Quantitative Stress Analysis Research Articles

Microstructure strengthening mechanisms in different equal channel angular pressed aluminum alloys

Microstructure characterization and identification of the different nature of boundary formation during severe plastic deformation is the basis for a quantitative analysis of material flow stress. In equal channel angular pressing, the microstructure evolves to form low-angle dislocation boundaries and high-angle boundaries whose origin is different. For this reason, boundary misorientation, size and fraction evolve differently with strain. The Hall–Petch relationship in severe plastic deformed aluminum and aluminum alloys has been extensively discussed by Niels Hansen and others in several published works. It appeared that in such cases, the dislocation boundary strengthening contribution is to be taken into account. This paper deals with further insights into the Hansen's and other authors approach to the Hall–Petch relationship. Present approach is based on a detailed microstructure characterization of the different strengthening contributions in severe plastic deformed aluminum alloys. AA1200, AA3103, AA6000 series, and AA2091 were quantitatively characterized by TEM inspections. The calculated alloys yield strengths were compared to measured tensile yield stresses obtaining a quite satisfactory matching. This, ultimately, confirmed the proposed approach and models. Finally, an experimental value of the hardness-to-yield stress, H/σy, was found for all the studied alloys and discussed accordingly.

Finite element modeling of the human pulmonary autograft: A quantitative analysis of wall stress after the Ross procedure

CONCLUSIONS: Underinsured patients are at the greatest risk of requiring non-elective thoracic aortic operations, likely due to decreased use of anti-hypertensive and lipid-lowering therapies, and aortic surveillance. After presentation for treatment, insurance status does not confer additional independent operative risk. These data suggest that greater access to preventative cardiovascular care may reduce the need for non-elective thoracic aortic surgery and lead to improved survival from thoracic aortic disease.

Fabrication of Large-Area Three-Dimensional Microstructures on Flexible Substrates by Microtransfer Printing Methods

This paper presents two robust microtransfer printing methods, namely, multiple transfer printing and peeling microprinting methods, to fabricate three-dimensional (3-D) and high-aspect-ratio microelectromechanical systems (MEMS) structures over large areas on flexible polydimethylsiloxane (PDMS) substrates. These techniques enable conformal wrapping of 3-D microstructures, initially fabricated in two-dimensional (2-D) layouts with standard fabrication technology onto a wide range of surfaces with complex and curvilinear shapes. The processes exploit the differential adhesive tendencies of the microstructures formed between a donor and a transfer substrate to accomplish an efficient release and transfer process. Experimental and theoretical studies show that the MEMS structures with a wide variety of pattern densities can be conformally transferred to bendable device substrates while keeping the structural integrity and density intact. Quantitative stress analysis on the micromechanics of such a curvilinear system suggests that the stress induced by wrapping the complete structure onto a cylinder is mostly in the flexible PDMS substrate, while the MEMS structures experience little stress.

In situquantitative analysis of stress and texture development in forsterite aggregates deformed at 6 GPa and 1373 K

The investigation of materials plastic properties at high pressure is a fast-growing field, owing to the coupling of high-pressure deformation apparatuses with X-ray synchrotron radiation. In such devices, materials strain and strain rate are measured by time-resolved radiography, while differential stress is deduced from the elastic response of thedspacing of the crystallographic planes as measured by X-ray diffraction. Here a new protocol is presented, which allows thein situmeasurement of stress and texture development in aggregates deformed at high pressure for experiments carried out with the recently installed ten-element energy-dispersive detector at the X17B2 beamline of the National Synchrotron Light Source (Brookhaven National Laboratory, Upton, NY, USA). Cycling deformation of a forsterite specimen was carried out at a pressure of ∼6 GPa and a temperature of ∼1373 K, using a deformation-DIA apparatus. Diffraction peak energies are analysed in terms of differential stress and principal stress direction, while the intensities of peaks obtained at different azimuths are analysed in terms of lattice preferred orientation (LPO). The development and evolution of a marked LPO, with the (010) plane perpendicular to the compression axis, is observedin situduring the run and is confirmed by electron backscatter diffraction measurements on the run product.

