• Journal of the Korean Ceramic Society
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• v.27 no.6
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• pp.729-734
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• 1990

The microstructural dependence of thermal conductivity of a high-alumina (ca. 70%) heat-insulating frebricks(ca. 75%porosity) was investigated under special consideration of the tailored-pore shape effects. Pores different shape could be incorporated into the insulators through pore formers : Styrofoam produces spherical pores while saw dust results in parallel plate pores. Concerning the pore-shape effectiveness of thermal insulation, the specimen with irregular plate pores showed much lower values of heat conductivity than those with spherical pores, the values being 0.31 to 0.38 at $600^{\circ}C$ and 0.35 to 0.47 at 100$0^{\circ}C$, respectively. On the contrary, however, other material properties such as strength and softening temeprature under load were turned out to be better in the case of the spherical pores.

• Computers and Concrete
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• v.20 no.6
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• pp.689-704
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• 2017

The paper presents experimental and numerical investigations of prefabricated composite structural building reinforced concrete slabs with the insulating material for a residential building construction. The building slabs were composed of concrete and expanded polystyrene. In experiments, the slabs in the full-scale 1:1 were subjected to vertical concentrated loads and failed along a diagonal shear crack. The experiments were numerically evaluated using the finite element method based on two different constitutive continuum models for concrete. First, an elasto-plastic model with the Drucker-Prager criterion defined in compression and with the Rankine criterion defined in tension was used. Second, a coupled elasto-plastic-damage formulation based on the strain equivalence hypothesis was used. In order to describe strain localization in concrete, both models were enhanced in the softening regime by a characteristic length of micro-structure by means of a non-local theory. Attention was paid to the formation of critical diagonal shear crack which was a failure precursor.

• Computers and Concrete
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• v.23 no.3
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• pp.171-188
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• 2019

This study proposed a new and efficient 2D damage-plasticity model within the framework of Isogeometric analysis (IGA) for the geometrically nonlinear damage analysis of concrete. Since concrete exhibits complicated material properties, two internal variables are introduced to measure the hardening/softening behavior of concrete in tension and compression, and an implicit gradient-enhanced formulation is adopted to restore the well-posedness of the boundary value problem. The numerical results calculated by the model is compared with the experimental data of three benchmark problems of plain concrete (three-point and four-point bending single-notched beams and four-point bending double-notched beam) to illustrate the geometrical flexibility, accuracy, and robustness of the proposed approach. In addition, the influence of the characteristic length on the numerical results of each problem is investigated.

• Coupled systems mechanics
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• v.8 no.2
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• pp.111-127
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• 2019

In this paper, we present a 2D multi-scale coupling computation procedure for localized failure. When modeling the behavior of a structure by a multi-scale method, the macro-scale is used to describe the homogenized response of the structure, and the micro-scale to describe the details of the behavior on the smaller scale of the material where some inelastic mechanisms, like damage or plasticity, can be defined. The micro-scale mesh is defined for each multi-scale element in a way to fit entirely inside it. The two scales are coupled by imposing the constraint on the displacement field over their interface. An embedded discontinuity is implemented in the macro-scale element to capture the softening behavior happening on the micro-scale. The computation is performed using the operator split solution procedure on both scales.

• Journal of Industrial and Engineering Chemistry
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• v.67
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• pp.1-11
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• 2018

Polymer composites offered broad engineered applications, however their diversity get restricted owing to fluctuations in thermomechanical properties during heating or cooling hence great concern required prior their applications through thermomechanical analysis (TMA). Traditionally, TMA or dilatometry found to be simple, ideal, reliable, sensitive, excellent and basic thermal analytical technique. TMA provides valuable information on thermal expansion, glass transitions temperature (Tg), softening points, composition and phase changes on material of having different geometries simply by applying a constant force as a function of temperature. This compilation highlights the basics and experimental of TMA for both research and technical applications and also provide literature on TMA of polymers, hybrid composites, nanocomposites and their diverse applications.

• Coupled systems mechanics
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• v.11 no.5
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• pp.411-438
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• 2022

In this paper, we present the parameter identification for inelastic and multi-scale problems. First, the theoretical background of several fundamental methods used in the upscaling process is reviewed. Several key definitions including random field, Bayesian theorem, Polynomial chaos expansion (PCE), and Gauss-Markov-Kalman filter are briefly summarized. An illustrative example is given to assimilate fracture energy in a simple inelastic problem with linear hardening and softening phases. Second, the parameter identification using the Gauss-Markov-Kalman filter is employed for a multi-scale problem to identify bulk and shear moduli and other material properties in a macro-scale with the data from a micro-scale as quantities of interest (QoI). The problem can also be viewed as upscaling homogenization.

