Compressive Damage Research Articles

Analysis of compression damage pattern and strength influencing factors in graphite-tailing-filled soilbags

To realize the resourceful use of soilbags filled with graphite tailings, their load-bearing and deformation characteristics must be fully understood. In this study, the following results were obtained by performing geometric testing of water-filled sealing bags and uniaxial compression tests of soilbags filled with graphite tailings. The volume of the soilbag expressed in rectangular form was approximately 0.773 times the actual volume. The types of compression damage to soilbags can be defined as surface damage and overall damage. The surface damage load increases with decreasing filling density and decreases with decreasing soilbag size. Moreover, the higher the tensile capacity of the soilbag material and the lower the friction between the soilbags, the greater the surface damage load. The overall damage load increased with an increase in the tensile strength of the soilbag material and decreased with an increase in the degree of filling; the overall damage load was greater for large-sized soilbags at high degrees of filling. Thus, the existing theoretical calculation method cannot accurately calculate the damage load of soilbags filled with graphite tailings, and the test results deviate from the theoretical calculation results, with the latter showing an increasing damage load with a decreasing filling degree.

Crack Propagation Law of Reinforced Concrete Beams

During the process of the shear and bending failure of reinforced concrete beams, the cracks generated on the side of the beam are mostly type I–II composite cracks. Considering the material nonlinearity and geometric irregularity of reinforced concrete, it is of great significance to study the dynamic evolution law of crack propagation in reinforced concrete members. Crack propagation consists of the elongation of the crack length at the surface of the concrete material, as well as the widening of the crack width. In this paper, a finite element model of simply supported reinforced concrete beams is established by considering material nonlinearity and geometric nonlinearity and considering the damage of the concrete. Comparing the experimental results, the finite element model can accurately reflect the strain changes of longitudinal reinforcement and stirrups with a maximum error within 10%. The crack development of concrete is basically consistent with the experimental results. It shows the accuracy of the finite element analysis. On this basis, a beam–column joint is analyzed and its crack propagation under reciprocating load is investigated. An important contribution is made to the preliminary analysis of the actual crack control project. The nonlinear finite element results show that the compressive damage to the concrete of the joint is insignificant at 0.1. but the tensile damage is significant at 0.96. The cracks in the connection between the frame and the floor slab mainly show bending cracks and the concrete damage in the floor slab is higher than that in the beam.

Study on the deterioration characteristics and mechanisms of recycled brick-concrete aggregate concrete under load-freeze-thaw coupling

