• Advances in concrete construction
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• 제15권2호
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• pp.115-126
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• 2023

This paper investigates creep analysis of a plate made of Al-SiC functionally graded material using Mendelson's method of successive elastic solution. All mechanical and thermal material properties, except Poisson's ratio, are assumed to be variable along the thickness direction based on the volume fraction of reinforcement and thickness. First, the basic relations of the plate are derived using the Love-Kirchhoff plate theory. The solution of governing equations yields an elastic solution to start creep analysis. The creep behavior is demonstrated through Norton's equation based on Pandey's experimental results extracted for Al-SiC functionally graded material. A linear variation is assumed for temperature distribution along the thickness direction. The creep strain, as well as the thermal strain, are included in the governing equations derived from classical plate theory for mechanical strain. A successive elastic solution based on Mendelson's method is employed to derive the history of stresses, strains, and displacements over a long time. History of stresses and deformations are obtained over a long time to predict damage to the plate because of various loadings, and material composition along the thickness and planar directions.

• 대한기계학회논문집
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• 제17권2호
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• pp.285-299
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• 1993

본 연구에서는 UBET를 이용한 프로그램을 개발하여 소성가공 문제에 적용하였 으며, 형단조 가공에서 형 내부의 재료의 비정상 유동을 해석할 수 있는 알고리듬을 제시하였다. 매 변형단계에서 요소별 가공경화를 고려하여 자동적으로 요소시스템 (element system)을 재구성함으로써, UBET에 의한 소성가공 문제 해석을 효율적으로 할 수 있도록 하였다. 축대칭 형단조 문제에 있어서 리브의 높이대 폭의 비가 1.0, 2.0일때 UBET 및 탄소성 유한요소법에 의하여 형 내부의 재료 층만 과정을 시뮬레이션 하였으며, 단조 하중, 다이 충만도 및 재료의 유동 경향을 분석하여 적절한 유동 모델 과 초기 소재의 형상을 구하였다. 모델 재료를 사용한 형단조 모의실험을 수행하여 재료유동 및 변형 단계별 단조 하중분포 등을 구하였으며, 해석결과와 비교 분석하였 다. 또한 후방압출(backward extrusion) 및 평두형 펀치에 의한 평판압입(flat pu- nch indentation) 문제를 해석하였다. 후방압출시 모서리부의 라운딩(rounding) 효 과가 재료 유동에 미치는 영향을 고려하였으며, 평두형 펀치에 의한 평판압입에서는 상당 소성변형률(equivalent plastic strain)의 분포를 탄소성 유한요소법(elastic plastic finite element method)에 의한 결과와 비교하였다.

• 한국해양공학회지
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• 제32권4호
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• pp.253-260
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• 2018

Recently, the application of non-steel materials in ships and offshore plants is increasing because of the development of various nonlinear materials and the improvement of performance. Especially, hyper-elastic materials, which have a nonlinear stress-strain relationship, are used mainly in marine plant structures or ships where impact relaxation, vibration suppression, and elasticity are required, while elasticity must be maintained, even under high strain conditions. In order to simulate and evaluate the behavior of the hyperelastic material, it is very important to select an appropriate material model according to the strain of the material. This study focused on the selection of material models for hyperelastic materials, such as rubber used in the marine and offshore fields. Tension and compression tests and finite element simulations were conducted to compare the accuracy of the nonlinear material models due to variations in the stretch ratio of hyper-elastic material. Material coefficients of nonlinear material models are determined based on the curve fitting of experimental data. The results of this study can be used to improve the reliability of nonlinear material models according to stretch ratio variation.

• 동력기계공학회지
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• 제11권1호
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• pp.127-133
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• 2007

SG-365 steel is an important material and used for manufacturing a pressure vessel which the gas piping. In this investigation, the elastic plastic fracture toughness of this material is evaluated by the unloading compliance method according to the ASTM E813-97 and E1152-97 method on the smooth and side groove 1CT specimens. The effect of smooth and side groove is studied on the elastic plastic fracture toughness. The side grooved specimen is very useful in estimation of the $J_{IC}$. It is much easier than the smooth specimen to the onset of the ductile tearing by the R curve method. Besides, it improves the accuracy of toughness values, decreases a phenomenon of the tunneling and shear lip by the side groove.

• 한국산업융합학회 논문집
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• 제23권1호
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• pp.83-91
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• 2020

The evaluation of the compression behavior of the cushioning material is of importance to achieve appropriate packaging design. In order to change packaging design from polymeric-based to more eco-friendly cellulose-based nire effectively, comparative study on the compression behavior between these two packaging materials is crucial. In this study, the stress-strain behavior, hysteresis loss, and response characteristics for cyclic loading were analyzed through compression tests on multi-layered corrugated structure (MLCS) and expanded polystyrene (EPS) packaging materials. MLCS produced in Korea is produced by winding a certain number of single-faced corrugated paperboard, and the compression behavior of this material was turned out to be 6 stages: elastic stage, first buckling stage, sub-buckling stage, densification stage, last buckling stage and high densification stage. On the other hand, EPS's compression behavior was in 3 stages: linear elastic stage, collapse plateau, and densification stage. The strain energy per unit volume (strain energy density) of MLCS did not differ depending on the material thickness, but it showed a clear difference depending on the raw material and flute type. Hysteresis loss of MLCS ranged from 0.90 to 0.93, and there were no significant differences in the raw material and flute type. These values were about 5 to 20% greater than the hysteresis of the EPS (about 0.78 to 0.87).

