Volume 55, Issue 2

This contribution highlights the implementation of different methods for early stage damage detection in very high cycle fatigue (VHCF) experiments by means of an ultrasonic testing machine developed by BOKU in Vienna. Basically three different methods are used for in-situ evaluation of degradation: the analysis of (i) the harmonics, (ii) the development of the resonance frequency, (iii) the damping behaviour of the specimen at the end of each testing pulse. The fatigue experiments and measurements of the relevant parameters are controlled using the software LabView. We demonstrate the sensivity of the different methods on two specimen variants: (i) round samples of the chromium steel X10CrNiMoV12-2-2 and (ii) flat samples of the aluminium alloy Al-2024.

The objective of this paper is the assessment of the toughness of glass fiber-reinforced polypropylene and polybutene-1 by means of fracture mechanics concepts to describe the resistance against unstable crack initiation for these materials. In addition, the acoustic emissions during the instrumented Charpy impact test were recorded, which allows the characterization of the damage kinetics. For this purpose, the recorded transient signals of the acoustic sensor were analyzed with the wavelet transform. Thus, it was possible to describe the onset of the damage in the time domain, as well as the load F s and the corresponding deflection f s . In dependence on the bonding conditions of the materials, the damage onset was detected for polypropylene before and for polybutene-1 at the transition from elastic to elastic-plastic behaviour.

The creep behaviour of near-equiatomic (50.8 at.-% Ni) NiTi wire with a diameter of 0.49 mm is studied between 82 MPa and 127 MPa tensile stress as well as in a temperature range of 575 °C to 650 °C. For 600 °C and between 82–107 MPa a stress exponent of n = 4.5 as well as for 82 MPa between 600–625 °C an activation energy of Q = 300 kJ mol -1 have been found, these results have been compared with previous creep studies. In contrast to previous studies, this investigation has been performed with high stresses for thin NiTi wires. Moreover, fracture surfaces and ductility of wires have been investigated. The main reasons for the various results are discussed.

Kurzfassung Für die luftgekoppelte Ultraschall-Prüfung wird der Prototyp eines neuartigen Prüfkopfes vorgestellt. Statt eines piezokeramischen Ultraschall-Wandlers mit einer λ/4-Anpassschicht wird eine Ferroelektret-Folie aus schaumförmigem Polypropylen eingesetzt. Durch die außerordentlich geringe akustische Impedanz der Folie reduzieren sich die Reflexionsverluste an den Grenzschichten zur Luft so stark, dass bei diesem Prüfkopf auf eine λ/4-Anpassschicht verzichtet werden kann. Außerdem ist die Folie hochspannungsfest. Sie konnte mit Spannungen von mehr als 3500 V angesteuert werden und erlaubte eine Vorspannung am Ultraschall-Wandler des Empfangsprüfkopfes von 2000 V. Mithilfe der hohen Anregungsspannung stieg die Amplitude des akustischen Prüfimpulses auf das 11,2-Fache. Die Empfindlichkeit des Empfängers erhöhte sich durch die Vorspannung weiter um den Faktor 4,3. Insgesamt steigt die Amplitude am Empfänger also auf das 48-Fache, bei gleichbleibendem Rauschpegel. Ein abschließender Vergleich mit kommerziellen Luftultraschall-Prüfköpfen belegt die Überlegenheit der Folien-Prüfköpfe. Damit rückt der Einsatz einer vollwertigen Impuls-Echo-Technik auch bei der luftgekoppelten Ultraschallprüfung deutlich näher.

In this study, the sliding wear behaviour of the materials utilized in manufacturing of load-bearing orthopedic implants (316 L, Ti6Al4V, and CoCrMo nickel alloys) was examined by a reciprocating wear tester under ceramic-on-metal configuration in a simulated body fluid (SBF). During the tests the generated wear debris were transferred into the SBF and increased its optical density. In accordance with its poor wear resistance, Ti6Al4V alloy provided a large amount of wear debris transfer into the SBF along with the heavy material attachment to the contact surface of the counterface. Dissolution of wear debris led to an increase of the metal ion concentration in the SBFs. Even though few wear debris were generated, trace elements were detected in the SBFs of the 316 L and CoCrMo alloy, besides the main elements.

