Stages Of Damage Evolution Research Articles

Dynamic uniaxial compression mechanical properties of self-compacting rubber concrete subjected to different strain rates

Rubber concrete is a kind of light green building material, which is prepared by mixing rubber powder or rubber crumb into ordinary concrete in a certain proportion and then introducing rubber concrete through vibration-free technology to prepare self-compacting rubber concrete. Uniaxial compression tests were carried out on self-compacting rubber concrete with two particle sizes at different strain rates, and the effects of strain rate and rubber content on the dynamic mechanical properties of self-compacting rubber concrete were studied. The microstructure of self-compacting rubber concrete before and after damage was analyzed. Compared with ordinary concrete, the self-compacting rubber concrete is capable of maintaining good integrity during damage, when the rubber powder content exceeds 10% and the rubber crumb content exceeds 15%. The results indicate that as the strain rate increases, both the peak stress and the elastic modulus increase, indicating the strain rate enhancement effect, while the strain rate effect of the peak strain is not evident. Moreover, the model equations of peak stress and elastic modulus strain rate effect were established, the dynamic damage constitutive model was proposed, the damage evolution was analyzed, and the stress intervals were assigned to the various stages of damage evolution.

Multi-method comparison and multi-index evaluation of cracking characteristics of asphalt mixture

The micro crack inside asphalt pavement are potential and antecedent factors for macroscopic cracking of the pavement. The position and quantity of micro cracks have a significant impact on the service life and failure mode of asphalt pavement. The purpose of this study was to conduct multi-scale analysis and multi-index evaluation on the whole process of generation, expansion, and transformation of micro-crack inside asphalt pavement (asphalt mixture) based on multiple testing methods. Firstly, synchronous tests were conducted on the cracking process of asphalt mixture by using three-point bending loading method, acoustic emission (AE) monitoring method, and digital image correlation (DIC) analysis method. Secondly, a three-dimensional finite element model of the asphalt mixture beam was established for AE source location simulation. Finally, the advantages and limitations of multi-methods were compared and analyzed. The principal strain points with different sizes were randomly distributed in the tensile area of the asphalt mixture beam bottom at the initial loading stage, and the number of the principal strain points increased with the decrease of the loading rate. The macroscopic main crack of the asphalt mixture beam generated and expanded from the maximum principal strain point (P1) at the later loading stage. The AE dominant-frequency distribution ranges of micro-crack expanding process, macro-crack generating process, and failure process of asphalt mixture beam were 78.125–156.25 kHz, 234.375–312.5 kHz, and 0–78.125 kHz, respectively. Four stages of damage evolution and cracking process inside the asphalt mixture beam were obtained by the AE source location simulation. A comprehensive and systematic evaluation of bending cracking characteristics of asphalt mixture beam was realized by obtaining multiple indexes from multiple scales with multiple methods.

Influence of Uneven Subgrade Frost Heave on Deformation and Damage of CRTSIII Slab Track

The problem of uneven frost heave deformation of high-speed railway subgrade in seasonal freezing areas seriously affects the service state and service life of slab track structures and threatens the safe operation of high-speed vehicles. Based on the damage plasticity theory of concrete, in this study, an analytical model is established for CRTSIII slab track with damage plasticity and reinforcement. The influences of various frost heaving parameters on track structure deformation, interlayer seam, as well as the stress and damage behaviors were analyzed in detail. The results show that, as compared with a linear elastic model, the damage plastic model better reflects the softening behavior and stress attenuation of track structure concrete after reaching its tensile strength. The deformation and the interlayer seam reach their maximum values when the frost heaving wave peak acts at the position that is one-sixth of the base length from the edge of the concrete base. When the frost heaving wave peak acts on grooves at the base center, initially, the track structure is seriously damaged. The interlayer seam and damage decrease with an increase in frost heaving wavelength and increase with an increase in frost heaving wave amplitude. The interlayer seam of the track structure is more sensitive to frost heave deformation having a wavelength of less than 10 m. The extent of damage to the concrete base gradually increases with a decrease in the wave/amplitude ratio. It undergoes three stages of damage evolution: (i) no damage, (ii) upper surface bending damage, (iii) reverse bending damage. In order to improve efficiency, it is recommended, during track maintenance, to focus on the position of the central groove of the base and the position that is one-sixth of the base length from the edge of the concrete base.

