Transverse Cracks Research Articles

A Numerical Simulation of UIC60 Rail-Weld's Fatigue and Crack Growth under Wheel Frictional Contact and Bending

In service condition rail joints, especially the weldments are under the action of various loadings which are not only working in multiple axis direction but also time-dependent having a cyclic and mixed-mode in nature and non-relative to each other. The surface of the rail and its weldment is acted by very high repetitive stress through the wheel and because of this contact stress the running surface or subsurface may have cracks or fractures due to fatigue. This work is based on numerical simulation of an aluminum thermite weldment on a UIC 60 rail under multi-axial fatigue crack propagation under the friction with surficial interaction between weldment and wheel with bending load due to vertically applied load through the wheel on the weld. Since contact is highly influenced by vertical load and also for minimizing the simulation time the lateral and longitudinal traction forces are not included in this study. The work formulation and discretization have been done with the finite element method and a non-linear lagrangian algorithm solver is applied. A 3-D rail-weld wheel model assembly and a semi-elliptical crack as a flaw on the weld surface are used to identify 3-Modes of SIFs along with its graphical plot generation. Simulation is performed under multi-axial weld wheel surface contact at different locations on weld running surface, taking into account varying position of fracture crack on weld 3-D model to calculate fracture life of weld joint and observation of fatigue crack propagation. This work involves the numerical and theoretical approach of fracture mechanics on created FE fatigue model using the Linear Elastic Fracture Mechanics (LEFM) method following Paris law for fracture mechanics. All the numerical simulation for critical fracture dimension and cycle count with stress intensity factor for weld failure data is estimated using software ANSYS 2020 academic and plotted, then comparison of predicted and observed transverse crack growth behavior and fatigue life of weld, based on Millions Gross Tonnes (MGT) is discussed.

Analysis on Cracking of a Pipeline Steel Pipe during Hydraulic Burst Test

Through macroscopic and microcosmic analysis of fracture, chemical composition analysis, fracture microscopic analysis and other methods, the causes of longitudinal and transverse fracture (only longitudinal cracking commonly through thousands of columns) in hydraulic burst test of L360M LSAW pipe were analyzed. Test results showed that the causes of transverse cracks in the steel pipe were the poor toughness of the pipe material which was related to the serious ferrite-pearlite banded structure. The serious band structure in the pipe was related to the high manganese content in the steel, which leaded to manganese segregation. We can use some measures to reduce the banded structure including controlling the element manganese content reasonably, reducing the final rolling temperature, controlling cooling rate and micro alloying.

Investigation on Flaw Evolution of Additively Manufactured Al2O3 Ceramic by In Situ X-ray Computed Tomography.

The additive manufacturing process may create flaws inside ceramic materials. The flaws have a significant influence on the macroscopic mechanical behavior of ceramic materials. In order to reveal the influence of flaws on the mechanical behavior of additively manufactured ceramic, flaw evolution under mechanical loads was studied by in situ X-ray computed tomography (XCT) in this work. In situ compression XCT tests were conducted on stereolithographic additively manufactured Al2O3 ceramic. The three-dimensional full-field morphologies at different compressive loads were obtained. The evolution of flaws, including pores, transverse cracks, and vertical cracks, during compressive loading was observed. The number and volume of pores, transverse cracks, and vertical cracks were extracted. It was found that most pores and transverse cracks tend to be compacted. However, high compressive loads cause vertical cracks near the upper surface to expand, leading to the failure of the specimen. Real flaws with morphological and positional information were introduced into the finite element models. The influence of different types of flaws on the mechanical behavior is discussed. It was found that vertical cracks have a greater influence on mechanical behavior than do transverse cracks under compression. The presence of transverse cracks contributes to the evolution of vertical cracks. This study may be helpful for process optimization and performance enhancement of additively manufactured ceramic materials.

