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An instrumented macro-indentation test was used to determine the viscoelastic parameters and hardness of the shell of Coco Nucifera from Cameroon in order to promote their use in the manufacture of abrasives. Samples measuring 10 mm x 10 mm x 3 mm were cut out from the bottom of the fruit, close to the natural indentations (the eye) of an approxima...
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... difference could be attributed to difference in test method. The values of Young's modulus obtained in this study are closer to values for polymers and gypsum (Table 2), an indication that the instrumented macroindentation test may be more suitable for characterising the mechanical properties of this material. ...Similar publications
An instrumented macro-indentation test was used to determine the viscoelastic parameters and hardness of the shell of Coco Nucifera from Cameroon in order to promote their use in the manufacture of abrasives. Samples measuring 10 mm x 10 mm x 3 mm were cut out from the bottom of the fruit, close to the natural indentations (the eye) of an approxima...
Citations
The present work deals with the valorization of agro-industrial by-products to realize bonded abrasives. Four by-products were studied because of their wide availability and mechanical properties: palm nuts shells (Elaeis guineensis), Coco Nucifera shells, fruit kernels of Canarium schweinfurthii and fruit kernels of Raffia Vinifera. The Oliver and Pharr hardness and Young’s modulus of the raffia cores are obtained by instrumented macro indentation, giving the values 101 MPa and 1.82 GPa, respectively. The development of the abrasive wheels was based on the experimental method of full factorial design at 2 levels. Porosity, hardness, resilience, material removal rate and wear were determined. Leeb 280 HL hardness shoe sole material was used for tribological testing. The optimal formulations have 20% binder content and 1 mm grain size of the four agro-industrial by-products used with a higher material removal rate and a longer life than commercial grinding wheels. These results presage their use in the shoe industry and abrasive disc huskers.
The aim of this study was to show how temperature modifies the mechanical characteristics of the Cocos nucifera (CN) shells and the Canarium schweinfurthii (CS) cores. The test consisted in performing an instrumented macroindentation on prismatic specimens in an adiabatic chamber; the indentation carried out according to four temperature ranges (30°C, 50°C, 70°C, 90°C). The Oliver and Pharr method is used for the analysis of mechanical parameters in indentation: reduced Young's modulus, hardness, creep coefficient. These parameters have enabled to estimate indirect characteristics such as toughness and ultimate mechanical stress to be obtained. The creep data are simulated to have the rheological model to these materials by considering the statistical criteria. As a global observation, when the temperature increases, the mechanical parameters decrease; although CN is more sensitive to the temperature gradient than CS, these 2 materials show performances that allow them to be classified as engineering polymer materials according to the Ashby diagram.
Traditionally, the material’s stress-strain relationship is acquired from uniaxial testing, which is widely used to describe its behavior under plastic deformation. When it comes to traditional hardness tests, such as in the Brinell, Knoop, Rockwell, and Vickers, they have been mostly used as a way to assess the capability a material has to resist plastic deformation. The technique developed and presented here has gone beyond that by determining other material properties in addition to hardness. This is performed by relating the applied load to the resultant indentation profile impressed in the material. Similar approaches have been devised aided by instrumented indentation devices. However, the methodology presented here does not require the use of such a device. It considers that the use of three configurations of the Brinell hardness test is enough to represent the material behavior within the boundaries of the plastic deformation experienced by it. Therefore, it is simpler than the usual approaches in this aspect. On the other hand, the indentation profile is also assessed along with the load-depth information obtained for each of those configurations. For that, a multi-image analysis of the indention impressions is performed in a confocal laser microscope. The indentation profile informs the amount of pile-up/sink-in experienced by the material. These phenomena are directly related to the strain hardening of the material, and therefore influence the description of the plastic stress-strain curve. The extracted profiles are used as a reference which with the predicted output of repeated FEM modeling is compared. In this process, several trial stress-strain curves are provided to minimize the discrepancy between numerical and experimental data in an iterative FEM modeling of the indentation process. The process runs until reaching the established tolerance and thus providing the hardening parameters that best fit the experimental data. The SAE 1524 is analyzed in the present work employing the Kleinermann-Ponthot constitutive hardening model, which is composed of four parameters. It is shown that the determined parameters conform closely to the experimental data. Therefore, the procedure is viable for the material characterization task.
Fruit and nut shells can exhibit high hardness and toughness. In the peninsula of Yucatan, Mexico, the fruit of the Cocoyol palm tree (Acrocomia mexicana) is well known to be very difficult to break. Its hardness has been documented since the 1500 s, and is even mentioned in the popular Maya legend The Dwarf of Uxmal. However, until now, no scientific studies quantifying the mechanical performance of the Cocoyol endocarp has been found in the literature to prove or disprove that this fruit shell is indeed “very hard”. Here we report the mechanical properties, microstructure and hardness of this material. The mechanical measurements showed compressive strength values of up to ~150 and ~250 MPa under quasi-static and high strain rate loading conditions, respectively, and microhardness of up to ~0.36 GPa. Our findings reveal a complex hierarchical structure showing that the Cocoyol shell is a functionally graded material with distinctive layers along the radial directions. These findings demonstrate that structure-property relationships make this material hard and tough. The mechanical results and the microstructure presented herein encourage designing new types of bioinspired superior synthetic materials.
