FRACTURE BEHAVIOR AFTER HOT TENSILE TEST IN THE SHAPE MEMORY ALLOY NI-RICH NITI PRODUCED BY VACUUM INDUCTION MELTING

In this work, samples of the alloy (composed of 50.9% at Ni) were machined and solubilized so all had the same condition for the hot tensile test between the temperatures 350-650 °C. The results showed that yield stress was between 800 and 597.1 MPa and area reduction between 17 and 75% during the hot tensile test in the respective temperatures. The test at 350 °C shows a fragile fracture characteristic verified by the presence of “river marks”, which are characteristic of this type of fracture, because this condition does not promote much plastic deformation. At the other temperatures ductile fracture was observed, with “dimples” that also characterize this type of fracture. This work shows the temperature relationship in the mechanical properties, more specifically the hot tensile test, in NiTi alloy.

Structural and physico-chemical transformations of modified with epoxy resin pericardia implants

Bovine pericardium samples modified with ethylene glycol diglycidyl ether, designed for surgical correction of congenital heart defects and large blood vessels, were studied by scanning electron microscopy, X-ray diffraction, IR spectroscopy, and differential thermal analysis. It was found that the initial samples of pericardium, before implantation, contain sites of disorganization of the collagen matrix, fragile fracture of collagen fibrils and destruction of the interstitial membranes promoting the penetration of immunocytes into the deep layers of the pericardium. Ossifying calcification with amorphized hydroxyapatite deposition and bone tissue formation as well as multiple erosions and hypertrophic proliferation in the endothelial membrane were detected in the implantation pericardium samples.

A Case of an Insufficiency Fracture of the Medial Proximal Tibia Secondary to Osteomalacia Associated with Long-Term Saccharated Ferric Oxide Administration

This article presents a case of insufficiency fracture of medial proximal tibia caused by long-term administration of saccharated ferric oxide (SFO) in a 77-year-old female. In this case, 2-year administration of SFO for iron deficit anemia induced hypophosphatemic osteomalacia and finally resulted in an insufficiency fracture of medial proximal tibia. Hypophosphatemia and pain due to the insufficiency fracture were recovered promptly by withdrawing SFO administration and rest. This case represented varus deformity of the knee associated with osteoarthritis, which may also cause the insufficiency fracture of medial proximal tibia in addition to osteomalacia due to long-term administration of SFO. Long-term SFO administration should be avoided because of a definitive risk of osteomalacia and fragile fracture.

Mechanical behavior of honeycomb lattices manufactured by investment casting for scaffolding applications

Lightweight metallic lattices in the form of honeycombs are long known to exhibit a good mechanical strength/weight relation, given their geometry and relative density, in comparison with bulk materials. Due to the current developments in additive manufacturing techniques, the production of honeycombs by investment casting is now easier and may be a competitive route when compared to welding and gluing of sheet metal. This study explores the importance of the manufacturing design when producing honeycombs by investment casting. It is shown by numerical simulation and experimental procedures that mold filling in directions where horizontal ribs are present may induce defects such as interdendritic porosities. These defects have a relevant role in the elastic domain of the lattices, decreasing the apparent Young’s modulus and the plastic collapse stress. In terms of energy absorption, it is shown that these porosities have no significant effect due to the fragile fracture of both casting directions.

PATTERN FORMATION IN NONCOHESIVE AND COHESIVE GRANULAR MEDIA

We studied pattern formation in granular media in two distinct states: in the dry and non-cohesive (powder) state, on the one hand, and in the wet and cohesive (paste) state, on the other. In the first case, we have shown that gas injection in a thin layer of powder within a Hele Shaw cell leads to fractal patterns remarkably similar to viscous fingering patterns obtained with complex fluids. In the second case, we have shown that the tensile cohesive viscoplastic fracture of a layer of paste leads to self-affine rough surfaces with a Hurst exponent close to 0.88, very close to the value obtained for fragile fracture by other authors.18 Our observations reinforce the universality of two fractal growth processes and add a new element to the ambivalent nature of the granular state of matter.