Crack Initiation Angle Research Articles

Investigating the influence of geometric configurations and loading modes on mixed mode I/II fracture characteristics of rocks: Part I-Numerical simulation

The influence of geometric configurations and loading modes is a bottleneck that restricts the accurate determination of rock fracture parameters and the precise understanding of fracture mechanisms. Therefore, the phase field method is employed to analyze the influences of specimen geometry and loading modes on the dimensionless stress intensity factors, peak load, fracture toughness, and crack initiation angle during the rock mixed mode I/II fracture process. Three new configurations of specimens are proposed to test rock mixed mode I/II fracture. The research results indicate that as the prefabricated crack inclination angle increases, the peak load of three-point bending type specimen increases, while the peak load of diametric-compression type specimen decreases. Moreover, the influence of geometric configurations on the fracture parameters of three-point bending specimens is greater than that of diametric-compression disk specimens. The research findings of this work can provide basic supporting data for the establishment of mixed mode I/II fracture testing standards.

Dynamic behavior of fractured gabbro treated by high temperatures

Rock masses in deep engineering are often subjected to high geothermal effect, and blasting is a key technique for deep rock excavation. It is crucial to study the dynamic characteristics of fractured rock masses under high geothermal conditions and blasting excavation. This paper focuses on fractured gabbro, examining the effects of high temperatures on its surface chromaticity and mass. Dynamic splitting tests were conducted using a Split Hopkinson Pressure Bar (SHPB) apparatus, and the microstructure was analyzed with scanning electron microscopy (SEM). The results indicate that: (1) High temperatures significantly affect the surface chromaticity and mass of gabbro samples. (2) Elevated temperatures lead to the progression from a microstructure with no noticeable microcracks to the development of extensive microcracks and mineral particle fragmentation. (3) The impacts of high temperatures on the splitting strength, peak strain, and dynamic elastic modulus of gabbro samples reach a critical point around 500 °C. At this temperature, the strengthening effect of high temperature is evident, whereas at 800 °C, these properties significantly decrease due to extensive mineral crystal fragmentation and microcrack expansion, weakening the sample's strength, stiffness, and deformation resistance. (4) From 25 °C to 600 °C, the fissure angle significantly influences the splitting strength, peak strain, and dynamic elastic modulus of gabbro. Although the fissure angle still impacts these properties at 800 °C, the overall effect of high temperature is more pronounced. (5) The failure of fractured gabbro samples is primarily characterized by tensile and shear failures, with the crack initiation angle closely related to the fissure angle.

Validity for measuring mode II fracture toughness using the short beam in compression method

Mode II fracture toughness is a crucial intrinsic property of rocks, and accurately measuring this parameter is a challenge in rock fracture mechanics. Among the various approaches for measuring the mode II fracture toughness, the short beam in compression (SBC) method is a convenient and effective option. Nevertheless, the validity of measuring the mode II fracture toughness using the SBC method is controversial. This study conducted numerical analyses and experiments on the SBC specimen with different geometries (C/H) to identify the fracture mode and initiation location. In addition, the improved fracture criterion was developed by introducing three components of T-stress to determine the fracture mode at crack tips and the crack initiation angle. The results reveal that the pure shear fracture can occur on notch tips of SBC specimens with C/H=0.1 and 0.2, indicating that the SBC method is valid for measuring the mode II fracture toughness of rocks. The modified fracture criterion can predict the fracture mode and the angle of shear crack initiation observed in the SBC experiment well. Another important finding is that, due to the compressive stress on the notch tip, the measured mode II fracture toughness of rocks using the SBC method should be corrected using the Coulomb friction model. It is also discovered that the length of the fracture process zone and the corrected mode II fracture toughness depend on the value of C/H. A small C/H leads to a significant error between the measured and corrected mode II fracture toughness.