Examination of the Effects of Different Frequencies on Rock Fracturing via Laboratory-Scale Variable Amplitude Fatigue Loading Experiments

In this study, the characteristics of the fracture evolution of argillaceous shale under increasing-amplitude loading were investigated. The GCTS RTR-2000 test system and in-situ acoustic emission (AE) monitoring were employed to execute the tests. The following results were observed. (1) The strength, deformation, and fatigue life increased with the frequency, and the morphology of the hysteresis curve changed regularly with time. (2) The cumulative damage of the rock at the location in which the stress amplitude suddenly increased exceeded that at the fatigue loading stage. The AE count and AE energy were affected by the loading frequency. (3) The secant modulus exhibited different values for different loading frequencies; the smaller the loading frequency, the fewer loading stages the samples experienced, and the faster the secant modulus decreased. The change in Poisson’s ratio over the entire process was composed of a steady growth stage and a rapid growth stage. (4) The rock exhibited two stages of damage evolution, with rapid damage accumulation occurring at the beginning of the loading and relatively smooth damage occurring thereafter. This study developed a cumulative fatigue damage model that can adequately fit the accumulated damage during the fracturing process. The experiments revealed that variable amplitude fatigue loading at different frequencies significantly influences the damage deterioration and the failure law of the rock. The results are expected to improve the understanding of the frequency effect on the fracture behavior and help predict the lifespan of rock structures. This is of great significance to the promotion of slope management, landslide disaster prevention, and mine reuse at the West Open-pit Mine.

Structural phenomenological concept of monitoring the load-bearing capacity of structural elements of composite materials

The authors demonstrate the potential of a methodological approach for monitoring the damage kinetics and evaluating the load-bearing capacity of composite structural elements based on the method of acoustic emission. This methodology was developed by specialists of the Blagonravov Mechanical Engineering Research Institute of the Russian Academy of Sciences. The methodology was implemented for a fatigue test of an aircraft panel represented by a complex hybrid structure with a lining made of layered composite and a cellular internal structure of aluminum foil with polymeric filler that has a continuous layered structure in the gripping area. Fatigue tests were carried out at 4 Hz from the zero-loading cycle with an amplitude of 145 kN. To record the accumulation of damages, R15–AST transducers by Mistral (USA) and an A-line 32D 8-channel acoustic emission system by Interunis-IT LLC were used. Comparing the weight content of location impulses with their threshold values in energy clusters characterizing the kinetics of micro-, meso-, and macro-damages of the composite material structure made it possible to determine the bearing capacity of the aircraft panel at respective stages of damage kinetics. The results of the acoustic emission diagnostics are given for the examined aircraft panel during cyclic loading, including the coordinate location of acoustic emission sources, accumulation of acoustic emission events by channels, the dynamics of partial activity changes, and weight content of location impulses at damage evolution stages of a composite material. Therefore, the acoustic emission diagnostics of the aircraft panel made it possible to identify the areas of intensive damage accumulation in the hybrid structure of the panel and control the actual bearing capacity by defining the extent of its damages at various scale and structural levels during cyclic loading. The described methodology of using acoustic emission diagnostics for monitoring the damage kinetics and actual bearing capacity of highly loaded composite elements extends the research potential of the acoustic emission method.

Assessment of tensile behaviour of plain weave fabric CFRP composites using acoustic emission technique and deep learning

The applications of Carbon Fibre Reinforced Plastic (CFRP) composites in aerospace applications have increased exponentially in the last decade. CFRP composites are now replacing conventional materials used in high temperature applications. Different types and strategies of reinforcements are used in these composites to improve their applicability to high temperature applications. One of the reinforcement strategies that has been used frequently in the recent years is the plain weave fabric configuration of reinforcing fibres in polymer matrix. A comprehensive damage assessment is essential to evaluate the characteristics of these composites at elevated temperatures. The Acoustic Emission (AE) signals generated during the damage evolution stages are used for studying the damage evolution stages when the plain weave fabric composites are tested at temperatures close to their glass transition state. A new information-theoretic parameter, Lempel-Ziv (LZ) complexity and the deep learning neural network is used for understanding the damage evolution stages. Furthermore, the neural network is used for validating the utilization of LZ complexity as a potential AE parameter for damage classification applications. The results are promising with the damage classification strategy using LZ complexity exhibits an accuracy of 85.1% which is validated through the neural network.

