Level Of Stress Concentration Research Articles

Vibration analysis of composite exhaust manifold for diesel engine using CFD

Researchers used computer-aided design and computational fluid dynamics methodologies to establish the flow simulation process and find the critical level temperatures. CATIA V5 R20 has been used to create the geometric model. As a result, the normal study state conditions are performed at varied coefficient levels in all boundary areas. Three solid dimensioning approaches were used in the simulation process. The internal flow structures and velocity contours were obtained using computational fluid dynamics flow software. As a result, the structural elements in the exhaust manifold were mapped from a minimum range of 0.2933 to a maximum range of 0.99995 under various thermal conditions. The gradient temperature and velocity contour findings were absorbed in a flow process with maximum energy transmit of 0.2917 m/s and a temperature of 350 °C calculated using Computational fluid dynamics (CFD) techniques. The simulated data found the failure areas at the bottom of the exhaust manifold. At 0.005% of the input conditions, the stress concentrations were detected. Computational fluid dynamics simulation techniques reduced stress concentration levels by 14%.

Design of Triaxial Tests with Polymer Matrix Composites.

Multiaxial testing in composites may generate failure modes which are more representative of what occurs in a real structure submitted to complex loading conditions. However, some of its main handicaps include the need for special facilities, the correct design of the experiments, and the challenging interpretation of the results. The framework of this research is based on a triaxial testing machine with six actuators which is able to apply simultaneous and synchronized axial loads in the three space directions. Then, the aim was to design from a numerical point of view a triaxial experiment adapted to this equipment. The methodology proposed could allow for an adequate characterization of the triaxial response of a polymer-based composite with apparent isotropic behaviour in the testing directions. The finite element method (FEM) is applied in order to define the geometry of the triaxial specimen. The design pursues to achieve homogeneous stress and strain states in the triaxially loaded region, which should be accessible for direct measurement of the strains. Moreover, a fixing system is proposed for experimentally reproducing the desired boundary conditions imposed on the numerical simulations. The procedure to determine the full strain tensor in the triaxially loaded region is described analytically and with the help of FEM virtual testing. The hydrostatic component and the deviatoric part of the strain tensor are proposed for estimating the susceptibility of the polymer-based composite to fail due to the triaxial strain state imposed. Then, the loading scenarios that cause higher values of the deviatoric components in the triaxially loaded region are considered to be more prone to damage the region of interest. Nevertheless, the experimental failure is expected to be produced in the arms of the specimen which are uniaxially loaded, since in all of the loading cases the simulations show higher levels of stress concentration out of the triaxially loaded region. Thus, although the triaxial strength could not be accurately determined by the proposed tests, they can be utilized for observing the triaxial response before failure.

Influence of posterior pedicle screw fixation at L4\u2013L5 level on biomechanics of the lumbar spine with and without fusion: a finite element method

BackgroundPosterior pedicle screw (PS) fixation, a common treatment method for widespread low-back pain problems, has many uncertain aspects including stress concentration levels, effects on adjacent segments, and relationships with physiological motions. A better understanding of how posterior PS fixation affects the biomechanics of the lumbar spine is needed. For this purpose, a finite element (FE) model of a lumbar spine with posterior PS fixation at the L4–L5 segment level was developed by partially removing facet joints (FJs) to imitate an actual surgical procedure. This FE study aimed to investigate the influence of the posterior PS fixation system on the biomechanics of the lumbar spine before and after fusion by determining which physiological motions have the most increase in posterior instrumentation (PI) stresses and FJ loading.ResultsIt was determined that posterior PS fixation increased FJ loading by approximately 35% and 23% at the L3–L4 adjacent level with extension and lateral bending motion, respectively. This increase in FJ loading at the adjacent level could point to the possibility that adjacent segment disease has developed or progressed after posterior lumbar interbody fusion. Furthermore, analyses of peak von Mises stresses on PI showed that the maximum PI stresses of 272.1 MPa and 263.7 MPa occurred in lateral bending and flexion motion before fusion, respectively.ConclusionsThe effects of a posterior PS fixation system on the biomechanics of the lumbar spine before and after fusion were investigated for all physiological motions. This model could be used as a fundamental tool for further studies, providing a better understanding of the effects of posterior PS fixation by clearing up uncertain aspects.

