Analysis Of Surface Cracks Research Articles

Experimental study on improving the performance of imitation earthen site soil in carbon dioxide environment

This study aims to explore the performance of lime-treated soil for repairing the lime soil of the earthen city wall of Kaifeng and to standardize the construction technology of lime-treated soil. The research comprehensively considered factors such as carbonation time, lime particle size, aging conditions, and lime content, and conducted various tests and analyses including triaxial mechanical properties, surface crack analysis, particle size distribution, pH measurement, composition analysis, and electron microscopy on different samples. The results indicate that the significant effect of high-concentration CO2 carbonation enhances the chemical reactions of lime soil, and an appropriate carbonation process can strengthen the bonding and density between soil particles. Under the maintenance condition of 5 % CO2, with increasing carbonation time, the crack ratio, average crack length, and average crack width of the samples decreased. Cohesion and internal friction angle of the samples exhibited an initial increase followed by a decrease, while shear strength of the samples increased by 22.93 %–75.09 %. The lime particle size has a critical impact on the formation of cracks in lime soil. With increasing lime particle size, the crack ratio, average crack length, and average crack width of the samples increased. Cohesion and internal friction angle of the samples gradually increased with increasing lime content. The increase in crack ratio, average crack length, and average crack width during natural curing of lime-treated soil samples was proportional to the lime content. Appropriate carbonation time, smaller lime particle size, and curing conditions with 5 % CO2 contribute to improving the particle size distribution of lime-treated soil samples, reducing surface cracks, and enhancing performance. However, prolonged carbonation may lead to larger lime particle size, resulting in rough and loose particles, disorganized arrangement of CaCO3 crystals, and the inability to form a cross-linked network skeleton, causing a reduction in shear strength of the samples. These research findings provide important theoretical basis and construction technology guidance for the application of lime-treated soil combined with CO2 carbonation in repairing earthen city walls.

Analysis of cracking failure of gast iron brake disc

To investigate the causes of crack initiation and propagation in brake discs, a comprehensive analysis of surface cracks was conducted using macroscopic observation, metallographic observation, scanning electron microscopy, and microhardness testing. The results revealed that the internal structure of the brake disc material consists mainly of pearlite and a small amount of ferrite. Near the friction surface, the internal structure undergoes grain refinement and the formation of a small amount of granular pearlite, with a microhardness range of 350 ∼ 410 HV. Based on metallographic observations, it is evident that there are loose defects within the brake disc. When the brake disc is subjected to external loads and thermal stress, stress concentration occurs around these defects, initiating cracks and their outward propagation, thereby accelerating the crack propagation rate. The crack growth exhibits a combination of transgranular and intergranular characteristics. Analysis of the crack width in the brake disc reveals that the width of the radial primary cracks is approximately three times that of the micro-cracks, and the depth of the micro-cracks is relatively shallow, with a maximum depth of 4 mm. In contrast, the primary crack extends to a depth of 9 mm. This implies that the failure of the brake disc is associated with the extension and deepening of cracks.

Surface crack analysis of 8Cr4Mo4V steel based on Crystal/Phase microstructure model by grinding

Metal polycrystalline materials tend to be homogeneous and isotropic at the macroscopic level, which leads it difficult to visually characterize the sprouting and expansion of cracks by traditional grinding simulation. In this study, the Johnson–Cook constitutive model was used for the finite element method (FEM) based on grinding characteristics with a high strain rate and large plastic deformation. The models are focused on the actual microstructure distribution, one of them contains grains and grain boundaries, and another contains phase organization (martensite and acicular martensite) and carbides. The study pinpoints the changes in microstructure under different grinding parameters during the grinding process and the influences on the formation of microscopic cracks. Ultimately, it was found that the shedding of large primary carbide is a critical factor for inducing surface cracks. The uncoordinated deformation between brittle carbides with the other phases is the main cause of carbide shedding. Therefore, this article visualized shows the influence of grinding parameters on surface cracks from the perspective of microstructure modeling, which is of great significance in guiding practical processing.

