Multi-directional Crack Research Articles

Detecting Multi-directional Cracks on Catalyst Tubes of Reformer Furnace using a Saturated Low-Frequency Eddy Current Array

Detecting Multi-directional Cracks on Catalyst Tubes of Reformer Furnace using a Saturated Low-Frequency Eddy Current Array

Poromechanical approach to blast‐induced dynamic fracture in concrete

AbstractThis study introduces a novel poromechanical approach to analyze blast‐induced dynamic fracture in concrete considering gaseous kinetics. The objective is to establish a framework for examining the fracture mechanisms during demolition. The simulation employs finite element analysis, incorporating three‐dimensional non‐orthogonal multidirectional cracks induced by gas inflation, through which the gaseous media flows too. The study investigates the principles governing crack network development and the influence of pressurized gas using a multiphase scheme and verifies its findings experimentally. It was also emphasized that benchmark blast experimental data are essential for validating the model, for practical applications in the demolition and renovation of existing structural concrete.

Investigation on the multidirectional crack vibration induced by rock fracture

Understanding crack vibrations in rock under load is crucial for comprehending and predicting rock failure. With this motive, a novel multidirectional crack vibration (MCV) monitoring experiment is carried out using miniature vibration acceleration sensors with directional sensing. The obtained results show that the crack surface produced by uniaxial compression failure of rock is rough and its direction is variable. Furthermore, the volume distribution of the sample after failure is uneven, and there is a noticeable difference in mass between the broken samples on either side of the crack. Different directions of crack vibration signals were detected during rock failure, all exhibiting a strong temporal correspondence with the stress drop, but the amplitudes and main frequencies of the vibrations differ across directions. The fracture-induced crack vibration is a typical low-frequency signal, with the highest recorded frequency at 55.63 kHz and the lowest being 0.86 kHz, with the main frequency mostly below 25 kHz, which is notably lower than acoustic emission. This difference suggests that fracture-induced crack vibration and acoustic emission are distinct physical quantities. The disparities in rock vibration amplitude and main frequency among different directions, especially those perceived by opposing sensors, indicate that the two sides of the crack cannot be considered as the same vibration system. The analysis shows that the fracture-induced crack vibration of rock under load is damped vibration with a small and variable damping. Besides, due to the difference in vibration parameters on both sides of the crack, their vibration amplitude and frequency are also different. The miniature acceleration sensors used in this work can effectively capture MCV during rock failure and can be employed to further investigate the vibration precursor of rock instability failure, so as to develop appropriate assessment and prediction methods for underground dynamic disasters.

Deformation behavior and microstructure formation mechanism at the interface of Mg/Al composite plate during vibration assisted rolling process

The poor metal mobility and insufficient fragmentation of the oxide film and hardened layer, which caused by low misalignment rate of the interface in traditional rolling (TR) process, lead to challenges to improve the interfacial bonding strength of Mg/Al composite plates. In this paper, a novel technology for manufacturing Mg/Al composite plates with excellent interfacial bonding quality by vibration assisted rolling (VAR) technology was proposed. VAR technology achieves high interfacial bonding quality of Mg/Al composite plates by introducing active shear stress through the misalignment of rollers. As a result, the interfacial bonding strength significantly increased from 28.5 MPa to 46.7 MPa, displaying an obvious improvement of over 64%. VAR technology enhances the degree of microstructures evolution and promotes the interdiffusion of elements in Mg/Al composite plates due to the frictional heat by the periodic misalignment of the rollers. Moreover, it promotes the multi-directional cracking of the hardened layer, and the cracking changes from strip cracking to cross cracking. It was attributed to the stress state of the Mg/Al composite plates change from biaxial compressive stress to state where biaxial tensile and compressive stress alternate periodically. In addition, the original shear stress in the rolling direction (RD) was increased and introducing an additional tangential direction (TD) shear stress at the interface. The technology could be beneficial for manufacturing Mg/Al composite plates with high interfacial bonding quality as well as provide a new technique for other metal composite plates.

