Small Flaws Research Articles

Elizabeth Clarke Politics, Religion and the Song of Songs in Seventeenth-Century EnglandPolitics, Religion and the Song of Songs in Seventeenth-Century England. Elizabeth Clarke. Basingstoke: Palgrave Macmillan, 2011. Pp. v+265.

<i>Elizabeth Clarke</i> Politics, Religion and the Song of Songs in Seventeenth-Century England<i>Politics, Religion and the Song of Songs in Seventeenth-Century England</i>. Elizabeth Clarke. Basingstoke: Palgrave Macmillan, 2011. Pp. v+265.

An integrated TTCN-3 test framework architecture for interconnected object-based internet applications

The internet is being transformed by rich interconnected object–based applications that support session–based interactions between users and applications over a variety of protocols (HTTP/s, SOAP, SIP). In this paper, we analyse and demonstrate the key benefits and advantages of TTCN–3, especially in terms of costs, as a test language and framework for testing internet applications. The integration of TTCN–3 and object–based unit test frameworks can provide superior testing of interconnected object–based internet applications but is currently limited by a small flaw in the TTCN–3 concrete layer architecture. We propose a refinement to the TTCN–3 standard which enables seamless integration with object–based unit test–frameworks. An existing TTCN–3 vendor has already incorporated the changes in the latest version of their tool and ETSI has established a committee to modify the TTCN–3 standard accordingly. We demonstrate the benefits with a series of examples involving both SIP and HTTP–based internet applications.

Modeling dynamic brittle behavior of materials with circular flaws or pores

Compressive failure of brittle materials is driven primarily by crack growth from pre-existing flaws in the material. These flaws, such as grain boundaries, pores, preexisting cracks, inclusions and missing grains, are randomly spaced and have a range of possible shapes and sizes. The current work proposes a micromechanics-based model for compressive dynamic failure of brittle materials with circular pore flaws, which incorporates both the number density and the size distribution of flaws. Results show that the distribution of flaw sizes is very important, particularly at moderate strain rate, since analyses based solely on the mean flaw size overpredict strength. Therefore, in order to increase dynamic strength at low to moderate strain rates, it is most effective to control the presence of large flaws. At very high strain rates, however, crack growth is activated even in small flaws and therefore controlling the total number density rather than the size of the flaws is effective for increasing dynamic strength. Finally, the model shows that neglecting very small flaws in the pore population may not have significant effects on the results in many cases, suggesting that the model is a useful tool for identifying a minimum resolution required for experimental characterization of microstructure.

Unanticipated Large-Diameter Pipe Rupture Accidents in the RBMK-1000 Circulation Loop with Reactor Emergency Cooling System Failure

The results of calculations of large-diameter pipe rupture accidents in the RBMK circulation loop (pressure header of the main circulation pump, down pipe of the steam drum, and distribution group header) with failure of the reactor emergency cooling system are presented. The main computational problem is to evaluate the onset time of fuel-element cladding depressurization in the damaged half of the core and the integrity of the channel tubes. It is shown that for rupture of the pressure header fuel-element cladding depressurization starts at the 10th minute after the initial event and depressurization of the down-pipe near the steam drum and distribution group header start at the 17th and 40th minutes, respectively. The possible rupture of the channel tubes can have the form of only individual small flaws, for which the structural integrity of the reactor space is preserved. The calculations were performed with the RELAP5/mod3.2 computer code adapted for RBMK.

