Consistent model predictions for isothermal cure kinetics investigation of high performance epoxy prepregs

An accurate kinetics model is essential for understanding the curing mechanism and predicting the end properties of polymer materials. Graphite/epoxy AS4/ 8552 prepreg is a recent high-performance thermosetting composite modified with thermoplastic, which is being used in the manufacture of aircraft and military structures. The isothermal cures of this system along with another thermoplastic toughened high-performance prepreg, the T800H/3900-2 system, were investigated by real-time Fourier transform infrared (FTIR) spectroscopy. The cure rate was quantitatively analyzed based on the concentration profiles of both the epoxy and primary amine groups. Three autocatalytic models were used to determine kinetics parameters for both composite systems. The model which utilizes an empirical term, the final relative conversion (at different isothermal curing temperatures), describes the experimental data of both systems more satisfactorily than the model which applies a diffusion factor. The modeling results suggest that the curing of epoxy within both prepregs can be assumed to be a second order process.

Facial age estimation by nonlinear aging pattern subspace

Human age estimation by face images is an interesting yet challenging research topic emerging in recent years. This paper extends our previous work on facial age estimation (a linear method named AGES). In order to match the nonlinear nature of the human aging progress, a new algorithm named KAGES is proposed based on a nonlinear subspace trained on the aging patterns, which are defined as sequences of individual face images sorted in time order. Both the training and test (age estimation) processes of KAGES rely on a probabilistic model of KPCA. In the experimental results, the performance of KAGES is not only better than all the compared algorithms, but also better than the human observers in age estimation. The results are sensitive to parameter choice however, and future research challenges are identified.

Decay of electrical conductivity in p-toluene sulfonate doped polypyrrole films

Long term performance of conductivity of p-toluene sulfonic acid (pTSA) doped electrochemically synthesized polypyrrole (PPy) films was estimated from accelerated aging studies between 80 °C and 120 °C. Conductivity decay experiments indicated that overall aging behavior of PPy films deviated from first order kinetics at prolonged aging times at elevated temperatures. However, an approximate value for the activation energy of the conductivity decay of PPy was calculated as E=47.4 kJ/mol, enabling an estimate of a rate constant of k=8.35×10⁻⁶/min at 20 °C. The rate of decrease of conductivity was not only temperature dependent but also influenced by the dopant concentration. A concentration of 0.005 M pTSA in the electrolyte resulted in a conductive film and when this film was exposed to 120 °C for a period of 40 h, the conductivity decayed to about 1/20 of its original value. The concentration of pTSA was increased to 0.05 mol/l and when the resulting film was aged in the same way, it showed a decrease in the conductivity to about 1/3 of its original value. Both microwave transmission and dc conductivity data revealed that highly doped films were considerably more electrically stable than lightly doped films. The dopant had a preserving effect on the electrical properties of PPy.

Relationship between hypoactive sexual desire disorder and aging

Objective: Explore the association between Hypoactive Sexual Desire Disorder (HSDD) and aging. The American Foundation of Urologic Disease and the American Psychiatric Association stipulate that HSDD is only diagnosed when both low sexual desire and sexually related personal distress are present.
Design : Community-based, cross-sectional study.
Setting : Europe (UK, Germany, France, Italy) and the USA.
Patient(s) Women aged 20-70 in sexual relationships participating in the Women’s International Study of Health and Sexuality (n=1998 Europe, n=1591 USA).
Intervention(s) : No interventions were administered.
Main Outcome Measures : Self-administered questionnaire that included two validated instruments: Profile of Female Sexual Function© measured sexual desire; Personal Distress Scale© measured sexual distress. Women with low desire and distress were considered to have HSDD.
Results : The proportion of European women with low desire increased from 11% amongst women aged 20-29 years to 53% amongst women aged 60-70 years. The proportion of American women with low desire displayed a trend towards an increase with age. In the 20-29 year age group 65% of European women and 67% of American women with low sexual desire were distressed by it. This decreased to 22% and 37%, respectively, in the 60-70 year age group. In Europe and the USA the prevalence of HSDD in the population did not change significantly with age (6-13% in Europe, 12-19% in the USA).
Conclusions: The proportion of women with low desire increased with age while the proportion of women distressed about their low desire decreased with age. Consequently, the prevalence of HSDD remained essentially constant with age. This may explain why no association between HSDD and age is often reported in the literature.

