Stress Intensity Factor Analysis Research Articles

Cutting-edge insights: Crack growth rates in 9% Ni steel from room to cryogenic conditions influenced by crack closure and effective stress intensity factors

This study investigates the fatigue crack growth rate of 9% Ni steel at varying stress ratios under both room and cryogenic temperatures, attributing different growth rates to the phenomenon of crack closure. Traditional methods of studying crack closure, including the opening force, compliance ratio, and adjusted compliance ratio techniques, are assessed. Our results are juxtaposed with previous formulae for the opening force technique, leading to the introduction of a new formula that incorporates temperature effects by normalising the stress intensity factor with the yield strength at the respective test temperature. We highlight the adjusted compliance ratio (ACR) technique's limitations at cryogenic temperatures due to challenges in measuring notch open-crack compliance. As a solution, we present an innovative method that determines compliance using the effective elastic modulus. The mechanics behind the ACR technique are elucidated through the lens of the wedging mechanism. Our insights reveal that the ACR technique precisely calculates the effective stress intensity factor range (ΔKeff) under specific conditions. We address existing limitations by introducing a novel method, the triple compliance ratio (TCR) technique. A comparative analysis of effective stress intensity factors from all four techniques reveals the TCR technique's superior ability to correlate crack closure with crack growth. By eliminating the crack closure effect, the TCR technique offers a more accurate prediction of fatigue crack growth rate across diverse load ratios.

Residual stress effects on short crack propagation behavior in friction stir welded 7075-T6 aluminum alloy panel under biaxial loading: An experimental and numerical study

The effects of residual stress on short crack propagation behavior of friction stir welded (FSWed) 7075-T6 aluminum alloy panel was investigated under biaxial loading. The biaxial fatigue tests were carried out on three kinds of cruciform samples, including base material (BM) cruciform sample and FSWed cruciform sample with crack perpendicular or parallel to the weld. Scanning electron microscope (SEM) fractography was conducted to identify and relate fracture surface features to governing fatigue damage mechanisms. Finite element method combined with stress intensity factor (SIF) analysis was used to simulate the biaxial fatigue propagation. In a comparison of the crack path in BM and FSWed cruciform samples, experimental and numerical results showed that residual stress can change the nominal biaxiality ratio, leading to crack path changes in FSWed cruciform sample with crack parallel to the weld, and the curved fatigue crack front formed on the fracture surface due to the non-uniform distribution of the residual stress through the thickness. The fatigue damage mechanisms are different depending upon the biaxiality ratio as well as the weld direction.

Analysis and calculation of stress intensity factors for type I cracks on the edge of elliptical holes under internal pressure

Analysis and calculation of stress intensity factors for type I cracks on the edge of elliptical holes under internal pressure

Stress intensity factor analysis for mixed-mode fracture behavior of inclined semi-elliptical surface crack in stiffened plate under tension load

This study aims to investigate the mixed-mode fracture behavior of stiffened plates with inclined semi-elliptical surface cracks (ISSCs). For this purpose, a new numerical model is developed for the fracture analysis using FRANC 3D in combination with ABAQUS. Normalized stress intensity factors (SIFs) are used to analyze the fracture behavior at the surface and deepest points of the surface crack. Additionally, an arrest parameter ψ is proposed to quantify the level of crack arrest under mixed-mode conditions. Then, a thorough investigation is conducted to examine the fracture behavior of stiffened plates with ISSCs, focusing on the effects of aspect ratio, relative depth, spacing ratio, stiffness coefficient, crack angle, and loading mode. The findings indicate that the restraint effect of stiffeners on the fracture of large surface cracks is significantly stronger compared to small surface cracks. It is also identified that the restraint effect is more pronounced at the surface point than at the deepest point. Finally, a set of novel formulas is derived to evaluate the mixed-mode SIFs in stiffened plates through statistical analysis of the results.

Conventional shot peening treatment effects on thermal fatigue crack growth and failure mechanisms of a solid solution alloy

This study presents the effects of conventional shot peening as a surface post-treatment method on the fatigue crack growth behavior and failure mechanism of a solid solution alloy used in the flat seal component under thermal fatigue conditions. The study employs a combination of experimental tests and finite element simulations to evaluate the effect of shot peening on thermal fatigue crack growth behavior. The corrected J-integral and Paris model are used to calculate the stress intensity factor and predict the thermal fatigue crack growth behavior, respectively. Additionally, the ZENCRACK method is employed to predict thermal fatigue life. The results indicate that shot peening induces compressive residual stress, leading to a decreased distribution of thermal stress, particularly along the crack propagation path. The simulated fatigue life curve obtained by ZENCRACK demonstrated a good agreement between the simulated and experimental crack growth results. The incorporation of shot peening caused a significant reduction in the rate of thermal fatigue crack growth, and the simulated stress intensity factor analysis revealed an increase during the heating stage. Consequently, the thermal fatigue crack propagated during the heating-up process. SEM evaluation reveals that the shot peening post-treatment impacts both thermal fatigue crack initiation and propagation. Furthermore, the failure mode of shot-peened specimens involves inter- and trans-granular cracking, while non-shot-peened specimens exhibit trans-granular cracking.

