Multiple Cracks Research Articles

Mechanical Behavior of Multiple Edge‐Cracked Nanobeams by Taking Into Account the Multiple Cracks Effects

ABSTRACTBy exploiting the stress‐driven model, within the Euler–Bernoulli beam theory, a novel nonlocal analytical model is proposed in order to simulate the mechanical behavior of multiple edge–cracked nanobeams by taking into account the multiple cracks effects. According to the present model, the nanobeam is split in correspondence with each of the edge cracks, thus obtaining beam segments, connected to each other by means of massless elastic rotational springs. Firstly, the proposed model is validated by considering experimental data available in the literature, related to bending tests on two cantilever microbeams, each of them containing a single edge crack (i.e., ). Then, the model is employed to simulate a bending test on a cracked cantilever microbeam containing two edge cracks (i.e., ) and a parametric study is performed by varying both the crack depth, the distance between cracks, and the characteristic length of the material in order to investigate the influence of such parameters on the microbeam mechanical response.

Flexural behaviour of stone slabs with prefabricated prestressed CFRP-reinforced stone strips

A strengthening technique incorporating prefabricated, prestressed, carbon-fibre-reinforced polymer (CFRP)-reinforced stone strips for stone slabs was proposed. To investigate the flexural behaviour of strengthened stone slabs, an experimental campaign consisting of 11 stone-slab specimens was conducted by considering the reinforcement ratio, the prestress level, the length of stone strip and the strengthening method as the main parameters. By installing strain gauges on the CFRP bars and stone slabs, the stress-transfer efficiency between different components of the strengthened stone slab during prestressing and strengthening processes were monitored. The results showed that the temporary device could effectively maintain the prestress imposed in the CFRP bars and transfer it to the stone slabs to be strengthened. Further four-point bending tests indicated that the prefabricated stone strips shifted the failure mode of bare stone slabs from brittle fracture to ductile, with obvious deflection and multiple flexural cracks. The load plotted against deflection responses of the strengthened slabs showed three stages, and a significant increase in the load-carrying and deformation capacities was observed when compared to those of the bare stone slabs. Finally, simplified theoretical models for predicting the flexural strength and initial stiffness of the strengthened stone slabs were proposed and assessed.

Influence of Water Ingress at the Shield Tunnel Portal on Tunnel Deformation and Load Capacity Weakening

Abstract. During the construction of shield tunnels, adverse geological conditions can lead to tunnel segment settlement and damage. This study investigates the deformation patterns and changes in load capacity of shield tunnels under water ingress conditions at the portal, using a segment of the Jinan Metro as a case study. Through field measurements and numerical simulations, we analyzed the structural deformation and weakening of load capacity caused by water ingress. The results indicate that significant settlement occurs at both the tunnel crown and invert after water ingress, with a maximum settlement of 181.2 mm compared to the original design axis. The deformation profile of the tunnel primarily resembles a transverse "duck egg" shape, while the segments near the portal exhibit vertical "duck egg" deformations due to grouting and other factors. Multiple cracks and damages were observed in the segments, with up to 16 cracks found in a single ring. Compared to the original design conditions, the bending moment in the tunnel lining increased by approximately 7%, and the axial force increased by about 9%, leading to an 11% reduction in tunnel resistance effects. The findings of this study regarding tunnel lining deformation and load capacity weakening provide valuable insights for similar engineering projects.

Uniqueness and modified Newton method for cracks from the far field patterns with a fixed incident direction

Abstract We consider the inverse cracks scattering problems from the far field patterns with a fixed incident direction. We firstly show that the sound-soft cracks can be uniquely determined by the multi-frequency far field patterns with a fixed incident direction. The proof is based on a low frequency asymptotic analysis of the scattered field. One important feature of the uniqueness result is that the background can even be an unknown inhomogeneous medium. A modified Newton method is then proposed for the numerical reconstruction of the shapes and locations of the cracks. Compared to the classical Newton method, the modified Newton method relaxes the dependence of a good initial guess and can be applied for multiple cracks. Numerical examples in two dimensions are presented to demonstrate the feasibility and effectiveness of the modified Newton method. In particular, the quality of the reconstructions can be greatly improved if we use the measurements properly with two frequencies or two incident directions.

