Metallschaume - insbesondere Aluminiumschaume - werden heute zur Klasse der porosen Metalle gezahlt. Das Buch gibt einen Uberblick uber die verschiedenen Herstellungsmoglichkeiten, Eigenschaften und ...aktuelle Anwendungen bis hin zu Forschungsthemen der letzten Jahre fur offen- und geschlossenporige Metallschaume.
Abstract
In this study, we analyze the influences of carbon nanotube (CNT) addition on the martensite transformation and internal friction of Cu–Al–Ni shape-memory alloys (SMAs). X-ray diffraction ...and differential scanning calorimetry results demonstrate that Cu–13.5Al–4Ni–
x
CNT (
x
= 0, 0.2, 0.4, 0.6, and 0.8 wt%) SMA/CNT composites exhibit a
$${\upbeta }_{1}({\mathrm{DO}}_{3})\rightleftarrows {\upbeta }_{1}^{\mathrm{^{\prime}}}(18\mathrm{R})$$
β
1
(
DO
3
)
⇄
β
1
′
(
18
R
)
martensitic transformation. The martensitic transformation temperatures and transformation enthalpies of the martensitic transformation peaks for the Cu–13.5Al–4Ni–
x
CNT (
x
= 0–0.8 wt%) composites gradually decrease with the increase in the amount of CNT addition. Compared to the Cu–13.5Al–4Ni SMA, the Cu–13.5Al–4Ni–
x
CNT (
x
= 0.2–0.8 wt%) SMA/CNT composites exhibit significant improvements in the amount of dissipation of energy (storage modulus (
$${E}^{\prime}))$$
E
′
)
)
and mechanical strength. However, the tan δ of the internal friction peak gradually decreases with the increase in the CNT content above 0.6 wt%. The reduction in tan
δ
is attributed to the decrease in the magnitude of the austenite-to-martensite transformation and precipitation of γ
2
(Cu
9
Al
4
) phase particles, which impede the interface motion in between the parent/martensitic phase and martensitic phase.
The input of combustion heat in engines has a major impact on the piston friction
and the resulting wear of the piston skirt. The new methodology presented here
enables the simulation of combustion ...heat input during motored operation, and
thus a detailed investigation of the piston friction under realistic piston
temperature profiles of real engine operation is possible.
For this purpose a standardized engine test bench for motored friction
evaluations was expanded to include, among other things, a movable high-power
diode laser with special defocusing optics. The setup of the test engine is
based on the FEV teardown step methodology 1 and has open access to the engine piston from above due to a
cylinder head dummy. Thus, the heat input by means of a high-power diode laser
into the piston crown can be made. The reduced engine structure also enables a
precise and highly accurate evaluation of the piston friction. A previously
conducted validation process of the methodology ensures the most accurate
possible replication of fired piston temperature profiles. The comparison
between the piston temperatures measured in fired operation and those simulated
in motored operation for a partial load operating point shows a maximum variance
deviation of only 15°C depending on the measuring point.
The new methodology is also used in particular for the evaluation and detection
of critical piston friction conditions. Experiments in this context are
presented and discussed exemplary by using three measurement series at different
operating temperatures and engine speeds.
There is a gradual increase in the laser power for each series of measurements
and thus in the heat input into the piston. The increase in heat input leads to
a significant increase in friction at all operating points due to thermal
expansion and the associated decrease reduction in piston clearance. Depending
on the operating temperature and the engine speed, a critical piston friction
condition is achieved and detected by the level of friction increase. The
additional use of ultrasonic sensors and the knock sensor installed as standard
makes a simultaneous measurement of the structure-borne sound signals possible.
The increase in the acceleration levels of all sensors correlates here with the
increase in piston friction. An evaluation of the noise, vibration, and
harshness (NVH) measurement in both the frequency range and the crank angle (CA)
range shows conspicuous high-frequency excitation levels that occur in the top
dead center area. This correlation can be proven for all three measurement
series.
The results obtained here may open a path to an improved piston cooling strategy
in the future.
