Fatigue Crack Propagation Analysis Research Articles

Analysis of biaxial proportional low-cycle fatigue crack propagation for hull inclined-crack plate based on accumulative plasticity

Fracture failures of ship plates subjected to in-plane biaxial low-cycle fatigue loading are generally the coupling result of accumulative plasticity and biaxial low-cycle fatigue damage. A biaxial low-cycle fatigue crack growth analysis of hull structure that accounts for the accumulative plasticity effect can be more suitable for the actual evaluation of the overall fracture performance of the hull structure in severe sea conditions. An analytical model of biaxial low-cycle fatigue crack propagation with a control parameter for ∆CTOD is presented for hull inclined-crack plate. A test was conducted for cruciform specimens made of Q235 steel with an inclined crack to validate the presented analysis. The biaxial accumulative plasticity behavior and the effects of biaxiality and stress ratios were investigated. The results of this study reveal a strong dependence of biaxial low-cycle fatigue crack propagation on biaxial accumulated plasticity.

Fatigue crack propagation analysis of a CT test specimen with cladding

In this study, a system for fatigue crack propagation analysis based on XFEM referred to as sim2d, which can model crack independently of finite elements, has been developed. A fatigue crack propagation analysis of a carbon steel CT specimen with stainless steel cladding has been performed by the system. The stress intensity factor for initial crack front obtained by sim2d is compared with that by FEM. In addition, crack propagation analysis was performed and the geometry of propagating crack front was simulated.

Investigating the Structural Dynamics and Crack Propagation Behavior under Uniform and Non-Uniform Temperature Conditions.

The robustness and stability of the system depend on structural integrity. This stability is, however, compromised by aging, wear and tear, overloads, and environmental factors. A study of vibration and fatigue cracking for structural health monitoring is one of the core research areas in recent times. In this paper, the structural dynamics and fatigue crack propagation behavior when subjected to thermal and mechanical loads were studied. It investigates the modal parameters of uncracked and various cracked specimens under uniform and non-uniform temperature conditions. The analytical model was validated by experimental and numerical approaches. The analysis was evaluated by considering different heating rates to attain the required temperatures. The heating rates were controlled by a proportional-integral-derivative (PID) temperature controller. It showed that a slow heating rate required an ample amount of time but more accurate results than quick heating. This suggested that the heating rate can cause variation in the structural response, especially at elevated temperatures. A small variation in modal parameters was also observed when the applied uniform temperatures were changed to non-uniform temperatures. This study substantiates the fatigue crack propagation behavior of pre-seeded cracks. The results show that propagated cracking depends on applied temperatures and associated mass. The appearance of double crack fronts and multiple cracks were observed. The appearance of multiple cracks seems to be due to the selection of the pre-seeded crack shape. Hence, the real cracks and pre-seeded cracks are distinct and need careful consideration in fatigue crack propagation analysis.

A reliability approach to fatigue crack propagation analysis of ship structures in polar regions

Fatigue is a common failure mode in ship structures. For structures with an initial crack, the fatigue crack propagation behavior needs to be considered. The purpose of this study is to establish a procedure for analysis of fatigue crack propagation of ship structures in combination with reliability methods. The stress intensity factor (SIF) and geometry correction factor are calculated by means of finite element analysis. Validation for the SIF calculation is achieved by comparing the computed results with those based on related solutions. Since fatigue damage usually occurs in weld areas, the effect of such components on the fatigue crack propagation behavior was also considered in this work. The Paris law in combination with the Monte Carlo technique are employed for the fatigue crack propagation analysis in this study. Reliability updating based on inspection for cracks is also carried out. A computer program was developed for the purpose of fatigue crack propagation analysis within the framework of reliability methods. An application example of fatigue crack propagation in relation to the hull of the icebreaker Xuelong 2 is presented. The sensitivity of the procedure to key analysis parameters (sample size, initial crack size) is also considered. Finally, the effect of low temperatures on the computed results is also analyzed.

