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Die in zunehmenden Maße Mitte der 80er Jahre einsetzende Substitution von metallischen Materialien z. B. durch hochleistungsfähige polymere Werkstoffe und Verbundwerkstoffe wurde u. a. von der DGM zum Anlass genommen, ihre zukünftigen Aufgaben neu zu definieren und gleichzeitig mit der Gründung des Fachausschusses "Gefüge und Eigenschaften von Polymerwerkstoffen" dieser neuen Entwicklung in der Materialkunde auf dem Gebiet der Kunststoffe und ihrer Anwendungen Rechnung zu tragen.
Characterization of the fcc/bcc orientation relationship by EBSD using pole figures and variants
(2004)
The orientation relationship (OR) between fcc and bcc lattices are described by crystallographic fundamentals using the example of Kurdjumov-Sachs (K-S) and Nishiyama-Wassermann (N-W). Complete pole figures containing all variants will be used to distinguish even between slightly different ORs. EBSD on iron meteorites and duplex steel has been used to analyse a large number of crystal orientations with regard to a high statistical significance and a high probability to capture all variants in a single measurement. It is shown that the use of fixed OR models like K-S, N-W, Bain, Pitsch, or Greninger-Troiano does not satisfacturally reflect the observed experimental pole distributions. It is not convenient to use high-indexed lattice planes and directions to describe the small deviations from the given models. The Euler subspace representation offers a readily comprehensible tool to get an idea about the characteristic of the experimentally detected OR.
ür die Berücksichtigung mechanischer Belastungen unterhalb der Streckgrenze ist im Rahmen einer zuverlässigen Bauteilauslegung die Kenntnis der elastischen Konstanten von besonderer Bedeutung. Für die experimentelle Bestimmung des Elastizitätsmoduls wurde eine Vielzahl von Verfahren entwickelt, die zum Teil werkstoffspezifisch Eingang in die Normung gefunden haben.
Prinzipiell können diese Verfahren in zwei Gruppen unterteilt werden: die statischen und die dynamischen Prüfverfahren. Die statischen Verfahren beruhen auf der direkten Messung des Spannungs-Dehnungs-Zusammenhangs während einer mechanischen Belastung im elastischen Verformungsbereich (Zug, Biegung, Druck). Die dynamischen Verfahren basieren auf der Schwingungsanregung eines Prüfkörpers und der Analyse der resultierenden Schwingungen (Resonanzmethode oder Impulsanregungsmethode) oder auf der Messung der Ultraschallausbreitungsgeschwindigkeit.
Stellvertretend für die dynamischen Verfahren wird im ersten Teil dieses Beitrages die Resonanzmethode vorgestellt. Der zweite Teil dieses Beitrages fasst die werkstoffabhängigen Ergebnisse der E-Modulbestimmung mit statischen Verfahren im Zug- und Biegeversuch zusammen.
For the safety and cost efficiency of welded high-strength steel structures, precise knowledge of the level and distribution of welding- and cooling-specific stresses and residual stresses is essential, since they exert a decisive influence on strength, crack resistance, and finally on the bearable service load. This paper presents innovative filler materials, of which the phase transformation temperature was deliberately adjusted via the chemical composition. The transformation behaviour of these martensitic Low Transformation Temperature (LTT-) filler materials shows direct effects on the local residual stresses in the weld and the HAZ. These effects can purposefully be exploited to counteract the thermally induced shrinkage of the material and to produce significant compressive residual stresses in the weld. Comparative welding experiments were carried out on 690 MPa high-strength base materials using various LTT-filler materials. High energy synchrotron radiation was used for residual stress measurement. Particularly the use of high energy synchrotron radiation makes it possible to detect the residual stress condition fast without destruction of material. Thereby, residual stress depth gradients can be determined simultaneously without removing material. In steel, gradients of up to 150 µm can be resolved in such a way. Furthermore, the application of high energy radiation permits determination of residual stresses of any available residual austenite contents. Results show significant dependence of transformation temperatures on the resulting residual stress level and distribution.
Cold cracking resistance is a relevant evaluation criterion for welded joints and affected by residual stresses which result from the welding procedure. Compressive residual stresses can thereby have a positive influence on preventing cracking. A unique possibility of generating compressive residual stresses already during the welding procedure is offered by the so-called Low Transformation Temperature (LTT) filler wires. Compared to conventional wires, these materials show decreased phase transformation temperatures which can work against the cooling-specific contraction. In consequence, distinct compressive residual stresses can be observed within the weld and adjacent areas. The strength of these fillers makes them potentially applicable to high-strength steel welding. Investigations were carried out to determine the phase transformation behaviour of different LTT-filler materials. Transformation temperatures were identified using Single Sensor Differential Thermal Analysis (SS-DTA). Additionally Synchrotron radiation was used to measure the transformation kinetics of all involved crystalline phases during heating and cooling of a simulated weld thermal cycle.
