scholarly journals Effects of Spatially Varying Seismic Ground Motions and Incident Angles on Behavior of Long Tunnels

2018 ◽  
Vol 2018 ◽  
pp. 1-6 ◽  
Author(s):  
Yundong Zhou ◽  
Yongxin Wu ◽  
Ziheng Shangguan ◽  
Zhanbin Wang
Keyword(s):  
Stress State ◽  
Strain Rate ◽  
Ground Motions ◽  
Pure Shear ◽  
Radial Strain ◽  
Complex Stress State ◽  
Asymmetric Effect ◽  
Principal Stresses ◽  
Input Motion ◽  
Spatially Varying

Seismic behavior of long circle tunnels is significantly influenced by the nature of input motion. This study, based on the 3D finite-element method (FEM), evaluates the effects of spatially varying seismic ground motions and uniform input seismic ground motions and their incident angles on the diameter strain rate and tensive/compressive principal stresses under different strata. It is found that (1) the spatially varying seismic ground motions induced larger diameter strain rate (radially deformation) than the uniform input seismic motion, (2) the spatially varying seismic ground motions had an asymmetric effect on the radial strain rate distributions, and (3) the rising incident angles changed the pure shear stress state into a complex stress state for tunnels under specified input motion.

Anisotropic Behavior of Geomaterial under Three-Dimensional Stress States

2010 ◽  
Vol 160-162 ◽  
pp. 1425-1431
Author(s):  
Kun Yong Zhang ◽  
Yan Gang Zhang ◽  
Chi Wang
Keyword(s):  
Stress State ◽  
Principal Stress ◽  
Three Dimensional ◽  
Complex Stress State ◽  
Triaxial Tests ◽  
Induced Anisotropy ◽  
Principal Stresses ◽  
True Triaxial ◽  
Stress Effects ◽  
Stress Induced Anisotropy

Most soil constitutive models were developed based on the traditional triaxial tests with isotropic assumption, in which the load is applied as the major principal stress direction and the other two principal stresses are symmetric. When such isotropic models are applied to practical analysis, stress induced anisotropy under complex stress state and the middle principal stress effects are often neglected, thus there are many disagreements between the calculated results and the infield testing data. To simulate the practical loading process, true triaxial tests were carried out on geomaterial under three-dimensional stress state. It was found that the stress induced anisotropy effects are remarkable and the middle principal stress effects are obvious because of the initial three-dimensional stress state. Such kind of stress-induced anisotropy could have important impact on the numerical analysis results and should be taken into consideration when developing the constitutive model.

scholarly journals An analytical approach to deformation of anisotropic ice-crystal aggregates

2001 ◽  
Vol 47 (158) ◽  
pp. 507-516 ◽  
Author(s):  
Throstur Thorsteinsson
Keyword(s):  
Shear Stress ◽  
Stress State ◽  
Strain Rate ◽  
Deformation Rate ◽  
Stress Component ◽  
Pure Shear ◽  
Cone Angle ◽  
Complex Stress ◽  
Transverse Strain ◽  
Maximum Enhancement

AbstractDeformation rates of single hexagonal crystals, deforming by glide on the basal plane, are described as a function of stress state and crystal orientation. These results are used to infer the deformation rate of crystal aggregates assuming that the stress distribution within the crystal aggregate is homogeneous. Analytical equations for the deformation rate of anisotropic ice aggregates are derived for vertically symmetric girdle fabric. This type of fabric is approximated by a uniform distribution of c-axis orientations between a cone angle and a smaller girdle angle relative to the symmetry axis. For simple shear stress acting on a single-maximum fabric there is a slight de-enhancement for cone angles of 60–90°. In uniaxial compression a maximum enhancement of ∼1.7 occurs at a cone angle of 57°. A pure shear stress state has similar features, with the additional complication that it causes a non-zero transverse strain rate, except for perfect vertical alignment of crystals and isotropic fabric. In combined states of stress the contribution of each stress component to the strain rate depends on fabric. A single enhancement factor is not adequate to describe the effects of anisotropy for complex stress states.

scholarly journals LOCALIZATION OF PLASTIC DEFORMATION IN COMMERCIALLY PURE TITANIUM IN A COMPLEX STRESS STATE UNDER HIGH-SPEED TENSION

2021 ◽  
pp. 89-102
Author(s):  
V.V. Skripnyak ◽  
◽  
K.V. Iokhim ◽  
V.A. Skripnyak ◽  
◽  
...  
Keyword(s):  
Plastic Deformation ◽  
Stress State ◽  
Strain Rate ◽  
High Speed ◽  
Pure Titanium ◽  
Complex Stress ◽  
Complex Stress State ◽  
Strain Rates ◽  
Commercially Pure Titanium ◽  
Commercially Pure

