Kwang Soo Kim

Ratcheting of Stainless Steel 304 Under Multiaxial Nonproportional Loading

Multiaxial ratcheting is often simulated by use of nonlinear kinematic hardening models, while in reality materials show cyclic hardening/softening and additional hardening under nonproportional loading. The effect of isotropic hardening on ratcheting needs to be addressed in simulation. In this study, ratcheting tests are conducted on stainless steel 304 under uniaxial, torsional, and combined axial-torsional loading. The ratcheting strain is predicted based on the constitutive theory that incorporates a modified OhnoWang kinematic hardening rule and Tanakas isotropic hardening model. The results show that the main features of the stress-strain response can be simulated with the constitutive model. Ratcheting strain under axial mean stress depends highly on the loading path and load level, and the degree of cyclic changes in shear stress under torsional strain control is not as influential. The torsional ratcheting strain under mean shear stress with (or without) fully reversed axial strain cycling is found close to the axial ratcheting strain under equivalent mean stress with (or without) torsional strain cycling. In all, the experimental and predicted ratcheting strains for nonproportional paths are found in decent correlation. However, overprediction still prevails for some loading paths, and ratcheting rates deviate considerably from experimental values.

Strain Rate Dependent Constitutive Model of Multiaxial Ratchetting of 63Sn–37Pb Solder

A series of multiaxial ratcheting tests were conducted on 63Sn-37Pb solder A unified viscoplastic constitutive model was developed on the basis of the Ohno-Wang kinematic hardening model, and the rate dependence of the material was taken into consideration by introducing a viscous term. The stress-strain hysteresis loop of 63Sn-37Pb under different strain rates can be simulated reasonably well bythe model. However, since the axial ratcheting strain rate of 63Sn-37Pb solder is strongly dependent on the applied shear strain rates in axial/torsional ratcheting, the original constitutive model fails to describe the effect of shear strain rate on the ratcheting strain. To improve the rate sensitivity of the model, the material parameter μ i was correlated to the strain rate. Comparisons of the experimental and simulated results verify that the modified constitutive model is able to predict the complicated deformation of 63Sn-37Pb. The effects of axial stress, shear strain range, loading history, and strain rate on ratcheting behavior can be reflected fairly well.

Experimental Study of Ratcheting for SUS304 Stainless Steel and A1070 Aluminum Alloy

This paper studies the cyclic ratcheting for two materials under multiaxial stress state. The two materials are SUS304 austenitic stainless steel and A1070 pure aluminum. The former material is known as a material that gives strong additional hardening and the latter material shows little additional hardening under nonproportional cyclic loading. The ratcheting behavior under 12 stress-strain waveforms was extensively studied using hollow cylinder specimen. Ratcheting strain depended on the material and stress-strain waveform. Anisotropic ratcheting was found in A1070 but isotropic ratcheting was observed in SUS304 steel.Copyright

Effects on Transmission Loss of Soundproof Panel Depending on Material and Thickness of Air Layer

Abstract Shortage of site suitable for housing caused by rapid urban development has led to a construction of the high-rise apartmentcomplex along the roadside. This gave rise to the increasing number of population exposed to the traffic noise. Nowadays, trans-parent noise barriers are used to replace the conventional noise barriers to solve the problems such as maintenance and urban land-scape. However, transparent noise barriers have also several problems such as discoloration, stains and scratching to lose initialadvantages. In this study, it was focused to compare the soundproofing performance according to the type of polymer materialsand panel structure to development of eco noise barrier. As a result, it was observed that PE and PP showed similar a soundproofperformance with PC. And in case of soundproofing panel with double layer, sound insulation performance is improved about17% compare to soundproofing panel with single layer.Key words : Noise Barrier, Polymer, Soundproofing panel, Sound insulation, Double layer

Preliminary Study on Dust Removal by Electrode-Plate Coated with Activated Carbon

The purposes of this research are to know the optimal gab and electric pressure (voltage) of electrode-plates coated with activated carbon and also to study their arrangement through dust removal efficiency. From the experimental results of attached dust mass at different electrode-plate gab, the frequency of attachment and detachment of dust was more increased as electrode-plate gab was closer. In attached dust mass per unit area of electrode-plate, the farther electrode gab, the more increased. But in total attached dust mass, the closer electrode gab, the more removed. From the experimental results, the optimal electrode arrangement in dust removal chamber was considered that the forward parts of chamber need to be increased the number of electrode-plate, the backward parts to be increased them. The dust attachment have no relation with electric pressure while showing high removal efficiency under condition of 5 kV of voltage and 2 cm of electrode-plates gab.

Sound Insulation Properties of Polymer Soundproof Panels

It is widely known that the sound insulation of soundproof panel is highly correlated to two factors, surface density of material and the frequency of noise. Accordingly, the character of traffic noise released in actual situation is important requisite for determining thickness to determine surface density and material of soundproof panel. This present study selected polymer panel with advantage of light weight and workability and evaluates according to frequency of traffic noise. Polypropylene (PP) and high-density polyethylene (HDPE) were selected as subjects based on economic valuation and efficiency. The sound transmission loss of selected polymer panels were compared with the currently used panels such as polycarbonate (PC) and polymethyl methacrylate (PMMA) depending on thickness and materials. As a result, PC showed the highest sound transmission loss followed by PMMA, HDPE, and PP in range of mass law. In terms of acoustic performance on thickness, the transmission loss increased with thickness of soundproof panel meanwhile coincidence dip was observed in lower frequency where had reduced transmission loss. Therefore, it is suggested that after determining target frequency, the kind of materials and thickness of soundproof panel need to be designed so that traffic noise can be more efficiently reduced.

Removal of Dust in Positive and Negative Plates of Electrode Coated with Activated Carbon

The purposes of this research are to know the dust removal efficiency according to the changes of gab between positive and negative plates in dust removal chamber. The experiments for dust removal efficiencies were conducted with changing the electrode-plate gab from 2 cm to 1 cm while the electric pressure, influent flow, and linear velocity were kept 5 kV, 80 L/min, and 6 cm/sec, respectively. From the experimental results of the electrode-plate gab of 2 cm, dust removal efficiencies were decreased to as low as about 50%. Attached dust on the surface of electrodes was released due to a reverse electric charge of dust. From the experimental results of the electrode-plate gab of 1 cm, dust removal efficiencies were increased to as high as about 80% due to the dust attachment velocity to the electrodes to be far more fast than influent linear velocity. Finally, to protect a attached dust from occurring a reverse electric charge it is needed to install the non-conductor between positive and negative electrodes and also to remove air humidity.