Compressive Stress Distribution Research Articles

Humerus osteology, myology, and finite element structure analysis of Cheloniidae.

Adaptation of osteology and myology lead to the formation of hydrofoil foreflippers in Cheloniidae (all recent sea turtles except Dermochelys coriacea) which are used mainly for underwater flight. Recent research shows the biomechanical advantages of a complex system of agonistic and antagonistic tension chords that reduce bending stress in bones. Finite element structure analysis (FESA) of a cheloniid humerus is used to provide a better understanding of morphology and microanatomy and to link these with the main flipper function, underwater flight. Dissection of a Caretta caretta gave insights into lines of action, that is, the course that a muscle takes between its origin and insertion, of foreflipper musculature. Lines of action were determined by spanning physical threads on a skeleton of Chelonia mydas. The right humerus of this skeleton was micro-CT scanned. Based on the scans, a finite element (FE) model was built and muscle force vectors were entered. Muscle forces were iteratively approximated until a uniform compressive stress distribution was attained. Two load cases, downstroke and upstroke, were computed. We found that muscle wrappings (m. coracobrachialis magnus and brevis, several extensors, humeral head of m. triceps) are crucial in addition to axial loading to obtain homogenous compressive loading in all bone cross-sections. Detailed knowledge on muscle disposition leads to compressive stress distribution in the FE model which corresponds with the bone microstructure. The FE analysis of the cheloniid humerus shows that bone may be loaded mainly by compression if the bending moments are minimized.

Evaluation of stress on metal surfaces by laser-induced breakdown spectroscopy

In this study, we evaluated the feasibility of using laser-induced breakdown spectroscopy (LIBS) to determine the stress generated in metal materials by comparing measured stress levels with those determined by x-ray diffraction (XRD). Magnesium (Mg) alloy specimens underwent impact stress generated under ultrasonic peening. Stainless steel specimens were subjected to bending stress. The reference stress for each specimen was measured using XRD. LIBS measurements were performed to determine the correlation between stress distribution and the ratio of ionic to atomic spectral line intensity. The stress distribution from the surface to the interior of the ultrasonic-peened specimens measured by LIBS showed a similar tendency to that measured by XRD, but there was a difference in the maximum measurable depth. Additionally, the tensile and compressive stress distributions measured by LIBS on bending specimens showed similar trends to those of XRD. From these results, it was possible to measure the correlation between the stress state of the metal matrix and the spectral line strength of LIBS, thus confirming the potential for stress measurement using LIBS.

Laser 3D printed bio-inspired impact resistant structure: failure mechanism under compressive loading

ABSTRACT This work presents a comprehensive failure mechanism study of the bi-directionally corrugated panel (DCP) structures inspired by the telson of mantis shrimp. The DCP structures were fabricated by selective laser melting (SLM) with AlSi10Mg powder. The influence of key structural parameters, namely wave number (N), on the compressive behaviours, stress distribution, deformation modes and fracture mechanism of SLM-processed DCP components was systematically investigated. Results revealed that with the increase of wave number (N), the structural expansion effect became more obvious, which led to the disappearance of the plateau region on the compressive force-displacement curve, the decrease of specific energy absorption (SEA) growth rate and the energy absorption per periodicity cell. Three deformation modes were observed, namely full-folded mode (N = 4), transitional mode (N = 5), and global-buckling mode (N = 6). Finally, the fracture morphologies elucidated that the fracture mechanism changed from ductile fracture to brittle fracture with the increase of wave number.