Three-dimensional modeling of non-planar fatigue crack growth in spur gear tooth using tetrahedral finite elements

In this paper, a numerical methodology for prediction of crack growth path and life of structures containing cracks and its application to three different case studies on spur gear tooth are presented. Three-dimensional non-planar fatigue crack propagation analyses are carried out using FRAC3D, which is part of Fracture and Crack Propagation Analysis System (FCPAS), employing fully unstructured tetrahedral elements along the crack front and in the whole model. Fatigue crack growth path predictions are performed using recently developed crack growth criteria that combine different equations used to predict crack deflection angle and to determine equivalent stress intensity factor. Comparisons of obtained results from numerical simulations with available data from the literature in terms of crack growth trajectories show very close agreement. Therefore, it is concluded that FCPAS is capable of performing three-dimensional non-planar crack growth modeling using fully tetrahedral elements in the whole finite element model, which requires less user intervention, time and effort for modeling. Moreover, the presented methodology and the recently developed crack growth criteria can be used for three-dimensional crack growth analysis.

Crack Propagation in the Tibia Bone within Total Knee Replacement Using the eXtended Finite Element Method

Understanding of fracture mechanics of the human knee structures within total knee replacement (TKR) allows a better decision support for bone fracture prevention. Numerous studies addressed these complex injuries involving the femur bones but the full macro-crack propagation from crack initiation to final failure and age-related effects on the tibia bone were not extensively studied. The present study aimed to develop a patient-specific model of the human tibia bone and the associated TKR implant, to study fatigue and fracture behaviors under physiological and pathological (i.e., age-related effect) conditions. Computed tomography (CT) data were used to develop a patient-specific computational model of the human tibia bone (cortical and cancellous) and associated implants. First, segmentation and 3D-reconstruction of the geometrical models of the tibia and implant were performed. Then, meshes were generated. The locations of crack initiation were identified using the clinical observation and the fatigue crack initiation model. Then, the propagation of the crack in the bone until final failure was investigated using the eXtended finite element method (X-FEM). Finally, the obtained outcomes were analyzed and evaluated to investigate the age-effects on the crack propagation behaviors of the bone. For fatigue crack initiation analysis, the stress amplitude–life S–N curve witnessed a decrease with increasing age. The maximal stress concentration caused by cyclic loading resulted in the weakening of the tibia bone under TKR. For fatigue crack propagation analysis, regarding simulation with the implant, the stress intensity factorand the energy release rate tended to decrease, as compared to the tibia model without the implant, from 0.152.5 to 0.111.9 (MPa) and from 10240 to 5133 (J), respectively. This led to the drop in crack propagation speed. This study provided, for the first time, a detailed view on the full crack path from crack initiation to final failure of the tibia bone within the TKR implant. The obtained outcomes also suggested that age (i.e., bone strength) also plays an important role in tibia crack and bone fracture. In perspective, patient-specific bone properties and dynamic loadings (e.g., during walking or running) are incorporated to provide objective and quantitative indicators for crack and fracture prevention, during daily activities.

Fatigue crack separation and merging simulation using the smoothed particle hydrodynamics

The present paper proposes a new computational method for the fatigue crack propagation in a metallic structure using the smoothed particle hydrodynamics (SPH). First, we discuss how to model the crack front line with C0 continuous elements called chained crack front lines, which resemble those that were experimentally observed. In the second, the detailed algorithm for the chained crack front line is proposed and implemented into the fatigue crack propagation analysis program based on the SPH named as SPH-Fatigue. Third, the present method is applied to the fatigue crack propagation problems with crack separation and merging phenomena, such as the crack propagation passing through a hole or passing through a slit in a T-joint structure. The calculated results show an excellent agreement with time-dependent crack shapes experimentally obtained. We conclude that the idea of chained crack front line discussed in this paper is useful to estimate the time dependent crack shape of real materials and structures.

Three-dimensional fatigue crack propagation analysis of welded steel beam based on global-local numerical model

The existing fatigue assessment approaches were mainly conducted on the component level. The interaction of local component damage and the global response cannot be well addressed. In this study, three-dimensional (3D) fatigue crack propagation analysis approach based on global-local numerical model was implemented, and examined to be accurate and effective through a series of systematic experimental data obtained by Fisher. Afterwards, the approach was introduced into a typical steel truss bridge for realizing more refined fatigue assessment from the global structural level. The fatigue performance of the longitudinal steel welded beam in the steel truss bridge was investigated based on global-local model and local model respectively. It was found that there is no difference in terms of the fatigue crack growth mechanism between the simulation between global-local model and local model due to that the stress level of the whole structure is relatively low. At last, the effect of heavy haul train operation on the fatigue performance of the steel truss bridge was analyzed. It was observed that the residual life of the longitudinal steel welded beam would have an obvious reduction when the axle load was increasing. The research work in this study presents a technical solution for the fatigue assessment of the global structure and can provide beneficial reference for relevant practical engineering projects.

