Crack Analysis Research Articles

Failure Analysis of the Crack and Leakage of a Crude Oil Pipeline under CO2-Steam Flooding

This paper presents the failure analysis of the crack and leakage accident of a crude oil pipeline under CO2-steam flooding in the western oilfield of China. To analyze the failure behavior and cause, different testing, including nondestructive testing, chemical composition analysis, tensile property testing, metallographic analysis, and microanalysis of fracture and chloride stress corrosion cracking (SCC) testing, are applied in the present study. The obtained results showed that the pipeline under the insulation layer of high humidity, high oxygen content, and high Cl− environment occurred pit corrosion, and the stress concentration area at the bottom of the corrosion pit sprouted cracks. Besides, it is demonstrated that the cracks were much branched, mostly through the crystal, and the fracture showed brittle, which is consistent with the typical characteristics of chloride SCC. Meanwhile, the insufficient Ni content of the pipeline material promoted the process of chloride SCC, and the high-temperature working conditions also aggravated the rate of chloride SCC. In addition, efficient precautions were provided to avoid fracture.

Influence of flexoelectricity on interface crack problems under a dynamic load

In the present paper, the influence of flexoelectricity on behavior of the interface crack between two dissimilar dielectric materials under a dynamic mechanical load is investigated. The induced electric field affects the distribution and evolution of mechanical fields in dielectric materials. Large strain gradients induce the electric polarization in the direct flexoelectricity. Due to the large strain gradients at the crack tip vicinity it is needed to consider the strain gradient theory model. Governing equations in this theory contain higher-order derivatives than in the conventional continuum mechanics approach. The mixed finite element method (FEM) is developed here for a general boundary value problem, where the standard C0 continuous finite elements are applied for independent approximations of displacements and strains. The constraints between them are satisfied by collocation at appropriate internal points in elements. Interface cracks are observed in layered structures frequently due to a poor adhesion of layers. The incorporation of flexoelectricity and micro-inertial effects is needed into the failure analysis of interface cracks in nano-sized structures under dynamic loading. In numerical examples, we discuss the influence of flexoelectricity coefficients as well as the ratio of elastic coefficients and the geometrical size to microstructural (micro-stiffness and micro-inertia) length scale parameters of the bilayer composite on the crack opening displacement, stresses ahead the crack tip and induced electric intensity vector.

Analysis Method for Post-Impact Damage Development in Carbon Fiber Reinforced Laminate under Repeated Loading

In the current work, an analysis method for obtaining post-impact damage propagation under cyclic compressive load in flat carbon fiber reinforced plastic (CFRP) panels is presented. The solution for damage growth life is given based on the introduced hypothesis of reference damage mode (RDM). The critical size of damage for obtaining damage growth life was informed by the analysis of crack driving force versus damage size conducted using finite element analysis (FEA). The applicability of the damage tolerance principle for the case of compression–compression cyclic loading of the structural element containing impact damage is discussed and illustrated by the example. The results of using the introduced simplified approach to the calculation of characteristics of damage growth life suggest that the use of the slow-growth approach in composite structures is possible, though the necessity of obtaining the exact parameters of the damage growth rate equation with regard to the chosen crack driving force measure must be addressed.

Enriched physics-informed neural networks for 2D in-plane crack analysis: Theory and MATLAB code

In this paper, a method based on the physics-informed neural networks (PINNs) is presented to analyze 2D in-plane crack problems in the linear elastic fracture mechanics. Instead of using a discretizing mesh, the PINNs-based method is meshless and can be trained on batches of discretely sampled collocation points. In order to capture the asymptotic behavior of the near-tip displacement and stress fields, the standard PINNs formulation is enriched here by including the crack-tip asymptotic functions such that the local behavior in the crack-tip region can be modeled accurately without a nodal refinement. The trainable parameters of the enriched PINNs are learned to satisfy the governing partial differential equations of the cracked elastic solid and the corresponding boundary conditions. It is found that the incorporation of the crack-tip enrichment functions in the PINNs is substantially simpler and more feasible than in the conventional finite element method (FEM) or boundary element method (BEM). The present PINNs-based algorithm is tested and verified by several representative benchmark examples for different loading and crack-mode types. Numerical results show that the present PINNs-based method can provide highly accurate stress intensity factors (SIFs) with only few degrees of freedom. For interested readers, a self-contained MATLAB code and data-sets supplementing this paper are also provided in the Supplementary material.

