Failure Angle Research Articles

Designing optimized geometry and fiber orientation of composites for dynamic tension via artificial intelligence

Machine learning is quickly becoming an invaluable tool for examining large databases to find patterns and predictions based on similar parameters tested in previous studies. A natural application of this subset of artificial intelligence revolves around material data sets where tests are repeated for basic studies (e.g. tension, compression, bending, or shear) and extrapolating the data for tests not yet considered. Dynamic testing and validation with machine learning is examined here, as a significant time and cost is required for understanding larger-sized specimens (cm scale and larger) especially when the samples are composite materials in tension. This is due in part to the challenges involved in ensuring failure at the region of interests for an anisotropic material and minimizing the number of repeated tests. In this study, the data sets were generated artificially via finite element analysis with failure, and a machine learning code applied to infer the shape of the tensile test coupon knowing only the failure and stress field. Then the algorithm was run to generate a library of ideal coupon geometries based on ply angle and area location of failure within the test specimen. The result is a highly efficient prediction algorithm that can create the ideal specimen shape for tensile testing at speeds orders of magnitude faster than comparable finite element codes.

Numerical simulation of mechanical properties and damage process of carbon nanotube concrete under triaxial compression and splitting conditions

To investigate the mechanical properties and failure processes of carbon nanotube concrete, a three-dimensional meso-scale finite element model of concrete was constructed. Using ABAQUS software, numerical simulations were conducted on concrete samples with different carbon nanotube concentrations under triaxial compression and splitting conditions. The results indicate that under splitting conditions, the failure of the specimens initially occurs along the loading direction from both ends, with few cracks and slow propagation. Subsequently, the cracks rapidly expand, penetrating the entire specimen, leading to the formation of a macro-fracture surface with a crack aligned with the loading direction. This failure mode manifests as a straight crack. At the same loading rate, the tensile strength of the specimens with different carbon nanotube concentrations increases to varying degrees during splitting failure, with a maximum increase of 45.10% to 4.15 MPa. nder triaxial compression conditions, the main failure mode of the specimens exhibits shear failure characteristics. As the confining pressure gradually increases, the failure angle of the specimens enlarges. Under low confining pressure, there are fewer wing-shaped tensile cracks at the shear failure surface of the specimens. As the confining pressure increases, irregular shear failures and multiple shear planes appear in the specimens, resulting in more complex failure modes. For specimens with the same carbon nanotube concentration, the triaxial compressive strength of carbon nanotube concrete specimens increases with increasing confining pressure. The triaxial compressive strengths of the specimens under confining pressures of 5 MPa, 10 MPa, 15 MPa, and 20 MPa are 90.48 MPa, 122.72 MPa, 137.22 MPa, and 172.65 MPa, with strength increases of 35.63%, 51.66%, and 90.81%, respectively.

Failure mechanism of a tunnel in a soil–rock mixture based on a new combined finite–discrete element method

The mechanical properties and failure characteristics of soil–rock mixtures (SRMs) directly affect the stability of tunnels constructed in SRMs. A new SRM modelling method based on the combined finite–discrete element method (FDEM) was proposed. Using this new SRM modelling method based on the FDEM, the mechanical characteristics and failure behaviour of SRM samples under uniaxial compression, as well as the failure mechanism of SRMs around a tunnel, were further investigated. The study results support the following findings: (1) The modelling of SRM samples can be achieved using a heterogeneous rock modelling method based on the Weibull distribution. By adjusting the relevant parameters, such as the soil–rock boundaries, element sizes and modelling control points, SRM models with different rock contents and morphologies can be obtained. (2) The simulation results of uniaxial compression tests of SRM samples with different element sizes and morphologies validate the reliability and robustness of the new modelling method. In addition, with increasing rock content, VBP (volumetric block proportion), the uniaxial compressive strength and Young’s modulus increase exponentially, but the samples all undergo single shear failure within the soil or along the soil–rock interfaces, and the shear failure angles are all close to the theoretical values. (3) Tunnels in SRMs with different rock contents all exhibit X-shaped conjugate shear failure, but the fracture network propagation depth, the maximum displacement around the tunnel, and the failure degree of the tunnel in the SRM roughly decreases via a power function as the rock content increases. In addition, as the rock content increases, such as when VBP = 40%, large rocks have a significant blocking effect on fracture propagation, resulting in an asymmetric fracture network around the tunnel. (4) The comparisons of uniaxial compression and tunnel excavation simulation results with previous theoretical results, laboratory test results, and numerical simulation results verify the correctness of the new modelling method proposed in this paper.

