Journal articles: 'Evolution of longitudinal cracks'

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Klocke, Fritz, A. Timmer, and F. Schongen. "Investigation of Surface Crack Types under Axial Compression Loading for a Case-Hardening Steel." Key Engineering Materials 452-453 (November 2010): 741–44. http://dx.doi.org/10.4028/www.scientific.net/kem.452-453.741.

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During cold-forming operations the formability of the materials can be reached due to the low process temperature, leading to crack initiation. For the investigated case-hardening steel 16MnCrS5 longitudinal cracks and shear cracks are identified as the main crack types. The evolution of both crack types is determined by scanning electron microscope (SEM)-investigations and a simplified finite element method (FEM)-model. The results reveal that the initiation point of shear cracks is located at the surface. In contrast thereto longitudinal cracks emanate from second phase particles in the rim zone.

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SUN, YADONG, SENJIANG YU, YAOPENG DU, HONG ZHOU, and MIAOGEN CHEN. "CONTROLLED MORPHOLOGICAL EVOLUTIONS OF SILVER FILMS ON COMPLIANT SUBSTRATES BY TUNING MECHANICAL STRAIN." Surface Review and Letters 27, no. 01 (May 3, 2019): 1950094. http://dx.doi.org/10.1142/s0218625x1950094x.

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Controlled surface morphologies of stiff films on compliant substrates possess a variety of applications, ranging from stretchable electronics, surface engineering to biomimics. Here, we report on the morphological evolutions of silver films deposited on prestretched compliant PDMS substrates by tuning the film strain in unloading, reloading and further stretching processes. It is found that the silver films generate transverse (perpendicular to the loading direction) wrinkles and longitudinal (parallel to the loading direction) cracks during the unloading process. On the contrary, longitudinal wrinkles and transverse cracks can be observed during the further stretching process. The morphological characteristics, evolution behaviors and mechanical mechanisms of the crack and wrinkle patterns are investigated in detail. The report in this work could promote a better understanding of the morphological evolutions of stiff films on compliant substrates by tuning the mechanical strain.

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Giordano, Luca, and Francesco Tondolo. "Crack Width Evolution of R/C Structures Subject to Corrosion and Fatigue." Key Engineering Materials 452-453 (November 2010): 417–20. http://dx.doi.org/10.4028/www.scientific.net/kem.452-453.417.

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Corrosion modifies the steel-concrete interface in reinforced concrete structures. Moreover in structures subjected to cyclic load, a simultaneous mechanical deterioration due to the load is present. Both phenomena can lead to an evolution of cracks width during the service life. In order to evaluate the crack openings increase, an experimental campaign on reinforced concrete ties subjected to simultaneous loading and corrosion have been realized. Transversal crack opening, initially due to loading and longitudinal corrosion cracks evolution is monitored. Results highlight the differences in terms of corroded and uncorroded specimens, static and cycling test and also different loading amplitude. Finally it can be observed as the growing of the damage is significantly different when a cycling action, combined with a chemical attack is present.

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Chang, Yan Jun, Shuang Feng Zeng, Ke Shi Zhang, and Zhuo Li. "Study of Q345 Steel under Tensile Failure with Bilateral Parallelcracks." Applied Mechanics and Materials 574 (July 2014): 368–72. http://dx.doi.org/10.4028/www.scientific.net/amm.574.368.

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The parallel crackswere prefabricated on both sides of theQ345 steel specimensand the tensile failure tests were performed.The effects of parallel crack spacing and crack length on the crack propagation behavior were studied and the fracture modes were investigated with electronic scanning microscope.The finite element analysis of tensile fracture process was also fulfilled based on the ductile metal damage theory, and the crack propagation and the crack stress field evolution around the crack tips were studied. The simulation was agreed with experimental results, and these analysis shows that the crack propagation related with double crack tip of horizontal distance ratio. When the longitudinal and horizontal distance ratio of the two crack tip is less than 1, the linkage between two cracks occurs, or two cracks expand independently. Simulation analysis shows that cracks deflect and connect with another one when the two high Mises plastic stress zones are met with each other; on the contrary, cracks propagate separately.

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5

Fisher, John W. "Evolution of Fatigue-Resistant Steel Bridges." Transportation Research Record: Journal of the Transportation Research Board 1594, no. 1 (January 1997): 5–17. http://dx.doi.org/10.3141/1594-01.

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Fatigue cracking was seldom found in welded highway and railroad bridges from the time of their introduction in the 1950s until the late 1960s. The fatigue design specifications used in that era were developed from a limited knowledge base and largely with small-scale specimens that simulated welded details. During the AASHO Road Test in 1960 fatigue cracks were observed to develop in cover-plated steel bridge beams as a result of the heavy loads and high stress ranges. This observation subsequently resulted in a series of experimental studies supported by NCHRP starting in 1967. The laboratory studies with full-scale details were designed to evaluate the significance of many factors thought to influence fatigue resistance, including loading history (and associated stress states including residual stresses), type of steel, design details, and quality of fabrication. These studies indicated that small-scale specimens overestimated fatigue resistance and that only the stress range for a given detail was critical. As a result fatigue resistance design provisions in use since the 1950s were inadequate and overly optimistic, particularly at longer lives, because the assumption of a fatigue limit of 2 million cycles proved to be incorrect. The results of laboratory studies with full-size specimens and their impact on changing the concept of fatigue design and the bridge fatigue design provisions used for highway and railroad bridges today are reviewed. During the 1970s and 1980s fatigue cracking associated with low-fatigue-strength details (Categories E and E′), such as cover plates and lateral gusset plates, increased. Cracks were also found in transverse groove welds, particularly in attachments such as longitudinal stiffeners, gusset plates and even flange splices. These groove weld cracks generally occurred because large defects were inadvertently fabricated into the welded joint. The occurrence of these cracks was found to be predictable and in agreement with the laboratory fatigue resistance results. The 1970s also exposed an unexpected source of cracking due to the distortion of small web gaps that were frequently used in welded bridge structures. Web gap cracking continues to develop in a wide range of bridge types. It is the source of most fatigue cracks in steel bridges. Existing bridges that are susceptible to fatigue cracks or that develop fatigue cracks at primary details or from web gap distortion are easily repaired or retrofitted to ensure long-term performance. Examples of such repairs are reviewed. The future is bright for welded bridges because the knowledge base and current design provisions make it possible to design and build fatigue-resistant bridges.

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Zhao, Libin, Tianliang Qin, Jianyu Zhang, and Yuli Chen. "3D Gradual Material Degradation Model for Progressive Damage Analyses of Unidirectional Composite Materials." Mathematical Problems in Engineering 2015 (2015): 1–11. http://dx.doi.org/10.1155/2015/145629.

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A new 3D constitutive model for progressive damage analyses of unidirectional composite materials is presented, in which several important damage phenomena for the composite materials, such as the interfiber crack orientation, coupling of fiber failure and interfiber failure under longitudinal loads, closure effect for interfiber cracks, and longitudinal compressive behaviors under transversal constraints, have been considered comprehensively. A modified maximum stress failure criterion has been used for the damage onset prediction and a linear damage model has been adopted to establish the evolution rules of different damage. Numerical analyses with the model proposed have been implemented by using the subroutine UMAT in commercial software ABAQUS. Progressive damage analyses and static tensile experiments of a group of double-lap composite bolted joints have been carried out to validate the model proposed. Good agreements between the numerical and experimental results have been obtained.

