Great Engineering Value Research Articles

Disc cutter wear prediction based on the friction work principle

As the main rock-breaking tool of the tunnel boring machine, wear of the disc cutter is affected by geological conditions, equipment factors, and tunneling parameters when it interacts with rock. Because of the complex factors affecting disc cutter wear, it is difficult to accurately predict the wear of the disc cutter. In this study, the rock-breaking mechanism and the force of the disc cutter were analyzed, and a theoretical prediction model of disc cutter wear was established based on the friction work principle. The parameters in the disc cutter wear prediction model were determined by simulation, and a prediction method of disc cutter wear is proposed. Finally, the wear prediction model of the disc cutter was verified by field wear data. The results show that the average error between the predicted value of the disc cutter and the actual wear data from the field is 16.1%. The wear prediction model of the disc cutter has high accuracy and adaptability. The research results provide an effective method for wear prediction of the disc cutter, which is of great significance and engineering value for cutter replacement and construction management.

Energy Saving in Flow-Shop Scheduling Management: An Improved Multiobjective Model Based on Grey Wolf Optimization Algorithm

Currently, energy saving is increasingly important. During the production procedure, energy saving can be achieved if the operational method and machine infrastructure are improved, but it also increases the complexity of flow-shop scheduling. Actually, as one of the data mining technologies, Grey Wolf Optimization Algorithm is widely applied to various mathematical problems in engineering. However, due to the immaturity of this algorithm, it still has some defects. Therefore, we propose an improved multiobjective model based on Grey Wolf Optimization Algorithm related to Kalman filter and reinforcement learning operator, where Kalman filter is introduced to make the solution set closer to the Pareto optimal front end. By means of reinforcement learning operator, the convergence speed and solving ability of the algorithm can be improved. After testing six benchmark functions, the results show that it is better than that of the original algorithm and other comparison algorithms in terms of search accuracy and solution set diversity. The improved multiobjective model based on Grey Wolf Optimization Algorithm proposed in this paper is conducive to solving energy saving problems in flow-shop scheduling problem, and it is of great practical value in engineering and management.

Study on the corrected hyperbolic model of liquefaction evaluation for fine-grained sand

Through the investigation and research for seismic liquefaction cases, it is found that a certain amount of fine-grained sand is usually contained in the sand field where the seismic liquefaction occurs. Since the existence of fine particles in sand will affect the distribution of soil particles and the contact of between soil particles, further affect the liquefaction resistance of soil, it is of great practical significance and engineering value to study the seismic liquefaction evaluation of fine-grained sand. Based on the original hyperbolic model of liquefaction evaluation for clean sand, a corrected hyperbolic model of liquefaction evaluation for fine-grained sand is established in this study. Firstly, according to Chi-Chi seismic data, the relationship between clay content and fines content in sand is statistically analyzed, and the fine-grained correction term in the hyperbola model is determined; then the model of liquefaction evaluation for fine-grained sand is established and improved by the regression calculation of data samples, and the applicability of the corrected hyperbolic model is verified; on this basis the results of liquefaction evaluation for deep soil are compared between the corrected hyperbolic model and the simplified method proposed by Seed. The results show that the scope of application of the original hyperbolic model is expanded through the corrected hyperbolic model, and the success rate of seismic liquefaction evaluation in shallow soil is improved; compared with the simplified method proposed by Seed, the corrected hyperbolic model shows the good rationality when the liquefaction evaluation results in deep soil are estimated.

Joint Distribution of the Wave Crest and Its Associated Period for Nonlinear Random Waves of Finite Bandwidth

The theoretical treatment of statistical properties relevant to nonlinear random waves of finite bandwidth, such as the joint distribution of wave crest and its associated wave period, is an overdue task hampered by the complicated form of the analytical model for sea surface elevation. In this study, we first derive the wave crest distribution based on the simplified version of the Longuet-Higgins’ wave model and proceed to derive the joint distribution of the wave crest and its associated period, and the conditional wave period distribution with a given wave crest, which are of great engineering value. It is shown that the bandwidth of the wave spectrum has a significant influence on the crest distribution, and the significant wave crest is getting larger in an increasing manner as nonlinearity is increased as expected. It also turns out that the positive correlation of wave crest height with its associated period is extended to more massive waves as nonlinearity is enhanced contrary to the general perception in the coastal engineering community that the wave crest is a statistically independent random process with wave period over large waves. The peak period decreases due to the destructive interference of second-order free harmonics.

