Mechanical Stress Distribution Research Articles

Plant ramifications inspire branched lightweight composites

The junctions between stems and branches in arborescent monocotyledons and columnar cacti are structurally and functionally poorly understood to date. Therefore, the functional anatomy and morphology of these junctions as well as the arrangement and biomechanics of mechanically relevant tissues were investigated. Both plant groups share distinctive anatomical features. Due to restricted secondary growth, newly formed tissues connecting stem and branch clasp around the main shoot, resulting in a “flange-mounted” structure. In addition, an indentation or a distinct necking forming a specific shape characterizes the area of attachment. As a result, the distribution of mechanical stresses is modified by increasing the resistance against high stresses upon static and presumably also upon dynamic loading. The mechanically important fibrous bundles or wood lamellae are collinearly aligned with the occurring stresses leading to a lateral shift of the stress trajectories and a shape adjustment. This particular branching type shows a remarkable potential to improve joints in braided fiber-reinforced composites. In the near future, a fully automated fabrication of biomimetic branched composites will be possible. First promising demonstrators have already been produced on lab scale.

A comparative evaluation of the hybrid technique for fixation of the sagittal split ramus osteotomy in mandibular advancement by mechanical, photoelastic, and finite element analysis

This study evaluated the mechanical characteristics and stress distribution of the hybrid technique fixation of the sagittal split ramus osteotomy. In the mechanical test, 10 polyurethane replicas of human hemimandibles of each group were submitted to linear loading test. For the photoelastic evaluation, 3 hemimandible replicas of photoelastic resin were subjected to photoelastic analysis. In the finite element analysis, 3 computer models simulated the displacement and the results of maximum principal stress were analyzed. The results of this study demonstrated that the fixation technique with 3 bicortical screws presented better mechanical resistance and stress distribution pattern when compared with the hybrid technique that, on the other hand, presents better results in comparison with a miniplate and monocortical screws. The results suggest that the hybrid technique increased the resistance and improved stress distribution of miniplate/monocortical screw fixation, maintaining most of the advantages of this technique.

Spatial distribution of dynamic mechanical stresses in ionic crystals under the action of a pulsed electron beam

We report on the results of experimental and theoretical investigation of the shape of an acoustic pulse generated in alkali-halide crystals by a pulsed electron beam with a maximal electron energy of 0.28 MeV and an energy density of 0.10–0.65 J/cm2. It is found that the shape of the acoustic pulse for the given beam parameters substantially differs from the absorbed energy density profile. The formation of the fine structure of the acoustic pulse is associated with local release of energy due to the evolution of multichannel electrical breakdown.

Mechanical Stress on Double Stranded DNA Drives Homology Recognition

RecA performs a homology search that compares a single stranded DNA (ssDNA) to a double stranded DNA (dsDNA) and accurately recognizes homologous sequences in a background containing non-homologous and near-homologous sequences. This recognition process can occur in the absence of ATP hydrolysis, indicating that it must be thermodynamically reversible and free energetically favorable. In this poster, we examine the mechanism by which RecA performs comparisons over sequences that are much longer than an individual protein while avoiding kinetic trapping in regions with local accidental homology. We present a model of RecA bound to DNA that uses a simplified version of its known structure to calculate the distribution of mechanical stress in the protein/DNA complex. In addition, we use computer simulations to model the dynamic polymerization process. We propose that the lattice mismatch between the more strongly and weakly bound strands of DNA results in a mechanical stress that increases non-linearly with the number of bound base pairs. The distribution of stress combined with an iterative homology search may explain several previously unexplained features of the structure and function of RecA. The model is consistent with mechanical data obtained from magnetic tweezer measurements of polymerization of RecA on double stranded DNA (dsDNA) and the extension of RecA-ssDNA filaments on dsDNA. RecA's mechanism can also be instructive for artificial self-assembled systems.

Piezooptic Effect and Dislocation Structure in Paratellurite Single Crystals

Theoretically and experimentally the possibility of revealing the dislocation structure of paratellurite with the aid of piezooptic effect is demonstrated. Calculations are given of the mechanical stress distribution around dislocations. Both photoelastic and chemical etching methods were employed to delineate the dislocations in plane-parallel and spherical samples. Data on the distribution of dislocations in Czochralsky-grown crystals are presented.

