Predict Crack Initiation Research Articles

Sequential thermomechanical stress and cracking analysis of photovoltaic modules with full and half-cut cells

The transition from conventional full-cell patterns to half-cell modules in the photovoltaic (PV) industry promises enhanced stability and efficiency. This study investigates the thermomechanical behaviour and stress distribution within half-cell and full-cell PV modules during the manufacturing and operational phases. Using finite element modeling, the research simulates sequentially the manufacturing and operating processes such as laser cutting, soldering, lamination, mechanical loading and thermal cycling. The Extended Finite Element Method (XFEM) predicts crack initiation and propagation in the crack-sensitive regions in PV modules during their entire life. Key findings highlight stress concentrations during manufacturing, influenced by parameters like laser power, scribing length and Silicon wafer size. Mechanical loading (ML) and thermal cycling (TC) induce additional stresses, impacting module reliability. The results are useful for the optimization of material properties and the development of advanced design strategies contributing to the durability and efficiency of PV systems.

Investigation on fatigue parameters in railway wheels using a critical plane model

The contact areas between rail and wheel are critical in determining the performance of rail vehicles. Analyzing the mechanics, materials, tribology, and geometry of the interface is important to understand the contact damage mechanisms, fatigue parameter and fatigue life. Developing a simplified and novel approach to predict crack initiation and fatigue life is key for investigating contact fatigue of rail wheel interaction. This study aims to investigate rolling contact fatigue (RCF) cracks and fatigue life in railroad wheels using Finite Element Model (FEM). Using a proper material model that accounts for plastic shakedown, ratchetting, and cyclic hardening for both the rail and wheel materials, the FEM model is analyzed with the help of Abaqus 2020 tool. The submodelling technique was implemented to reduce computation demand. Stress and strain history outputs extracted from the submodel (at 0 mm, 1.3 mm, 2.6 mm, and 3.6 mm depths) were used to predict critical plane orientation, crack initiation and fatigue life using critical plane models. The orientation of critical (crack) plane was found using a novel MATLAB algorithm by searching for a plane with maximum fatigue parameter (FPmax). The investigation reveals that the location of maximum damage is the subsurface and the crack angles fall within the range of (0°, 40°), (62°, 123°) and (143°, 180°) with a 5 % margin and at a depth of 2.6 mm below the wheel surface. The determined fatigue crack initiation and life at this specific location were 6178 and 7174 cycles, respectively. Predicting the critical zone which is susceptible to shorter crack initiation and fatigue life is a crucial to prevent wheel failure.

Study on crack initiation mechanism of notched TC4 titanium alloy plate based on acoustic emission information entropy

ABSTRACT Titanium alloys are widely used in high-end manufacturing fields such as aerospace and nuclear energy due to their excellent mechanical properties and corrosion resistance, but it is prone to cracking under load, seriously affecting its performance and safety. Therefore, studying the crack initiation process of titanium alloys is of great significance for improving their service life and safety. In this study, TC4 titanium alloy material is taken as the research object, and the crack emergence mechanism during its tensile fracture process is investigated by combining tensile test and AE test. The experiments were carried out under displacement-controlled conditions, and crack emergence detection was carried out by two methods: AE characterisation parameters and AE information entropy, and SEM was used to observe and analyse the specimen fracture. The results indicate that the AE characteristic parameters of different notched specimens have the same evolution pattern, and this method can be used to predict crack initiation, but there is a certain degree of uncertainty. Compared with the former, the information entropy theory can more accurately predict crack initiation. Therefore, the analysis of the entropy of AE information can be used as a highly practical real-time condition detection method to provide effective detection means for engineering applications.

