Propagation Of Edge Crack Research Articles

Influence of Edge Crack Propagation on Critical Current Degradation of REBCO Tape Studied by Phase-Field Fracture Method and Current Shunting Model

For efficiency and cost savings during manufacturing, a fixed wide REBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> -x (REBCO) tape is usually mechanically slit to a width required by varying applications, whereas the multiple edge cracks are induced in this process. In physics, it is widely recognized that the critical current of REBCO tape is degraded with tensile strain, and excessive strain causes crack growth. We are curious about how the edge crack grows under tensile strain, thereby further affecting the critical current performance. Therefore, we first introduced the phase-field method (PFM) to analyze the cracking and fracture behavior. After building a numerical model containing an edge crack and solving it by the finite element method, we presented the propagation path of the edge crack under tension and obtained the quantitative correlation between fracture ratio (crack depth/tape width) and tensile strain. Furthermore, since cracks impede the current flow and make the current shunted to the metal layer, resulting in critical current degradation, we adopted a current shunting model that considers the obstacle of cracks to investigate the relationship between critical current degradation and fracture ratio. Moreover, employing the intermediate variable of fracture ratio, we obtained the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${I}_c - \varepsilon $</tex-math></inline-formula> curve of REBCO tape. By comparing the calculated <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${I}_c - \varepsilon $</tex-math></inline-formula> curve with previous experimental data, the critical current degradation with tensile strain was very well interpreted by the propagation of the edge crack induced by mechanical slitting.

Fatigue crack propagation under corrosion of high-strength steel

Corrosion is nearly unavoidable phenomenon in most of the metal materials. In this paper, its effect on the sharp edge crack propagation under tensile loading is investigated. A rectangular plate with a perpendicular crack and an elliptical corrosion pit nearby is modelled via finite elements and fracture behavior of the crack is analyzed. The multi-parameter fracture mechanics concept is applied, i.e. the higher-order terms of the Williams expansion are calculated by means of the over-deterministic method and utilized for tangential stress approximation in the vicinity of the crack tip. Thus, the generalized MTS criterion could be used for estimation of the crack deflection angle. The calculations were performed for a selected corrosion pit size and location considering various crack lengths. The results are discussed and a crack length with the highest probability to deflect from its original perpendicular propagation direction is found.

A coarse-grained concurrent multiscale method for simulating brittle fracture

This paper proposed a concurrent multiscale method for modeling crack propagation in brittle solids. The method couples the continuum finite element domain with a recently-developed coarse-grained atomistic potential, which has been developed to simulate crack nucleation and propagation within the molecular dynamics domain. The main advantage of this potential is to suppress dislocation nucleation from the crack tip which significantly eases the coupling procedure. In this multiscale framework, complexities like large deformation, crack nucleation and propagation are simulated in the atomistic domain while the rest such as elastic wave propagation and boundary conditions are modeled in the continuum domain. As a result, the atomistic area will be limited around the cracking zone which increases the computational efficiency. Two examples of edge crack propagation and sliding surfaces in contact are presented and compared with the fully atomistic models to verify and check the efficiency of the proposed multiscale method. The comparison shows that the proposed method can accurately capture the crack formation while the computation cost reduces significantly.

Comparison of edge crack behavior of Mg sheets prepared by online heating rolling

Low-alloying and low-cost magnesium alloy sheets have the potential for large-scale application. Therefore, the edge cracking developed during the rolling is of great importance. In this work, Mg-1.0Mn-0.5Al (MA10), Mg–2Zn-1.5Mn (ZM21), and Mg-3.0Al-1.0Zn (AZ31) alloy sheets were rolled at 150 °C in different single-pass reductions using online heating rolling. Their edge cracking behaviors at the edge of rolled sheets after large strain rolling were investigated and compared through the scanning electron microscope (SEM), electron backscatter diffraction (EBSD), and digital image correlation (DIC) technique. The results show that compared with ZM21 and AZ31 rolled sheets, MA10 rolled sheets exhibit the most severe edge cracking behavior after large strain rolling. This is mainly attributed to the lower recrystallization degree and ultimate compressive strength, as well as higher strain localization during the plastic deformation. Meanwhile, both coarser second phase particles at the edge and larger grain size difference also promote the initiation and propagation of edge crack in MA10 alloy rolled sheets. In addition, the small crack is developed in front of the crack tip in all of Mg alloys rolled sheets after a single-pass reduction of 75% due to the stress concentration at triple junctions caused by large rolling reduction and maximum shear stress along the plane collinear with the major crack.

