Low Creep Deformation Research Articles

Facile Fabrication of Graphene Oxide Nanoribbon-Based Nanocomposite Papers with Different Oxidation Degrees and Morphologies for Tunable Fire-Warning Response.

Smart fire-warning sensors based on graphene oxide (GO) nanomaterials, via monitoring their temperature-responsive resistance transition, have attracted considerable interest for several years. However, an important question remains as to whether or not different oxidation degrees of the GO network can produce different impacts on fire-warning responses. In this study, we synthesized three types of GO nanoribbons (GONRs) with different oxidation degrees and morphologies, and thus prepared flame retardant polyethylene glycol (PEG)/GONR/montmorillonite (MMT) nanocomposite papers via a facile, solvent free, and low-temperature evaporation-induced assembly approach. The results showed that the presence of the GONRs in the PEG/MMT promoted the formation of an interconnected nacre-like layered structure, and that appropriate oxidation of the GONRs provided better reinforcing efficiency and lower creep deformation. Furthermore, the different oxidation degrees of the GONRs produced a tunable flame-detection response, and an ideal fire-warning signal in pre-combustion (e.g., 3, 18, and 33 s at 300 °C for the three PEG/GONR/MMT nanocomposite papers), superior to the previous GONR-based fire-warning materials. Clearly, this work provides a novel strategy for the design and development of smart fire-warning sensors.

Location-specific mechanical response and morphology of facial soft tissues.

The facial tissue of 9 healthy volunteers (m/f; age: 23-60y) is characterized at three different locations using a procedure combining suction measurements and 18MHz ultrasound imaging. The time-dependent and multilayered nature of skin is accounted for by adopting multiple loading protocols which differ with respect to suction probe opening size and rate of tissue deformation. Over 700 suction measurements were conducted and analyzed according to location-specific mechanical and morphological characteristics. All corresponding data are reported and made available for facial tissue analysis and biomechanical modeling. Higher skin stiffness is measured at the forehead in comparison to jaw and parotid; these two regions are further characterized by lower creep deformation. Thicker tissue regions display a tendency towards a more compliant and less dissipative response. Comparison of superficial layer thickness and corresponding mechanical measurements suggests that connective tissue density determines the resistance to deformation in suction experiments.

Rheological and electrical behavior of poly(methyl methacrylate)/carbon black composites as investigated by creep recovery in shear

The rheological and electrical behavior of poly(methyl methacrylate) (PMMA)/carbon black (CB) composites has been studied as a function of CB concentration by simultaneous electrical and rheological measurements during creep and creep-recovery experiments in the linear and nonlinear regimes. The creep compliance and recoverable compliance were strongly influenced by the CB concentration in the linear regime, especially above the percolation threshold. The creep compliance remained almost unchanged in the linear and nonlinear regimes, but the recoverable compliance was strongly influenced by the creep stress. The electrical conductivity increased under low creep deformation, but under high creep deformation, the electrical conductivity decreased rapidly at the beginning of the creep experiment. After a sufficiently long creep time under shear, the electrical conductivity again increased. The results provide a deeper insight into structural changes in conductive polymer composites induced by shear deformation.

Investigation of in-service damage accumulation of Alloy 800HT methanol reformer outlet tubes

Methanol outlet reformer tubes, or pigtails, transport reformed syngas from reformer tubes to outlet manifolds at high temperature (800–900°C). These outlet tubes tend to have a convoluted geometry to accommodate thermal expansion of the reformer tubes, outlet tubes and manifolds, hence the term pigtails. The industry standard material for reformer outlet tubes is Alloy 800HT, a creep resistant austenitic Ni–Cr steel. A number of anomalous in-service failures of Alloy 800HT reformer outlet tubes have occurred at lower than expected service life and at low creep deformation. A discussion of the failures is presented in this paper, covering the parameters which affect potential damage mechanisms.

The effect of mullite seeding on reaction-sintered mullite-zirconia multiphase ceramic

Reaction sintering of alumina and zircon is an easy and inexpensive route to obtain homogeneous mullitezirconia composites, and has been extensively studied by many workers [1–5]. Due to mullization during firing, however, a lot of closed pores are easily formed, and the fully dense compacts are difficult to achieve. Two different ways have been employed in order to obtain dense composites. The first [1], is a two-stage process, separating densification and reaction after attrition milling and isostatic pressing (600 MPa) of the raw materials. In the second method, additives are used to promote the reaction sintering processes by enabling reaction and densification simultaneously [6]. The study of various compounds as sintering aids has been carried out in the past [7–9]. However, the use of additives usually leads to a large amount of glassy phase present in the material, which is undesirable to keep high mechanical properties and low creep deformation at elevated temperature. Koyama et al. [10] showed that the mechanical strength at high temperature could be improved by a seeding method, but no further information concerning the effect of mullite seeds on the reaction sintering processes was available in their paper. The aim of the present work is to investigate the effect of seeding on reaction-sintered mullite-zirconia composites when a small amount of mullite seeds is added, and special attention is paid to reaction and densification mechanisms during firing. All the samples were prepared starting from highpurity (99.9 wt%) alumina and fine zircon (ZrO2> 65 wt%) powders. The main impurities of the zircon powders were Al2O3 (0.50 wt%), CaO (0.40 wt%) and Fe2O3 (0.10 wt%). The average particle sizes of these two kinds of powder were 0.35 μm and 0.48 μm respectively. The mullite particle used as seeds has a mean size of 1.87 μm, with the main impurities being CaO (0.29 wt%), Fe2O3 (0.27 wt%) and Na2O (0.21 wt%). The sample composition was determined by the following equation: