Volume 54, Issue 11-12

The need for reliable fatigue predictions arises with an increasing application of fibre-reinforced composites in primary light-weight structures with intended service times of up to 30 years. Only few data about very high cycle fatigue (VHCF) of polymer composites are available, because VHCF testing is rather challenging due to time consuming tests. Moreover, problems arise when testing at high frequencies. Two alternative approaches are presented in this article, a bending test rig for high-frequency testing of flat specimens and a resonant test rig for tube specimens.

Fatigue designing of high-stressed engine components is a key factor for reliable power train systems in automotive industry. In this context load assumptions are very important since this is attended with a pre-designing of important machine elements. Load analyses are usually performed by using experimental methods since the accuracy of load simulations are often not precise enough. An example for VHCF problems occurs in modern high pressure pumps for gasoline direct injection systems, which have load spectra with a large amount of cycles up to 10 9 including a very powerful shape of the spectra. At the same time it is necessary to consider the properties of fuels in service since they might affect the fatigue strength significantly. For example, ethanol-based gasoline fuels are used in a lot of countries worldwide and especially their additives may lead to significant corrosion fatigue effects. In addition, it is well known that material inclusions play an important role for the VHCF behaviour especially for high-strength steels. This paper deals with possibilities to avoid VHCF problems of components in service to maintain reliable systems.

Cyclic low amplitude loading and a huge number of cycles characterizes the Very High Cycle Fatigue (VHCF) regime. The challenge in research of the Very High Cycle Fatigue regime is to apply this large number of cycles to fracture in an acceptable time frame. For this reason, it is essential to use a machine, which is able to operate at high frequencies of cycles. Two testing machine concepts with piezo actuators are presented in this study. In the first concept, a high performance piezo stack actuator is presented, in which the specimen and the load cell are mechanically assembled in series. This set-up applies forces up to 10 kN and testing frequencies up to 1000 Hz. The second testing facility is a hybrid testing system, which consists of an inertial mass actuator and a servo hydraulic actuator connected in parallel. Both systems are capable of testing normal specimen dimensions and provide the possibility to work with variable as well as constant amplitude loading.

At the Institute of Materials Science and Engineering of the University Kaiserslautern an ultrasonic testing facility was developed to perform fatigue tests in the VHCF regime. The individual design of the ultrasonic testing facility allows to control the process parameters and to measure relevant data with a frequency of up to 500 kHz in reasonable time. This permits a high-resolution measurement of the ultrasonic oscillation and the dissipated energy as well as a determination of microstructural reactions inside the specimens. With the described ultrasonic testing facility constant amplitude tests and load increase tests were carried out with the alloy Ti6Al4V. The results show that the innovative test and measuring techniques are best suited to describe the fatigue behaviour of Ti6Al4V. Additionally, for the first time high resolution 3D scanning laser vibrometry were carried out to determine the oscillation behaviour of specimens under ultrasonic cyclic load.

The rapidly developing market for high strength and high stiffness carbon fibre-reinforced composites demands among others for reliable damage evaluation methods for very high cycle fatigue loading (VHCF). For the analysis of the widely unknown damage behaviour at VHCF loading specific test principles and a shaker based fatigue test stand are developed. Key requirements herein are: high frequency fatigue (f > 150 Hz) without significant warming of the specimen, homogeneous stress distribution and minor through thickness stress gradients as well as adjustable mean stresses for the fatigue testing regarding specific failure modes. Using numerical and experimental investigations a promising solution for the given problem has been found in form of a shear force free bending test stand and a specifically layered specimen.

The effect of various Co additions to P/M 316L stainless steel on α ’-martensite formation and mechanical properties (bending strength and hardness) were investigated. Powder mixtures were compacted using a single action press at 498 MPa and sintered at 1,300°C for 30 min under hydrogen atmosphere, followed by heat-treating in air at 800°C and 900°C for 25 h, 50 h, 75 h, and 100 h, respectively. It is found that oxide formation in closed pores at high temperatures can induce the α ’-martensite formation and reduce the area fraction of porosities, resulting in higher hardness of the heat-treated specimens than that of the sintered specimens. The Co additions can also reduce the amount of α ’-martensite. Long-term heating results in a slight decrease of bending strength due to high connected oxide formation in the internal pores.