Using construction waste to prepare recycled concrete is an important way to realize the resource utilization of construction waste and solve the shortage of sand and gravel resources in China. However, the current separation process makes it difficult to completely separate recycled brick aggregate (RBA) and recycled concrete aggregate (RCA), and the cost of high-precision separation is high. Therefore, the mixed-use of RBA and RCA to prepare recycled brick-concrete aggregate concrete (RB-CAC) can effectively reduce the pre-separation cost and has good economic and engineering applicability.In northern China, concrete is often subjected to load-freeze-thaw coupling. However, there are few studies on RB-CAC, and there are fewer studies on its degradation characteristics and degradation mechanism under load-freeze-thaw coupling. Therefore, based on the previous research on the mechanical properties of RB-CAC, RB-CAC was prepared by mixing RBA and RCA in a ratio of 1:1 and replacing natural coarse aggregate (NA) with a replacement rate of 30%. The macroscopic properties and degradation mechanism of RB-CAC under load-freeze-thaw coupling were studied by compressive strength tests, SEM, microhardness tests, and NMR tests. The quantitative relationship between microstructure and compressive strength damage was established, and the deterioration characteristics and mechanism of RB-CAC were explored. The results show that: (1) With the increase in stress ratio, the frost resistance of RB-CAC decreases gradually. Under the stress ratios of 0, 0.2, 0.4, and 0.6, the maximum number of freeze-thaw cycles that can be tolerated is 170 times, 150 times, 130 times, and 60 times (brittle fracture occurs when the stress ratio is 0.6, and freeze-thaws 70 times). After 60 freeze-thaw cycles, compared with 0 stress ratio, the mass loss rate under 0.2, 0.4, and 0.6 stress ratio increased by 0.33%, 0.42%, 1.61%, and the relative dynamic elastic modulus and compressive strength decreased by 4.73%, 2.71%, 14.13%, and 0.25 MPa, 1.07 MPa, 3.58 MPa, respectively. (2) The performance of RCA and the old mortar interface area is better than that of RCA and the new mortar interface area, and the performance of RBA and the new mortar interface area is better than that of RBA and the old mortar interface area. With the increase in stress ratio and freeze-thaw times, the interface thickness of RCA-old mortar is lower than that of RCA-new mortar, the interface thickness of RBA-old mortar is higher than that of RBA-new mortar, the interface hardness of RCA-old mortar is higher than that of RCA-new mortar, and the interface hardness of RBA-old mortar is lower than that of RBA-new mortar. (3) With the increase of the applied stress and the number of freeze-thaw cycles, the effective pore of the specimen shows a gradually decreasing trend, and the invalid pore shows a gradually increasing trend. The total porosity increased by 0.78%, 2.13%, 7.39%, and 0.71%, 2.766%, 3.50%, 4.83%, respectively, indicating that the size of the stress ratio has a greater influence on the porosity than the number of freeze-thaw cycles. (4) The fractal dimension was introduced to characterize the deterioration characteristics of RB-CAC, and the macro-micro relationship was established. The regression coefficients were 0.8784 and 0.9938, respectively. (5) The correlation analysis between the parameters of the multiple interface transition zone and the compressive strength was carried out, and the regression coefficients were all greater than 0.9. The greater the thickness of the interface zone, the smaller the hardness and the lower the compressive strength of the concrete.The research results provide a reference for reducing the separation process requirements of RBA and RCA, reducing the preparation cost of recycled concrete, and further developing high-frost resistance RB-CAC suitable for engineering applications in cold regions.

Complete constitutive model of CFRP including continuous damage in low strain rate compression and temperature generation in high strain rate impact

AbstractThis paper reports a method to construct the complete constitutive model of carbon fiber‐reinforced plastic (CFRP) by distinguishing the strain rate state and modifying the material stiffness. In quasistatic (low strain rate) compression, the initial nonlinear effect caused by the material defects was described by introducing an nonlinear increasing factor. In dynamic (high strain rate) impact, the nonlinear strengthening effect was described by introducing the dynamic amplification factors of stress and strain based on the reference state. Considering the instantaneous temperature rise obtained from the impact work–temperature generation equation and the influence of temperature on modulus and strength, the coupled thermomechanical constitutive models combining the strain rate effect and the temperature effect were established. The user‐defined material subroutines (VUMAT) were developed, and then these constitutive models were verified by finite element analysis (FEA). Finally, the developed material subroutine was applied to predict the impact penetration of CFRP laminates, and the results show that the opening holes, damage and energy dissipation are in good agreement with the reference experiment. This work comprehensively analyzed the construction method of CFRP constitutive models, which would provide a guidance for the coupled thermomechanical behavior under dynamic impact.Highlights An anisotropic continuum mechanical constitutive behavior considering strain rate effect and damage evolution behavior was established. A macroscopic anisotropic constitutive model including the coupled impact temperature generation‐mechanical behavior was established. Combined with the incremental finite element method, the three‐dimensional user‐defined material subroutines (VUMAT) were developed and verified. The thermomechanical impact penetration behaviors of CFRP laminates was predicted, and the stress field, temperature field and failure characteristics were visualized.

