Von Mises Stress Research Articles

A finite element analysis of stress distribution with various directions of intermaxillary fixation using orthodontic mini-implants and elastics following mandibular advancement with a bilateral sagittal split ramus osteotomy.

This finite element analysis (FEA) aimed to assess the stress distribution in the mandible and fixation system with various directions of the intermaxillary fixation (IMF) using mini-implants (MIs) and elastics following mandibular advancement with a bilateral sagittal split ramus osteotomy (BSSRO). A total of nine mandibular advancement models were set according to the position of the MIs (1.6 mm in diameter, 8 mm in length) and direction of the IMF elastics (1/4 inch, 5 oz). Major and minor principal stresses in the cortical and cancellous bones, von Mises stresses in the fixation system (miniplate and monocortical screws), and bending angles of the miniplate were analysed. Compressive and tensile stress distributions in the mandible and von Mises stress distributions in the fixation system were greater in models with a Class III IMF elastic direction and a higher IMF elastic force than in models with a Class II IMF elastic direction and a lower IMF elastic force. The bending angle of the miniplate was negligible. Stress distributions in the bone and fixation system varied depending on the direction, amount of force, and position of IMF elastics and MIs. Conclusively, IMF elastics in the Class II direction with minimal load in the area close to the osteotomy site should be recommended.

Effect of loading paths on hydroforming ability of stepped hollow shaft components from double layer pipes

The step hollow shaft components are composed of two layers of different materials, they are formed using tube hydroforming process due to its high strength and rigidity, low weight and flexible profiles, compared to traditional casting, welding, and forming methods. These products are effectively used in industries such as the automotive, shipbuilding, aerospace and defense, and oil and gas sectors. The success of various double layer pipe hydroforming process depends on several factors, with the most important being the internal pressure path and axial loading path. This paper presents research on the effect of input loading paths on the hydroforming ability of a different two-layer metal structure - an outer layer of SUS304 stainless steel and an inner layer of CDA110 copper - using 3D numerical simulations on Abaqus/CAE software. Output criteria were used to evaluate the forming ability of the formed components, including Von Mises stress, Plastic strain component (PEmax), wall thinning, and pipe profile, based on which the input loading paths were combined during the forming process. These output criteria allow for more accurate predictions of material behavior during the hydroforming process, as well as deformation and stress distribution. This can support the design process, improve product quality, reduce errors, and increase production efficiency. The research results can be applied as a basis for optimizing load paths for the next experimental step in the near future, for undergraduate and graduate training, as well as allowing designers and engineers to optimize the process of hydroforming of different 2-layer tubes, reducing costs, improving accuracy, flexible design, minimizing risks, and increasing efficiency

Head Impact Analysis Terhadap Pillar Aluminium Dan Mild Steel St37 Menggunakan LS-Dyna

Head Impact analysis is research that can be used as a basis for other research. Head impact analysis is used to determine safety factor, HIC, displacement and others, but in this simulation the focus is on determining displacement using the finite element method. This simulation is designed using LS-DYNA software, a software used to solve finite element model problems. This simulation consists of an analysis of the head hitting the pillar that are made for the simulation process. The output of this simulation is X-displacement and Von-Mises Stress. In modeling and simulating the speed used is 40 km/h (11 m/s) which is the safe limit and one of the most common speed values when an accident occurs.