Mechanical Properties and Martensitic Transformation Behavior of 316LN Stainless Steel Under Cryogenic Deformation

Digital image correlation (DIC) technology can capture strain anomalies and predict crack initiation providing early warning of material failure. Herein, DIC technique is used to calculate the full‐field strain by analyzing the grayscale patterns of speckle images during the tensile process. This allowed for an analysis of the microstructure evolution of the 316LN austenitic stainless steel (SS) at cryogenic temperatures. Deformation behavior of the 316LN SS at cryogenic temperatures is further analyzed using electron backscatter diffraction technology and transmission electron microscopy. Based on the strain field obtained by the DIC technique, a comprehensive analysis of the martensite volume fraction at different strains can be conducted. The results show that the strain localization under cryogenic deformation is related to martensitic transformation, while the random distribution of slip bands aligns with local strain peak values. Notably, fracture under cryogenic deformation occurs in regions where the strain field reaches its peak, rather than at locations with the maximum strain value.

Unraveling the plastic deformation, recrystallization, and oxidation behavior of Waspaloy during thermal fatigue crack propagation

Thermal fatigue is one typical failure mode for engine components involving cyclic thermal stresses/strains. However, the microstructure evolution and its microscopic interaction with thermal fatigue cracking in Ni-based superalloys featuring intragranular γ′ and intergranular carbides have yet to be clarified. In this study, cyclic temperature variations ranging from 25 °C to 700 °C were conducted on Waspaloy to unravel the synergistic damage mechanisms including stress distribution, plastic deformation, recrystallization, oxidation, and crack propagation. The thermal fatigue cracks are found to predominantly propagate along grain boundaries with a gradually descending rate from 3.5 μm/cycle to 1.5 μm/cycle. Compared with the macroscopic thermal stress up to ∼800 MPa, the local thermal stress induced by different sizes of M23C6 carbides marginally affects the crack propagation. Intensive slip bands and sparse deformation twins in the deformed matrix are observed, indicating the plastic deformation is mainly achieved by dislocation slipping and supplemented by twinning. Trans-granular cracks parallel to {111} planes form occasionally when the propagation directions of intergranular cracks are almost parallel to the {111} slip bands. Besides, dislocations promote the oxidation damage of the crack surface through pipe diffusion of solutes, and the γ′-precipitate free zones (PFZs) and recrystallized areas are produced accordingly. The quantitation analysis of the PFZ thickness provides a reference for predicting crack initiation time during thermal fatigue.

A phase field method for predicting hydrogen-induced cracking on pipelines

An accurate determination of the threshold conditions to initiate cracks on aged hydrogen pipelines is paramount for ensuring energy transport safety. In this work, a finite element-based phase field method was developed to assess the crack initiation on dented pipelines while considering the hydrogen (H) impact. Theoretical and multi-physics numerical formulas were derived for prediction of the elastic-plastic fracture behavior of H-contained steel. A critical phase field parameter, ϕ=0.69, is defined for predicting crack initiation at the dent on pipelines. The presence of H within the steel decreases the threshold dent depth for initiating H-induced cracks. When the initial H concentration increases from 0 to 0.5 wppm, the maximum dent depth for crack initiation reduces from 17.5 mm to 10.7 mm. The maximum dent depth required for crack initiation reduces from 17.5 mm to 7.8 mm when an internal pressure of 8 MPa is applied on the steel pipe. The site with the maximum phase field parameter changes during indentation, implying that the location initiating cracks depends on the dent dimension. The existing criteria in ASME B31.12 standard are not applicable for predicting H-induced crack initiation on dented pipelines. This study proposes a new method to predict hydrogen-induced cracking on aged pipelines when transporting hydrogen.

Triaxiality and Plastic-Strain-Dependent Proposed PEAK Parameter for Predicting Crack Formation in Polypropylene Polymer Reservoir Subjected to Pressure Load.

This article raises the topic of the critical examination of polypropylene, a key polymeric material, and its extensive application within the automotive industry, particularly focusing on the manufacturing of brake fluid reservoirs. This study aims to enhance the understanding of polypropylene's behavior under mechanical stresses through a series of laboratory destruction tests and numerical simulations, emphasizing the finite element method (FEM). A novel aspect of this research is the introduction of the PEAK parameter, a groundbreaking approach designed to assess the material's resilience against varying states of strain, known as triaxiality. This parameter facilitates the identification of critical areas prone to crack initiation, thereby enabling the optimization of component design with a minimized safety margin, which is crucial for cost-effective production. The methodology involves conducting burst tests to locate crack initiation sites, followed by FEM simulations to determine the PEAK threshold value for the Sabic 83MF10 polypropylene material. The study successfully validates the predictive capability of the PEAK parameter, demonstrating a high correlation between simulated results and actual laboratory tests. This validation underscores the potential of the PEAK parameter as a predictive tool for enhancing the reliability and safety of polypropylene automotive components. The research presented in this article contributes significantly to the field of material science and engineering by providing a deeper insight into the mechanical behavior of polypropylene and introducing an effective tool for predicting crack initiation in automotive components. The findings hold promise for advancing the design and manufacturing processes in the automotive industry, with potential applications extending to other sectors.

