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

  • Mixed Mode Fracture analysis using generalized averaged strain energy density criterion for linear elastic materials
    International Journal of Solids and Structures, 2017
    Co-Authors: Rashidi M Moghaddam, M R Ayatollahi, Filippo Berto
    Abstract:

    Abstract A modified energy-based Model called the generalized averaged strain energy density (ASED) criterion is proposed to predict the Mixed Mode I/II Fracture resistance of brittle and quasi-brittle materials. The proposed criterion takes into account the effect of T -stress in addition to the stress intensity factors K I and K II when calculating the strain energy density averaged in a control volume around the crack tip. The effect of T -stress on the Mixed Mode Fracture resistance of materials is investigated by using the generalized ASED criterion and the generalized SED criterion. The results predicted by these criteria are compared with the experimental results reported in the literature from Fracture tests conducted on the Brazilian disc specimens and the semi-circular bend specimens made of Harsin marble and Guiting limestone. It is shown that the theoretical estimates of the generalized ASED criterion are consistent very well with the experimental results. The theoretical results also show that the specimens having a negative T -stress require higher loads in order their averaged strain energy density around the crack tip attains its critical value.

  • a generalized strain energy density criterion for Mixed Mode Fracture analysis in brittle and quasi brittle materials
    Theoretical and Applied Fracture Mechanics, 2015
    Co-Authors: M R Ayatollahi, Rashidi M Moghaddam, Filippo Berto
    Abstract:

    Abstract In this paper, a modified Mixed Mode Fracture Model called the generalized strain energy density criterion is proposed. The criterion uses three key crack parameters including: the Mode I and Mode II stress intensity factors (KI and KII) and the T-stress for predicating the Mixed Mode Fracture resistance in brittle and quasi-brittle materials. The main purpose of this paper is to show that the T-stress has a major role in Mixed Mode I/II brittle Fracture when an energy-based criterion is employed. The theoretical results obtained from the generalized strain energy density criterion are compared with the experimental results reported in previous papers for semi-circular bend specimens made of PMMA and Harsin marble and also for cracked triangular specimens made of Neiriz marble. It is shown that the results predicted using the modified criterion are in significantly better agreement with the experimental results compared with the conventional minimum strain energy density criterion.

  • Mixed Mode Fracture resistance of asphalt concrete mixtures
    Engineering Fracture Mechanics, 2012
    Co-Authors: Mahmoud Ameri, M R M Aliha, Ahmad Mansourian, Sadjad Pirmohammad, M R Ayatollahi
    Abstract:

    Abstract Fracture resistance of hot mix asphalt (HMA) is an important parameter for characterizing the asphalt concrete probable performance in cold climates. In this research study, two types of semi-circular bend (SCB) specimens containing an edge vertical crack are used and subjected to asymmetric three-point bending load to measure the critical load needed for calculation of HMA Fracture resistance. The numerical and experimental results indicate that the proposed test specimens would allow the measurement of critical loads under complete combinations of Mixed Mode deformation ranging from pure Mode I to pure Mode II and therefore can be used as suitable specimens for investigating Mixed Mode crack deformation of HMA mixtures at low temperatures.

  • typical upper bound lower bound Mixed Mode Fracture resistance envelopes for rock material
    Rock Mechanics and Rock Engineering, 2012
    Co-Authors: M R M Aliha, M R Ayatollahi, J Akbardoost
    Abstract:

    Mixed Mode Fracture experiments were conducted on Harsin marble using two disc-shape samples namely the Brazilian disc (BD) and the semi-circular bend (SCB) specimens. For each specimen, a complete Fracture toughness envelope ranging from pure Mode I to pure Mode II was obtained. The experimental results indicate that the Mixed Mode Fracture toughness depends on the geometry and loading conditions such that for any similar Mode mixture, the BD test data were significantly greater than the SCB Fracture toughness results. Therefore, the conventional Fracture criteria which present a unique Mixed Mode Fracture curve, fail to predict the test results. It is shown that a generalized criterion, which takes into account the effects of geometry and loading conditions, is able to provide individual Fracture curves for theses specimens with very good estimates for the test results obtained from both BD and SCB specimens. The BD and SCB specimens can be suggested as appropriate specimens for obtaining typical upper bound and lower bound envelopes for Mixed Mode Fracture toughness of rocks.