Biaxial tensile test and meso damage numerical simulation of HTPB propellant

Aiming at the shortcomings of the current research on the mechanical properties of solid propellants under complex stress conditions, an effective cross-shaped test piece configuration and variable-scale biaxial tensile test method are designed in this paper, and the meso-simulation model of propellant is constructed by Micro-CT test and random filling algorithm. Then, based on the Hook-Jeeves method and the cohesive force model, the mechanical performance parameters of each mesoscopic component were obtained, and finally the damage evolution process of the propellant was numerically simulated. The results show that the stress–strain curve of the propellant under biaxial loading is similar to that of uniaxial stretching, and has obvious rate dependence and stress state dependence. The mechanical properties of the propellant under biaxial tensile loading are significantly lower than those in uniaxial stretching, and the maximum elongation is only 45–85% of that in uniaxial stretching. The fracture process of propellant can be divided into initial linear stage, damage evolution stage and fracture stage. The dewetting phenomenon generally occurs at the interface between the large-sized AP particles and the matrix. With the loading of the load, the pores formed by the dewetting and matrix tearing continue to converge into cracks and expand in the direction perpendicular to the resultant force, and finally fracture. The propellant dehumidifies more easily under high strain rate loading, but the degree of dewetting is lower when the same strain is reached.

Damage Progress Classification in AlSi10Mg SLM Specimens by Convolutional Neural Network and k-Fold Cross Validation.

In this study, the damage evolution stages in testing AlSi10Mg specimens manufactured using Selective Laser Melting (SLM) process are identified using Acoustic Emission (AE) technique and Convolutional Neural Network (CNN). AE signals generated during the testing of AlSi10Mg specimens are recorded and analysed to identify their time-frequency features in three different damage evolution stages: elastic stage, plastic stage, and fracture stage. Continuous Wavelet Transform (CWT) spectrograms are used for the processing of the AE signals. The AE signals from each of these stages are then used for training a CNN based on SqueezeNet. Moreover, k-fold cross validation is implemented while training the modified SqueezeNet to improve the classification efficiency of the network. The trained network shows promising results in classifying the AE signals from different damage evolution stages.

Seismic behaviour of a novel hollow-core precast shear wall with cast-in-situ boundary elements

A novel reinforced concrete hollow-core precast shear wall (HCPSW), including a precast hollow-core wall panel and cast-in-situ boundary elements is proposed in this study with two anti-seismic defence lines. To analyse the seismic behaviour of this wall, six full-scale specimens were tested under cyclic loading, including two types of HCPSWs with different reinforcements in the boundary elements and one group of solid shear walls for comparison. The test results indicated that the solid shear wall fractured suddenly along the inclined section after the peak load. In contrast, the HCPSW had one more damage evolution stage from the peak load to the ultimate load and could still support the vertical load by boundary elements after achieving the ultimate lateral load. The lateral bearing capacity of the HCPSW specimens was mainly determined by the shear behaviour of the precast wall panel. At the same concrete dosages, the HCPSWs had a comparable lateral bearing capacity and better energy dissipation than the walls with a solid section. To calculate the lateral bearing capacity of this novel wall, a theoretical calculation method based on the softened strut-and-tie model was developed, which had good prediction accuracy for the tested specimens.

Improved tensile and single-lap-shear mechanical-electrical response of epoxy composites reinforced with gridded nano-carbons

A new carbon nanotube (CNT)/graphene (GN) grid structure is prepared and used to reinforce and health-monitor the epoxy composites. Results reveal that with a 30–50% mesoscopic-porosity of the CNT/GN grid, tensile strength and single-lap-shear (SLS) strength of the CNT/GN/epoxy composites can be improved by 27–41% and 28–49%, respectively. Also, relative resistance change (ΔR/R0%) at damage initiation would sudden change more than 10% for the tensile testing and 6% for the SLS testing. Meanwhile, during the damage evolution stage, the gauge factor obtained from tensile testing reaches 10.2–24.9 improved by 23–200%, and ΔR/R0% from SLS testing achieves 47.4–60.4% increased by 69–116%, respectively, when compared to the baseline composite. Moreover, an equivalent resistance prediction mode for the CNT/GN grid composites is proposed and which can well explain the resistance response mechanism. The result reveals that the gridded CNT/GN sensor is potential in reinforcing and structural health monitoring the epoxy resin-based composites.