Wheel–rail stochastic dynamics and rail wear analysis of small radius curved sections of a tram line based on generalized probability density evolution

Compared with ordinary railways, the curve radius of tram lines tends to be smaller, with minimum values of only 30 m. Therefore, wheel–rail interaction is more intense and complicated in sections of small radius tram line curves. Using a stochastic variable sample set based on a generalized probability density evolution method, the stochastic variable–spectrum representation method was used to generate a time-domain sample set of stochastic track irregularities. By inputting the stochastic set of track irregularities into a tram-track coupled dynamic system model, the stochastic dynamic response of the coupled dynamic system can be obtained. Moreover, by substituting the stochastic dynamic system response into the generalized probability density evolution formula, the process of probability density evolution of each evaluation index can be obtained by the finite difference method. Finally, the dynamic response of the tram-track coupled dynamic system can be evaluated by the probability distribution of each index. By setting a series of specific groove rail wear values, a tram-track coupled dynamic analysis was carried out, and compared with the specification requirements, vehicle safety limits under different wear values were obtained. This research has great engineering value for guiding the routine maintenance of small radius curve sections of trams.

Failure analysis and revamping methods for loading threaded joints of raiseboring machine

The process of raise boring (or back reaming) has been successfully employed for vertical mine development. The technology has successfully evolved from early small borehole diameter less than 2m to large diameter greater than 8m without incident. However, in our developed raise boring machines, the threaded joints connecting reamers and drill rods suffered several fracture accidents during reaming in different geological and geotechnical conditions. Under this background, it is undoubtedly of great engineering value to explore the failure mechanisms and put forward systematic quality control and risk control measures.The fractured threaded joints were visually examined on-site, and then examined in the laboratory using fractographic and metallographic examination, mechanical testing and chemical composition analysis. Firstly, the end faces of threaded joints could not to be installed to fit the end faces of spindles due to over-specified tolerances or insufficient preload. Secondly, it was found that the manganese (Mn) contents in material samples are higher than the national standards values. Thirdly, the heat treatment of water-quenching of workpieces perhaps caused a certain degree of residual stresses. Clearly this systematic inspection suggested we should take overall improvements to eliminate the potential failure mechanisms. After check and measurement of product and process performance, the cause-and-effect relationships undoubtedly were complex and multifaceted. Therefore, the component was redesigned using revamping methods including material compositions upgrade, fitting tolerances control, optimization of heat treatment process. Moreover, a systems approach and the institution of quality management system including increasing the preload, adding anti-dropping device and executing a Plan-Do-Check-Act cycle were implemented. Through this investigation and recommendations, the device has been in operation for more than two years without any problems.

Study on Torsional Vibration of RV Reducer Based on Time-Varying Stiffness

The torsional vibration of RV reducer is the key factor affecting the positioning accuracy and trajectory accuracy of industrial robots. It is of great significance to study the torsional stiffness periodic fluctuation and parametric torsional vibration to improve the torsional vibration performance and transmission accuracy of RV reducer. Based on the torsional stiffness test device of RV reducer, the torsional stiffness is measured and the torsional stiffness curve with periodic fluctuation is obtained. The trigonometric function fitting and mathematical description of torsional stiffness curve are carried out, and the torsional vibration equation of RV reducer parameters is established. The parametric torsional vibration response of RV reducer is simulated by Runge–Kutta method, and the combined frequency characteristics and system stability are analyzed. The torsional vibration test device of RV reducer is developed to study the torsional stiffness fluctuation and torsional vibration fault. The torsional stiffness fluctuation of RV reducer can be divided into a short period and long period, corresponding to different manufacturing errors, and the mechanism of torsional stiffness fluctuation is found out. The frequency spectrum of torsional vibration under working condition is highly consistent with the simulated response spectrum, and the harmonic resonance interval obtained by frequency sweeping is close to the peak of the torsional vibration–speed curve, so the correctness of the established torsional vibration model is verified. Using the mechanism of RV reducer stiffness fluctuation to realize rapid diagnosis of defective parts of RV reducer has a strong engineering application value. The time-varying torsional stiffness of RV reducer will cause the phenomenon of parametric torsional vibration. The vibration response characteristic frequency is a linear combination of internal reference variation frequency and external excitation frequency. The parametric torsional vibration will cause the harmonic resonance of RV reducer and aggravate the torsional vibration. Therefore, it is of great engineering value to study the time-varying torsional stiffness and torsional vibration of RV reducer.

