Edge Fracture Research Articles

Oxidation-creep interactions for an Hf-doped Ni-based superalloy with different wall thickness at 760 °C

Stress rupture tests of an Hf-containing Ni-based superalloy with different wall thicknesses were carried out at 760 °C/691 Mpa using the RD-100 electronic machine. At the fracture edge, electron backscatter diffraction (EBSD) analysis showed that recrystallization (RS) occurred, and the width of RS increased with increasing sample thickness. The RS induced the intergranular corrosion cracking and accelerated the failure of the sample. At the interior of the substrate, voids were preferentially nucleated at the site of the Hf(Ta)C carbides, and the thinner sample suffered lighter creep damage than the thicker sample. Consequently, the thinner sample had a superior creep life.

Devising procedures for design and verification calculations of the beam-wall with edge breaks under static and cyclic loads

This paper considers a thin-walled steel beam-wall with broken edges, which is part of many structures. The wall of this beam consists of two prismatic parts with a straight transition from a lower wall height to a higher one, forming a broken upper edge together with the edges of the prismatic parts. The bottom straight edge of the wall is attached to the cladding. The beam-wall is affected by static and cyclic nominal loads, which can cause the appearance of elastic-plastic deformations in the stress concentrator. This causes non-fulfillment of static strength and the appearance and growth of fatigue cracks. In the current work, procedures of design and verification calculation of a steel beam-wall with fractured edges at elastic static and cyclic elastic-plastic deformation in the stress concentrator are proposed. The material of the beam is ideal elastic-plastic. Features of the procedures are the possibility of optimal design under conditions of elastic and elastic-plastic deformation, using dependences only for optimal elastic design. A distinctive signature of the procedures is that, through Neiber's formula, elastic-plastic characteristics are not determined by known elastic ones, as usual, but vice versa. According to the established dependences for cyclic elastic-plastic deformations in the concentrator, the theoretical concentration coefficient is determined, which, in turn, is involved in determining the optimal geometric parameters. The procedures give reliable results with nominal symmetrical cyclic loads up to 0.6 of the yield strength. This is because Naber's formula always yields conservative results, causing excess strength. The procedures can be applied separately for stretching-compression and bending, and with their combined action

Traumatic Fracture Treatment: Calcium Phosphate Bone Substitute Case-Control Study in Humerus, Radius, Tibia Fractures-Assessing Efficacy and Recovery Outcomes.

To date, insufficient investigation has been carried out on the biocompatibility of synthetic bioactive bone substitute materials after traumatically induced bone fractures in clinical conditions. This study encompasses the safety, resorption, healing process, and complications of surgical treatment. Our current hypothesis posits that calcium phosphate-based bone substitutes could improve bone healing. In this retrospective case-control study, over 290 patients who underwent surgical treatment for acute fractures were examined. Bone defects were augmented with calcium phosphate-based bone substitute material (CP) in comparison to with empty defect treatment (ED) between 2011 and 2018. A novel scoring system for fracture healing was introduced to assess bone healing in up to six radiological follow-up examinations. Furthermore, demographic data, concomitant diseases, and complications were subjected to analysis. Data analysis disclosed significantly fewer postoperative complications in the CP group relative to the ED group (p < 0.001). The CP group revealed decreased risks of experiencing complications (p < 0.001), arthrosis (p = 0.01), and neurological diseases (p < 0.001). The fracture edge, the fracture gap, and the articular surface were definably enhanced. Osteosynthesis and general bone density demonstrated similarity (p > 0.05). Subgroup analysis focusing on patients aged 64 years and older revealed a diminished complication incidence within the CP group (p = 0.025). Notably, the application of CP bone substitute materials showed discernible benefits in geriatric patients, evident by decreased rates of pseudarthrosis (p = 0.059). Intermediate follow-up evaluations disclosed marked enhancements in fracture gap, edge, and articular surface conditions through the utilization of CP-based substitutes (p < 0.05). In conclusion, calcium phosphate-based bone substitute materials assert their clinical integrity by demonstrating safety in clinical applications. They substantiate an accelerated early osseous healing trajectory while concurrently decreasing the severity of complications within the bone substitute cohort. In vivo advantages were demonstrated for CP bone graft substitutes.

