Papers by Author: Dan Sheng Wang

Abstract: Nondestructive detection evaluation technique which based on the electro-mechanical impedance (EMI) method is widely used for structure health monitoring (SHM). The arrangement of piezoelectric transducer (PZT) includes two types, surface-mounted and embedded. A lot of researches have been done about two kind of transducer based on EMI method, however the effect of two types on the same damage condition requires to be researched deeply. Therefore, the objective of this investigation is comparing the effect of two kind types of PZT in detecting local damage of concrete beam end. An experiment was set up to detect local damage of the beam by EMI method with both embedded and surface-mounted PZT. The experiment result shows that EMI method is available to detect local damage of concrete beam end. The surface-mounted PZT is more sensitive to local damage of concrete beam end, meanwhile surface-mounted PZT is more vulnerable to the environment and other factors.

Abstract: The corrosion of the steel structure not only causes the economic losses, but also poses a threat to the safety of the structure. The steel structure corrosion form is divided into uniform corrosion and local corrosion. Lead zirconate titanate (PZT) as a smart material was widely used in structural health monitoring (SHM) in recent years. For local corrosion damage in the form, a steel beam local corrosion monitoring experiments based on Electro-Mechanical Impedance (EMI) technique was designed. Marine environment was simulated and the steel beam local corrosion condition was designed firstly. Then the surface-mounted PZT transducer was used on the structure for long-term monitoring. The development process of corrosion and the admittance change was researched. The result shows that EMI technique is available to the beam local corrosion monitoring by analyzing the change rule of admittance signal and resonant frequency deviation ratio index with the steel beam corrosion.

Abstract: In recent two decades, the issues on structural damage detection and health monitoring have been paid considerable attention in mechanical and civil engineering communities. A lot of researchers have developed many methods to try to resolve the problems. To this day, detection of the small damage of structures, however, has still been a difficulty. The correlation theories of proper orthogonal decomposition (POD) and the basic principle of a new structural damage detection method based on the slope of POD are introduced in this paper. Numerical study on beam structures for small damage detection based on the proposed method is implemented. From the study results one can find that the method based on the slope of the difference of proper orthogonal modes (POMs) has the abilities to localize the small damage of beam structures.

Abstract: In this paper, a new time-domain method for detecting structural local damage has been developed, which is based on the measured strain signals. The “pseudo strain energy density (PSED)” is defined and used to build two major damage indexes, the “average pseudo strain energy density” (APSED) and the “average pseudo strain energy density changing rate” (APSEDR). A probability and mathematical statistics technique is utilized to derive a standardized damage index. Afterwards, these indexes are used to establish the damage identification strategies for beam structures and plate structures respectively. Furthermore, the wavelet packet transform is used to pre-process the measured dynamic strain signals. Then, the effectivity of the new damage identification method is confirmed by numerical simulations. Finally, a laboratory beam model experiment is conducted to verify this method examine the feasibility and applicability of the new method.

Abstract: Structural crack identification has been received considerable attention in recent decade. A lot of different techniques like acoustic emission, ultrasonic, or X-ray, etc have been used for structural crack detection. However, it is still difficult to identify the small crack in structures. A new method for identification of small crack in beam structures using the first anti-resonant frequency curve is proposed in this paper. The method makes use of the driving-point mechanical impedance characteristics of beam structures and a simplified rotational spring model to model the edge crack of beam. After the first anti-resonant frequency curve is obtained, signal process based on wavelet transformation will be carried out and the small crack in beam structures can be explored. The proposed method is validated by a numerical example of cracked beam with pinned-pinned or fixed-free boundary. It is concluded that not only the location of beam crack can be determined, but also the extent of crack damage can be identified qualitatively based on the first anti-resonant frequency curve and wavelet analysis.

Abstract: Crack damage brings a serious threat to the safety of mechanical and civil structures, and the problem of incipient damage identification of structures has been paying attention as a puzzle by many researchers in recent years. To seek for an alternative solution of the problem, a method for incipient crack localization using the slope of the anti-resonance curve is proposed in this paper. The method makes use of the driving-point mechanical impedance characteristics of cracked beams stimulated by harmonic force. To characterize the local discontinuity due to the presence of crack, a simplified rotational spring model is presented to model the crack. Subsequently, the proposed method is verified by a numerical example of cracked beam under simple support or cantilever boundary conditions.

Abstract: Cracks bring a serious threat to safety of structures. Most of the failures and fractures of engineering structures are due to initial cracks or fatigue cracks of materials. So it is very important to analyze the vibration characteristics and to identify the damage of cracked structures. A method for multi-crack identification based on wave propagation is proposed in this paper, which makes use of the driving-point mechanical impedance characteristics of the cracked beams stimulated by harmonic force. The proposed identification method is used to characterize the local discontinuity due to cracks, and a simplified rotational spring model is introduced to model cracks. Subsequently, the proposed method is verified by a numerical example of a simply supported steel beam with three cracks. The effect of crack depth on driving-point impedance is investigated. Combined with the first anti-resonances information, the proposed method can identify the presence of cracks, localize the multiple cracks, and qualitatively identify the extent of the crack damages.