Characteristics of earthquake swarm activity observed in the Palghar region of Indian Peninsula from January 2019 to October 2020

The present study emphasizes the seismic characteristics of earthquake swarm activity of the Palghar region that occurred in the hard strata of Deccan traps of the Indian peninsula. This activity is well monitored by National Centre for Seismology (NCS) from December 2018 to October 2020. The related data inferred that initially before the swarm activation there was a barricade to stop the entry of fluids into the permeable zone. Later the fluids are injected into the fault zone at a feasible place may be near the surface at the time of swarm initiation. Further the associated fluids percolated through several channels in many directions forming a multi-dimensional system of cracks and fissures at the level of swarm progression through two distinctive clusters during the time of present study along normal fault orientations. During this process, the heterogeneous material within the subsurface layers might have experienced a decrease in the effective stress due to the increase in the pore pressure which is the resultant of the percolation of fluids within the permeable zone. The outcome of the results shows a comparable strategic increase in the seismicity after the soil saturation during and after the rainfall in the affected zone. Also, the study of the seismicity accompanying fluid injections indicates that the fluid triggering seismicity is demonstrated by the increased slope of the magnitude frequency distribution in the form of spatial b-value which has been found reliable for a catalogue for Palghar swarm activity. The coulomb stress change is also examined to find out the consistency of stress patterns with the earthquake occurrences in the Palghar region which gives the characteristics of swarm sequence. The study emphasized the fundamental and geo-mechanical behavior of fluid migration through multi-directional cracks and fissures as the cause for the evolution and further growth of the Palghar swarm activity.

Assessment of the residual life of turbine runners with operational defectiveness

The residual life of the runners of hydraulic turbines in the presence of operational defects is estimated. The main problems of the operation of hydraulic turbines associated with technological defects and exhaustion of the standard resource are described. The main requirements for initial data to be used in estimation of the residual resource and the requirements for predicting the residual resource of runners based on the results of surveys and analysis of their technical condition are specified. We have classified and briefly described the applied approaches and techniques used in estimation of the residual resource. The main damaging factors affecting the residual life of the runners are revealed: deformation aging of the metal, cavitation, corrosion and fatigue damage to the elements of runners. The most characteristic defects are divided into three groups: zones of cavitation erosion; corrosion-fatigue cracks; and weld defects. Particular attention is paid to corrosion-fatigue cracks identified using flaw detection. The mechanism of crack formation and the most probable location of the cracks in the runner are shown. Statistical data on the number of cracks at the onset of the runner operation and at the time of shutdown maintenance are presented. The main statistical parameters of the sample and the parameters of crack size distributions including the distribution law are determined. The distribution law is exponential for the crack length parameter; whereas for the crack opening width it is log-normal. The revealed multidirectional cracks are located at the surface, subsurface or inner layer of the metal. They arise from operational defects (ulcers, craters, undercuts or delamination) and grow during operation of the turbine units. We also present the design schemes of elements with cracks used for quantification of resources according to the criteria of fracture mechanics. The results of calculations for static and dynamic crack resistance are presented as the dependence of stress intensity factors on the crack size. The levels of the total accumulated damage to the runners, the values of the residual life at the stage of crack nucleation and development were determined for 11 hydraulic units in the «start-stop» and «working» cycles. The main conclusion is that the total operating time of the hydraulic turbine runners significantly exceeds the standard operating life, while the residual resource is insufficient for a further period of long-term operation.

Normal Magnetizing-Based Eddy Current Testing Method for Multidirectional Cracks on Steel Plate Surface Based on Permeability Perturbation

Normal Magnetizing-Based Eddy Current Testing Method for Multidirectional Cracks on Steel Plate Surface Based on Permeability Perturbation

Extended Multi-directional Crack Model Applied to the RC Precast Joint Interface with Shear Dowel

Extended Multi-directional Crack Model Applied to the RC Precast Joint Interface with Shear Dowel

Influence of the second phase on relative fracture behavior of friction stir welded 7A52 aluminum alloy

The mechanical properties of welded joints play a decisive role in service life of the materials, and the second phase particles significantly affect the fracture behavior of the welded joint. In present work, 7A52 aluminum alloy welded joints were prepared by friction stir welding (FSW), the morphologies of different second phases distributed in the joints were observed by SEM, TEM, EBSD and the fracture behavior of the advance side was investigated by in-situ tensile testing. The results show that the fracture is located at the thermo-mechanically affected zone of advance side, where are serious crystal mutation and second phase segregation. Because of poor mechanical properties of the incoherent Mg2Si phase, the cracking initiated at the interface and showed a characteristic with multi-directional cracking. The incoherent AlFe phase cracked along the direction of shear force, and the separated phase interface provided the main cracking propagation path, which would reduce the energy consumption in the process of cracking propagation and accelerate the propagation speed. The semi-coherent AlMgCu phase with excellent mechanical properties hindered the movement of dislocations and improved the mechanical properties of the joints.