A Deep Learning and Morphological Method for Concrete Cracks Detection

Concrete crack detection is essential for infrastructure safety, and its detection efficiency and accuracy are the key issues. An improved YOLOV5 and three measurement algorithms are proposed in this paper, where the original prediction heads are replaced by Transformer Heads (TH) to expose the prediction potential with one self-attention model. Experiments show that the improved YOLOV5 effectively enhances the detection and classification of concrete cracks, and the Mean Average Precision (MAP) value of all classes increases to 99.5%. The first method is more accurate for small cracks, whilst the average width obtained based on the axial traverse correction method is more exact for large cracks. The crack width obtained from the concrete picture sample is the same as that obtained from the manual detection, with a deviation rate of 0–5.5%. This research demonstrates the recognition and classification of concrete cracks by integrating deep learning and machine vision with high precision and high efficiency. It is helpful for the real-time measurement and analysis of concrete cracks with potential safety hazards in bridges, high-rise buildings, etc.

Deep learning approaches for prediction of adiabatic temperature rise of concrete with complex mixture constituents

Temperature control and crack prevention of mass concrete are significant to the safety and durability of structures such as dams and long-span bridges. Adiabatic temperature rise is the key issue in thermal and crack risk analysis of mass concrete. Due to the substantial diversity of admixtures influencing the hydration process in modern concrete, it is challenging to develop a comprehensive analytical model to predict adiabatic temperature rise based on theoretical frameworks. As a data-driven approach, deep learning (DL) provides a potential solution for predicting the properties of complex materials in recent years. DL model based on artificial neuron network (ANN) and recurrent neuron network (RNN) were employed in this study to predict adiabatic temperature rise considering 15 variables as input parameters. The determination coefficient (R2) of the prediction results given from ANN and RNN was 0.7616 and 0.8542, respectively. Segmentation technique and bidirectional deep (BD) neuron network algorithm were implemented to improve the performance of RNN. It was demonstrated that BD-RNN provided better results with promising statistical parameters (R2 = 0.9245) and curve fitting of adiabatic temperature rise profiles. Through optimization and k-fold cross-validation, an evolutionary DL model was developed for reliable prediction of adiabatic temperature rise of concrete with complex admixtures.

Crack analysis and modeling in concrete beams reinforced with FRP composite sheets

In this article using the principles and relationships governing fracture mechanics and finite elements cracking in the first mode for reinforced concrete beams reinforced with FRP sheets are analyzed and modeled. In this method to simulate the crack in reinforced beams, the relations for determining the stress intensity coefficients with the presence of rebars and reinforcement sheets are developed. Here, it is assumed that a composite sheet is completely bound to the bottom surface of the beam under pure bending moment. In the proposed method beam components are divided into two categories, including components without cracks and components with cracks. In components without cracks, relations, equations, and the conventional stiffness matrix governing the beam are used, taking into account the changes in the moment of inertia caused by the presence of reinforcements and FRP sheets. In the finite component with a crack, the crack profile is simulated by creating a geometric defect in the beam section. So that the reduction in the hardness of the component with a crack is equivalent to the change in the dimensions of the discontinuity. Here, the changes in the hardness of the cracked component are calculated and presented as a function of the modified stress intensity coefficients. To ensure the correctness and accuracy of the presented method, all the analyzes are implemented in Abaqus software. The comparison of the obtained results shows that the presented method is a suitable method for the analysis of reinforced concrete structures resistant to cracking. So that it can be extended and developed for other models with proper accuracy.

Finite element analysis of three-dimensional cracks by connecting global and local meshes

In this paper, a novel method for the finite element analysis of three-dimensional cracks is developed by connecting global and local meshes using polyhedral elements. A local mesh including a fine spider-web mesh around the crack tip is arbitrary placed in a coarse global mesh of hexahedral elements. Polyhedral elements are generated by modifying the hexahedral elements at the interface between global and local meshes. The present polyhedral elements provide a seamless connection between global and local meshes. Numerical results show that the present method can be effectively used to analyze three-dimensional cracks by connecting global and local meshes using polyhedral elements.

Analysis of Intergranular Corrosion Cracking of Austenitic Stainless Steel Tubes for Utility Boilers

The cracking failure accidents of austenitic stainless steel pipes of utility boilers often occur. The intergranular corrosion cracking caused by improper control of welding, heat treatment and cold working processes is an important reason for its failure. Through the analysis of typical cases, this paper expounds on the influence of welding, heat treatment and cold working processes on the service safety of austenitic stainless steel pipes and puts forward protective measures.