Influence of the longitudinal welded joint microstructure of X52 and X70 large diameter pipes on resistance to hydrogen embrittlement

The article covers influence of a set of gradient microstructures of large diameter pipes (LDP) on resistance to hydrogen embrittlement. The object of the study were specimens of longitudinal welded joints of X52 and X70 LDP before and after slow strain rate tensile tests (SSRT) in gaseous nitrogen and hydrogen. It was found that fracture of X52 specimens during SSRT occurred with multiple crack initiation centres at the interfaces of the pearlite–ferrite structural constituents, while fracture of X70 specimens resulted in a single crack propagation. Steels Х52 and Х70 fractured not in the heat-affected zone (HAZ) recrystallisation area containing islands of martensite-austenite phase, but in the high-temperature tempering zone, which is characterised by anisotropic ferrite-perlite (Х52) and ferrite-bainite (Х70) microstructure. Finely dispersed uniform structure of bainite ferrite despite the content of martensite-austenite component is not a source of hydrogen crack initiation. Although a welded joint of X70 steel is characterised by higher strength, it is less susceptible to the embrittlement effects of gaseous hydrogen than X52, which is probably due to the finer and more uniform structure of X70 steel. Presence of ferrite-pearlite banding in the structure of X52 steel has a more negative effect on resistance to hydrogen embrittlement than increased hardness of the HAZ high-temperature tempering area of X70 steel.

Evaluation of polyester high-tenacity fabric and carbon nanotube reinforcements for improving flexural response in concrete beams.

This research scrutinized the effectiveness of utilizing polyester high tenacity fabrics to enhance the functionality of concrete panels. Two distinct woven fabrics with comparable strength resistance were fabricated and assessed. Concrete beams were compared in their original form and those reinforced with woven fabrics, along with beams reinforced with carbon nanotubes (CNTs) (B, BC2, BC4, BS1, and BS2). Results indicated that the textile-reinforced concrete panels displayed notably greater energy absorption capabilities post-failure under flexural loads in comparison to the control and CNT-reinforced panels. This enhanced performance was credited to the development of multiple cracking patterns in the textile-reinforced panels. The flexural behavior of the textile-reinforced panels was characterized by four discernible phases: a linearly increasing segment, a crack propagation phase featuring multiple cracking, a post-cracking phase with reduced stiffness, and ultimately, failure due to fabric rupture or debonding. Conversely, the control and CNT-reinforced panels exhibited a more brittle response post-initial cracking, with a limited number of cracks and reduced deformation capacity. The performance of the textile samples was largely unaffected by their specific characteristics, except for the fabric wrapping angle. The introduction of 0.04% CNTs marginally enhanced crack flexural resistance compared to the control and 0.02% CNT panels, owing to the varied distribution of CNTs within the matrix. Overall, the textile-reinforced concrete panels demonstrated superior load-bearing capacity, ductility, and energy absorption when compared to the other reinforcement techniques examined.

Reduced basis method for the elastic scattering by multiple shape-parametric open arcs in two dimensions

We consider the elastic scattering problem by multiple disjoint arcs or cracks in two spatial dimensions. A key aspect of our approach lies in the parametric description of each arc's shape, which is controlled by a potentially high-dimensional, possibly countably infinite, set of parameters. We are interested in the efficient approximation of the parameter-to-solution map employing model order reduction techniques, specifically the reduced basis method. Initially, we utilize boundary potentials to transform the boundary value problem, originally posed in an unbounded domain, into a system of boundary integral equations set on the parametrically defined open arcs. Our aim is to construct a rapid surrogate for solving this problem. To achieve this, we adopt the two-phase paradigm of the reduced basis method. In the offline phase, we compute solutions for this problem under the assumption of complete decoupling among arcs for various shapes. Leveraging these high-fidelity solutions and Proper Orthogonal Decomposition (POD), we construct a reduced-order basis tailored to the single arc problem. Subsequently, in the online phase, when computing solutions for the multiple arc problem with a new parametric input, we utilize the aforementioned basis for each individual arc. To expedite the offline phase, we employ a modified version of the Empirical Interpolation Method (EIM) to compute a precise and cost-effective affine representation of the interaction terms between arcs. Finally, we present a series of numerical experiments demonstrating the advantages of our proposed method in terms of both accuracy and computational efficiency.

