Evaluation of soft adhesives containing dual-curable melamine-based compounds

Park, Ji-won,Lee, Seong-Ju,Jung, Hyun-Woo,Ahn, Hyun-Suk,Kim, Hyun-Joong,Cho, Jin Ku,Kim, Baekjin,Shin, Seunghan,Hwang, Taek-Sung Butterworth-Heinemann Ltd. 2016 International journal of adhesion & adhesives Vol.70 No.-

<P><B>Abstract</B></P> <P>Although pressure-sensitive adhesives can be used in a wide variety of applications, their durable temperature range is generally limited due to their weak cohesive power. In this study, melamine-based compounds bearing UV-curable <I>N</I>-methyl acrylate groups and thermal-curable <I>N</I>-methoxylmethyl groups were evaluated as dual-curable materials for PSAs. The photo-curing abilities of MAOs are slightly inferior to those of TMP(EO)TA due to their rigid melamine core, but they could be improved by substituting acrylate groups onto the melamine core. In photo shrinkage, MAOs are less shrunk than TMP(EO)TA because of their greater size. Following the dual curing process, the storage modulus of MAO-containing PSA was maintained at approximately 3E6 dyne/cm<SUP>2</SUP>, even at high temperature. In particular, MAOs are very tolerant to heat exposure and thus could afford highly cohesive cured materials with a sufficient thermal curing process.</P>

Interfacial microstructures and properties of aluminum alloys/galvanized low-carbon steel under high-pressure torsion

Liu, Y.,Bian, X.,Zhang, K.,Yang, C.,Feng, L.,Kim, H.S.,Guo, J. BUTTERWORTH - HEINEMANN 2014 MATERIALS AND DESIGN Vol.64 No.-

A new composite processing technology characterized by hot-dip Zn-Al alloy process was developed to achieve a sound metallurgical bonding between Al-7wt% Si alloy (or pure Al) castings and low-carbon steel inserts, and the variations of microstructure and property of the bonding zone were investigated under high-pressure torsion (HPT). During hot-dipping in a Zn-2.2wt% Al alloy bath, a thick Al<SUB>5</SUB>Fe<SUB>2</SUB>Zn<SUB>x</SUB> phase layer was formed on the steel surface and retarded the formation of Fe-Zn compound layers, resulting in the formation of a dispersed Al<SUB>3</SUB>FeZn<SUB>x</SUB> phase in zinc coating. During the composite casting process, complex interface reactions were observed for the Al-Fe-Si-Zn (or Al-Fe-Zn) phases formation in the interfacial bonding zone of Al-Si alloy (or Al)/galvanized steel reaction couple. In addition, the results show that the HPT process generates a number of cracks in the Al-Fe phase layers (consisting of Al<SUB>5</SUB>Fe<SUB>2</SUB> and Al<SUB>3</SUB>Fe phases) of the Al/aluminized steel interface. Unexpectedly, the Al/galvanized steel interface zone shows a good plastic property. Beside the Al/galvanized steel interface zone, the microhardnesses of both the interface zone and substrates increased after the HPT process.

Numerical and experimental investigation of the deformation behavior during the accumulative back extrusion of an AZ91 magnesium alloy

Faraji, G.,Jafarzadeh, H.,Jeong, H.J.,Mashhadi, M.M.,Kim, H.S. BUTTERWORTH - HEINEMANN 2012 MATERIALS AND DESIGN Vol.35 No.-

<P><B>Highlights</B></P><P>► The accumulative back extrusion (ABE) was introduced as a high straining method suitable for AZ91. ► The strain distribution and deformation behavior during the ABE process using the finite element simulation was investigated. ► The deformation ratio and die stroke led to better deformation homogeneity and more plastic strains.</P> <P><B>Abstract</B></P><P>In the present study, the finite element method (FEM) and an experimental investigation were performed during the accumulative back extrusion (ABE) processing of an AZ91 magnesium alloy in order to investigate the effects of the deformation ratio (= inner punch diameter/outer punch diameter) and die stroke (DS) on the plastic deformation behavior. The results showed that increasing the deformation ratio and DS led to better deformation homogeneity and more plastic strains. There are two distinct regions in the ABE processed samples containing low and high plastic strain areas and the metallurgical investigations showed that more grain refinement with a mean grain size of 1.5μm takes place in high strain regions while the grain sizes are larger in other regions. A comparison between the FEM and experimental results of the required loads and developed microstructures showed good agreement.</P>