Structural Integrity of a Shaft Subjected to Multiaxial Fatigue Loads in Presence of Short Crack

The behavior of short cracks, focusing on the study of small manufacturing flaws in a critical structure working under a high frequency load spectrum, is a complex and very current topic and its investigated in this study. The modeling and predicting of the effect of these flaws is a matter of interest also for industrial manufacturers with regards to the future design of high stressed components. Aeronautical components in general, but particularly helicopter components, are subjected to a high number of fatigue cycles that potentially cause the propagation of very small flaws and thus require careful analysis. The application of multi-axial loading conditions such as axial and torsional load complicate the assessment by provoking a multimode propagation. A high cycle multi-axial fatigue loading condition (torsional and axial) on a tube that is representative of a helicopter main transmission shaft has thus been investigated in this work. The presence of a small flaw has been artificially created on the surface of the tube and the behavior of the defect in terms of the threshold of the propagation of a crack emanating from it under high cycles fatigue due to axial and torsional stresses has been investigated by means of analytical and FE models. Experimental test have also been carried out to validate the results of the simulations.

Predicting flaw-induced resonance spectrum shift with theoretical perturbation analysis

Resonance inspection is an emerging non-destructive evaluation (NDE) technique used by the automotive casting industry which uses the resonance spectra differences between the good part population and the flawed parts to identify anomalous parts. It was previously established that finite-element (FE)-based modal analysis can be used to predict the resonance spectrum for an engineering scale part with relatively good accuracy. However, FE-based simulations can be time consuming in examining the spectrum shifts induced by all possible structural flaws. This paper aims at developing a computationally efficient perturbation technique to quantify the frequency shifts induced by small structural flaws, based on the FE simulated resonance spectrum for the perfect part. A generic automotive connecting rod is used as the example part for our study. The results demonstrate that the linear perturbation theory provides a very promising way in predicting frequency changes induced by small structural flaws. As the flaw size increases, the discrepancy between the perturbation analysis and the actual FE simulation results increases due to nonlinearity, yet the perturbation analysis is still able to predict the right trend in frequency shift.

DAMAGE DETECTION IN COMPOSITE CYLINDRICAL PANELS BASED ON FORCED VIBRATION

The current work is devoted to the problem of the damage detecting inside the composite cylindrical panels. The applied method is based on the analysis of the forced vibration and corresponding mode shapes of the structure. The presented study has theoretical character (numerical experiment) but it can be easily adopted in practice, for example in case of the SLDV technique. The analysis is performed with use of finite element method. The internal GHIHFWLVPRGHOHGE\�WKHUHGXFWLRQRIWKHFRPSRVLWHPDWHULDOVW LIIQHVVDQGGHQVLW\�LQDUELWUDU\�FKRVHQHOHPHQWV��,QWKH� first step the natural frequencies of the intact structure are computed with use of the modal analysis. Next, the corresponding mode shapes are determined (harmonic analysis) for the damage and intact structure. For the each mode shape the curvature in the longitudinal and circumferential direction are determined. Generally, the change of the curvature are very similar in case of damage and intact structure. However, in the location of the damage the change of mode shape curvature are quite different in comparison with intact ones. This fact can be further used in order to detect any kind of flaws inside the analyzed structure. The appropriate damage index is also introduced. Moreover, the simplified analysis of the measurement error influence on the accuracy of the proposed approach is also investigated. The discussed method of the damage detecting in the investigated here multilayered cylindrical panel are very sensitive. Even single small flaws with relatively low reduction of the material stiffness as well as its position can be effectively detected and localized

Segmenting mammographic microcalcifications using a semi-automatic procedure based on Otsu s method and morphological filters

