Equivalent Flaw Size Research Articles

Sizing Small Crack-like Flaws through Non-ideal Part Surface Using Ultrasonic Measurement Model

ABSTRACTTo accurately size small crack-like flaws in components with non-ideal surface conditions, such as curvature, roughness, and coating, we developed a flaw sizing method based on an ultrasonic measurement model. First, the effects of surface curvature on the sound beam profile, as well as the effects of surface coating and roughness on the wave energy are investigated theoretically and experimentally. Then, correction methods for curvature, roughness, and coating are introduced into the ultrasonic measurement model, and the flaw response in components with different surface conditions is predicted. Lastly, by accounting for the effects of surface conditions, a set of model-based flaw sizing curves is generated for predicting the equivalent size of crack-like flaws. These model-based curves can guide the setting of system parameters and improve the flaw sizing accuracy. Experiments are then conducted to verify the effectiveness of the proposed method. This work demonstrates the utility of the ultrasonic method for measuring the equivalent flaw size in practical applications.

Corrosion modified fatigue analysis for next-generation damage-tolerant management

Abstract Although a great deal of success in structural integrity management has been achieved, it may be realized by excessively conservative assumptions, high inspection burdens, and aggressive maintenance and repair strategies. Corrosion has been found to reduce fatigue life, but methods to account for it in fatigue modeling are still limited. There is a recognized need to improve structural integrity calculations through the inclusion of the effect of existing corrosion damage on fatigue. The feasibility of a corrosion modified fatigue analysis process that uses finite element analysis and linear elastic fracture mechanics techniques to predict fatigue life of a corroded aircraft component based on the corrosion damage location is demonstrated in this work. A corrosion modified equivalent flaw size was successfully used to predict fatigue crack growth from AA7075-T651 specimens with two different notch geometries and corrosion damage at the notch center.

Stress intensity factors for surface flaws in toughened glasses

An approximate method of deriving stress intensity factors as a function of angle for semicircular surface flaws is outlined. The method can be applied to a wide range of load distributions including non‐polynomial distributions. The method is used to calculate stress intensity factors for thermally and chemically tempered glasses. The stress intensity factor equations developed are also used to calculate equivalent flaw sizes for some toughened glasses subjected to bending loads.

NEW APPROACHES TO ULTRASONIC EQUIVALENT SIZING FOR SMALL FLAWS

Ultrasonic equivalent flaw sizing methods size defects in a material by obtaining a best-lit simple defect shape (such as an ellipsoid or ellipse) from relatively small amounts of ultrasonic data. In these equivalent flaw sizing methods, it is essential that the origin of time be determined precisely with respect lo a fixed spatial location. Current methods for this determination are not entirely adequate, leading to an important “ zero-of-lime” problem In this work, two new approaches to equivalent flaw sizing for relatively small flaws are developed: (1) an amplitude-based equivalent (ABE) sizing method for obtaining best-lit equivalent flaws by the use of amplitude ratios measured at different transducer orientations, and (2) a first moment (FM) method for estimating the equivalent radius from a first moment calculation of the lime domain flaw response. We show how these approaches can address the zero-of-lime problem and demonstrate the performance of these methods with experiments

New approaches to model-based ultrasonic flaw sizing

Ultrasonic equivalent flaw sizing methods have been recently used to size a flaw in a material by obtaining a best-fit simple equivalent shape that matches the ultrasonic scattering data. However, current ultrasonic equivalent flaw sizing methods have a number of important limitations: (1) they are both iterative and highly nonlinear in nature, and (2) they require the availability of flaw classification information. Here, a series of approaches are outlined that address both of the above problems. Both numerical and experimental results that validate these new approaches are also given. First, when the flaw shape is determined in terms of a best-fit equivalent ellipsoid, a new linear least-squares/eigenvalue method is described that can replace existing nonliner routines and provide a computationally fast and robust sizing procedure. Second, it is shown that if the shape is determined instead in terms of an expansion in spherical harmonics, the sizing problem again reduces to a simpler linear least-squares/differentiation process. Third, a way to do equivalent flaw sizing even when flaw classification information is not present is demonstrated. When such classification information is available, however, one can see how it can be used to improve sizing estimates for cracks, by the elimination of systematic measurement errors due to finite transducer bandwidth effects.

