Initiation Stress Research Articles

Solidification cracking susceptibility of alloy 718 during additive manufacturing and evaluating method

Although hot cracks frequently occur during metal additive manufacturing (AM), there are very few fundamental studies on the cracking behaviour and susceptibility. In this study, a horizontal tensile-type hot cracking test was investigated for evaluating the solidification cracking susceptibility of alloy 718 quantitatively during AM, particularly in laser powder bed fusion. The factors influencing the cracking susceptibility were also examined. The solidification cracking was reproduced by the melting of the AMed specimen with a tensile load under conditions of heat source simulating the AM process. The critical initial tensile stress for solidification crack initiation could apply as an evaluation index for cracking susceptibility. The critical initial stress decreased with increasing the laser power. A similar tendency was observed during the melting of the powders set on tiny groove for simulating AM process. The critical strain rate for solidification cracking (CST) was derived by a thermal elastic–plastic analysis using the critical initial stress measured experimentally. The CST at the laser power of 1125 W was higher than that of 1000 W for no crack condition. Therefore, high CST corresponding to penetration shape with high laser power induce to deteriorate the solidification cracking susceptibility.

Theoretical stability of ice shelf basal crevasses with a vertical temperature profile

Abstract Basal crevasses threaten the stability of ice shelves through the potential to form rifts and calve icebergs. Furthermore, it is important to determine the dependence of crevasse stability on temperature due to large vertical temperature variations on ice shelves. In this work, considering the vertical temperature profile through ice viscosity, we compare (1) the theoretical crack depths and (2) the threshold stress causing the transition from basal crevasses to full thickness fractures in several fracture theories. In the Zero Stress approximation, the depth-integrated force at the crevassed and non-crevassed location are unbalanced, violating the volume-integrated Stokes equation. By incorporating a Horizontal Force Balance (HFB) argument, recent work showed analytically that the threshold stress for rift initiation is only half of that predicted by the Zero Stress approximation. We generalize the HFB theory to show that while the temperature profile influences crack depths, the threshold rifting stress is insensitive to temperature. We compare with observations and find that HFB best matches observed rifts. Using HFB instead of Zero Stress for cracks in an ice-sheet model would substantially enlarge the predicted fracture depth, reduce the threshold rifting stress and potentially increase the projected rate of ice shelf mass loss.

Does a polymer film due to Rayleigh-instability affect interfacial properties measured by microbond test?

ABSTRACT The microbond (MB) test, which is primarily used to characterise the interface of fibrous composites, requires a large number of droplets to be tested and analysed in order to make a reliable conclusion about the fibre–droplet interface. The conventional method of depositing single droplets on fibre and performing the MB test can be improved by depositing multiple droplets using the Rayleigh plateau instability phenomenon (an additional film is formed between the droplets). Although the latter method has significant advantages and higher statistical reliability, the role of the additional film affecting MB test results has not been investigated. In this work, both methods are experimentally evaluated for glass and flax fibres with two different resin systems and the interfacial constants, namely critical stress for damage initiation and critical energy release rate, are validated by finite element (FE) models. The study reveals that the thickness of the additional film shows incorrect interfacial shear strength (IFSS) when determined from simple force-displacement data ( ≈ 18% increase for the fibre-droplet system in this study). The FE models confirm that the damage onset at the interface occurs at a higher force with this method, but the interfacial strength constants remain the same as with the conventional method.

A New Rock Brittleness Index Based on Crack Initiation and Crack Damage Stress Thresholds

A New Rock Brittleness Index Based on Crack Initiation and Crack Damage Stress Thresholds

Effect of Boron on Microstructures and Low-Temperature Impact Toughness of Medium-Carbon CrMo Alloy Steels with Different Quenching Temperatures

The effect of boron (B) on the microstructures and low-temperature impact toughness of medium-carbon CrMo steel quenched at 870~1050 °C and tempered at 600 °C was studied via Charpy impact testing and microstructure characterizations. The results showed that with an increasing B content from 0 to 50 ppm, the low-temperature impact toughness deteriorated significantly at quenching temperatures (Tq) lower than 950 °C but increased at a higher Tq of 1050 °C. Undissolved M2B particles remained and coarsened during the holding process due to the low Tq, decreasing the critical stress required for crack initiation and deteriorating the impact toughness accordingly. However, this detrimental effect of B could be mitigated by a higher Tq, and the favorable influences on the impact toughness improvement could be attributed to (1) the finer M2B particles formed during quenching effectively pinning the austenite grain boundaries (GBs), leading to a finer block size and a high density of high-angle grain boundaries, which reduced the critical stress for crack initiation; and (2) the fact that the coarsening of M23C6 on the GBs during tempering was slightly suppressed by the segregated B, eventually increasing the energy required for crack propagation. However, the degree of the favorable effect due to B was still lower than the negative effect of a high Tq.

Influence of prior austenite grain size on martensite-austenite islands morphology and decomposition characteristics during two-step tempering in Mn-Ni-Mo steel

Martensite-austenite (M/A) islands are typical in the quenched microstructure of Mn-Ni-Mo steel, frequently utilized for fabricating reactor pressure vessels (RPV). These islands can decompose into harmful long rod-shaped Fe3C carbides during tempering above 600°C, quantifying the negative effect of M/A island decomposition on mechanical properties and indicating a potential issue in RPV fabrication. To address this issue, the present study investigates a two-step tempering process on three different prior austenite grain size (PAGS) specimens (5 µm, 47 µm, and 119 µm). The effect of PAGS on M/A island decomposition characteristics during sub-600°C tempering and their impact on precipitated carbide morphology is investigated. A preliminary pre-tempering treatment at 200°C, 350°C, and 500°C for 2 hours was followed by a 3-hour final tempering step at 650°C. The findings revealed unique temperature-dependent decomposition characteristics of M/A islands. For example, at 200°C, partial M/A island decomposition took place, resulting in long rod-shaped carbides during final tempering. Meanwhile, the 350°C pre-tempering specimen revealed aggregated carbide precipitates of varying sizes in former M/A island locations. In contrast, the 500°C pre-tempering specimen showed coarse globular carbides and the absence of carbide precipitate clustering. This result can be attributed to the decrease in surface energy associated with the carbide-matrix interface as size increases. After tempering, all specimens produced three types of precipitates: rod-shaped Fe3C carbides, rhombus-shaped Mn7C3, and globular-shaped Mn23C6 carbides. The formation of long rod-shaped carbides during M/A island decomposition reduces the critical cleavage stress for micro-crack initiation, jeopardizing steel mechanical properties. Aggregated carbides cause the simultaneous formation of numerous micro-voids in close proximity, which eventually merge to form a large crack, resulting in material failure. When compared to other pre-tempered and directly tempered specimens, pre-tempering at 500°C produced the most favorable microstructure in terms of impact properties.

Field observations and interpretation of extensional fracture in hard rock surrounding deep underground openings

Extensional fracturing often occurs in hard rock masses during excavation at depths, for example, >1000 m below the ground surface. Surface-parallel fractures are created in the surrounding rock mass, which is typically subjected to stresses parallel to the free rock surfaces after excavation. These are called extensional fractures because the strains perpendicular to the fracture planes are extensional and the opposite surfaces of each fracture tend to separate from each other as soon as the fracture is created. These fractures predominantly propagate parallel to the maximum principal stress σ1 in the surrounding rock mass. This study analyses extensional fractures observed during excavations in cut-and-fill mining stopes in a deep metal mine. This analysis explores the process of extensional fracturing during excavation in an undisturbed rock mass. In general, intensive spalling occurred on the roof surfaces immediately after the excavation of the undisturbed rock mass. This spalling terminated after a certain depth of rock failure, while burst sounds intermediately emitted from the surrounding rock mass, indicating that rock fracturing was ongoing at depth. In the subsequent cutting slices, the spacing between the extensional fractures decreased with increasing mine-out space in the stope. An extensional fracturing criterion was proposed based on microscopic observations of microcrack development in the rock in response to applied stress. The crack initiation and extensional fracturing processes are associated with two critical extensional strains which are related to the secondary stress state in the position. In areas close to the free rock surface where σ3 = 0, the stress for crack initiation is (σ1+σ2) = 0.4σc, whereas the stress for extensional fracturing is (σ1+σ2) = 0.8σc.

New method for determining the mode I fracture toughness of shotcrete: edge-notched partial disc test

The fracture toughness (mode I) of shotcrete specimens was obtained using edge-notched partial disc (ENPD) specimens. Notched Brazilian discs (NBDs) were also tested to validate the results of the ENPD experiments. Numerical analysis was also conducted on the ENPD results to compare the measured and numerically obtained fracture toughness values. The notch lengths in the ENPD specimens were 15, 30, 45 and 60 mm, while the notch lengths in the NBD specimens were 10, 20, 30, 40, 50 and 60 mm. It was found that the flat joint model accurately predicted the potential crack growth path and crack initiation stress as compared with the experimental results. It was also deduced that the fracture toughness was roughly the same with an increase in the notch length. The tensile strength (σt) and fracture toughness (KIC) of the shotcrete specimens were found to be meaningfully correlated (σt = 7.92KIC). The ENPD tests yielded the lowest fracture toughness values because of the pure tensile stress distribution on the failure surface. It was also found that the derived fracture extension patterns from the laboratory investigations were in acceptable agreement with the outputs of numerical simulations.

A viscoelastic–plastic constitutive model incorporating creep initiation stress for surrounding rock in deep roadways and its practical application

AbstractWith the increasing depth of engineering in rock masses, the issue of significant rheological deformation becomes notably prominent. To accurately characterize the deformation and failure behavior of the surrounding rock near the goaf in deep small coal pillars, we have developed a viscoelastic–plastic constitutive model that takes into account the initial stress associated with creep. This model builds upon an existing viscoelastic–plastic constitutive framework and is implemented numerically using C++ in the FLAC3D. The Oedometer test method is used to check the creep components and the calculated parameter (η/G) ensure convergence of numerical operations. We conducted both pre‐improvement and post‐improvement tests of the constitutive model in a simple numerical analysis of roadways. The enhanced model demonstrates improved accuracy in deviational stress calculations and proves suitable for modeling deep, soft roadways. Furthermore, we applied the improved model to simulate actual working conditions at Zhaozhuang Mine, where mining operations near the working face induce a fracture zone of approximately 3 m in the small coal pillar located at the goaf's edge. The new model closely aligns with the observed results, further validating its suitability for tunneling along the goaf. Tunneling and mining activities result in significant deformation at various locations, including the shoulder socket of the working face, the top angle of the coal pillar, and the bottom angle of the floor. The crushing zone at the working face extends up to 4 m. Rheological effects transform the triangular elastic core, from its original high‐pressure elastic state to a fracture and plastic zone in the deep coal. Stress in deep coal is transmitted along the triangular elastic core. Numerical simulation results closely match the excavation profile of the tunneling, providing valuable insights into the impact of mining activities. This study can provide reference for deformation of similar geological conditions and engineering situation.

Damage and failure characteristics of single fractured cyan sandstone subjected to freeze–thaw cycles under uniaxial compression

In order to explore the freeze–thaw (FT) damage characteristics of fractured rock masses, FT cycle tests and uniaxial compression tests were conducted on intact and pre-cracked cyan sandstone samples, respectively. The degradation laws of physical and mechanical properties of samples under FT cycle conditions were analyzed, and the FT damage mechanism and failure mechanism were explored accordingly. The results indicate that as the number of FT cycles (N) increases, the saturation weight change rate and porosity of the sample continue to increase, while the P-wave velocity continues to decrease. The closure stress, initiation stress, damage stress, and peak stress decrease linearly with increasing FT cycles, and increase linearly with increasing crack inclination angle (β). Moreover, as FT cycles increase, the geological strength index GSI decreases linearly, while the damage factor (D) increases linearly. A Hoek Brown strength degradation model for fractured rocks subjected to FT damage under uniaxial compression was obtained, and its high reliability was verified using test results. The FT damage of cyan sandstone is mainly dominated by the frost heave force inside the rock, and the degree of FT damage of fractured samples is much higher than that of intact ones. The concentration of frost heave force at the crack tip leading to cracking is the key to exacerbating the FT damage in fractured rock masses. However, the crack initiation mechanism is still controlled by β. Whenβ = 90°, it exhibits tensile initiation mode, and whenβ = 45°, it mainly exhibits shear initiation mode. Moreover, the fracture of the single crack sample conforms to the compression-shear fracture criterion. Taking the sample with pre-crack inclination angle of 45° as an example, the variation of KI and KII, and the relationship between them are discussed accordingly. The results of this paper are beneficial to clarify the influence of FT cycles on the mechanical properties of cyan sandstone, and can provide reference for the study of related issues.