Bone remodelling: A combined biomechanical and systems‐biological challenge

AbstractBone tissues are formed by cells, bone matrix and fluids. The bone matrix is a porous structure, which is remodelled by bone‐cells. To describe this process, a coupled systems‐biological and biomechanical model is presented.The macroscopic mechanical behaviour of bone is specified by a biphasic model embedded in the Theory of Porous Media, where the solid phase represents cells and bone matrix, and the fluid phase summarises the extracellular fluids and its components. In this context, the bone remodelling process is described on the macro‐scale by a distinct mass exchange that also results in a change of the constituents'material properties.On the micro‐scale, the description of the bone remodelling process stems from a systems‐biological cell interaction model. Therein, the bone matrix formation and resorption are a result of the stress‐regulated activity of cells.Here, a staggered solutions strategy is presented. Therein, snapshots of the mechanical stress distribution are calculated on the macro‐scale by use of the finite element method. The snapshots are locally evaluated on the micro‐scale by use of a cell interaction model, which calculates the long term remodelling process. The evaluation results of the micro‐scale are then used to update the reference configuration of the mechanical simulation. As an integrative modelling platform scientific workflows and web‐service technologies are employed. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim

Multi-scale Simulation Methodology for Stress Assessment in 3D IC: Effect of Die Stacking on Device Performance

Potential challenges with managing mechanical stress distributions and the consequent effects on device performance for advanced 3D integrated circuit (IC) technologies are outlined. A set of physics-based compact models for a multi-scale simulation, to assess the mechanical stress across the device layers in silicon chips stacked and packaged with the 3D through-silicon-via (TSV) technology, is proposed. A calibration technique based on fitting to measured stress components and electrical characteristics of the test-chip devices is presented. For model validation, high-resolution strain measurements in Si channels of the test-chip devices are needed. At the nanoscale, the transmission electron microscopy (TEM) is the only technique available for sub-10 nm strain measurements so far.

Static response and free vibration of two-dimensional functionally graded metal/ceramic open cylindrical shells under various boundary conditions

The free vibration and static response of a two-dimensional functionally graded (2-D FGM) metal/ceramic open cylindrical shell are analyzed using 2-D generalized differential quadrature method. The open cylindrical shell is assumed to be simply supported at one pair of opposite edges and arbitrary boundary conditions at the other edges such that trigonometric functions expansion can be used to satisfy the boundary conditions precisely at simply supported edges. This paper presents a novel 2-D power-law distribution for ceramic volume fraction of 2-D FGM that gives designers a powerful tool for flexible designing of structures under multifunctional requirements. Various material profiles in two radial and axial directions are illustrated using the 2-D power-law distribution. The effective material properties at a point are determined in terms of the local volume fractions and the material properties by the Mori–Tanaka scheme. The 2-D generalized differential quadrature method as an efficient and accurate numerical tool is used to discretize the governing equations and to implement the boundary conditions. The convergence of the method is demonstrated, and to validate the results, comparisons are made with the available solutions for FGM cylindrical shells. The interesting results indicate that a graded ceramic volume fraction in two directions has a higher capability to reduce the mechanical stresses and natural frequency than conventional 1-D FGM. The achieved results confirm that natural frequency and mechanical stress distribution can be modified to a required manner by selecting an appropriate volume fraction profile in two directions.

Tensile Properties, Collagen Content, and Crosslinks in Connective Tissues of the Immature Knee Joint

