scholarly journals Numerical Simulation of Strength, Deformation, and Failure Characteristics of Rock with Fissure Hole Defect

2020 ◽  
Vol 2020 ◽  
pp. 1-15 ◽  
Author(s):  
Shaojie Chen ◽  
Zhiguo Xia ◽  
Fan Feng
Keyword(s):  
Elastic Modulus ◽  
Stress Concentration ◽  
Compressive Stress ◽  
Failure Modes ◽  
Elliptical Hole ◽  
Major Axis ◽  
Minor Axis ◽  
Peak Strain ◽  
Secondary Cracks ◽  
The Right

Using discrete element software, namely, particle flow code as two-dimensional program (PFC2D), two types of models were established: vertical fissure hole combination and horizontal fissure hole combination with ratios of major and minor axis of ellipse being 1, 1.2, 1.5, 2, and 3, which corresponded to a total of ten samples. The failure mode, mechanical behavior, and stress state before and after crack generation in elliptical hole crack combination models with different ratios of major and minor axis were analyzed. The crack development, stress field evolution, and acoustic emission characteristics of the vertical fissure model and horizontal fissure model were studied at the optimized ratio of major and minor axis of ellipse being 1.5. The results showed that elliptical hole fissure with different ratios of major and minor axis resulted in the decrease in the strength and elastic modulus of rock and increase in the peak strain of rock. The effect of the horizontal fissure model on the peak strength, peak strain, and elastic modulus of rock was found to be greater than that of the vertical fissure hole model. Ellipses with different ratios of major and minor axis in various models slightly influenced the rock failure modes, and their failure modes corresponded to tensile shear failure and tensile failure. Before crack formation, the tensile stress concentration areas of each model were, respectively, distributed at the upper and lower ends of the vertical fissure and the major axis of ellipse, and the compressive stress concentration areas were distributed at both ends of the major axis of ellipse and the fissure in the horizontal direction. After the model failed, the compressive stress concentration areas of the vertical fissure model and the horizontal fissure model transferred to the left upper part and the right upper part of the model along the left end of the hole and the right end of the fissure, respectively. When the ratio of major and minor axis of ellipse was 1.5, cracks in the vertical model and the horizontal model of fissure developed along the axial direction at the ends of cracks and holes, respectively, and then secondary cracks were generated at the ends of left and right sides. The maximum compressive stress in each stage of the vertical fissure model was greater than that of the horizontal fissure model, and when the model was damaged, its stress release was more.

scholarly journals Numerical Study of the Strength and Characteristics of Sandstone Samples with Combined Double Hole and Double Fissure Defects

2021 ◽  
Vol 13 (13) ◽  
pp. 7090
Author(s):  
Junbiao Ma ◽  
Ning Jiang ◽  
Xujun Wang ◽  
Xiaodong Jia ◽  
Dehao Yao
Keyword(s):  
Mechanical Properties ◽  
Stress Concentration ◽  
Crack Initiation ◽  
Compressive Stress ◽  
Uniaxial Compression ◽  
Failure Modes ◽  
Numerical Study ◽  
Simulation Software ◽  
Particle Flow Code ◽  
Peak Strain

To explore the failure mechanism of rock with holes and fissures, uniaxial compression tests of sandstone samples with combined double hole and double fissure defects were carried out using Particle Flow Code 2D (PFC2D) numerical simulation software. The failure behaviour and mechanical properties of the sandstone samples with combined double hole and double fissure defects at different angles were analysed, and the evolution results of the stress field and crack propagation were studied. The results show that with a decrease in fissure angle, the crack initiation stress, damage stress, elastic modulus and peak stress of the defective rock decrease, while the peak strain increases, and the brittleness of the rock is weakened. Rocks with combined double hole and double fissure defects at different angles lead to different failure modes, crack initiation positions and crack development directions. After uniaxial compression, both compressive stress and tensile stress concentration areas are produced in the defective rock, but the compressive stress concentration is of primary importance. The concentration area is mainly distributed around the holes and fissures and the defect connecting line, and the stress concentration area decreases with the decreasing fissure angle. This study can correctly predict the mechanical properties of rock with combined double hole and double fissure defects at different angles and provide a reference for actual rock engineering.

