Strain-life fatigue predictions for sintered steels with nonzero mean stress

Several approximate models have been utilized for fatigue life prediction. Some of these models are available for mean stress (or strain) correction on fatigue life, when nonzero mean stress (or strain) is applied. In this paper, the most commonly used empirical strain-life models for fatigue life predictions, for materials subjected to variable amplitude loads, are described. Experimental results of fatigue tests, where the specimens of sintered steels were subjected to partial random loads, are presented and compared with those results obtained theoretically by the models. The utilization of the various models and their influence on results are discussed.     

The Multimode Resource‐Constrained Project Scheduling Problem for Repetitive Activities in Construction Projects

In construction projects, resource availability might limit the implementation of ideal schedules. Especially, when repetitive activities are involved, traditional resource‐constrained project scheduling problem (RCPSP) models fail to allocate the resource consumption in an efficient manner. Besides, actual models only provide local optimal solutions and do not incorporate activity acceleration routines. To fulfill this gap, partially, a mathematical optimization model, the multimode RCPSP for repetitive activities in construction projects, is proposed and solved to optimality; it takes into account acceleration routines under real construction scenarios using spreadsheets. The article shows a complete computational experimentation over a real construction project, considering several scenarios of resource availabilities and continuity conditions. The model allows analyzing the resources efficiency indexes comparing them to resource consumptions, continuity of activities, and objective functions that reveal that fragmented activities do not provide better resource efficiency outcomes.     

Study of the transient response of microcompensated amorphoussilicon detector in the near infrared range

A detailed investigation of the near infrared detection process of an hydrogenated amorphous silicon sensor is presented. Single junction devices with micro-compensated absorber layer show photocurrent response to radiation up to 2 μm at room temperature. This sensitivity is ascribed to both the high number of trap states existing in the absorber material and to the electric field distribution in the device. Results of transient and frequency responses under different bias voltage and illumination conditions confirm the existence of a conduction mechanism controlled by traps. In particular, the exponential increase of the signal current with forward applied voltage suggests the re-excitation of the injected carriers from shallow localized states into extended states. Finally, a preliminary optimization of the response of the device achieved by including it in a front-end circuit allows detection of modulated radiation up to 100 kHz