A high-speed stereo-vision system is employed to quantify dynamic material response during buried blast loading. Deformation measurements obtained using 3D image correlation of synchronized, ...patterned stereo-vision images obtained with an inter-frame time in the range 16
μs
≤
t
≤
40
μs indicate that (a) buried blast loading initially induces highly localized material response directly under the buried blast location, with severity of the blast event a strong function of depth of explosive burial, (b) for relatively shallow (deep) depth of explosive burial, plate surface velocities and accelerations exceed 220
m
s
−1 (100
m
s
−1) and 6
×
10
6
m
s
−2 (1.5
×
10
6
m
s
−1) during the first 30
μs (80
μs) after detonation, respectively.
In addition, full-field plate deformation measurements demonstrate that the specimen experienced (c) measured effective strains exceeding 8% (5%) and effective strain rates exceeding 4000
s
−1 (1500
s
−1) during the first 50
μs (80
μs), respectively and (d) a blast-induced, circularly symmetric, transient bending wave was induced in the plate that travels with radial velocity of Mach 2 (1.25) during blast loading.
By combining the Cowper–Symonds constitutive relation with full-field strain and strain rate measurements, well-defined yield boundaries are evident on the plate surface during blast loading; the presence of spatial gradients in yield stress has the potential to affect plate failure processes during transient blast loading events.
Mining exploitation influence range Kwinta, Andrzej; Gradka, Robert
Natural hazards (Dordrecht),
12/2018, Volume:
94, Issue:
3
Journal Article
Peer reviewed
Open access
Mining exploitation has a negative impact on the natural environment. Voids created in the rockmass result in displacements and deformations of land surface. During planning and conducting the ...exploitation, the range of exploitation influence in the form of linear deformations is being determined. On the basis of mining-geological parameters of exploitation, the exploitation range of influences is calculated. According to the literature, many different ranges of exploitation influences can be determined depending on what has been the purpose of it. Different types of exploitation influence ranges can be distinguished, such as theoretical, damage or measurable. In the paper, the matters connected with determining those three types of the influence range are taken under consideration. The comparison of magnitudes of determined influence ranges is illustrated with two practical examples.
Summary
Remote measurements using images are particularly useful in structural health monitoring cases in which the installation of contact sensors is difficult. Some limitations, though, associated ...with photogrammetry‐type optical metrology involve the application of speckle patterns, which become even more important with variable working distance or when the required resolution and sensitivity are not a priori known which are both very practical common issues. In this context, multispectral sensing can circumvent some of the challenges of acquiring data at different working distances. The objective of this investigation is therefore to use multispectral imaging combined with the method of digital image correlation to demonstrate an approach for remote sensing related to deformation measurements at the structural level. To demonstrate this novel approach, two speckle patterns were designed for measurements at specified working distances; one was set to work in the visible and the second in the ultraviolet spectrum. The results show that the spectral specific reflectivity of the speckle patterns can be used for spatial overlay without affecting imaging in either spectral range considered, which allows the extraction of multiscale deformation information.
The stiffness evolution of binder ‘cement paste’ is triggering the stiffness of concrete. In the engineering practice, concrete formworks are typically removed 24 h after production. This underlines ...that knowledge on mechanical properties of cementitious materials during the second, third and fourth day after production is of high relevance for the ongoing construction process. This provides the motivation to perform early‐age stiffness characterisation on hydrating cement pastes, by means of the following three test methods. Unloading modulus is determined using a novel setup for non‐destructive uniaxial compression testing including overdetermined deformation measurements. Dynamic Young's moduli are obtained from ultrasonics experiments. Isothermal differential calorimetry allows for linking the observed temporal evolution of early‐age stiffness to the hydration degree of cement. Pastes with three different compositions are investigated, defined in terms of the initial water‐to‐cement mass ratio w/c and the initial water‐to‐solid (binder) mass ratio w/s. Pure cement pastes exhibit w/c = w/s = 0.50 and w/c = w/s = 0.42, respectively. A fly ash‐blended cement paste refers to a cement mass replacement level of 16%, and this is related to w/c = 0.50 and w/s = 0.42. Both unloading moduli and dynamic Young's moduli of all three materials increase practically linearly with increasing hydration degree, in the investigated regime of hydration degrees ranging from 40 to 60%. Fly ash does not contribute significantly to the early‐age hydration of the material, i.e. it represents a quasi‐inert part of the material's microstructure, exhibiting a significant stiffening effect.
