Research on the effects of surface modification of ceramic powder on cure performance during digital light processing (DLP)

Digital light processing (DLP) is one of the most important additive manufacture technologies to fabricate ceramic parts with complex geometries. Compared with pure photosensitive resin, the cure performance of ceramic suspensions is obviously different due to the optical property change after the addition of ceramic powders. In this paper, a unique oxidation process was used to modify the optical properties of nitride powders including AlN and Si₃N₄. The properties of oxidized ceramics were investigated and the cure performance of ceramic suspensions was then characterized. The effect of oxidation time on cure performance was evaluated. The results showed that for AlN, oxidation process leads to the smaller cure depth and smaller excess cure width as compared with non-oxidized AlN and for Si₃N₄, oxidation process leads to the larger cure depth and larger excess cure width as compared with non-oxidized Si₃N₄, indicating that both refractive index and light absorbance of ceramic powders have obvious effects on cure behaviors. Additionally, the cure behavior of oxidized ceramic suspension in this study shows that the relationship of cure depth vs. incident energy agrees well with Beer- Lambert model, but the excess cure width vs. incident energy is not consistent with quasi Beer-Lambert model due to the nature of digital micromirror device (DMD).     

Cure monitoring of thermoset coatings

The combination of favorable features of tensile mode dynamic mechanical analysis and torsional braid analysis leads to a useful method for cure monitoring of thermoset coatings. This sensitive technique allows the observation of cure reactions over a wide time and temperature range, thus including gelation and long-term curing in one measurement. Isothermal baking can be simulated realistically, since evaporation of volatile compounds like solvents or blocking agents is not hindered and the sample film is in direct contact with the heating atmosphere. Examples are given showing the cure behavior of automotive clear coats and electro coats depending on parameters like crosslinker type and catalytic agents.     

Bayesian bivariate generalized Lindley model for survival data with a cure fraction

The cure fraction models have been widely used to analyze survival data in which a proportion of the individuals is not susceptible to the event of interest. In this article, we introduce a bivariate model for survival data with a cure fraction based on the three-parameter generalized Lindley distribution. The joint distribution of the survival times is obtained by using copula functions. We consider three types of copula function models, the Farlie–Gumbel–Morgenstern (FGM), Clayton and Gumbel–Barnett copulas. The model is implemented under a Bayesian framework, where the parameter estimation is based on Markov Chain Monte Carlo (MCMC) techniques. To illustrate the utility of the model, we consider an application to a real data set related to an invasive cervical cancer study.     

Synthesis of novel bisphenol containing phthalazinone and azomethine moieties and thermal properties of cured diamine/bisphenol/DGEBA polymers

A novel bisphenol(1,2-dihydro-2-(4-((4-hydroxy)phenyliminomethylidene)phenyl)-4-(4-((4-(4-hydroxy)phenyliminomethylidene)phenoxy)phenyl)(2H)phthalazin-1-one, DPP) and a diamine(1,2-dihydro-2-(4-aminophenyl)-4-(4-(4-aminophenoxy)phenyl)(2H)phthalazin-1-one, DAP) were synthesized and characterized. The novel epoxy polymers containing phthalazinone and/or azomethine moieties were prepared by binary polymerization of DAP (or DPP) with diglycidyl ether of biphenyl A (DGEBA) and ternary polymerization of hybrid curing agents, DAP/DPP (DAP and DPP under different molar ratios) with DGEBA. The cure behaviors of these new epoxy systems were studied by dynamic differential scanning calorimeter (DSC) and Infrared (IR) scans. Especially, the activation energy of DAP/DGEBA calculated by Kissinger and Ozawa methods were 73.8 and 77.4 kJ/mol, respectively. For ternary epoxy system, it was found that hybrid curing agents of DAP/DPP exhibited significant associated effect on their reactivity towards the oxirane group. Glass transition temperatures (T_g's) of these new epoxy polymers were all above 150 °C from the results of DSC, and the initial thermal decomposition temperatures (T_d,5%'s) and integral procedure decomposition temperatures (IPDT's) of these new epoxy polymers are above 350 and 850 °C, respectively from results of thermogravimetric analyses (TGA). These results show that new epoxy polymers containing phthalazinone and/or azomethine moieties exhibited excellent thermal properties. Especially, thermal properties of the ternary epoxy polymers could be modified by changing the content of DAP and DPP. The linear relationships between char yield (Y_c,wt%) and the structural compositions of these new polymers (weight percentage of phthalazinone, azomethine and nitrogen, C/H weight ratio) were built.     