Modeling of the mechano-electrochemical effect at corrosion defect with varied inclinations on oil/gas pipelines

A 3-dimensional finite element model was built to determine the effect of inclination angle of a corrosion defect on local mechano-electrochemical (M-E) effect in a simulated soil solution. Because of the high effect of the defect inclination angle on the M-E effect, when the inclination angle is 0° (i.e., the primary axis of the defect parallel to the longitudinal direction of the pipe), the greatest stress concentration level at the defect can be observed, which is associated with the lowest corrosion potential, the greatest anodic current density and the most serious accelerated localized corrosion. When the inclination angle is 90°, the stress concentration level reduces and the corrosion potential becomes less negative, accompanying with the decreased anodic/cathodic current densities. Besides, when the ratio ( r ca ) of the primary axial length of the defect to its secondary axial length is 1, the defect inclination does not affect the stress and the electrochemical corrosion rate at the defect. With the increase of r ca , the effect of the defect inclination angle is more apparent.

Evaluation of facial tissue stresses under medical devices post application of a cyanoacrylate liquid skin protectant: An integrated experimental-computational study.

Medical device‐related pressure ulcers (PUs) (injuries) are a subclass of PUs, associated with pressure and/or shear applied by a medical device onto the skin. Clinical application of a cyanoacrylate liquid skin protectant (CLSP) under the contours of skin‐contacting medical devices to shield an intact skin from the sustained mechanical loads that are applied by medical devices is a preventative option, but no computer modelling work has been reported to assess the biomechanical efficacy of such interventions. Here, we investigated the biomechanical protective effect of a polymerised cyanoacrylate coating using three‐dimensional, anatomically realistic finite element models of the ear with oxygen cannula and the mouth with endotracheal attachment device, informed by experimental studies. We have compared tissue stress exposures under the devices at these facial sites between conditions where the cyanoacrylate skin protectant has been applied or where the device was contacting the skin directly, without the shielding of the cyanoacrylate coating. The CLSP considerably reduced the skin stress concentration levels and overall tissue stress exposures under the aforementioned medical devices. This demonstrates strong biomechanical effectiveness of the studied cyanoacrylate‐based skin protectant in prevention of facial medical device‐related injuries at small, curved and thereby difficult to protect facial sites.

Vibration and acoustic radiation characteristics of cylindrical piezoelectric transducers with circumferential steps

Circular cylindrical transducers have a wide range of applications in ultrasound generation. Introducing axial or circumferential stepped-thickness variations affects the performance of these transducers. This paper investigates the effect of circumferential stepped-thickness variations on the vibration and acoustic characteristics of a circular cylindrical piezoelectric shell. FEM software ANSYS is used to simulate these characteristics and experiments are performed to validate the simulations. Stress concentration levels due to these steps are observed in order to avoid exceeding the material limit. The results show that these steps can excite certain mode shapes which produce strong ultrasound fields and these modes have circumferential wave numbers commensurate with the number of stepped regions. These steps localize the vibration within the thin-walled regions leading to higher amplitude acoustic waves produced by constructive interference. Superiority of a circumferentially stepped transducer over an axially stepped one is demonstrated in this study through a much more uniform acoustic field along the length of the transducer as well as a lower frequency of operation at the intended mode shape. The effect of input excitation is also investigated and it is shown that introducing circumferential steps is more effective in terms of acoustic amplification than increasing the input excitation for the uniform-thickness transducer.