The hydrogen embrittlement mechanisms and hydrogen induced cracking process of selective laser-melted GH4169

This study investigates the hydrogen embrittlement sensitivity and brittle failure mechanism of selective laser-melted GH4169 alloy under hydrogen precharged conditions. Fractographic analysis reveals that a high concentration of hydrogen facilitates the formation of small quasi-cleavage steps near the fracture edge. Additionally, hydrogen promotes the migration of {111} planar dislocations, resulting in shear failure of the δ phases and the nucleation of microvoids. These microvoids then propagate, leading to the development of hydrogen-assisted transgranular cracks along the dislocation slip bands. The deformation behaviors of the δ and γ" phases were characterized using high-resolution transmission electron microscopy.

Aluminium foil-aided ultrasonic welding of NiTi and 304 stainless steel: a study of mechanical properties and interface microstructure

The achievement of an effective connection between superelastic NiTi and 304 stainless steel (304 SS) using ultrasonic welding with varying welding energy inputs has been studied. It has been observed that the addition of aluminium foil serves to a tight joint, which displays two kinds of interfaces where no defects were observed. With the increase in input energy, the peak load exhibits an initial growth phase followed by a decrement phase, and the interfacial heat production intensifies gradually, leading to subsequent interfacial oxidation. When the input energy is 750 J, the joint peak load reaches its maximum at 890 N. The fracture pattern of the joint exhibited both interfacial fracture and edge fracture. In high welding energy situations, Fe4Al13 (a brittle phase) is produced, which deleteriously impact on the joint's performance. Conversely, low welding energy results in the absence of any brittle phase formation.

Microstructural Influence on Fracture Toughness of IF Steel and DP Steel

Interstitial free steels (IF) and Dual-phase (DP) steels are widely used in the automotive industry, their specific application is driven by requirements to optimize the strength-to-weight ratio. Utilizing the full capacity of their plasticity and strain hardenability requires an assessment of edge fracture susceptibility and flangeability. In this work, the ability of the mentioned steels to spreading of deformation along initiated cracks is evaluated by structural and fractographic analyzes. Microstructural restrictions of plasticity are correlated with fracture toughness results, adopting the essential work of fracture (EWF) methodology. Crystallographic analyzes (EBSD) are focused on the role of anisotropy and the deformation texture evolution, affecting the development of plasticity and thus the energy consumption to the fracture.

A non-isothermal phase-field hydraulic fracture modeling in saturated porous media with convection-dominated heat transport

This research aims to extend the isothermal continuum mechanical modeling framework of hydraulic fracturing in porous materials to account for the non-isothermal processes. Whereas the theory of porous media is used for the macroscopic material description, the phase-field method is utilized for modeling the crack initiation and propagation. We proceed in this study from a two-phase porous material consisting of thermomechanically interacting pore fluid and solid matrix. The heat exchange between the fluid in the crack and the surrounding porous environment through the diffusive fracture edges is carefully studied, and new formulations here are proposed. Besides, temperature-dependent solid and fluid material parameters are taken into account, which is of particular importance in connection with fluid viscosity and its effect on post-cracking pressure behavior. This continuum mechanical treatment results in strongly coupled partial differential equations of the mass, the momentum, and the energy balance of the thermally non-equilibrated constituents. Using the finite element method, two-dimensional initial-boundary-value problems are presented to show, on the one hand, the stability and robustness of the applied numerical algorithm in solving the emerged strongly coupled problem in the convection-dominated heat transport state. On the other hand, they show the capability of the modeling scheme in predicting important instances related to hydraulic fracturing and the role of the temperature field in this process. Additionally, they show the importance of using stabilization techniques, such as adding an artificial thermo-diffusivity term, to mitigate temperature fluctuations at high flow velocity.

Perspective on edge fracture

Edge fracture is a viscoelastic instability characterized by the sudden indentation of a fluid’s free surface when the fluid is subjected to a high enough shear rate. During shear rheometry, the fracture can invade the fluid sample, decreasing its contact area with the rheometer fixture and rendering the measurement of viscosity and normal stresses at high-shear rates invalid. Edge fracture can also induce apparent shear banding in the fluid, complicating the interpretation of experimental results. Over the past several decades, empirical and theoretical research has unraveled the physics underlying edge fracture. The knowledge obtained has allowed rheologists to develop techniques to minimize the adverse effect of fracture in their experiments. In recent years, edge fracture has also been used to break up viscoelastic liquid bridges quickly and cleanly, showing its potential to be adapted to the design of functional dispensing nozzles. This Perspective article aims to give a historical overview of edge fracture and suggests research directions to develop methods for suppressing or harnessing the phenomenon to benefit applications of both fundamental and technological importance.