Mechanical behaviors and failure characteristics of coal-rock combination under quasi-static and dynamic disturbance loading: a case based on a new equipment

The dynamic disasters of deep mining coal and rock mass are frequent and easy to be instable. Aiming at the deformation of coal-rock roadway under the coupled static and dynamic load, a new equipment which can simulate the actual situation dynamic environment is used to carry out the coupled static-dynamic loading test of coal-rock combination. The failure law and mechanical behavior of combination are studied. Test results show that weak structure significantly affects mechanical response of coal-rock combination. The coal part with lower strength firstly reaches the crack initiation stress. The strength of the combination is dominated by the coal part. The post-peak stage of the stress–strain curve under the coupled static and dynamic load presents a stepped reduction, which shows yield process. The dynamic load level has a significant effect on the mechanical behaviors of the combination. The elastic modulus decreases under dynamic loading. The peak stress of the combination is positively correlated with the dynamic load level in a certain range, and the peak strain was negatively correlated. The energy accumulation and dissipation are closely related to the failure of the samples. The strain energy is more concentrated in the area where the failure occurs first. The AE energy under dynamic load is developed from the traditional “four-stages” characteristic under static load to three stages. The interval release stage appears because of the appearance of intermittent disturbance load makes the AE energy of the sample change intermittently. The dynamic instability of samples accompanies a sudden increase in AE energy rate, hysteresis loop area and strain. Compared with the shear failure of single lithology sample, the failure mode of the combinations is mainly tensile, and it turns into tensile-shear failure under dynamic load. The fragmentation of samples is different under different failure modes. The fragmentation index can characterize the failure mode and crack propagation characteristics of coal-rock combination. The research provides reference for large deformation dynamic disasters of surrounding rock.

Intermittent disturbance mechanical behavior and fractional deterioration mechanical model of rock under complex true triaxial stress paths

Mechanical excavation, blasting, adjacent rockburst and fracture slip that occur during mining excavation impose dynamic loads on the rock mass, leading to further fracture of damaged surrounding rock in three-dimensional high-stress and even causing disasters. Therefore, a novel complex true triaxial static-dynamic combined loading method reflecting underground excavation damage and then frequent intermittent disturbance failure is proposed. True triaxial static compression and intermittent disturbance tests are carried out on monzogabbro. The effects of intermediate principal stress and amplitude on the strength characteristics, deformation characteristics, failure characteristics, and precursors of monzogabbro are analyzed, intermediate principal stress and amplitude increase monzogabbro strength and tensile fracture mechanism. Rapid increases in microseismic parameters during rock loading can be precursors for intermittent rock disturbance. Based on the experimental result, the new damage fractional elements and method with considering crack initiation stress and crack unstable stress as initiation and acceleration condition of intermittent disturbance irreversible deformation are proposed. A novel three-dimensional disturbance fractional deterioration model considering the intermediate principal stress effect and intermittent disturbance damage effect is established, and the model predicted results align well with the experimental results. The sensitivity of stress states and model parameters is further explored, and the intermittent disturbance behaviors at different f are predicted. This study provides valuable theoretical bases for the stability analysis of deep mining engineering under dynamic loads.

Predicting Sandstone Brittleness under Varying Water Conditions Using Infrared Radiation and Computational Techniques

The brittleness index is one of the most integral parameters used in assessing rock bursts and catastrophic rock failures resulting from deep underground mining activities. Accurately predicting this parameter is crucial for effectively monitoring rock bursts, which can cause damage to miners and lead to the catastrophic failure of engineering structures. Therefore, developing a new brittleness index capable of effectively predicting rock bursts is essential for the safe and efficient execution of engineering projects. In this research study, a novel mathematical rock brittleness index is developed, utilizing factors such as crack initiation, crack damage, and peak stress for sandstones with varying water contents. Additionally, the brittleness index is compared with previous important brittleness indices (e.g., B1, B2, B3, and B4) predicted using infrared radiation (IR) characteristics, specifically the variance of infrared radiation temperature (VIRT), along with various artificial intelligent (AI) techniques such as k-nearest neighbor (KNN), extreme gradient boost (XGBoost), and random forest (RF), providing comprehensive insights for predicting rock bursts. The experimental and AI results revealed that: (1) crack initiation, elastic modulus, crack damage, and peak stress decrease with an increase in water content; (2) the brittleness indices such as B1, B3, and B4 show a positive linear exponential correlation, having a coefficient of determination of R2 = 0.88, while B2 shows a negative linear exponential correlation (R2 = 0.82) with water content. Furthermore, the proposed brittleness index shows a good linear correlation with B1, B3, and B4, with an R2 > 0.85, while it shows a poor negative linear correlation with B2, with an R2 = 0.61; (3) the RF model, developed for predicting the brittleness index, demonstrates superior performance when compared to other models, as indicated by the following performance parameters: R2 = 0.999, root mean square error (RMSE) = 0.383, mean square error (MSE) = 0.007, and mean absolute error (MAE) = 0.002. Consequently, RF stands as being recommended for accurate rock brittleness prediction. These research findings offer valuable insights and guidelines for effectively developing a brittleness index to assess the rock burst risks associated with rock engineering projects under water conditions.

