MGPCC fracture performance evaluation method and system based on improved boundary effect model

Abstract

The invention discloses an MGPCC fracture performance evaluation method and system based on an improved boundary effect model, and belongs to the technical field of material fracture performance testing. On the basis of a traditional boundary effect model, influence parameters of a macro-fine-micro level are fused, a more accurate improved model is constructed, then fracture parameters of a material are calculated, and the fracture performance of the material is evaluated. And a fracture and failure curve is constructed by combining different types of test pieces (sizes, fracture height ratios and span-height ratios), and the fracture and failure types are accurately evaluated. According to the method, multi-level factors are integrated, so that the model is more practical, the evaluation accuracy is improved, the fracture behavior can be effectively predicted, a basis is provided for engineering design and safety evaluation, and the method has important significance in promoting scientific application of an MGPCC material in the engineering field.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of material fracture performance testing, and more particularly to a MGPCC fracture performance evaluation method and system based on an improved boundary effect model. BACKGROUND

[0002] Geopolymer-cement composite (GPCC) has attracted extensive attention due to its low carbon emission in production process and excellent mechanical properties and corrosion resistance. However, the polycondensation reaction of GPCC leads to a high drying shrinkage, which affects the development of internal microcracks and pore structure, and deteriorates the toughness and deformation resistance of GPCC, thereby limiting its wide application in hydraulic structure engineering. Based on this, a small amount of cement (OPC) is introduced into GPCC, which not only enhances the cementitious ability, but also accelerates the polycondensation reaction of GPCC as an additional calcium source. In order to improve the brittleness and deformation resistance of GPCC, researchers have prepared multi-scale geopolymer cement composite (MGPCC) by adding hybrid fibers and nanomaterials.

[0003] At present, there are few studies on the fracture performance of MGPCC, and the fracture process is more complex after adding hybrid fibers and nanomaterials, and the multi-scale fracture mechanism is not clear. The traditional fracture parameter testing method has a size effect problem, and it is difficult to accurately evaluate the true fracture performance of MGPCC.

[0004] Therefore, how to provide a MGPCC fracture performance evaluation method and system is a problem that those skilled in the art need to solve. SUMMARY

[0005] Therefore, the present application provides a MGPCC fracture performance evaluation method and system based on an improved boundary effect model, which accurately evaluates the size effect-free fracture parameters of MGPCC by considering the relationship between the microstructure characteristics and the macroscopic mechanical properties of the material, and realizes accurate evaluation of the intrinsic fracture performance of the material under the condition of small-size test specimens.

[0006] In order to achieve the above purpose, the present application adopts the following technical solutions:

[0007] On the one hand, the present application provides a MGPCC fracture performance evaluation method based on an improved boundary effect model, comprising:

[0008] Based on the traditional boundary effect model, the influence parameters of the macro-micro-microscopic level are considered, and an improved boundary effect model is established;

[0009] calculating the fracture parameters of the MGPCC specimen based on the improved boundary effect model and the test data;

[0010] constructing a fracture failure curve according to the fracture parameters and different specimen types;

[0011] evaluating the fracture failure type of the MGPCC specimen according to the fracture failure curve.

[0012] Preferably, the macro-meso-micro level influence parameters include:

[0013] macro parameters: size of specimen, height ratio, span ratio, initial crack;

[0014] meso parameters: aggregate particle size, fiber size;

[0015] micro parameters: porosity.

[0016] Preferably, based on the traditional boundary effect model, an improved boundary effect model is established by considering the macro-meso-micro level influence parameters, including:

[0017] constructing a basic analytical expression of the traditional boundary effect model based on the macro parameters:

[0018]

[0019] wherein σ n is the nominal stress considering the influence of initial crack; P max is the measured peak load of the MGPCC specimen; Δa fic is the virtual crack extension corresponding to the peak load; a e is the equivalent crack length; is the characteristic crack length;

[0020] Considering the influence of the virtual crack extension Δa fic corresponding to the peak load, the analytical expression of the traditional boundary effect model is:

[0021]

[0022] According to the stress distribution, the calculation formula of the nominal stress σ n considering the influence of initial crack obtained by force and moment balance is:

[0023]

[0024] wherein S is the span of the three-point bending beam, W is the height of the three-point bending beam, B is the width of the three-point bending beam, and α is the crack height ratio of the specimen;