Raman scattering investigations on disorder and recovery induced by low and high energy ion irradiation on 3C-SiC

The cubic polytype of SiC (3C-SiC) epilayer grown on Si has been irradiated with 200 keV Si+ ions for various ion doses (0.025 dpa- 0.6 dpa) followed by 14 MeV Si+ ion irradiation (ion fluences: 1 × 1014 –1 × 1015 ions/cm2) at room temperature to study the recovery of damage caused by low energy ions. The disorder was estimated using Raman Scattering results and it is explained by direct impact model. From the total disorder and chemical disorder values, the three stages of damage evolution is clearly observed upon 200 keV Si+ ion irradiation. Upon 14 MeV Si+ ion irradiation on 3C-SiC, the sample has not amorphized even upto the ion fluence of 1 × 1015 ions/cm2. The present experimental results show that when the damage(caused by low energy ion) is less (<0.05dpa), the recovery of damage occurred upon high energy Si+ ion irradiation and it is mainly due to ionization induced annealing of defects.

Infrared radiation test on the influence of water content on sandstone damage evolution

The rock mechanics uniaxial compression testing system and a thermal imaging camera were used to research the influence of water on sandstone damage evolution and the concurrent infrared radiation (IR) characteristics on sandstone samples with different water contents. The field of view of the thermal imaging camera divided the sandstone surface into several small areas of equal area. When one of the small areas of sandstone ruptured (that was when a damage point was generated in the sandstone) the IR information from that area underwent abrupt changes. Based on this monitoring, a quantitative index of infrared radiation, the IR count (IRC), was adopted and investigated as the indicator for damage evolution of rocks that also linked damage intensity with the corresponding IR temperature. The research results showed that when the sandstone stress experienced a stress drop, the IRC will simultaneously undergo a sudden increase indicating that the IRC was controlled by the stress. However, this stress control on IRC decreased with increasing water content due to the softening effect of water on the sandstone. Among them, the control effect of stress on IRC reaches 100% for dry sandstone, which is reduced to 75% for sandstone with a water content of 0.5% and 66.7% for sandstone with a water content of 1.5%. The control effect of stress of saturated sandstone on IRC is 57.1%. For sandstones with other water contents, but at the same damage evolution stage, the average IRC (IRC¯) for sandstones showed an upward trend as the water content increased. Compared with other damage evolution stages, the IRC¯ of the water-bearing sandstone had the most significant difference in the failure stage, indicating that water had the most significant influence on the damage evolution of the sandstone in the failure stage. This IRC was generated at the location of a new damage point on the sandstone surface. Therefore, based on the instant of time node when the sandstone IRC suddenly increased, the IRC spatial distribution map at that corresponding time was drawn to accurately locate the sandstone damage and fracture area. The characteristics of the damage evolution process of sandstones with different water contents were the same over the time before the sudden increase in IRC, the damage points formed were disorderly distributed, and the number of damage points was less. The difference was that as the water content increased, the number of sandstone damage points became larger and more concentrated.

A novel and robust method to quantify fatigue damage in fibre composite materials using thermal imagine analysis

This work proposes a novel and robust thermal imaging-based method suitable to quantify damage evolution stages in fibre-reinforced composite materials under fatigue loading. The method uses adiabatic hysteretic heating of the material to calculate the change of enthalpy by thermal imaging when the material undergoes fatigue damage. This work analytically corroborates the validity of using the calculated change of enthalpy to identify the three different fundamental fatigue damage stages of the material. The method is applied to two different types of notched sandwich specimens subject to constant amplitude fatigue loading. It is practically demonstrated that the characteristic curve progressions of the mechanically measured hysteretic dissipation curves are in good agreement with those of the enthalpy change computed by the proposed method.

Bending Stiffness of Damaged Cross-Ply Laminates

The bending stiffness of carbon/epoxy and glass/epoxy cross-ply laminates with intralaminar cracks in the surface 90° plies and local delaminations were studied experimentally using 4-point bending tests. The bending stiffness is defined as the slope of the relation between the applied bending moment and the corresponding midplane curvature. To measure the midplane curvature of laminates with different damage states, the digital image correlation system was used. The reduction in the bending stiffness with increasing density of transverse cracks and delamination length was also analyzed using a 3-D FEM model. The analysis and optical microscopy observations showed that, in the initial stage of damage evolution, local delaminations were small, but with increasing load, the delaminations grew rapidly from the tips of existing and newly created cracks, enhancing the bending stiffness degradation. As an alternative to the 3-D FEM modelling of the test, analytical approaches in conjunction with the classical laminate theory were suggested. The analytical approach was based on the concept of the “effective stiffness of damaged ply,” where the initial stiffness of the damaged ply was replaced by the effective stiffness depending on the damage state. In the present work, two routines were used to determinate the effective stiffness of the damaged ply: a) back-calculation from the difference in the stiffnesses of damaged and undamaged laminates employing the FEM model of the representative volume element; b) simple analytical fitting functions. It is shown that the analytical approach suggested is accurate and convenient for predicting the degradation of bending stiffness of a laminate with an evolving microdamage.

