• Title, Summary, Keyword: Damage matrix

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An efficient method for structural damage localization based on the concepts of flexibility matrix and strain energy of a structure

  • Nobahari, Mehdi;Seyedpoor, Seyed Mohammad
    • Structural Engineering and Mechanics
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    • v.46 no.2
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    • pp.231-244
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    • 2013
  • An efficient method is proposed here to identify multiple damage cases in structural systems using the concepts of flexibility matrix and strain energy of a structure. The flexibility matrix of the structure is accurately estimated from the first few mode shapes and natural frequencies. Then, the change of strain energy of a structural element, due to damage, evaluated by the columnar coefficients of the flexibility matrix is used to construct a damage indicator. This new indicator is named here as flexibility strain energy based index (FSEBI). In order to assess the performance of the proposed method for structural damage detection, two benchmark structures having a number of damage scenarios are considered. Numerical results demonstrate that the method can accurately locate the structural damage induced. It is also revealed that the magnitudes of the FSEBI depend on the damage severity.

Damage assessment in periodic structures from measured natural frequencies by a sensitivity and transfer matrix-based method

  • Zhu, Hongping;Li, Lin;Wang, Dansheng
    • Structural Engineering and Mechanics
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    • v.16 no.1
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    • pp.17-34
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    • 2003
  • This paper presents a damage assessment procedure applied to periodic spring mass systems using an eigenvalue sensitivity-based method. The damage is directly related to the stiffness reduction of the damage element. The natural frequencies of periodic structures with one single disorder are found by adopting the transfer matrix approach, consequently, the first order approximation of the natural frequencies with respect to the disordered stiffness in different elements is used to form the sensitivity matrix. The analysis shows that the sensitivity of natural frequencies to damage in different locations depends only on the mode number and the location of damage. The stiffness changes due to damage can be identified by solving a set of underdetermined equations based on the sensitivity matrix. The issues associated with many possible damage locations in large structural systems are addressed, and a means of improving the computational efficiency of damage detection while maintaining the accuracy for large periodic structures with limited available measured natural frequencies, is also introduced in this paper. The incomplete measurements and the effect of random error in terms of measurement noise in the natural frequencies are considered. Numerical results of a periodic spring-mass system of 20 degrees of freedom illustrate that the proposed method is simple and robust in locating single or multiple damages in a large periodic structure with a high computational efficiency.

Monitoring Failure Behaviour of Pultruded CFRP Composites by Electrical Resistance Measurement

  • Mao, Yaqin;Yu, Yunhua;Wu, Dezhen;Yang, Xiaoping
    • Carbon letters
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    • v.5 no.1
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    • pp.18-22
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    • 2004
  • The failure behaviours of unidirectional pultruded carbon fiber reinforced polymer (CFRP) composites were monitored by the electrical resistance measurement during tensile loading, three-point-bending, interlaminar shear loading. The tensile failure behaviour of carbon fiber tows was also investigated by the electrical resistance measurement. Infrared thermography non-destructive evaluation was performed in real time during tensile test of CFRP composites to validate the change of microdamage in the materials. Experiment results demonstrated that the CFRP composites and carbon fiber tows were damaged by different damage mechinsms during tensile loading, for the CFRP composites, mainly being in the forms of matrix damage and the debonding between matrix and fibers, while for the carbon fiber tows, mainly being in the forms of fiber fracture. The correlation between the infrared thermographs and the change in the electrical resistance could be regarded as an evidence of the damage mechanisms of the CFRP composites. During three-point-bending loading, the main damage forms were the simultaneity fracture of matrix and fibers firstly, then matrix cracking and the debonding between matrix and fiber were carried out. This results can be shown in Fig. 9(a) and (b). During interlaminar shear loading, the change in the electrical resistance was related to the damage degree of interlaminar structure. Electrical resistance measurement was more sensitive to the damage behaviour of the CFRP composites than the stress/time curve.

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Evaluation of Thermal Shock Damage of Metal Matrix Composite Using Ultasonics (초음파를 이용한 금속기지 복합재료의 열충격 손상 평가)

  • Kang, Moon-Phil;Lee, Min-Rae;Lee, Joon-Hyun
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.29 no.11
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    • pp.1480-1487
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    • 2005
  • Metal matrix composites(MMCs) have been rapidly becoming one of the strongest candidates for structural materials fur many high temperature application. However, among the various high temperature environments in which metal matrix composites was applied, thermal shock is known to cause significant degradation in most MMC system. Due to the appreciable difference in coefficient of thermal expansion(CTE) between reinforcement and metal matrix, internal stresses are generated following temperature changes. Infernal stresses affect degradation of mechanical properties of MMC by causing microscopic damage in interface and matrix during thermal cycling. Therefore, the nondestructive evaluation on thermal shock damage behavior of SiC/A16061 composite has been carried out using ultrasonics. For this study, SiC fiber reinforced metal matrix composite specimens fabricated by a squeeze casting technique were thermally cycled in the temperature range 298$\~$673 K up to 1000cyc1es. Three point bending test was conducted to investigate the efffct of thermal shock damage on mechanical properties. The relationship between thermal shock damage behavior and the propagation characteristics of surface wave and SH-ultrasonic wave was discussed by considering the result of SEM observation of fracture surface.