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Baensch, Franziska, Michaela Zauner, Sergio J. Sanabria, Markus G. R. Sause, Bernd R. Pinzer, Andreas J. Brunner, Marco Stampanoni, and Peter Niemz. "Damage evolution in wood: synchrotron radiation micro-computed tomography (SRμCT) as a complementary tool for interpreting acoustic emission (AE) behavior." Holzforschung 69, no. 8 (October 1, 2015): 1015–25. http://dx.doi.org/10.1515/hf-2014-0152.

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Abstract Tensile tests of miniature spruce wood specimens have been performed to investigate the damage evolution in wood at the microscopic scale. For this purpose, the samples were stepwise tensile loaded in the longitudinal (L) and radial (R) directions and the damage evolution was monitored in real-time by acoustic emission (AE) and synchrotron radiation micro-computed tomography (SRμCT). This combination is of outstanding benefit as SRμCT monitoring provides an insight on the crack evolution and the final fracture at microscopic scale, whereas AE permits the detection of the associated accumulation and interaction of single damage events on all length scales with high time resolution. A significant drawback of the AE testing of wood has been overcome by means of calibrating the AE amplitudes with the underlying crack length development. Thus, a setup-dependent and wood species-dependent calibration value was estimated, which associates 1 μm2 crack area generating of 0.0038 mV in the detected AE amplitude. Furthermore, for both L and R specimens, AE signals were classified into two clusters by using a frequency-based approach of unsupervised pattern recognition. The shares of AE signals of both clusters correlate with the ratio of the relative crack area of the interwall and transwall cracks gained from the fractographic analysis of SRμCT scans.

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Zhang, Zhiqiang, Changshu He, Ying Li, Jingxun Wei, Menggang Zhai, Su Zhao, and Xiang Zhao. "Fatigue Behaviour of 7N01-T4 Aluminium Alloy Welded by Ultrasonic-Assisted Friction Stir Welding." Materials 13, no. 20 (October 14, 2020): 4582. http://dx.doi.org/10.3390/ma13204582.

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This study investigates the effects of axial ultrasonic vibration on the microstructure evolution, residual stresses distribution and fatigue fracture behaviour of a 7N01-T4 joint, and demonstrates that ultrasonic vibration can significantly promote the flow of plasticised metals, expand the stirred zone (SZ) width and refine the grain size. The longitudinal residual stresses of the joints are dominant, and the peak longitudinal residual stresses of the thermo-mechanically affected zone (TMAZ) on the advancing side (AS) (TMAZ-AS) in the ultrasonic-assisted friction stir welding (UAFSW) joint are 31.5 MPa lower than those in the friction stir welding (FSW) joint. Compared to that of FSW joints, the fatigue strength of UAFSW joints increases by 20 MPa at 107 cycles (stress ratio of R = 0.1). At high-stress levels, crack initiation occurs at the TMAZ-AS, and is mainly attributed to high residual stresses and second-phase particles. At low-stress levels, fatigue cracks are likely to initiate in the transition zone (TZ).

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9

Kasapi, M. A., and J. M. Gosline. "Design complexity and fracture control in the equine hoof wall." Journal of Experimental Biology 200, no. 11 (June 1, 1997): 1639–59. http://dx.doi.org/10.1242/jeb.200.11.1639.

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Morphological and mechanical studies were conducted on samples of equine hoof wall to help elucidate the relationship between form and function of this complex, hierarchically organized structure. Morphological findings indicated a dependence of tubule size, shape and helical alignment of intermediate filaments (IFs) within the lamellae on the position through the wall thickness. The plane of the intertubular IFs changed from perpendicular to the tubule axis in the inner wall to almost parallel to the tubule axis in the outer wall. Morphological data predicted the existence of three crack diversion mechanisms which might prevent cracks from reaching the sensitive, living tissues of the hoof: a mid-wall diversion mechanism of intertubular material to inhibit inward and upward crack propagation, and inner- and outer-wall diversion mechanisms that prevent inward crack propagation. Tensile and compact tension fracture tests were conducted on samples of fully hydrated equine hoof wall. Longitudinal stiffness decreased from 0.56 to 0.30 GPa proceeding inwardly, whereas ultimate (maximum) properties were constant. Fracture toughness parameters indicated that no compromise results from the declining stiffness, with J-integral values ranging from 5.5 to 7.8 kJ m-2 through the wall thickness; however, highest toughness was found in specimens with cracks initiated tangential to the wall surface (10.7 kJ m-2). Fracture paths agreed with morphological predictions and further suggested that the wall has evolved into a structure capable of both resisting and redirecting cracks initiated in numerous orientations.

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KENNEALLY, JAMES P., and TERENCE J. HUGHES. "Fracture and back stress along the Byrd Glacier flowband on the Ross Ice Shelf." Antarctic Science 16, no. 3 (September 2004): 345–54. http://dx.doi.org/10.1017/s0954102004002056.

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East Antarctic ice discharged by Byrd Glacier continues as a flowband to the calving front of the Ross Ice Shelf. Flow across the grounding line changes from compressive to extensive as it leaves the fjord through the Transantarctic Mountains occupied by Byrd Glacier. Magnitudes of the longitudinal compressive stress that suppress opening of transverse tensile cracks are calculated for the flowband. As compressive back stresses diminish, initial depths and subsequent growth of these cracks, and their spacing, are calculated using theories of elastic and ductile fracture mechanics. Cracks are initially about one millimeter wide, with approximately 30 m depths and 20 m spacings for a back stress of 83 kPa at a distance of 50 km beyond the fjord, where floating ice is 600 m thick. When these crevasses penetrate the whole ice thickness, they release tabular icebergs 20 km to 100 km wide, spaced parallel to the calving front of the Ross Ice Shelf.

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11

Cao, Zhou Hong, Ji Jian Lian, and Xi Zhu Liu. "An Improvement of General Design Methods for Lock Castle Structures." Advanced Materials Research 594-597 (November 2012): 1897–900. http://dx.doi.org/10.4028/www.scientific.net/amr.594-597.1897.

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Longitudinal cracks often appear on the top of the large locks’ floor built on soft foundations, but the cause can’t be explained by general design methods. Based on the simulation of lock’s construction and clay’s consolidation, the paper analyses the evolution process of the floor stress, and find the regular pattern of stress’ change over the time, then improves general design methods by omitting the floor’s deadweight when calculating the negative moment. The conclusion serves as a reference for the design and the construction of similar projects.

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12

He, Fulian, Xiaobin Li, Wenrui He, Yongqiang Zhao, Zhuhe Xu, and Quansheng Li. "The Key Stratum Structure Morphology of Longwall Mechanized Top Coal Caving Mining in Extra-Thick Coal Seams: A Typical Case Study." Advances in Civil Engineering 2020 (August 28, 2020): 1–13. http://dx.doi.org/10.1155/2020/7916729.