Laser powder bed fusion of bio-inspired reticulated shell structure: Optimization mechanisms of structure, process, and compressive property

Recent researchers show that the shell structure and truss structure are emerging categories of light weight structure with unique mechanical properties and high customization potential, but they are difficult to manufacture by traditional methods. Inspired by the diving bell of water spider, the reticulated shell structure designed in this work combines the characteristics of the truss structure and the shell structure, and is fabricated by laser powder bed fusion (LPBF). The effect mechanism of strut angle on the manufacturability, compressive behaviors, energy absorption property, stress distribution, and fracture morphology were studied by experiment and simulation methods. The results showed that the relative densities of reticulated shell structures increased with the increase of strut angle, which was due to the existence of a large proportion of overhang structures in the reticulated shell structures. The compressive load-displacement curves of all reticulated shell structures showed a similar trend, including three stages, which were elasticity, subsidence, and densification. The reticulated shell structure with the strut angle of 75° had the highest specific energy absorption and energy absorption capacity. Finite element simulation results revealed that, with the change of the strut angle, the stress concentration in the reticulated shell structure significantly changed and directly affected the compression behavior of structures. The structure with the strut angle of 75° exhibited the lowest stress concentration level at key locations, leading to the best compressive behavior among structures.

Experimental assessment of drilling-induced damage in impacted composite laminates for resin-injection repair: Influence of open/blind hole-hole interaction and orientation

An experimental study of drilling-induced damage in barely visible impact damaged (BVID) carbon fibre reinforced polymer (CFRP) laminates where small circular holes were intentionally drilled into the impacted zone as an intermediate step of the resin-injection repair process was described. In-plane compression testing was conducted to determine the mechanical properties of BVID specimens containing open/blind, single and binary holes. Binary-hole specimens at fixed distance apart were tested in parallel or normal to the applied uniaxial force. As expected, BVID specimens experienced significant diminution of property value (compared to pristine ones). No dependence of mechanical properties on hole-hole orientation was observed. Owing to the large hole-hole separation, this significantly mitigated the hole-hole interactions, even though the predicted stress concentration (around the holes) level was above the residual strength. Interestingly, single/binary-hole BVID laminates generated counter-intuitive laminate stiffening effects that the stiffness was significantly higher than that of undrilled BVID specimens.

Modeling coupled gas flow and geomechanics process in stimulated coal seam by hydraulic flushing

Hydraulic flushing (HF) is an efficient technique for improving coal mine gas extraction. Although much research has been conducted in recent decades, many problems on its mechanism of enhancing permeability still exist. For example, how does coal strength affect the enhanced permeability by HF? Can a larger borehole generate a higher gas flowrate? Therefore, a coupled gas flow-geomechanics model was developed based on an equivalent fractured-coal model to solve these issues. Plastic volumetric strain was introduced in this model to quantify the coal structure, which can improve the numerical models for coal permeability, gas flow in fracture and diffusion in matrix, respectively. The model was used to describe gas flow in the virgin and disturbed coal seams. Results show that neglecting coal failure can cause erroneous stress and permeability distributions, and lead to an overestimation of gas pressure and an underestimation of gas extraction amount. Effects of coal strength and borehole diameter on the distributions of stress, plastic zone, permeability and gas pressure were systematically studied. It indicates that the stress relief, plastic and enhanced-permeability zones around the boreholes in soft coal are obviously larger than those in hard coal. The stress-concentration level and permeability reduction in soft coal are greater than those in hard coal. After 500 d extraction, gas pressure in soft coal has a higher decrease than that in hard coal, indicating that the enhanced permeability by HF of soft coal is larger than that of hard coal. Besides, the investigation on the effects of borehole diameter shows that there exists an optimal borehole diameter. Gas pressure between the boreholes decreases before the optimal diameter, and increases sharply after the optimal diameter due to the high stress concentration. For the Pingmei 8th mine, the optimal borehole diameter is about 1.0 m. Field tests indicate that the optimized HF can considerably eliminate the risk of coal and gas outburst.

Aluminum beam reinforced by externally bonded composite materials

A recently popular method for retrofitting reinforced structure beams is to bond composite plates to their tensile faces. An important failure mode of such plated beams is the debonding of the composite plates from the base material of the beam due to high level of stress concentration in the adhesive at the ends of the composite plate. This paper, shows and presents in more detail a closed-form rigorous solution for interfacial stress in cantilever aluminum beams strengthened with bonded composite (sika wrap) plates and subjected to a uniformly distributed load. The results show that there exists a high concentration of both shear and normal stress at the ends of the laminate, which might result in premature failure of the strengthening scheme at these locations. A parametric study has been conducted to investigate the sensitivity of interface behavior to parameters such as laminate and adhesive stiffness, the thickness of the laminate; the effect on plate length of the strengthened cantilever beam region, the effect of adhesive (modules, thickness) and the effect of loading and geometry for the cantilever beam; where all were found to have a marked effect on the magnitude of maximum shear and normal stress in the composite member. The theoretical predictions are compared with other existing solutions. Finally, this research is helpful for the understanding on mechanical behaviour of the interface and design of the composite-aluminum hybrid structures.

