Ribs of Pinna nobilis shell induce unexpected microstructural changes that provide unique mechanical properties

The reinforcement function of shell ribs depends not only on their vaulted morphology but also on their microstructure. They are part of the outer layer which, in the case of the Pinna nobilis bivalve, is built from almost monocrystalline calcitic prisms, always oriented perpendicular to the growth surfaces. Originally, prisms and their c-axes follow the radii of rib curvature, becoming oblique to the shell thickness direction. Later, prisms bend to reach the nacre layer perpendicularly, but their c-axes retain the initial orientation. Calcite grains form nonrandom boundaries. Most often, three twin disorientations arise, with two of them observed for the first time. Nano-indentation and impact tests demonstrate that the oblique orientation of c-axes significantly improves the hardness and fracture toughness of prisms. Moreover, compression tests reveal that the rib area achieves a unique strength of 700 MPa. The detection of the specific microstructure formed to toughen the shell is novel.The work was supported by the Polish National Agency for Academic Exchange (grant PPI/APM/2018/1/00049/U/001) and the National Science Center (grant UMO-2018/29/B/ST8/02200). MS was supported by the European Union from the resources of the European Social Fund (Project No.WNDPOWR. 03.02.00-00-I043/16). AGC was funded by project CGL2017-85118-P of the Spanish Ministerio de Ciencia e Innovación

Niepewność w określeniu prędkości EES zderzenia samochodów wyznaczanej metodą eksperymentalno-analityczną

One of the basic ways to estimate vehicle speeds at the reconstruction of vehicle collisions is the use of methods generally referred to as “energy methods”, where a relation between the “energy equivalent speed” (EES) and the size of permanent vehicle deformation is described. There are several mathematical models used in practice to describe such a relation. Usually, a linear relation between the deformation size (depth) and the energy consumed to cause the deformation (“deformation work”) is assumed. In contrast, the deformation itself and the deformation energy are described in various ways. In consequence, different EES values may be obtained from the calculations, depending on the model used. In the accident reconstruction practice, an increasingly important role is played by the uncertainty and reliability of the analysis results obtained. This article is dedicated to the uncertainty of estimation of the energy equivalent speed (EES). The uncertainty calculation results obtained with the use of one of the typical methods of determining it, i.e. the total differential method, have been presented. The calculations were carried out for five analytical models used to determine the deformation work, based on the deformation size, for several real cases of post-impact vehicle deformation. The calculation results have been presented in the form of tables and graphs, thanks to which comparisons between both the EES values and the values of their absolute and relative uncertainty could be made. The whole analysis has ended with conclusions concerning the values obtained; they may be a source of information on the uncertainty in determining the EES parameter depending on the computation model used.Jednym z podstawowych sposobów stosowanych przy rekonstrukcji zderzeń samochodów, wykorzystywanym w celu oszacowania ich prędkości, jest grupa tzw. metod energetycznych. W metodach tych opisuje się związek między prędkością równoważną energii EES (z ang. energy equivalent speed), a rozmiarem trwałego odkształcenia pojazdu. Istnieje kilka praktycznie wykorzystywanych modeli matematycznych opisujących ten związek. Zazwyczaj zakładają one liniową zależność między wspomnianym rozmiarem (głębokością) deformacji, a energią zużytą na jej powstanie (tzw. pracą deformacji). W różny sposób natomiast opisywana jest sama deformacja oraz energia deformacji. W zależności od zastosowanego modelu możemy otrzymać inne wartości poszukiwanej prędkości EES. W praktyce rekonstrukcji wypadków coraz istotniejszą rolę odgrywa niepewność i wiarygodność otrzymanych wyników. Przedmiotem artykułu jest niepewność oszacowania prędkości równoważnej energii EES. W pracy zostały przedstawione wyniki obliczeń otrzymane przy użyciu jednej z typowych metod jej określania – metody różniczki zupełnej. Obliczenia zostały wykonane dla pięciu modeli analitycznych wyznaczania pracy deformacji, na podstawie jej rozmiaru, dla kilku rzeczywistych odkształceń pozderzeniowych pojazdów. Wyniki przedstawiono w postaci tabelarycznej oraz wykresów, umożliwiających porównanie zarówno wartości parametru EES, jak i wyznaczonych dla niego niepewności bezwzględnych oraz względnych. Całość została podsumowana wnioskami odnoszącymi się do otrzymanych wartości. Mogą one być źródłem informacji na temat niepewności w wyznaczaniu prędkości EES w zależności od zastosowanego modelu obliczeniowego