Residual stress in electrodeposited nanocrystalline nickel-tungsten coatings

Abstract

2D and 3D finite element analysis of central incisor generated by computerized tomography

The purpose of this study was to compare the results of different hierarchical models in engineering analysis applied to dentistry with 2D and 3D models of a tooth and its supporting structures under 100 N occlusal loading at 45° and examine the reliability of simplified 2D models in dental research. Five models were built from computed-tomography scans: four 2D models with Plane Strain and Plane Stress State with linear triangular and quadratic quadrilateral elements and one 3D model. The finite element results indicated that the stress distribution was similar qualitatively in all models but the stress magnitude was quite different. It was concluded that 2D models are acceptable when investigating the biomechanical behavior of upper central incisor qualitatively. However, quantitative stress analysis is less reliable in 2D-finite element analysis, because 2D models overestimate the results and do not represent the complex anatomical configuration of dental structures. Therefore 3D finite element analyses of dental biomechanics cannot be simplified.

Rough faults, distributed weakening, and off‐fault deformation

We report systematic spatial variations in fault rocks along nonplanar strike‐slip faults cross‐cutting the Lake Edison Granodiorite, Sierra Nevada, California (Sierran wavy fault) and Lobbia outcrops of the Adamello Batholith in the Italian Alps (Lobbia wavy fault). In the case of the Sierran fault, pseudotachylyte formed at contractional fault bends, where it is found as thin (1–2 mm) fault‐parallel veins. Epidote and chlorite developed in the same seismic context as the pseudotachylyte and are especially abundant in extensional fault bends. We argue that the presence of fluids, as illustrated by this example, does not necessarily preclude the development of frictional melt. In the case of the Lobbia fault, pseudotachylyte thickness varies along the length of the fault, but the pseudotachylyte veins thicken and pool in extensional bends. We conduct a quantitative analysis of fault roughness, microcrack distribution, stress, and friction along the Lobbia fault. Numerical modeling results show that opening in extensional bends and localized thermal weakening in contractional bends counteract resistance encountered by fault waviness, resulting in an overall weaker fault than suggested by the corresponding static friction coefficient. The models also predict static stress redistribution around bends in the faults which is consistent with distribution of microcracks, indicating significant elastic and inelastic strain energy is dissipated into the wall rocks due to nonplanar fault geometry. Together these observations suggest that damage and energy dissipation occurs along the entire nonplanar fault during slip, rather than being confined to the region close to the dynamically propagating crack tip.

Serum concentrations of interleukin-6 in patients following unilateral versus bilateral total knee arthroplasty

BackgroundSurgical stress is known to affect body temperature, white blood cell (WBC) count, C-reactive protein (CRP), and interleukin-6 (IL-6). The aim of the present study was to investigate which parameter is most suitable for quantitative analysis of surgical stress. MethodsUnilateral total knee arthroplasty (U-TKA) and bilateral TKA (B-TKA) were selected for the subjects of this study because the B-TKA creates approximately double the surgical stress of the U-TKA. The temperature, WBC count, CRP, and IL-6 in the blood were measured pre- and postoperatively in both groups. The IL-6 in the drainage fluid was also measured after the operation. ResultsThe temperature, WBC count, CRP, and IL-6 in the blood significantly increased on the first day after the operation in both groups. There were significant differences between the two groups in the WBC count (P < 0.05) and the IL-6 level in the blood (P < 0.05) on the first day after the surgery. There were no significant differences between the two groups for the CRP and IL-6 levels in the drainage fluid. The relative proportions — (B-TKA/U-TKA) x 100 (%) — were 170.4% for the operating time, 219.4 % for total blood loss, 200.0% for blood transfusion, 100.3% for temperature, 128.9% for WBC count, 127.4% for CRP, and 246.5% for the IL-6 level in the blood. ConclusionsThe serum IL-6 level may best reflect surgical stress and could therefore be a quantitative marker of surgical stress.

