Increasing Crack Depth Research Articles

Study on the self-vibration characteristics of non-circular arches with cracks based on the transfer matrix method

As the span of reinforced concrete arch bridges continues to increase, so does the difficulty of construction. The structure is at risk of cracking. Most of the bridges under construction are non-circular arches, and there are few studies on such arches. The current study tried to investigate the self-vibration characteristics of non-circular arches with existing cracks. A computational approach proposed in the original non-circular arch is substituted with multiple infinitesimal arch segments having different radii of curvature, enabling the determination of natural frequencies and mode shapes of the non-circular arches with cracks. Furthermore, a finite element model (FEM) of the reinforced concrete structure with existing cracks is developed to assess the effects of various factors, including axial location, crack depth, and positions within the same cross-section. The results demonstrate the feasibility of the computational method using multiple infinitesimal arc segments with varied radii of curvature, yielding a maximum error of only 1.58 %, which satisfies engineering application standards. An increase in crack depth leads to a reduction in the natural frequencies of specific modes of the structure, while the effect on others is insignificant. For cracks situated at the top or bottom plates within the same cross-section, the impact differs based on the local deformation being convex or concave. If the deformation is convex, the top plate cracks exhibit a higher rate of change in natural frequencies compared to the bottom plate cracks; conversely, with concave deformation, the bottom plate cracks have a greater influence than the top plate cracks.

STUDY OF STRESS WAVE PROPAGATION PATH AND DEPTH IDENTIFICATION IN CRACKED WOOD BASED ON ACOUSTIC EMISSION

The propagation velocity models were built using AE sensors to capture stress wave on pine specimen surface.On the different specimens, cracks were made in different numbers and the depth was gradually increased from 0 mm to 90 mm at 10 mm intervals. AE experiment was combined with COMSOL to investigate propagation path.The results show that R-squared is 0.996 when fitting tangent of angle to propagation velocity.At smaller crack depths, stress wave is diffracted around crack tip and then continues to propagate in to sensor along a straight line.However, as the crack depth increases, the reflected wave at the end face will arrive at the detection location faster with significantly weaker diffraction.The area with dimensions of20×10 mm was identified about the crack tip by crack identification method.

The study on fracture response of cracked pipeline considering the Lüders effect

Since pipeline steel typically exhibits yield discontinuities, some pipelines may experience high local strains during service that exceed the strain limits required by existing fracture assessment methods, thereby posing a significant threat to pipeline integrity. By establishing a finite element fracture model of a cracked pipeline with the Lüders effect and incorporating a developed constitutive model with a trilinear stress-strain relationship, the mechanical and fracture responses of the cracked pipeline with the Lüders effect under uniaxial tensile loading are analyzed in this study. The effects of crack configurations and material parameters on the crack driving force are discussed in detail. The results indicate that an increase in crack length and strain hardening exponent lowers the crack driving force plateau and shortens its length. Conversely, increases in crack depth, softening modulus, and Lüders strain raise the crack driving force plateau. Specifically, as crack depth increases, the plateau length of the crack driving force shortens, while an increase in the softening modulus and Lüders strain extends the plateau length. These conclusions provide guidance for the fracture analysis and assessment of pipelines with cracks affected by the Lüders effect.

Propagation Effect Analysis of Existing Cracks in Box Girder Bridges Based on the Criterion of Compound Crack Propagation

Cracking in concrete box girder bridges will have a significant impact on the safety and durability of the structure, and many box girder bridges which are in service have undergone varying degrees of cracking. Currently, the safety design of actual bridge projects place an emphasis on the stress or the load value of a cross section at the limit value specified in the code for safety control. This design method assumes that the member itself is of uniform and continuous material and is internally undamaged. However, the bridge structure is more or less cracked to varying degrees during the period from casting to construction to operation of the concrete members. In this paper, a finite element computational model of a three-span prestressed concrete box girder bridge with existing cracks is established based on the fracture mechanics theory, and the critical parameters of crack extension are introduced to evaluate the extension state of cracks. At the same time, the extended stability of the existing cracks of the box girder bridge is analyzed by considering the temperature effect, vehicle loading, and prestressing loss, and the sensitivity of crack extension under each working condition is investigated. The results show that, with the increase in crack length and depth, the crack expansion is promoted, but the effect is relatively small, and the maximum stress intensity factor is only 6.48 MPa mm1/2. Under the multi-factor coupling effect, the cracks show a composite crack expansion dominated by type I cracks, the longitudinal cracks of the existing base plate are in a stable state, the maximum value of the crack expansion critical parameter of the vertical cracks of the webs reaches 1.087, and there is a tendency to expand locally. The maximum value of the critical parameter for crack extension of the vertical crack in the web plate reaches 1.087, and there is a tendency towards local expansion. The crack extension evaluation criteria proposed in this paper have a certain reference value for crack extension research on similar concrete box girder bridges and provide a scientific basis for the optimized design of similar bridges.