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Longwall mechanized top coal caving mining (LMTCCM) in extra-thick coal seams has its own characteristics. The law of mining pressure and overlying strata failure height in extra-thick coal seams are much larger than those of medium-thick and thick coal seams. The key stratum structure morphology also has an important influence on the law of overlying strata movement and stability of surrounding rock. Based on the engineering geological conditions, this paper used the method of theoretical analysis and numerical simulation to study the key stratum structure morphology of LMTCCM in extra-thick coal seams. The results show that under the condition of LMTCCM in extra-thick coal seams, the key stratum forms the structure of low cantilever beam and high hinged rock beam. With the increase of coal seam thickness, the breaking position of cantilever beam is closer to the coal wall. Through theoretical calculation, it is obtained that the breaking length of cantilever beam is 31.5 m and the breaking position of cantilever beam is 15.4 m away from coal wall. With the increase of cycle, key strata will undergo the evolution law from the generation of longitudinal cracks to the hinged structure and then to the cantilever beam structure. The breakage of key strata will cause the expansion of longitudinal cracks and the overall synchronous movement of overlying strata. With the increase of coal seam thickness, the distribution of longitudinal cracks will gradually transfer from the upper part of goaf to the deep part of coal body in space and increase in quantity. This research is of great significance for improving the stability of overlying strata and ensuring the safe and efficient mining of extra-thick coal seams.

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13

Meng, Xiangxi, and Weitao Liu. "Study on Failure Process and Permeation Evolution of Single-Cracked Rock." Advances in Materials Science and Engineering 2018 (2018): 1–9. http://dx.doi.org/10.1155/2018/7915652.

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To evaluate the mechanical properties and permeation evolution of cracked rock mass, failure evolution tests were designed by RFPA software for single-cracked rock mass with (i) different inclination angles under uniaxial compression and (ii) different confining pressures and pore pressures under triaxial compression. The results show the following: (1) Angle of the crack significantly affects the crack propagation mode and slightly affects the bearing capacity of rock. During the crack propagation, the peak of permeation is delayed at the peak of stress. The stress-strain curve shows a different behavior in the postcritical part of the curve, especially in the case of 45°, where a smooth postcritical curve was clearly observed instead of an abrupt decrease in the stress of other two cases. (2) When the confining pressure is constant, the trend is almost the same when varying pore pressures, and with the increase in pore pressure, crack propagation is accelerated. At a low confining pressure, the crack is extended vertically to the upper and lower ends of the specimen, forming a longitudinal macroscopic crack. At a high confining pressure, the crack gradually extends to the left and right boundaries of the specimen, forming a transverse macroscopic crack. (3) The rate of crack initiation and destruction first decreases and then increases with the increase in confining pressure when pore pressure is constant.

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Fradette, Nicolas, Guy Doré, Pascale Pierre, and Serge Hébert. "Evolution of Pavement Winter Roughness." Transportation Research Record: Journal of the Transportation Research Board 1913, no. 1 (January 2005): 137–47. http://dx.doi.org/10.1177/0361198105191300114.

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The functional service level of roads is quantified in terms of roughness. This parameter considers every road surface defect that causes passenger vehicle discomfort. Roughness is measured by a quality index, the international roughness index (IRI). Roughness gives an overall appreciation of road profile quality without, however, permitting a deeper analysis. The overall value of the IRI does not discriminate between the two main factors responsible for winter deterioration of roughness: the subgrade differential heave and crack heaving (winter tenting). Differential heave is the result of variability in frost susceptibility of subgrade. This phenomenon can be detected by isolating the long wavelengths produced at the road surface from the longitudinal profile. Crack heaving is a superficial phenomenon greatly influenced by the application of deicing salts. By isolating the short wavelengths from the profile, it is possible to highlight the influence of this phenomenon on deterioration. The goal of this research is to establish, with the use of a filtering technique of road profile, the contribution of these two main factors to winter deterioration of roughness on five road sections in the Quebec City, Canada, area. This study will then allow for the development of a tool to determine the dominant factor for longitudinal profile deterioration and therefore the use of the best technique to rehabilitate roads.

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Giordano, Luca, Giuseppe Mancini, and Francesco Tondolo. "Durability of R/C Structures under Mechanical and Environmental Action." Key Engineering Materials 462-463 (January 2011): 949–54. http://dx.doi.org/10.4028/www.scientific.net/kem.462-463.949.

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In the present work, an experimental campaign on reinforced concrete elements subjected to simultaneous loading and degradation due to corrosion is presented. The specimens are loaded in tension and the cycling action is designed in order to simulate in terms of stress peak and stress variation, the effect of the passage of vehicles under fatigue design situations. The environmental action is simulated by means of corrosion induced with an electrochemical process; the corrosion rate is chosen in order to obtain about 27 years of equivalent carbonation attack within 25 days of test. In the mean time, 6.5·106 loading cycles are achieved. In addition to those standard tests, also other static tests were conducted in order to have a comprehensive analysis of the deterioration processes. Evolution of transversal crack due to loading and of longitudinal cracks due to corrosion is monitored. They can be related to the internal bond condition between steel and concrete. Results highlight the differences in terms of corroded and uncorroded specimens, static and cycling test and also different loading amplitude. Finally it can be observed as the growing of the damage is significantly different when a cycling action, combined with a chemical attack, is present.

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Prassack, Kari Alyssa. "The effect of weathering on bird bone survivorship in modern and fossil saline-alkaline lake environments." Paleobiology 37, no. 4 (2011): 633–54. http://dx.doi.org/10.1666/10041.1.

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A modern Lesser Flamingo (Phoeniconaias minor) assemblage was collected along the shoreline of Lake Emakat, a saline-alkaline lake in northern Tanzania. Taphonomic analysis found the assemblage to be heavily weathered. This is likely due to the bone's heightened exposure to solar radiation and corrosive soil and water chemistries, as is expected to occur in such depositional environments.Analysis found that deep, wide, longitudinal cracks penetrate the medullar cavities of both weathered and unweathered long bones. The cause and taphonomic consequence of these cracks are addressed here, using data from Lake Emakat and from controlled studies. Results support repeated (episodic) submersion, followed by drying, as the causal mechanism behind thesewet-drycracks. Mineral salt uptake by bone may explain the early appearance and prevalence of these cracks in saline-alkaline lake settings, as compared to other depositional settings.The rate of weathering and incidence of wet-dry cracking varies significantly across limb elements. This difference correlates to element specific resistance properties to external loading forces. Heavy weathering weakens the structural integrity of bone and can accelerate its fragmentation. This can lead to bird bone loss in nearshore and ephemeral wetland settings, which may then affect resulting skeletal part, diversity, and richness profiles. Heavy weathering can therefore obscure important taphonomic and paleoecological information.The weathering data collected here are then applied to a fossil bird assemblage from the FLK Complex, (late Pliocene), Olduvai Gorge, in Tanzania. Results provide evidence for the effect of weathering on paleoecological and behavioral interpretations. Weathering should be considered when analyzing fossil bird assemblages.

