Formation Of Transverse Cracks Research Articles

Experimental Study on the Damage Evolution Mechanism of Siltstone by Water Content and Confining Pressure

ABSTRACTProlonged exposure of deep coal mines to erosion from groundwater results in a gradual accumulation of rock mass damage, which can lead to geological hazards such as deformation and instability. These challenges significantly impact the safe operation of deep coal mines. To understand the mechanisms behind siltstone damage progression related to water content and confining pressure, this study explores the influence of these factors on the deformation and damage evolution of siltstone, employing a combination of rock mechanics testing, numerical simulation, and CT scanning techniques. Results demonstrate that increasing water content reduces the compressive strength of rock, leading to more complex failure modes. In contrast, higher confining pressure strengthens the compressive capacity, thereby suppressing the formation and growth of transverse cracks under compression. Using Avizo software, a three‐dimensional model of siltstone was developed to visualize the distribution of fractures in a three‐dimensional field. In the MATLAB platform, a box dimension algorithm based on three‐dimensional digital volume imaging was developed, employing box dimension theory and digital image storage methods. Fractal analysis reveals that the fractal dimension of internal fractures in loaded samples increases linearly with water content, indicating more extensive fracture development and greater specimen damage. Applying the box dimension from three‐dimensional digital volume images as a metric facilitates characterizing the damage evolution in siltstone under different water content conditions. This approach provides a new means to quantitatively evaluate the growth and complexity of internal fractures in siltstone, offering insights into rock damage progression under varying moisture conditions.

Development of the reinforced concrete resistance theory in the zone about reinforcement

The actual problem of resistance of near-reinforcement zone of concrete is solved as a problem of volumetric stress-strain state with "closure" of output integral parameters of this zone on the rod scheme of the whole reinforced concrete element synthesizing hypotheses and dependencies of various disciplines of mechanics of solid deformation body, including fracture mechanics. The calculation model of the reinforced concrete element takes into account the effect of reinforced concrete of prof. Vl.I. Kolchunov describing the mechanism of formation and development of transverse and longitudinal cracks. In this case, generalized hypotheses of linear and angular deformations for warping and gradients of jumps of relative mutual displacements of reinforcement and concrete are adopted. New functionals of reinforced concrete are constructed, which are consistent with the ideas about resistance of crosssections of rod elements in near-reinforcement zones. Physical equations for a concrete matrix modeled between transverse cracks are written. The displacement components for the near-reinforcement area are found in relation to the crack opening width at the boundary of the "concrete-reinforcement" contact in transverse, longitudinal and radial cracks, respectively. The use of the accepted assumptions and multi-level calculation scheme for the near-reinforcement region significantly brings the calculation model closer to a real assessment of physical phenomena.

Analysis of the mechanical behavior of asphalt pavement under multiple coupling effects

To reveal the damage mechanism of asphalt pavement caused by the spatial rotation of the stress principal axis, and the influence range of excess pore water pressure on the pavement under the coupling action of multiple fields, the finite element software was used to build the three-dimensional highway asphalt pavement models. Under the consideration of gravity's impact on dynamic computation results, the study investigated the variation patterns of the direction cosines of the principal stress axes of asphalt structural pavement elements under the action of moving loads, as well as the distribution laws of excess pore water pressure. The results indicate that the influence of gravity on dynamic computation results increases gradually with the depth of the pavement, reaching an error of first principal stress of 40.1 % at the bottom of the lower layer. During the movement of loads, the pavement elements directly under the load undergo rotation of the principal stress axes in the xy, xz, and yz planes under different physical fields. With increasing pavement depth, the angle between the first principal stress and the z-axis primarily fluctuates between −90° to 0° and 90° to 180°. The cosine of the angle between the first principal stress and the x-axis and z-axis undergoes instantaneous positive and negative conversion, which can easily lead to transverse and longitudinal cracks on the road surface. The influence widths of excess pore water pressure along the longitudinal and transverse directions of the pavement increase with the pavement depth, with maximum widths of 5.426 m and 2.075 m, respectively. These findings offer new insights into the mechanisms behind the formation of transverse and longitudinal cracks on asphalt pavement and hold significant implications for the improvement of asphalt design methods.

