Materials Science Forum Vols. 580-582

Abstract: The trend of the welding technology of lightweight alloys such as aluminum alloy and magnesium alloy has been studied. The lightweight alloys in the automobile, high-speed light aircraft and modern aerospace industry can reduce vehicle weight, while stringently demanding the high quality and efficienct welding techniques, to produce the best weldments. Among the production technologies, welding plays an important role in the fabrication of lightweight vehicle structure. This has led to an increasing attention towards the use of modern welding technology such as laser beam welding process, ultrasonic welding process, friction stir welding technology and laser hybrid welding technology, etc. This paper covers the recent technical trends of welding technologies of lightweight alloys including the COMPENDEX DB analysis of welding metallurgy, welding process, and welding fabrications.

Abstract: Currently, the most important objective in designing automobiles is to focus on environment-friendly and safety performance aspects. For the environment-friendly aspect, the issues relate to the shift towards lightweight automobile production, for improving fuel-efficiency and reducing exhaust fumes. However, in contrast, the issues of the safety performance such as crash safety, comfort level and muti-functional programs demand increase of automobile’s weight. Therefore, the design of automobile should be inclined towards the safety aspects, but at the same time, it also should consider reducing the structural weight of an automobile. In this study, for lightweight design of side member, CFRP side member was manufactured from CFRP unidirectional prepreg sheet. The stacking condition related to the energy absorption of composite materials, is being considered as an issue for the structural efficiency. Therefore, the axial collapse tests were performed with change of the stacking condition, such as fiber orientation angle and interlaminar number. The collapse modes and energy absorption characteristics were analyzed according to fiber orientation angle and interlaminar number.

Abstract: Sandwich panels are widely used in the main structure of aircrafts and ships because of their lightweight, high strength, stiffness, durability, and corrosion resistance. The present paper proposes a manufacturing process of a carbody structure of rolling stock using a composite honeycomb sandwich panel. The panel is made of carbon/epoxy composite faces and an aluminum core. The faces bear bending loads and the core shearing load. A product is manufactured by lay-up of composite material on the mold of the product in final dimensions; then cured in a large autoclave for obtaining one body of a structure. In this study, in order to evaluate the mechanical properties of the honeycomb sandwich panel, tensile test, compressive test, flexural test and shear test of the face in honeycomb sandwich panel were performed. Impact test for the honeycomb sandwich panel was also carried out. Moreover, end compression test was conducted. The results show that the composite honeycomb sandwich panel has good properties for the carbody structure of rolling stock.

Abstract: In this study, the effect of thickness on the fracture toughness of the steel plate with the thickness of 80mm has been investigated by the wide plate tensile test and ESSO test. The fracture toughness for crack initiation and propagation was evaluated quantitatively for the full thickness specimen. It was found that EH-36 grade steel with the thickness of 80mmt showed the KIC value of 164kgf/mm1.5 at -145°C. Also, large-scale ESSO test result showed that the steel with the thickness of 80mm had 520kgf/mm1.5 at -10°C. Although it was known that the fracture toughness decreases with the increase of the plate thickness, EH-36 grade steel with the thickness of 80mm had enough values of fracture toughness to prevent the crack initiation and arrest the brittle crack propagation.

Abstract: The American Welding Society has developed its first welding design code for titanium alloy welded structures, through its consensus standards process and the work of many volunteers,. Defining the provisions of this new code required collecting and summarizing both strength and fatigue data for titanium structural welds. The design provisions were based on these data, but only in context of other provisions of the code in areas of welding procedure qualification, fabrication, and inspection. For instance, the allowable imperfection sizes found on inspection had to be correlated with the expected fatigue performance of imperfect welds. Test data from welds in the primary structural alloy Ti-6Al-4V are described for several weld configurations, both with and without welding imperfections.

Abstract: Mechanical post treatments for welded structures have been applied in various industrial fields and, in most cases, have been found to cause substantial increase in their fatigue strength. These methods, generally, consist of the modification of weld toe geometry and the introduction of compressive residual stresses. In hammer peening, the weld profile is modified due to removal or reduction of minute crack-like flaws; compressive residual stresses are also induced by repeated hammering of the weld toe region with blunt-nosed chisel. In this study, a hammer peening procedure, using commercial pneumatic chipping hammer, was developed; a quantitative measure of fatigue strength improvement was performed. The fatigue life of hammer-peened specimen was prolonged by approximately 10 times in
S=240MPa, and was doubled for the as-welded specimen.

Abstract: Previously, object-oriented inspections have been conducted by the regulatory authority for the welding of electric power generating equipment (hereinafter referred to as “electric structures”) of nuclear power stations in Japan. However, the law related to the welding was recently amended and enforced. The soundness of the welding of the electric structures is verified in a manner that the regulatory authority reviews the utilities’ implementation conditions of welding inspections instead of directly inspecting the welded joints by the authority. This report presents an outline of the Welding Safety Management Review System, which is a review-type inspection.

Abstract: Since Power Plant has tens of thousands welded parts in its structures, the quality on the welded parts are always a key factor for ensuring the reliability of the structures. Film based Radiography Test (hereinafter called “FRT”) is a generally accepted solution in inspecting the welded structure. However, the RT demands complex workflow, high cost, hazardous waste disposal, and etc…. In an effort to get over such shortcomings from FRT and present alternative inspection tools, this study was intended to evaluate a Digital Radiography Test (hereinafter called “DRT”). In this study, the evaluation were focused on if a DRT is applicable to the inspection of Welded structure in Power Plants, and what benefits can be generated in a use of DRT.

Abstract: This paper presents a study on the relationship between feedrate and fatigue life of Al7075-T6 specimens before and after shotpeening. For this purpose, six groups of specimens, each of which consists of eight specimens, were first machined at six different feedrates (0.05, 0.10, 0.15, 0.20, 0.25, 0.30 mm/rev). Half of eight specimens in each group were then peened and the others remained un-peened. Next, the fatigue life was measured by using 4-point rotary bending machine. One observation was that the fast the feedrate was, the large the mean diameter of a specimen was. To apply the same bending stresses in all cases, different loading conditions were thus recalculated and applied to specimens based on their mean diameters. Finally, the effect of feedrate on the fatigue life was estimated by comparing twelve sets of specimens (six groups times two sets, peened and un-peened).

Abstract: Development of a non-contact method for measuring the degree of corrosion is highly desired by those who are involved in the maintenance and control of steel structures. Increasingly, it is expected that application of an electromagnetic acoustic technology that does not require a coupling medium will meet this demand. Various problems have been reported regarding measuring thickness of a corroded material using the resonance method. In order to clarify these problems, it is important to make evaluations based on the resonance spectrum that corresponds to the thickness of each plate. In this paper, experiments using grooved specimens for a basic investigation were performed and a new method for wall-thinning measurement based on the resonance spectrum amplitude was proposed. In addition, examination was performed by using a numerical simulation about this method’s detection principle.