Tensile Cracking Failure Research Articles

Investigation of the mechanical behavior of rock-like material with two flaws subjected to biaxial compression

The biaxial compression experiments of rock-like materials with two flaws are carried out under different flaw inclination angle, rock bridge ligament angle, lateral stress. The experimental studies show that crack propagation modes of rock-like material are as follows: wing crack through mode (Y mode), shear crack through mode (J mode), mixed crack through mode (wing shear JY mode), longitudinal extension of crack and transverse shear splitting. prefabricated fractured rock specimens have experienced the closing stage of prefabricated fractures, the elastic deformation stage, the generation and expansion of cracks (or plastic strengthening), and the residual loading stage. The peak strength of the specimen is increases with the increase of flaw inclination angle and lateral stress. With the increase of the rock bridge ligament angle, the failure of the rock bridge region changes from the shear crack failure to composite failure of shear crack and the wing type tensile crack failure, and then to the wing crack failure. With the increase of the lateral pressure, the failure of the specimen changes from the wing type tensile crack failure to the wing type and shear crack failure, and then to shear crack failure. The flaw inclination angle mainly changes the form of crack growth but does not effect on the failure modes. The counting number of acoustic emission events at the center of the sample is relative large, indicating that the cacks appear in the part of the rock bridge firstly. With the increasing of loads, the cracks of the rock bridge expanding constantly and connecting finally. The changes of acoustic emission event counts is consistent with the macroscopic damage form obtained from the experiments.

Nonlinear Performance Curve Estimation of Unreinforced Masonry Walls Subjected to In-Plane Rocking Behavior

This study focused on the in-plane rocking behavior of unreinforced masonry (URM) walls. Three URM wall specimens were designed and fabricated based on a typical masonry house in Korea. The experimental parameters were the layout of openings (its presence or absence) and configuration of openings (window or door). Static cyclic loading tests were conducted to investigate nonlinear performance curves of masonry walls subjected to a rocking behavior in the in-plane direction. In this paper, the mortar-joint tensile crack strength and rocking strength of masonry walls (i.e., peak and residual strengths) were evaluated, and the effects of opening configurations on the masonry wall strength were examined, due to the proposed procedure. The deformation capacity of a rocking behavior was also identified by the procedure. As a result, specimens without initial cracks showed the rocking behavior after mortar-joint tensile crack failure, whereas a specimen with initial cracks exhibited only the rocking behavior. Since no remarkable strength deterioration was found until final loading in all specimens, an in-plane rocking URM wall may have very good deformation performance. The estimated mortar-joint tensile crack strength, rocking strength, stiffness, and ultimate deformation were in good agreement with the experimental results, regardless of the layout and configuration of openings.

Numerical simulation of creep fracture evolution in fractured rock masses

The initiation, expansion, and penetration of microscopic cracks in rock is the macroscopic manifestation of creep. This paper investigates mechanical creep characteristics and fracture evolution processes in rock masses with different fracture angles, lengths, and rock bridge dip angles. Single fractures, dual parallel fractures, and fracture groups are considered. The approach comprises discrete element simulation based on continuum mechanics, utilizing the continuous and discontinuous software, GDEM. Single-fracture rock masses are characterized by a progressive fracture development mode dominated by tensile shear failure. The rate of creep and fracture magnitude both increase according to fracture length. With increasing fracture inclination angle, creep rate and fracture magnitude increase and decrease. The creep rate and degree of rupture are highest for fractures inclined at 30°. The dual-fracture rock mass exhibits both tensile crack failure and compressional shear failure. Creep rates are highest, and rupture effects are most apparent at rock bridge inclination angles of 90°. If the rock bridge is too long or too short, the stable creep stage is prolonged, but the creep acceleration stage intensifies due to interaction between fracture-bounded rock masses. The failure mode, in this case, involves collective failure by tension fractures and compressional shear. Creep rate and fracture magnitude increase with the number of fractures, which accelerates rock mass deformation to a certain extent. However, when the number of fractures reaches a certain threshold, a relatively stable structure may become established, slowing down the creep rate, especially during the creep acceleration stage. This study can provide a theoretical basis and reference for investigating the creep rupture law of rock mass engineering and the prevention and control of fractured rock mass geological disasters.

