Lateral Strain Distribution Research Articles

Experimental hysteretic behavior of CFST column-foundation connections with novel detailing in embedded region

This paper presents a novel CFST column-foundation connection detail to improve stress transfer and damage control. To achieve this aim, seven specimens were created in the lab in three different configurations: exposed connection (base plate), embedded connection without reinforcement, and embedded connection with reinforcement. These specimens were subjected to cyclic lateral load and constant axial load tests. The effect of using internal reinforcement (including reinforcing anchor bar and internal tube) and external reinforcement (including shear studs, external diaphragm, and through diaphragm) in the embedded region on the reduction of the embedded depth was assessed. Performance indices of the tested connections, including the stiffness, lateral loading capacity, energy-dissipation capacity, ductility, and strain distribution of steel tubes, were analyzed based on hysteresis and pushover graphs. The test data demonstrated that all the specimens experienced flexural failure, and consequently, the local buckling of the steel tube was observed in all experiments with the exception of the specimen that had an exposed connection. The specimens with reinforcement in the embedded region had acceptable behavior with ductility coefficients higher than 4.8. The seismic response of the connection with the novel detail showed that the performance indices of the connection with reinforcing anchor rebars and reinforcing internal steel tube in the embedded region were considerably higher than those of the connection without reinforcement in the embedded region and the one in the exposed form. Moreover, the depth at which the connection is embedded was reduced by up to 0.7 times the diameter of the column due to the utilization of reinforcement in the embedded region.

Structural behaviour of tyre-bale sandwich wall under axial load

This paper presents structural behaviour of tyre-bale sandwich wall that is made of two outer reinforced concrete walls and tyre-bale as core material. The thickness of tyre-bale and each concrete wall is 650 mm and 125 mm respectively. The concrete walls are reinforced with 6 mm diameter steel bars in each direction. Four sandwich walls were casted and tested on full scale under different compression loadings. In the first test, the axial load was applied directly to the tyre-bale to investigate the tyre-bale compressibility. The effect of eccentric loading was studied in the second test by applying the compression load on one concrete wall. In the third test, load was applied simultaneously on both concrete walls and finally, the fourth compression test was conducted by cutting-off the tie wires to simulate the severe corrosion conditions. The structural behaviour of sandwich wall is discussed in terms of ultimate load, vertical and lateral deflections, strain distribution and failure mechanism. In addition, the change in structural behaviour of sandwich wall under the effect of severe corrosion is presented. A significant reduction in structural capacity of sandwich wall was observed, when simulating corrosion conditions. Finite element modeling (FEM) of the sandwich wall was conducted in ABAQUS to simulate the damage of concrete in compression using concrete damage plasticity model. The difference in experimental and FEM results was found to be 15%. Furthermore, the experimental peak loads are compared with the existing empirical equations, which provided conservative design values to estimate the ultimate design load of sandwich wall.

Lattice strain enhanced acidic etching on as cut sawn silicon wafer

The mechanical processing of silicon wafers leads to a heterogeneous lateral strain distribution and various modifications of the silicon, both of which influence the resulting topography after acid etching. In this study we investigate the influence of local strains and the initial topography of slurry and diamond wire saw wafers on the acid etching mechanism. The strain distribution is quantified and qualified by Raman microscopy before and after thermal treatment, while the topography is characterized by confocal microscopy before and after etching. The thermal treatment was used to selectively relax strains and investigate the effect of the individual strains on the etching mechanism. We found that amorphous silicon and compressive strained silicon are mainly present on the top most surface of the saw damage and do not influence the chemical reactivity of acid etching. In contrast, highly reactive tensile strained silicon is found up to 2.7 μm deep in the saw damage and acts as an etching mask. Rapid etching of the tensile strained silicon by HF/HNO3/H2SiF6 leads to the formation of cracks with high local concentrations of intermediate species. These strains induced cracks are etched out together with the original saw damage induced cracks and trenches and form the final surface after etching. Furthermore, we can show how the tensile strain strength must have a relative Raman shift of at least −2 cm−1 to have an effect on the local etch rate. Our data demonstrate how mechanical treatment in combination with thermal treatment and acidic etching can be used to optimize the resulting topography for applications like photovoltaics. In addition, it provides a deeper insight into the acid etching mechanism for non-planar silicon wafers.

