• 소성∙가공
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• 제14권6호
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• pp.541-546
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• 2005

Apparent mechanical properties in structural components can be different from the initially designed values due to the formation of the residual stress in metal forming and welding. Therefore, the evaluation of residual stress has great importance in the reliability diagnosis of structural components. A nondestructive continuous indentation technique has been proposed to evaluate various strength concerning mechanical properties from the analysis of load-depth curve. In this study, quantitative residual stress estimation on API X65 welded joints for natural gas pipeline was performed by analyzing the variation of indentation loading curve by residual stress through a new proposed theoretical model. The residual stress from the indentation method was compared with that from the saw-cutting method.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 춘계학술대회 논문집
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• pp.126-129
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• 2005

Apparent mechanical properties in structural components can be different from the initially designed values due to the formation of the residual stress in metal forming and welding. Therefore, the evaluation of residual stress has great importance in the reliability diagnosis of structural components. A nondestructive continuous indentation technique has been proposed to evaluate various strength concerning mechanical properties from the analysis of load-depth curve. In this study, quantitative residual stress estimation on API X65 welded joints for natural gas pipeline was performed by analyzing the variation of indentation loading curve by residual stress through a new proposed theoretical model. The residual stress from the indentation method was compared with that from the saw-cutting method.

• Earthquakes and Structures
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• 제25권1호
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• pp.15-26
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• 2023

It is of great importance to assess the residual displacement demand in the performance-based seismic design. In this paper, a hybrid deep learning model for predicting the residual displacement spectra under near-fault (NF) ground motions is proposed by combining the long short-term memory network (LSTM) and back-propagation (BP) network. The model is featured by its capacity of predicting the residual displacement spectrum under a given NF ground motion while considering the effects of structural parameters. To construct this model, 315 natural and artificial NF ground motions were employed to compute the residual displacement spectra through elastoplastic time history analysis considering different structural parameters. Based on the resulted dataset with a total of 9,450 samples, the proposed model was finally trained and tested. The results show that the proposed model has a satisfactory accuracy as well as a high efficiency in predicting residual displacement spectra under given NF ground motions while considering the impacts of structural parameters.

• Steel and Composite Structures
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• 제25권5호
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• pp.617-624
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• 2017

In this study, a new empirical method is presented to obtain Dynamic Increase Factor (DIF) in nonlinear static analysis of structures against sudden removal of a gravity load-bearing element. In this method, DIF is defined as a function of minimum ratio of difference between maximum moment capacity ($M_u$) and moment demand ($M_d$) to plastic moment capacity ($M_p$) under unamplified gravity loads of elements. This function determines the residual strength of a damaged building before amplified gravity loads. For each column removal location, a nonlinear dynamic analysis and a step-by-step nonlinear static analysis are carried out and the modified empirical DIF formulas are derived, which correspond to the ratio min $[(M_u-M_d)/M_p]$ of beams in the bays immediately adjacent to the removed column, and at all floors above it. Therefore, the new DIF can be used with nonlinear static analysis instead of nonlinear dynamic analysis to assess the progressive collapse potential of a moment frame structure. The proposed DIF formulas can estimate the real residual strength of a structure based on critical member.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2006년도 춘계학술대회 논문집
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• pp.579-580
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• 2006

In this study, an injection mold of tensile test specimen was manufactured by international standard. Pressure and temperature in the cavity of the injection mold was measured by sensors. Simulation of injection molding process was performed with the same condition of experiment and linear structural tensile analysis was also performed with the initial condition of the residual stress induced by injection molding analysis. Normalized elastic coefficient of tensile test was compared with that of structural analysis. It was shown that the residual stress induced by injection molding has an effect on both the experiment of tensile test and linear structural analysis.

