Effects of electron beam irradiation on the gel fraction, thermal and mechanical properties of poly(butylene succinate) crosslinked by multi-functional monomer

Kim, B.K.,Cho, D.,Kwon, O.H.,Park, W.H.,Lee, J.H. Scientific and Technical Press ; Elsevier Science 2015 Materials & Design Vol.87 No.-

In the present work, a multi-functional monomer triallyl isocyanurate (TAIC) of 4wt.% is incorporated into neat poly(butylene succinate) (PBS) by twin screw extrusion technique and the PBS sheets are irradiated at various electron beam absorption doses. It has been found that electron beam irradiation at an appropriate absorption dose plays an effective role in crosslinking the PBS molecules in the presence of TAIC. As a result, the irradiation influences the gel fraction, glass transition temperature, thermal stability, thermo-dimensional stability, dynamic storage modulus, and tensile properties of PBS, depending on the electron beam absorption dose applied. The improvement of the thermal and mechanical properties of PBS is most significant in the range of 50 to 70kGy. The results are consistent with each other, supporting the electron beam irradiation effect on the property improvement of PBS.

Characterization of laser welds in Al-10wt.%Si coated ferritic stainless steel

Kong, J.P.,Park, T.J.,Kim, J.K.,Uhm, S.H.,Woo, I.S.,Lee, J.S.,Park, B.G.,Kang, C.Y. Scientific and Technical Press ; Elsevier Science 2011 Materials & design Vol.32 No.2

409L stainless steel hot-dipped with Al-10wt.%Si was welded using CO<SUB>2</SUB> laser and the microstructure and hardness of the weld were investigated. When the specimen was welded with laser power of 5kW and welding speed of 5m/min, full-penetrated sound weld was obtained. With that specimen, the relationship between the microstructure and hardness of the weld was examined. The hardness of the weld was the highest in the fusion zone (FZ) and decreased to the base metal (BM) via heat affected zone (HAZ). The hardness of the HAZ near bond line was also higher than that near the base metal. The maximum hardness in the fusion zone could be explained by the existence of the precipitates, that is, TiN, Ti(C,N), Al<SUB>2</SUB>O<SUB>3</SUB> and Al<SUB>2</SUB>O<SUB>3</SUB>+TiN mixed compounds with the size of 500nm, and solution strengthening due to the elements Al and Si dissolved from the coating layer to the fusion zone. There were subgrains within the HAZ and more in the area near the bond line. In addition, fine TiC particles with the size under 50nm was precipitated in the sub-grain boundaries. The formation of sub-grain boundaries and the particles precipitated in the boundaries might contributed to the high hardness in the HAZ.

Microwave absorbers of two-layer composites laminate for wide oblique incidence angles

Kim, J.W.,Kim, S.S. Scientific and Technical Press ; Elsevier Science 2010 MATERIALS AND DESIGN Vol.31 No.3

Advanced microwave absorbers for wide oblique incidence angles are required in many applications including wireless communication or vehicle identification in Intelligent Transport System (ITS) where 5.8GHz Dedicated Short Range Communication (DSRC) system is applied. In this study, two-layer microwave absorbers are designed for the achievement of low reflection coefficient over wide incidence angles at 5.8GHz. The absorbing layer of rubber composite containing magnetic iron flake particles and the surface layer of low dielectric constant (carbon black composite and glass fiber composite) have been used in the absorber design. On the basis of transmission line theory, the reflection loss has been calculated with variation of incident angles for both Transverse Electric (TE) and Transverse Magnetic (TM) polarization. At the optimum thickness of the composite layers, a low value of reflection loss (less than -10dB) has been predicted for wide incidence angles up to 60<SUP>o</SUP> for both TE and TM polarization, which is well consistent with the reflected power measured by free-space arch test. The two-layer composite laminate consisted of magnetic absorbing layer with high magnetic and dielectric loss and surface impedance-matching layer of a controlled dielectric constant can be proposed for high potential microwave absorbers in ITS.