This research studies the effect of multi-wall carbon nanotube (MWCNT) coated nickel to foaming time on the foam expansion and the distribution of pore sizes MWCNT reinforced AlMg4Si8 foam composite ...by powder metallurgy process. To control interface reactivity and wettability between MWCNT and the metal matrix, nickel coating is carried out on the MWCNT surface. Significantly, different foaming behavior of the MWCNT coated nickel reinforced AlMg4Si8 was studied with a foaming time variation of 8 and 9 min. Digital images generated by the imaging system are used with the MATLAB R2017a algorithm to determine the porosity of the surface and the pore area of aluminum foam efficiently. The results can have important implications for processing MWCNT coated nickel reinforced aluminum alloy composites.
This study investigates the damping properties of Cu–Al–Mn shape memory alloys (SMAs) with various chemical compositions and the effects of the addition of quaternary alloying elements Ag and Nb on ...the microstructure, martensitic transformation behavior, and damping capacity of SMAs. Compared to other Cu–12Al–xMn (x = 4–7 wt%) SMAs, Cu–12Al–5Mn has a more significant inherent and intrinsic internal friction (IFPT + IFI) peak above room temperature. The addition of Ag or Nb to Cu–12Al–5Mn reduced the grain size, thereby increasing the hardness of the alloys; however, the damping capacity and temperature of the IFPT + IFI peak decreased simultaneously. The addition of Ag to Cu–12Al–5Mn significantly reduced the damping capacity (IFPT+IFI peak) because of the notable decrease in the amount of transformed martensite. Moreover, the addition of Nb to Cu–12Al–5Mn caused the AlNb3 phase to precipitate, limiting the mobility of the martensite variant interfaces and slightly decreasing the damping capacity (IFPT + IFI peak). Among the Ag- and Nb-doped Cu–12Al–5Mn SMAs, Cu–12Al–5Mn–1 Nb showed not only a significantly higher hardness but also a higher IFPT + IFI peak, with tan δ exceeding 0.01 at approximately 50 °C.
Display omitted
•In Cu-based SMAs, damping capacity depends on microstructure and the volume fraction of the transformed martensite.•Alloying elements with different mechanisms affect the damping performance of Cu-based SMAs.•In Cu-based SMAs, both damping capacity and mechanical strength improve by optimizing chemical composition.
Training effects reported for stepping exergames on stepping performances in older adults often based on not comprehensively validated outcomes measures, and follow-up data on their sustainability ...are lacking. The aim of this study is to evaluate the effectiveness and sustainability of a motor-cognitive stepping exergame training on the stepping performance in older adults.
Fifty-eight older adults (78.3 ± 6.5 years) participated in the randomized controlled trial with a 10-week intervention and 10-week follow-up period. The intervention group (IG:
= 29) took part in a once-weekly exercise program including strength and balance exercises supplemented with an additional stepping exergame training. The control group (CG:
= 29) only performed the strength and balance exercises. Outcome measures included stepping reaction times (SRTs) and games scores for individual stepping exergame levels and for the overall exergame performance, as measured by an assessment strategy previously validated in older adults.
SRTs and/or games scores for 7 out of 10 levels and the overall exergame performance significantly improved in the IG compared to the CG during the intervention (
≤ 0.001-0.039,
= 0.090-0.445). Training gains were sustained for 2 levels and for the overall exergame performance (
= 0.017-0.033,
= 0.127-0.193).
The study demonstrates that the additional stepping exergame training effectively and sustainably improves the performance in complex motor-cognitive stepping exergame tasks in older adults, which can be relevant for preventing falls. Future research is needed to evaluate the effectiveness of such training on reducing the number of falls.
ISRCTN registry, ISRCTN14855620, 06/06/2019 (retrospectively registered).
This study assessed the feasibility of using a plasma-modified Ni foam as an anode to improve the electrochemical performance of double-chamber microbial fuel cells (MFCs). Scanning electron ...microscopy results showed that Ni foam exhibited an open cellular structure and rough surface morphology, providing a large contact area between bacteria and anodes in the MFCs. N 2 plasma modification did not influence the surface morphology of the Ni foam, whereas the hydrophobic surfaces of the Ni foam became highly hydrophilic. X-ray photoelectron spectrometer results revealed that Ni–N and NH 3 functional groups, formed on the surface of the Ni foam during the N 2 plasma modification, were responsible for its highly hydrophilic surface. Electrochemical measurements demonstrated that the highest power density of the MFC configured with an unmodified Ni foam anode electrode (166.9 mW m −2 ) was much higher than those of the MFCs configured with dense Ni rod (5.1 mW m −2 ) or graphite rod (29.5 mW m −2 ) anodes because Ni foam combined the advantages of an open cellular structure and good electrical conductivity. The highest power density of MFC configured with Ni foam was further improved to 247.1 mW m −2 after 60 min N 2 plasma treatment owing to the high hydrophilicity of the N 2 plasma-modified Ni foam electrodes, which facilitated bacteria adhesion and biofilm formation.
