Tensile Strength of Threaded Rods Made by 3D Printing of Polymeric Material

The extension of 3D printing processes for parts made of polymeric materials highlighted the possibility of manufacturing threaded surfaces through such processes. In principle, the operation of a threaded joint involves tensile forces in the threaded rod. The dimensional characteristics of the threaded surface and some input factors in the 3D printing process can influence the tensile strength of threaded rods made of polymeric materials. An experimental research aimed at the tensile behavior of a threaded joint was designed, using a plastic screw and a special steel nut. A factorial experiment was designed and implemented to identify an empirical mathematical model capable of highlighting the influence of the dimensional characteristics of the threaded surface and some of the input factors in the 3D printing process on tensile strength. The test samples from polymeric materials were manufactured by 3D printing, then subjected to tensile tests. The mathematical processing of the experimental results allowed the determination of a mathematical model that allows the inclusion of the ordering of the factors taken into account in terms of the intensity of the influence that these factors exert on the tensile strength of the threaded rods. It was found that the diameter of the threaded rod exerts the strongest influence on the tensile strength of the threaded rod obtained by 3D printing, increasing the diameter of the threaded rod causing an increase in the maximum deformation of the rod. Increasing the thread pitch leads to a decrease in the maximum deformation of the threaded rod.

SOURCE PARAMETERS of CRIMEAN-BLACK SEA EARTHQUAKES in 2015

The spectral and dynamic source parameters (М0, r0, , , ησ, , u, Eu and Mw) of 16 Crimean earthquakes with КП=6.5–10.8, restored by amplitude spectra of compression and shear seismic waves recorded by digital regional seismic stations are analyzed. Approximation of the spectra and source parameters calculation is performed in the framework of the Brune dislocation model. The highest values of dynamic parameters (М0, r0, , , ησ, u, EU и Mw) are obtained for the earthquakes on June 13 and August 16 with h=11 km, h=7 km respectively and КП=10.8, which occurred in the Azov-Kuban and Kerch-Anapa areas. The radiation friction r for all earthquakes had a negative value, pointing to a complex slide of the rupture in the source. Within the whole energy range, the average value of the released stress did not exceed Δσ=8∙105 PA (8 bar) and apparent stress ησ <11∙105 PA (11 bar). For most 2015 earthquakes, the average M0 и r0 values were within the confidence intervals of long-term dependencies M0(КП), r0(КП). The values of r0 were evenly distributed concerning the regression r0(КП) and М0 is mostly located below the average according to М0 (КП). The maximum deviations of M0 from the long-term М0(КП) dependence were obtained for the most strong earthquakes on June 13 and August 16 with КП=10.8. These deviations can be associated with participation in average M0 of the "Sevastopol" station data which give low values of М0 and possible errors in determining the focal depths influencing the choice of environment velocity models to calculate М0. For the most strong earthquake of August 16 with Мw=3.8, which occurred in the Kerch-Anapa region, a solution of focal mechanism was obtained. The earthquake occurred under the action of horizontal latitudinal tensile forces. The type of movement in the source is an oblique normal fault. Both nodal planes have near-meridional (STKNP1=167°) and near-diagonal (STKNP2=336°) strike.

Slit-Robo Signalling Establishes a Sphingosine-1-Phosphate Gradient to Polarise Fin Mesenchyme and Establish Fin Morphology

SUMMARYImmigration of mesenchymal cells into the growing fin and limb buds drives distal outgrowth, with subsequent tensile forces between these cells essential for fin and limb morphogenesis. Morphogens derived from the apical domain of the fin, orientate limb mesenchyme cell polarity, migration, division and adhesion. The zebrafish mutant stomp displays defects in fin morphogenesis including blister formation and associated loss of orientation and adhesion of immigrating fin mesenchyme cells. Positional cloning of stomp identified a mutation in the gene encoding the axon guidance ligand, Slit3. We provide evidence that Slit ligands derived from immigrating mesenchyme act via Robo receptors at the Apical Ectodermal Ridge (AER) to promote release of sphingosine-1-phosphate (S1P). S1P subsequently diffuses back to the mesenchyme to promote their polarisation, orientation, positioning and adhesion to the interstitial matrix of the fin fold. We thus demonstrate coordination of the Slit-Robo and S1P signalling pathways in fin fold morphogenesis. Our work introduces a mechanism regulating the orientation, positioning and adhesion of its constituent cells.