In this work, the effect of a triaxiality stress state on the mechanical behavior and fracture of commercially pure titanium VT1-0 (Grade 2) in the range of strain rates from 0.1 to 1000 s−1 is studied. Tensile tests are carried out using a servo-hydraulic testing machine Instron VHS 40 / 50-20 on flat specimens with a constant cross-sectional area and on flat specimens with a notch. To study the effect of the complex stress state on the ultimate deformation before fracture, the samples with the notch of various radii (10, 5, 2.5 mm) are used in the experiments. Phantom V711 is employed for high-speed video registration of specimen’s deformation. Deformation fields in a working part of the sample are investigated by the digital image correlation method. It is shown that the effect of the strain rate on the ultimate deformations before fracture has a nonmonotonic behavior. An analysis of strain fields in the working part of the samples shows that the degree of uniform deformation of the working part decreases with an increase in the strain rate. At strain rates above 1000 s−1, the shear bands occur at the onset of a plastic flow. Commercially pure titanium undergoes fracture due to the nucleation, growth, and coalescence of damages in the bands of localized plastic deformation oriented along the maximum shear stresses. The results confirm that the fracture of commercially pure titanium exhibits ductile behavior at strain rates varying from 0.1 to 1000 s−1, at a triaxiality stress parameter in the range of 0.333 ≤ η <0.467, and at a temperature close to 295 K.

An octahedral stress-based fracture criterion for hyperelastic materials

2020 ◽  
pp. 095440622097213
Author(s):  
A Hamdi ◽  
A Boulenouar ◽  
N Benseddiq
Keyword(s):  
Pure Shear ◽  
Thermoplastic Elastomer ◽  
Styrene Butadiene Rubber ◽  
Butadiene Rubber ◽  
Principal Stresses ◽  
Hyperelastic Materials ◽  
Biaxial Tests ◽  
Set Up ◽  
Loading Modes ◽  
Styrene Butadiene

No unified stress-based criterion exists, in the literature, for predicting the rupture of hyperelastic materials subjected to mutiaxial loading paths. This paper aims to establish a generalized rupture criterion under plane stress loading for elastomers. First, the experimental set up, at breaking, including various loading modes, is briefly described and commented. It consists of uniaxial tests, biaxial tests and pure shear tests, performed on different rubbers. The used vulcanizate and thermoplastic rubber materials are a Natural Rubber (NR), a Styrene Butadiene Rubber (SBR), a Polyurethane (PU) and a Thermoplastic elastomer (TPE). Then, we have investigated a new theoretical approach, based upon the principal stresses, to establish a failure criterion under quasi-static loadings. Thus, we have proposed a new analytical model expressed as a function of octahedral stresses. Quite good agreement is highlighted when comparing the ultimate stresses, at break, between the experimental data and the prediction of the proposed criteria using our rubber-like materials.

scholarly journals Left ventricular and left atrial deformation imaging early after pPCI: does diabetes mellitus make any difference?

2021 ◽  
Vol 22 (Supplement_1) ◽  
Author(s):  
D Trifunovic Zamaklar ◽  
G Krljanac ◽  
M Asanin ◽  
L Savic-Spasic ◽  
J Vratonjic ◽  
...  
Keyword(s):  
Heart Failure ◽  
Strain Rate ◽  
Myocardial Function ◽  
Radial Strain ◽  
Left Ventricular ◽  
Deformation Analysis ◽  
Syntax Score ◽  
Deformation Imaging ◽  
Early Diastole