A strain-based J-integral formulation for an internal circumferential surface crack of pipeline under inner pressure and large axial deformation

The presence of cracks on pipelines poses a potential threat to their operational status, and it is critical to assess the permissibility of pipelines containing cracks. The dimensional analysis combined with the finite element method is applied to investigate the fracture behavior of circumferential crack on the internal surface of pipe under internal pressure and large axial deformation. Dimensionless parameters are determined to represent the effects of crack size, pipe geometry, pipe material, and external load on the crack front driving force, and a strain-based J-integral formulation is obtained by a stepwise coefficient fitting approach rather than a polynomial fitting method. This J-integral formula can be used to quickly assess the crack front driving force of a pipe in service condition and subjected to axial displacement. The diameter-to-thickness ratio of the pipe and the dimensionless pressure of the pipe are found to act together in a combined form on the crack front driving force. Increases in dimensionless crack depth, dimensionless crack length, the ratio of circumferential stress to yield strength of the pipe, and strain hardening exponent cause an increase in the crack front driving force. The effect of dimensionless crack depth on crack front driving force is more significant than other dimensionless parameters. Changes in the other dimensionless parameters do not significantly change the crack front driving force when the dimensionless crack depth is small. Other dimensionless parameters have a progressively greater influence on the crack front driving force as the crack dimensionless crack depth increases. Large deformations in the ligament zone and increasing axial stress are the main reasons for the high crack front driving force. The J-integral formula has a similar form to that of the J-integral in the Electric Power Research Institute (EPRI) method when the effect of internal pressure is not considered. It can be reduced to predict the crack front driving force of a surface cracked plate subjected to uniaxial tensile loading. For the interaction between an internal surface crack and an embedded crack, re-characterizing the crack size using BS 7910 will overestimate the equivalent crack depth, and a more accurate equivalent crack size can be obtained using the J-integral formula proposed.

Characteristics of Center-blast Tube with V-grooves During Blasting

The prediction of fracture time and crack development of metal shell under the impact load is a very significant research direction in engineering. In this paper, a coupling method is used to solve the dynamic expansion fracture process of center-blast tube with V-grooves under the pressure. A one-dimensional two-fluid model was utilized to govern the transient combustion. The nonlinear mechanical behaviors were predicted based on the finite element software ABAQUS, and the pressure and the structure were coupled by applying a user subroutine interface VUAMP in ABAQUS. The coupling approach was validated by comparing the predicted results with experimental results. Based on the validated approach, the characteristics of expansion fracture and the process of crack propagation on the center-blast tube with V-grooves were studied, and the effect grooves depth were analyzed. The results show that the crack propagation on tube can be divided into two stages that stable propagation stage and unstable propagation stage. The burst pressure of the center-blast tube with V-grooves decreases with the increase of crack depth, and the burst pressure decreases by about 7MPa with every depth increase of 0.25mm.

Finite Element Analysis Study of Buried Crack Defects in B-Sleeve Fillet Welds

Finite Element Analysis Study of Buried Crack Defects in B-Sleeve Fillet Welds

Experimental and Numerical Studies on the Vibration of Hybrid Composite with an Edge Crack

The hybrid composite plate is increasingly used in marine, robotic arm, and other applications. Edge crack is the greatest common fault in the structural systems during its working time. In this research, the successful fabrications of a hybrid composite of epoxy-based composites reinforced with bamboo and glass fibers have been done to examine the vibration characteristics under free vibration. First-order shear deformation theory is used to study the fundamental natural frequencies of asymmetrically hybrid composite beam with edge cracks for cantilever beam boundary conditions. Both numerical (FEM) using ABAQUS software and experimental investigations are done for the vibration analysis of unidirectional bamboo/glass fiber epoxy hybrid composite (BGHC) beam with edge cracks using fracture mechanics theory. It is observed that implications edge crack with different crack depth and various fiber weight ratio parameters have a major effect on vibration analysis. Also, it is clear that the natural frequencies of the hybrid composite are significantly affected due to the fiber weight ratio and crack depth of the hybrid composite materials. So, crack lengths are playing a vital role in the dynamic or vibration characteristics of the hybrid composite materials. The results of natural frequencies have been shown that they are decreased with an increase in crack depth and an increase in the bamboo fiber weight. Thus, BGHC-2 made from 30% bamboo and 10% glass fiber can be a viable candidate for applications that will produce good vibration properties. Generally, the first-third natural frequency of the hybrid composite beam decreases within the increase of bamboo fiber and decreases in glass fiber. The composite materials having 60% of epoxy with 20% bamboo and 20% glass fiber, and 60% of epoxy with 10% glass and 30% bamboo fibers, are observed with a gradual decrease in the values of natural frequencies with respect to increasing in crack depth. A fine agreement was accomplished between the simulation and experimental results. Therefore, the present approach can be used to identify cracks for mechanical health monitoring by linking the variation in natural frequencies of the hybrid composite beams.

