The Experts below are selected from a list of 6027 Experts worldwide ranked by ideXlab platform

M Heidarirarani - One of the best experts on this subject based on the ideXlab platform.

  • Delamination r curve behavior of curved composite laminates
    Composites Part B-engineering, 2019
    Co-Authors: A Ghadirdokht, M Heidarirarani
    Abstract:

    Abstract The effect of curvature on the Delamination R-curve behavior of composite unidirectional laminates is investigated in both the experimental and numerical manners. The flat and curved double cantilever beam specimens with different radii of curvatures are manufactured and tested subjected to mode I loading. A new data reduction method is developed for the curved specimens by adopting the Timoshenko curved beam theory. Experimental R-curves indicate that curvature has no effect on the initiation toughness, while it significantly affects the steady-state toughness and fiber bridging length. Variation of the steady-state toughness and fiber bridging length vs. The different curvatures is formulated for the curved specimens with R/h > 25 (R/h: the ratio of the radius of curvature to thickness). Finally, Delamination Propagation is simulated in the curved double cantilever beam specimens in commercial finite element software, ABAQUS, by applying both the virtual crack closure technique and cohesive zone model.

  • dependency of bridging traction of dcb composite specimen on interface fiber angle
    Theoretical and Applied Fracture Mechanics, 2017
    Co-Authors: Mahmood M. Shokrieh, Mazaher Salamattalab, M Heidarirarani
    Abstract:

    Abstract In this paper, the role of interface fiber angle on the bridging traction of double cantilever beam (DCB) specimens is investigated experimentally. In order to eliminate the effect of the remote ply orientation on the bridging traction during Delamination initiation and Propagation, DCB specimens with stacking sequences of [0 11 /θ//0 12 ] where θ  = 0, 30, 45 and 90 were considered. An experimental test set-up was established for measuring the Initial crack tip opening displacement (ICTOD) using image processing method and conducting the fracture tests. The J -integral approach was used for obtaining the bridging laws from the experimental data. The experimental results show that by increasing the interface fiber angle, the maximum bridging traction in the bridging zone increases, but the ICTOD at the end of the bridging zone is independent of the interface fiber angle. Finally, the measured bridging laws were used with cohesive elements in ABAQUS software to model the Delamination Propagation in DCB specimens accurately.

  • effect of interface fiber angle on the r curve behavior of e glass epoxy dcb specimens
    Theoretical and Applied Fracture Mechanics, 2016
    Co-Authors: Mahmood M. Shokrieh, Mazaher Salamattalab, M Heidarirarani
    Abstract:

    Abstract In this study, the effect of interface fiber angle on the R-curve behavior of double cantilever beam (DCB) specimens made of E-glass/epoxy under mode I loading is investigated experimentally. For this purpose, DCB specimens with stacking sequences of [0 11 /θ//0 12 ] and θ  = 0, 30, 45, 90 are manufactured by hand lay-up method. These stacking sequences are chosen to eliminate the effect of remote ply orientation on the R-curve behavior of DCB specimens during the Delamination Propagation. In order to obtain the critical strain energy release rate, fracture tests are conducted on these specimens. Results show that DCB specimens with 0°//0° interface have the lowest initiation interlaminar fracture toughness and the greatest bridging zone length due to good penetration of two adjacent layers of the Delamination interface. Moreover, results indicate that the interface fiber angle has significant effect on the steady-state interlaminar fracture toughness as well as the bridging zone length.

  • effect of initial crack length on the measured bridging law of unidirectional e glass epoxy double cantilever beam specimens
    Materials & Design, 2014
    Co-Authors: Mahmood M. Shokrieh, Mazaher Salamattalab, M Heidarirarani
    Abstract:

    Abstract In this paper, the effect of initial Delamination length is experimentally investigated on obtaining the mode I bridging law of unidirectional E-glass/epoxy double cantilever beam (DCB) specimens manufactured by hand layup method. To this end, an experimental test set-up is established for accurate measurement of crack tip opening displacement (CTOD) using digital image processing method. DCB tests are performed for three different Delamination lengths and the corresponding bridging laws are calculated using J -integral approach. Results showed that the maximum bridging stress, the shape of bridging law and energy dissipation in bridging zone are slightly affected by changing initial crack length. In other words, the measured bridging law acts independent of initial Delamination length. Therefore, the obtained bridging law can be used with the cohesive elements available in the commercial finite element software to simulate the Delamination Propagation behavior in unidirectional DCB specimens.