  • Mixed Mode i ii brittle Fracture evaluation of marble using scb specimen
    Procedia Engineering, 2011
    Co-Authors: M R M Aliha, M R Ayatollahi
    Abstract:

    Abstract The failure of cracked rock masses is mainly due to the influence of both opening (Mode I) and sliding (Mode II) of deformation. In this paper, Mixed Mode I/II Fracture toughness of an Iranian white marble (Harsin marble) was investigated both experimentally and theoretically. Several Mixed Mode Fracture tests were conducted on Harsin marble using cracked semi circular bend (SCB) specimens to obtain the Mixed Mode Fracture resistance envelope in the complete range from pure Mode I to pure Mode II. However, the experimental results were not consistent with the classical Mixed Mode brittle Fracture criteria. It was demonstrated that the low Fracture resistance of the tested rock was mainly due to the influence of large positive T -stresses that exist in the SCB specimen when the specimen is subjected to Mixed Mode loading. It was also shown that the GMTS criterion which uses three Fracture parameters i.e. K I, K II and T can provide significantly better estimates for Mixed Mode Fracture in the Harsin marble when tested by the SCB specimens.

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

  • Mixed Mode Fracture toughness testing of pmma with different three point bend type specimens
    European Journal of Mechanics A-solids, 2016
    Co-Authors: M R M Aliha, A Bahmani, Sh Akhondi
    Abstract:

    Abstract Mixed Mode Fracture behavior of PMMA, was studied experimentally and theoretically using four different test configurations and with different crack types. Although all the test samples were subjected to three-point bend loading but completely different Mixed Mode Fracture behaviors were observed for the tested samples. For each test configuration, especial Mixed Mode Fracture toughness curves were obtained for Fracture initiation direction and Fracture toughness in the whole ranges of Mixed Mode I/II loading conditions. The level of crack tip constraint in the tested samples (which is related to the stress intensity factors ( K ) and the T -stress) was used as the main affecting parameter for predicting the Mixed Mode Fracture results based on a two parameter ( K-T ) Fracture theory. It was observed that the loss of crack tip constraint in the tested samples increases the Mixed Mode Fracture resistance and decreases the Fracture initiation direction and vice versa.

  • strain based criteria for Mixed Mode Fracture of polycrystalline graphite
    Engineering Fracture Mechanics, 2016
    Co-Authors: Mirmilad Mirsayar, M R M Aliha, Filippo Berto, Philip Park
    Abstract:

    Abstract The Mixed-Mode brittle Fracture of two types of commercial graphite is investigated focusing on strain-based Fracture criteria. The previously published experiments using centrally-cracked Brazilian disk specimens subjected to Mixed-Mode loadings are simulated by two strain-based Fracture criteria: the traditional maximum tangential strain (MTSN) criterion only considering the singular terms, and the extended maximum tangential strain (EMTSN) criterion, which considers the first nonsingular strain term as well as the singular terms. Numerical simulations on the centrally-cracked Brazilian disk specimen show that the first nonsingular tangential strain term significantly influences the tangential strain distribution around the crack tip. The comparison of the evaluations by the MTSN and EMTSN criteria with the experimental data shows that the EMTSN criterion is more capable of successfully estimating the Fracture resistance of graphite materials rather than the traditional MTSN criterion. In addition, when the first nonsingular term is considered, the strain-based Fracture criterion provides better predictions for near Mode II loadings than the stress-based Fracture criterion.

  • the effects of thickness and poisson s ratio on 3d Mixed Mode Fracture
    Engineering Fracture Mechanics, 2013
    Co-Authors: M R M Aliha, H Saghafi
    Abstract:

    Abstract The effects of specimen thickness and Poisson’s ratio are investigated on Mixed Mode Fracture parameters of a test sample using numerical analyses. A large number of three dimensional finite element Models of semicircular bend specimen containing an inclined edge crack are analyzed to compute Mixed Mode Fracture parameters (i.e. KI, KII and T). While for the two dimensional Models the Fracture parameters are independent of thickness and Poisson’s ratio, the three dimensional results showed that the stress intensity factors (KI and KII) and the T-stress are generally increased by increasing Poisson’s ratio. The T-stress decreases when the thickness of specimens is increased. A comparison between the two and three dimensional solutions shows that the available KI, KII and T results obtained from two dimensional conditions, present lower estimate data for the real three dimensional cracked semicircular bend specimen. Also, the influence of specimen thickness and Poisson’s ratio, is more pronounced for dominantly Mode I condition in the semicircular bend specimen.