Ultrasonic hardening of the gear wheels of helicopter transmission

Purpose. Evaluation of the effect of ultrasonic hardening on endurance strength, the magnitude and nature of the distribution of residual stresses in the surface layer of samples of gear wheels from steel 16Х3НВФМБ-Ш of helicopter transmission is done.Methods of research. For comparative tests on fatigue, special samples were made with a fillet in a number of 34 pieces, samples material of gear wheels is steel 16Х3НВФМБ-Ш, the technological process of making fillet samples is similar to the technological process of processing the cavities of the teeth of helicopter transmission gear wheels were used.Some samples (17 pcs.) were tested in the initial state, the rest of samples were subjected to ultrasonic hardening with balls. The tests were carried out on a ВЭДС-400 vibrostand at room temperature and resonant vibrations in the first bending form of cantilevered samples.Received results. In the work, based on the results of experimental studies, the effect of ultrasonic hardening on fatigue resistance, the magnitude and nature of the distribution of residual compressive stresses in the surface layer of samples of steel 16Х3НВФМБ-Ш were schown.Scientific novelty. Experimental studies have shown that ultrasonic hardening increases the fatigue resistance of samples from steel 16Х3НВФМБ-Ш and forms in their surface layer the residual compressive stresses in the range from -533 to -23 MPa. The endurance limit of the original samples is σ-1 = 588 MPa. The endurance limit of samples with a fillet, which surface was subjected to ultrasonic hardening with steel balls, is σ-1 = 666 MPa.Practical value. Based on the results of this experiment, it is possible to develop a rational technological process for the manufacture of gear wheels from steel 16Х3НВФМБ-Ш of helicopter transmission, ensuring their high performance.

Longer collagen fibers trigger multicellular streaming on soft substrates via enhanced forces and cell-cell cooperation.

Grouped cells often leave large cell colonies in the form of narrow multicellular streams. However, it remains unknown how collective cell streaming exploits specific matrix properties, like stiffness and fiber length. It is also unclear how cellular forces, cell-cell adhesion and velocities are coordinated within streams. To independently tune stiffness and collagen fiber length, we developed new hydrogels and discovered invasion-like streaming of normal epithelial cells on soft substrates coated with long collagen fibers. Here, streams arise owing to a surge in cell velocities, forces, YAP activity and expression of mesenchymal marker proteins in regions of high-stress anisotropy. Coordinated velocities and symmetric distribution of tensile and compressive stresses support persistent stream growth. Stiff matrices diminish cell-cell adhesions, disrupt front-rear velocity coordination and do not promote sustained fiber-dependent streaming. Rac inhibition reduces cell elongation and cell-cell cooperation, resulting in a complete loss of streaming in all matrix conditions. Our results reveal a stiffness-modulated effect of collagen fiber length on collective cell streaming and unveil a biophysical mechanism of streaming governed by a delicate balance of enhanced forces, monolayer cohesion and cell-cell cooperation.This article has an associated First Person interview with the first authors of the paper.

A multi-step chemical ion-exchange process for alkali/alkaline-earth aluminosilicate glasses

The paper describes a multi-step chemical ion exchange method, also known as "Kailly Method", to increase the impact resistance of Na2O–Al2O3–SiO2 based glasses and derivatives. The chemical strengthening methodology comprises of three steps where the first step is a chemical ion-exchange process (labeled as IOX1) in KNO3 melt followed by a second step involving high temperature ion migration (HTIM), and the final step of another chemical ion-exchange (IOX2) step in KNO3 melt. The effect of the proposed strengthening mechanism on the compressive stress layer depth (DOL), diffusion coefficient (D) and surface compressive stress (CS) of a glass with composition 16.11 Na2O-1.47 K2O-2.73 MgO-20.02 Al2O3-59.08 SiO2-0.1 CaO-0.49 SnO2 (wt.%) has been evaluated. The results show that the "Kailly Method" can promote a DOL to 120–150 μm which is 50–80% higher than the conventional one-step ion exchange process. The distribution of compressive stress has been positively correlated with K+ concentration and modulus of elasticity. Further the impact strength of a 0.5 mm thick glass specimen has been demonstrated to be linearly related to the compressive stress and the square root of DOL thus, indicating that the increase of DOL on the glass surface contributes to the improvement of impact resistance.