An ultrasonic time-of-flight equivalent flaw sizing method

One of the challenging tasks in the field of ultrasonic NDE is to obtain quantitative flaw size, shape, and orientation information. In an equivalent flaw sizing approach, flaws in a material are reconstructed in terms of a best-fit simple shape such as an ellipsoid or ellipse. In this work, a new time-of-flight equivalent (TOFE) flaw sizing method is developed for obtaining best-fit equivalent flaws from a relatively small number of timing measurements at different transducer orientations. The performance of the method is demonstrated on synthetic numerical data and with experiments, including examples of sizing in anisotropic composite materials and in welds.

An Ultrasonic Time-of-Flight Equivalent Flaw Sizing Method

Abstract One of the challenging tasks in the field of ultrasonic NDE is to obtain quantitative flaw size, shape, and orientation information. In an equivalent flaw sizing approach, flaws in a material are reconstructed in terms of a best-fit simple shape such as an ellipsoid or ellipse. In this work, a new time-of-flight equivalent (TOFE) flaw sizing method is developed for obtaining best-fit equivalent flaws from a relatively small number of timing measurements at different transducer orientations. The performance of the method is demonstrated on synthetic numerical data and with experiments, including examples of sizing in anisotropic composite materials and in welds.

Liquid impact on toughened glasses

Stresses induced by thermal or chemical means are commonly used to toughen glass. This is known to result in large increases in the quasi-static strengths of the glass. The impact performance of such materials has, however, received less study. In this paper the performance of a thermally toughened and two chemically toughened glasses under liquid impact are studied. The results are compared to data obtained on annealed soda-lime glass. The increase in damage threshold is not as great as the increase in quasi-static strength would suggest. In addition, the behaviour of these materials under multiple impact is different from that seen in non-toughened materials. These features are discussed in terms of a crack extension model. A computer simulation based on the interaction of Rayleigh waves and toughening stresses with an idealised flaw distribution supports this model. Finally the concept of equivalent flaw size is applied to these materials and this lends further backing to the crack extension model used to describe the liquid impact results.

A unified constrained inversion model for ultrasonic flaw sizing

Equivalent flaw sizing using ultrasonic waves is an approach whereby shape and orientation information of a defect are obtained in terms of a best-fit simple geometry that is able to represent the major aspects of the flaw. Separate examples of this approach have previously been developed for volumetric flaws and cracks using the Born and Kirchhoff approximations, respectively. Here, these separate algorithms are unified into a single algorithm capable of sizing both volumetric flaws and cracks. Some examples of the performance of this unified algorithm on both synthetic and experimental data are also given.

Mechanical Reliability of Z5u Multilayer Capacitors

AbstractDynamic fatigue experiments were performed on Z5U multilayer capacitors in an attempt to correlate microflaw fracture behavior due to intrinsic processing defects within the material with predictions of fracture behavior based on macrocrack fracture mechanics determinations. A direct correlation between microflaw fracture behavior and predictions based upon macrocrack fracture mechanics techniques was not observable due to the wide size range of processing defects. A systematic post-mortem examination of fracture surfaces was used to identify fracture origins and sort individual test specimens into groups with equivalent flaw sizes. The correlation between microflaw and macrocrack fracture behavior became more “sorting” the dynamic fatigue data into groups withm oereq uoibvvailoeunst aflfatwer sizes.

An improved strength-measurement technique for brittle materials

An improved apparatus for determining the fracture strength of brittle materials by a hydraulic bursting technique is described. The new design greatly reduces the number of specimens which fail at their edge and reduces the scatter in the results. To complement this, a more detailed theory is developed to analyse results. An investigation of the strength of silicon nitride as a function of the impact velocity of a water jet illustrates the use of the apparatus. A method for converting fracture stress data to equivalent flaw size data is given which allows a more physically meaningful and useful presentation of results.