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17

Yu, Xiang, Cheng Biao Wang, and Zhi Jian Peng. "Improving Ag-DLC Film Adherence on High-Speed Steel by Varying Ag Contents in A Mid-Frequency Dual-Magnetron Sputtering." Key Engineering Materials 434-435 (March 2010): 462–65. http://dx.doi.org/10.4028/www.scientific.net/kem.434-435.462.

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Aiming at improving their tribological behaviors, adhesion of diamond-like carbon (DLC) films on high-speed steel was investigated by varying doping silver (Ag) contents in a mid-frequency dual-magnetron sputtering system. Scratch testing was performed on the Ag-DLC films under a progressive normal load from 3 to 80 N, along with a Rockwell C indenter at a relative displacement speed for a Rockwell testing. A microscopic analysis of the scratch evolution under a progressive normal load permits identification of the various traces and the damage mechanisms of the films. A process of the film adhesion failure typically in turn appears like this, germination of the cracks along the longitudinal edges of the scratch traces; propagation in front of the indenter; and, detachment in the subsurface by shearing. An Ag-DLC film of 15.2 at% Ag exhibits a superior adherence on the steel substrate as compared with the three Ag DLC films of the other doping silver contents.

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18

Ezzedine El Dandachy, Mohamad, Matthieu Briffaut, Stefano Dal Pont, and Frederic Dufour. "Induced Anisotropic Gas Permeability of Concrete due to Coupled Effect of Drying and Temperature." Key Engineering Materials 711 (September 2016): 871–78. http://dx.doi.org/10.4028/www.scientific.net/kem.711.871.

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An experimental campaign is carried out to study the effect of drying shrinkage and temperature on multi-directional gas permeability of dry concrete. Thermal loadings up to 250°C are applied on concrete samples in cylinder (11×22) and dog-bone forms (total length of 61 cm). Samples are sliced for permeability measurements. Permeabilities in longitudinal and radial directions are addressed. The cylinder samples are first sliced then dried or heated whilst the dog-bone samples are first dried or heated then sliced. The average of initial intrinsic permeability for the slices (5 cm height, 11 cm diameter) obtained from the (11×22) samples is found isotropic and equal to 2.93×10-17 m2. In this case, drying shrinkage is isotropic. Furthermore, it is shown that for the dog-bone samples, drying shrinkage may induce micro-cracks preferentially in a certain direction which induces permeability anisotropy. Finally, the evolution of the normalized intrinsic permeability with respect to initial permeability versus temperature is found isotropic. An exponential fitting of intrinsic permeability versus temperature is found based on experimental measurements.

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19

Luzin, Vladimir, C. Rathod, D. Wexler, Paul Boyd, and Manicka Dhanasekar. "Residual Stresses in Rail-Ends from the in-Service Insulated Rail Joints Using Neutron Diffraction." Materials Science Forum 768-769 (September 2013): 741–46. http://dx.doi.org/10.4028/www.scientific.net/msf.768-769.741.

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Insulated rail joints (IRJs) are an integral part of the rail track signaling system and pose significant maintenance and replacement costs due to their low and fluctuating service lives. Failure occurs mainly in rail head region, bolt- holes of fishplates and web-holes of the rails. Propagation of cracks is influenced by the evolution of internal residual stresses in rails during rail manufacturing (hot-rolling, roller-straightening, and head-hardening process), and during service, particularly in heavy rail haul freight systems where loads are high. In this investigation, rail head accumulated residual stresses were analysed using neutron diffraction at the Australian Nuclear Science and Technology Organisation (ANSTO). Two ex-service two head-hardened rail joints damaged under different loading were examined and results were compared with those obtained from an unused rail joint reference sample in order to differentiate the stresses developed during rail manufacturing and stresses accumulated during rail service. Neutron diffraction analyses were carried out on the samples in longitudinal, transverse and vertical directions, and on 5mm thick sliceed samples cut by Electric Discharge Machining (EDM). For the rail joints from the service line, irrespective of loading conditions and in-service times, results revealed similar depth profiles of stress distribution. Evolution of residual stress fields in rails due to service was also accompanied by evidence of larger material flow based on reflected light and scanning electron microscopy studies. Stress evolution in the vicinity of rail ends was characterised by a compressive layer, approximately 5 mm deep, and a tension zone located approximately 5- 15mm below the surfaces. A significant variation of d0 with depth near the top surface was detected and was attributed to decarburization in the top layer induced by cold work. Stress distributions observed in longitudinal slices of the two different deformed rail samples were found to be similar. For the undeformed rail, the stress distributions obtained could be attributed to variations associated with thermo-mechanical history of the rail.

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Borrero-Lopez, Oscar, Paul J. Constantino, Mark B. Bush, and Brian R. Lawn. "On the vital role of enamel prism interfaces and graded properties in human tooth survival." Biology Letters 16, no. 8 (August 2020): 20200498. http://dx.doi.org/10.1098/rsbl.2020.0498.

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Teeth of omnivores face a formidable evolutionary challenge: how to protect against fracture and abrasive wear caused by the wide variety of foods they process. It is hypothesized that this challenge is met in part by adaptations in enamel microstructure. The low-crowned teeth of humans and some other omnivorous mammals exhibit multiple fissures running longitudinally along the outer enamel walls, yet remain intact. It is proposed that inter-prism weakness and enamel property gradation act together to avert entry of these fissures into vulnerable inner tooth regions and, at the same time, confer wear resistance at the occlusal surface. A simple indentation experiment is employed to quantify crack paths and energetics in human enamel, and an extended-finite-element model to evaluate longitudinal crack growth histories. Consideration is given as to how tooth microstructure may have played a vital role in human evolution, and, by extension, to other omnivorous mammals.

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Xiangan, Kong, K. Saanouni, and C. Bathias. "On the Fatigue at Very High Frequency — Part I: Theoretical and Variational Formulation." Journal of Engineering Materials and Technology 113, no. 2 (April 1, 1991): 205–9. http://dx.doi.org/10.1115/1.2903393.

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This first part of our study is concerned with the theoretical and variational formulations of the problem of elastic cyclic loading at very high frequency (or acoustic fatigue). The problem is treated by using the theory of longitudinal thermoelastic wave motion in a finite medium with and without running crack. Two methods are used to formulate the evolution problem: the first one deals with the use of classical time integration schema, and the second uses the Fourier transformation to solve the evolution problem in the frequency space. Comparison of our results with some closed form solutions of some classical problem is presented. In a second paper this method is used to calculate thermo-mechanical fields in specimens used in ultrasonic fatigue tests (endurance tests and crack growth tests).

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Betke, Ulf, Marcel Scheunemann, and Michael Scheffler. "Refitting of Zirconia Toughening into Open-Cellular Alumina Foams by Infiltration with Zirconyl Nitrate." Materials 12, no. 12 (June 12, 2019): 1886. http://dx.doi.org/10.3390/ma12121886.

