Development of a time-of-flight spectrometer at the Ruder Boškovi? Institute in Zagreb

A new TOF telescope has been constructed for thin film and surface analysis. The timing system consists of two electrostatic mirror type detectors of Busch design. The detection efficiency of timing stations for very light ions was significantly improved using DLC (diamond like carbon) foils coated with LiF instead of the conventionally used carbon foils. Ion energy is measured by a 300 mm² ULTRA ion-implanted silicon detector. For the ERDA measurements with heavy and energetic ion beams, a time-of-flight (TOF) spectrometer is positioned at 37.5°. Spectrometer can be easily moved to 120° backward angle for time-of-flight RBS analysis with low energy beam of light ions. Positioning and fine adjustments of sample orientation are performed with a motorized sample stage. The same spectrometer can be also installed at the ion microprobe scattering chamber for 3D elemental imaging.     

Investigating the behaviour of fluid-filled polyethylene containers under base drop impact: A combined experimental/numerical approach

In this work, the behaviour of fluid-filled plastic containers under base drop impact is investigated using a combined experimental/numerical approach. In addition, theoretical predictions from two approaches, waterhammer theory and a mass-spring model, are also given. Experimental tests are conducted using a specially designed rig for testing plastic containers (bottles). Tested containers are fully instrumented with pressure transducers and strain gauges. The experiments are simulated using a two-system fluid-structure interaction procedure based on the Finite Volume Method. Good agreement is found between measured and predicted pressure and strain histories. Results obtained are in favour of waterhammer theory.     

Finite volume method and multigrid acceleration in modelling of rapid crack propagation in full-scale pipe test

Rapid Crack Propagation (RCP) along pressurised plastic pipes is by far the most dangerous pipe failure mode. Despite the economic benefits offered by increasing pipe size and operating pressure, both strategies increase the risk and the potential consequences of RCP. It is therefore extremely important to account for RCP in establishing the safe operational conditions. Combined experimental-numerical study is the only reliable approach of addressing the problem, and extensive research is undertaken by various fracture groups (e.g. Southwest Research Institute – USA, Imperial College – UK). This paper presents numerical results from finite volume modelling of full-scale test on medium density polyethylene gas pressurised pipes. The crack speed and pressure profile are prescribed in the analysis. Both steady-state and transient RCPs are considered, and the comparison between the two shown. The steady-state results are efficiently achieved employing a full multigrid acceleration technique, where sets of progressively finer grids are used in V-cycles. Also, the effect of inelastic behaviour of polyethylene on RCP results is demonstrated.     

Noise robust F0 determination and epoch-marking algorithms

This paper presents a combined pitch frequency (F0) determination and epoch (pitch period) marking procedure CPDMA using merged normalized forward–backward correlation. The algorithm consists of several processing steps: preprocessing of the input speech signal, voicing detection using artificial neural networks, F0 determination stage based on normalized correlation, F0 contour postprocessing applying partial Viterbi traceback, and finally, epoch (or pitch period) marking. To evaluate the proposed CPDMA procedure against any other algorithm, a manually segmented PDA/PMA reference database based on real-life SPEECON Spanish speech database has been created. A set of criteria was proposed to objectively and compactly evaluate the performance of any evaluated PDA/PMA or voicing detection algorithm. The performance of the proposed CPDMA was compared with the performance of well-known and publicly available PRAAT toolkit. The PDA and PMA performances achieved with the proposed CPDMA algorithm significantly outperformed the performance of the PRAAT toolkit in all its three considered configurations: autocorrelation method (PRAAT_AC), cross-correlation method (PRAAT_CC), SHS (PRAAT_SHS), and point process (PRAAT_PP). The superior noise robustness of CPDMA is achieved at the expense of a more complex algorithm and consequently leads to worse real time factor when compared to PRAAT.     

Characterization of the fracture behavior of polyethylene using measured cohesive curves. I: Effects of constraint and rate

The damage and failure mechanisms in polyethylene are investigated using a circumferentially notched tensile specimen subject to constant rate displacement conditions. The fracture process can be quantified, independent of the bulk deformation, using a local traction–separation relation. The study found that the mechanisms of deformation under quasi‐static test speeds depend on the degree of crack tip constraint in addition to rate. This dependency can lead to contrasting deformation‐failure behavior between different grades of polyethylene and hence the overall energy dissipation process. Based on this approach, both gross and subtle differences in the fracture behavior between the grades were readily detected and differentiated. In general, the damage mechanisms changed from a brittle mode under conditions of high constraint to a ductile mode as the level of constraint is reduced. POLYM. ENG. SCI., 46:763–777, 2006. © 2006 Society of Plastics Engineers     

Limiting crack speeds in dynamic tensile fracture tests

The spring mass model is used to determine a crack speed, crack length and loading relationship in terms of energy release rate. An essential feature of the analysis is the inclusion of the contact stiffness and a geometry dependent limiting speed. The analysis is used to describe crack speed data taken over a wide range of geometry changes. A good fit to the data is obtained but a low wave speed is predicted. This is rationalised on the basis of a low, local strain dependent modulus.     

Mathematical Modelling of Cutting Force as the Most Reliable Information Bearer on Cutting Tools Wearing Phenomenon

Being one of their prominent exploitative characteristics, cutting tools durability depends on the character, intensity and the speed of wearing. Identification of tool wearing is of great significance for the purpose of avoiding sooner or later replacement of tools. The parameters of tool wearing can be measured by out-process and in-process-measuring systems. Given the extremely limiting role of the former in modern production lines, development of the latter （the indirect measuring systems） has gained prominence, The basis of indirect measuring systems comprises a set of various signals originating from the units of the system under treatment which stand in certain correlations with the wearing parameters. The paper presents mathematical models of axial force designed on the basis of experimental research in drilling tempered steel by twist drills made of high-speed steel manufactured by powder metallurgy.