Direction Of Maximum Principal Strain Research Articles

Experimental study on the deterioration of mechanical properties of sandy mudstone under different water-gas interactions

Based on the water-rock-gas coupling test system, the work combined the scanning electron microscope and XTDIC 3D full-field strain measurement system. The Brazilian splitting test was performed on four groups of sandy mudstone specimens under contrast (CO), mash-gas soaking (MS), water-mash gas soaking (WM), and water-soaking (WS) conditions. The tensile strength, deformation failure, and microscopic characteristics of fractures were studied to reveal the deterioration mechanism of the tensile properties of sandy mudstone under water-gas coupling. The results showed that the uniaxial tensile strength of sandy mudstone specimens under the three soaking conditions was less than that of the contrast conditions. Compared with specimens in the CO group, the tensile strength of specimens in MS-WS groups was reduced; the WS group decreased the most. Specimens changed from brittle failure to plastic failure after soaking. The decrease rate in strength after the peak was consistent with the change trend in tensile strength. It led to a larger localized deformation zone of specimens and more obvious displacement. The deformation localization zone of the WS group was the broadest, with the most intense displacement. Besides, stress concentration first occurred in the submerged part of the WM group. Fractures expanded in the direction of maximum principal strain. The internal pore structure of sandy mudstone specimens in each group changed after soaking. The average porosity, maximum pore area, and probability entropy of specimens in WS-MS groups increased compared to the CO group. The WS group had the largest reduction and the MS group had the smallest. The pre-peak energy storage capacity of sandy mudstone specimens was gradually weakened. Compared with the CO group, that in the WS-MS groups was reduced. The WS group had the greatest reduction, and the MS group had the smallest. The deterioration effect of water on the interior of sandy mudstone was stronger than that of gas. The work is of great significance for understanding the stability of coal and rocks in closed-pit high-gas mines.

Mechanical properties measurement and micro-damage characterization of ITZ in concrete by SEM-DIC method

Due to the limitation of current experimental measurements, there is an almost insurmountable challenge to determine the mechanical tensile properties of interfacial transition zone (ITZ) in concrete. The present work aims to experimentally characterize micro-mechanical properties of ITZ under tensile load with the combined strategy of scanning electron microscope (SEM), digital image correlation (DIC), nanoindentation and wavelet packet technology. A bi-material sample composed of aggregate and mortar in the same volume and shape is designed for convenience to conduct tensile experiments using the proposed SEM-DIC method. By analyzing the stress obtained from the loading device and full-field strain calculated through DIC technique, the mechanical properties including tensile strength, nominal fracture energy (GNF) and nominal tensile elastic modulus (ENT) of ITZ are evaluated. Nanoindentation tests are also conducted, and their results are briefly compared with that of SEM-DIC method. The micro-damage distribution in ITZ area is further evaluated by wavelet packet analysis. Results reveals that a region with apparently lower ENT values can be characterized as the ITZ area, in which the average ENT value is about 55% of that of the mortar. In addition, growing path of microcracks can be estimated by the direction of maximum principal strain, and the degree of micro-damage could be well characterized by energy change rate (ECR) through wavelet packet analysis.

遠心圧縮機インペラに発生する衝撃波形成角度の計測

In a compressor, shock waves are generated when the impeller blade velocity reaches supersonic speed relative to the air drawn in from the air inlet. The shock interacts with the tip-leakage vortex and the boundary layer on the impeller blade surface. The interaction causes the pressure rise and the reverse flow. Thus, it is important to predict the formation of shock on the blades in compressor design. This study focused on a position of the shock in a centrifugal compressor. In general, simultaneous measurement by multiple pressure sensors is necessary to measure the angle of the shock formed near the leading edge of the impeller blade. In this study, a pressure history was measured at a single point near the leading edge of the blade using a semiconductor pressure transducer. The semiconductor pressure transducer has a diaphragm onto which a semiconductor strain gauge is glued. The pressure acting on the diaphragm is proportional to the strain at the center of the diaphragm. The direction of maximum principal strain of the diaphragm corresponds to the shock direction or its perpendicular direction. The strains in three different directions on the diaphragm were obtained and the direction of maximum principal strain was calculated using Rosette analysis. As a result, the angle of formation of the shock wave generated in the centrifugal compressor impeller was estimated.