Irradiation-Assisted Microstructure Evolution and Mechanical Properties Loss of 310S Welded Joints

In order to reveal the effect of irradiation damage caused by high-level liquid radioactive wastes on the welded joint of the container, the irradiation-induced microstructure evolution and mechanical properties degradation of the 310S stainless steel welded joints were investigated in this study. For this purpose, the 1.3 MeV 60Co and 2 MeV accelerators were used to simulate irradiation experiments on 310S welded joints. The uniaxial tensile tests characterized the specimens' mechanical properties and fracture morphology. The results revealed that elongation was reduced by about 5% of irradiation damage by 60Co, and the fracture morphology shows a large number of secondary cracks. In contrast, the elongation was recovered irradiated by the accelerator, and the fracture morphology showed a large number of dimples. Following the interrupted creep deformation, creep fracture tests were conducted for irradiation specimens. The 60Co irradiation damage significantly decreases the creep resistance, leading to deformation of creep, which is increased to 1.5 times that of those unirradiated specimens. At the same time, the ductility is seriously degraded for the irradiated creep fracture specimens. As a result, the creep fracture strain of 60Co specimens is reduced to 70% of that of unirradiated specimens. Further, ductility reduction was related to the irradiated hardening by 60Co, while Nano-indenter hardness was 5.9 GPa, higher by 44% than the unirradiated specimens. The results are shown in an enrichment of Cr, C and P elements at phase boundaries for 60Co irradiation specimens, while the magnitude of element segregation increased by the accelerator combination irradiation. Finally, the creep cracking analysis results show intergranular cracking was observed on the surfaces of the irradiated specimens, while the M23C6 has a primary relationship with the intergranular cracks. The synergic effect of irradiation promoted damage, and element segregation was the primary cause of the intergranular cracking of the 310S welded joints.

Studies on the post cracking behaviour of Recycled Aggregate Concrete beams at elevated temperature

PurposeThe majority of previous studies made on Recycled Concrete Aggregates (RCA) are limited to the utilisation of non-structural grade concrete due to unfavourable physical characteristics of RCA including the higher absorption of water, tending to increased water requirement of concrete. This seriously limits its applicability and as a result it reduces the usage of RCA in structural members. In the present study, the impact of hybrid fibres on cracking behaviour of RCA concrete beams along with the inclusion of reinforcing steel bars under two-point loading system exposed to different sustained elevated temperatures are being investigated.Design/methodology/approach RCA is substituted for Natural Coarse Aggregates (NCA) at 0, 50 and 100 percentages. The study involves testing of 150 mm cubes and beams of size (700 × 150 × 150) mm, i.e. with steel reinforcing bars along with the addition of 0.35% Steel fibres+ 0.15% polypropylene fibres. The specimens are being exposed to temperatures from 100° to 500°C with 100° interval for 2 h. Studies were made on the post crack analysis, which includes the measurement of crack width, crack length and load at first crack. The crack patterns were analysed in order to understand the effect of fibres and RCA at sustained elevated temperatures.FindingsThe result shows that ultimate load carrying capacity of reinforced concrete beams and load at first crack decreases with the raise in temperatures and increased percentage of RCA content in the mix. Further that 100% RCA replacement specimens showed lesser cracks when compared to the other mixes and the inclusion of fibres enhances the flexural capacity of members highlighting the importance of fibres.Practical implicationsRCA can be used for structural purposes and the study can be projected for assessing the performance of real structures with the extent of fire damage when recycled aggregates are used.Social implicationsMost of recycled materials can be used in the regular concrete which solves two problems namely avoiding the dumping of C&D waste and preventing the usage of natural aggregates. Hence the study provides sustainable option for the production of concrete.Originality/valueThe reduction in capacity of flexural members due to the utilisation of recycled aggregates can be negated by the usage of fibres. Hence improved flexural performance is observed for specimens with fibres at sustained elevated temperatures.

Analysis of Cracking Causes of AISI 416 Martensitic Stainless Steel During Hot Rolling

Analysis of Cracking Causes of AISI 416 Martensitic Stainless Steel During Hot Rolling

Nonlinear extension of the Kolosov-Muskhelishvili stress function formalism.