Improved hot ductility of an as-cast high Mn TWIP steel by direct implementation of an MnS-containing master alloy

Transverse cracking is the main issue during continuous casting of TWIP steels due to degraded hot ductility at 700–950 °C. In this study, we improve the hot ductility of an 18.1Mn-0.68C-1.5Al (wt.%) TWIP steel by refining the as-cast structure via inoculation. Inoculation was implemented by direct addition of MnS-containing master alloy to the melt. Since MnS did not dissolve in the melt, they acted as heterogeneous nucleation sites for austenite nucleation. Consequently, MnS-inoculated steel shows finer grain sizes than reference steel. Additionally, MnS particles are found to have a polygonal shape, randomly distribute, and share a cube-on-cube orientation relationship with austenite; both habit planes are parallel to {111}. A periodic array of b= 1/6<112> edge dislocations at every fourth {222} planes of MnS is necessary to accommodate the large lattice misfit of the cube-cube relationship. The MnS-inoculated TWIP steel shows significantly improved hot ductility compared to previously reported TWIP steels.

Enhanced efficiency of enzymatic hydrolysis of wheat straw via freeze–thaw pretreatment

This research investigated enhancing the efficiency of enzymatic hydrolysis of wheat straw via freeze-thaw pretreatment and assessed the physicochemical structural changes after this pretreatment. The enzymatic hydrolysis efficiency of cellulose and hemicellulose was enhanced, and hemicellulose was more susceptible to pretreatment. The highest enzymatic hydrolysis efficiency of cellulose and hemicellulose was 57.06 and 70.66%, respectively, at - 80 ℃ for 24h and - 10 ℃ for 24h, respectively, which were 2.23 and 3.13-fold higher than the control levels, respectively. Scanning electron microscopy images indicated that transverse cracks appeared before longitudinal cracks with stronger pretreatment conditions, and holes were found in every sample after this pretreatment. Fourier transform infrared spectroscopy and X-ray diffraction analysis indicated that freeze-thaw pretreatment affected both the crystalline and amorphous regions and disrupted the hydrogen bonds within them. This study provides a physical pretreatment method to improve the efficiency of enzymatic hydrolysis of wheat straw.

Experimental and computational study on dynamic analysis of cracked simply supported structures under moving mass

In this study, the influences of crack parameters like crack location from the left end, crack height, number of cracks and the magnitude of mass and the velocity of the transit load on the vertical displacements of the cracked simply supported beams subjected to transit mass are investigated. The transverse open cracks with numerous damage scenerios are considered for the mathematical modelling of the system. The governing equations of motion for the system have been obtained and the equations have been solved by the help of Duhamel integral technique. The theoretical formulation has been exemplified with numerical studies. By utilizing ANSYS Workbench 2020, transient structural analysis has been carried out. The mode shapes and the frequency ratios of damaged simply supported beam have also been determined. To validate the numerical and FEM models, the experiments with damaged beams have been carried out in the laboratory. It has been proven that the results of the theoretical and FEM models are well convergent with the experimental data. The results gathered from the numerical analysis, FEA as well as experimental study have been presented with comparative graphs and tables. The outcomes of the examinations have been interpreted in the conclusions part. It has been observed that subject parameters are of considerable significance on the time dependent response of the cracked beams.

Active crack control approach applied to a horizontal rotating machine

The present contribution proposes an active vibration control technique devoted to shafts with cracks aiming to minimize their propagation. The existence of a crack in rotating shafts can be characterized by 2X and 3X super-harmonic amplitudes in the vibration responses of the rotor, which can increase as the crack propagates along the shaft’s cross-section. A proportional-integral-derivative control technique is applied to suppress the 2X and 3X vibration amplitudes of a cracked shaft, which is performed by using a bandpass filter applied to the vibration responses of the rotor. Numerical and experimental results are obtained through both a representative finite element model of a horizontal rotor and its corresponding test-rig. In this case, electromagnetic actuators are used to apply the control effort to the rotor. The Mayes model is applied for simulating the breathing behavior of the transverse crack. The linear fracture mechanics theory is considered to correlate the crack depth with the corresponding additional rotor flexibility. Both numerical and experimental results demonstrate the possibility of reducing the effects of a transverse crack through active control on the dynamic behavior of a rotating machine. Moreover, it is shown that the proposed control law is capable of controlling the crack effects with the rotor operating in different rotation speeds.