Crack Initiation in Compacted Graphite Iron with Random Microstructure: Effect of Volume Fraction and Distribution of Particles.

Thanks to the distinctive morphology of graphite particles in its microstructure, compacted graphite iron (CGI) exhibits excellent thermal conductivity together with high strength and durability. CGI is extensively used in many applications, e.g., engine cylinder heads and brakes. The structural integrity of such metal-matrix materials is controlled by the generation and growth of microcracks. Although the effects of the volume fraction and morphology of graphite inclusions on the tensile response of CGI were investigated in recent years, their influence on crack initiation is still unknown. Experimental studies of crack initiation require a considerable amount of time and resources due to the highly complicated geometries of graphite inclusions scattered throughout the metallic matrix. Therefore, developing a 2D computational framework for CGI with a random microstructure capable of predicting the crack initiation and path is desirable. In this work, an integrated numerical model is developed for the analysis of the effects of volume fraction and nodularity on the mechanical properties of CGI as well as its damage and failure behaviours. Finite-element models of random microstructure are generated using an in-house Python script. The determination of spacings between a graphite inclusion and its four adjacent particles is performed with a plugin, written in Java and implemented in ImageJ. To analyse the orientation effect of inclusions, a statistical analysis is implemented for representative elements in this research. Further, Johnson-Cook damage criteria are used to predict crack initiation in the developed models. The numerical simulations are validated with conventional tensile-test data. The created models can support the understanding of the fracture behaviour of CGI under mechanical load, and the proposed approach can be utilised to design metal-matrix composites with optimised mechanical properties and performance.

Revealing crack initiation and extension of brittle rock via time-lapse acoustic attenuation: Insights from active ultrasonic experiments

Predicting brittle rock failure is essential for rock mechanics research and early disaster alerts in deep rock engineering. Successful prediction relies on identifying crack initiation and extension. However, currently, there is no universally accepted method for accurately identifying and tracking crack evolution to predict brittle failure of the surrounding rock. In this study, the propagation parameters of transmission ultrasonic waves were used to characterize crack behaviors at the laboratory scale. The differential acoustic attenuation term was proposed by modifying the spectral ratio method to evaluate the dissipation capability of the corresponding medium to the transmitted ultrasonic waves. In addition to acoustic attenuation, velocity and amplitude attenuation were introduced to characterize the damage evolution during brittle failure. The indicators were analyzed by conducting a uniaxial compression test on a sandstone sample with a single flaw. During compression, active ultrasonic surveys were conducted to attain the propagation parameters. The two-dimensional digital image correlation method was simultaneously applied to capture the full-field strain on the front surface of the sample. The shear and tensile strain profiles indicated that the shear damage initially accumulated at the tips of the flaw, causing a reduction in the velocity and amplitude of the transmitted ultrasonic waves. The acoustic attenuation indicator in the flaw-tip regions increased before the shear strain began. As the damage developed further, the acoustic attenuation increased overall, with numerous local fluctuations in the flaw-tip regions due to stress rearrangement and damage development, while the velocity and amplitude remained consistently low. In contrast, intact regions that were far away from the tips of the flaw exhibited different characteristics. The velocity and amplitude variations were more staged, while the acoustic attenuation changed gradually. The results indicated that the variations in the propagation parameters exhibited specific patterns before the damage was initiated, offering a potential for predicting crack initiation. The variations in the acoustic attenuation, velocity, and amplitude attenuation allow for tracking the crack propagation.

