Key Engineering Materials Vols. 525-526

Abstract: In this paper, the electromagnetic shielding function composite fiberboards were made by filling with stainless steel nets dipped with urea-formaldehyde resin adhesive (UF) and the influence of different mesh and layers of nets on its electromagnetic shielding performance, static bending strength (MOR), modulus of elasticity (MOE) and internal bonding strength (IB) were studied. The results showed that: when the mechanical strength was enough and the frequency was in range of 50MHz to 1GHz, of all the composite fiberboards filled with one-layer stainless steel net, the one filled with 60 mesh was best and the minimum shielding effectiveness (SE) was 36.22 dB; when filled with two-layers nets, the one filled with 80 mesh was best and the minimum SE was 42.54dB; when filled with three-layers nets, the one filled with 60 mesh was best and the minimum SE was 50.77dB.

Abstract: The low cycle fatigue behaviors of TI-6AL-4V alloy controlled by strain were investigated by experiment. The fatigue tests were performed at room temperature, and cyclic strain and stress ratio are 0.1 with triangle load wave. The results show that TI-6AL-4V alloy is soften rapidly under the cyclic tensile stresses and it is harden rapidly under the cyclic compressive stresses during the initial-stage of strain controlled fatigue, and the rates of cyclic soften and cyclic harden are decreased with the fatigue progress. The soften rate is related to the cyclic strain but little to the cyclic stress during the overall fatigue progress. The change of cyclic stress is related to the macro friction stresses. The results of experiment show that obvious cyclic creep occurs under the stress controlled low cycle fatigue conditions, and the magnitude of cyclic creep strain is related to the maximum cyclic stress. The softening of tensile friction stresses is the main factor of cyclic creep.

Abstract: A generalized expression of the stress-singularity function at the tip of artificial crack is proposed, and a formula to calculate the stress intensity factor of artificial crack is obtained in the paper. The solutions of stress singularity of a cracked bi-materials beam under uniform tension and bending were computed. The results show that the degree of stress-singularity is determined by the exponent λ at the tip of artificial crack, and the exponent λ is, not only determined by materials parameter of artificial crack but also by angle. Key words: artificial crack; bi-material; stress singularity; eigen value; stress extrapolation method

Abstract: Since ultra-high performance concrete (UHPC) is subject to large occurrence of shrinkage at early age due to its low water-to-cement ratio, the mixing of large quantities of powdered admixtures and the absence of coarse aggregates, UHPC presents large risks of shrinkage cracking caused by the restraints provided by the form and reinforcing bars. Accordingly, this study intends to evaluate the shrinkage behavior of UHPC under restrained state by performing restrained shrinkage test using ring-test. The test results reveal that increasing thickness of the inner ring increases the tensile creep at early age leading to the reduction of the average strain and residual stress of the inner ring.

Abstract: This study is an experimental research on using stainless steel car body structure for urban railway vehicles. The car body used in the experiment was made of stainless steel. To evaluate the structural characteristics and safety of the stainless car body, static load test was carried out by means of "Performance Test Standard for Electrical Multiple Unit" with the reference code JIS E 7105. The structural safety of the car body was evaluated by implementing vertical load, horizontal compressive load, twist load, and 3-point support tests. Test results verified that the structural safety of a car body was very stable and safe under design load conditions.

Abstract: A sandwich construction is applied to wing skins and fuselages, along with many other structures in aeronautical applications, due to its increased stiffness and reduced weight. In this paper, a face-sheet composed of plain-woven composite laminate that uses prepregs (HPW193/RS3232) and a core material of aluminum honeycomb (Al5052/F40-0.0025) is used. Launch vehicle structures have cut-out areas to check the status of the payload and electric equipment. Cut-out areas reduce the structural stiffness of the launch vehicle structure. Changes in the shape of cut-outs can cause a difference in load support ability of the structure. Compression tests and FEM analysis were performed on composite sandwich panels with various types of cut-out, but with the same overall area.

Abstract: PHE (Process Heat Exchanger) is a key component for transferring the high-temperature heat generated from a VHTR (Very High Temperature Reactor) to a chemical reaction for massive production of hydrogen. Recently, Korea Atomic Energy Research Institute (KAERI) has manufactured a small-scale and a medium-scale PHE prototype made of Hastelloy-X of high-temperature alloy and a performance test on the PHE prototype is scheduled in a small-scale nitrogen gas loop established at KAERI. In this study, in order to compare the high-temperature structural integrity of the PHE prototypes under the normal test condition of the gas loop, high-temperature structural analyses on the PHE prototypes were carried out and the analyses results were compared to each other. As a result of comparisons, the high-temperature structural integrity of the medium-scale PHE prototype gets worse due to higher thermal expansion by a size effect.

Abstract: PHE (Process Heat Exchanger) is a key component for transferring the high-temperature heat generated from a VHTR (Very High Temperature Reactor) to a chemical reaction for massive production of hydrogen. Korea Atomic Energy Research Institute has established a small-scale nitrogen gas loop for the performance test on VHTR components and has manufactured a small-scale PHE prototype made of Hastelloy-X of high-temperature alloy. A performance test on the PHE prototype is underway in the gas loop. In this study, in order to evaluate the high-temperature structural integrity of the PHE prototype under the test condition of the gas loop, structural analysis on the PHE prototype was carried out to gauge the stiffness of pipelines connected to the PHE prototype in the gas loop.

Abstract: A ductile failure is characterized by pronounced plastic deformations which involve significant plastic strains. The modeling of this failure behavior requires a precise description of the material plasticity starting from the crack initiation, its propagation through the material to the final fracture. The classical theory of metal plasticity based on the von Mises or Tresca formulations assumes that the effect of hydrostatic pressure on the flow potential is insignificant. Furthermore, it postulates that the flow stress is independent of the third stress invariant of the deviatoric stress tensor. The scientific findings from last few years show, however, that these both quantities should be considered for the precise description of plasticity, especially, of the real materials [1-4].

Abstract: With the sustainable construction the emphasis is placed on saving energy, reducing of consumption of natural resources, extending the life cycle of recycling, etc. One of the important groups of materials that can be reused are polymers. Polymers and waste polymers can be used as a base material for products used in civil engineering. One of these products, which were developed, is an insulation block from modified recycled polymer HDPE for direct solution of thermal bridges in wall footing detail. Design of the insulation block has been done using the MAP method together with long-time experimental testing of specimens and in a testing wall in scale 1:1. In the mathematic modeling the installation block was assessed in terms of statics and thermal technology. Static assessment was performed using Standard Solid rheological model, which represents the most accurate approximation of long-time behaviour.