Reactive diffusion in nanostructures of spherical symmetry

To investigate reactive diffusion in nanosized spherical geometries, a clear model experiment has been designed. Thin film {Al/Cu/Al} and {Cu/Al/Cu} triple layers were deposited on tips of 25 nm apex radius and investigated by atom probe tomography (APT). At the interfaces within both samples, the growth of the reaction product proceeds parabolically from the very beginning but with remarkably different rates. Growth appears to be always faster if Cu is stacked to the outer side of Al. The complex quantitative analysis of reaction-induced stress, surface tensions and partial mobilities suggests that the different growth rates represent the Darken and the Nernst–Planck limits of interdiffusion. Since the curvature radius of the model samples ranges down to a few tens of nanometers, it is anticipated that an analogous effect may play a role in the oxidation of nanospheres or in chemical reactions of core–shell structures.

Calibration of the thermoelastic constants for quantitative thermoelastic stress analysis on composites

The application of thermoelastic stress analysis in composite materials is particularly complicated because of the anisotropy of the material, that determines the thermoelastic constant to be dependent on the direction of the fibers. A further difficulty depends on the constructive stratification of the material, whose mechanical properties vary with the depth from the surface and this causes thermoelastic constants to be dependent on the frequency of the load applied. By using an analytical two layer model, it has been possible to interpret experimental data, thus proposing an explanation of the dependence on the frequency of the measured thermoelastic constants. This has shown that the practical use of the thermoelastic effect for quantitative stress analysis on composites needs constants calibrated at the correct frequency, also considering the thin layer of superficial resin present in every composite material.

Correlating Raman peak shifts with phase transformation and defect densities: a comprehensive TEM and Raman study on silicon

AbstractSilicon is the most often used material in micro electromechanical systems (MEMS). Detailed understanding of its mechanical properties as well as the microstructure is crucial for the reliability of MEMS devices. In this paper, we investigate the microstructure changes upon indentation of single crystalline (100) oriented silicon by transmission electron microscopy (TEM) and Raman microscopy. TEM cross sections were prepared by focused ion beam (FIB) at the location of the indent. Raman microscopy and TEM revealed the occurrence of phase transformations and residual stresses upon deformation. Raman microscopy was also used directly on the cross‐sectional TEM lamella and thus microstructural details could be correlated to peak shape and peak position. The results show, however, that due to the implanted Ga+ ions in the lamella the silicon Raman peak is shifted significantly to lower wavenumbers. This hinders a quantitative analysis of residual stresses in the lamella. Furthermore, Raman microscopy also possesses the ability to map deformation structures with a lateral resolution in the submicron range. Copyright © 2009 John Wiley &amp; Sons, Ltd.

An investigation of pulsatile flow in a model cavo‐pulmonary vascular system

AbstractThe complexities in the flow pattern in a cavo‐pulmonary vascular system—after application of the Fontan procedure in the vicinity of the superior vena cava, inferior vena cava, and the confluence at the T‐junction—are analysed. A characteristic‐based split (CBS) finite element scheme involving the artificial compressibility approach is employed to compute the resulting flow. Benchmarking of the CBS scheme is carried out using standard problems and with the flow features observed in an experimental model with the help of a dye visualization technique in model scale. The transient flow variations in a total cavo‐pulmonary connection (TCPC) under pulsatile conditions are investigated and compared with flow visualization studies. In addition to such qualitative flow investigations, quantitative analysis of energy loss and haemodynamic stresses have also been performed. The comparisons show good agreement between the numerical and experimental flow patterns. The numerically predicted shear stress values indicate that the pulsatile flow condition is likely to be more severe than steady flow, with regard to the long‐term health of the surgically corrected TCPC. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Regional myocardial perfusion reserve determined using myocardial perfusion magnetic resonance imaging showed a direct correlation with coronary flow velocity reserve by Doppler flow wire