Bisphenol A polycarbonate/acrylonitrile–butadiene–styrene (PC/ABS) with and without bisphenol A bis(diphenyl phosphate) (BDP) and 5 wt.% zinc borate (Znb) were investigated. The pyrolysis was studied by thermogravimetry (TG), TG-FTIR and NMR, the fire behaviour with a cone calorimeter applying different heat fluxes, LOI and UL 94. Fire residues were examined with NMR. BDP affects the decomposition of PC/ABS and acts as a flame retardant in the gas and condensed phases. The addition of Znb results in an additional hydrolysis of PC. The fire behaviour is similar to PC/ABS, aside from a slightly increased LOI and a reduced peak heat release rate, both caused by borates improving the barrier properties of the char. In PC/ABS + BDP + Znb, the addition of Znb yields a borate network and amorphous phosphates. Znb also reacts with BDP to form alpha-zinc phosphate and borophosphates that suppress the original flame retardancy mechanisms of BDP. The inorganic–organic residue formed provides more effective flame retardancy, in particular at low irradiation in the cone calorimeter, and a clear synergy in LOI, whereas for more developed fires BDP + Znb become less effective than BDP in PC/ABS with respect to the total heat evolved.
Die Analytik von Phthalaten (DMP bis DEHP) in der Luft ist mit thermischer Desorption unter Verwendung von Quarzwolle als Adsorbens erfolgreich realisierbar. Dies wurde durch eine Methodenvalidierung bestätigt. Es wurden sowohl Messungen im Innenraum als auch in Emissionskammern vorgenommen. In den Emissionskammermessungen wurden mögliche Senkeneffekte der Kammeroberfläche (Glas) untersucht. Unter Zuhilfenahme der idealen Abklingkurve wird bestätigt, dass diese Oberfläche eine Senke darstellt.
Phosphorus-based flame retardancy mechanisms - Old hat or a starting point for future development?
(2010)
Different kinds of additive and reactive flame retardants containing phosphorus are increasingly successful as halogen-free alternatives for various polymeric materials and applications. Phosphorus can act in the condensed phase by enhancing charring, yielding intumescence, or through inorganic glass formation; and in the gas phase through flame inhibition. Occurrence and efficiency depend, not only on the flame retardant itself, but also on its interaction with pyrolysing polymeric material and additives. Flame retardancy is sensitive to modification of the flame retardant, the use of synergists/adjuvants, and changes to the polymeric material. A detailed understanding facilitates the launch of tailored and targeted development.
Structural changes in the condensed phase of bisphenol A polycarbonate (containing 0.45 wt% poly (tetrafluoroethylene))/silicone acrylate rubber/bisphenol A bis(diphenyl-phosphate) (PC/SiR/BDP) and PC/SiR/BDP/zinc borate (PC/SiR/BDP/ZnB) during thermal treatment in nitrogen atmosphere and in fire residues were investigated by solid-state NMR. H-1, B-11, C-13 and P-31 NMR experiments using direct excitation with a single pulse and H-1-P-31 cross-polarization (CP) were carried out including 31P(1 H) and C-13{P-31}double-resonance techniques (REDOR: Rotational Echo Double Resonance) on a series of heat-treated samples (580 K-850 K). Because many amorphous phases occur in the solid residues, and solid-state NMR spectroscopy addresses the most important sites carbon, phosphorus and boron, this paper is the key analytical approach for understanding the pyrolysis and flame retarding phenomenon in the condensed phase of PC/SiR/BDP and PC/SiR/BDP/ZnB.
For the system PC/SiR/BDP it is shown that (i) at temperatures around 750-770 K (main decomposition step) carbonaceous charring of PC occurs and arylphosphate structures are still present, reacted in part with the decomposing PC; (ii) for higher temperatures from 770 K the phosphorus remaining in the solid phase increasingly converts to amorphous phosphonates and inorganic orthophosphates with a minor amount of crystalline orthophosphates; and (iii) H-1-P-31{H-1} CP REDOR and H-1-C-13{P-31} CP REDOR NMR experiments suggest that the phosphates and phosphonates are bound via oxygen to aromatic carbons, indicating the interaction with the carbonaceous char.
When ZnB is added to the system PC/SiR/BDP, (i) ZnB leads to a slightly enhanced PC decomposition for temperatures below 750 K; (ii) alpha-Zn-3(PO4)(2) and borophosphate (BPO4) are formed in small amounts at high temperatures suggesting a reaction between BDP and ZnB during thermal decomposition; and (iii) most of the borate remains in the solid residues, forming an amorphous pure borate network, with the BO3/BO4 ratio increasing with higher temperatures.
