Mechanical Stress Concentration Research Articles

Design of intelligent drill bit embedded structure based on multi-objective topology optimization method

To address the issues of mechanical performance changes, stress concentration, and displacement in the original drill bit structure caused by the design of embedded structures in intelligent drill bits, the optimal topology of the drill bit was calculated using multi-objective topology optimization methods. Optimal values under various load conditions were obtained using single-objective topology optimization methods combined with penalty functions. Based on these optimal values, calculations for the intelligent drill bit embedded structure were performed using a trade-off planning method. Following this, the initially optimized results were redesigned using NURBS modeling methods to create an embedded structure that meets structural performance requirements. The embedded structure meeting these requirements was then tested through orthogonal simulation to verify its mechanical performance under various complex load conditions. The results show that the embedded structure drill bits designed based on multi-objective optimization generally surpass traditional drill bit structures and those optimized using multi-objective methods in terms of maximum Mises stress and maximum deformation, particularly in external and internal petal configurations, demonstrating good performance in enhancing structural strength.

Determination of the maximum mechanical stresses in the insulating material around a defect with a high dielectric permittivity in an electrostatic field

Introduction. All insulating macrohomogeneous solid materials change shape under the influence of an electric field. Problem. The presence of minor defects changes the distribution of an electric field and causes a significant concentration of mechanical stresses in a given section of the material, which, under certain circumstances, can cause partial or complete destruction of this material. Goal. The purpose of the work is to determine maximum mechanical stresses according to the von Mises criterion in insulating materials around defects with ionized air and water in an electrostatic field. Also, to analyze the influence of the following parameters on the indicated stresses: the location of the defect, the orientation angle of the semi-major axis of the defect cross-section, the ratio of semi-major and semi-minor axes, elastic and dielectric properties of the insulating material and the defect. Methodology. The study is based on the interrelated equations of electrostatics and structural mechanics for an isotropic piecewise homogeneous medium. The solution of these equations is obtained by the finite element method. Results. Graphs of dependences of maximum mechanical stresses on the ratio of semi-major and semi-minor axes of the ellipsoidal cross-section of the defect have been obtained. The minimum ratio of the greatest stresses in the insulating materials around the surface cracks and pores for ionized air has been 9.3 times for the maximum ratio of major and minor semi-axes of the cross-section of the defect considered in the work, which is 10. For a water defect, the similar ratio has been 2...5.6 times, increasing when the relative dielectric permittivity of the insulating material changes from 7 to 2. When Young’s modulus of the insulating material increases from 1 MPa to 100 GPa, the angles of the inclination of the linearized dependences of maximum mechanical stresses around bounded pores with ionized air (water) to the axis of the ratio of major and minor semi-axes of the defect cross-section have been increased by 35.9° (58.0°) and 18.6° (20.1°) at orientations of major semi-axes at angles of 0° and 45°, respectively. Originality. The numerical-field mathematical two-dimensional model has been developed for the first time, which consists of sequentially solved equations of electrostatics and structural mechanics, for the determination of the distribution of mechanical stresses in an insulating material with a liquid or gaseous defect. It has been established for the first time that the ratio of the elastic properties of the insulating material and the defect determines the angle of the inclination of the linearized dependence of the maximum mechanical stress to the axis of the ratio of major and minor semi-axes of the defect cross-section. Practical value. The types of defects that contribute to the aging of insulation materials under the combined action of an electric field and a stress field to the greatest extent have been established.

Analysis of the influence of the stress-strain state of oil and gas equipment metal on the parameters of electromagnetic-acoustic conversion

In the oil and gas industry, to assess the technical condition of equipment, diagnostic methods and tools are used aimed at identifying defects that are unacceptable, according to regulatory documents. In places where mechanical stress is concentrated, microdefects in the metal structure arise, which, under the influence of static and dynamic loads, develop into macrodefects that cause equipment destruction. To identify areas of concentration of mechanical stress and localize metal microdamages, it is proposed to use a non-contact, high-performance electromagnetic-acoustic diagnostic method. But existing electromagnetic-acoustic diagnostic tools lack sensitivity and information content. The article provides an analysis of the influence of the stress-strain state of the metal on the parameters of electromagnetic-acoustic transformation in order to identify additional informative parameters and methods for their processing to solve the problem of identifying the stress-strain state and damage to the metal structure of oil and gas equipment.

