Except for aerodynamics forces, all vehicle excitation forces are generated at the tyre-road interface. Considering low speed applications, such as terramechanics where the aerodynamics force are negligible, the road-tyre interaction is of extreme importance. Crucial variables which govern the forces generated at the tyre-road interface are tyre side-slip angle, tyre longitudinal slip ratio and terrain pro le. Solutions to measure these variables exist for smooth hard roads but the solutions experience challenges on rough and o -road terrain. Digital Image Correlation is concerned with tracking the changes of a scene in a sequence of images or in images obtained from multiple viewpoints. These methods are frequently used in micro and nano-scale mechanical testing due to its ease of implementation and use as well as its non-contact approach. As a result these techniques are being implemented in many elds from material testing, physics, lm animations and engineering. The aim of this thesis is to investigate the applications of Digital Image Correlation in vehicle dynamics using cost e cient o -the-shelf digital cameras and lenses. The following three vehicle dynamic problems are investigated: The measurement of the vehicle side-slip angle, longitudinal slip-ratio of a pneumatic tyre and high delity terrain pro ling. The vehicle side-slip angle can be used as a measure of the vehicle stability and therefore be used to improve the e ectiveness of vehicle stability controllers. The tyre side-slip angle is also a vital measurement in characterising the lateral force characteristics of pneumatic tyres. A planar measuring method using Digital Image Correlation is shown to accurately measure the side-slip angle. The method is expanded by developing two additional algorithms which can measure all translational and rotational velocities. These methods are validated on both smooth surfaces and rough o -road terrain. A method is also implemented whereby the longitudinal slip ratio of a tyre can be measured using a single camera. Therefore, doing away with the conventional method of using three independent measurement systems. Features in the contact patch, encompassing both the tyre and the road, are tracked in a sequence of images. The features are classi ed into features lying on the tyre, road and outliers using a clustering algorithm. This enables the system to determine the tyre and road velocities from which the slip ratio is determined. High delity terrain pro ling is performed using a calibrated stereographic rig to obtain a three dimensional point cloud of the scene which is being viewed. The point cloud generated at one sample contains a grid of points encompassing a large area with points spaced both laterally and longitudinally. Overlapping point clouds are generated and joined using various registration techniques. The joined point clouds are sub-sampled to obtain a regularised grid of point containing a single point cloud of non overlapping points. The proposed techniques create new possibilities in the eld of vehicle dynamics. Enabling the side-slip angle to be measured in rough of road conditions while providing additional measurements. The longitudinal slip ratio which is measured directly at the contact patch could pave the way for better understanding the mechanism of the longitudinal tyre force generation. The inexpensive road pro ling systems enables multiple sensors to be used in terramechanics tests to determine the impact of a vehicle on the environment. The thesis presents the mere tip of the ice berg concerning digital image correlation used in vehicle dynamics with many more possibilities waiting to be discovered. / Thesis (PhD)--University of Pretoria, 2015. / tm2015 / Mechanical and Aeronautical Engineering / PhD / Unrestricted

As traffic loads increase and bridges age the need for structural health monitoring is growing. With the digitalization of our society, new non-contact full-field measurement techniques have been developed. These techniques have the potential to be used in monitoring of existing bridges. Today visual inspections are carried out every sixth year. These only give a rough estimate of the structure's health and only provide information about the surface of the structure. In addition to these inspections, traditional sensors like linear variable differential transformers and strain gauges are used to measure parameters such as displacement and strain. For existing bridges in reinforced concrete it is especially important to monitor reinforcement strains, as high strains could be indicative of overloading of the structure or even that a failure is about to occur. The methods available to measure reinforcement strain in existing bridges today are not very effective and have some limitations. The aim of this thesis is thus to evaluate the possibility to predict reinforcement strain based on surface strain measurements obtained by a non-contact full-field optical measurement system. In this study the software ARAMIS was used to measure surface strains, and traditional strain gauges were used to measure reinforcement strain. Strain distribution were evaluated at the initiation of cracks, during sections of cyclic loading and at a load close to the yielding point of the reinforcement. A correlation factor between the strain registered in the software and the strain obtained from the strain gauges was introduced. Based on the results in this study it is not possible to predict exact reinforcement strain based on surface measurements. Digital image correlation does however show potential to be used as a non-contact full-field measurement technique for in-situ measurements. Before this is reality there is still a need for further research in this area.

