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We have developed a new digital image correlation (DIC) algorithm for non-contact, two-dimensional, whole-field displacement and strain measurement. Relative to existing algorithms, our algorithm substantially reduces the calculation expense by using neighborhood information while processing the data to determine the displacement field in a sub-region of interest. The new algorithm also uses higher-order interpolations of the displacement field, allowing for better accuracy in estimating strain distributions when the deformation field is non-homogeneous. Numerically-generated digital images are used to show that the new algorithm accurately reproduces the imposed displacement fields. The algorithm is also tested on actual images from deformed specimens from a variety of experiments, and shown to perform satisfactorily. / Singapore-MIT Alliance (SMA)

The measurement of strain is critical in many engineering design, test, and health monitoring procedures. Despite the promise of non-contacting and remote strain measurement, optical techniques have not been widely adopted by industry; the preference being the use of electrical resistance strain gauges. This is due to the perceived and real complexities of many optical techniques.

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Strain detecting with carbon nanotube (CNT) networks is one of the encouraging findings in sensor technologies. Two types of CNT based films are available for strain detection, namely CNT composite films and CNT films. Configurations of the CNT networks in these films can be made into random and aligned distributions. Understanding of fundamental knowledge regarding piezoresistive response in CNT networks in particular of the CNT film is not quite available, and this is the motivation of the present thesis. In this thesis, piezoresistive response of CNT networks under in-plane straining was studies in details first. Based on the stick percolation model, the relation between the density and conductance in CNT networks (with randomly distributed) was established and then the models which describe the relation between the density and piezoresistive sensitivity and the relation between density and piezoresistive linearity, respectively, were developed. After that, fabrication of CNT networks with aligned distributions was studied. Likewise, the models as developed for CNT network with random distributions were developed for ones with aligned distributions. Finally, modeling of the stress transfer between the nanotubes and polymer matrix was studied. This study has led to the following conclusions: (1) piezoresistive response in CNT networks of the CNT film follows the stick percolation model with the critical exponent coefficient (α) in the model being 1.938; (2) it is feasible to fabricate aligned CNT networks of varying densities with the technique which combines the spray deposition and externally applied magnetic field; (3) the configuration of CNT networks, in addition to their density, was a primary factor governing their piezoresistive response; (4) slipping occurs at the interface between the nanotube and polymer matrix when the films are subject to in-plane straining. The contributions of this study are: (1) the knowledge along with a percolation model for piezoresistive response of CNT networks of the CNT film, (2) a fabrication technique to align CNT networks of the CNT film, and (3) the knowledge along with a model for interaction between the CNT and polymer substrate in the CNT film.

Since the development of knockout and transgenic mouse models, mice have become the most widely used mammalian animal model to study bone. Despite the advances in knowledge of bone biology and function that have occurred from use of mouse models, many studies use primarily qualitative techniques, which may result in overlooking important subtle pathophysiologic changes. The hypothesis of this dissertation is that quantitative techniques to measure bone structure and function could identify the physiologic role of carbonic anhydrase II and calbindin-D28k in mouse bone, despite earlier qualitative studies indicating mice without these proteins have normal bone structure and function. Furthermore, a method to quantify bone function in vivo will be tested in a mouse model.Although carbonic anhydrase II deficient mice are less severely affected than patients, the mice demonstrate features of osteopetrosis including metaphyseal widening and a 50% increase in trabecular bone volume. The mice partially compensate for inhibited osteoclast function by increasing osteoclast number.Calbindin-D28k knockout mice demonstrated an increase in bone volume that results from additional bone at the endosteal surfaces. The higher bone volume results in increased stiffness and failure loads, highlighting the potential use of drugs that inhibit calbindin-D28k to treat diseases such as osteoporosis.Finally, calcium phosphate ceramic and hydroxyapatite particles used as strain gauge coatings demonstrated bone bonding to mouse femora after two months in vivo. The use of hydroxyapatite particles to coat strain gauges is the first time this method has been used with all commercially available materials, and will allow other research groups to use this technique. The major limitation to in vivo bone strain measurement in mice is the relatively large size of the sensors, which resulted in increased second moments of inertia in the implanted bones.Overall, this dissertation demonstrates that the use of quantitative techniques, including histology, histomorphometry, µCT imaging, and mechanical testing can measure subtle changes in bone properties that have been previously overlooked. Development of additional quantitative methods to study bone biomechanics in mouse models may encourage other research groups to quantify bone properties if no changes are noted using primarily qualitative methods.

