• Journal of Biosystems Engineering
• /
• 제14권3호
• /
• pp.181-187
• /
• 1989

The mechanical and rheological properties of agricultural materials which influence the machine design or handling are not completely understood. Agricultural materials do not react in a purely elastic manner, and their responses when subjected to stress and strain appear a combination of elastic and viscous behavior. Many researchers have studied the mechanical and rheological properties of the various agricultural materials, but those properties are available mostly for foreign varieties of agricultural products. Rheological properties of rice seedlings become important to formulate the principles governing their mechanical behavior. The objectives of this study were to experimentally determine the creep and recovery behavior of rice seedlings of one japonica-type and one Indica x japonica hybrid in the transplanting age. The results of this study are summarized as follows; 1. The compression creep and recovery behavior of mat-type seedlings could be described by 4-element Burger's model. 2. The steady-state creep appeared at the stress larger than 0.8 MPa and the logarithmic creep appeared at the stress smaller than 0.8 MPa. 3. In the compression creep test of the rice seedlings, the instantaneous elastic modulus of Burger's model showed the range from 20 to 40 MPa. The higher value of absolute viscosity for the rice seedling explained that the rice seedlings were viscoelastic materials. 4. In the recovery test of the rice seedlings, there was a tendency that the higher permanent strain of all samples was observed under the smaller stress being appeared, and the larger permanent strain in Dongjin was observed than in Samkang.

• 한국식품과학회지
• /
• 제26권2호
• /
• pp.103-109
• /
• 1994

응력완화 현상을 측정하여 생선단백질 겔의 선형적 점탄성과 열처리 공정에 따른 물성의 변화를 수식적 모델로 분석하였다. 생선단백질 겔은 정변형도 $0.105{\sim}0.693$, 압축속도 $50{\sim}250\;mm/min$의 범위에서 선형적 점탄성을 나타내었으며, generalized Maxwell 모형에 의해 분석한 결과, 압축변형도과 압축속도가 증가함에 따라 가열에 의해 형성된 내부조직 중 탄성 성분의 증가와 점성성분의 감소현상을 보였다. $4^{\circ}C$와 $40^{\circ}C$에서 전처리하여 $90^{\circ}C$에서 제조한 겔은 전처리 없이 $90^{\circ}C$에서 직접 열처리한 겔보다 탄성율(E) 및 평형탄성율$(E_e)$이 높았으나, 점성성분$({\eta})$은 적용된 모델에 따라서 그 값의 차이가 나타났다. 따라서 식품의 물성을 측정하는데 있어서 두 수학적 모델의 접근방법 및 정확도에 대하여 설명하였다.

• 한국도로학회논문집
• /
• 제17권3호
• /
• pp.77-83
• /
• 2015

PURPOSES : In this study, a fracture-based finite element (FE) model is proposed to evaluate the fracture behavior of fiber-reinforced asphalt (FRA) concrete under various interface conditions. METHODS : A fracture-based FE model was developed to simulate a double-edge notched tension (DENT) test. A cohesive zone model (CZM) and linear viscoelastic model were implemented to model the fracture behavior and viscous behavior of the FRA concrete, respectively. Three models were developed to characterize the behavior of interfacial bonding between the fiber reinforcement and surrounding materials. In the first model, the fracture property of the asphalt concrete was modified to study the effect of fiber reinforcement. In the second model, spring elements were used to simulated the fiber reinforcement. In the third method, bar and spring elements, based on a nonlinear bond-slip model, were used to simulate the fiber reinforcement and interfacial bonding conditions. The performance of the FRA in resisting crack development under various interfacial conditions was evaluated. RESULTS : The elastic modulus of the fibers was not sensitive to the behavior of the FRA in the DENT test before crack initiation. After crack development, the fracture resistance of the FRA was found to have enhanced considerably as the elastic modulus of the fibers increased from 450 MPa to 900 MPa. When the adhesion between the fibers and asphalt concrete was sufficiently high, the fiber reinforcement was effective. It means that the interfacial bonding conditions affect the fracture resistance of the FRA significantly. CONCLUSIONS : The bar/spring element models were more effective in representing the local behavior of the fibers and interfacial bonding than the fracture energy approach. The reinforcement effect is more significant after crack initiation, as the fibers can be pulled out sufficiently. Both the elastic modulus of the fiber reinforcement and the interfacial bonding were significant in controlling crack development in the FRA.

