Fictitious Crack Research Articles

Improved probabilistic design method to quantify the fracture properties of roller compacted concrete

In this paper, the material parameters pertaining to fracture properties of Roller Compacted Concrete (RCC) were evaluated using the boundary element method (BEM). The fictitious crack growth length Δafic is determined by the relative size (T-a0)/di, while the individualized values of material parameters (KIC&ft) of RCC for different water-to-cement ratios were obtained. In this study, the three-parameter Weibull fracture statistical model was proposed for the first time to analyze the discreteness of these individualized values of material parameters (KIC&ft) of RCC. The statistical analysis minimum value of material parameters (KIC&ft) of each group is obtained. The failure curves of each group of RCC were predicted from the three-parameter Weibull fracture statistical model, and the simple calculation model for material parameters (KIC&ft) was validated. Further, a two-point design method was proposed for RCC material parameters (KIC&ft) with varying strengths and water-to-cement ratios.

Numerical investigation on flexural performance of dowel laminated timber with laminas made of laminated veneer lumber

Horizontal dowel laminated timber (H-DLT) is a doweled engineered wood product with laminas made of solid timber. H-DLT has excellent bending resistance. However, the height of cross-section of H-DLT as a beam is limited by the width of solid wood laminas. Laminated veneer lumber (LVL) is an engineered wood product formed by hot-pressed gluing thin veneers, which is flexible in cross-section size compared to solid timber. Horizontal dowel laminated veneer lumber (H-DLVL) was developed by utilizing the H-DLT production methods and LVL material characteristics. H-DLVL has flexible size and good mechanical properties, and it can be made into beams and panels with large cross-sections. In this paper, the flexural performance of H-DLVL beams was investigated. A predictive finite element model of H-DLVL beams was created by the extended finite element method (XFEM) with cohesive zone model (CZM). The numerical models using solid-beam elements without fictitious cracks were verified and calibrated by experimental results. The influence of five variables, including lamina width, thickness, and quantity, dowel spacing along the grain, and dowel row (edge distance), on the flexural performance of H-DLVL beams was analyzed, and the flexural strength of H-DLVL beams was parameterized. The results showed that the failure mode of H-DLVL beams could be well predicted by XFEM without considering fictitious cracks combined with CZM, and the error range of simulated flexural strength of H-DLVL beams was within ±10 %. The flexural strength of H-DLVL beams was directly affected by lamina thickness and dowel spacing along the grain. The flexural strength of H-DLVL beams increased with the increase of those two variables. Lamina width and dowel row (edge distance) affected the flexural strength of H-DLVL beams indirectly by influencing the failure mode of H-DLVL beams. Based on this research, the recommended dowel spacing along the grain of H-DLVL beams was 6.25–12.5 times the wood dowel diameter, and the recommended edge distance of H-DLVL beams was 5–7 times.

Experimental and numerical investigations on rate-dependent fracture behavior of concrete-rock interface

To ensure the safety and stability of the concrete gravity dams built in the seismic regions, this study investigated the rate-dependent fracture behavior of the concrete-rock interfaces with different roughness degrees. Firstly, direct tensile tests and three-point bending tests were conducted to measure the mechanical and fracture properties of the concrete-rock interface with three roughness degrees, i.e. the 4 × 4 interface, natural interface, and 7 × 7 interface, and under four strain rates, i.e. 10-5/s, 10-4/s, 10-3/s, and 10-2/s. By employing the fictitious crack model and initial fracture toughness-based crack propagation criterion, numerical simulations were conducted to analyze the crack propagation processes of the concrete-rock interfaces under different strain rates. The results indicated that the tensile strength and initial fracture toughness exhibited an obvious increasing tendency with the increase of the strain rates, and they showed a nearly linear relationship with the logarithms of the strain rates. Prediction models were proposed to calculate the tensile strength and initial fracture toughness of the concrete-rock interface under different strain rates. In addition, the initial fracture toughness-based crack propagation criterion was proved to be applicable to analyze the crack propagation processes of the concrete-rock interfaces under both quasi-static and seismic strain rates. It was found that the fully-formed fracture process zone lengths and the corresponding crack length decreased obviously with the increase of the strain rates, indicating that the boundary effect of the concrete became stronger under the higher strain rates, which approached to the fracture behaviors of the large-size specimens.

The microscopic fracture model for determining the fracture behavior of self-compacting lightweight concrete

The fracture toughness (KIC) and tensile strength (ft) of concrete are critical parameters governing crack resistance. Concrete usually exhibits brittleness under flexure and tension, so this brittle fracture first occurs at the micro level. Many researchers have studied its fracture properties at the micro level. However, the theoretical model and calculation formulae do not reflect the influence of micro-material parameters on the corresponding fracture properties. In this paper, the microscopic fracture model of self-compacting lightweight aggregate concrete (SCLC) was developed, considering the parameters of micro-nano silica materials. First, the characteristic parameters, such as particle size, specific surface area, and unit weight of micro silica (MS) and colloidal nano-silica (CNS), were considered, and the calculation equation for fictitious crack growth length was proposed. Then, the micro-fracture model was developed, which was further used to calculate the fracture parameters KIC and ft of SCLC incorporated with micro-nano silica. The results are found to be consistent with the fracture parameters determined by the size effect model. In addition, the failure curves of different structural fracture modes of SCLC were established through the fracture parameters KIC and ft obtained from the microscopic fracture model, and the fracture modes of SCLC incorporated with MS and CNS were identified. The peak load of the minimum specimen size satisfying linear elastic fracture was also predicted. This research provides a new perspective for evaluating concrete fracture parameters, realizes the progressive prediction of concrete fracture performance from macro to micro, and fills in the research gaps in the existing knowledge base on the synergistic effect of MS and CNS to enhance the fracture performance of SCLC.

Analytic solution of pull-out failure on bond-slip relationship between deformed rebar and ultra-high-performance concrete

Numerous studies have explored the bond performance between deformed rebar and ultra-high-performance concrete (UHPC), yet an analytical solution to the bond-slip relationship remains elusive. This study presents an analytical solution of pull-out failure for the staged bond-slip constitutive relationship between rebar and UHPC, taking into account the meso-scale bond properties of fibers. The critical point coordinates for different stages are determined by the analytical solution. Utilizing the elastic mechanic solution of thick-walled cylinder under uniform internal pressure, the fictitious crack model, and the fiber-matrix discrete model, analytical solutions and simplified formulas for bond stress and slip at the critical points are provided respectively. The simplified formulas for predicting bond characteristics are proposed. The bond-slip test data are composed of 107 groups from 15 literatures, and the predictions of different formulas are compared. The average ratios of the theoretical ultimate bond stress and peak slip to the test results are 0.995 and 1.033, with a standard deviation of 0.179 and 0.231, and the error is generally within 20%. Compared with the bond-slip relationship, it is more reasonable that the ascending and descending sections are exponential. Moreover, the parameters in the bond-slip relationship can be calculated by the theoretical predictions of bond characteristics at each critical point.

Investigation on interfacial shear performance of concrete strengthened with bonded steel plate

This study investigated the interfacial shear performance of concrete strengthened with bonded steel plate through tests, fracture energy based theoretical analysis and numerical simulation. Firstly, the interfacial shear bearing capacity of concrete strengthened with bonded steel plate having various lengths was experimentally investigated, and the failure mode and bearing capacity were discussed. Secondly, based on fracture theory, fictitious crack hypothesis, concrete failure criteria and bilinear linear softening shear slip model, the interfacial shear capacity was theoretically derived, including the effective interfacial shear stress transfer length, fracture energy and peak interfacial shear bearing capacity. Moreover, the interfacial shear failure behavior was also numerically simulated, and the interfacial shear stress and normal stress during the whole loading and failure process were discussed. The results confirmed that the numerical simulation using the theoretically derived interfacial fracture energy and peak shear strength could give simulation results in good agreement with experimental results. Also, the calculated interfacial bearing capacity using the theoretical approach showed excellent agreement with the experimental results. Furthermore, the influence of bonding length was also theoretically derived using the numerical parametric simulation results, and a revised interfacial shear bearing capacity considering bonding length was further proposed, which was also in good agreement with both experimental and numerical simulation results.