Fatigue Crack Propagation Analysis of Orthotropic Steel Bridge with Crack Tip Elastoplastic Consideration

Abstract: Due to the complex structure of the orthogonal steel bridge deck and dense weld, fatigue cracks are prone to occur in the typical welding details. Welding residual stress will cause a plastic zone at the crack tip. In this paper, an elastoplastic constitutive model of Chaboche material was introduced, and the extended finite element method (XFEM) was used to study the influence of material elastoplasticity and crack tip plastic zone on the law of fatigue crack propagation. By judging the stress state of the residual stress field at the crack tip and selecting different crack propagation rate models to investigate the crack propagation law when plastic deformation was considered, the propagation path and propagation rate of fatigue crack of the orthotropic bridge deck were obtained. The results show that, whether the residual stress field is considered or not, the plastic deformation at the crack tip will not cause the obvious closure of the fatigue crack at the U-rib toe during the crack propagation process, but will significantly affect the crack propagation path. When material plasticity is considered, the propagation angle of fatigue crack at the U-rib toe basically remains unchanged along the short-axis direction of the initial crack, but increases along the long-axis direction, and the crack tip plastic zone inhibits the propagation of the crack tip on one side. Compared with linear elastic materials, the crack propagation law considering material plasticity is more consistent with the actual fatigue crack propagation law in bridge engineering. In terms of the propagation rate, if the residual stress field is not considered, the fatigue crack propagation rate at U-rib toe with plasticity considered is slightly higher than that without plasticity considered, because plastic deformation will affect the amplitude of energy release rate. When considering the welding residual stress field, the fatigue crack propagation rate at U-rib toe is increased due to the combined actions of plastic deformation and stress ratio R.

Novel Fatigue Crack Propagation Analysis of Solder Joint Using Singularity of Strain Energy Density in the Crack Tip Near Field

Novel Fatigue Crack Propagation Analysis of Solder Joint Using Singularity of Strain Energy Density in the Crack Tip Near Field

A procedure to generate design load-time histories for fatigue strength assessment of offshore structures

This paper presents general procedures to generate loading histories for fatigue strength assessment of offshore structures based on a storm model and seasonal wave data. Using hindcast wave data of 11 years at one point in the North Atlantic Ocean, the relations among the storm duration, storm crest and the number of levels in a storm are formulated and the statistics of storm duration are obtained. One year, including four seasons is chosen as the reference period of the loading history. Based on the generated loading histories, fatigue crack propagation analyses are performed on a tubular T-joint using a fatigue crack growth model considering the load interaction and R-ratio effect. The crack size uncertainty caused by randomly generated loading histories is investigated. The proposed procedures can lead to a good agreement with the observed significant wave height distribution. The generated loading histories result in median crack growth curves, comparing with those from measured wave data. The crack size is subjected to considerable uncertainty after a period of crack propagation. Ignoring the load interaction effect leads to faster crack growth, which may be the most convenient way to achieve a conservative fatigue crack propagation analysis using only one generated load history.

Analysis of fatigue crack propagation in rails under combined action of wheel load and residual stress

Fatigue crack is one of the main damages that reduce rail service life and raise rail maintenance costs. In this paper, a three-dimensional elastic–plastic finite element model of wheel-rail contact is established, in which a three-dimensional oblique crack is inserted in the rail. Taking crack tip displacements as fracture parameters, the effect of residual stress on fatigue crack propagation of rails is quantitatively analyzed, and the fatigue crack propagation mechanism of rails under the combined action of wheel load and residual stress are studied. Results show that crack tip displacements under the action of wheel load are quite different from that under the combined action of wheel load and residual stress. For the oblique crack with crack tip entering the residual tensile stress zone, crack tip sliding displacement amplitude increases with the increase of wheel-rail friction coefficient. Under the combined action of wheel load and residual stress, the oblique crack propagates as the combined type of II/III dominated by type II.