Does double pre-notches have a greater impact than single pre-notch on the mechanical and fracture behavior of rock? Insights from three-point bending tests using the numerical approach of grain-based model

The mechanical performance of rock masses is significantly impacted by the existence of cracks. Distribution of the cracks may result in different mechanical or fracture behaviors of rock. To gain a preliminary understanding of such problems, a series of numerical tests of three-point bending (TPB) are designed and carried out with the consideration of single pre-notch and double pre-notches. The numerical method of grain-based model (GBM) approach is employed in this paper, with a validation implemented by comparing the results with previous experiments to demonstrate the reliability of this model. Afterward, a comprehensive investigation, including the mechanical behavior, strength characteristics, crack evolution and progressive failure mechanism of the above mentioned TPB tests are conducted. The conclusions are as follows: (1) During TPB tests, as the offset distance increases, the fracture mode of the single pre-notched specimens gradually transitions from Mode I to Mode II, with the peak fracture toughness occurring at a mixed Mode I-II fracture condition (2p/s = 0.4). Moreover, the failure angle, notch open degree and expansion area all tend to rise regardless of specimens of single or double pre-notches. (2) A thorough exploration of crack evolution shows that the specimens primarily fracture during the crack propagation and failure stages. Shear failure predominates among these stages, with microcracks mostly occurring inside the rock mineral grains. (3) When offset distance increases to a certain degree (2p/s = 0.8), the fracture of specimen ceases to be governed by the pre-notch; instead, it occurs directly from the middle of the beam specimen. This phenomenon can be attributed to the reduction of stress concentration at the notch tip, as inferred from analysis of the contact force chain. (4) In double pre-notched specimen, microcracks initiate at both pre-notches, but the final failure results from crack propagation at one notch tip. Compared to single pre-notched specimen, the presence of double pre-notches exhibits superior fracture resistance performance.

Borehole Condition and Limit Pressure Differential Analysis in Carbonate Reservoirs

In deep carbonate reservoirs, testing and production with open-hole completion can help release the maximum production capacity. However, because the reservoir is subjected to high in situ stress, if the test pressure differential is too large, the wellbore collapse and instability will occur easily, causing downhole accidents. Therefore, it is necessary to determine the state of the borehole during the open-hole test in the carbonate reservoir and analyze the ultimate test pressure differential accordingly to ensure test safety. Considering the characteristics of open-hole completion, based on the mechanical properties of the carbonate reservoir and the stress distribution around the borehole during testing, a calculation method of the elastic zone, plastic zone, and residual failure zone around the open-hole wellbore was proposed. Regarding actual engineering data, a criterion for the overall stability of the open-hole section had been established from three aspects: the volume ratio of the plastic zone; the failure zone around the wellbore; and the failure angle on the borehole wall. According to this criterion, it is possible to determine the ultimate pressure differential during the open-hole test process and provide theoretical support for designing the open-hole completion test and production parameters for deep carbonate reservoirs.

Tensile resistance and shear-tension interaction relationship of T-type perfobond rid shear connectors

This study aims to investigate the mechanical performance of T-type perfobond rib (T-type PBL) shear connectors under complex load cases. Initially, the experimental tests were conducted and finite element analyses (FEA) were performed. Subsequently, a parametric study was carried out to assess the impact of geometric parameters on tensile resistance and the effect of tension ratio on the shear-tension interaction resistance of T-type PBL connectors. Finally, based on the test and FEA results, prediction methods were developed for evaluating the tensile resistance and shear-tension interaction relationship of T-type PBL connectors. The test results showed that the pull-out of the concrete below the flange led to the failure of T-type PBL shear connectors under tension. The concrete failure angles were approximately 33°. The failure under shear was manifested as concrete collapse and connector yielding. The ultimate capacity decreased with the increase in tension ratio. The specimens with tension ratios of 25%, 45%, and 65% decreased 7.9%, 16.3%, and 24.2%, respectively, compared to the specimen under pure shear. The parametric study suggested that the rib height and perforated rebars were the main factors impacting the tensile resistance of T-type PBL shear connectors. When the tension ratio reached 55% of the ultimate, the failure mode of the shear connectors was dominated by the pull-out of the concrete. The tensile resistance evaluation formula was verified by the test and FEA results, demonstrating an average calculated-to-FE-results ratio of 0.99 with a standard deviation of 0.04. The suggested shear and tension interaction relationship for T-type PBL connectors had reliable predictive outcomes, with a coefficient of variation of 0.02. This study could provide guidance for the design of T-type PBL shear connectors and promote the application in long-span composite structures.