Experimental analysis of glass failure criteria under different thermal conditions

The initiation of the first crack mainly determines the criteria for glass failure. However, the extended consequences of cracking, with the formation of multiple cracks merging, result in fallout conditions under varying thermal loads that become more critical. Point-supported glass arrangements are globally used in high-rise and energy-efficient buildings for architectural ingenuity aimed at a low budget. However, the formation of cracks due to thermal load resulting in glass breakage could infuriate the overall fire dynamics of the enclosed area. Therefore, experimental study and prediction of glass failure become very crucial. The present experimental study focuses on finding the most critical parameter that may quantify the cause of glass failure and further breakage in fallout conditions under varying thermal loads. 45 experiments were carried out on float glass of 300 × 300 mm2 with 4 mm, 6 mm, 8 mm, 10 mm, and 12 mm with continuous fuel supply arrangements. Critical parameters analysed were the time of crack initiation, glass temperature at the time of cracking, maximum temperature difference at glass failure, and thermal strain caused by the temperature difference on the glass surface. The range of minimum and maximum temperature difference recorded on the glass surface for the present study was between 30–35°C and 55–60°C at the breakage time for all the experiments. The Maximum temperature difference measured was 56.99°C on the 12 mm glass surface, and the corresponding maximum thermal strain found was 482 × 10−6 mm/mm. The maximum heat release rate was found to be approximately 200 kW. Maximum heat flux was found in the range of 10.33 kW/m2 to 21.14 kW/m2. A correlation was also developed using the least square method for all the thicknesses, which is well correlated with the glass thickness per unit length.

Experimental and numerical evaluation of fibre-reinforced concrete vault forming slabs subjected to low-velocity impact loading

Vaults and dome structures are attractive in architecture due to their ability to evenly distribute weight and support substantial loads without internal columns. Fibre-reinforced concrete is ideal for these compressive structures, which experience low tensile stress. Assessing their performance under impact loading is crucial for safety, financial protection, and preserving cultural heritage. In this study, twelve arch-shaped slabs with thicknesses of 50, 75, and 100 mm, incorporating varying fibre percentages, were tested using a drop-weight impact test machine. Finite element analysis, validated against experimental results, was employed to evaluate the slabs’ behaviour under low-velocity impacts. The analysis revealed multiple flexural cracks in fibre-reinforced specimens, with maximum crack widths decreasing as fibre ratios increased. Although the number of microcracks rose with higher fibre content, crack spacing diminished. Results indicated that adding steel fibres significantly enhances tensile strength and energy absorption—showing a 90% increase in the 100 mm thick dome with 1.5% fibres—while reducing cracking. These improvements contribute to the durability, stability, and safety of concrete domes, lowering maintenance costs. Thus, incorporating steel fibres in the design and construction of impact-resistant concrete domes is highly recommended.

Fabrication and characterization of nacre-inspired metal/ceramic composites containing AlN nanowhiskers

Nacre-like composites prepared by infiltrating ice-templated porous ceramic-scaffolds with molten metal phases have successfully imitated the strengthening and toughening mechanisms of nacre at different lengthscales from macro to micro, but have not yet been able to replicate the nanoscale toughening mechanisms of nacre, which limits the further improvement in mechanical properties of the nacre-inspired composites. To resolve this issue, we prepared nacre-inspired Al/SiC composites containing AlN nanowhiskers by in-situ growth of whiskers during the spontaneous infiltration process of Al-10wt.%Mg alloy into an ice-templated porous SiC skeleton. It was found that the oxidation of the SiC skeleton had a significant impact on the growth of AlN nanowhiskers, as well as the phase composition and mechanical properties of the composites. When the skeleton was oxidized at 1100 ° C in air for 2 hours, the composite exhibited a large number of AlN whiskers and the optimal phase composition, while the flexural strength and fracture toughness of the composite reached their maximum values. The strengthening and toughening mechanisms, such as plastic deformation, crack deflection, multiple cracking, crack bridging, crack branching, and delamination, caused by the lamellar structure were observed. It was also found that the pull-out and bridging of the AlN whiskers provided strengthening and toughening effects at the nanoscale for the nacre-like composites.

A Hybridization of CSA DEA Approach for Detection of Multiple Transverse Crack Rotor Shaft Rotating in Fluid Environment under Axial and Bending Loading

A Hybridization of CSA DEA Approach for Detection of Multiple Transverse Crack Rotor Shaft Rotating in Fluid Environment under Axial and Bending Loading

Partially insulated cracks in orthotropic materials under steady state thermo-mechanical loadings

An attempt has been made to investigate the cracked composite medium with thermally conducting multiple cracks at its interface of the dissimilar orthotropic media subjected to thermal and mechanical loadings. The present article examines the governing equations, the associated differential constraints and boundary conditions those govern the temperature field and stress field. Fourier integral transforms, together with their corresponding inverses, have been employed to convert the singular integral equations into a set of linear equations by using the concept of orthogonality and completeness. The numerical technique, namely the Schmidt method, which employs a polynomial expansion of the unknown functions, is used to solve algebraic equations to determine the desired temperature and stress fields. The semi-analytical findings of the expressions for heat flux intensity factor (HFIF), stress intensity factor (SIF), and crack displacements have been mentioned in the article. Both mode-I and II types of cracks have been studied to investigate the effect of thermal conductivity. Detailed graphical representations effectively illustrate the numerical results and the interrelations between crack lengths, bonded strip width, and the partial conductivity coefficient of the crack surface. As the thermal conductivity coefficient increases, the temperature difference tends to zero. The results reveal that an increase in thermal conductivity decreases the SIFs.

