Volume 56, Issue 1

Fires in homes develop very fast nowadays, because the amount of combustible materials in furniture and electrical devices has increased significantly in recent years. Especially fires in children's rooms can be very hazardous as several recent fires in Germany showed. To investigate the fire and smoke development in such a fire the test room was furnished like a typical children's room and equipped with 36 thermocouples and a pressure measurement device. Also smoke detectors were installed. The fire was ignited by a small candle which was in contact with a mattress only for one second. Flashover occurred only after 4 minutes. The fire load and the fire and smoke development were investigated. The fire safety regulations for the furnishings, electrical devices and toys were discussed. Additionally the temperature rise in the compartment was predicted according to the method of McCaffrey.

Kurzfassung Der Einfluss von Korrosion auf die Mikrostruktur und die damit einhergehenden mechanischen Eigenschaften der kriechbeständigen bariumhaltigen Mg-Al-Ca-Legierung DieMag422 wurden untersucht. Zur Bewertung des Korrosionsverhaltens wurden potenziodynamische Polarisationsmessungen und Immersionsversuche in pH7 mit und ohne Natriumchlorid durchgeführt. Die Korrosionsmechanismen wurden an Proben mit definierten Korrosionszuständen mikrostrukturell im REM analysiert. Die Festigkeits- und Verformungseigenschaften nichtkorrodierter und korrodierter Proben wurden in quasistatischen Zugversuchen verglichen, wobei ein signifikanter Abfall der Zugfestigkeit und Bruchdehnung mit steigendem Grad an korrosiver Schädigung festgestellt wurde. Die Ermüdungseigenschaften wurden in mehrstufigen und einstufigen Versuchen mithilfe von Hysteresis-, Temperatur- und elektrischen Widerstandsmessungen für verschiedene Korrosionszustände charakterisiert. Der Laststeigerungsversuch ermöglicht eine Abschätzung der Dauerfestigkeit und die Bestimmung der zum Bruch führenden Spannungsamplitude mit einer Probe. Die Ermüdungsergebnisse belegen einen signifikanten Abfall der Dauerfestigkeit und Bruchspannungsamplitude mit steigendem Korrosionsgrad. Die eingesetzten Messverfahren erlauben gleichermaßen die Charakterisierung der Ermüdungseigenschaften und die Darstellung des aktuellen Ermüdungszustands. Die thermische und elektrische Werkstoffreaktion verhält sich proportional zur zyklischen plastischen Verformung und bietet die Möglichkeit den aktuellen Ermüdungszustand von Bauteilen selbst unter Betriebsbedingungen im Sinne eines Condition-Monitorings zu bewerten.

Alumina (Al 2 O 3 ) is one of the most important technical ceramic materials due to its good properties and its acceptable price. For some purposes, it is important to achieve either a very smooth or a rough surface of the ceramic object. The aim of this study was to evaluate the influence of different surface finish processes on the surface roughness of alumina and, consequently, on the measured Knoop hardness. Four types of samples were prepared, each with a different surface finish – ground with different SiC abrasive papers or polished with diamond pastes with different granulation. For each sample three indentation loads were used: 0.4903 N (HK 0.05), 4.903 N (HK 0.5) and 49.03 N (HK 5). It has been noticed that all samples exhibited a decrease in hardness with the increasing applied test load, a phenomenon known as the normal indentation size effect (ISE). In order to investigate this occurrence, three mathematical models were applied, i. e., Meyer's law, the proportional specimen resistance model (PSR) and modified proportional specimen resistance model (MPSR). The results showed that the alumina surface roughness significantly affects the measured Knoop hardness. Dependence of Knoop hardness and the indentation load can be quantified by all three mathematical models.

As a more economical cathode material than conventional Ni/YSZ cermet for high temperature electrolysis (HTE) cell, CuO/YSZ composites (40 vol.-% and 60 vol.-% CuO powder with balance YSZ) were successfully fabricated by high energy ball-milling of CuO and YSZ powders, pressing into pellets (Φ 13 mm × 2 mm) and subjecting them to a subsequent reduction-sintering process at 900 °C under purging with a 5 % H 2 /Ar gas. The Cu/YSZ cermet material thus fabricated was characterized using various analytical methods such as XRD, SEM, and laser diffraction as well as scattering method. Electrical conductivity of reduction-sintered Cu/YSZ cermet pellets thus fabricated was measured both at room temperature and temperature range between 600 °C and 800 °C by using the 4-probe technique for comparison with those of previously published literature conductivity data of Ni/YSZ and Cu/YSZ cermets produced by the same high-energy ball milling of blended elemental metal with YSZ powders. The effect of composite composition on the electrical conductivity was investigated and a slight decrease in electrical conductivity for CuO content of 60 vol.-% was explained by a greater porosity accompanying reduction-sintering of 60 vol.-% CuO/YSZ composite than that with 40 vol.-%. Lastly, CuO/YSZ was used as a HTE cathode of a self-supporting planar unit cell and its electrochemical performance was investigated.