During the ultrasound defectoscopy the ultrasound absorption factor inside the material is raised to the fourth power of frequency. In conjunction with the previously stated, the attenuation of the sound signal which is caused by the reflections of the sound inside the sample, the application of high frequency ultrasound in porous and hollow materials is very limited or even impossible. The frequencies are the reason for this, because they are in the range of just several megahertz, which are currently the main trend in the ultrasound examination. This paper presents a principle of this new method, including the experimental results from its application on the typical represent of product packaging material. Also, it is shown that the expressed absorption of ultrasound waves from porous and hollow structures can be avoided by applying the method with such low frequencies.

A crack identification method for beam type structures under moving vehicle is proposed. The basic of the method is to formulate damage detection as an inverse problem, and solve for damage locations and extents. With respect to this, an objective function is defined based on the difference of damaged beam dynamic response and the response calculated by the mathematical model of the beam. The optimization problem is solved by the particle swarm optimization (PSO) with linearly increasing inertia weight to obtain crack locations and their depths. By the numerical simulations, it was observed that cracks with depth ratio of 0.1 can be identified with reasonable error by the present method in spite of noise interference of 3 %.

The current practice of periodic retesting of composite pressure receptacles primarily based on the hydraulic pressure test has to be evaluated as critical. This is justified by micro damages caused to the specimen by the test itself and by a lack of informative values. Thus, BAM Federal Institute of Materials Research and Testing uses a new validation approach in the case of retest periods of more than 5 years. It enables the description of the condition of a specific design type series based on destructive tests parallel to operation. With respect to this approach it is explained how the statistical evaluation of sample tests and their extrapolation to end of life or at least to the time of next retesting can be achieved. In addition, it is explained how the reliability limits may be linked to the size and pressure level of the respective composite pressure receptacle. The frame of this safety approach includes the influence of the maximum working pressure on the safety assessment. One topic of this approach is the introduction of the working diagram essential for safety assessments that allows graphical evaluation of load cycle strength by mean value, scatter and survival rate of samples as well as instruction how to use it. For this, it is explained how the number of filling cycles and the reduction of the respective hydraulic residual cycle strength interacts with the newly introduced value of specific filling sensitivity.

This paper reports an improved constitutive model for the shear creep behaviour of offwhite marbles which are selected from slope or underground cavern and contain greenschist's weak structural planes. The shear creep behaviour of the samples is characterized by rheological tests. Based on the experimental measurements on mechanical properties under different normal stress conditions, an improved model is proposed to analyze the experimental results. It is demonstrated from a further discussion that such model can reflect the non-linear creep characteristics of structural planes, and especially, it is suitable for description of the viscoelastic and viscoplastic deformation behaviour of structural planes.

Lead frames are generated in large quantities by modern semiconductor packaging industry and they contain significant concentrations of valuable tin, nickel, and copper. For electrowinning of tin from waste lead frames, hydrochloric acid leaching of tin is quite advantageous, but solution stability, electrolytic efficiency and deposit morphology should be optimized before commercialization. HCl electrolyte was diluted (distilled water: HCl = 350:150) for electrowinning of waste lead frames at 40 °C with 0.2 A/cm 2 and Ti-Ir cathode. After 4 h electrowinning, 99% pure Sn with 99.1% recovery rate was produced. Therefore, aqueous HCl electrolyte was quite effective for electrowinning of Sn leaching solution, and a higher recovery rate of purer Sn within shorter electrowinning time was obtained.

As an important analytical method for thin film growth, spectroscopic ellipsometry plays an active role in investigating thin film growth mechanism of molecular beam epitaxial especially under in-situ and real-time environment. In this paper, the dynamic data presenting p-6P molecule film growth on mica substrates at different evaporation temperatures have been obtained under ultra-high vacuum by a self-designed in-situ and real-time spectroscopic ellipsometry system. It is shown that the strength of p-6P molecular ellipsometry signal increases as the amount of molecule deposited increases, and there is a negative characteristic peak at 3.9 eV, caused by electron transition of the p-6P molecule from the highest occupied molecular orbital to the lowest unoccupied molecular orbital, which can be considered to be an optical characteristics of p-6P molecule.