Investigating the modal behaviors of a beam with a transverse crack on a high-frequency bending node

There is a premise that the reduction of the bending modal frequency does not occur in the presence of a transverse crack on the bending node of a beam. This study investigated the modal behaviors of a beam with a transverse crack on a bending node and revealed that this premise does not hold, particularly for a deep crack on a high-frequency bending node. Mode II crack (sliding crack mode) of fracture mechanics, which has not been considered in most previous studies, was found to cause the reduction of the modal frequency of a beam with a crack on a bending node. A new frequency equation that accounts for mode II crack was devised. The implications of the new frequency equation were demonstrated through the normalized modal frequency shift factor. Further, the validity of the proposed frequency equation was demonstrated by comparing the quantitative results with finite element analysis results and experimental data.

НАУКОВИЙ СУПРОВІД РЕМОНТУ МОСТА НА КМ 159 + 267 ПРИ РЕКОНСТРУКЦІЇ АВТОМОБІЛЬНОЇ ДОРОГИ Н-31 ДНІПРО – ЦАРИЧАНКА – КОБЕЛЯКИ – РЕШЕТИЛІВКА

Abstract Introduction. Bridges are one of the most important components of transport infrastructure. And transport structures are built of complex structures, and the cost of their operation is high. In the last period, the traffic intensity and weight of vehicles on the roads of Ukraine have significantly increased. Ensuring reliable and trouble-free operation is a priority, complex and responsible task. Problem statement. After the installation of a cement-concrete surface on the bridge on KM 159+267 of the H – 31 Dnipro – Tsarichanka – Kobelaki-Reshetilovka road, cracks were found on the cement-concrete surface across the entire passage after some time. Oblique and transverse cracks soon appeared in the surface on both adjacent bridges (separate bridges for different directions of movement). The opening of cracks reached 1 mm. Materials and methods. On the bridge at Km 159+267, an experimental design was applied – a cement-concrete coating made of concrete of class B40. It provides for the device of dense waterproof concrete of the roadway slab, 110 mm thick, made of monolithic concrete of Class B40 F300 W12 (C32/40, XF4, C1 0,20 according to DSTU b v. 2.7-176:2008, crushed stone fraction 5-10 mm), after the device of a monolithic slab with a thickness of 200 mm, combining the beams of the superstructure. To study damaged structures, methods for measuring the opening of cracks using probes and tape measures were used. To determine the adhesion of the coating to a monolithic slab, samples were taken – round cores using a core collector. The strength of the concrete was measured with a sclerometer. Results. As a result of the conducted research, the lack of adhesion of the cement-concrete coating to the monolithic slab of the bridge was revealed. To achieve high performance, it is necessary to disassemble the damaged cement-concrete surface and install a new coating to eliminate defects in the bridge surface on km 159 + 267 of the H-31 highway. Conclusions. Studies have shown that more and more new cracks appear in the cement-concrete coating, and the opening of old ones increases. The cause of cracks is shrinkage of concrete. Since concrete shrinkage can last up to 1.5 years, even more cracks should have been expected to appear. It also turned out that the cement-concrete coating does not adhere to the monolithic slab of the superstructure. Given the above reasons, it is impractical to repair individual cracks. To achieve high performance, it is necessary to disassemble the damaged cement-concrete coating and install a new one. Taking into account the capabilities of the contractor, the construction of the bridge bed and asphalt concrete pavement was developed. Keywords: bridge, highway, cement-concrete pavement, asphalt concrete.