Effect of ECAP on fracture toughness and fatigue endurance of DED-processed Ti-6Al-4V investigated on miniaturized specimens

Additive manufacturing (AM) has revolutionised the production of complex components with custom mechanical properties. However, as-deposited AM-ed materials often exhibit inferior mechanical behaviour compared to conventionally manufactured counterparts because of defects generated during the deposition. In this study, the effects of equal channel angular pressing (ECAP) on fracture toughness and fatigue endurance of Ti-6Al-4V titanium alloy manufactured by direct energy deposition (DED) are investigated. The aim of this study is to compare the mechanical performance of the material in the as-deposited and ECAP-ed states, exploiting the potential benefits of ECAP in improving the properties of additively manufactured components. ECAP processing is used to induce severe plastic deformation (SPD) and create a unique microstructure in Ti-6Al-4V specimens. As-deposited and ECAP-ed specimens were evaluated using stress intensity factor (SIF) analysis, fatigue crack growth, and high cycle fatigue tests using miniaturized specimens. Fractographic analysis was performed using scanning electron microscopy (SEM) to examine the fracture surfaces and identify the underlying failure mechanisms. The results revealed that while ECAP led to a slight increase in porosity, it significantly reduced fracture toughness and had a negligible effect on the rate of propagation of fatigue cracks. In addition, the ECAP-ed specimens showed reduced fatigue endurance of the material.

Theoretical analysis of stress intensity factors and interactions of collinear flaws with unequal lengths in brittle solids under uniaxial tensile conditions

Interactions between multiple flaws with different sizes in brittle solids are a key factor that induce failure. Previous studies have focused on the initiation, propagation and coalescence behaviors of multiple flaws in brittle solids. Nevertheless, there have been few theoretical or quantitative analyses of interactions between multiple flaws. In the present study, based on the Kachanov method, we first proposed theoretical analytical solutions of the stress intensity factors (SIFs) for two and three collinear flaws with unequal lengths under uniaxial tensile conditions. Then, a theoretical analysis of the effects of various geometric factors, such as flaw interval, flaw length and flaw number, was performed. The results supported the following findings: (1) For two collinear flaws, interactions between the primary and secondary flaws gradually weakened with increasing flaw interval, and the flaw length ratio gradually became the main factor that determined the interaction. (2) For three collinear flaws, when the interval between the primary and secondary flaws was not less than 1.5 times the length of the secondary flaw, the interaction had no effect on the propagation of the primary flaw. (3) The increase in the number of collinear flaws significantly enhanced the effect on propagation reinforcement between the flaws. Finally, numerical simulations were conducted to verify the results of the theoretical analysis, and good consistency was found. These research results are of great theoretical significance and engineering value for quantitatively understanding the failure mechanism of brittle solids containing multiple flaws and proposing effective measures to prevent cracking and ensure the safety of brittle solid structures.

Effect of basal texture on small crack behavior of magnesium alloy in very high cycle fatigue regime

AbstractThe behavior of small cracks in magnesium alloy is key to understanding very high cycle fatigue (VHCF), which is influenced by microstructure and deformation mechanism. This study explores how basal texture affects VHCF failure mechanisms in extruded magnesium alloys. Findings reveal that faceted and rough morphologies characterize fracture surfaces during crack initiation and early propagation, respectively. Basal texturing inhibits basal slipping during faceted‐like crack initiation while compression twinning dominates deformation during early propagation, contributing to rough zones. Stress intensity factor and plastic zone size analysis indicates significant influence of basal texture on VHCF failure mechanisms but with limited effect on stable propagation.

Intensity of Dynamic Stresses of Longitudinal Shear in a Periodically Layered Composite with Penny-Shaped Cracks

We consider the problem of harmonic torsional loading of an infinite elastic composite formed by alternating plane layers made of two different materials in the presence of a penny-shaped crack in one of the components of periodic structure. By using the integral representations for displacements and stresses in the frequency domain and satisfying the conditions of periodicity and perfect contact on the interfaces, we deduce a system of uncoupled boundary integral equations for the functions of tangential dynamic crack-opening displacement in a two-layered representative element of the composite. We perform the numerical analysis of the mode-III dynamic stress intensity factors in the vicinity of the analyzed crack depending on the wave number, the thicknesses of constituent layers, and the properties of their materials.

