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Aging Tests (aging + test)
Selected AbstractsIn vivo aging test for a bioactive bone cement consisting of glass bead filler and PMMA matrix,JOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 2 2004Shuichi Shinzato Abstract The degradation of a new bioactive bone cement (GBC), comprised of an inorganic filler (bioactive MgO-CaO-SiO2 -P2O5 -CaF2 glass beads) and an organic matrix [high-molecular-weight polymethyl methacrylate (PMMA)], was evaluated in an in vivo aging test. Hardened rectangular specimens (20 × 4 × 3 mm) were prepared from two GBC formulations (containing 50% w/w [GBC50] or 60% w/w [GBC60] bioactive beads) and a conventional PMMA bone cement control (CMW-1). Initial bending strengths were measured with the use of the three-point bending method. Specimens of all three cements were then implanted into the dorsal subcutaneous tissue of rats, removed after 3, 6, or 12 months, and tested for bending strength. The bending strengths (MPa) of GBC50 at baseline (0 months), 3, 6, and 12 months were 136 ± 1, 119 ± 3, 106 ± 5 and 104 ± 5, respectively. Corresponding values were 138 ± 3, 120 ± 3, 110 ± 2 and 109 ± 5 for GBC60, and 106 ± 5, 97 ± 5, 92 ± 4 and 88 ± 4 for CMW-1. Although the bending strengths of all three cements decreased significantly from 0 to 6 months, those of GBC50 and GBC60 did not change significantly thereafter, whereas that of CMW-1 declined significantly between 6 and 12 months. Thus, degradation of GBC50 and GBC60 does not appear to continue after 6 months, whereas CMW-1 degrades progressively over 12 months. Moreover, the bending strengths of GBC50 and GBC60 (especially GBC60) were significantly higher than that of CMW-1 throughout. It is believed that GBC60 is strong enough for use under weight-bearing conditions and that its mechanical strength is retained in vivo; however, its dynamic fatigue behavior will need assessment before application in the clinical setting. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 68B: 132,139, 2004 [source] Thermal aging of a blend of high-performance fibersJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2010Carlos Arrieta Abstract The focus of this work is the study of the thermal aging of high-performance fibers used in the making of fire protective garments. Accelerated thermal aging tests were carried out on fabric samples made up of a blend of Kevlar® (poly p -phenylene terephthalamide) and PBI (poly benzimidazole) staple fibers, as well as on yarns pulled from this fabric, by means of exposure to elevated temperatures, comprised between 190°C and 320°C. All samples underwent loss of breaking force retention. The material thermal life, defined as the time required for the fibers to attain a 50% reduction of the original breaking force, ranged between a dozen of days at the lowest exposure temperature, to less than an hour at the highest. Breaking force data were fitted using the Arrhenius model following two different approaches, namely the extrapolated thermal life value and the shift factors yielded by the time-temperature superposition (TTS). The Arrhenius model seemed to describe appropriately the overall aging process, as inferred from the excellent fit obtained when using both approaches, although activation energies provided from both approaches are different. To follow the chemical evolution of the material with thermal aging, Fourier-transform infrared (FTIR) analyses were conducted. The qualitative analysis of the FTIR spectra showed little evidence of chemical changes between the aged and the nonaged samples, indicating either that the aging process carries on without significant modification of the chemical structure of the fibers, or that FTIR is not an appropriate method to spot such a modification. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Evaluation of heat and oxidative damage during storage of processed tomato products.JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 11 2002Abstract The evolution of heat damage during storage of tomato pulp, puree and paste was studied by accelerated aging tests. Heat damage indices,5-hydroxymethyl-2-furfural (HMF), furosine and colour changes (,E),were evaluated for tomato products stored at 30, 40 and 50,°C for up to 90 days. Furosine and ,E values increased following pseudo-zero-order kinetics, and the higher the solid content of the products, the higher were the rate constant values. HMF formation followed pseudo-first-order kinetics in tomato pulp and pseudo-zero-order kinetics in puree and paste samples. Data show that heat damage reactions in tomato products proceed even at room temperature, and the kinetic model provided can be used to predict changes occurring during shelf-life. © 2002 Society of Chemical Industry [source] Short term instabilities of InGaN GaN light emitting diodes by capacitance,voltage characteristics and junction spectroscopyPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005A. Castaldini Abstract We present a combined capacitance-voltage, Deep Level Transient Spectroscopy (DLTS) and electroluminescence (EL) study of short-term instabilities of InGaN/GaN LEDs submitted to forward current aging tests at room temperature. In the early stages of the aging tests at low forward current levels (15 and 20 mA), LEDs present a decrease in optical emission, which stabilizes within the first 50 hours and never exceeds 20% (measured at an output current of 1 mA after stressing the LEDs for 50 hours with 15 mA stress). The spectral distribution of the EL intensity does not change with stress, while C-V profiles detect changes consisting in apparent doping and/or charge concentration increase within quantum wells. This increase is correlated with the decrease in optical power. DLTS has been carried out to clarify the DC aging induced generation/modification of the energy levels present in the devices. Remarkable changes occur after the stress, which can be related to the doping/charge variation and thus to the efficiency loss. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||