Investigation of the Effect of Nanometakaolin on the Compression Behavior of Concrete by Acoustic Emission.

To investigate the influence of nanometakaolin (NMK) on the compression behavior of concrete, acoustic emission (AE) is applied to monitor the development of cracks on ordinary concrete as a control sample and concrete with the addition of 1% or 3% NMK during the whole compressive process. The AE parameters (event, count, RA-AF, etc.) and Gaussian Mixture Model (GMM) were analyzed. The results show that the addition of NMK results in a decrease of crack number and crack width. Compared to the control concrete, the concrete with NMK inhibits the initial crack, increases the crack initiation stress and crack damage stress, and improves the energy of crack propagation. Correspondingly, we proposed a critical point where the ringing counts and amplitude fit parameters are less than a certain threshold. This index can be used as a failure precursor for crack instability. According to the criterion and the GMM, what is found from the relation between RA and AF is that the resistance to tensile and shear is improved in the case of the concrete with NMK.

Pressure-Shear Crack Initiation and Expansion Mechanism of Complex Cracked Rock Mass under the Seepage Stress

This work was to analyze and discuss the propagation mechanism of compressive shear initiation of complex fractured rock mass with seepage stress. The dense marble of Daye Iron mine with bulk density of 26.6 kN/m3 and uniaxial compressive strength of 52.4 MPa was selected as the material, and the upper and lower fracture surfaces were polished smoothly. The crack initiation criterion under compressive shear stress state is analyzed by taking the theory of fracture mechanics and classical mechanics. The coupling equation in the extended finite element simulation is established. The influence of lateral pressure on the crack propagation law, the relationship between lateral pressure and fracture, the initial expansion angle and pressure change law, and the effect of working face length on the crack expansion are analyzed. Results. The initial expansion angle of cracks increases with the increase of lateral pressure, and that of a single crack decreases with the increase of pressure. When other conditions are constant, the crack angle of the crevice also shows a trend of increasing with the increase of lateral pressure. When the lateral pressure becomes smaller, the initial expansion angle is relatively small. With the progress of the step size, the expansion angle shows a gradually decreasing trend, that is, the initial expansion angle gradually decreases with the increase of water pressure. The smaller the working face length, the smaller the expansion length of the floor crack. Conclusion. The expansion of the floor cracks is mainly formed by the tensile shear failure, and the fracture water pressure will reduce the initiation stress, which makes the rock mass more prone to the fracture failure.

Effect of Hydration under High Temperature and Pressure on the Stress Thresholds of Shale

The stress threshold of deep reservoir shale subjected to fracturing fluid immersion is an important factor affecting fracture initiation and propagation during fracturing. However, little information has been reported on the effect on shale of soaking at high temperature and high pressure (HTHP). In this study, immersion tests and triaxial compression tests were carried out at reservoir temperature and in-situ stress on the downhole cores with different mineral compositions. The characteristics of stress thresholds, i.e., crack initiation stress (σci), crack damage stress (σcd), and peak deviator stress (σp), of shale affected by the different times of soaking with low-viscosity fracturing fluid (a) and the different viscosity fracturing fluids (a, b, and c) were investigated. The results show that hydration at HTHP has a significant softening effect on the stress thresholds (σci, σcd, σp) of reservoir shale, but the softening rate varies for samples with different mineral compositions. The crack initiation stresses of quartz-rich and clay-rich shales treated with different soaking times and different soaking media remain almost unchanged in the range of 47 to 54% of the corresponding peak strength, while the crack initiation stresses of carbonate-rich shales are significantly affected. The ratio σcd/σp of quartz-rich shale is significantly affected by the different viscosity fracturing fluids (a, b) and the different times of soaking with low-viscosity fracturing fluid (a), while clay- and carbonate-rich shales are less affected. The results of this study can provide a reference for the fracturing design of deep shale gas development.