Investigation on Springback Behavior of Cu/Ni Clad Foils during Flexible Die Micro V-Bending Process

With the increasing demand for micro parts using metal laminates in modern production, the manufacturing processes of thin sheet parts have been elevated. However, it is difficult to predict the deformation behavior with miniaturization because of size effects in micro-scale. In this study, the flexible die micro V-bending behavior of Cu/Ni clad foils was investigated. The bending experiments with three different punch angles and Cu/Ni clad foils under different annealed temperatures were performed. The results show that the springback angle increases with the increase of bending angle and annealing temperature. The placement of Cu/Ni clad foils induced compressive stress results in the more obvious thinning of thickness and decreasing of springback angle. The interactive effects of the distribution of deformation zones and compressive stress induced by the interface layer result in the springback behavior of Cu/Ni clad foils during the flexible die micro V-bending process.

A study on the surface morphology evolution of the GH4619 using warm laser shock peening

Compared with the laser shock peening, the warm laser shock peening has been demonstrated to get a stable compressive stress distribution under heating and cyclic loading, which is mainly due to warm laser shock peening combined with the advantages of laser shock peening and dynamic strain aging. The surface morphology evaluation of warm laser shock peening was investigated systematically in this work, the GH4169 nickel-base super-alloy is selected as the material with which to conduct experiments of laser shock peening and warm laser shock peening. It can be found that there are a lot of surface ripples appearing after the treatment of warm laser shock peening, which is different from the surface reliefs by the treatment of laser shock peening. Under high temperature and strain rate, δ phase transformed into γ″ phase. Simultaneously, compared with the δ phase of the larger grain size, the grain size of γ″ phase is much smaller, and is unable to form the surface relief. Warm laser shock peening produced a higher dislocation density and more stabilized dislocations that are pinned by the “Cottrell Clouds” formed by γ″ phase, which can inhibit the residual stress failure at the high temperature-alternating load.

Theoretical study of stress and strain distribution in coupled pyramidal InAs quantum dots embedded in GaAs by finite element method

Stress and strain distributions in and around a single or two-coupled pyramidal InAs quantum dots (QDs) embedded in GaAs are calculated by finite element methods according to the continuum elasticity theory. By changing the quantum dot spacing and thickness of cap layer, the results about strain and stress distributions show compressive strain and stress distribution in the QDs and relaxation undergoes two stages with different speeds for different quantum dot height, quantum width and thickness of cap layer. The stress and strain distributions of pyramidal QDs would not vary monotonously with geometric dimensions. The height of quantum dot and cap layer thickness can effectively adjust the vertical correlation of self-assembly QDs according to the calculation. The shape of stress distribution at surface of cap layer can be tuned from a quadrangle into a circle by increasing the thickness of cap layer or decreasing the height of quantum dot. Also, a new approach to grow quantum ring is found in this paper. The calculations of two-coupled QDs show that the self-assembly technology might fail if the horizontal distance between two QDs is not large enough. The stress induced by upper QDs will be relaxed to zero with a longer distance downwards is found in this paper.

A Screening Approach for Rapid Qualitative Evaluation of Residual-Stress States – Application to Laser-Hardened Microalloyed Steel

Abstract Surface hardening and compressive residual stresses are keys to superior part performance in numerous applications. In this context the development of advanced laser surface treatments for new materials and complex sample shapes is a time consuming process. Eventually, determination of residual stress states by means of X-ray diffraction in the whole surface and subsurface region, respectively, is one of the main time consuming facors in terms of characterization. In many applications the provision of an adequate distribution of compressive residual stresses, however, is needed for approval of parts. In the present work it is shown that micrograph analysis can be used to provide the zero transition zone of residual stresses revealing the relevant penetration depth of the laser treatment conducted. One single surface stress scan employing standard techniques only is needed to verify the sign of residual stresses induced by the treatment. In fact, the screening approach introduced in this study enables time- and cost-efficent development processes for studying new sets of laser hardening parameters.