Method for detecting and locating cracks in aluminum plates based on balanced field electromagnetic technique

Aluminum plates are susceptible to environmental and fatigue loads producing randomly distributed cracks and thus compromising safety performance. This paper proposes a detection and location method based on the balanced field electromagnetic technique (BFET) for the detection of cracks on the upper and backside surfaces. The self-zero nature of BFET and the principle of high-sensitivity crack detection are analyzed. The signal characteristics and variation laws are clarified theoretically. The results show that the amplitude and phase of the upper surface crack signal both vary linearly with the crack depth. The signal amplitude of the backside crack decays exponentially with depth and the phase lags linearly. The two-dimensional amplitude phase diagram is rotated at a fixed angle with increasing crack depth and can locate the crack. BFET can detect cracks below the skin depth and provides a reference to increase the detection penetration depth for other electromagnetic detection methods.

Research on Magnetic Field-Based Damage Detection Technology for Ferromagnetic Microwires

Composite materials are frequently exposed to external factors during their operational service, resulting in internal structural damage which subsequently impacts their structural performance. This paper employs ferromagnetic materials for their sensitivity to magnetic field strength. By detecting variations in the magnetic field within the embedded ferromagnetic microwires of composite materials, the aim is to indirectly assess the health status of the composite materials. Firstly, a theoretical numerical model for magnetic field intensity at the crack site was established. Subsequently, a finite element model was employed to analyze the variations in the magnetic characteristics of ferromagnetic microwires at the crack site. Under different parameter conditions, the patterns of magnetic signals at the crack site were determined. The results indicate that with an increase in the angle between the external magnetic field and the crack, the fitted curve of the magnetic signal shows a linear increase. The distance between the peak and valley of the radial magnetic signal in the axial direction decreases, and the axial magnetic signal transitions from double-peak to single-peak. With the increase in crack depth, the fitted curve of the magnetic signal shows a linear increase, and the magnetic signal at the crack tip also exhibits a linear increase. An increase in crack width leads to a non-linear decrease in the fitted curve of the magnetic signal, and after reaching a certain width, the magnetic signal stabilizes. For two identical cracks at different distances, the magnetic signal exhibits a transition from a complete pattern to two complete patterns. With the increase in the external magnetic field, the magnetic signal shows a completely regular linear increase. By analyzing and calculating the variations in magnetic signals, the patterns of magnetic characteristics under the damaged state of ferromagnetic microwires were obtained. This serves as a basis for assessing whether they can continue in service and for evaluating the overall health status of composite materials.

Study on Stress Intensity Factor of Girth Weld with Crack Defects

In order to study the safety performance of the girth weld with cracks in the pressure vessel in use, based on fracture mechanics, this paper adopts ABAQUS and FRANC3D joint simulation to calculate the crack tip stress intensity factor(SIF). The influence of crack location, length and depth on the stress intensity factor of crack tip is analyzed. The results show that the crack SIF at different crack locations (inner crack > buried crack > outside crack) increases with the increase of crack length and increases with the increase of crack depth.

Experimental and numerical investigation of impact behavior in honeycomb sandwich composites

This paper presents an experimental and numerical study on the low-energy impact fatigue and bending behavior of sandwich panels reinforced with composite laminate glass and carbon fabric facesheets, supported by a honeycomb core made of Nomex. The crushing behavior of honeycomb sandwich specimens subjected to the impact test was compared and discussed. Our results indicate that the carbon composite facesheets have a significant effect on the impact, resulting in an increase in impact resistance and a 157.14% increase in crack depth in the elastic region compared to glass facesheets reinforcement. This increase serves as an indicator of the laminate's ability to resist damage initiation and impact fracture mechanisms. Also, an increasing in flexural strength about 45.72% was observed in carbon facesheets honeycomb specimens compared to glass facesheets reinforcement. Microscopic illustration of the damaged honeycomb sandwich specimens was conducted to evaluate the interfacial characteristics and describe the damage mechanics of the composite facesheets and core adhesion under the impact test. The numerical approach proves to be efficient in terms of accuracy and simplicity compared to existing methods for predicting the damage mechanisms of honeycomb sandwich structures. It was noted that results of numerical study show best agreements with experiment results and the model can be used to predict the low-energy impact fatigue.