Strain-rate effects on the mechanical behavior of the AISI 300 series of austenitic stainless steel under cryogenic environments

Park, W.S.,Yoo, S.W.,Kim, M.H.,Lee, J.M. Scientific and Technical Press ; Elsevier Science 2010 MATERIALS AND DESIGN Vol.31 No.8

A series of uni-axial tensile tests were carried out under various low temperatures and strain-rate ranges for AISI 300 austenitic stainless steel. The strain-rate dependencies of the materials under investigation were evaluated at temperatures ranging from ambient to cryogenic. Non-linear mechanical behavior such as phase transformation, discontinuous yielding and micro-damage of four kinds of commercial stainless steel-based material were quantitatively investigated by measuring transformation induced plasticity (TRIP) and threshold strain for 2nd hardening. In this study, the main properties of each material were analyzed and compared based on the conditions of strain-rates and temperature. Test results showed that all the test materials were strongly dependent on temperature and strain rate. It is expected that the findings in this study could be used for the cryogenic design and further research of structure materials under cryogenic environments.

Effect of the rolling speed on microstructural and mechanical properties of aluminummagnesium alloys prepared by twin roll casting

Das, S.,Lim, N.S.,Seol, J.B.,Kim, H.W.,Park, C.G. Scientific and Technical Press ; Elsevier Science 2010 MATERIALS AND DESIGN Vol.31 No.3

In the present investigation the microstructures and mechanical properties of Al-Mg alloys prepared by twin roll casting (TRC), varying rolling speed, (i.e., 3, 4, and 5rpm) were studied. Optical microstructures of the all the samples show dendritic morphology. Scanning electron microscopy (SEM) and energy dispersive X-ray spectrometer (EDS) studies show segregation of alloying elements at the interdendritic regions. Transmission electron microscopy (TEM) observation confirms the presence of intermetallic phase (Mg<SUB>5</SUB>Al<SUB>8</SUB>) at the grain boundaries. It was observed that the secondary dendritic arm spacing (SDAS) increases (marginally) with rolling speed. Also the microhardness and tensile strength decreases with increase in rolling speed.

Fracture limit prediction for a double safety structure in cylindrical-type lithium secondary batteries

Ku, T.W.,Song, W.J.,Kim, J.,Kang, B.S. Scientific and Technical Press ; Elsevier Science 2010 MATERIALS AND DESIGN Vol.31 No.10

In this study, a double safety structure used for cylindrical-type lithium secondary batteries is newly introduced. The structure is necessary to prevent users and the cylindrical-type secondary batteries from unpredictable explosions due to a temporary increase in the inner pressure of the batteries. The double safety structure consists of a primary safety component as micro half-blanked component, and a secondary safety device as V-notched part. For the double safety device, both the mentioned components are considered by the micro half-blanking and the V-notch forming processes with numerical and experimental predictions for the fracture limit. The mechanical properties are investigated with both a raw and an annealed thin sheet material of 1050-H16 aluminum alloy. The main process parameters are considered to be the clearance and punch-die corner radius for the micro half-blanking process, and the remaining thickness, tip radius, and shape angle of the V-notch. In this study, finite element simulations are carried out to verify the manufacturing process with the mentioned process parameters. The ductile fracture criterion is also adopted to predict the fracture limit for each component. Furthermore, experimental investigations are included to verify the fracture limit predicted from the numerical approach. From the systematic approaches, it is confirmed that the fracture limit for the double safety structure is well predicted, and satisfies the required fracture limit.

Ultrasound-assisted brazing of Cu/Al dissimilar metals using a Zn-3Al filler metal

Xiao, Y.,Ji, H.,Li, M.,Kim, J. Scientific and Technical Press ; Elsevier Science 2013 Materials & design Vol.52 No.-

Ultrasound-assisted brazing of Cu/Al dissimilar metals was performed using a Zn-3Al filler metal. The effects of brazing temperature on the microstructure and mechanical properties of Cu/Al joints were investigated. Results showed that excellent metallurgic bonding could be obtained in the fluxless brazed Cu/Al joints with the assistance of ultrasonic vibration. In the joint brazed at 400<SUP>o</SUP>C, the filler metal layer showed a non-uniform microstructure and a thick CuZn<SUB>5</SUB> IMC layer was found on the Cu interface. Increasing the brazing temperature to 440<SUP>o</SUP>C, however, leaded to a refined and dispersed microstructure of the filler metal layer and to a thin Al<SUB>4.2</SUB>Cu<SUB>3.2</SUB>Zn<SUB>0.7</SUB> serrate structure in the Cu interfacial IMC layer. Further increasing the brazing temperature to 480<SUP>o</SUP>C resulted in the coarsening of the filler metal and the significantly growth of the Al<SUB>4.2</SUB>Cu<SUB>3.2</SUB>Zn<SUB>0.7</SUB> IMC layer into a dendrite structure. Nanoindentation tests showed that the hardness of the Al<SUB>4.2</SUB>Cu<SUB>3.2</SUB>Zn<SUB>0.7</SUB> and CuZn<SUB>5</SUB> phase was 11.4 and 4.65GPa, respectively. Tensile strength tests showed that all the Cu/Al joints were failed in the Cu interfacial regions. The joint brazed at 440<SUP>o</SUP>C exhibited the highest tensile strength of 78.93MPa.