Cracking mechanism of CMAS-corroded thermal barrier coatings based on a coupled thermo-chemo-mechanically phase-field fracture model

A thermo-chemo-mechanically coupled theoretical framework is proposed to describe the calcium-magnesium-alumina-silicate (CMAS) corrosion process during the cooling process. A phase-field fracture model is developed to investigate the effect of cooling temperature and CMAS concentration on the degree of corrosion reaction, the stress evolution and the crack initiation and propagation. σ11 concentrates in the region beneath the overlay of CMAS and σ22 appears at the interface between top ceramic coating (TC) and bond coating (BC). The higher stress concentration of σ11 and σ22 contribute to the formation of both vertical and transverse cracks. Transverse cracks first emerge at the interface between TC and BC in the edge region, followed by the formation of vertical cracks in the CMAS-coated region. Vertical cracks propagate to the interface and deflect into transverse cracks. The transverse cracks at the interface further propagate and merge, ultimately leading to the coating delamination. The higher initial cooling temperature and CMAS concentration contribute to the accelerated development of vertical cracking and the increase of the quantity and length of transverse and vertical cracks. The model provides a significant advantage in predicting the failure of TBCs during the cooling stage of CMAS corrosion.

Transverse cracking signal characterization in CFRP laminates using modal acoustic emission and digital image correlation techniques

The process of formation and subsequent propagation of transverse cracks in 90° plies of carbon-fiber laminated composites was studied using modal acoustic emission approach and digital image correlation techniques. The results from modal acoustic emission approach, which included a newly developed processing tool for acoustic emission waveforms, provided information for identification and subsequent characterization or localization of signals originating from transverse cracking by analysis of the separated flexural and extensional Lamb wave modes in terms of their modal parameters. The digital image correlation method served as a verification tool of the acoustic emission data outputs in the terms of activity of significant localized events originating from the formation of the transverse crack in the 90oply. This made it possible to specify more locally the accompanying activity belonging to the formation or propagation of the magistral transverse crack. The manuscript also presents results related to the evolution of flexural/extensional wave modal parameters as the function of loading force for both [0/0/0/90]S and [90/0/0/0]S panels. It can be concluded that the detection of transverse cracks requires the need for applying a more complex acoustic emission data analysis methodology, while the standard parametric analysis, including the waveform peak frequency, is not sufficient. The presented methodology may serve as a basis for development of robust analysis tool capable of detecting the investigated phenomena.

Failure mechanisms for Gd2O3–Yb2O3 co-doped YSZ thermal barrier coatings under high-temperature gradient

In this study, Gd2O3–Yb2O3 co-doped YSZ thermal barrier coatings with a top coat thickness of 400 μm were prepared on a nickel-based superalloy by atmospheric plasma spraying. The samples underwent multiple short-term and single long-term thermal exposures through burner rig tests under high-temperature gradients. The short-term thermal exposure duration of the coating was 25 s and the long-term thermal exposure duration was 1200 s. The microstructures and phase compositions of the samples were characterized, and their failure mechanism was discussed. The results demonstrate that during the burner rig tests, the coating surface temperature reached 2600K, resulting in coating sintering and sintered zone formation comprising coarse equiaxed grains. The short-term thermal exposure life of the coating is 3 cycles, and the long-term life is more than 1200s. After the single 1200s thermal exposure, the coating exhibited a stable cubic phase. However, under multiple 25s thermal exposures, the depth of the sintered zone increased with increasing number of cycles, leading to the formation of various vertical and transverse cracks within the coating. Coating failure was due to a combination of sintering and thermal-mismatch-induced stress.The early-stage coating delamination was attributed to sintering-induced transverse cracks, while the overall spallation was primarily ascribed to thermal-mismatch-induced transverse cracks.

Formation of transverse cracks in cross ply laminates in an environment of nonuniformly distributed fibers

This work is concerned with extracting characteristic features of transverse crack formation in cross ply laminates under axial tension considering nonuniform distribution of fibers in the ply cross section. The fiber-matrix debond crack initiation sites are determined first by the dilatation induced cavitation criterion for an epoxy matrix. The growth of the debond cracks is analyzed by calculating the energy release rates using the virtual crack closure technique. The kink-out of the debond cracks into the matrix is determined in short incremental steps by the maximum energy release rate criterion. Different scenarios are considered for the linking up of the kinked-out cracks to form continuous transverse cracks. By studying two different degrees of fiber distribution nonuniformity, the interactive effects due to the fiber distribution on the transverse crack formation are clarified.