Optimal intensity measure selection and probabilistic seismic demand models for dam-reservoir-layered foundation system

This study evaluates the optimal intensity measures (IMs) for the seismic fragility analysis of dam-reservoir-layered foundation (DRLF) system. Probabilistic seismic demand models (PSDMs) for the DRLF system are developed that are plotted between engineering demand parameters (EDPs) and intensity measures. Optimal IMs are evaluated based on the selection measures: efficiency, practicality, proficiency, sufficiency, and hazard computability. In addition, finest IM, based on coefficient of determination (COD) in linear regression analysis, is assessed. Prior to that, the numerical model of DRLF system is developed in finite element method software, Abaqus. The concrete damaged plasticity model and Mohr-Coulomb failure model are adopted to provide the non-linear behavior to dam and foundation, respectively. The screening experiments are performed to examine the modeling parameter's effect on the tensile cracking failure in the dam. Ground motions are selected using the conditional mean spectrum approach. Dynamic structural analysis is performed through the incremental dynamic analysis method and a total of 110 non-linear time-history analyses are performed. Further, based on damage index, an analytical approach is used to construct the seismic fragility curves. Various damage states, based on tensile crack failure, are proposed. The screening experiment shows that concrete damping, rock to rock elastic modulus of different layers, concrete elastic modulus, concrete mass density and rock to rock frictional angle have a significant effect on the seismic response of the dam. While investigating the uncertainties associated with the modeling parameters of DRLF system, the elastic modulus of different layers should be chosen with care. Further, based on the IMs selection measures, ASI, EDA, MIV, IP_I and PGD are recognized as optimal IMs. However, ASI and EDA are observed to have excellent predictability and show best correlation for the considered EDPs of the dam.

Stability of the Rock Mass Reserved in front of Anti-slide Piles

To study the stability evaluation method and failure mode of reserved rock masses, the Yueyang landslide project was taken as the research object. First, based on the limit equilibrium method and elastic mechanics, the formulas for calculating the stability of a reserved rock mass were analyzed. Second, the failure modes of the reserved rock mass were tested by the experiment model. The results show that the failure modes of the reserved rock mass can be divided into three modes: upward sliding failure, downward sliding failure and tensile crack failure, which are mainly related to the strength and width of the reserved rock mass. Therefore, it is unreasonable to regard a reserved rock mass as a unified failure form in the design of anti-slide pile reinforcement. In addition, although both moderate-strength and strong-strength reserved rock masses exhibit tensile crack failure, moderate-strength rock masses under triangular loading are prone to tension-sliding failure, while strong-strength rock masses under parabolic loading are prone to tension-overturning failure. Finally, the displacement and stress monitoring results in the experiment are basically consistent with the theoretical analysis, indicating that the theoretical analysis results have high reliability.

Seismic fragility analysis of the Koyna gravity dam with layered rock foundation considering tensile crack failure

In the present investigation, the seismic fragility analysis of the Koyna dam-reservoir-layered rock foundation system is performed, considering foundation flexibility. For material non-linearity, the Concrete Damaged Plasticity (CDP) model and Mohr-Coulomb failure model are adopted for dam and foundation, respectively. The finite element modelling takes into account the material flexibility, inertial, and damping properties. For the seismic analysis, ground motions are picked according to the Conditional Mean Spectrum approach. An Incremental Dynamic Analysis (IDA) method is used in which each ground motion is scaled at different intensity levels and directly these ground motions are adopted for the time-history analysis. The ground motion Peak Ground Acceleration (PGA), Peak Ground Velocity (PGV), and Acceleration Spectrum Intensity (ASI) are preferred as an intensity measure (IM) parameter. For the seismic fragility analysis, the tensile crack failure in the dam is considered as a limit state. Analytical fragility curves are plotted for the various vulnerability states of the gravity dam based on the damage indices which are evaluated using crack length and dissipation energy in the dam. Numerical results indicate that the dam with more flexible rock layers is more sensitive against seismic forces; however, the dam with hard rock layers is on the safer side. The crest displacement and heel stress can be viewed as a damage measure (DM) parameter for the IDA method. It is observed that the ground motion PGV shows a distinct result in IDA curves as compared to PGA and ASI. However, in fragility analysis, the seismic risk of a gravity dam can be evaluated better against PGA and ASI as compared to PGV.

Comparative Investigation and Characterization of the Scratch and Wear Resistance Behavior of TiN, CrN, AlTiN and AlCrN Cathodic Arc PVD Coatings

The scratch resistance and wear behavior at relatively high normal loads of binary (TiN, CrN) and ternary (Al0.50Ti0.50N, Al0.68Cr0.32N) coatings were comparatively investigated. Scratch test results showed that based on the adhesive strength the coatings can be ranked thus: CrN > TiN > Al0.68Cr0.32N > Al0.50Ti0.50N. The binary coatings were found to possess superior adhesion strength mainly exhibiting a tensile cracking failure mechanism. In contrast, the ternary coatings failed more severely by through-thickness cracking with spallation. The ternary coatings exhibited an average of 68, 67 and 55% improvement in the wear resistance at 15, 20 and 25 N normal loads, respectively, over the binary coatings. Abrasive and oxidation wear were the main wear mechanisms of the binary coatings. The formation of protective tribo-oxide layers is associated with the improved wear resistance behavior of the ternary coatings. High surface roughness due to large amount of surface defects coupled with low plastic deformation resistance and high Al content are reasons for low wear resistance of Al0.68Cr0.32N in comparison with Al0.50Ti0.50N coating.

