L.C.S. Nunes

Simultaneous measurement of temperature and pressure using single fiber Bragg grating and fixed filter demodulation technique

Fiber Bragg grating (FBG) sensors offer many advantages for monitoring strain and temperature, other physical parameters can be measured through the use of mechanical transducers. However, FBGs are sensitive to strain and temperature and, in many cases, it is difficult to discrminate both measurements. To overcome this problem several techniques have been proposed, most of them employing more than one grating. This work demonstrates the possibility to discriminate temperature and pressure measurements using only one FBG sensor and a low cost demodulation technique based on two fixed filters. A pressure transducer has been used to transfer a lateral force to the fiber, proportional to the applied pressure, generating birefringence in the Bragg grating. The system allowed to measure pressure in the range of 0 to 400 psi with uncertainty of 4 psi and, simultaneously, measure temperature in a range of 22°C with uncertainty of 0.1°C.

Experimental investigation of mixed-mode-I/II fracture in polymer mortars using digital image correlation method

The purpose of this work is to investigate experimentally the effects of mixed-mode I/II loading on the fracture behavior of polymer mortars. Three point bend beam specimens with offcenter notch were used in plane-strain fracture toughness tests. Two approaches have been simultaneously used to determine the crack opening displacements. The crack mouth opening displacement was measured by means of a clip gauge, while the crack tip opening displacement was estimated through the Digital Image Correlation method. Fracture parameters, such as critical values of crack opening displacement, energy release rate and mixed-mode stress intensity factor were estimated. In addition, the values of crack mouth opening displacement and crack tip opening displacement were used to evaluate the rotational factor. Finally, the effect of sliding mode-II in fracture was not easily observed using clip gage, however this effect was noticed employing Digital Image Correlation method.

Mechanical Characterization Using Optical Fiber Sensors of Polyester Polymer Concrete Made with Recycled Aggregates

The sustainable management of solid wastes encourages metallurgic and metal-mechanic industries to look for safety applications for their wastes, thereby attenuating the environmental impact or lowering the costs. The study herein proposes strain monitoring the recycling of foundry sand with organic pollutants, as inert, in the manufacturing process of polymer concrete using optical fiber sensors. This work also analyzes the compressive strength of polyester polymer concrete made with foundry waste, i.e., recycled foundry sand and polyester polymer concrete made with fresh sand. The foundry sands are contaminated with Sodium Silicate from the mould-making process. Polymer Concrete (PC) is a composite material in which the binder consists entirely of a synthetic organic polymer. Optical fiber sensors present a great deal of potential in monitoring the structural health condition of materials. Experimental results show that the use of the embedded FBG sensor can accurately measure strain, providing information to the operator that the structure is subjected to failure. Multiplexed FBG strain sensors enable measuring strain in different locations by occupying only one tiny optical fiber.

Shear strain determination of the polymer polydimethysiloxane (PMDS) using digital image correlation in different temperatures

In the present work a digital image correlation (DIC) method is used in order to analyze the adhesive shear modulus of poly-dimethylsiloxane (PDMS) submitted to different loads and temperatures. This is an optical-numerical full-field surface displacement measurement method. It is based on a comparison between two images of a specimen coated by a random speckled pattern in the undeformed and in the deformed states. A single lap joint testing is performed. This is a standard test specimen for characterizing adhesive properties and it is considered the simplest form of adhesive joints. For the single lap joint specimen, steel adherends are bonded using a flexible rubber elastic polymer (PDMS), which is a commercially available silicone elastic rubber