Investigation of the possibility detection of defects in rail foot by mfl method

The article investigates the possibility of detecting defects in the form of transverse cracks in the rail foot at continuous inspection of rails during their operation. Magnetic method is chosen as an alternative to ultrasonic inspection. Computer modeling was carried out, based on the results of which a working model of the magnetization system and registration of control signals was developed and manufactured. Experimental studies of detection of crack models in the rail foot were carried out in laboratory conditions. The studies confirmed the results of computer modeling and proved the possibility of detecting such crack models. The minimum sizes of detectable crack models in rail foot in the zone of rail fasteners and between them have been estimated.

Stress field model for bond in reinforced concrete ties

The interaction of the reinforcing bars and the surrounding concrete plays an important role in structural concrete as it is decisive for the reinforcing bar anchorage and the load-deformation behaviour, including stiffness and deformation capacity. Therefore, understanding this interaction – commonly known as bond – is highly relevant to a safe and efficient structural concrete design. Bond depends on many parameters, which affect the local reinforcing bar-concrete interface as well as the global load transfer between the reinforcing bars and the surrounding concrete. The latter governs the formation of transverse and longitudinal cracks and the activation of transverse confinement, which are as decisive for bond as the local interface characteristics. Nonetheless, most bond models and code provisions focus on the local interface and merely account for the global configuration by means of empirically calibrated factors accounting, e.g. for good or bad bond conditions in confined or unconfined situations, respectively.This study investigates the potential of stress fields for modelling bond based on the lower-bound theorem of plasticity theory. Stress fields facilitate the investigation of the local interface and the global load transfer consistently in one model, providing valuable insight into the flow of forces. For simplicity, the fundamental case of a concrete tie reinforced with one deformed steel bar is studied in this paper, superimposing axisymmetric discontinuous stress fields originating at each reinforcing bar rib. Each stress field consists of a triaxial nodal zone adjacent to a rib and a conical compression field that spreads the bond force radially, and is equilibrated along its outer perimeter by axial tensile stresses and confining hoops. The model relies on geometric parameters and basic material properties. The validation against experiments on reinforced concrete ties shows a good correlation between the predicted and observed bond strength and the crack spacing. The predictions can be improved by assigning stiffnesses to the stress field components and requiring interface compatibility, i.e. ensuring contact between the concrete and the reinforcing bar at every rib. Even when assuming a simplified, linearly elastic constitutive behaviour for concrete, the consideration of interface compatibility allows for reproducing the steel strain dependency of the local and average bond stresses and the occurrence and impact of splitting cracks.

Accelerated in vitro oxidative degradation testing of polypropylene surgical mesh.

Polypropylene (PP) surgical mesh had reasonable success in repair of hernia and treatment of stress urinary incontinence (SUI); however, their use for the repair of pelvic organ prolapse (POP) resulted in highly variable results with lifelong complications in some patients. One of several factors that could be associated with mesh-related POP complications is changes in the properties of the implanted surgical mesh due to oxidative degradation of PP in vivo. Currently, there are no standardized in vitro bench testing methods available for assessing the susceptibility to oxidative degradation and estimating long-term in vivo stability of surgical mesh. In this work, we adapted a previously reported automated reactive accelerated aging (aRAA) system, which uses elevated temperatures and high concentrations of hydrogen peroxide (H2 O2 ), for accelerated bench-top oxidative degradation testing of PP surgical mesh. Since H2 O2 is highly unstable at elevated temperatures and for prolonged periods, the aRAA system involves a feedback loop based on electrochemical detection methods to maintain consistent H2 O2 concentration in test solutions. Four PP mesh samples with varying mesh knit designs, filament diameter, weight, and % porosity, were selected for testing using aRAA up to 4 weeks and characterized using thermal analysis, Fourier-transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR) and scanning electron microscopy (SEM). Additionally, the oxidation index (OI) values were calculated based on the FTIR-ATR spectra to estimate the oxidative degradation and oxidation reaction kinetics of PP surgical mesh. The OI values and surface damage in the form of surface flaking, peeling, and formation of transverse cracks increased with aRAA aging time. The aRAA test method introduced here could be used to standardize the assessment of long-term stability of surgical mesh and may also be adopted for accelerated oxidative degradation testing of other polymer-based medical devices.