A Numerical Evaluation of Forming Failure of an Aluminum Sheet due to Splitting Damage in Hole Expansion Process

Abstract The reduction of car body weight is the principal issue of car manufacturers for reducing fuel consumption. Aluminum alloys are attractive materials for the automotive industry because they have low density and adequate strength, but they may exhibit crack formation during manufacturing processes. Generally, crack formations emerge because of tool geometry and material anisotropy. Accordingly, determination of the forming limits of aluminum alloys is essential. The hole expansion test (HET) is a significant formability process used in the automotive industry because it gives information about the stretch-flangeability limits of the material. Edge splitting (edge fracture) is a failure type seen in HET, and it limits the stretch-flangeability of the material. Therefore, the prediction of edge splitting is an essential issue for engineers in the automotive industry. In this work, HET of AA6016-O aluminum alloy was simulated with the finite element (FE) method to assess the influence of yield functions on failure prediction in HET. To this end, Hill48, Yld91, and a homogeneous fourth-order polynomial type yield criteria (HomPol4) were selected to identify the anisotropic behavior of the sheet. Analyses were carried out in Marc commercial FE software, and the Hypela2 user subroutine was incorporated into FE code. Thickness distributions in the rolling direction (RD), diagonal direction, and transverse direction (TD) of the part and around the hole edge were also predicted, and it was observed that only the HomPol4 criterion predicted excessive thinning at two locations near the RD and TD, separately. On the other hand, Yld91 and Hill48 predicted lower strain levels when compared with HomPol4. Finally, plastic work distribution around the hole edge was considered, and the predictions were compared with the experimental damaged sample. This comparison showed that HomPol4 predicted a robust plastic work localization in RD, which is consistent with the damaged sample.

Effects of load waveforms on stress corrosion behavior of pipeline steel

The effects of different load waveforms on stress corrosion cracking (SCC) of X70 pipeline steel were studied by means of fluctuating slow strain rate tensile test (F-SSRT). The results show that the SCC sensitivity of F-SSRT specimens with square wave loading is weak, and the fracture is straight; the SCC sensitivity of F-SSRT specimens with superimposed triangular wave loading is in the middle, and the fracture edge is serrated; The F-SSRT specimens with superimposed sine wave loading own the strongest SCC sensitivity, and the fracture is an oblique section fracture extending along the 45° direction. Different superimposed loads with different waveforms result in different SCC test results including different fracture morphology and change rules, which are caused by the change of the direction and magnitude of the applied force of the superimposed load, not only attributing to the different superimposed load energy.

Optimization of Mathematical Function-Shaped Fracture Distribution Patterns for Multi-Stage Fractured Horizontal Wells

A conventional oil and gas well does not have a natural production capacity, which necessitates a hydraulic fracturing operation. The effectiveness of the fracturing directly impacts the economic benefit of a single well. Among the various parameters, including fracture spacing, fracture width, and conductivity, fracture half-length is one of the main influencing factors on the productivity of horizontal wells. For conventional homogeneous reservoirs, research mainly focuses on fracture patterns with equal fracture lengths. However, in actual production processes, due to mutual interference and the superimposition of drainage areas between fractures, the production distribution of each fracture is non-uniform. Typical fracture distribution patterns mainly include uniform, staggered, dumbbell, and spindle. While many believe that the dumbbell-shaped fracture distribution pattern has the best effect, there has been no quantitative study on the length of each fracture under the dumbbell-shaped pattern. Based on this, this paper proposes a modeling approach for function-shaped fracture distribution that takes advantage of the high production of edge fractures and the low output of middle fractures in horizontal wells. The influence of this approach on production capacity is studied. Constant, linear, and parabolic functions are used to establish the relationship between fracture position and fracture half-length, optimizing the fracture distribution function to achieve the best production effect. This method can guide the horizontal well fracture distribution in the block to maximize productivity. The results show that the parabolic function-shaped model is better than the linear function-shaped model and the constant function-shaped model is the least effective. The research presented in this paper offers a new idea for optimizing on-site fracturing plans. It utilizes mathematical expressions to describe the parameters that affect productivity, which provides valuable guidance for designing multi-stage fractured horizontal wells in the field. In the future, this research will be extended by exploring the optimal fracture distribution function under different formation conditions.