  • finite element modeling of mode i Delamination growth in laminated dcb specimens with r curve effects
    Composites Part B-engineering, 2013
    Co-Authors: M Heidarirarani, Mahmood M. Shokrieh, P P Camanho
    Abstract:

    This paper proposes a three-linear cohesive zone model (CZM) to capture the mode I Delamination initiation and Propagation behavior of unidirectional DCB specimens under large-scale fiber bridging conditions (R-curve behavior). This CZM is produced by superposing two bilinear CZMs and the required parameters are obtained from the experimental R-curve of a DCB specimen only knowing the initiation fracture toughness (Gi), the fiber bridging length (lFPZ) and the steady state toughness (Gss). The proposed method does not need the measurement of the crack tip opening displacement during the experiments and, therefore, it eliminates the current difficulties of the traditional CZMs in the simulation of Delamination Propagation under large-scale bridging.

Jianyu Zhang - One of the best experts on this subject based on the ideXlab platform.

  • a modified mode i cohesive zone model for the Delamination growth in dcb laminates with the effect of fiber bridging
    International Journal of Mechanical Sciences, 2020
    Co-Authors: Libin Zhao, Yu Gong, Yixin Hou, Jianyu Zhang
    Abstract:

    Abstract Fiber bridging has a significant influence on the Delamination Propagation behavior in multidirectional composite laminates. Traditional pure mode I bilinear cohesive zone models (CZM) do not consider the effect of fiber bridging and result in an inaccurate simulation on the Delamination behavior. This study proposed a physical-based three-linear CZM superposed by two bilinear CZMs, which represent two different phenomena including the quasi-brittle matrix fracture characterized by a higher peak stress and a shorter critical opening displacement, and the fiber bridging characterized by a lower peak stress and a longer critical opening displacement, respectively. The three-linear CZM was implemented in the commercial FE software using a user-subroutine UMAT. Double Cantilever Beam (DCB) tests on the multidirectional composite laminates with 0°/5° and 45°/−45° interfaces conducted in our previous studies are shown to have large-scale fiber bridging in mode I Delamination and are used to provide experimental data for calibrating the new CZM. Good agreements between the predicted and tested results can be achieved by adopting this new CZM, demonstrating its applicability on predicting the mode I Delamination behavior in composite laminates with the effect of fiber bridging.

  • an analytical model for evaluating the buckling Delamination Propagation and failure behaviors of delaminated composites under uniaxial compression
    Composite Structures, 2019
    Co-Authors: Kangkang Wang, Libin Zhao, Yu Gong, Haiming Hong, Jianyu Zhang
    Abstract:

    Abstract Laminated carbon fibre reinforced composite materials are very susceptible to Delamination, which is one of the most serious failure modes in composite laminates. According to the requests of damage tolerance evaluation, to completely evaluate the buckling responses and failure behaviors of delaminated composites under uniaxial compression, an analytical model was established. Based on the principle of minimum potential energy and brittle damage mechanics, the analytical model incorporated both the Delamination Propagation and failure evaluation into the buckling analysis. Uniaxial compression tests of three specimens containing embedded Delaminations were conducted. The predicted results are highly consistent with the experimental outcomes, thus validating the applicability and accuracy of the proposed analytical model. It is found that the out-of-plane deflections and energy release rate of the delaminated laminate are closely related to the buckling states; the choice of G C in a range from G IC to G IIC has little effect on the predicted results with the proposed model.

