Mixed mode I/II fracture criterion for orthotropic materials based on damage zone properties

Fakoor, Mahdi; Khansari, Nabi Mehri

doi:10.1016/j.engfracmech.2015.11.018

Cited by 42 publications

(15 citation statements)

References 34 publications

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“…The former is a stress-based theory and the other two are energy-based ones. These failure theories were extended to orthotropic materials and modified for prediction of the mixed mode I/II delamination growth by some researchers [24][25][26]. Based on the MTS criterion, a mixed mode crack extends from the crack tip along the direction of the maximum tangential stress, and that crack growth occurs when the maximum tangential stress exceeds a critical value.…”

Section: Strain Energy Density Theory For Crack Onset In Orthotropic mentioning

confidence: 99%

Physics of delamination onset in unidirectional composite laminates under mixed-mode I/II loading

Daneshjoo

Shokrieh

Fakoor

et al. 2019

Engineering Fracture Mechanics

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A B S T R A C TIn order to understand the physics of the delamination onset in laminated composites, an experimental investigation of delamination growth is presented. The main objective of this paper is to demonstrate that delamination onset occurs at lower values than G c defined by the ASTM standards, and that the strain energy release rate level at which the crack growth onset occurs under any mixed mode I/II loading is governed by the critical strain energy density (SED) approach. Quasi-static delamination experiments have been performed under mode I, mode II and mixed mode I/II loadings. The value of the strain energy release rate at the observed crack onset and the angle of the initial crack growth were correlated with the SED theory to test the validity. The acoustic emission was also used to provide more insight into the physics of the delamination growth. The investigation shows that the onset of delamination growth occurs at the strain energy release rate levels predicted by the critical SED approach, and well before reaching the critical strain energy release rate determined via delamination tests following the ASTM standards. Moreover, results indicated that the predicted angle of the initial crack for delamination onset was in a good agreement with the experimental data. linearity (NL), the point at which the delamination growth is visually observed (VIS) or the intersection of a 5% offset line (5% Max).

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Section: Strain Energy Density Theory For Crack Onset In Orthotropic mentioning

confidence: 99%

Physics of delamination onset in unidirectional composite laminates under mixed-mode I/II loading

Daneshjoo

Shokrieh

Fakoor

et al. 2019

Engineering Fracture Mechanics

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“…Some test setup and specimens are already introduced for estimation of damage zone properties Anaraki and Fakoor 2010a . Also some theoretical approaches have been introduced for calculation of damage moduli of elastic solids Horii andNemat-Nasser 1983, Fakoor andMehri Khansari 2016 .…”

Section: Implicit Approachmentioning

confidence: 99%

A New Approach for Investigation of Mode II Fracture Toughness in Orthotropic Materials

Fakoor

Khansari

2018

Lat. Am. j. solids struct.

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Estimation of mode II fracture toughness KIIC in composite materials is known as a troublous and crucial problem. Dissipated values of KIIC that are reported in different fracture mechanics references is the evidence of the mentioned claim. This problem can signify the necessity of modification on common test methods and fixtures. The present study focuses on the causes of shear test results scattering in composite materials and presents some solutions in the form of necessary corrections that should be performed on the common test fixtures. Mixed mode I/II fracture limit curves are employed to show that the scattering in test results have strong relation with the creation of a considerable Fracture Process Zone FPZ. It is shown that common test fixtures are blind in confrontation with FPZ and are not able to active toughening mechanisms in pure mode II, correctly. Therefore, estimation of KIIC with available test fixtures has considerable standard deviation. After that, by employing some structural modifications on common fixtures, a new scheme of a shear fixture is proposed that in addition to include the FPZ effects, prepare suitable condition in order to activate the mode II toughening mechanisms. In this regard, it could be found that by applying these reforms, shear load concentration as well as the accuracy of empirical test and repeatability and reproducibility are enhanced. Furthermore, a 3D finite element method FEM was considered as the numerical method in which the Iosipesque and new fixture's specimens were analyzed by ANSYS software. It was found that by applying major amendments in the new shear test fixture, a remarkable precision in results can be obtained in comparison with the previous Iosipesque one

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“…In a similar case, a geometrical approach named "Representative Circular Elements (RCEs)" was proposed for simulation of variety in directions and dimensions of damage zone at crack tip vicinity of orthotropic media (Fakoor & Khansari 2016). A general mixed mode I/II fracture failure criterion is proposed in which it is assumed that the fracture occurs in the isotropic matrix and it is the effect of the fibers modeled as tensile or shear reinforcements (Fakoor & Khansari, 2018a).…”

Section: Introductionmentioning

confidence: 99%

Orthotropic mode II shear test fixture: Iosipesque modification

Khansari¹,

Farrokhi²,

Mosavi³

2019

10.5267/j.esm

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In-plane strength and constitutive properties of composite materials is known as crucial problems. Although, several studies have been made for obtaining the in-plane mode II properties, the common test fixtures are blind in confrontation of shear zone. Furthermore, toughening mechanisms and consequently mode II fracture toughness cannot be evaluated, precisely. Also, proposing the convenient configuration of shear test fixture increase the accuracy of evaluation for the shear-zone energy dissipation, especially in orthotropic materials. Hence in the present research, a novel shear fixture configuration is proposed based on Iosipesque structural modification. Hereof, some arbitrary composite materials (e.g. graphite/epoxy and wood) were studies on the basis of DOE and E-691 ASTM. Furthermore, as the numerical method for indicating the comparison of the uniform and non-uniform shear stress distribution in the modified and common shear test fixture, a statistical procedure is used based on ASTM standard in addition to FEM analysis. The obtained results reveal that applying major amendments through the new scheme of the shear test fixture, would provide a remarkable precision and a reasonable estimation of the shear strength in comparison with the previous Iosipesque experiments.

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Mixed mode I/II fracture criterion for orthotropic materials based on damage zone properties

Cited by 42 publications

References 34 publications

Physics of delamination onset in unidirectional composite laminates under mixed-mode I/II loading

Physics of delamination onset in unidirectional composite laminates under mixed-mode I/II loading

A New Approach for Investigation of Mode II Fracture Toughness in Orthotropic Materials

Orthotropic mode II shear test fixture: Iosipesque modification

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