Study of microcellular injection-molded polypropylene/waste ground rubber tire powder blend

Xin, Z.X.,Zhang, Z.X.,Pal, K.,Byeon, J.U.,Lee, S.H.,Kim, J.K. Scientific and Technical Press ; Elsevier Science 2010 MATERIALS AND DESIGN Vol.31 No.1

Microcellular polypropylene/waste ground rubber tire powder blend processing was performed on an injection-molding machine with a chemical foaming agent. The molded samples produced based on the design of experiments (DOE) matrices were subjected to tensile testing and scanning electron microscope (SEM) analyses. Molding conditions and waste ground rubber tire (WGRT) powder have been found to have profound effects on the cell structures and mechanical properties of polypropylene (PP) and waste ground rubber tire powder composite samples. The result shows that microcellular PP/WGRT blend samples exhibit smaller cell size and higher cell density compare with polypropylene resin. Among the molding parameters studied, chemical foaming agent weight percentage has the most significant effect on cell size, cell density, and tensile strength. The results also suggest that tensile strength of microcellular PP/WGRT composites is sensitive to weight reduction, and skin thickness.

Design of high strength Cu alloy interlayer for mechanical bonding Ti to steel and characterization of their tri-layered clad

Ha, J.S.,Hong, S.I. Scientific and Technical Press ; Elsevier Science 2013 Materials & design Vol.51 No.-

Cu-8wt.% Ag alloy is proposed as a good interlayer alloy with good deformability, high strength, least reactivity and low melting temperature for low temperature joining of Ti and carbon steel. Titanium and carbon steel plates with a Cu-8Ag interlayer plate were joined by high pressure torsioning (HPT) at room temperature and the effect of post-HPT annealing on their mechanical performance was examined. The most pronounced increase of the Vickers microhardness (from 88 to 248Hv) was observed in Cu-8Ag, suggesting Cu-Ag is the ideal bonding interlayer with a lower melting temperature, an initial excellent deformability and high strength after joining. With the increase of heat-treatment temperature, the tensile strength increased initially up to 350<SUP>o</SUP>C and then decreased with increase of annealing temperature above 350<SUP>o</SUP>C. The maximum strength after annealing at 250<SUP>o</SUP>C is due to the combined effect of the precipitation strengthening of Cu-8Ag interlayer and static strain aging of both S20C and Ti. The stress-strain curves exhibited the step-wise fracture, with the first step resulting from the fracture of S20C plate and the next from co-fracture of Ti plate and Cu-Ag interlayer. The co-fracture of Cu-8Ag and Ti suggests that the bonding strength between two layers is fairly high even in the presence of intermetallic layer.

Microstructure and joint properties of ultrasonically brazed Al alloy joints using a Zn-Al hypereutectic filler metal

Xiao, Y.,Ji, H.,Li, M.,Kim, J.,Kim, H. Scientific and Technical Press ; Elsevier Science 2013 Materials & design Vol.47 No.-

The ultrasound-assisted brazing of 1060 Al alloy using a Zn-14Al hypereutectic filler metal was investigated at different temperatures. The effects of brazing temperature on the bonding ratio, shear strength and microstructure of the joints were studied. Cavities and discontinuous cracks were found in the joint ultrasonically brazed at 410<SUP>o</SUP>C, and the joint showed a low bonding ratio and poor shear strength. Excellent bonding ratios and high shear strength were obtained in the joints ultrasonically brazed at 440<SUP>o</SUP>C and 470<SUP>o</SUP>C. The primary α-Al phase showed a refined spherical shape in the joint ultrasonically brazed at 440<SUP>o</SUP>C, but showed a coarse dendritic structure in the joint ultrasonically brazed at 470<SUP>o</SUP>C and that brazed at 440<SUP>o</SUP>C without ultrasonic vibration. The refined spherical microstructure shown in the joint ultrasonically brazed at 440<SUP>o</SUP>C was attributed to cavitation-aided grain refinement effects.