In situ synchrotron radiation µCT indentation of cortical bone: Anisotropic crack propagation, local deformation, and fracture

The development of treatment strategies for skeletal diseases relies on the understanding of bone mechanical properties in relation to its structure at different length scales. At the microscale, indention techniques can be used to evaluate the elastic, plastic, and fracture behaviour of bone tissue. Here, we combined in situ high-resolution SRµCT indentation testing and digital volume correlation to elucidate the anisotropic crack propagation, deformation, and fracture of ovine cortical bone under Berkovich and spherical tips. Independently of the indenter type we observed significant dependence of the crack development due to the anisotropy ahead of the tip, with lower strains and smaller crack systems developing in samples indented in the transverse material direction, where the fibrillar bone ultrastructure is largely aligned perpendicular to the indentation direction. Such alignment allows to accommodate the strain energy, inhibiting crack propagation. Higher tensile hoop strains generally correlated with regions that display significant cracking radial to the indenter, indicating a predominant Mode I fracture. This was confirmed by the three-dimensional analysis of crack opening displacements and stress intensity factors along the crack front obtained for the first time from full displacement fields in bone tissue. The X-ray beam significantly influenced the relaxation behaviour independent of the tip. Raman analyses did not show significant changes in specimen composition after irradiation compared to non-irradiated tissue, suggesting an embrittlement process that may be linked to damage of the non-fibrillar organic matrix. This study highlights the importance of three-dimensional investigation of bone deformation and fracture behaviour to explore the mechanisms of bone failure in relation to structural changes due to ageing or disease. Statement of significanceCharacterising the three-dimensional deformation and fracture behaviour of bone remains essential to decipher the interplay between structure, function, and composition with the aim to improve fracture prevention strategies. The experimental methodology presented here, combining high-resolution imaging, indentation testing and digital volume correlation, allows us to quantify the local deformation, crack propagation, and fracture modes of cortical bone tissue. Our results highlight the anisotropic behaviour of osteonal bone and the complex crack propagation patterns and fracture modes initiating by the intricate stress states beneath the indenter tip. This is of wide interest not only for the understanding of bone fracture but also to understand other architectured (bio)structures providing an effective way to quantify their toughening mechanisms in relation to their main mechanical function.

Analytical and finite element analysis of the concrete stress intensity factor with carbon fibers

Concrete is a material with low tensile strength and fracture resistance. One way to improve these properties is through the insertion of synthetic fibers such as carbon fibers into the concrete. This work determined the stress intensity factor for concrete with aligned carbon fibers (laminate) using an analytical model and finite element methods – macro-mechanical analysis of the composite laminate using the ABAQUS finite element package. Symmetrical laminate models were used with carbon fibers ranging from ± 15° to ± 75°. A single-edge notch bending specimen geometry was used to determine the KI of the laminates. The mechanical properties of the laminate were obtained through analytical models of the laminate theory. Results indicate that the fiber angles influence the stress intensity factor. The behavior is practically linear and a strong correlation was observed between the angle of the fibers and the KI through Pearson’s r. The laminate with a fiber angle of ± 75° showed a higher KI value compared to the others (x14 about ± 15°). Comparisons of the analytical and numerical results showed good agreement in the determined KI.

Analysis of Stress Intensity Factor of a Fibre Embedded in a Matrix

The analytical or numerical determination of the stress intensity factor (SIF) in cracked bodies usually assumes the body to be isolated. However, in fibre-reinforced composites, the fibre, which is the main load-carrying component, is embedded in a matrix. To clarify the effect the embedding matrix has on the SIF of the fibre, we propose a 3D computational model of an orthotropic fibre embedded in an isotropic matrix, and compute the SIF using the J-integral method. A parametric analysis based on dimensionless variables explores the effect of the fibre–matrix stiffness ratio as well as the effect of the degree of elastic orthotropy of the fibre. The results show that the SIF is strongly influenced by both factors, and that the matrix reduces the SIF by limiting the crack opening.

Analysis of stress intensity factor of a finite plate with centre crack containing different hole shapes

Analysis of stress intensity factor of a finite plate with centre crack containing different hole shapes

Out-of-plane bending stress intensity factor analysis of cracks in a strip using single-element strain gage

Out-of-plane bending stress intensity factor analysis of cracks in a strip using single-element strain gage

Cleavages along {110} in bcc iron emit dislocations from the curved crack fronts

Body-centered-cubic (bcc) transition metals, such as alpha -Fe and W, cleave along the {100} plane, even though the surface energy is the lowest along the {110} plane. To unravel the mechanism of this odd response, large-scale atomistic simulations of curved cleavage cracks of alpha -Fe were conducted in association with stress intensity factor analyses of straight crack fronts using an interatomic potential created by an artificial neural network technique. The study provides novel findings: Dislocations are emitted from the crack fronts along the {110} cleavage plane, and this phenomenon explains why the {100} plane can be the cleavage plane. However, the simple straight crack-front analyses did not yield the same conclusion. It is suggested that atomistic modeling, at sufficiently large scales to capture the inherent complexities of materials using highly accurate potentials, is necessary to correctly predict the mechanical strength. The method adopted in this study is generally applicable to the cleavage problem of bcc transition metals and alloys.