The method of stress function in elasticity theory is a powerful analytical tool with applications to a wide range of physical systems, including defective crystals, fluctuating membranes, and more. A complex coordinates formulation of stress function, known as the Kolosov-Muskhelishvili formalism, enabled the analysis of elastic problems with singular domains, particularly cracks, forming the basis for fracture mechanics. A shortcoming of this method is its limitation to linear elasticity, which assumes Hookean energy and linear strain measure. Under finite loads, the linearized strain fails to describe the deformation field adequately, reflecting the onset of geometric nonlinearity. The latter is common in materials experiencing large rotations, such as regions close to the crack tip or elastic metamaterials. While a nonlinear stress function formalism exists, the Kolosov-Muskhelishvili complex representation had not been generalized and remained limited to linear elasticity. This paper develops a Kolosov-Muskhelishvili formalism for the nonlinear stress function. Our formalism allows us to port methods from complex analysis to nonlinear elasticity and to solve nonlinear problems in singular domains. Upon implementing the method to the crack problem, we discover that nonlinear solutions strongly depend on the applied remote loads, excluding a universal form of the solution close to the crack tip and questioning the validity of previous studies of nonlinear crack analysis.

Improved XFEM for multiple crack analysis: Accurate and efficient implementations for stress intensity factors

The extended finite element method (XFEM) has achieved unprecedented success in crack analysis. However, challenges still remain for a multiple crack simulation. One issue is the difficulty of level set construction, where cracks are generally represented by combinations of different level set functions. Another issue is the rapidly increasing condition number of the global stiffness matrix, which is even more severe than the single crack case. In order to overcome these issues, we make two improvements as follows. On the one hand, inspired by the discontinuous description via cover cutting in Numerical Manifold Method (and later phantom node method in XFEM), we propose a level set templated cover cutting method, which makes use of level set values to cut a nodal patch and then to add virtual nodes. This method, which combines the advantages of both the level set method and the cover cutting technique, is simple and straightforward to implement. The method also plays a role in templated subdivision of discontinuous elements and hence presents an efficient and robust integration scheme. On the other hand, we extend the Improved XFEM (IXFEM), previously proposed by our research group, to the scenario of multiple crack problems. The method fundamentally eliminates the daunting issues of linear dependence and ill-conditioning of the standard XFEM, because it uses an extra-dof-free singularity enrichment around the crack tip. Numerical studies on multiple crack problems show that the developed approach offers various advantages: (1) Highly accurate SIF evaluation over the standard XFEM; (2) Well-conditioning of the global stiffness matrix independent of the number of cracks — condition number being of the same order as the standard FEM; (3) Efficient and robust linear system solving and geometric computations. Thus the developed approach is well capable of modeling arbitrary multiple crack problems.

The role of the strengthening phases on the HAZ liquation cracking in a cast Ni-based superalloy used in industrial gas turbines

This work presents the influence of microstructural constituents on liquation crack formation in the cast Ni-based superalloy, René 108. The investigation was divided into three parts: characterisation of the material's microstructure in pre-weld condition, hot ductility studies and analysis of liquation cracking induced by the gas tungsten arc welding process. Using advanced electron microscopy techniques it is shown that the base material in pre-weld condition is characterised by a complex microstructure. The phases identified in René 108 include γ matrix, γ' precipitates, MC and M23C6 carbides, and M5B3 borides. Based on Gleeble testing, it was found that René 108 is characterised by high strength at elevated temperatures with a maximum of 1107 MPa at 975 °C. As a result of constitutional liquation, the superalloy’s strength and ductility were significantly reduced. The nil strength temperature was equal to 1292 °C, while the nil ductility temperature was 1225 °C. The low ductility recovery rate (32.1), ratio of ductility recovery (36.2) and hot cracking factor (Rf = 0.05) values confirmed the low weldability of Renѐ 108. In the heat-affected zone (HAZ) induced by welding, constitutional liquation of mainly γ' precipitates, with a contribution of M23C6 carbides and M5B3 borides, was observed. The thin non-equilibrium liquid film, which formed along high-angle grain boundaries, led to crack initiation and their further propagation during cooling. The eutectic γ–γ' re-solidification products are visible on the crack edges.

Mechanistic analysis of bottom-up crack in asphalt pavement using cohesive zone model

The bottom-up crack (BUC), one kind of reflective crack that initiates at the bottom of asphalt layer and propagates upwards, has become one of the major distresses of asphalt pavement. The Mode Ⅰ dominated bilinear cohesive zone model (CZM) after calibration was introduced into finite element (FE) model to simulate the BUC propagation in asphalt pavement under displacement load. The mechanism of crack propagation under different types of periodic load was analyzed based on two indexes from Mode Ⅰ dominated bilinear CZM. The FE model and corresponding periodic load were modified to limit the occurrence of top-down crack propagation. A combined method based on the developed model was adopted to predict the BUC propagation velocity at varied heights and the remaining life of pavement. The results showed that the acceleration of BUC propagation decreased with the crack tip height. Moreover, the predicted remaining life of pavement based on the proposed method was reasonable referring to the engineering design specifications.