Experimental and Numerical Analysis of Qinling Mountain Engineered Rocks during Pulse-Shaped SHPB Test

2015 ◽  
Vol 16 (3-4) ◽  
pp. 165-171
Author(s):  
Shi Liu ◽  
Jinyu Xu
Keyword(s):  
Compressive Strength ◽  
Elastic Modulus ◽  
Strain Rate ◽  
Energy Absorption ◽  
Absorption Rate ◽  
Failure Modes ◽  
Dynamic Compression ◽  
Peak Strain ◽  
Compression Stress ◽  
Dynamic Compressive Strength

AbstractIn order to study the dynamic compression mechanical properties of engineering rock under high strain rate （100~102 S−1）loads, dynamic compression tests of three common engineering rocks (marble, sandstone and granite) taken from the Qinling Mountain are studied subjected to five different kinds of shock air pressure using Φ 100 mm split Hopkinson pressure bar test system improved with purple copper waveform shaper. The dynamic compression stress-strain curves, dynamic compressive strength, peak strain, energy absorption rate and elastic modulus of three rocks variation with strain rate are researched. The dynamic compression failure modes under different strain rates are analyzed. Then the three-dimensional numerical simulations of waveform shaper shaping effects and stress wave propagation in the SHPB tests are carried out to reproduce the test results. The research results show that the dynamic compression stress-strain curves show certain discreteness, and there is an obvious rebound phenomenon after the peak. With the increase in strain rate, the dynamic compressive strength, peak strain and energy absorption rate are all in a certain degree of increase, but the elastic modulus have no obvious change trend. Under the same strain rate, the dynamic compressive strength of granite is greatest while of sandstone is least. With the increase in strain rate, the margin of increase in peak strain and energy absorption rate of granite is greatest while of sandstone is least. The failure modes of the sample experience a developing process from outside to inside with the increase of strain rate.

Numerical Simulation in Deep Drawing of Cylindrical Cup with Elliptical Shape Die Shoulder

2010 ◽  
Vol 148-149 ◽  
pp. 1355-1359
Author(s):  
Yu Qing Shi ◽  
Ai Zhi Guan
Keyword(s):  
Sheet Metal ◽  
Deep Drawing ◽  
Metal Forming ◽  
Failure Modes ◽  
Major Axis ◽  
Minor Axis ◽  
Drawing Process ◽  
Deep Drawing Process ◽  
Elliptical Shape ◽  
Cylindrical Cup

Wrinkling and tearing are the main failure modes in sheet-metal forming. The radius of die is important for deep-drawing because of an effective way to promote deep formability sheet metal .This paper presents an attempt to determine the effect of various elliptical shape die shoulder on the fracture and wrinkling and was investigated using 08Al sheet metal .The ellipse with minor axis of b=4.5mm and major axis of a=6.5mm,a=7mm,a=8mm ,a=10mm were analyzed to eliminate wrinkling and fracture in deep-drawing .The aim of this study is to investigate the effect of elliptical major axis and elliptical minor axis variables in elliptical shape die shoulder on formability in the deep-drawing process and to obtain useful date from the industrial field .The experiment show that limit formability promote with elliptical shape die shoulder in deep-drawing process.

scholarly journals An Experimental Study on the Compressive Dynamic Performance of Polypropylene Fiber Reinforced Concrete for Retaining Structure under Automobile Collision Magnitude

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Furong Li ◽  
Guoxing Chen ◽  
Guizhong Xu ◽  
Yongyi Wu
Keyword(s):  
Reinforced Concrete ◽  
Strain Rate ◽  
Compressive Stress ◽  
Failure Modes ◽  
Polypropylene Fiber ◽  
Fiber Content ◽  
Fiber Reinforced Concrete ◽  
Peak Strain ◽  
Fiber Reinforced ◽  
Polypropylene Fiber Reinforced Concrete