[0025] the virtual crack extension Δa ficIn connection with the mesoscopic parameters, the virtual crack propagation amount Δa corresponding to the modified peak load is obtained fic :

[0026]

[0027] wherein β i is a dispersion coefficient; d i represents the particle size of the aggregate or the morphological size of the fiber, d1 is the average particle size of the aggregate, d2 is the average diameter of the steel fiber, and d3 is the average diameter of the PVA fiber;

[0028] The micro-parameters are introduced into the virtual crack propagation amount Δa corresponding to the modified peak load fic :

[0029] Δa fic-ρ = β(1-ρ)d av

[0030] wherein Δa fic-ρ is the virtual crack propagation amount considering the micro-parameters, and ρ is the porosity;

[0031] According to the virtual crack propagation amount Δa corresponding to the modified peak load fic , the calculation formula of the characteristic crack length is derived:

[0032]

[0033] According to the basic analytical expression of the traditional boundary effect model, the calculation formula of the nominal stress σ n considering the influence of the initial crack obtained by force and moment balance, the virtual crack propagation amount calculation formula considering the micro-parameters, and the characteristic crack length, the combined formula is obtained:

[0034]

[0035] wherein, and are equivalent areas.

[0036] Preferably, the specimen size includes 40 mm, 80 mm, 160 mm, 320 mm, the crack height ratio includes 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, and the span height ratio includes 2.5, 4.0.

[0037] Preferably, the fracture failure curve is obtained based on the basic analytical expression of the traditional boundary effect model.

[0038] Preferably, the fracture failure type of the MGPCC specimen is evaluated according to the fracture failure curve, including:

[0039] in combination with a ratio of an equivalent crack length to a characteristic crack length, to predict a fracture behavior of the MGPCC specimen, when a fracture process of the MGPCC specimen is controlled by a strength criterion; when a fracture process of the MGPCC specimen is controlled by a toughness criterion; and when a fracture process of the MGPCC specimen is controlled by both the strength criterion and the toughness criterion.

[0040] In another aspect, the present application provides a system for evaluating a fracture performance of a MGPCC based on an improved boundary effect model, which is used to implement any one of the above-mentioned methods for evaluating a fracture performance of a MGPCC based on an improved boundary effect model, comprising:

[0041] a model construction unit configured to establish an improved boundary effect model based on a traditional boundary effect model and considering influence parameters at macroscopic, mesoscopic and microscopic levels;

[0042] a fracture parameter calculation unit configured to calculate fracture parameters of the MGPCC specimen based on the improved boundary effect model and the test data;

[0043] a fracture failure curve construction unit configured to construct a fracture failure curve according to the fracture parameters and different specimen types;

[0044] a fracture type determination unit configured to evaluate a fracture failure type of the MGPCC specimen according to the fracture failure curve.

[0045] According to the above technical solutions, compared with the prior art, the present application provides a method and system for evaluating a fracture performance of a MGPCC based on an improved boundary effect model. The traditional boundary effect model is optimized by comprehensively considering various influence parameters at macroscopic, mesoscopic and microscopic levels. Not only macroscopic factors such as specimen size and initial crack are covered, but also mesoscopic characteristics such as aggregate particle size and fiber size and microscopic parameters such as porosity are integrated, so that the improved model is more consistent with the complex characteristics of actual materials, thereby the fracture parameters of the MGPCC specimen can be more accurately calculated and the construction precision of the fracture failure curve is improved. Secondly, the virtual crack extension amount is associated with the mesoscopic parameters and the microscopic porosity is introduced for correction, which reveals the specific influence mechanism of different factors on the fracture behavior of the MGPCC. Meanwhile, according to the fracture failure curve and the ratio of the equivalent crack length to the characteristic crack length, the fracture process of the specimen can be clearly predicted to be controlled by the strength criterion, the toughness criterion or both, which provides a strong basis for engineering design and safety evaluation and effectively prevents fracture accidents. BRIEF DESCRIPTION OF DRAWINGS

[0046] In order to make the technical solutions in the embodiments of the present application or the prior art clearer, the accompanying drawings needed in the embodiments or prior art description will be briefly introduced below. Obviously, the accompanying drawings in the following description only aim at the embodiments of the present application, and other accompanying drawings can be obtained by those skilled in the art without any creative effort on the basis of the provided accompanying drawings.

