Analysis Of Mechanical Structures Research Articles

Structure design and mechanical performance analysis of three kinds of bioresorbable poly-lactic acid (PLA) stents

Vascular stent implantation has become an important choice for the treatment of severe cardiovascular and cerebrovascular blockage. Rational design is vital to ensure the mechanical properties of the vascular stents, which are important both to the implantation and service as for clinical treatment of coronary heart disease. Therefore we proposed a wholly new non-uniform honeycomb stent E and compared with an inverted honeycomb-like shaped stent F and a honeycomb-like shaped stent G. To evaluate their properties, a finite element method (FEM) was used to simulate the implantation process (crimp, crimp recoil, expand, and expand recoil) of these three different kinds of stents. Results showed that the stent E exhibits better mechanical behaviour than the other two stents F and G as far as radial strength and axial shortening performances and that the distribution of equivalent stress among the stent E is more uniform than that among the other two stents F and G. After that, a three-point bending method was used to study the bending flexibility of these three vascular stents. Stent E shows high bending stiffness compared with stents F and G due to the existence of additional support bridges in its structure. This study can be helpful to the rational design of optimizable PLA stents for its practical clinical performance and therefore possibly improve the prognosis of patients.

The sculpture of the Christ of the blood: Structural mechanical analysis based on 3D models and video techniques for the study of recurrent pathologies

The Christ of the Blood is an emblematic work of Spanish baroque sculpture. A sculptural heritage from the 17th century, unique for its symbolism and turbulent history. It was badly damaged during the Spanish Civil War and was divided into thirty fragments, which were recomposed by important local sculptors of the time through complex interventions. As is tradition, after the war, the sculpture has continued to be paraded in a procession every year on the occasion of Holy Week. The movements derived from this parade affect the integrity of the sculpture, although in a particular and critical way on the right foot, which requires recurrent interventions from the 1940s to the present day. There is a dilemma between tradition and preservation, between devotion and integrity. The studies and tests carried out so far are limited to the evaluation of the state of the structure, the materials and the application of new conservation treatments, but they do not contribute decisively to the prevention of its degradation. The research presented here aims to develop a dynamic structural study of the forces and stresses to which the sculpture is subjected during its annual parade. To do this, computer simulation by finite elements is chosen, which requires a three-dimensional model which is available as a result of previous research. At the same time, advanced video measurement techniques are used to obtain initial data for the simulation process, such as maximum acceleration. Finally, possible solutions are provided that allow the repair, prevention and conservation of this invaluable heritage asset, as well as a technical assessment and economic investment of the application of each of them.

Isogeometric analysis with embedded stiffened shells for the hull structural mechanical analysis

Isogeometric analysis with embedded stiffened shells for the hull structural mechanical analysis

Study on Mechanical Problems of Complex Rock Mass by Composite Material Micromechanics Methods: A Literature Review

The mechanical analysis of complex rock mass is a difficult problem, which often occurs in scientific research and practical engineering. Many achievements have been made in the study of rock mass composite problems by composite material micromechanics method, but it has not been well summarized so far. This paper summarizes in detail the research status of complex rock mass problems by composite material micromechanics method at home and abroad, including the application of the Eshelby equivalent inclusion theory and self-consistent model in rock mass composite problems, and the application of the homogenization method in jointed rock mass and other rock mass composite problems such as anchored rock mass, layered rock mass, and salt rock mass with impurities. It is proposed that the structural similarity and mechanical analysis similarity should be satisfied when the composite material micromechanics method is used to study the complex rock mass. Finally, the problems that need to be further studied are put forward. The research results provide a valuable reference for the study of complex rock mass by the composite material micromechanics method.

Porous Structure Design and Mechanical Properties Analysis of Femoral Stem Based on Selective Laser Melting

Porous Structure Design and Mechanical Properties Analysis of Femoral Stem Based on Selective Laser Melting

Low-cost and highly efficient production of bacterial cellulose from sweet potato residues: Optimization, characterization, and application

Bacterial cellulose (BC) is an emerging biological material with unique properties and structure, which has attracted more and more attention. In this study, Gluconacetobacter xylinus was used to convert sweet potato residues (SPR) hydrolysate to BC. SPR was directly used without pretreatment, and almost no inhibitors were generated, which was beneficial to subsequent glucan conversion and SPR-BC synthesis. SPR-BC production was 11.35 g/L under the optimized condition. The comprehensive structural characterization and mechanical analysis demonstrated that the crystallinity, maximum thermal degradation temperature, and tensile strength of SPR-BC were 87.39%, 263 °C, and 6.87 MPa, respectively, which were superior to those of BC produced with the synthetic medium. SPR-BC was added to rice straw pulp to enhance the bonding force between fibers and the indices of tensile, burst, and tear of rice straw paper. The indices were increased by 83.18%, 301.27%, and 169.58%, respectively. This research not only expanded the carbon source of BC synthesis, reduced BC production cost, but also improved the quality of rice straw paper.