The NMR data of thermal and fire residues are highly correlated, underlining the importance of this work for understanding the pyrolysis and flame retardancy mechanisms in the condensed phase during the burning of the PC/SiR blends. (C) 2010 Elsevier Ltd. All rights reserved.
The pyrolysis and fire behavior of halogen-free flame-retarded DGEBA/DMC, RTM6 and their corresponding 60 vol.-% carbon fibers (CF) composites were investigated. A novel phosphorous compound (DOPI) was used. Its action is dependent on the epoxy matrix. DGEBA/DMC and DOPI decompose independently of each other. Only flame inhibition occurs in the gas phase. RTM6 shows flame inhibition and a condensed phase interaction increasing charring. Both mechanisms decrease with increasing irradiance, whereas in RTM6-CF charring is suppressed at low ones. RTM6+DOPI shows a higher LOI (34.2%) than DGEBA/DMC+DOPI and a V-0 classification in UL 94. Adding CF only enhances the LOI, DOPI+CF leads to a superposition in LOI for DGEBA/DMC-CF+DOPI (31.8%, V-0) and a synergism for RTM6-CF+DOPI (47.7%, V-0).
Pyrolysis, flammability, fire behavior, melt viscosity, and gas diffusion of bisphenol A polycarbonate/acrylonitrile-butadiene-styrene (PC/ABS) were investigated, with bisphenol A bis(diphenyl phosphate) (BDP), with 10 wt.% talc and with BDP in combination with 5, 10 and 20 wt.% talc, respectively. Compared to PC/ABS, PC/ABS + BDP results in an increased decomposition temperature of PC, a higher char yield, a significantly increased LOI, a V-0 classification in UL 94, a reduced peak heat release rate (pHRR), and a reduced total heat release (THR) in the cone calorimeter. This efficient flame retardancy is due to mechanisms in both the gas and condensed phases. PC/ABS + 10 wt.% talc shows a decrease in the PC decomposition temperature. The fire behavior is improved in part compared to PC/ABS, with an increased LOI and reduced pHRR. PC/ABS + BDP + 10 wt.% talc shows a strong synergism in LOI, a V-0 classification, and a decrease in pHRR, whereas THR is slightly increased compared to PC/ABS + BDP. Talc decreases the gas diffusion and enhances the flow limit for low shear rates, both of which influence the pyrolysis and flammability results. Further, talc improves the protection properties of the fire residues. Nevertheless it also partly suppresses flame inhibition and the charring effect of BDP. The synergism between BDP and talc in LOI is obtained even for low talc loadings in PC/ABS + BDP + talc, whereas for higher loadings saturation is observed.
Downsizing (power-to-weight ratio) and higher speeds lead to a rise in Hertzian contact pressures in combination with an increase in surface or oil temperatures. Under such conditions, commonly used bearing steels, such as 100Cr6, reach their limits, creating a demand for alternative slip-rolling resistant steel alloys. The present work therefore compares the slip-rolling performance of various steel types with Maraging- and PM-type steel alloys such as e.g. CSS-42L™, ASP2012, BIMAX42+, in the Hertzian contact pressure range up to P0max of 4 GPa. Through-hardened 100Cr6H (AISI 52100), case-hardened 20MnCr5 (AISI 5120H) and nitrogen alloyed Croni-dur30 (AMS 5898) still compete in terms of slip-rolling and wear resistance and load carrying capacity, whereas Maraging- and PM-type steel alloys offer superior strength and toughness properties.
Several construction and building materials, including wood, glue and coatings, are possible sources of very volatile organic compounds (VVOCs) and volatile organic compounds (VOCs) like formic and acetic acid. Due to very high air tightness and very low air exchange rates in new buildings concentrations of these harmful substances can increase considerably. To minimize the risk, emissions from building products should be identified and quantified. With the common standard method, this means Tenax® sampling followed by thermal desorption and GC-MS analysis, these acids could not be detected sufficiently. The aim oft this study is the comparison of two different methods for the determination of acetic and formic acid. The sampling of method one, which is usually used for identification and quantification of VOCs, is done in accordance with ISO 16000-6 and ISO 16017-1 on Carbotrap® 202 multi-bed thermal desorption tube by subsequent identification and quantification with GC-MS. Method two is based on sampling on 2,4-dinitrophenylhydrazine (DNPH) cartridges, derivatisation, elution, identification and quantification of the derivatives with LC-MS/MS (liquid chromatography mass spectrometry/mass spectrometry).