Numerical Approach for Residual Strengths of Fiber-Reinforced Concrete Beams with Different Densities

A numerical approach is proposed to predict the flexural stress–crack mouth opening displacement (CMOD) relationship of fiber-reinforced concrete (FRC) beams. The compressive strength and density of concrete as well as various fiber parameters are considered in the compressive and tensile stress–strain relationships of concrete employed in the analysis. The nonlinear hinge model for fictitious crack propagation generalized by Olesen is also utilized to calculate the CMOD from the curvature determined from critical beam sections. The theoretical flexural stress–CMOD curves corresponded well with the measured curves. They indicated that the mean and standard deviation of normalized root mean square error values determined from 136 FRC beams were 0.237 and 0.118, respectively. A comprehensive parametric study is then conducted by numerically analyzing the primary variables influencing the CMOD response of FRC beams at extensive ranges. This enables the formulation of simple closed-form equations to determine the residual flexural strengths straightforwardly. The residual flexural strengths yielded by the derived equations agree better with the test results than with those given by previous empirical equations, yielding fewer scatters in the ratios between the experimental results and predictions is observed. Consequently, the present equations have potential in reliably assessing the residual flexural strengths of FRC with a wide range of variables, such as compressive strength, density, aggregate size, and fiber parameters.

Normal statistical fracture analysis of Roller-compacted concrete on the basis of non-linear elastic fracture mechanics

Roller-compacted concrete (RCC) is widely used in dam structures; the fracture properties of RCC directly affect the cracking resistance of RCC dams. Solving the discrete problem of the RCC fracture properties and obtaining real material parameters is important for the healthy and stable operation of RCC structures. The tensile strength (ft) and fracture toughness (KIC) are two critical parameters that have a direct impact on the fracture properties of RCC structures. In this study, the relative ligament depth [(W − a0)/di] is associated with the fictitious crack growth length (Δafic). A normal statistical fracture model is developed to describe the dispersion of the RCC ft and KIC to obtain the real material parameters of RCC with different cement-to-aggregate (C/A) ratios. For an increase in the C/A ratio from 12 % to 17 %, the ft and KIC for each group of RCC structures are 4.05–6.35 MPa and 0.90–1.41 MPa·m1/2, respectively. Based on the results of the normal statistical analysis, fracture failure curves are constructed with 95 % reliability, revealing that the fracture behavior of RCC is quasi-brittle fracture. Additionally, a relationship between the peak load (Pmax) and the material parameters is proposed, this confirms the correctness of the proposed model. Finally, the relationship between indoor small-size specimens and actual engineering-scale RCC dams regarding fracture failure is discussed based on the fracture failure curve.

Fracture model of meso-ceramics based on relative size and prediction of fracture toughness and bending strength

Based on grain size effect of ceramics and boundary effect model, the concept of relative size is introduced. In addition, meso-fracture model of ceramics with different relative sizes is established. Experimental data of nine ceramic materials with different relative sizes are statistically analyzed. It is found that fictitious crack growth length Δafic is k (W − a0) (where k is a constant, W is the specimen depth, and a0 is the initial crack length). Furthermore, k value is 0.02 when relative size is less than 200, while it is 0.2 when relative size is in the range from 200 to 1500. Fracture parameter values determined by considering relative size are basically consistent with fracture parameter values reported in the literature. Combined with normal distribution, full fracture failure curves of ceramics with different relative sizes are constructed. No brittle failure controlled by fracture toughness occurs in ceramic specimens with relative size less than 200, while brittle failure controlled by fracture toughness occurs in ceramic specimens with relative size ranging from 200 to 1500. Main reasons for the occurrence of brittle failure controlled by fracture toughness are that with increasing relative size, grain size is reduced, the number of grain boundaries increases, crack growth length increases gradually, and the interaction between fracture process zone of ceramics and the boundary of specimens becomes stronger. At the same time, an expression for predicting the peak load Pmax of ceramics with relative size (W–a0)/dav≤1500 is established. It is found that peak load can be predicted based on relative size and geometric parameters of ceramics, which is of great significance for conveniently and accurately obtaining fracture parameters of ceramics.

Experimental and meso-scale investigation of size effect on fracture properties in three-point concrete beams (TPB)

In this study, the size effect on concrete fracture parameters has been investigated in three distinct groups. While the geometry is similar across each group, the span-to-height ratio varies among the three groups. The study investigates the impact of three different span-to-height ratios (1.85, 2.65, and 4) and five different notch-to-beam height ratios (0.1, 0.2, 0.3, 0.4, and 0.5) by using three-point notched beams (TPB). Beams with identical spans but different heights are used. A new method is proposed to determine the fracture properties of concrete based on the Boundary Effect Method (BEM). A proposed formula for the fictitious cracks is presented based on the results of numerical analyses at the mesoscale and used in the BEM to determine the values of tensile strength and fracture toughness with the effects of span-to-height ratio. The established mesoscale fracture model reproduces the load-displacement curves of 3 PB specimens concrete, which verifies the rationality of the model with the experimental results. Numerical simulation reveals that the fictitious crack length in concrete is highly sensitive to the size of aggregates, their distribution and spacemen’s dimensions. Discussion on BEM based on principles of mathematical fitting and data processing is provided for more objective quasi-brittle fracture experiments and modeling. The size effect law (SEL) is limited by its requirement for sample geometries to be similar, which introduces some additional error when applied to samples with dissimilar geometries. To minimize this error, this study proposes a new formulation within the BEM method. It is found that the fracture parameters predicted by the BEM method using the proposed formulation for different geometries are consistent with the size effect law (SEL) for similar geometries.

