Focusing on application aspects of the rubber nanocomposites and the production and testing of industrial-sized samples, this study was performed in two phases. First, natural rubber (NR)/organomontmorillonite (OMMT) nanocomposites containing 2-14 phr OMMT were prepared on a laboratorysized two-roll mill. The vulcanization behavior and mechanical properties of NR/OMMT composites were compared with a referent NR compound containing 60 phr carbon black (N330) as a reinforcing filler. The x-ray diffraction (XRD) analyses showed a predominant intercalated structure for all OMMT nanocomposites. As a result, the organoclay behaved as an effective reinforcement for NR, even at loadings as low as 2 phr. This nanocomposite exhibited an improvement in tensile strength of 29% and in elongation at break of 61% in comparison with the referent NR/N330 compound. With the estimated optimal filler content, in the second phase, bulk NR/OMMT-5/steel samples were successfully produced for dynamic testing. The dynamic moduli were investigated by the method of forced vibrations. Compared to the NR/N 330 samples, NR/OMMT-5 samples showed improved hysteresis, with very low dissipating energy per cycle and significantly reduced Mullins effect.Keywords: organo-montmorillonite; nanocomposites; natural rubber; dynamic properties ДОБИВАЊЕ И СВОЈСТВА НА ПРИРОДНА ГУМА НАПОЛНЕТА СО ОРГАНСКИ МОДИФИЦИРАН МОНТМОРИЛОНИТ: ОД ЛАБОРАТОРИСКИ ПРИМЕРОЦИ ДО МАСИВЕН МАТЕРИЈАЛИстражувањата во овој труд се направени во две фази фокусирајќи се на применливоста на нанокомпозитите на база на гума и на добивањето и карактеризација на примероци со индус-триски димензии. Прво беа подготвени лабораториски примероци нанокомпозити природна гума (NR)/органски модифициран монтморилонит (OMMT) со 2-14 phr OMMT на лабораториски дво-валјак. Вулканизацијата и механичките својства на композитите NR/OMMT се споредувани со референтен примерок на природна гума наполнета со саѓи (N330). Рендгенската дифракција (XRD) покажа дека кај сите нанокомпозити со OMMT доминира интеркалирана структура. Како резултат на тоа, органски модифицираната глина се однесува како ефикасен зајакнувач на природната гума, дури и при концентрации од само 2 phr. Нанокомпозитот се одликува со јачина на истегнување за 29 % поголема од онаа на референтниот примерок со саѓи (NR/N330), како и со зголемено издолжување (за 61 %). Во втората фаза, по определување оптимална количина на полнилото, произведени беа индустриски примероци NR/OMMT и сендвич-структура NR/OMMT-5/челична A. Ivanoska-Dacikj, G. Bogoeva-Gaceva, A. Buzarovska, I. Gjorgjiev, L. Raka Maced. J. Chem. Chem. Eng. 33 (2), 249-265 (2014) 250 плоча наменета за динамичко тестирање. Динамичкиот модул на материјалот е испитуван со методот на принудни вибрации. Произведениот масивен нанокомпозитен материјал NR/OMMT-5 се одликува со подобрена хистереза, многу ниска енергија на дисипација за циклус и значително намален Mullin-ов ефект во споредба со референтниот материјал NR/N330. Клучни зборови: органски модифициран монтморилонит; нанокомпозити; ...
The moment resisting frames (MRF) are one of the three main structural steel typologies used for seismic design of steel frames. They are characterized as the most ductile structural type possessing a large number of possible dissipative zones, following the fact that plastic hinges can develop both in the beams and the columns. Possessing the feature of being the most ductile type, these structures exhibit very large deflections before the structural damage occurs. Additionally, the strength and stiffness deterioration of the steel material due to cyclic loading increases the effect of the lateral forces and represents the most realistic behaviour of this structural system. Hence, in this research study an improved approach using updated material model for evaluating the steel MRFs' behaviour is implemented in order to tackle the deficiency in the assessment of this type of structures. Firstly, the modelling is performed using the nonlinear beam -column elements with distributed plasticity for both the beams and the columns. Then, the same frame model is developed using the elastic beam -column elements ending with zero-length plastic hinges modelled by a stiffness deteriorating steel material referred to as Ibarra -Krawinkler (IK) model. Two sets of seven acceleration records are chosen as realistic earthquake loading to represent the medium hazard seismicity (MH) and high hazard seismicity (HH) scenarios. Incremental nonlinear dynamic analysis of the frames is conducted by scaling the records in order to attain various levels of relative intensities. They are extracted from the database and scaled to match the EC8 elastic spectra for the two hazard scenarios.
Structural Health Monitoring is essential when it comes to damage detection and quantification of civil infrastructure under dynamic excitations. Lately, seismic interferometry has been frequently used for damage identification of structures under earthquake excitations. The method uses data from vibrational sensors to detect changes in travel times of seismic waves propagating trough the structure. The propagating waves’ travel time between pairs of sensors (and consequently their velocity) is related to the local stiffness of the structure enabling to follow possible degradation caused by damage during an extreme event. In this study an analytical uniform Timoshenko beam model that accounts for dispersion due to bending deformation, was implemented for system definition and damage identification of a 3 storey, 1:2 large scale shaking table model. The model is coupled wall RC structure and it was tested in the dynamic testing laboratory in IZIIS, in the frames of SERA project. A full testing programme consisted of random excitation and shaking table tests with gradually increasing intensity of the input excitation. We collected the data consisted of accelerograms from the distributed accelerometers of all tests and recorded damages of the model after each test, defining four damage states. In our research we focus on fitting uniform Timoshenko beam model in the recorded response of the shaking table model after each test. The structure was modelled with large shear stiffness and its compressional wave velocity, cL, was identified and analyzed. We monitored the change in cL after each damage state and compared it with the shift in the fundamental frequency of vibration f1 as well as the observed damage to discuss on the effectiveness of the method. We concluded that it is possible to detect and quantify damages of the structure induced by the increasing earthquake amplitude in each test by wave propagation analysis.
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