Design and milling performance investigation of a new PCBN multi-edge ball milling and grinding composite tool

The structure and material of micro tools have a significant impact on their machining performance. To improving the machining performance and wear resistance of micro milling tools, a new PCBN multi-edge ball milling and grinding composite tool (ME-BMGT) with multi-edge and spherical flank is proposed. The micro milling experiment results show that, compared with the cemented carbide double-edged ball-end milling tool (OMBMT), the micro groove morphology machined by the ME-BMGT has grinding texture characteristics, the micro groove surface quality is better, and the burr height is smaller. The wear morphology shows that the wear form of ME-BMGT is adhesive wear, while the wear form of OMBMT is cutting edge fracture and adhesive wear. The ME-BMGT provides superior wear resistance.

Edge fracture of the first and third-generation high-strength steels: DP1000 and QP1000

Advanced high-strength steels (AHSS) have shown profound progress in improving tensile ductility or global formality in the last decades over three generations. For a complete assessment of both the global and local formability, this study aims to characterize and compare the tensile and edge fracture behavior of the first and third-generation AHSS (dual-phase steel and quenching & partitioning steel) with the same nominal strength level of 980 MPa. Uniaxial tensile tests are performed to characterize the tensile properties. Hole expansion tests are conducted with two edge conditions based on separated preparation techniques (waterjet with polishing and punching) to investigate the edge fracture for both materials. The hole expansion ratios and edge fractures are compared between two materials and two edge conditions. It is concluded that the investigated QP1000 has promoted global formability while the DP1000 shows better local formability due to its damage-tolerant and crack-resistant responses.

Effect of pre-strain on edge formability of high strength steels for chassis applications

There is a high level of uncertainty in the prediction of edge cracking during the design and manufacturing of high strength sheet metal products. Edge ductility is a complex parameter to measure since it is not an intrinsic property of the material, but it also depends on the trimming strategy/parameters that have been applied to the edge (edge preparation method, cutting/punching clearance, etc.). Furthermore, most forming processes involve more than one operation where the material can be deformed in a first stage, then trimmed or punched and further deformed in a final forming step to obtain the desired shape. Therefore, in order to design a robust and safe forming process able to predict the risk of edge cracking, it is crucial to understand the influence of pre-strain on the residual formability of trimmed edges. This paper analyses the effect of different pre-strain levels and paths (uniaxial tension, plane strain and equi-biaxial stretching) on the sheared edge ductility of a Complex Phase (CP) steel and a high strength low alloy (HSLA) steel used for automobile chassis applications. To this purpose, rectangular specimens are cut out from pre-strained samples and punched. Hole Tension Tests (HTTs) in combination with Digital Image Correlation (DIC) are carried out to determine the edge fracture strain of undeformed and pre-strained samples. The results are discussed in terms of major strains obtained from DIC. The proposed methodology allows describing the edge cracking sensitivity of high-strength steel sheets as a function of the pre-deformation state and can be useful to predict the risk of edge cracking more accurately in forming simulations.

Intelligent Detection Method for Concrete Dam Surface Cracks Based on Two-Stage Transfer Learning

The timely identification and detection of surface cracks in concrete dams, an important public safety infrastructure, is of great significance in predicting engineering hazards and ensuring dam safety. Due to their low efficiency and accuracy, manual detection methods are gradually being replaced by computer vision techniques, and deep learning semantic segmentation methods have higher accuracy and robustness than traditional image methods. However, the lack of data images and insufficient detection performance remain challenges in concrete dam surface crack detection scenarios. Therefore, this paper proposes an intelligent detection method for concrete dam surface cracks based on two-stage transfer learning. First, relevant domain knowledge is transferred to the target domain using two-stage transfer learning, cross-domain and intradomain learning, allowing the model to be fully trained with a small dataset. Second, the segmentation capability is enhanced by using residual network 50 (ResNet50) as a UNet model feature extraction network to enhance crack feature information extraction. Finally, multilayer parallel residual attention (MPR) is integrated into its jump connection path to improve the focus on critical information for clearer fracture edge segmentation. The results show that the proposed method achieves optimal mIoU and mPA of 88.3% and 92.7%, respectively, among many advanced semantic segmentation models. Compared with the benchmark UNet model, the proposed method improves mIoU and mPA by 4.6% and 3.2%, respectively, reduces FLOPs by 36.7%, improves inference speed by 48.9%, verifies its better segmentation performance on dam face crack images with a low fine crack miss detection rate and clear crack edge segmentation, and achieves an accuracy of over 85.7% in crack area prediction. In summary, the proposed method has higher efficiency and accuracy in concrete dam face crack detection, with greater robustness, and can provide a better alternative or complementary approach to dam safety inspections than the benchmark UNet model.