Prediction of transverse crack progression based on continuum damage mechanics and its application to composite laminates and filament-wound cylindrical pressure vessels

To predict the damage variable of a 90° ply in an arbitrary lay-up laminate subjected to a certain loading, we formulated a damage progression law that represents the damage variable as a function of the damage-associated variable based on continuum damage mechanics (CDM). Utilizing the three-dimensional laminate theory and this CDM model, we predicted the damage progression of a 90° ply in cross-ply and quasi-isotropic laminates. In this analysis, the effective compliance of Lopes’ model was adopted. Additionally, the failure pressure of a filament-wound (FW) cylindrical vessel was predicted by coupling the analytical solution with the present CDM model, and the predicted failure pressure was compared with the results obtained using Christensen’s failure stress criteria. As a result, it was indicated that the prediction of the final fracture of FW vessel requires the CDM approach.

Formation mechanism and control of transverse corner cracks in fine blanking steel

Owing to the extreme difficulty in their prevention, transverse corner cracks have been frequently observed in fine blanking steel produced on straight arc caster. In this study, the transient thermal module of Ansys was used to calculate the corner temperature distribution of a continuous casting slab. According to the actual cooling rate, a Gleeble 3500 thermal simulator was used to simulate the bending process of continuous casting, and the thermoplastic curves of test steel grades were drawn. Through the observation of fracture morphology and metallographic examination, typical precipitation detection and phase transformation temperature detection, the mechanism of corner cracks in experimental steel grades was determined and the corresponding control measures were formulated. The results showed that under the original process conditions, the corner temperature of the continuous casting slab was in the brittle temperature range of the steel grade when it entered the bending section. During the cooling process of the continuous casting slab, all Ti elements dissolved into the matrix, and the main precipitates were (Cr, Fe)XCY, while the grain boundary pinning was weak. In the high temperature brittle region, deformation-induced ferrite was produced at grain boundaries, which formed a stress concentration during the bending process which led to plastic reduction. The mixed control mode of strong cooling in the cooling stage and weak cooling in the reheating stage could not only ensure the strength of the slab shell in the vertical section, but also promoted the growth of the ferrite film induced by intergranular deformation in the strong cooling stage. It increased the maximum allowable stress of ferrite at the grain boundary. By controlling the temperature and cooling rate in the reheating stage, the growth of ferrite at the grain boundaries and the nucleation of ferrite in grains were accelerated, the stress distribution at grain boundaries and grains was uniform, and the corner cracks were eliminated.

Centrifugal model test on a riverine landslide in the Three Gorges Reservoir induced by rainfall and water level fluctuation

Frequent soil landslide events are recorded in the Three Gorges Reservoir area, China, making it necessary to investigate the failure mode of such riverside landslides. Geotechnical centrifugal test is considered to be the most realistic laboratory model, which can reconstruct the required geo-stress. In this study, the Liangshuijing landslide in the Three Gorgers Reservoir area is selected for a scaled centrifugal model experiment, and a water pump system is employed to retain the rainfall condition. Using the techniques of digital photography and pore water pressure transducers, water level fluctuation is controlled, and multi-physical data are thus obtained, including the pore water pressure, earth pressure, surface displacement and deep displacement. The analysis results indicate that: Three stages were set in the test (waterflooding stage, rainfall stage and drainage stage). Seven transverse cracks with wide of 1–5 mm appeared during the model test, of which 3 cracks at the toe landslide were caused by reservoir water fluctuation, and the cracks at the middle and rear part were caused by rainfall. During rainfall process, the maximum displacement of landslide model reaches 3 cm. And the maximum deformation of the model exceeds 12 cm at the drainage stage. The failure process of the slope model can be divided into four stages: microcracks appearance and propagation stage, thrust-type failure stage, retrogressive failure stage, and holistic failure stage. When the thrust-type zone caused by rainfall was connected or even overlapped with the retrogressive failure zone caused by the drainage, the landslide would start, which displayed a typical composite failure pattern. The failure mode and deformation mechanism under the coupling actions of water level fluctuation and rainfall are revealed in the model test, which could appropriately guide for the analysis and evaluation of riverside landslides.