  • Mixed Mode Fracture resistance of asphalt concrete mixtures
    Engineering Fracture Mechanics, 2012
    Co-Authors: Mahmoud Ameri, M R M Aliha, Ahmad Mansourian, Sadjad Pirmohammad, M R Ayatollahi
    Abstract:

    Abstract Fracture resistance of hot mix asphalt (HMA) is an important parameter for characterizing the asphalt concrete probable performance in cold climates. In this research study, two types of semi-circular bend (SCB) specimens containing an edge vertical crack are used and subjected to asymmetric three-point bending load to measure the critical load needed for calculation of HMA Fracture resistance. The numerical and experimental results indicate that the proposed test specimens would allow the measurement of critical loads under complete combinations of Mixed Mode deformation ranging from pure Mode I to pure Mode II and therefore can be used as suitable specimens for investigating Mixed Mode crack deformation of HMA mixtures at low temperatures.

  • typical upper bound lower bound Mixed Mode Fracture resistance envelopes for rock material
    Rock Mechanics and Rock Engineering, 2012
    Co-Authors: M R M Aliha, M R Ayatollahi, J Akbardoost
    Abstract:

    Mixed Mode Fracture experiments were conducted on Harsin marble using two disc-shape samples namely the Brazilian disc (BD) and the semi-circular bend (SCB) specimens. For each specimen, a complete Fracture toughness envelope ranging from pure Mode I to pure Mode II was obtained. The experimental results indicate that the Mixed Mode Fracture toughness depends on the geometry and loading conditions such that for any similar Mode mixture, the BD test data were significantly greater than the SCB Fracture toughness results. Therefore, the conventional Fracture criteria which present a unique Mixed Mode Fracture curve, fail to predict the test results. It is shown that a generalized criterion, which takes into account the effects of geometry and loading conditions, is able to provide individual Fracture curves for theses specimens with very good estimates for the test results obtained from both BD and SCB specimens. The BD and SCB specimens can be suggested as appropriate specimens for obtaining typical upper bound and lower bound envelopes for Mixed Mode Fracture toughness of rocks.

Mirmilad Mirsayar - One of the best experts on this subject based on the ideXlab platform.

  • emtsn criterion for evaluating Mixed Mode i ii crack propagation in rock materials
    Engineering Fracture Mechanics, 2017
    Co-Authors: Mirmilad Mirsayar, A Razmi, Filippo Berto
    Abstract:

    Abstract This paper investigates the results of brittle Fracture in rock materials subjected to the Mixed Mode I/II loading using different Fracture criteria. Two sets of Mixed Mode Fracture test data in the entire range of Mode mixity, from pure Mode I to pure Mode II, reported in the literature for semi-circular and triangular shape specimens and subjected to three point bend loading (i.e. SCB and ECT specimens) are utilized to study the brittle Fracture in two marble rocks. First, the onset of Fracture initiation is examined by different conventional Fracture criteria including Maximum Tangential Stress (MTS) and Maximum Tangential Strain (MTSN) criteria. It is shown that these two conventional Fracture criteria, which only consider singular crack tip stress/strain terms, are not able to accurately predict the Mixed Mode Fracture test data. The experimental Mixed Mode Fracture toughness data are then predicted by an extended version of the maximum tangential strain (EMTSN) criterion which takes into account the effect of first nonsingular strain term as well as the singular strain components. It is found that both Mixed Mode Fracture toughness results of the investigated rock materials and the crack propagation direction can be predicted successfully by the EMTSN criterion.

  • strain based criteria for Mixed Mode Fracture of polycrystalline graphite
    Engineering Fracture Mechanics, 2016
    Co-Authors: Mirmilad Mirsayar, M R M Aliha, Filippo Berto, Philip Park
    Abstract:

    Abstract The Mixed-Mode brittle Fracture of two types of commercial graphite is investigated focusing on strain-based Fracture criteria. The previously published experiments using centrally-cracked Brazilian disk specimens subjected to Mixed-Mode loadings are simulated by two strain-based Fracture criteria: the traditional maximum tangential strain (MTSN) criterion only considering the singular terms, and the extended maximum tangential strain (EMTSN) criterion, which considers the first nonsingular strain term as well as the singular terms. Numerical simulations on the centrally-cracked Brazilian disk specimen show that the first nonsingular tangential strain term significantly influences the tangential strain distribution around the crack tip. The comparison of the evaluations by the MTSN and EMTSN criteria with the experimental data shows that the EMTSN criterion is more capable of successfully estimating the Fracture resistance of graphite materials rather than the traditional MTSN criterion. In addition, when the first nonsingular term is considered, the strain-based Fracture criterion provides better predictions for near Mode II loadings than the stress-based Fracture criterion.