Recycled polystyrene/polyvinylpyrrolidone/reduced graphene oxide nanocomposites for optoelectronic devices

Polymer nanocomposites based on recycled polystyrene (PS) and polyvinylpyrrolidone (PVP) with various reduced graphene oxide (rGO) loadings were prepared through a facile casting technique for enhancing the electrical conductivity of the insulator waste polystyrene to be applicable in electronic devices. The prepared nanocomposites were investigated by different techniques. FTIR analysis shows a reduction and shift of the main vibrational peaks of the blend, which confirms the introduction of (rGO) to the polymeric matrix, while XRD diffractograms provide complementary evidence for the transformation of graphene oxide into (rGO). The SEM image of the fractured edge of the sample points to a homogenous distribution of the PVP inside the major phase of the PS matrix. Moreover, the TEM image shows graphene oxide nanoparticles appearing in the form of dark lamellar structures with some light dots on a gray background, representing the polymeric domain. Besides, the TGA shows the existence of (rGO) led to some shifts in the PS and PVP onset decomposition temperatures when compared to the reference blend sample. Besides, the conductivity and dielectric properties of the prepared nanocomposites were characterized over a wide frequency range. Introducing (rGO) considerably enhanced their dielectric constant and ionic conductivity. The conductivity of these nanocomposites ranged from 10−11 to 10−6 S/m. The dielectric constant and dielectric loss of these composites were tested through frequencies, 0.1 Hz - 1 MHz, at 30 °C. The obtained values of the dielectric constant, loss tangent, and DC conductivity (σdc) suggested that the prepared nanocomposites could be used in various technological sectors such as energy storage, electronics, anti-static, and electro-static dissipation applications.

Enhancing endoscopic foraminal decompression in adult isthmic spondylolisthesis: the potential influence of lateral recess isthmic spur and our case series of an innovative craniocaudal interlaminar approach via unilateral biportal endoscopic spinal surgery

BackgroundThe NASS guideline cannot recommend any of the surgical treatment options toward adult isthmic spondylolisthesis (AIS) since 2014. After the introduction of endoscopic decompression, instead of treating the spondylolysis itself, treatment can specifically target the refractory radicular pain developed during the degeneration progress without devastating the peripheral soft tissue. However, we noticed that endoscopic transforaminal decompression seems to be less effective in AIS compared to other types of degenerative spondylolisthesis. Thus, we came up with a novel craniocaudal interlaminar approach, utilizing the proximal adjacent interlaminar space to perform bilateral decompression and observed the pathoanatomy of pars defect directly and tried to identify the cause of decompression failure.MethodsFrom January 2022 to June 2022, 13 patients with AIS underwent endoscopic decompression via the endoscopic craniocaudal interlaminar approach and were followed up for at least 6 months. Visual Analogue Scale, Oswestry Disability Index and MacNab scores were recorded to monitor patients’ clinical recovery. All endoscopic procedures were recorded and reviewed to illustrate the pathoanatomy.ResultsFour patients required minor revision via the same technique. One of them required it due to incomplete isthmic spur resection, two due to neglected disc protrusion, and the other due to root subpedicular kinking in higher grade anterolisthesis. All patients’ clinical condition improved significantly subsequently. After reviewing the endoscopic video, we have observed that the hook-like, ragged spur originating from the isthmic defect extends beyond the region around the foramen. Instead, it extends proximally into the adjacent lateral recess, resulting in impingement along the fracture edge above the index foramen and, in some cases, even in the extraforaminal area.ConclusionsThe broad spanning isthmic spur extending to the proximal adjacent lateral recess might be the reason why the transforaminal approach yielded less satisfactory results due to the incomplete decompression result from approach related restriction. Our study demonstrated an optimistic outcome by applying decompression from the upper level. Therefore, we propose that the craniocaudal interlaminar approach might be a better route for decompression in adult isthmic spondylolisthesis.