Design of Low-Stress robust silicon and Silicon-Carbide anode with high areal capacity and high energy density for Next-Generation Lithium-Ion batteries

Utilization of biomass-converted products in the energy industry is a pathway to sustain the demand of high energy lithium cells, and silicon anode could be a solution before the lithium metal. The high percentage of silicon (>10 wt%) in the anode for capacity gain can’t prevent crack generation during cycling and results in capacity fading and cell failure. Here, we present a unique anode structure like an in-situ nano-layer of carbon-coated silicon–silicon carbide (Si-SiC@C) from black rice husk ash (BRHA)-biomass. A specific proportion of the “SiC” phase in Si-SiC@C plays a crucial role in the formation of a stable interface, passivation of the Si surface, and suppression of Si cracking, resulting in improved battery cycling performance. Furthermore, the distribution of relaxation times (DRT) experiment was carried out in MATLAB software to more understand the interface mechanism. Nano-indentation and Von-mises stress generation method was used to analyze the mechanical properties of samples. The ‘Si’ and ‘SiC’ phases were distinguished by X-ray Diffraction (XRD) and are thoroughly analyzed via the advanced characterization tools (i.e., FETEM, c-AFM, XPS, etc.). The optimized Si-SiC@C composition showed excellent cyclic stability up to 700 cycles with an areal capacity of ∼2.3 mAh cm−2 at a rate of 0.2 A g−1 vs. Li/Li+. Moreover, a pouch cell is fabricated with the Si-SiC@C (i.e., ∼3.8 mg cm−2) as anode and NMC811 as cathode (∼11.5 mg cm−2). The developed 300 mAh pouch cell performed excellently (>85 % capacity retention) over 200 cycles. In light of easy and energy-efficient synthesis, robustness, and cyclic stability, the specially designed Si-SiC@C from BRHA can be a promising choice as the next-generation anode material for rechargeable battery applications, particularly for lithium-ion batteries.

FINITE ELEMENT ANALYSIS OF HUMAN AND ARTIFICIAL ARTICULAR CARTILAGE

Joint diseases, such as osteoarthritis, induce pain and loss of mobility to millions of people around the world. Current clinical methods for the diagnosis of osteoarthritis include X-ray, magnetic resonance imaging, and arthroscopy. These methods may be insensitive to the earliest signs of osteoarthritis. This study investigates a new procedure that was developed and validated numerically for use in the evaluation of cartilage quality. This finite element model of the human articular cartilage could be helpful in providing insight into mechanisms of injury, effects of treatment, and the role of mechanical factors in degenerativeconditions, this three-dimensional finite element model is a useful tool for understanding of the stress distributions within articular cartilage in response to external loads and investigating both the prevention of injury and the pathological degeneration of the joints.In this study, 21 models were analysed by using ANSYS workbench v12.1: four normal articular cartilage models (distal femur, patella, medial and lateral tibia). A redesign to the distal femur model was done to get osteoarthritis articular cartilage (simple and deep) seven models by making partial cut without affecting the subchondral bone, and full cut with part of the subchondral bone in different diameters. Finally a treatment done by replacing the defective parts with artificial articular cartilages with different types of treatment. The finite element analysis studied depending on a Von Mises criteria and total deformation in different activities. The results shows that Autologous Chondrocyte Implementation is the best treatment way and it is close by 87.50% to normal cartilage. This procedure can be used as a diagnostic procedure for osteoarthritic patients and to choose the best treatment options.

Mechanical influence of tissue scaffolding design with different geometries using finite element study.

The mechanical properties of tissue scaffolds are essential in providing stability for tissue repair and growth. Thus, the ability of scaffolds to withstand specific loads is crucial for scaffold design. Most research on scaffold pores focuses on grids with pore size and gradient structure, and many research models are based on scaffolding with vertically arranged holes. However, little attention is paid to the influence of the distribution of holes on the mechanical properties of the scaffold. To address this gap, this research investigates the effect of pore distribution on the mechanical properties of tissue scaffolds. The study involves four types of scaffold designs with regular and staggered pore arrangements and porosity ranging from 30% to 80%. Finite element analysis (FEA) was used to compare the mechanical properties of different scaffold designs, with von-Mises stress distribution maps generated for each scaffold. The results show that scaffolds with regular vertical holes exhibit a more uniform stress distribution and better mechanical performance than those with irregular holes. In contrast, the scaffold with a staggered arrangement of holes had a higher probability of stress concentration. The study emphasized the importance of balancing porosity and strength in scaffold design.