[0047] Figure 1 The flowchart provided by the present application.

[0048] Figure 2 The schematic diagram of the fracture process for BEM.

[0049] Figure 3 The stress distribution diagram of the 3-P-B test piece under the peak load.

[0050] Fig. 4(a) is the fracture failure curve of all MGPCC test pieces; Fig. 4(b) is the fracture failure curve of MGPCC test pieces with S / W of 2.5 and 4.0 respectively; Fig. 4(c) is the fracture failure curve of MGPCC test pieces with different sizes; Fig. 4(d) is the fracture failure curve of MGPCC test pieces with different slit height ratios.

[0051] Figure 5 The a of MGPCC. e The curve with the change of a.

[0052] Figure 6 The minimum size of MGPCC meeting the LEFM criterion control.

[0053] Figure 7 The structural schematic diagram provided by the present application. DETAILED DESCRIPTION

[0054] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without any creative effort belong to the protection scope of the present application.

[0055] The embodiments of the present application disclose a method for evaluating the fracture performance of MGPCC based on an improved boundary effect model, as shown in the formula (1), which comprises the following steps. Figure 1

[0056] Based on the traditional boundary effect model, the influence parameters in the macro-microscopic level are considered to establish an improved boundary effect model;

[0057] Based on the improved boundary effect model and the test data, the fracture parameters of the MGPCC test piece are calculated; ​

[0058] According to the fracture parameters and different specimen types, the fracture failure curve is constructed;

[0059] According to the fracture failure curve, the fracture failure type of the MGPCC specimen is evaluated.

[0060] Preferably, the macro-meso-micro level influence parameters include:

[0061] Macro parameters: size of specimen, aspect ratio, span ratio, initial crack;

[0062] Meso parameters: aggregate particle size, fiber size;

[0063] Micro parameters: porosity.

[0064] Further, the boundary effect basic theory believes that the fundamental reason for the size effect of small size specimens is the mutual influence between the FPZ at the initial crack tip and the specimen boundary, rather than caused by the absolute size change of the specimen. The basic analytical expression of the boundary effect theory model is:

[0065]

[0066] In the formula, σ n is the nominal stress considering the influence of the initial crack. P max is the measured peak load of the specimen. Δa fic is the virtual crack propagation amount corresponding to the peak load. a e is the equivalent crack length, which is only related to the size of the specimen and the initial crack length a0, and can be regarded as a geometric parameter of the specimen itself. is the characteristic crack length, which is a material parameter and can be determined by f t and K IC :

[0067]

[0068] BEM divides the fracture process of the material into three parts, respectively, when , formula (1) can be degenerated into σ n = f t , then the structural failure of the specimen is controlled by the strength criterion f t . When , i.e. , then the structural failure of the specimen is controlled by the fracture toughness criterion K IC . When , then the specimen is in a quasi-brittle fracture state, as shown in Figure 2 .

[0069] Substituting into formula (1), a linear form can be obtained, and the following formula can be obtained:

[0070]

[0071] From equation (3), once the nominal stress σ n and the equivalent crack length a e are determined, the corresponding fracture parameter—K IC and f t can be obtained simultaneously by curve regression of experimental data. n Thus, the theoretical relationship between σ IC , K t and f e is established.

[0072] The calculation formula of a e is as follows:

[0073]

[0074] In the formula, Y(α) is a geometric influence parameter related to the macroscopic size of the specimen, and is different for different span-height ratios, as follows:

[0075] S / W = 2.5,

[0076]

[0077] S / W = 4.0,

[0078]

[0079] The FPZ is a nonlinear region of macroscopic cracks composed of multiple microcracks, and the development of the FPZ is affected by the specimen boundary, fracture energy, microcracks, aggregate and fiber diameter, and loading rate. Due to the existence of the FPZ, it has a great influence on the fracture process of cement-based composites. BEM mainly focuses on the length of the virtual crack extension Δa fic , and assumes that the stress distribution in this region is uniform and the size is limited. As shown in Figure 3 , based on the bilinear stress distribution diagram of finite virtual crack extension under peak load P max , σ n has a close relationship with P max and Δa fic .

