Proc. SPIE. 10168, Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2017
KEYWORDS: Optical fibers, Modeling, Aerospace engineering, Fiber Bragg gratings, Sensors, Composites, Structural health monitoring, Finite element methods, System identification, Optical networks, Chemical elements, Systems modeling
Technologies based on optical fibers provide the possibility of installing relatively dense networks of sensors that can perform effective strain sensing functions during the operational life of structures. A contemporary trend is the increasing adoption of composite materials in aerospace constructions, which leads to structural architectures made of large monolithic elements. The paper is aimed at showing the feasibility of a detailed reconstruction of the strain field in a composite spar, which is based on the development of reference finite element models and the identification of load modes, consisting of a parameterized set of forces. The procedure is described and assessed in ideal conditions. Thereafter, a surrogate model is used to obtain realistic representation of the data acquired by the strain sensing system, so that the developed procedure is evaluated considering local effects due to the introduction of loads, significant modelling discrepancy in the development of the reference model and the presence of measurement noise. Results show that the method can obtain a robust and quite detailed reconstruction of strain fields, even at the level of local distributions, of the internal forces in the spars and of the displacements, by identifying an equivalent set of load parameters. Finally, the trade-off between the number of sensor and the accuracy, and the optimal position of the sensors for a given maximum number of sensors is evaluated by performing a multi-objective optimization, thus showing that even a relative dense network of externally applied sensors can be used to achieve good quality results.
The manufacturing and the preliminary numerical and experimental testing results of a fiber optic based sensor, able to recognize different load paths, are herein presented. This device is conceived to identify load directions by strain detection along a circumferential geometry. A demonstrator is realized by manufacturing a circular shaped, flexible glass/epoxy laminate hosting the sensible elements. Three loops of optical fiber, laying at different quotes along its thickness, are there integrated. The sensor system is supposed to be bonded on the structural element and then able to follow its deformations under load. The working principle is based on the comparison of the strain paths detected at each fiber optic loop at homologous positions. Rayleigh backscattering optical technology is implemented to measure high spatial resolution strains. A finite element model is used to simulate the sensor behavior and assess its optimal configuration. A preliminary experimental campaign and a numerical correlation are performed to evaluate sensor performance considering in-plane and bending loads.
In the search for new deposits petrochemical extraction Companies are searching in challenging environments as deep
sea-beds. At the same time, especially following the Gulf of Mexico disaster, there is a justified concern about the
assessment of the installed asset condition. The Aerospace Engineering Department of the Politecnico di Milano and
Prysmian Group R&D Department are currently carrying over a joint research project aiming to the development of new
methods for the testing and evaluation of health status and conditions to be applied in the field of deep sub-sea umbilical
normally employed for the petrochemical hydrocarbon extraction. The monitoring methods and the measurement system
under joint development will enable Prysmian to validate vs. full scale measurement the design analytical tools currently
utilized to analyze the developed elements versus the operational scenarios for which any particular umbilical is
currently designed. Additionally, together with the Politecnico di Milano, Prysmian will develop a real-time
measurement system to be utilized, during operational lifetime, for the asset management of the produced sub-sea
Deformable mirrors actuated by smart structures are promising devices for next generation astronomical instrumentation.
Thermal activated Shape Memory Alloys are materials able to recover their original shape, after an
external deformation, if heated above a characteristic temperature. If the recovery of the shape is completely
or partially prevented by the presence of constraints, the material can generate recovery stress. Thanks to this
feature, these materials can be positively exploited in Smart Structures if properly embedded into host materials.
This paper will show the technological processes developed for an efficient use of SMA-based actuators embedded
in smart structures tailored to astronomical instrumentation. In particular the analysis of the interface with the
host material. Some possible modeling approaches to the actuators behavior will be addressed taking into account
trade-offs between detailed analysis and overall performance prediction as a function of the computational
time. We developed a combined Finite Element and Raytracing analysis devoted to a parametric performance
predictions of a SMA based substrate applicable to deformable mirrors. We took in detail into account the possibility
to change the focal length of the mirror keeping a satisfactory image quality. Finally a possible approach
with some preliminary results for an efficient control system for the strongly non-linear SMA actuators will be
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 Turner's 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).