Numerical modeling of circular, square and rectangular concrete columns wrapped with FRP under concentric and eccentric load

Abstract In this paper, the finite element method was used for the numerical modeling of columns with square, rectangular and circular cross sections wrapped with FRP. The numerical modeling was successfully calibrated with the experimental data considering axial load, axial strain and transverse strain. The distribution of compressive stresses in the cross section of the column indicates that for centered load, circular cross sections have uniform distribution and for square and rectangular sections the effective confined concrete was defined by parabolas and concentrates next to the rounded corners. For eccentric load, the effective confined region moves to the most confined edge, thus, this does not reduce the gain for square and rectangular columns, but is unfavorable for circular columns.

Biomechanical Effect of an Exposed Dental Implant's First Thread: A Three-Dimensional Finite Element Analysis Study.

BackgroundThe purpose of this study was to assess the effect of different exposure levels of a dental implant’s first thread on adjacent bone stress and strain using the finite element analysis method.Material/MethodsThree-dimensional models of 2 threaded implants and abutments with a mandibular bone segment were constructed to represent the covered (C) and exposed models. In the exposed models, the implant was first placed in the bone, and rotated around its axis a quarter-turn each time to simulate 4 different levels of first thread exposure at the mid-lingual side: Upper Flank (UF), Thread Crest (TC), Lower Flank (LF), and Thread Root (TR) models. Oblique forces were applied and analysis was performed.ResultsMaximum compressive stress magnitude and distribution varied according to the exposed thread profile. In the exposed group, peak stress ranged from 136 MPa to 197 MPa in TC and LF models, respectively, compared to 141 MPa in C model. In LF, UF, and C models, peak stress was observed at the mid-lingual side of the crestal region, while in TC and TR models, peak stress shifted distally in accordance with thread profile. However, alveolar bone volumes which exhibited compressive microstrain levels within the physiological loading and maintenance windows were relatively close in all models.ConclusionsResults suggest that the exposed thread profile influences stress and strain outcomes in the adjacent bone; however, this influence is only limited to a small region around the exposed thread.

Study on the enhancement coefficient of the local compressive strength improvement of masonry under a cantilever beam

Locally compressed masonry under a cantilever beam is restrained by the surrounding masonry, resulting in improved local compressive strength. The code for design of masonry structures stipulates that the enhancement coefficients of the local compressive strength of masonry(γ) with single- and T-wall supporting cantilever beams are 1.25 and 1.5, respectively; however, these two values, which stem from the material performance test of masonr’s local compressive strength, are not testified from the local compression of masonry under cantilever beam. Further, the γ of L-shaped wall supporting cantilever beam is not presented in the Code. This study theoretically deduced the effective length of the masonry’s compressive stress distribution based on the elastic foundation beam theory, obtaining the theoretical results in good agreement with the test values. The theoretical, test, and code values of the effective length of the masonry’s compressive stress distribution were adopted for calculating γ with single- and T-wall supporting cantilever beams, revealing the code value of γ was relatively small. Herein, the enhancement coefficient of the local compressive strength of masonry has been investigated using an L-shaped wall supporting cantilever beam; according to the calculation results, an enhancement coefficient of 1.4 is recommended for safety reasons.

To the determination of the actual stress state of the elements of flat precast-monolithic slabs