NEURAL NETWORK PROCESSING OF ELECTROMAGNETIC ACOUSTIC SIGNALS TO IDENTIFY THE STRESS-STRAIN STATE AND DAMAGE OF POWER EQUIPMENT

The purpose of the study is to develop and train an artificial neural network to identify the stress-strain state and damage to the metal of power equipment based on the values of the parameters of the harmonic components of the electromagnetic-acoustic transducer signal.
 
 Materials and methods. Experimental study of the relationship between the parameters of the harmonic components of the signal of an electromagnetic-acoustic transducer with the stress-strain state and damage to the structure of standard metal samples, development of an artificial neural network and methods for its training to identify the stress-strain state and damage to the structure of the metal according to the loading diagram.
 
 Results. Analysis of changes in the microstructure and frequency models of standard steel samples used in power engineering confirmed the possibility of identifying the stress-strain state and damage to the structure of metals based on the values of the parameters of the harmonic components of the electromagnetic-acoustic transducer signal. To solve this problem, an artificial neural network has been developed and trained. After training, the effectiveness of the network in identifying the stress-strain state and damage to the structure of metals reached 92.16%, which is acceptable for the tasks of recognizing the technical condition of metal structural elements of electrical installation equipment.
 
 Conclusions. The use of an artificial neural network to identify the stress-strain state and damage to metal structures based on the harmonic parameters of the electromagnetic-acoustic transducer signal enables to identify areas of concentration of mechanical stress and damage to the metal structure at the early stage of development, thereby increasing reliability and safety operation of electrical equipment.

Predicting mechanical and electrical failure of nanowire networks in flexible transparent electrodes

Flexible transparent electrodes employing metal nanowires (NWs) find extensive use in various applications such as optoelectronic devices, solar cells, light-emitting diodes, and transparent heaters. NW networks in flexible transparent electrodes can withstand mechanical deformations and conduct electricity but are susceptible to localized damage caused by mechanical stress and current density concentration. This localized damage ultimately results in electrode failure. Our study aims to track locally induced damage from both mechanical and electrical sources and assess their collective influence on electrode performance until failure occurs. To this end, we create two-dimensional digital samples that represent the NW networks, transform them into beam networks and equivalent resistor networks, and perform finite element simulations of the mechanical and electrical network responses while varying the NW content.Our simulations reveal crack-like patterns in the distribution of damaged elements at network failure that depend on the process inducing the damage. While our results suggest that the impact of electrically induced damage on overall network stability is more significant than that of mechanically induced damage, the latter must not be ignored.

P‐BT‐16 | Low Mechanical Stress and High Throughput Concentration of Cells with Acoustophoresis

P‐BT‐16 | Low Mechanical Stress and High Throughput Concentration of Cells with Acoustophoresis

Armadillo-inspired ultra-sensitive flexible sensor for wearable electronics

Flexible sensors are receiving growing attention as a valuable technology in application areas such as wearable electronics, soft robotics and e-skin. Unfortunately, most flexible sensors generally suffer from low sensitivity, narrow application range and single detection function. Herein, we present an uneven deformation strategy inspired by armadillo skin to construct ultra-sensitive flexible sensors. ASR-CLNS sensor consists of a silicone rubber substrate imitating the armadillo skin (ASR) and a continuously laminated conductive network (CLN). Mechanical deformation-induced stress concentration substantially contributes to ultra-high sensitivity. Noteworthily, the non-uniform substrates have specific stress concentration responses in different tensile directions, and the stretch sensitivity can be easily adjusted by microstructure customization or simply changing the sensor placement angle, which enables it to meet the detection requirements of more scenarios. Simultaneously, the laminated structure of the CLN endows the sensor pressure sensitivity, which allows sensors to be used to detect small pressures such as human breathing. Additionally, CLN demonstrated fast heat transfer capability, which can effectively improve the thermal management properties of composites. In short, this work provides an unexplored strategy to develop tunable/ultra-high sensitivity and multifunctional flexible sensor devices.