Metal nanoparticle-doped epoxy resin to suppress surface charge accumulation on insulators under DC voltage

In high-voltage direct current (HVDC) transmission systems, electric charge accumulates on insulator surfaces, causing surface electric field distortion and flashover voltage reduction. Therefore, studying a material that can improve the insulator surface insulation strength is of great engineering value. In this work, several types of metal nanoparticles with different particle sizes and concentrations are doped into epoxy resin. The experimental phenomena enables some interesting conclusions: when no agglomeration of doped nanoparticles occurs, a higher doping concentration provides a better insulation performance. The larger the doping particle size is, the lower the insulation performance. Additionally, under the same conditions, different types of metal nanoparticles lead to slightly different results after doping. Especially after doping with low concentration (approximately 120 parts per million (ppm)) and small particle size (approximately 10 nm) nanocopper particles, the insulator surface charge accumulation was effectively suppressed, and the flashover voltage was significantly improved. Our analysis suggests that it may be related to the single-electron tunneling phenomenon. Relevant results provide a new way to improve the surface insulation strength of insulators in the future.

Further Study of the Vehicle Rattle Noise with Consideration of the Impact Rates and Loudness

<div class="section abstract"><div class="htmlview paragraph">With the prevalent trend of the pure electric vehicle, vehicle interior noise has been reduced significantly. However, other noises become prominent in the cabin. Especially, the BSR noise generated by friction between parts and the clearance between components become the elements of complaints directly affect the quality of vehicles. Currently, the BSR noises are subjectively evaluated by experts, and the noise samples are simply labeled as ‘qualified’ or ‘unqualified’. Therefore, it is necessary to develop an evaluation model to assess the BSR noise objectively. In this paper, we study the vehicle rattle noise intensively. Several types of rattle noise were recorded in a semi-anechoic room. The recorded signals were then processed in the LMS test lab. to extract the single impact segments. A pool of simulated signals with different impact rates (number of impacts per second) and various loudness was synthesized for analyzation. To verify the universality of the assessment, the in-vehicle background noises were also recorded. The in-vehicle background noises were added to the rattle noise samples to simulate the in-vehicle test environment. Sound metrics were calculated and compared for all the processed samples. Jury assessment with 5 experts were performed to evaluate the rattle noise samples. The correlation between the subjective evaluation and the impact rates as well as sound metrics were studied. Consequently, an objective assessing model for vehicle rattle noise was developed based on the above analysis. This study can be used to assess the rattle noise effectively, and it has bright prospect and great value in engineering.</div></div>

Uniaxial Compression Fractal Damage Constitutive Model of Rock Subjected to Freezing and Thawing

Mechanical properties of the rock in the cold regions are often affected by freeze-thaw cycles and loads. It is of great theoretical significance and engineering value to establish a uniaxial compression damage constitutive model of the rock under freeze-thaw cycles that can reflect the relationship between macroscopic and mesoscopic structural damage. In this paper, macroscopic and mesoscopic methods are combined with statistical methods to quantitatively analyze the damage degree of rock under freeze-thaw cycles and loads. Combined with the fractal features of the macroscopic image of the section, a fractal damage constitutive model considering the residual strength of rock is established. In addition, the model is subsequently verified by the experiment. The experiment shows that the mechanical properties of rocks subjected to freeze-thaw cycles and loads are determined by freeze-thaw damage variables, load damage variables, and their coupling effects. As the number of freeze-thaw cycles increases, the uniaxial compressive strength and elastic modulus of rocks decrease, and peak strain increases. By using the fractal dimension of the compression fracture surface as a bridge considering the residual strength of the rock, the constitutive model can better reflect the compaction stage, elastic deformation stage and plastic deformation stage of the uniaxial compression process of the freeze-thaw rocks.

Influence of the Mineral Powder Content on the Asphalt Aging Resistance in High-Altitude Areas Based on Indoor Ultraviolet Light Tests.

