This article presents results from investigation of the effects of variation in autoclave pressure, temperature, and vacuumapplication time on porosity, hot/wet (H/W) and room temperature/dry (RT/D) short beam shear (SBS) strength, and failure mechanism of a commercial carbon fiber/epoxy prepreg, Cycom IM7/977-2 unidirectional tape. Fourteen cure cycles were designed to study a wide range of curing pressures, curing temperatures, and two different vacuumapplication durations, including vacuum vented at recommended pressure and vacuum held throughout the cure cycle. The results showed that the SBS strength did not vary significantly over a relatively wide range of curing temperatures and pressures if vacuum was vented at recommended curing pressure; however, after a certain point, a decreasing trend in the SBS strength was observed by reducing the curing temperature and pressure. The C-scan images of panels cured with the vacuum held throughout the cure cycles revealed presence of a high-porosity crossshaped defect at the center of the panels. The observed defect became larger as the curing pressure decreased. The correlation between the SBS strength and the void content was studied using theoretical models and experimental data. The investigation of the failure modes for each panel showed a change in both the H/W and the RT/D failure mechanism as a result of variation in curing temperature and pressure.

Thermal, rheological, and mechanical properties of a commercial carbon fiber epoxy prepreg, Cycom 977-2 UD, were obtained for isothermal cure temperatures ranging from 149 C to 182 C. For each cure profile, an encapsulated-sample rheometer (ESR) was used to measure the storage modulus. Each ESR cure profile was followed by the glass transition temperature (T g ) test. The degree of cure () during cure and the heat of reaction of the prepreg were obtained using a differential scanning calorimeter (DSC). Combined loading compression (CLC) and short-beam shear (SBS) tests were performed to obtain compressive properties and SBS strength, respectively. It was observed that the compressive properties did not vary significantly for the studied isothermal cure temperatures; likewise, the compressive failure mode was the same for all the CLC specimens. However, the SBS strength for the specimens cured at 149 C was approximately 10% less than that of those cured at isothermal cure temperatures ranging from 160 C to 182 C. Further, the failure mode of the SBS specimens cured at 149 C was also different from other specimens. The storage modulus of the ESR sample cured at 149 C also showed a 10% decrease compared to other ESR samples. The SBS strength exhibited a good correlation with the storage modulus and a weak correlation with T g and .

Here, we propose a new method for estimating the extent of curing of thermosetting prepregs. In the proposed method, the extent of curing is estimated with the curing index (C i ), defined as the ratio of the glasstransition temperature (T g ) to the ultimate glass-transition temperature of the material. The advantages of this new method over the conventional degree of conversion (a) for estimating the extent of curing of thermosetting prepregs are discussed in detail. C i and a of a toughened epoxy prepreg (977-2 unidirectional) were obtained for a wide range of isothermal curing temperatures with a differential scanning calorimeter. The ultimate heat of reaction varied inconsistently with decreasing curing temperature; this resulted in erratic behavior of a. However, C i provided a more consistent estimate of the extent of curing because T g , unlike a, did not need to be modified on the basis of the curing history of the material and was measured directly with the heat-flow data from differential scanning calorimetry. V C 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121: [883][884][885][886][887][888][889][890][891] 2011

This paper reviews various studies carried out on thermal issues in lithium-ion batteries. Although thermal behavior of Li-ion batteries plays an important role in performance, life cycle and safety of these batteries, it has not been studied as intensely as chemical characteristics of these batteries. In this review paper, studies concerning thermal issues on Li-ion batteries are classified based on their methodologies and the battery components being investigated. The methodologies include mathematical thermal modeling, calorimetry, electrochemical impedance spectroscopy and thermal management system method. The battery components that have been studied include anode, cathode, electrolyte and the whole cell.

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