Charpy impact properties of stainless steel weldment in liquefied natural gas pipelines: Effect of low temperatures

Kim, J.H.,Choi, S.W.,Park, D.H.,Lee, J.M. BUTTERWORTH - HEINEMANN 2015 MATERIALS AND DESIGN Vol.65 No.-

In this study, an austenitic stainless steel pipe for the transportation of liquefied natural gas (LNG) was gas tungsten arc welded with a wall thickness of 15.1mm. Low-temperature Charpy V-notch (CVN) impact tests were performed to investigate the effect of low temperatures on the fracture toughness of the welded zone (WZ), heat-affected zone (HAZ), and base metal (BM) of the LNG pipe. For design and safety reasons, it is necessary to investigate the low-temperature impact properties of weld metals, because weld metals have higher susceptibility to embrittlement than their counterpart base metals. In addition, the effects of cubic crystal structures on the CVN impact response were examined to compare the absorbed energy and fracture surfaces of the materials. Charpy impact tests were performed on mild steels with body-centered cubic (BCC) crystal structures for comparison with the test results of welded austenitic stainless steels with face-centered cubic (FCC) crystal structures. The applicable temperatures were examined, and a scanning electron microscope was used to examine the fracture surface morphology of V-notched specimens tested under various temperature conditions. The results revealed that the absorbed energy of the WZ was slightly higher than that of the BM and HAZ in the FCC-crystal-structured welded pipe specimens. In addition, the ductile-to-brittle transition temperature of the BCC-crystal-structured mild steels was examined.

Evaluation of combined hardening coefficients of zircaloy-4 sheets by simple shear test

Rickhey, F.,Kim, M.,Lee, H.,Kim, N. BUTTERWORTH - HEINEMANN 2015 MATERIALS AND DESIGN Vol.65 No.-

Springback prediction in the simulation of multi-step stamping of zircaloy-4 metal sheets requires accurate understanding of the material behavior and in particular of the Bauschinger effect. In this study, issues concerning the one-sided simple shear test (specimen size, tightening torque and measurement of simple shear displacement) are discussed and suggestions regarding the test set-up are made. Forward/reverse simple shear tests are then performed with zircaloy-4 sheets to obtain shear load-displacement (P-δ) curves. In addition, applying the combined isotropic/kinematic hardening model the test is simulated in Abaqus/Explicit. Finally, the hardening coefficients for the combined isotropic/kinematic hardening model for zircaloy-4 sheets are determined by fitting the P-δ curve from finite element analysis (FEA) to the experimental curve. Applying the results to springback analysis will serve to improve the accuracy of multi-step stamping of zircaloy-4 sheets.

Effect of spark plasma sintering pressure on mechanical properties of WC-7.5wt% Nano Co

Rumman, Md.R.,Xie, Z.,Hong, S.J.,Ghomashchi, R. BUTTERWORTH - HEINEMANN 2015 MATERIALS AND DESIGN Vol.68 No.-

In this study, Spark Plasma Sintering (SPS), a relatively fast consolidation method assisted with simultaneous application of heat and pressure, was used to produce bulk carbides from mixed WC-7.5wt% Nano Co powders. Different pressures ranging from 30 to 80MPa were applied during sintering to explore its effect on the mechanical properties of resulting carbides. The maximum hardness was found for the samples pressed at 80MPa, which is ~1925HV (18.88GPa), higher than that of the commercially available cemented carbide tools. The marked changes in porosity, hardness, and crack propagation observed in the samples show that the sintering pressure have considerable impact on the mechanical properties of cemented carbides. In particular, the nature of crack initiation and propagation, which is indicative of the fracture toughness of materials, was studied and clarified.

Mode separation and characterization of torsional guided wave signals reflected from defects using chirplet transform

Kim, C.Y.,Park, K.J. Butterworth-Heinemann 2015 NDT AND E INTERNATIONAL Vol.74 No.-

The sensor configuration of a magnetostrictive guided-wave system can be described as a single continuous transducing element which makes it difficult to separate the individual modes from the reflected signal. In this work, we develop the mode decomposition technique employing chirplet transform, which is able to separate the individual modes from dispersive and multimodal waveforms measured using the magnetostrictive sensor, and estimate the time-frequency centers and individual energies of the reflection, which would be used to locate and characterize defects. The reflection coefficients are calculated using the modal energies of the separated modes. Experimental results on a carbon steel pipe are presented, which show that the accurate and quantitative defect characterization could be enabled using the proposed technique.