Determination of equivalent fracture toughness and tensile strength of steel fibre reinforced cementitious composite based on boundary effect model

A theoretical method for determining the equivalent fracture toughness and tensile strength of steel fibre reinforced cementitious composite (SFRC) was established based on boundary effect model (BEM). The characteristic parameter Cf and discrete number γ were introduced to the analytical expression of BEM, which considered the influence of orientation, length and diameter of steel fibre on SFRC. The fictitious crack propagation corresponding to the peak load was evaluated by parameter combination γ⋅Cf. SFRC specimens with different depths were analyzed to verify the applicability and feasibility of the proposed method. The full failure curves for SFRC were further established.

Crack extension at the concrete–rock interface damaged by high-pressure water environment: DIC research

As a weak link in hydraulic structures such as arch dams, the fracture property of the concrete–rock interface is impacted by various factors, including the material properties of the individual constituents and the fracture process zone (FPZ) at the crack tip. Because the heel area of an extra-high dam has been exposed to a high-pressure water environment, this paper aims to investigate the whole fracture process of the concrete–rock interface after the water pressure effect. In this test, the water pressure was set at 0, 1, 2, and 4 MPa, and the crack deformation of the concrete–rock composite beam under three-point bending (TPB) was monitored in real-time by the digital image correlation (DIC) technique. DIC has been discovered to aid in understanding the damage caused by a high-pressure water environment to material properties. The stable crack extension of TPB composite beams after the high-pressure water exposure was greatly limited, and the corresponding crack length was decreased by up to 35%. The FPZ characteristic length was reduced by 19% when exposed to a high-pressure water environment, resulting in a drop in cohesive toughness on the fictitious crack. KR resistance curves for the concrete–rock interface fracture were constructed to consider the damage to material properties and FPZ evolution by high-pressure water exposure. For a reference for fracture analysis in the dam heel of extra-high dams, the calculation model of critical crack size in elastic fracture and the prediction equation of FPZ characteristic length in nonlinear fracture were constructed for a TPB composite beam.

Analytical method for predicting mode I crack propagation process of concrete under low-cycle fatigue loading

The fatigue failure of concrete structures is preceded by the formation of microcracks and the propagation of macrocracks. Therefore, the fatigue fracture properties of concrete should be investigated thoroughly to guarantee the safety of structures. In this paper, an analytical method for predicting the mode I crack propagation in concrete under low-cycle fatigue loading is proposed according to the fictitious crack model, where the fatigue tension-softening constitutive relationship is introduced, and the initial fracture toughness-based crack propagation criterion is applied. The fatigue crack propagation process can be determined by solving two governing equations. To validate the effectiveness of the method, the fatigue crack propagation in three-point bending (TPB) beams is calculated, and the results are compared with the simulated and experimental results. It is shown that, although the linearization assumption of the crack opening displacement (COD) along the depth direction leads to slight differences between the analytical and simulated results, there is still a reasonable agreement between the analytical and experimental results. The effectiveness of the analytical method is verified. Therefore, when Young’s modulus, initial fracture toughness, and fatigue tension-softening constitutive relationship are determined, the mode I fatigue crack propagation in concrete can be predicted based on the analytical method. It is expected that the method will contribute to the safety assessment of concrete structures under low-cycle fatigue loading.

