Volume 55, Issue 1

Recently, a couple of methods for the physically based fatigue life calculation of metallic materials were developed at the Institute of Materials Science and Engineering at the University of Kaiserslautern. The focus of these “PHYBAL”-methods is the reduction of the necessary experiments in comparison to the conventional determination of fatigue data. The application of the “PHYBAL”-method requires a limited number of high-precision fatigue experiments. In addition to conventional mechanical stress-strain hysteresis measurements temperature and electrical resistance measurements have to be carried out to characterize the cyclic deformation behaviour. So far the “PHYBAL”-versions “PHYBAL W ” (σW = endurance limit), “PHYBAL LIT ” (LIT = load increase test), “PHYBAL SB ” (SB = scatter bands) and “PHYBAL mean ” (mean = mean stress) are available and were successfully applied on different unalloyed carbon steels as well as austenitic steels, cast irons and light alloy metals.

Kurzfassung Die Untersuchung der Wälzfestigkeit linearer Bauteile, die durch ein neuartiges Kaltumformverfahren höhere Oberflächenhärten und geringere Rauigkeiten aufweisen, stellt prozessbedingt eine sehr große Herausforderung dar und erscheint in diesem Zusammenhang sinnvoll. Denn die momentan auf dem Markt befindlichen Prüfmethoden zur Wälzfestigkeitsermittlung basieren auf der rotationssymmetrischen Geometrie der Prüfkörper und stellen somit ein Ausschlusskriterium für lineare Bauteile dar. Um jedoch die spezifischen Eigenschaften, die aus dem Spaltprofilierprozess resultieren und die an die lineare Form der Spaltprofile gebunden sind, so real wie möglich simulieren zu können, wurde ein neuartiger Wälzfestigkeitsprüfstand für lineare Bauteile konstruiert, entwickelt und in Betrieb genommen. Mit diesem Prüfstand ist eine Bewertung der Wälzfestigkeit linearer Bauteile möglich.

The further development from polymer testing to polymer diagnostics leads to test methods with higher amount of information per test procedure as conventional tests. These changes contribute to fulfill the increased requirements in polymer testing and diagnostics. Selected examples of practice of industrial polymer testing show that these new methods can be applied appropriately to solve the issues of the automotive industry.

Titanium and its alloys which have been widely used in many prostheses carry the major joint load and cause stress shielding. Thus, the bone might become osteoporotic due to lack of physiological stress flow in common hip replacement. Therefore, the optimization of hip joint materials is one of the most challenging tasks in prosthetic design. It is found in the literature that there is a great contradiction regarding the use of hydroxyapatite (HAP) coating. In this study a finite element analysis (FEA) and optimization techniques have been carried out in order to find a new design of hip stem coating using functionally graded material (FGM) to reduce stress shielding at the proximal medial part of the femur, as well as reducing the interface shear stress at the interface between the coating and the bone which directly affects the implantation and long-term stability. This work is divided into two parts: in the first part, the gradation of the elastic modulus of the coating material has been changed in the vertical direction, while the second part changes the elastic modulus in the horizontal direction. The optimal design of the first and second models was compared with HAP coating and with homogenous uncoated titanium stem. The design optimization of the first model revealed, using a coating material consisting of HAP at the upper layer of the coating graded to collagen at the lower layer, increases the maximum von Mises stress in bone at the proximal medial part of the femur by 65% and 19% compared to titanium stem and titanium coated with HAP, respectively. The maximum lateral interface shear stress in the bone at the bone/coating interface is reduced by 23% and 12%, respectively. However, the maximum medial interface shear stress in the bone at the bone/coating interface is reduced by 39% and 14% compared to titanium stem and titanium coated with HAP, respectively. The design optimization of the second model revealed, using a coating material consisting of collagen at the inner layer adjacent to stem graded to HAP at the outer layer adjacent to bone, increases the maximum von Mises stress at the proximal medial part of the femur by 60% and 15% compared to titanium stem and titanium coated with HAP, respectively. The maximum lateral interface shear stress is reduced by 18% and 6%, respectively. However, the maximum medial interface shear stress is reduced by 35% and 8% compared to titanium stem and titanium coated with HAP, respectively.