Application of cohesive soil flow limit and slope critical flow angle

To investigate the relationship between moisture content in cohesive soils during spontaneous liquefaction and their corresponding critical slope failure angles. This study modified the liquid limit test apparatus originally developed by A. Atterberg in 1911, adapting it into a liquid-flow limit test apparatus. On-site soils from three actual cases of slope failures in Xiaolin Village, Jiasian District, Kaohsiung City, as well as soils from slope failures along the banks of Meilong River and Zengwun River were used for experiments involving different soil moisture content and slope failure angles. Based on the experimental findings, the moisture content which cohesive soils undergo spontaneous liquefaction was designated as the Flow Limit (FL), corresponding to the downslope angle at which circular failure occurs. This value represents the critical sliding angle at which spontaneous liquefaction occurs as a results of soil saturation. It also represents the maximum slope angle for exposed mudrock or clay slopes, and establishes the critical slope angle for vegetated slopes. Beyond this critical FL angle, all vegetation is susceptible to loss due to soil liquefaction. Furthermore, this study conducted FL tests on soils from thirteen tree holes in Kaohsiung City, two mountain slopes in Fengshan District, and the silty clay responsible for property damage and injuries during a landslide in Yanchao District on September 29, 2016, as a means of validation. The consistent test results observed reaffirm that different soils exhibit similar spontaneous liquefaction angles and flow limit behavior. These FL test results demonstrate a consistent pattern, reinforcing the notion of distinct curve characteristics that can be replicated across diverse soil compositions.

Development of a rock-bit interaction analytical model by considering the in-situ stresses for a bottom-hole element

PDC drill bits are an important part of drilling engineering, but improper selection or design can lead to decreased performance and increased costs. Then, accurate modeling of rock-bit interaction for Oil/gas well drilling is critical. Although several mathematical models are presented for this purpose, they have not been able to present a comprehensive model for the rock-bit interaction. In-situ stresses in real drilling conditions affect the force required for rock failure. However, the models proposed so far either have not considered the effects of in-situ stresses or have assumed that the rock failure angle in the downhole conditions is equal to the one calculated in the atmospheric conditions. In this work, after reviewing the background of studies conducted on the rock and bit interaction, with an analytical method, stresses applied to the bottom hole element are examined, including stresses resulting from bit and in-situ stresses. Based on the principle of superposition, the total stress imposed on the bottom hole element is calculated to determine the angle and force of rock cutting. Finally, a novel mathematical model of rock-bit interaction in vertical and deviated oil/gas wells drilling by Considering In-Situ Stresses is presented. Also, the study compares the current model to the Nishimatsu and Xin Ling models using data from a southwest field in Iran. The results show that the simplifying assumption made by previous models leads to a significant underestimation of the failure angle and the amount of force required to the rock failure, with reductions of up to 21% and 48%, respectively, in the case of a vertical well. In an inclined well, the current model predicts cutting force at about 0.14 of that predicted by the previous model.

Experimental study on the physical and mechanical properties of carbonatite rocks under high confining pressure after thermal treatment

AbstractOil and gas exploration studies have been increasingly moving deeper into the earth. The rocks in deep and ultra‐deep reservoirs are exposed to a complex environment of high temperatures and large geo‐stresses. The Tarim oilfield in the Xinjiang Uygur Autonomous Region (Xinjiang for short), China, has achieved a breakthrough in the exploration of deep hydrocarbon reservoirs at a depth of over 9000 m. The mechanical properties of deep rocks are significantly different from those of shallow rocks. In this study, triaxial compression tests were conducted on heat‐treated carbonatite rocks to explore the evolution of the mechanical properties of carbonatite rocks under high confining pressure after thermal treatment. The rocks for the tests were collected from reservoirs in the Tarim oilfield, Xinjiang, China. The experiments were performed at confining pressures ranging from atmospheric to 120 MPa and temperatures ranging from 25 to 500°C. The results show that the critical confining pressure of the brittle–ductile transition increases with increasing temperature. Young's modulus is negatively correlated with the temperature and positively correlated with the confining pressure. As the confining pressure increases, the failure mode of the specimens gradually transforms from shear fracture failure into “V”‐type failure and finally into bulging failure (multiple shear fractures). With increasing temperature, the failure angle tends to decrease. In addition, an improved version of the Mohr‒Coulomb strength criterion with a temperature‐dependent power function was proposed to describe the failure strength of carbonatite rocks after exposure to high temperature and high confining pressure. The surface of the strength envelope of this criterion is temperature dependent, which could reflect the strength evolution of rock under high confining pressures after thermal treatment. Compared with other strength criteria, this criterion is more capable of replicating physical processes.