  • An improved power law criterion for the Delamination Propagation with the effect of large-scale fiber bridging in composite multidirectional laminates
    Composite Structures, 2018
    Co-Authors: Yu Gong, Libin Zhao, Jianyu Zhang
    Abstract:

    Abstract Large-scale fiber bridging can significantly enhance Delamination resistance, which makes the use of traditional Delamination Propagation criterion failed to accurately evaluate the Delamination behavior in multidirectional laminates. This paper proposed an improved power law criterion to take account for the effect of fiber bridging on the Delamination behavior. The key of the improved criterion lies on the introducing of R-curves, which can typically be determined by the standard Delamination tests. A numerical Delamination model based on the available cohesive elements was established with implementation of the improved criterion. The efficacy of the improved criterion is validated by the simulation of mixed mode bending Delamination tests. Numerical results in terms of load-displacement curves agreed well with the experiment ones. The improved criterion can accurately evaluate the mixed-mode Delamination with the effect of fiber bridging in a cost and time effective way, is convenient for applications.

  • Delamination Propagation criterion including the effect of fiber bridging for mixed mode i ii Delamination in cfrp multidirectional laminates
    Composites Science and Technology, 2017
    Co-Authors: Yu Gong, Libin Zhao, Jianyu Zhang, Yana Wang
    Abstract:

    Abstract Large-scale fiber bridging developed in the CRFP multidirectional (MD) laminates upon mixed-mode I/II fracture has a significant effect on the Delamination behavior. Without considering the effect of fiber bridging, traditional Delamination Propagation criteria fail to evaluate the Delamination behavior in MD laminates. To solve this problem, an improved criterion is proposed here, which accounts for the Delamination resistance curve (R-curve) induced by fiber bridging. Systematic Delamination tests under mode I, II and mixed I/II loadings were carried out to determine the unique parameter in the criterion and a numerical Delamination model based on the cohesive zone model (CZM) was established with implementation of the improved criterion. Initial and ultimate damage loads from numerical predictions and experiments show good agreements, verifying the accuracy of the improved criterion on evaluating the mixed-mode I/II Delamination behavior in MD laminates. Additional mixed-mode I/II Delamination test was conducted, which was used to validate the applicability of the improved criterion on evaluating the Delamination behavior with any other mode-mixity ratios (φ-ratios).

  • xfem based model for simulating zigzag Delamination growth in laminated composites under mode i loading
    Composite Structures, 2017
    Co-Authors: Libin Zhao, Yana Wang, Jianyu Zhang, Yu Gong
    Abstract:

    Abstract Interfaces adjacent to a 90° ply in laminated composites show a typical zigzag path during the mode I Delamination Propagation process, which is considered to be closely related to high Propagation values of fracture toughness. DCB (double cantilever beam) tests of specimens with a starter crack inserted into two 90° mid-layers were carried out, during which the zigzag Delamination growth and pronounced R-curve behavior were obtained. To simulate the zigzag Delamination Propagation path, four XFEM-based Delamination growth models were proposed which were comprised of a crack initiation model and a crack Propagation model, respectively. In the framework of the Delamination growth model, a new crack initiation model was developed, which took a quadratic criterion as the crack initiation criterion and the direction orthogonal to the maximum principal stress as the crack growth direction. Based on the mechanism of the Delamination resistance, four crack Propagation models considering whether the Delamination follows a pure or mixed mode damage evolution law and whether a constant or varying critical fracture toughness dominates the damage evolution were introduced. By comparing the predictions from the four Delamination growth models and the experimental results, the mode I Delamination mechanism with a zigzag path was investigated. The Delamination growth model that adopted a critical fracture toughness function and the mixed mode damage evolution law showed the best agreement with the experimental results and was recommended.

Yu Gong - One of the best experts on this subject based on the ideXlab platform.