Microstructure of Commercial Purity Titanium Subjected to Complex Loading by the Kobo Method

Observations of refined microstructure of Commercial Purity titanium for applications in biomedical devices has been carried out. Refinement of titanium microstructure has been performed in process with complex strain scheme. Materials investigated in this work were: Commercial Purity titanium grade 2 and grade 4. Samples of as received materials were subjected to plastic deformation in complex loading process of extrusion combined with oscillation twisting (KoBo extrusion). Both types of samples were deformed in single step of extrusion, in temperature of 450 °C, with extrusion ratio 19.14 and 12.25 for grade 2 titanium and grade 4 titanium, respectively. Initial mean grain diameter for both types of materials was approximately 30 μm. Samples were investigated by means of crystal orientation microscopy. In both cases considerable microstructure refinement has been observed. Microstructures of deformed samples are heterogenous and consist of both elongated and fine equiaxed grains. Elongated grains (lamellae) are separated by High Angle Grain Boundaries and feature internal structure with subgrains and dislocation walls. Grain refinement is stronger in material with higher extrusion ratio and mean grain diameter in this case is equal to 1.48 μm compared to 8.07 μm. in material with lower extrusion ratio. Mean misorientation angle (24° and 27° for grade 4 and grade 2 titanium) indicates high fraction of HAGBs in microstructures of KoBo deformed samples. Misorientation fluctuations inside grains have been analyzed and distinct curvature of crystal lattice have been observed. Hardness of samples after plastic deformation increased from 174.6±3.4 and 234.9±3.5 to 205.0±3.2 and 251.2±2.2 for titanium grade 2 and grade 4 respectively

Microstructure of Commercial Purity Titanium Subjected to Complex Loading by the Kobo Method

Observations of refined microstructure of Commercial Purity titanium for applications in biomedical devices has been carried out. Refinement of titanium microstructure has been performed in process with complex strain scheme. Materials investigated in this work were: Commercial Purity titanium grade 2 and grade 4. Samples of as received materials were subjected to plastic deformation in complex loading process of extrusion combined with oscillation twisting (KoBo extrusion). Both types of samples were deformed in single step of extrusion, in temperature of 450 °C, with extrusion ratio 19.14 and 12.25 for grade 2 titanium and grade 4 titanium, respectively. Initial mean grain diameter for both types of materials was approximately 30 μm. Samples were investigated by means of crystal orientation microscopy. In both cases considerable microstructure refinement has been observed. Microstructures of deformed samples are heterogenous and consist of both elongated and fine equiaxed grains. Elongated grains (lamellae) are separated by High Angle Grain Boundaries and feature internal structure with subgrains and dislocation walls. Grain refinement is stronger in material with higher extrusion ratio and mean grain diameter in this case is equal to 1.48 μm compared to 8.07 μm. in material with lower extrusion ratio. Mean misorientation angle (24° and 27° for grade 4 and grade 2 titanium) indicates high fraction of HAGBs in microstructures of KoBo deformed samples. Misorientation fluctuations inside grains have been analyzed and distinct curvature of crystal lattice have been observed. Hardness of samples after plastic deformation increased from 174.6±3.4 and 234.9±3.5 to 205.0±3.2 and 251.2±2.2 for titanium grade 2 and grade 4 respectively