Study on the Damage Characteristics and Internal Variable Modeling of Single-Fracture Sandstone under the Coupling Effect of Freeze–Thaw and Fatigue Load

The fractured rock mass in the western cold region is affected by freezing and thawing disasters and is prone to local damage and fracture along the fissures’ ends. The fatigue damage induced by repeated frost heave and traffic loads seriously endangers the stability of cold region roadbed. This paper selects sandstone as the research object. Firstly, 20 freeze–thaw cycles were performed on fractured sandstone samples with different inclination angles of 30°, 45°, 60°, and 90°. Subsequently, triaxial compression and triaxial fatigue loading tests were conducted to explore the mechanical properties and fracture morphology evolution mechanism during the compression process of freeze–thaw fractured sandstone. Nuclear magnetic resonance technology (NMR) was used to measure the H-containing fluid inside rock pores. The microscopic damage characteristics inside the rock were analyzed from the NMR T2 relaxation spectrum signal and pore size distribution characteristics. Based on the internal variable theory of continuum mechanics, a fatigue model of freeze–thaw fractured sandstone with different inclination angles was established. The results show that sandstone strength was negatively correlated with the fracture dip angle, and the axial deformation and shear failure angle were positively correlated with the fracture dip angle. The mechanical properties of the sandstone were deteriorated by fatigue loading. When the crack angle was 90°, the fatigue failure strength of the rock sample was the lowest. The T2 spectrum distribution of the fractured sandstone mainly had three peaks and the pore size was mainly medium and small pores. There was a small leftward shift after freeze–thaw cycles and fatigue loading. The T2 spectrum area was significantly affected by fatigue loading, with the highest rate of change at a crack angle of 30°. Through the fine correspondence between the axial residual deformation and the deformation modulus, a fatigue model with different crack inclination angles was established using the axial residual deformation as the internal variable, and the rationality of the model was verified by fatigue loading tests.

Combination effect of Chinese kidney-tonifying granules and platelet-rich plasma gels on enhancing bone healing in rat models with femur defects

BackgroundThe traditional Chinese kidney-tonifying granules, known as Bushen Zhongyao Keli (BSZYKL), have been found to stimulate calcium salt deposition, enhance bone formation, and foster bone growth within the bone matrix at sites of bone defects. On the other hand, platelet-rich plasma (PRP) is enriched with various growth factors capable of facilitating the repair of bone defects and enhancing bone strength following fractures. This study is dedicated to investigating the combined efficacy of BSZYKL and PRP gel (PRP-G) in the treatment of bone defects.MethodsWe established a femur defect model in male Sprague-Dawley (SD) rats and filled the defect areas with autologous coccygeal bone and PRP-G. For 8 consecutive weeks, those rats were given with intragastric administration of BSZYKL. Biomechanical characteristics of the femur were assessed 28 days after intramuscular administration. On day 56, bone formation was examined using X-ray, micro-CT, and transmission electron microscopy. Additionally, we analyzed the expression of bone formation markers, Runx2 and Osterix, in femur tissues through qPCR, Western blotting, and immunohistochemistry.ResultsRats receiving the combined treatment of BSZYKL and PRP-G exhibited drastically enhanced femoral peak torsion, failure angle, energy absorption capacity, and torsional stiffness as compared to control group. This combination therapy also led to marked improvements in bone volume, mass, and microarchitecture, accompanied by elevated expressions of Runx2 and Osterix when compared to control group. Notably, the synergistic effects of BSZYKL and PRP-G in treating bone defects surpassed the effects of either treatment alone.ConclusionsThese findings revealed the potential of BSZYKL in combination with PRP-G in improving bone defects.