Cause analysis of surface cracks in flash butt welding joint of high manganese steel frog

Surface cracking is one of the typical failures in butt welding joints of high manganese steel railway frogs. Understanding the formation mechanism of such cracks can effectively prevent similar failures from occurring. Herein, assisted with multiple macro and micro characterization tools, we discussed the causes of surface crack formation for a flash butt welding joint of a high manganese steel frog. The results show that the surface cracks are typical intergranular stress corrosion cracks (IGSCC) distributed near the fusion line between the carbon steel rail and the stainless steel medium in the stainless steel side. Acicular martensite exists near the fusion line between carbon steel rail and stainless steel medium, and the residual stress is large. At the same time, there are continuous network chromium carbide precipitates on the austenitic grain boundary of stainless steel. The above two points should be the main reasons for the initiation of cracks on the weld surface. Reduce the proportion of martensite structure by reasonably optimizing the welding cooling rate. Properly temper martensite to reduce the hardness and internal stress in the transition zone. These measures can prevent the occurrence of intergranular cracks on the weld surface.

Study on low cycle fatigue of ferritic-martensitic steel at high temperature

In 2011, a serious nuclear accident occurred in Fukushima, Japan, and one of the major causes was the destruction of the cladding material mainly made of Zr alloy due to a violent chemical reaction with high-temperature water vapor. Since then, scholars in various countries have been trying to find a better nuclear fuel cladding material. Because of its high temperature strength, ferritic/martensitic(F/M) steel is used in thermal power units. Over the past hundred years, the high temperature performance of ferritic/martensitic steel has developed simultaneously with the operating temperature of thermal power system. F/M steel is widely used in nuclear power system as well as thermal power, The fatigue life of nuclear fuel cladding material is an important parameter to study its service life, due to the special shape of the cladding material, especially for the pipe with a thickness of less than 0.5mm, it is difficult to directly measure its mechanical properties, this paper through special experimental materials and fixtures F/M pipe steel at room temperature and high temperature tensile test, as well as low cycle fatigue performance test, and its fracture port, surface crack analysis. Through the analysis and processing of experimental data, typical stress-cycle life curves, total strain amplitude-life curves, elastic strain amplitude-life curves, hysteresis curves with different strain amplitudes, and fatigue life prediction curves were obtained.

Enhancement of compressive strength and strain ductility of SMA fiber reinforced concrete considering fiber’s aspect ratios

In this study, the effect of recovery stress on the toughness of cementitious materials was investigated using randomly distributed SMA fibers in concrete. The composite was reinforced by cold drawn crimped SMA fibers due to their great potential in developing a prestressing effect as well as providing sufficient bond resistance. To this end, considering the same volumetric fraction, different aspect ratios of the SMA fibers were embedded into the matrix and then molded into different reinforced concrete cylinders. Compression tests were performed where several parameters, including compressive strength, ductility, axial, and volumetric strain were examined before and after inducing the prestressing effect. Furthermore, the present study dealt with fracture modes, as well as internal and surface crack analysis via X-ray and digital image correlation (DIC) equipment to investigate the effect of prestressing with different aspect ratios. The results showed that not only the current geometry of SMA fibers in concrete could improve the ductility of the composite, but also elevate the compressive strength demonstrating a considerable rise in energy absorption capacity.

Surface crack analysis of the steering shaft gear after carburizing and quenching

The phenomenon of surface cracks in steering shaft gear after carburizing and quenching was analyzed by combining experimental research, theoretical analysis, and numerical simulation. The chemical composition, crack morphology, non-metallic inclusions, microstructure, microhardness, and forging process were analyzed and studied by means of directly reading spectrometer, metallographic microscope, scanning electron microscope, energy dispersive spectrometer, and micro hardness tester. The evolution process of surface crack morphology was numerically simulated and reproduced with the help of Deform 3D point tracking technology. The results show that linear surface cracks are formed on the surface of the round steel because of Alumina-type non-metallic inclusions, which destroy the continuity of the steel matrix during the rolling process. Surface cracks become arc-shaped due to the regular plastic flow direction of the material and propagate in the depth direction during the forging process. Crack provide a channel for the diffusion of C atoms during carburizing and quenching process, therefore carburized layer with gradient distribution is formed on both sides of the crack. The carburized layer reacts with oxygen during quenching and subsequent tempering, resulting in a certain degree of oxidation on both sides of the crack and the crack tail. Therefore, the surface cracks found in the steering shaft gear after carburizing and quenching are originated from the rolling cracks formed by non-metallic inclusions of steel. The rolling cracks have undergone further evolution in the subsequent forging and carburizing quenching process.

