A three-function numerical model for the prediction of vulcanization-reversion of rubber during sulfur curing

The cross-linking mechanisms of sulfur vulcanization are not analytically known and, therefore, reticulation kinetics has to be deduced macroscopically from standardized tests. One of the most popular laboratory test to characterize curing and reversion is the oscillating disk rheometer ODR, which gives a quantitative assessment of scorch, cure rate, and state of cure. In this article, a numerical two-step approach, which is based on the utilization of experimental ODR data and aimed at predicting the degree of vulcanization of thick rubber items cured with accelerated sulfur, is presented. In step one, a composite numerical three-function curve is used to fit experimental rheometer data, able to describe the increases of the viscosity at successive curing times and at different controlled temperatures, requiring only few points of the experimental cure curve to predict the global behavior. Both the case of indefinite increase of the torque and reversion can be reproduced with the model. In step two, considering the same rubber compound of step one, numerical cure curves at different temperatures are collected in a database and successively implemented in a Finite Element software, which is specifically developed to perform thermal analyzes on complex 2D/3D geometries. As an example, an extruded thick EPDM section is considered and meshed through eight-noded isoparametric plane elements. Several FEM simulations are repeated by changing exposition time tc and external curing temperature Tn, to evaluate for each (tc,Tn) couple the corresponding mechanical properties of the item at the end of the thermal treatment. A recently presented bisectional approach, alternating tangent (AT), is used to drastically reduce the computational efforts required to converge to the optimal solution associated with the maximum value of an output property, tensile strength

Multiple organizational identification levels and the impact of perceived external prestige and communication climate

sEarlier studies have shown that perceived external prestige and communication climate influence organizational identification. In this paper we present the results of a study of the influence of communication climate and perceived external prestige on organizational identification at various organizational levels of a regional police organization. In total, 314 respondents filled out a questionnaire on communication climate, perceived external prestige and organizational identification. The results of this study show that communication climate has the strongest link with employee identification when it concerns the identification with the daily work group and a weaker one with the organization as a whole. It also appears that perceived external prestige has a stronger influence on the identification with the organization as a whole than on the identification at the more concrete organizational levels (such as department or work group). This research offers reasons to presuppose that organizational identification and communication climate are multiple constructs. If management wishes to influence organizational identification through a bottom-up process, it is wise to pay particular attention to the communication climate in the work groups. Influencing organizational identification with the organization as a whole is better conducted through perceived external prestige

Oscillating between a relationship-based and a market-based model: The Salim Group

Crony capitalism, Oscillatory dynamics, Salim Group,