This thesis investigates the appropriateness of a simplified, open-source digital image correlation (DIC) software for use in quasi-static, structural testing utilizing two-dimensional (2D) DIC measurements. DIC is a non-contact optical measurement technique that uses computer vision to track unique attributes on the surface of an object. For structural testing, traditional instrumentation such as displacement sensors and strain gages are impractical for full field measurements due their limited ability to capture large amounts of data. However, over the past decade, DIC has proven a successful method for full-field kinematics measurements, making it an appealing tool for collecting high densities of accurate data. This thesis specifically studies the accuracy and limitations of the DIC software, MODEM, for various test specimens and loading conditions. This research work is part of an experimental program comprised of three phases. The first stage was conducted by another investigator on aluminum coupons tested in pure tension. These results were used to calibrate parameters (speckle pattern density, lighting, and camera settings) used with the DIC software. The second stage included pure compression tests on concrete cubes and concrete cylinders to compare the difference in results between: (i) surface curvature, (ii) camera distance, (iii) surface treatment, and (iv) speckle pattern color. The final stage involved analysis of a tension test of a concrete prism completed at the University of Auckland in an effort to assess how MODEM could be utilized to accurately detect onset and propagation of concrete cracking. Results showed the most accurate DIC strains were within 5% error when compared to traditional instrumentation for aluminum loaded in tension and within 6% error for concrete loaded in compression/tension. This level of accuracy is comparable to existing open source and commercial DIC software utilizing 2D DIC analysis. Therefore, MODEM can be used to provide accurate 2D DIC strain measurements for small and medium scale structural test specimens when using the following parameters: (i) the surface of the specimen is planar, (ii) the camera is placed accordingly so the maximum amount of zoom can be used, (iii) the surface of a test specimen is free of debris or imperfections, and (iv) a high contrast and evenly distributed speckle pattern is used. Computational analysis of the results showed that known material properties can be used to calibrate, or remove errors from, the DIC results when traditional instrumentation is not available. Additionally, results showed MODEM strain contours can be used for initial detection of cracks in concrete loaded in tension while MODEM tracking performance can be used to characterize the centerline and orientation of cracks. The experimental tests provide critical information on how to set up, run, and analyze DIC results when using MODEM. The full field measurements are of value in providing accurate data for structural testing to develop a better understanding of material response and structural performance, since large-scale tests are typically limited by a sparse number of data points when using traditional instrumentation.

Ultra-high performance concrete (UHPC) was evaluated as a potential material for future bridge deck designs. Material characterization tests took place to identify potential challenges in mixing, placing, and curing UHPC. Biaxial testing was performed to evaluate behavior of UHPC in combined tension and compression stress states. A UHPC bridge deck was designed to perform similarly to a conventional concrete bridge deck, and a single unit bridge deck section was tested to evaluate the design methods used for untreated UHPC. Material tests identified challenges with placing UHPC. A specified compressive strength was determined for structural design using untreated UHPC, which was identified as a cost-effective alternative to steam treated UHPC. UHPC was tested in biaxial tension-compression stress states. A biaxial test method was developed for UHPC to directly apply tension and compression. The influence of both curing method and fiber orientation were evaluated. The failure envelope developed for untreated UHPC with random fiber orientation was suggested as a conservative estimate for future analysis of UHPC. Digital image correlation was also evaluated as a means to estimate surface strains of UHPC, and recommendations are provided to improve consistency in future tests using DIC methods. A preliminary bridge deck design was completed for untreated UHPC and using established material models. Prestressing steel was used as primary reinforcement in the transverse direction. Preliminary testing was used to evaluate three different placement scenarios, and results showed that fiber settling was a potential placement problem resulting in reduced tensile strength. The UHPC bridge deck was redesigned to incorporate preliminary test results, and two single unit bridge deck sections were tested to evaluate the incorporated design methods for both upside down and right-side up placement techniques. Test results showed that the applied design methods would be conservative for either placement method. / Ph. D.