• Korea-Australia Rheology Journal
• /
• 제17권4호
• /
• pp.181-190
• /
• 2005

Rheological characterisation of flocculated kaolinite pulps has been undertaken to elucidate particle interactions underpinning the dewatering behaviour induced by flocculation with polyethylene oxide (PEO), anionic polyacrylamide (PAM A) and their blends. Shear yield stress $(\tau_y)$ analysis indicated that polymer mediated particle interactions were markedly amplified upon shear of PEG based pulps. In contrast, PAM A based pulps showed a significant decrease in yield values upon shear. Steady stress measurements analysed using a modified Ellis model indicated subtle differences between the respective linear viscoelastic plateaus of the pulps. Furthermore, modified shear thinning behaviour was evident in PEG based pulps. Estimation of elastic and viscous moduli (G', G') was made using dynamic stress analysis for comparison with values determined from vane measurements. Despite a noticeable difference in the magnitude of G' between the two methods, similar trends indicating sheared PEG-based pulps to be more elastic than PAM based pulps, were observed. Floc microstructural observations obtained in support of rheological properties indicate that PEG flocculant induces significantly more compact particle aggregation within the clay pulps under shear consistent with the yield stress data, in contrast to PAM A, or indeed unsheared PEG based pulps. Consequentially, sheared PEG based pulps show significantly improved dewatering behaviour. The implications of the results, potential benefits and drawbacks of flocculation with PEG and PAM A are discussed with respect to improvements in current dewatering processes used in the minerals industry.

• 한국구조물진단유지관리공학회 논문집
• /
• 제8권1호
• /
• pp.109-119
• /
• 2004

목표 성능수준을 만족하기 위하여 필요한 점성과 점탄성감쇠기와 같은 속도-의존형 부가 감쇠기의 설계절차를 변위스펙트럼을 이용하여 제시하였다. 주어진 성능 한계상태를 만족하기 위하여 필요한 부가 감쇠량은 변위스펙트럼을 이용한 비선형 정적해석에 의해 산정한 다음 필요 감쇠비를 달성하기 위하여 각 층에 적당하게 분배하였다. 다층 철골조 건물에 제안된 방법을 적용하고 설계절차의 정확성을 검증하기 위하여 시간이력해석을 수행하였다. 해석결과에 의하면 부가 감쇠기로 보강한 예제 구조물의 최대 변위가 목표변위까지 잘 제어됨을 알 수 있다.

• 한국지진공학회논문집
• /
• 제19권1호
• /
• pp.37-43
• /
• 2015

This paper presents a detailed procedure for a nonlinear soil-structure interaction of a seismically isolated NPP(Nuclear Power Plant) structure using the boundary reaction method (BRM). The BRM offers a two-step method as follows: (1) the calculation of boundary reaction forces in the frequency domain on an interface of linear and nonlinear regions, (2) solving the wave radiation problem subjected to the boundary reaction forces in the time domain. For the purpose of calculating the boundary reaction forces at the base of the isolator, the KIESSI-3D program is employed in this study to solve soil-foundation interaction problem subjected to vertically incident seismic waves. Wave radiation analysis is also employed, in which the nonlinear structure and the linear soil region are modeled by finite elements and energy absorbing elements on the outer model boundary using a general purpose nonlinear FE program. In this study, the MIDAS/Civil program is employed for modeling the wave radiation problem. In order to absorb the outgoing elastic waves to the unbounded soil region, spring and viscous-damper elements are used at the outer FE boundary. The BRM technique utilizing KIESSI-3D and MIDAS/Civil programs is verified using a linear soil-structure analysis problem. Finally the method is applied to nonlinear seismic analysis of a base-isolated NPP structure. The results show that BRM can effectively be applied to nonlinear soil-structure interaction problems.