4D imaging of chemo-mechanical membrane degradation in polymer electrolyte fuel cells - Part 1: Understanding and evading edge failures

This work is a two-part article series on chemo-mechanical membrane degradation in fuel cells, wherein the present work in Part 1 investigates edge failure and Part 2 investigates failure within the active area of an edge-protected cell. Membrane electrode assembly (MEA) edges are sensitive regions that can cause premature failure. Here, two different MEA frame designs are implemented to study their robustness during a combined chemical/mechanical membrane degradation accelerated stress test. 4D in situ visualization by periodic, identical-location X-ray computed tomography is performed to understand and thus mitigate the design issues responsible for edge failures. Interfacial interaction of adhesive-containing polyimide gasket and MEA and non-uniform load distribution along MEA edges are identified as the two key contributors to premature edge failures, which introduce significant cell voltage decay due to permanent membrane deformation. Edge failure mitigation is demonstrated by using a non-adhesive sub-gasket along with increased gasket coverage area, which leads to: (i) delayed onset of edge failure; (ii) five times reduction in edge crack size; (iii) elimination of membrane tearing; and (iv) minimal impact of edge failures on cell performance, thus enabling a robust MEA edge wherein the performance-impacting failure is shifted to the more important active area regions. • 4D in situ visualization scheme is applied to study membrane failure at MEA edges. • Edge crack propagation at identical MEA locations is captured for the first time. • Edge failure occurs primarily due to non-uniform interfacial stress distribution. • A robust MEA frame design is demonstrated that can endure chemo-mechanical stress.

Influence of the interphase between laser-cladded metal layer and steel substrate on fatigue propagation of a short edge crack

Laser cladding is a relatively new technology how to combine properties of various materials. Thus, bi-material interfaces are presented in real structures and can affect the fatigue crack propagation. A cracked bar subjected to pure tensile loading is numerically simulated in this work in order to analyze the effect of the interphase layer between the cladded metal layer and the steel substrate on crack growth in the surface layer. Particularly, the influence of various Young’s modulus of the interphase on the stable/unstable edge crack propagation is assessed. Moreover, the number of cycles necessary for achievement of the defined critical crack length is calculated and it is summarized that knowledge of elastic properties of the thin interphase is crucial for fracture and fatigue analyses.

Molecular dynamics simulation of edge crack propagation in single crystalline alpha quartz

Edge crack propagation of single-crystalline alpha quartz under mode I loading condition was investigated using a molecular dynamics simulation. Five different crack lengths are used to analyze the effects of crack length on each sample's crack growth behavior. The effect of crack length was studied in terms of the material's stress-strain curve, strain energy, fracture toughness, atomic analysis of crack propagation, and crack opening deformation. The results revealed that during tensile loading, the pre-cracked crystalline quartz samples are fractured in a brittle approach. The fracture stress in the pre-cracked sample (40 Å length) is dropped about 70% compared to pristine quartz. Moreover, the effect of loading velocity on the mechanical properties is investigated. According to the findings, maximum stress rises by enhancing the loading velocity, and fracture toughness improves. The fracture surface energy of the single crystalline alpha quartz is calculated, and based on the results, there is a good agreement with experimental data.

Weighted adaptive Kalman filtering-based diverse information fusion for hole edge crack monitoring

The information fusion of different sensors is an effective means of improving the damage quantification of aircraft structures operating in a complex environment. A weighted adaptive Kalman filtering-based information fusion method (WAKFIFM) is proposed to achieve the feature-level fusion of diverse signals of the hybrid piezoelectric-fiber optic sensor network. The damage identification results obtained from guided wave signals and strain signals are described by the quantification curves of damage index (DI) and crack length. A new fusion curve is obtained by fitting the above two quantification curves using the quadratic polynomial method. The mean square error and the root mean square error of the fusion curve and the actual curve are used as the error and the covariance of the proposed WAKFIFM, respectively. The weighted value in WAKFIFM is the reciprocal of the square of the actual measured maximum DI. The hole edge crack propagation experiments are conducted on both an aluminum plate and a carbon fiber reinforced polymer plate in a load-temperature changing environment.A new damage location method integrated with DI information is developed to obtain a more accurate result. The feature-level fusion results show that the proposed WAKFIFM can improve the accuracy of damage quantification, compared against that obtained from the single guided wave signals or fiber optic sensor signals.

