Crack Location Research Articles

New Analytical Solutions for Free Vibration of Cracked Functionally Graded Rectangular Plates

In aerospace engineering, the existence of cracks highly alters the mechanical behaviors of structural components. As a new class of key structural components, functionally graded material (FGM) rectangular plates with an interior/side crack are focused on in this study. New analytical free vibration solutions are put forward for such cracked FGM plates. First, a cracked plate is decomposed into several subplates with the necessary continuity conditions to address the physical discontinuity issue caused by the crack. The challenge then becomes deriving analytical free vibration solutions for each subplate. To accomplish this task, a symplectic superposition method (SSM) is developed to deal with FGM rectangular plates with various boundary conditions, including the complex continuity conditions. The SSM eliminates the need for a predefined solution form, and its solution procedure, including variable separation and eigen expansion, is mathematically rigorous. Afterward, the analytical solutions obtained via the SSM are integrated to serve as the final free vibration solution of the cracked FGM plate. Comprehensive results based on the obtained analytical solutions, including natural frequencies and vibration modes, are presented and validated. The solutions are further used to investigate the effects of some important parameters, such as crack length and crack location.

Fatigue life prediction of cracked cross beam of mining linear vibrating screen under cyclic load

The cross beam of a mining linear vibrating screen is prone to cracking under long-term cyclic load. In order to accurately predict the fatigue life of the cracked cross beam, a coupled analysis method of vibration and crack propagation is proposed. A 2D dynamic model of the vibrating screen is established based on the finite element method, which is verified by the vibration test platform. The cracked Euler beam element is used to model the cracked cross beam. The effects of crack depth, amplitude of excitation force, frequency of excitation force, and crack location on the crack-tip stress intensity factor of the cracked cross beam are investigated in detail. In addition, an iterative method is proposed on the basis of the Paris model. The residual service life of the beam under different frequencies of excitation force, amplitudes of excitation force, spring stiffness, crack positions, and degrees of stiffness imbalance are discussed. The results demonstrate that the fatigue life of the beam increases as the frequency of excitation force and spring stiffness increase. The increase of the amplitude of excitation force and spring permanent deformation reduces the fatigue life. The conclusion obtained provide some theoretical guidance for the design and routine maintenance of mining linear vibrating screens.

Multiscale modeling of diffuse damage and localized cracking in quasi-brittle materials under compression with a quadratic friction law

The diffuse damage and localized cracking of quasi-brittle materials (i.e., rocks and concretes) under compression can be delineated by a matrix-microcrack system, wherein a solid matrix phase is weakened by a large number of randomly oriented and distributed microcracks, and the macroscopic cracking is formed by a progressive evolution of microcracks. Several homogenization-based multiscale models have been proposed to describe this matrix-microcrack system, but most of them are based on a linear friction law on the microcrack surface, rendering a linear strength criterion. In this paper, we propose a new quadratic friction law within the local multiscale friction-damage (LMFD) model to capture the plastic distortion due to frictional sliding along the rough microcrack surface. Following that, a macroscopic Ottosen-type nonlinear strength criterion is rationally derived with up-scaling friction-damage coupling analysis. An enhanced semi-implicit return mapping (ESRM) algorithm with a substepping scheme is then developed to integrate the complex nonlinear constitutive model. The performance of LMFD model is evaluated compared to a wide range of experimental data on plain concretes, and the robustness of ESRM algorithm is assessed through a series of numerical tests. Subsequently, to effectively describe the localized cracking process, a regularization scheme is proposed by combining the phase-field model with the established LMFD model, and the discretization independent crack localization is numerically verified.

Effect of welding residual stresses on the fatigue life assessment of welded connections

Welding residual stresses impose significant influences on the fatigue behavior and structural integrity of welded connections in various engineering applications. Understanding the effects of these residual stresses on fatigue life is crucial for ensuring the reliability and safety of welded structures. This paper proposes a damage-incorporated thermal–mechanical simulation method to examine the effect of welding residual stresses on the fatigue life prediction of welded plates and circular hollow section (CHS) X-joints. Compared to the experimental X-ray diffraction measurements and the fatigue tests, the predicted residual stresses and fatigue life demonstrate good agreement with experimental results for both high-cycle and low-cycle fatigue. The location of fatigue cracks resembles closely the estimation from a uniform fatigue damage indicator. The fatigue life prediction without incorporating the welding residual stresses does not affect significantly the life estimation for low-cycle fatigue but can cause substantial over-predictions for high-cycle fatigue.