Seismic Behaviour of Beris Dam Under Six Earthquake Excitations by using Finite Element Method

This paper focused on the behavior of the dam when exposed to seismic loading and ability of the dam to withstand the applied loads from various seismic events. The chosen concrete dam to be referred to in the two- dimensional analysis is Beris Dam located in Kedah, Malaysia. A nonlinear dynamic analysis is chosen to analyse the behavior of Beris Dam under selected ground motion. Analysis of the dam is performed using the finite element method by utilizing ABAQUS software. From the cracking analysis pattern, a crack appeared at the upstream face of the dam caused mainly by the excessive tensile stress. Based on the results, the displacement of the dam is increased with the increasing of ground motion data where the displacement occurred in the horizontal direction. The maximum stresses exerted by the dam structure do not exceed the allowable capacity of concrete dams. The stress behaviour of the dam was satisfactorily acceptable as the maximum normal stress and shear stress of the dam when numerous seismic loadings are applied do not exceed the allowable stress capacity which is 800 kN/m2.

Phase-field ductile fracture analysis of multi-materials and functionally graded composites through numerical and experimental methods

Despite extensive studies on material models for fracture applicable to homogenous materials, the demand for advanced numerical methods to predict the failure in multi-materials and functionally graded materials (FGMs) remains substantial. This study aims to address this gap by using a phase-field approach for analyzing crack development and ductile fracture in FGMs via numerical and experimental methods. To account for the failure induced by material plastic deformations, we introduce the elastoplastic material framework within the damage driving force. This framework enables us to analyze fracture in the FGM setting, whereby the gradual spatial changes of the elastoplastic and fracture properties across the functionally graded medium are modelled by considering the effective property values calculated via rule of mixtures. The influence of the gradation profiles and orientations on the problems of crack initiation, propagation, and fully-developed crack pattern is elucidated via mixed-mode crack analyses on a representative numerical example. In particular, the fracture resistance changes resulting from the property mismatches between the constituent FGM materials are assessed. To determine the efficacy of the numerical model in predicting the fracture behavior, it is evaluated against the experimental tensile test data obtained from miniaturized tensile test specimens excised from an FGM block consisting of 316L and IN718 powders, deposited via Laser powder blown Directed Energy Deposition (LDED).

Cracking Analysis of a Brass Clamp Mounted on the Main Transformer in the Power Grid System

Cracking of conductive brass accessories in substations causes overheating or an open circuit, seriously affecting the safe and stable operation of the power grid system. A deep understanding of failure mechanisms could provide more safety, as well as lower down costs and save time for the power grid system, which have been seldomly involved in the literature. This paper presents a cracking analysis of a brass clamp in service for seven years that is mounted on the main transformer. The fracture morphology, chemical composition, and metallographic structure of the brass clamp were systematically analyzed, and the stress conditions were obtained by finite element simulation. The clamp exhibits transgranular brittle fracture with high oxygen content in the fracture, containing a crack propagation along the Pb particle connecting pathways, and the stress concentration was confirmed at the crack position. It is concluded that the failure was a result of the stress corrosion cracking and excessive content of Pb. Suggestions were proposed to avoid malfunction of the main transformer caused by the clamp crack.

Superposed element method for the numerical simulation of structure crack

Crack is a key factor for the normal operation of structures. In this paper, a new method called Superposed Element Method (SEM) is proposed for the numerical simulation of crack analysis. Firstly, the structure containing crack is divided into two independent meshes. One is the global mesh without crack, the other is the local mesh of the crack and its vicinity. Then, the two independent meshes are coupled together, finite element method (FEM) is used for the local mesh and the complete elements outside of the coverage of the local mesh, and numerical manifold technique is applied to the incomplete elements. Finally, in order to couple the global mesh with the local mesh, the penalty stiffness is imposed on the boundaries of local mesh. The results of the numerical examples show that the pre-processing of SEM is quite simple, and the accuracy of the solution is relatively high. The method proposed is expected to be widely used for dynamic simulation of crack propagation.