Experimental investigation of the effect of infill parameters on dynamic compressive performance of 3D-Printed carbon fiber reinforced polyethylene terephthalate glycol composites

The current investigation evaluates the compressive response of 3D-printed carbon fiber-reinforced PETG thermoplastics to optimize different infill parameters when loaded at high impact pressures (strain rates). The selected parameters for the 3D printing of different samples are the filling pattern (rectilinear and honeycomb) and the filling density (25%, 50%, and 75%). Compression-split Hopkinson pressure bars (SHPBs) combined with a high-speed camera were used to monitor the evolution of the mechanical behavior and damage kinetics of 3D-printed samples in real-time with the variation in strain rate. The results revealed a significant improvement in compressive strength and compressive modulus when the filling density was increased from 20% to 75% for both patterns. However, the combination of a honeycomb pattern with 75% filling presented the best compressive strength, stiffness and damage resistance, irrespective of impact pressure. In particular, the highest compressive strengths, ranging from 35.5 to 56.16 MPa for impact pressures of 1.4 to 2.4 bar, respectively, were obtained with this configuration (75% honeycomb pattern). This represents a substantial difference of 25 to 38% compared with the 75% rectilinear pattern, which showed values below 35 MPa. Another significant result was observed for the compressive modulus, which reached 2787.8 MPa for the honeycomb-filled samples, whereas this value remained below 2000 MPa for the rectilinear pattern.

Investigation on damage behavior of composite T-shaped stiffened panels under compression after multi-point impact considering impact positions

Considering the randomness and non-uniqueness of the impact damage distribution of composite structures, both experimental and numerical simulation methods are employed to systematically explore the multi-point impact damage and compression-after-impact damage behavior of composite T-shaped stiffened panels under three types of impact positions. Non-destructive testing, and numerical simulation methods are used to examine the morphology of multi-point impact damage. The compression failure process of the impacted specimens and the intact specimens (reference group) is investigated by the electrometric method. In addition, the impact failure mechanism and compression failure mechanism is further studied by combining with the numerical simulation method. The results demonstrate that impact position B (the edge of each stiffener flange), the type of impact damage is more complex, in addition to fiber/matrix damage, it contains skin/stiffener debonding damage/layer fracture damage. Especially layer fracture damage, which significantly affects the compression damage behavior of structures.

Seismic Behavior of Demountable Reinforced Concrete (RC) Beam-to-Column Joints with Damage-Control Fuses

In this paper, a new type of assembled RC beam–column joint with a beam-end steel cover-plate connection is proposed to achieve seismic toughness and damage control of the joint. Energy-dissipation plates with different structural forms are proposed, and a series of seismic performance indexes of the joints are calculated and analyzed by using the finite element method. The energy-dissipation plate with an arc notch can reach the yield condition faster, and the ultimate bearing capacity of the joint reaches the maximum. The bending design of energy-dissipation plates is carried out by calculating the demand bending moment, and energy-dissipation plates of different structural forms are simulated and verified. The results show that the proposed design formula can ensure that the bending moment at the beam end still maintains elastic deformation when the energy-dissipation plate yields. The important parameters affecting the bending moment of the weakened part in the middle of the energy-dissipation plate are analyzed. Finally, this paper also analyzes the important parameters affecting the seismic performance of the joints. The results show that the seismic performance of the newly assembled RC beam–column joints proposed in this paper is better than that of cast-in-place joints. Increasing the longitudinal reinforcement ratio appropriately can greatly improve the ultimate bearing capacity and ductility of the joints. Increasing the thickness of the energy-dissipation plate, increasing the strength of the energy-dissipation plate, increasing the axial compression ratio of the column, increasing the strength of the concrete, and increasing the strength of the shear web can improve the ultimate bearing capacity of the joints but also reduce their ductility. Under different axial compression ratios, the strain in the core area of the joints is low, and the compressive damage of the concrete is zero, which verifies the effectiveness of the damage-control design of the proposed model.

Numerical analysis on the failure characteristics of hot dry rock subjected to axial-torsional coupled percussion with single cutter