Structural behavior of sandwich composite wall with truss connectors under compression

Sandwich composite wall consists of concrete core attached by two external steel faceplates. It combines the advantage of steel and concrete. The appropriate composite action between steel faceplate and concrete core is achieved by using adequate mechanical connectors. This research studied the compressive behavior of the sandwich composite walls using steel trusses to bond the steel faceplates to concrete infill. Four short specimens with different wall width and thickness of steel faceplate were designed and tested under axial compression. The test results were comprehensively evaluated in terms of failure modes, load versus axial and lateral deformation responses, resistance, stiffness, ductility, strength index, and strain distribution. The test results showed that all specimens exhibited high resistance and good ductility. Truss connectors offer better restraint to walls with thinner faceplates and smaller wall width. In addition, increasing faceplate thickness is more effective in improving the ultimate resistance and axial stiffness of the wall.

Comprehensive effects of TGO growth on the stress characteristic and delamination mechanism in lamellar structured thermal barrier coatings

To clarify the role of thermally grown oxide (TGO) in the failure of thermal barrier coating system (TBCs) is beneficial to further understand coating spallation mechanism and optimize the spraying process. In this study, the influences of TGO growth on the stress state and crack growth behavior upon temperature cycling are quantitatively examined based on a novel model with lamellar structure. Three kinds of TGO growth modes are employed to explore the TGO growth effect. The non-uniform distribution of lateral growth strain through TGO thickness is included in the model. TGO growth is dynamically modeled using the material property change step by step. The successive propagation and coalescence of multi-crack are materialized by a fracture mechanics analysis. The results suggest that the continuous increase of tensile and shear stress with cycles can occur only when the lateral growth strain is considered into the TGO. Large stress concentration arises at the crack tip and near the pore, which is responsible for the early crack growth. The successive growth and linkage of multi-crack can be expected in the model with TGO lateral growth. The spallation path and the variation trend of total crack length achieved in the current model are in line with the results in experiments. The large gradient of lateral strain distribution in TGO will result in a higher cycle to failure and incubation period. However, the overall crack propagation behavior and linkage mechanism are not affected by the lateral strain distribution. The computational results in the current model can provide a theoretical foundation for developing advanced TBCs with long lifetime.

Stress states in plasma-sprayed thermal barrier coatings upon temperature cycling: Combined effects of creep, plastic deformation, and TGO growth

Abstract To ascertain material parameter effects on the stress states is beneficial to comprehend the crack growth behavior and delamination mechanism in thermal barrier coatings (TBCs). In this work, numerical models are established to explore the combined effects of material parameters including creep, plastic deformation, and thermally grown oxide (TGO) growth on the stress states upon temperature cycling. For all layers, thermal-physical properties reliant on temperature are incorporated into the model. The process of bond coat (BC) oxidation, namely TGO growth, is materialized by changing material properties with cycles. Based on the principle of a single variable, the residual stress states are explored using many different material combinations. The results indicate that the tensile stress in the ceramic top coat (TC) decreases with the increase in the TGO lateral strain distribution gradient. Increasing the BC yield strength or decreasing the TGO growth stress can reduce the tensile stress in TC if there is no creep in the model. When BC yield strength is relatively high (≥150 MPa), BC creep will strengthen the TC tensile stress. TGO creep can decrease the tensile stress in TC irrespective of TGO growth stress and BC creep. When TGO creep rate is higher than 10 B tgo , an exceedingly small tensile stress can always be achieved. This work could provide significant theory direction for material selection and composition control towards advanced TBCs with prolonged lifetime.

