 to 7, and groove depth-to-width (H/D) from 0.15 to 0.2. The results show that the magnitudes in the average Nusselt number on the grooved surface are maximum 92.8% higher than those on the flat surface without groove. A computer program utilizing the coupled FEM numerical technique that can predict the temperature distributions on the disc brake to analyze the thermal deformation has been developed.