  • a modified mode i cohesive zone model for the Delamination growth in dcb laminates with the effect of fiber bridging
    International Journal of Mechanical Sciences, 2020
    Co-Authors: Libin Zhao, Yu Gong, Yixin Hou, Jianyu Zhang
    Abstract:

    Abstract Fiber bridging has a significant influence on the Delamination Propagation behavior in multidirectional composite laminates. Traditional pure mode I bilinear cohesive zone models (CZM) do not consider the effect of fiber bridging and result in an inaccurate simulation on the Delamination behavior. This study proposed a physical-based three-linear CZM superposed by two bilinear CZMs, which represent two different phenomena including the quasi-brittle matrix fracture characterized by a higher peak stress and a shorter critical opening displacement, and the fiber bridging characterized by a lower peak stress and a longer critical opening displacement, respectively. The three-linear CZM was implemented in the commercial FE software using a user-subroutine UMAT. Double Cantilever Beam (DCB) tests on the multidirectional composite laminates with 0°/5° and 45°/−45° interfaces conducted in our previous studies are shown to have large-scale fiber bridging in mode I Delamination and are used to provide experimental data for calibrating the new CZM. Good agreements between the predicted and tested results can be achieved by adopting this new CZM, demonstrating its applicability on predicting the mode I Delamination behavior in composite laminates with the effect of fiber bridging.

  • an analytical model for evaluating the buckling Delamination Propagation and failure behaviors of delaminated composites under uniaxial compression
    Composite Structures, 2019
    Co-Authors: Kangkang Wang, Libin Zhao, Yu Gong, Haiming Hong, Jianyu Zhang
    Abstract:

    Abstract Laminated carbon fibre reinforced composite materials are very susceptible to Delamination, which is one of the most serious failure modes in composite laminates. According to the requests of damage tolerance evaluation, to completely evaluate the buckling responses and failure behaviors of delaminated composites under uniaxial compression, an analytical model was established. Based on the principle of minimum potential energy and brittle damage mechanics, the analytical model incorporated both the Delamination Propagation and failure evaluation into the buckling analysis. Uniaxial compression tests of three specimens containing embedded Delaminations were conducted. The predicted results are highly consistent with the experimental outcomes, thus validating the applicability and accuracy of the proposed analytical model. It is found that the out-of-plane deflections and energy release rate of the delaminated laminate are closely related to the buckling states; the choice of G C in a range from G IC to G IIC has little effect on the predicted results with the proposed model.

  • An improved power law criterion for the Delamination Propagation with the effect of large-scale fiber bridging in composite multidirectional laminates
    Composite Structures, 2018
    Co-Authors: Yu Gong, Libin Zhao, Jianyu Zhang
    Abstract:

    Abstract Large-scale fiber bridging can significantly enhance Delamination resistance, which makes the use of traditional Delamination Propagation criterion failed to accurately evaluate the Delamination behavior in multidirectional laminates. This paper proposed an improved power law criterion to take account for the effect of fiber bridging on the Delamination behavior. The key of the improved criterion lies on the introducing of R-curves, which can typically be determined by the standard Delamination tests. A numerical Delamination model based on the available cohesive elements was established with implementation of the improved criterion. The efficacy of the improved criterion is validated by the simulation of mixed mode bending Delamination tests. Numerical results in terms of load-displacement curves agreed well with the experiment ones. The improved criterion can accurately evaluate the mixed-mode Delamination with the effect of fiber bridging in a cost and time effective way, is convenient for applications.

  • Delamination Propagation criterion including the effect of fiber bridging for mixed mode i ii Delamination in cfrp multidirectional laminates
    Composites Science and Technology, 2017
    Co-Authors: Yu Gong, Libin Zhao, Jianyu Zhang, Yana Wang
    Abstract:

    Abstract Large-scale fiber bridging developed in the CRFP multidirectional (MD) laminates upon mixed-mode I/II fracture has a significant effect on the Delamination behavior. Without considering the effect of fiber bridging, traditional Delamination Propagation criteria fail to evaluate the Delamination behavior in MD laminates. To solve this problem, an improved criterion is proposed here, which accounts for the Delamination resistance curve (R-curve) induced by fiber bridging. Systematic Delamination tests under mode I, II and mixed I/II loadings were carried out to determine the unique parameter in the criterion and a numerical Delamination model based on the cohesive zone model (CZM) was established with implementation of the improved criterion. Initial and ultimate damage loads from numerical predictions and experiments show good agreements, verifying the accuracy of the improved criterion on evaluating the mixed-mode I/II Delamination behavior in MD laminates. Additional mixed-mode I/II Delamination test was conducted, which was used to validate the applicability of the improved criterion on evaluating the Delamination behavior with any other mode-mixity ratios (φ-ratios).