Superior crack propagation inhibitory effectiveness of MWCNT reinforced SBS toward improving oil/gas well cement integrity

The brittleness and low cracking resistance of oil- and gas-well cement threaten its integrity, specially under the high stress concentrations at bottom-hole conditions. Fortunately, the excellent mechanical properties of carbon nanotubes and elastomers motivate researchers to utilize them as versatile candidates that can positively modify the breakage behaviors of cement-based materials. Herein, we investigated the hybridization effects of multi-walled carbon nanotubes (MWCNTs) and styrene–butadiene–styrene (SBS) on the mechanical properties and breakage behaviors of oil- and gas-well cements. MWCNTs and SBS were synthesized and then, characterized with a wide range of techniques, signifying successful syntheses of these two materials. Afterward, SBS was dry mixed with cement powder and then added to the aqueous suspension of MWCNT prepared via sonication method. The mechanical testing (e.g., uniaxial, triaxial, and Brazilian tests), numerical simulation, and imaging analysis showed that incorporation of the SBS into the cement matrix promoted the ductility and macro-scale cracking resistance. The introduction of MWCNTs improved the cohesion, micro-scale cracking resistance, and strength properties of the cement matrix. Thereupon, the hybridization of 0.075 wt% of MWCNT and 9 wt% of SBS endowed great mechanical behavior and cracking resistance to the conventional oil-well cement in both micro and macro structures. These specifications can maintain cement’s durability under the critical thermal and mechanical stress concentrations at various bottom hole conditions. This improvement contains the increasing of strain energy, tensile strength, cohesion, and Poisson’s ratio by 219.27%, 141.17%, 750% and 100%, respectively and reducing the elastic modulus by 41.67%. Fourier Transform Infrared Spectroscopy (FTIR) analysis exhibited that these enhancements can be attributed to favorable interactions between MWCNT and SBS in the cement matrix.

МЕТОДЫ ОЦЕНКИ КОНЦЕНТРАЦИЙ МЕХАНИЧЕСКИХ НАПРЯЖЕНИЙ

Methods of estimation of mechanical stress concentrations by conducting a computer experiment on models of welds with defects having zones with increased stress concentration in the form of non-welding of the root of the weld are considered. The paper notes that a full-scale study of the stress state with the determination of stress concentration coefficients on the equipment itself is difficult due to the duration of the development of degradation processes, wear and aging, therefore, their conduct is associated with risk and high time and material costs. Analytical research methods using mathematical models and application packages are increasingly being used

АНАЛИЗ МЕТОДОВ ОЦЕНКИ ПРОЧНОСТИ КОНСТРУКЦИЙ В ЗОНАХ КОНЦЕНТРАЦИЙ МЕХАНИЧЕСКИХ НАПРЯЖЕНИЙ

The analysis of methods for assessing strength in areas of mechanical stress concentrations in structures with defects is considered. As examples, the connections of a pipe with a welded shell and a technological pipeline with a through crack in the metal stratification zone delamination are given. It is shown that the calculation of structures with defects is based on the determination of the type of stress state that occurs under load, which is usually characterized by the value of the stiffness coefficient. Analysis of the study of a fragment of a technological pipeline in the zone of wall de-struction showed that the rupture occurred in the zone of the greatest wall thinning caused by the de-lamination of the wall metal, and the cause of the destruction was an excess of internal pressure

Highly conformable chip-in-foil implants for neural applications

Demands for neural interfaces around functionality, high spatial resolution, and longevity have recently increased. These requirements can be met with sophisticated silicon-based integrated circuits. Embedding miniaturized dice in flexible polymer substrates significantly improves their adaptation to the mechanical environment in the body, thus improving the systems’ structural biocompatibility and ability to cover larger areas of the brain. This work addresses the main challenges in developing a hybrid chip-in-foil neural implant. Assessments considered (1) the mechanical compliance to the recipient tissue that allows a long-term application and (2) the suitable design that allows the implant’s scaling and modular adaptation of chip arrangement. Finite element model studies were performed to identify design rules regarding die geometry, interconnect routing, and positions for contact pads on dice. Providing edge fillets in the die base shape proved an effective measure to improve die-substrate integrity and increase the area available for contact pads. Furthermore, routing of interconnects in the immediate vicinity of die corners should be avoided, as the substrate in these areas is prone to mechanical stress concentration. Contact pads on dice should be placed with a clearance from the die rim to avoid delamination when the implant conforms to a curvilinear body. A microfabrication process was developed to transfer, align, and electrically interconnect multiple dice into conformable polyimide-based substrates. The process enabled arbitrary die shape and size over independent target positions on the conformable substrate based on the die position on the fabrication wafer.