A framework of modelling slip-controlled crack growth in polycrystals using crystal plasticity and XFEM

Short cracks tend to develop at high and irregular rates compared to macroscopic cracks, making the prediction of fatigue life a challenging task. In this work, a numerical framework combining crystal plasticity model and the Extended Finite Element Method (XFEM) is applied to study the slip-controlled short crack growth in a polycrystal superalloy RR1000. The model is calibrated from experiments and used to evaluate short crack growth paths and rates. Two fracture criteria are used and compared: the onset of fracture is controlled by the total and individual cumulative shear strain respectively, and the crack grows either perpendicular to the direction of maximum principal strain or along crystallographic directions.

Measurement of in vitro cardiac deformation by means of 3D digital image correlation and ultrasound 2D speckle-tracking echocardiography

Ultrasound-based 2D speckle-tracking echocardiography (US-2D-STE) is increasingly used to assess the functionality of the heart. In particular, the analysis of cardiac strain plays an important role in the identification of several cardiovascular diseases. However, this imaging technique presents some limitations associated with its operating principle that result in low accuracy and reproducibility of the measurement.In this study, an experimental framework for multimodal strain imaging in an in vitro porcine heart was developed. Specifically, the aim of this work was to analyse displacement and strain in the heart by means of 3D digital image correlation (3D-DIC) and US-2D-STE. Over a single cardiac cycle, displacement values obtained from the two techniques were in strong correlation, although systematically larger displacements were observed with 3D-DIC. Notwithstanding an absolute comparison of the strain measurements was not possible to achieve between the two methods, maximum principal strain directions computed with 3D-DIC were consistent with the longitudinal and circumferential strain distribution measured with US-2D-STE. 3D-DIC confirmed its high repeatability in quantifying displacement and strain over multiple cardiac cycles, unlike US-2D-STE which is affected by accumulated errors over time (i.e. drift).To conclude, this study demonstrates the potential of 3D-DIC to perform dynamic measurement of displacement and strain during heart deformations and supports future applications of this method in ex vivo beating heart platforms, which replicate more fully the complex contraction of the heart.

Determination of the block movements in the eastern section of the Gediz Graben (Turkey) from GNSS measurements

The source parameters of an earthquake should be determined in detail to calculate deformations caused by that earthquake and to identify faults that are likely to break. Today, the GNSS method is frequently used to determine these source parameters. However, to date, no detailed study has been conducted for this purpose in the eastern section of the Gediz Graben. Therefore, in this study, the GNSS technique was used to determine the tectonic movements in the area between Alaşehir and Sarıgöl in the Gediz Graben. For the implementation of the GNSS technique, 11 benchmark sites, which had been previously established for different purposes in the area, were used, and the measurements were performed in 2013, 2014, and 2015. The GNSS measurements obtained at these sites were evaluated by GAMIT/GLOBK software, and the annual velocity values of the sites were obtained (with respect to the Eurasian plate). The resulting annual horizontal velocity values obtained at the GNSS sites ranged from 12 mm/yr to 27 mm/yr. It was observed that the sites with the highest vertical movements were within the graben. The annual vertical velocity value at the TRAZ site located in the east of the graben was obtained to be approximately −90 mm/yr. This site was followed by BGCL (-33 mm/yr) and AKCL (−13 mm/yr) toward the west of the graben. Furthermore, significant strain accumulations were derived in the study area, and their compliance with the tectonic structure of the region was revealed. The maximum and minimum principal strain parameters and the direction of maximum principal strain that provided the average drift and compression directions for the region were obtained to be 0.604 μs/yr, -0.375 μs/yr, and 11.27 °, respectively. Block modeling in the study area revealed that the annual strike slip ranged from 4 ± 1.2 mm/yr to 19.3 ± 0.6 mm/yr, and the dip slip varied between -23.3 ± 0.5 mm/yr and -16.0 ± 0.5 mm/yr.