Prediction of crack initiation for notched concrete beam from FPZ at maximum load

The initial cracking load (Pi) of a notched concrete beam, difficult to measure, has been predicted from the maximum fracture load (Pmax) together with the notch-tip fracture process zone (FPZ) at Pmax. A simple analytical model is used to link Pi and Pmax together through the FPZ. The corresponding initiation and unstable fracture toughness, Ki and Kun, have also been determined. The model assumes that the lower limit of Pmax from a group of identical notched concrete beams corresponds to the lower limit of the FPZ length FPZL, so that the lowest limit Pmax = Pi is established for FPZL = 0. Detailed FPZ measurements before and at Pmax using a digital image correlation technique were analysed and used to predict the initial cracking load Pi. Six different specimens with various sizes (W = 40, 60 and 80 mm), initial notches (a0 = 12 to 48 mm) and FPZL (7 to 13 mm) at Pmax showed the average ratio of FPZL/(W – a0) was around 0.25, indicating the Pi/Pmax ratio was around 0.67 based on the analytical model. The crack growth resistance KR-curve between the crack initiation toughness Ki at Pi and the unstable fracture toughness Kun at Pmax was also established approximately by the simple model. Estimated intrinsic fracture toughness KIC was compared with Ki and Kun. The influence of average aggregate size dav on Pi and FPZL at Pmax was also discussed.

Deep learning approach for predicting crack initiation position and size in a steam turbine blade using frequency response and model order reduction

Deep learning approach for predicting crack initiation position and size in a steam turbine blade using frequency response and model order reduction

Influence of different heat treatments on fracture behavior of rolling element bearing steels

Rolling element bearings (REB), one of the critical components of mechanical power transmissions, operate under high contact loads concentrated over small volumes of material. The damage caused by fatigue to REBs happens in two stages: the initiation of cracks and the propagation of cracks from areas of stress concentration. To select bearing steels for different applications, it is important to have knowledge about the material’s ability to resist fracture. This study presents results from an experimental investigation of bearing steels manufactured using different heat treatments. Steels were induction-hardened, carburized, and through-hardened, generating varying microstructures. Fracture mechanics tests were conducted using ASTM standards. The data generated is useful for predicting crack initiation and growth behavior under different loading conditions. Microscopic-level investigations are also presented to discern the fracture mechanisms associated with different microstructures.

Non-dimensionalization and scaling of fracture processes in concrete and rock

Many types of engineering structures may fracture, due to extreme external loads or due to inherent damages arising while in service or during their manufacturing/creation. The fractures may form at various scales, particularly within geological or cementitious materials like rock and concrete. Understanding and simulating accurately the fracturing processes at different scales, from laboratory to field, assists with the optimization of structural design and enhances reliability. This paper proposes novel non-dimensional scaling laws for fracture mechanics problems. They improve the prediction and interpretation of crack initiation and evolution and the subsequent mechanical response of structures. They have direct applicability in advanced numerical models like phase field models, where the governing parameters and mesh sizes can be appropriately scaled prior to conducting the numerical simulation. This leads to a unique dimensionless model output for any given loading configuration. Rescaling the unique non-dimensional output, which may incorporate varying pre-peak and post-peak fracture resistances, allows for the fracture behavior of a structure at any scale to be determined. The non-dimensionalization and rescaling techniques are demonstrated and validated against independent analytical and experimental benchmark problems. The scaling laws enable the adoption of coarse meshes in numerical models, significantly reducing computational cost while maintaining accuracy and capturing the fundamental mechanics. It is shown that the challenges associated with modeling fracture processes across scales can be mitigated as long as the problem is appropriately scaled.