811 - Process Development and Manufacturing: LOW MECHANICAL STRESS AND HIGH THROUGHPUT CONCENTRATION OF CELLS WITH ACOUSTOPHORESIS

811 - Process Development and Manufacturing: LOW MECHANICAL STRESS AND HIGH THROUGHPUT CONCENTRATION OF CELLS WITH ACOUSTOPHORESIS

Modeling the mechanism of reducing enamel mineral density in the vicinity of the fisure tip

A distinctive feature of the enamel surface of molars and premolars is the presence of a certain number of fissures - wedge-shaped (V-shaped) notches, the tops of which are natural stress concentrators in the enamel of the tooth crown. To determine the degree of concentration of mechanical stresses in the vicinity of the fissure tip, the problem of the stress-strain state of enamelin the form of an elastic wedge imitating a fissure is considered. The bite force, acting on the food, wedges the fissure and causes a stress-strain state in the vicinity of its tip. The resulting formulas made it possible to estimate the stress-strain state in the vicinity of the fissure tip depending on the fissure opening angle, food diameter, and relative deformation of the lateral surface of the fissure.

Influence of Radial Stiffness Gradients on Porous Composite Bulk Mechanics

Functionally gradient materials, characterized by a smooth compositional change over space, have gained attention in recent years due to their tunable properties and ability to reduce mechanical stress concentrations. Specifically, attaining high stiffness without compromising toughness is a challenge, as the properties are inversely related. Varying moduli gradients, as seen abundantly in biological materials, do not present this trade‐off, facilitating increased rigidity without altering maximum elongation. Herein, the application of stiffness gradients in porous structures is investigated through compressive mechanical testing, computerized tomography imaging, and finite element modeling. Gradients are compared to several alternative designs to investigate the importance of a smooth material transition and increased radial stiffness. All groups are compressed to 50% strain and the pre‐ and postpore closure modulus, toughness, and dimensional change in the transverse and radial directions are measured. The findings indicate that a mechanical gradient with increasing radial stiffness allows for balance of mechanical integrity and favorable recovery characteristics, crucial for long‐lasting performance. Furthermore, the structures with an increasing radial stiffness outperform those with a decreasing radial stiffness in all aspects. The results emphasize the mechanical advantages and optimization potential of a radial stiffness gradient for a wide range of load‐bearing applications.

Effects of gradient structure and modulation period on mechanical performance and thermal stress of TiN/TiSiN multilayer hard coatings

Gradient structure and modulation period of multilayer hard coatings are effective to improve the mechanical performance of cutting tools. However, the effects of gradient structure and modulation period on mechanical and thermal performances of hard coatings have not been clarified. In this study, seven groups of TiN/TiSiN multilayer coating models with diverse gradient structure and various modulation period were established using finite element method (FEM). Nanoindentation and cooling process were simulated to study the effects of gradient structure on mechanical performance and thermal stress. Coatings with thicker layers at the top have more excellent mechanical performance. Mechanical performance and stress concentration are both weakened with the increase of modulation period number, while stress fluctuation becomes more severe. Thicker layers at the upper and bottom of coatings cause maximum stress reduced during applied loads and thermal stress, respectively. Structure of decreasing-increasing modulation periods helps the coating to reduce stress impacts while having better mechanical performance.