The use of coconut fiber (CF) agricultural waste was considered as an environmentally friendly and inexpensive alternative in flame retarded biocomposites. To decrease the high content of aluminum trihydrate (ATH) required, the thermal decomposition (thermogravimetry), flammability [oxygen index (LOI) and UL 94 test] and fire behavior (cone calorimeter) of a combination of CF and ATH were investigated in a commercial blend of thermoplastic starch (TPS) and cellulose derivatives. CF induced some charring activity, slightly decreasing the fire load and burning propensity in cone calorimeter test. ATH decomposes endothermically into water and inorganic residue. Significant fuel dilution as well as a pronounced residual protection layer reduces the fire hazards. Replacing a part of ATH with coconut fibers resulted in improved flame retardancy in terms of ignition, reaction to small flame, and flame-spread characteristics [heat release rate (HRR), fire growth rate (FIGRA), etc.]. The observed ATH and CF synergy opens the door to significant reduction of the ATH contents and thus to interesting flame retarded biocomposites.
Effect of well dispersed amorphous silicon dioxide in flame retarded styrene butadiene rubber
(2013)
Spherically shaped amorphous silicon dioxide with broad size particle distribution was used in combination with aluminium trihydroxide (ATH) in styrene butadiene rubber composites. The pyrolysis, flammability, fire properties, flame spread and gas diffusion were investigated. The kind and amount of ATH, but in particular the fine silicon dioxide chosen as an additive, influenced the thermal decomposition and fire behaviour of styrene butadiene rubber composites. Gravimetric gas sorption measurements showed that the gas diffusion was systematically lower with silicon dioxide. The initial pyrolysis gas release was hindered, increasing the temperature at which decomposition begins as well as the ignition time in fire tests. During combustion, ATH and silicon dioxide accumulate on the surface of the specimen, forming a residual protective layer. A reduced peak heat release rate and fire spread were observed. The addition of a special kind of silicon dioxide is proposed to play a key role in optimising fire retardancy.
We use a dynamic scanning electron microscope (DySEM) to analyze the movement of oscillating micromechanical structures. A dynamic secondary electron (SE) signal is recorded and correlated to the oscillatory excitation of scanning force microscope (SFM) cantilever by means of lock-in amplifiers. We show, how the relative phase of the oscillations modulate the resulting real part and phase pictures of the DySEM mapping. This can be used to obtain information about the underlying oscillatory dynamics. We apply the theory to the case of a cantilever in oscillation, driven at different flexural and torsional resonance modes. This is an extension of a recent work (Schr¨oter et al 2012 Nanotechnology 23 435501), where we
reported on a general methodology to distinguish nonlinear features caused by the Imaging process from those caused by cantilever motion.
In welding experiments conducted on heavy wall pipes, the penetration mode (full or partial penetration) occurred to be a significant factor influencing appearance of solidification cracks. To explain the observed phenomena and support further optimization of manufacturing processes, a computational model was developed, which used a sophisticated strategy to model the material. High stresses emerged in the models in regions which showed cracking during experiments. In partial penetration welding, they were caused by the prevention of weld shrinkage due to the cold and strong material below the joint. Another identified factor having an influence on high stress localization is bulging of the weld.
Odour measurements become increasingly important in view of the assessment of indoor air quality and the emissions of building products. Hence they need to be implemented into evaluation schemes such as the AgBB scheme. While there are already standards like DIN ISO 16000-28 and VDI 4302 Part 1 specifying the procedure of odour measurements using a comparison scale, no final validation of the method has been carried out so far. Therefore, a round robin test was conducted in 2012 with 12 participating laboratories that mainly consisted of the following two parts: 1) testing of the available comparison scales with respect to their operational performance and 2) execution of an odour assessment of an acrylic sealant using emission test chambers. Part one included the measurement of the air flow rates and the provided concentrations of the reference substance (acetone). Part two was conducted to test the performance of the laboratories and the applicability of DIN ISO 16000-28 and supplementary VDI 4302 Part 1 by assessing the perceived intensity and the hedonic tone of the air samples. Moreover, samples for VOC analysis were taken from the air in the emission test chamber on the 7th day of testing to allow for quality control. Resulting from this round robin test main deficits were detected and suggestions for the improvement of the odour measurement procedure were made.
A method for the determination of very volatile organic compounds (VVOC) in air was developed and successfully tested for methanol and ethanol. Carbotrap300® (a multi-bed tube using Carbopack C®, Carbopack B® and Carbosive SIII®) was selected as sorption material for thermal desorption and tested for its suitability for emission test chamber measurements. The adsorption behaviour and the chromatographic results are influenced negatively by spiking aqueous solutions on the adsorption medium for calibration purposes. The latter effect can be reduced by blowing dry air across the adsorbent to remove the adsorbed water. Detection and quantification limits were determined for a GC-FID system and compared to GC-MS. The applicability of the method was tested with a methanol eliminating silane modified polymeric adhesive (SMP-adhesive for parquet) in an emission test chamber