Analysis of Fracture Modes and Acoustic Emission Characteristics of Low‐Frequency Disturbed Water‐Bearing Soft Rock With Different Cyclic Initial Value

ABSTRACTIn the complex geological environment of deep mining area, water‐bearing soft rock is more prone to damage and destruction by low‐frequency disturbance. In this paper, the dynamic–static combination test was conducted on the basis of uniaxial compression test by using creep dynamic disturbance impact loading system and acoustic emission technique. The test results show that with the increase of the initial value of disturbance loading, the fracture morphology of sandstone gradually changes from a single major crack to multiple cracks coexisting, and some saturated sandstones lose the bearing capacity in the process of disturbance, presenting a cone‐shaped fracture surface. The increase of the initial value of the disturbance changes the bearing capacity of the sandstone, and the peak energy of acoustic emission reaches the maximum value when the initial value of the disturbance is 80% UCS. The results of the study can provide some reference for the stability analysis of deep water‐rich soft rock mines.

Crack Growth and Fatigue Strength of Deck‐Rib Welded Joints in Orthotropic Steel Decks Integrating Mean Stress Effect

ABSTRACTFatigue tests were conducted to investigate the effects of mean stress, stress range, and deck thickness on crack growth and fatigue failure of the deck‐rib welded joint. According to the experimental results, a fatigue failure criterion and a fatigue evaluation method for deck‐rib welded joints, which consider mean stress effect, was proposed. The results indicated that the stress range remains the dominating factor, but the influence of mean stress cannot be ignored. It was proposed that the crack length reaching approximately 150 mm and the depth reaching around 70% deck thickness can be taken as the fatigue failure criterion, while increase in mean stress would reduce the critical crack length but increase the critical crack depth. Besides, multiple cracks will weaken the fatigue strength. It is recommended to use Walker method and the FAT 71 curve with enhancement factor to evaluate the fatigue strength under symmetrical stress cycle.

Multiple damage detection in sandwich composite structures with lattice core using regression-based machine learning techniques

The abstract discusses the importance of Structural Health Monitoring (SHM) in ensuring the reliability and health of structures. It introduces a novel approach for recognizing cracks and delamination in sandwich composite structures using advanced methods for data analysis and machine learning algorithms. The research leverages artificial intelligence and machine learning to accurately identify and locate damage such as delamination and cracks in composite sandwich layers, which can significantly enhance troubleshooting performance, improve detection accuracy, and reduce the time and cost associated with repairs. The article presents a damage detection technique utilizing regression analysis for sandwich composite structures with a lattice core, capable of identifying and locating multiple cracks and delamination, as well as simultaneous defects in the structure. The analysis is conducted based on the sandwich composite structure’s healthy and damaged conditions in Abaqus software, and acceleration responses under random forces obtained through the finite element method were used to train various machine learning models, including regression algorithms like k-Nearest Neighborhood Regression (KNN), Light Gradient Boost Machine (LGBM), and Decision Tree Regression (DTR) to detect the damage location. The results indicate that the regression (LGBM), k-Nearest neighborhood, and decision tree regression (DTR) were the most successful functions, respectively, and the damage classification models accurately identified the damage and its location in the composite structure, achieving an accuracy rate of approximately 98.8%.

Stress Field near Crack Tips in Pressurized Thick-Walled Cylinders with Single and Multiple Cracks in Linear Elastic Fracture Mechanics: Analytical and Numerical Analysis of Stress Field and Crack Behavior

<div>Arrays of radial cracks often appear at the bore of pressurized cylinders, posing potential safety risks and leading to possible structural failures. This article presents an analytical approach to evaluate the stress field arising from single or multiple uniform radial cracks in thick-walled pressurized cylinders within the context of linear elastic fracture mechanics (LEFM) under mode-I loading. This formulation is based on the fundamental equations of elasticity and approximations of stress intensity factors (SIF) reported in the literature. Hence, the SIF were revisited and their range of validity was highlighted. The study considers two types of internal pressure loading: one applied only to the cylinder’s inner surface with no pressure on the crack faces and another applied to both the inner surface and the crack faces. The influence of the number and length of cracks relative to cylinder thickness on the stress field is analyzed. A finite element model of the pressurized vessel is constructed to verify the proposed analytical solution, showing good agreement with numerical results for a limited number of cracks.</div>