A unified approach for the derivation of the known equations describing damage accumulation as a result of loading of fibre-reinforced polymers is proposed. The investigated materials are short glass fibre-reinforced polyoxymethylene (GF/POM) and long glass fibre-reinforced epoxyresin (GFRP). The damage structures themselves consist of the accumulation of additional internal surfaces within the entire material volume as measured by small angle scattering X-ray refractometry. On the basis of the concept for a loading percentage under creep, damage accumulations applying short-term and long-term loading are compared. It is shown that for the investigated materials our approximations by a double exponent function are more effective than the approximations according to Weibull. It is also shown how the coefficients of the double exponent cumulative function can be found.

The results of experimental investigation of creep rate and rupture time of the alloys of Pt-Rh system are presented in this paper. Selected alloys with 7–40 wt.-% Rh content were examined using a universal device for tensile testing of materials at high temperatures, and monitoring structure changes of the samples by electron microscopy. Investigations were performed in the temperature range between 1200°C and 1700°C at a stress between 2 MPa and 15 MPa.

SPM 10 and ASP 2052 alloys fabricated by powder metallurgy have a higher alloying elements content than rolled types. Such higher alloying contents improve the mechanical properties of tool steels and provide a longer tooling life. In this study, the effects of alloying elements and different heat treatments processes on the properties of SPM 10 and ASP 2052 were investigated. Also, the effects of alloying elements and process parameters on the mechanical properties as well as tooling abilities of the specimens were studied. The specimens were characterized by Rockwell hardness tests and the tooling abilities of the specimen were determined by characterizing the number of screws that could be fabricated with specimens. According to the results of the experiments, higher hardness values were obtained at elevated austenitization temperatures. Besides, the presence of Co as an alloying element evolved better hot work properties of the specimens.

WC/10Co4Cr and WC/20CrC7Ni powders were sprayed onto the surface of low-carbon steel substrates using the high velocity oxygen fuel (HVOF) spraying method. Microstructure of the obtained coatings was evaluated by scanning electron microscopy (SEM). X-ray diffraction (XRD) analysis as well as hardness and porosity testing were performed on the samples. The abrasion wear resistance of the coatings was determined using the rubber wheel abrasion test. The mass loss rate (mg/h) of the samples was measured and the test results showed that the WC-CrC-Ni coating has better abrasion wear properties than the WC-CoCr coating.

The grainary substructure of 30CrMnSi steel has been studied after rolling deformation. It has been found that in the studied material the bulk share of anisotropic grains amounts to 25% and the isotropic grains to 75%. It has been observed that the martensitic structure is completely broken in the rolling process.

ZnO:Tm,Gd materials with high quality blue light-emitting were successfully prepared using the chemical co-precipitation method. The surface morphology, composition, crystal structure and fluorescence properties were investigated using the thermogravimetric analysis/differential thermal analysis (TG/DTA), scanning electronic microscopy (SEM), X-ray diffraction (XRD), and photoluminescence (PL). The results showed that the lowest sintering temperature was 580°C, the optimal sintering temperature was 900°C, ZnO:Tm 3+ , Gd 3+ had two emission peaks: 1 D 2 → 3 H 4 and 1 G 4 → 3 H 6 , the optimal heat preservation time was 3 h, the proportion of matrix and doping elements was 100: 2, and the optimal proportion of Tm and Gd was 3: 2.

Cellular metals differ from the other materials by a lower density which is their characteristic property. Besides, they show unusual physical, mechanical, thermal, acoustic and electrical properties. Even though they have lots of pores compared to solid materials they can show a unique combination of several properties that cannot be obtained in a conventional material at the same time. There are several kinds of production methods for cellular materials. Nowadays, lots of researches have been carried out with respect to new production methods. The lost foam process, which bases on evaporating the polystyrene foam model, reduces the process steps of investment casting and can be an alternative method to many production methods. In this study, open cell samples were produced with two different aluminium alloys by using the lost foam casting technique. A413 as a casting alloy and A6063 as a wrought alloy were selected for casting experiments. After production of these two aluminium alloys, the decrease in weight, compression strengths, deformation ratios were determined and compared to each other.