磁碟机病毒破坏机制与防治策略研究

磁碟机病毒及其变种是近几年来病毒技术含量最高、破坏性最强的病毒,已感染数十万台计算机,造成的损失远远超过"熊猫烧香"。为了能有效地防御和查杀该病毒,该文特地对磁碟机病毒进行了深入的研究,分析了磁碟机的破坏机制,指出了磁碟机的种种危害,提出了防治磁碟机的几种技术方法,这对当前防御和清除磁碟机病毒具有一定的现实意义。     

活化体系加快丁基橡胶硫化速度的探索

对丁基橡胶五种硫黄－促进剂组合配用常规活化体系及两种新活化体系，表明新活化体系可加快丁基橡胶及其同三元乙丙橡胶、溴化丁基橡胶并用胶的硫化速度，而且具有较好的耐热氧老化性，但抗硫化还原性差。     

Thermal press curing of advanced thermoset composite laminate parts

An alternative process to autoclaving, called Thermal Press Curing (TPC), is proposed, whereby an uncured composite laminate is pressed between a heated curing mold and customized rubber-faced mold that are designed to provide uniform temperature and pressure conditions. TPC was demonstrated by designing a complex 3-D ‘benchmark’ part shape, applying a simple computational algorithm to derive the required tool shapes, and fabricating the tooling. A comparative study was performed involving the benchmark part made from four plies of woven carbon/epoxy prepreg material. Identical laminates were pre-formed by double diaphragm forming and then cured and consolidated by autoclaving, Quickstep, and TPC using standard industry practice. Results of the study indicate that the TPC part is of similar quality as compared to those made by autoclaving and Quickstep, but, more importantly, requiring significantly less energy and resource consumption, lower cost (capital and recurring), and less preparation and cycle time.     

Chemical and thermal shrinkage in thermosetting prepreg

A methodology for predicting residual cure deformation and stresses in composite laminates during cure is proposed. The technique employs an unbalanced cross-ply strip denoted as a “bi-lamina” strip to measure the in situ development of chemical and thermal shrinkage deformation during a specified thermal cycle. The constitutive model of the composite material was developed based on self-consistent micro-mechanical homogenization with variable resin thermo-mechanical material properties during the cure cycle. The resin properties were determined as a function of cure and temperature using different experimental techniques, including differential scanning calorimetry, digital image correlation, rheometry and dynamic mechanical analysis. The predicted bending deflection profiles of the strip agreed closely with experimental observations. The proposed methodology can be used to validate the material model of the resin and composite during the cure cycle.     

Cure cycle optimization of an inorganic polymer matrix material for high temperature fiber reinforced composites

We investigated the potential effects of inorganic polymer processing conditions on the residual stress generation of fiber reinforced inorganic polymer matrix composites. By optimizing various stages of processing it was found that process-induced shrinkage can be reduced by as much as 20%, while simultaneously, the compression strength can be improved by over 30% compared to baseline processing parameters. Further with the optimization of the process parameters, the pore diameter reduced by over 65%, while the relative density increased by a little over 5%. These results suggest high temperature dimensional stability and reduced pore content. Also SEM images indicate a continuous thermodynamic transformation in the bonding strength between the precipitated particles. Thus, it is demonstrated that, through the process modification, a path exists to reduced cure shrinkage, high mechanical strength and thermodynamic stability that results in a potential reduction in residual stresses in continuous fiber reinforced, inorganic matrix composites.     

Preparation, characterization and application of advanced isoconversional kinetics to epoxy/1,4-Bis(3-aminopropoxy) butane/MWCNT nanocomposite

A novel nanocomposite consisting bisphenol A diglycidyl ether/1,4-Bis(3-aminopropoxy) butane (1,4-APB)/multiwall carbon nanotube (MWCNT) was synthesized and characterized. Kinetics of the reaction was described by applying differential scanning calorimetry (DSC) data to isoconversional methods of Flynn-Wall-Ozawa (FWO), advanced isoconversional method of Vyazovkin, and non-linear integral isoconversional algorithm (NLN). It was found that at the presence of MWCNT the thermal decomposition temperature increased by rising the curing temperature and time. Data from dynamic mechanical thermal analysis (DMTA) showed that the glass transition temperature of the cured nanocomposite is 7 °C higher than that value found for the system without carbon nanotube. Scanning electron microscopy (SEM) was used to observe the fracture surface morphology and results indicated evidence of the interfacial interaction improvement and adhesion strength due to good dispersion of MWCNT.