Quantitative analysis of rest-stress myocardial perfusion magnetic resonance imaging (MRI) can provide assessments of regional myocardial perfusion reserve (MPR). The purpose of this study was to compare regional MPR determined by myocardial perfusion MRI with coronary flow reserve (CFR) by intracoronary Doppler flow wire. Twenty patients with suspected coronary artery disease (CAD) were studied. Average peak velocity was measured by Doppler flow wire in the resting state and during adenosine triphosphate (ATP) stress in 36 coronary arteries. CFR measurements for each patient were performed in the culprit and one non-culprit non-stenotic artery. First-pass, contrast-enhanced myocardial perfusion MR images were obtained in the resting state and during ATP stress within the week before the Doppler wire procedure. Regional myocardial blood flow (MBF) was quantified in 16 myocardial segments by analysing arterial input and myocardial output using a Patlak plot method. MPR was calculated as stress MBF divided by rest MBF. CFR measured by Doppler flow wire was compared with MPR in the myocardial segments corresponding to vessel territories. The average MPR measured by perfusion MRI was 1.77 +/- 0.62 for the culprit arteries and 3.45 +/- 0.78 for the non-culprit arteries, respectively (P < 0.001). The averaged CFR by Doppler flow wire was 1.72 +/- 0.44 in the culprit arteries and 3.14 +/- 0.74 in the non-culprit arteries, respectively (P < 0.001). For both culprit and non-culprit vessel groups, significant direct correlations were observed between MR assessments of MPR and Doppler assessments of CFR (culprit artery: R = 0.87, Non-culprit artery: R = 0.86) On Bland-Altman analysis, the mean differences between MPR determined by myocardial perfusion MRI and CFR measured by Doppler wire were 0.05 in culprit arteries (95% limit of agreement; -0.65 to 0.56) and 0.36 in non-culprit arteries (95% limit of agreement; -1.24 to 0.44). The sensitivity and specificity of MR measurement of MPR for predicting physiologically significant reduction of Doppler CFR (<2) was 88% (95% CI 61.7-98.5) and 90% (95% CI 68.3-98.8), respectively. The current results using Doppler flow wire as a reference method demonstrated that quantitative analysis of stress-rest myocardial perfusion MRI can provide a non-invasive assessment of reduced MPR in patients with CAD.

Factors Influencing the Suitability of Thermal Methods for Stress Analysis of NiTi Shape Memory Alloys

The material assumptions made to facilitate Thermoelastic Stress Analysis (TSA) are linear elasticity, material homogeneity and isotropy, and mechanical properties that are independent of temperature. The unusual shape memory and superelastic properties of near equiatomic NiTi alloys complicate the application of any experimental stress analysis technique, and in the case of TSA, make these assumptions invalid. This paper describes a detailed analysis conducted to characterise the material properties of NiTi shape memory alloys and to identify loading conditions suitable for quantitative stress analysis using TSA. The mechanical behaviour of the material in three distinct regions is considered and the suitability of each region for TSA is discussed. It is shown that the thermoelastic response is dependent on the mean stress when tested at room temperature in the pre-martensitic phase, due the presence of an intermediate R-phase. Theoretical calculations are used to confirm that this effect is related to the high temperature dependence of the material’s Young’s modulus.

Optimizing Silica Encapsulation of Living Cells: In Situ Evaluation of Cellular Stress

The encapsulation of living cells in materials with good optical and mechanical properties often produces death or stress due to the release of toxic byproducts originated during the synthesis. We present here a method to assess the cellular stress that silica entrapment exerts over living cells taking into account the main preparation variables such as the nature of the silica source, protecting functional groups, total solid concentration, or indirect procedures. Measurement of the cellular stress status of genetically modified Sacharomyces cerevisiae, a true biological probe, allowed us to perform a quantitative analysis of cellular stress in a short time basis (compared to conventional long-term viability tests), opening the gate for a more sophisticated approach to optimize the synthesis conditions. In addition, the aforementioned findings allowed the preparation of novel materials with enhanced optical and mechanical properties. The relation of cellular stress with initial viability is also discussed.

Rapid qualitative phase analysis in highly textured thin films by x-ray diffraction

Phase analysis of highly out-of-plane textured specimens using x-ray diffraction is usually complicated due to the disappearance of most of the x-ray peaks in a common theta/2 theta diffraction geometry. In this paper, we propose a technique, where powderlike spectra of textured samples are obtained by multiaxial x-ray diffraction scans. This technique is a simple, yet powerful method which allows for significant improvement in thin film characterization and provides several types of information about the samples, such as the rapid qualitative identification of phases using common powder x-ray diffraction spectra databases, texture distribution, and quantitative residual stress analysis.