• Journal of Welding and Joining
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• 제32권1호
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• pp.71-78
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• 2014

Although the fatigue design curve of ASME Code has enough margin with respect to alternating stress and cycles, the welding residual stress(WRS) should be included in fatigue analysis. In this paper, WRS distribution in a nozzle with dissimilar metal weldment was obtained by finite element analysis and was added in fatigue analysis. The fatigue analysis was performed by following the ASME Code including thermal and stress analysis applying with postulated 30 transient conditions. The calculated results of a cumulative fatigue usage factors(CUF) were compared for the case of the models with or without WRS effects. The results showed that the CUF at weldment and heat affected zone was affected by the WRS.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2001년도 춘계학술발표대회 논문집
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• pp.126-129
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• 2001

LIPCA (LIghtweight Piezo-composite Curved Actuator) is an actuator device which is lighter than other conventional piezoelectric ceramic type actuator. LIPCA is composed of a piezoelectric ceramic layer and fiber reinforced light composite layers, typically a PZT ceramic layer is sandwiched by a top fiber layer with low CTE (coefficient of thermal expansion) and base layers with high CTE. LIPCA has curved shape like a typical THUNDER (thin-layer composite unimorph feroelectric driver and sensor), but it is lighter an than THUNDER. Since the curved shape of LIPCA is from the thermal deformation during the manufacturing process of unsymmetrically laminated lay-up structure, an analysis for the thermal deformation and residual stresses induced during the manufacturing process is very important for an optimal design to increase the performance of LIPCA. To investigate the thermal deformation behavior and the induced residual stresses of LIPCA at room temperature, the curvatures of LIPCA were measured and compared with those predicted from the analysis using the classical lamination theory. A methodology is being studied to find an optimal stacking sequence and geometry of LIPCA to have larger specific actuating displacement and higher force. The residual stresses induced during the cooling process of the piezo-composite actuators have been calculated. A lay-up geometry for the PZT ceramic layer to have compression stress in the geometrical principal direction has been designed.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.218-223
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• 2000

The shot peening is largely used for a surface treatment in which small spherical parts called shots are blasted on a surface of a metallic components with velocities up to 100m/s. This treatment leads to an improvement of fatigue behavior due to the developed compressive residual stresses, and so it has gained widespread acceptance in the automobile and aerospace industries. The residual stress profile on surface layer depends on the parameters of shot peening, which are, shot velocity, shot diameter, coverage, impact angle, material properties etc. and the method to confirm this profile is only measurement by X-ray diffractometer. Despite its importance to automobile and aerospace industries, little attention has been devoted to the accurate modelling of the process. In this paper, the simulation technique is applied to predict the magnitude and distribution of the residual stress and plastic deformation caused by shot peening with the help of the finite element analysis.

• 한국지진공학회논문집
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• 제12권6호
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• pp.35-45
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• 2008

구조물의 응답에 대한 잔류변위의 영향을 평가하기 위하여, 초기 잔류변형이 있는 상태에서 작용하는 설계지진에 대한 좌굴방지 가새골조(BRBF)와 특수 모멘트골조(SMRF)의 응답을 평가하였다. 초기 잔류변형은 구조물에 두 가지 방법으로 적용하였다. 첫 번째 방법은 첫 지진에 대하여 구조물이 정지 상태에 도달한 이후 같은 크기의 지진을 적용하는 것이다. 두 번째 방법은 소요 잔류층간 변형이 발생할 때까지 일방향으로 가력한 다음 지진하중을 적용하였다. 해석결과에 따르면 초기 잔류층간변위는 BRBF와 SMRF의 응답에 큰 영향을 주었다. SMRF 시스템보다 BRBF의 응답이 초기 잔류변형에 크게 의존하였다. 그러므로 지진발생 이후 보수비용을 최소화하기 위하여 잔류층간변위를 줄이는 것이 필요하다.

• 한국항공우주학회지
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• 제43권12호
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• pp.1116-1123
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• 2015

정지궤도위성의 수명은 추진제 잔여량에 좌우되고 정확한 잔여추진제량 측정은 조기 수명종료로 야기되는 경제적 손실을 완화시킬 뿐만 아니라 후속위성의 대체나 위성망 운용계획 등에 매우 중요하다. 본 논문에서는 열질량법과 그 불확실성 추정방법에 대한 기본이론에 대해 소개한다. 열질량법 잔여추진제 분석은 무궁화위성 데이터를 기초로 분석하였고 이러한 열질량법 불확실성 분석은 몬테카를로 방법을 사용하여 수행하였다. 이러한 연구 결과를 통해 열질량법을 사용한 잔여추진제 추정의 중요 파라미터를 알 수 있다.