Crack Arrest Research Articles

Analysis of tensile damage characteristics of single filled bolt hole in laminate

AbstractThe strength of filled bolt holes of composites is an important parameter in developing the bearing bypass envelope curves for bolted joint structures in engineering design. This paper presents the procedures of tensile failure strengths and damage for a laminate with a filled bolt hole. Tests of two different cases, open‐hole tension (OHT) and filled‐hole tension (FHT), were performed and repeated seven times, respectively. A new type of virtual testing based on the LaRC05 criteria coupling with XFEM crack technique was developed to predict and analyze the crack initiation and early propagation around the bolt hole in the laminates. Two analytical methods were also adopted to predict the residual strength for a laminate after drilling. The results show that the thinner sample would present a higher strength with the same material system. It is also shown that the virtual test can well capture the failure modes, revealing that the 0° fiber has a natural function of crack arrest, the 90° layers that are the fracture pioneers with matrix tensile failure trigger the fiber breakage of 0° layers, and the failure of 45° layers occurs at the last. Additionally, an interesting phenomenon is observed that the initial failure around the filled hole edge does not affect the structural stiffness. Finally, a good agreement is achieved among the experimental, analytical and numerical results. It suggests that the results could provide a valuable guidance for the design of multi‐bolted joint structure.

Flexural Performance of Composite RC Beams Having an ECC Layer at the Tension Face

This paper presents an experimental study on the flexural behavior of composite Reinforced Concrete (RC) beams having a monolithic Engineered Cementitious Composites (ECC) layer at the tension face. Due to the brittle nature of normal concrete, clear cover on the tension side of beam cracks results in spalling and corrosion of reinforcement. The proposed technique overcomes the inherent brittle behavior of normal concrete with the incorporation of ECC on the tension face. This also helps in reducing bond-splitting, cover-spalling, and buckling of reinforcement in RC flexural members. For testing purposes, six full-scale beam specimens (225 mm x 300 mm x 2400 mm) with the same reinforcement were cast and tested. Out of six, two specimens were made of conventional concrete, whereas the remaining four (two each) had an ECC layer of 75mm and 100mm thick at the tension face respectively. Each specimen was installed with three strain gauges (one each at the midspan top & bottom surface of concrete and one midspan rebar on the tension face) and one LVDT at midspan. The samples were then subjected to simple monotonic loading under a third-point bending test as per ASTM C78. The load-displacement, stress-strain and moment-curvature curves were obtained for all the tested specimens. It was found that ECC-strengthened beam samples displayed an increased flexural performance at first crack, yield, and ultimate load-carrying capacity as compared to conventional RC specimens. Whereas a better crack arrest with even distribution of cracks and improvement in ductility was observed for the ECC-strengthened composite beams.

A Literature Review on Crack Arrest Features for Composite Materials and Composite Joints with a Focus on Aerospace Applications

Crack propagation within composite materials or along the interface of composite joints is a phenomenon that might result in catastrophic failure of a structure. When the factor of safety is involved in the integrity of a structure, fail-safe design becomes crucial by embedding failure-confining features. This article reviews the research work that has been carried out on such crack-arresting features (CAFs) for composite laminates, composite-to-composite joints and composite-to-metal joints. The methodology of descriptive–narrative systematic literature review was employed in order to present the state of the research in the field. Crack stopping along adhesively joined interfaces was the most common subject encountered in the literature, while other types of secondary bonding such as thermoplastic welding were quite limited. The types of the CAFs were mainly categorized by means of their integration into the structure, namely “production” and “post-production”. For each method reviewed, the common aspects of the CAFs in question are discussed as well as the outcome of the work.

Research on the dynamic failure behavior of fissured tunnel subjected to combined dynamic and static loads

With the development of mining shifting to deep underground, the effect of in-situ stress on the stability of deep tunnels cannot be ignored acted upon by dynamic disturbance loads. Numerical simulations of the failure behavior of fissured tunnel model acted upon by the effect of coupled dynamic disturbance loads and in-situ stresses are conducted by using finite difference software AUTODYN. The tunnel model containing a mode I crack was made with green sandstone, a large-scale drop-hammer impact test equipment was used as dynamic disturbance loading device. The crack initiation time (CIT), crack growth rate and crack arrest time were obtained by using the crack propagation gauge (CPG). Subsequently, a series of simulations were conducted under 0.5 ∼ 3 MPa in-situ stress and dynamic loads combined conditions. The obtained results indicate that with an increasing in the level of in-situ stress in the practical tunnel, the CIT, crack propagation length, and average crack growth rate are less than that of the tunnel in the absence of in-situ stress. The dynamic circumferential tensile stress concentration at tunnel spandrel and foot increases with the level of in-situ stress. In addition, the maximum value of the dynamic initiation toughness (DIT) reaches at in-situ stress of 1.5 MPa, and then the DIT decreases with the level of in-situ stress.

