scholarly journals Dynamic Behavior and Fatigue Damage Evolution of Sandstone under Uniaxial Cyclic Loading

2020 ◽  
Vol 2020 ◽  
pp. 1-9 ◽  
Author(s):  
Yidan Sun ◽  
Yu Yang ◽  
Min Li
Keyword(s):  
Cyclic Loading ◽  
Fatigue Damage ◽  
Mechanical Response ◽  
Compressive Strain ◽  
Damage Model ◽  
Testing Machine ◽  
Strain Curve ◽  
Peak Stress ◽  
Creep Theory ◽  
Cycle Number

The mechanical response characteristics of sandstone specimens under different stress amplitudes and loading frequencies were tested by a TAW-2000 rock triaxial testing machine. The characteristics of the stress-strain curve and the evolution process of strain damage under cyclic loading are analyzed. Based on creep theory and the disturbance state concept, a theoretical model between the axial compressive strain, axial compressive stress, and cycle number is established. The results show that there exists an upper threshold value of stress in cyclic loading above which the specimen will be damaged. As peak stress increases, the energy loss and irreversible deformation caused by damage gradually increase. When loading to an unstable peak stress under cyclic loading, the fatigue damage of sandstone under cyclic loading undergoes three characteristic stages: the initial stage; the stable stage; and the accelerated failure stage. The parameters of the strain damage model based on the disturbance state concept of sandstone are identified by test data, and the rationality of the model is validated by comparing theoretical values with experimental measurements.

scholarly journals Compressive Test Characteristics and Constitutive Relationship of Wet Polypropylene Macrofiber-Reinforced Shotcrete

2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Fenghui Li ◽  
Yunhai Cheng ◽  
Fei Wu ◽  
Chang Su ◽  
Gangwei Li
Keyword(s):  
Mechanical Response ◽  
Average Energy ◽  
Strain Curve ◽  
Peak Stress ◽  
Constitutive Relationship ◽  
Compression Tests ◽  
Response Characteristics ◽  
Test Characteristics ◽  
High Crack ◽  
Relationship Of

Shotcrete is often subject to poor ductility and cracking problems, particularly under high stresses. In order to deal with these issues, the feasibility of adding polypropylene macrofibers to shotcrete was verified. To ascertain the supporting effect, dry shotcrete, wet shotcrete, and wet polypropylene macrofiber-reinforced shotcrete (WPMS) were used as samples. Furthermore, the mechanical response characteristics thereof in uniaxial compression tests were compared and analyzed by acoustic emission (AE) monitoring. The results showed that the three materials were brittle, but the ductility, residual strength, and bearing capacity of polypropylene macrofiber-reinforced shotcrete were significantly enhanced. The energy absorption value of plain shotcrete was higher in the cracking stage, while that of polypropylene macrofiber-reinforced shotcrete was greater in the postpeak stage, which showed that the polypropylene macrofiber-reinforced shotcrete had the characteristics of a high crack-initiation strength and toughness. Besides, the energy release from fiber shotcrete occurred after the peak stress rather than near the peak stress. The average energy absorbed by polypropylene macrofiber-reinforced shotcrete was significantly higher than that in dry shotcrete and wet shotcrete, which implied that polypropylene macrofiber-reinforced shotcrete could mitigate the brittle instability of a shotcrete layer. A constitutive model of damage statistics was established based on the test data. The comparison between the experimental data and the fitting results can reflect the characteristics of the total stress-strain curve of such shotcrete. The results provide a basis for the optimization of polypropylene macrofiber-reinforced shotcrete layers.

scholarly journals Mechanical Behavior of Shale Rock under Uniaxial Cyclic Loading and Unloading Condition

2018 ◽  
Vol 2018 ◽  
pp. 1-8 ◽  
Author(s):  
Baoyun Zhao ◽  
Dongyan Liu ◽  
Ziyun Li ◽  
Wei Huang ◽  
Qian Dong
Keyword(s):  
Cyclic Loading ◽  
Mechanical Behavior ◽  
Creep Behavior ◽  
Peak Stress ◽  
Creep Model ◽  
Cycle Number ◽  
Shale Rock ◽  
Cyclic Loading And Unloading ◽  
Residual Strains ◽  
Loading And Unloading