Analysis of the causes and clinical results of vertebral fracture during oblique lateral lumbar interbody fusion

To analyze the causes of vertebral fracture during oblique lateral interbody fusion in the treatment of lumbar spondylopathy, summarize the clinical results, and propose preventive measures. Retrospective analysis was made on the data of 8 cases of lumbar spondylopathy and vertebral fracture treated by oblique lateral interbody fusion in three medical centers from October 2014 to December 2018. All were female, aged from 50 to 81 years with an average of 66.4 years. Disease types included 1 case of lumbar degenerative disease, 3 cases of lumbar spinal stenosis, 2 cases of lumbar degenerative spondylolisthesis and 2 cases of lumbar degenerative scoliosis. Preoperative dual energy X-ray bone mineral density test showed that 2 cases had T-value >-1 SD, 2 cases had T-value -1 to -2.5 SD, and 4 cases had T-value <-2.5 SD. Single segment fusion was in 5 cases, two segment fusion in 1 case and three segment fusion in 2 cases. Four cases were treated with OLIF Stand-alone and 4 cases were treated with OLIF combined with posterior pedicle screw fixation. Postoperative imaging examination showed vertebral fracture, and all of them were single vertebral fracture. There were 2 cases of right lower edge fracture of upper vertebral body at fusion segment, 6 cases of lower vertebral body fracture at fusion segment, and 6 cases with endplate injury and fusion cage partially embedded in vertebral body. Three cases of OLIF Stand-alone were treated with pedicle screw fixation via posterior intermuscular approach, while one case of OLIF Stand-alone and four cases of OLIF combined with posterior pedicle screw fixation were not treated specially. The 5 cases of initial operation and 3 cases of reoperation did not show wound skin necrosis or wound infection. The follow-up time was from 12 to 48 months with an average of 22.8 months. Visual analogue scale (VAS) of low back pain was preoperative decreased from 4 to 8 points (averagely 6.3 points) and postoperative 1 to 3 points (averagely 1.7 points) at the final follow-up. Oswestry disability index (ODI) was preoperative 39.7% to 52.4% (averagely 40.2%), and postoperative 7.9% to 11.2% (averagely 9.5%) at the final follow-up. During the follow-up, there was no loosening or fracture of the pedicle screw system, and no lateral displacement of the fusion cage;however, the fusion cage at the vertebral fracture segment had obvious subsidence. The intervertebral space height of vertebral fracture segment was preoperaive 6.7 to 9.2 mm (averagely 8.1 mm), and postoperative 10.5 to 12.8 mm (averagely 11.2 mm). The improvement rate after operation was 37.98% compared to preoperative. The intervertebral space height at final follow-up was 8.4 to 10.9 mm (averagely 9.3 mm), and the loss rate was 16.71% compared with that after operation. At the final follow-up, interbody fusion was achieved in all cases except for one that could not be identified. The incidence of vertebral fracture during oblique lateral interbody fusion in the treatment of lumbar spondylopathy is lower, and there are many reasons for fracture, including preoperative bone loss or osteoporosis, endplate injury, irregular shape of endplate, excessive selection of fusion cage, and osteophyte hyperplasia at the affected segment. As long as vertebral fracture is found in time and handled properly, the prognosis is well. However, it still needs to strengthen prevention.

Numerical study of abrasive water jet rotational slits in hard rock using a coupled SPH-FEM method

Use of abrasive water jet (AWJ) to break rock is a promising technology for improving the speed of tunnelling hard rock roadways. In this study, smooth particle hydrodynamics (SPH) and the finite element method (FEM) were coupled to develop a method that was used to simulate the abrasive water jet slit rock. The failure patterns and crack evolution were analysed. Moreover, the effects of parameters of AWJ on rock slit were studied. Furthermore, the motion behaviour of abrasive particles after collision with hard rock is discussed. The results indicated that the optimum mass concentration and diameter of AWJ were 15% and 1.6 mm, respectively, and the depth of slits cut in rocks increased nonlinearly with increasing pressure. Instantaneous failure and multi-step cumulative failure occurred at the centres and edges of rock fractures, respectively. For impacts at large incident angles, the cumulative damage velocities were greater for the central cracks than the radial cracks. The impact velocity had the greatest effect on the propagation of the central cracks, while the effect on the radial cracks was relatively small. The equivalent stress caused by impact was the primary reason for the failure of rock elements at the main impact site, and the cracks in rock were mainly caused by tensile stress. The damage of rock elements accumulated in steps similar to the shape of stairs. Damage accumulated faster when the pressure peak was large and the pressure undulated frequently. The findings of this study provide a theoretical reference for optimizing the parameters of AWJ and increasing the speed of excavating in hard rock.

Water-induced weakening retrogressive landslides: a study on the progressive failure process and formation mechanism of trailing edge fracture surfaces

Water-induced weakening retrogressive landslides: a study on the progressive failure process and formation mechanism of trailing edge fracture surfaces