Modelling the influence of root position and growth on pavement tensile crack failure when occurring under three thicknesses of asphaltic concrete

Root-pavement conflicts are a common challenge in urban forest management. Given the expense of pavement installation and the time needed to develop large trees, there is a preference for modelling design solutions to integrate trees and pavement with shared soil volumes. While Finite Element (FE) models are used in pavement analysis and design, and have been used to describe root growth in soils, there are few examples exploring of integration of the two applications with respect to designing urban root zones under pavements. Four series of FE models were developed to test the influence of an asphaltic concrete wearing surface layer thickness and base layer thickness (the top two layers in a pavement design) in surface crack formation from a growing tree root simulation in positions within the top zone of the base layer and below the base layer. The expected pavement damage was defined at places where horizontal tensile stresses exceeded 862 kPa. The testing series were developed from a common group of 18 FE pavement layer configurations using 3 asphalt concrete (AC) thicknesses and 3 granular base thicknesses with a growing root element at 2 root elevations. In the first series, an AC layer of a thickness of 7.6 cm did not exceed the horizontal stresses needed to develop a crack when a simulated root element increased from 3.6 to 5.1 cm when the root element was below the base layer at least 10.16 cm below the bottom of the AC layer. A second series of 77 model runs with a refined root simulation verified the impact of a changed root simulation (shift of element shape with a material modeling change that accounted for soil hardening during deformation). For the second series, a 2.54 cm diameter circular root was expanded to a final size ranging from 3.8 to 10.16 cm. Results of the second series confirmed and added detail to the first, but required a significant increase in computational time to accommodate the added model and data output details. The third series developed root simulations from an initial 0.508 cm diameter (the smallest diameter available in the PLAXIS FEM modeling platform) to a maximum 5.08 cm diameter in a series of 55 tests. The third set allowed a method to observe and compare the colonization step to a series of radial growth steps, which caused minimal influence to the stress state of the AC as a consequence of soil displacements from the root growth. Finally, in the fourth testing series of 58 simulations, we tested a cluster of three root elements at a 10.16 cm spacing 0.635 cm below the AC or the base layer, growing from an initial 2.54 cm to 6.35 cm diameter. Modeling three root elements at the 10.16 cm spacing generated tensile stress-induced cracks in all AC-base-root depth configurations. Displacements in those models exceeded the imposed upward displacement limit of 1.27 cm after doubling in size from an initial 2.54 cm diameter.

On the load capacity and fracture mechanism of hard rocks at indentation loading

The load capacity of selected hard rocks subjected to circular flat punch indentation is investigated. The compacted zone underneath the indenter is assumed to be limited and only responsible for the load transition to the rest of the material. Therefore, the theory of elasticity is used to define the stress state in a semi-infinite medium loaded by a flat punch indenter. The final load capacity is related to the formation of a sub-surface median crack that initiates due to tensile hoop (circumferential) stresses. Therefore the final failure should occur at a force level in which the hoop stress is greater than the tensile strength of the rock. Since the tensile stress is distributed over a volume of material, tensile crack failure can occur at different locations with tensile hoop stress depending on where the most critical flaw is located. Therefore, the initiation of the median crack that should be responsible for the final load capacity is treated as a probabilistic phenomenon. This process is described by Weibull theory which will be used as a failure criterion. It is assumed here that the opening of median crack triggers a final violent rupture, therefore the assumption in Weibull theory, that the final failure occurs as soon as a macroscopic fracture initiates from a microcrack is fulfilled. The effective volume is calculated for a semi-infinite medium loaded by a flat punch indenter. The material properties of Bohus granite obtained from three point bending tests are used as reference values in describing the Weibull size effect. The experimental results for the stamp load capacity of three selected hard rocks are taken from the literature. They are considered similar rocks to the reference material in this paper, which is Bohus granite. The model describes the observed load capacity with a very good accuracy for all three rocks. It is likely that the presently proposed methodology is applicable for other types of semi-brittle materials and indenter shapes.