Crack coalescence prediction and load-bearing mechanism of defective specimen based on computer vision recognition model

The coalescence of cracks in rock, triggered by external stress or geological activities, plays a pivotal role in determining the mechanical properties and stability of rock structures. Consequently, the prediction method of crack coalescence become critical tools in ensuring the safety and stability of geotechnical engineering facilities. In this paper, based on the strain field data obtained by digital image correlation (DIC), a set of programs was developed to automatically identify the values and percentage changes of different strain intervals in the strain field of the specimen. Then, a computer vision recognition (CVR) model is established to study the process and prediction of crack coalescence in sandstone specimens with open flaws. This method overcomes the limitations, subjectivity and unpredictability of the traditional method of identifying cracks through artificial vision. The results show that the increase of the flaw width causes the displacement trend to be squeezed and deflected along the width direction, thereby changing the angle of crack initiation and exhibiting different forms of crack coalescence. The increase in the inclination angle of the flaw leads to an increase in the effective compressive area (ECA) of sandstone, and the magnitude of ECA is positively correlated with the uniaxial compressive strength (UCS) of the sandstone. Additionally, the CVR model identifies two types of numerical fluctuation signals before crack coalescence, namely the plastic characteristic signal (PCS) in the early stage of the experiment and the early-warning signal (EWS) near the period of crack coalescence, where EWS can be used as a predictive signal for crack coalescence. The research results provide a new algorithm technical support for the process analysis and prediction of crack coalescence, and provide a basis for early warning of rock mass engineering disasters.

Assessing the Effect of Twisting and Twisting Fatigue on ZnO:Al Thin Film Performance on PEN and PET Substrates.

This study examines the electromechanical characteristics of aluminium-doped zinc oxide (AZO) films. The films were produced using the RF magnetron sputtering process with a consistent thickness of 150 nm on various polymer substrates. The study focuses on assessing the electro-mechanical failure processes of coated segments using flexible substrates, namely polyethylene naphthalate (PEN) and polyethylene terephthalate (PET), with a specific emphasis on typical cracking and delamination occurrences. This examination involves conducting twisting deformation together with using standardised electrical resistance measurements and optical microscope monitoring instruments. It was found that the crack initiation angle is mostly dependent on the mechanical mismatch between the coating and substrate. Higher critical twisting angle values are observed for the AZO/PEN film during twisting testing. Relative to the perpendicular plane of the untwisted sample, it was found that cracks initiated at a twist angle equal to 42° ± 2.1° and 38° ± 1.7° for AZO/PEN and AZO/PET, respectively, and propagated along the sample length. SEM images indicate that the twisting motion results in deformation in the thin film material, leading to the presence of both types of stress in the film structure. These discoveries emphasise the significance of studying the mechanical properties of thin films under different stress conditions, as it can impact their performance and reliability in real-world applications. The electromechanical stability of AZO was found to be similar on both substrates during fatigue testing. Studying the electromechanical properties of various material combinations is important for selecting polymer substrates and predicting the durability of flexible electronic devices made from polyester.

Experimental and numerical study on the damage evolution and acoustic emission multi-parameter responses of single flaw sandstone under uniaxial compression