Numerical analysis of hydrogen atom diffusion and trapping at an unconstrained dent on pipelines

In this work, a three-dimensional finite element-based mechanics-diffusion coupling model is developed to determine the stress/strain distribution and hydrogen (H) atom concentration at an unconstrained dent on an X52 steel pipe which is to be used for transport of high-pressure hydrogen gas. Both von Mises stress and equivalent plastic strain concentrations and a high hydrostatic stress gradient exist at the dent. The distribution of H atom concentration coincides with that of the hydrostatic stress. The maximum H atom concentration in the steel lattice locates at the dent bottom, while the distribution of the H atom concentration at metallurgical traps is consistent with that of the equivalent plastic strain. A competitive effect exists between the hydrostatic stress and the plastic strain on the H atom distribution. At low initial H atom concentrations (e.g., 0.001 mol/m3), the equivalent plastic strain dominates the distribution of H atoms. At high initial H atom concentrations (e.g., 0.1 and 1 mol/m3), the hydrostatic stress is more important to determine the distribution of H atom concentration. As the dent depth increases, both the von Mises stress and plastic strain at the dent increases, while the total H atom concentration decreases due to decreased hydrostatic stress. When the internal pressure increases from 5 MPa to 15 MPa, there are slightly increases in von Mises stress, equivalent plastic strain and the total H atom concentration.

Experimental investigation on the performance of Cable-Girder anchorage structure of hybrid Cable-Stayed suspension bridges

As the key component of the stay cable connecting the girder and tower in the hybrid cable-stayed suspension system, the cable anchorage structure needs to bear the powerful cable force transmission function. Compared with normal anchorages, the structural features of a new type of anchor box structure cable-girder anchorage (CGA) that has strong bearing capacity and more uniform stress distribution for a long-span hybrid cable-stayed suspension bridge with steel box girder was investigated by a 1:2 scale specimen test and a series of finite-element analysis. Through finite element analysis (FEA) and test results, the stress distribution and cable load transfer pathway of anchor box structure are obtained. The test results show that the CGA design is reasonable and reliable. The four welds connected to the anchor box support plates and the steel box girder webs bear 87% of the cable force load transfer, and the remaining 13% of the cable load is delivered from the anchor box bearing plate to webs. A large stress concentration in the six welds, but the maximum von Mises stress (VMS) of welds is 130–151 MPa. According to the parametric studies,the installation angle of the anchor box considerably affects the stress characteristics. Also, the thickness and length of the anchor box plate are changed, the transmission and distribution proportion of the cable force between the main welds of the anchor box increase alternately.

Seismic performance of bolted T-stub Beam-to-Box column connection

Using internal continuity plates in box columns due to accessibility problems and complicated detailing of connection was perceived as fraught with shortcomings and limitations. To overcome this deficiency, the effectiveness of external continuity plates in conjugation with T-stub connectors in I-beam to box-column connections under cyclic action is investigated in this study. Three damage control strategies based on the fuse action of T-stubs (T-F), strengthening the connections (T-S), and using reduced beam section (RBS) connections (T-R) are pursued and are compared to a corresponding end-plate connection (E). Nonlinear finite element analyses are conducted using the ABAQUS/STANDARD software on the connections under the qualification cyclic loading conditions to elucidate all the main seismic behavioral aspects, including the strength, initial stiffness, energy dissipation, ductility, von-Mises stress, and equivalent plastic strain distributions of models. First, the accuracy of numerical models is validated by a series of available experimental results. Then, a parametric study is performed on the effects of the moment ratio of the beam to column, the number of continuity plates, stiffeners embedded on the beam, and using high strength materials on the seismic performance of the connections. From the results, it is found that the T-S model was the most efficient among the different connections studied, supplying the stiffness, strength, energy absorption, and ductility increases by 2%, 21%, −17%, and 22%, respectively with respect to the E model, satisfying the requirements of AISC Seismic Provisions for SMF. Increasing the beam-to-column moment ratio and the number of continuity plates, had limited effects by less than 10% on the seismic performance of the connections. In the absence of continuity plates, the connections exhibited worse inelastic seismic performance with decreases in stiffness, strength, and energy dissipation up to 67%, 44%, and 74%, respectively. The T-F connection gained a 13% strength increase and satisfied the AISC requirements when high-strength T-stubs are used. Based on the numerical observations, design strength and rotational stiffness of the proposed connections on the component-based joint design strategies, are finally outlined.