Temporal evolution of crack propagation characteristics in a weak snowpack layer: conditions of crack arrest and sustained propagation

Abstract. For a slab avalanche to release, we need sustained crack propagation in a weak snow layer beneath a cohesive snow slab – a process we call dynamic crack propagation. Field measurements on crack propagation are very scarce. We therefore performed a series of crack propagation experiments, up to 9 m long, over a period of 10 weeks and analysed these using digital image correlation techniques. We derived the elastic modulus of the slab (0.5 to 50 MPa), the elastic modulus of the weak layer (50 kPa to 1 MPa) and the specific fracture energy of the weak layer (0.1 to 1.5 J m−2) with a homogeneous and a layered-slab model. During crack propagation, we measured crack speed, touchdown distance, and the energy dissipation due to compaction and dynamic fracture (5 mJ m−2 to 0.43 J m−2). Crack speeds were highest for experiments resulting in full propagation, and crack arrest lengths were always shorter than touchdown lengths. Based on these findings, an index for self-sustained crack propagation is proposed. Our data set provides unique insight and valuable data to validate models.

Influence of SiC particles orientation on fretting crack extension in an Al-SiC metal matrix composite

The effect of SiC particle orientation regarding the fretting cracking process of an Al-SiC metal matrix composite (MMC) is investigated. Focusing on the crack extension below a sphere-on-flat fretting contact after 106 loading cycles, it is shown that the maximum crack extension is observed when the SiC particles are collinear with the crack path (i.e. perpendicular to the fretting tensile stress). The minimum extension is by contrast observed when the SiC particles are perpendicular to this latter. The crack extension seems favoured when the crack path follows the interface between the SiC particle and the Al matrix but slows down when the particles are perpendicular to the crack path. The crack must then fracture the reinforcing particle. These various experiments are simulated using a 3D finite element modelling (FEM) including the presence of a 3D crack shape. Considering that the crack arrest condition is reached (i.e. plain fretting cracks do not extend anymore after 106 loading cycles), the crack arrest thresholds ΔKth from short to long crack regimes as a function of the SiC particles orientation are extracted from a reverse analysis of the experiments.

Strain-rate sensitivity of brittle deformation and removal mechanisms of monocrystalline 3C–SiC induced by nano cutting process

In this work, the dynamic crack propagation mechanism of 3C–SiC at the micro-scale and the influence mechanism of the strain rate effect are studied, and the deformation mechanism under different strain rate is deeply analyzed. These simulations show many new phenomena, such as crack nucleation, deflection and arrest, defect accumulation and evolution near crack, strain rate effect on material deformation and removal. When the cutting velocity is equal to 5 m/s, the deformation mode of 3C–SiC is mainly sliding deformation, and the chip is separated from the matrix in the form of massive slump. When the cutting velocity reaches 500 m/s, the plastic deformation mode of the material in the machining region is the same, but the dislocation density is significantly reduced, and the material removal mode is transformed into a pure fracture mode. The brittle removal mode of monocrystalline SiC is closely related to the strain rate. The results will not only enhance the understanding the strain rate sensitivity of the damage evolution and removal behaviors of monocrystalline 3C–SiC involved at nano- and micro-scales, but also provide a theoretical guidance for optimizing process parameters during the SPDT process of monocrystalline 3C–SiC.

The effect of thermal aging on fracture properties of a narrow-gap Alloy 52 dissimilar metal weld

In nuclear power plants, dissimilar metal welds belong to safety class 1. The effect of thermal aging at 400 °C up to 15000 h on ductile-to-brittle transition (DBT) region was investigated for an Alloy 52 dissimilar metal weld (DMW). The cracks and the notches were placed close to the fusion boundary between the low-alloy steel (LAS) and the weld metal. In previous work for DMWs, the shifts in different DBT temperatures have not been investigated, including reference temperature T0, impact toughness-based T28J and reference temperature for arrest toughness, TKIa. The results show that the T0 reference temperature does not change significantly with aging time, only 10 °C, but the shift in T28J is 49 °C after 15000 h. The shift in TKIa is 35 °C. The results indicate that the aging mechanism affects more the crack propagation and arrest properties than brittle fracture initiation.

