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Figure from:Mechanics of composite sandwich structures with bioinspired core

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Fig. 3. Macroscale flexural, compressive and shear strain fields in the sandwich core corresponding to 8 MPa flexural stress in the elastic regime (point A in Fig. 2 The modulus, E, and damage initiation strain ¢g, and model fitting parameters obtained from the new damage model that includes plasticity in Eqs. (2)-(4). Table 1

Figure 3 Macroscale flexural, compressive and shear strain fields in the sandwich core corresponding to 8 MPa flexural stress in the elastic regime (point A in Fig. 2 The modulus, E, and damage initiation strain ¢g, and model fitting parameters obtained from the new damage model that includes plasticity in Eqs. (2)-(4). Table 1

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This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Provided for non-commercial research and education use. Not for reproduction, distribution or commercial use.
This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Provided for non-commercial research and education use. Not for reproduction, distribution or commercial use.
Fig. 1. (a) Palmetto wood, (b) sandwich composite with bioinspired polymeric foam core and carbon fiber-epoxy face sheets and (c) hierarchical structure of the bioinspirec sandwich composites. The materials used to prepare the composite sandwich speci- mens with bioinspired core are polymeric soft foam (density 35 kg/m?), epoxy carbon fiber laminates and pultruded carbon rods (density 1600 kg/m?) from The Composites Store and epoxy resin 105 and slow hardener 206 from West System. The bioinspired core of sandwich specimens was reinforced by carbon rods to mi- mic the hierarchical structure of Palmetto wood. The face sheets of carbon epoxy laminates (The Composite Store) of 0.05 inch thick- ness were adhered to the core using the epoxy based adhesive pre- pared from resin 105 and hardener 206 mixed by 5:1 ratio by weight. The reinforcement of carbon rods have been used by pene- trating the carbon rods in the soft foam core after dipping them in the adhesive to achieve better adhesion with the foam. The glued and reinforced specimens were cured in a closed chamber at 80°C for 30h under a weight. The sandwich core thickness was Inspired by the structure of Palmetto wood (Fig. 1(a)), we have developed a bioinspired core for sandwich composite structures (Fig. 1(b)) consisting of pultruded carbon fiber rods within polymer foam. However the reinforcement in these structures is fundamen- tally different from the Z-pinned sandwich composites, where the
Fig. 1. (a) Palmetto wood, (b) sandwich composite with bioinspired polymeric foam core and carbon fiber-epoxy face sheets and (c) hierarchical structure of the bioinspirec sandwich composites. The materials used to prepare the composite sandwich speci- mens with bioinspired core are polymeric soft foam (density 35 kg/m?), epoxy carbon fiber laminates and pultruded carbon rods (density 1600 kg/m?) from The Composites Store and epoxy resin 105 and slow hardener 206 from West System. The bioinspired core of sandwich specimens was reinforced by carbon rods to mi- mic the hierarchical structure of Palmetto wood. The face sheets of carbon epoxy laminates (The Composite Store) of 0.05 inch thick- ness were adhered to the core using the epoxy based adhesive pre- pared from resin 105 and hardener 206 mixed by 5:1 ratio by weight. The reinforcement of carbon rods have been used by pene- trating the carbon rods in the soft foam core after dipping them in the adhesive to achieve better adhesion with the foam. The glued and reinforced specimens were cured in a closed chamber at 80°C for 30h under a weight. The sandwich core thickness was Inspired by the structure of Palmetto wood (Fig. 1(a)), we have developed a bioinspired core for sandwich composite structures (Fig. 1(b)) consisting of pultruded carbon fiber rods within polymer foam. However the reinforcement in these structures is fundamen- tally different from the Z-pinned sandwich composites, where the
Fig. 2. Effect of reinforcement volume fraction in the flexural behavior of sandwich composite structure with bioinspired core under quasi-static flexure.
Fig. 2. Effect of reinforcement volume fraction in the flexural behavior of sandwich composite structure with bioinspired core under quasi-static flexure.
Fig. 4. (a) Image of the core of the bioinspired sandwich composite structure at magnification of 5x and (b) compressive and shear strain fields at the carbon rod- foam core interface and under flexure at high magnification. Dotted white line represents the reinforced pultruded carbon rod in foam core, (c) evolution of local strain components and global flexural stress with global flexural strain at encircled point shown in (a).
Fig. 4. (a) Image of the core of the bioinspired sandwich composite structure at magnification of 5x and (b) compressive and shear strain fields at the carbon rod- foam core interface and under flexure at high magnification. Dotted white line represents the reinforced pultruded carbon rod in foam core, (c) evolution of local strain components and global flexural stress with global flexural strain at encircled point shown in (a).
Fig. 6. Evolution of local strain components at encircled point shown in Fig. 4 compared with the flexural plastic strain obtained from the damage model consistent with a pore collapse mechanism near the fiber-matrix interface controlling the macroscopic response of the bioinspired core. Fig. 5. (a) Damage evolution; (b) evolution of plastic strain with the total global flexural strain; (c) closed view of (b) and (d) comparison of experimentally obtained flexura behavior of sandwich with bioinspired core and the response obtained using the model.
Fig. 6. Evolution of local strain components at encircled point shown in Fig. 4 compared with the flexural plastic strain obtained from the damage model consistent with a pore collapse mechanism near the fiber-matrix interface controlling the macroscopic response of the bioinspired core. Fig. 5. (a) Damage evolution; (b) evolution of plastic strain with the total global flexural strain; (c) closed view of (b) and (d) comparison of experimentally obtained flexura behavior of sandwich with bioinspired core and the response obtained using the model.
S. Haldar, H.A. Bruck / Composites Science and Technology 95 (2014) 67-74
S. Haldar, H.A. Bruck / Composites Science and Technology 95 (2014) 67-74
Fig. 8. Comparison of energy density of the bioinspired sandwich composite with other composites [32]. In the present work, it is demonstrated that the flexural behavior can be improved by using reinforcements in the foam core through bioinspired concept. Apart from that, the mechanical behavior of the sandwich composites can be suitably tuned by changing the volume fraction of the reinforcements. It is
Fig. 8. Comparison of energy density of the bioinspired sandwich composite with other composites [32]. In the present work, it is demonstrated that the flexural behavior can be improved by using reinforcements in the foam core through bioinspired concept. Apart from that, the mechanical behavior of the sandwich composites can be suitably tuned by changing the volume fraction of the reinforcements. It is
Fig. 7. Summary of the evolution of plastic strain with damage accumulation in sandwich composite materials with different cores with respect to Palmetto wood.
Fig. 7. Summary of the evolution of plastic strain with damage accumulation in sandwich composite materials with different cores with respect to Palmetto wood.