Multidirectional crack monitoring of concrete structures using 3D piezoceramic sensing array

Multidirectional crack monitoring of concrete structures using 3D piezoceramic sensing array

Fabrication and mechanical property of three-dimensional carbon fiber reinforced Mg-based bulk metallic glass matrix composite

Carbon fiber (CF) reinforced bulk metallic glass matrix composites (BMGMCs) have received widespread attention due to their light weight, but subsequent development is facing urgent challenges of uncontrollable interface reaction and poor plasticity. Here, we report a three-dimensional CF-reinforced Mg-based BMGMC, which significantly improves the microstructure and compressive plasticity by adjusting the pressure infiltration parameters. It has been found that the electroless copper plating improves the wettability of the CF and the melt without inducing the crystallization of the matrix, in spite of the partially dissolving and diffusing of the coating to the matrix. Under a similar infiltration pressure difference, high vacuum conditions are beneficial to reduce the capillary resistance of the porous CF preform, thereby improving the formability of BMGMC. Compression test results prove that the introduction of three-dimensional CF effectively improves the plasticity of the composite material and reduces its brittleness tendency. It can be attributed to the fact that the carbon fibers distributed in different directions effectively bridge the multi-directional cracks and prevent the early rapid shear band propagation. The present work provides meaningful enlightenment for the development of CF-reinforced BMGMC materials.

Influence of Fibers on High Performance Concretes: Fibers Fabricated in Cameroon

In this article, steel fibers (sf) and Alcohol polyvinyl fibers (apvf) are used as addition with the aim to obtain high performances concrete (hpc). Some mechanical properties of high performances concrete containing these materials have been studied through bending and compressive tests on prismatic and cylindrical test tubes. The results showed that the addition of fibers in a formulation of high performances concrete gives results that varies from one solicitation to another and from a type of fiber to another: in the case of the simple compressive strength test, strengths are rather reduced, despite the fact that pieces of test- tube remain sewn after rupture. This is due to the phenomena of multidirectional cracking that appear at the time of the solicitation. The compressive strength decreases more when apvf is used; ii) concerning the bending test, steel fibers improve considerably the strength and the ductility of concretes thanks to their nature and their geometry. This improvement is favored by the compactness of the matrix; iii) there is no interest using apvf to improve the ductility or the strength of the hpc in bending. They rather decrease the resistance to the cracking and the rigidity of the material.

Multi-Directional Fixed Crack Model Extended to Masonry Structures

The mechanical nonlinearity of a masonry structure depends on debonding and slip of masonry joints and the fracture of blocks like bricks and concrete. The present study proposes a behavioral simulation to idealize masonry joints by allocating three orthogonal planes, which are governed by the existing multi-directional crack model, and to represent the damage of blocks by using another three crack planes. The shear stiffness of the joint changes due to the disintegration of the infilling mortar caused by the shear slip of the joint, as well as the confining pressure dependence of the shear strength. Shear response analysis of a masonry structure considering this disintegration was carried out, and the applicability of the analysis model was validated. The following three types of structures were selected for validation: 1) masonry structures in which both joints and masonry blocks are damaged, 2) structures in which masonry blocks are primarily damaged but deformation is not concentrated in the joints, and 3) structures in which mortar joints are exclusively damaged but the masonry blocks are exempt of damage. It was confirmed that the proposed analysis model can analyze the damage mode of masonry structures. It evaluates yield strength as well and deformability is estimated on the safe side of an engineering viewpoint.

Warm deformation enhances strength and inhibits hydrogen induced fatigue crack growth in metastable 304 and 316 austenitic stainless steels

The effect of deforming temperature on fatigue crack growth rate (FCGR) was investigated for cold/warm deformed 304 and 316 stainless steels under 5.0 MPa hydrogen and argon gas atmospheres. The slope of the FCGR vs ΔK curve in both steels declined with increasing deforming temperature, especially in type 304 steel. Strain-induced α′ martensite was prone to flat-facetted, step-like and quasi-cleavage fracture. Warm deformation (400 °C) can inhibit the formation of α′ martensite around crack tip and cause cellular dislocation structures, which led to multi-directional crack pathway and lower FCGR. The microstructure was adjusted by warm deformation, and then hydrogen embrittlement resistance was improved on the basis of high-strength in metastable austenitic stainless steels.