Cracks are generally the weakest position in engineering rock mass. It is of great practical significance to study the influence of cracks on the fracture process of rock mass and the precursor criterion of failure for disaster prevention and mitigation projects. In this paper, particle flow program (PFC2D) is used to analyze the mechanical strength and damage evolution of fractured rock. The multi-parameter stage characteristics of acoustic emission (AE) and the difference of fracture precursor information of fractured rock mass under uniaxial compression (UC) are explored. The results are as follows: (1) The strength and modulus of elasticity of fractured rock samples are smaller than that of intact rock mass, and increase in quadratic function with the increase of fracture angle, and the strength of B-90 sample is closest to intact rock samples; (2) The PFC analysis shows that the cracks in the defective rock samples all originate from the tip of the prefabricated crack, and the crack initiation angle is basically in the range of 60°∼90°. The loading process mainly produces tensile damage, and the number of tensile cracks are far more than that of shear cracks. Compressive stress and tensile stress increase with the increase of load, but the force chain of failure surface is the smallest after complete failure of rock; (3) The acoustic emission ringing number, RA/AF value, b value and entropy value of sandstone have obvious stage characteristics, the main frequency signal is mainly low frequency signal, and large-scale cracks are mainly produced in the failure process. The sudden increase point of AE ringing times and RA/AF value accumulation curve can be used as critical failure point. The fluctuation of B value and entropy value reflects the instability of fracture development, and “cliff-like” descending point and ascending point can be regarded as the precursor of critical failure of rock; (4) The failure precursor of acoustic emission parameters of sandstone appears in the peak load period of 85 %–98 %. The order of response time of different parameters is: cumulative RA/AF value, cumulative event number, entropy value, B value. The response time of B-45 and B-15 is earlier, while that of B-60 and B-30 is later. The research results are expected to deepen the understanding of the relevant standards of damage evolution and failure precursors of defective rocks in engineering applications.

Study on the mechanism of energy evolution and bearing degradation in pre-cracked sandstone under non uniform cyclic loading

The engineering rock mass is affected by the original cracks, which increases the uncertainty of instability and failure mechanisms. Under the action of excavation unloading or other disturbance loads, its bearing properties are more complex and the deformation characteristics is more special, which has always been a difficult issue in the analysis of rock mechanics. In order to explore the propagation and failure mechanism of spatial micro cracks in fractured rock masses, acoustic emission (AE) experiment of sandstone was carried out under pre-static loading and low-frequency stepwise cyclic loading–unloading. The research results indicate that the peak strain and crack initiation stress of rocks with different pre-cracked positions have the highest differences of 12.62% and 18.65%, respectively. The difference between peak stress and crack initiation strain is within 4%. The pre-cracked position mainly affects the peak strain and crack initiation stress of pre-cracked rocks, and its effect on peak stress and crack initiation strain is limited. The crack initiation angle of prefabricated cracks is mainly distributed within the range of 45° − 90°, and it decreases with the increase of quantities of prefabricated cracks. The crack initiation angle of rocks with prefabricated three cracks is 30% lower than that of single crack. The research results have deepened the analysis of energy evolution and deformation damage of fractured rock masses.

Effect of high-temperature and strain rate on the mechanical and cracking behaviors of flawed sandstone under dynamic impact loading

A deep understanding of how flawed rock cracks under high temperatures and dynamic impacts is crucial for safe deep rock engineering design and operation. Dynamic impact tests were conducted on sandstones with various flaw inclinations using a Split Hopkinson Press bar (SHPB) system at room temperature and after high-temperature treatment at 600 °C. The results show that the dynamic peak stress and energy consumption of rock were reduced by thermal treatment. The study identified the circular tensile- and compressive-tangential stress zones around the flaw boundary using elastic theory. The strain accumulation zones gradually shift from the tensile- to the compressive-tangential stress zones as the flaw inclination increases, resulting in a larger crack initiation angle and opening displacement, while also constraining the propagation path. Additionally, the high-temperature treatment strengthened the deformation in the circular tensile-tangential stress zone. In contrast to the severe failure of specimens at room temperature, the clear failure pattern of the specimens after high-temperature treatment merely consists of wing cracks. Finally, this study presents a detailed theoretical explanation of the cracking behavior under various conditions, which is consistent with the experimental results. This research enhances the understanding of dynamic crack propagation in deep high-temperature rocks and provides scientific references for engineering safety design and protection.

