Volume 55, Issue 10

Hydraulic pressure testing of composite gas cylinders damages the cylinders, but provides very limited information. For this reason, the Federal Institute of Materials Research and Testing (BAM) demands the assessment of the safety of design types for retest periods of more than three years by employing destructive testing of small samples. This gives insight in properties not quantified by current standards. Depending on the cycle fatigue behaviour of the individual design type either cycle tests or slow burst tests are employed. In this paper methods are introduced for a statistical assessment of sample results of both test methods. This includes gathering the average and load cycle burst strength, and the scatter of a sample as well as analysing and plotting them as a pair of values. Each pair of values representing a sample can be assessed approximately regarding its survival rate in service, if the introduced performance charts are employed.

The paper describes a novel testing method for mechanical joints between fibre-reinforced plastics and metals. As an example, the paper discusses a connection between a continuous carbon-fibre-reinforced plastic and aluminium via a flow drill screw. The failure load of the joints under different loading angles was tested with the help of a modified KS-II testing facility. A detailed analysis of the damage and failure behaviour of the connection was performed by means of optical recordings and micrographs. The results indicate that the tested material combination has nearly the same failure load at different loading angles with various failure mechanisms. The experimental results can be used to devise new failure criteria for these connections and to detect limit values for the design process.

During the exploitation of a steam turbine, mainly because of non-adequate purity of fresh steam, salts can be deposited on the components in the through-flow area. Deposited salts decrease the reliability and efficiency of the steam turbine, while thicker layers, i. e. higher quantities of deposited salts, could cause serious damage to the turbine. This paper gives a description of deposited salt layers in the through-flow area of a 210 MW steam turbine and presents the results of research and analysis. In order to determine the cause of salt deposition on turbine surfaces, a chemical analysis of deposited layers was carried out. This paper proposes measures to reduce the salt deposition as well as methods for the removal of deposited layers in the through-flow area of a steam turbine.

This research investigated the effects of various cobalt and nickel/cobalt additions to P/M 304L stainless steel on oxidation behavior at 900 °C, hardness and bending strength. A single action press at 498 MPa was used for compacting powder mixture specimens. They were then sintered at 1300 °C for 30 minutes in hydrogen atmosphere and heat treated at 900 °C for 2, 5, 10, 20, 25, 40, 60, 80 and 100 hours in air for oxidation tests. It is clearly shown in the results that cobalt addition could improve density, hardness and bending strength. However, only 1 wt.-% Co addition was the best condition for oxidation resistance. The detrimental effect of Ni addition dominated the beneficial effect of Co addition, because its bigger powder size led to more pore formation. The resulting mechanical properties and oxidation behaviour depend on microstructures, porosity and powder size.

In order to investigate the strain gauge characteristics of NiCr thin films, 500 nm NiCr (80 wt.-% and 20 wt.-%, respectively) thin films were deposited on glass substrates by DC magnetron sputtering. After deposition, NiCr thin films were characterized by using X-Ray diffraction analysis, scanning electron microscope and four-point probe techniques inview of crystallization, phases, film structure and electrical resistivity. After characterization, NiCr thin films were shaped into strain gauges by photo lithography and wet etching techniques. Strain gauges were tested with different loads, and strain values were calculated by comparing the results with commercial NiCr strain gauges with the same surface area. Resistivity change vs. strain was plotted, and the gauge factor of fabricated thin film strain gauges was evaluated as 1.23.

Digital detectors such as phosphor imaging plates (IP) and digital detector arrays (DDA) enable radiographic inspection with higher efficiency and improved image quality in comparison to the classic film technique. The mobile mechanised tomographic system TomoCAR (tomographic computer aided radiology) was developed first for inspection of circumferential welded seams of pipes. It consists of the manipulator based position control of an X-ray tube in front of the region to inspect and a digital detector array behind it. The high contrast sensitivity technique was combined with planar tomography. The tomographic reconstruction allows the three-dimensional (3D) representation of the material structure and included defects, equivalent to a metallographic cross sectioning. The hardware design is based on a specially developed flat X-ray tube and a direct converting CMOS detector array on CdTe basis. TomoCAR is applied for sizing of volumetric and planar defects. It allows the reliable detection of planar defects with openings larger than 25μm by subpixel resolution due to the achieved high signal-to-noise ratio. TomoCAR was successfully qualified as the result of a German pilot study on the basis of the European Network of Inspection and Qualification (ENIQ) guidelines for application in the nuclear power industry. Application examples are presented. The TomoCAR design was modified for in situ inspection of large aircraft components under production conditions. A gantry gate based planar tomograph was constructed and tested for inspection of the integrity of large flat CFRP panel components of up to 3 m × 9 m size. The integrity of imbedded stringers has been successfully observed. Different trials were performed to prove the finding rate of cracks in embedded stringers, which will be presented and discussed.