In order to investigate the mechanical behavior of shale rock under cyclic loading and unloading condition, two kinds of incremental cyclic loading tests were conducted. Based on the result of the short-term uniaxial incremental cyclic loading test, the permanent residual strain, modulus, and damage evolution were analyzed firstly. Results showed that the relationship between the residual strains and the cycle number can be expressed by an exponential function. The deformation modulus E50 and elastic modulus ES first increased and then decreased with the peak stress under the loading condition, and both of them increased approximately linearly with the peak stress under the unloading condition. On the basis of the energy dissipation, the damage variables showed an exponential increasing with the strain at peak stress. The creep behavior of the shale rock was also analyzed. Results showed that there are obvious instantaneous strain, decay creep, and steady creep under each stress level and the specimen appears the accelerated creep stage under the 4th stress of 51.16 MPa. Based on the characteristics of the Burgers creep model, a viscoelastic-plastic creep model was proposed through viscoplastic mechanics, which agrees very well with the experimental results and can better describe the creep behavior of shale rock better than the Burgers creep model. Results can provide some mechanics reference evidence for shale gas development.

Damage Evolution Analysis of Calcareous Mudstone with Different Water Content under Uniaxial Compression

2010 ◽  
Vol 168-170 ◽  
pp. 1388-1395
Author(s):  
Ming Ji ◽  
Nong Zhang ◽  
Feng Gao
Keyword(s):  
Acoustic Emission ◽  
Water Content ◽  
Uniaxial Compression ◽  
Damage Evolution ◽  
Testing Machine ◽  
Strain Curve ◽  
Peak Stress ◽  
Damage Evolution Equation ◽  
Emission Activity ◽  
Hydraulic Servo

Uniaxial compression and acoustic emission experiments of calcareous mudstone with different water content were carried out by using microcomputer controlled electro-hydraulic servo compression testing machine control system of YAW series equipped by coal-rock acoustic and electric data acquisition system of CTA-1-type. Mchanical properties and acoustic emission law of calcareous mudstone were studied. It is concluded from experiment result that rock’s elastic modulus and compressive strength both decrease with increase water content but peak stress shows the opposite trend. It is also found that calcareous mudstone is brittleness with low water content but when water content reaches saturation, calcareous mudstone presents plastic features. Acoustic emission curve fits well with stress-strain curve: acoustic emission activity begins intensifying when stress reaches 70% of peak stress, correspondingly, acoustic emission is up to maximum at peak stress. Based on Weibull hypothesis and acoustic emission experiment, damage law of water bearing calcareous mudstone is researched and damage evolution equation with time variable is advanced.

TMF of Directionally Solidified and Single Crystal Superalloy

2011 ◽  
Vol 233-235 ◽  
pp. 2227-2230
Author(s):  
Qing Wu Wang ◽  
Shi Hui Zhang ◽  
Mao Pang
Keyword(s):  
Single Crystal ◽  
Fatigue Damage ◽  
Evaluation Method ◽  
Mechanical Response ◽  
Coupling Effect ◽  
Damage Model ◽  
Equivalent Strain ◽  
Single Crystal Superalloy ◽  
Thermomechanical Coupling ◽  
Directionally Solidified

Directional solidification and single crystal technology reduces material defects, improves material mechanical property and improves resistances to the high temperature fatigue, creep and corrosion. Accumulation of fatigue damage is a method of life prediction analysis and many fatigue damage models are proposed. Based on foregone research achievements, this paper presents a fatigue damage model, which could reflect material anisotropy and thermomechanical coupling effect. Based on equivalent strain, a fatigue damage evaluation method of directionally solidified and single crystal superalloy is presented and by this method, the linear fit of published fatigue experiment data is proceeded. Directionally solidified and single crystal superalloy is of strong anisotropy and crystal orientation has strong effect on component mechanical response. Comparative life of different location on component could be analyzed.

