Results 1 - 10 of 4717
Results 1 - 10 of 4717. Search took: 0.032 seconds
|Sort by: date | relevance|
[en] Present article is devoted to study of spectral characteristics and properties of polymer material surface using in micro fluidic devices. The analysis of some spectral characteristics and properties of polymer material surface using in micro fluidic devices before and after plasma processing has been conducted. On the basis of carried out studies it has been defined that processing by high frequency plasma in argon medium leads to change of polymer material surface.
[en] In this paper, the heating/ethanol-response of a commercial poly methyl methacrylate (PMMA) is investigated. All PMMA samples are pre-deformed by means of impression (surface compression with a mold) to introduce a gradient pre-strain/stress field. Two types of molds are applied in impression. One is a Singaporean coin and the other is a particularly designed mold with a variable protrusive feature on top. Two potential applications—temperature sensors to monitor overheating temperatures and anti-counterfeit labels with a water-mark that appears only upon heating to a particular temperature—are demonstrated. Since the heating-responsive shape memory effect (SME) is an intrinsic feature of almost all polymers, other conventional polymers may be used in such applications as well. (technical note)
[en] It is actually well known that the accumulated charges in insulators subjected to various external stress, involve an irreversible decrease in their performances, and present, in this way, a serious danger to the electric insulation systems. In this work, we have been interested in the effect of space charges on the local field and the mechanisms of conduction in the PMMA subjected to thermal and electric constraints. Measurements by thermal step and thermally stimulated depolarization currents techniques realized after conditioning under an electric field of 7.5 kV/mm at Tc=90deg. C during 2 hours show the presence of polarization phenomenon and the injected charges by the electrodes in PMMA, which influences local field value. Polarization of PMMA is confirmed by a complementary dielectric experiment. I(V) characteristics show a space charges limited conduction in PMMA. Conduction mechanisms were found to be well described by Schottky and Mott models. Indeed, at low fields (< VTFL) conduction was dominated by the interfaces effects, while at high fields (>VTFL) the bulk presents a majoritory contribution to the conduction mechanism. Comparison of the experimental results shows a good agreement.
[en] Percutaneous vertebroplasty has gained widespread popularity and demonstrated clinical efficacy in the treatment of spinal osteoporotic compression fractures and pathologic osteolytic lesions. Despite its rapid pain relief and safety, this minimally invasive intervention has exhibited some rare complications over the past decade. In this case study, we describe a patient with an uncommon complication of polymethylmethacrylate (PMMA) cement pulmonary embolism following fluoroscopy-guided percutaneous vertebroplasty for treatment of pain associated with an osteoporotic vertebral fracture. We present this case to highlight that vertebroplasty is not risk-free and that knowledge of such potentially severe complication is necessary for prevention and optimal operative outcomes
[en] The complex stress intensity factor at the tips of obliquely cracked plates subjected to a biaxial load at infinity was studied by an interferometric method. The effect of higher-order terms in the series expression of the isopachics on their size and shape was studied. Thus, the optical evaluation of the stress intensity factor at the tips of the crack was improved by theoretically determining the appropriate number of terms in the series expansion of the expression defining the isopachics. The possibility of determining the optimal number of terms presents the advantage of allowing to select experimental information from any area far from the crack tip, in a zone where the validity of the experimental method is incontestable and the results do not include significant errors. In this way the values for the respective stress intensity factors approach closer to their theoretical values. The method was examplified with the evaluation of the stress intensity factor at the tip of a transverse internal crack in a plexiglas plate submitted in simple tension. (orig.)
[de]Der komplexe Spannungsintensitaetsfaktor an der Rissspitze einer Schraegrisse enthaltenden unendlich ausgedehnten Platte, die einer zweiachsigen Belastung ausgesetzt ist, wurde mittels der interferometrischen Methode untersucht. Es wurde der Einfluss von Gliedern hoeherer Ordnung in der Reihendarstellung der Isopachen auf die Form und Groesse ermittelt. Die optische Abschaetzung des Spannungsintensitaetsfaktors an der Rissspitze wurde verbessert. Die entsprechende Anzahl von Gliedern in der Reihentwicklung der die Isopachen bestimmenden Ausdruecke wurde theoretisch bestimmt. Die Moeglichkeit zum Bestimmen der optimalen Anzahl der Glieder gestattet die experimentelle Auswahl von Informationen aus jedem Gebiet, das weit weg von der Rissspitze liegt und bei dem die Gueltigkeit der experimentellen Methode nicht bestreitbar ist - wobei die Ergebnisse keine signifikanten Fehler enthalten. Auf diese Weise naehern sich die Werte fuer die entsprechenden Spannungsintensitaetsfaktoren besser den theoretischen Werten an. Die Methode wurde unter Abschaetzung der Spannungsintensitaetsfaktoren an der Spitze des transversalen Zentralrisses einer Plexiglasplatte unter einfacher Dehnung geprueft. (orig.)
[en] Despite of a lot of attempts during recent years, complex mechanical behaviour of polymers remains incompletely modelled, making industrial design of structures under complex, cyclic and hard loadings not totally reliable. The non linear and dissipative viscoelastic, viscoplastic behaviour of those materials impose to take into account non linear and combined effects of mechanical and thermal phenomena. In this view, a visco-hyperelastic, viscoplastic model, based on network description of the material has recently been developed and designed in a complete thermodynamic frame in order to take into account those main thermo-mechanical couplings. Also, a way to account for coupled effects of strain-rate and temperature was suggested. First experimental validations conducted in the 1D limit on amorphous rubbery like PMMA in isothermal conditions led to pretty goods results. In this paper a more complete formalism is presented and validated in the case of a semi crystalline polymer, a PA66 and a PET (either amorphous or semi crystalline) are used. Protocol for identification of constitutive parameters is described. It is concluded that this new approach should be the route to accurately model thermo-mechanical behaviour of polymers using a reduced number of parameters of some physical meaning.