This thesis examines the feasibility of combining Digital Image Correlation (DIC) with laser speckle based methods to form a new hybrid deformation measurement method called Digital Laser Speckle Image Correlation (DilSIC). Consequently, this method does not require any sample preparation and allows for the measurement of displacement of micro structures in addition to large displacements. In this technique, a coherent 30mW-632nm laser beam is expanded with 40X lens and then illuminated on the target surface to produce a fine, homogenous laser speckle pattern. Images were captured before and after deformation due to external load and the whole field displacement and strain were determined by the DIC method. This technique could measure displacement less than 30-μm with high accuracy when a 120mm × 80mm area of the surface was inspected. Up to 10% strain was measured by this technique with high accuracy during the whole range. Eventually the sub-surface crack was located successfully, which is a revolutionary achievement in NDT optical methods. This method was tested in different material, with different roughness. Aluminum sheet and rubber material were used mostly. This method could broaden the capability of displacement measurement and subsurface crack detection in wide range of materials.

Structural health monitoring (SHM) is an emerging field in civil engineering in recent years. The main objectives of the SHM are to identify structural integrity issues at early stage and improve the structural safety through measuring and analyzing structural behaviors. Sensing systems for SHM can be used to identify applied vehicle loads for bridge structures. Bridge weigh-in-motion (BWIM) is one type of such vehicle load identification. As a tool to monitor the vehicle weight moving on the bridges, BWIM uses the structural responses induced by moving vehicle on the bridge to back-calculate vehicle information. In this thesis, optimized BWIM systems using multimetric measurements will be investigated. In Chapter 1, the concept and background of BWIM systems will be introduced. The objective of this research will be also demonstrated in this chapter. Chapter 2 is the literature review section. In Chapter 3, the finite element bridge model adopted for this study will be described. In this section, the moving-load time history analysis, sectional properties for bridge members, and other structural parameters of bridge model will be introduced. The methodology of BWIM systems used in this study will be demonstrated in Chapter 4. In Chapter 5, optimized sensor locations for BWIM using normal and shear strain measurements and acceleration measurement will be discussed for the case without measurement noise. In Chapter 6, sensor location optimization for the case considering measurement noises will be investigated. A new acceleration-based BWIM method is proposed in this section. Non-drift displacement reconstruction technique using acceleration measurement and FIR filtering is applied for BWIM. Finally, Chapter 7 is the conclusion part of this thesis.

[Truncated abstract] Characterising the behaviour of calcareous sediments that possess some degree of bonding between their constituents has attracted worldwide research interest in recent years. Although many recent studies have made significant contributions in delineating the behaviour of these sediments, there is still paucity of information particularly on the cyclic behaviour of cemented calcareous soils. This thesis describes in detail the characteristic features of cemented calcareous soils and proposes methods for characterising their cyclic behaviour. Two different calcareous soils Goodwyn (GW) and Ledge Point (LP) soils representing extreme depositional environments were examined in this study. Artificially cemented sample were created using the CIPS (Calcite Insitu Precipitation Systems) technique, considering its superiority over other most commonly available cementation techniques in replicating the natural pattern of cementation, and the behaviour of natural calcarenite under monotonic loading conditions. The experimental program involved triaxial testing of both uncemented and calcite-cemented calcareous soils under different loading conditions, i.e. isotropic compression tests to high-pressure (16 MPa), monotonic shearing tests, undrained cyclic shearing tests and undrained monotonic post-cyclic shearing tests. Significant emphasis has been placed on the cyclic behaviour of these soils. Internal submersible LDVTs were used for the accurate and continuous measurement of strain down to about 10-5