scholarly journals New Nonlinear Cumulative Fatigue Damage Model Based on Ecological Quality Dissipation of Materials

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Hongsong Li ◽  
Yongbao Liu ◽  
Xing He ◽  
Wangtian Yin
Keyword(s):  
Fatigue Life ◽  
Cyclic Loading ◽  
Fatigue Damage ◽  
Damage Model ◽  
Fatigue Loading ◽  
Ecological Quality ◽  
Aircraft Structures ◽  
Variable Amplitude ◽  
Fatigue Damage Accumulation ◽  
Cumulative Fatigue Damage

The failure of many aircraft structures and materials is caused by the accumulation of fatigue damage under variable-amplitude cyclic loading wherein the damage evolution of materials is complicated. Therefore, to study the cumulative fatigue damage of materials under variable-amplitude cyclic loading, a new nonlinear fatigue damage accumulation model is proposed based on the ecological quality dissipation of materials by considering the effects of load interaction and sequence. The proposed new model is validated by the test data obtained for three kinds of material under multilevel fatigue loading. Compared with the Miner model and Kwofie model, the proposed model can more effectively analyse the accumulative damage and predict fatigue life of different materials under variable-amplitude cyclic loading than others. The study provides a basis for predicting fatigue life accurately and determining reasonable maintenance periods of aircraft structures.

Numerical Simulation of CFRP Reinforced Steel Pipe Elbows Subjected to Cyclic Loading

2016 ◽  
Author(s):  
Giannoula Chatzopoulou ◽  
Ioannis Skarakis ◽  
Spyros A. Karamanos ◽  
Nicholas G. Tsouvalis ◽  
Aglaia E. Pournara
Keyword(s):  
Cyclic Loading ◽  
Structural Integrity ◽  
Mechanical Response ◽  
Numerical Models ◽  
Experimental Testing ◽  
Strain Curve ◽  
Steel Pipe ◽  
Cyclic Plasticity ◽  
Loading Conditions ◽  
Piping Systems

Strengthening of pipelines and piping systems under extreme loading conditions increases their operation safety level towards safeguarding their structural integrity. Motivated by the structural integrity of pipelines and piping systems, the present study aims at investigating the effect of Carbon Fiber Reinforced Plastic (CFRP) wrapping on the mechanical response of cyclically-loaded steel pipe elbows. Based on experimental testing results, a finite element model is developed, which simulates reinforced and non-reinforced pipe elbows specimens subjected to low-cyclic fatigue. For the description of the material nonlinearities, an efficient cyclic-plasticity material model is also employed, capable of describing both the yield plateau region of the steel stress-strain curve and the Bauschinger effect that appears under reverse plastic loading conditions. The results from the numerical models are compared successfully with the experimental data. Furthermore, a parametric analysis is conducted in order to examine the effect of internal pressure on the structural behavior of unreinforced and reinforced elbows, subjected to cyclic loading.

Thermal performance of self-compacting concrete: destructive and nondestructive evaluation

2013 ◽  
Vol 40 (12) ◽  
pp. 1205-1214 ◽  
Author(s):  
Rami H. Haddad ◽  
Ruba A. Odeh ◽  
Hala A. Amawi ◽  
Ayman N. Ababneh
Keyword(s):  
Compressive Strength ◽  
Elastic Modulus ◽  
Elevated Temperature ◽  
Elevated Temperatures ◽  
Mechanical Response ◽  
Compressive Strain ◽  
Peak Stress ◽  
Pulse Velocity ◽  
Self Compacting Concrete ◽  
Damage Indices