  • xfem based model for simulating zigzag Delamination growth in laminated composites under mode i loading
    Composite Structures, 2017
    Co-Authors: Libin Zhao, Yana Wang, Jianyu Zhang, Yu Gong
    Abstract:

    Abstract Interfaces adjacent to a 90° ply in laminated composites show a typical zigzag path during the mode I Delamination Propagation process, which is considered to be closely related to high Propagation values of fracture toughness. DCB (double cantilever beam) tests of specimens with a starter crack inserted into two 90° mid-layers were carried out, during which the zigzag Delamination growth and pronounced R-curve behavior were obtained. To simulate the zigzag Delamination Propagation path, four XFEM-based Delamination growth models were proposed which were comprised of a crack initiation model and a crack Propagation model, respectively. In the framework of the Delamination growth model, a new crack initiation model was developed, which took a quadratic criterion as the crack initiation criterion and the direction orthogonal to the maximum principal stress as the crack growth direction. Based on the mechanism of the Delamination resistance, four crack Propagation models considering whether the Delamination follows a pure or mixed mode damage evolution law and whether a constant or varying critical fracture toughness dominates the damage evolution were introduced. By comparing the predictions from the four Delamination growth models and the experimental results, the mode I Delamination mechanism with a zigzag path was investigated. The Delamination growth model that adopted a critical fracture toughness function and the mixed mode damage evolution law showed the best agreement with the experimental results and was recommended.

Stephen R. Hallett - One of the best experts on this subject based on the ideXlab platform.

  • cohesive element formulation for z pin Delamination bridging in fibre reinforced laminates
    International Journal of Solids and Structures, 2018
    Co-Authors: Galal F A Mohamed, Mehdi Yasaee, Gabriella Allegri, Stephen R. Hallett
    Abstract:

    Abstract Z-pins are an effective method of reinforcing laminated composite materials for resisting the Propagation of Delamination. In this paper, a novel numerical method combines the classical cohesive finite element (FE) method with a semi-analytical z-pin crack bridging model. Special purpose cohesive elements, in which the generalized traction-displacement characteristics are provided by the semi-analytical model z-pin bridging map, are implemented in macro-scale FE models. This cohesive element offers the flexibility to employ two cohesive laws concurrently for prediction of Delamination Propagation, for both the pinned and unpinned behaviour. Its efficacy is evaluated by the simulation of double cantilever beam (DCB), mixed-mode bend (MMB), and pure mode II End-Loaded Split (ELS) fracture tests at 2% z-pin areal density. The numerical results in terms of load-deflection predictions agree well with experiments. The different simulations were all performed using a single set of input parameters derived from single z-pin tests with no fitting factors.

  • cohesive element formulation for z pin Delamination bridging in fibre reinforced laminates
    International Journal of Solids and Structures, 2018
    Co-Authors: Galal F A Mohamed, Mehdi Yasaee, Gabriella Allegri, Stephen R. Hallett
    Abstract:

    Abstract Z-pins are an effective method of reinforcing laminated composite materials for resisting the Propagation of Delamination. In this paper, a novel numerical method combines the classical cohesive finite element (FE) method with a semi-analytical z-pin crack bridging model. Special purpose cohesive elements, in which the generalized traction-displacement characteristics are provided by the semi-analytical model z-pin bridging map, are implemented in macro-scale FE models. This cohesive element offers the flexibility to employ two cohesive laws concurrently for prediction of Delamination Propagation, for both the pinned and unpinned behaviour. Its efficacy is evaluated by the simulation of double cantilever beam (DCB), mixed-mode bend (MMB), and pure mode II End-Loaded Split (ELS) fracture tests at 2% z-pin areal density. The numerical results in terms of load-deflection predictions agree well with experiments. The different simulations were all performed using a single set of input parameters derived from single z-pin tests with no fitting factors.