Simulation of crack propagation in piping components using phase field approach

Understanding the fracture behaviour in pipelines transporting steam and other resources is vital for its longevity and structural integrity. The prediction of crack initiation and propagation, involving crack branching, and the nucleation of new cracks, etc. in fracture processes are challenging tasks. The phase field method (PFM), based on variational formulation, emerged as a competitive mathematical tool to address fracture mechanics problems. PFM does not require the presence of predefined cracks, handles the crack initiation and propagation within the same system. This feature provides an added advantage to PFM and overcomes the limitations of Griffith’s approach-based linear elastic fracture mechanics (LEFM). In the present work, simulation of the crack propagation in the piping components by employing phase field methodologies has been carried out. Two parameters namely; a phase field parameter (ϕ) that varies between 0 and 1 differentiating between broken and intact material, and a length scale parameter (l_0) that approximates the sharp crack into the diffused crack with exponential distribution are introduced in the mathematical modeling. Numerical modeling is solved using the staggered algorithm in three layered scheme defining the displacement field and phase field within a 3-D finite element framework and implemented in Abaqus via user-defined element (UEL) subroutine codes. PFM simulates the crack path and predicts the load-displacement response, which is validated with benchmark problems, and extended for piping components under monotonic loading. The proposed study accurately captures the crack growth behaviour as observed in experiments on SA312 Type 304LN stainless steel pipes and hence, demonstrated the robustness of the proposed formulation.

Prediction of Crack Initiation at Die Corner of Molded Underfill Flip-Chip Packages Under Thermal Load by New Criteria—Part I: Accurate Formulation of Singular Stress Fields

Prediction of Crack Initiation at Die Corner of Molded Underfill Flip-Chip Packages Under Thermal Load by New Criteria—Part I: Accurate Formulation of Singular Stress Fields

Phase Field Fracture Modelling of Crack Initiation and Propagation in Dual-Phase Microstructures

Dual-phase (DP) steel's spread in the industry has been fueled by its highly desirable qualities, which include a unique balance of strength and ductility, making it a valuable material for applications ranging from automotive manufacturing to construction. Despite the continued progress in the research of DP steels, the complex failure mechanisms at the microscale, resulting from the coexistence of brittle martensite phases within the ductile ferrite phase, remain an area of ongoing exploration. This study aims to investigate the micro structural evolution, as well as crack initiation and propagation, in DP steels at the microscale. In this context, to accurately capture the microstructural evolution of DP steels, a rate-dependent crystal plasticity formulation is utilized for the ferrite phase alongside a phenomenological isotropic J2 plasticity model for the martensite phase. A novel ductile phase-field fracture framework has been implemented to predict crack initiation and propagation, integrating both crystal plasticity and J2 plasticity constitutive models with the phase field fracture model. Generic 3D polycrystalline Representative Volume Elements (RVEs) are created and simulated to analyze the trends influencing the failure behavior of DP steels. The numerical study includes examples with two different martensite volume fractions (15% and 37%), each characterized by varying random crystallographic orientation sets and morphologies. The obtained results suggest that despite the similarity in stress concentration regions within two different random orientation sets in a simulation with fixed volume fraction and morphology, the resulting crack paths exhibit significant differences. Additionally, it is inferred that damage appears to accumulate at the junction points of the martensite islands. Moreover, an increase in the martensite volume fraction is found to diminish the influence of crystallographic orientation on the resultant crack path. Therefore, given the aforementioned findings, it is essential to analyze the microstructural evolution, as well as crack initiation and propagation in DP steels, utilizing appropriate material and fracture modeling frameworks at the microscale.

An effective free-meshing and linear Step-Wise procedure to predict crack initiation and propagation

An automated procedure is proposed to calculate fracture initiation and propagation in two-dimensional structures. The application uses and enriches the Hybrid Semi-Analytical Method to calculate mixed-mode stress intensity factors in linear elastic fracture mechanics framework. The strategy does not necessitate prior knowledge of the starting crack tip location within the structure, resulting in suitable for analyzing structures without initial defects. When neither a priori invitation nor pre-existing notch is provided, the fracture initiation is assumed to occur when the structure reaches its elastic limit, and a non-linear analysis is conducted under the prescribed load to identify the first occurrence of permanent strain and to locate where the crack opening occurs. As the crack propagates, solely linear elastic analyses are performed to calculate the stress intensity factors. Relying upon these parameters, the procedure implements an evolutionary algorithm based on a step-by-step evaluation of the crack increment and direction. A global–local energy-based criterion is employed to drive fracture propagation. Neither local refinement nor mapped meshes around the crack tip are required, resulting in a streamlined and efficient free-meshing strategy.The calculation has been implemented in a standard finite element environment, and several numerical examples have been investigated, both from a qualitative and quantitative point of view. Qualitative crack paths have been shown for a square hollow plate under pure tensile and shear loads, and a modified Single Edge Notched specimen in bending, as a function of the mutual void positions, distance from the plate edges, and different notch lengths. Finally, an effective comparison in terms of forces-displacement curves has been presented between the proposed procedure, and a lab test for a modified Compact Tension specimen under tensile loading, demonstrating the overall accuracy and reliability of the presented strategy.It is felt that the proposed procedure could pave the way for designing hollowed structures and investigating the corresponding evolutionary laws that relate structural geometries to the insurgence and spread of fractures, and envisaging crack initiation and propagation within inhomogeneous media.