This study assessed the feasibility of using a plasma-modified Ni foam as an anode to improve the electrochemical performance of double-chamber microbial fuel cells (MFCs). Scanning electron ...microscopy results showed that Ni foam exhibited an open cellular structure and rough surface morphology, providing a large contact area between bacteria and anodes in the MFCs. N
2
plasma modification did not influence the surface morphology of the Ni foam, whereas the hydrophobic surfaces of the Ni foam became highly hydrophilic. X-ray photoelectron spectrometer results revealed that Ni-N and NH
3
functional groups, formed on the surface of the Ni foam during the N
2
plasma modification, were responsible for its highly hydrophilic surface. Electrochemical measurements demonstrated that the highest power density of the MFC configured with an unmodified Ni foam anode electrode (166.9 mW m
−2
) was much higher than those of the MFCs configured with dense Ni rod (5.1 mW m
−2
) or graphite rod (29.5 mW m
−2
) anodes because Ni foam combined the advantages of an open cellular structure and good electrical conductivity. The highest power density of MFC configured with Ni foam was further improved to 247.1 mW m
−2
after 60 min N
2
plasma treatment owing to the high hydrophilicity of the N
2
plasma-modified Ni foam electrodes, which facilitated bacteria adhesion and biofilm formation.
Plasma-modified Ni foam electrodes are suitable for MFCs because they combine the advantages of high surface area structures and good electrical conductivity.
Key summary points
Aim
To examine different mobility outcomes of acute geriatric care in acutely hospitalized older adults and identify associated factors.
Findings
Patients showed significant ...increases in locomotor capacity, physical activity, and life-space mobility from hospital admission to discharge, for which frailty was consistently identified as a negative independent predictor. A higher mean daily physical activity level was independently predictive of improvements in locomotor capacity.
Message
Older hospitalized patients benefit from acute geriatric care in terms of distinct mobility outcomes; however, frailty-specific adaptations may be needed for frail patients to optimize their mobility outcomes.
Purpose
To examine distinct mobility outcomes (locomotor capacity, physical activity, life-space mobility) of acute geriatric care (AGC) in acutely hospitalized older adults and identify predictors associated with these outcomes.
Methods
The PAGER study was designed as a prospective observational study
.
Mobility outcomes of 107 hospitalized older patients (age = 83.2 ± 6.4 years, female:
n
= 68, 63.6%) receiving AGC were measured at hospital admission and discharge. Locomotor capacity was assessed with the Short Physical Performance Battery (SPPB), 24-h physical activity (step count) with an activity monitor, and life-space mobility with the Life-Space Assessment in Institutionalized Settings (LSA-IS). Baseline demographical, clinical, physical, cognitive, and psychological characteristics were analyzed as candidate predictors of mobility outcomes.
Results
SPPB (median interquartile range 4.0 2.8–5.0 pt. vs. 5.0 3.0–6.3 pt.), step count (516 89–1806 steps vs. 1111 228–3291 steps), and LSA-IS total score (10.5 6.0–15.0 pt. vs. 16.3 12.0–24.1 pt.) significantly improved during AGC (all
p
< 0.001). Adjusting for baseline status, frailty was identified as an independent negative predictor of SPPB, step count, and LSA-IS at discharge (
p
= 0.003–0.005). Barthel Index was also independently positively associated with step count (
p
= 0.017) at discharge, as was the mean daily PA level with SPPB (
p
= 0.027) at discharge, both independent of baseline status.
Conclusion
AGC improves distinct mobility outcomes in hospitalized older patients. Frailty was consistently found to be an independent negative predictor of all mobility outcomes. Frailty assessment in AGC may be important to identify patients at risk for decreased treatment gains in mobility. Early PA promotion in AGC seems to be beneficial in improving patients’ locomotor capacity.
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