A generalized 2D Bézier-based solution for stress analysis of notched epoxy resin plates reinforced with graphene nanoplatelets

In this study, a robust Bezier-based multi-step method is extended to accurately solve the governing fourth-order complex partial differential equation (PDE) in linear elastic fracture mechanics (LEFM) problems. The Bezier technique was first introduced by the authors to solve initial value problems in one dimension. Now, the method is further extended to simultaneously solve Boundary Value Problems (BVPs) in orthogonal directions. To examine the accuracy and performance of the present method, the first-mode normalized stress intensity factor (SIF) of a 2D epoxy resin plate having an initial edge crack and reinforced with randomly oriented graphene nanoplatelets (GnP) is determined and compared with the associated exact analytical solution using the Bayesian statistical analysis. Besides, the impact of GnP aspect ratio on the normalized crack opening displacement (COD) of the reinforced matrix is elaborated for the first time in the literature. Results of the present study suggest that GnPs with maximum aspect ratio are most effective to enhance elastic properties of the plate and potentially limit the edge crack propagation. Specifically, inclusion of 0.5 and 1.0% of needle-shaped GnPs in a notched epoxy resin plate decrease the maximum normalized COD by 33 and 50%, respectively, while for square-shaped GnPs, these reductions are limited to 20 and 37%, respectively.

Theoretical Limits in Detachment Strength for Axisymmetric Bi-Material Adhesives

AbstractReversible dry adhesives rely on short-ranged intermolecular bonds, hence requiring a low elastic modulus to conform to the surface roughness of the adhered material. Under external loads, however, soft adhesives accumulate strain energy, which release drives the propagation of interfacial flaws prompting detachment. The trade-off between the required compliance, for surface conformity, and the desire for a reduced energy release rate, for better strength, can be achieved with a bi-material adhesive having a soft tip and a rigid backing (RB). This design strategy is widely observed in nature across multiple species. However, the detachment mechanisms of these adhesives are not completely understood and quantitative analysis of their adhesive strength is still missing. Based on linear elastic fracture mechanics (LEFM), we analyze the strength of axisymmetric bi-material adhesives. We observed two main detachment mechanisms, namely (i) center crack propagation and (ii) edge crack propagation. If the soft tip is sufficiently thin, mechanism (i) dominates and provides stable crack propagation, thereby toughening the interface. We ultimately provide the maximum theoretical strength of these adhesives obtaining closed-form estimation for an incompressible tip. In some cases, the maximum adhesive strength is independent of the crack size, rendering the interface flaw tolerant. We finally compare our prediction with experiments in the literature and observe good agreement.

Laboratory study on the propagation of edge cracks in rock-like material and its implication in coal mining

Rock fracture propagation is a major hazard for mining and tunnel excavation in fractured rock masses or coal seams. A longwall mining panel with a typical dimension of 200m (width)×1000m (length)×3m (height) can be considered as an open edge crack. The fracturing processes in the vicinity of the edge crack (or the longwall panel) particularly in the roof and floor are critically important for the safety of mining operation because fracturing can lead to water inrush and dynamic loading on the working face. It’s therefore important to understand and predict the pre-existing edge crack initiation and propagation in rock masses. This paper describes a study investigating the mechanisms and pathways of rock fracture under uniaxial compression. In this study, a rock-like material which consists of model gypsum, water and diatomaceous earth at a mass ratio of 165:75:2 was used. The uniaxial compression strength of the material decreased with the increase of the length of pre-existing edge crack. During the tests, wing (tensile) cracks were first observed at the tip of the pre-existing edge crack. This was followed by secondary cracks as the loading increased. The final failure of the specimens however was dominated by tensile cracks throughout the specimens. Due to the sudden crack initiations in the specimens, the loading stress in the specimen varies stepwise, and acoustic emission (AE) energy and amplitude showed abrupt changes when crack initiated. When the crack initiation occurred, the loading stress of the specimens showed a notable retreat in the stress-strain curve, and the recorded AE energy and amplitude showed a sharp spike. These findings from this experimental study have been applied to the underground longwall mining to explain the failure mechanisms in the floor of the mining panel. The fracturing process associated with the pre-existing edge crack resembles the formation of flow channels for water inrush during longwall mining.