  • Mixed Mode Fracture analysis using extended maximum tangential strain criterion
    Materials & Design, 2015
    Co-Authors: Mirmilad Mirsayar
    Abstract:

    Abstract The maximum tangential strain (MTSN) criterion is modified in this paper to predict Fracture initiation in cracked specimens under Mixed Mode loading conditions. Theoretical investigations were performed to study the role of both first nonsingular strain term (T-strain) and Poisson's ratio on prediction of the crack propagation direction and Fracture toughness. An extended version of the MTSN (EMTSN) criterion is proposed by taking into account the T-strain as well as the singular strain field. The EMTSN criterion is then examined using the experimental data reported for angled cracked plates made from polymethylmethacrylate (PMMA). It is shown that the EMTSN criterion provides more accurate estimation of the experimental results than conventional MTSN criterion.

  • on Fracture of kinked interface cracks the role of t stress
    Materials & Design, 2014
    Co-Authors: Mirmilad Mirsayar
    Abstract:

    Abstract This paper presents a modified maximum tangential stress criterion (MMTS) for prediction of the Fracture initiation conditions in kinked bi-material cracks. The criterion takes into account the effect of T -stress as well as the stress intensity factors ( K I and K II ) to predict the Mixed Mode Fracture toughness of interface cracked specimens. First the Fracture criterion is developed and the effect of sign and magnitude of T -stress on Mixed Mode Fracture toughness is studied analytically. Then, the suggested criterion is evaluated using the experimental data reported for some epoxy/Aluminum Brazil-nut-sandwich specimens in the literature. The MMTS criterion is also compared with the conventional maximum tangential stress (MTS) criterion and hence, significantly improved estimates were achieved for Mixed Mode Fracture toughness of the tested specimens.

Filippo Berto - One of the best experts on this subject based on the ideXlab platform.

  • emtsn criterion for evaluating Mixed Mode i ii crack propagation in rock materials
    Engineering Fracture Mechanics, 2017
    Co-Authors: Mirmilad Mirsayar, A Razmi, Filippo Berto
    Abstract:

    Abstract This paper investigates the results of brittle Fracture in rock materials subjected to the Mixed Mode I/II loading using different Fracture criteria. Two sets of Mixed Mode Fracture test data in the entire range of Mode mixity, from pure Mode I to pure Mode II, reported in the literature for semi-circular and triangular shape specimens and subjected to three point bend loading (i.e. SCB and ECT specimens) are utilized to study the brittle Fracture in two marble rocks. First, the onset of Fracture initiation is examined by different conventional Fracture criteria including Maximum Tangential Stress (MTS) and Maximum Tangential Strain (MTSN) criteria. It is shown that these two conventional Fracture criteria, which only consider singular crack tip stress/strain terms, are not able to accurately predict the Mixed Mode Fracture test data. The experimental Mixed Mode Fracture toughness data are then predicted by an extended version of the maximum tangential strain (EMTSN) criterion which takes into account the effect of first nonsingular strain term as well as the singular strain components. It is found that both Mixed Mode Fracture toughness results of the investigated rock materials and the crack propagation direction can be predicted successfully by the EMTSN criterion.

  • Mixed Mode Fracture analysis using generalized averaged strain energy density criterion for linear elastic materials
    International Journal of Solids and Structures, 2017
    Co-Authors: Rashidi M Moghaddam, M R Ayatollahi, Filippo Berto
    Abstract:

    Abstract A modified energy-based Model called the generalized averaged strain energy density (ASED) criterion is proposed to predict the Mixed Mode I/II Fracture resistance of brittle and quasi-brittle materials. The proposed criterion takes into account the effect of T -stress in addition to the stress intensity factors K I and K II when calculating the strain energy density averaged in a control volume around the crack tip. The effect of T -stress on the Mixed Mode Fracture resistance of materials is investigated by using the generalized ASED criterion and the generalized SED criterion. The results predicted by these criteria are compared with the experimental results reported in the literature from Fracture tests conducted on the Brazilian disc specimens and the semi-circular bend specimens made of Harsin marble and Guiting limestone. It is shown that the theoretical estimates of the generalized ASED criterion are consistent very well with the experimental results. The theoretical results also show that the specimens having a negative T -stress require higher loads in order their averaged strain energy density around the crack tip attains its critical value.