Dynamic propagation behavior of mode I crack in MSF/PVA-MKPC NSCB specimens after high-temperature exposure

In order to improve the high-temperature resistance of engineering cementitious composite (ECC), magnesium potassium phosphate cement (MKPC) was used to replace portland cement, and micro steel fiber (MSF) was used to replace polyvinyl alcohol (PVA) fiber in equal volume. And the fiber-reinforced potassium magnesium phosphate cement matrix composites (MSF/PVA-MKPC) were prepared. The microstructure of the MKPC matrix and the condition of the fibers after subjecting to high temperature were observed by scanning electron microscope (SEM), and the split Hopkinson pressure bar (SHPB) was used to conduct the impact test on notched semi-circular bend (NSCB) specimens after thermal treatment. The dynamic propagation behavior of mode I crack of MSF/PVA-MKPC after heat treatment was studied by crack propagation gauge (CPG) and experimental–numerical method. The results showed that: (1) MSF/PVA-MKPC remained intact after high temperature exposure and did not completely lose the strain hardening and strain softening ability; (2) Dynamic fracture toughness is negatively correlated with crack propagation speed; (3) Dynamic fracture toughness increases with the increase of loading rate and first decreases and then increases with the increase of maximum exposure temperature; (4) Crack arrest exists in the process of crack propagation, and the crack arrest toughness is greater than the initial toughness and the average propagation toughness.

Some Features of Cleavage Cracks in Rocks and Metals

The cracking of some rocks, namely granite, serpentinite and sandstone under tensile stress is examined in details. Brazilian testing or diametral compression, three points bending and explosion testing are used as the loading schemes in air at room temperature. Morphology of cracks in the model rocks are compared with cracks in silicon crystals, as the standard of a brittle crack, with cleavage cracks in iridium single crystals and with cracks in gallium-covered aluminum single crystals. The comparison of cracks between themselves has shown that there is additional channel for stress accommodation in the model rocks. This channel does not lead to transformation of a rock into a macroscopically ductile material, but it causes the arrest of the dangerous crack in it under tensile stress. Its influence causes transition from the brittle crack to the pore-like crack on the microscopic scale. The most probable mechanism of this transition is the dislocation emission from crack, which becomes possible in such a natural covalent solid as a rock due to Rehbinder's effect.

Verification of the master curve concept (ASTM E1921) and inhomogeneity analysis of a German RPV weld for various loading rates

Fracture-mechanical investigations were carried out on the weld metal of a German reactor pressure vessel steel 22NiMoCr3-7. The crack tip loading rate and test temperature were varied in the brittle-ductile transition region, while the results were evaluated using the Master Curve methodology (ASTME1921), including inhomogeneity analyses in Appendix X5. The highly inhomogeneous datasets could be uniformly described with a bimodal distribution function with good accuracy compared to the standard procedure. However, this agreement decreases with increasing crack tip loading rate. In contrast, a modified Master Curve with a shape factor of p = 0.03/°C progressively matches the data better with increasing crack tip loading rate. The weld metal has a significantly higher toughness than the base material. SEM analysis suggests that the inhomogeneity is due to the stochastic distribution of sharp microcracks, while the observed inhomogeneity is additionally superimposed by dynamic effects (adiabatic heating and local crack arrest) at increased crack tip loading rates. It is argued that the microstructural inhomogeneity is hereby »neutralized« and could instead be interpreted as a possible artifact of the standard Master Curve under dynamic conditions.