In order to examine the compressive dynamic performance of polypropylene fiber reinforced concrete to be used for the retaining structure under the automobile collision magnitude, an experimental study was carried out by using hydraulic servo on concrete specimens with 4 different polypropylene fiber contents under 6 loading strain rates. The failure modes and stress-strain curves of concrete under different loading conditions were obtained. Then, by comparatively analyzing the mechanical characteristic parameters of polypropylene fiber reinforced concrete under different loading conditions, the following conclusions are drawn: with the increase of the polypropylene fiber content, the integrity of concrete upon compressive failure is gradually improved. When the polypropylene fiber content is relatively high, the static and dynamic failure modes are basically similar. With the increase of the loading strain rate, the peak compressive stress and elastic modulus of the polypropylene fiber reinforced concrete gradually increase. The increase in the polypropylene fiber content gradually intensifies the effect of loading strain rate on the peak compressive stress dynamic improvement coefficient. The peak strain of polypropylene fiber reinforced concrete is gradually increased with the increase of polypropylene fiber content, while the effect of the loading strain rate on the peak strain shows an obvious discreteness characteristic. Meanwhile, we proposed a relationship equation for describing the peak compressive stress dynamic improvement coefficient based on the coupling effect of the polypropylene fiber content and loading strain rate and further discussed the underlying stress mechanism in detail. Our research findings are of important research significance for the application and promotion of polypropylene fiber reinforced concrete in the engineering practice of retaining structures.

scholarly journals Effect of Multiple Hole Distribution and Shape Based on Particle Flow on Rocklike Failure Characteristics and Mechanical Behavior

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Zhiguo Xia ◽  
Ning Jiang ◽  
Huisan Yang ◽  
Liu Han ◽  
Haiyang Pan ◽  
...  
Keyword(s):  
Stress Concentration ◽  
Tensile Stress ◽  
Compressive Stress ◽  
Particle Flow ◽  
Peak Strain ◽  
Vertical Orientation ◽  
Failure Characteristics ◽  
Horizontal Orientation ◽  
Orientation Model ◽  
Different Shapes

Based on the particle flow code, numerical models of vertical and horizontal orientations of holes with different shapes were established, and the effects of preexisting holes with different shapes and arrangement patterns on the mechanical behaviors and failure characteristics of rocklike materials were studied. The evolution trend of the stress field is discussed by taking a circular hole as an example. The results show that the existence of holes reduces the peak stress, peak strain, and elastic modulus of the sample, and different shapes of holes and different arrangement patterns have different effects on the mechanical properties and damage degree of the sample and significantly affect the horizontal orientation model. Before crack formation, the compressive stress and tensile stress concentration areas of each sample are located at the left and right ends and the upper and lower ends of the hole, respectively. After model failure, the compressive stress and tensile stress concentration areas of each sample are relatively scattered. In the vertical orientation model, the middle area of vertical holes is the main compressive stress concentration area, which is approximately “columnar” distribution. In the horizontal orientation model, the compressive stress concentration area between the holes is cross distribution and approximately “X” type distribution. The vertical orientation model sample forms a “columnar” distribution to bear the applied load with a more favorable bearing orientation.

The Conventional Triaxial Compressive Test of Plain Reactive Powder Concrete

2014 ◽  
Vol 670-671 ◽  
pp. 401-406
Author(s):  
Xiao Fei Wang ◽  
Yang Ping Wang
Keyword(s):  
Elastic Modulus ◽  
Failure Modes ◽  
Shear Failure ◽  
Poisson Ratio ◽  
Confining Pressure ◽  
Peak Strength ◽  
Reactive Powder Concrete ◽  
Peak Strain ◽  
Confining Pressures ◽  
Reactive Powder

