Marco Riva

Carbon Fiber Reinforced Smart Laminates with Embedded SMA Actuators—Part I: Embedding Techniques and Interface Analysis

Up to now one of the main limits for a large use of shape memory alloys (SMA)-based smart composite structures in the aerospace industry is the lack of useful numerical tools for design. Moreover, technological aspects still need a more detailed investigation. This paper shows how to overcome issues regarding embedding of NiTiNOL wires in carbon fibre/epoxy laminates. A crucial aspect of those structures is related to the load transfer capabilities between the SMA actuators and the host material during their activation. Embedding techniques developed for taking into account problems like thermal and electrical compatibility between actuators and host material and passive/active invasivity are reported in this paper. Simple smart laminates with several actuators were manufactured, tested, and deeply analyzed. In order to characterize the interface in the real operative conditions, pull-out tests were conducted on NiTiNOL wires embedded in composite fiber laminates. The results were compared to standard experiments on wires embedded in pure epoxy resin blocks.

Carbon Fiber-Reinforced Smart Laminates with Embedded SMA Actuators—Part II: Numerical Models and Empirical Correlations

Up to now one of the main limitations for a large use of shape memory alloys (SMA)-based smart composite structures in the aerospace industry is the lack of useful numerical tools for design; in addition, some technological aspects still need a more detailed investigation. This article shows numerical modeling approaches adopted for the implementation of SMA constitutive laws in commercial codes such as ABAQUS. Two different approaches were selected. The first one is based on the thermomechanical model proposed by Turner and the other one follows the thermodynamic macromechanical constitutive law developed by Lagoudas. The implementation in ABAQUS code was followed by a procedure to evaluate model parameters and to experimentally validate the reliability of code predictions for specifically designed test situations. This article presents the test campaign carried out for the definition of these parameters and the numerical-experimental correlation for both the models.

Path to the stars: the evolution of the species in the hunting to the GRBs

During the last years, a number of telescopes and instruments have been dedicated to the follow-up of GRBs: recent studies of the prompt emission (see for instance GRB080319B) and of their afterglows, evidenced a series of phenomena that do not fit very well within the standard fireball model. In those cases, optical observations were fundamental to distinguish among different emission mechanisms and models. In particular, simultaneous observation in various optical filters became essential to understand the physics, and we discovered the need to have a detailed high time resolution follow up. Finally, recent observations of the polarization in GRB 090102 clearly indicate the presence of an ordered magnetic field favoring the electromagnetic outflows models. This is, however, only one case and, in order to detail properly the model, we need a bit of statistics. But, after the Swift launch, the average observed intensity of GRB afterglows showed to be lower than thought before. Robotic telescopes, as demonstrated by REM, ROTSE, TAROT, etc. (but see also the GROND set up) is clearly the winning strategy. Indeed, as we will also briefly discuss later on, the understanding of the prompt emission mechanism depends on the observations covering the first few hundreds seconds since the beginning of the event with high temporal resolution. To tackle these problems and track down a realistic model, we started the conceptual design and phase A study of a 4 meter class, fast-pointing telescope (40 sec on target), equipped with multichannel imagers, from Visible to Near Infrared (Codevisir/Pathos). In the study we explored all the different parts of the project, from the telescope to the instrumental suite to data managing and analysis, to the dome and site issue. Contacts with industry have been fruitful in understanding the actual feasibility of building such a complex machine and no show stoppers have been identified, even if some critical points should be better addressed in the Phase B study. In this paper, we present the main results of the feasibility study we performed.

Shape Memory Composite Deformable Mirrors

This paper deals with some of the critical aspects regarding Shape Memory Composite (SMC) design: firstly some technological aspects concerning embedding technique and their efficiency secondarily the lack of useful numerical tools for this peculiar design. It has been taken into account as a possible application a deformable panel which is devoted to act as a substrate for a deformable mirror. The activity has been mainly focused to the study of embedding technologies, activation and authority. In detail it will be presented the how to manufacturing of some smart panels with embedded NiTiNol wires in order to show the technology developed for SMC structures. The first part of the work compares non conventional pull-out tests on wires embedded in composites laminates (real condition of application), with standard pull-out in pure epoxy resin blocks. Considering the numerical approach some different modeling techniques to be implemented in commercial codes (ABAQUS) have been investigated. The Turners thermo-mechanical model has been adopted for the modeling of the benchmark: A spherical panel devoted to work as an active substrate for a Carbon Fiber Reinforced Plastic (CFRP) deformable mirror has been considered as a significant technological demonstrator and possible future application (f=240mm, r.o.c.=1996mm).