Intense ultraviolet irradiation is an important environmental factor affecting the service performance of asphalt mixtures in high-altitude areas, and the asphalt mortar is the main factor affecting the durability of asphalt mixtures. It is of great theoretical significance and engineering value to study the performance of the asphalt mortar at medium and low temperatures under ultraviolet irradiation. Therefore, this paper focuses on the evolution of the effect of the filler content on the rheological properties of different asphalt materials at low and medium temperatures under quantitative UV irradiation. Taking the average amount of UV irradiation observed annually in Northwest China as the indoor aging condition, the matrix asphalt mortar and modified asphalt mortar with different mass ratios of asphalt mortar are selected for indoor aging tests. Physical property tests, low-temperature performance tests, and dynamic shear rheological tests are carried out. The effects of the UV irradiation intensity and mineral powder content on the low temperature performance of the asphalt mortar are studied by variance analysis method, and the reasonable mass ratio range of the asphalt mortar under UV irradiation is proposed based on the standard residual square sum (STRSS) method. The results show that the temperature sensibility and low-temperature deformation energy significantly decrease with the increase in the filler content, while the values of the softening point, fatigue factor (G*sin δ), and creep stiffness modulus of the asphalt mortar increase. In addition, the variance analysis of the creep stiffness modulus aging index (SAI) shows that the ultraviolet radiation intensity has a significant impact on the performance of the asphalt mortar. When the mineral powder content is less than 40%. When the filler content is greater than 40%, the filler content effects the performance of the asphalt mortar. According to the standard residual square sum (STRSS) method, the best mass ratio of the base asphalt mortar is 1.096, and the best mass ratio of the modified asphalt mortar is 0.9091.

State Evolution of Dry Gas Seal during Repeated Start–Stop Operation Using Acoustic Emission Method

Seal failure is a common phenomenon that occurs when using a dry gas seal. Many seal failures occur during the start-up process of the seal. In this study, the state evolution of a dry gas seal during repeated start–stop operations was investigated using an acoustic emission (AE) method and a modified empirical mode decomposition using masking signals (MS-EMD). It was evident that the liftoff speed and root mean square (RMS) of the full-speed period changed in stages. According to the change in these parameters, the state evolution of the dry gas seal during the experiment occurred in four stages: the running-in stage, normal working stage, transition stage, and abnormal stage. During the normal working stage, the RMS curve of the late liftoff period oscillated, but its wave trough was flattened due to misalignment of the seal face. After entering the transition stage, the period flattened at the wave trough disappeared and was replaced by a period of slow decline, which is attributed to the existence of abrasive particles between the seal faces. The unsteady accumulation of abrasive particles caused the liftoff speed to fluctuate significantly. By monitoring the liftoff speed of the seal and the RMS of the full-speed period, seal operators may assess the state of the seal and take intervention measures. This has great engineering value for the safe operation and life management of the seal.

Study on Strength Variation of Permeable Concrete Based on Differential Calorimetry Method and Multi-Index Test

With the implementation of the Xiongan New Area and the urbanization construction plan surrounding the Beijing-Tianjin satellite, it is urgent to study and apply the sponge-permeable paving materials to solve the “urban waterlogging and heat island effect.” In this paper, the hydration microscopic characteristics of cementitious materials are analyzed by means of the differential scanning calorimetry (DSC) test. The test of water-cement ratio, porosity, and gradation structure on the strength and permeability coefficient is emphasized, and the strength change rule of porous permeable concrete is obtained. The research results are shown as follows: (1) The DSC test shows that the effect of temperature on the hydration process of cement is obvious. With the increase of temperature, the two exothermic peaks of cement hydration increase significantly and tend to overlap and the exothermic process is shortened. At 85°C, only one exothermic peak appeared, indicating that C3S hydration and ettringite formation process were completed at the same time in a relatively short time. (2) The optimal water-binder ratio of pervious concrete ranges from 0.24 to 0.30, and the optimal porosity ranges should be controlled within the range of 15%–25%. Moreover, the open gradation of pervious concrete mix ratio design is selected, and the cement content should be within the range of 20%–25%. (3) The mathematical model of permeability coefficient and porosity ratio of permeable concrete is established: k=−0.0003n2+0.0057n−0.0044; the mathematical model of permeability coefficient and compressive strength of open-graded pervious concrete: k=0.99006−0.05389c+8.02×10−4c2. The research results can provide theoretical support and technical guidance for the design and construction of permeable materials of sponge cities in Xiongan New Area and surrounding ring new area, which are of great engineering value.