A prediction method of stress intensity factor for mode-I crack in coal rock based on deep learning

The stress intensity factor (SIF: K) analysis is of utmost importance in the evaluation of the coal-rock mass damage. However, the existing calculation processes seem cumbersome, even failing to meet the remote real-time determination of the SIF. Against this background, this paper introduces a prediction method of the SIF for the mode-I crack in the coal rock based on deep learning (DL). As soon as the model training is completed, the SIF can be acquired only by inputting the coal-rock image. To obtain extensive images of the mode-I crack of coal rock during the three-point bending test, a high-speed camera is used. The digital image correlation (DIC) and a crack-tracking algorithm (CTA) are further utilized to calculate the SIF corresponding to each image. Afterward, the model is trained and validated based on the self-designed convolutional neural network (CNN) architecture. The final results demonstrate that the fitting coefficient between the true value and the predicted one reaches 0.961, which indicates that the trained model is able to accurately predict the SIF.

A novel analysis of stress intensity factors for distributed non-planar surface cracks and its application to material quality control

A novel method for the numerical analysis of stress intensity factors (SIFs) was developed for multiple, 3-d-distributed, semi-elliptical cracks on the surface of a semi-infinite elastic body under arbitrary loading conditions. Emphasis was placed on the nature of interactions between cracks, with examination by the distributed infinitesimal dislocation loop technique, an eigenstrain method. SIFs of 100 distributed surface cracks were acquired in approximately 15 min when calculated on a standard personal computer, owing to the numerical integration approaches and meshing procedure adopted. The validity of the obtained results is verified and its applicability to some engineering problems is discussed.

Effects of local fiber discontinuity on the fatigue strength parameter at the fiber inclusion corner in fiber-reinforced composites

Abstract To comprehend the fatigue failure mechanism at the fiber discontinuity in fiber-reinforced composites, it is necessary to evaluate the local mechanical behaviors. The fatigue strength depends on the stress distribution at the fiber inclusion corner. An improved advanced finite element method (IAFEM) is proposed for the stress intensity factor (SIF) analysis at the fiber inclusion corner. In the IAFEM, the element stiffness matrix of singular inclusion corner element (SICE) is obtained, and the singular elastic field at the tip of the fiber inclusion is determined. The effects of load direction, fiber distribution, fiber geometry, and material properties on SIFs are analyzed numerically using the IAFEM. The difference in stress field distribution between two-dimensional and three-dimensional fiber inclusions is discussed. The IAFEIM and calculation results can provide reference for fatigue strength analysis and preparation of composite materials.

Analysis of Stress Intensity Factor for Cracked Non-load-carrying Fillet Welded Joint Under High-Temperature Tensile Loading

Analysis of Stress Intensity Factor for Cracked Non-load-carrying Fillet Welded Joint Under High-Temperature Tensile Loading

Theoretical Analysis of Stress Intensity Factor for Two Asymmetric Cracks Emanating from Water Conveyance Tunnel

The water conveyance tunnel has been widely applied in tunnel engineering, which may be subjected to compressive stress and shear stress from rock and faults, respectively. The internal pressure caused by water in the tunnel will make the appearance of cracks and propagation, resulting in disasters. In order to study the effects of the cracks and compressive stress on the cracked tunnel model, a plane model containing a circular hole with two unequal cracks under the compression loads, shear stress and internal pressure was established in this study. Complex variable function and conformal mapping function were implemented to theoretically derive the stress intensity factors (SIFs) at the crack tip in the rock mass, the numerical simulation was conducted to validate the theoretical solutions. The results indicate that the numerical results using the ABAQUS code were in good agreement with the theoretical solutions. The effects of compressive stress, shear stress, internal pressure, crack length and crack inclination angle on model II SIFs were discussed, the initiation angle and initiation pressure of different rock materials were also studied. When the crack inclination angle changes from [Formula: see text] to [Formula: see text], the tunnel is easily destroyed. With the increase of the right crack length, the increasing rate of the SIFs increases quickly first and then linearly, however, the left crack length has a slight effect on SIFs. When the crack inclination angle is [Formula: see text], the crack initiation angle reaches the maximum value.