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The present work describes the combination of the well-established dispersion infiltration of the hollow struts in reticulated porous ceramics (RPCs) and the salt solution infiltration of the remaining strut porosity. This approach is applied on alumina foams, which are loaded subsequently with a dispersion of sub-micrometer alumina particles and a ZrO(NO3)2 solution. The zirconyl nitrate is converted into a ZrO2 transformation toughening phase during the final sintering step. As a consequence of the complex microstructure evolution during the consecutive infiltration cycles, the reinforcement phase concentrates selectively at the weak spots of RPC structures—namely, the hollow strut cavities and longitudinal cracks along the struts. As a consequence, a severe improvement of the compressive strength is observed: The average compressive strength, normalized to a porosity of 91.6 vol.%, is 1.47 MPa for the Al2O3/ZrO2 infiltrated foams, which is an improvement by 40% with respect to alumina-only loaded foams (1.05 MPa) or by 206% compared to uninfiltrated alumina RPCs (0.48 MPa). The compressive strength results are correlated to infiltration parameters and the properties of the infiltration fluids, for example the rheological behavior and the size of the Zr solute species in the respective ZrO(NO3)2 solution.

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Ghiban, Brandusa, Iulian Antoniac, Gheorghe Dan, Alexandru Ghiban, and Razvan Ene. "Metallurgical Failure Analysis of Intramedullary Nail Used for Femoral Fracture Stabilization." Key Engineering Materials 695 (May 2016): 178–82. http://dx.doi.org/10.4028/www.scientific.net/kem.695.178.

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Currently orthopedics challenge is the use of intramedullary nails to straighten diaphyseal femoral fractures. In this paper it was conducted a case study on an intramedullary nail used for femoral fracture stabilization, in the case of one young patient. The evolution was unfavorable to the fracture site and the implant failed after three month of first surgical intervention. Intramedullary nail dimensions were 300mm length and 10mm in diameter. The following investigations were made in order to establish the failure causes: determination of the chemical composition through spectral analysis, macrostructural analysis using stereomicroscopy, optical microstructural analysis using optical microscopy, fractographic analysis using scanning electron microscopy. The final conclusions showed that the metallic biomaterial used for manufacturing the intramedullary nail was approximately an austenitic stainless steel AISI 316L, but with major microstructural defects. Macro-structural analysis revealed the presence of two zones of cracking, which are very rare at austenitic stainless steels. Also breaking with a fragile character has radial front tear propagation. In longitudinal section, cracks were evidenced due to the extraction operation and also the presence of corrosion products was shown. From fractographic analysis it was determined that intramedullary nail failure was predominantly through the mechanism of brittle fracture that took place at the point of maximum bending of the implant fragile.

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Yu, Ying, Weihang Zeng, Wen Liu, He Zhang, and Xiaohong Wang. "Crack Propagation and Fracture Process Zone (FPZ) of Wood in the Longitudinal Direction Determined Using Digital Image Correlation (DIC) Technique." Remote Sensing 11, no. 13 (July 2, 2019): 1562. http://dx.doi.org/10.3390/rs11131562.

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As a state-of-the-art method, the digital image correlation (DIC) technique is used to capture the fracture properties of wood along the longitudinal direction, such as the crack propagation, the strain field, and the fracture process zone (FPZ). Single-edge notched (SEN) specimens made of Douglas fir (Pseudotsuga menziesii) from Canada with different notch-to-depth ratios are tested by three-point-bending (3-p-b) experiment. The crack mouth opening displacements (CMOD) measured by the clip gauge and DIC technique agree well with each other, verifying the applicability of the DIC technique. Then, the quasi-brittle fracture process of wood is analyzed by combing the load-CMOD curve and the strain field in front of the preformed crack. Additionally, the equivalent elastic crack length is calculated using the linear superposition hypothesis. The comparison between the FPZ evolution and the equivalent elastic crack shows that specimens with higher notch-to-depth ratios have better cohesive effect and higher cracking resistance.

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Wang, Ying, Lars Mikkelsen, Grzegorz Pyka, and Philip Withers. "Time-Lapse Helical X-ray Computed Tomography (CT) Study of Tensile Fatigue Damage Formation in Composites for Wind Turbine Blades." Materials 11, no. 11 (November 21, 2018): 2340. http://dx.doi.org/10.3390/ma11112340.

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Understanding the fatigue damage mechanisms in composite materials is of great importance in the wind turbine industry because of the very large number of loading cycles rotor blades undergo during their service life. In this paper, the fatigue damage mechanisms of a non-crimp unidirectional (UD) glass fibre reinforced polymer (GFRP) used in wind turbine blades are characterised by time-lapse ex-situ helical X-ray computed tomography (CT) at different stages through its fatigue life. Our observations validate the hypothesis that off-axis cracking in secondary oriented fibre bundles, the so-called backing bundles, are directly related to fibre fractures in the UD bundles. Using helical X-ray CT we are able to follow the fatigue damage evolution in the composite over a length of 20 mm in the UD fibre direction using a voxel size of (2.75 µm)3. A staining approach was used to enhance the detectability of the narrow off-axis matrix and interface cracks, partly closed fibre fractures and thin longitudinal splits. Instead of being evenly distributed, fibre fractures in the UD bundles nucleate and propagate locally where backing bundles cross-over, or where stitching threads cross-over. In addition, UD fibre fractures can also be initiated by the presence of extensive debonding and longitudinal splitting, which were found to develop from debonding of the stitching threads near surface. The splits lower the lateral constraint of the originally closely packed UD fibres, which could potentially make the composite susceptible to compressive loads as well as the environment in service. The results here indicate that further research into the better design of the positioning of stitching threads, and backing fibre cross-over regions is required, as well as new approaches to control the positions of UD fibres.

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Li, Rong, and Jun Xiong. "A numerical prediction of residual stress for a thin-walled part with geometrical features fabricated by GMA-based additive manufacturing." Rapid Prototyping Journal 26, no. 2 (September 19, 2019): 299–308. http://dx.doi.org/10.1108/rpj-08-2018-0193.

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Purpose An accurate prediction of process-induced residual stress is necessary to prevent large distortion and cracks in gas metal arc (GMA)-based additive manufactured parts, especially thin-walled parts. The purpose of this study is to present an investigation into predicting the residual stress distributions of a thin-walled component with geometrical features. Design/methodology/approach A coupled thermo-mechanical finite element model considering a general Goldak double ellipsoidal heat source is built for a thin-walled component with geometrical features. To confirm the accuracy of the model, corresponding experiments are performed using a positional deposition method in which the torch is tilted from the normal direction of the substrate. During the experiment, the thermal cycle curves of locations on the substrate are obtained by thermocouples. The residual stresses on the substrate and part are measured using X-ray diffraction. The validated model is used to investigate the thermal stress evolution and residual stress distributions of the substrate and part. Findings Decent agreements are achieved after comparing the experimental and simulated results. It is shown that the geometrical feature of the part gives rise to an asymmetrical transversal residual stress distribution on the substrate surface, while it has a minimal influence on the longitudinal residual stress distribution. The residual stress distributions of the part are spatially uneven. The longitudinal tensile residual stress is the prominent residual stress in the central area of the component. Large wall-growth tensile residual stresses, which may cause delamination, appear at both ends of the component and the substrate–component interfaces. Originality/value The predicted residual stress distributions of the thin-walled part with geometrical features are helpful to understand the influence of geometry on the thermo-mechanical behavior in GMA-based additive manufacturing.