Cellularization characteristics of ethyl acetate spherical expanding flame

The cellular instability of ethyl acetate (EA) premixed flame has been studied theoretically and experimentally under different initial temperature, pressure and equivalence ratio. The constant pressure method (CPM) was used to determine the laminar burning velocity of EA spherical expanding flame in this research. In addition, the cellular evolution image of EA spherical expansion flame surface was obtained using high-speed schlieren technology. The image processing technology combined with three-dimensional reconstruction algorithm was used to extract and reconstruct the flame surface crack length, the number of cells on the flame surface, cellular area and cellular length scale. From the quantitative analysis of surface crack and cellular structure of EA flame, it can be seen that the evolution of flame surface crack and surface cellular structure is largely affected by equivalence ratio and initial pressure. With the increase of initial pressure or equivalence ratio, the earlier the flame surface cracks and cell formation. Furthermore, according to the cellular length scale in different radius, the wavenumber was deduced, and compared with the theoretical curve, it is found that the experimental wave numbers have the same evolution trend. Although, when the equivalence ratio is 1.4 with high Peclet number, the experimental wave numbers are somewhat beyond the boundary of the peninsula curve due to the influence of the nonlinear effects, the trend is consistent with the theoretical results.

Development of Automated Model Generation and Analysis of Surface-Cracked Plates in Bending for Interpolated Elastic–Plastic J-Integral Solutions

Abstract NASA’s Tool for Analysis of Surface Cracks (TASC) has been used since 2014 to perform elastic–plastic J-integral (J), crack mouth opening displacement (CMOD), crack front constraint, and deformation limit calculations for plates in tension. To date, no comparable database or tool exists for surface-cracked plates in bending. Existing tools and prior ASTM standards are limited to linear-elastic materials or simpler 2-D crack geometries. TASC uses a database of 600 models for interpolated solutions over a wide range of semielliptical surface crack geometries (0.2≤a/c≤1.0, 0.2≤a/t≤0.8) and material properties (100≤E/Sys≤1,000, 3≤n≤20). Here, a is the crack depth, c is the half-width of the crack, and t is the plate thickness, so that a/c is the crack aspect ratio and a/t is a normalized measurement of crack depth. E, Sys, and n are the plate’s elastic modulus, yield strength, and the Ramberg–Osgood power law hardening exponent, respectively. This report details the development of a bending model database covering the same range of crack geometries and material properties. It includes developing new criteria to determine if a model has reached sufficient plastic deformation and modifications to model boundary conditions to accurately capture the behavior of deeply cracked plates in bending. Python is the primary automation tool used in this process, including running FEACrack to create meshes, modifying material properties, iterating WARP3D boundary conditions to meet plastic deformation requirements, and converting WARP3D output into a reduced set of MATLAB-compatible data files. Bending model results from WARP3D are validated against Abaqus results for identical meshes. This report then shows the initial integration of bending models and results into the existing TASC code, laying the groundwork for a single tool for analysis of surface-cracked plates in tension or bending.

Root Cause Analysis of Surface Cracks in Heavy Steel Plates during the Hot Rolling Process

This paper investigates the root cause of the formation of surface cracks on hot-rolled C–Mn constructional steel heavy plates. Cracks are rather evenly distributed over the surface in the form of colonies of cracks. Samples were cut from the heavy plate. The microstructure of samples in the as-cast and hot-rolled states were studied using optical and electron microscopes as well as energy dispersive X-ray spectroscopy (EDS). Results show that cracks are heavily oxidized. De-carburized areas are also seen alongside cracks. The crack tip is in the form of a deer-horn, indicating that crack branching has taken place during deformation. The crack initiation sites are V-shaped grooves on the surface of as-cast slabs. Correlations between microstructures, processing parameters, and crack formation are discussed.