An approach for fatigue crack propagation analysis by smoothed particle hydrodynamics method

An approach for fatigue crack propagation analysis by smoothed particle hydrodynamics method

Three-dimensional fatigue crack growth simulation of embedded cracks using s-version FEM

PurposeSince the most of structures and structural components suffers from cyclic loadings, the study on the fatigue failure due to the crack growth has a great importance. The purpose of this paper is to present a three-dimensional fatigue crack growth simulation of embedded cracks using s-version finite element method (SFEM). Using the numerical results, the validity of the fitness-for-service (FFS) code evaluation method is verified.Design/methodology/approachIn this paper, three-dimensional fatigue crack propagation analysis of embedded cracks is performed using the SFEM. SFEM is a numerical analysis method in which the shape of the structure is represented by a global mesh, and cracks are modeled by local meshes independently. The independent global and local meshes are superimposed to obtain the displacement solution of the problem simultaneously.FindingsThe fatigue crack growth of arbitrary shape of cracks is slow compared to that of the simplified circular crack and the crack approximated based on the FFS code of the Japan Society of Mechanical Engineers (JSME). The results tell us that the FFS code of JSME can provide a conservative evaluation of the fatigue crack growth and the residual life time.Originality/valueThis paper presents a three-dimensional fatigue crack growth simulation of embedded cracks using SFEM. Using this method, it is possible to apply mixed mode loads to complex shaped cracks that are closer to realistic conditions.

Analyses of fatigue crack propagation with smoothed particle hydrodynamics method

In this paper, a new fatigue crack propagation analysis method based on the linear fracture mechanics, the Paris-Erdogan Law and the smoothed particle hydrodynamics (SPH), is proposed. At first, a crack is simply modeled as an aggregate of particle voids for handling crack propagation. Then, the crack front line is given the feature of changing its shape naturally as a chained crack front line based on the experimental observation. Third, the crack propagation algorithm with the SPH including the method to handle the cracks merging problems is developed. Finally, some numerical and experimental data of the fatigue crack propagation behavior are compared to confirm the utility and the validity of the proposed method. In case of a crack propagation from a corner crack, the present numerical solution shows almost the same crack propagation as observed in the experimental data. In case of a two cracks merging problem, the numerical result shows a smoothed time dependent crack propagation behavior. Also, the case in which a crack is passing a hole is successfully solved, showing a smooth crack separation and cracks merging process.

Stress fatigue crack propagation analysis of crane structure based on acoustic emission

Gantry crane is a widely used equipment in logistics fields. Stress fatigue crack propagation is an important fatigue mode of gantry crane in services. Based on theoretical analysis and acoustic emission (AE) test, A new crack propagation analysis method was proposed in this investigation. A two-parameter basis function was adopted to analyze crack propagation of steel Q235B, and the response surface was modeled to predict the fatigue life of steel specimen, moreover AE technique was advanced to detect the crack propagation, where layout of AE sensors was optimized to achieve a precise result. Consequently the proposed method was applied in practical box-girder crack propagation analysis. By comparison with theoretical analysis, it indicated that this method was precise and could be applied in practical engineering.

Fatigue crack propagation analysis in structures with random parameters based on polynomial chaos expansion method

Fatigue fracture is the most common failure for aircraft structures, therefore fatigue life prediction plays an important role in structure design. However, uncertainties widely existing in engineering structures make it difficult to analyze crack propagation and predict fatigue life. This paper presents a novel efficient and accurate approach to crack propagation analysis in structures with random uncertainties based on polynomial chaos expansion (PCE) method. For short fatigue crack in aircraft skin or armor plate of tank, the structure can be regarded as an infinite plate. In this situation, the stress intensity factor range has a simple analytical expression and a basic crack propagation equation is derived based on it. Considering uncertain parameters, crack length is regarded as a random variable and expanded into orthogonal polynomial series after introducing Hermite polynomials. Because crack length is a time-dependent variable, the coefficients in polynomial series are regarded to be time-dependent. In order to determine values of these coefficients, orthogonal polynomial series of crack length is substituted into Paris law and a series equations are obtained considering the orthogonality of Hermite polynomials. Time history of the coefficients is acquired by solving these equations using numerical algorithm. Furthermore, expectation and standard deviation of crack length can be easily obtained. The proposed method is verified based on three numerical examples and Monte-Carlo Simulation (MCS) is applied for the sake of validation. The results demonstrated the accuracy and efficiency of the proposed method for crack propagation analysis of structures with random parameters.