Параметры оксидативного стресса и провоспалительный статус пациенток с нарушениями менструального цикла на фоне терапии ожирения

Objective. To study the effect of cyclical vitamin therapy on the parameters of oxidative stress and pro-inflammatory status of patients with menstrual disorders against the background of obesity treatment. Patients and methods. The study included 49 women aged 20 to 35 years (29.4 (26.5; 33.2) years) with obesity and various menstrual disorders. Twenty-six (53.06%) patients had polycystic ovary syndrome (PCOS). To treat obesity, 26 patients followed a diet and received Orlistat 120 mg three times a day. Twenty-three women received similar treatment and additionally took micronutrient supplements. In both groups, treatment was continued for 4 months. Results. Body mass index decreased by 1.9 (0.3; 2.3) kg/m2 in the group of women who received Orlistat, and by 1.6 (0.5; 2.7) kg/m2 in the group of women who received Orlistat and vitamins. Menstrual cycle normalized in more than a third of patients in each group. Baseline levels of oxidative stress and C-reactive protein concentrations were abnormal in all patients, especially in PCOS. Decrease of tocopherol (12.8 (6.6; 14.7) μg/mL; 7.1 (3.4; 9.1) μg/mL, p = 0.04) and beta-carotene (680.1 (320.3; 810.3) μg/mL; 420.3 (150.4; 510.1) μg/mL, p = 0.01) concentrations in the blood of patients who did not receive vitamins during treatment was expected, as was their increase in those who took vitamins (tocopherol 10.1 (4.5; 15.1) μg/mL; 13.2 (7.1; 15.9) μg/mL, p = 0.045; beta-carotene 610.4 (450.3; 710.5) μg/mL; 630.4 (570.3; 790.5) μg/mL, p > 0.05). In the blood of those patients who received vitamins, the concentration of the antioxidant ubiquinone (0.6 (0.3; 1.4) μg/mL; 1.1 (0.5; 1.7) μg/mL, p = 0.002) increased, and the positive dynamics of oxidative stress parameters were more considerable and statistically more significant. Conclusion. Supplementation of micronutrient complex in the treatment of obesity helps to improve the parameters of antioxidant protection and pro-inflammatory status. Key words: obesity, menstrual disorders, oxidative stress, pro-inflammatory status, cyclical vitamin therapy

Developing a system and criteria for directed choice of technology to provide required quality of surfaces of flexible coupling parts for rotor machines

The paper discusses the process of normal friction and wear as a result of fretting corrosion, as well as measures to reduce its level. There are considered the issues of reliability and accuracy of the connection of “shaft - sleeve with key” type, which is of particular danger. The disadvantages of the considered connections are shown, namely the relative complexity of the disassembly-assembly processes; high level of stress concentration; the tendency to corrosion at contact. There has been proposed a physically based mathematical model of the wear process for the strengthened surfaces of the flexible coupling parts on the friction conditions. By using the friction work value, the model allows determining the wear expressed through the change in the surface roughness. A method has been developed for determining the constant of the wear equation for various materials of friction pairs. Using the energy and economic criteria, the technique of the integral description of the method for achieving the required quality of the surface layers of the elastic coupling parts is given. A mathematical model has been developed to reliably allow predicting the wear amount for the surfaces of the elastic coupling parts whose surface layers are formed in various ways. It is proposed a system for the directed choice of the technologies to produce the surface layers of the flexible coupling parts taking into account all the stages of their life cycles. In doing so, both economic and environmental requirements are also taken into consideration. The use of the system for the direct choice of the technology to ensure the required quality of the flexible coupling parts at the repair stage allows more economically solving the problem of restoring their performance. As practice shows, at this stage, the application of the results of the scientific research gives a significant economic effect.