• Applied Biological Chemistry
• /
• 제40권6호
• /
• pp.525-530
• /
• 1997

생분해성 포장재질에 대한 달걀의 기능성 변화를 알아보기 위해 달걀의 저장중 pH변화, 파손강도 및 응력완화현상을 측정하고 무포장 및 복합 필름에 포장한 달걀과 비교하였다. 생분해성 포장재질을 달걀에 사용한 경우 pH는 초기 8.39에서 최종 pH 9.3으로 최종 pH 9.48을 보인 무포장의 경우와 유사한 pH변화를 보이며, 파손강도의 변화에 있어서도 초기 14.25 N에서 생분해성 포장재질로 포장한 경우 6.76 N, 무포장의 경우 9.31 N의 변화를 보였다. 생분해성 포장재질이나 무포장에 비해 공기투과도가 상대적으로 무척 낮은 복합 필름 포장재를 사용한 경우는 저장이 진행됨에 따라 pH는 8.39에서 8.81로 적은 변화량을 보였으나 파손 강도값은 14.25 N에서 5.29 N으로 크게 감소하는 것으로 보아 달걀내부의 물성학적 기능이 크게 저하됨을 보여주었다. 내부조직변화를 감지할 수 있는 응력완화 현상을 측정하여 3-elements Maxwell model에 적용하고 구하여진 점탄성의 값을 비교시 무포장한 달걀과 생분해성 포장재를 사용한 경우에는 큰 차이가 없었으나 복합 필름 포장재의 경우에는 저장이 진행됨에 따라 그 기능이 현저하게 떨어짐을 보여주었으며 따라서, 달걀의 기능성 변화를 살펴볼 때 공기 및 수분투과도가 큰 영향을 미치는 것으로 나타났다. 생분해성 포장재질의 많은 인장력 증가가 현 단계에서 요구되나 환경적인 문제를 고려할 때 기존의 달걀 포장재인 PE포장재의 대체품으로서 사용 가능성이 긍정적으로 여겨진다.