Attitude Decoupling Control for Quadrotor Aircraft Based on Linear Active Disturbance Rejection Control Technique

An attitude decoupling controller based on linear active disturbance rejection control (LADRC) is designed for small quadrotor aircraft, considering the problems existing in the controller based on active disturbance rejection control (ADRC), such as complicated design and parameters tuning difficulties in project implementation. First, the nonlinear and couple model of small quadrotor aircraft were established, and the LADRC was introduced, which described the principles of the ability of decoupling rejection control for multiple-input and multiple-output (MIMO) system and tuning method, then the model was decoupled. After that, the attitude controller based on second-order LADRC is designed and parameters is turned according to the desired settling time. F. Finally, the simulation test of the design was carried out. The simulation results indicate that the designed controller has strong robustness and anti-disturbance performance, and does not have accurate models. Moreover, there is only one parameter needs tuning in this controller, which makes the design easy to be realized and shows great engineering value.

Variation and removal of 2-MIB in full-scale treatment plants with source water from Lake Tai, China

2-Methylisoborneol (2-MIB) is one of the most common taste and odor (T&O) compounds in waterbodies and causes complaints from drinking water consumers. This is a case study of two water treatment plants taking the raw water from Lake Tai, the third largest lake in China. The relationships between the 2-MIB concentration and algae density, light change and nutrients of the raw water for the most recent four years were comprehensively investigated. The yearly variation pattern of the 2-MIB concentration in the raw water is closely related to the algae cell density. Both values reached peaks in July or August with concentrations as high as ∼500 ng/L and ∼1000 × 104 count/L, respectively. For the diurnal 2-MIB variation, the concentrations increase from 5 to 6 am, reach a peak value at ∼12 p.m., and then gradually decrease and achieve the lowest value at night. These results further confirm that 2-MIB is highly related to algae cell activity (e.g., photosynthesis). In addition, 2-MIB exists both inside and outside algae cells (i.e., intracellular and extracellular or bound and dissolved 2-MIB, respectively), and the percentage of the extracellular/dissolved portion was as high as 60% during the study period. Conventional water treatment processes (usually referrings to coagulation sedimentation and sand filtration, CSF) in WTPs have extremely unstable 2-MIB removal efficiencies (from −20% to >95%), which is mainly related to the existing forms of 2-MIB. The intracellular/bound portion can be effectively removed by CSF, especially sand filtration, while advanced water treatment processes are required to remove the dissolved 2-MIB. An ozone-activated carbon process is recommended, and the 2-MIB removal rate can reach 100%. This research has great theoretical and engineering value for treating water containing T&O compounds.

A Microcrack Location Method Based on Nonlinear S0 Mode Lamb Wave and Probability Scan Positioning Imaging Matrix

Early damage, such as microcrack, occupies most of the fatigue life of materials, and timely detection of early damage and positioning has great engineering and economic value. In this paper, a matrix scanning and positioning imaging method based on a probabilistic algorithm is proposed. Cooperating with the single-mode (S0) lamb wave, the microcrack in the thin plate material can be efficiently positioned. Taking the S0 mode lamb wave as the fundamental wave can effectively reduce the influence of the dispersion effect on the signal analysis. Meanwhile, in order to reduce the noise interference, the signal is reconstructed by empirical mode decomposition (EMD) to achieve the filtering effect. Then, the ABAQUS finite element simulation software is used to compare the positioning results under different locations of microcrack and different arrangements of probe. Finally, the feasibility of the localization algorithm is verified by the RAM-5000 SNAP nonlinear ultrasound system. The experimental results are consistent with the simulation theory, and the microcrack is effectively positioned. This facilitates our timely remedial action or further assessment of the remaining value of the material.

Effect of Orthotropic Mechanical Property on the Limit Load of Cylindrical Shell under Internal Pressure