Study by finite element modeling of hydrogen atom diffusion and distribution at a dent on existing pipelines for hydrogen transport

Pipelines, especially existing natural gas pipelines, provide an efficient and economical means for hydrogen transport, accelerating realization of a full-scale hydrogen economy. However, the existing aged pipelines usually contain dents, which serve as effective traps to accumulate hydrogen atoms, potentially causing hydrogen embrittlement and pipeline failures. To date, there has been a strong interest in development techniques for assessment of hydrogen atom distribution at a dent on pipelines. In this work, a three-dimensional nonlinear finite element-based model was developed to investigate the hydrogen atom diffusion and distribution at a constrained dent on an X52 steel pipe. Parametric effects, including dent depth and internal pressure, were determined. The presence of a dent on pipelines drastically changes the local stress and strain distributions, facilitating diffusion and accumulation of hydrogen atoms at the dent. The minimum hydrogen atom concentration at the crystalline lattice sites, (i.e., 3.8 mol/m3) is located on the outer surface of the dent center, and the maximum hydrogen atom concentration (i.e., 12.1 mol/m3) is found on both sides of the dent with 103 mm from the dent center in the circumferential direction. The hydrogen atom concentration at trap sites at the dent is much lower than that at the lattice sites. The diffusion and accumulation of hydrogen atoms at the dent area is affected by two competitive mechanisms, i.e., hydrostatic stress and plastic strain, depending on the initial concentration of hydrogen atoms entering the interior of the pipe steel. At a low initial concentration such as 0.001 mol/m3, the equivalent plastic strain dominates the distribution of hydrogen atoms at the dent, and the hydrogen atom concentration at the lattice sites is much lower than the concentration at the trap sites. At high initial hydrogen atom concentrations such as 0.1 and 1 mol/m3, the hydrostatic stress is the dominant factor to determine the distribution of hydrogen atoms, which mainly accumulate at the lattice sites. With an increased depth of the dent, both the von Mises stress and plastic strain concentrations increase, and so is the hydrogen atom concentration. The increase of internal pressure from 5 MPa to 15 MPa only slightly elevates the von Mises stress, equivalent plastic strain and the hydrogen atom concentration.

In-plane impact dynamics of angular gradient honeycomb structure with adjustable Poisson’s ratio multi-arc concave cell

The honeycomb structure with negative Poisson’s ratio has many advantages. The development of lightweight and high-strength materials requires researchers to construct new negative Poisson’s ratio honeycomb structures from the gradient structure design method. In this paper, a new angular gradient multi-arc concave honeycomb structure has been constructed based on a multi-arc concave cell. By setting different cell arrangement modes, four angular gradient honeycomb structures were established: positive gradient, negative gradient, symmetrical positive gradient and symmetrical negative gradient. The relative density expression of the angular gradient multi-arc concave honeycomb structure was deduced. The deformation failure modes, Von Mises stress contours, dynamic response curves, energy absorption per unit mass and plateau stress of the different gradient arrangement and impact velocity were numerically studied. The results show that the gradient arrangement and the impact compression velocity have significant effects on the deformation failure modes and the dynamic response curve of the honeycomb structures. The energy absorption effect of the negative gradient honeycomb structure is the best. The plateau stress of the honeycomb structure is mainly affected by the impact compression velocity, while the gradient arrangement has little effect on the plateau stress.

