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In this article, we propose an approach suitable for modeling isothermal fatigue in amorphous polymers. The theory is formulated in a rate form within continuum mechanics framework without the need to measure damage changes per loading cycles. Using the approach, contribution of ratcheting to fatigue of polycarbonate (PC) was investigated and the results were compared to previous experimental observations. When subjected to uniaxial stress-controlled cyclic loadings, ratcheting deformation apparently occurs and increases with mean stress and amplitude. The development of ratcheting deformation shows an initial growth followed by a decrease to almost a constant growth rate which occupies majority of the total lifetime. Ratcheting behavior under multiaxial stress states was also investigated based on finite element analyses of a dogboneshaped test specimen. The results show that fatigue damage develops at the sites following closely the localized plastic deformation and increases with ratcheting deformation during cyclic loadings. The results indicate that the ratcheting behavior can be exploited in the evaluation of the entire fatigue lifetime.

Business process reengineering (BPR) is following a typical maturity cycle as a business fad. Some of the more radical and flashy elements are omitted as the basic principles integrate into common sense and business and engineering school curricula. The ways of evaluating benefits become more precise. This is illustrated by three case studies, in which the benefits are classified into customer perceived value, cost savings and business option value. The latter is not a direct consequence of an implemented reengineering project, but a set of new abilities that an organization must exercise separately as a part of a strategy process. This provides a conceptual link between reengineering and some of its critics arguing for a more proactive approach to value creation. The lasting contribution of the reengineering movement is the insistence on using both technology and organizational change together.

An approach suitable for modeling viscoelastic-viscoplastic response with isothermal fatigue damage in amorphous solids is proposed. The theory explicitly accounts for frame-indifference and dependence of the free energy on both the viscoelastic-viscoplastic deformation and fatigue damage in a thermodynamically consistent manner. The damage evolution per se is formulated by utilizing an endurance surface that shifts in an effective stress space independent on damage. The idea is suitable for solids in which the fatigue behavior is ductile, i.e. localized damage during the creation of micro-cracks governs majority (up to 95%) of the total fatigue life. Based on implicit numerical integration, the solution procedure is presented, and the capability for technologically important polycarbonate (PC) polymer is addressed. To simulate the fatigue in real specimens, the approach is implemented in a finite-element program. The results show that fatigue life can be predicted using a single point at which fatigue most intensively initiates. A microscopic, rectangular region representing a RVE of the specimen is also investigated. Simulations, in accordance with the model assumption, indicate that damage develops in small zones around involved inhomogeneities while majority of the material remains undamaged.