A comparison of high strain rate response and adiabatic shear band formation in additively and traditionally manufactured Inconel 718

3D printing of Inconel 718 has been increasingly commercialized, as such research comparing the mechanical properties of additively manufactured (AM) and traditionally manufactured (TM) components in both quasi-static and high rate regimes should be conducted. Herein, the high strain rate material response, as well as the formation of adiabatic shear bands (ASBs) in AM and TM Inconel 718 are studied using a split Hopkinson pressure bar (SHPB) system. A top-hat cylindrical specimen geometry was used to convert the compressive load to shear and conduct high rate shear tests in the SHPB. The quasi-static and high rate stress-strain data reported herein indicates that TM components have at least a 70 MPa higher compressive yield strength. Interestingly, the AM specimens were more susceptible to ASB formation than their TM counterparts. The critical shear strain at which an ASB forms was higher for the TM specimens compared to the AM specimens. This was attributed to the TM material having a higher critical stress for dynamic recrystallization initiation, which is required to ASB formation. The microstructures of the shear zone in the top-hat specimens were examined using an optical microscope (OM), scanning electron microscope (SEM), and transmission electron microscope (TEM). Dynamic recrystallization was observed at the center of the shear affected zone (SAZ) using TEM from material lifted out from the ASB. Due to the plastic deformation in the shear region, the material strain hardens and therefore has a higher hardness than the bulk material. At the center of the shear region, a peak in nano-hardness of 585 HV was recorded on the ASB. The outcome of this research will lead to the prevention, containment, and control of shear instability in AM structures.

Constitutive response and failure progression in digitally fabricated (3D printed) concrete under compression and their dependence on print layer height

Among the several geometry and process-related characteristics that determine the ultimate product quality of 3D printed concrete, one that has gained considerable importance is the height/thickness of the individual layers. Layer height dictates the number of interlayer interfaces, and influences the properties of the layer and the interfaces (both interlayer and inter-filament), for a given mixture and printer characteristics. This paper examines the influence of layer height on the constitutive response and failure of 3D printed concrete specimens under compression, investigated along the direction of layer build-up (or perpendicular to the layer interfaces), which is the dominant plane of loading in 3D printed walls and columns. Plain and steel fiber-reinforced wall elements with two different layer heights (7.5 mm and 15 mm) are printed, from which cylindrical and prismatic specimens are extracted and tested. The uniaxial compressive strength is seen to decrease with increasing layer height. The constitutive relationships of the specimens with different layer heights, along with volumetric strains, enable the extraction of crack initiation stress and unstable crack propagation stress, which are influenced by layer height and the presence of fiber reinforcement. The unstable crack propagation stress is lower than the peak stress, and it decreases with increasing layer height. Digital image correlation (DIC) is used to demonstrate the dominant effect of inter-filament interfaces on the crack propagation response and resultant failure.

Numerical investigation of the mechano-electro-chemical effect of X100 buried pipelines with pre-existing corrosion defects

This study investigates the corrosion kinetics and crack propagation in buried transmission pipelines made of high-strength low alloy steel API X100. Despite its cost-effectiveness and ability to withstand high operating conditions without increasing pipe wall thickness, the corrosion kinetics in near-neutral pH environments for this steel grade is not fully understood. To address this gap, two numerical models were developed. The first model, using COMSOL Multiphysics v5.6, showed higher electrolyte potential at the corrosion defect center due to stress-induced defect growth, increasing corrosion susceptibility. The second model, employing the XFEM approach, evaluated crack initiation, propagation, and von Mises stress distribution along the crack path. This research contributes to a better understanding of corrosion and crack behavior in corroded pipelines, aiding in their performance improvement in near-neutral pH soil environments.

A new method for predicting multi-crack fracture mechanism in the finite plate of red sandstone

A novel theoretical approach was put forth to forecast multi-crack propagation trajectories in a finite plate. First, a weighted residual approach and complex function are used to create the formula for computing the maximum (stress intensity factor) SIF of multi-crack in the finite plate. And then, three cracks were then chosen as a model for computation to determine how the plate size affects the SIF. The formula of multi-branch crack in finite plate is derived and the crack initiation and propagation criterion of multi-crack in finite plate was established. Finally, the propagation paths of three cracked red sandstone in a finite plate were predicted and verified by the uniaxial compression test. It demonstrates that the SIF of multiple cracks in a finite plate is consistently larger than that of an infinite plate. Under the uniaxial compression test, the first crack initiation point is often A2 or B2, and each specimen’s first crack initiation time increases and subsequently reduces when the relative horizontal spacing (Ds’) of cracks varies. The crack initiation stress increases and the unstable stress first increases and then decreases with Ds’. The total crack extension length initially goes down and then goes up. All of the fracture initiation and propagation mechanisms are Mode I. The effectiveness of the multi-crack propagation theory in finite plates is established by the good agreement between predicted and test findings.