Abstract Funding Acknowledgements Type of funding sources: None. onbehalf PREDICT-VT More extensive coronary atherosclerosis in diabetes mellitu (DM) induces poorer clinical outcomes after STEMI, but there are data suggesting that impaired myocardial function in DM, even independently from epicardial coronary lesions severity, might have detrimental effect, predominately on heart failure development in DM. Aim the current study is a sub-study of PREDICT-VT study (NCT03263949), aimed to analyse LV and LA function using myocardial deformation imaging based on speckle tracking echocardiography after pPCI in STEMI patients with and without DM. Methods in 307 consecutive pts enrolled in PREDICT-VT study early echocardiography (5 ± 2 days after pPCI) was done including LA and multilayer LV deformation analysis with longitudinal (L), radial (R) and circumferential (C) strain (S; %) and strain rate (SR, 1/sec), LV index of post systolic shortening for longitudinal (PSS LS) and circumferential (PSS CS) strains and analysis of LV rotation mechanic. Results from 242 patients who completed 1 year follow up, 48 (20%) had DM. Pts with DM were older (60 ± 1,01 vs 57 ± 10; p = 0.067) and had insignificantly higher SYNTAX score (18.5 ± 9.2 vs 15.8 ± 9.8, p = 0.118) . However, diabetics had more severely impaired EF (44.2 ± 8.6 vs 49.2 ± 9.8, p = 0.001), E/A ratio (0.78 ± 0.33 vs 0.90 ± 0.34; p = 0.036) and MAPSE (1.18 ± 0.32 vs 1.32 ± 0.33; p = 0.001).  Global LV LS on all layers (endo: -13.6 ± 4.0 vs-16.2 ± 4.7; mid: -11.9 ± 3.5 vs -14.1 ± 4.1; epi: -10.4 ± 3.1 vs -12.3 ± 3.6; p &lt; 0.005 for all) was impaired in DM patients, as well as longitudinal systolic SR (-0.71 ± 0.23 vs -0.84 ± 0.24; p = 0.001) and SR during early diastole (0.65 ± 0.26 vs 0.83 ± 0.33, p &lt; 0.001). Patients with DM had more pronounced longitudinal posts-systolic shortening throughout LV wall (endo: 21.4 ± 16.1 vs 13.7 ± 13.3, p = 0.005; mid: 21.9 ± 16.1 vs 14.3 ± 13.1, p = 0.006; epi: 22.4 ± 16.5 vs 15.3 ± 13.7, p = 0.010) and higher LV mechanical dispersion (MDI: 71.3 ± 38.3 vs 59.0 ± 18.9, p = 0.037). LA strain was significantly impaired in DM patients (18.9 ± 7.7 vs 22.6 ± 10.0, p = 0.011) and even more profoundly LA strain rate during early diastole (-0.73 ± 0.48 vs -1.00 ±0.58, p = 0.002). Patients with DM also had more impaired LV global (15.7 ± 9.1 vs 19.8 ± 10.4, p = 0.013) radial strain, global LV circumferencial strain, especially at the mid-wall level (-13.9 ± 4.2 vs -16.0 ± 4.3, p = 0.005) and impaired circumferential SR E (1.25± 0.44 vs 1.49 ± 0.46, p = 0.003). End-systolic rotation of the LV apex was more impaired in DM (4.7 ± 5.1 vs 6.8 ± 5.5, p= 0.022). During 1 year follow-up heart failure and all-cause mortality tend to be higher among DM pts (46.7% vs 35.2%, p = 0.153). Conclusion STEMI patients with DM have more severely impaired LV systolic and diastolic function estimated both by traditional parameter and advanced echo techniques. These results might, at least partially, explain why outcomes after STEMI in DM might be poorer, even in the absence of more complex angiographic findings, pointing to the significance of impaired myocardial function DM itself.

scholarly journals Crystal rotations and alignment in spatially varying magma flows: Two-dimensional examples of common subvolcanic flow geometries

2021 ◽  
Author(s):  
Rémi Vachon ◽  
Mohsen Bazargan ◽  
Christoph F Hieronymus ◽  
Erika Ronchin ◽  
Bjarne Almqvist
Keyword(s):  
Shear Flow ◽  
Magma Chamber ◽  
Simple Shear ◽  
Thermal Convection ◽  
Pure Shear ◽  
Simple Shear Flow ◽  
Two Dimensional ◽  
Crystal Orientations ◽  
Volcanic Plumbing System ◽  
Spatially Varying

Summary Elongate inclusions immersed in a viscous fluid generally rotate at a rate that is different from the local angular velocity of the flow. Often, a net alignment of the inclusions develops, and the resulting shape preferred orientation (SPO) of the particle ensemble can then be used as a strain marker that allows reconstruction of the fluid’s velocity field. Much of the previous work on the dynamics of flow-induced particle rotations has focused on spatially homogeneous flows with large-scale tectonic deformations as the main application. Recently, the theory has been extended to spatially varying flows, such as magma with embedded crystals moving through a volcanic plumbing system. Additionally, an evolution equation has been introduced for the probability density function (PDF) of crystal orientations. Here, we apply this new theory to a number of simple, two-dimensional flow geometries commonly encountered in magmatic intrusions, such as flow from a dyke into a reservoir or from a reservoir into a dyke, flow inside an inflating or deflating reservoir, flow in a dyke with a sharp bend, and thermal convection in a magma chamber. The main purpose is to provide a guide for interpreting field observations and for setting up more complex flow models with embedded crystals. As a general rule, we find that a larger aspect ratio of the embedded crystals causes a more coherent alignment of the crystals, while it has only a minor effect on the geometry of the alignment pattern. Due to various perturbations in the crystal rotation equations that are expected in natural systems, we show that the time-periodic behavior found in idealized systems is probably short-lived in nature, and the crystal alignment is well described by the time-averaged solution. We also confirm some earlier findings. For example, near channel walls, fluid flow often follows the bounding surface and the resulting simple shear flow causes preferred crystal orientations that are approximately parallel to the boundary. Where pure shear deformation dominates, there is a tendency for crystals to orient themselves in the direction of the greatest tensile strain rate. Where flow impinges on a boundary, for example in an inflating magma chamber or as part of a thermal convection pattern, the stretching component of pure shear aligns with the boundary, and the crystals orient themselves in that direction. In the field, this local pattern may be difficult to distinguish from a boundary-parallel simple shear flow. Pure shear also dominates along the walls of a deflating magma chamber and in places where the flow turns away from the reservoir walls, but in these locations, the preferred crystal orientation is perpendicular to the wall. Overall, we find that our calculated patterns of crystal orientations agree well with results from analogue experiments where similar geometries are available.

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