Establishment of finite element model of varus-type ankle arthritis and biomechanical analysis of different correction models for tibial anterior surface angle

To establish the finite element model of varus-type ankle arthritis and to implement the finite element mechanical analysis of different correction models for tibial anterior surface angle (TAS) in supramalleolar osteotomy. A female patient with left varus-type ankle arthritis (Takakura stage Ⅱ, TAS 78°) was taken as the study object. Based on the CT data, the three-dimensional model of varus-type ankle arthritis (TAS 78°) and different TAS correction models [normal (TAS 89°), 5° valgus (TAS 94°), and 10° valgus (TAS 99°)] were created by software Mimics 21.0, Geomagic Wrap 2021, Solidworks 2017, and Workbench 17.0. The 290 N vertical downward force was applied to the upper surface of the tibia and 60 N vertical downward force to the upper surface of the fibula. Von Mises stress distribution and stress peak were calculated. The finite element model of normal TAS was basically consistent with biomechanics of the foot. According to biomechanical analysis, the maximum stress of the varus model appeared in the medial tibiotalar joint surface and the medial part of the top tibiotalar joint surface. The stress distribution of talofibular joint surface and the lateral part of the top tibiotalar joint surface were uniform. In the normal model, the stress distributions of the talofibular joint surface and the tibiotalar joint surface were uniform, and no obvious stress concentration was observed. The maximum stress in the 5° valgus model appeared at the posterior part of the talofibular joint surface and the lateral part of the top tibiotalar joint surface. The stress distribution of medial tibiotalar joint surface was uniform. The maximum stress of the 10° valgus model appeared at the posterior part of the talofibular joint surface and the lateral part of the top tibiotalar joint surface. The stress on the medial tibiotalar joint surface increased. With the increase of valgus, the stress of ankle joint gradually shift outwards, and the stress concentration tends to appear. There was no obvious obstruction of fibula with 10° TAS correction. However, when TAS correction exceeds 10° and continues to increase, the obstruction effect of fibula becomes increasingly significant.

A comparison of the biomechanical properties of three different lumbar internal fixation methods in the treatment of lumbosacral spinal tuberculosis: finite element analysis

There are various internal fixation methods in treating lumbosacral spinal tuberculosis. The study compared the stability and stress distribution in surrounding tissues/implants, such as discs, endplates and screw-rod internal fixation system, etc. when applying three different lumbar internal fixation methods to treat lumbosacral spinal tuberculosis. A finite element model was constructed and validated. The spinal stability was restored using three methods: a titanium cage with lateral double screw-rod fixation (group 1), autologous bone with posterior double screw-rod fixation (group 2), and a titanium cage with posterior double screw-rod fixation (group 3). For comparison, group 4 represented the intact L3-S1 spine. Finally, a load was applied, and the ranges of motion and Von Mises stresses in the cortical endplates, screw-rod internal fixation system and cortical bone around the screws in the different groups were recorded and analyzed. All six ranges of motion (flexion, extension, left/right lateral bending, left/right rotation) of the surgical segment were substantially lower in groups 1 (0.53° ~ 1.41°), 2 (0.68° ~ 1.54°) and 3 (0.55° ~ 0.64°) than in group 4 (4.48° ~ 10.12°). The maximum stress in the screw-rod internal fixation system was clearly higher in group 2 than in groups 1 and 3 under flexion, left/right lateral bending, and left/right rotation. However, in extension, group 1 had the highest maximum stress in the screw-rod internal fixation system. Group 2 had the lowest peak stresses in the cortical endplates in all directions. The peak stresses in the cortical bone around the screws were higher in group 1 and group 2 than in group 3 in all directions. Thus, titanium cage with posterior double screw-rod fixation has more advantages in immediate reconstruction of lumbosacral spinal stability and prevention of screw loosening.