[0080] Considering the influence of Δa fic , the analytical expression of BEM is as follows:

[0081]

[0082] According to the stress distribution, the calculation formula of σ n obtained from force and moment balance is as follows:

[0083]

[0084] Based on microscopic studies of concrete and rock, the propagation of microcracks primarily bypasses steel fibers, PVA fibers, or aggregates. Due to the crack deflection effect resulting from the intrinsic brittle fracture characteristics of the cement matrix and the differences in the fiber or aggregate interface, the long axis dimension of the aggregate or fiber is the most important material structural parameter.

[0085] Based on the above, Δa fic With respect to aggregate particle size or fiber diameter d i Related to: Δa fic =β·d i , where β is the dispersion parameter, which incorporates the dimensions of aggregates and fibers into Δa. fic Δa of MGPCC fic The formula is as follows:

[0086]

[0087] In the formula, β i β1, β2, and β3 are the dispersion coefficients, where β1, β2, and β3 are the dispersion coefficients of aggregate, steel fiber, and PVA fiber in MGPCC, respectively. i This represents the aggregate particle size or fiber morphology, where d1 is the average particle size of the fine aggregate that accounts for the majority of MGPCC, and d2 and d3 are the average diameters of steel fibers and PVA fibers, respectively. Based on the study of the boundary effect model of multi-scale hybrid fiber reinforced cementitious composites, the fracture parameter (K... IC and f t The value can be determined by different specimen sizes and initial crack lengths, and based on different β values. i The study of the values ​​of β found that, i When taking a uniform value, the fracture parameter (K) is measured. IC and f t A simple approximation method can be used to obtain K that is independent of size. IC and f t That is, formula (9) can be transformed into formula (10). Since β i A unified value can standardize the size of aggregates and mixed fibers, i.e., d. av =d1+d2+d3.

[0088]

[0089] Based on the micro level, the propagation of micro cracks in the FPZ during the fracture process is related to the pore structure of the MGPCC. At the micro level, the micro cracks in the FPZ fully propagate, in which part of the micro cracks propagate through the micro pores, while others encounter the micro pores, leading to the crack blunting without further propagation, which may be related to the size and surface morphology of the micro pores. In order to further study the root cause of the size effect in the fracture performance of the MGPCC, it is necessary to consider the micro pore structure when calculating Δa fic .

[0090] It is found through research that the fracture parameters of the MGPCC are greatly related to the total fractal dimension of the micro pore structure and the harmful pores (50-200 nm), but the total fractal dimension cannot be directly substituted into Δa fic in terms of physical performance parameters, and the size (50-200 nm) of the harmful pores is smaller than the size of the aggregate and the hybrid fibers, which can be ignored, so the overall parameter of the pore structure, the porosity (ρ), is introduced into the calculation of Δa fic , and the formula is as follows:

[0091] Δa fic-ρ = θ Δa fic (11)

[0092] In the formula, Δa fic-ρ is the virtual crack propagation amount considering the porosity (ρ); θ is related to the porosity (ρ) of the MGPCC, and in Δa fic , the pore structure in the ligament participating in the tensile softening process needs to be removed, that is, θ = 1-ρ. In summary, the calculation expression of Δa fic-ρ is as follows:

[0093] Δa fic-ρ = β (1-ρ) d av (12)

[0094] According to a large amount of research, the characteristic crack length is related to the microstructure of the aggregate and the fibers, and according to the determined d av , the calculation formula of is obtained:

[0095]

[0096] According to the formulas (3), (8), (12) and (13), the combined formula is as follows:

[0097]

[0098]

[0099] wherein, and For the equivalent area, and (or ) entirely determined by specimen size W, initial crack a0 and d av Decide.

[0100] A was obtained based on the geometric parameters of each specimen and the 3-PB fracture test. e and P max Substituting these values ​​into formulas (14) and (15), the fracture parameters (f) of each specimen can be calculated. t and K IC Based on the calculated fracture parameters (f) t and K IC It can predict its peak load P in reverse. max And compare and analyze the results with the experimental values.

[0101] Preferably, the specimen size includes 40mm, 80mm, 160mm, and 320mm, the seam height ratio includes 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6, and the span-to-height ratio includes 2.5 and 4.0.

[0102] Preferably, the fracture failure curve is obtained based on the basic analytical expression of the traditional boundary effect model.

