بهبود مدل شكست مود پيچ خوردگي الياف در مواد كامپوزيت لايه اي تك جهته

چكيده انگليسي :

Abstract The main aim of this research is to improve the fiber kinking stress based model inunidirectional laminated composites and to propose a new fiber kinking strain based model sothat it can predict the compressive strength and the kink band angle in the fiber kinking failuremode To achieve the goal the 2D and 3D fiber kinking model proposed by Pinho on the basisof Argon and Davila s works is first explained The Pinho model is based on the idea that thefiber kinking failure mode is different from the micro buckling failure mode and thephenomenon mainly occurs due to the matrix failure In the stress based model by knowingthe compressive strength and assumption that the fiber kinking is due to the matrix failure themisalignment angle at failure point is calculated by using matrix failure criterion and by usingthe constitutive shear stress strain law the initial misalignment angle can also be calculated The initial misalignment angle is used as a material parameter in the proposed fiber kinkingmodel In the stress based model after damage initiation by use of the damage variable thestresses in the plane perpendicular to the fiber direction are reduced In order to implement the above mentioned model into a finite element code a subroutineis developed and is used for all numerical calculations Investigation of the model and theobtained numerical results show that this model can be improved due to compressive strengthand kink band angle prediction Therefore in this research by means of the stress based model a new model based on strain is proposed The new model is different from the stress basedmodel in several cases such as fracture plane selection and calculation of fiber misalignmentangle Next the strain based model is implemented into the finite element code and thenumerical results for several case studies are obtained and compared with the results ofPinho s model In order to investigate the fiber kinking phenomenon some experiments are carried out onsome specimens made of Glass Epoxy prepreg composite material The specimens are smallblocks with different sizes and have 0 5 10 15 and 20o off axis angles and compressed with afixture Experimental observations show that 0 degree off axis specimens failed under severalfailure mechanisms namely kink band formation delamination splitting fiber breakage andthe final failure occurred catastrophically with a loud voice For these specimens kinking mayoccurred in the plane of lamina or through the thickness direction With increasing the off axisangle the fiber kinking failure mode becomes dominate Therefore for 10 15 and 20o off axisspecimens only this type of failure mode was observed These specimens failed softly and novoice was heard at their final failure These observations confirm that shear behavior of theunidirectional composite materials has an important role in kink band formation Comparisonbetween numerical results obtained from two stress and strain based models and experimentalresults show that there is large difference between experimental and numerical results for0$ off axis specimens which can be due to the fact that in the experiments more than onefailure mode may happen while in the numerical analysis only the fiber kinking failure modeis considered In other specimens 5 10 15 and 20o which the fiber kinking is the dominantfailure mode good agreement is observed between the experimental and the numerical results Finally the results show that the strain based model has advantage over the stress based modelbecause in addition to simplicity it predicts the compressive strength and kink band anglemore accurately and physically is more compatible with the initial assumptions of kink bandformation

كبيري عطا آبادي، عبدالرضا

بهبود مدل شكست مود پيچ خوردگي الياف در مواد كامپوزيت لايه اي تك جهته

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