BackgroundThe major connective tissues of the knee joint act in concert during locomotion to provide joint stability, smooth articulation, shock absorption, and distribution of mechanical stresses. These functions are largely conferred by the intrinsic material properties of the tissues, which are in turn determined by biochemical composition. A thorough understanding of the structure-function relationships of the connective tissues of the knee joint is needed to provide design parameters for efforts in tissue engineering.Methodology/Principal FindingsThe objective of this study was to perform a comprehensive characterization of the tensile properties, collagen content, and pyridinoline crosslink abundance of condylar cartilage, patellar cartilage, medial and lateral menisci, cranial and caudal cruciate ligaments (analogous to anterior and posterior cruciate ligaments in humans, respectively), medial and lateral collateral ligaments, and patellar ligament from immature bovine calves. Tensile stiffness and strength were greatest in the menisci and patellar ligament, and lowest in the hyaline cartilages and cruciate ligaments; these tensile results reflected trends in collagen content. Pyridinoline crosslinks were found in every tissue despite the relative immaturity of the joints, and significant differences were observed among tissues. Notably, for the cruciate ligaments and patellar ligament, crosslink density appeared more important in determining tensile stiffness than collagen content.Conclusions/SignificanceTo our knowledge, this study is the first to examine tensile properties, collagen content, and pyridinoline crosslink abundance in a direct head-to-head comparison among all of the major connective tissues of the knee. This is also the first study to report results for pyridinoline crosslink density that suggest its preferential role over collagen in determining tensile stiffness for certain tissues.

Comparison of SOI and Partial-SOI LDMOSFETs Using Electrical–Thermal–Stress Coupled-Field Effect

The requirement of electrical-thermal-stress (E-T-S) modeling of semiconductor devices as indicated by ITRS2006 demands the use of finite-element analysis (FEA) for device simulation. In this paper, we perform E-T-S coupled-field simulation from the first principle by considering the stress-induced modification of the Si band structures and employ FEA software COMSOL to apply the E-T-S model on lateral double-diffused MOS field-effect transistors (LDMOSFETs) as an example. From the comparison of the electrical characteristics computed using the models with and without the mechanical stress caused by material thermal mismatch in the device structures, we found that the effect of the mechanical stress is insignificant in the forward-bias condition but it does have impact in the reverse-bias condition, namely, the reverse leakage current is higher if the mechanical stress is considered. Simulations are performed on two types of LDMOSFETs, namely, silicon-on-insulator (SOI) and partial-SOI (PSOI) LDMOSFETs, because the temperature and mechanical stress distributions are very different in these LDMOSFETs even under the same operating conditions. From the comparison of the computational results of SOI and PSOI LDMOSFETs, the results indicate that PSOI power LDMOSFET structure enables efficient heat conduction from the hot junctions and offers higher breakdown voltage.

Mode excitation efficiency for contour vibrations of piezoelectric resonators

This paper addresses a theoretical procedure for control of the contour mode excitation efficiency in thin piezoelectric arbitrarily-shaped resonators by adjusting the surface electrode configuration to the mechanical stress distribution. The procedure allows accurate determination of at least five efficiently excited modes for various electrode configurations. This is validated by experimentally measured data for rectangular resonators. For the first time, electrode configurations are suggested that provide high values of the dynamic electromechanical coupling factor for the longitudinal edge mode in a rectangular resonator, while the excitation of spurious modes is suppressed.

Mechanical Analysis of Steel Beam and Steel-Concrete Combined Section Pavement in Long-Span Hybrid Girder Bridge

Firstly the pavement compound system model of steel beam and steel-concrete combined section are established based on structure characteristics of long-span hybrid girder bridge, and the worst loading locations and their characteristics of two beams are obtained. Then, mechanical responses of pavement under the worst loading locations are analyzed to compare mechanical control indices and stress distribution of two beam model. parameters and suggestions are provided for formulation of standards of long-span hybrid girder bridge pavement, at the same time theoretical basis is and selecting pavement materials and pavement structural optimization design.

Electrical–Thermal–Stress Coupled-Field Effect in SOI and Partial SOI Lateral Power Diode

The requirement of electrical-thermal-stress (E-T-S) modeling of semiconductor devices, as indicated by ITRS2006, demands the use of finite-element analysis (FEA) for device simulation. In this study, we perform E-T-S coupled-field simulation from the first principle by considering the stress-induced modification of the Si band structures, and employ the FEA software COMSOL to apply the E-T-S model to the study of lateral power diodes as an example. This power diode is a basic building block for power electronic devices and circuits, and as a first attempt for the ETS model application, only the steady-state characteristics of the lateral power diodes are considered. Simulations are performed on two types of diodes, namely, silicon-on-insulator (SOI) and partial SOI (PSOI) lateral power diodes because the temperature and mechanical stress distributions are very different in these diodes even under the same operating conditions. From the comparison of the computational results of SOI and PSOI diodes, the results indicate that PSOI power diode structure enables efficient heat conduction from the hot junctions and offers higher breakdown voltage. However, it has larger reverse current, higher thermomechanical stress that can lead to reliability issues.