Torsional Behavior of CFRP Strengthening of SCC Box Beams with Web Openings under Repeated Loading

Monotonic and repeated torsional loading frequently occur in many concrete structures. The loading and unloading action of repeated torsion places structures under greater damage and risk of failure than other types of loading. Therefore, keeping old infrastructure maintained, repaired, and upgraded has become an important priority and requirement. In this research, experimental work was done on pre-cracked self-compacted reinforced concrete box beams repaired (strengthened) with CFRP sheets to investigate the effect of web openings and CFRP sheets on the torsional behavior of tested specimens. Two groups of sixteen half-scale CFRP-strengthened RC box beams with different numbers of circular openings in the web, with a diameter of about 30% of the hollow box depth, were investigated. The first group (I), tested under monotonic torsional loading, comprised four unstrengthened RC beams and another four beams strengthened with CFRP strips, whereas the second group (II) consisted of the same details as the first one tested under repeated loading. The range of the repeated loading was about 30% and 60% of the ultimate load of the monotonic tests. The effect of opening and repairing (strengthening) with CFRP on the ultimate and cracking Torques, Torque-Twist Angle, steel strains, and modes of failure were displayed and discussed. Cracking and ultimate torques and the angle of twist of the tested beams were significantly reduced due to openings in the web, accompanied by increased values for the steel strains due to the presence of openings. However, the results showed that using CFRP strengthening techniques increased torsional strength, angle of twist, and decreased steel strain for all the tested beam specimens. Results revealed that repeated loading causes inelastic deformations in proportion to the number of loading cycles, more than static load deformations. Doi: 10.28991/CEJ-2023-09-12-06 Full Text: PDF

Teardrop and Parabolic Lens Yield Curves for Viscous‐Plastic Sea Ice Models: New Constitutive Equations and Failure Angles

AbstractMost viscous‐plastic sea ice models use the elliptical yield curve. This yield curve has a fundamental flaw: it excludes acute angles between deformation features at high resolution. Conceptually, the teardrop (TD) and parabolic lens (PL) yield curves offer an attractive alternative. These yield curves feature a non‐symmetrical shape, a Coulombic behavior for the low‐medium compressive stress, and a continuous transition to the ridging‐dominant mode, but their published formulation leads to negative or zero bulk and shear viscosities and, consequently, poor numerical convergence with stress states at times outside the yield curve. These issues are a consequence of the original assumption that the constitutive equations of the commonly used elliptical yield curve are also applicable to non‐symmetrical yield curves and yield curves with tensile strength. We derive a corrected formulation for the constitutive relations of the TD and PL yield curves. Results from simple uni‐axial loading experiments show that with the new formulation the numerical convergence of the solver improves and much smaller nonlinear residuals after a smaller number of total solver iterations can be reached, resulting in significant improvements in numerical efficiency and representation of the stress and deformation fields. The TD and PL yield curves lead to smaller angles of failure that better agree with observations. They are promising candidates to replace the elliptical yield curve in high‐resolution pan‐Arctic sea ice simulations.

Cohesive granular columns collapsing: Numerics questioning failure, cohesion, and friction

Simulations of the failure of cohesive granular steps with varying intensities of the contact adhesive force are presented. The simulations are compared with experimental and numerical studies of wet shear flows [Badetti et al., J. Rheol. 62, 1175–1196 (2018) and Khamseh et al., Phys. Rev. E 92, 022201 (2015)], computing the apparent friction coefficient. We observe consistent behaviors. We reproduce the dependence between the macroscopic cohesion and the contact adhesion [Rumpf, Chem. Ing. Tech. 42, 538–540 (1970) and Richefeu et al., Phys. Rev. E 73(5), 051304 (2006)] observed experimentally for sticky polymer-coated grains, as well as the range of friction explored [Gans et al., Phys. Rev. E 101, 032904 (2020)]. Focusing on the interface between moving and static materials, and assuming a linear failure, we infer the orientation of the failure plane with the horizontal. We disclose a nonmonotonous evolution with the intensity of the contact adhesion. Assuming an ideal Coulomb material allows for proposing an interpretation to this nonmonotonous behavior. Although the systems are past incipient failure, we consider an edge of material at equilibrium, for which the failure angle is related to the internal frictional properties of the material. In this framework, the nonmonotonous evolution of the failure orientation may hint at a cohesion-induced weakening mechanism, by which stronger contact adhesion involve weaker friction.

