For the first time, an experimental investigation is presented quantifying out-of-plane wrinkle formation and in-plane deformations occurring in prepreg slit tape specimens during automated fiber ...placement (AFP). The AFP process is conducted on 6.35 mm wide individual prepreg tows that are placed along a straight path and steered along circular paths with radii of curvature, ρ = 2540 mm, 1270 mm and 305 mm. Full-field shape, displacement and strain measurements are obtained using StereoDIC in three successive stages; (i) immediately after lay-up of the tow, (ii) one hour after lay-up and (iii) after reheating of the as-placed tow by traversing the AFP head close to the tow path and exposing the specimen to the same levels of heating as employed during the initial lay-up (without compaction pressure). Measurements obtained in stage (i) showed that (a) all tows exhibited local wrinkling at locations where the underlying substrate had defects (e.g., gaps, overlaps), (b) excluding the substrate defect locations, tows steered with ρ = 2540 mm showed no evidence of additional out-of-plane wrinkling after placement, (c) tows steered with ρ = 1270 mm exhibited several small amplitude wrinkles initiated at locations outside the substrate overlap regions and (d) tows steered with ρ = 305 mm incurred significant additional localized wrinkling along the inner radius of the tow with an increase in both the amplitude and frequency of the wrinkles. In addition, higher variability in the wrinkle wavelength is observed for ρ = 305 mm. Measurements obtained in stages (ii) and (iii) showed an increase in wrinkle amplitude, indicating that wrinkle amplitude is a function of both time and temperature for an as-placed tow.
•Vision-based measurements of deformations and cracks are developed for RC specimens.•The method accurately estimates flexural, shear and sliding deformations of RC walls.•A program is developed for ...characterizing the pattern, width and angle of cracks.•Vision-based system achieves efficient measurements of complex crack fields.
This paper develops vision-based measurement methods for experimental tests of reinforced concrete (RC) structures. The methods can measure deformations and characterize cracks from images of RC specimens. The coordinates of objects of interest (OOIs) in the specimen are measured using a target tracking approach, and then deformation components (e.g., flexural, shear and sliding deformations) of the specimen are computed from the coordinates of OOIs through geometry analysis. The cracks are (i) identified using binary images converted from color images, (ii) and then quantified using the filter-based algorithm. The morphological operations, separation algorithm and connected component labeling algorithm are used in the image processing for crack measurements. The developed vision-based measurement methods were applied to cyclic tests of RC wall specimens. The accuracy of the vision-based measurements was validated by comparison with the results of traditional measurement techniques using the displacement transducers and crack scales. The proposed vision-based measurement methods demonstrate much higher efficiency and provide more useful information than the traditional measurement techniques. The paper also discusses a few application issues such as the specimen surface requirements and resolution of the vision-based measurements.
The aim of this study is to present an inverse thermomechanical methodology to identify thermal boundary conditions and the thermal expansion coefficient from experimental deformation measurements. ...By means of an analytical approach, we establish a thermoelastic mechanical transfer function between the temperature of a heated surface and the mechanical deformation of a solid at a given abscissa far from the surface. Subsequently, we measure this deformation at discrete time intervals using strain gauge and we apply a deconvolution product for those measurements to identify the temperature of the heated surface. By this way, it is no longer necessary to know the temperature field to solve the thermomechanical problem of our experimental device. We demonstrate that the inversion procedure can be applied successfully even in situations where the measured signal is affected by noise, through using the Tikhonov or a truncated singular value decomposition as regularization method. Lastly, the surface temperature identified from the deformation measurements is compared to a temperature measurement. The deformation and temperature measurements are used to estimate the thermal expansion coefficient.
•An inverse problem to identify temperature from deformation measurements.•Identification using analytical transfer function and convolution product.•Regularization is implemented by using two technics: truncated singular value decomposition and the Tikhonov penalization.
Interferometric synthetic aperture radar (InSAR) has been a valuable tool for mapping topography and subtle deformations. However, dealing with a wide imaging integral angle (IIA), especially for ...low-frequency band unmanned aerial vehicle (UAV) InSAR systems, introduces challenges. The conventional interferometric phase model depends on the difference in two slant ranges between the synthetic aperture centers and the target in two observations. Accuracy limitations emerge when variations are encountered in differences of slant range history across the entire wide IIA. This article explores the impact of IIA on interferometric measurements and proposes a modified interferometric phase model to address these limitations. For a wide IIA, the proposed model focuses on the integral of differences in slant range history throughout IIA by considering the nonlinear trajectory of the UAV platform. Additionally, measurement models for the IIA are deduced, in which an additional scale factor expanded by the Bessel function is introduced. Simulated and experimental datasets are utilized to demonstrate improvements in the accuracy of topography and deformation measurements. These results validate the effectiveness of the modified model in overcoming the challenges posed by wide IIAs in UAV InSAR systems.
The diffusion of electronics in everyday life requires for the development of sensing systems, based on new materials and technologies. Deformation sensors are of interest in many application fields, ...ranging from assisted rehabilitation, virtual reality and augmented reality, and gaming applications, juts to mention a few. The diffusion of low-cost sensing systems outlines the need for environmentally friendly and low-cost sensors. Cellulose is one of the most abundant materials on earth. Eventually, it is green, cheap, and flexible. In this article, the deformation sensing properties of a three-layer structure-based bacterial cellulose (BC) compound based on BC, impregnated by ionic liquids, and covered by conducting polymers are investigated. More specifically, it is shown that this novel composite is capable of sensing flexural deformations and producing a corresponding open-circuit voltage. The obtained results pave the road to the possibility of realizing a new class of deformation sensors that fit the requirements of more sustainable sensor technologies.
