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Abstract.In this paper we analyze, using the Finite Element Method, the process of brittle-ductile transition in the failure mode observed in polycarbonate notched specimens under impact loads. In order to analyze this transition we have implemented, through a user subroutine, a damage model which combines a tensional fracture criterion and an energetic, acting simultaneously. The competition between both criteria predicts the difference in material behavior from a critical impact velocity, and how this transition is produced on different planes through the thickness of the specimen. These results show the necessity of employing three-dimensional models for its study. IntroductionThe good relationship between the impact resistance of certain polymeric materials with respect to their weight and cost has prompted its use in the industry over the last decades. During its service lifetime, these components can be subjected to dynamic and impact loads, which requires a deeper understanding of the mechanical behavior of these materials under high strain rates, as well as their fracture behavior. Polymeric materials have called the attention from the scientific community [1,2,3,4,5], showing the importance to predict the failure conditions of a component.The brittle-ductile transition in the failure mode has been studied mainly in metals [6,7], but it has been also observed in polymeric materials, such as PolyMethylMethAcrylate (PMMA) [8] and PolyCarbonate (PC) [9]. This phenomenon of transition in the failure mode was analyzed by Kalthoff [6] in steel specimens subjected to dynamic mode-II loading. He observed that at low impact velocities, the fracture mechanism of cleavage was the dominant, and cracks propagated at an angle of about 70 degrees relative to the plane of the notch. However, from a certain impact velocity, adiabatic shear bands appear and cracks propagate at a much smaller angle, about 10º. The change in the failure mode, from a mechanism of brittle fracture to a ductile one, is called brittleductile transition in the failure mode.Most published analysis [6,8,9], either on metals or polymers, focus on the qualitative description of the phenomenon. Recently, Dolinski et al. [7] proposed a damage model applied to metallic materials able to predict this transition. However, as it has been experimentally observed, the failure modes produced in polymeric materials are similar to those reported by [7], so it might be interesting to extend the proposed methodology to polymers.In this paper, using the Finite Element Method, a full 3D numerical model has been build, to reproduce tests made on PC simple notched specimens [9], incorporating a damage model by means of a user subroutine. This damage model is an extension of the one published by Dolinski et al. [7], to be applicable to polymeric materials, in particular the PC. In the analysis, a special attention to the process of brittle-ductile transition in the failure mode has been paid. The results highlight the distinctly three-dimensional character of the cr...
Abstract.In this paper we analyze, using the Finite Element Method, the process of brittle-ductile transition in the failure mode observed in polycarbonate notched specimens under impact loads. In order to analyze this transition we have implemented, through a user subroutine, a damage model which combines a tensional fracture criterion and an energetic, acting simultaneously. The competition between both criteria predicts the difference in material behavior from a critical impact velocity, and how this transition is produced on different planes through the thickness of the specimen. These results show the necessity of employing three-dimensional models for its study. IntroductionThe good relationship between the impact resistance of certain polymeric materials with respect to their weight and cost has prompted its use in the industry over the last decades. During its service lifetime, these components can be subjected to dynamic and impact loads, which requires a deeper understanding of the mechanical behavior of these materials under high strain rates, as well as their fracture behavior. Polymeric materials have called the attention from the scientific community [1,2,3,4,5], showing the importance to predict the failure conditions of a component.The brittle-ductile transition in the failure mode has been studied mainly in metals [6,7], but it has been also observed in polymeric materials, such as PolyMethylMethAcrylate (PMMA) [8] and PolyCarbonate (PC) [9]. This phenomenon of transition in the failure mode was analyzed by Kalthoff [6] in steel specimens subjected to dynamic mode-II loading. He observed that at low impact velocities, the fracture mechanism of cleavage was the dominant, and cracks propagated at an angle of about 70 degrees relative to the plane of the notch. However, from a certain impact velocity, adiabatic shear bands appear and cracks propagate at a much smaller angle, about 10º. The change in the failure mode, from a mechanism of brittle fracture to a ductile one, is called brittleductile transition in the failure mode.Most published analysis [6,8,9], either on metals or polymers, focus on the qualitative description of the phenomenon. Recently, Dolinski et al. [7] proposed a damage model applied to metallic materials able to predict this transition. However, as it has been experimentally observed, the failure modes produced in polymeric materials are similar to those reported by [7], so it might be interesting to extend the proposed methodology to polymers.In this paper, using the Finite Element Method, a full 3D numerical model has been build, to reproduce tests made on PC simple notched specimens [9], incorporating a damage model by means of a user subroutine. This damage model is an extension of the one published by Dolinski et al. [7], to be applicable to polymeric materials, in particular the PC. In the analysis, a special attention to the process of brittle-ductile transition in the failure mode has been paid. The results highlight the distinctly three-dimensional character of the cr...
Fragmentation occurs in structures when subjected to large-strain-rate loading that commonly occurs in ballistic and asteroid impacts. In ductile materials, fragmentation is preceded by localized plastic deformation forming multiple adiabatic shear-bands. The shear-band-spacing thus formed controls the final fragment-size distribution. The observed fragment-size distribution is different from the theoretically predicted values. The above discrepancy can be deciphered by simulating multiple-shear-band formation that accounts for both thermal-and shear-void-growth-softening (which is often ignored). We model the shear-void-growth-softening by using the extended Gurson-model (Nahshon-Hutchinson model) in our method of characteristics-based finite-difference solution methodology. We perform parametric simulations varying the shear-void-growthrate. Our results indicate that the number of shear-bands increases linearly with increase in the shear-voidgrowth-rate for any applied strain-rate. The average shear-band-spacing thus predicted is reduced, signifying the important role of shear-void-growth-softening in the simulations of multiple-shear-band formation.
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