Analysis and experimental verification of dynamic characteristics of cantilever plate with fatigue crack

Fatigue cracks in aero-engine blades seriously threaten the stability and reliability of the engine. It is very necessary to identify and diagnose the crack state through vibration signals, and predicting its vibration rules through dynamic analysis is the basis of crack identification. At present, the dynamic model of cracked blades with breathing cracks is mainly established by implanting cracks, and there is a lack of relevant experimental validation. To address the above deficiencies, this paper firstly obtains the real extension path of the cracked plate through the fatigue testing machine, and then introduces it into the cantilever plate finite element model. Then the correctness of the proposed model is verified by natural frequency obtained from hammering test and frequency sweeping test. Finally, the effect of different crack parameters such as crack depth, crack location and plate length on the crack vibration characteristics is investigated based on simulations and experiments. The results indicate that (1) the real fatigue crack obtained by tensile test has larger amplitude peaks under excitation frequency compared with wire-cut crack, and it has stronger nonlinearity to better reflect the vibration characteristics; (2) Specimens show obvious nonlinear characteristics that significant amplitude peaks occur at multiples of excitation frequencies in both experiments and simulations; (3) For the cantilever plate containing breathing cracks, the vibration amplitude totally increased by 18.5% with the increase of crack depth, and it decreased by 41.5% throughout as the crack location became further away from the plate root. This study provides a theoretical basis for detection and diagnosis of blade cracks.

Improvement of Safety and Reliability of SCM440 Steel with Induction Hardening

In this study, structural SCM440 steel was used to investigate harmless crack size using compressive residual stresses by induction hardening (IH). The fatigue limits of base metal (BM), quenching–tempering (QT), and IH specimens were obtained. The harmless crack size (ahml) was evaluated using the fatigue limits, threshold stress intensity factor using the Ando equation, and the sum of the stress intensity factor using the Newman-Raju and API-RP579 equations. Because as the crack depth increases, the compressive residual stress rapidly decreases, the harmless crack was determined from the intersection of depth for all aspect ratios (As). However, the outermost surface crack did not intersect because the compressive residual stress (σr,s) on the surface is always present. The ahml values based on BM and QT are 1.04−1.45 and 1.02−1.39 mm, respectively. These values can be evaluated as the ∆Kth(l) of a long crack. ahml did not significantly depend on As. If the crack detected after nondestructive inspection (NDI) is not surface modified after repair, then NDI1 with a very high resolution must be performed.

Vibration based damage detection for hybrid composite cantilever beam using finite element analysis and artificial neural network

Damage in mechanical structure causes a change in its physical properties and it will affect the real-time application. Cracks in a structure that distressed in model parameters like mode shape, and natural frequency. Its need to the identification of damage early to avoid catastrophic failure and increase the life of the mechanical structure. In this paper, a model for natural fundamental vibration analysis of cantilever beam with the inclined crack with different depths and different locations has been presented. The natural frequency of crack reduces by an increase in crack depth. The performances of results have been verified with finite element analyses software ANSYS, Experimental analysis and finally compare results with a neural network.

Effect of hydrogen embrittlement on the safety assessment of low-strength hydrogen transmission pipeline

Currently, no systematic approach exists for the safety assessment method of hydrogen transmission low-strength pipeline, it is necessary to study the effect of hydrogen embrittlement (HE) on the method of failure assessment diagram (FAD) for the defective pipe. The hydrogen charging experiments of tensile and Charpy impact specimens for the L245 pipe steel were carried out with charging time of 0, 30, 90, and 120 h, and then the tensile and Charpy impact tests were immediately conducted. The HE indexes of tensile and Charpy impact properties were presented to quantitatively analyze the effect of HE under tensile and impact deformation processes. Subsequently, the FAD method coupled with the effect of HE was investigated to analyze the difference in the safety assessment method between hydrogen and non-hydrogen environments. Finally, the fracture morphology of tensile and Charpy impact specimens was observed to analyze the responses of microscopic fracture modes between hydrogen and non-hydrogen environments. The results show that the effect of HE on the tensile properties of the base material is more sensitive than that of the weld joint. The FAC with the effect of HE for safety assessment of defective pipes shrinks by reducing the safe zone. The decrease ratio of safety factors affected by HE presents an increasing tendency as the increase of crack depth while showing a decreasing tendency as the increase of internal pressure.