Prediction of crack initiation in single-crystal sapphire during ultra-precision machining using MD simulation-based slip/fracture activation model

In this paper, material deformation during ultra-precision machining (UPM) on the C-, R-, and A-planes of sapphire was investigated using the slip/fracture activation model where the likelihood of activation of individual plastic deformation and fracture systems on different crystallographic planes was calculated. The stress data obtained from molecular dynamics (MD) simulations were utilized, and the slip/fracture activation model was developed by incorporating the principal stresses in calculating the plastic deformation and fracture cleavage parameters. The analysis methodology was applied to study material deformation along various cutting orientations in sapphire. The stress field at crack initiation during UPM on C-, R-, and A-planes of sapphire was calculated using molecular dynamics (MD) simulations. An equation describing the relationship between crack initiation and its triggering parameters was formulated considering the systems' plastic deformation and cleavage fractures. The model can qualitatively predict the crack initiations for various cutting orientations. The proposed model was verified through ultra-precision orthogonal plunge cut experiments along the same cutting orientations as in the MD simulations.

Numerical Study on Fracture Behavior of Printed Circuit Heat Exchanger Core Based on Elasto-Plastic Phase Field Method

Abstract Printed circuit heat exchanger (PCHE) is a type of compact heat exchanger with high thermal efficiency, more compact, and suitable for high pressure and high temperature conditions. The safety assessment of PCHE is very important, especially for PCHE core. Because PHCE core is different from the PCHE headers which are typical pressure vessel components. However, there is no standard design method to ensure the structural integrity for PCHE core. Some failure modes of PCHE core are studied in recent years, but seldom researches have been conducted concerning the fracture behavior of PCHE core. In addition, the phase field method for fracture has developed rapidly in recent years with its advantages in predicting crack initiation, bifurcation, and merging. In this work, the fracture behavior of PCHE core with and without defects is investigated based on elasto-plastic phase field method. The model parameter of Ni-based Alloy for elasto-plastic phase field method is first calibrated by comparing the numerical results with tensile test data of diffusion-bonded PHCE core specimen. Then, the influence of loading directions, defect locations, and defect sizes on the fracture behavior of PCHE core with semicircular and semicircular-rectangular channels are analyzed. Some conclusions are discussed.

A novel defect-related cyclic damage model driven by strain energy density for LPBF titanium alloy

The unavoidable defects in additive manufacturing (AM) material have an impact on the deformation behavior and fatigue lifetime. In this study, a series of experiments on Laser powder bed fusion (LPBF) Ti-6Al-4 V under symmetrical tension–compression cyclic loading were conducted, and the corresponding damage mechanism was then investigated. It is revealed that due to the nucleation, growth, and coalescence of micro-voids, LPBF Ti-6Al-4 V exhibits accelerated softening behavior after reaching cyclic stability. Based on the physical mechanism, a cyclic damage model with a critical initiation criterion was developed using fracture mechanics principles, in which plastic strain energy as the driving parameter is introduced to describe the defect evolution, and the void’s closure effect during the tension–compression cycle is considered. Experimental validation has demonstrated that the damage model can accurately predict the cyclic stress–strain curves for LPBF Ti-6Al-4 V vertical and horizontal specimens, with errors in predicting crack initiation and growth lifetime falling within the ± 1.6 and ± 2.5 scatter bands.