a system for the investigation of cracks

This work aims to deal with the problem of identifying, analysing, and classifying cracks in figurative works. The recent, considerable progress made in techniques for processing visual information has broadened the number of scientific applications in which the display and graphic processing of data play a fundamental role. Cracks consist of many elements; distinguishing and studying them has made it possible to develop a classification that in some cases can also be used as tool to verify a work's authenticity. RESTART, the system presented here, is deemed suitable for use in numerous and varied settings, such as teaching, conservation, study and research. It is able to investigate, study, research and 'restore' the digital, in accordance with the criteria dictated by knowledge. Also of considerable interest is the investigation of a crack based on such characteristics as origin and pathology, and the possibility of analysing the cracks in a fresco. The use of RESTART for such case examples is investigated and proposed

Integration of an Ultrasonic Sensor within a Robotic End Effector for Application within Railway Track Flaw Detection

The rail industry is constantly facing challenges related to safety with regard to the detection of surface cracks and internal defects within rail tracks. Significant focus has been placed on developing sensor technologies that would facilitate the detection of flaws that compromise rail safety. In parallel, robot automation has demonstrated significant advancements in the integration of sensor technologies within end effectors. This study investigates the novel integration of an ultrasonic sensor within a robotic platform specifically for the application of detecting surface cracks and internal defects within rail tracks. The performance of the robotic sensor system was assessed on a rail track specimen containing sacrificial surface cracks and internal defects and then compared against a manual detection system. The investigation concludes that the robotic sensor system successfully identified internal defects in the web region of the rail track when utilising a 60° and 70° wedged probe, with a frequency range between 4 MHz and 5 MHz. However, the surface crack investigation proved that the transducer was insensitive to the detection of cracks, possibly due to the inadequate angle of the wedged probe. The overall outcome of the study highlights the potential that robotic sensor systems have in the detection of internal defects and characterises the limitations of surface crack identification to assist in enhancing rail safety

The Role of Structural Dynamics and Testing in the Shuttle Flowliner Crack Investigation

During a normal inspection of the main propulsion system at Kennedy Space Center, small cracks were noticed near a slotted region of a gimbal joint flowliner located just upstream from one of the Space Shuttle Main Engines (SSME). These small cracks sparked an investigation of the entire Space Shuttle fleet main propulsion feedlines. The investigation was initiated to determine the cause of the small cracks and a repair method that would be needed to return the Shuttle fleet back to operation safely. The cracks were found to be initiated by structural resonance caused by flow fluctuations from the SSME low pressure fuel turbopump interacting with the flowliner. The pump induced backward traveling wakes that excited the liner and duct acoustics which also caused the liner to vibrate in complex mode shapes. The investigation involved an extensive effort by a team of engineers from the NASA civil servant and contractor workforce with the goal to characterize the root cause of the cracking behavior of the fuel side gimbal joint flowliners. In addition to working to identify the root cause, a parallel path was taken to characterize the material properties and fatigue capabilities of the liner material such that the life of the liners could be ascertained. As the characterization of the material and the most probable cause matured, the combination of the two with pump speed restrictions provided a means to return the Shuttle to flight in a safe manner. This paper traces the flowliner investigation results with respect to the structural dynamics analysis, component level testing and hot-fire flow testing on a static testbed. The paper will address the unique aspects of a very complex problem involving backflow from a high performance pump that has never been characterized nor understood to such detail. In addition, the paper will briefly address the flow phenomena that excited the liners, the unique structural dynamic modal characteristics and the variability of SSME operation which has ultimately ensured the safe and reliable operation of the shuttle main engines for each flight

System of edge parallel cracks in contact area of rolling bodies

Записано сингулярні інтегральні рівняння для системи крайових паралельних нерівних нахилених тріщин у пружній півплощині, береги яких контактують без тертя під час переміщення герцівського навантаження вздовж краю півплощини. Запропоновано алгоритм визначення меж ділянок контактування берегів тріщин та коефіцієнтів інтенсивності напружень у їх вершинах. Числові результати отримано для випадку двох паралельних рівних тріщин.The surface (edge) parallel cracks system is one of typical contact fatigue damages of elements of wheel-rail technical pair. So, the important task for estimation of a contact strength and durability of such pair is determination of a stress-strain state or stress intensity factors (SIF) at crack tips under operational conditions. In given investigation the model scheme, where in a two-dimensional case damaged bodies are simulated by elastic halfplane with cuts, and counterbody action by forward unidirectional movement of model contact load along halfplane boundary, has been used for simulation of contact rolling interaction. Other parameters have been chosen according to operational conditions for wheel-rail pair and typical features of damages. Singular integral equations of contact problem of elasticity theory for halfplane with the system of parallel inclined cracks, the faces of which are in contact without friction under action of a moving model load (Hertzian pressure with tangential component) have been constructed. The algorithm (iterative procedure) for finding of opened segments of a cracks faces has been developed. Numerical results for the case of two equal parallel cracks, inclined at angle β = 5π/6 to direction of a tangential contact efforts and, respectively, at angle π –β = 30° to direction of a counterbody movement for different values of a friction coefficient (f = 0.1 and f = 0.3) in a contact between rolling bodies and different relative distances between cracks δ = b/a depending on a contact load position in relation to cracks have been obtained. The maps of cracks faces contacting during a contact load movement along halfplane boundary (change of parameter λ = х0/а) have been constructed and stress intensity factors KI, KII and mixed SIF KIθ have been calculated. It was determined that cracks begin to close mainly from the mouth during contact load movement. The value of ∆KII = maxKII(λ) – minKII(λ) parameter, that controls the fracture by shear mechanism significantly depends on a distance between the cracks and a substantial weakening of rolling body nearsurface area (maximum of ∆KII) is achieved under distance, that commensurable with the contact segment length. Maximum and minimum of KII(λ) are realized if both cracks are contacting along all its length. So, partial opening of cracks has little influence on ∆KII range. The analysis of K I∗θ = max K Iθ (λ , θ ) parameter, that controls the fracture by opening mechanism, showed: when the contact load is directly above the crack(s) not only shear fracture can occur, but fracture by opening can occur too. Generally, the presence of a fully closed crack with contacting faces can significantly influence the SIF of another opened crack. Therefore, this influence can not be neglected