Thermoelastic analysis of surface cracks in FGMs hollow cylinders using the interaction energy integral method

The present work is focused on the analysis of surface cracks in functionally graded hollow cylinders subjected to thermal loading. The interaction energy integral is deployed in the finite element framework and an un-coupled thermo-mechanical analysis is carried out to extract the mixed-mode stress intensity factors (SIFs). The effective thermal and mechanical properties, as well as the critical energy release rate of the graded material, are obtained resorting to micromechanics models. Material gradation is considered in both radial and axial directions. The obtained results allow to elucidate the role played by material gradation profile on the severity of surface cracks and can therefore be effectively used in the design of FGMs hollow cylinders.

Phase II Results of an Analytical Round Robin for Elastic-Plastic Analysis of Surface Cracked Plates

Abstract The second phase of an analytical round robin for the elastic-plastic analysis of surface cracks in flat plates was conducted under the auspices of ASTM Interlaboratory Study 732. The interlaboratory study (ILS) had ten participants with a broad range of expertise and experience, and experimental results from a surface crack tension test in 4142 steel plate loaded well into the elastic-plastic regime provided the basis for the study. The participants were asked to evaluate a surface crack tension test according to the version of the surface crack initiation toughness testing standard published at the time of the ILS, ASTM E2899-13, Standard Test Method for Measurement of Initiation Toughness in Surface Cracks under Tension and Bending. Data were provided to each participant that represented the fundamental information that would be provided by a mechanical test laboratory prior to evaluating the test result. Participants were asked to interpret the test according to E2899, including evaluation of crack-front constraint, determination of a critical initiation angle along the crack front, determination of the deformation regime of the test, and determination of the critical J-integral value. The choice of finite element analysis constitutive models and treatment of the stress-strain data was left to the discretion of the participants. The hope was that this process would familiarize participants with the standard and provide the task group with very helpful feedback regarding the interpretation of the requirements as they are written. Overall the participants’ test analysis results were in good agreement and constructive feedback was received that has resulted in an improved published version of the standard E2899-15.

Analysis of surface cracks in round bars using dual boundary element method

A closed-form solution for stress intensity factors (SIFs) of a semi-elliptical surface crack in round bars subjected to torsional loading using the dual boundary element method are presented in this paper. The SIFs of surface cracks having different crack aspect ratios and inclination angles were calculated using the numerical software BEASY. In general, the results revealed that the Mode III SIF was strongly affected by both the crack size and crack shape whereas that crack aspect ratio had the greatest influence on the SIFs regardless of the fracture modes.

Propagation of surface breathing cracks in shafts under quasi-static rotary bending

Due to cyclic loading conditions, cracks frequently appear in rotating machines. The propagation of fatigue cracks in shafts can provoke severe accidents with high risks of people. During the rotation of the cracked shaft, the crack opens and closes in what is called the breathing mechanism, and consequently the behavior of the shaft becomes nonlinear. In the present paper, the propagation of a semi-elliptical crack contained in a rotating shaft has been analyzed considering the nonlinear effect of the crack as the shaft rotates. To this end, an integration algorithm which allows obtaining the crack front evolution has been improved. This procedure uses the Paris-Erdogan Law to determine the advance at a few points along the crack front and uses the general expression proposed previously by the authors that gives the Stress Intensity Factor along the crack front of an elliptical crack in a rotating shaft in terms of the crack depth ratio, the crack aspect ratio, the relative position on the front and the angle of rotation. Several initial semi-elliptical surface crack geometries have been analyzed. For each geometry, the evolution of the crack front has been studied, analyzing the variation of the crack aspect ratio against the crack depth ratio. By the moment, no fatigue growth analyses of surface cracks in rotating shafts, taking into account the breathing mechanism and considering the nonlinear behavior of the shaft, have been found in the literature.

