Fragestellung: Die Evaluierung der posturalen Stabilität mittels Posturographie wird häufig als Diagnoseinstrument und auch zur Überprüfung des Therapieergebnisses im rehabilitativen Management bei chronischen, idiopathischen Rückenschmerzen (CLBP) eingesetzt. Ziel dieser Studie war die Überprüfung der Kurz- und Langzeit-Reliabilität posturographischer Messungen bei Patienten mit CLBP.
Due to their high specific strength, good corrosion resistance and high temperature strength Magnesium alloys containing Rare Earth additions are promising candidates for structural and engine applications in the transportation industry. Also medical applications, like bone screws and nails, benefit from their moderate corrosion rate and biocompatibility. All applications need materials which show a high strength, ductility and fracture toughness in case a crack has formed during service to keep safety against rupture. In this study four extruded Mg10Gd based alloys modified with Nd and La have been 3-point-bend tested at low a deformation speed to evaluate the influence of the microstructure on crack growth. A comparison to the cast material (subjected to T4 to increase ductility and to reduce the dendritic microstructure) shows an increase in strength and ductility due to the fine grained microstructure as a result of recrystallization during extrusion. The maximum bending strength and outer strain to crack initiation is also strongly influenced by the alloying system itself. The influence of Nd and La to the binary alloy Mg10Gd is discussed in using tensile, compression and bending tests. The increase in strength results in reduced elongation to fracture in tension loading as well as the outer strain for the crack initiation during bending tests. Tensile tests are often discussed to be not a reliable method for determining the Young’s modulus of magnesium. Therefore resonance frequency damping analysis has been applied to determine the dynamic modulus of elasticity, which is compared with the flexural (bending) modulus. Crack growth is discussed using light microscopy and correlated with bending stress-strain curves. The crack growth rate of the extruded, fine grained material is many times higher than of the cast, coarse grained material. Crack propagation is mostly transgranular and assisted by twinning.
The influence of post-heat treatment on the mechanical properties of complexly deformed low carbon steel is studied in this work to improve a forming process to ensure and enhance the overall product quality. Since there is no constant deformation degree, there are big differences in the mechanical properties within the part: material seen a high deformation degree shows increased strength but decreased ductility, which carries the risk of formation of cracks. A post heat treatment reduces that risk by reducing inner stresses and work/strain hardening. This study involves two steel component varying in thickness and forming process: stretching plus bending and stretching only. Post heat treatment after cold forming is necessary to provide the safety margin needed in the application. The forming process which consists of stretching only delivers a more uniform deformation over the length of the nozzle. However, adding bending to stretching keeps the deformation degree lower and leads to a more homogenous property distribution after annealing. Material only exposed to stretching shows strong softening by deforming above critical deformation degree with resulting values below initial properties. Even during annealing of around 40 min, recrystallization took part: more globular grains can be seen. Post heat treatment also homogenizes hardness over the cross-section of the work piece. Increased hardness towards the tension and compression surface side as a result of friction between tool and work piece should be avoided to provide the safety margin also on the more local level. Annealing retrieves the yield point phenomenon and strongly increases ductility up to 35 % and reduces the ratio of tensile yield strength to ultimate tensile strength to more moderate levels of around 0.6.
'%3e%3cpath fill='%23012169' d='M0 0v30h60V0z'/%3e%3cpath stroke='%23fff' stroke-width='6' d='m0 0 60 30m0-30L0 30'/%3e%3cpath stroke='%23C8102E' stroke-width='4' d='m0 0 60 30m0-30L0 30' clip-path='url(%23b)'/%3e%3cpath stroke='%23fff' stroke-width='10' d='M30 0v30M0 15h60'/%3e%3cpath stroke='%23C8102E' stroke-width='6' d='M30 0v30M0 15h60'/%3e%3c/g%3e%3c/svg%3e)
