Dr. Vaziri’s research focuses on the development of analytical and numerical modelling techniques to solve a variety of inter-disciplinary problems in materials and structures. His most significant contributions have been in modelling the response of structures, notably those made of advanced composite materials, to high intensity impact and blast loading as well as process modelling of composite structures. Address: Canada
In this work, two intralaminar damage models with different underlying assumptions are utilized t... more In this work, two intralaminar damage models with different underlying assumptions are utilized to predict the damage response of notched composite laminates. One is a sub-laminate based continuum damage model, CODAM2, implemented in LS-DYNA, and the other is a ply-based damage model, ABQ_DLR_UD, that uses the Ladeveze damage model as its basis and is implemented as a user-material model (VUMAT) in Abaqus/Explicit. Aside from the base-formulations, different variations of the models including local and nonlocal integration (smearing) schemes are also considered. These models are employed to predict the damage response of Over-height compact tension (OCT) and scaled center-notched specimens made out of IM7/8552 CFRP laminates with quasi-isotropic layup. For each geometry and loading scenario, sensitivity of the predictions with respect to various damage parameters including peak stress and fracture energy as well as assumptions made on the shape of the strain-softening curve are inve...
Numerical Modelling of Failure in Advanced Composite Materials, 2015
The literature abounds with models for progressive damage and fracture behaviour of composite mat... more The literature abounds with models for progressive damage and fracture behaviour of composite materials at various scales of resolution. We present a brief review of these models with an emphasis on continuum approaches used for modelling the intralaminar damage mechanisms in laminated composites. We also address challenges involved in experimental calibration and numerical implementation of such models.
International Journal of Solids and Structures, 1987
The analysis of a rigid, perfectly plastic rectangular beam with constrained ends subjected to a ... more The analysis of a rigid, perfectly plastic rectangular beam with constrained ends subjected to a rectangular pressure pulse of finite duration is presented. Closed form expressions are obtained for the maximum permanent deflection for both simply supported and clamped boundary ...
Process modelling has been a successful strategy for simulating the behaviour of composites durin... more Process modelling has been a successful strategy for simulating the behaviour of composites during their manufacturing process. The simplest approach for modelling the viscoelastic behaviour of thermoset composites (unidirectional or woven) during cure would be to incorporate the effect of the fibre-bed structure into the micromechanics equations. To demonstrate this for unidirectional composites, the fibre-bed is represented as a cellular solid with its characteristics (e.g. fibre waviness and diameter) being determined based on the experimental data in the literature. Then, the generalized cellular solid model proposed recently by Malek & Gibson [1] is described and employed to estimate the effective properties of the fibre-bed. Model predictions are compared with experimentally measured values for a typical unidirectional fibre reinforced composite. These properties are then incorporated into the micromechanics equations for predicting the effective viscoelastic behaviour of comp...
Impact damage formation and resistance is of great importance to all designers of structural comp... more Impact damage formation and resistance is of great importance to all designers of structural components whether mobile or stationary. This is particularly true in the case of composite materials where the lack of a local plastic deformation mechanism means that even small impacts can result in complete fracture of constituent members, accompanied with a substantial or complete loss of the load carrying capabilities in the region of damage. This paper presents the experimental approach used to examine the structural response and resulting damage in non-crimp fabric carbon fibre reinforced epoxy composite samples at varying strain rates. The strain rates considered are those associated with quasistatic, low-velocity impact, and highvelocity impact loading rates. The differentiating characteristics of these regimes is discussed, and their effect on the samples is shown through experimental damage characterisation including physical measurements and ultrasonic C-scans. It is found that ...
Composite tubular structures are of interest as viable energy absorbing components in vehicular f... more Composite tubular structures are of interest as viable energy absorbing components in vehicular front rail structures to improve crashworthiness [1-9]. Desirable tools in designing such structures are models capable of simulating damage growth in composite materials. Our model (CODAM for COmposite DAMage), which is a continuum damage mechanics based model for composite materials with physically based inputs, has shown promise in predicting the complete tensile behaviour from initiation of damage to complete failure [10-13]. This study focuses on extending the model to capture the complete compressive response of composite materials. Refinements to the model are based on the experimentally observed compressive failure mechanisms presented in the literature [14-19]. In particular, the mechanical consequences of kinking and kink band broadening, in conjunction with matrix cracking and delamination, are represented in the model. This is accomplished by including a plateau stress in the ...
A structural modelling framework for prediction of damage development and failure of composite la... more A structural modelling framework for prediction of damage development and failure of composite laminates
Inter-ply slippage is known to be an important mechanism taking place during forming processes of... more Inter-ply slippage is known to be an important mechanism taking place during forming processes of textile composites, especially with respect to multi-layer fabric lay-ups. The coefficient of friction between the plies strongly depends on the structure and the orientation of forming fabric. Despite many numerical and experimental investigations, this dependency and its effect on the interaction between the plies has been overlooked. In this paper, the effect of fiber orientation on the interlayer friction of a typical thermoplastic fabric prepreg at room temperature is investigated. Results, through a polar representation of data, revealed that both static and dynamic coefficients of friction are statistically dependent on the lay-up orientation, applied normal load, along with their interaction. Further, it was identified that the repeated frictional loading of the plies results in a hysteresis, particularly for asymmetric layups due to non-negligible movement and realignment of filaments at the micro-scale. Finally, an empirical model was developed using an interpolation function (for pressure dependency) combined with a Fourier series (for orientation dependency), to predict the coefficients of friction.