Failure cause assessment of steam reformer radiant tube after long‐term service

AbstractThis study investigates the damage, microstructure, and mechanical evolution of service‐exposed HP40NbTi radiant tubes of a steam reformer furnace. Tube failure was reported after 6‐year of working at 525°C–830°C in the form of visible longitudinal and transverse cracks. The microstructure was evaluated using optical and scanning electron microscopy equipped with energy‐dispersive X‐ray spectrum analysis. The carbide phase transformation was determined by the method based on the matrix dissolution technique and X‐ray diffraction. The results of this study showed that the primary cause of the longitudinal crack formation is the local overheating and the oxidation of the dendritic grain boundaries. The M7C3 carbide transforms completely into the metastable M23C6 phase during high‐temperature service. Metallographic examinations revealed the shrinkage cavities and creep voids that are nucleated on both Cr‐ and Nb‐carbides. The continuous oxide layers of Cr2O3 and SiO2 formed near the inner and outer tube surfaces and the matrix's chemical composition near the outer tube surface was found to be depleted of Cr and C. Mechanical properties are irregular across the samples. A little margin of safety is noted, while the complete ductility dip is detected at room temperature. The root cause analysis of the failure under investigation showed that the tube failed due to the creep.

High-rate mode II fracture toughness testing of polymer matrix composites using the Transverse Crack Tension (TCT) test

This paper describes the novel high-rate transverse crack tension (TCT) test to determine mode II fracture toughness for high strain rates and compares this to quasi-static fracture toughness obtained with the standardized End Notch Flexure (ENF) test and the modified Transverse Crack Tension (mTCT) test suggested in the literature. The novel, miniaturized mTCT specimen is used to determine the fracture toughness under quasi-static and high-rate loading conditions with an electro-mechanical test machine and a Split Hopkinson Tension bar, respectively. For the high-rate tests, almost no interfering oscillations were observed in the load signal. A novel data reduction scheme allows achieving repeatable results with a very small standard deviation. The fracture toughness for the tested composite at a loading rate of about 5 m/s was found to be at least 50% higher than the one obtained under quasi-static loading.

Multi-fidelity progressive damage simulation of notched composite laminates with various ply thicknesses

In this study, a multi-fidelity fracture simulation scheme of composite laminates that accomplishes a seamless transition between medium- and high-fidelity crack models, namely, smeared crack models (SCMs) and discrete crack models (DCMs), is developed. The proposed scheme is based on the adaptive discrete-smeared crack (A-DiSC) method and a theoretical model for saturated crack density. The A-DiSC method first employs a DCM to model the transverse cracks in the laminates. If the crack density of each ply reaches the saturation value calculated using the theoretical model, the DCM is converted to an SCM. At this point, some cracks that are longer than a certain critical length remain explicitly modeled by the DCM, as they can significantly affect the subsequent path to final failure. By combining the two models, this method reduces the computational cost while preserving a sufficient prediction accuracy particularly in the case with numerous noncritical cracks up to failure. A simulation of the open-hole tensile test of composite laminates with various ply thicknesses was performed to verify the prediction accuracy of the developed scheme, and the predicted results were compared with the experimental results.

Experimental and numerical analysis of a novel curved sandwich panel with pultruded GFRP strip core

Curved sandwich structure made of glass fiber-reinforced polymer (GFRP) composite is emerging in the construction of non-linear architectures and wind turbine blades. In this work, a novel curved sandwich panel with pultruded GFRP strip core was proposed and studied. Compared with the common core materials such as foam and wood, pultruded GFRP strips can provide a higher stiffness and strength, particularly when used in large-scale sandwich structures. The proposed sandwich panel was manufactured through vacuum-assisted resin transfer molding process. A series of three-point bending tests was conducted to study the flexural behavior. The effect of surface thickness on the load-carrying capacity and failure mode was addressed. Then, a finite element analysis was conducted via ABAQUS and validated by the experimental results. The parametric study was performed to address the key design parameters. Both experimental and numerical results indicated that with the increased surface thickness, the failure mode could transition from the damage of glue seam to the transverse cracking inside the pultruded GFRP strip. Moreover, the load-carrying capacity can be improved with the thickened face sheet. In the end, this work successfully demonstrated the use of multilayer shell elements in the finite element modelling of the cracking behavior of glue seams.