Numerical modeling of dip-slip faulting through granular soils using DEM

A GPU-based DEM modeling methodology with rolling resistance is employed to study comprehensively dip-slip faulting through granular soils from both engineering and fundamental viewpoints. From engineering viewpoints, the results of engineering significances, including the ruptures path, the fault outcropping location, the ground surface distortion zone, the near surface stress path within the rupture and the fault outcropping strain are studied. From fundamental viewpoints, the orientation of the ruptures (shear bands) is discussed using the Roscoe theory. The analyses show that the fault ruptures deviate from the fault projection surfaces as propagating up toward the ground surface; the deviation depends on the faulting type, faulting angle and soil density. The reverse ruptures may deviate from the fault projection surfaces toward the hanging wall or foot wall, depending on the fault dip angle; however, both primary and secondary normal ruptures refract at the soil-bedrock interface, deviating toward the hanging wall. In addition, the analyses show that by increasing the fault dip angle, the slopes of the near surface stress paths within the reverse ruptures increase from about the slope of the biaxial compression stress path to about that of the p-constant stress path (compressional regime); conversely, these slopes within the normal ruptures decrease from about the slope of the biaxial extension stress path to about that of the p-constant stress path (extensional regime). Moreover, the analyses show that the fault outcropping strains of reverse faulting are comparatively higher than those of normal faulting. In addition, the fault outcropping strains are proportional to the soil ductility. From fundamental viewpoints, the analyses show that all of the reverse and normal fault ruptures through the denser and looser sands do propagate in parallel with zero-extension lines of the localized areas located along the ruptures paths, provided that the variations of the maximum principal strain directions and dilatancy rates along the ruptures are taken into account; this is in accord with the Roscoe theory.

The Ratcheting Behaviour of Stainless Steel Pressurized Piping Elbows Subjected to Dynamic Out-of-Plane Moments

In this paper the ratcheting behavior of four pairs of stainless steel elbows is studied under conditions of steady internal pressure and dynamic conditions that induced out-of-plane external moments at frequencies typical of seismic excitations. The finite element analysis with the nonlinear kinematic hardening model has been used to evaluate ratcheting behavior of the piping elbows under mentioned loading condition. Material parameters have been obtained from several stabilized cycles of specimens that are subjected to symmetric strain cycles. The direction of maximum strain is at about 45° between the hoop and axial directions. The results show that the direction of highest ratcheting is along the hoop direction rather than the direction of maximum principal strain. Also, the initial rate of ratcheting is large and then it decreases with the increasing cycles. Also, the FE method gives over estimated values compared with the experimental data.

Strain estimation from single forms of distorted fossils — A computer graphics and MATLAB approach

Most of the existing methods of strain analysis can estimate strain in a single form of distorted brachiopod, or trilobite provided independent evidence, such as the association of the fossil with cleavage and/or stretching lineation is available for inferring the direction of maximum principal strain. This article proposes a simple computer graphics based method and its MATLAB code that determine the minimum amount of strain in a single distorted fossil form even if data for inferring the maximum principal strain direction are lacking. Our method is a rapid computer-graphics alternative to some of the existing analytical methods.

Dynamic Rupture Propagation during the 1891 Nobi, Central Japan, Earthquake: A Possible Extension to the Branched Faults

The dynamic rupture process of the 1891 Nobi, Japan, earthquake was closely reinvestigated by using a boundary integral equation method based on currently available observations. We discussed mainly a possibility of the rupture propagation on branched faults, including a buried fault called the Gifu-Ichinomiya line. Several numerical simulations were made incorporating the information on the fault geometry based on the active fault traces on the ground surface and the maximum principal strain direction observed by the triangular surveys for the past 100 years. The results suggest that the rupture should propagate along the buried fault during the Nobi earthquake if a weak geological discontinuity exists along the Gifu- Ichinomiya line and is connected to the Neodani fault, which is one of the major surface faults appearing during the Nobi earthquake.

Remodeling of biological tissue: Mechanically induced reorientation of a transversely isotropic chain network

A new class of micromechanically motivated chain network models for soft biological tissues is presented. On the microlevel, it is based on the statistics of long chain molecules. A wormlike chain model is applied to capture the behavior of the collagen microfibrils. On the macrolevel, the network of collagen chains is represented by a transversely isotropic eight chain unit cell introducing one characteristic material axis. Biomechanically induced remodeling is captured by allowing for a continuous reorientation of the predominant unit cell axis driven by a biomechanical stimulus. To this end, we adopt the gradual alignment of the unit cell axis with the direction of maximum principal strain. The evolution of the unit cell axis’ orientation is governed by a first-order rate equation. For the temporal discretization of the remodeling rate equation, we suggest an exponential update scheme of Euler-Rodrigues type. For the spatial discretization, a finite element strategy is applied which introduces the current individual cell orientation as an internal variable on the integration point level. Selected model problems are analyzed to illustrate the basic features of the new model. Finally, the presented approach is applied to the biomechanically relevant boundary value problem of an in vitro engineered functional tendon construct.