Sedimentation of particles with various shapes and orientations in a closed channel using smoothed particle hydrodynamics

The sedimentation of particles with various shapes and orientations in a closed channel using smoothed particle hydrodynamics is investigated in this paper. The continuity and momentum equations of both fluid and solid are discretized using kernel approximation in the Lagrangian frame. The sedimentation behavior of different general shapes, including circle, pentagon, square, ellipse, rectangle, and triangle, at various initial orientations in the suspending fluid is simulated. The stable equilibrium orientation (SEO) of these shapes is examined, excluding the circle which serves as a validation case. Specifically, the major axis of the ellipse and rectangle tends to align horizontally, whereas the orientations of the pentagon and square seem to be random due to the lack of a major axis and the finite channel height. The settling behavior of the three types of triangles is also discussed, and the von Mises stress of these shapes during their settling is presented. This study offers valuable insights into fluid-particle interactions, specifically regarding the SEO and internal stress of settling particles with varying shapes and orientations.

Prevention of sclerosis around cannulated screw after treatment of femoral neck fractures with bioceramic nails: a finite element analysis

PurposeConventional cannulated screws (CS) are the main treatment method for femoral neck fractures (FNF). However, the rate of femoral head necrosis remains high after FNF treatment. The study aimed to compare the biomechanical features of different internal fixation materials for the treatment of Pauwel type III FNF to explore new strategies for clinical management.MethodsA new material was prepared by applying casting, freeze drying and sintering process. The independently developed calcium magnesium silicate ceramic powder and hydrogel solution were evenly mixed to obtain a high-viscosity bio-ink, and a bioceramic nail (BN) with high mechanical strength and high fracture toughness was successfully prepared. Four internal fixations were developed to establish the Pauwel type III FNF and healed fracture finite element models: A, three CSs; B, three BNs; C, two BNs and one CS; D, one BN and two CSs. Von Mises stress and displacement of the implants and femur were observed.ResultsThe measured Mg content in ceramic powder was 2.08 wt%. The spectral data confirmed that the ceramic powder has high crystallinity, which coincides with the wollastonite-2 M (PDF# 27–0088). The maximum von Mises stresses for the four models were concentrated in the lower part of the fracture surface, at 318.42 Mpa, 103.52 MPa, 121.16 MPa, and 144.06 MPa in models A, B, C, and D, respectively. Moreover, the maximum Von-mises stresses of the implants of the four models were concentrated near the fracture end at 243.65 MPa (A) and 58.02 MPa (B), 102.18 MPa (C), and 144.06 MPa (D). The maximum displacements of the four models were 5.36 mm (A), 3.41 mm (B), 3.60 mm (C), and 3.71 mm (D). The displacements of the three models with BNs were similar and smaller than that of the triple CS fracture model. In the fracture healing models with and without three CSs, the greatest stress concentration was scattered among the lowest screw tail, femoral calcar region, and lateral femur shaft. The displacement and stress distributions in both models are generally consistent. The stress distribution and displacement of the three healed femoral models with BNs were essentially identical to the healing models with three CSs. The maximum von Mises stresses were 65.94 MPa (B), 64.61 MPa (C), and 66.99 MPa (D) while the maximum displacements of the three healed femoral models were 2.49 mm (B), 2.56 mm (C), and 2.49 mm (D), respectively.ConclusionsBioceramic nails offer greater advantages than conventional canulated screws after femoral neck fractures. However, the combination of bioceramic nails and CSs is more clinically realistic; replacing all internal fixations with bioceramic nails after the healing of femoral neck fractures can solve the problem of sclerosis formation around CSs and improve bone reconstruction by their bioactivity.