Effect of reflected stress wave on dynamic crack propagation and arrest behavior of sandstone specimens under impact loading

The interaction of stress waves generated by blasting or excavation disturbance with cracks or joints significantly affects the mechanical behavior of rock masses with some pre-existing cracks. To better understand the dynamic damage evolution mechanism of fractured rock mass, the influence of stress waves on cracks in rock mass must be investigated. Thus, to study the effect of reflected stress wave on dynamic fracture behavior of fissured rock mass, a large-size arc-shape boundary single cleavage triangle (ABSCT) configuration sandstone specimen was proposed in the present study. A series of impact tests were performed on the specimen with 0°, 65°, 95°, and 125° ABSCT using the drop plate impact testing system to determine dynamic fracture properties. The test was numerically simulated using the modified finite difference software and the traditional finite element software. The effect of the reflected stress wave caused by the arc-shape boundary of the ABSCT specimen on the crack propagating speed, crack fracture toughness, and compressive stress along the crack trajectory under dynamic loads was analyzed and discussed. The results show that the ABSCT specimen has a crack arresting effect on a propagating crack. The average crack propagation speed of three specimens with arc-shape boundaries is almost 0.63 times that of the flat-bottom specimen, indicating that the arc boundary has an obvious effect on the crack propagating velocity. The average crack propagating speed decreases with the increase in arc boundary radian. The compressive stress on the crack path of three arc boundary specimens is found to be greater than that of the flat-bottom specimen. Furthermore, the crack arrest toughness is greater than the average crack propagating toughness at the arc-shape boundary specimen.

Prediction of fatigue crack propagation in center cracked steel plate strengthened with prestressed CFRP strip

Evaluating the fatigue behavior of steel structures strengthened with prestressed carbon fiber reinforced polymer (CFRP) is of great significance for structural repair and rehabilitation. In this paper, an analytical model based on linear elastic fracture mechanics considering the additional elongation of the steel plate caused by the central crack opening was proposed to predict the fatigue behavior of prestressed CFRP strips strengthened steel plates. The finite element model calibrated by experiments was used to verify the proposed model. The results showed that the proposed model can predict the stress state of various components, the stress intensity factor SIF amplitude, the fatigue crack growth life, and the minimum prestress of CFRP strips required for crack arrest under different strengthening conditions with high accuracy. This study will be conducive to a better application of the prestressed CFRP strengthening of thin-walled steel structures under fatigue loading.

Large-scale testing of the mortise and tenon joint performance of the tunnel lining of prefabricated frame tunnels

Although prefabricated frame tunnels are widely used, research on their structural performance is limited, especially research on the weakest joints in prefabricated tunnels. In this study, a large-scale physical model test is used to study the mechanical properties of joints with bolts and without bolts under static loading, mainly considering the joint concrete and steel strain, opening amount, deflection, rotation angle, toughness, and ductility. The failure of the two joint types is quantitatively analysed using the virtual hinge angle and plasticity index. In addition, a finite element model is established, the model test results are compared, and the effects of the axial force and bolt preload on the joint performance are evaluated. The results show that the concrete strain and steel strain of the two joint types do not exceed the limit values under the ultimate load, providing sufficient ductility. The mechanical properties of the bolted joint are improved by the anchoring and crack arrest mechanism of the bolt. The deflection produced in each stage is lower and the deformation resistance is stronger for the bolted joint than for the boltless joint. Due to its larger damage area and greater number of cracks, the bolted joint exhibits a smaller rotation angle and stronger load-bearing capacity, and the material performance of the joint concrete is fully utilized. Increasing the axial force of a joint can significantly improve its bearing performance, but increasing the bolt preload has no significant effect. In the design of prefabricated frame tunnel joints, bolts can be added to improve the bearing capacity and deformation resistance.

To Investigate the Mechanical Properties of Concrete by Partial Replacement of Cement with Ceramic Tiles Waste Powder and Addition of Jute Fiber