Radiographic changes of the femoral neck after total hip resurfacing

Significant femoral neck narrowing following hip resurfacing arthroplasty has been observed. Several factors contributing to the physiopathology of femoral neck narrowing have been suggested. The aim of this study was to evaluate the femoral neck radiographic changes observed after hip resurfacing at a minimum follow-up period of 5 years and to determine their causes. We conducted a prospective study of 57 hip resurfacing arthroplasties performed in 53 patients (30 men, 23 women) of mean age 49.2 years (32-65) at surgery. These patients were clinically reviewed (inguinal pain during walking, WOMAC and UCLA scores) at 2 years and radiographically examined at 1, 2 and 5 postoperative years. The accuracy of our computer-aided measurement method was 1mm. Measurement of femoral neck to implant ratio was performed to assess the amount of neck thinning at the femoral neck-implant junction (N/H) and midway between the implant and the inter-trochanteric line (N(1/2)H) on an AP radiograph. Neck-thinning greater than 10% was considered as significant. Any other radiographic morphologic change in the femoral neck was investigated. Metallic ion concentration in blood was measured. A uni- and multivariate analysis was performed to determine the correlation with radiographic changes. In one third of the patients, femoral neck narrowing was greater than 1mm at 2 and 5 postoperative years. Such result corresponds to a mean decrease in neck to implant ratio (N/H) of 5.9% (range, 2.3 to 9.4) at 2 years and 8.3% (range, 2.5 to 23.8) at 5 years. At 5 postoperative years, an overall neck thinning greater than 10% was reported in 3 patients (with a 10- to 17-% increase in femoral neck narrowing between the 2nd and the 5th postoperative year). In one case, neck thinning was associated with fracture of the femoral stem managed with revision surgery during which femoral neck necrosis was confirmed. Neck thinning was, in these cases, circumferential to the neck-implant junction. There was no significant negative impact on clinical scores and no relationship could be established between neck thinning and factors such as BMI or patient activity. Moreover, neck thinning greater than 10% was reported in two cases after 2 postoperative years through the appearance of a localized femoral neck notching which was absent in the postoperative period, secondary to a femoroacetabular impingement. Femoral neck narrowing used to be a common phenomenon after HR when polyethylene acetabular bearings were implanted thus inducing osteolysis secondary to PE wear debris. The incidence of such phenomenon has decreased but still occurs after HR when using a metal-on-metal bearing surface. It has an early occurence but stabilizes after 2 postoperative years. Changes in mechanical stress distribution in the neck region after hip resurfacing have been hypothesized to be a cause of neck thinning. Other aetiologies may be suggested. An overall evolutive femoral neck narrowing after 2 postoperative years should raise the suspicion of necrosis leading to a risk of loosening, fracture or implant failure. Therefore, radiographic monitoring should be conducted. The presence of femoral neck notching secondary to femoroacetabular impingement represents a differential diagnosis which conservative treatment is advocated in the absence of any associated symptoms.

Burrowing and subsurface locomotion in anguilliform fish: behavioral specializations and mechanical constraints

Fish swimming is probably one of the most studied and best understood locomotor behaviors in vertebrates. However, many fish also actively exploit sediments. Because of their elongate body shape, anguilliform fishes are not only efficient swimmers but also very maneuverable. Consequently, many species live in complexly structured environments near the bottom and many are known to burrow into the sediment. To better understand burrowing and subsurface locomotion in anguilliform fish we provide descriptive kinematic data on subsurface locomotion in a burrowing eel (Pisodonophis boro) using videofluoroscopy. We also measured the maximal forces that can be exerted by this species during head-first and tail-first burrowing, and explored the implications of head-first burrowing on mechanical stress distribution in the skull. Our data show that P. boro uses lateral undulation to penetrate and move in sandy sediments under water. The kinematics of subsurface locomotion are different from those observed during swimming and are characterized by a very high slip factor. These observations differ considerably from recently published data in terrestrial sand-swimming lizards, and suggest that the sediment behaves like a solid rather than a frictional fluid. Finally, our finite element models show that the cranial shape and structure in the head-first burrowing P. boro is mechanically more suited for head-first burrowing than that of an obligate tail-first burrowing species, Heteroconger hassi.