Analysis of two-dimensional fatigue crack propagation in thin aluminum plates using the Paris law modified by a closure concept

A general procedure is applied to analyze fatigue crack propagation in isotropic materials under mixed mode conditions, the Paris law modified by a closure concept. The dual boundary element method (DBEM) provides an stress and strain analysis on the solid, with reliable results for the mechanical fields in the region near to the crack tip. For validating purposes, thin plates made of 2024-T3 aluminum alloy are used with two horizontal notches. Throughout the J-Integral the stress intensity factors (SIFs) can be evaluated and with digital image processing, the displacement information from the experimental tests is obtained. Then, the effect of the crack closure during unloading is considered to attain remarkable numerical results compared to those experimentally collected, showing the feasibility of the proposed model.

Effect of temperature on the probability and cost analysis of mixed-mode fatigue crack propagation in patched aluminium plate

By the present paper, a numerical model for cost and probability analysis of mixed mode fatigue crack propagation in a patched 2024-T3Aluminium plate is developed. The finite element method is used to analyse the temperature effect on the bonded composite repair performance of the Aluminium plate. Using a fine mesh, mid-plane finite element results are in good experimental results given by literature. Different patch shapes are proposed like; circle, rectangle, square, ellipse, regular octagon, and prolonged octagon. The stress intensity factors at the crack tip are chosen as fracture criteria in order to estimate the repair performance. According to the temperature variation, the lifespan of the repaired fatigue crack growth is estimated using Paris law. The repair done on a central inclined crack with a single-side composite patch show that, best results are given by prolonged octagon and patch is damaged under at elevated temperature. The life-cycle of the patched Aluminium plate is obtained by Monte Carlo simulation, and the probability of failure is quantified according to various geometrical and mechanical parameters. At elevated temperature, the most dominant input parameters are thicknesses of adhesive and patch. In sensitivity analysis effect of thickness of the adhesive layer reaches 35%.Finally, a code source has been developed and implanted in ANSYS software, to consider the manufacturing process and optimal maintenance costs to prove the performance of patch operation from both safety and economical point of view.

Analysis of Fatigue Crack Propagation of an Orthotropic Bridge Deck Based on the Extended Finite Element Method

As one of the most fatigue‐sensitive parts of an orthotropic steel bridge deck, the weld between the U‐rib and the top deck is prone to fatigue cracking under the actions of the stress concentration, welding residual stress, and vehicle load. To investigate the mechanism of fatigue crack propagation and the influence of the welding residual stress on the propagation patterns of fatigue cracks, a multiscale modeling method was proposed, and the static analysis and the dynamic propagation analysis of fatigue crack were carried out in this paper. First, a multiscale finite element model was established, including whole bridge models with a scale feature of 102 m, orthotropic bridge deck models with a scale feature of 100 m, and crack models with a scale feature of 10−3 m. Then, a segmental model of the bridge deck was extracted, which is regarded as a critical location of the bridge, and the shell‐solid coupling method is adopted in the segmental model in order to further analyze the crack propagation rule. Moreover, based on the extended finite element method (XFEM), the static crack and dynamic crack propagation in this critical position were analyzed. Finally, thermoelastoplastic analysis was carried out on the connection of the U‐rib and deck with a length of 500 mm to obtain the residual stress, and then the results of residual stress were introduced into the segmental model to further study its influence on the evolution of fatigue crack propagation. The analysis of the welding process shows that near the weld region of the connection of the U‐rib and deck, the peak value of the residual tensile stress can reach the material yield strength. The static analysis of fatigue cracks shows that under the single action of a standard fatigue vehicle load, the fatigue details at the weld toe of the deck cannot reach the tensile stress required for fatigue crack propagation, and only the fatigue details at the weld toe of the U‐rib can meet the requirements of fatigue crack propagation. The dynamic analysis of fatigue cracks reveals that the crack in the weld toe of the U‐rib is a mixed‐mode crack with modes I, II, and III. The propagation of a fatigue crack without a residual stress field will be terminated until the crack length is extended to a certain length. Nevertheless, when the residual stress field was introduced, the growth angle and size of the fatigue crack would increase, and no crack closure occurs. For the crack in the weld toe of the deck, the crack is in the closed state under the standard fatigue vehicle load. When the residual stress field is introduced, the tensile stress of the fatigue details increases. Meanwhile, the fatigue crack will become a mixed‐mode crack with modes I, II, and III that will be dominated by mode I and extend toward the weld at a slight deflection angle. The results of various initial crack sizes at the weld toes of the top deck are analyzed, which shows that the initial crack size has a certain effect on the fatigue crack growth rate, especially the initial crack depth.