Stress states and crack behavior in plasma sprayed TBCs based on a novel lamellar structure model with real interface morphology

Abstract To ascertain the crack growth behavior and coalescence mechanism in thermal barrier coatings (TBCs) is beneficial for understanding the failure of TBCs and proposing the probable optimization methods. In this work, a novel lamellar structure model with real interface morphology is developed to explore the crack growth behavior and the failure mechanism of TBCs during thermal cycling. Three typical defects which include pore, inter-splat crack, and intra-splat are incorporated in the model. To simulate the oxidation process of the bond coat (BC) realistically, The oxidation growth process is simulated via changing the BC properties to thermally grown oxide (TGO) properties layer by layer. The effects of the lateral growth strain distribution through TGO thickness on the stress states are executed. Moreover, the influences of BC creep on the crack growth and coating lifetime are further elaborated. The results show that the larger the lateral growth strain gradient, the smaller the residual tensile stress. The irregular interface morphology results in the redistribution of residual stresses. Although the pores and cracks can alleviate the tensile stress near the valley, large stress concentration will occur near them. At the early phase of thermal cycling, the cracks grow steadily. After more cycles, the cracks propagate rapidly and merge with others. The simulated delamination path is in agreement with the experiment results. Not only does BC creep change the crack coalescence mechanism, it also decreases the thermal cyclic lifetime of TBCs. The coating optimization method proposed in this study provides another option for developing advanced TBCs with longer lifetime.

Strain analysis of a seismically imaged mass‐transport complex, offshore Uruguay

AbstractStrain style, magnitude and distribution within mass‐transport complexes (MTCs) are important for understanding the process evolution of submarine mass flows and for estimating their runout distances. Structural restoration and quantification of strain in gravitationally driven passive margins have been shown to approximately balance between updip extensional and downdip contractional domains; such an exercise has not yet been attempted for MTCs. We here interpret and structurally restore a shallowly buried (c. 1,500 mbsf) and well‐imaged MTC, offshore Uruguay using a high‐resolution (12.5 m vertical and 15 × 12.5 m horizontal resolution) three‐dimensional seismic‐reflection survey. This allows us to characterise and quantify vertical and lateral strain distribution within the deposit. Detailed seismic mapping and attribute analysis shows that the MTC is characterised by a complicated array of kinematic indicators, which vary spatially in style and concentration. Seismic‐attribute extractions reveal several previously undocumented fabrics preserved in the MTC, including internal shearing in the form of sub‐orthogonal shear zones, and fold‐thrust systems within the basal shear zone beneath rafted‐blocks. These features suggest multiple transport directions and phases of flow during emplacement. The MTC is characterised by a broadly tripartite strain distribution, with extensional (e.g. normal faults), translational and contractional (e.g. folds and thrusts) domains, along with a radial frontally emergent zone. We also show how strain is preferentially concentrated around intra‐MTC rafted‐blocks due to their kinematic interactions with the underlying basal shear zone. Overall, and even when volume loss within the frontally emergent zone is included, a strain difference between extension (1.6–1.9 km) and contraction (6.7–7.3 km) is calculated. We attribute this to a combination of distributed, sub‐seismic, ‘cryptic’ strain, likely related to de‐watering, grain‐scale deformation and related changes in bulk sediment volume. This work has implications for assessing MTCs strain distribution and provides a practical approach for evaluating structural interpretations within such deposits.

Evaluating the Performance of Geosynthetic Reinforced Soil-Integrated Bridge System (GRS-IBS) under Working Stress Condition

This paper evaluates the performance of geosynthetic reinforced soil-Integrated Bridge System (GRS-IBS) in terms of lateral facing deformation and strain distribution along geosynthetics. Simulations were conducted using 2D PLAXIS program. The hardening model proposed by Schanz et al. [1] was used to simulate the behavior of backfill material; the backfill-reinforcement interface was simulated using Mohr-Coulomb model, and the reinforcement and facing block were simulated using linear elastic models. The numerical model was verified using the results of a case study conducted at Maree Michel GRS-IBS, Louisiana. Parametric study was carried out to investigate the effects of span length, reinforcement spacing, and reinforcement stiffness on the performance of GRS-IBS. The results indicate that span length have significant impact on strain distribution along geosynthetics and lateral facing deformation. The reinforcement stiffness has significant impact on the GRS-IBS behavior up to a certain point, beyond which the effect tends to decrease contradictory to reinforcement spacing that has a consistent relationship between the GRS-IBS behavior and reinforcement spacing. The results also indicate that reinforcement spacing has higher influence on the lateral facing deformation than the reinforcement stiffness for the same reinforcement strength/spacing ratio (Tf/Sv) due to the composite behavior of closely reinforcement spacing.