Biomechanical effects of transverse connectors on total en bloc spondylectomy of the lumbar spine: a finite element analysis

BackgroundThe influence of total en bloc spondylectomy (TES) on spinal stability is substantial, necessitating strong fixation to restore spinal stability. The transverse connector (TC) serves as a posterior spinal instrumentation that connects the left and right sides of the pedicle screw-rod system. Several studies have highlighted the potential of a TC in enhancing the stability of the fixed segments. However, contradictory results have suggested that a TC not only fails to improve the stability of the fixed segments but also might promote stress associated with internal fixation. To date, there is a lack of previous research investigating the biomechanical effects of a TC on TES. This study aimed to investigate the biomechanical effects of a TC on internal fixation during TES of the lumbar (L) spine.MethodsA single-segment (L3 segment) TES was simulated using a comprehensive L spine finite element model. Five models were constructed based on the various positions of the TC, namely the intact model (L1-sacrum), the TES model without a TC, the TES model with a TC at L1–2, the TES model with a TC at L2–4, and the TES model with a TC at L4–5. Mechanical analysis of these distinct models was conducted using the Abaqus software to assess the variations in the biomechanics of the pedicle screw-rod system, titanium cage, and adjacent endplates.ResultsThe stability of the surgical segments was found to be satisfactory across all models. Compared with the complete model, the internal fixation device exhibited the greatest constraint on overextension (95.2–95.6%), while showing the least limitation on left/right rotation (53.62–55.64%). The application of the TC had minimal effect on the stability of the fixed segments, resulting in a maximum reduction in segment mobility of 0.11° and a variation range of 3.29%. Regardless of the use of a TC, no significant changes in stress were observed for the titanium cage. In the model without the TC, the maximum von Mises stress (VMS) for the pedicle screw-rod system reached 136.9 MPa during anterior flexion. Upon the addition of a TC, the maximum VMS of the pedicle screw-rod system increased to varying degrees. The highest recorded VMS was 459.3 MPa, indicating a stress increase of 335.5%. Following the TC implantation, the stress on the adjacent endplate exhibited a partial reduction, with the maximum stress reduced by 27.6%.ConclusionThe use of a TC in TES does not improve the stability of the fixed segments and instead might result in increased stress concentration within the internal fixation devices. Based on these findings, the routine utilisation of TC in TES is deemed unnecessary.

Enhanced mechanical and tribological properties of polymer nanocomposites by improving interfacial properties by hexagonal boron nitride nanosheets: Molecular dynamics simulations

AbstractTo comparatively investigate the mechanical, tribological, and interfacial properties of polytetrafluoroethylene (PTFE) strengthened by graphene (Gr) and hexagonal boron nitride (h‐BN) nanosheets, molecular models of PTFE nanocomposites containing a similar weight fraction of Gr and h‐BN nanosheets were established. The constant‐strain approach, the three‐layer friction structures, and the pull‐out simulations were respectively employed to calculate the mechanical, tribological, and interfacial properties of the nanocomposites. Results indicate that the Young's, shear, and bulk moduli of the nanocomposites are increased by 17.22%, 20.72%, and 4.78%, respectively, by introducing h‐BN nanosheets than those by introducing Gr nanosheets. Meanwhile, a decrease of 8.49% in the friction coefficient of the nanocomposites is obtained by incorporating h‐BN nanosheets than that by incorporating Gr nanosheets. In addition, 84.71% and 5.18 times higher in the interfacial cohesive strength and interfacial shear strength, and 91.58% and 128.7% higher in the interfacial fracture toughness of PTFE nanocomposites in the normal separation and shear separation, respectively, are achieved by incorporating h‐BN nanosheets than those by incorporating Gr nanosheets. To provide a deeper understanding of the enhancement mechanisms of h‐BN nanosheets, the interfacial interaction energies, radial distribution functions, and von Mises stress distributions of the two PTFE nanocomposites were evaluated and interpreted accordingly.