Cements with supplementary cementitious materials for high-temperature geothermal wells

This paper discusses self-healing ability, characterized by the strength recovery and crack sealing, thermal shock and acid resistance of several cementitious composites in water, alkali carbonate or geothermal brine at 300 °C. The tested formulations included a common high-temperature OPC/SiO2 formulation, a calcium-aluminate cement with alkali activated FAF blend (TSRC), alkali-activated granulated blast furnace slag (GBFS/SiO2) and fly ash C/fly ash F (FAC/FAF) cementitious blends. Compressive strength recoveries and visual observations of cracks sealing using 3D imaging after the compressive damage and then after the 5-day healing period were used to evaluate the self-healing abilities of these composites. The strength recoveries were evaluated for composites after 1-, 5-, 10-, 15-, and 30- day initial curing periods at 300 °C and after repeated damage and 5-day healing treatments. The nature of the failure was classified depending on the Young’s modulus (YM) of the tested blends. Composites with moderate values of YM, such as OPC/SiO2 and TSRC developed slim cracks while brittle and very brittle FAC/FAF and GBFS/SiO2 cementitious blends produced multidirectional cracks or near-fragment failures resulting in poor strength recoveries. In comparison with the common high-temperature OPC/SiO2 blend, composites with alkali activated pozzolanic materials demonstrated a decrease in crack size during the short healing periods. Fly ash-containing composites showed better acid resistance surviving 28 days in sulfuric acid (pH 0.2) at 90 °C. The TSRC demonstrated the best thermal shock resistance losing only about 20 % of the original strength in five 350 °C heat→25 °C water thermal cycles. In all the tests the TSRC outperformed the rest of the composites with average strength recoveries of more than 85 %. Alkali carbonate was the most favorable for both strength recovery and crack sealing. The short-term strength recoveries could be further improved to above 100 % by addition of micro-glass fibers (MGF). However, the MGF raised the brittleness of the samples after longer initial curing times, which decreased recovery rates of the aged samples. Crystalline phase analysis demonstrated that different products assisted in strength recoveries and crack sealing. The later included for the most part silica and analcime while the former were hydrogrossulars (ferrian) with various stoichiometries, iron-magnesium minerals, cancrinite, quartz and boehmite. These phases formed thanks to the slow high-temperature alkaline reactions of fly ash and glass fibers for MGF-modified samples.

Development of oral‐fluid‐impervious and fracture‐resistant silver–poly(methyl methacrylate) nanoformulations for intra‐oral/extra‐oral rehabilitation

ABSTRACTPoly(methyl methacrylate) (PMMA) based dental prosthetic materials have an inferior transverse resistance value and a high water‐retention capacity. These drawbacks cause frequent prosthesis fractures both inside and outside the mouth, which require the remaking or repair of the prosthesis. The mechanical and physical durability of the polymer matrix can be improved by the incorporation of a multifunctional filler. In this study, we focused on the reinforcing effect of silver nanoparticles (AgNPs) on the flexural properties of PMMA. Apart from that, the transport behavior of water and saliva through this composite matrix was also studied extensively. Morphological analyses with scanning electron microscopy (SEM) and atomic force microscopy imaging techniques confirmed the uniform distribution of nanoparticles in the matrix with an increased surface roughness proportionate to the amount of AgNPs. The flexural strength and modulus were enhanced by the addition of up to 5 wt % AgNPs (p < 0.05); we also observed a significant increase in the fracture resistance. The SEM micrographs of the fractured ends of AgNP‐reinforced groups had smaller cracks compared to the large multidirectional cracks in the unreinforced group. The diffusion of oral fluid through the composite was investigated in detail as a function of the AgNP content, the nature of the solvent (water or saliva), and the temperature (5, 28, 37, or 60°C). The water and saliva uptake, diffusion, sorption, and permeation constants were investigated and were found to decrease with increasing AgNP loading. The transport properties could have been related to the morphology of the nanocomposites and followed the Korsmeyer–Peppas model. At high concentrations, the AgNPs formed a local filler–filler network in the polymer matrix. This network hindered the transport of water and saliva through the polymer. The outcome deduced from this study confirmed that the reinforced nanocomposites improved the durability of the denture base and could be an effective replacement for the conventional denture base. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47669.