INTRODUCTION: Breast cancer has the second highest world's incidence rate, according to the Brazilian National Cancer Institute (INCa). Clinical examination and mammography are the best methods for early diagnosis. Computer-aided detection (CADe) and computer-aided diagnosis (CADx) systems are developed to improve mammographic diagnosis. Basically, CADx systems have three components: (i) segmentation, (ii) parameters extraction and selection, (iii) lesion classification. The first step for a CADx system is segmentation. METHODS: A microcalcification segmentation method is proposed, based on morphological operators, Otsu's Method and radiologists' knowledge. Pre-processing with top-hat operators improves contrast and reduces background noise. The Otsu's method automatically selects the best grey-level threshold to segment microcalcifications, obtaining binary images. Following, inferior reconstruction and morphological dilatation operators are applied to reconstruct lost structure details and fill small flaws in the segmented microcalcifications. Finally, the Canny edge detection is applied to identify microcalcifications contour candidates for each region-of-interest (ROI). Two experienced radiologists intervene in this semi-automatic method, firstly, selecting the ROI and, then, analyzing the segmentation result. The method was assessed in 1000 ROIs from 158 digital images (300 dpi, 8 bits). RESULTS: Considering the radiologists opinion, the rates of ROIs adequately segmented to establish a diagnosis hypothesis were 97.8% for one radiologist and 97.3% for the other. Using the Area Overlap Measure (AOM) and the 2136 microcalcifications delineated by an experienced radiologist as gold standards, the method achieved an average AOM of 0.64±0.14, being 0.56±0.09 for small microcalcifications and 0.66±0.13 for the large ones. Moreover, AOM was 0.64±0.13 for the benign and 0.64±0.14 for the malignant lesions with no statistical differences between them. CONCLUSION: Based on these findings, the proposed method could be used to develop a CADx system that could help early breast cancer detection.

Reference-free damage detection by means of wavelet transform and empirical mode decomposition applied to Lamb waves

Guided ultrasonic waves are increasingly used in all those structural health monitoring applications that benefit from built-in transduction, moderately large inspection ranges, and high sensitivity to small flaws. This article describes a monitoring system based on the generation and detection of the guided ultrasonic waves from an array of sparse transducers. In a round-robin manner, ultrasonic waves are generated and measured from all possible different pairs of excitation and sensing transducers. The ultrasonic signals are then processed using continuous wavelet transform and empirical mode decomposition to extract few damage-sensitive features that enable the detection and localization of damage. With respect to most of the existing guided ultrasonic wave–based methods, the proposed approach does not require to record data from a pristine structure (baseline data), and damage is inferred by examining the selected features obtained from all the possible combinations of actuator–sensor pairs of the array. In this study, the method is validated using commercial finite element software to model the presence of 10 ultrasonic transducers bonded onto an aluminum plate. The results are promising and ongoing studies are focusing on the experimental validation and the application to other waveguides.

Time-Frequency Analysis of Long Range Ultrasonic Signals

Long range ultrasonic testing (LRUT) is a relatively new development within the non-destructive testing sector. Traditionally, conventional ultrasonic testing (UT) is performed at high frequencies, in the MHz range, and is capable of detecting small flaws within a range of millimetres; whereas long range ultrasonic inspection is carried out at lower frequencies, typically between 20 and 100kHz, and is capable of highlighting structural detail and discontinuities tens of metres from a test position. Conventional ultrasonic testing relies on the transmission of bulk waves, the velocities of which are independent of frequency and can usually be predicted easily if the elastic properties of the material under test are known. The dynamics of guided waves, however, are dependent upon frequency making the analysis of received data from a specimen complex. This paper will serve as an introduction to time-frequency representation and may allow a clearer understanding of the non-stationary raw signals produced by this inspection process. Currently, LRUT data are assessed in the time or distance domain using the amplitude vs. time 'A-Scan', therefore structural features and potential flaws are highlighted on a time-of-flight basis. However, as the data obtained are dynamic in time and frequency (non-stationary), time-frequency distributions could provide a mode identification or de-noising process to deal with the problem of coherent noise.