  • a new semi empirical law for variable stress ratio and mixed mode fatigue Delamination growth
    Composites Part A-applied Science and Manufacturing, 2013
    Co-Authors: G Allegri, Michael R Wisnom, Stephen R. Hallett
    Abstract:

    Abstract A new semi-empirical equation that describes the fatigue Delamination growth in fibre reinforced toughened epoxies is presented and validated against data available in the literature. The new law accounts for the simultaneous effects of the stress-ratio and mode-mixity on the interlaminar crack Propagation. If Delamination Propagation thresholds are ignored, the proposed semi-empirical equation allows describing interlaminar crack Propagation employing only three material dependent parameters, whereas alternative models presented in the literature require four. If reliable threshold data are available from experimental tests, the new semi-empirical law can be extended to a unified description of stress-ratio, mode-mixity and thresholds effects using six material dependent parameters.

  • a concise interface constitutive law for analysis of Delamination and splitting in composite materials and its application to scaled notched tensile specimens
    International Journal for Numerical Methods in Engineering, 2007
    Co-Authors: W G Jiang, Stephen R. Hallett, B G Green
    Abstract:

    A concise constitutive law for cohesive interfaces is proposed in this paper. A new state variable is introduced to track the extent of damage accumulated at the interface. The constitutive equations not only account for mixed-mode Delamination Propagation in composite materials, but also satisfactorily deal with mode ratio change during the debonding process. The interface model is implemented in the LS-DYNA explicit finite element code. The model has been applied to scaled open hole tension tests on laminated composite material. Comparison between numerical results and experiments shows good correlation for failure modes and strengths for a range of different specimen sizes. Copyright © 2006 John Wiley & Sons, Ltd.

Libin Zhao - One of the best experts on this subject based on the ideXlab platform.

  • a modified mode i cohesive zone model for the Delamination growth in dcb laminates with the effect of fiber bridging
    International Journal of Mechanical Sciences, 2020
    Co-Authors: Libin Zhao, Yu Gong, Yixin Hou, Jianyu Zhang
    Abstract:

    Abstract Fiber bridging has a significant influence on the Delamination Propagation behavior in multidirectional composite laminates. Traditional pure mode I bilinear cohesive zone models (CZM) do not consider the effect of fiber bridging and result in an inaccurate simulation on the Delamination behavior. This study proposed a physical-based three-linear CZM superposed by two bilinear CZMs, which represent two different phenomena including the quasi-brittle matrix fracture characterized by a higher peak stress and a shorter critical opening displacement, and the fiber bridging characterized by a lower peak stress and a longer critical opening displacement, respectively. The three-linear CZM was implemented in the commercial FE software using a user-subroutine UMAT. Double Cantilever Beam (DCB) tests on the multidirectional composite laminates with 0°/5° and 45°/−45° interfaces conducted in our previous studies are shown to have large-scale fiber bridging in mode I Delamination and are used to provide experimental data for calibrating the new CZM. Good agreements between the predicted and tested results can be achieved by adopting this new CZM, demonstrating its applicability on predicting the mode I Delamination behavior in composite laminates with the effect of fiber bridging.

  • an analytical model for evaluating the buckling Delamination Propagation and failure behaviors of delaminated composites under uniaxial compression
    Composite Structures, 2019
    Co-Authors: Kangkang Wang, Libin Zhao, Yu Gong, Haiming Hong, Jianyu Zhang
    Abstract:

    Abstract Laminated carbon fibre reinforced composite materials are very susceptible to Delamination, which is one of the most serious failure modes in composite laminates. According to the requests of damage tolerance evaluation, to completely evaluate the buckling responses and failure behaviors of delaminated composites under uniaxial compression, an analytical model was established. Based on the principle of minimum potential energy and brittle damage mechanics, the analytical model incorporated both the Delamination Propagation and failure evaluation into the buckling analysis. Uniaxial compression tests of three specimens containing embedded Delaminations were conducted. The predicted results are highly consistent with the experimental outcomes, thus validating the applicability and accuracy of the proposed analytical model. It is found that the out-of-plane deflections and energy release rate of the delaminated laminate are closely related to the buckling states; the choice of G C in a range from G IC to G IIC has little effect on the predicted results with the proposed model.