A new micromechanics based CDM model and its application to CMC's

A CDM theory is further developed in order to better model the non linear and dissipative behavior of Ceramic Matrix Composites. A new damage deactivation rule is developed, directly based on mechanics of microcrack behavior, considering both closure effects and the corresponding elastic energy storage. The complete model uses two sets of damage state variables, the scalar ones correspond to microcracks oriented by reinforcements and a second order tensor that evolves with the maximum principal strain directions. The model is applied to uniaxial and multiaxial monotonic and cyclic tests on a SiC/SiC composite. In addition, the new version of the damage deactivation rule allows a progressive effect and a better description of the residual strain.

New progress in micromechanics-based CDM models and their application to CMCs

A previously developed continuum-damage theory for modeling ceramic-matrix composites is modified relative to the deactivation rule. The new deactivation is directly based on mechanics of microcrack behaviour, considering both closure effects and the corresponding elastic energy storage. The model uses two sets of damage state variables, scalar ones corresponding to microcracks oriented by reinforcements and a second rank tensor that evolves with the maximum principal strain directions. The model is applied to uniaxial and multiaxial monotonic and cyclic tests on a SiC/SiC composite.

ＳＵＳ３０４ステンレス鋼の高温多軸低サイクル疲労寿命に及ぼす最大主ひずみ軸方向変化の影響

Low cycle fatigue tests were carried out using cruciform specimens of Type 304 stainless steel under fully ranged multiaxial strain states at 823K. Strain paths employed in the tests were not only proportional strain histories but also severe strain histories including out-of-phase strain in order to examine the effect of stain history on multiaxial fatigue life. The crack mode was also discussed by observing the crack direction on specimen surface. For the cruciform specimen, the principal strain axes are always fixed but the maximum principal strain direction is changed into the one of three principal strain axes due to the severe strain histories. The change in direction of the maximum principal strain from one principal axis to the others had no effect on fatigue life because the additional interaction between slip systems did not occur resulting in no large additional hardening. Only the strain multiaxiality influenced the fatigue life which can be predicted as well as the multiaxial fatigue life under proportional strain histories. The strain history also did not influence the mode of crack initiation.

Crack Growth Behavior in Ti-Ni SMA Coil Spring under Cyclic Thermal and Extension Fatigue.

The fatigue characteristics of Ti-Ni SMA coil springs under cyclic thermal and extension fatigue were investigated. The crack growth behavior and the fracture aspect were observed at several strain levels at three heating temperatures (60, 70 and 80°C). The cracks initiated on the inside surface of the coil springs and propagated in a direction almost perpendicular to the direction of maximum principal strain near the crack origin. The relations between crack growth rate (da/dN) and stress intensity factor range (ΔKσ) and strain intensity factor range (ΔKc) were found to be almost linear in a bilogarithmic graph. In particular, the da/dN-(ΔKc) relation in the case of a 60°C heating temperature was almost same as that in the case of an 80°C heating temperature.

Response and cyclic strain accumulation of pressurized piping elbows under dynamic out-of-plane bending

In a previous publication (1),† an experimental programme, involving four carbon and four stainless steel pairs of 2 inch NPS, 90° welding elbows tested under conditions of steady internal pressure and dynamic inputs that induced resonant in-plane bending at frequencies typical of seismic excitations, was described and some results reported. In this contribution, a similar test programme using identical pressurized components under dynamic conditions that induced out-of-plane external moments at similar frequencies is considered. For each material, two thicknesses (extra strong and standard weight specifications) were chosen and for each thickness two bend radius geometries (long and short) were tested. The similarities and differences in instrumentation, response and behaviour between the two programmes are highlighted. While the dynamic responses and the levels of moment achieved were similar for both types of external loads, there was an important difference in strain behaviour. Firstly, the direction of maximum strain was found to be at about 45° between the hoop and axial directions. Secondly, while there was practically no strain accumulation in the axial direction, ratcheting in both hoop and maximum principal strain directions was initiated at about the same level of input. Thirdly, the direction of highest ratcheting was found to be along the hoop direction rather than the direction of maximum principal strain. The cyclic strain accumulation against response moment for each component is assessed and ratios of applied to limit moment at onset of ratcheting are given for each material.