• Composites Research
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• v.28 no.3
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• pp.112-117
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• 2015

Mechanical properties of nonwoven alfa fiber based reinforced biocomposite were evaluated to assess the possibility of using it as a new material in engineering applications such as orthopedic application. Samples were fabricated by needle punching, thermal bonding and Hydroentanglement, by blending alfa fibers with wool fibers or Polypropylene fibers. The mechanical properties were tested and showed that the nonwoven NW3 (alfa fiber/PP/PLA, with hydroentanglement) is the best. It has a value of stress at break of 1.94 MPa, a strain of 54.2% and a young's module of 7.95 MPa, in a production normal direction. A biocomposite has been made with NW3 mixed with PMMA matrix. The use of nonwoven based alfa fiber in reinforcing the composite material increases its rigidity and the tensile strength; the elongation was found to be 1.53%, the Young's Module of 1.79 GPa and the tensile at break of 15.06 MPa. Results indicated that alfa fibres are of interest for low-cost engineering applications and can compete with glass fibres in orthopedic application.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.6
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• pp.222-229
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• 2003

The purpose of this study is to evaluate the mechanical properties of 6061 Al foams, which were fabricated by P/M and multi-step induction heating method, and to build the database, which is needed for computer aided modeling or foam components design. Aluminium foams, consisting of solid aluminium and large quantities of porosities, is widely used in automotive, aerospace, naval as well as functional applications because of its high stiffness at very low density, high impact energy absorption, heat and fire resistance, and greater thermal stability than any organic material. In this study, 6061 Al foams were fabricated for variation of fraction of porosities (%) according to porosities (%)-final heating temperature ( $T_{a3}$) curves. Mechanical properties such as compressive strength, energy absorption capacity, and efficiency were investigated to evaluate the feasibility of foams as crash energy absorbing components. Moreover, effect of the surface skin thickness on plateau stress and strain sensitivity of the 6061 Al foams with low porosities (%) were studied.d.

• Transactions of Materials Processing
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• v.9 no.4
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• pp.395-403
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• 2000

Formation of Shear Band under the adiabatic condition is widely observed In the engineering materials during rapidly forming process lot a thermally rate-dependent material. The shear band stems from evolution of a narrow region in which an intensive plastic flow occurs. The shear band often plays a role of a precursor of the ductile fracture during a forming process. The objective of this study is to investigate the localization behavior using numerical method. In this work, the implicit finite difference scheme is employed due to the ease of convergence and the numerical stability It is noted that physical and mechanical properties of materials determine how the shear band is formed and then localized. Material properties can be characterized with inertia number dissipation number and diffusion number. It is observed that the dimensionless numbers effect on localization. Using a parametric study, comparison was made between CRS-1018 steel with WHA (tungsten heavy alloy). The deformation behavior of material in this study include an isotropic hardening as well as thermal softening. Moreover, this study suggests that a kinematic hardening constitutive relation be required to predict a more accurate strain level at a shear band.

• Journal of Powder Materials
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• v.6 no.1
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• pp.27-35
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• 1999

A study was made on the fabrication of nanostructured Fe-Co powders by mechanical alloying and their magnetic properties. Microstrural development during the process of MA was inverstigated by means of X-ray diffraction, differential thermal analyzer, scanning electron microscopy and transmission electron microscopy. The magnetic properties of NS Fe-Co powders were evaluated through the measurements of the saturation magnetization $(M_s)$ as well as the coercivity $(H_c)$. The average grain size calculated from line braodening in XRD peak was about 10nm or less and confirmed by TEM. In this experiment, two different milling methods (cycle opertion and conventional milling) were used. Cycle operation had an advantage over the conventional milling method in that more refined powders can be obtained. Solid state alloying of the components was confirmed from both the change of the saturation magnetization and the change of lattice parameter with Co contentration. Maxium $M_s$ was obtained at the composition of 30at.%Co. Relatively high coercivities of 10~150e were obtained for the compositions investigated, and this seems to be due to the high amount of internal strain introduced during milling.

• International Journal of Aeronautical and Space Sciences
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• v.18 no.1
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• pp.70-81
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• 2017

Various components of an engine nozzle are modeled as flexible multi-body components that are operated under high temperature and pressure. In this paper, in order to predict complex behavior of an engine nozzle, thermo-fluid-flexible multi-body dynamics coupled analysis framework was developed. Temperature and pressure on the nozzle wall were obtained by the steady-state flow analysis for a two-dimensional nozzle. The pressure and temperature-dependent material properties were delivered to the flexible multi-body dynamics analysis. Then the deflection and strain distribution for a nozzle configuration was obtained. Heat conduction and thermal analyses were done using MSC.NASTRAN. The present framework was validated for a simple nozzle configuration by using a one-way coupled analysis. A two-way coupled analysis was also performed for the simple nozzle with an arbitrary joint clearance, and an asymmetric flow was observed. Finally, the total strain result for a realistic nozzle configuration was obtained using the one-way and two-way coupled analyses.