Abstract: The need for natural and non-renewable resources has grown as a result of the continuing development of society and human endeavours. As a result, the amount of industrial solid waste products kept growing. The most widely used man-made material in the world, concrete, has generated a lot of interest as a potential method for recycling solid waste. About the same amount of CO2 is produced during the manufacture of 1 tonne of Portland cement. The cement sector is thought to be responsible for 5% to 8% of yearly global greenhouse gas emissions. The use of waste materials in our current concrete can lessen the environmental pollution. Put the scenario in a critical state employing alternate approaches and come up with a better material recycling solution. As additional cementitious materials, a variety of by-products, including fly ash, slag, and silica fume, are successfully used every day in the manufacturing of concrete (SCM). According to the research it has been found that about 150 million tons of ceramic have been produced per year. From that total production, around 25% to 35% has become waste material without recycling from the ceramic industry at present. The ceramic powder has various advantages such as cost - saving, energy Saving and reduces the hazards materials to the environment. Ceramic waste can be used in concrete to increase the compressive strength and physical and chemical properties of concrete. It has been established that the addition of evenly distributed, tightly spaced Fibers to concrete will significantly enhance its static and dynamic properties and act as a crack arrester. Concrete that has been reinforced with fibrous material, or fiber-reinforced concrete (FRC), has a higher structural stability. It is important to note that jute is sometimes referred to as the golden fibre owing to its high cash value and its colour. It improves the shear and punching resistance of concrete, aid in recovering post-cracking strength losses, increases the toughness and become an effective way for reinforcement. In this experimental work, partial replacement of cement by ceramic tiles waste powder by percentages of 0%, 15%, 20%, 25% and 30% with expansion of Jute Fiber at different rate as 0%, 0.25%, 0.50%, 0.75% and 1.0% are done to make sustainable concrete. All specimens were cured for 7days and 28 days before testing. From the study it has been observed that the test results shows optimum proportion for concrete mix and are within acceptable limits.

Analysis of Impact Tendency and Sensitivity of Fractured Rock with Different Crack Arrest Measures

Crack propagation leads to rock instability and failure, which seriously influence the safe and efficient operation of coal mines. According to the characteristics of fracture development and expansion, this paper takes a fractured rock with different crack numbers as the research background and studies the effects of the grouted arrest measure, anchored crack arrest measure, and grouted anchored arrest measure on the mechanical properties, energy evolution, crack expansion, and progressive instability of the fractured rock. The sensitivity of different crack arrest measures to the peak strength, elastic modulus, total crack number, and impact tendency of the fractured rock are analyzed based on the sensitive percentage. The experimental results show that the more cracks in the rock, the greater the increase of peak stress of grouted rock and grouted anchored rock, and the smaller the increase of peak stress of anchored fractured rock. With the increase of the crack number, the total crack number in anchored fractured rock specimens gradually decrease, the total crack number in grouted rocks, and grouted anchored rock specimens gradually increase. The anchored fractured rock with more cracks produces a lower total crack number when it is destroyed. The grouted rock and grouted anchored rock with more cracks produce a higher total crack number when it is destroyed. The pre-peak energy of anchored single-fractured rock is larger, the pre-peak energy of grouting multi-fractured rock is larger, and the grouted rock has a strong impact tendency. The grouted arrest measure is an important sensitive parameter to the impact energy index; the anchored crack arrest measure is the primary sensitive parameter to the peak stress, elastic modulus, and total crack number; and the grouted anchored arrest measure is an important sensitive parameter to the elastic modulus. The research results of this paper provide some guidance on the selection of crack arrest parameters and scheme design in practical rock engineering.

Effect of Testing Conditions, Gauge, and Temper on Stress Corrosion Cracking of AA7xxx Aluminum Aerospace Plate Alloys

The European Aviation Safety Agency’s recent safety information bulletin (SIB 2018-04R2) describes a brittle intergranular cracking phenomenon in 7xxx aluminum alloys and recommends testing conditions. These testing conditions are severe compared with expectations regarding, temperature, humidity, and stress in aerostructures. In this study, strong increases in time to failure of smooth specimens tested in humid air were observed when reducing either temperature or stress to levels closer to what is representative of in-service conditions. The cracking morphologies after testing in hot, humid air were identical to those described in the literature for in-service occurrences of stress corrosion cracking (SCC), including the observation of crack arrest markings consistent with a mechanism of alternate local corrosion and crack propagation by hydrogen embrittlement. The differences between such fracture surfaces and those observed in the industry standard SCC screening test, which uses a chloride-containing solution to accelerate initiation and propagation, can be attributed to the pitting of the crack surface in a chloride-containing solution in the wake of the propagating crack. The performances of 7xxx-T7 aluminum plates SCC testing in either hot, humid air or a chloride-containing aqueous solution have been compared as a function of thickness, over-aging treatment, and composition. There is a strong effect of plate thickness in both tests, with substantial decreases in initiation time and lifetime for thinner plates. The effect of plate gauge is such that “legacy” materials (such as 7010-T7651, 7050-T7651, and 7050-T7451) passing the SIB 2018-04R2 test at high thicknesses, fail at lower gauges, yet have been flying for nearly 50 y. An increase in SCC performance with increased overaging is observed in both tests. As a consequence, comparisons of SCC performance of alloy compositions should be made wherever possible at identical plate thickness and for aging treatments that result in comparable strengths. When this is done, high Zn concentration 7449-T76++ (7449-T7651 with additional aging) shows a slightly worse strength-SCC balance than 7010-T7651 and 7050-T7651. The observed trends in SCC performance in the two tests are consistent, suggesting that similar repeated initiation and propagation mechanisms are responsible for cracking in humid air and in aqueous NaCl environments.