The formation mechanism of metal-ceramic interlayer interface during laser powder bed fusion

ABSTRACT Experiments on Laser powder bed fusion (LPBF) of powdered Ti on Al2O3 substrate were conducted and the interface formation was studied using a multi-material fluid dynamics model. Results show that the melt pool is relatively shallow, with relatively flat interlayer interface under LPBF’s conduction mode. In this condition, a thin sheath of molten Al2O3 forms and acts as a lubricating film for the molten Ti, leading to Rayleigh instability due to high flow inertia. Keyhole formation penetrates the Al2O3 substrate, resulting in a wavy interlayer interface. The recoil pressure from the keyhole and overall melt inertia are suppressed by the highly viscous molten Al2O3, thereby improving single-track melt pool stability. However, the thermal expansion coefficient difference between Ti and Al2O3 led to the formation of transverse cracks. Achieving a defect-free metal-on-ceramic single track remains a challenge, despite this study serving as a guide for melt track and interface control.

Effects of micro voids on the early stage of transverse crack formation in unidirectional composites

Effects of micro voids on the early stage of transverse crack formation in unidirectional composites

Elastic–Plastic Stage of Transverse Deformations in the Compressed Zone of Real Reinforced Concrete Beams

The relationship between transverse and longitudinal deformations (Poisson ratio) in the compressed zone of bending reinforced concrete elements is still not properly considered in designs. This factor is important as it is related to the formation of transverse cracks in the compressed zone of the elements. The main aim of the present research was an experimental investigation of the Poisson ratio in the compressed zone of real single- and two-layer reinforced concrete beams as well as a comparison with the theoretical model proposed in this study. The elastic and elastic–plastic stages were analyzed using experimental data for real beams with a span of 8 m. It was shown that the term “Poisson coefficient” had a limited validity for elastic longitudinal deformations up to 0.5‰. After reaching this limit, the suitable term was “Poisson ratio”. The obtained results allowed a more accurate prediction of transverse deformations and the corresponding cracks, defining a new limit state for bending reinforced concrete elements. Therefore, the authors recommend that the obtained results are considered in order to increase the design accuracy of reinforced concrete bending elements. The outcomes of this study and the proposed theoretical concept should be included in modern design provisions.

Методы гидроразрыва труднообрушающейся кровли и угольного пласта для исключения динамических явлений в угольных шахтах

The paper demonstrates the need to develop methods of managing poorly caving roofs in the stoping and development faces as well as the ways of intensifying the degassing process of unrelieved coal seams to improve the technical and economic performance and safety of operation. Methods of the directional hydraulic fracturing (DHF) of the roof and the interval hydraulic fracturing (IHF) of the coal seam are suggested to eliminate the dynamic phenomena in coal mines as well as technological charts of their implementation. The DHF method consists in creating an initiating slot in the borehole walls, which acts as a stress concentrator, followed by its sealing with an insulating device, i.e. a packer. When a fluid is injected into this slot, the tensile stresses are created in the borehole walls and the fracture is forced to develop in a predetermined direction. The IHF method of the coal seam from the development workings using non-cased degassing holes of large and variable diameter consists in creation of transverse hydraulic fractures in the hole relative to its axis and increasing its gas recovery by an order of magnitude. This is achieved by using a double-sided packer with elastically expanding elements and a valve installed between them. Additional tangential stresses created in the borehole walls ensure the development of inelastic strain zone, leading to the formation of transverse cracks in the borehole. The results of numerical modeling of the stress-and-strain state of the rocks near the borehole where packer seals are installed using the finite element method are presented in the paper. Techniques and means to monitor the processes of hydraulic impact on the coal-rock massif are shown.

Modelling the thermoelectric behaviour of composite laminates in the presence of transverse cracks

Composite materials, based on carbon fibres and/or nano-modified polymers, are characterised by a thermoelectric coupling. Indeed, an electric potential drop is generated in the presence of a thermal gradient (Seebeck effect), which makes them suitable for thermoelectric applications.In this work, novel analytical models are presented for the calculation of the apparent in-plane electric, thermal and thermoelectric properties of composite cross-ply laminates in the presence of transverse cracks. The aim of this analysis is to understand the variation in the apparent laminate properties if damage takes place in the form of transverse cracks, this being typically the first damage mode occurring in composite laminates under static and cyclic tensile loadings.