Fatigue life prediction for Q420qFNH weathering steel welded joints considering the effect of multiple cracks

Multiple semi-elliptical cracks frequently develop at the weld toes of welded joints. These interfering multiple cracks significantly accelerate crack growth rates and reduce the fatigue life of a welded joint compared to a single crack. This study proposes a method for predicting the fatigue life of a welded joint with multiple cracks, considering weld toe amplification effect, multiple crack interference amplification effect, and crack closure effect. The method is validated through fatigue tests on Q420qFNH weathering steel welded joints. The main factors influencing the interference amplification effect are investigated, and theoretical formulas for the interference amplification factor of the stress intensity factor are derived using the finite element method and the superposition principle. The initiation, aggregation, and morphological evolution during the propagation process of multiple cracks is accurately simulated, and the fatigue life of both cruciform-welded and butt-welded joints is predicted. Additionally, a quantitative analysis is conducted to assess the impact of the number of fatigue cracks on fatigue strength. The results indicate that the interference amplification effect of cracks depends on their distance and mainly affects the surface point where the crack front is closest. The proposed fatigue life prediction method can accurately estimate the fatigue life of Q420qFNH steel welded joints considering the effect of multi-cracks. The interference and coalescence of multiple cracks significantly reduce the fatigue life of welded joints. An increase in the number of fatigue cracks notably decreases the fatigue strength.

A multi-scale modeling method for tensile properties of strain-hardening cementitious composites

The synergistic design of components of Strain-Hardening Cementitious Composites (SHCC) based on micromechanics is the critical to realize its high strength and ductility. We have developed a mesoscale model for revealing effects of mesoscopic parameter of SHCC on its multiple cracking behavior. However, the heterogeneity of mortar in SHCC, which may influence the saturated multiple cracking, was usually absent in the existing mesoscale model. In this paper, a sub-mesoscale model of mortar considering the fine aggregates, hydrated cement paste, and interfacial transition zones (ITZ) are introduced into the previous SHCC mesoscale model. A parameter transfer method linking these two scales is proposed. By linking them, the parameter design of SHCC of different scales can be considered comprehensively. The proposed model is validated by the three-point bending test and uniaxial tensile test of SHCC. The effects of fine aggregate volume, tensile strength of hydrated cement paste and tensile strength of interfacial transition zone on the mechanical behavior are parametrically analyzed via the validated model. The results show that the increase of the volume content of fine aggregate will reduce the tensile strength and elastic modulus of SHCC mortar matrix, while the strength of hydrated cement paste has a significant increase in the first crack stress of SHCC, and the ITZ strength mainly affects the elastic modulus of SHCC mortar. The developed model provides a reference for the material optimization design of SHCC.

Analysis and Repair of Cracks in Welding Tee of Main Steam Pipelines in Thermal Power Units

Abstract During the maintenance process of a certain thermal power unit, multiple intermittent cracks were found in the Y-type welding tee weld of the main steam pipeline. This paper expounds the detection situation and treatment process of the welding tee weld, and analyzes the material, operating condition, structural characteristics and stress state of the test parts. The results show that the cracks are reheat crack, which is greatly related to the material. In addition, the structure of the welding tee is not reasonable, which increases the stress of the weld and accelerates the generation and expansion of the cracks. In this paper, the optimization suggestions are put forward for the welding repair and heat treatment process of the main steam pipeline, and the defects are successfully treated, which provides a reference for the detection and repair of the weld defects of similar and thick-wall pipe fittings.

Multiple edge cracks in a coated semi-infinite medium due to non-Fourier thermal shock

In this wok, based on the non-Fourier C-V model, the problem for multiple edge cracks is investigated for a coating-substrate pair subjected to a sudden temperature drop at the surface of coating. The temperature and resulting thermal stresses without cracks are obtained by the method of Laplace transform. By numerically solving the singular integral equations, the thermal stress intensity factors (SIFs) are evaluated. The results from the Fourier model and C-V heat conduction model are presented for comparison. Two dimensionless quantities are proposed to account for the coupling effects of heat conduction parameters (i.e., thermal conductivity, thermal diffusivity, and thermal relaxation time). Numerical results are presented for the thermal SIF as a function of normalized quantities such as time, crack depth, material constants and crack spacing. The findings in this work are expected to provide references for maintaining the integrity of the coating-substrate pair in the extreme heat transfer applications.