A unified approach for the structural health monitoring of waveguides

In this article, the simultaneous use of ultrasonic testing and impedance-based technique to monitor the health of structural waveguides is proposed. Methods based on the propagation of guided waves are increasingly used in all those structural health monitoring applications that benefit from built-in transduction, moderately large inspection ranges, and high sensitivity to small flaws. In the meantime, impedance-based method promises to adequately assess the structural integrity of simple and complex structures that include welds and bolts. As both wave-based and impedance-based approaches can utilize piezoelectric transducers (lead zirconate titanate) bonded or embedded to the structure being monitored, this article describes a unified structural health monitoring paradigm where these techniques are employed simultaneously, driven by the same sensing/hardware/software unit. Specifically, we propose to use two lead zirconate titanates controlled by a National Instruments–PXI running in LabVIEW. An ad hoc LabVIEW Virtual Instrument controls signal output and input as well as processing and storage. To assess the feasibility of this unified system, an aluminum plate and a steel pipe were monitored. Damage was simulated by changing the boundary conditions of each structure. The results show that the proposed system is robust and can be developed further to address the challenges associated with the structural health monitoring of complex structures.

Zuclopenthixol acetate for acute schizophrenia and similar serious mental illnesses.

Medication used for acute aggression in psychiatry must have rapid onset of effect, low frequency of administration and low levels of adverse effects. Zuclopenthixol acetate is said to have these properties. To estimate the clinical effects of zuclopenthixol acetate for the management of acute aggression or violence thought to be due to serious mental illnesses, in comparison to other drugs used to treat similar conditions. We searched the Cochrane Schizophrenia's Group Trials Register (July 2011). We supplemented this by citation searching and personal contact with authors and relevant pharmaceutical companies. All randomised clinical trials involving people thought to have serious mental illnesses comparing zuclopenthixol acetate with other drugs. Two review authors extracted and cross-checked data independently. We calculated fixed-effect relative risks (RR) and 95% confidence intervals (CI) for dichotomous data. We analysed by intention-to-treat. We used mean differences (MD) for continuous variables. We found no data for the primary outcome, tranquillisation. Compared with haloperidol, zuclopenthixol acetate was no more sedating at two hours (n = 40, 1 RCT, RR 0.60, 95% CI 0.27 to 1.34). People given zuclopenthixol acetate were not at reduced risk of being given supplementary antipsychotics (n = 134, 3 RCTs, RR 1.49, 95% CI 0.97 to 2.30) although additional use of benzodiazepines was less (n = 50, 1 RCT, RR 0.03, 95% CI 0.00 to 0.47). People given zuclopenthixol acetate had fewer injections over seven days compared with those allocated to haloperidol IM (n = 70, 1 RCT, RR 0.39, 95% CI 0.18 to 0.84, NNT 4, CI 3 to 14). We found no data on more episodes of aggression or harm to self or others. One trial (n = 148) reported no significant difference in adverse effects for people receiving zuclopenthixol acetate compared with those allocated haloperidol at one, three and six days (RR 0.74, 95% CI 0.43 to 1.27). Compared with haloperidol or clotiapine, people allocated zuclopenthixol did not seem to be at more risk of a range of movement disorders (< 20%). Three studies found no difference in the proportion of people getting blurred vision/dry mouth (n = 192, 2 RCTs, RR at 24 hours 0.90, 95% CI 0.48 to 1.70). Similarly, dizziness was equally infrequent for those allocated zuclopenthixol acetate compared with haloperidol (n = 192, 2 RCTs, RR at 24 hours 1.15, 95% CI 0.46 to 2.88). There was no difference between treatments for leaving the study before completion (n = 522, RR 0.85, 95% CI 0.31 to 2.31). One study reported no difference in adverse effects and outcome scores, when high dose (50-100 mg/injection) zuclopenthixol acetate was compared with low dose (25-50 mg/injection) zuclopenthixol acetate. Recommendations on the use of zuclopenthixol acetate for the management of psychiatric emergencies in preference to 'standard' treatment have to be viewed with caution. Most of the small trials present important methodological flaws and findings are poorly reported. This review did not find any suggestion that zuclopenthixol acetate is more or less effective in controlling aggressive acute psychosis, or in preventing adverse effects than intramuscular haloperidol, and neither seemed to have a rapid onset of action. Use of zuclopenthixol acetate may result in less numerous coercive injections and low doses of the drug may be as effective as higher doses. Well-conducted pragmatic randomised controlled trials are needed.