Forecasting and Detection of Fatigue Cracks in Polycrystalline Alloys With Ultrasonic Testing Via Discrete Wavelet Transform

Abstract Forecasting and detection of fatigue cracks play a key role in damage mitigation of mechanical structures (e.g., those made of polycrystalline alloys) to enhance their service life, and ultrasonic testing (UT) has emerged as a powerful tool for detection of fatigue cracks at early stages of damage evolution. Along this line, the work reported in this paper aims to improve the performance of fatigue crack forecasting and detection based on a synergistic combination of discrete wavelet transform (DWT) and Hilbert transform (HT) of UT data, collected from a computer-instrumented and computer-controlled fatigue-testing apparatus. Performance of the proposed method is evaluated by comparison with the images generated from a digital microscope, which are treated as the ground truth in this paper. The results of comparison reveal that forthcoming fatigue cracks can be detected ahead of their appearance on the surface of test specimens. The proposed method apparently outperforms both HT and conventional DWT, when they are applied individually, because the synergistic combination of DWT and HT provides a better characterization of UT signal attenuation for detection of fatigue crack damage.

Effect of combination variation of particle and matrix on the damage evolution and mechanical properties of particle reinforced metal matrix composites

Abstract In this article, SiCp/Al composites with matrices of different strengths reinforced by three sizes particles were manufactured by powder metallurgy process. The yield strength and ultimate strength of these composites ranged from 95 MPa to 379 MPa and 131 MPa–561 MPa respectively. In particular, in addition to the expected strengthening behavior, a weakening of the composite's yield strength and ultimate strength was found. This abnormal phenomenon was correlated with the effects of the combination variation of the particle and matrix. To study the mechanisms driving these effects, images and statistical data describing the evolution of the whole damage process were analyzed through in situ tensile testing. Two major types of damage, particle cracking and matrix slippage, were identified by the particle cracking rate f c and the slip band density ρ s . Based on the growth characteristics of these two major damage types, three stages of damage evolution were defined, and the effect of these stages on the strengthening limit of the composites' mechanical properties was discussed. Furthermore, through the analysis of the microstructures and fracture morphologies of the composites, a damage factor Q was defined to describe the different failure mechanism and the strengthening limits of the composites. This work provides a better understanding of the relation between the composite components and the mechanical properties.

A Study of the Structural Evolution and Strength Damage Mechanisms of PishaSandstone Cement Soil Modified with Fly Ash

In the present study, in order to investigate the effects of fly ash on the structural evolution and strength damage mechanism of Pisha-sandstone cement soil, unconfined compressive strength tests of Pisha-sandstone cement soil with different fly ash content levels and various ages were carried out. The apparent morphology, microstructures, and chemical compositions of the samples were observed and analyzed using ultra-depth three-dimensional microscopy, scanning electron microscopy, and XRD methods. The results revealed that the unconfined compressive strength levels of Pisha-sandstone cement soil samples displayed increasing trends with the increases in fly ash content and age. For example, when the fly ash content levels were increased from 12% to 15%, the strength of Pisha-sandstone cement soil had only slightly increased under the curing ages of 7, 28, and 60 days. In addition, the unconfined compressive strength levels of the samples with 15% fly ash content only increased 0.02%, 0.51%, and 0.54%, respectively, when compared with the samples containing 12% fly ash. It was observed that with the increases in the fly ash content, the number of pores on the outer surfaces of the samples were significantly reduced. Also, the height differences of cross-sectional gullies were reduced, and the apparent morphology was observed to be flatter. Since cement hydration creates a strong alkaline environment for reaction systems, the active degrees of the pozzolanic reactions of the fly ash were stimulated in this study. Moreover, a significant amount of the C-S-H gel phase and the stable five-membered ring structure of the mordenite and ettringite were generated, which connected the loose Pisha-sandstone particles to form a skeleton. The internal microstructures were then observed to be denser and more uniform. At the same time, the micro-pores were filled and refined by the unreacted micro-bead fly ash. Consequently, the defects in the internal microstructures were improved. Also, based on the Weibull distribution, a damage evolution model of the Pisha-sandstone cement soil was established. The analysis results of the damage variable D values during the initial damage stage, damage evolution stage, and residual damage stage of the damage process showed that the damage variables during all three stages displayed decreasing trends with the increases in the fly ash content levels and age. Therefore, based on this study’s findings, it was considered that the incorporation of fly ash could effectively improve the damage degrees of Pisha-sandstone cement soil under external force conditions.