High-hardness and poor-drillability of hot dry rock (HDR) impose great challenges on drilling-rate improvement, limiting the economic exploitation of HDR geothermal. Axial-torsional coupled percussive drilling (ATCPD), as a potential drilling-rate improvement method, might provide solutions for achieving efficient breaking of HDR. To determine the rock breaking performance of ATCPD in HDR, we investigate the failure behaviors of high temperature rocks under percussion loads. Three loading modes, i.e., static loading, axial percussion loading, and torsional percussion loading, are compared with axial-torsional coupled percussion loading (A-TCPL) mode, with respect to rock breaking capacity and failure behaviors. The effect of some important engineering parameters, e.g., rock temperature, impact amplitude and frequency, is put particular emphasis to obtain the great rock breaking performance. Results show that ATCPD is characterized by the higher amplitude force, lower torque and larger cracking volume as compared to other loading modes, thereby resulting in a growth drilling efficiency. A-TCPD shows greater performance to high temperature rocks in stress response and material damage. The maximum principal stress, tensile and compressive damage factors are positively correlated with rock temperatures under A-TCPL mode. Increasing the impact amplitude and frequency are beneficial for inducing damage on rocks with temperatures ranging from 200 to 600 °C. By using the rock breaking total displacement as the evaluation index, the optimal ratio of axial to torsional impact frequencies for greater rock breaking capacity is obtained. For rocks at 200 °C, 400 °C, and 600 °C, the optimal ratio of axial to torsional impact frequencies is 1:2, 1:3, and 2:3, respectively. The results are expected to provide new insights to enhance drilling rate for geothermal well and HDR excavation.

Effect of ultraviolet radiation on the low‐velocity impact and compression after impact performances of aerospace composite laminates

AbstractThe low‐velocity impact (LVI) characteristics and compression after impact (CAI) properties of aircraft composite laminates under the influence of ultraviolet (UV) radiation were studied. Firstly, 0, 30, 60, 90 days of UV radiation experiments were carried out on the specimens to analyze the characteristics of the surface topography. Secondly, LVI experiments, the impact energies of 10, 17, and 25 J, were carried out on specimens to analyze the impact response laws and the characteristics of the impact instantaneous deformation. Finally, through CAI experiments and scanning electron microscope (SEM) techniques to clarify the influence mechanism of UV radiation on the residual compressive strength of specimens. The results showed that with the increase of UV radiation time, the shrinkage and erosion phenomena of the surface matrix and the exposure degree of the surface fibers were gradually increased, and the surface fibers were completely exposed after 90 days of radiation. At the same impact energy, with longer radiation time, the peak force gradually decreased (from 8673.86 to 7851.68 N at 17 J), the absorbed impact energy (from 9.48 to 11.13 J at 17 J) and maximum displacement (from 4.1 to 4.73 mm at 17 J) increased, the depth of pit on the impact surface decreased (from 0.213 to 0.14 mm at 17 J), and the internal damage projection area increased (from 906.68 to 1158.66 mm2 at 17 J). The compression damage of the specimens not exposed to/ exposed to UV radiation was mainly fiber cracking/interlayer delamination, respectively.Highlights Ultraviolet (UV) radiation makes the matrix of surface shrink, the fibers exposure increase. The Stage II has obvious oscillation phenomenon in four stages of the low‐velocity impact process. With prolonged UV radiation, the projected area of internal damage expands. The residual compressive load increases with the increase of UV radiation time.

Mechanical characteristics and energy evolution of rock with circular hole defects

In this paper, the uniaxial compression damage characteristics of specimens are analyzed containing holes using PFC2D. In addition, the crack propagation, stress distribution and energy development characteristics of the specimens were systematically discussed. The findings indicate that the strength parameters of various specimens drop initially and then increase with increasing center point connecting angle, in comparison to intact rock. The most significant reduction in strength parameters is observed at a center point connecting angle of 45°. The stress concentration around the holes occurs prior to crack initiation and vanishes upon specimen failure. The number of cracks in the specimens is small and the propagation length is short before touching the peak value, while the cracks expand rapidly in a short period of time after the stress touches the peak value, and the crack development rules in the two stages are quite different. With increasing center point connecting angle, the pre-peak energy and total energy drop first and then increase. After touching the peak value, the specimen is dominated by energy release and the ability to absorb energy is weakened. In the case of center point connecting angle of 45°, the specimen has the largest energy difference coefficient and the worst ability to resist damage. The damage behavior can be composed of no damage, initial damage and accelerated damage take into account the damage change rules of the specimens.