Computational fluid dynamic analysis of the initiation of cerebral aneurysms

OBJECTIVE Relationships between aneurysm initiation and hemodynamic factors remain unclear since de novo aneurysms are rarely observed. Most previous computational fluid dynamics (CFD) studies have used artificially reproduced vessel geometries before aneurysm initiation for analysis. In this study, the authors investigated the hemodynamic factors related to aneurysm initiation by using angiographic images in patients with cerebral aneurysms taken before and after an aneurysm formation. METHODS The authors identified 10 cases of de novo aneurysms in patients who underwent follow-up examinations for existing cerebral aneurysms located at a different vessel. The authors then reconstructed the vessel geometry from the images that were taken before aneurysm initiation. In addition, 34 arterial locations without aneurysms were selected as control cases. Hemodynamic parameters acting on the arterial walls were calculated by CFD analysis. RESULTS In all de novo cases, the aneurysmal initiation area corresponded to the highest wall shear stress divergence (WSSD point), which indicated that there was a strong tensile force on the arterial wall at the initiation area. The other previously reported parameters did not show such correlations. Additionally, the pressure loss coefficient (PLc) was statistically significantly higher in the de novo cases (p < 0.01). The blood flow impact on the bifurcation apex, or the secondary flow accompanied by vortices, resulted in high tensile forces and high total pressure loss acting on the vessel wall. CONCLUSIONS Aneurysm initiation may be more likely in an area where both tensile forces acting on the vessel wall and total pressure loss are large.

Centrifuge study of seismic response of soil-nailed walls supporting a footing on the ground surface

Seismic design of soil-nailed walls requires demonstrations of tolerable ranges of wall movements, especially when a surcharge load exists near the wall. In this study, the effect of surcharge location on seismically induced wall movements was investigated using four centrifuge tests. The axial tensile forces, developed along the soil nails during the seismic loadings, were also measured during the tests. At 50g centrifugal acceleration, model tests represented a 12-m-high prototype wall reinforced with five rows of soil nails. To apply a surcharge stress of 30 kPa at the specified location relative to the wall for each model test, a rigid footing was placed on the soil surface. The model soil-nailed walls were subjected to three successive earthquake motions. Surprisingly, it was found that the model wall with the footing located behind the soil-nailed region experienced the largest seismic movements, even more than when the footing was directly behind the wall. Further, the tests showed that the lower soil nails played a key role in the wall stability during earthquake shaking, acting as a pivot for the pre-collapse cases tested, whereas the upper soil nails needed to be sufficiently extended to properly contribute to the seismic stability of the wall.

Analysis and Design of Cable Stayed and Suspension Bridge Subjected to Wind Loading

Bridge can be defined as a structure which is built to pass a physical obstacle such as river road or valley and this structure does not close the way underneath it. The main objective of the bridgeis to provide a passage which can surpass any obstacle. A bridge is designed according to various specific purposes depending upon the need function and various physical factors. Cable-stayed bridge is having one or more columns called towers or pylons, with the cables directly supporting the bridge deck. Cable-stayed bridge is the bridge form in which the weight of the deck is supported by a number of nearly straight diagonal cables in tension running directly to one or more vertical towers. The towers transfer the cable forces to the foundations through vertical compression. The tensile forces in the cables also put the deck into horizontal compression. A suspension bridge is able to carry vertical loads with the help of curved cables in tension. Transfer of load takes place to both the towers, which is transferred by vertical compression to the ground, and anchorages, which is able to withstand the inward and occasionally vertical pull of the cables. The suspension bridge is often looked as an upside-down arch in tension with only the towers as compression members. In this research work, analysis and design of cable stayed and suspension bridge subjected to wind loading has been carried out.