Although the ice phase greatly influences the properties of ice cream, other structural components also affect its rheological behavior, particularly after melting. In this study, mix viscosity ...(serum phase viscosity), extent of fat destabilization (FD), and overrun were manipulated to produce different microstructures. The effects of these structural components were evaluated on the rheological properties of the ice creams and melted ice creams. In oscillatory thermorheometry, mix viscosity and then overrun, influenced G’ and tanδ below −10 °C. When ice phase decreased (between −10 and −2.7 °C), mix viscosity had reduced effects, but continued to strongly affect G’ and tanδ, followed by FD, and with lower effects from overrun. When the ice phase was completely melted at 0 °C, FD had most influence on G’ and tanδ, followed by overrun, and with lower effects from mix viscosity. In creep/recovery test, six‐element model described well creep behavior of melted ice cream at 0 °C. Viscous behavior at lower shear rate (η0 0 °C) was most influenced by mix viscosity, followed by FD, and lower overrun effects. In stress growth measurement, transient behavior, represented by σY 0 °C, of melted matrix at 0 °C was most influenced by FD, followed by mix viscosity, with lower overrun effects. In flow ramp measurement, Hysteresis Area was most affected by mix viscosity, followed by overrun, and with lower FD effects. Moreover, correlation between Hyst 0 °C and tanδ Peak suggested that structure formation affected the magnitude of tanδ Peak. These results document the importance of microstructure on properties of melted ice cream.
Practical Application
The understanding of how structural components, such as mix viscosity, fat destabilization, and overrun, affect the ice cream matrix can help manufacturers to control its rheological behavior. The influence of these structural components on the G’, tanδ, η0 0 °C, σY 0 °C, and Hyst 0 °C can be also used to understand the structural rearrangements that occur in meltdown tests and sensory analyses for future studies. Therefore, elucidation of these mechanisms on the rheological properties can directly assist in quality control and new product development in the ice cream industry.
Continuous welded rail has become the standard in modern railway track construction around the world because it alleviates well-documented disadvantages of rail joints in a track. Continuous welded ...rail practice results in long segments of continuous rail in track that will develop significant thermal longitudinal stresses due to the absence of expansion joints. Before a continuous welded rail is laid, the rail is free of thermal stresses; the temperature at that time is known as the rail neutral temperature. The design rail neutral temperature is calculated based on local climate projections. As a continuous welded rail is laid, it may be stretched or compressed if the current temperature is not within the calculated design rail neutral temperature range, prior to anchoring the rail down. Upon anchoring, as temperatures deviate from the rail neutral temperature, significant tensile or compressive longitudinal stresses develop, leading to a track buckling or rail pull-apart that compromise the integrity of the track and the safety of train operation. Existing methods to estimate the rail neutral temperature and determine the state of stress in the rail have significant shortcomings related to the ease of implementation, system complexity, practicality, reliability, simplicity, cost, and instrumentation demands. We propose a novel concept for measuring stress in rail segments and determining the rail neutral temperature. The proposed method is based on measurements of nonuniform deformations of the rail under thermal loading, as observed in computer simulations and laboratory investigations. The implementation uses thermal imaging and three-dimensional stereo-digital image correlation technology to acquire full-field deformations. The acquired data are processed to estimate rail neutral temperature and quantify the longitudinal stress in the rail. This article presents the analytical and experimental work that led to the conception of the method and introduces the systematic approach to develop the method along with verification and validation studies.
A series of baseline displacement measurements have been obtained using 2D Digital Image Correlation (2D-DIC) and images from Scanning Electron Microscopes (SEM). Direct correlation of subsets from a ...reference image to subsets in a series of uncorrected images is used to identify the presence of non-stationary step-changes in the measured displacements. Using image time integration and recently developed approaches to correct residual drift and spatial distortions in recorded images, results clearly indicate that the corrected SEM images can be used to extract deformations with displacement accuracy of +/-0.02 pixels (1 nm at magnification of 10,000) and mean value strain measurements that are consistent with independent estimates and have point-to-point strain variability of +/-1.5X10.
Mechanically Defined Microgels by Droplet Microfluidics Heida, Thomas; Neubauer, Jens W.; Seuss, Maximilian ...
Macromolecular chemistry and physics,
January 2017, 2017-01-00, 20170101, Volume:
218, Issue:
2
Journal Article
Peer reviewed
Over the last two decades, droplet‐based microfluidics has evolved into a versatile tool for fabricating tailored micrometer‐sized hydrogel particles. Combining precise fluid handling down to ...femtoliter scale with diverse hydrogel precursor design, it allows for excellent control over microgel size and shape, but also functionalization and crosslinking density. Consequently, it is possible to tune physicochemical and mechanical properties such as swelling, degradation, stimuli sensitivity, and elasticity by microfluidic droplet templates. This has led to a recent trend in applying microgels as experimental platform in cell culturing, drug delivery, sensing, and tissue engineering. This article highlights advances in microfluidic droplet formation as templates for microgels with tailored physicochemical properties. Special focus is put on evolving design strategies for the synthesis of mechanically defined microgels, their applications, and methods for mechanical characterization on single‐particle level.
Microfluidic emulsion formation combined with hydrogel design via droplet templates has greatly advanced the application of microgels in cell culturing, sensing and actuation. On that account, exact knowledge and control over physicochemical and mechanical properties is crucial. We discuss recent progress in droplet microfluidics‐based design of mechanically defined microgels, their latest applications and characterization methods on single‐particle level.
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