Stress imagining of semiconductor surface by tip‐enhanced Raman spectroscopy

Tip-enhanced Raman imaging of strained silicon reveals the property of nanoscale stress imposed on the lattice. Our approach relies on the highly localized excitation provided by a metallized tip. Surface sensitive detections in nanoscale are realized by a reflection-mode configuration combined with 442-nm excitation and a silver-coated silicon nitride tip. The background signals from an underlying silicon germanium layer and a tip are well suppressed. The quantitative stress analysis is made on the basis of the Raman shift of the Si-Si phonon mode. We succeeded in visualizing the localized stress with a spatial resolution down to 25 nm whereas a conventional micro Raman technique provides only a uniform image because of the averaging effect within a diffraction-limited focused spot.

Determination of stored elastic energy in plastically deformed copper

The quantitative analysis of stresses in plastically deformed copper samples was performed using the self-consistent model and X-ray diffraction measurements of lattice strains. The {220} strain pole figures were determined for the samples subjected to different magnitude of tensile deformation. Using diffraction data and self-consistent model, the tensor of plastic incompatibility stress, was found for each orientation of a polycrystalline grain. The distribution of elastic stored energy was presented in the Euler space and correlated with preferred orientations of grains. Moreover, using the model prediction, variation of the critical resolved shear stress with grain orientation was shown.

Quantitative real-time analysis of nucleolar stress by coherent phase microscopy

We develop a method of coherent phase microscopy (CPM) for direct visualization of nonfixed, nonstained mammalian cells (both cultured cells and freshly isolated tumor biopsies) followed by computer-assisted data analysis. The major purpose of CPM is to evaluate the refractive properties of optically dense intracellular structures such as the nucleus and the nucleoli. In particular, we focus on quantitative real-time analysis of the nucleolar dynamics using phase thickness as an equivalent of optical path difference for optically nonhomogenous biological objects. Pharmacological inhibition of gene transcription leads to a dramatic decrease of the phase thickness of the nucleoli within the initial minutes of cell exposure. Furthermore, the acute depletion of intracellular ATP pool, depolymerization of microtubules and inhibition of DNA replication resulted in a rapid decrease of the nucleolar phase thickness. These optical effects were paralleled by segregation of nucleolar components as documented by electron microscopy. Thus, CPM detects early changes of nucleolar dynamics, in particular, the nucleolar segregation as part of general cellular response to cytotoxic stress, regardless of whether the nucleolus is or is not the primary target of the toxin. CPM is applicable for monitoring and quantitative analysis of the "nucleolar stress" in living mammalian cells.

Measurement techniques and preliminary results of drop tests with full scale spent fuel transport and storage casks

The experimental testing and quantitative stress analysis of new cask designs becomes more and more important with increasing size of casks and their impact limiters, in order to assess the safety margins as well as for calculation validation reasons. Full scale drop testing of spent fuel transport and storage casks is performed by the Federal Institute for Materials Research and Testing within the type B package approval procedure and for safety demonstration reasons respectively. In drop tests for demonstrating ability of a package to withstand normal and accident conditions of transport, the instrumentation of a specimen is an important tool to evaluate its mechanical behaviour during impact. Generally, the instrumentation incorporates the measurement of strains and accelerations at the package. Test results as deceleration–time and strain–time functions constitute a main basis for the validation of assumptions in the safety analysis, for the evaluation of calculations based on finite element methods and extrapolation of scale model testing on full sized package within approval design tests. Besides, all of the above mentioned instrumentation, the flatness of the sealing area and the circularity of the cask lid flange are determined by using three-dimensional coordinate measurements to evaluate the mechanical impact behaviour of the cask flange region after the drop test sequence. Indispensable are measurements concerning leak tightness of the closure lid system. Additionally, specific photogrammetric measurements are used to characterise the conditions of the closure lid system after drop test in more detail. The preparation and interpretation of the results is in progress and indicates possible correlations between the leak tightness rate and measures of the relative movement of the lid.