Analytical study on creep shear failures of RC slender beams without web reinforcement

Sustained load problems, which can cause excessive deformation and severe damage to concrete structures, have been considered in current worldwide design codes by applying reduction factors on the compressive and tensile strength of concrete. A reduction factor in the shear design may also be required due to the decrease of shear-transfer action corresponding to the increases of the shear cracks opening. However, only a few studies are examining the effect of creep on shear performance of concrete structures, and the results are still inconclusive. As a complement to the previous experimental works, this study aims to investigate the effect of loading rate on the shear capacity of RC slender beams by non-linear finite element (FE) analysis. A spaceaveraged constitutive model with fixed multi-directional cracks was employed in the simulation of diagonal shear failure. The present study analytically examines the time-dependent effects on the beams under different loading rates until the delayed failure and compares the results with the previous experimental ones.

Pervasive cracking of heterogeneous brittle materials using a multi-directional smeared crack band model

A numerical methodology is presented for the plane stress analysis of pervasive cracking in heterogeneous materials. The smeared crack band concept is used in conjunction with the multi-directional crack model to objectively model cracking in a finite element analysis while allowing cracks to form at different orientations. The multi-directional crack approach is able to reduce stress-locking behavior that plagues conventional fixed crack models. An advanced meshing technique is used to generate meshes with smooth grain boundaries and high-quality elements of uniform size. The sequentially linear analysis procedure is used in place of an iterative method to avoid instability issues and to capture the snap-type behavior of brittle materials. The implementation is generalized to allow for the analyses of heterogeneous materials composed of anisotropic constituents; furthermore, elastic stiffnesses and fracture parameters of the materials studied can vary with orientation. The proposed methodology is used to study cracking in a concrete microstructure obtained using X-ray computed tomography. Bulk constitutive behavior and crack patterns are compared with results of other crack methods in the literature. The proposed methodology is also used to analyze cracking within a computer-generated polycrystalline microstructure composed of Voronoi-like grains with the properties of alumina. Using the capabilities of the proposed methodology, a comparative study is performed by varying the tensile strengths along grain boundaries relative to their interiors.

Tracking multi-directional intersecting cracks in numerical modelling of masonry shear walls under cyclic loading

In-plane cyclic loading of masonry walls induces a complex failure pattern composed of multiple diagonal shear cracks, as well as flexural cracks. The realistic modelling of such induced localized cracking necessitates the use of costly direct numerical simulations with detailed information on both the properties and geometry of masonry components. On the contrary, computationally efficient macro-models using standard smeared-crack approaches often result in a poor representation of fracture in the simulated material, not properly localized and biased by the finite element mesh orientation. This work proposes a possible remedy to these drawbacks of macro-models through the use of a crack-tracking algorithm. The macro-modelling approach results in an affordable computational cost, while the tracking algorithm aids the mesh-bias independent and localized representation of cracking. A novel methodology is presented that allows the simulation of intersecting and multi-directional cracks using tracking algorithms. This development extends the use of localized crack approaches using tracking algorithms to a wider field of applications exhibiting multiple, arbitrary and interacting cracking. The paper presents also a novel formulation including into an orthotropic damage model the description of irreversible deformations under shear loading. The proposed approach is calibrated through the comparison with an experimental test on a masonry shear wall against in-plane cyclic loading.

Behavioral Simulation Model for SFRC and Application to Flexural Fatigue in Tension

A fatigue behavioral simulation for steel fiber reinforced concrete (SFRC) subjected to high cycle repetition of loads is presented. The fatigue constitutive models for normal strength concrete developed in the past decades are extended to those for SFRC with regard to tension, compression and shear transfer along dispersed cracking. The hysteretic path-dependency of SFRC is extensively focused on as well as post-cracking tension softening, because it greatly affects the stress-strain amplitudes of SFRC inside structures. The interaction of multi-directional cracks is taken into account based upon the fixed crack approach for enabling the damage evolution under the principal stress rotation. The rate effect on the stress and strain relation is also formulated to take into account the nonlinearity related to both loading rates and numbers of cycles. These proposed models for SFRC are experimentally verified in view of S-N diagrams of flexural tension for practical use.