Numerical analysis of surface cracks repaired with single and double patches of composites

In this work, the performances of circular single- and double-sided composite patch repairs are compared by computing the maximum stress intensity factor of a repaired surface crack. The three-dimensional finite-element method is used to calculate the stress intensity factor along the crack. The effects of the crack depth, composite patch thickness and patch material on the stress intensity factor variation are highlighted. The obtained results show that the selection of single- or double-sided patches depends on both the crack depth and patch thickness.

Code Verification of Surface Crack Analysis Program SCANP

Code Verification of Surface Crack Analysis Program SCANP

Visual analytics and rendering for tunnel crack analysis

The visual analysis of surface cracks plays an essential role in tunnel maintenance when assessing the condition of a tunnel. To identify patterns of cracks, which endanger the structural integrity of its concrete surface, analysts need an integrated solution for visual analysis of geometric and multivariate data to decide if issuing a repair project is necessary. The primary contribution of this work is a design study, supporting tunnel crack analysis by tightly integrating geometric and attribute views to allow users a holistic visual analysis of geometric representations and multivariate attributes. Our secondary contribution is Visual Analytics and Rendering, a methodological approach which addresses challenges and recurring design questions in integrated systems. We evaluated the tunnel crack analysis solution in informal feedback sessions with experts from tunnel maintenance and surveying. We substantiated the derived methodology by providing guidelines and linking it to examples from the literature.Electronic supplementary materialThe online version of this article (doi:10.1007/s00371-016-1257-5) contains supplementary material, which is available to authorized users.

Sampling method in probabilistic S-version finite element analysis for initial flaw size

The aim of this paper is to demonstrate the accuracy of the sampling method in probabilistic fatigue surface crack growth analysis. A finite thickness plate with surface crack subjected to a fatigue load is considered for fracture analysis using the newly developed Probabilistic S-version Finite Element Model (ProbS-FEM). Two sampling methods, Monte Carlo and Latin Hypercube are employed in the ProbS-FEM. Two different sampling methods are used to generate the random variables in the analysis. The results from the strategies are compared to highlight the advantages of each sampling strategy. The distribution of the initial surface crack length and depth are extracted from the fatigue tests. The accuracy and consistency between the two sampling methods are evaluated. The Latin Hypercube sampling (LHS) shows advantages compared to the Monte Carlo. Then, the developed ProbS-FEM is demonstrated on a four-point bending model. The developed ProbS-FEM shows that the code is capable of modelling the uncertainty in the fatigue surface crack analysis with better accuracy and consistency of sampling process.

Elastic-Plastic Fracture Mechanics Analyses of Surface Cracks in Drill String Subjected to Combined Loading

The drill pipe near the surface stands the largest tension and torsion load for the full hole during drilling operation. And fatigue crack growth is always the major cause of failure of drill string. As an example, 5ʺ drill pipe that was near the well head of an ultra-deep straight well and made of 30CrMo, whose constitutional relation was fitted by experiment, was analyzed here. Simplifying the initial crack of the drill pipe as circumferential semi-elliptical surface crack, we simulated the elastic-plastic fracture feature of the drill string with surface crack, partly through-wall crack and fully through-wall crack under combined loading of axial force and torsion. Crack front geometry evolvement is simulated for the different stages of crack propagation. This work would provide a basis for the full-range analysis of fatigue crack growth.

Analysis of surface cracks in multi-crystalline thin silicon wafers

Surface cracks are the most common defects in solar silicon wafers. The stress intensity factors (SIFs) calculated by the semi-analytical equation derived by Newman and Raju have been compared with results of 3D finite element analysis for a wide range of semi-elliptical surface crack configurations in thin silicon wafer subjected to bending. It has been shown that the geometrical nonlinearity of silicon wafers significantly influences the SIF values. The discrepancy between nonlinear and linear models is 19% for a surface crack with 20μm depth and 1mm length, while it is 74% for a surface crack with 160μm depth and 100mm length. Furthermore, the results show that for long surface cracks (a/c⩽0.01) finite element models should be used to calculate the SIF and the existing semi-analytical solution is not reliable.