Research on target-matching method in ultrasonic testing

Ultrasonic echoes contain ample flaw information in nondestructive testing. However, bad coupling or small flaw often leads to low SNR (signal-to-noise ratio), so the result provided by conventional amplitude detection may not be accurate enough. To solve this problem, the finite element method is used to investigate the frequency domain characteristics of flaw echoes. Furthermore, a target-matching method based on the maximum output SNR criteria is proposed. The transducer is excited by a certain electrical signal obtained by adaptive filtering deconvolution algorithm for each flaw, so we get a maximum SNR when the excitation signal and flaw match. This is further verified in ultrasonic test for a series of samples containing different sizes of flat-bottom holes. This work is supported by the National Natural Science Foundation of China (Grant Nos. 10834009, 11074272)

The effect of volumetric defectiveness on the spatiotemporal characteristics of an electromagnetic response during acoustoelectric transformations in dielectric specimens

The effect of a local bulk flaw has been preliminary studied using a multisensory control system based on the phenomenon of mechanoelectrical transformations in dielectric structures. A hole with a variable depth served as a bulk flaw. The high efficiency of the multisensory system, which allows reliable recording of small local bulk flaws is demonstrated.

Microwave Dielectric-Loaded Rectangular Waveguide Resonator for Depth Evaluation of Shallow Flaws in Metals

This paper presents the design and performances of a partially filled dielectric-loaded waveguide resonator for sensing application, in particular, for evaluating very small flaws on a metal surface. The resonator consists of a rectangular waveguide loaded with a transversally and longitudinally finite dielectric insert that concentrates the electromagnetic field within it and effectively creates a quarter-wavelength resonator. The quarter-wavelength resonator is short-circuited at one end, whereas the other end is formed by tapering the dielectric insert. It is shown that the coupling between the resonator and the feeding waveguide can be widely varied by changing the geometrical and dielectric properties of the insert. Simulations are performed to demonstrate the characteristics of this resonator using a standard K-band (18-26.5 GHz) rectangular waveguide. To demonstrate the potential practical usefulness of such a resonator as a sensor, small perturbations, such as shallow pits or notches (representing damage or flaws), in the surface of the shorting plate of the resonator were used to evaluate the change in the resonator characteristics. These changes can be used for sensing and sizing such surface flaws in nondestructive testing applications (i.e., inspection of aircraft fuselage panels). Measurements are conducted to verify the potential of this sensor for shallow-pit-depth evaluation.

Guided waves for the health monitoring of sign support structures under varying environmental conditions

SUMMARY Guided ultrasonic waves are increasingly used in all those structural health monitoring applications that benefit from built-in transduction, moderately large inspection ranges, and high sensitivity to small flaws. The wave-based structural health monitoring of complex or thick structures can be difficult because of factors such as simultaneous propagation of many modes, large number of overlapping reflections, and mode conversion. Moreover, if the structures are subjected to environmental changes, variations on the characteristics of the detected signals are observed. This paper describes a health monitoring system for large trusses that combines the advantages of guided ultrasonic waves with the extraction of defect-sensitive features aimed at performing a multivariate diagnosis of damage. The system was tested on a chord of a dismantled overhead sign support structure subjected to changing environmental conditions. Cold/warm temperatures and wet/snow boundary conditions were created. The system's hardware consisted of a data acquisition unit that controlled the generation and detection of ultrasonic signals by means of an array of piezoelectric transducers. The signals were processed using a feature-based approach whereby features between two signals collected simultaneously or between a signal and a baseline were compared. The features were then fed into an unsupervised learning algorithm based on outlier analysis. Experimental results show that damage can be detected even in the presence of temperature and boundary condition variations. Copyright © 2011 John Wiley & Sons, Ltd.