<p>In the last two decades, there has been significant improvements in pile design methods. These methods include variables that have been studied using laboratory and full-scale experiments. Refined understanding of the underlying mechanisms controlling pile response to loading enables introduction of variables in the design equations that reflect observations made in high-quality experimental data.</p><p>The mechanisms involved in the mobilization of the pile resistance (both base and shaft resistance) are studied in this thesis using a large-scale model pile testing facility consisting of a half-cylindrical calibration chamber with image analysis capabilities, instrumented model piles, and data and digital image acquisition systems. The thesis focuses on the effect of the pile surface roughness on the mobilization of tensile shaft resistance, the effect of the pile base geometry on the mobilization of base resistance, the analysis of possible mechanisms responsible for time-dependent increases in pile axial capacity, and particle crushing produced by pile installation. </p><p>A set of model pile tests were performed to study the effects of three different surface roughnesses on the shaft resistance of model piles jacked in the half-cylindrical calibration chamber. Digital images of the model piles and surrounding sand captured during tensile static loading were analyzed using the digital image correlation (DIC) technique. The base and shaft resistance measured for the instrumented model piles and the displacement and strain fields obtained with the DIC technique show that an increase in the roughness of the pile shaft results in an increase in the average unit shaft resistance and in the displacements and strains in the sand next to the shaft of the pile. Guidance is provided for consideration of pile shaft surface roughness in the calculation of the tensile limit unit shaft resistance of jacked piles in sand.</p><p>Base geometry effects were studied using jacked and pre-installed model piles with flat and conical bases tested in the DIC calibration chamber. The results show that the mobilized base resistance of a model pile with a conical tip was less than that of an equal pile with a flat base, all other things being equal, by a factor ranging from 0.64 to 0.84. The displacement and strain fields obtained with DIC also show that the slip pattern below the pile with a conical base differs from that of a pile with a flat base. </p><p>Finally, the degree of crushing of silica sand particles below the base of model piles jacked in sand samples is studied. The particle size distribution curves are obtained before and after pile installation. Relationships between the load mobilized at the base of the model piles and two well-known breakage parameters are proposed. This work also provides detailed measurements of the trajectories followed by crushed and uncrushed particles during pile installation, and characterizes the typical particle crushing modes produced by piles jacked in silica sand.</p><div><br></div>

This thesis deals with measurement of residual stress by hole drilling method. This method is based on drilling a hole and measurement of deformation in the area around this hole. Measured deformations are then converted to residual stresses by using calibration coefficients. The deformation around the drilled hole is measured by optical non contact method called digital image correlation (DIC). First part of the thesis is focused on current state of research. The thesis contains evaluation of residual stresses by using different methods and evaluation of used methods.

Digital Laser Speckle Image Correlation (DiLSIC) is a technique that utilizes a laser generated speckle pattern with Digital Image Correlation (DIC). This technology eliminates the need to apply an artifact speckle pattern to the surface of the material of interest, and produces a finer speckle pattern resulting in a more sensitive analysis. This investigation explores the parameters effecting laser speckle patterns for DIC and studies DiLSIC as a tool to measure surface strain and detect subsurface defects on pressure vessels. In this study a 632.8 nm 30 mW neon-helium laser generated the speckle pattern by passing through the objective end of an objective lens. All experiments took place in a lab setting on a high performance laminar flow stabilizer optical table.This investigation began with a deeper look at the camera settings that effect the effectiveness of using laser speckles with DIC. The first studies were concentrated on the aperture size (f-stop), shutter speed, and gain (ISO) of the camera. Through a series of zero-correlation studies, translation tests, and settings studies, it was discovered that, much like white light DIC, an increased gain allowed for more noise and less reliable measurements when using DiLSIC. It was shown that the aperture size and shutter speed will largely depend on the surface composition of the material, and that these factors should be investigated with each new sample of different surface finish.To determine the feasibility of using DiLSIC on pressure vessels two samples were acquired. The first was a standard ASTM filament wound composite pressure vessel (CPV) which had an upper load limit of 40 psi. The second was a plastic vessel that had internal subsurface defects added with the use of an air pencil grinder. Both vessels were put under a pressure load with the use of a modified air compressor that allowed for multiple loading cycles through the use of a pressure relief valve. The CPV was mapped out in 10-degree increments between the 90° and 180° markings that were on the pressure vessel, occurring in three areas, each one inch apart. The CPV had a pressure load applied to at 10, 20, 30,and 40 psi. DiLSIC was able to measure increasing displacement with increased loading on the surface of the CPV, however with a load limit of 40 psi no strains were detected. The plastic vessel had known subsurface defects, and these areas were the focus of the investigation. The plastic vessel was loaded with a pressure load at 5, 10, 12, 15, 17, and 20 psi. The 5 psi loaded image was used as a reference image for the correlation and decorrelation consistently occurred at 20 psi. This investigation proved that DiLSIC can detect and locate subsurface defects through strain measurement. The results were verified with traditional white light DIC, which also showed that the subsurface defects on pressure vessels were detectable. The DIC and DiLSIC results did not agree on maximum strain measurement, with the DiLSIC prediciting much larger strains than traditional DIC. This is due to the larger effect out-of-plane displacement has on DiLSIC. DiLSIC was able to detect subsurface defects on a pressure vessel. The median measured hoop strain was in agreement for DiLSIC, DIC and the predicted hoop strain for a wall thickness of 0.1 inches. However, DiLSIC also produced unreliable maximum strain measurements. This technique shows potential for future applications, but more investigations will be needed to implement it for industrial use. A full investigation into the parameters surrounding this technique, and the factors that contribute the most to added noise and unreliability should be conducted. This technology is being developed by multiple entities and shows promising results, and once further advanced could be a useful tool for rapid surface strain measurement and subsurface defect detection in nondestructive evaluation applications. Therefore, it is recommended to continue further investigations into this technology and its applications.