Flexural mechanical properties of H-shaped steel-bamboo scrimber composite beams

To improve the torsional buckling resistance and enhance the load-bearing capacity and ductility of H-shaped steel beams with carbon reduction materials, the concept of combining H-shaped steel with bamboo scrimber has been proposed, in which the bamboo scrimber, an eco-friendly, lightweight, and high-strength material, promises significant structural benefits. Five full-scale specimens were designed and tested, including one H-shaped steel, two bamboo scrimber beams, and two composite beams. Additionally, further simulation tests were conducted using the verified finite element model (FEM). The experimental results revealed a remarkable increase in the ultimate bearing capacity of the composite beams by 96.5 % compared to bamboo scrimber-only beams and 72.7 % compared to steel-only beams. Meanwhile, distinct from the brittle fracture characteristics of the bamboo scrimber beams, which include instantaneous crack propagation and interlaminar cracking, the composite beams exhibited localized vertical cracks within the beam's tensile zone, effectively avoiding the torsional buckling issue of the H-shaped steel beam. The results further demonstrated that increasing the cross-sectional size of the composite beams can significantly enhance their flexural stiffness (up to 669 %), and reduce the deflection at the ultimate flexural moment. When the area of the bamboo scrimber in the cross-section was reduced with an unchanged steel profile, the initial stiffness dropped to 79 % without incurring any structural instability. Furthermore, by integrating the experimental and simulation results, a fiber element model for this composite beam structure is proposed to predict the maximum flexural moment value in the ultimate state. A corresponding calculation program was developed, and it is found that the calculated predicted ultimate flexural moment values exhibited negligible deviation from both experimental and FEM results, with AV of 1.0001, AAE of 2.21 %, and COV of 3.28 %.

Study on fracture characteristics of surrounding rock of twin tunnels under various crack inclination and location conditions

In some practical projects, two neighboring tunnels are often constructed in natural rock bodies that have a significant number of fractures with unpredictable inclination angles and locations. To study dynamic fracture characteristics of the surrounding rock mass of the twin tunnels containing a crack with different crack inclinations and crack locations, an experimental model of a cracked twin tunnel was designed and proposed, dynamic experimental analyses were carried out by using a traditional split Hopkinson pressure bar (SHPB) device and digital image correlation (DIC) method, followed by simulation conducted by using LS-DYNA code. The findings indicate that the spandrels and corners of the twin tunnels nearest the pre-cracks are more vulnerable to failure under dynamic loads, resulting in tunnels joining the ends of the pre-cracks. With various crack inclinations and crack locations, the initial cracks are typically produced at the roof and floor of the tunnel, as well as at the points of the pre-cracks. The specimen's kind of crack and its emergence site are connected. Crack inclination and location have little influence on the maximum displacement value in the twin tunnels. The study's findings could offer a fresh theoretical direction for evaluating the stability of twin tunnels when there are numerous joints and flaws.

Microstructure-sensitivity of CPFEM models on fretting fatigue crack initiation of AA2024-T351 alloy

The AA2024-T351 alloy is widely used in civil engineering, machinery, and aerospace industries for bolts, rivets, and thin plate components. When in service within these fields, the components are susceptible to performance degradation and fracture failure due to fretting fatigue. In this study, a crystal plastic finite element method (CPFEM) model incorporating microstructure sensitivity is employed to predict the fretting fatigue crack initiation (FFCI) location and lifetime. The submodel method is utilized to simulate various microstructures in the contact region of the specimen under fretting fatigue. This research focuses on two fatigue indicator parameters (FIPs): accumulated plastic slip p and FIPFS, used to determine the hotspots for crack nucleation on the contact surface and subsurface in fretting fatigue. The study explores the impact of different grain size and orientation on crack nucleation and analyzes how various microstructural characteristics influence the crack initiation lifetime. The findings indicate that the influence of grain orientation distribution in fretting fatigue on the initiation location of contact surface cracks is not significant, but it has a notable impact on subsurface cracks. Different grain textures combinations exhibit a more pronounced anisotropy based on the accumulated plastic slip p than FIPFS. Additionally, the effect of grain orientation distribution on the FFCI lifetime is influenced by the average grain size, showing remarkable influence within a specific range of grain sizes.