Trifunctional Laves precipitates enabling dual-hierarchical FeCrAl alloys ultra-strong and ductile

The synergy of ultra-high strength and large ductility is a vital requirement in particular for single-phase structural alloys; unfortunately these two properties are generally mutually exclusive. The hard-yet-deformable precipitates in alloys not only act as the strengthener that can block dislocation motion thus enhance the work hardening capability to strengthen materials, but also act as the stress buffer via self-deformation that releases local stress concentrations and as the cracking modulator that triggers multiple micromechanisms that resist crack propagation to ductilize materials. Here, taking the advanced FeCrAl-based alloy as an example, we confirmed a strategy that combines these triple functions of precipitates in a dual-hierarchical alloy by controllably embedding the multi-scaled hard-yet-deformable Laves precipitates in the lamellar coarse-grained matrix, where the lamellar boundary decorated by equiaxed ultra-fine grains serving as crack arresters. The proposed design concept of dual-hierarchically heterogeneous structure can achieve a substantial increase in yield strength up to the ultrahigh level ∼1.0 GPa by far with enhanced uniform elongation. These trifunctional Laves precipitates exhibit the interface-controlled mechanisms transited from dislocation cutting through coherent nanoscaled Laves precipitates to stacking fault-mediated plasticity of incoherent micro-scaled Laves precipitates. The present dual-hierarchical design strategy opens a new avenue to engineer materials with exceptional properties for superior fracture resistance.

Experimental study on the energy evolution law during crack propagation of cracked rock mass under impact loads

Rock dynamic fracture is usually accompanied by numerous energy loss, to reveal energy evolution laws during rock dynamic fracture, the single cleavage triangle (SCT) specimens made by two types of sandstone are implemented to conduct dynamic fracture tests by using the split Hopkinson pressure bar (SHPB) device. The dynamic stress distribution law and the energy evolution law can be obtained according to the strain history of cracked rock mass subjected to impact loads. Crack propagation gauges (CPG) were applied to measure crack propagation speed, dynamic stress intensity factor (DSIF) and dynamic energy release rate can be determined by using an experimental–numerical method with the help of the software COSMOL. The experimental results show a physical pseudo-healing of the crack due to the short closure of the crack after its arrest under impact loads. The crack propagation speed and the DSIF show a certain oscillatory with the increase of crack length, the DSIFs at crack initiation are 0.2 ∼ 0.8 of the maximum value. The history of dissipated energy has a slow decrease after they reach a peak during 300 μs ∼ 350 μs, whose curves after the peak contain two stages: stage I is that the absorbed energy of the SCT specimen is mainly transformed into the transmitted energy; stage II is that it will be reflected energy. The input energy overtakes the consumed energy by new crack formation to drive the crack propagation and the test results of sandstone specimens show that 2.11 ‰ to 4.44 ‰ dissipated energy is implemented to drive crack propagation. The energy and stress are released more significantly around the crack tip before the crack arrest.

Experimental study on failure characteristics of rock-fiber concrete composite under compression load

To study the failure characteristics of the rock-fiber concrete composite structure under compressive load, the experimental research was conducted with the aid of the 3D-DIC full-field strain test experimental system. The three-dimensional space deformation field information of the composite layer was obtained. The deformation characteristics, damage characteristics and failure modes of the composite layer were analyzed. (1) The local strain field and the overall strain field of the composite layer will increase to different degrees when subjected to compressive load. When the failure is approaching, the local strain field in the crack initiation area will increase rapidly. (2) The changes in the three-dimensional displacement field and strain field of the composite layer will retain the characteristics of brittle materials. The horizontal strain field and the vertical strain field show different distribution patterns, respectively. (3) The damage change of the specimen undergoes four stages: micro damage, damage accumulation, damage manifestation and complete damage. (4) The test results show that the binding site of the composite can play a certain effect of crack arrest.