Depth evaluation of damage to aircraft fuselage skins using microwave and millimeter wave methods

The depth of damage to metal surfaces is a particularly useful, sought after, and difficult to obtain piece of information, and is used to guide repair decisions. For this investigation such damage is represented as rectangular slots (cracks) or cylindrical pits. Several millimeter wave methods are presented to evaluate depth. The quarter-wavelength resonant response of cracks, excited by a probing rectangular waveguide, allows evaluation of depth using the phase of reflection coefficient. A theoretical derivation is also supplied, modeling the system as the junction of two rectangular waveguides, the probing waveguide and the crack. If the crack is filled with a dielectric material, shallower cracks may be evaluated and the magnitude of reflection coefficient may be used instead of phase. This approach has the advantage of low sensitivity to crack width and probe position, but has some limitations in the minimum depth and the smallest openings which can be evaluated. The depth of pits and shorter cracks may be evaluated using the phase in a non-resonant approach, by comparison with reference curves. A dielectric slab-loaded waveguide probe is also developed which theoretically would allow measurement of smaller damages, of both opening and depth, as a resonance perturbation. Sensitivity to very small damage is apparent, but high sensitivity to probe position is also evident. Extensive simulation results are presented for each approach, with supporting measurements. Evaluation of the depth of filled cracks, using the quarter-wavelength resonance approach, is, in particular, demonstrated in measurements for depths from 0.7- 2.7 mm for three frequency bands and three filling materials --Abstract, Page iii

Geotechnical Forensic Investigation of Observed Cracks on a Building in Tallahassee, Florida

In July 2010, two vapor extraction wells were installed about 15 feet from a building at an angle of 50 degrees to the horizontal using rotosonic drilling technique (RDT). In June 2011, a crack approximately 0.5 inch wide on the wall of the building was reported. Several other small cracks were observed on the building following inspection by the authors. The owner of the building expressed concerns that the rotosonic drilling was the cause of the cracks and wanted assurance that subsequent drillings would not exacerbate the problem. Geotechnical forensic investigation was performed to evaluate the potential cause(s) of cracking in the building and whether future drilling would impact the building and the foundation structure system. The investigations involved performing site reconnaissance surveys, site-specific field investigations, real-time vibration monitoring, crack monitoring, and geotechnical laboratory analyses. This paper presents the results from the forensic investigations. Based on these results, potential causes for the development of cracks in the wall of the building and recommended repair measures are discussed

A phased array-based method for damage detection and localization in thin plates

A method for damage localization based on the phased array idea has been developed. Four arrays oftransducers are used to perform a beam-forming procedure. Each array consists of nine transducersplaced along a line, which are able to excite and register elastic waves. The A0 Lamb wave mode hasbeen chosen for the localization method. The arrays are placed in such a way that the angulardifference between them is 458 and the rotation point is the middle transducer, which is common for allthe arrays. The idea has been tested on a square aluminium plate modeled by the Spectral Element Method. Two types of damage were considered, namely distributed damage, which was modeled asstiffness reduction, and cracks, modeled as separation of nodes between selected spectral elements.The plate is excited by a wave packet. The whole array system is placed in the middle of the plate.Each linear phased array in the system acts independently and produces maps of a scanned fieldbased on the beam-forming procedure. These maps are made of time signals (transferred to spacedomain) that represent the difference between the damaged plate signals and those from the intactplate. An algorithm was developed to join all four maps. The final map is modified by proposed signal processing algorithm to indicate the damaged area of the plate more precisely. The problem fordamage localization was investigated and exemplary maps confirming the effectiveness of theproposed system were obtained. It was also shown that the response of the introduced configurationremoves the ambiguity of damage localization normally present when a linear phased array is utilized.The investigation is based exclusively on numerical data