In Vivo Stress Analysis of a Pacing Lead From an Angiographic Sequence

In this paper, a method is presented to analyze the mechanical stress distribution in a pacing lead based on a sequence of paired 2D angiographic images. The 3D positions and geometrical shapes of an implanted pacemaker lead throughout the cardiac cycle were generated using a previously validated 3D modeling technique. Based on the Frenet-Serret formulas, the kinematic property of the lead was derived and characterized. The distribution of curvature and twist angle per unit length in the pacing lead was calculated from a finite difference method, which enabled a rapid and effective computation of the mechanical stress in the pacing lead. The analytical solution of the helix deformation geometry was used to evaluate the accuracy of the proposed numerical method, and an excellent agreement in curvature, twist angle, and stresses was achieved. As demonstrated in the example, the proposed technique can be used to analyze the complex movement and deformation of the implanted pacing lead in vivo. The information can facilitate the future development of pacing leads.

Quantifying Mechanical Interactions between Cells in Small Clusters

Tissue cells typically utilize their actomyosin contractile machinery to actively pull on their environment, which can be either the extracellular matrix or neighboring cells. The mechanical forces that a cell exerts and experiences have been shown to regulate fundamental cellular processes, including cell growth, proliferation, differentiation and migration. However, little is known about the spatial distribution of mechanical stress in tissues. In particular, the extent to which mechanical forces are communicated through cell-cell interactions across a tissue is not well understood.

Моделирование химически индуцированных напряжений в трубчатых мембранах со смешанной кислород-ионной и электронной проводимостью

By the example of tubular oxygen-permeable membrane of mixed-conducting LaGa0.65Mg0.15Ni0.20O3-Δ operating under oxygen chemical potential gradients in the regime of hydrocarbon oxidation, modeling of chemically induced strains in the dense ceramic material has been carried out. The membranes with various radii in different reactor configurations were simulated. Analysis of the distributions of oxygen chemical activity and chemically induced stresses showed that, for minimization of mechanical stresses, the most advantageous basic configuration involves supplying atmospheric air inside a tubular membrane and opposite directions of the gas flows. The maximum stresses are observed in the region of reducing gas mixture injection, where a zone with an essentially constant oxygen chemical potential on the membrane surface may exist for many reactor configurations. The size of such zones formed due to specific features of the gaseous phase component distribution and/or ceramic reactor configurations, has a significant effect on the mechanical stress distribution.

Nanosensitive Silicon Microprobes for Mechanical Detection and Measurements

Nanosensitive mechanical microprobes with CMOS transistors, inverters, inverters cascades and ring oscillators, integrated on the thin silicon cantilevers are presented. Mechanical stress shifts linear, steep switching fragment of the inverters’ electrical characteristics. Microprobes were fabricated with use of the standard CMOS technology (3.5 μm design rules, one level polysilicon gate and one level of the metal interconnections) and relief MEMS technique. Control of the silicon cantilever thickness was satisfactory in the range above the few micrometers. Several computer simulations were done to analyze and optimize transistors location on the cantilever, in respect to the mechanical stress distribution. Results of the microprobes electromechanical tests confirm high deflection sensitivity 1.2 - 1.8 mV/nm and force sensitivity 2.0 - 2.4 mV/nN, both in nano ranges. Microprobes, with the ring oscillators revealed sensitivities 5 - 8 Hz/nm. These microprobes seem to be appropriate for applications in precise chemical and biochemical sensing.

Modeling the effects of particle size and intercalation-deintercalation rate of LiMn2O4 cathode material on the level of mechanical stresses in lithium-ion batteries

A mathematical model of the appearance and development of intercalation-deintercalation (ID) mechanical stresses in particles of an electrode material is presented. Results of simulations of the effects of particle size (including submicron level) and ID rate on the magnitude of mechanical stresses are presented. Analytical expressions are obtained that describe the distribution of mechanical stresses in a submicron particle, depending on the dimensionless ion current density. Results are illustrated by examples for LiMn2O4 cathode material.