  • An improved power law criterion for the Delamination Propagation with the effect of large-scale fiber bridging in composite multidirectional laminates
    Composite Structures, 2018
    Co-Authors: Yu Gong, Libin Zhao, Jianyu Zhang
    Abstract:

    Abstract Large-scale fiber bridging can significantly enhance Delamination resistance, which makes the use of traditional Delamination Propagation criterion failed to accurately evaluate the Delamination behavior in multidirectional laminates. This paper proposed an improved power law criterion to take account for the effect of fiber bridging on the Delamination behavior. The key of the improved criterion lies on the introducing of R-curves, which can typically be determined by the standard Delamination tests. A numerical Delamination model based on the available cohesive elements was established with implementation of the improved criterion. The efficacy of the improved criterion is validated by the simulation of mixed mode bending Delamination tests. Numerical results in terms of load-displacement curves agreed well with the experiment ones. The improved criterion can accurately evaluate the mixed-mode Delamination with the effect of fiber bridging in a cost and time effective way, is convenient for applications.

  • Delamination Propagation criterion including the effect of fiber bridging for mixed mode i ii Delamination in cfrp multidirectional laminates
    Composites Science and Technology, 2017
    Co-Authors: Yu Gong, Libin Zhao, Jianyu Zhang, Yana Wang
    Abstract:

    Abstract Large-scale fiber bridging developed in the CRFP multidirectional (MD) laminates upon mixed-mode I/II fracture has a significant effect on the Delamination behavior. Without considering the effect of fiber bridging, traditional Delamination Propagation criteria fail to evaluate the Delamination behavior in MD laminates. To solve this problem, an improved criterion is proposed here, which accounts for the Delamination resistance curve (R-curve) induced by fiber bridging. Systematic Delamination tests under mode I, II and mixed I/II loadings were carried out to determine the unique parameter in the criterion and a numerical Delamination model based on the cohesive zone model (CZM) was established with implementation of the improved criterion. Initial and ultimate damage loads from numerical predictions and experiments show good agreements, verifying the accuracy of the improved criterion on evaluating the mixed-mode I/II Delamination behavior in MD laminates. Additional mixed-mode I/II Delamination test was conducted, which was used to validate the applicability of the improved criterion on evaluating the Delamination behavior with any other mode-mixity ratios (φ-ratios).

  • xfem based model for simulating zigzag Delamination growth in laminated composites under mode i loading
    Composite Structures, 2017
    Co-Authors: Libin Zhao, Yana Wang, Jianyu Zhang, Yu Gong
    Abstract:

    Abstract Interfaces adjacent to a 90° ply in laminated composites show a typical zigzag path during the mode I Delamination Propagation process, which is considered to be closely related to high Propagation values of fracture toughness. DCB (double cantilever beam) tests of specimens with a starter crack inserted into two 90° mid-layers were carried out, during which the zigzag Delamination growth and pronounced R-curve behavior were obtained. To simulate the zigzag Delamination Propagation path, four XFEM-based Delamination growth models were proposed which were comprised of a crack initiation model and a crack Propagation model, respectively. In the framework of the Delamination growth model, a new crack initiation model was developed, which took a quadratic criterion as the crack initiation criterion and the direction orthogonal to the maximum principal stress as the crack growth direction. Based on the mechanism of the Delamination resistance, four crack Propagation models considering whether the Delamination follows a pure or mixed mode damage evolution law and whether a constant or varying critical fracture toughness dominates the damage evolution were introduced. By comparing the predictions from the four Delamination growth models and the experimental results, the mode I Delamination mechanism with a zigzag path was investigated. The Delamination growth model that adopted a critical fracture toughness function and the mixed mode damage evolution law showed the best agreement with the experimental results and was recommended.