Dental implantation treatment has developed into one of the most successful prosthetic technologies. A critical progress made in this area was the development of biocompatible materials to enable an engineered device (implant) to integrate within its surrounding bony tissues. Titanium and its alloys have been widely adopted as such materials due to their excellent biocompatibility. However, their mechanical properties largely differ from those in host bony tissues, which is problematical in osseointegration and bone remodeling. The challenge to face in prosthetics is to develop both biologically and mechanically compatible biomaterials for this purpose. Few existing research has been reported to develop an optimized design of functionally graded material (FGM) dental implant for promoting a long-term success. One of the authors of the present Contributions has previously designed a new FGM dental implant coating graded in axial direction from titanium at the apex to collagen at the basis of the dental implant. The aim of this investigation is to design a new gradation direction of FGM dental implant coating as well as studying the effect of coating thickness on the maximum von Mises stresses in bone adjacent to the coating layer. The gradation of the elastic modulus is changed along the longitudinal direction. Stress analysis using a finite element method showed that using a coating of 150 μm thickness, which is functionally graded from titanium at the outer shell adjacent to the bone to collagen at the inner shell adjacent to the implant, will reduce the maximum von Mises stress by 16 % and 13 % compared with the common conventional coating materials such as collagen and hydroxyapatite coatings, respectively. However, using FGM coating graded from hydroxyapatite at the outer shell to titanium at the inner shell reduces the maximum von Mises stress by 8 % and 5 % compared with collagen and hydroxyapatite coatings, respectively, but this gradation can improve the biocompatibility and can also achieve a full integration of the implant within the living bone, which increases the life of the implant.

The goal of this study is to reinforce the compression strut ties of space truss systems by increasing the load carrying capacities of them. Therefore, 28 steel bar ties each having 900 mm length and 60.3 mm diameter were reinforced in six different ways and subjected to an axial compression test in the Structure Laboratory of the Civil Engineering department, Faculty of Engineering and Architecture, Selçuk University, Konya, Turkey. The results obtained from tests were examined by making comparisons between the plotted graphics. The applied reinforcement has not increased the buckling load, but it has increased the energy absorption capacity of reinforced bars under yielding and maximum stresses. When the negative effect due to welding is eliminated, a further increase in the energy absorption capacity at the yielding and proportionality limits and an increase in the maximum load carrying capacity can be expected.

The present study has been aimed to investigate the preparation and analysis of calcium phosphate (CaP) based hydroxyapatite (HA, Ca 10 (PO 4 ) 6 (OH) 2 ) coatings formed on Ti6Al4V alloys in a new buffer environment. The coating process has been performed by means of biomimetic method. In the study, a synthetic body fluid (SBF), which is fully compatible with human blood plasma, has been prepared for the first time in the literature by using the citric acid – sodium citrate buffer system. Using this buffer system will not cause any toxic reactions in the human body. CaP coating of the Ti6Al4V surface has been performed in this new SBF. The surface roughness and thickness specifications of the coatings have been determined, their microstructures have been analyzed by using a scanning electron microscope (SEM), the elemental analysis (EDX) of the coating surfaces and the XRD analysis have been done. The results are presented and discussed.

The objective of the present study was it to design a type-2 fuzzy set and system in order to predict surface roughness and hardness depending on the parameters (material thickness, cutting speed, arc voltage and current) of the plasma arc cutting process of S235JR sheet materials. Therefore, some experimental studies were conducted. The experimentally determined data were used to describe the type-2 fuzzy set and system. Type-2 fuzzy set and system was found to be usefull to predict surface roughnes and hardness. According to the obtained values, the best surface roughness and the values closest to the hardness of the raw material were obtained at 1500 mm/min cutting speed, 8 mm material thickness, 115 V arc voltage and 80 A current.

In this contribution, performances of well-known population based algorithms, the artificial bee colony (ABC), contemporary particle swarm optimization (CPSO), genetic algorithm (GA), and differential evolution (DE) are compared in a basic model for damage identification (DI). DI is modeled as an inverse problem with the objective function based on the difference of the frequency response functions (FRF) computed by the finite element model of the structure and the reference data measured from damaged structure. Damage parameters are determined solving the problem with the aforementioned algorithms. It was observed that DE is the best one of a given number of function evaluations and gives the most accurate results in spite of noise interference to the reference data. According to the relevant literature, this is the first study including a comparison of these algorithms in an FRF based DI study.