Ductility‐oriented design of UHPC T‐beams: Mechanical model and design recommendations

AbstractUltrahigh performance concrete (UHPC) has recently become a major focus garnering substantial attention due to its remarkable mechanical properties. UHPC has been increasingly employed across diverse projects in the construction industry. However, the structural ductility of UHPC members has yet to be fully established and is often compromised by the manifestation of the crack localization phenomenon. This paper presents the flexural test results of five T‐beams and introduces a model for predicting the flexural capacity and failure modes of UHPC T‐beams. The model employs the curvature ductility index as a measurement for evaluating and ensuring the member's ductility. The results show that the flexural behavior of UHPC T‐beams can be characterized by four key points representing cracking, reinforcement yielding, crack localization, and post‐localization capacity. The validity of the model is substantiated by experimental data from this study and complemented by test data collected from the literature. The proposed model is then employed to derive ductility‐oriented design limits, including minimum and maximum reinforcement ratios and minimum localization strain capacity. Finally, the paper summarizes the design recommendations and provides a classification of section conditions, reinforcement limits, localization strain limits, adequate ductility range, and the feasible ductile design range.

Unveiling the quantitative relationship between microstructural features and quasi-static tensile properties in dual-phase titanium alloys based on data-driven neural networks

The quasi-static mechanical properties of α+β dual-phase titanium alloys are susceptible to their microstructural features, presenting a complex, high-dimensional nonlinear relationship, which hinders the rapid development of high-performance materials. In this work, 4065 micro-representative models were virtually constructed with varying volume fractions of α and β phases and characteristic dimensions via high-throughput finite element simulation, incorporating a cohesive zone model to simulate the interfaces between the two phases. Especially, the established representative models were experimentally verified by two groups of real material microstructures, and the results showed that the relative errors were not more than 9.5 % in microstructural characteristics and quasi-static mechanical properties. Afterward, a neural network model was developed to correlate the quasi-static tensile properties with the microstructural features of the dual-phase TC6 titanium alloys, achieving an 88.2 % accuracy in predicting overall mechanical performance. Utilizing the Shaply Additive Explanation method, it was found that the primary α phase's volume fraction and the secondary α phase's width were the most significant microstructural features affecting quasi-static strength. Specifically, the volume fraction of the primary α phase and the width of the secondary α phase negatively affected strength, while the width of the secondary α phase positively influenced plasticity. Notably, the primary α phase's volume fraction had a quadratic curve pattern of influence on plasticity. The intrinsic mechanisms behind these laws were further revealed based on local stress-strain responses and crack propagation analysis. Ultimately, the optimal microstructural features with strength-plasticity balance were identified through the lower threshold method: a secondary α phase width of about 1 μm and a primary α phase volume fraction ranging from 0.1 to 0.2, effectively facilitating microstructure design.

Formulation of dynamic damage features sensitive to local fatigue cracks in steel bridges: Numerical study

Fatigue cracks commonly emerge within welding areas of steel bridges with orthotropic decks during the long-term operation. Dynamic-based detection presents an appealing method for detecting such fatigue cracks within steel bridges. Traditional linear dynamic indexes are not significantly affected by the small size of the damage, exhibiting the insensitivity to local fatigue cracks across the entire steel bridges. This study aims to address the dynamic insensitivity and find some potential damage features with practical utility. The fatigue cracks found on the Türr Istvan bridge spanning the Danube River in Hungary are presented, and the bridge models with two types of cracks are established. The local dynamic characteristics of the concerned substructures are isolated from the global characteristics of the entire bridge and used to reflect the local damage information. Accordingly, three potential strategies, namely, (i) impacting vertical ribs to obtain local frequencies, (ii) frequency sweeping the entire bridge system to induce local modes of the longitudinal girders, and (iii) pairwise monitoring of local strains near the crack, are proposed. Numerical results highlight that the sensitivity of local frequencies of vertical ribs is higher than that of global frequencies. The correlation coefficients of the pairs of strains between a crack are significantly decreased compared with those of the uncracked areas. The resonance peaks of the local modes induced by the local frequency-swept excitation migrate leftward while the resonance peaks of the global modes remain unchanged when a crack occurs. The superiorities of three damage features are numerically validated and expected to overcome the insensitivity of the existing dynamic detection methods in detecting local fatigue cracks within steel bridges.