Structural investigations of CaO-CaF₂-SiO₂-Si₃N₄ based glasses by Raman spectroscopy and XPS considering its application to continuous casting of steels

Shin, S.H.,Cho, J.W.,Kim, S.H. BUTTERWORTH - HEINEMANN 2015 MATERIALS AND DESIGN Vol.76 No.-

Structural analysis of CaO-CaF<SUB>2</SUB>-SiO<SUB>2</SUB>-Si<SUB>3</SUB>N<SUB>4</SUB> based glass was conducted in order to understand its viscoelastic properties. CaO-CaF<SUB>2</SUB>-SiO<SUB>2</SUB>-Si<SUB>3</SUB>N<SUB>4</SUB> based glass has been adapted in various industries because a small amount of nitrogen incorporation leads to enhancing many properties such as fracture toughness, viscosity and chemical durability. Recently, few metallurgists have begun to use CaO-CaF<SUB>2</SUB>-SiO<SUB>2</SUB>-Si<SUB>3</SUB>N<SUB>4</SUB> based glass as a lubricant of continuous casting process of steel in order to maximize its viscoelastic property by controlling degree of polymerization (DP). The present study provides structural understanding of CaO-CaF<SUB>2</SUB>-SiO<SUB>2</SUB>-Si<SUB>3</SUB>N<SUB>4</SUB> based glass, specifically designed for the continuous casting process of steel by Raman spectroscopy and XPS. With Raman spectroscopy, the degree of polymerization (DP) was evaluated by the Q<SUB>3</SUB>/Q<SUB>2</SUB> ratio. The qualitative analysis of nitrogen and non-bridging oxygen was conducted by XPS within a range between 0.1 and 6wt.% of nitrogen. According to the results, the introduced nitrogen was incorporated with non-bridging oxygen of silicate network units, resulting in increase on degree polymerization (DP) of silicate network units. Such structural changes would potentially enhance shear thinning property of CaO-CaF<SUB>2</SUB>-SiO<SUB>2</SUB>-Si<SUB>3</SUB>N<SUB>4</SUB> based glass, resulting in a positive influence on continuous casting process of steel.

Microstructure and mechanical properties of twin roll cast AM31 magnesium alloy sheet processed by differential speed rolling

Chang, L.L.,Cho, J.H.,Kang, S.K. BUTTERWORTH - HEINEMANN 2012 MATERIALS AND DESIGN Vol.34 No.-

<P><B>Highlights</B></P><P>► Fine and homogenous microstructure of AM31 was obtained by DSR of TRC AM31. ► Texture characteristics of AM31 in subsequent rolling were inherited from TRC. ► Strength and ductility of the AM31 alloy was improved by TRC combined with DSR.</P> <P><B>Abstract</B></P><P>Twin roll cast AM31 alloys were rolled at a warm temperature of 350°C and subsequently rolled at 300°C using equal speed rolling and differential speed rolling with speed ratios of top roll to bottom roll, 1.2 and 1.5, respectively. Microstructures, textures and mechanical properties of the as-rolled AM31 sheets were examined. Ductility was improved by differential speed rolling due to inclined and weakened basal texture. Fine grain size and higher solution elements contents in the twin roll casted AM31 resulted in high ductility and strength in the rolled AM31 sheets. Texture characteristics inherited from the twin roll cast AM31 sheets had great influence on the evolution of microstructure and texture during the subsequent rolling and annealing process. Strength and ductility were improved by twin roll casting combined with differential speed rolling due to grain refining, inclination of basal poles and weakened texture.</P>

In-plane compression response of wire-woven metal cored sandwich panels

Lee, M.G.,Yoon, J.W.,Han, S.M.,Suh, Y.S.,Kang, K.J. BUTTERWORTH - HEINEMANN 2014 MATERIALS AND DESIGN Vol.55 No.-

This article presents the buckling behaviors of two types of WBK (Wire-woven Bulk Kagome) cored sandwich panels subjected to in-plane compression. Classical theories are introduced, and the experimental and numerical results are presented. The effects of several design parameters are analyzed. For both types, the peak loads were governed by macroplastic buckling. Low shear modulus and strength of the WBK core substantially influenced the buckling behaviors of the sandwich panels before and after their peaks. A small initial deflection greatly decreased the resistance against buckling of the sandwich panels with thinner cores, as confirmed by a two-stage FEA (Finite Element Analysis) and the analytic solution accounting for eccentricity.