In the past several decades, many papers have been published on fluid–structure coupled calculations to analyse the hydro-elastic response of flexible (composite) propellers. The flow is usually ...modelled either by the Navier–Stokes equations or as a potential flow, by assuming an irrotational flow. Phenomena as separation of the flow, flow transition, boundary layer build-up and vorticity dynamics are not captured in a non-viscous potential flow. Nevertheless, potential flow based methods have been shown to be powerful methods to resolve the hydrodynamics of propellers. With the upcoming interest in flexible (composite) propellers, a valid question is what the consequences of the potential flow simplifications are with regard to the coupled fluid–structure analyses of these types of propellers. This question has been addressed in the following way: calculations and experiments were conducted for uniform flows only, with a propeller geometry that challenges the potential flow model due to its sensitivity to leading edge vortex separation. Calculations were performed on the undeformed propeller geometry with a Reynolds-averaged-Navier–Stokes (RANS) solver and a boundary element method (BEM). These calculations show some typical differences between the RANS and BEM results. The flexible propeller responses were predicted by coupled calculations between BEM and finite element method (FEM) and RANS and FEM. The applied methodologies are briefly described. Results obtained from both calculation methods have been compared to experimental results obtained from blade deformation measurements in a cavitation tunnel. The results show that, even for the extreme cases, promising results have been obtained with the BEM-FEM coupling. The BEM-FEM calculated responses are consistent with the RANS-FEM results.
Measurements of surface deformations as part of the “Contact Mechanics Challenge” were collected using digital image correlation (DIC). For these experiments, a scaled version (1000×) of the periodic ...and random roughness surface provided for the “Contact Mechanics Challenge” was used. A 100 mm × 100 mm scale replica of the surface, approximately 10 mm thick, was 3D-printed using an opaque polymethylmethacrylate and pressed into contact against flat, transparent polydimethylsiloxane (PDMS) sheets with dead weight loads. Four different formulations of PDMS were used, and the resulting elastic moduli ranged from 64 kPa to 2.1 MPa. The DIC technique was used in situ to measure the deformation of the PDMS surface at each load increment from 22.5 to 450 N. Surface deformations in and out of contact were measured across the entire apparent area of contact and overlaid with the measurements of contact area to provide a complete description of the surface profile during loading. A direct comparison between these experiments and the simulations regarding the gap within the contact at a reduced pressure of 0.164 agrees to within ±10% when normalized to the maximum gap.
For the measurement of abrupt and large surface movements caused by earthquakes, volcanic eruption and melting glacier, Synthetic aperture radar (SAR) offset tracking method would be a feasible ...solution because it can provide unambiguous ground displacements in both the ground range and azimuth directions when the interferometric phase is not coherent. However, the measurement performance of the method largely depends on the kernel size, which denotes the size of search window to estimate the azimuth and range offsets between reference and target SAR images. Thus, there is a trade-off between sensitivity and measurement density depending on the search kernel size. In this study, an enhanced SAR offset tracking method based on multi-kernel processing has been developed to find an optimized measurement from the trade-off between resolution and measurement accuracy. It can obtain optimal surface displacement measurements by calculating multiple offset measurements and determining a final measurement from the statistical properties of the multiple measurements. The measurement performance of the proposed method was evaluated by using European Remote Sensing 2 (ERS-2) satellite SAR data sets of the Hector Mine earthquake event in 1999 and Advanced Land Observing Satellite-2 Phased Array type L-band Synthetic Aperture Radar-2 (ALOS-2 PALSAR-2) data sets of the 2016 Kumamoto earthquake event. Our results showed that an optimized measurement from the trade-off between the observation accuracy and resolution can be effectively determined by our proposed processing strategy. The results are improved results for measurement density and accuracy over previously published results. It further confirmed that our new method is allowed for the optimal measuring the large-scale fast surface displacements that cannot be sufficiently observed with the phase-based SAR method.
The denaturation and gelling properties of mixed systems of β‐lactoglobulin and sodium‐alginate have been investigated as a function of alginate molecular weight, chemical composition, concentration, ...pH and ionic strength. Differential scanning calorimetry and small strain oscillatory measurements showed that denaturation temperature were lower than the gelling temperatures under the conditions examined. The denaturation temperatures were dependent on both pH and ionic strength, but unaffected by alginate concentration and type. The mechanical and textural properties of mixed gels of β‐lactoglobulin and sodium alginate were dependent on several factors; the gel strength increased as a function of alginate concentration under ambient conditions, and decreased as the pH and/or the ionic strength were changed. High molecular weight alginate gave the most pronounced effects, probably due to the accessibility of the alginate for protein binding. The chemical composition of the alginate had negligible effect on the mechanical properties of the gels.
Practical Applications
As both proteins and polysaccharides are widely used in the food industry, it is important to understand the interactions between these two biopolymers in order to envisage final product properties. The present article gives an overview of several important parameters when mixing β‐lactoglobulin and sodium alginate. β‐Lactoglobulin is the main protein in whey and one of the major food protein ingredients. Alginate is a polysaccharide that is often used in the food industry because of its functional properties. This study shows that if the conditions and the alginate type are adequately chosen, the textural properties of food products can be controlled and tailored.
The paper discusses the results of selected fatigue tests of a motor glider’s insulated spar structure. The results of the experimental tests were used to assess the potential of the strain-gauge ...method for diagnosing the spar damage involving the unbolting of one of metal fittings in the spar pin. The usefulness of the deformation measurement method in the composite structure diagnostic process was confirmed, while simultaneously drawing attention to the need for conducting a process optimizing the number of sensors and their distribution on a tested object, in the context of the sensitivity of diagnostic signals received.
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