PREVENTING THE INCREASE IN THE RISK OF BONE FAILURE IN OSTEOPOROTIC CERVICAL SPINE VERTEBRA WITH A NOVEL COMPUTATIONAL APPROACH

Osteoporosis is a bone disease characterized by a low bone mass that may seriously lead to vertebral fractures. Nowadays, especially elderly people, are most vulnerable to this complication. Hence, it is essential to prevent and predict the high-risk of mechanical stress that causes bone fractures. In this paper, a new computational methodology is developed to prevent the increase in the risk of bone failure in osteoporotic cervical vertebra based on mechanical stress assessment. The cortical bone thickness and the trabecular bone density from computed tomography (CT) scan data are the main initial input parameters for the computation. The methodology is based on a combination of finite element (FE) modeling of the lower cervical spine and the design of experiment (DoE) technique to establish surface responses assessing mechanical stress in healthy and osteoporotic vertebrae. The results reveal that the mechanical stress applied to an osteoporotic cervical vertebra is higher by an average of 35% compared to a healthy vertebra, respecting the applied conditions. Based thereon, a safety factor ([Formula: see text]) is introduced to predict and indicate the state of osteoporosis in the vertebra. A safety factor [Formula: see text] is found to correspond to a healthy state, 1.85 [Formula: see text] 2.45 for an osteopenic state, 1 [Formula: see text] 1.85 for an osteoporotic state, and [Formula: see text] 1 to indicate a severe osteoporosis state. The developed computational methodology consists of an efficient tool for clinicians to prevent early the risk of osteoporosis and also for engineers to design safer prostheses minimizing both mechanical stress concentration and stress shielding.

Mechanical Stress in Rotors of Permanent Magnet Machines—Comparison of Different Determination Methods

In this work, different analytical methods for calculating the mechanical stresses in the rotors of permanent magnet machines are presented. The focus is on interior permanent magnet machines. First, an overview of eight different methods from the literature is given. Specific differences are pointed out, and a brief summary of the analytical approach for each method is provided. For reference purposes, a finite element model is created and simulated for each rotor geometry studied. A total of seven rotors rom representative automotive powertrains are considered in their specific speed range. The analytical methods are used to determine the maximum mechanical stress concentration factors for the seven rotor geometries, in which we are determined to find maximum mechanical stress as a final step of the analytical process. For each geometry and each respective operating speed range, the deviations from the finite element reference are determined. In addition, the error in the selected geometry variations is evaluated. A recommendation for the method with the lowest error considering all cases studied is given specifically for the stress in the airgap bridge and the central bridge.

Improving metal surface integrity by integrating mechanical stress fields during micron- and nano-abrasive machining

The micron-scale fixed-abrasive machining can assure micro-shape accuracy through mechanical cut removal and copying, but the machined surface integrity depends on the nanoscale loose-abrasive machining without mechanical stress concentration. Hence, the mechanical stress fields are synthesized by the hybrid machining of loose-Al2O3-abrasive machining and fixed-diamond-abrasive machining. The objective is to improve the surface integrity in the mechanical machining of difficult-to-cut metals. In order to hold the loose-abrasive in fixed-abrasive mechanical machining, the bonding behaviour and the hydrodynamic pressure were first analysed in relation to flow viscosity and fixed-abrasive-tool rotation, respectively. In the hybrid machining, the surface formation was then modelled in relation to mechanical stress distribution, fixed-abrasive-tool vibration, hydrodynamic pressure, etc. Finally, the surface integrity was investigated in micro-machining of die steel, titanium alloy and Inconel alloy, respectively. It is shown that the nanoscale hydrated particle cluster flexibly bonds the loose-abrasive with the hydrodynamic pressure beyond the critical tool rotation. It can absorb the micron-scale tool vibration to the surface formation, fixed-abrasive wear without ground traces and micro-cut edge burrs. The resulted homogeneous stress also can restrain the uneven residual stress derived from the cut copying of fixed-abrasive machining. The hybrid machining decreases the subsurface damage (SSD), residual compressive stress and surface roughness to the polishing ones in micro-shape grinding, but it is subject to the nanometre-scale size of loose-abrasive, the hydrodynamic pressure and the micron-scale cutting depth of fixed-abrasive. The fixed-abrasive wear rate is higher with larger metal hardness, and the residual stress associated with elastic modulus is more greatly improved. As a result, die steel shows better machinability with a low fixed-abrasive wear rate and residual stress compared to titanium alloy and Inconel alloy.