• 농업과학연구
• /
• 제14권1호
• /
• pp.98-133
• /
• 1987

The mechanical and rheological properties of agricultural materials are important for engineering design and analysis of their mechanical harvesting, handling, transporting and processing systems. Agricultural materials, which composed of structural members and fluids do not react in a purely elastic manner, and their response when subjected to stress and strain is a combination of elastic and viscous behavior so called viscoelastic behavior. Many researchers have conducted studies on the mechanical and rheological properties of the various agricultural products, but a few researcher has studied those properties of rice plant, and also those data are available only for foreign varieties of rice plant. This study are conducted to experimentally determine the mechanical and the rheological properties such as axial compressive strength, tensile strength, bending and shear strength, stress relaxation and creep behavior of rice stems, and grain detachment strength. The rheological models for the rice stem were developed from the test data. The shearing characteristics were examined at some different levels of portion, cross-sectional area, moisture content of rice stem and shearing angle. The results obtained from this study were summarized as follows 1. The mechanical properties of the stems of the J aponica types were greater than those of the Indica ${\times}$ Japonica hybrid in compression, tension, bendingand shearing. 2. The mean value of the compressive force was 80.5 N in the Japonica types and 55.5 N in the Indica ${\times}$ Japonica hybrid which was about 70 percent to that of the Japonica types, and then the value increased progressively at the lower portion of the stems generally. 3. The average tensile force was about 226.6 N in the Japonica types and 123.6 N in the Indica ${\times}$ Japonica hybrid which was about 55 percent to that of the Japonica types. 4. The bending moment was $0.19N{\cdot}m$ in the Japonica types and $0.13N{\cdot}m$ in the Indica ${\times}$ Japonica hybrid which was 68 percent to that of the Japonica types and the bending strength was 7.7 MPa in the Japonica types and 6.5 MPa in the Indica ${\times}$ Japonica hybrid respectively. 5. The shearing force was 141.1 N in Jinju, the Japonica type and 101.4 N in Taebaeg, the Indica ${\times}$ Japonica hybrid which was 72 percent to that of Jinju, and the shearing strength of Taebaeg was 63 percent to that of Jinju. 6. The shearing force and the shearing energy along the stem portion in Jinju increased progressively together at the lower portions, meanwhile in Taebaeg the shearing force showed the maximum value at the intermediate portion and the shearing energy was the greatest at the portion of 21 cm from the ground level, and also the shearing strength and the shearing energy per unit cross-sectional area of the stem were the greater values at the intermediate portion than at any other portions. 7. The shearing force and the shearing energy increased with increase of the cross-sectional area of the rice stem and with decrease of the shearing angie from $90^{\circ}$ to $50^{\circ}$. 8. The shearing forces showed the minimum values of 110 N at Jinju and of 60 N at Taebaeg, the shearing energy at the moisture content decreased about 15 percent point from initial moisture content showed value of 50 mJ in Jinju and of 30 mJ in Taebaeg, respectively. 9. The stress relaxation behavior could be described by the generalized Maxwell model and also the compression creep behavior by Burger's model, respectively in the rice stem. 10. With increase of loading rate, the stress relaxation intensity increased, meanwhile the relaxation time and residual stress decreased. 11. In the compression creep test, the logarithmic creep occured at the stress less than 2.0 MPa and the steady-state creep at the stress larger than 2.0 MPa. 12. The stress level had not a significant effect on the relaxation time, while the relaxation intensity and residual stress increased with increase of the stress level. 13. In the compression creep test of the rice stem, the instantaneous elastic modulus of Burger's model showed the range of 60 to 80 MPa and the viscosities of the free dashpot were very large numerical value which was well explained that the rice stem was viscoelastic material. 14. The tensile detachment forces were about 1.7 to 2.3 N in the Japonica types while about 1.0 to 1.3 N in Indica ${\times}$ Japonica hybrid corresponding to 58 percent of Japonica types, and the bending detachment forces were about 0.6 to 1.1 N corresponding to 30 to 50 percent of the tensile detachment forces, and the bending detachment of the Indica ${\times}$ Japonica hybrid was 0.1 to 0.3 N which was 7 to 21 percent of Japonica types. 15. The detachment force of the lower portion was little bigger than that of the upper portion in a penicle and was not significantly affected by the harvesting period from September 28 to October 20. 16. The tensile and bending detachment forces decreased with decrease of the moisture content from 23 to 13 percent (w.b.) by the natural drying, and the decreasing rate of detachment forces along the moisture content was the greater in the bending detachment force than the tensile detachment force.

• 한국지반공학회논문집
• /
• 제22권9호
• /
• pp.37-43
• /
• 2006

지반구조물의 동적해석은 모델의 영역이 커짐에 따라 에너지가 감소하는 현상을 표현할 수 있는 방법을 필요로 한다. 이러한 현상은 흔히 방사 감쇠(radiation damping) 또는 기하학적 감쇠(geometric attenuation)로 알려져 있으며, 탄성에너지가 점성 또는 이력현상에 의해 감소되는 재료 감쇠현상과는 구별된다. 따라서 수치해석으로 지반구조물의 동적거동을 해석할 경우 모델의 영역 구축은 특별한 고려를 필요로 한다. 인공적인 경계조건은 유한요소내의 지반상태를 무한상태로 변형시킬 수 있어야 하며, 경계에 도달하는 응력 파동을 모델내로 반사시키지 않고 흡수 할 수 있어야 한다. 본 논문에서는 간단한 점 탄성 반무한 불연속 요소를 이용하여 지반구조물의 동적해석을 수행할 경우 에너지를 투과하는 경계조건을 수립하는 방법을 보여준다. 반무한 요소의 실행은 OpenSees라는 유한요소 해석프로그램을 이용하여 수행되었으며, 예를 통하여 불연속 요소가 경계에 도달하는 응력 파동을 충분히 흡수하여 유한요소 모델을 반무한 상태로 전환 시킬 수 있다는 것을 보여준다. 본 논문에서 제시된 방법은 간단하게 실용적으로 사용할 수 있는 반무한 경계조건이지만, 입사각이 매우 예리할 경우는 에너지의 흡수정도가 충분치 않은 것으로 알려져 있다.