Fiber Rearrangement and Matrix Compression in Soft Tissues: Multiscale Hypoelasticity and Application to Tendon

It is widely accepted that the nonlinear macroscopic mechanical behavior of soft tissue is governed by fiber straightening and re-orientation. Here, we provide a quantitative assessment of this phenomenon, by means of a continuum micromechanics approach. Given the negligibly small bending stiffness of crimped fibers, the latter are represented through a number of hypoelastic straight fiber phases with different orientations, being embedded into a hypoelastic matrix phase. The corresponding representative volume element (RVE) hosting these phases is subjected to “macroscopic” strain rates, which are downscaled to fiber and matrix strain rates on the one hand, and to fiber spins on the other hand. This gives quantitative access to the fiber decrimping (or straightening) phenomenon under non-affine conditions, i.e. in the case where the fiber orientations cannot be simply linked to the macroscopic strain state. In the case of tendinous tissue, such an RVE relates to the fascicle material with 50 μm characteristic length, made up of crimped collagen bundles and a gel-type matrix in-between. The fascicles themselves act as parallel fibers in a similar matrix at the scale of a tissue-related RVE with 500 μm characteristic length. As evidenced by a sensitivity analysis and confirmed by various mechanical tests, it is the initial crimping angle which drives both the degree of straightening and the shape of the macroscopic stress-strain curve, while the final linear portion of this curve depends almost exclusively on the collagen bundle elasticity. Our model also reveals the mechanical cooperation of the tissue’s key microstructural components: while the fibers carry tensile forces, the matrices undergo hydrostatic pressure.

Overview of the modified magnetoelastic method applicability

<p class="Abstract">A requirement of axial force determination in important structural elements of a building or engineering structure during its construction or operational state is very frequent in technical practice. In civil engineering practice, five experimental techniques are usually used for evaluation of axial tensile forces in these elements. Each of them has its advantages and disadvantages. One of these methods is the magnetoelastic method, that can be used, for example, on engineering structures for experimental determination of the axial forces in prestressed structural elements made of ferromagnetic materials, e.g., prestressed bars, wires and strands. The article presents general principles of the magnetoelastic method, the magnetoelastic sensor layout and actual information and knowledge about practical application of the new approach based on the magnetoelastic principle on prestressed concrete structures. Subsequently, recent results of the experimental verification and the in-situ application of the method are described in the text. The described experimental approach is usable not only for newly built structures but in particular for existing ones. Furthermore, this approach is the only one effectively usable experimental method for determination of the prestressed force on existing prestressed concrete structures in many cases in the technical practice.</p>

Measurement of Axial Strain of Geogrid by Optical Sensors

In recent years, the technology of optical fibers has rapidly gained ground in many areas of science and industry, including the construction industry. In this article, the technology of optical fibers based on a fiber Bragg grating (FBG) was used to determine tensile forces acting in a basal reinforcement of a scaled down physical model, which included piled embankment and basal reinforcement. Installing FBG sensors on the geogrid made monitoring of axial strains possible, thus allowing determination of the behavior of the basal reinforcement of the piled embankment. On the basis of three tests performed on the physical model, numerical model calibration with the physical model was carried out using the software PLAXIS 3D Tunnel 2.4. The results showed accurate predictions, especially for the low and middle part of the measured deformations where the numerical analysis proposed a solution that can be considered as safe. Installing FBG sensors on biaxial geogrids was a bold idea that was not easy to implement. However, other possibilities have been successfully tested, such as high-frequency measurements of the response of reinforced soil structure under dynamic loading.