The complex interface between tyre and terrain is a largely studied topic in terramechanics and vehicle dynamics research. This interface, known as the contact patch, is however hidden from view and cannot easily be measured. Several studies have focused on measuring tyre strain on the inside surface of the tyre to indirectly determine tyre parameters. The inner surface is separated from the contact patch by the tyre thickness however this difference can be considered small in comparison to the bene t gained by a safe environment for measurement systems. Static studies of tyre strain have been successful however lacks the important phenomena occurring in a rolling tyre. Tyre strain measurements in dynamic tyres have been limited to discrete points and/or once per revolution, which is an insufficient sampling rate for vehicle stability controllers such as ABS. This study performs full-fi eld and point strain measurements of the inner tyre surface of a rolling agricultural tyre at low speeds. Stereo cameras mounted on a mechanically stabilised rim will record full-fi eld measurement of the contact patch kept in constant view. Digital Image Correlation techniques are used to determine full-fi eld deformation and strain from successively captured images. Point measurements, such as strain gauges, are included in the study for a comparative measurement. An agricultural tyre hosts large lugs which include large strain concentrations within the contact patch. The complex tyre structure signi ficantly influences the strain measurements, other factors such as inflation pressure, vertical load and slip angle is also studied. Since most vehicle forces are transmitted through the tyre at the tyre-terrain interface, capabilities to measure this area will be a great benefi t for tyre research and leading towards a smart tyre. / Dissertation (MEng (Mechanical Engineering))--University of Pretoria, 2020. / Mechanical and Aeronautical Engineering / MEng (Mechanical Engineering) / Unrestricted

The thesis aimed to identify fracture strain for multiaxial loading for laminate material of Al and LDPE that is mostly used in the food packing technology specially in liquid packaging industry. These materials are thin and flexible which make it difficult to handle and test it. The investigation was through applying new Nakajima test setup on such a material by designing a custom setup and 3D printing the Nakajima setup prototype to be able to use it in this study. DIC technique was used to get the results from the Nakajima test and the software used to apply the DIC technique is GOM correlate. As a validation for measurement from such a technique, a tensile test has been done and measured strains were compared with those from the specimen from the Nakajima that has smallest width as it was close to a uniaxial loading. One more validation technique was by creating a FE-model using (Abaqus software) for the biaxial loading and comparing it to the biaxial loading results that obtained from the DIC analysis.