  • strain based criteria for Mixed Mode Fracture of polycrystalline graphite
    Engineering Fracture Mechanics, 2016
    Co-Authors: Mirmilad Mirsayar, M R M Aliha, Filippo Berto, Philip Park
    Abstract:

    Abstract The Mixed-Mode brittle Fracture of two types of commercial graphite is investigated focusing on strain-based Fracture criteria. The previously published experiments using centrally-cracked Brazilian disk specimens subjected to Mixed-Mode loadings are simulated by two strain-based Fracture criteria: the traditional maximum tangential strain (MTSN) criterion only considering the singular terms, and the extended maximum tangential strain (EMTSN) criterion, which considers the first nonsingular strain term as well as the singular terms. Numerical simulations on the centrally-cracked Brazilian disk specimen show that the first nonsingular tangential strain term significantly influences the tangential strain distribution around the crack tip. The comparison of the evaluations by the MTSN and EMTSN criteria with the experimental data shows that the EMTSN criterion is more capable of successfully estimating the Fracture resistance of graphite materials rather than the traditional MTSN criterion. In addition, when the first nonsingular term is considered, the strain-based Fracture criterion provides better predictions for near Mode II loadings than the stress-based Fracture criterion.

  • a generalized strain energy density criterion for Mixed Mode Fracture analysis in brittle and quasi brittle materials
    Theoretical and Applied Fracture Mechanics, 2015
    Co-Authors: M R Ayatollahi, Rashidi M Moghaddam, Filippo Berto
    Abstract:

    Abstract In this paper, a modified Mixed Mode Fracture Model called the generalized strain energy density criterion is proposed. The criterion uses three key crack parameters including: the Mode I and Mode II stress intensity factors (KI and KII) and the T-stress for predicating the Mixed Mode Fracture resistance in brittle and quasi-brittle materials. The main purpose of this paper is to show that the T-stress has a major role in Mixed Mode I/II brittle Fracture when an energy-based criterion is employed. The theoretical results obtained from the generalized strain energy density criterion are compared with the experimental results reported in previous papers for semi-circular bend specimens made of PMMA and Harsin marble and also for cracked triangular specimens made of Neiriz marble. It is shown that the results predicted using the modified criterion are in significantly better agreement with the experimental results compared with the conventional minimum strain energy density criterion.

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

  • Mixed Mode Fracture analysis using generalized averaged strain energy density criterion for linear elastic materials
    International Journal of Solids and Structures, 2017
    Co-Authors: Rashidi M Moghaddam, M R Ayatollahi, Filippo Berto
    Abstract:

    Abstract A modified energy-based Model called the generalized averaged strain energy density (ASED) criterion is proposed to predict the Mixed Mode I/II Fracture resistance of brittle and quasi-brittle materials. The proposed criterion takes into account the effect of T -stress in addition to the stress intensity factors K I and K II when calculating the strain energy density averaged in a control volume around the crack tip. The effect of T -stress on the Mixed Mode Fracture resistance of materials is investigated by using the generalized ASED criterion and the generalized SED criterion. The results predicted by these criteria are compared with the experimental results reported in the literature from Fracture tests conducted on the Brazilian disc specimens and the semi-circular bend specimens made of Harsin marble and Guiting limestone. It is shown that the theoretical estimates of the generalized ASED criterion are consistent very well with the experimental results. The theoretical results also show that the specimens having a negative T -stress require higher loads in order their averaged strain energy density around the crack tip attains its critical value.

  • a generalized strain energy density criterion for Mixed Mode Fracture analysis in brittle and quasi brittle materials
    Theoretical and Applied Fracture Mechanics, 2015
    Co-Authors: M R Ayatollahi, Rashidi M Moghaddam, Filippo Berto
    Abstract:

    Abstract In this paper, a modified Mixed Mode Fracture Model called the generalized strain energy density criterion is proposed. The criterion uses three key crack parameters including: the Mode I and Mode II stress intensity factors (KI and KII) and the T-stress for predicating the Mixed Mode Fracture resistance in brittle and quasi-brittle materials. The main purpose of this paper is to show that the T-stress has a major role in Mixed Mode I/II brittle Fracture when an energy-based criterion is employed. The theoretical results obtained from the generalized strain energy density criterion are compared with the experimental results reported in previous papers for semi-circular bend specimens made of PMMA and Harsin marble and also for cracked triangular specimens made of Neiriz marble. It is shown that the results predicted using the modified criterion are in significantly better agreement with the experimental results compared with the conventional minimum strain energy density criterion.