Numerical Simulation of Impact Effect on Stability of Transmission Tower Foundation

The impact effect can cause structural damage to a transmission tower’s foundation and affect its overall stability. In order to study the influence of the impact effect on the stability of transmission tower foundations, a three-dimensional finite element numerical simulation method was used to investigate the variations in the extent of damage, displacement, and inclination degree of a transmission tower foundation under different impact velocities, impact durations, impactor shapes, and impact locations. The results show that as the impact velocity increases, the damage value of the transmission tower foundation continuously increases, and the damaged area expands. The lateral displacement value increases continuously with the duration of the impact effect, and the variation in lateral displacement follows a linear function distribution. The inclination degree of the transmission tower foundation increases continuously with increased impact duration and can lead to overturning failure. A smaller impact contact area results in a larger compressive damage value for the transmission tower foundation, and different impact contact areas lead to different modes of failure for the transmission tower foundation. The damage value and damaged area of the transmission tower foundation vary with the location of the impact. By comparing the deformation of the transmission tower foundation before and after reinforcement, it is evident that the reinforcement design can significantly improve the deformation resistance and anti-overturning capacity of the transmission tower foundation.

Influence of near-fault velocity pulse on the seismic response of subway station structure

This research aims to explore the influence of near-fault velocity pulse on the seismic response of subway station under the condition of acceleration response spectra being consistent. Two suites of seismic motions are utilized, one suite is twelve as-recorded seismic motions with velocity pulses, and the other one suite is the corresponding artificial seismic motions synthesized with the response spectra of seismic motions in the first suite as target spectra. For each seismic motion with velocity pulse, the corresponding synthetic seismic motion without velocity pulse is generated by using the method of superimposing narrow-band time histories. Numerical model of soil-subway station interaction is developed by using the commercial software ABAQUS with a practical 3-span, 3-story subway station as the prototype. Numerical results indicate that with the engineering sites change from hard to soft and the burial depths change from shallow to deep, the adverse effect of velocity pulse is more significant, and the maximum inter-story drift ratio of subway station with a burial depth of 20 m embedded in site classes I, II and III has increased by 16.5%, 20.1% and 21.7%, respectively. However, the influence of velocity pulse on the concrete compression damage of subway station is not obvious.

An experimental and numerical study on the hybrid effect of basalt fiber and polypropylene fiber on the impact toughness of fiber reinforced concrete

As the civil aviation industry advances, higher requirements are put forward for the performance of airport cement pavement. The frequent takeoffs and landing of aircraft will cause continuous and large impact load on airport pavement, and combined with long-term natural factors, there will be various structural diseases. These diseases not only affect the service life of pavement, navigation safety. To enhance the impact resistance and durability of concrete, the incorporation of fiber has proven an effective approach, and basalt fibers (BF) and polypropylene fibers (PF) are selected as reinforcement materials in this study. Firstly, the effects of single BF and hybrid BF and PF on the mechanical properties of concrete were explored through compressive and flexural tests considering fiber volume contents (0.1%, 0.15, 0.2%) and lengths (6 mm, 9 mm, 12 mm). Then, the drop hammer impact test method, recommended by ACI committee 544, was refined to evaluate the impact resistance toughness of concrete. Finally, the numerical simulation of the impact test was established to explain the concrete impact damage mechanism. The results show that under less than 0.15% volume content, the single BF can effectively enhance the compressive strength, flexural strength, and impact resistance of concrete. Compared with the single BF, the combination of 12 mm BF and 6 mm PF yields favorable results, encompassing improved mechanical properties and impact resistance, thus exhibiting a positive hybrid effect. The increase in PF length (9 mm) leads to a reduction in compressive strength but an improvement in flexural strength and impact resistance. The simulation of the impact test is constructed and the accuracy is confirmed by comparing the impact times and failure patterns of the specimens. The tensile damage of plain concrete is much greater than the compressive damage, and the cracks will spread rapidly from the upper surface to the lower surface. Compared with plain concrete, the crack width of hybrid fiber reinforced concrete is larger, but the damage degree is more uniform. Fiber can absorb a large amount of impact energy, reduce the emergence of micro-cracks, and improve the impact toughness and toughness coefficient of concrete.