The Analytical Aspect of Pressure Dependence and the Change of Edge Crack Propagation of Horizontal Layer

The receiving of plain problem by analytical appearance with horizontal edges on the endless layer of propagation of the vertical crack and the dependence of the inner pressure of crack is observed. It supposed that the bottom edge of the layer is fixed to absolutely hard semi-flatness, but the upper edge is free. In this respect, we have tried to get the propagation measure of the opening and the analytical aspect of pressure change dependence acting inside it, by method of local modifications using the received solutions. The corresponding methods of approximate illustration of functional dependence are used. In the environment of the opening and the received measure of crack propagation the analytical expressions of distribution of stresses give the full image of peculiarities of those dependences for that immeasurable domain and correspond to the received results by method of modifications. The received formulas may be applied by solving concrete applicable problems and in studies of opportunities of cracks’ propagation for environment of fragile material. Those opportunities are increasing moreover if we take into account that the solutions are received for immeasurable environment.

Increasing cold workability of Ti-6Al-4V alloy via thermo-mechanical processing: simulation and experiment

AbstractRolling temperature is thought to have a significant effect on the cold workability of Ti-6Al-4V alloy. To investigate the extent of this effect, four Ti-6Al-4V strips were hot rolled at different rolling temperatures in the range of 650–950 °C while other process parameters were invariant. The specimens revealed an increase in work hardening capacity with increase in rolling temperature, based on tensile and plane strain compression testing. After 10 % cold rolling, the same annealed samples exhibited propagation of edge cracks in specimens that had been hot rolled at 650, 750 and 850 °C while no cold rolling defect was found in the specimen hot rolled at 950 °C. The results of finite element method reveal that during cold rolling, the von Mises stress field is decreased as a result of increasing previous hot rolling temperature. In accordance with X-ray diffraction results, increasing previous hot rolling temperature is associated with lower lattice strain storage during subsequent cold rolling.

Microstructure and fatigue damage mechanism of Fe[sbnd]Co[sbnd]Ni[sbnd]Al[sbnd]Ti[sbnd]Zr high-entropy alloy film by nanoscale dynamic mechanical analysis

Micro-electromechanical system (MEMS) films are subjected to a large number of impact during the working process. The fatigue life of the films need be measured to evaluate the reliability of the film's impact resistance. In this work, a new kind of MEMS soft magnetic non-equimolar high-entropy alloy (HEA) film (FeCoNi)25(TiZrAl)75 was prepared by magnetron sputtering. The fatigue damage behaviors of the HEA film was investigated by nanoscale dynamic mechanical analysis (nanoDMA) technique. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM) were adopted to analyze the microstructure and damage surfaces pattern. The results showed that the HEA film displayed a polycrystalline structure with the fcc solid solution uniformly distributed in the amorphous phase. There were three stages during the process of fatigue damage, the compressional deformation stage, the buckling and layering stage, and the edge crack propagation leads to the delamination stage. The contact stiffness suddenly decreased at the moment of fatigue damage happening.

On the Role of the Plaque Porous Structure in Mussel Adhesion: Implications for Adhesion Control Using Bulk Patterning

Mussel adhesion is a problem of great interest to scientists and engineers. Recent microscopic imaging suggests that the mussel material is porous with patterned void distributions. In this paper, we study the effect of the pore distribution on the interfacial-to-the overall response of an elastic porous plate, inspired from mussel plaque, glued to a rigid substrate by a cohesive interface. We show using a semi-analytical approach that the existence of pores in the vicinity of the crack reduces the driving force for crack growth and increases the effective ductility and fracture toughness of the system. We also demonstrate how the failure mode may switch between edge crack propagation and inner crack nucleation depending on the geometric characteristics of the bulk in the vicinity of the interface. Numerically, we investigate using the finite element method two different void patterns; uniform and graded. Each case is analyzed under displacement-controlled loading. We show that by changing the void size, gradation, or volume fraction, we may control the peak pulling force, maximum elongation at failure, as well as the total energy dissipated at complete separation. We discuss the implications of our results on design of bulk heterogeneities for enhanced interfacial behavior.