Finite Element Analysis for First Metatarsophalangeal Joint Arthrodesis Demonstrates Reduction in Stress Across Bio-Integrative Fixation Over Traditional Metal Fixation

Category: Midfoot/Forefoot; Bunion Introduction/Purpose: During each step-in gait, the first metatarsophalangeal joint (MTPJ) is stressed by 90% of body weight, while loading the metatarsal head and base with up to 29% (228N/80Kg patient) of body weight (188N) during each foot push-off. To withstand these high mechanical forces, a successful fusion is dependent on joint preparation and rigid fixation. In this study we assessed a novel bio-integrative fiber-reinforced screw and nail construct. This material technology may provide improved mechanical fixation profile through its high flexural strength and flexural modulus that is closely matched to that of cortical bone. Finite Element Analysis (FEA) was performed to evaluate the mechanical strength and stress concentrations acting on the 1st MTPJ fusion following the use of these implants, compared to conventional metal fixation. Methods: CT-based FEA of the 1st MTPJ fusion fixed by two fixation methods was simulated for mechanical strength and stress concentrations acting on the surrounding cortical bone. The 1st MTPJ of an adult male weighing 80kg was segmented from a left foot CT scan (120 KVP, SL 1mm) and was incorporated in a 3-dimensional CAD model. Bio-integrative fiber-reinforced 4.0mm partially threaded headless compression screw, and a 3.0mm fiber-reinforced cannulated nail were inserted in this computational model in crossed fashion (Fig. 1A). The bio-integrative implants are composed of continuous reinforcing mineral fibers (50% w/w), comprised of elements found in native bone and bound together by a degradable polymer [poly (L-lactide-co- D,L-lactide), PLDLA]. Two 4.0mm partially threaded headless titanium screws were inserted in similar trajectories and served as control (Fig. 1B). The FEA algorithm was based on published known forces acting on the first ray during push-off. Post-processing was performed on FEA results. Results: The relative displacement between the Metatarsal and Phalangeal heads upon simulated loading was 1.6mm for metal fixation and 0.2mm for the fiber-reinforced bio-integrative fixation, demonstrating this technology to be mechanically stable at least as conventional metal fixation. In both models, the Von-Mises maximum stresses were found between the implant thread and shank. However, maximum localized stresses in cortical bone regions interacting with the metal implants were substantially higher (up to 8 times) compared to the bio-integrative implant-bone interactions. Moreover, stresses in the implant body were remarkably higher with metal implants compared to bio-integrative fixation (Fig. 1C, D&E). These results indicate that for physiological loading conditions applied on the 1st MTPJ, the use of bio-integrative fixation construct may reduce stress concentrations at the implant-cortical bone interface. Conclusion: FEA results indicate that bio-integrative screw-nail construct provides equivalent mechanical fixation strength to metal fixation, while resulting in lower bone-implant stress concentrations. The closely matched flexural modulus of the bio- integrative material to that of cortical bone, decreases implant-bone resistance level and the probability of bone/implant failure and risk for implant loosening, all common complications in foot and ankle surgery. This study demonstrates a new methodology of CT-FEA for the evaluation of 1st MTPJ fusion arthrodesis and suggests the bio-integrative screw-nail combination as an alternative to traditional metal fixation. This model is currently being investigated in an ongoing clinical series.

Effect of S addition on mechanical and machinability properties in austenitic Fe–Mn–Al–C lightweight steels

In this study, the machinability of austenitic LWS and the effect of MnS formation on the mechanical and machinability properties were investigated. For this purpose, S was added over a wide range from 0.0048 to 0.0713 wt% to control MnS inclusions. As the S content increased, the number and area fraction of the MnS inclusions increased linearly, whereas the inclusion size first rapidly increased, and then its slope decreased. The tensile properties hardly changed regardless of the S content, whereas the Charpy impact energy deteriorated linearly with increasing S content. Furthermore, the machinability of LWS was considerably improved by the formation of MnS inclusions, which play a role in the site of mechanical stress concentration and thermal cavity and pore generation during machining.