Prediction of the Damage in the Structure with Damping Using the Modified Dynamic Characteristics (동특성 변화를 이용한 감쇠 구조물의 손상예측)

  • Lee, Jung Youn
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.22 no.11
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    • pp.1144-1151
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    • 2012
  • A damage in structure alters its dynamic characteristics. The change is characterized by changes in the modal parameter, i.e., modal frequencies, modal damping value and mode shape associated with each modal frequency. Changes also occur in some of the structural parameters; namely, the mass, damping, stiffness matrices of the structure. In this paper, evaluation of changes in stiffness matrix of a structure is presented as a method not only for identifying the presence of the damage but also locating the damage. It is shown that changed stiffness matrix can be accurately estimated a sensitivity coefficient matrix derived from modifying mode shapes, First, with 4 story shear structure models, the effect of presence of damage in a structure on its stiffness matrix is studied. By using these analytical model, the effectiveness of using change of stiffness matrix in detecting and locating damages is demonstrated. To validate the predicted changing stiffness and its location, the obtained results are compared to the reanalysis result which shows good agreement.

Optimized finite element model updating method for damage detection using limited sensor information

  • Cheng, L.;Xie, H.C.;Spencer, B.F. Jr.;Giles, R.K.
    • Smart Structures and Systems
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    • v.5 no.6
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    • pp.681-697
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    • 2009
  • Limited, noisy data in vibration testing is a hindrance to the development of structural damage detection. This paper presents a method for optimizing sensor placement and performing damage detection using finite element model updating. Sensitivity analysis of the modal flexibility matrix determines the optimal sensor locations for collecting information on structural damage. The optimal sensor locations require the instrumentation of only a limited number of degrees of freedom. Using noisy modal data from only these limited sensor locations, a method based on model updating and changes in the flexibility matrix successfully determines the location and severity of the imposed damage in numerical simulations. In addition, a steel cantilever beam experiment performed in the laboratory that considered the effects of model error and noise tested the validity of the method. The results show that the proposed approach effectively and robustly detects structural damage using limited, optimal sensor information.

Optimal sensor placement for bridge damage detection using deflection influence line

  • Liu, Chengyin;Teng, Jun;Peng, Zhen
    • Smart Structures and Systems
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    • v.25 no.2
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    • pp.169-181
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    • 2020
  • Sensor placement is a crucial aspect of bridge health monitoring (BHM) dedicated to accurately estimate and locate structural damages. In addressing this goal, a sensor placement framework based on the deflection influence line (DIL) analysis is here proposed, for the optimal design of damage detection-oriented BHM system. In order to improve damage detection accuracy, we explore the change of global stiffness matrix, damage coefficient matrix and DIL vector caused by structural damage, and thus develop a novel sensor placement framework based on the Fisher information matrix. Our approach seeks to determine the contribution of each sensing node to damage detection, and adopts a distance correction coefficient to eliminate the information redundancy among sensors. The proposed damage detection-oriented optimal sensor placement (OSP) method is verified by two examples: (1) a numerically simulated three-span continuous beam, and (2) the Pinghu bridge which has existing real damage conditions. These two examples verify the performance of the distance corrected damage sensitivity of influence line (DSIL) method in significantly higher contribution to damage detection and lower information redundancy, and demonstrate the proposed OSP framework can be potentially employed in BHM practices.

Analysis of Fatigue Damage at Wheel under Variable Load (불규칙 하중을 받는 휠에서의 피로 파손 해석)

  • Cho, Jae-Ung;Han, Moon-Sik
    • Journal of The Korean Society of Manufacturing Technology Engineers
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    • v.19 no.6
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    • pp.753-759
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    • 2010
  • The variable fatigue load is simulated in this study. The stability and the life of the material are analyzed theoretically by Ansys program. These results are successfully applied to the practical wheel to predict the prevention of fracture and the endurance. The life and the damage on the every part of the fatigue specimen can be predicted. As the available lives are compared for every loading variation, the rain flow and damage matrix results can be helpful in determining the effects of small stress cycles in any loading history. The rainbow and damage matrices illustrate the possible effects of infinite life. The safety and stability of wheel and the other practical structures according to the variable load can be estimated by using the results of this study.

The Analysis of Fatigue Damage in Structure under Variable Load (변동 하중을 받는 구조물에서의 피로 파손 해석)

  • 한문식;조재웅
    • Transactions of the Korean Society of Automotive Engineers
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    • v.12 no.4
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    • pp.85-93
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    • 2004
  • The variable fatigue load is simulated in this study, The stability and the life of the material are analyzed theoretically by the program of Ansys workbench. These results are successfully applied to the practical structures to predict the prevention of fracture and the endurance, The life and the damage on the every part of the fatigue specimen can be predicted. As the available lives are compared for every loading variation, the rainflow and damage matrix results can be helpful in determining the effects of small stress cycles in any loading history. The rainflow and damage matrices illustrate the possible effects of infinite life. The safety and stability of fatigue specimen according to the variable load can be estimated by using the results of this study.

A Study on Evaluation of Thermal Shock Damage of Metal Matrix Composite using Ultrasonics (초음파를 이용한 금속복합재료의 열충격 손상 평가 연구)

  • 강문필;이준현
    • Proceedings of the Korean Society For Composite Materials Conference
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    • pp.31-37
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    • 2000
  • Metal matrix composites(MMCs) are rapidly becoming one of the strongest candidates for structural materials for many high temperature application. Among the high temperature environment, thermal shock is known to cause significant degradation in most MMC system. Therefore, the nondestructive evaluation on thermal shock damage behavior of SiC/A16061 composite has been carried out using ultrasonic surface and SH-waves. For this study, Sic fiber reinforced metal matrix composite specimens fabricated by a squeeze casting technique were thermally cycled in the temperature range 25~$400^{\circ}C$ up to 1000 cycles. Three point bend test was conducted to investigate the effect of thermal shock damage on mechanical properties. The relationship between thermal shock damage behavior and the change of ultrasonic velocity and attenuation were discussed by considering SEM observation of fracture surface.

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