Through the conventional triaxial test about plain reactive powder concrete under different confining pressures at 0Mpa, 25 Mpa,50 Mpa and 75 Mpa, this paper obtained the stress-strain curves in axial direction and radial direction of plain reactive powder concrete under different confining pressures, compared and analyzed the effects of confining pressures on peak strength, peak strain, Elastic modulus, Poisson ratio and failure modes of plain reactive power concrete also. The results showed that peak strength increases with the increase of confining pressure, when confining pressure increases from 0Mpa to 25Mpa, the peak strength increases most rapidly. The results also showed that peak strain increases linearly with the increase of confining pressure, when confining pressure increase from 0Mpa to 75Mpa gradually, the peak strain increases from 0.2 percent to 0.93 percent, meanwhile Poisson ratio increase with the increase of confining pressures, yet Elastic modulus changes slight at different confining pressures, failure modes of plain reactive powder concrete at different confining pressures exhibit different modes, when confining pressure is 0Mpa, failure mode presents as splitting failure, shear failure mode at 25Mpa, while shear failure merge local crushing at 50MPa and 75MPa.

The Effect of Stress Concentration on Bone Remodeling: Theoretical Predictions

1989 ◽  
Vol 111 (4) ◽  
pp. 355-360 ◽  
Author(s):  
K. Firoozbakhsh ◽  
M. Aleyaasin
Keyword(s):  
Stress Concentration ◽  
Bone Resorption ◽  
Bone Remodeling ◽  
Compressive Stress ◽  
Bone Structure ◽  
Compressive Load ◽  
Elliptical Hole ◽  
Special Cases ◽  
Theoretical Predictions ◽  
Elastic Coefficients

Theoretical predictions of internal bone remodeling around an elliptical hole are studied. The internal remodeling theory due to Cowin and Hegedus is employed. The bone is modeled as an initially homogeneous adaptive elastic plate with an elliptical hole under a superposed steady compressive load. It is shown that there will exist a final inhomogeneous remodeling distribution around the hole that will disappear away from the hole. The remodeling is such that the compressive stress concentration causes the bone structure to evolve to one of greater density and stiffer elastic coefficients. The speed of remodeling around the hole and its variation with respect to distance is investigated and discussed. It is shown that the rate of bone reinforcement in the area of compressive stress concentration is much higher than the rate of bone resorption in the area of existing tensile stress. Special cases of a circular hole and vertical and horizontal slots are studied and discussed.

scholarly journals Experimental Study on the Mechanical Properties and Compression Size Effect of Recycled Aggregate Concrete

Materials ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2323
Author(s):  
Yubing Du ◽  
Zhiqing Zhao ◽  
Qiang Xiao ◽  
Feiting Shi ◽  
Jianming Yang ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Size Effect ◽  
Compressive Stress ◽  
Failure Modes ◽  
Recycled Concrete ◽  
Recycled Aggregate Concrete ◽  
Recycled Aggregate ◽  
Aggregate Concrete ◽  
Substitution Ratio ◽  
The Impact

To explore the basic mechanical properties and size effects of recycled aggregate concrete (RAC) with different substitution ratios of coarse recycled concrete aggregates (CRCAs) to replace natural coarse aggregates (NCA), the failure modes and mechanical parameters of RAC under different loading conditions including compression, splitting tensile resistance and direct shear were compared and analyzed. The conclusions drawn are as follows: the failure mechanisms of concrete with different substitution ratios of CRCAs are similar; with the increase in substitution ratio, the peak compressive stress and peak tensile stress of RAC decrease gradually, the splitting limit displacement decreases, and the splitting tensile modulus slightly increases; with the increase in the concrete cube’s side length, the peak compressive stress of RAC declines gradually, but the integrity after compression is gradually improved; and the increase in the substitution ratio of the recycled aggregate reduces the impact of the size effect on the peak compressive stress of RAC. Furthermore, an influence equation of the coupling effect of the substitution ratio and size effect on the peak compressive stress of RAC was quantitatively established. The research results are of great significance for the engineering application of RAC and the strength selection of RAC structure design.

