Microcomputed tomography imaging in a rat model of delayed union/non-union fracture

We aimed to develop a clinically relevant delayed union/non-union fracture model to evaluate a cell therapy intervention repair strategy. Histology, three-dimensional (3D) micro-computed tomography (micro-CT) imaging and mechanical testing were utilized to develop an analytical protocol for qualitative and quantitative assessment of fracture repair. An open femoral diaphyseal osteotomy, combined with periosteal diathermy and endosteal excision, was held in compression by a four pin unilateral external fixator. Three delayed union/non-union fracture groups established at 6 weeks-(a) a control group, (b) a cell therapy group, and (c) a group receiving phosphate-buffered saline (PBS) injection alone-were examined subsequently at 8 and 14 weeks. The histological response was combined fibrous and cartilaginous non-unions in groups A and B with fibrous non-unions in group C. Mineralized callus volume/total volume percentage showed no statistically significant differences between groups. Endosteal calcified tissue volume/endosteal tissue volume, at the center of the fracture site, displayed statistically significant differences between 8 and 14 weeks for cell and PBS intervention groups but not for the control group. The percentage load to failure was significantly lower in the control and cell treatment groups than in the PBS alone group. High-resolution micro-CT imaging provides a powerful tool to augment characterization of repair in delayed union/non-union fractures together with outcomes such as histology and mechanical strength measurement. Accurate, nondestructive, 3D identification of mineralization progression in repairing fractures is enabled in the presence or absence of intervention strategies. (c) 2007 Orthopaedic Research Society.

Fracture surface, impact energy and hardness of Ni-free high-Mn steels

Two manganese steels were investigated: Fe-19.7%Mn (VM339A) and Fe-19.7%Mn stabilized with 0.056%C, 0.19%Ti and 0.083%Al (VM339B). The toughness of VM339A was higher than VM339B, but VM339B had higher hardness. Tempering does not affect the toughness of the alloys. SEM images of the fracture surface for both the alloys revealed ductile fractures. A further alloy with a lower manganese content, Fe-8.46%Mn-0.24%Nb-0.038%C, and thus even lower cost than the conventional 3.5Ni cryogenic steel, was tested for its impact toughness after heat treatment at 600°C, giving promising results.

Micro-Satellite Structure Fracture Investigation techniques

Mounting accuracy of satellite payload and
ADCS (attitude determination and control subsystem) seats
is one of the requirements to achieve the satellite mission
with satisfactory performance. Deviation of the position of
the mounting seat for Multi-Band-Earth-Imager (MBEI) is
caused by cracks in the plate of the basis unit and bracket
for attachment of MBEI. These cracks were detected during
inspection of the satellite strength mock-up after vibration
testing for air transportation phase. Most probable reason of
the cracking is fatigue damage as strength mock-up
structure was subjected to prolonged vibration loading
during various loading cases. Total vibration duration
during testing is about 56 hours. In order to study the
cracking reasons, finite element modeling of the structural
parts of the basis unit including MBEI bracket and
instrument MBEI is subjected to harmonic response to
simulate vibration loading for the case of air transportation.
Numerical results are compared with the experimental ones,
and mechanical design of the basis-plate unit is modified