Physical and mechanical properties of sandstone containing a single fissure after exposure to high temperatures

In order to investigate the physical and mechanical properties of sandstone containing fissures after exposure to high temperatures, fissures with different angles α were prefabricated in the plate sandstone samples, and the processed samples were then heated at 5 different temperatures. Indoor uniaxial compression was conducted to analyze the change rules of physical properties of sandstone after exposure to high temperature, and the deformation, strength and failure characteristics of sandstone containing fissures. The results show that, with increasing temperature, the volume of sandstone increases gradually while the quality and density decrease gradually, and the color of sandstone remains basically unchanged while the brightness increases markedly when the temperature is higher than 585°C; the peak strength of sandstone containing fissures first decreases then increases when the temperature is between 25°C and 400°C. The peak strain of sandstone containing fissures increases gradually while the average modulus decreases gradually with increasing temperature, and the mechanical properties of sandstone show obvious deterioration after 400°C. The peak strain of sandstone containing fissures increases gradually while the average modulus decreases gradually with increasing temperature; with increasing angle α of the fissure, the evolution characteristics of the macro-mechanical parameters of sandstone are closely related to the their own mechanical properties. When the temperature is 800°C, the correlation between the peak strength and average modulus of sandstone and the angle α of the fissure is obviously weakened. The failure modes of sandstone containing fissures after high temperature exposure are of three different kinds including: tensile crack failure, tensile and shear cracks mixed failure, and shear crack failure. Tensile and shear crack mixed failure occur mainly at low temperatures and small angles; tensile crack failure occurs at high temperatures and large angles.

Dynamic tensile strength of terrestrial rocks and application to impact cratering

Abstract— Dynamic tensile strengths and fracture strengths of 3 terrestrial rocks, San Marcos gabbro, Coconino sandstone, and Sesia eclogite were determined by carrying out flat‐plate (PMMA and aluminum) impact experiments on disc‐shaped samples in the 5 to 60 m/sec range. Tensile stresses of 125 to 300 MPa and 245 to 580 MPa were induced for gabbro and eclogite, respectively (with duration time of ˜1 μs). For sandstone (porosity 25%), tensile stresses normal to bedding of ˜13 to 55 MPa were induced (with duration times of 2.4 and ˜1.4 μs). Tensile crack failure was detected by the onset of shock‐induced (damage) P and S wave velocity reduction.The dynamic tensile strength of gabbro determined from P and S wave velocity deficits agrees closely with the value of previously determined values by post‐impact microscopic examination (˜150 MPa). Tensile strength of Coconino sandstone is 20 MPa for a 14 μs duration time and 17 MPa for a 2.4 μs duration time. For Sesia eclogite, the dynamic tensile strength is ˜240 MPa. The fracture strength for gabbro is ˜250 MPa, ˜500 MPa for eclogite, and ˜40 MPa for sandstone. Relative crack‐induced reduction of S wave velocities is less than that of post‐impact P wave velocity reductions for both gabbro and eclogite, indicating that the cracks were predominantly spall cracks.Impacts upon planetary surfaces induce tensile failure within shock‐processed rocks beneath the resulting craters. The depth of cracking beneath impact craters can be determined both by seismic refraction methods for rocks of varying water saturation and, for dry conditions (e.g., the Moon), from gravity anomalies. In principle, depth of cracking is related to the equations‐of‐state of projectile and target, projectile dimension, and impact velocity. We constructed a crack‐depth model applicable to Meteor Crater. For the observed 850 m depth of cracking, our preferred strength scaling model yields an impact velocity of 33 km/s and impactor radius of 9 m for an iron projectile.

The structure and residual stress in Si containing diamond-like carbon coating

Silicon (Si) containing diamond-like carbon films are deposited by RF plasma CVD with reactant gases of CH 4, SiH 4 and Ar. The effects of substrate temperature and RF power on film structure, residual stress and adhesion are studied. The tensile cracking failure mode for films on Corning 7059 glass shows full adherence properties. A structure model is proposed, and the residual stress of the films is compressive. The relation between the structure and the residual compressive stress is investigated.

The effect of residual stress on the adhesion of PECVD-coated aluminum oxide film on glass

Transparent, amorphous and hard aluminum oxide films were deposited on glass at low temperatures (≤ 773 K) by r.f. plasma-enhanced chemical vapor deposition with AlCl 3, H 2 and CO 2 as the reactants. The adhesion of films, a predominant factor in determining the performance and reliability of a coating-substrate system, evaluated by the critical load in scratch testing strongly depends on the deposition conditions (substrate temperature and CO 2 flow rate) and compressive residual stress in the films measured by radii of curvature determinations. These films have shown a tensile cracking failure mode in scratch testing and as opposed to the prediction based on energy balance and the critical shear stress criteria, which indicates that the critical load will vary inversely with internal stress, the compressive residual stresses increase the adherence strength by increasing the resistance to the tensile cracking failure. Hence, it is important to characterize the failure modes associated with the scratch adhesion test to account for the dependence of critical load on internal stresses in the films.