In this work, two intralaminar damage models with different underlying assumptions are utilized t... more In this work, two intralaminar damage models with different underlying assumptions are utilized to predict the damage response of notched composite laminates. One is a sub-laminate based continuum damage model, CODAM2, implemented in LS-DYNA, and the other is a ply-based damage model, ABQ_DLR_UD, that uses the Ladeveze damage model as its basis and is implemented as a user-material model (VUMAT) in Abaqus/Explicit. Aside from the base-formulations, different variations of the models including local and nonlocal integration (smearing) schemes are also considered. These models are employed to predict the damage response of Over-height compact tension (OCT) and scaled center-notched specimens made out of IM7/8552 CFRP laminates with quasi-isotropic layup. For each geometry and loading scenario, sensitivity of the predictions with respect to various damage parameters including peak stress and fracture energy as well as assumptions made on the shape of the strain-softening curve are inve...
Numerical Modelling of Failure in Advanced Composite Materials, 2015
The literature abounds with models for progressive damage and fracture behaviour of composite mat... more The literature abounds with models for progressive damage and fracture behaviour of composite materials at various scales of resolution. We present a brief review of these models with an emphasis on continuum approaches used for modelling the intralaminar damage mechanisms in laminated composites. We also address challenges involved in experimental calibration and numerical implementation of such models.
International Journal of Solids and Structures, 1987
The analysis of a rigid, perfectly plastic rectangular beam with constrained ends subjected to a ... more The analysis of a rigid, perfectly plastic rectangular beam with constrained ends subjected to a rectangular pressure pulse of finite duration is presented. Closed form expressions are obtained for the maximum permanent deflection for both simply supported and clamped boundary ...
Process modelling has been a successful strategy for simulating the behaviour of composites durin... more Process modelling has been a successful strategy for simulating the behaviour of composites during their manufacturing process. The simplest approach for modelling the viscoelastic behaviour of thermoset composites (unidirectional or woven) during cure would be to incorporate the effect of the fibre-bed structure into the micromechanics equations. To demonstrate this for unidirectional composites, the fibre-bed is represented as a cellular solid with its characteristics (e.g. fibre waviness and diameter) being determined based on the experimental data in the literature. Then, the generalized cellular solid model proposed recently by Malek & Gibson [1] is described and employed to estimate the effective properties of the fibre-bed. Model predictions are compared with experimentally measured values for a typical unidirectional fibre reinforced composite. These properties are then incorporated into the micromechanics equations for predicting the effective viscoelastic behaviour of comp...
Impact damage formation and resistance is of great importance to all designers of structural comp... more Impact damage formation and resistance is of great importance to all designers of structural components whether mobile or stationary. This is particularly true in the case of composite materials where the lack of a local plastic deformation mechanism means that even small impacts can result in complete fracture of constituent members, accompanied with a substantial or complete loss of the load carrying capabilities in the region of damage. This paper presents the experimental approach used to examine the structural response and resulting damage in non-crimp fabric carbon fibre reinforced epoxy composite samples at varying strain rates. The strain rates considered are those associated with quasistatic, low-velocity impact, and highvelocity impact loading rates. The differentiating characteristics of these regimes is discussed, and their effect on the samples is shown through experimental damage characterisation including physical measurements and ultrasonic C-scans. It is found that ...
Composite tubular structures are of interest as viable energy absorbing components in vehicular f... more Composite tubular structures are of interest as viable energy absorbing components in vehicular front rail structures to improve crashworthiness [1-9]. Desirable tools in designing such structures are models capable of simulating damage growth in composite materials. Our model (CODAM for COmposite DAMage), which is a continuum damage mechanics based model for composite materials with physically based inputs, has shown promise in predicting the complete tensile behaviour from initiation of damage to complete failure [10-13]. This study focuses on extending the model to capture the complete compressive response of composite materials. Refinements to the model are based on the experimentally observed compressive failure mechanisms presented in the literature [14-19]. In particular, the mechanical consequences of kinking and kink band broadening, in conjunction with matrix cracking and delamination, are represented in the model. This is accomplished by including a plateau stress in the ...
A structural modelling framework for prediction of damage development and failure of composite la... more A structural modelling framework for prediction of damage development and failure of composite laminates
Inter-ply slippage is known to be an important mechanism taking place during forming processes of... more Inter-ply slippage is known to be an important mechanism taking place during forming processes of textile composites, especially with respect to multi-layer fabric lay-ups. The coefficient of friction between the plies strongly depends on the structure and the orientation of forming fabric. Despite many numerical and experimental investigations, this dependency and its effect on the interaction between the plies has been overlooked. In this paper, the effect of fiber orientation on the interlayer friction of a typical thermoplastic fabric prepreg at room temperature is investigated. Results, through a polar representation of data, revealed that both static and dynamic coefficients of friction are statistically dependent on the lay-up orientation, applied normal load, along with their interaction. Further, it was identified that the repeated frictional loading of the plies results in a hysteresis, particularly for asymmetric layups due to non-negligible movement and realignment of filaments at the micro-scale. Finally, an empirical model was developed using an interpolation function (for pressure dependency) combined with a Fourier series (for orientation dependency), to predict the coefficients of friction.
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Papers by Reza Vaziri