Papers by Keyword: Flaw

Abstract: Power transmission towers are major equipment of State Grid,the safety of the tower foundation is very important to the power system,nondestructive testing to foundations is necessary when excavation is impossible.In this paper, the dynamic response analysis of the impact-echo method for power transmission tower foundation with flaws is solved based on finite element method; the result of numerical analysis is consistent with the depth of the setting flaw, which shows the feasibility of detecting flaws in transmission tower foundations with the impact-echo method.

Abstract: This paper adopts the program Ansys and its secondary exploit platform tools to construct three-dimensional model to simulate the destroy process of cave depot. The method that damage surface and yield surface are dealt separately, and dispersion model is forward to simulate flaws. And the results of numerical simulation have been debated to find the laws of flaws growth and distribution with increasing of explosion pressure. It can be found that with the the linear increase of explosion pressure, flaws and distribution regions of flaws grow and expand. Tension flaws are precede to shear flaws. Flaws regions appear in the order , namely, the center of the arch--arch foot-- flaws in the center arch propagation - flaws in other else regions propagation. The research result has important value for online monitor, maintain and reinforce of cave depot. And the technology that has been forwarded in this paper also supplies for the numerical simulation researcher.

Abstract: Sizing of material flaw is addressed in the multipath scene, and a method is developed to detect an isolated sized flaw and estimate its height based on imaging theory of different path profiles. A signal model based on the multipath higher order reflections of the flaw is built to detect the sized flaw. Multipaths are predicted and identified on the basis of the direct reflection path, which is relatively easy to be identified using the conventional flaw detection techniques. Direct reflection path and combined path are applied to detect the flaw from the top, and multipath w is to detect its bottom of the flaw. Ultrasonic imaging is formed and synthesized by all the identified multipaths, which shows the size of the material flaw. Simulations and experimentations demonstrate that the flaw sizing can be calculated utilizing the time-of-arrivals of the multipath signals.

Abstract: Based on the magnetic theory, the paper reviewed the factors of affecting the distribution of magnetic flux leakage (MFL) on the ferromagnetic material and analyzed the wire rope defects characters from MFL signal. A non-destructive testing (NDT) instrument of steel wire rope using magnetic flux leakage was presented in this paper. By using permanent magnets to magnetize wire rope and using Hall element arrays to test MFL, Intelligent signal processing was applied for effective discrimination of wire rope’s flaws. The experiment results show the degree and the width of defects, the annular distribution of localized flaws such as concentrated or dispersive broken wires can be well distinguished. The instrument can be used conveniently with good resolution and repeatability and can meet the requirement of real time.

Abstract: A widely used organic polymer textile material, which is made of polyester fibers and then cured in the resin afterwards to fix the original pattern of the textile, is used to study the flaw’s influence in the mechanical properties as well as its influence in the failure behavior of the textile. This kind of textile is preferably applied and acts as the re-enforcement part or component in the composite design or composite manufacturing. To mathematically and theoretically analyze the relationship between the mechanical behavior of the polyester textile and the flaw within the material, a model based on the fracture mechanics is proposed to explain the experimental results from the mechanical tests of polyester textile specimens.

Abstract: Ultrasonic signature of flaw is studied in the multipath scene, and a method is developed to localize the flaw by only single mono/bi-static measurement. A signal model based on the concept of multipath is built to construct flaw position, of which multipath scenarios are reviewed for signature of flaw depth. Multipath scenarios may be identified by direct path, which is relatively easy to be detected. Algebraic solution is proposed to solve the multipath equations to obtain the position of the flaw depth. Experiments show that the solution of the flaw depth is valid.

Abstract: The effect of the heat treatment on the fracture toughness and flexural strength of the silicon carbide – silicon nitride composites prepared by liquid-phase-sintering was investigated. The results were compared to those obtained for a reference silicon carbide material, prepared by the same fabrication route. The fracture toughness increased from 3.19 to 5.15 MPa.m1/2 due to the toughening mechanisms (crack deflection, mechanical interlocking, crack branching) occurring in the heat treated materials during the crack propagation. However, the flexural strength decreased after the heat treatment of the experimental materials. The strength of the investigated materials was degraded by the presence of processing flaws mainly in the form of pores, clusters of pores, and SiC agglomerates.

Abstract: The theta test specimen is a versatile tool for evaluating the strength of extremely small structures. Round and hexagonal rings are compressed vertically on their ends creating a uniform tension stress in the middle gauge section. The simple compression loading scheme eliminates the need for special grips. A conventional nanoindentation hardness machine with a flat indenter applied load, monitored displacement, and recorded fracture loads. Prototype miniature specimens with web sections as thin as 7.5 m were fabricated by deep reactive ion etching (DRIE) of single crystal silicon wafers. The strength limiting flaws were 200 nm to 500 nm deep surface etch pits.

Abstract: Evidence regarding a fracture event is absolutely and definitively recorded by Nature during the fracture process. That record is in the form of the general macrocrack pattern and the surface topological features of the newly formed fracture surface. In reality, it is the only perfect record of what actually occurred during a fracture. Whenever a conflict or controversy arises regarding a fracture, it is the moral and scientific responsibility of the fractographer to analyze and interpret the record of the fracture as it was created by Nature. It is further necessary for the fractographer to then inform and educate the members of the legal community (lawyer, judge and jury) as to exactly what happened during the failure. This educational process is necessary so that the legal community can collectively understand the history of the fracture and arrive at a just and fair decision regarding responsibility and potential liability for the failure. This paper describes the overall process from the beginning of the fracture examination of the failed artifact to the final appearance in court leading to a decision by the judge or a jury. Both the technical and the human factors are addressed with varying degrees of detail.

Abstract: In this paper, Lifted Wavelet Transform (LWT) and BP neural network are used for automatic flaw classification of pipeline girth welds. LWT is proposed to extract flaw feature from ultrasonic echo signals, ideally matched local characteristics of original signal and increasing the computational speed and flaw classification efficiency. After extracting features of all flaw echoes, a feature library is constructed. A modified BP neural network is followed as a classifier, trained by the library. When feature of any flaw echo is extracted and sent to BP network, flaw type is the output, realizing automatic flaw classification. Experiment results prove the proposed method, LWT with BP neural network, is more fit for automatic flaw classification than traditional methods.