Exact solution of burst pressure for thick-walled pipes using the flow theory of plasticity

This paper develops an exact solution of burst pressure for defect-free, thick-walled pipes using the flow theory of plasticity in terms of the average shear stress yield criterion (or Zhu-Leis yield criterion). The pipe steel is assumed to obey the power-law strain hardening rule, and large plastic deformation is described by the finite strain theory. On this basis, internal pressure is obtained as a power series function of the effective strains on the inside and outside surfaces of the thick-walled pipe with use of the second Bernoulli numbers. At burst failure, the Zhu-Leis flow solution of burst pressure is determined as a power series solution, and the burst effective strains, the burst effective stresses, and the burst pressure are functions of the diameter ratio (Do / Di), strain hardening exponent (n), and ultimate tensile strength (UTS). Similarly, the Tresca and von Mises flow solutions of burst pressure are also determined as a power series solution in terms of the Tresca and von Mises yield criteria. A general closed-from exact solution of burst pressure is then proposed for the three yield criteria, and the results showed that the proposed exact solution matches well with the power series solution for each yield criterion. Moreover, the von Mises flow solution is an upper bound prediction, the Tresca flow solution is a lower bound prediction, and the Zhu-Leis flow solution is an intermediate prediction that agrees well with the finite element analysis results of burst pressure for thick-walled pipes. Two datasets of full-scale burst tests are then utilized to evaluate and validate the proposed flow solutions of burst pressure for both thin and thick-walled pipes.

The machining parameter optimisation during the machining of the Cr-Mn austenitic stainless steel by the topsis method

The Cr-Mn stainless steel (austenitic) was dry turned in a lathe. A carbide tool (Indoloy) was used for the machining. The speed (v), feed (f), and depth of cut (DOC, d) were the input parameters. The experimental work was done following the Taguchi L 27 design plan. The chip reduction coefficients (CRC) and the von Mises stresses (VMS) were determined for all the experimental conditions. The TOPSIS (Technique for Order of Preference by Similarity to the Ideal Solution) method was used to optimise the process parameters. The optimal conditions were attainable at high speed (v = 100 m/min.), moderate feed (f = 0.1 mm/rev.), and moderate DOC (d = 1 mm). At optimized machining conditions, the VMS was 3429.5 MPa and the CRC was 1.6. The VMS was higher for the lower speed, and the VMS was lower for the higher speed. The higher VMS was attributed to the formation of strain-induced martensite (SIM). The lower VMS was due to the dynamic recrystallization (DRX) at the higher temperature for the higher speed. For the higher speed, the DRX and the dynamic precipitation (DP) occurred at the chip surface (under).

Study on the performance characteristics and failure analysis of exhaust valves

Abstract Exhaust valves are a type of valve that can commonly be found in the top section of the cylinder block in an engine. When failures occur on the exhaust valve, the engine has a high possibility to result engine failure or breakdown. This will affect the user where the user requires to spend a huge amount on repairing costs or engine replacement. Thus, this research aims to investigate the effect of the exhaust valve’s material on its performance and identify the appropriate material which could increase its fatigue life in a four-stroke internal combustion diesel engine. A three-dimension (3D) Computer-aided design model of the exhaust valve was generated by using SOLIDWORKS and undergo static structural analysis as well as thermal analysis. The measure variables are von-mises stress, total deformation, temperature, total heat flux and directional heat flux by using ANSYS Finite Element Analysis. Stainless steel 304 alloy and Aluminium-Silicon Carbide (Al-Sic) materials are the manipulated variable that was applied to the 3D CAD model exhaust valve to undergo all the analyses. Before performing all the analyses, the appropriate mesh method and mesh sizing was identified by referring to the mesh metrics spectrum and performing a mesh independence test. The results from the analysis were collected and tabulated for comparison and discussion purposes. From the analysis, the maximal thermal stress was determined in the valve stem region. By appointing Stainless Steel 304 alloy on the exhaust valve, the durability and the fatigue life are improved as the material can achieve a smaller value of temperature distribution, total heat flux, total deformation, and higher von-mises stress. This research provided a better understanding of the effect of an exhaust valve material on its performance characteristic.