Fatigue life prediction of in-situ TiB2/2024 aluminum matrix composite

Fatigue performances of an in-situ TiB2 particle reinforced 2024-T4 alloy matrix composite (TiB2/2024Al) and 2024-T4 aluminum alloy (2024Al) were investigated. Stress- and strain-controlled fatigue experiments were conducted to obtain the fatigue lives. High-cycle fatigue performance was experimentally studied under different stress concentration levels. The results showed that the addition of in-situ particles enhances the fatigue resistance. A fatigue life prediction method was developed based on a damage-coupled Chaboche elastic–plastic constitutive model. Fatigue life predictions were performed using the established method and compared with the experiments. It was observed that the proposed method achieves fatigue life predictions with satisfactory accuracy.

Experimental study on dynamic fracture behaviors of Beishan NSCB and CCNSCB granite specimens under different loading rates

Beishan area in Gansu province of China has been listed as a major candidate for underground constructions of high-level radioactive waste repository. Therefore, to explore the dynamic responses of Beishan granite is important to the related excavation engineering. This paper investigates the rate dependent effect on the dynamic fracture behaviors of the Beishan granite. The notched semi-circular bend (NSCB) and cracked chevron notched semi-circular bend (CCNSCB) specimens are prepared with speckles uniformly distributed on surface for digital image correlation (DIC) image processing. An ultra-high-speed camera is employed for the modified split Hopkinson pressure bar (SHPB) system to capture the complete cracking process of the rock specimen. The dimensionless stress intensity factors (SIFs) of NSCB and CCNSCB specimens are calculated numerically by the J-integral method in ABAQUS simulation software. To systematically reveal the dynamic fracture mechanisms of Beishan granite specimens, the key dynamic fracture parameters including the dynamic fracture toughness, the evolution of dynamic stress intensity factor (DSIF) during fracturing and the dynamic fracture energy are obtained for further investigations and comparisons. The results show that the dynamic fracture toughness of NSCB and CCNSCB specimens exhibits a distinct rate dependence-the fracture toughness increases with the loading rate rises. Furthermore, the toughness value of the CCNSCB specimen are mostly higher than that of the NSCB specimen due to a more severe stress concentration level near the notch tip. The evolutions of DSIFs of Beishan NSCB and CCNSCB specimens are quite similar to each other, and the corresponding variation curves are all subjected to three typical developing phases until specimens are totally fractured. The dynamic fracture energy of NSCB and CCNSCB specimens is relatively consistent and shows a positive relationship with the loading rate. However, the fracture energy absorption rate (defined as the ratio between the fracture energy and the energy generated in the incident bar) gradually decreases with the loading rate rising, indicating a lower loading rate may be more suitable to improve rock fragmentation efficiency.

Analytical solution for the stress field of hierarchical defects: multiscale framework and applications

Hierarchical defects are defined as adjacent defects at different length scales. Involved are the two scales where the stress field distribution is interrelated. Based on the complex variable method and conformal mapping, a multiscale framework for solving the problems of hierarchical defects is formulated. The separated representations of mapping function, the governing equations of potentials, and the stress field are subsequently obtained. The proposed multiscale framework can be used to solve a variety of simplified engineering problems. The case in point is the analytical solution of a macroscopic elliptic hole with a microscopic circular edge defect. The results indicate that the microscopic defect aggregates the stress concentration on the macroscopic defect and likely leads to global propagation and rupture. Multiple micro-defects have interactive effects on the distribution of the stress field. The level of stress concentration may be reduced by the coalescence of micro-defects. This work provides a unified method to analytically investigate the influence of edge micro-defects within the scope of multiscale hierarchy. The formulated multiscale approach can also be potentially applied to materials with hierarchical defects, such as additive manufacturing and bio-inspired materials.