ТРІЩИНОСТІЙКІСТЬ БЕТОНІВ З ПОЗИЦІЇ МЕХАНІКИ РУЙНУВАННЯ (ОГЛЯД)

This paper presents the generalized results of the analysisand synthesis of scientific and technical sources of investigation the heavy concrete on the basis of fracture mechanics for the last 25-30 years.New criteria and models for heavy concrete, which were obtained during this period have been described and generalized, in particular, a new deformation model of concrete crack resistance on the basis of fracture mechanics. The analysis of results of experimental and theoretical researches of heavy concrete crack resistance on disk-shaped samples at eccentric stretching by concentrated forces has been presented. A number of methods have been elaborated i.e. a method for experimental determination of the concrete crack resistance characteristics under static loads, a method for determining the length of the fracture zone in the crack, the relationship between the mechanical characteristics of heavy concrete and the parameters of acoustic emission measurement. The method of concrete cracking resistance with the addition of basalt fiber was also developed and the influence of basalt fiber on crack resistance and crack opening was studied in field tests. The generalized results have been presented.It has been stated about the significant development over the last three decades of methods for determining the strength, crack resistance and deformation of concrete in reinforced concrete elements from the standpoint of reinforced concrete mechanics and mechanics of concrete destruction. The conclusions about the expediency of using the Leonov-Panasyuk deformation model for concrete and the prospects for fictitious crack model have been made.On the basis of the generalized data given in the specified publications the technique of technical diagnostics and a technique of repair and restoration works at strengtheningwith use of modern technologies and materials has been developed that gives the chance to increase considerably a resource and reliability of reinforced concrete buildings and constructions

Аналитическая модель квазихрупкого разрушения пластины с трещиной

The paper considers a rectangular plate with the edge crack of mode I of normal separation from the elastoplastic material with the ultimate strain. This class of materials includes, for example, the low-alloy steels used in structures operating at temperatures below the cold brittleness threshold. The strength of the plate was studied within the framework of the Neuber --- Novozhilov approach. The crack propagation criterion was formulated using the modified Leonov --- Panasyuk --- Dugdale model using an additional parameter, i.e., the plasticity zone diameter (pre-fracture zone width). Under conditions of small-scale yielding in the presence of the stress field singular feature in the vicinity of the crack tip, the two-parameter (dual) criterion for quasi-brittle fracture was formulated for mode I cracks in the elastoplastic material. The fracture dual criterion included deformation criterion at the crack tip, as well as the force criterion at the fictitious crack tip. The lengths of the original and fictitious cracks were differing by the length of the pre-fracture zone. Diagrams of the plate quasi-brittle fracture under conditions of plane deformation and plane stress were constructed. The parameters included in the proposed quasi-brittle fracture model were analyzed. It was proposed to select model parameters according to the approximation (σ--ε)-diagram of uniaxial tension and the KIc critical stress intensity factor

Time-Dependent Fracture Behavior of Rock–Concrete Interface Coupling Viscoelasticity and Cohesive Stress Relaxation

This study investigated the time-dependent crack propagation of the rock–concrete interface under sustained loading. First, sustained loading tests were performed on the composite rock–concrete beams under three-point bending with respect to three interface roughness degrees, i.e., natural, 4×4, and 7×7 interfaces, and three sustained load levels, i.e., 80% of the maximum load, the initial cracking load, and 97% of the maximum load. Then, by employing the Norton-Bailey model and the time-dependent fictitious crack model, the constitutive relationships of bilateral materials and the rock–concrete interface were established and the mechanical responses of the rock–concrete interface under sustained loading were simulated. In addition, a crack propagation criterion proposed in this study was applied in the numerical procedure to simulate the time-dependent crack propagation process under sustained loading. The criterion implied that the interface crack propagated when the difference between the average elastic strain energy densities near the crack tip caused by the external load and cohesive stress exceeded that at the initial fracture status under quasi-static loading. The results indicated that the crack propagation under sustained loading could be interpreted from the view of energy balance between the driving energy from the external load and the resistance energy from the cohesive stress. The time-dependent crack propagation under sustained loading experienced three stages, i.e., decelerated propagation, uniform propagation, and accelerated propagation. A linear relationship between the logarithms of the crack mouth opening rate in the uniform propagation period and the failure time was established to predict the failure time of the rock–concrete interface under sustained loading.