Experimental investigations of vertical post-tensioned connection for modular steel structures

Modular construction is an off-site construction technique. In this method, structural volumetric modular components are produced in a factory and assembled on-site to form a larger, permanent building. Typical vertical connections of modular steel buildings (MSBs) are provided by on-site welding. Welding may interfere with the finishing of the modules and also when several modules are placed together at a given floor level complete access for welding is compromised. As an alternative to on-site welding, the present paper proposes a new vertical post-tensioned (PT) connection for MSBs. This connection is comprised of a post-tensioned threaded rod installed inside hollow structural sections (HSS) columns and a steel box placed between two modules. In order to evaluate the general and the seismic performance of the proposed connection, eight quasi-static cyclic loading tests were performed in T-shaped subassemblies. A combination of three different steel boxes and three initial post-tensioning loads levels were considered. Additionally, two quasi-static cyclic loading tests were performed using standard welded connections. No local buckling was observed in any of the specimens and no welding fractures occurred up to 3% drift demand. Results indicated that in comparison to the welded connection the proposed PT connection have similar lateral stiffness and strain distribution, and a higher cumulative energy dissipation capability. Therefore, the proposed connection has the potential to eliminate on-site welding in the assembly of the modules while providing the lateral resistance required.

Quasi‐Static Cyclic Test on a Concrete‐Encased Frame‐Reinforced Concrete Tube Building Model

This paper experimentally investigated the seismic behavior of a 1:5 reduced‐scale model of concrete‐encased steel frame‐reinforced concrete core tube building. The quasi‐static testing with multipoint loading was carried out, and mode‐superposition response spectrum method was adopted to control the amplitude of displacement. The damage process, crack pattern, and failure mode were observed. Various parameters were obtained, including lateral deformation, hysteretic characteristics, strain distribution, ductility, and energy dissipation capacity. The test revealed the distributions of base shear between the core tube and frame. The result indicated that the core tube bears major loading and exhibited overturning failure, afterwards frame carry the surplus load and exhibited column tensile failure and joint panel shear failure. The characteristic of two seismic resistant systems are reflected by the excellent cooperation of core tube and frame.

X‐ray characterization of self‐organized periodic body‐centered tetragonal lattices of SiGe dots

Modern nanotechnology offers new possibilities to create artificial materials such as three‐dimensional (3D) ordered island crystals that might be of interest e.g., for optoelectronic applications. We demonstrate that a completely self‐organized body‐centered tetragonal lattice of SiGe dots can be achieved by reduced pressure chemical vapor deposition (RPCVD). Main subject of this paper is the application of different X‐ray diffraction techniques to study the structural properties of a large ensemble of buried SiGe dots with the target to optimize deposition conditions. This includes specular ω‐2Θ scans to reveal vertical periodicity and strain state, reciprocal space mapping to determine lateral arrangement and symmetry of dots, and in‐plane diffraction to get better inside to the lateral strain distribution close to the surface for further growth simulations.SEM cross‐section images of a SiGe/Si superlattice of imperfect lateral periodic structure of SiGe dots.

Improved Correlation of Strain Indices with Cognitive Dysfunction with Inclusion of Adventitial Layer with Carotid Plaque.

Plaque instability may lead to chronic embolization, which in turn may contribute to progressive cognitive decline. Accumulated strain tensor indices over a cardiac cycle within a pulsating carotid plaque may be viable biomarkers for the diagnosis of plaque instability. Using plaque-only carotid artery segmentations, we recently demonstrated that impaired cognitive function correlated significantly with maximum axial and lateral strain indices within a localized region of interest in plaque. Inclusion of the adventitial layer focuses our strain or instability measures on the vessel wall-plaque interface hypothesized to be a region with increased shearing forces and measureable instability. A hierarchical block-matching motion tracking algorithm developed in our laboratory was used to estimate accumulated axial, lateral, and shear strain distribution in plaques identified with the plaque-with-adventitia segmentation. Correlations of strain indices to the Repeatable Battery for the Assessment of Neuropsychological Status Total score were performed and compared with previous results. Overall, correlation coefficients (r) and significance (p) values improved for axial, lateral, and shear strain indices. Shear strain indices, however, demonstrated the largest improvement. The Pearson correlation coefficients for maximum shear strain and cognition improved from the previous plaque-only analyses of -0.432 and -0.345 to -0.795 and -0.717 with the plaque-with-adventitia segmentation for the symptomatic group and for all patients combined, respectively. Our results demonstrate the advantage of including adventitia for ultrasound carotid strain imaging providing improved association to parameters assessing cognitive impairment in patients. This supports theories of the importance of the vessel wall plaque interface in the pathophysiology of embolic disease.