Numerical analysis of rubberized engineered cementitious composite (RECC) RC beams under impact loads

The environmental hazards of unrecycled rubber products and the current movement of developing more sustainable materials shed the light on utilizing recycled rubber as aggregates in concrete. The use of recycled scrab tire rubbers as aggregates in concrete can not only reduce environmental damages but also enhance the concrete’s dynamic mechanical properties such as an increase in the overall compression strain at failure and the material’s fracture energy. Previous research has investigated using rubber aggregates in concrete for reinforced concrete (RC) structural elements under static loads. However, this study aims to utilize the improved dynamic properties of concrete with rubber to resist impact loads on beams. This article presents a novel numerical investigation of the static and impact loading response of rubberized engineered cementitious composite (RECC) beams. A three-dimensional (3D) non-linear finite element (FE) model was constructed to analyze the behavior of conventional concrete (NC), crumb RECC, and powder RECC beams under impact loads. The study employs an accurate FE model that captures the non-linear behavior of RECC materials, including their properties in compression and tension, and the strain rate effect. Moreover, the strength and toughness of concrete beams can be improved by using a hybrid section of NC and RECC. Therefore, in the current study, the behavior of crumb or powder RECC layers in compression or tension sides of NC beams was studied under impact loads as well as the effect of low-impact energy, high-impact energy and the impactor nose type (hemispherical and flat-nose cylinder) on RECC beams. The outcomes of the FE model demonstrated good agreement with the available experimental results from the literature. The dynamic response of RECC beams was analyzed using FE model outputs, including time histories of impact forces, reaction forces, internal forces (shear force and flexural moment), mid-span displacements, and dissipated energy. Results indicated that RECC enhanced the performance of RC beams under impact loads. The tension performance of RC beams under impact loads was enhanced by using RECC on the tension side or in full depth since RECC limited flexural cracks and improved flexural capacity. In Comparison with NC Beams, the RC beams mid-span displacement was reduced and the energy dissipation capacity of concrete was improved when using RECC under low and high impact energies. CRECC on the compression side or in full depth improved the distribution of impact force on the NC and reduced compression damage.

Compression damage mechanism and damage detection of Aronia melanocarpa based on nuclear magnetic resonance tests

Compression damage mechanism and damage detection of Aronia melanocarpa based on nuclear magnetic resonance tests

Different effects of interfacial properties on the tensile and compressive damage mechanisms of 3D woven composites: Multiscale damage model and numerical comparative study

A multiscale damage model is proposed based on a micro-mesoscale bridging model and a multiscale kinking model, which can predict the damage development processes of 3D woven composites (3DWCs) under different loading conditions using only few material parameters. At the microscale, the various mesoscopic damage modes of yarns, including tensile fiber breakage, compressive fiber kinking and transverse inter-fiber crack, can be simply divided into matrix- and fiber-dominated damage. Using this multiscale damage model, a numerical comparative study is conducted to investigate the effect of interfacial properties on the mechanical performances and damage mechanism of 3DWCs. The numerical results indicate that the interfacial properties exhibit different effects on the tensile and compressive strengths and damage mechanisms of 3DWCs. The interaction of different damage modes controls the overall trend of the tensile strength of 3DWCs. There is an optimum point for the tensile strength of 3DWCs at different interfacial fracture toughness. Beyond the optimum point, the tensile strength of 3DWCs is negatively correlated with interfacial properties. Unlike the tensile loading case, the better the interfacial properties, the later fiber kinking occurs, resulting in higher compressive strength of 3DWCs.

Effects of compressive damage on the corrosion protection performance of offshore wind power coating systems

AbstractDamage to multilayer organic coating systems due to compressive loads can deteriorate the corrosion protection performance of the coatings under offshore exposure. The contribution is concerned with statistical investigations into the effects of load‐based and coating‐based factors on the protection performance of different coating systems. Accelerated cyclic laboratory tests (ISO 12944‐9) were performed on four multilayer coating systems, and the results were statistically analyzed. Results of analysis of variance investigations revealed that the effects on the anticorrosive performance of the coatings (anticorrosive effect [AE]) were dominated by coating‐based factors, namely coating system and total dry film thickness. These factors could explain 86% of all effects. Coating system was the only extremely significant factor. Load‐based factors did not deliver notable effects (5%). Except for the contact stiffness, these factors were insignificant. The load intensity was insignificant for all target parameters (blistering, delamination, AE). Coating regions, plastically deformed during the compression tests, did not lead to a reduction in the protection performance.