[0103] Preferably, the fracture failure type of the MGPCC specimen is evaluated based on the fracture failure curve, including:

[0104] By combining the ratio of equivalent crack length to characteristic crack length, the fracture behavior of MGPCC specimens is predicted. At that time, the fracture process of the MGPCC specimen was controlled by the strength criterion; when At that time, the fracture process of the MGPCC specimen was controlled by the toughness criterion; when At that time, the fracture process of the MGPCC specimen was jointly controlled by the strength criterion and the toughness criterion.

[0105] Specifically, based on the MGPCC fracture parameters (f) determined above... t and K IC Using formula (3), the fracture failure curve of MGPCC can be obtained, as shown below. Figures 4(a)-4(b) As shown. Based on the positions of different types of specimens in the fracture failure curves, it can be seen that all test results are within... and Within the range. According to relevant research, the BEM model... It can predict the fracture failure behavior of the test specimen, when At that time, the fracture process of the specimen was mainly controlled by the strength criterion (f t );when At that time, the fracture process of the specimen was mainly controlled by the LEFM criterion, namely the toughness criterion (K).IC );when At that time, the fracture process is affected by f t and K IC The common control of quasi-brittle fracture, such as Figure 2 As shown. Therefore, when W is 40, 80, 160, and 320 mm, the fracture type of MGPCC is quasi-brittle fracture. Even the largest MGPCC specimen with a height of 320 mm cannot meet the LEFM criterion control. Small-sized specimens under laboratory conditions exhibit obvious quasi-brittle characteristics, which has a significant impact on determining the true fracture parameters of non-homogeneous materials such as MGPCC.

[0106] like Figures 4(c)-4(d) As shown, W and α of the MGPCC specimen have a significant impact on the type of fracture failure. With the increase of W in the MGPCC specimen, the fracture failure type gradually tends towards the quasi-brittle fracture criterion control region. Simultaneously, with the increase of α in the MGPCC specimen, the fracture failure type transitions towards the quasi-brittle fracture criterion control region during the period α = 0.1–0.2, and then transitions towards the strength criterion control region as α changes from 0.2 to 0.6. Because the equivalent crack length a of the specimen increases with the increase of α... e First increase and then decrease, such as Figure 5 As shown, when the crack tip approaches the sample boundary (the front boundary when α→0 or the rear boundary when α→0.6), a e The rapid decrease causes tensile stress conditions to dominate, leading to a transition to the strength criterion-controlled region.

[0107] like Figures 4(a)-4(d) As shown, even though the maximum height of the MGPCC specimen in this embodiment is 320 mm, it is still far from meeting the LEFM condition. In order to obtain the minimum MGPCC specimen size that meets the LEFM criterion, the formula can be used. Obtain the equivalent crack length a e Then, based on formula (4), the initial crack length a0 can be deduced, and the minimum MGPCC specimen size W that satisfies the LEFM condition can be obtained according to the crack height ratio α. Figure 6 As shown, in the 3-PB fracture test, when α = 0.2, the minimum MGPCC specimen size W = 634.84 mm that satisfies the LEFM criterion can be obtained, which is still much larger than the maximum specimen size W = 320 mm set in this embodiment. Therefore, a larger specimen size is required to obtain accurate fracture parameters, which not only causes a lot of waste, but also cannot meet the specimen forming and mechanical testing conditions under most laboratory conditions. Based on the improved BEM model, accurate fracture parameters (f) without size effects can be obtained through small-sized specimens. t and K IC), which provides convenience for practical engineering application and experimental research.

[0108] In another aspect, the present application provides a MGPCC fracture performance evaluation system based on an improved boundary effect model, which is used to implement the MGPCC fracture performance evaluation method based on the improved boundary effect model of any one of the above aspects, such as Figure 7 as shown, comprising:

[0109] A model construction unit is configured to establish an improved boundary effect model based on a traditional boundary effect model and considering influence parameters at the macro-meso-microscopic level.

[0110] A fracture parameter calculation unit is configured to calculate fracture parameters of the MGPCC test piece based on the improved boundary effect model and test data.

[0111] A fracture failure curve construction unit is configured to construct a fracture failure curve according to the fracture parameters and different test piece types.

[0112] A fracture type determination unit is configured to determine the fracture failure type of the MGPCC test piece according to the fracture failure curve.