Imaging Structure and Composition Homogeneity of 300 mm SiGe Virtual Substrates for Advanced CMOS Applications by Scanning X-ray Diffraction Microscopy.

Advanced semiconductor heterostructures are at the very heart of many modern technologies, including aggressively scaled complementary metal oxide semiconductor transistors for high performance computing and laser diodes for low power solid state lighting applications. The control of structural and compositional homogeneity of these semiconductor heterostructures is the key to success to further develop these state-of-the-art technologies. In this article, we report on the lateral distribution of tilt, composition, and strain across step-graded SiGe strain relaxed buffer layers on 300 mm Si(001) wafers treated with and without chemical-mechanical polishing. By using the advanced synchrotron based scanning X-ray diffraction microscopy technique K-Map together with micro-Raman spectroscopy and Atomic Force Microscopy, we are able to establish a partial correlation between real space morphology and structural properties of the sample resolved at the micrometer scale. In particular, we demonstrate that the lattice plane bending of the commonly observed cross-hatch pattern is caused by dislocations. Our results show a strong local correlation between the strain field and composition distribution, indicating that the adatom surface diffusion during growth is driven by strain field fluctuations induced by the underlying dislocation network. Finally, it is revealed that a superficial chemical-mechanical polishing of cross-hatched surfaces does not lead to any significant change of tilt, composition, and strain variation compared to that of as-grown samples.

Postannealing Effects on Strain/Crystal Quality of Lateral Source Relaxed/Strained Layer Heterostructures Fabricated by O+ Ion Implantation

We have experimentally studied postannealing effects on the relaxation rate of strain and crystal quality of a lateral relaxed/strained heterostructure layer after the O+ ion implantation process. We have demonstrated the critical annealing temperature as well as the critical recoil energy ER of implanted O+ ions for relaxing the strained layers, using UV-Raman spectroscopy. Moreover, we have shown that the crystal quality increases with increasing postannealing temperature, and high-resolution transmission electron microscopy (HRTEM) images of the cross sections and plane views of the O+-ion-implanted strained-Si layers also show the high crystal quality. Moreover, we have observed a threading dislocation of about 15 nm length between high-quality lateral abrupt-relaxed/strained layer heterostuctures, and the threading dislocation area is a stress buffer layer to form the abrupt lateral-strain distribution.

Lateral Distribution of Anodic Oxides and Strain on Self-Organized Fractal Silicon Photoelectrodes

Fractal microtopographies were prepared on n-type Si(100) photoelectrodes by self-organized anodic dissolution in concentrated ammonium fluoride. The concurrent formation of etch structures, extending along preferential crystallographic directions, and inhomogeneous anodic oxide layers was investigated by synchrotron radiation photoelectron spectroscopy (SRPES) and electrochemical analysis. It is shown that two types of SiO2 layers are forming at the surface, distinguishable by the layer thickness and a shift in the Si(4+) binding energy. The finding is based on chemical analysis with spatial resolution using Photoelectron Emission Microscopy (PEEM): at the tip of fractal branches, reversed contrasts were obtained by detection of the PEEM photoelectron yield of the respective SiO2 layers. Electrochemical analysis was applied for the first time to assess the etching behavior of inhomogeneously distributed oxides in real-time. Oxide thicknesses of about 3–4 nm within microstructures and 5–8 nm on planar areas could be derived. The observation of locally attenuated PEEM signals at the structure boundaries after oxide removal is tentatively assigned to residual strain in a surface-near region. This interpretation thereby complements a recently developed theoretical model for the physicochemical evolution of fractal microstructures on silicon.