A new analytical method for stability analysis of rock blocks with basal erosion in sub-horizontal strata by considering the eccentricity effect

Abstract. The basal cavity of a rock block formed due to differential weathering is an important predisposing factor for rockfall in hard–soft interbedded rocks, which induces an eccentricity situation at the base of the rock block. Rock block falling due to the non-uniform distribution with the failure modes of toppling or sliding is defined as biased rockfall in this study. Taking into account the non-uniform stress distribution due to the eccentricity effect, a new analytical method is proposed for three-dimensional stability analysis of biased rockfall. The development of non-uniform stress distribution stress calculated by this analytical method was verified by numerical simulation. The biased rockfall progresses from partial damage of the soft underlying layer, caused by non-uniform distributed stress, to toppling and sliding of overhanging hard rock block due to overall unbalanced force. Therefore, a set of factors of safety (Fos's) against partial damage (compressive and tensile damage of the soft underlying layer) and overall failure (toppling and sliding of the hard rock block) are used to determine the rockfall susceptibility level. The analytical method is applied and validated using biased rockfalls on the northeastern edge of the Sichuan Basin in southwest China, where a significant number of rockfalls consisting of overhanging thick sandstone and underlying mudstone occur. The evolution process of biased rockfalls is divided into four stages, initial state, basal cavity formation, partially unstable and failure. The proposed method is validated by calculating Fos's of the typical unstable rock blocks in the study area. As the cavity continues to grow, the continuous retreat of mudstone causes stress redistribution between the hard and soft rock layers. This results in damage to the underlying soft rock layer due to the development of the non-uniform distribution, ultimately leading to the failure of the hard rock block. The critical retreat ratio is determined to be 0.33, which is used to classify the low and moderate rockfall susceptibility in the eastern Sichuan Basin. The proposed analytical method provides insights into the evolution of biased rockfall and a means for early identification and susceptibility assessment of rockfall.

Study on AE characteristics of concrete with different w/c ratio under uniaxial compression

Concrete material is a three-phase composite material. Its acoustic emission (AE) characteristics are influenced by the properties of its components. The water-cement ratio has significant influence on the mechanical properties and components of concrete. To clarify the relationship between water-cement ratio and AE characteristics of concrete, in this study, AE characteristics of concrete with different water-cement ratio were discussed through parameter analysis and frequency domain analysis. A damage evaluation model of concrete was established based on AE events,cumulative AE ringing count (CR) and cumulative energy (CE).The results show that AE parameters can characterize the three-stage failure process of concrete, namely the initial stage, the stable stage and the active stage.The water-cement ratio has obvious influence on the damage process of concrete and the time distribution of AE parameters.With the development of the damage process, AE signals shift from 30 kHz to 300 kHz and higher frequencies, and the number of main frequency segments increases. On this basis, the evaluation model D of concrete compression damage based on the CR and CE was established. The tangent slope of D was used to observe the change of damage stage, which is in good agreement with the experimental results.

A novel pultrusion method and axial compression behavior of 3-D braiding-winding-pultrusion composite tubes at different temperatures

The 3-D carbon fiber reinforced resin matrix composite tubes were designed and formed via a type of novel braiding-winding-pultrusion processing technique. The effects of temperature environments (lower, normal and high temperature) on the axial compressive mechanical responses and damage behaviors of novel 3-D braiding-winding-pultrusion composite (BWPC) tubes were investigated. It was found that the BWPC tubes combined with three forming process features has a complex compression failure mode. The CT image was show that the fiber damage methods of braiding, winding and pultrusion layer were different, and the structural design of the tubes directly affects the axial bearing capacity. The axial quasi-static compression failures of tubes were the flowering failure of petals at one end. The fiber fracture and fiber block falling off was more apparent when under the lower temperature environment. The research also indicated that, when the temperature exceeds 180 °C, the resin softening and stratification will be destroyed.