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Zhao, Xingdong, Lei Deng, and Jitao Xu. "Defining Stress Thresholds of Granite Failure Process Based on Acoustic Emission Activity Parameters." Shock and Vibration 2020 (July 28, 2020): 1–8. http://dx.doi.org/10.1155/2020/8812066.

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In order to study the crack closure stress threshold σcc of hard rock, crack initiation stress threshold σci, stress threshold σcs of crack interaction, and damage stress threshold σc d, uniaxial compression test was carried out on granite samples. Stress sensor and dynamic strain gauge are used to measure the load, longitudinal, and lateral deformation of rock in real time. The acoustic emission characteristic parameters of rock fracture process are obtained by using the acoustic emission system. According to the change rule of the AE event rate, cumulative energy, energy rate, duration, and amplitude in the whole process of granite sample fracture, the stress threshold (σcc, σci, σcs, and σc d) of each loading stage in the process of rock sample fracture is obtained. The relationship between the stress threshold (σcc, σci, σcs, and σc d) of each stage and the uniaxial compressive strength σUCS of rock samples in the whole process of fracture is analyzed, which shows that the deformation characteristics and crack evolution law of the rock are unified. The research results can provide some reference for further understanding of rock damage evolution mechanism in engineering field.

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Li, Ke, Xin Ling Wang, and Shuang Yin Cao. "Fatigue Performance of Partially Prestressed RC Beams with HRBF500 Bars." Applied Mechanics and Materials 174-177 (May 2012): 1463–70. http://dx.doi.org/10.4028/www.scientific.net/amm.174-177.1463.

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500 MPa level hot-rolled ribbed bars of fine grains (HRBF500) is a successfully developed new-type steel in Chain. The fatigue behavior of partially prestressed reinforced concrete (RC) beams with HRBF500 bars was investigated in fatigue tests of pre-tensioned T-beams. The beams are simply supported with the same overall dimensions, and the main parameter in the study is prestress degree and longitudinal steel ratio. Four beams were constructed and tested under constant-amplitude fatigue loading. All beams are initially cracked before the application of repeated loading. The stress evolution of HRBF500 bars and prestressed strands, the information about crack growth and the deflection developments of test beams were presented. The main factors that affect the fatigue properties of prestressed concrete test beams were fully discussed. Test results indicate that, the prestressed concrete beams reinforced with appropriate amount of HRBF500 bars and reasonable prestressing conﬁgurations can survive 2.5 millions cycles of constant-amplitude fatigue loading using an upper-bound fatigue load producing tensile stress of less than 150 MPa in HRBF500 bars. The results provide important guidance for the fatigue design of prestressed concrete beams with HRBF500 bars.

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Kasapi, M. A., and J. M. Gosline. "Micromechanics of the equine hoof wall: optimizing crack control and material stiffness through modulation of the properties of keratin." Journal of Experimental Biology 202, no. 4 (February 15, 1999): 377–91. http://dx.doi.org/10.1242/jeb.202.4.377.

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Small-scale components of the equine hoof wall were tested to determine their mechanical roles in the morphological hierarchy. Macroscale tensile tests conducted on samples of the inner wall tubules and intertubular material showed a sixfold difference in mean initial stiffnesses (0.47 and 0.08 GPa, respectively), indicating that the inner wall tubules stiffen the wall along its longitudinal axis. The similarity in material properties of tubule and intertubular samples from the mid-wall suggests that tubules in this region offer only minor reinforcement along the longitudinal axis.Microscale tests conducted on rows of keratin strands from the inner wall tubules and intertubular material, and on intertubular keratin strands of the mid-wall, produced estimates of the stiffnesses of the hydrated matrix (0.03 GPa) and intermediate filament (IF; 3–4 GPa) components of the nanoscale (α -keratin) composite. The results from these tests also suggest that the properties of the keratin composite vary through the wall thickness. Birefringence measurements on inner wall and mid-wall regions agree with these observations and suggest that, although the keratin IF volume fraction is locally constant, the volume fraction changes through the thickness of the wall. These findings imply that modulation of the hoof wall properties has been achieved by varying the IF volume fraction, countering the effects of specific IF alignments which serve another function and would otherwise adversely affect the modulus of a particular region.

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Ilczyszyn, Florent, Abel Cherouat, and Guillaume Montay. "Mechanical Modeling of Hemp Fibres Behaviour Using Digital Imaging Treatment." Advanced Materials Research 423 (December 2011): 143–53. http://dx.doi.org/10.4028/www.scientific.net/amr.423.143.

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These last years, hemp fibres are using as reinforcement for compounds based on polymer in different industrial manufacturing for their interesting mechanical and ecological properties. The hemp fibres present a non constant cross section and complex geometry that can have a high effect on their mechanical properties. The mechanical properties of hemp fibres (Young moduli, longitudinal stress and failure strain) are rather difficult and request a specific characterization method. In this study, a micro-traction test coupled with a numerical imaging treatment and a finite elements method are used. The mechanical tensile test allows to determinate the evolution of the traction load in function of the displacement until the fibre crack. The numerical imaging allows to measure finely the hemp cross section along the fibre and aims to reconstruct a 3D hemp fibre object model from an image sequence captured by a mobile camera. And lastly, the finite elements method allows to take the real fibre geometry into consideration for the mechanical characterization using inverse optimization simplex method.

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Shabovta, V. P., A. K. Torgovets, and E. V. Maksimov. "Formation of longitudinal cracks on slabs." Steel in Translation 40, no. 6 (June 2010): 558–61. http://dx.doi.org/10.3103/s0967091210060100.

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Sun, Yan-hui, You-jin Ni, Hai-tao Wang, Zhong-bo Xu, and Kai-ke Cai. "Longitudinal surface cracks of thin slabs." International Journal of Minerals, Metallurgy, and Materials 17, no. 2 (April 2010): 159–66. http://dx.doi.org/10.1007/s12613-010-0207-x.

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Zhang, Nian, Xuejian Zhu, and Yifan Ren. "Analysis and Study on Crack Characteristics of Highway Tunnel Lining." Civil Engineering Journal 5, no. 5 (May 21, 2019): 1119–23. http://dx.doi.org/10.28991/cej-2019-03091316.

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Lining cracks are one of the most common diseases in highway tunnels, and the existence of lining cracks directly affects the overall stability and durability of tunnels, which has an important impact on the safe operation of tunnels, and it is necessary to analyze and study the characteristics of tunnel lining cracks. Combining with the detection data of multiple highway tunnels in the field, the different types of tunnel cracks are divided, and the classification numerical statistics method is used to obtain that the number and length of annular cracks in highway tunnel cracks are significantly higher than those of the other two kinds of cracks, and the longitudinal cracks in tunnel crack cracking degree are greater than the circumferential cracks and the inclinded cracks. The influence degree of cracks on the safety of tunnel structure longitudinal cracks are relatively the largest, the inclinded cracks are second only to longitudinal cracks, and the influence of cyclic cracks is relatively small. It provides reference for tunnel engineering design, construction, operation management and comprehensive improvement work.