Problem statement. Recently, a constructive system with the use of frame and frame-bced frameworks with precast reinforced concrete elements (flat precast-monolithic slabs) has been widely spread. The design of the frame uses monolithic or prefabricated columns and prefabricated monolithic flat slabs. A constructive solution is a flat floor slab consisting of precast hollow-core slabs adjacent in one level to monolithic bearing girders (conditional girders), using concrete dowels located in round cavities open at the plate ends and made monolithically with bearing girders. The work of the joints of the ends of the plates with bearing girders is of great interest. It appears that below in the above mentioned joints there are deformations of compression, as a result of the work of hollow-core slabs as the part of the floor slab for bending with an emphasis on bearing crossbars according to the hypothesis of flat sections that should affect the stressed state of the slab elements. It is established that the distribution of the main tensile and compressive stresses in the longitudinal central section of the multi-tensile plates clamping through the apertures in the linear and physically nonlinear problem, based on the performed studies, is not the same. In the linear and physically nonlinear formulation of the problem one can see that the distribution of the main compressive stresses is different by nature. Thus, in the case of a linear problem in the quarter of the slab, there is a zone of zero stresses, which is the boundary between the distribution of the main compressive stresses in the lower edge and the upper passage of the section of the element. In the nonlinear formulation of the problem, the zero-voltage zone is absent. Under the influence of the arched effect, the initial bending moment in the middle bores under the action of the distributed load is partially reduced.

Influence of the stressed state of the surface layer on the endurance of gas turbine engine compressor blades

Different types of final strengthening treatment of gas turbine engine (GTD) compressor blades are considered. The influence of each type of treatment on the formation of roughness of the surface with favorable microrelief, as well as on the level and depth of distribution of residual compressive stresses in the compressor blade airfoil is analyzed. The causes of blade fatigue failure are described and methods of controlling this kind of failure are presented. The results of testing special specimens made of VT9 titanic alloy are presented to establish the influence of final strengthening treatment modes on the compressor blade resistance to fatigue stress. The results of testing residual stress distribution along the thickness of compressor blade airfoil are presented. A method of improving dynamic strengthening of specimens due to the protection of compressor blade edges is discussed. The results of semi-graphical analysis of the stressed state of low-pressure and medium-pressure compressor blades made of VT9 alloy are presented. They take into account residual stresses, as well as operating load stresses in the process of operation. We show that it is possible to increase the limit of the blade endurance due to the optimization of residual stress diagrams by improving the final strengthening technology with the use of dust blasting.

Development of Live Load Distribution Factor Equation for Concrete Multicell Box-Girder Bridges under Vehicle Loading

The evaluation and design of concrete bridges in large part depend on the transverse distribution characteristics of the live load carried and the service level. The live load distribution for continuous concrete multicell box-girder bridges varies according to bridge configuration, so when designing such bridges, it is important to determine the maximum negative stress at the piers, the midspan positive (tensile) stress and the deflection of the bridge when subjected to live loads. This paper reports an extensive parametric study to determine the maximum stress, deflection, and moment distribution factors for two span multicell box-girder bridges based on a finite element analysis of 120 representative numerical model bridges. Bridge parameters were selected to extend the parameters and ranges of current live load distribution factors defined by AASHTO LRFD specifications. The results indicate that the span length, number of boxes, and the number of lanes all significantly affect the positive (tensile) and the negative (compression) stress distribution factors. A set of equations proposed to describe the behavior of such bridges under AASHTO LRFD live loads yielded results that agreed closely with the numerically derived results for the stress and deflection distribution factors.

Study on the influence of residual stress on the mechanical characteristics of free-standing Si-membranes processed by deep reactive ion etching

The mechanical behavior of free-standing Si-membranes (diaphragms) fabricated by deep reactive ion etching (DRIE) was studied in order to emphasis the magnitude of process-induced stress and/or strain distribution in both square and circular diaphragms. For this purpose, 25 μm thick circular and square diaphragms with 4 mm diameter (or side-size) were fabricated using silicon-on-insulator wafer. The thickness and surface homogeneities of the DRIE processed Si-diaphragms were analyzed by SEM and AFM, respectively. Micro-Raman spectroscopy studies revealed a non-uniform distribution of compressive stresses throughout the diaphragm surface. Using the synchrotron based Laue diffraction measurements, the residual stress values were quantitatively estimated as 19.88 and −22.83 MPa for the unloaded circular and square diaphragms, respectively. The pressure vs. displacement experiments were conducted using the bulge testing method and these studies yielded maximum mid-point deflection values of 25 and 30 μm for the circular and square diaphragms, respectively against applied pressure of 25 kPa. Based on the deflection characteristics, the average residual stress and equivalent biaxial modulus were estimated by means of standard analytical equations. Using the finite element analysis, the mid-point deflection characteristics of the diaphragms were simulated through considering the residual stresses as input parameters and the results are compared with that of those obtained by the experimental and analytical methods. The residual stress information such as those inferred in this study would help in tuning the resonant frequency of Si-diaphragms towards sensor/actuator applications.

