• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.34 no.7
• /
• pp.911-917
• /
• 2010

In this study, we performed structural and fatigue analyses of the engine exhaust manifold that was subjected to thermo-mechanical cyclic loading. The methodologies used in this study are based on an approach in which the techniques for modeling the exhaust system, the temperature-dependent properties of the material, and thermal cyclic loading are taken into consideration and a reliable strategy is adopted for failure prediction. An application example shows that at an elevated temperature, considerable compressive plastic deformation is observed and that at a low temperature, tensile stresses remain in those parts of the test exhaust manifold where failure is observed. In order to predict fatigue life, mechanical damage is determined on the basis of the stress.strain hysteresis loops by using the classical Coffin.Manson equation and by adopting a method in which the dissipated plastic energy is taken into consideration.

• Korean Journal of Materials Research
• /
• v.8 no.3
• /
• pp.200-205
• /
• 1998

The nature, degree, and evolution of contact damage from Hertzian contacts in silicon nitride-boron nitride composites($Si_3N_4-BN$) are investigated as a function of boron nitride content. The strong deviations of indentation stress-strain from elastic response indicate exceptional plasticity in $Si_3N_4-BN$. The absence of ring cracks or cone cracks on the surfaces is observed, indicating a high damage tolerance. Subsurface quasi- plastic deformation by shear stress is considerable and microdamage is widely distributed within the region below the contact. Shear faults associated with local microfailures play a precursor role in plasticity of this material. When boron nitride content increases, $Si_3N_4-BN$ becomes softer and more quasi-plastic.

• Journal of the Korean Ceramic Society
• /
• v.40 no.3
• /
• pp.273-278
• /
• 2003

The effects of content and particle size of sewage sludge slag on the sound absorption was investigated and the physical$.$mechanical properties of porous ceramics for sound absorbent material was studied. The physical$.$mechanical properties of specimens have depended on sintering temperature and slag content without particle size effect of slag. As water glass content increase and particle size of slag decrease at the same slag content, physical$.$mechanical properties of them have been improved. The bulk density and compressive strength of specimens with the batch composition of 77∼89 wt% of slag content and particles with 1∼3 mm, and sintered at 1,050$^{\circ}C$ for 2 h were 1.48∼1.71 and 86∼163 kgf/$\textrm{cm}^2$, respectively. The specimens with 1∼3 mm and <1 mm of particles size showed good sound absorption property at low frequency and high frequency region. With increasing thickness of specimens, sound absorption properties at low frequency region were increased.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.11 no.3
• /
• pp.488-500
• /
• 1987

The improvement of surface roughness of machined cylindrical rods through the plastic polishing process was studied in this paper. The criterion and limits for the plastic polishing process due to the wave motion of the ridge were established with respect to process variables: ridge shape and size, semi-cone die angle as well as friction factor, by the application of the upper-bound approach. The surface roughness of the plastic polished products was measured, and compared with that of the original specimen. Also the depth of the surface deformation layer was tested, and compared those of the theoretical values. Qualitative agreement exists between the experimental plastic polishing loads and theoretical loads. The wave motion of the ridge was mostly occurred within the established limits. The surface roughness of specimens was sufficiently improved through the present process. Also the predicted depth of the surface deformation layer was in good agreement with experimental results.

• Geotechnical Engineering
• /
• v.11 no.1
• /
• pp.113-126
• /
• 1995

Both resonant column (RC) and torsional shear(TS) tests were performed at small to intermediate strain levels to investigate deformational characteristics of cohesive soils. The effects of variables such as strain amplitude, loading frequency, and number of loading cycles were studied. Plasticity index was found to be an important variables in evaluating these effects. Soils tested include undisturbed silts and clays and compacted subgrade soils. At small strains below the elastic threshold, shear modulus is independent of number of loading cycles and strain amplitude. Small strain material damping exists wi th ranges be tween 1.1% and 1.7% for 75 tests. The elastic threshold strain increases as confining pressure and plasticity index increases. Above the cyclic threshold strain, the modulus of cohesive soil decreases with increasing number of cycles while damping ratio is almost independent of number of load cycles. Moduli and damping ratios of cohesive soils obtanined by RC test are higher than those from 75 test because of the frequency effect. Shear modulus of cohesive soil increases linearly as a function of the logarithm of loading frequency.