Recently, self-compacting concrete (SCC) has been increasingly used in high-rise buildings and industrial units, susceptible to accidental fires. The probable degradation of these structures necessitates understanding SCC behavior under elevated temperatures. For this, an extensive experimental investigation was undertaken to evaluate the effect of elevated temperature (300–600 °C) on the mechanical compressive properties of SCC; considering the effect of water-to-cement ratio (0.40–0.50), type of mineral aggregate and filler (limestone and basalt), and internal humidity. Standard cylinder (150 mm × 300 mm) and prism (100 mm × 100 mm × 300 mm) specimens were prepared from various SCC mixtures, cured for 28 d in limewater, and then stored at different environments for an additional 90 d to create varying internal humidity levels; ranging from 28 to 95%. Later, specimens were subjected to elevated temperatures in an electrical furnace, then cooled and tested for compressive mechanical response or non-destructively using resonance frequency, ultrasonic pulse velocity, and rebound hammer evaluation techniques. The results showed significant reduction in residual compressive strength, and elastic modulus, and an increase in compressive strain at peak stress and toughness as elevated temperature was increased. The SCC mixtures at upper water-to-cement ratios with basalt aggregate showed higher resistance to elevated temperatures than corresponding ones with limestone. Internal humidity in SCC had a detrimental impact on compressive strength and elastic modulus; especially at exposure temperatures below 400 °C. The statistical correlations between residuals for compressive strength or elastic modulus and nondestructive damage indices can be classified as very good. Furthermore, the nonlinear empirical models, developed to predict residuals for compressive strength and elastic modulus in terms of the study parameters, showed relatively high prediction potential, hence are recommended to be used in designing SCC mixtures for best resistance against possible fire attack.

scholarly journals Experimental Study on the Effect of Freeze-Thaw Cycles on Axial Tension and Compression Performance of Concrete after Complete Carbonization

2021 ◽  
Vol 2021 ◽  
pp. 1-16
Author(s):  
Dafu Cao ◽  
Jiaqi Liu ◽  
Yanling Zhou ◽  
Wenjie Ge ◽  
Xin Zhang
Keyword(s):  
Compressive Stress ◽  
Axial Compression ◽  
Compressive Strain ◽  
Strain Curve ◽  
Peak Stress ◽  
Experimental Result ◽  
Peak Strain ◽  
Freeze Thaw ◽  
Axial Tension ◽  
Thaw Cycle

The effect of freeze-thaw cycles on the axial tension and axial compression properties of completely carbonized concrete are investigated in this study. Three grade concrete specimens (C30, C40, and C45) were fabricated. The freeze-thaw cycle test was carried out on the completely carbonized specimens, followed by axial tension and axial compression tests. The results show that completed carbonization increases the axial tensile peak stress of C30, C40, and C45 concrete specimens by 8.7%, 9.7%, and, 12.1%, respectively. The peak axial tension strain increased by 1.9%, 7.2%, and 9.6%, respectively. The peak axial compressive stress increased by 10.5%, 19.1%, and 24.1%, respectively. The peak axial compressive strain decreased by 13.7%, 14.1%, and 14.3%, respectively. With the increase of freeze-thaw cycles, the peak stress of tensile stress, peak strain, and compressive stress of concrete decrease continuously. The peak strain of compressive strain increases. The lower the strength grade of concrete, the faster the decline rate of stress and strain. According to the data changes of peak stress and peak strain at different times of freeze thaw after carbonization, the stress-strain curve fitting formula for concrete under freeze-thaw cycles after complete carbonization is put forward, which has a good coincidence with the experimental result.

A Damage Model for Low Cycle Fatigue Analysis of Stiffened Plates

2014 ◽  
Vol 496-500 ◽  
pp. 561-566
Author(s):  
Qin Dong ◽  
Ping Yang ◽  
Jun Lin Deng ◽  
Hong Wang
Keyword(s):  
Cyclic Loading ◽  
Plastic Strain ◽  
Fatigue Damage ◽  
Damage Mechanics ◽  
Integral Transformation ◽  
Low Cycle Fatigue ◽  
Damage Model ◽  
Stiffened Plates ◽  
Cycle Fatigue ◽  
Cyclic Loading Condition

A low-cycle fatigue damage model for stiffened plates has been derived based on the theory of damage mechanics. The fatigue damage variable equation of the stiffened plate under cyclic loading was introduced into the accumulative plastic strain equation. Then by means of integral transformation, the evolution equation of axial plastic strain was derived under low cyclic loading condition. The analysis results by the presented model compare well with those by the finite element method.

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