Prediction of Equivalent Chloride Ion Diffusion Coefficient in Cracked Concrete of the in-Service RC Element

Considering the influence of the visible load-induced transverse cracks on chloride ion diffusion in cracked concrete of the in-service reinforced concrete (RC) elements under marine environment, a typical concrete volume with one transverse crack was taken to establish the governing equation. Assuming the crack widths at the outer lateral and bottom surfaces were equal, a model to predict the equivalent chloride diffusion coefficient in cracked concrete was put forward to consider the influence of the average transverse crack width, crack spacing and crack extending lengths in beam height and width directions on chloride diffusion. Results show that the proposed model can better reflect the variation trend of the equivalent chloride diffusion coefficient with different crack widths in in-service RC elements under marine environment.

Mechanistic–Empirical Model for Cracking Prediction in Unbonded Concrete Overlays on Concrete Pavements

Unbonded concrete overlays (UBOL) are a preferred rehabilitation solution for distressed concrete pavements because the remaining pavement can be used as a strong support layer while an interlayer between the UBOL and the existing pavement mitigates potential distress reflections. Nevertheless, UBOL, as other types of jointed concrete pavements, experiences fatigue cracking as a major distress because of critical stress inflicted by traffic and environmental loading. Therefore, for proper UBOL performance, a cracking model that considers the specific UBOL characteristics is necessary. The AASHTO Mechanistic–Empirical Pavement Design (AASHTO M-E) cracking model, although the most advanced model for UBOL design currently available, still presents significant limitations. The model considers only transverse cracking, ignoring longitudinal cracking which has been reported by Departments of Transportation. Additionally, UBOL unique design features such as the effect of temperature variation throughout the existing concrete slab thickness and different interlayer properties are overlooked, resulting in crack predictions with unreliable trends. To address these issues, this paper proposes a modified UBOL cracking model. The proposed model was developed with a new approach for stress analysis and damage calculation considering different positions in the UBOL as well as modifications of the temperature data processing, and built-in curl analysis. The model was calibrated and validated using Long-Term Pavement Performance UBOL sections, and two sensitivity analysis are presented with a modified reliability analysis.

Damage evolution in cross-ply laminates under tension–compression and compression-compression cyclic loads

Tension-Compression and Compression-Compression fatigue tests were carried out on glass/epoxy cross-ply laminates, with different values of the minimum to maximum load ratio R (−1, −3, −5, −7, −10 and 20). During the tests, the damage evolution in the 90° ply was monitored at the macro-and micro-scales. Three damage scenarios were observed, depending on the load ratio: i) initiation and propagation of transverse cracks for R ≥ −3, ii) initiation of multiple inclined short cracks for R = 20, iii) a mixed damage type with the presence of both transverse cracks and inclined short cracks for −10 ≤ R ≤ −5. Finite Element analyses of micro-scale Representative Volume Elements, combined with a recently developed crack initiation criterion, revealed the role of the Local Hydrostatic Stress in the matrix in controlling the different damage scenarios. Eventually, quantitative analyses showed a highly detrimental effect of the compressive part of the cycle on the transverse crack initiation and propagation.

Early fatigue damage accumulation of CFRP Cross-Ply laminates considering size and stress level effects

Ply-block size and stress level effect on accumulation of transverse cracks and delamination are investigated during early fatigue life of CFRP laminates. Tension-tension fatigue tests under different stress levels were performed for two cross-ply configurations. Edge observation with digital cameras, digital image correlation and acoustic emission were employed for in-situ damage monitoring. Transverse cracks were dominant for [0/902]s laminates with almost non-existent delamination, while different interactive levels between both damage mechanisms occurred for [02/904]s laminates. Poisson’s ratio identifies whether early fatigue damage is dominant by transverse cracks or involves delamination. Cumulative AE energy is a helpful indicator of crack density.