Experimental study of the effect of crack distribution on the failure mechanism of sandstone specimens based on inclination angles and number of parallel flaws

Discontinuous joints are prevalent in engineered rock masses and play a significant role in the stability of the rock mass. This study aims to analyze the impact of the inclination angle and number of prefabricated flaws on the crack evolution and failure pattern of sandstone specimens. Uniaxial compression tests, along with acoustic emission technology and digital image technology, were employed to monitor and analyze the effects. The findings indicate that: (1) With the increase in the flaw inclination angle, the damage mode of the specimen transitions from tensile to compressive-shear failure. The localized high-strain region on the surface of the specimen predicts the propagation path for the formation of macroscopic cracks. (2) When the number of prefabricated flaws is small, the flaws mainly expand through tensile wing cracks. As the number of flaws increases, the inner flaw tip does not produce cracks. Instead, the failure of the entire specimen occurs along the direction of the outer flaw's tensile wing crack, with the inner flaw running through it. (3) The winged tensile crack is the first crack to appear in all rock samples, regardless of the flaw initiation angles. Finally, the stress intensity factor at the crack tip under uniaxial compression conditions, without considering the closure effect, was expressed based on fracture mechanics theory. The crack initiation angle was then calculated. The results of the theoretical calculation of the initiation angle were found to be consistent with the test results. These research findings can serve as theoretical references and provide insights into the failure mechanisms of cracked rocks and the development of disaster control methods in rock engineering.

3D-generalized maximum tangential strain criterion for predicting mixed-mode I/II/III fracture initiation of brittle materials considering T-stress effects

To overcome the difficulty of predicting the initiation and conditions of three-dimensional (3D) cracks, we proposed a novel 3D-generalized maximum tangential strain (3D-GMTSN) criterion for mixed-mode I/II/III loading conditions, considering the effects of T-stress and Poisson’s ratio. The proposed strain-based criterion can predict the initiation direction and conditions of cracks under mixed-modes I/II, I/III, II/III, and I/II/III. The criterion was compared with the existing criteria for mixed-modes, and the results were compared with the experimental results. Our study indicated that the criterion considering T-stress effects can predict the crack initiation angles and the critical stress intensity factors (CSIFs) for arbitrary mixed-mode fractures. Specifically, the criterion provides better predictions of the CSIFs under the mode II-dominant conditions. The 3D-GMTSN criterion was better for predicting the out-of-plane crack initiation angles and CSIFs of brittle materials containing mode III cracks as compared to the existing criteria.

Experimental study on crack propagation characteristics of unconventional reservoir rocks

This study investigates the fracture behaviour of three types of specimens (shale, sandstone, and coal), which are commonly found in unconventional reservoirs, based on mode Ⅰ single-edge notch beam (SENB) test. We employ the Digital Image Correlation technique to track the strain evolution and crack propagation paths of the three types of materials and compare their fracture characteristics. The experimental results show that both the surface roughness and crack initiation angle of the coal are larger comparing with that of sandstone and shale, which demonstrates the ductile property of coal and fracturing difficulty in coal seam. Moreover, the average velocity difference of crack propagation is obvious, which is 53.76 × 103, 453, and 0.33 mm/s in shale, sandstone, and coal, respectively. The elastoplastic J-R curves, which reflects the influence of the plastic zone, are presented to analyze the energy dissipation characteristics of three types of specimens during crack propagation. It is found that the J-integral of shale and sandstone does not increase with crack propagation, but the J-integral of coal shows obvious increasing trend with crack propagation due to the effect of plasticity. In addition, microscopic analysis is conducted using a petrographic microscope and scanning electron microscope (SEM) to explain the plastic zone differences at the notch tips of shale, sandstone, and coal. This study is a preliminary and significant step of hydraulic fracturing application in unconventional reservoirs for efficient recovery of the berried natural gas.