Structural optimization design and mechanical performance analysis of laminated six-ring redundant axial magnetic bearings

Targeting at the axial magnetic bearing, a structure of laminated six-ring redundant axial magnetic bearing, which is featured in both high redundancy and low heat, was designed in this paper. Meanwhile, the design criteria of the laminated redundant axial magnetic bearing was proposed, and the theoretical research, numerical simulation and empirical research on the redundancy and electromagnetic force of the laminated redundant axial magnetic bearing were conducted as well in this study.

Detailed Deformation Behaviors and Tensile Parameters for Coated Warp-Knitted Fabrics in 2D Stress Space

AbstractUnderstanding the mechanical properties of membrane materials in two-dimensional (2D) stress space is critical for structural design and mechanical analysis of membrane structures. In this ...

Table-Top Lithium Disilicate Ceramic Restoration Thickness Effect on the Stress Distribution in Upper Premolars: 3D Finite Element Analysis

To evaluate the stresses generated in upper premolars rehabilitated with ceramic fragments (table-top) of lithium disilicate on the occlusal surface. An upper premolar was modeled following its anatomical references using computer aided design software (Rhinoceros version 5.0 SR8, USA). The dental tissues were individually designed containing enamel, dentin and periodontal ligament. The main anatomical points were used as parameters for model creation. Ceramic fragments were modeled varying their maximum thicknesses as: 0.5 mm, 1.0 mm and 1.5 mm. Solid geometries were exported to the analysis software (ANSYS 17.2, USA) in STEP format. The materials were considered isotropic, homogeneous and linear, and the values of the elastic modulus of the materials and structures were used to perform a static structural mechanical analysis. The set was submitted to 200 N load. The system fixation was defined on the basis of the three- dimensional model, and the results were obtained in MPa according to the failure criteria of the analyzed materials (tensile stress). Occlusal restoration was not detrimental to mechanical behavior. Stress distribution in the internal region of the restoration was similar between the groups. Thicker fragments presented a lower concentration of tensile stress, therefore suggesting better prognosis in attenuating tensile stresses in the tooth region. More conservative occlusal ceramic fragments presented worse prognosis. However, all evaluated thickness for table-tops support the occlusal rehabilitation of upper premolars when submitted to 200 N loading.

Safety supervision of tower crane operation on construction sites: An evolutionary game analysis

Tower crane is one of the most widely used equipment on the construction sites, but followed by a high accident rate. How to prevent the tower crane operation accident has already been an urgent mission. Although researchers carried out a number of studies about accident causes analysis, monitoring technology and structural mechanics analysis, one of the important gaps is that crane stakeholders and supervision bodies, as the components of a holistic crane safety system, were neglected, resulting in that the prevention of tower crane accidents is seldom solved fundamentally. To bridge these gaps, this paper takes the main stakeholders involved in the tower crane operation, namely, the tower crane users (TCU), the responsible party for repair (RPR) and the responsible party for supervisor (RPS), as research objects. A tripartite evolutionary game model is established. The accident risk perception of each stakeholder is considered in the proposed model and an accident preference coefficient is used to express the important factor. The evolution laws of safety strategy selection of the stakeholders are revealed by solving the proposed model. The numerical simulation is applied to verify the rationality of the solution results of the model. The results find that when the sum of penalty amount and safety reward performance is greater than the safety input cost, RPS, RPR and TCU will adopt the favorable safety supervision strategies of tower crane operation; the accident risk perception of RPR has a greater impact on the evolution and the strategy stability of the three stakeholders.