Reasons for formation of transverse cracks in longitudinal weld of a pipe of the main gas pipeline

Investigations of transverse cracks in a longitudinal weld of a main gas pipeline pipe are presented, and the reasons for the formation of defects are analyzed. A comparative analysis of the results of in-line diagnostics and additional non-destructive testing with the actual parameters of cracks in microsections was carried out. The microhardness of the weld metal was measured in the crack zone and at a distance of up to 20 mm from it in both directions, which showed the presence of residual stresses in the region of the crack tip. The methods of optical and electron scanning microscopy were used to study the crack zone with the determination of the chemical composition of the weld base metal and inclusions in the crack zone. The results obtained made it possible to classify defects as “cold cracks” that formed in the weld metal after a long period of operation and developed further according to the stress corrosion cracking mechanism.

Prediction of transverse crack multiplication of CFRP cross-ply laminates under tension-tension fatigue load

This study aims to predict the transverse crack accumulation behavior of CFRP cross-ply laminates for evaluation of their remaining life. The tension-tension fatigue tests of CFRP cross-ply laminates were used to investigate the relationship between transverse crack accumulation behavior and the number of cycles of the fatigue tests. We also studied the damage accumulation behavior, including delamination of cross-ply laminates under fatigue loading, and it was indicated that the damage accumulation behavior depends on the maximum load of the fatigue tests. We proposed a method that can predict transverse crack accumulation behavior using a power-law between transverse crack density growth rate and the energy release rate associated with single transverse crack formation. As a result, the proposed method can estimate the applied number of cycles on CFRP cross-ply laminates.

Mitigation of cracks in laser welding of titanium and stainless steel by in-situ nickel interlayer deposition

• Fusion joining of SS-Ti by directed energy deposition of Ni interlayer demonstrated. • Ni interlayer restricted brittle intermetallic formation of Fe and Ti. • Ni between SS and Ti formed joint with graded thermal expansion coefficient. • Thus, Ni interlayer eliminated longitudinal and transverse cracks in SS-Ti joint. • Directed energy deposition of Ni interlayer improved the weld strength. In-situ laser deposition of Ni powder as an interlayer has been exploited to join dissimilar metals, titanium and stainless steel. Direct fusion joining of these materials often suffers from longitudinal cracks due to the formation of hard and brittle intermetallics of Ti and Fe, and also transverse cracks because of large difference in their thermal expansion coefficients. The Ni-interlayer mitigated the longitudinal cracks by acting as an effective barrier to elemental diffusion, thus restricting the growth of brittle intermetallics. As the thermal expansion coefficient of Ni lies between that of SS and Ti, this acted as a functionally graded layer to reduce the thermal residual stresses, thus preventing the formation of transverse cracks across the joint. Maximum ultimate tensile strength of the weld joints obtained was 375 MPa. Results were analyzed by performing various microstructural characterizations using scanning electron microscopy, x-ray diffraction, and energy-dispersive X-ray spectroscopy. The novelty of this method is its easy adaptability in three dimensions contour welding any dissimilar metals using an interlayer of a compatible material.

КРИТЕРИИ ОЦЕНКИ ТЕХНИЧЕСКОГО СОСТОЯНИЯ ЖЕЛЕЗОБЕТОННЫХ ПЛИТ ПРИ КОРРОЗИИ АРМАТУРЫ

To prevent premature wear and reduce the bearing capacity of reinforced concrete slabs, it is necessary to conduct a timely examination of their technical condition with the determination of the causes of defects with their subsequent elimination. At present, GOST 31937, which regulates the inspection rules, does not contain quantitative values of the technical condition criteria, according to which it is possible to assign a category of the technical condition of structures, including within the framework of a visual inspection. To identify the frequency of occurrence of defects associated with corrosion of reinforcement in reinforced concrete slabs of buildings and structures, as well as to determine the causes of their occurrence, 738 archival survey reports of TsNIIPromzdaniy JSC were considered. An analysis of previous surveys showed that defects caused by corrosion of reinforcement are among the most common and require more detailed instructions on the designation of the category of technical condition of structures. To develop criteria for the technical condition of reinforced concrete slabs with defects resulting from reinforcement corrosion, a calculation analysis of the effect of reinforcement corrosion on the bearing capacity was performed, the effect of corrosion products on the formation of longitudinal and transverse cracks, experimental data, and the requirements of regulatory documents were considered.

Cause analysis on tube brust of T23 steel water-wall in a ultra-supercritical unit

During the hydrostatic test of an ultra supercritical unit, the water wall burst occurred. The causes of leakage were analyzed by means of macro observation, chemical composition analysis, metallographic examination and hardness test. The results show that the formation of cracks is related to fatigue, extending from the inner wall to the outer wall, accompanied by corrosion and oxidation. Fatigue is the main cause of transverse crack formation.