Finite element analysis of fretting fatigue properties of GH4169 superalloy considering the surface treatments

In the present work, the fretting fatigue properties of GH4169 superalloy at 650℃ were investigated through numerical simulation considering the influences of the surface treatments. As a detrimental phenomenon, fretting fatigue involves fatigue and wear simultaneously, where the coefficient of friction and residual stress fields induced by the surface coating or modification techniques may affect the fretting fatigue lifetimes by changing the complex stress state between the two contacting surfaces. The numerical solutions were implemented to compare the crack initiation angles and paths under different surface conditions. The simulation results indicated that fretting fatigue cracks in residual stress fields were tendentiously parallel to the surface resulting in crack retardation and debris peeling, as verified by experimental observations. Additionally, three propagation models were compared to study the effect of compressive loading on the driving force of crack propagation rates, especially where compressive residual stresses was present. The combination of the linear superposition model with the Harter-T method was proven to be more accurate in the fretting fatigue life prediction, which may provide a modeling basis for service life prediction of engineering components in many practical applications.

Multiaxial fatigue behavior and crack orientation prediction for steel and cast iron

This study investigates multiaxial fatigue behavior of ductile construction steel S355 and cast iron EN-GJS-500-14. Fatigue lives and crack initiation orientations are measured. Three critical plane models are evaluated for predicting fatigue life and crack initiation angles. While all models achieve decent accuracy in predicting fatigue life, crack initiation angle predictions are less satisfactory. Weak correlation is observed between the quality of fatigue life and crack orientation prediction, particularly for the Smith–Watson–Topper (SWT) and Fatemi-Socie (FS) models. The SWT model performs better in predicting fatigue life and crack angles for cast iron, while the FS model shows higher accuracy for S355. The short-crack model (SC) provides the best overall fatigue life prediction but crack orientation estimation is not superior.

Stress-Based Model for Calculating the Opening Angle of Notch Cracks in a Magnesium Alloy under Multiaxial Fatigue

This paper presents a model to calculate the opening angle of crack initiation in notched fractures subjected to multiaxial loading. To validate the proposed model, a study was performed on polished AZ31B-F magnesium alloy specimens under multiaxial high-cycle fatigue loading. The specimens exhibited a notch in the smaller cross-sectional area, which was created with a special drilling jig to promote the formation of fatigue cracks in this localized area of the specimen. The load paths used in the experiments and numerical analyses were proportional and non-proportional, resulting in different stress states in the crack front opening, which were determined by finite element analysis to validate the proposed model. To obtain more accurate numerical results for these estimates, these finite element analyses were performed using the nonlinear Chaboche plasticity model of ABAQUS® 2021 software. A sensitivity analysis was also performed to determine which load component—axial or torsional—has a greater influence on the fatigue strength and contributes significantly to the crack opening process. The results show that the type of load path and the stress level of each load component—axial and torsional—has a strong influence on the opening angle of the notch crack and the fatigue lifetime of the specimen. This result is confirmed not only by the experimentally determined fatigue strength, but also by a fractographic analysis performed on the surface of the specimens for both load paths. Moreover, the results show an acceptable correlation between the experimental results and the estimates obtained with the proposed model and the stresses obtained with the finite element analysis.

Investigation of T-stress and tensile strength effect on crack tip conditions and crack initiation angle in off-axis laminate composite

In this work, five different yield criteria have been used, maximum tangential stress (MTS), maximum energy release rate (MERR), Hill-48, Hill-90, and Barlat-93, in order to determine crack initiation angle. A study is performed to investigate the effect of T-stress on crack initiation angle. For this purpose, the elastic–plastic core region is plotted, and the R-criterion suggests that the crack initiates along local minimum (negative value) or global minimum (positive value) direction depending on the stress state at the crack tip. It is found that a negative value of T-stress makes the crack move toward the loading direction (T-axis), or in other words, the crack initiation angle decreases. It also turns out that MERR and Barlat criteria show a better result for crack initiation angle. The yield surface and elastic–plastic core region have also been plotted for different tensile strengths. For the case when transverse tensile strength equals to z-direction tensile strength, Hill-48, Hill-90, and Barlat show the same yield surface, and approximately, the same crack initiation angle. Also, when transverse tensile strength is smaller than longitudinal tensile strength, crack tends to move toward x-direction (local coordinate placed on crack tip). Finally, a FE simulation is performed to numerically determine SIFs.

