Journal of Engineering Materials and Technology, 2020
Heavily cross-linked epoxy was characterized under different types of loading. The scope of work ... more Heavily cross-linked epoxy was characterized under different types of loading. The scope of work involves detailed testing procedures utilizing high-precision digital image correlation (DIC) system for all strain measurements. Fractographic analyses using scanning electron microscopy (SEM) were also provided. Besides, computed tomography (CT) scans were employed to characterize existing manufacturing imperfections, i.e., voids. Numerical modeling using extended finite element method (XFEM) utilizing the actual microstructure is conducted. Testing results and fractographic analyses showed that microvoids led to failure initiation at micro lengths. An unstable fracture behavior dominated the final failure under different types of loading. Global plastic deformation was observed in the case of uniaxial tension, while local plasticity was observed in specimens under three-point loading. It can be concluded that epoxies failure under a combined state of stresses is sophisticated, and str...
This article proposes a damage initiation criterion based on the total strain energy density (SED... more This article proposes a damage initiation criterion based on the total strain energy density (SED) for glassy polymers such as epoxy resins. The proposed damage initiation model was developed and implemented in a user-defined subroutine in the finite element code Abaqus using eXtended Finite Element Method (XFEM). Numerical results were verified with uniaxial and three-point bending tests. To accurately assess predictions, a high precision Digital Image Correlation (DIC) system was utilized for precise strain measurements. Also, synchronized image processing was used for efficient identification of yielding whenever it occurred. Furthermore, a microscopic investigation of fractured surfaces using optical microscopy was conducted. Micro-cavitation were consistently observed in all failed specimens identifying that brittle behavior dominated the final fracture. Comparisons with built-in damage models in Abaqus concluded enhanced and conservative predictions of the currently developed ...
This article proposes an extended Ramberg–Osgood (R–O) relationship accounting for the effect of ... more This article proposes an extended Ramberg–Osgood (R–O) relationship accounting for the effect of porosity on porous metal behavior under tension. Initially, microstructural unit cells satisfying continuity boundary conditions were employed to account for pore intensity and its effect on elastic-plastic behavior. Results obtained from micromechanical simulations coupled with regression analyses were utilized to express elastic-plastic behavior as a function of porosity. Therefore, mathematical relationships were successfully developed to extend the R–O model to account for porosity. Finally, for validation and assessment of the developed relation, analytical and macromechanical finite element (FE) results were compared with those of testing. Comparisons at low-porosity range, i.e., < 10 pct, proved to have excellent agreement. It is concluded that multiscale FE analyses conducted successively on the micro- and macro-scales efficiently delineated the effect of porosity on mechanical behavior. Moreover, these analyses enabled extending the R–O relationship for accurate modeling of porous metals with low-range porosity.
Porosity in metals is well known to influence the mechanical behavior, namely, the elastic respon... more Porosity in metals is well known to influence the mechanical behavior, namely, the elastic response, the plastic behavior, and the material loading capacity. The main focus of the current work is to investigate the failure of porous metals. Extensive literature search was conducted to identify failure mechanisms associated with the increase of porosity for up to 15% by volume. Consequently, micromechanical modeling is utilized to investigate the damage process at microlengths. Finally, a complete macromechanical modeling approach is proposed for specimen-sized models. The approach utilizes the extended Ramberg–Osgood relationship for the elastoplastic behavior, while the failure is predicted using a strain energy-based failure criterion capturing the effect of porosity. The proposed approach is validated against several testing results for different metals at various porosity levels.
Journal of Engineering Materials and Technology, 2020
Heavily cross-linked epoxy was characterized under different types of loading. The scope of work ... more Heavily cross-linked epoxy was characterized under different types of loading. The scope of work involves detailed testing procedures utilizing high-precision digital image correlation (DIC) system for all strain measurements. Fractographic analyses using scanning electron microscopy (SEM) were also provided. Besides, computed tomography (CT) scans were employed to characterize existing manufacturing imperfections, i.e., voids. Numerical modeling using extended finite element method (XFEM) utilizing the actual microstructure is conducted. Testing results and fractographic analyses showed that microvoids led to failure initiation at micro lengths. An unstable fracture behavior dominated the final failure under different types of loading. Global plastic deformation was observed in the case of uniaxial tension, while local plasticity was observed in specimens under three-point loading. It can be concluded that epoxies failure under a combined state of stresses is sophisticated, and str...
This article proposes a damage initiation criterion based on the total strain energy density (SED... more This article proposes a damage initiation criterion based on the total strain energy density (SED) for glassy polymers such as epoxy resins. The proposed damage initiation model was developed and implemented in a user-defined subroutine in the finite element code Abaqus using eXtended Finite Element Method (XFEM). Numerical results were verified with uniaxial and three-point bending tests. To accurately assess predictions, a high precision Digital Image Correlation (DIC) system was utilized for precise strain measurements. Also, synchronized image processing was used for efficient identification of yielding whenever it occurred. Furthermore, a microscopic investigation of fractured surfaces using optical microscopy was conducted. Micro-cavitation were consistently observed in all failed specimens identifying that brittle behavior dominated the final fracture. Comparisons with built-in damage models in Abaqus concluded enhanced and conservative predictions of the currently developed ...
This article proposes an extended Ramberg–Osgood (R–O) relationship accounting for the effect of ... more This article proposes an extended Ramberg–Osgood (R–O) relationship accounting for the effect of porosity on porous metal behavior under tension. Initially, microstructural unit cells satisfying continuity boundary conditions were employed to account for pore intensity and its effect on elastic-plastic behavior. Results obtained from micromechanical simulations coupled with regression analyses were utilized to express elastic-plastic behavior as a function of porosity. Therefore, mathematical relationships were successfully developed to extend the R–O model to account for porosity. Finally, for validation and assessment of the developed relation, analytical and macromechanical finite element (FE) results were compared with those of testing. Comparisons at low-porosity range, i.e., < 10 pct, proved to have excellent agreement. It is concluded that multiscale FE analyses conducted successively on the micro- and macro-scales efficiently delineated the effect of porosity on mechanical behavior. Moreover, these analyses enabled extending the R–O relationship for accurate modeling of porous metals with low-range porosity.
Porosity in metals is well known to influence the mechanical behavior, namely, the elastic respon... more Porosity in metals is well known to influence the mechanical behavior, namely, the elastic response, the plastic behavior, and the material loading capacity. The main focus of the current work is to investigate the failure of porous metals. Extensive literature search was conducted to identify failure mechanisms associated with the increase of porosity for up to 15% by volume. Consequently, micromechanical modeling is utilized to investigate the damage process at microlengths. Finally, a complete macromechanical modeling approach is proposed for specimen-sized models. The approach utilizes the extended Ramberg–Osgood relationship for the elastoplastic behavior, while the failure is predicted using a strain energy-based failure criterion capturing the effect of porosity. The proposed approach is validated against several testing results for different metals at various porosity levels.
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