LOAD RATE EFFECTS IN ADHESIVE SINGLE LAP JOINTS BONDED WITH EPOXY/CERAMIC COMPOSITES

THE PRESENT PAPER IS CONCERNED WITH THE ANALYSIS OF THE EFFECT OF THE LOADING RATE IN A PARTICULAR CLASS OF SINGLE LAP JOINTS USED IN THE OIL INDUSTRY. THE ADHESIVE/ADHEREND SYSTEM CONSISTS OF ASTM A36 STEEL PLATES BONDED WITH AN EPOXY/CERAMIC COMPOSITE. THE LOADING RATE SENSITIVITY IS ANALYSED CONSIDERING TWO DIFFERENT SITUATIONS: (I) STRAIN CONTROLLED QUASI-STATIC RUPTURE TESTS AND (II) APPLICATIONS IN WHICH THE JOINT MAY OSCILLATE LIKE A SPRING. THIS SECOND SITUATION IS MOTIVATED BY A SPECIFIC APPLICATION: THE TRANSPORT OF AN ETHANOL RESERVOIR BY A CRANE USING A SPECIAL TRUSS LIFTING SYSTEM ATTACHED TO THE TANK THROUGH BONDED JOINTS. QUASI-STATIC TENSILE TESTS ALLOW OBSERVING A RATE-DEPENDENT BEHAVIOUR OF THE JOINT WITH HIGHER STRENGTHS FOR HIGHER CROSS-HEAD VELOCITIES. AN ALGEBRAIC EQUATION IS PROPOSED TO PREDICT THE DEPENDENCE OF THE RUPTURE FORCE ON THE ELONGATION RATE IN TENSILE TESTS AND THE MODEL PREDICTIONS ARE IN GOOD AGREEMENT WITH EXPERIMENTAL RESULTS. HOWEVER, IN THE CASE OF THE TRANSPORT OF A TANK WITH MASS M (SITUATION (II)), THE LIFTING SYSTEM CANNOT BE ONLY DESIGNED TO RESIST THE STATIC LOAD (THE WEIGHT). FAST LOADING MAY INDUCE VIBRATION. LIKE IN A SPRING-MASS SYSTEM, EVEN A VERY SMALL OSCILLATION OF THE JOINT INDUCES A DYNAMIC LOAD THAT IS HIGHER THAN THE STATIC LOAD. A SIMPLE ANALYSIS ALLOWS PROPOSING CONDITIONS FOR A SAFE OPERATION IN THIS CASE.

Digital holographic interferometry applied to mixed-mode fracture analysis

In the present work digital holographic interferograms obtained by digital Fourier transform holography are used to analyze fracture propagation. Digital holography is a non-contact optical technique that consists in recording digitally a hologram with a CCD sensor as holographic media. The image reconstruction of the object is obtained numerically. Holographic interferograms are obtained by superposition of two holograms of object, being the first one in its initial state and the second one after some modification produced in this object. Basically, the main purpose is to use interferograms for investigating mixed-mode I/II fracture. Tests on cracked specimen under combined loading are performed.

Thermal Conductivity Augmentation in Polymeric Nanocomposites

This paper presents an experimental analysis of the thermal conductivity of a nanocomposite system composed of a unsaturated polyester resin as matrix and alumina nanoparticles as filler. The nano particles used are 30–40 nanometers gamma alumina particles. Samples are fabricated using simple molding and no specialized homogenization equipment is used for mixing the particles with the liquid resin. The thermal conductivity is measured using the Fox-50 device, manufactured by LaserComp. Measurements are taken at different temperatures (from 0° to 50°C) for different batches of samples varying the fraction of nanoparticles used in the composite system. Finally, the thermal conductivity measurements are compared with models for predicting the thermal conductivity of composite materials with nanoparticles, showing that the obtained results are over the values estimated by these models.Copyright

Identification of material properties using full-field and non contact measurements

In the present work, the Digital Image Correlation (DIC) measurement method is used to obtain the displacement field of specific regions of a cantilever beam under bending. These fields are used within an inverse analysis scheme in order to obtain the elasticity modulus of the beam material. The parameter estimation is performed by means of the minimization of an error function comprising of the difference between the displacement fields obtained from the experiment and from an appropriate mathematical model. The inverse problem is solved by means of the classical Levenberg-Marquardt nonlinear parameter estimation technique. The estimate obtained for the elasticity modulus is validated taking into account new experimental data obtained through modal analysis of another beam-like specimen which, in turn, is made of the same material as the original one.

Analysis of cantilever beam test using digital holography

In the present work an interferometric approach based on the implementation of a digital holography setup is discussed. It is used to determine interferograms of materials under small deformations. In order to do this, a fixed-free cantilever beam subjected to a concentrated force applied at the free end is taken into account. The experimental procedure to estimate displacements is carried out using digital Fourier transform holography (DFTH) technique. This is obtained making a very simple modification in the classical setup architecture of the DFTH setup. It is also demonstrated the easy and practical viability of the setup in an interferometric application for mechanical parameters determination.

Bragg wavelength deviation for TDM/WDM multiplexing systems

An analysis of the Bragg wavelength deviation generated by TDM/WDM multiplexing of large number of fiber Bragg grating (FBG) sensors has been proposed. Demodulation technique based on Fixed Spectrum Filters is compared with peak position of full wavelength spectrum. Results indicate that the fixed filter approach is less sensitive to wavelength distortion due to shadow of other sensors operating at the same nominal wavelength, allowing much larger number of FBG sensors. A simulated result show less than 1 pm deviation with up to 100 sensors at same wavelength, with 1% peak reflectivity for each sensor.