Acoustic emission parameters and energy dissipation law of cyclic load and unload damage of dihydrate gypsum under different loading rate

In order to explore the effect of loading rate on physical and mechanical properties of dihydrate gypsum, cyclic loading and unloading mechanical tests were carried out at different loading rates. Test results were analyzed from the aspects of stress-strain curve, energy distribution mode, damage law and failure mode of specimen. The main research results obtained in the thesis are as follows: with the increase of the loading rate, the peak value of specimen damage first increases rapidly, and then in-creases slowly, and there is a damage threshold. In the early stage of loading, the dissipated energy of the specimen accounts for about 70% of the total energy, most of the total energy input is converted into dissipated energy. The elastic energy density shows an increasing trend with the increase of the loading rate. The elastic energy density is the highest when the loading rate is 400 ​N/s, and more elastic energy can be stored. The ratio of elastic energy ue/u increases with the in-crease of loading rate and tends to be stable. The acoustic emission data show that the acoustic emission signals present a certain agglomeration phenomenon at the unloading point, and there is a “blank period” between the unloading point and the emergence of the next acoustic emission activity. In the early stage of specimen loading, friction-type acoustic emission is mainly generated. The cumulative ringing count when the load reaches the peak failure stress at low loading rate is more, indicating that low loading rate will produce more acoustic emission activities. With the increase of loading rate, the cumulative ringing number per unit time increases, indicating that the increase of loading rate accelerates the damage and failure of dihydrate gypsum near the peak value. The failure mode of gypsum specimens is shear failure, and the increase of loading rate of shear failure angle shows an increasing trend. The larger the loading rate is, the higher the strength of the specimen is. The more energy the press inputs during the loading process, the higher the energy absorbed by the unit volume specimen, which aggravates the development, expansion and penetration of the internal cracks of the specimen, resulting in the larger shear angle of the specimen. The test results provide a more comprehensive theoretical basis for the study of damage characteristics of dihydrate gypsum during cyclic loading and unloading.

Experimental investigation on mechanical behavior of T-type perfobond rid shear connectors under combined shear and tension

The stress of shear connectors becomes more complicated as the span length of steel-concrete composite bridges increases. To bear the great shear and uplift forces, a T-type perfobond rib (T-type PBL) shear connector with sufficient stiffness and ductility is proposed. While the shear behavior of T-type PBL connectors has been evaluated in previous studies, its mechanical performance under combined shear and tension is not well understood due to the particular shape and numerous impact factors. Therefore, one pull-out test considering pure tension and seven modified push-out tests considering combined shear and tension were carried out to investigate the failure mode, bearing capacity, and load-slip behavior of T-type PBL connectors under combined actions. The pull-out test was performed to determine the tensile resistance, followed by a series of modified push-out tests with constant horizontal tension to investigate the structural behaviors. Additionally, the effects of the rib height, flange width, and hole numbers were evaluated. Based on the test results, conical failure surfaces formed from the flange of the T-type PBL to the concrete surface for all specimens, and the concrete failure angle was approximately 32°. The bearing capacity of the specimen improved by 26% when the perfobond rib height increased from 100 mm to 120 mm, but the flange width barely had any effect. The capacity of 1-hole specimen dropped by 20% while 2-hole specimen increased by 8% compared to the standard specimen, which may relate to the distance between adjacent holes. Increasing the rib height by 25% and 50% reduced the initial relative slip (S90) by 30% and 32%, respectively, indicating the improvement in initial stiffness. Generally, the pull-out resistance of the T-type PBL shear connector was enhanced by increasing the flange width, rib height, and number of holes. An evaluation equation considering the hole number and hole spacing was suggested for the bearing capacity of T-type PBL shear connectors under the combined actions. The validity was verified by test results, with a calculated-to-test-result ratio of 1.12 and standard deviation of 0.15. This study could enhance the understanding of the behavior of T-type PBL connectors under the combined actions, and promote the potential application in long-span composite bridge decks.