Stamping dies are used in the Sheet Metal Forming (SMF) process for manufacturing of car body parts. The lead time for design and manufacturing of a stamping die is long, and therefore costly. In the final step of the manufacturing process, manual rework is performed to reach a desired pressure distribution on the forming surfaces in order to achieve a robust process and an approved part within tolerance. The main purpose for this work is to study and further develop a Virtual Rework Method that alters the shape of the forming surfaces of a die to compensate for the displacements of a stamping press that occur during stamping. Measurements were performed to obtain the displacements that occur in the stamping press during stamping. These measurements were performed on a double action deep drawing press of the brand Danly, located at Volvo Cars Tool &amp; Die department in Olofström, Sweden. The measurement yields information of how the stamping press is deflecting and deforming during operation. The measurements are recorded with a Digital Image Correlation (DIC) system that records the displacements of the press during stamping. The displacements obtained in the measurements are then used as constraints to inverse FE- model a press table with topology optimization. This optimized press table is used in the Virtual Rework Method to be able to simulate both the deformations of the press and the internal deformations that occur in the die. Pre-simulations were performed before the measurements to ensure that the blank holder plate used in the measurements would withstand the applied blank holder force. These simulations also yield if the displacements were large enough for the ARAMIS DIC system to capture. The FE-model used in this work consisted of a die, blank holder, blank holder plate, outer ram and the optimized press table. The Virtual Rework Method was applied on the FE-model, where the result concludes that the altered shape of the deformed forming surfaces is almost identical to the shape of the nominal forming surfaces. However, an inversed modelled structure that represents the behavior of the outer ram is required to apply the Virtual Rework Method on the blank holder. This inversed modelled structure could be created from the displacements obtained in the measurements. To apply the Virtual Rework method on the punch, further measurements are required, where the position of the ARAMIS DIC system is altered, or an additional ARAMIS DIC system is used. / Pressverktyg används i plåtformningsprocessen vid tillverkning av karossdelar. Ledtiden för konstruktion och tillverkning av ett pressverktyg är lång och därför kostsam. I det sista steget i tillverkningsprocessen utförs manuell bearbetning för att nå en önskad tryckfördelning på formningsytorna, vilket ger en robust process och en godkänd del inom toleranserna. Huvudsyftet med detta arbetet är att studera och vidareutveckla en virtuell fläckningsmetod som korrigerar formningsytorna på dynan för att kompensera för de förskjutningar som uppstår i en stämplingspress under stämpling. Mätningar har utfördes för att erhålla förskjutning som uppstår i en stämplingspress under stämpling. Dessa mätningar utfördes på en dubbelverkande djupdragningspress av märket Danly, som finns hos Volvo Cars Tool &amp; Die avdelning i Olofström, Sverige. Mätningen gav information om hur pressen deformeras under stämpling. Mätningarna registreras med ett Digital Image Correlation (DIC) system som registrerar pressens förskjutningar under stämpling. Förskjutningarna som erhållits i mätningarna användes sedan som randvillkor för en inversmodell för topologioptimering av ett pressbord. Detta optimerade pressbord används sedan i den Virtuella fläckningsmetoden för att kunna simulera både pressens stelkroppsrörelse och de interna deformationer som uppstår i pressverktyget. En förstudie utfördes innan mätningarna för att säkerställa att den plåthållarplattan som användes i mätningarna skulle motstå den applicerade plåthållarkraften. Denna förstudie gjordes även för att säkerhetsställa att förskjutningarna som uppstår i plåthållarplattan var stora nog för att ARAMIS DIC systemet skulle registrera dem. FE-modellerna som användes i detta arbete bestod av en dyna, plåthållare, plåthållarplatta, yttre slid och det optimerade pressbordet. Den Virtuella fläckningsmetoden applicerades på FE- modellen, där resultatet gav slutsatsen att den korrigerade formningsytan med applicerad belastning är nästintill identisk med formen på den nominella formningsytan. En inversmodellerad struktur som representerar beteendet hos den yttre sliden krävs emellertid för att tillämpa den Virtuella fläckningsmetoden på plåthållaren. Denna inversmodellerade struktur kunde erhållas från de förskjutning som erhölls i mätningarna. För att tillämpa den Virtuella fläckningsmetoden på stansen krävs ytterligare mätningar, där ARAMIS DIC systemets position ändras eller ett ytterligare ARAMIS DIC system används. / Reduced Lead Time through Advanced Die Structure Analysis - Vinnova