The kinetics of two-stage formation of TiAl3 in multilayered Ti/Al foils prepared by accumulative roll bonding

The solid-state reactions of Ti/Al multilayered samples produced by Accumulative Roll Bonding (ARB) have been investigated using differential scanning calorimetry, X-ray diffraction and scanning electron microscopy. The kinetics of the formation of the intermetallic compound TiAl3 was highlighted. Experimental evidence and analysis of the data shows that, there was a two-stage process in the formation of TiAl₃ in the ARB Ti/Al reactive multilayered samples. Calorimetric and microstructural analyses also suggest that the interdiffusion of Al and Ti which led to solid solutions preceded the formation of intermetallic compounds. Despite the apparent chaos in the thickness of the ARB multilayered samples, the distribution of layer spacing did not become broad enough to lose the main features of the double exothermal behaviour. Isothermal DSC shows a larger Avarami constant in ARB Ti/Al multilayered structures than was found in Ti/Al thin films. A modified model based on thin films was set up to describe the kinetic characteristics of the formation of the intermetallic compound TiAl₃ in ARB samples.

Martensite/particle interactions and the shape memory effect in an Fe–Mn–Si-based alloy

The effect of carbide precipitates with a size range of 30–300 nm on the austenite to martensite transformation has been studied. Such particles are known to enhance shape memory, and it was the aim of this work to clarify how the particles exert a favourable effect on shape memory. Differential scanning calorimetry revealed that the presence of particles increases the amount of thermally induced martensite. X-ray diffraction showed that the presence of particles increases the amount of stress-induced martensite also. Surface-relief produced on a pre-polished surface by bending deformation showed that the particle-containing samples exhibited a more complex and highly tilted surface-relief indicative of the formation of a larger volume fraction of martensite. The reversion characteristics of the particle-containing and solution-treated samples were similar: both showed co-reversion of multiple variants of martensite within the same volume of microstructure. However, a higher volume fraction of martensite reverted for the particle-containing sample on recovery annealing. The increased density of nucleation sites for martensite formation and a higher volume fraction of stress-induced martensite for a given strain are therefore considered to be the main contributions of relatively coarse carbide particles to the improvement of shape memory performance.

Austenite stability in Fe-Mn-Si-based shape memory alloys

The stability of austenite in a number of Fe–Mn–Si-based shape memory alloys has been investigated. It was found that a grain boundary precipitate of BCC structure is formed over a wide range of alloy compositions and heat treatment temperatures. This grain boundary phase has been identified as the chi (χ) phase. Although up to 3 vol.% of the grain boundary precipitate was generated by isothermal aging in the range 500–800 °C, it was found not to markedly affect the mechanical properties or the shape memory effect. Nano-indentation indicated that the hardness and strength of the parent and precipitate phase are very similar, as are their compositions.

Thermal degradation kinetics and morphology of natural rubber/silica nanocomposites

A novel natural rubber/silica (NR/SiO₂) nanocomposite with a SiO₂ loading of 4 wt% is developed by incorporating latex compounding with self-assembly techniques. The SiO₂ nanoparticles are homogenouslydistributed throughout the NR matrix as spherical nano-clusters with an average size of 75 nm. In comparison with the host NR, the thermal resistance of the nanocomposite is significantly improved. The degradation temperatures (T), reaction activation energy(E), and reaction order (n) of the nanocomposite are markedly higher than those of the pure NR, due to significant retardant effect of the SiO₂ nanoparticles.