Study on the mixed fracture characteristics of concrete-rock Brazilian disks with different fracture angles

The fracture characteristics of cracked straight-through Brazilian discs for concrete-rock composites (CSTBD-CRC) with different fracture inclination angles (Mode I-II) were investigated to evaluate the stability of concrete reinforcement engineering. Acoustic emission (AE) and digital image correlation (DIC) techniques were employed to study crack propagation and fracture modes in CSTBD-CRC Brazil splitting tests, as well as the entropy evolution of AE and DIC. Additionally, 3D scanning technology and fractal theory were utilized to investigate the effect of the fracture mode on the fracture surface morphology. The results indicate that both the fracture energy and peak load of the CSTBD-CRC increase with increasing fracture inclination angle. Moreover, the section fractal dimensions of 0°, 10°, 15° and 25° samples are 2.01879, 2.01528, 2.01186, and 2.01072. Shear fracture mode increases as the dip angle increases and the fracture surface morphology decreases in fractal dimension. Notably, sharp increases in entropy values for both AE and DIC occurred at peak load, suggesting their use as failure criteria for CSTBD-CRC specimens. Furthermore, cracks were found to initiate at the tips of preexisting cracks within the concrete. The displacement in the x direction undergoes the most significant changes on both sides of the crack during crack growth, while the strain in the x direction experiences its greatest variations at the crack location.

On sensitivity analysis of the fundamental frequency of cracked fiber metal laminated (FML) beams using experimental survey and finite element method

PurposeIn this research, the free vibration sensitivity analysis of cracked fiber metal laminated (FML) beams is investigated numerically and experimentally. The effects of single and double cracks on the frequency of the cantilever beams are simulated using the finite element method (FEM) and compared to the experimental results.Design/methodology/approachIn FEM analysis, the crack defect is simulated by the contour integral technique without considering the crack growth. The specimens are fabricated with an aluminum sheet, woven carbon fiber and epoxy resin. The FML specimens are constructed by bonding five layers as [carbon fiber-epoxy/Al/carbon fiber-epoxy/Al/carbon fiber-epoxy]. First, the location and length of cracks are considered input factors for the frequency sensitivity analysis. Then, the design of the experiment is produced in the cases of single and double cracks to compute the frequency of the beams in the first and second modes using the FEM. The mechanical shaker is used to determine the natural frequency of the specimens. In addition, the predicted response values of the frequency for the beam are used to compare with the experimental results.FindingsConsequently, the results of the sensitivity analysis demonstrate that the location and length of the crack have significant effects on the modes.Originality/valueEffective interaction diagrams are introduced to investigate crack detection for input factors, including the location and length of cracks in the cases of single and double cracks.

Enhancing crack detection in railway tracks through AI-optimized ultrasonic guided wave modes

The utilization of ultrasonic guided wave technology for detecting cracks in railway tracks involves analyzing echo signals produced by the interaction of cracks with guided wave modes to achieve precise crack localization, which is extremely important in a real-time railway crack robotic detection system. Addressing the challenge of selecting the optimal detection mode for cracks in various regions of railway tracks, this paper presents a method for optimal crack detection mode selection. This method is based on the sensitivity of guided wave modes to cracks. By examining the frequency dispersion characteristics and mode shapes of guided wave modes, we establish indicators for crack zone energy and crack reflection intensity. Our focus is on the railhead of the railway track, selecting guided wave modes characterized by specific cracks for detection purposes. Experimental findings validate the accuracy of our proposed mode selection method in detecting cracks in railway tracks. This research not only enhances crack detection but also lays the groundwork for exploring advanced detection and localization techniques for cracks in railway tracks.

Error analysis for determining transverse tensile delamination strength of REBCO coated conductors by anvil test: numerical simulation demonstrations

RE–Ba–Cu–O (REBCO, where RE = Y, Gd, Sm, and other rare earth elements) coated conductor (CC) tapes exhibit considerable potential for application within the domains of high-energy physics and high-field science. Nevertheless, weak interfacial properties pose a significant obstacle, impeding the progress and practical implementation in high-field scenarios. The anvil tension method has been extensively employed for the assessment of transverse delamination strength of REBCO CC tapes. However, the outcomes derived from anvil tension exhibit severe dispersion, thereby impeding its efficacy in evaluating material performance. The underlying cause of this phenomenon remains unidentified. In this study, error analysis of anvil measurement method in determining the transverse tensile delamination strength (TTDS) of REBCO CC tapes was conducted based on finite element (FE) numerical simulations. A two-dimensional multilayer elastic-plastic delamination FE model with main layers of REBCO CC tapes, solder connecting layers and anvil materials were developed based on the bilinear cohesive zone model. The effects of anvil test conditions and the structural configuration of the conductor itself on the test results were discussed. Simulation results show that localized premature cracking of the interface due to stress concentration and plastic yielding of the CC tape around the loading boundary is the root reason for the discrepancy between the anvil test results and the true interfacial strength. Therefore, anvil test conditions (including top anvil dimensions, soldering conditions, loading eccentricity angle, and anvil material properties) as well as the structural configuration of the conductor itself (including edge initial crack length, edge encapsulation width, and stabilizer thickness) have a significant impact on anvil test-based TTDS results.

Analysis of CFRP inter‐laminar cracking location under laser impacts

AbstractIn this study, a combination of theoretical analysis and experimental verification was used to investigate the effects of laser parameters and shock wave shape on the location of layer cracks in carbon fiber‐reinforced plastics specimens. Firstly, the propagation coupling process of trapezoidal, rectangular, and triangular pulses in the material was investigated based on the one‐dimensional stress wave propagation theory. The study analyzed the effects of shock wave pressure amplitude, pulse width, and other factors on the location of layer cracks in the material. Subsequently, laser impact experiments with varying energies and pulse widths were conducted on specimens of different thicknesses to investigate the impact of shock wave pressure amplitude and laser pulse width on the location of layer cracking. The results show that the theoretical analysis of triangular shock waves has broader applicability and can serve as a representative analytical model to describe single‐layer crack damage.Highlights Laser impact experiments with various specimen thicknesses. Laser pulse width determines the initial location of inter‐laminar cracking. The applicability of the triangular pulsed layer cracking formula. The effect of laser energy on pulse amplitude.

An Investigation of the Energy-Absorption Characteristics of Thin-Walled Polymer Composite C-Channels: Experiment and Stacked Shell Simulation.

Polymer composite materials are increasingly used in civil aircraft structures. The failure mode and energy-absorption characteristics of polymer composite structures have garnered significant attention from academia and industry. For thin-walled polymer composite C-channels with layups of [0/90]3s, [45/-45]3s, and [45/90/-45/0]3, low-speed axial compression tests were performed to investigate the failure modes, failure mechanisms, and energy-absorbing characteristics. After parametric studies using [0] and [90] single-element models, stacked shell models of thin-walled composite C-channels were established using the Lavadèze single-layer damage constitutive model, Puck 2000, and Yamada Sun failure criteria. The results show that these thin-walled composite C-channels exhibit a stable progressive crushing process with a local buckling failure mode, encompassing local buckling, fiber break-age, matrix cracks, delamination, and corner cracking. The stacked shell model demonstrates reasonable agreement with the progressive crushing process of thin-walled composites, accurately capturing interlayer matrix failure and interface delamination cracking behavior. A comparison of the specific energy absorption (SEA) and mean crushing force (Fmean) between the simulation and test results yields a difference of less than 6%, indicating a strong correlation between the simulation results and the experimental energy-absorbing characteristics. It also shows that a deep understanding of the parameters is helpful for accurate numerical modeling.

A neural network‐based automated methodology to identify the crack causes in masonry structures

AbstractMost masonry constructions exhibit significant crack patterns caused by differential foundation settlements. While modern numerical methods effectively address forward displacement‐based problems, identifying the settlement causing a specific crack pattern remains an unsolved yet crucial challenge. For the first time, this research solves this highly non‐linear back‐engineering problem by proposing a robust and automated methodology synergizing artificial neural networks (ANNs) and the piecewise rigid displacement (PRD) method. The PRD's fast computational solving allows the generation of large datasets used to train specific ANNs through Levenberg–Marquardt and conjugate gradient algorithms. Using the location and widths of the main structural cracks as input, the proposed approach offers an instantaneous and accurate ANN‐based identification of foundation settlements that cause the detected damage scenario. The method is first validated on semicircular arches, and after that, its potential and effectiveness are demonstrated in a real engineering scenario, represented by the Deba bridge in Spain.

Analysis of crack propagation of PLA fabricated by the additive manufacturing technique

Understanding crack propagation is crucial for evaluating the structural integrity and reliability of additive manufacturing components, as cracks can compromise mechanical properties and potentially lead to catastrophic failures. The study of crack propagation in additive manufacturing components is used to develop strategies for mitigating crack initiation and growth, improving material properties, and optimising the design and manufacturing processes. Crack propagation in additive manufacturing components can be influenced by various factors, including material properties, design considerations, manufacturing defects, and loading conditions. Due to the identified issue, the study was carried out to investigate the crack propagation of the Fused Deposition Modeling (FDM) component using compact tension fracture testing. The experimental work started with fabricating the samples using PLA material, followed by a fracture test based on the compact tension specimen test to get a response of the structure and its crack propagation under tensile. Material properties were also collected using the dog bone tensile test. The material properties of the testing were then imported to Finite Element Analysis for further investigation of fracture mechanics. It was found that the maximum force of the sample was 141.7 ± 28 N at 1.70 ± 0.26 mm displacement, and cracks initiated around the tip and propagated upward or downward based on the initial crack location. The deformation patterns of PLA material have shown it to be brittle plastic deformation and low energy absorption before fracture.

Crack initiation and propagation from a closing flaw with frictional contact in a natural quasi-brittle orthotropic solid

This work considers the frictional closing of a pre-existing flaw in a natural quasi-brittle orthotropic medium (wood) under compression. The effect of the flaw face friction at multiple orientations of the flaw, on the peak load-bearing capacity are investigated. The failure due to crack growth initiation from the periphery of the pre-existing flaw and its propagation was investigated experimentally and modelled numerically. The experimental investigation was carried out using New Zealand Pine wood with a pre-existing flaw under a quasi-static compression test. In the numerical investigation, an eXtended Finite Element Method (XFEM)-based cohesive zone model (CZM) is employed in the modelling of the local crack initiation and propagation. The onset of the crack initiation is modelled using a stress-based criterion and the progressive degradation due to crack propagation is traction-separation based damage evolution. The XFEM-based CZM captures the crack initiation and propagation consistent with the experimental results. The numerical results also show the influence of flaw face friction on the peak load bearing capacity as well as the local stress response.

Scale model test and numerical analysis on the anchorage zone of a cable-stayed bridge with the cross-anchor structure

In this paper, scale model test and numerical analysis are conducted to investigate the stress distribution and crack development in the anchorage zone of a cable-stayed bridge with a cross-anchor structure. Initially, scale model test is performed on the tower-crossbeam connection zone to observe the stress distribution at key positions. Then, the anchorage zone is simulated using ABUQUS, considering the material's nonlinearity. The correctness of the finite element model is verified through model test. Finally, we analyze the stress and crack development under 2.7 times the design load. Results show that cracks are prone to occur on the concrete sidewalls. Cracks appear under 1.14 times the design load, and through cracks appear under 1.56 times the design load, initially in the upper-middle part of the anchorage zone. The stress distribution in the stirrups is the most complex among the rebar stresses. After local cracks and through cracks appear in the concrete, the stress in the stirrups increases rapidly.