• Journal of Welding and Joining
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• v.22 no.6
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• pp.25-29
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• 2004

Some industrial steel structures are composed by components linked by several welding joints to constitute an assembly. The main interest of assembly simulation is to evaluate the global distortion of welded structure. The general method, thermo-elasto-plastic analysis, leads to excessive model size and computation time. In this study, a simplified method called "Local and Global approach" was developed to break down this limit and to provide a accurate solution for distortion. Local and global approach is composed of 3 steps; 1) Local simulation of each welding joint on a dedicated mesh (usually very fine due to high thermal gradients), taking into account for the non linearity of the material properties and the moving heat source. 2) Transfer to the global model of the effects of the welding joints by projection of the plastic strain tensors. 3) Elastic simulation to determine final distortions in global model. The welding deformation test for mock-up structure was performed to verify this approach. The predicted welding distortion by this approach had a good agreement with experiment results.

• Journal of the Korean Geosynthetics Society
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• v.14 no.2
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• pp.57-70
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• 2015

This paper presents the results of an investigation into the effect of forced temperature change cycles on physical and mechanical properties of sand and weathered granite soil. The effect of forced temperature change cylecs on the particle arrangement and the thermal conductivity was first investigated. A series of triaxial compression tests on the soils were also performed to look into the effect of temperature change cycles on the stress-strain-strength behavior. The results indicated that the forced temperature change cycle does not significantly affect the particle arrangement and thermal conductivity. It is shown however that the heating duration showed some effect on the deviatoric stress at failure while no significant effect due to the number of heating-cooling cycle was observed.

• Journal of Korean Society of Steel Construction
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• v.12 no.6
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• pp.759-767
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• 2000

In this study, the time dependent internal stress changes of a Concrete Filled Steel Tube(CFT) column during a fire test were quantitatively analyzed. The strain ratio of a CFT column on the different loads was measured by tensile strength tests in terms of yield strength, tensile strength average extensibility and elasticity modulus. To understand the internal material properties change of concrete in CFT column damaged due to a fire, the compressive strength and elastic modulus tests were measured on a core sample from the center of the steel tube after the fire test. The elastic modulus test measured the strain from the stress. To determine the fire temperature of the test material, a differential thermal analysis was done. From the tested result, the gained data were conducted and an analysis method was suggested. The purpose of this work is to suggest a basic data for structure regulation enactments of the internal fire design of CFT.

• Journal of Soil and Groundwater Environment
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• v.6 no.1
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• pp.53-62
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• 2001

Effects of surface defect on thermal stability and stress crack resistance of high density polyethylene geomembranes in environmental conditions were examined by comparing the mechanical properties, chemical resistance and failure times of geomembranes between defective cases under different temperatures. Artificial surface defects were added to the surface of geomembranes by scratch apparatus designed specially. The number of surface defects was increased with the smaller size of scratch induced particles, and the more scratch addition numbers at the shear rate of scratch induced mechanism, 100mm/min. The tensile strength were decreased but the tensile strain was increased with the above conditions. In chemical resistance of defective geomembranes, the tensile strength were decreased but the tensile strain was increased with the longer immersion period and the higher temperature under the same scratch induced conditions. Finally, failure times of defective geomembranes by ESCR test were shifted to the shorter time ranges by increasing temperatures.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.370-376
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• 2001

When an adhesive joint is exposed to high environmental temperature, the tensile load capability of the adhesive joint decreases because the elastic modulus and failure strength of structural adhesive decrease. The thermo-mechanical properties of structural adhesive can be improved by addition of fillers to the adhesive. In this paper, the elastic modulus and failure strength of adhesives as well as the tensile load capability of tubular single lap adhesive joints were experimentally and theoretically investigated with respect to the volume fraction of filler (alumina) and the environmental temperature. Also the tensile modulus of the fille containing epoxy adhesive was predicted using a new equation which considers filler shape, filler content and environmental temperature. The tensile load capability of the adhesive joint was predicted by using the effective strain obtained from the finite element analysis and a new failure model, from which the relation between the bonding length and the crack length was developed with respect to the volume fraction of filler.