[0113] The various embodiments in the specification are described in a progressive manner, and each embodiment focuses on the difference from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0114] The above description of the disclosed embodiments enables a person skilled in the art to implement or use the present application. Various modifications to the embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for MGPCC fracture performance evaluation based on an improved boundary effect model, characterized in that, The method comprises the following steps: An improved boundary effect model is established based on a traditional boundary effect model and considering the influence parameters of macro-meso-micro levels; Fracture parameters of the MGPCC specimen are calculated based on the improved boundary effect model and the test data; A fracture failure curve is constructed according to the fracture parameters and different specimen types; The fracture failure type of the MGPCC specimen is evaluated according to the fracture failure curve.

2. The method for MGPCC fracture performance evaluation based on the improved boundary effect model according to claim 1, characterized in that, The influence parameters of the macro-meso-micro levels comprise: Macroscopic parameters: specimen size, crack height ratio, span height ratio, initial crack; Meso parameters: aggregate particle size, fiber size; Micro parameters: porosity.

3. The method of claim 1, wherein the method is based on an improved boundary effect model. The improved boundary effect model is established based on the traditional boundary effect model and considering the influence parameters of macro-meso-micro levels, comprising: A basic analytical expression of the traditional boundary effect model is constructed based on the macroscopic parameters: where σ n is the nominal stress considering the effect of initial crack; P max is the measured peak load of the MGPCC specimen; Δa fic is the virtual crack length corresponding to the peak load; a e is the equivalent crack length; is the characteristic crack length; Considering the influence of the virtual crack propagation amount Δa corresponding to the peak load fic The analytical expression of the conventional boundary effect model: According to the stress distribution, the formula of the nominal stress σ n considering the effect of initial crack obtained from the force and moment equilibrium is: Wherein, S is the span of the three-point bending beam, W is the height of the three-point bending beam, B is the width of the three-point bending beam, and a is the crack height ratio of the specimen; The virtual crack propagation amount Δa corresponding to the peak load is calculated fic The virtual crack propagation amount Δa corresponding to the peak load is calculated fic : where β i is the dispersion coefficient; d i denotes the aggregate particle size or the fiber form size, d1 is the average particle size of the aggregate, d2 is the average diameter of the steel fiber; d3 is the average diameter of the PVA fiber; The micro-parameters are introduced into the virtual crack propagation amount Δa corresponding to the modified peak load fic : Δa fic-ρ = β(1 - p)d av where Δa fic-ρ is the virtual crack growth quantity considering micro-parameters, and p is the porosity. According to the virtual crack propagation amount Δa corresponding to the modified peak load fic The calculation formula of the characteristic crack length The calculation formula: The formula of σ n n, the formula of virtual crack growth, and the characteristic crack length, the combined formula is obtained: wherein and is the equivalent area.

4. The method of claim 1, wherein the method is based on an improved boundary effect model. The specimen size comprises 40mm, 80mm, 160mm, and 320mm, the crack height ratio comprises 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6, and the span height ratio comprises 2.5 and 4.

0.

5. The method of claim 3, wherein the method is based on an improved boundary effect model. The fracture failure curve is obtained based on the basic analytical expression of the traditional boundary effect model.

6. The method of claim 4, wherein the method is based on an improved boundary effect model. The fracture failure type of the MGPCC specimen is evaluated according to the fracture failure curve, comprising: in combination with a ratio of an equivalent crack length to a characteristic crack length, to predict a fracture behavior of the MGPCC test piece, when the fracture process of the MGPCC test piece is controlled by a strength criterion; when the fracture process of the MGPCC test piece is controlled by a toughness criterion; and when the fracture process of the MGPCC test piece is controlled by both a strength criterion and a toughness criterion.

7. A system for MGPCC fracture performance evaluation based on modified boundary effect model, characterized in that, The system is used to realize the MGPCC fracture performance evaluation method based on the improved boundary effect model according to any one of claims 1-6, comprising: A model construction unit is configured to establish an improved boundary effect model based on a traditional boundary effect model and considering the influence parameters of macro-meso-micro levels; A fracture parameter calculation unit is configured to calculate the fracture parameters of the MGPCC specimen based on the improved boundary effect model and the test data; A fracture failure curve construction unit is configured to construct a fracture failure curve according to the fracture parameters and different specimen types; A fracture type determination unit is configured to evaluate the fracture failure type of the MGPCC specimen according to the fracture failure curve.

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