Kurzfassung Fatigue crack growth and active corrosion processes are the main causes for structural failures of transport products like road tankers, railway tank cars, and ships. Within the 7 th EC framework programme the aim of project CORFAT is to develop a new monitoring technology based on acoustic emission testing (AT) of the structural integrity in terms of proceeding degradation. Differentiation of acoustic emission (AE) signals of real degradation processes by fatigue crack growth or active corrosion from operational or environmental background noise requires the signal classification using also pattern recognition. Therefore, a data base of AE signals related to the different source mechanisms was built up experimentally. In this article selected results of corrosion and fatigue tests in the laboratory as well as results of monitoring background noise during moving of a road tanker are described.

This study investigated the multi-response optimization of turning process for an optimal parametric combination to yield minimum cutting forces and surface roughness with maximum material removal rate (MRR) using the combination of Grey relational analysis (GRA) and Taguchi method. Nine experimental runs based on an orthogonal array of Taguchi method were performed to derive objective functions to be optimized within experimental domain. The objective functions have been selected in relation to parameters of cutting process: cutting force, surface roughness and MRR. The Taguchi approach followed by Grey relational analysis to solve the multi-response optimization problem. The significance of factors on overall quality characteristics of the cutting process has also been evaluated quantitatively by the analysis of variance method (ANOVA). Optimal results have been verified through additional experiments. This shows proper selection of the cutting parameters produces, high material removal rate with better surface roughness and lower cutting force.

Kurzfassung Viele Bauteile sind während ihrer Nutzungsdauer schwingenden Beanspruchungen ausgesetzt. Ermüdungsfestigkeitsnachweise sollen den sicheren Betrieb schwingend beanspruchter Bauteile garantieren. Ein wichtiger Kennwert zur Führung von Ermüdungsfestigkeitsnachweisen ist die Bauteildauerfestigkeit. Ihre experimentelle Bestimmung ist zeit- und kostenintensiv. Häufig stehen nur wenige Prüfkörper zur Verfügung, sodass eine statistische Auswertung unmöglich wird. Um dennoch Aussagen über die Bauteildauerfestigkeit abzuleiten, können so genannte Durchläufer wiederholt eingesetzt werden. Im vorliegenden Beitrag werden die Auswirkungen des Wiedereinsatzes von Durchläufern diskutiert. Hierbei werden keine werkstoffmechanischen Betrachtungen zur Vorschädigung oder zur Trainierwirkung angestellt. Vielmehr werden Simulationsmethoden vorgestellt, mit denen sich maximale Fehler bei der 50%-Dauerfestigkeitsschätzung ableiten lassen. Durch nachträgliche Berücksichtigung des maximalen Fehlers kann ein Bemessungskennwert auch mit wenigen Proben abgeleitet werden.

The purpose of this work was to investigate the coatings made of Cr 3 C 2 and SiC powder manufactured on AISI 304 stainless steel applied by the plasma transferred arc (PTA) welding process. SiC content in the produced coated layer was varied between 0–100 wt.% and the effect of SiC concentration on the microstructure and hardness of the coating was measured experimentally. SEM analyses revealed that the composite coatings had a homogeneous, nonporous, and crack-free microstructure. Dendrites and interdendrite eutectics formed on the coating layer, subject to the temperature gradient and the solidification ratio. There was a significant increase in the hardness of coating layers with the effect of the γ -(Fe,Ni), Cr 7 C 3 , Cr 23 C 6 , Fe 5 C 2 , Cr 3 Si, CrSi 2 , Fe >0.64 Ni 0.36 , CFe 15.1 , C-(Fe,Cr)-Si phases formed in the microstructure. In comparison to the substrate, the microhardness of the coatings produced by PTA were 2.5–3.5 times harder.

Traditional Iznik ceramics (tile and pottery) are known as “unproducible” due to their high quartz content and unique processing steps. During the course of this study, a comparison of traditional and modern Iznik tiles in colour and brightness carried out. As latest insights of recent studies showed that the production techniques and the size of pigments are crucial parameters for the quality of colours of ceramics. Therefore, Iznik tiles were shaped by dry press without changing their quartz content. Secondly, paints to be applied in the decor stage were prepared with both traditional and nanometersized pigments and used in production process. Finally, characterization techniques were used in order to understand and compare the results and also the effects of nanometer sized pigments on Iznik tiles.

Greenhouse gas (GHG) emissions cause global warming and climate changing. This review summarizes the up-to-date applications that contribute to greater fuel economy and reduce CO2 emissions. A detailed explanation of the recent developments in the main concepts of fuel economy and CO2 reducing in automotive industry is given with a special relation to the materials to be selected. In the study, the past, present and future projection of fuel economy and CO2 emission is evaluated. The result of the study conclude that mass of the vehicle, kind of energy for engine, driving techniques and the technology level of the vehicles affect the fuel economy and CO2 emissions.