Prediction of titanium alloy Ti-6A1-4V lifetime under consecutive shock-wave and gigacycle fatigue loads

The influence of consecutive shock-wave and gigacycle fatigue loads on the lifetime of titanium alloy VT6 (Ti-6A1-4V) was investigated. An experimental methodology for estimating the ultra-high cycle lifetime was developed with reference to accidental high-speed collision of solid particles with fan blades and subsequent fatigue failure under the flight cycle conditions normal for operating aircraft engines. The program of ultra-high cycle loading (the number of cycles is 107-109) of specially made specimens was implemented experimentally. In these experiments, massive flat targets made of titanium alloy VT6 after shock-wave loading were impacted by a flat striker (explosive generator method), which initiated controlled damage in the material. Ultra-high cycle loading tests were carried out on the Shimadzu USF-2000 ultrasonic testing machine, which made it possible to conduct fatigue loading tests up to 108-1010 cycles and frequency of 20 kHz.The "in situ" method of determining the accumulation of irreversible fatigue damage was applied. It is based on the analysis of nonlinear features of the feedback signal in a closed system of an ultrasonic fatigue installation, which allowed us to relate the microscopic mechanisms of fatigue with model representations, as well as to consider the stages of damage evolution based on the nonlinear kinetics of defect accumulation during cyclic loading in high - and gigacycle fatigue modes. In the mode of ultra-high cycle (gigacycle) fatigue, the material exhibits abnormalities of elastic properties, which lead to the effect of non-linearity in the oscillation amplitude.

Quantitative Assessment of Damage in Buried Polyethylene Pipe Subjected to Land Subsidence

AbstractTraditional investigation of polyethylene pipe (PE) subjected to external loads focused only on the study of mechanical behavior or the failure judgment, but could not predict the damage evolution process. In this paper, a quantitative assessment was conducted for the damage of PE pipe subjected to land subsidence. Specifically, a static damage model was proposed based on failure pressure. Then, a finite element model of the buried PE pipe was established to calculate the failure pressure of smooth or notched pipe. Finally, the damage of the buried PE pipes suffering from land subsidence was computed by the damage model. The results show that the failure pressure and damage curves of smooth PE pipe can be divided into increased, steady, and reducing stages. For notched PE pipe, the damage curve can be divided into initial, middle, and late stages when the notch depth coefficient A (notch depth/thickness) equals to 0.1. But when A surpasses 0.2, the damage curve loses its middle stage and rapid damage follows. The threshold of the late stage of damage can be regarded as the last warning value of the damage of PE pipe under land subsidence, which indicates the maintenance measures should be taken immediately. The defects on the pipe accelerated the speed of damage and the late stage of damage evolution.

On the effect of stress amplitude on fracture and energy evolution of pre-flawed granite under uniaxial increasing-amplitude fatigue loads

Rock mass containing discontinues is often subjected to fatigue loads in many mining and civil engineering. The stress amplitude (SA) as an important factor impacts rock fracture evolution during fatigue loading condition. Existing effects to investigate the impacts of SA on rock fatigue behaviors were mainly on constant SA loading condition, the influences of incremental stress amplitude (ISA) for rock subjected to cyclic uniaxial increasing-amplitude conditions is not well understood. In this work, uniaxial increasing-amplitude fatigue loads and post-test 3D CT scanning experiments were conducted on granite containing two pre-existing flaws. Our experimental results reveal the impact of four applied ISA (i.e., 5, 10, 20 and 30 MPa) on rock fracture evolution, energy conversion and crack network pattern at rock bridge segment. The damage accumulation and volumetric deformation increase with the increase of applied ISA. The accelerated damage evolution stage is different for sample with different ISA, and it starts to appear the earliest for a sample subjected to ISA of 30 MPa. Energy conversion analysis reveals that the dissipated energy used to drive the crack propagation is relatively large for a sample with higher ISA. Post-test 3D CT visualization reveals a most striking finding that the crack network pattern becomes complicated as the applied ISA increases. It is suggested that crack coalescence between the flaws is easy to be formed for rock subjected to low ISA, rock bridge segment fracturing is stress amplitude dependent. The testing results are expected to improve the understanding of the influence of stress amplitude on the fatigue behaviors of pre-flawed rock when rock mass is subjected to increasing-amplitude stress disturbance.