Spatially resolved luminescence spectroscopy of single GaN/(Al,Ga)N quantum disks

AbstractThe dependence of the optical transition energy Et of GaN quantum disks (Qdisks) embedded within (Al,Ga)N nanocolumns grown on a (111) Si substrate on disk thickness, disk diameter, barrier thickness, and barrier composition has been investigated by both spatially resolved cathodoluminescence spectroscopy and applying a theoretical model. Results of Et on the disk and barrier thickness, as well as barrier composition resemble those of corresponding quantum wells, whereas results on the disk diameter are essentially determined by the lateral strain distribution of the Qdisks. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Plastic strain distribution underneath a Vickers Indenter: Role of yield strength and work hardening exponent

The effects of yield strength, σ y, and strain hardening exponent, n, on the plastic strain distribution underneath a Vickers indenter were explicitly examined by carrying out macro- and micro-indentation experiments on Al–Zn–Mg alloy that was aged for different times so as to obtain materials with different σ y but with similar n, or the same σ y but different n. Large Vickers indents were made (using a load of 700 N) that were subsequently sectioned along the median plane and the plastic strain distribution was determined by recourse to microindentation mapping. Comparison of the iso-strain contours shows that for similar values of n, higher σ y leads to a smaller deformation field in both the indentation ( z) and lateral ( x) directions. Higher n, at the same σ y, leads to a shallower deformation field. In all cases, it was found that strain fields are elliptical, with the long axis of the ellipse coinciding with the z-direction. The strain field ellipticity is sensitive to the work hardening behavior of the material, with higher n leading to lower ellipticity. While the lateral strain distribution is in agreement with the expanding cavity model, strain distribution directly ahead of the indenter tip appears to follow the Hutchison, Rice, and Rosengren fields ahead of a crack tip in an elastoplastic solid.

Biomechanical evaluation of the ventral and lateral surface shear strain distributions in central compared with dorsolateral placement of cages for lumbar interbody fusion

The purpose of this study was to measure and compare the ventral and lateral surface strain distributions and stiffness for two types of interbody cage placement: 1) central placement for anterior lumbar interbody fusion (ALIF); and 2) dorsolateral placement for extraforaminal lumbar interbody fusion (ELIF). Two functional spine units were obtained for testing in each of 13 cadaveric spines, yielding 26 segments (three of which were not used because of bone abnormalities). Bilateral strain gauges were mounted adjacent to the endplate on the lateral and ventral walls of each vertebral body in the 23 motion segments. Each segment was cyclically tested in compression, flexion, and extension in the following conditions: while intact, postdiscectomy, and instrumented with interbody fusion cages placed using both insertion techniques. No significant differences were observed between ALIF and ELIF in compressive stiffness, bending stiffness in flexion and extension (p > or = 0.1), ventral and lateral strain distribution during the intact tests (p > or = 0.24), and during the flexion tests after fusion (p > or = 0.22). In compression, higher ventral and lower lateral strain was observed in the ALIF than in the ELIF group (ventral, p = 0.05; lateral, p = 0.04), and in extension, higher ventral (p = 0.01) and higher lateral strain (p = 0.002) was observed in the ELIF than in the ALIF group. Preservation of the ventral anulus and dorsolateral placement of the interbody cages during ELIF allow alternate load transfer pathways through the dorsolateral vertebral wall and ventral anulus that are not observed following ALIF. These may be associated with a lower incidence of subsidence and a higher rate of fusion due to a more concentrated application of bone healing-enhancing compression forces during the fusion and healing process.

Misfit dislocation dipoles in Si/SiGe/Si heterostructures on SOI

Transmission electron microscopy (TEM) and synchrotron radiation double-crystal topography (SRDT) have been employed to investigate Si/SiGe/Si heterostructures grown by ultra-high vacuum chemical vapor deposition (UHVCVD) on bonded Si-on-insulator (SOI) wafers. A configuration of misfit dislocation dipoles is observed by high-resolution transmission electron microscopy (HRTEM). The dislocation dipoles are mostly of 60° type and three types of 60° dislocation dipoles, extrinsic, intrinsic, and null, are presented. Dark-field images (DFIs) indicate no lateral compositional modulations but strain distribution appearing in the SiGe layer, which is supported by the SRDT topograph. We suggest that the lateral strain modulation in the SiGe layer and subsequent annealing play an important role in the introduction of the dislocation dipoles.