Effect of the diffusion annealing process in the indentation properties of cobalt boride layer

New results about the indentation properties of cobalt boride layer exposed to a diffusion annealing process (DAP) are presented in this study. Initially, the cobalt boride layer (CoB-Co2B) was developed at the surface of the ASTM F1537 alloy using the powder-pack boriding process (PPBP) at 1273 K with 6 h of exposure. The DAP was conducted on the borided ASTM F1537 alloy considering the theoretical values (temperature and exposure time) estimated by a diffusion model to dissolve entirely the CoB layer. After that, the distribution of hardness, Young's modulus, and residual stresses across the depth of cobalt boride layer, obtained by both treatment conditions, were estimated using the depth-sensing Vickers microindentation test at a constant load. In addition, Vickers indentation fracture toughness tests were performed on the “pure zone” of the CoB layer (obtained by PPBP) considering a range of applied loads between 1.2 and 1.8 N, in contrast with the range of applied loads of 3–5 N performed in the cobalt boride layer obtained by the PPBP + DAP. Principally, the effect of the DAP resulted in a change of the microstructure of the cobalt boride layer and the modification of indentation properties; a distribution of compressive residual stresses was estimated along the depth of the cobalt boride layer, which drastically modified the fracture resistance to ~ 2.7 MPa m compared with a lower fracture value of ~ 0.5 MPa m obtained by the cobalt boride layer obtained by PPBP.

Numerical Analysis of Shot Peening with Incident Angle

Shot peening has been used to improve the fatigue strength of metal structural components because it can produce large compressive residual stress near the surface. The distribution of compressive residual stress is strongly dependent on shot peening conditions such as the material of the shot, the shot diameter, the shot velocity, the incident angle, and the peening time (coverage). In this study, a finite element model including multiple shots and the specimen was developed in order to investigate the influence of the incident angle on the compressive residual stress and the depth of its location from the surface in high-strength aluminum alloy. The residual stress and its distribution were analyzed when multiple shots were randomly impacted on the surface of the specimen. The analyzed residual stress distribution using the kinematic material model agreed very well with experimental ones at the incident angles of 90° and 30°. It can be concluded that the depth of the compressive residual stress is proportional to the velocity component perpendicular to the surface.

Prediction of residual stress profile and optimization of surface conditions induced by laser shock peening process using artificial neural networks

The purpose of this paper is to predict the compressive residual stress profile induced by the laser shock peening process and to optimize the surface conditions on a Ti-6Al-4V titanium super-alloy using the new technology based on the artificial neural networks. This study covers two principal cases: (i) The numerical analysis: the compressive residual stress distribution induced by the laser peening process is simulated based on the finite element method using ABAQUS software (ABAQUS/Explicit code). (ii) The mathematical modeling analysis: the using of the artificial neural network technique has been proposed to predict the residual stress profile induced by the laser shock processing in order to optimize the laser shock peening surface conditions. To train the artificial neural network, we use different numerical experiments measurements as training and test data. The best fitting training data set was obtained with four neurons in the hidden layers. After training and as seen from the mathematical experiments, the calculated residual stress and the damage state are obviously acceptable. The principal goal of this research paper is to predict the surface treatment state induced by the laser shock peening based on the artificial neural networks technique and on the numerical results without making multiple simulations that can take much more time.