REFINED ENGINEERING THEORY OF FRACTURE WITH A TWO-PARAMETER STRENGTH CRITERION

We present a refined engineering theory of cracks, based on a two-parameter strength criterion. Unlike the basic theory, the refined approach utilizes an improved algorithm for the regular stress component computation. This improvement allows extending the applicability range of the engineering theory to longer cracks. The two-parameter Leonov-Panasyuk-Dagdale fracture criterion serves as a basis. A coupled fracture criterion includes a strain-based criterion, which is formulated at the tip of the true crack, as well as a stress-based criterion, formulated at the tip of a fictitious crack. Based on the refined criterion, quasi-brittle fracture curves are constructed for a compact specimen, a strip with an edge crack, and a beam under four-point bending. To validate the new refined fracture criterion, we present simulation results of quasi-brittle fracture for structures made from various virtual materials. The corresponding virtual materials are modeled using a nonlocal damage accumulation theory accounting for the average size of the aggregate state of the material. Additionally, various classes of damage accumulation hypotheses are considered. Analysis of various types of virtual materials provides insights into the impact of hypotheses behind the engineering theory. For each type of material, the influence of the microstructural length scale on the overall structural strength is investigated. The analysis shows that the refined engineering theory has a wider range of applicability as compared to the basic theory based on two-parameter strength criteria.

Experimental Study on Fracture Properties of Hydraulic Concrete with Different Crack-Depth Ratios Based on Acoustic Emission and DIC Techniques

In order to study the fracture behavior of hydraulic concrete, wedge splitting tests are performed on notched cubic concrete specimens with different crack-depth ratios (0.3, 0.4, and 0.5). Meanwhile, acoustic emission and the digital image correlation method were used to monitor the crack propagation. Test results show that the initiation toughness of the hydraulic concrete specimen is independent of the crack-depth ratio. As the crack-depth ratio increases, the fracture toughness, the fracture energy, and the critical crack length decrease. The AE cumulative counts and hits can reflect not only the four-stages fracture process of hydraulic concrete but also the boundary effect of hydraulic concrete. The acoustic emission b value can reflect the two stages of postpeak damage of the hydraulic concrete. The length of fictitious crack, the propagation velocity of macrocrack and effective crack length decrease with the increase of the initial notch depth ratio. The effective crack length increases with the increase in the maximum aggregate size, and the growth time increases with the maximum aggregate size and an effective height of the specimen.

Statistical determination of fracture parameters of concrete with wide variation of water-cement ratio

The size effect and boundary effect fracture models were used to determine the fracture parameters of quasi-brittle materials through geometrically similar and non-geometrically similar specimens. Combining the characteristics of size effect and boundary effect, the concept of relative size was proposed. The simplified calculation method for quantitatively determining the fictitious crack growth length of concrete specimens with wide variation range of water-cement ratio under peak load. Based on the fracture test results of actual concrete, the tensile strength and fracture toughness of concrete with different water-cement ratios can be determined simultaneously. Using the normal distribution function, fracture curves with upper and lower limits covering all test data was established. According to the fracture failure curve, the minimum theoretical size of concrete specimens with different water-cement ratios satisfying linear elastic fracture mechanic was obtained. Furthermore, an analytical formula was established to directly determine the fracture parameters of concrete with different water-cement ratios from the peak load, and based on the analytical formula, the peak state of a large size structure meeting linear elastic fracture mechanic was predicted • The fracture toughness and tensile strength of concrete with different water-cement ratios can be determined by the proposed model in this paper. • The simplified calculation method of fictitious crack expansion Δafic for concrete samples with different water-cement ratio by determining peak load was quantitatively studied. • The relationship between the peak load and the fracture parameters is established, and the prediction of the peak state of the large-size specimen met LEFM was realized.

Fracture behavior of multi-scale nano-SiO2 and polyvinyl alcohol fiber reinforced cementitious composites under the complex environments

This paper aims to investigate the fracture properties and microscopic mechanisms of multi-scale nano-SiO2 (NS) and polyvinyl alcohol (PVA) fiber-reinforced cementitious composites (MNFRCC) in complex environments. The complex environment was the coupling effect of wet-thermal and chloride salt environments (CEWTSE) simulated by an environmental simulation test chamber. And the parameters of temperature, relative humidity (RH), mass fraction of NaCl solution, and action time were determined as 50 °C, 100 %, 5 %, and 30 d, respectively. The Double-K Fracture model (DKFM), boundary effect fracture model (BEM), and work fracture method (WFM) were used to reveal that PVA fiber and NS improved the fracture properties of MNFRCC under the CEWTSE. And when the contents of PVA fiber and NS were 1.2 % and 0.5 %, respectively, the fracture parameters were significantly improved. Based on the comparative analysis of DKFM and BEM, the reasonable fracture parameters could be obtained by linking them through the crack propagation length. Moreover, the fictitious crack growth lengths and characteristic cracks increased with the increase of PVA fiber contents. On the microscopic level, PVA fiber and NS improved pores, microcracks and interfacial transition zone in the MNFRCC.