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Barani, A., A. J. Keown, M. B. Bush, J. J. W. Lee, H. Chai, and B. R. Lawn. "Mechanics of longitudinal cracks in tooth enamel." Acta Biomaterialia 7, no. 5 (May 2011): 2285–92. http://dx.doi.org/10.1016/j.actbio.2011.01.038.

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Huang, Ru Qing, Zu Lai Li, Ye Hua Jiang, Rong Zhou, and Fan Gao. "Thermal Shock Cracks Initiation and Propagation of WCp / Steel Substrate Surface Composite at 500°C." Applied Mechanics and Materials 109 (October 2011): 253–60. http://dx.doi.org/10.4028/www.scientific.net/amm.109.253.

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In order to provide a theoretical basis for the study of thermal fatigue properties on surface composites, thermal shock cracks initiation and propagation of WCP reinforced high chromium steel substrate surface composites were studied by thermal shock test method at 500 °C. The results show that cracks initiation and propagation begin within a few thermal shock cycles, and after 15 thermal shock cycles, the composites remain intact, indicating a good thermal shock resistance. The thermal shock cracks consist mainly of longitudinal and transverse cracks. Within a few thermal shock cycles, the initiation and propagation of longitudinal cracks play a dominant role; however, with the increase in the number of thermal shock, the transverse cracks may play a key role as the length and number of both types of cracks increases. However, the increase is slow. The longitudinal cracks are mainly caused by the first class thermal stress and the transverse cracks result from the culminant effects of the first and second thermal stress, interacting with each other.

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Jokūbaitis, Vidmantas. "REGULARITIES IN PROPAGATION OF OPENED CORROSION‐INDUCED CRACKS IN CONCRETE." JOURNAL OF CIVIL ENGINEERING AND MANAGEMENT 13, no. 2 (June 30, 2007): 107–13. http://dx.doi.org/10.3846/13923730.2007.9636426.

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Long and short‐term (accelerated with simulation of pressure developed by compressed rust) experimental investigations were accomplished. It was investigated in long‐term tests the relationship between the width of the longitudinal cracks on the concrete surface and close to the reinforcement, and relation between these widths and corrosion‐induced damages in the reinforcement; parameters of these relationships were established. In short‐time investigations it was tried to clarify the influence of transverse reinforcement and opened normal cracks on the nature of longitudinal cracks propagation. It has been determined that the character and the rate of propagation of the longitudinal cracks depend on distribution of transverse reinforcement and normal cracks along a member.

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Yang, Shuo, Yang Zhang, Orhan Kaya, Halil Ceylan, and Sunghwan Kim. "Investigation of Longitudinal Cracking in Widened Concrete Pavements." Baltic Journal of Road and Bridge Engineering 15, no. 1 (March 17, 2020): 211–31. http://dx.doi.org/10.7250/bjrbe.2020-15.468.

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Widened slabs, widely employed in many US states in concrete pavements, have suffered from unexpected longitudinal cracks. These cracks suddenly appeared within 0.60 m to 1.20 m from widened slab edges and could be detrimental to the long-term pavement performance. The primary objective of this study was to identify possible causes for such longitudinal cracking observed on widened concrete pavements. Both field investigation and Finite Element Analysis were performed. Degrees of curling and warping were measured using a Terrestrial Laser Scanner. Concrete cores were also extracted to achieve a better understanding of how the cracking had developed. Field survey and numerical simulation results indicate that such longitudinal cracks could be primarily caused by a combination of excessive traffic loads, a high degree of curling and warping, inadequate support from underlying layers, pavement ageing, and skewed joints. It was also found that 4.30 m widened slabs coupled with tied Portland Cement Concrete shoulders outperformed others in terms of producing less cracking, even when they had experienced higher levels of truck traffic. The sites constructed in late afternoons also showed significantly less longitudinal cracks.

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Chen, Ling, and Guo Bin Tang. "Influence of Longitudinal Cracks in Bottom Flange of Concrete Continuous Box Girder." Applied Mechanics and Materials 744-746 (March 2015): 773–78. http://dx.doi.org/10.4028/www.scientific.net/amm.744-746.773.

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Longitudinal crack in bottom flange is one of the most common defects in concrete box girder bridges. This paper focuses on the influence of the longitudinal cracks on the mechanical properties of box girder using numerical method. Smear crack model and strain softening model was employed to simulate cracking process. Parameter analysis was also carried out to study the effect of length, crack depth and amounts of cracks in bottom flange. The results indicate longitudinal cracks in one span have a significant effect on the transverse stress and deflection, but have little effect on the other spans. The negative effects of longitudinal cracks increase with the crack length and depth. When the crack length is up to 10% of the girder span, the deflection of the span amplifies to 13%. Compared with the length and depth, the amounts of cracks don’t have much influence on the deformation of girder but affect stress.

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Ann Myers, Leslie, Reynaldo Roque, and Bjorn Birgisson. "Propagation Mechanisms for Surface-Initiated Longitudinal Wheelpath Cracks." Transportation Research Record: Journal of the Transportation Research Board 1778, no. 1 (January 2001): 113–22. http://dx.doi.org/10.3141/1778-14.

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Desjardins, J. L., D. J. Burns, R. Bell, and J. C. Thompson. "Stress Intensity Factors for Unequal Longitudinal-Radial Cracks in Thick-Walled Cylinders." Journal of Pressure Vessel Technology 113, no. 1 (February 1, 1991): 22–27. http://dx.doi.org/10.1115/1.2928723.

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Finite elements and two-dimensional photoelasticity have been used to analyze thick-walled cylinders which contain arrays of straight-fronted, longitudinal-radial cracks of unequal depth. The stress intensity factor K1 has been computed for the dominant crack and for some of the surrounding cracks. Cylinders with 2, 4, 6, 8, 16, 36 and 40 cracks have been considered. Good agreement has been obtained between the experimental and the numerical results and, for cylinders with 2 or 4 cracks, with previously published predictions. The results for all of the foregoing cases are used to develop simple, approximate techniques for estimating K1 for the dominant crack, when the total number of cracks is different from those that have been considered herein. Estimates of K1 obtained by these techniques agree well with corresponding finite element results.

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Gao, Xin Qiang, Gang Rong, and Yong Quan Zhu. "Analysis on the Development Trend of the Longitudinal Cracks During Tunnels Construction Based on the Strength Reduction Theory." Advanced Materials Research 368-373 (October 2011): 2949–54. http://dx.doi.org/10.4028/www.scientific.net/amr.368-373.2949.