In this study, machinability of AZ 91D magnesium alloy, which has been widely used in automotive and aircraft industries, was investigated by using HSS and carbide tools at dry cutting conditions. Taguchi's L 18 (2**1 3**2) mixed model was used for the experiments. Drilling parameters such as feed rate, spindle speed and cutting tool were optimized according to the multiple responses (diametral error, circularity and surface roughness) by grey relational analysis. The effects of machining parameters and their interactions on the hole diameter, circularity and surface roughness were determined. The analysis of Taguchi and ANOVA indicated that the influence of drill material on the surface roughness of the drilled hole was high, but on the hole diameter and circularity it was low. Furthermore, the results of grey relational analysis revealed that optimal combination of the drilling parameters (0.3 mm/rev feed rate, carbide tool and 3000 rpm spindle speed) can be used to obtain the minimum diametral error, circularity error and surface roughness.

The aim of this study was to investigate the different mechanical properties with respect to the impact behaviour on a single layer composite. For this, steel spheres have been used with low initial speed of v o = 2.5 m/s, 4 m/s and 5 m/s and three different diameters. The spheres have been dropped to the plate surface in the vertical direction. Sphere diameters of d = 7 mm, 8.5 mm and 10 mm have been chosen and the effect of impact on three different ply made composite materials has been calculated. The impact characteristics were evaluated by the pulse parameter λ, the reversal energy E, the contact force F, and the rebound velocity V.

In this study, thermal effects on the free vibration characteristics of composite beams are studied for different temperatures and boundary conditions by using numerical and experimental techniques. Different ply angles, stacking sequences and specimen thickness are also considered. The comparison revealed a good agreement between numerical and experimental results. It is also concluded that regardless of the type of boundary condition and thickness, natural frequencies are decreased with increasing temperature. In addition, a minimum natural frequency value occurs in the natural frequency-ply angle graph at 60° ply angle for all considered temperatures. It can also be stated that the natural frequencies of the composite beams can be adjusted by controlling the temperature as well as the stacking sequences.

Acrylonitrile-vinylidene chloride (AN-VDC) copolymer films containing activated carbon, manganese dioxide nanoparticles were fabricated via casting method. The formaldehyde degradation capacity of copolymer film was investigated. The results showed that formaldehyde eliminating rate was obviously improved when copolymer film was blended with MnO 2 or activated carbon, respectively. The HCHO removal rate increased with concentration of MnO 2 or activated carbon. HCHO degradation rate of AN-VDC copolymer film without addition was 45 % for 48 h, while it was up to 90–95 % with the treatment time of 36 h after 3 wt.-% MnO 2 or activated carbon addition. Furthermore, the complex effect of MnO 2 and activated carbon on the degradation has also been studied. When 3 wt.-% MnO 2 and 1 wt.-% activated carbon was mixed into copolymer, the HCHO removal rate was about 90 % for 36 h treatment. The results demonstrated that the formaldehyde eliminating rate was enhanced by complex addition of both MnO 2 and activated carbon compared to films with single additions. The enhancement of HCHO eliminating efficiency occured due to a double effect of physical absorption of activated carbon and catalytic oxidation of MnO 2 .

Several machines, such as crushers use the physical effect of compression to cause fragmentation “crushing” of brittle rocks. As a consequence of the complex fragmentation process, crushers are still sized by empirical approaches. This paper presents the results of a numerical study to understand some aspects of rock crushing phenomenon in terms of energy consumption. The study uses the discrete element approach of PFC2D code to simulate a stamp mill. The stamp mill has a simple crushing mechanism of a fixed kinetic energy delivered by a rigid ram impact. A single rock fragment crushing process dependent on the number of stamp mill ram blows is numerically examined. Both amount and type of energy generated by a ram blow are monitored besides the type of fractures generated. The model results indicate that the ram impact energy is mainly consumed in form of friction energy (up to 61 %) while strain energy stays at about 5 % of delivered energy. The energy consumed by crushing the rock represents only 32 % to 45 % of stamp mill energy and tends to decrease as the number of impacts increases. The rock fragmented matrix tends to convert into more friction energy with reduced number of new fractures as number of blows increase. The fragmentation caused by tensile is more often compared to those caused by shear, this behaviour increased with increasing number of ram blows.