• Journal of Advanced Marine Engineering and Technology
• /
• v.39 no.4
• /
• pp.489-494
• /
• 2015

This research focused on minimizing the response of fixed cylindrical offshore structures to a ship impact considering the seawater fluid part. A collision between a ship and offshore structure is generally a complex problem and it is often impractical to perform rigorous finite element analyses to include all the effects and sequences during the collision. The structural behavior of a fixed cylindrical type offshore substructure with a seawater fluid part has a simpler response and small deformation due to the dissipation of impact energy. Upon applying the impact force of a ship to the cylindrical structure, the maximum acceleration, internal energy, and plastic strain are calculated for each load cases using Ls-dyna finite element software. In the maximum cases 2.0 m/s velocity, the response result for the structure was carried out to compare between having a fluid region and no fluid region. Fluid-structure interaction analysis was performed using the ALE method, which make it possible to apply a fluid region on the impact problem. The case of a fixed cylindrical type offshore structure without a seawater fluid part can be a more conservative design.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.5 no.2
• /
• pp.101-109
• /
• 1981

균일 인장하중하에 있는 고체 내부에 고립된 제 1형 탄소성 크랙의 반취성 파괴를 경사슬립밴드모델(inclined slip band model)로서 연속크랙전위(conticuum crack dislocation) 및 연속격자 전위(continum lattice dislocation)을 이용하여 이론적으로 연구하였다. 크랙전위 및 격자전위에 관한 힘평형을 나타애는 연립특이적분방정식의 해는크랙전위 및 격자전위에 관한 적정밀도함수를 가지고 특이함을 해소하는 조건을 부가하여 얻는다. 이특이항 해소조건의 타당성은 처음으로 소성영역의 크기를 그 판단기준으로 검토되었으며, 그결과 합당한 것으로 확인되었다. 또한 상기방법으로부터 산출된 COD는 소규모 성역을 넘어서도 선형적으로 .KAPPA.$^{2}$.EPSILON..sigma.$_{Y}$ 에 따라 변화함을 알게 된다. 상기모델에서 위축적분경로(Shrunk path) 상의 J 적분치를 J=.delta..sigma.$_{Y/}$sin2.theta.의 형태로 유도하였는데, 이것은 J 적분에 관한 Eshelby의 힘개념을 구체적으로 표현한다: J는 크랙전파방향으로 탄소성크랙정점에 작용하는 가상적인 힘이며, 1/2 J의 한 슬립편면상에서의 분력은 그 슬립정면사으이 보든 격자전위에 작용하는 전단력의 총화와 같다. 같다.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.18 no.4 s.70
• /
• pp.453-458
• /
• 2005

This study deals with elasto-plasticity of granular micro-structures which recovers continuum elasto-plasticity in its counterpart. The theory is based on doublet mechanics that assumes particles of finite size and connecting linear springs, and it makes extensions to plasticity. The result shows that the micro model has one to one relationship with the continuum model in the simplest case. Micro-strain and micro-stress of two dimensional plane stress problem were calculated, which shows the behavior of the specimen and verifies the effectiveness of this model.

• Journal of the Society of Naval Architects of Korea
• /
• v.40 no.3
• /
• pp.45-53
• /
• 2003

Ships and ocean structures are subjected to random loads caused by irregular waves. The irregularity of amplitude from random loading affects on fatigue crack growth and fatigue life. However the effects of irregularity of loading on fatigue including random loading have not been explained exactly. Therefore in this paper crack growth tests on DENT specimens under constant-amplitude loading including a single tensile overload are conducted to investigate the effect of overload on crack growth rate. The size of plastic zone and crack growth rate before and after a single tensile overloading are measured using ESPI system. Crack growth retardation model that is characterized by crack growth length and the size of plastic zone was proposed and compared with test result. From the research, the validity of proposed model is examined on crack growth retardation, and consequently fatigue life.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
• /
• 2002.10a
• /
• pp.73-78
• /
• 2002

Ships and ocean structures are generally under random loading. Various type of variable-amplitude loading affects fatigue crack growth and fatigue life. However interaction effects due to irregularity of loading including random loading have not explained exactly and it is difficult to examined fatigue crack growth behaviour and fatigue life for this reason. Therefore in this paper crack growth tests with constant-amplitude loading including a single overload were conducted to measure plastic zone size near crack tip of DENT specimen. And the observed plastic zone sized were discussed in terms of crack growth rate. As a result of this the effect the plastic rue size due to the overload is examined on the effect on crack growth rate and, consequently, fatigue life.