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This article used the elastic-plastic finite element analysis method based on strength reduction theory and researched the regularity of longitudinal formation cracks during the loess tunnel construction. It analyzed the development trend of the crack dips and the distance between the surface crack and the tunnel center by different depth conditions when using the full section method and the bench cut method during the construction. From that it can get the boundary value of tunnel depth that the longitudinal crack can reach the ground. The result shows that: (1) Through the finite element analysis of the continuum structural model, it is feasible and effective to use the method, which is based on the area including the shear stress greater than the cohesive stress, the mutant horizontal displacement, and the change trend of the vertical displacement, to analyze the trend and the scope of longitudinal cracks after the excavation of the loess tunnels. (2) When using the full section method, the longitudinal cracks can reach the ground as long as the buried depth is less than 50m.With the increase of the buried depth, both of the depth of the cracks and the distance between the cracks and the tunnel center are all increased and the crack dips are changeable whose range is 56º~67º. However when the buried depth is more than 50m, the cracks can’t reach the ground and develop from the vault to the ground. The slip tendency near the ground is diminished. With the increase of the buried depth, the dips get larger, but the distance between the cracks and the tunnel center and the crack depth are invariable. (3) When using the-bench-cut method, the development trend of the formation crack is similar to that of the full section method. The cracks can reach the ground when the depth is less than 40m, and the range of the cracks is 56º~62º, or else the cracks can’t reach the ground. (4) From controlling the surface cracks, the bench cut method is superior to the full section method.

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Černý, Ivo, and Jiří Sís. "Experimental Assessment of Residual Fatigue Life of High Pressure Pipeline Section Containing Longitudinal Cracks." Key Engineering Materials 713 (September 2016): 163–66. http://dx.doi.org/10.4028/www.scientific.net/kem.713.163.

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Non-destructive inspection of an operated section of DN 300 high pressure gas pipeline (internal diameter 300 mm) indicated a quite frequent occurrence of longitudinal cracks of depths up to 50 % of the pipe wall thickness. As such cracks would be very dangerous from the viewpoint of further pipeline operation, selected sections of the pipeline were taken from the ground for an experimental programme aimed at evaluation of residual fatigue life. The first part of the programme concerned (i) experimental calibration of direct current potential drop (DCPD) method of crack depth estimation, complicated by the longitudinal position of the cracks, (ii) estimation of actual depths of selected, most distinct cracks and (iii) metallographical evaluation of profiles and depths of selected cracks. The DCPD calibration confirmed that for the specific configuration of electrodes used and characteristic crack profile, analytical calibration using Johnson´s formula corresponds to the actual crack depth quite exactly provided that the cracks are of radial direction. However, metallographical analyses showed that analysed actual cracks, though quite long, even more than 2 mm in some cases, were quite inclined, in some cases almost parallel to the pipe surface. These cracks occurred obviously in production during rolling process, which was a good sign for a relative safety of the affected pipeline. Further theoretical considerations were made to enable estimations of the inclined crack depths using the DCPD method, necessary for crack growth measurement during internal pressure fatigue tests, which followed.

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43

Perl, M., C. Levy, and J. Wang. "Interaction Effects in Combined Arrays of Radial and Longitudinal Semi-Elliptical Surface Cracks in Pressurized Thick-Walled Cylinder." Journal of Pressure Vessel Technology 119, no. 2 (May 1, 1997): 167–74. http://dx.doi.org/10.1115/1.2842279.

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In two previous papers, the interaction effects for two separate cases of large arrays of semi-elliptical, internal, surface cracks in a thick-walled, cylindrical pressure vessel were studied. First, arrays of radial cracks were considered followed by the study of longitudinal-coplanar crack arrays. Circumferential crack density and longitudinal crack spacing were found to have opposing effects on the prevailing stress intensity factors (SIFs). Consequently, in the present paper, combined arrays of both radial and longitudinal cracks are considered, and their interaction effects are studied. The mode I stress intensity factor (SIF) distribution for numerous configurations of combined semi-circular and semi-elliptical crack arrays are evaluated. The 3-D analysis is performed by the finite element (FE) method and the submodeling technique, employing singular elements along the crack front. The effects of crack density in the circumferential direction and of relative spacing in the longitudinal direction on the SIFs are studied for combined arrays of up to 32 circumferentially equispaced, radial cracks and having longitudinal relative spacing of 2c/d of 0.25 to 0.99; for a wide range of crack depth to wall thickness ratios, a/t, from 0.05 to 0.4; and for various ellipticities of the crack, i.e., the ratio of crack depth to semicrack length, a/c, from 0.2 to 1.5. The results clearly indicate that the SIFs are considerably affected by the interaction among the cracks, and that the SIF values depend upon the circumferential density and longitudinal spacing, the crack depth and ellipticity, as well as the three-dimensional nature of the problem.

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Yang, Gaiyan, Liguang Zhu, Wei Chen, Xingwang Yu, and Baomin He. "Initiation of Surface Cracks on Beam Blank in the Mold during Continuous Casting." Metals 8, no. 9 (September 11, 2018): 712. http://dx.doi.org/10.3390/met8090712.

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Surface cracking seriously affects the quality of beam blanks, a relatively new blank in the continuous casting in China. In order to study the mechanism of the initiation and propagation of surface cracks, this study established a 2D micro-segmented model of the solidification process for a beam blank in the mold, with a user subroutine DFLUX written in Fortran. Using a contact algorithm, the stress in the shell of the beam was analyzed considering the mechanical properties of the material (Q235B), thermal stress, surface friction force and ferrostatic pressure. The results showed that at the center of the web, surface longitudinal cracks were most likely to initiate at a height of 180 mm from the meniscus; at the fillet, surface longitudinal cracks were most likely to initiate at a height of 200 mm from the meniscus. Moreover, the casting speed showed a greater effect on surface crack initiation than the pouring temperature did. This study reveals the cause of longitudinal crack initiation, and the most likely positions of cracks on the strand. Thus, it is instructive for controlling surface cracks in production.

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45

Kornev, V. M. "Prefracture zone for longitudinal shear cracks in structured materials." Mechanics of Solids 46, no. 3 (June 2011): 416–24. http://dx.doi.org/10.3103/s0025654411030083.

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46

Il’gamov, M. A. "Longitudinal vibrations of a bar with incipient transverse cracks." Mechanics of Solids 52, no. 1 (January 2017): 18–24. http://dx.doi.org/10.3103/s0025654417010034.

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47

Kucheryavyi, V. I., and S. N. Mil’kov. "Estimation of oil-and-gas reliability at longitudinal cracks." Journal of Machinery Manufacture and Reliability 44, no. 1 (January 2015): 98–101. http://dx.doi.org/10.3103/s1052618814060041.

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Hosoda, Akira, Takayuki Higuchi, Masataka Eguchi, Haruaki Yoshida, and Hayato Aoki. "Self Healing of Longitudinal Cracks in Utility Concrete Pole." Journal of Advanced Concrete Technology 10, no. 8 (August 30, 2012): 278–84. http://dx.doi.org/10.3151/jact.10.278.

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49

Arafah, Diya, Mauro Madia, Uwe Zerbst, Stefano Beretta, and Mihaela Eliza Cristea. "Instability analysis of pressurized pipes with longitudinal surface cracks." International Journal of Pressure Vessels and Piping 126-127 (February 2015): 48–57. http://dx.doi.org/10.1016/j.ijpvp.2015.01.001.

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50

Budenkov, G. A., O. V. Nedzvetskaya, D. V. Zlobin, and S. A. Murashov. "Interaction of torsion waves with longitudinal cracks in tubes." Russian Journal of Nondestructive Testing 42, no. 6 (June 2006): 392–97. http://dx.doi.org/10.1134/s1061830906060064.

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Journal articles on the topic 'Evolution of longitudinal cracks'

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