Novel isocyanate-based matrix resins for high temperature composite applications

Polyoxazolidone composites were prepared from polymeric isocyanate (PAPI 901) and epoxides (Epon 828 and DEN 431) in the presence of an oxazolidone-forming catalyst, triphenylantimony iodide. The effects of isocyanate to epoxide equivalent ratio, type of epoxide, and amount of fiberglass reinforcement on the composite properties were studied as well as the effects of post-curing temperature and time. Increasing the fiberglass content of the polyoxazolidone composites resulted in an improvement of the thermal and mechanical strength properties. The heat deflection temperature of all polyoxazolidones was > 250°C. The retention of the tensile strength at 150°C was excellent, ∼90% or higher. Polyoxazolidone composites based on DEN 431 at 1.2 isocyanate to epoxide equivalent ratio with 70 wt.% of fiberglass and post-cured at 150°C for 48 h exhibited the best properties. According to the results of DMA, TMA and DSC, the maximum operating temperature for polyoxazolidone composites is around 200°C. The TGA data showed that the decomposition temperature was ∼330°C.     

Functionally Graded AA7075 Components Produced via Hot Stamping: A Novel Process Design Inspired from Analysis of Microstructure and Mechanical Properties

Herein, functionally graded AA7075 components manufactured via hot stamping are investigated by focusing on the effect of different process variables on localized microstructure evolution. To realize gradation through stamping, an active tool is designed and applied. The design of experiments allows to assess the impact of transfer time from the furnace to the tool, quenching time in the tool, and final quenching media. Related characteristics of mechanical properties throughout the hat-shaped profile are assessed via hardness and tensile tests. As expected, the sections of the samples formed in the cooled part of the tool are characterized by higher mechanical strength following subsequent aging, while sections formed in the heated part exhibit higher ductility. Moreover, the microstructural analysis reveals that fine precipitates with minimum interparticle distances only form in the cooled section of the samples. Increasing the tool temperature at the heated side to 350 °C results in the formation of coarse precipitates in the grain interior and along the grain boundaries. A sharp gradient in terms of microstructural and mechanical properties is found between these conditions. After reducing the transfer time, an increased volume fraction of fine precipitates leads to further improvements in hardness and mechanical strengths.     

A hybrid multiscale filter along with an improved adaptive SVR technique for fault diagnosis and machine learning modeling: forecasting the octane number of gasoline in isomerization reactor

Neural Computing and Applications - Using a reliable predictive model is important for modeling, controlling, and optimization of the isomerization process. This process has a significant impact on...     

Combination of acid‐demineralization and enzymatic desizing of cotton fabrics by using industrial acid stable glucoamylases and α‐amylases

In this study, the possibility of simultaneous acid‐demineralization and enzymatic desizing of cotton fabric in acidic conditions (pH 2) by using industrial acid stable enzymes has been investigated. Acid‐demineralization is necessary to remove undesired cationic metals and earth alkalis. Our experiments showed that by use of a mixture of two appropriate enzymes, a glucoamylase (Multifect GA 10L) and an α‐amylase (Optisize Next) in a solution of citric acid and presence of a chelating agent, enzymatic desizing, and acid‐demineralization can be successfully carried out at the same time. Therefore, two processes of pretreatment were integrated into a single process, which can effectively reduce time and costs for textile industry.     

Low-Cycle-Fatigue Performance of Stress-Aged EN AW-7075 Alloy

The effect of a novel heat treatment, that is, aging under superimposed external stress, on the fatigue performance and microstructural evolution of a high-strength aluminum alloy (EN AW-7075) is presented. Stress aging, a combination of heat treatment and superimposed external stress, can enhance the mechanical properties of EN AW-7075 under monotonic loading due to the acceleration of precipitation kinetics. Scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) reveal that a longer aging time and the presence of superimposed stress both promote the formation and growth of precipitates, that is, the precipitation of strengthening η´ precipitates. This is confirmed by differential scanning calorimetry (DSC) heating experiments of stressless and stress-aged states. Furthermore, stress aging leads to a reduction of dimensions of precipitate-free zones near grain boundaries. Cyclic deformation responses (CDRs) and half-life hysteresis loops are evaluated focusing on the low-cycle fatigue (LCF) performance of different conditions. A noticeable cyclic hardening seen in case of the specimens aged for a short time indicates the occurrence of dynamic strain aging (DSA). Eventually, stress aging allows for an enhancement of the monotonic mechanical properties of EN AW-7075 without degrading the cyclic performance in the LCF regime.