Study on small modulus modified gear damage fault and electromechanical coupling vibration characteristics under multiple working conditions

The fault of transmission system seriously affects the life of robot joints, so it is urgent to study the crack of the displacement wheel set. Firstly, the tooth profile equation of the modified gear is established, and the time-varying mesh stiffness (TVMS) is obtained. Secondly, the multi-degree-of-freedom electromechanical coupling dynamic equation is established. Finally, the vibration displacement under steady state, start-up and shock conditions is analyzed. The results show that: (a)The positive displacement can increase TVMS, while negative displacement is the opposite. (b) The appearance of cracks accelerates the damage to two adjacent teeth. (c) The decrease of TVMS increases with the increase of crack depth. (d) The crack causes the gear pair to generate vibration shock, and the vibration displacement increases significantly in the case of broken teeth. (e) Statistical analysis of the vibration displacement reveals that the root means square value can detect early cracks, and the kurtosis index can predict life. (f) Cracks have a large effect on the transient process at start-up and shock, but the effect of cracks is weakened during no-load steady-state operation.

An experimental and finite element investigation for determining critical speeds of a cracked jeffcott rotor model

Rotating machines like pumps, compressors, generators, and steam and gas turbines are widely used in Industry 4.0. The researchers have gained more attention by modeling a cracked Jeffcott rotor system through a finite element approach. The present work consists of theoretical and finite element analysis of the Jeffcott rotor model with consideration of different crack depths, crack locations, and shaft material. Finite element results and their experimental verification obtained by FFT analysis show that increasing crack depth decreases the first critical speed of the system. Also, an increasing number of cracks results in decreases in the system’s first critical speed. The presence of a crack changes the stiffness of the shaft which results in, a decreasing the natural frequency. The present study approach provides an improved platform for crack diagnostic information to the vibration condition monitoring community for using Ansys software effectively as a finite element tool for performing rotordynamic analysis in Industry 4.0.

Experimental and numerical study on the two-phase flow inside a cracked gas diffusion layer of PEMFC

The presence of cracks in the gas diffusion layer (GDL) can have a significant impact on the flow of two phases within Proton Exchange Membrane Fuel Cells (PEMFCs). This study focuses on investigating the transport process of two-phases flow in a GDL sample using both experimental and numerical methods. The porous structure of a hydrophobic carbon paper, serving as the macro-porous substrate (MPS) of the GDL, is examined using synchrotron radiation X-ray phase contrast Computed Tomography (CT). A 3-D model with various crack geometries is then created, and a Lattice Boltzmann Method (LBM) simulation is employed to analyze the flow behavior within the GDL model. The findings reveal that the water intrusion mode in the MPS primarily depends on its hydrophobic nature, but the width and depth of the cracks also significantly influence both the rate and path of water intrusion. Increasing the crack width from 7 μm to 28 μm results in a 30% increment in water intrusion rate, while the intrusion path remains unchanged. However, when the crack width reaches 42 μm, the crack itself becomes the primary path for water intrusion, doubling the intrusion rate. Furthermore, an increase in crack depth leads to a higher invasion rate of the liquid phase, consequently increasing the liquid storage volume within the GDL. This research provides a novel approach for analyzing cracked GDLs and demonstrates the potential to optimize the water management process of PEMFCs through GDL microstructure design.

Semi-analytical solution for internal forces of tunnel lining with multiple longitudinal cracks

Longitudinal cracks on the tunnel lining significantly influence the performance of tunnels in operation. In this study, we propose a semi-analytical method that provides a simple and effective way to calculate the internal forces of tunnel linings with multiple cracks. The semi-analytical solution is obtained using structural analysis considering the flexural rigidity for the cracked longitudinal section of the tunnel lining. Then the proposed solution is verified numerically. Using the proposed method, the influences of the crack depth and the number of cracks on the bending moment and modified crack tip stress are investigated. With the increase in crack depth, the bending moment of lining scetion adjacent to the crack decreases, while the bending moment of lining scetion far away from the crack increases slightly. The more the number of cracks in a tunnel lining, the easier the new cracks initiated.