The critical size of macroscopic imperfections in dry snow slab avalanche initiation

[1] Dry snow slab avalanches initiate after mode II fracture propagation within a thin, weak layer under a planar slab. Dry alpine snow in which avalanches form is a porous material, typically with volume fraction filled by solids of between 10% and 50%. If snow slab avalanches were caused by small scale flaws, there would be continuous avalanches and alpine snow would not survive on steep slopes. Instead, snow slab avalanches initiate from macroscopic imperfections or weak zones within the weak layer. These are called “sweet spots” by practitioners and deficit zones in the pioneering work by Conway and Abrahamson in the 1980s. In this paper, the results of 750 in situ shear fracture tests from 68 slab–weak layer combinations are summarized in relation to the critical sweet spot length and weak layer crystal form. The results show that the critical sweet spot lengths follow a gamma probability density function with a range from 0.14 to 1.3 m and most probable value 0.5 m. The results also imply that critical sweet spot length depends on weak layer grain type with significantly larger values for persistent forms (surface hoar and facets) than for nonpersistent forms (decomposing and fragmented grains).

Tensile properties of carbon fibres and carbon fibre–polymer composites in fire

The effect of fire on the tensile properties of carbon fibres is experimentally determined to provide new insights into the tensile performance of carbon fibre–polymer composite materials during fire. Structural tests on carbon–epoxy laminate reveal that thermally-activated weakening of the fibre reinforcement is the dominant softening process which leads to failure in the event of a fire. This process is experimentally investigated by determining the reduction to the tensile properties and identifying the softening mechanism of T700 carbon fibre following exposure to simulated fires of different temperatures (up to 700°C) and atmospheres (air and inert). The fibre modulus decreases with increasing temperature (above ∼500°C) in air, which is attributed to oxidation of the higher stiffness layer in the near-surface fibre region. The fibre modulus is not affected when heated in an inert (nitrogen) atmosphere due to the absence of surface oxidation, revealing that the stiffness loss of carbon fibre composites in fire is sensitive to the oxygen content. The tensile strength of carbon fibre is reduced by nearly 50% following exposure to temperatures over the range 400–700°C in an air or inert atmosphere. Unlike the fibre modulus, the reduction in fibre strength is insensitive to the oxygen content of the atmosphere during fire. The reduction in strength is possibly attributable to very small (under ∼100nm) flaws and removal of the sizing caused by high temperature exposure.

Comparative Investigation of Split Spectrum Processing over Classical Approach of Filtering for Non-Linear and Non-Stationary Signals

Ultrasonic welding defect signals are not processed, they are very difficult to identify the pattern of the defect, especially the TOFD welding defect signals are often mixed with noise and lead to confusion between grain noise and small flaws. It is very difficult to interpret the result defect and noise due to larger grain noise. This paper describes the comparative study of matlab simulation results of classic approach signal processing methodology and Split Spectrum Processing (SSP) with the Polarity Thresholding algorithm (PT) to the TOFD welding defect. A-scan signals are used to enhance SNR while suppressing the grain noise. The simulation results show that the welding defect TOFD signals after the SSP investigation are the best and produce the qualified output.

Flaw propagation and buckling in clay-bearing sandstones

Many historically and culturally significant buildings have sandstones that contain swelling clay inclusions in the binding phase. Differential strains that evolve during wetting and drying cycles can generate stresses that are on the order of the strength of the stone, leading to degradation. Most damage observed in the field is surface delamination and buckling of the stone over a flaw, indicating that the damage is occurring during wetting. Classical buckling theory predicts buckling to occur at a particular aspect ratio, or flaw size. The results of this study confirm buckling theory experimentally. Through finite-element simulation and experiment, the study then explores a potential flaw propagation mechanism whereby nonuniform wetting patterns generate stress intensities capable of flaw propagation. As a result, small natural flaws can grow to the critical size necessary for buckling.