Overall Design and Optimization of Mining Sequence in High-Stress Environment of Thick Orebody

After entering deep mining, the stress concentration level because of engineering excavation is considerably greater than the strength of the engineering rock mass. Here, we consider the engineering impact of a high stress environment in the deep mine plan, integrate the high-stress environment and its evolution with the mining process into the mining plan, and realize the balance of improving the stress state and getting the maximum net present value. Using Map3d boundary element simulation software, we planned two vertical and four horizontal mining sequences for deep and thick orebody backfill mining, respectively, and then analyzed the changes in stress and rock mass energy because of mining disturbance. The results show that the surrounding mining sequence can effectively improve the mining stress environment and increase production capacity. Using large-spaced dispersion and mining sequence from the middle to both ends can gradually redistribute the stress to adjacent areas, thus reducing the degree of stress concentration.

Failure Analysis of Metallic Orthopedic Implant for Total Knee Replacement

Fractures resulting from wear and fatigue process have been identified as the main causes of failure in biomaterials, especially in implants that act in place of bone or other hard tissue, as they are subject to conditions involving severe cyclic loadings. In biomaterialscase, the types of failures mentioned above must also be evaluated under the effect of degradation or corrosion, due to the direct contact with body fluids. The present research analyzed the fatigue induced by corrosion fracture of an orthopaedic implant for total knee replacementproduced with an austenitic ASTM F138 stainless steel. The morphology, compositions of the interfaces and subsequent corrosive pitting were characterized by stereoscopy and scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS). Stress concentration, inclusions and high carbon levels were the main reasons of failure.

Calculation method for evaluating the concentration coefficient in the elastic–plastic stress area

The presence of various types of defects that occur when using welding technologies requires taking into account the stress concentration factor that occurs near the defects, which significantly affects the level of allowable stresses and the nature of destruction. In this paper, we propose a simplified engineering technique based on the approach of A. Neuber, which allows us to estimate the level of stress concentration in plastic areas located in near the top of the concentrators based on the data obtained earlier about the theoretical concentration coefficients used in solving elastic problems, and on their basis to expand the possibilities of using existing approaches for solving elastic–plastic problems.

An ion beam layer removal method of determining the residual stress in the as-fabricated TSV-Cu/TiW/SiO2/Si interface on a nanoscale

Thermally induced residual stresses across the TSV-Cu/TiW/SiO2/Si interface in through‑silicon vias (TSVs) have raised serious concerns about mechanical and electrical reliability in 3D ICs. The lack of a nanometer-precision measurement technique for the TSV interfacial stress gradient makes the interface failure mechanism unclear. In this work, we propose an ion beam layer removal (ILR) method for determining the residual stress in the as-fabricated TSV-Cu/TiW/SiO2/Si interface on a nanoscale to facilitate identification of the failure mechanism of the TSV-Cu/TiW/SiO2/Si interface in as-fabricated TSVs. The measurement results showed that the residual stress fluctuates across the TSV-Cu/TiW/SiO2/Si interface and that both compressive stress and tensile stress existed within the interface system. Compressive stress occurred at all three interfaces, the TSV-Cu/TiW, TiW/SiO2, and SiO2/Si interfaces, but transitioned to tensile stress at a distance of 25–45 nm from these interfaces. The highest level of shear stress concentration appeared inside the TSV-Cu at a distance of approximately 45 nm from the TSV-Cu/TiW interface. This shear stress concentration explains the experimentally observed TSV interfacial cracking phenomenon.

Seismic analysis of plan irregular RC building frames

The presence of irregularity in buildings is a matter of concern when it is subjected to devastating earthquakes. A sudden change in vertical or plan configuration in buildings tends to weaken the structure. To prevent failure and minimize the hazard potential of irregular buildings, the responses of such buildings to lateral loads have to be studied in detail. In this paper, the responses of irregular buildings are analyzed using Pushover analysis. 10 re-entrant corner models are analyzed to study their effect as per IS 1893 (Part 1): 2016 codal provisions. The analytical tools used include ETABS v 16.2.0 software and SeismoMatch 2018 software. The parameters considered in this study are storey displacement, stress concentration and performance levels. Strengthening techniques to strengthen vulnerable models are also discussed. The results obtained are compared with that of a regular structure.