At present the orthotropic pressurized metal structure is generally used as the isotropic one, ignoring the anisotropic characteristics of material caused during rolling process. At the same time, the elastic stress analysis design method is commonly used in pressure vessel, and the load capacity coming from plasticity of material has not been utilized. Therefore, elastic-plastic analysis of orthotropic pressurized structure is of great theoretical significance and engineering value. In present paper the limit load of orthotropic titanium cylindrical shell under internal pressure was studied. By finite element method with twice elastic slope criterion the variations of limit load for orthotropic and isotropic titanium cylindrical shells under different diameter-thickness ratios were investigated. The effect of orthotropic mechanical property on limit load of titanium cylindrical shell was discussed. At the same time, the difference of limit loads between orthotropic and isotropic titanium cylindrical shells was compared. The calculation results show that the limit loads of orthotropic and isotropic titanium cylindrical shell increase with the diameter-thickness ratio, and the limit load of orthotropic titanium cylindrical shell increases more obviously. Additionally, if the yield strength of isotropic cylindrical shell is the same as or close to the yield strength of circumferential direction for orthotropic titanium cylindrical shell, the difference of limit load is smaller. While the yield strength of isotropic cylindrical shell is much different from the yield strength of circumferential direction for orthotropic titanium cylindrical shell, the difference of the limit load is higher.

A Combined Algorithm for Cleaning Abnormal Data of Wind Turbine Power Curve Based on Change Point Grouping Algorithm and Quartile Algorithm

There exist plenty of outliers in power curve of wind turbines, which is not conducive to the follow-up information mining. Improving the wind power curve data quality of wind turbines has great engineering value. According to the spatial distribution characteristics and shapes, the outliers of wind power curve are divided into four types: the bottom curve, the mid curve, and the top curve stacked outliers, as well as scattered outliers around the curve. Based on the outlier distribution characteristics, this paper proposes a method and process of cleaning the outliers based on the change point grouping algorithm and the quartile algorithm, followed by a theoretical analysis of its feasibility. Case studies and its comparisons with the quartile–change point grouping algorithm and the local outlier factor algorithm show that the proposed change point grouping–quartile algorithm can effectively identify the four types of outliers, with good cleaning effect, high efficiency, and strong versatility.

Research on Physical and Mechanics Properties of Metamorphic Sandstone Subjected to Freeze-thaw Cycles

The Sichuan-Tibet Railway passed through high-altitude metamorphic rock areas in western Sichuan, where rock freeze-thaw weathered intensely and geological disasters occured frequently, it was of great theoretical significance and engineering value to carry out freeze-thaw cycle tests on typical rocks. The metamorphic sandstone samples collected from the Lancang River Basin were divided into five groups, each group experienced freezing and thawing about 8h(4 h freezing and 4 h thawing) of wide temperature range whose freezing temperature was -40 °C and thawing temperature was 50 °. During the experiment, loss of quality, change in P-wave velocity of metamorphic sandstone were counted with observing deterioration in the appearance of rock specimens every certain number of cycles, combining with uniaxial compression tests after 22, 42, 65, 85, and 105 times of freeze-thaw cycles respectively. Comparing and analyzing the calculated physical and mechanical parameters, the result shows that with increasing cycles of freezing and thawing, the quality first drops, then reaches a minimum after 40∼50 cycles, and oscillates and stabilizes finally. The P-wave velocity of the sample is large after freezing, and is numerically higher than the P-wave velocity after thawing. Overall, the P-wave velocity and quality change trend have good consistency. The uniaxial compressive strength of specimens has no obvious regular pattern. The structural plane has an important influence on the freeze-thaw cycle test results, the research on the mechanism of structural freeze-thaw degradation is an important part of revealing the stability of rock mass in alpine region.

Influence of Replacement Level of Recycled Coarse Aggregate on Fracture Properties of Recycled Aggregate Concrete

recycled aggregate concrete made with recycled aggregate was one of the effective ways to reuse the construction and demolition waste. Due to the weak complex interface transition zone of recycled aggregate concrete, the defect had great effect on the bearing capacity and durability of recycled aggregate concrete. The fracture performance of recycled aggregate concrete was studied, which was of great practical significance and engineering value. The wedge splitting test of 200mm × 200mm × 230mm specimens was carried out using the fatigue testing machine (MTS). The elastic modulus of the specimens were measured and calculated by strain gauge and dynamic resistance strain gauge, and the elastic modulus was about 4GPa lower than that of standard test. Based on double-K fracture model of recycled aggregate concrete, the crack initiation fracture toughness and the unstable fracture toughness was obtained. The test results show that the replacement level of recycled aggregate is not obvious to the crack initiation fracture toughness, and the unstable fracture toughness is lower than that of natural concrete. Using the exponential function to fit the tail of the PH-COMD curve of the wedge splitting test, it is found that the fracture energy of the recycled aggregate concrete is not reduced with the increase of the replacement level of the recycled aggregate.