Application of the XFEM to Predict the Edge Crack Propagation of Steel Sheet in the Cold Rolling Process

Application of the XFEM to Predict the Edge Crack Propagation of Steel Sheet in the Cold Rolling Process

Application of the cohesive zone model for analysing the edge crack propagation of steel sheet in the cold rolling process

AbstractIn the cold rolling process, the expansion and coalescence of micro‐defects can make steel sheet quality descend and create edge crack in the steel sheet. And the edge crack can cause the strip rupture completely. In this research, the cohesive zone model (CZM) was used to analyse the initiation and propagation of edge crack in the cold rolling process with the non‐reversing two‐high mill. A bi‐linear traction–separation law was utilized which is primarily given by the CZM parameters including the cohesive stress, T, and the cohesive energy, Γ. Compared with other popular models such as the Gurson–Tvergaard–Needleman (GTN) model, the CZM presents certain advantages because it requires a smaller number of parameters to be defined. Comparison results of the experiments and simulation illustrated that the CZM can provide accurate prediction for the propagation of edge crack in the cold rolling process. Parametric analysis was carried out and showed that the extent of the crack propagation increases with the increasing of the reduction ratio.

Constitutive flow behaviour and finite element simulation of hot rolling of SiCp/2009Al composite

The material parameters of 17vol.%SiCp/2009Al composite in the Arrhenius-type constitutive equations were calculated using experimental data from hot compression tests. The constitutive equation was then implemented into the finite element software, ABAQUS/Explicit, to calculate the stress, deformation and edge damage in the hot rolling process. The initiation and propagation of edge cracks under the hot rolling condition were studied via the Gurson–Tvergaard–Needleman (GTN) damage model. The influence of the thickness reduction on the strip damage was assessed. The results indicate that the high tensile stress at the edge of the strip causes crack initiation and propagation, and the total reduction has a significant effect on the damage in the hot rolling of the SiCp/2009Al composites. When the reduction is less than 20%, no crack initiates and the damage occurs on the strip surface. With increase of the total reduction to 25% and larger, edge cracks occur and increase gradually. The distribution and direction of edge cracks are closely correlated with the stress components. The hot rolling experiments on 17vol.%SiCp/2009Al composite were conducted to evaluate the simulation results, and it is indicated that the finite element calculation results agreed well with the experimental results. This indicates that the finite element analysis is able to successfully simulate the rolling process and provide important information for the process optimization.

Prediction of crack location and propagation in stretch flanging process of aluminum alloy AA-5052 sheet using FEM simulation

The stretch flanging process is significantly affected by various geometrical, material and process parameters. The punch-die clearance and initial flange length are main parameters which have major effects on the edge crack location and strain distribution along die profile radius in the flange. Non-axisymmetric stretch flanging process of AA-5052 sheet metal blanks was carried out by numerical simulation to predict the deformation behavior of flange, location and propagation of crack in flange and to investigate the effect of punch die clearance, flange length, die and punch profile radius and friction in the stretch flanging process. The experimental investigations were made to validate the simulations results. The results reveal that the crack length increases with the increase in the flange length. It is found that the flange length has a significant effect in circumferential direction as compared with the radial direction. The punch die clearance has the most significant effect in crack propagation in comparison with flange length. The circumferential strain is found to be larger in the case of punch having the profile radius less than the die profile radius, which leads to faster edge crack propagation. A close agreement is found between simulation and experimental results in terms of location of edge crack and forming load.

FEM simulation of a crack propagation in a round bar under combined tension and torsion fatigue loading

An edge crack propagation in a steel bar of circular cross-section undergoing multiaxial fatigue loads is simulated by Finite Element Method (FEM). The variation of crack growth behaviour is studied under axial and combined in phase axial+torsional fatigue loading. Results show that the cyclic Mode III loading superimposed on the cyclic Mode I leads to a fatigue life reduction. Numerical calculations are performed using the FEM software ZENCRACK to determine the crack path and fatigue life. The FEM numerical predictions have been compared against corresponding experimental and numerical data, available from literature, getting satisfactory consistency.