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Experimental study on size effect in quasi-static compressive behavior of closed-cell aluminium foams
Koudelka_ml., Petr ; Zlámal, Petr ; Kytýř, Daniel ; Fíla, Tomáš ; Jiroušek, Ondřej
The size effect in compressive deformation behaviour of commercially available aluminium closed-cell foam Alporas was studied under quasi-static loading conditions with different boundary conditions. Dimensions of the specimen’s cross-section were selected to match those of sufficient representative volume element (RVE) obtained by spectral analysis of the macroscopic structure whereas different heights of specimens were tested to examine size-scaling factor. Mechanical properties were derived from three different data sources: I) using data captured by load-cell, II) by digital image correlation (DIC) of displacement of contact faces, III) by DIC of the specimen’s structure. Mechanical testing was performed in custom-built loading device as well as in Instron 4301 electromechanical testing system with custom computer control software.
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Comparative study on numerical and analytical assessment of elastic properties of metal foams
Koudelka_ml., Petr ; Jiroušek, Ondřej ; Doktor, Tomáš ; Zlámal, Petr ; Fíla, Tomáš
Recently, titanium metal foams are being considered as a suitable replacement for substituting trabecular bone microstructure especially for their similar pore distribution. The most common methods for determination of compressive effective elastic properties of such materials involve different approaches based on finite element analysis (FEA) of their microstructure. The internal geometry is usually modeled by two different methods - directly on the basis of a series of CT scans or using one of discretization schemes. However, all these techniques require highly specialized hardware, software and significant amount of computational time. In this paper, the effective elastic properties of the metal foam are instead obtained by analytical modulus-porosity relations and results are compared with previous FE based analysis.
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X-ray Observation of the Loaded Silicate Composite
Vavřík, Daniel ; Fíla, Tomáš ; Jandejsek, Ivan ; Veselý, V.
An intensive internal material damage evolution precedes a failure in quasi-brittle materials. Not only the existence of damage but also its quantification and the geometry of the Fracture Process Zone have to be identified in order to validate approaches on both numerical modelling of quasi-brittle behaviour and experimental determination of fracture properties. Radiographic techniques and Digital Image Correlation method are very appropriate for analysing of the Fracture Process Zone evolution during specimen loading.
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Investigation of composite material degradation indicators using acoustic measurement: comparison with laser vibrometry
Fíla, Tomáš ; Urushadze, Shota ; Kytýř, Daniel ; Valach, Jaroslav ; Šperl, Martin
This paper deals with investigation of acoustic material degradation indicator (attenuation decrement drop of selected natural frequency) measured by a custom-built experimental device. Samples of C/PPS fibre composite material were analyzed. Acoustic signals were recorded and processed using spectral analysis and sound signal regression. Data measured by this method were verified by comparative experiment. Specimens were simultaneously measured using both acoustic experimental device and laser vibrometer. Modal analysis of the specimen were carried out prior to the experiment. This enabled assessment of specimens natural modes and therefore the best impact zone. In total, 10 measurements were performed for each specimen at the same level of degradation. Measured data were then processed and compared. The specimens were repetitively measured after designated number of loading cycles.
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Design and use of novel compression device for microtomography under applied load
Fíla, Tomáš ; Zlámal, Petr ; Koudelka_ml., Petr ; Jiroušek, Ondřej ; Doktor, Tomáš ; Kytýř, Daniel
This paper deals with modification and usage of custom-designed compression device, that allows real time X-ray tomography scanning of specimen under applied pressure. In this case microtomography is used to obtain data required to determine specimens morphology and to develop 3D material model (especially for cellular materials such as bones, metal foams and quasi-brittle materials or particle composites such as concrete or cementitious composites). Important design changes were made in the existing device frame to increase its load capabilities, stiffness and to accomodate a larger specimen. Finally device displacement measurements were conducted and calibration experiment was carried out.
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Comparison of composite material degradation assesment methods using acoustic analysis and laser vibrometry
Urushadze, Shota ; Šperl, Martin ; Kytýř, D. ; Valach, J. ; Fíla, T.
Assessment of degradation rate of material can be carried out by many experimental techniques differing in complexity and sophistication. A relatively simple method based on acoustic analysis is described in this contribution. Degradation of material’s properties due to fatigue loading is detectable in decrease of their modulus of elasticity that can be derived from natural frequencies of specimens. These measurements utilize self-designed device capable of specimen excitation and acquisition of its vibration. The recorded signal is then processed by spectral analysis enabling determination of natural frequencies. Usefulness of the above mentioned acoustic method can be seen in the fact that the measured changes of material’s parameters are comparable to those obtained by laser vibrometry, which is by several orders more expensive technique.
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Investigation of C/PPS Composites Degradation Process Using Acoustic Measurement
Fíla, Tomáš ; Valach, Jaroslav ; Kytýř, Daniel ; Šperl, Martin
The article deals with assessment of fatigue degradation of C/PPS composites using simple acoustic measurement technique. Changes in natural frequency and attenuation decrement were chosen as indicators of fatigue damage accumulation in the studied composite material. New testing device was developed for acoustic measurement. The experimental setup was designed to chime the specimen by repeatable force of stiff striker exciting a specific natural mode of vibration and to record the acoustic response of the specimen to the impact simultaneously. From the power spectral density of the signal the natural frequency was obtained. Using the same signal, the attenuation decrement was estimated from regression of the its envelope.
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