• Archives of Metallurgy and Materials
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• v.65 no.4
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• pp.1293-1296
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• 2020

NdFeB anisotropic sintered permanent magnets are typically fabricated by strip casting or melt spinning. In this study, the plastic deformability of an NdFeB alloy was investigated to study the possibility of fabricating anisotropic sintered magnets using gas atomized powders. The results show that the stoichiometric composition Nd₁₂Fe₈₂B₆ softens at high temperatures. The aspect ratio and orientation factor of Nd₁₂Fe₈₂B₆ billets after plastic deformation were found to increase with increasing plastic deformation temperature, particularly above 800℃. This confirms that softening at high temperatures can lead to plastic deformation of Nd₂Fe₁₄B hard magnetic phases.

• Journal of Ocean Engineering and Technology
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• v.25 no.2
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• pp.134-144
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• 2011

In this paper, the global study trends for material behaviors are investigated regarding the static and dynamic hardenings and final fractures of marine structural steels. In particular, after reviewing all of the papers published at the 4th and 5th ICCGS (International Conference on Collision and Grounding of Ship), the used hardening and fracture properties are summarized, explicitly presenting the material properties. Although some studies have attempted to employ new plasticity and fracture models, it is obvious that most still employed an ideal hardening rule such as perfect plastic or linear hardening and a simple shear fracture criterion with an assumed value of failure strain. HSE (2001) presented pioneering study results regarding the temperature dependency of material strain hardening at various levels of temperature, but did not show strain rate hardening at intermediate or high strain rate ranges. Nemat-Nasser and Guo (2003) carried out fully coupled tests for DH-36 steel: strain hardening, strain rate hardening, and temperature hardening and softening at multiple steps of strain rates and temperatures. The main goal of this paper is to provide the theoretical background for strain and strain rate hardening. In addition, it presents the procedure and methodology needed to derive the material constants for the static hardening constitutive equations of Ludwik, Hollomon, Swift, and Ramberg-Osgood and for the dynamic hardening constitutive equations of power from Cowper-Symonds and Johnson-Cook.

• Journal of the Korean Ceramic Society
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• v.39 no.2
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• pp.194-198
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• 2002

Various composition of $K_2O{\cdot}CaO{\cdot}P_2O_5$ glasses were studied by melting process to identify glass forming region. Thermal properties were observed by DSC and TG-DTA, structural properties were investigated by FT-IR and Raman Spectroscopy. The glass transition temperature (Tg) and softening temperature (Ts) were decreased with increasing $K_2O\;and\;P_2O_5$ contents. The basic structural unit of phosphate glasses is the $PO_2\;and\;PO_4^{3-}$ groups to make a cross-link and P-O-P group to form skeleton structure. As CaO content was increased, the P-O-P field strength in these glass was increased and intensity of $PO_2\;and\;PO_4^{3-}$ stretch was decreased.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.7
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• pp.1241-1249
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• 2002

The extent of materials deterioration can be evaluated accurately by mechanical test such as impact test or creep test. But it is almost impossible to extract a large test specimen from in-service components. Thus material degradation evaluation by non-destructive method is earnestly required. In this paper, the material degradation for virgin and several aged materials of a Cr-Mo-V steel, which is an candidated as structural material of the turbine casing components for electric power plant, is nondestructively evaluated by reactivation polarization testing method. And, the results obtained from the test are compared with those in small punch(SP) tests recommended as a semi-nondestructive testing method using miniaturized specimen. In contrast to the aged materials up to 1,000hrs which exhibit the degradation behaviors with increased ${\Delta}[DBTT]_{SP}$, the improvement of mechanical property can be observed on the 2,000hrs and 3,000hrs aged materials. This is because of the softening of material due to the carbide precipitation, the increase of ferritic structures and the recovery of dislocation microstructure by long-time heat treatment. The reactivation rates($I_R/I_{Crit},\;Q_R/Q_{Crit}$) calculated by reactivation current densityt ($I_R$) and charge($Q_R$) in the polarization curves exhibit a good correlation with ${\Delta}[DBTT]_{SP}$ behaviors.