Experimental study and finite element modelling of the torsional behavior of self-compacting reinforced concrete (SCRC) beams strengthened by GFRP

The present study experimentally and numerically investigates the behavior of ten self-compacting reinforced concrete (SCRC) beams strengthened by various means of externally bonded glass fiber reinforced polymer (GFRP) strips and subjected to pure torsion. The experimental matrix is designed to explore the impact of the number of GFRP layers, the width of the strengthening layers, and the spacing between those layers on the ultimate torsional capacity, the ultimate angle of twist, ductility, and failure patterns with respect to an un-strengthened specimen. Tests revealed that the specimen that was strengthened along its whole length using three layers of GFRP sheets yielded the highest gain in the ultimate torsional moment of 33.3% compared to the un-strengthened specimen. Additionally, the highest gain in the energy dissipation capacity among all strengthened beams (209.4% higher than the control beam) was obtained when four layers of GFRP sheets spaced every 300 mm were installed. Moreover, a three-dimensional (3D) non-linear finite element analysis is carried out via ABAQUS software to predict the torsional characteristics of SCRC beams either strengthened by GFRP strips or kept bare. The numerical model well captured the failure patterns, torque versus angle of twist responses, stress distribution, and the ultimate load of SCRC beams strengthened by GFRP strips with respect to the experimental findings.

Effects of different joint wall lengths on in-plane compression properties of 3D braided jute/epoxy composite honeycombs

To comply with the trend in the development of engineering materials towards lightweight, high strength, eco-friendly, sustainable, and multi-functional, a three-dimensional braided integrated composite honeycomb is designed. The effects of geometrical parameters particularly joint wall lengths on the in-plane mechanical behavior of the honeycombs were investigated. The results show that the in-plane mechanical properties are related to the number of cell walls, and the angle between the cell wall and the loading direction. Increasing the number of cell rows to double and triple at similar areal density lead to an improvement of the maximum load up to 2.5, and 3.8 times, respectively. Similarly, the total absorbed strain energy increased up to 2.6 and 5.9 times, respectively. The displacement at the maximum load is increased by 1.6 and 2.7 times as a result of increasing the cell row number. The total absorbed strain energy increased to 1.7 and 1.3 times, respectively. The failure angle of the 3D braided composite honeycomb is about 4°–7°. This investigation presents the geometrical factors of a 3D braided composite honeycomb can be further designed and optimized, but it also provides a reference for the development and design of a new composite honeycomb.

Stochastic kinematic analysis of rock slope failure angle based on multi algorithm optimization, a case study of the proposed bridge project

ABSTRACT Due to the randomness and complexity of the discontinuity distribution, it is always complicated to analyse the three-dimensional stability problem of discontinuity-controlled rock slope in the field of engineering geology. Specifically, when restricted by poor sampling conditions, the discontinuity data obtained are very limited. To solve this problem, we propose a stochastic kinematic method to estimate the slope failure angle based on limited data. Taking the high-steep rock slope on the right bank of a proposed bridge as an example, the stochastic kinematic method based on multiple algorithms (Monte Carlo simulation, Latin hypercube, and Bayesian estimation) is used to analyse the failure angles of potentially unstable blocks in two modes of plane and wedge failure. After statistical optimisation, the slope failure angles are determined to be 65.69° (plane failure) and 58.65° (wedge failure); this approach is more objective than the empirical formula method and can be used as the basis for judging the slope stability. The method proposed in this study fully considers the randomness of discontinuity distribution and combination, and can use limited sample data to realise failure angle analysis and stability judgement. The result is important as a reference of significance for engineering construction and disaster prevention.

A failure envelope proposal based on the analysis of the requirements of nonlinear Mohr-Coulomb criteria

Nonlinear Mohr failure criterion is re-evaluated in this paper. It has been revealed that the polynomial failure criteria constructed by the normal stress σn and the shear stress τn predict the fracture angles unreasonably, and their predictions are also inconsistent with experimental observation that the two branches of failure envelope trend to be parallel to σn axis under high hydrostatic compression. In order to overcome the problems, first, the transformation of failure functions from the principal stress space (σ1, σ3) to the stress space (σn, τn) is derived. Then the failure function is expressed in terms of the principal stresses, and it is converted from the principal stress space (σ1, σ3) to the stress space (σn, τn) based on the transformation. The present failure criterion predicts more reasonable failure angles, and its envelope trends to be parallel to σn axis under high hydrostatic compression. In particular, the paper reveals that for brittle materials the fracture angle under the uniaxial tension is not 0° although the fracture surface is nearly perpendicular to the direction of the loading; under the pure shear stress the angle between the fracture surface and the direction of the loading is not 45° although it is close to 45°. The present criterion predicts this physical phenomenon reasonably.