Ingenieurwissenschaften und zugeordnete Tätigkeiten
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- 2014 (23) (entfernen)
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- AC weld pool support (2)
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Eingeladener Vortrag
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The influence of two different weld imperfections (gap/crack) on the fatigue behaviour of spot welded joints was tested
Surface cracks havenoinfluenceon thefatiguelife
Samples with cracks in the electrode indentation /HAZ where tested
Stiffness curves are not significantly influenced by surface cracks
3D FE-Simulation demonstrate no changes of stress due to surface imperfections
Drop-out of molten material was avoided by EM pressure
Compensation of the hydrostatic pressure of up to 20 mm thick
aluminum and stainless steel (experiment and FEM)
Mitigation of the weld bead dynamics
Significant changes in the velocity distributions in the weld pool
Weld pool geometry shape changes due to Hartmann effect
Significant porosity reduction
Surface quality improvements
Drop-out of molten material was avoided by EM pressure
Compensation of the hydrostatic pressure of up to 20 mm thick
aluminum and stainless steel (experiment and FEM)
Mitigation of the weld bead dynamics
Significant changes in the velocity distributions in the weld pool
Weld pool geometry shape changes due to Hartmann effect
Significant porosity reduction
Surface quality improvements
Computational Advances
(2014)
The term „Alternative Solvents“ often refers to ionic liquids (ILs), mainly to distinguish these substances from traditional (i.e., molecular) solvents.
In applications, any „alternative“ is required to perform better than something that is proven and tested.
To bring ILs into practical use, availability and costs are the fundamental points to be addressed.
There are two ways to proceed:
▬ tailoring a molecule, implanting the expected characteristics
advantage: optimization of the targeted performance possible
risks: outcome not always foreseeable, costly and time-intensive (“trial and error“)
▬ to target on mixtures of well-characterized ILs with molecular solvents
advantage: substance characteristics are known, less costly, less time-consuming,
mixture composition another tunable parameter
risks: the same but with less impact
For the basic engineering of technical processes, knowledge of phase equilibria, particularly of
mixtures, over a broad (p,T) range is mandatory.
This contribution reports on recent experimental results from our laboratory:
▬ the solubility of CO2 in a mixture of water and [bmim][CH3SO4]
▬ the solubility of CO2 in a mixture of methanol and [bmim][PF6]
Emergency response units increasingly use pressure cylinders made from fibre composites for breathing air as elements of personal protective equipment (PPE). Such applications expose the composite cylinders to harsh temperature and handling conditions. At least in Europe, standards have been used for certifying PPE, which are designed and mandatory for the approval of pressure receptacles for the transport of dangerous goods. Therefore, service conditions specific to PPEs are not accounted for in these standards. In this paper, BAM (Federal Institute for Materials Research and Testing) investigates the residual safety of a composite cylinder design at the end of their designated service life of 15 years. The cylinders (test pressure PH 450 bars; 6.8 Litres) are of one design type with aluminium liner and fully wrapped with carbon fibres, which is commonly considered a “Type III” cylinder. All cylinders were used as PPE by the Berlin fire department and randomly picked in three samples of 25 cylinders each before tested.
At BAM, the cylinder samples underwent hydraulic load cycle tests (LCT), conventional burst tests (BT) and so called slow burst tests (SBT). A concept for quantification of strength degradation already introduced by BAM was applied. This concept is based on a probabilistic assessment of the average strength and scatter of each sample of cylinders. The strength distributions of the used PPEcylinders is shown and analysed. Some unexpected effects are shown and a refinement of the statistical assessment is introduced.
The determination of the fatigue life in technical alloys containing large and small defects must rely on a propagation model which accounts for short and long crack growth. Recently an analytical model which incorporates propagation in the short crack regime and plastic correction for the crack driving force has been presented by two of the authors.
This work is intended to show further validation of the model, taking into account data sets for different materials with different testing conditions.
Despite the assumptions about missing parameters, the value of which had to be taken from the literature, the predictions showed a fairly good approximation of the fatigue lives. A possible interpretation of the results in terms of multiple crack initiation and propagation at higher loads is proposed.