• 대한기계학회논문집A
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• 제25권5호
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• pp.765-771
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• 2001

Elastic-plastic fracture toughness JIC can be used a s an effective design criterion in elastic-plastic fracture mechanics. Among the JIC test methods approved by ASTM, unloading compliance method was used in this study. In order to examine the relationship between fracture behavior of JIC test and AE signals, the post processing of AE signals has been carried out by Short Time Fourier Transform(STFT), one of the time-frequency analysis methods. The objective of this study is to evaluate the application of characterization of AE signals for unloading compliance method of JIC test. As a result of time-frequency analysis, we could extract the AE from the raw signal and analyze the frequencies in AE signal at the same time. AE signal generated by elastic-plastic fracture of material has some different aspects at elastic and plastic ranges, or the first portion of crack growth by fracture. First of all, increased energy recorded and detected by using AE count method increase rapidly from the start of ductile fracture. The variation of main frequency range with time-frequency analysis method could be confirmed. We could know fracture behavior of interior material by examination AE characteristics generated in real-time when elastic-plastic fracture occurred in material under loading.

• 한국도로학회논문집
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• 제19권1호
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• pp.37-44
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• 2017

PURPOSES : This study is primarily focused on evaluating the effects of the non-linear stress-strain behavior of RAP concrete on structural response characteristics as is applicable to concrete pavement. METHODS : A 3D FE model was developed by incorporating the actual stress-strain behavior of RAP concrete obtained via flexural strength testing as a material property model to evaluate the effects of the non-linear stress-strain behavior to failure on the maximum stresses in the concrete slab and potential performance prediction results. In addition, a typical linear elastic model was employed to analyze the structural responses for comparison purposes. The analytical results from the FE model incorporating the actual stress-strain behavior of RAP concrete were compared to the corresponding results from the linear elastic FE model. RESULTS : The results indicate that the linear elastic model tends to yield higher predicted maximum stresses in the concrete as compared to those obtained via the actual stress-strain model. Consequently, these higher predicted stresses lead to a difference in potential performance of the concrete pavement containing RAP. CONCLUSIONS : Analysis of the concrete pavement containing RAP demonstrated that an appropriate analytical model using the actual stress-strain characteristics should be employed to calculate the structural responses of RAP concrete pavement instead of simply assuming the concrete to be a linear elastic material.

• 대한기계학회논문집A
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• 제33권12호
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• pp.1455-1463
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• 2009

Theoretical mechanics analysis and finite element simulation were performed to investigate creep deformation behavior at the crack tip of transversely isotropic materials under small scale creep (SCC) conditions. Mechanical behavior of material was assumed as an elastic-$2^{nd}$ creep, which elastic modulus ( E ), Poisson's ratio ( ${\nu}$ ) and creep stress exponent ( n ) were isotropic and creep coefficient was only transversely isotropic. Based on the mechanics analysis for material behavior, a constitutive equation for transversely isotropic creep behavior was formulated and an equivalent creep coefficient was proposed under plain strain conditions. Creep deformation behavior at the crack tip was investigated through the finite element analysis. The results of the finite element analysis showed that creep deformation in transversely isotropic materials is dominant at the rear of the crack-tip. This result was more obvious when a load was applied to principal axis of anisotropy. Based on the results of the mechanics analysis and the finite element simulation, a corrected estimation scheme of the creep zone size was proposed in order to evaluate the creep deformation behavior at the crack tip of transversely isotropic creeping materials.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.729-732
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• 2003

The K-R design curve is an engineering method of linear-elastic fracture analysis under plane-stress loading conditions. By the way, linear-elastic fracture mechanics (LEFM) is valid only as long as nonlinear material deformation is confined to a small region surrounding the crack tip. Like general steels, it is virtually impossible to characterize the fracture behavior with LEFM, in many materials. Critical values of J contour integral or crack tip opening displacement (CTOD) give nearly size independent measures of fracture toughness, even for relatively large amounts of crack tip plasticity. Furthermore, the crack tip opening displacement is the only parameter that can be directly measured in the fracture test. On the other. the crack tip opening angle (CTOA) test is similar to CTOD experimentally. Moreover, the test is easier to measure the fracture toughness than other method. The shape of the CTOA curve depends on material fracture behavior and, on the opening configuration of the cracked structure. CTOA parameter describes crack tip conditions in elastic-plastic materials, and it can be used as a fracture criterion effectively. In this paper, CTOA test is performed for steel JS-SS400 hot-rolled thin plates under plane-stress loading conditions. Special experimental apparatuses are used to prevent specimens from buckling and to measure crack tip opening angle for thin compact tension (CT) specimens.

• Coupled systems mechanics
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• 제2권1호
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• pp.1-22
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• 2013

Under thermal environment, Magneto-Electro-Elastic (MEE) material exhibits pyroelectric and pyromagnetic effects which can be used for enhancing the performance of MEE sensors. Recently studies have been published on material constants such as pyroelectric constant and pyromagnetic constant for magneto-electro-thermo-elastic smart composite. Hence, the main aim of this paper is to study the pyroelectric and pyromagnetic effects on behavior of MEE plate under different boundary conditions subjected to uniform temperature. A numerical study is carried out using eight noded brick finite element under uniform temperature rise of 100 K. The study focused on the pyroelectric and pyromagnetic effects on system parameters like displacements, thermal stresses, electric potential, magnetic potential, electric displacements and magnetic flux densities. It is found that, there is a significant increase in electric potential due to the pyroelectric and pyromagnetic effects. These effects are visible on electric and magnetic potentials when CFFC and FCFC boundary conditions are applied. Additionally, the pyroelectric and pyromagnetic effects at free edge is dominant (nearly thrice the value in CFFC in comparison with FCFC) than at middle of the plate. This study is a significant contribution to sensor applications.