CMR markers for early right ventricular dysfunction in precapillary pulmonary hypertension

2020 ◽  
Vol 41 (Supplement_2) ◽  
Author(s):  
J Vos ◽  
T Leiner ◽  
A.P.J Van Dijk ◽  
F.J Meijboom ◽  
G.T Sieswerda ◽  
...  
Keyword(s):  
Pulmonary Hypertension ◽  
Right Ventricle ◽  
Right Ventricular ◽  
Circumferential Strain ◽  
Peak Strain ◽  
Healthy Controls ◽  
Free Wall ◽  
Global Circumferential Strain ◽  
The Right ◽  
Rv Function

Abstract Introduction Precapillary pulmonary hypertension (pPH) causes right ventricular (RV) pressure overload inducing RV remodeling, often resulting in dysfunction and dilatation, heart failure, and ultimately death. The ability of the right ventricle to adequately adapt to increased pressure loading is key for patients' prognosis. RV ejection fraction (RVEF) by cardiac magnetic resonance (CMR) is related to outcome in pPH patients, but this global measurement is not ideal for detecting early changes in RV function. Strain analysis on CMR using feature tracking (FT) software provides a more detailed assessment, and might therefore detect early changes in RV function. Aim 1) To compare RV strain parameters in pPH patients and healthy controls, and 2) to compare strain parameters in a subgroup of pPH patients with preserved RVEF (pRVEF) and healthy controls. Methods In this prospective study, a CMR was performed in pPH patients and healthy controls. Using FT-software on standard cine images, the following RV strain parameters were analyzed: global, septal, and free wall longitudinal strain (GLS, sept-LS, free wall-LS), time to peak strain (TTP, as a % of the whole cardiac cycle), the fractional area change (FAC), global circumferential strain (GCS), global longitudinal and global circumferential strain rate (GLSR and GCSR, respectively). A pRVEF is defined as a RVEF >50%. To compare RV strain parameters in pPH patients to healthy controls, the Mann-Whitney U test was used. Results 33 pPH-patients (55 [45–63] yrs; 10 (30%) male) and 22 healthy controls (40 [36–48] yrs; 15 (68%) male) were included. All RV strain parameters were significantly reduced in pPH patients compared to healthy controls (see table), except for GCS and GCSR. Most importantly, in pPH patients with pRVEF (n=8) GLS (−26.6% [−22.6 to −27.3] vs. −28.1% [−26.2 to −30.6], p=0.04), sept-LS (−21.2% [−19.8 to −23.2] vs. −26.0% [−24.0 to −27.9], p=0.005), and FAC (39% [35–44] vs. 44% [42–47], p=0.02) were still significantly impaired compared to healthy controls. The RV TTP was significantly increased in pPH patients compared to healthy controls (47% [44–57] vs. 40% [33–43], p≤0.001). Conclusions Several CMR-FT strain parameters of the right ventricle are impaired in pPH patients when compared to healthy controls. Moreover, even in pPH patients with a preserved RVEF multiple RV strain parameters (GLS, sept-LS, and FAC) remained significantly impaired, and TTP significantly prolonged, in comparison to healthy controls. This suggests that RV strain parameters may be used as an early marker of RV dysfunction in pPH patients. Funding Acknowledgement Type of funding source: None

scholarly journals Stress analysis of infinite laminated composite plate with elliptical cutout under different in plane loadings in hygrothermal environment

2021 ◽  
Vol 8 (1) ◽  
pp. 1-12
Author(s):  
Ashok Magar ◽  
Achchhe Lal
Keyword(s):  
Stress Concentration ◽  
Stress Distribution ◽  
Composite Plate ◽  
Volume Fraction ◽  
Elliptical Hole ◽  
Laminated Composite ◽  
Laminated Composite Plate ◽  
Concentration Changes ◽  
Hygrothermal Environment ◽  
Plate Analysis

Abstract This paper presents the solution of stress distribution around elliptical cutout in an infinite laminated composite plate. Analysis is done for in plane loading under hygrothermal environment. The formulation to obtain stresses around elliptical hole is based on Muskhelishvili’s complex variable method. The effect of fibre angle, type of in plane loading, volume fraction of fibre, change in temperature, fibre materials, stacking sequence and environmental conditions on stress distribution around elliptical hole is presented. The study revealed, these factors have significant effect on stress concentration in hygrothermal environment and stress concentration changes are significant with change in temperature.

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