STS-133/ET-137 Tanking Test Photogrammetry Assessment

Following the launch scrub of Space Shuttle mission STS-133 on November 5, 2010, an anomalous condition of cracked and raised thermal protection system (TPS) foam was observed on the External Tank (ET). Subsequent dissection of the affected TPS region revealed cracks in the feet of two Intertank (IT) metallic stringers. An extensive investigation into the cause(s) and corrective action(s) for the cracked stringers was initiated, involving a wide array of material and structural tests and nondestructive evaluations, with the intent to culminate into the development of flight rational. One such structural test was the instrumented tanking test performed on December 17, 2010. The tanking test incorporated two three-dimensional optical displacement measurement systems to measure full-field outer surface displacements of the TPS surrounding the affected region that contained the stringer cracks. The results showed that the radial displacement and rotation of the liquid oxygen (LO2) tank flange changed significantly as the fluid level of the LO2 approached and passed the LO2 tank flange

Test Analysis Correlation of the Single Stringer Bending Tests for the Space Shuttle ET-137 Intertank Stringer Crack Investigation

On November 5, 2010, Space Shuttle mission STS-133 was scrubbed due to a hydrogen leak at the Ground Umbilical Carrier Plate (GUCP). After the scrub, a crack in the foam thermal protection system (TPS) was observed on the External Tank (ET) near the interface between the liquid oxygen (LOX) tank and the Intertank. When the damaged foam was removed, two 9-in. long cracks were found on the feet of Intertank stringer S7-2, and the stringer failure was the cause of the TPS crack. An investigation was conducted to determine the root cause of the cracks, establish a remedy/repair for the stringers, and provide flight rationale for the damaged tank, ET-137. The Space Transportation System (STS) Super Lightweight ET (SLWT) is comprised of two propellant tanks (an aft liquid hydrogen (LH2) tank and a forward LOX tank) and an Intertank. The Intertank serves as the structural connection between the two propellant tanks and also functions to receive and distribute all thrust loads from the solid rocket boosters . The Intertank is a stiffened cylinder structure consisting of eight mechanically joined panels (two integrally-stiffened, machined thrust panels to react the booster loads and six stringer-stiffened skin panels). There are one main ring frame, four intermediate ring frames, and forward and aft flange chords that mate to the respective propellant tanks.. The skin/stringer panels utilize external hat-section stringers that are mechanically attached with rivets along most of their length and with specialty fasteners, such as GP Lockbolts and Hi-Loks, at the forward and aft ends where the stringers attach to the flange chords. During the STS-133 Intertank stringer crack investigation, cracks were found on a total of five stringers. All of the cracks were at the LOX end, in the feet of the stringers, and near the forward fasteners (GP Lockbolts). Video of tanking for the November 5 launch attempt was used to determine that the TPS failure, and thus the stringer failure, occurred as the LOX liquid level crossed the LOX tank / Intertank interface ring frame. Hence, cryogenically-induced displacements were suspected as a contributing cause of the stringer cracks. To study the behavior of Intertank stringers subjected to similar displacements, static load tests of individual stringers, colloquially known as "single stringer bending tests" were performed. Approximately thirty stringers were tested, many of which were cut from the partially completed Intertank for what would have been ET-139. In addition to the tests, finite element (FE) analyses of the test configuration were also performed. In this paper, the FE analyses and test-analysis correlation for stringer test S6-8 are presented. Stringer S6-8 is a "short chord" configuration with no doubler panels

Thermostructural responses of carbon phenolics in a restrained thermal growth test

The thermostructural response of carbon phenolic components in a solid rocket motor (SRM) is a complex process. It involves simultaneous heat and mass transfer along with chemical reactions in a multiphase system with time-dependent material properties and boundary conditions. In contrast to metals, the fracture of fiber-reinforced composites is characterized by the initiation and progression of multiple failures of different modes such as matrix cracks, interfacial debonding, fiber breaks, and delamination. The investigation of thermostructural responses of SRM carbon phenolics is further complicated by different failure modes under static and dynamic load applications. Historically, there have been several types of post-firing anomalies found in the carbon phenolic composites of the Space Shuttle SRM nozzle. Three major failure modes which have been observed on SRM nozzles are pocketing (spallation), ply-lift, and wedge-out. In order to efficiently control these anomalous phenomena, an investigation of fracture mechanisms under NASA/MSFC RSRM (Redesigned Solid Rocket Motor) and SPIP (Solid Propulsion Integrity Program) programs have been conducted following each anomaly. This report reviews the current progress in understanding the effects of the thermostructural behavior of carbon phenolics on the failure mechanisms of the SRM nozzle. A literature search was conducted and a technical bibliography was developed to support consolidation and assimilation of learning from the RSRM and SPIP investigation efforts. Another important objective of this report is to present a knowledge-based design basis for carbon phenolics that combines the analyses of thermochemical decomposition, pore pressure stresses, and thermostructural properties. Possible areas of application of the knowledge-based design include critical material properties development, nozzle component design, and SRM materials control