Application of modified fracture criteria incorporating T-stress for various cracked specimens under mixed mode I-II loading

Accurate assessment of fracture behavior and life prediction of cracked materials based on the mixed mode fracture criteria is of utmost importance in fracture mechanics. In this study, the modified fracture criteria incorporating T-stress for mixed mode I-II cracks were comprehensively reviewed. Additionally, a comparative analysis was conducted between the experimental results obtained from five different cracked configurations and the theoretical predictions according to these modified criteria. Moreover, a brief discussion was held regarding the effect of T-stress on both crack initiation angle and fracture toughness, accompanied by providing some suggestions. The results revealed that the predictive accuracy of modified criteria exhibited noticeable variations across different cracked configurations due to the significant disparities in both the sign and magnitude of T-stress around the crack tip. However, it was observed that the predicted curves based on the modified fracture criteria for the semi-circular bend and edge-crack triangular specimens had remarkable similarities owing to their similar biaxial stress ratio B. When the mode II loading dominated, the generalized maximum tangential stress, generalized minimum strain energy density and generalized averaged strain energy density criteria were suitable for the semi-circular bend, edge-crack triangular, central crack rectangular and short bend beam specimens with positive T-stresses, whereas the maximum tangential strain, generalized maximum tangential stress and generalized maximum tangential strain energy density criteria could provide better theoretical predictions for central cracked Brazilian disk specimens having a negative T-stress.

The Effect of Preloaded Compressive Stress and Curvature of Defect on Blast-Induced Fracture Behavior by Caustic and Numerical Models

In this study, the effects of preloaded uniaxial compressive stress and defect (prefabricated by laser cutting) curvature on blast-induced cracks and stress wave propagation were investigated in polymethyl methacrylate (PMMA) specimens using caustics theory. Based on the mathematical relationship between stress and optics, the fracture behavior (the propagation path, dynamic stress intensity factors (DSIFs), propagation velocity, initiation angle of the main crack, and damage degree between the defect and the blasthole) was calculated and analyzed quantitatively. The results show that the preloaded stress could mainly restrain the main crack propagation in the horizontal direction and reduce the initiation angle and damage degree at the defects. Meanwhile, the crack initiation position of the positive curvature defect was not at the end of the defect. In addition, the curvature of the defect significantly affected the blast-induced fracture compared to preloaded stresses. Comparing the main crack with other curvature defects, the DSIFs, velocity, crack arrest time, crack length, and horizontal offset distance of the main crack with negative curvature defect were the largest. The variation in the full stress field in the specimen under blasting and preloaded stress was simulated by a numerical model. The results show that the curvature of the defect has a significant effect on tensile waves at the end of defects, and the tensile stress from high to low was C-25, C0, and C25, in that order.

Damage effect and progressive failure mechanism of sandstone considering different flaw angles under dynamic loading

In many engineering applications, it is essential to have information about rocks that inherently contain pre-existing flaws under dynamic loading conditions. Dynamic impact tests are conducted on samples with varying flaw angles using the split Hopkinson pressure bar (SHPB) test system and the Digital Image Correlation system (DIC). The characteristics of the samples after dynamic loading, including dynamic strength, energy dissipation, and fractal fracture, are compared and analyzed. As the flaw angle increases, the peak stress and strain exhibit a typical V-shaped pattern, reaching the minimum value at 30°, and the initial initiation position shifts from the flaw tips to the middle of the flaw. Failure modes can be divided into three modes depending on the flaw angle. The progressive failure process, taking into account the heterogeneity of the rock, is demonstrated by developing an elastic damage constitutive model that uses dynamic compression and tensile tests to parameterize it. As the flaw angle increases, the initial damage zone also moves from the flaw tips to the middle of the flaw. Failures around the hole with redistributed stress are observed, and the failure mechanisms can be explained with the aid of strain energy density (SED). Using fracture mechanics, the analytical solution of stress around the flaw is provided, and the variation of crack initiation angle, stress distribution, and energy dissipation under different flaw angles is theoretically explained, which is in good agreement with the experimental and simulated results.

Effect of pad rotation angle and coefficient of friction on fretting fatigue crack nucleation behavior

Fretting fatigue may occur on surfaces that are in contact, subjected to a normal load, and where there is a cyclic small relative movement between them. It could occur in press-fitted shafts, bolted and dovetail joints, and many other engineering components. It is recognized that the coefficient of friction of the contacting bodies is a primary variable in the fretting process. Also, a recent study indicates that its behavior might be greatly affected by the possible rotation of the pad. Consequently, the aim of this investigation is to evaluate the impact of diverse angles of rotation of the pad and different coefficients of friction on crack initiation angle, location, and life. For this purpose, a numerical model based on a finite element model of a cylinder-plane test configuration is constructed. The Fatemi-Socie damage parameter for multiaxial fatigue is used to evaluate initiation behavior. Firstly, different angles of rotation are applied to the pad, in order to model a lack of stiffness of the test rig, while the coefficient of friction is kept constant and equal to 0.75. Secondly, several coefficients of friction between the pad and the specimen are utilized, while considering a cyclic rotation of the pad between 0.19° and – 0.19°. For the case studied, the results indicate that an increase of the coefficient of friction (μ) may cause a substantial reduction of crack initiation life. However, a variation of μ in the range 0.75 ≤ μ ≤ 0.85 does not produce a significant change in life estimation. This suggests that it cannot be stated that an increase in the coefficient of friction always leads to a reduction in nucleation life. Regarding the angle of initiation of the crack, the results show that an increase of μ causes an approximately linear reduction of the angle. In the case of an increase of the pad angle of rotation, this causes a longer nucleation life and a smaller crack nucleation angle. Even the rotation angle of 0.23° produces an increase of initiation life from 16.6 to 154 thousand cycles. It is concluded that there is a major impact on initiation behavior of the coefficient of friction and the rotation of the pad, which may be due to the lack of rigidity of the test setup. Therefore, controlling the stiffness of the test rig and measuring accurately the coefficient of friction are important factors to consider in fretting fatigue research.

Fracture parameters and crack initiation Assessment Employing Mixed-mode I/II Fracture Criterion in Laminate Composites Using Digital Image Correlation Method

The present study aims to have fracture parameters, such as stress intensity factors (SIFs) and J-integral, as well as the crack initiation angle, extracted through the utilization of a novel mixed-mode (I/II) fracture criterion founded on the maximum energy release rate (MERR) and maximum tangential stress (MTS). The digital image correlation (DIC) method is employed in the analysis of crack behavior. Of note, several key findings are highlighted by our research. Results show a slight decrease in the mode I stress intensity factor (KI) with an increase in the crack inclination angle (φ). Interestingly, a bell-shaped curve characterizes the mode II stress intensity factor (KII), with its peak occurring at φ = 45. Comparison of experimental outcomes with finite element (FE) based modeling reveals consistent trends in both KI and KII from both sources. The comparison of experimentally determined crack initiation angles with predictions from the MERR and MTS criteria offers insightful observations. For φ ≤ 30, both criteria closely match experimental outcomes, as the crack initiation corresponds to φ. However, for φ > 30, these criteria underestimate the crack initiation angles, leading to a slower decrease in kink angles compared to observations. Further analysis involves a comparison between the two criteria and experimental results. Here, MERR emerges as being more accurate in prediction than MTS. Lastly, Simpson's rule is employed to calculate the J-integral, contributing to a comprehensive understanding of crack behavior. The reliability of the new mixed-mode fracture criteria and the DIC method in evaluating crack tip conditions and predicting minor kink angles is established by our study. Not only is understanding enhanced by our findings, but practical applications in predicting crack initiation and behavior in complex materials are also offered.