Displacement detection based on Bayesian inference from GNSS kinematic positioning for deformation monitoring

Displacement is an important parameter in engineering analysis in structural mechanics and geomechanics. For decades, displacement detection based on the Global navigation satellite system (GNSS) has increasingly been important for a wide range of applications, from landslide monitoring, subsidence survey, to industrial measurement. However, due to the influence of measurement noise, it is still a challenge to identify and extract displacement from GNSS kinematic positioning results. To resolve this, we propose a novel displacement detection approach with the purpose of identifying and extracting displacement from GNSS kinematic positioning. Specifically, we use the Bayesian inference to obtain the displacement change time from the coordinate time series of GNSS kinematic positioning. By investigating the posterior distribution of the designed change point parameter, we can identify the change points. Furthermore, we derive the mean value from the posterior distribution of the mean parameter, and further obtain the displacement. Results from simulation and field experiments have demonstrated the effectiveness and flexibility of the proposed method. For significant displacement, it can be clearly identified; for small displacement, it can be identified by adding an interval constraint prior. The accuracy of vertical displacement extraction from GNSS real-time kinematic positioning can reach within 2 mm in 15 min.

Out-of-plane effect on the sharp V-notch tip fields in power-law creeping solids: A three-dimensional asymptotic analysis

Understanding the three-dimensional (3D) effect on the notch tip field is important for the fracture mechanics analysis of engineering materials and structures. This paper presents an asymptotic solution for 3D sharp V-notched structures subjected to mode Ⅰ creep loading condition. The asymptotic solution, including the singularities and stress field distribution functions, is obtained by introducing the out-of-plane constraint factor. It is found that the singular behavior is related to the notch angle, material creeping exponents, and the out-of-plane constraint factor. Specifically, singularity changes sharply near the free surface. KNt-Tz solution is presented to describe the mode Ⅰ stress field around the tip of 3D V-notch under creep condition. Its accuracy and advantages compared with plane strain or plane stress solutions are validated by finite element analysis. The difference between effective ranges of KNt-Tz solution and that of plane strain solution is clarified. Moreover, the effect of the creep time on the stress field is also shown. The solutions given in this paper could be beneficial for understanding the 3D effect on notch considering creep loading conditions.

Development of Novel Superabsorbent Hybrid Hydrogels by E-Beam Crosslinking.

In this study, several superabsorbent hybrid hydrogel compositions prepared from xanthan gum (XG)/sodium carboxymethylcellulose (CMC)/graphene oxide (GO) were synthesized by e-beam radiation crosslinking. We studied and evaluated the effects of GO content from the chemical structure of the hydrogels according to: sol-gel analysis, swelling degree, diffusion of water, ATR-FTIR spectroscopy, network structure, and dynamic mechanical analysis. The gel fraction and swelling properties of the prepared hydrogels depended on the polymer compositions and the absorbed dose. The hybrid XGCMCGO hydrogels showed superabsorbent capacity and reached equilibrium in less than 6 h. In particular, the XGCMCGO (70:30) hydrogel reached the highest swelling degree of about 6000%, at an irradiation dose of 15 kGy. The magnitude of the elastic (G′) and viscous (G″) moduli were strongly dependent on the absorbed dose. When the degree of crosslinking was higher, the G′ parameter was found to exceed 1000 Pa. In the case of the XGCMCGO (80:20) hydrogel compositions, the Mc and ξ parameters decreased with the absorbed dose, while crosslinking density increased, which demonstrated that we obtained a superabsorbent hydrogel with a permanent structure.

Nanoscale Extracellular Vesicles Carry the Mechanobiology Signatures of Breast Cancer Cells

Breast cancer cells secrete abundant nanometer-sized vesicles. Small extracellular vesicle (or sEV) cargos are known to have similar biomolecular signatures to their secreting parental breast cancer cells. However, whether malignant transformation modulates the physical and biomechanical profiles of secreted nanosized sEVs (40–120 nm) has not been established. Here, using multiparametric atomic force microscopy imaging, we directly compared the structure–mechanical properties (including topographic height, Young’s modulus, and adhesion) of breast cancer cell-derived sEVs and secreting cells. Our findings reveal that sEVs show reduced Young’s modulus concomitant with a decrease in cell stiffness as cells progress from nontumor to noninvasive to invasive breast cancer phenotypes across different probing forces, isolation techniques, and particle sizes. Further, single sEV structure–mechanical analysis of actual patient plasma samples showed alterations in biomechanical properties of sEVs in breast cancer patients compared to sEVs from benign healthy controls. Our study demonstrates that precise biomechanical fingerprinting of single nanoscale sEVs provides an attractive label-free, cell-free, and orthogonal approach to detect changes in parental cells, such as during malignant transformation.

Структурный анализ ромбического механизма с развитым шатуном рабочей группы двигателя Стирлинга

Designing the mechanisms of modern machines is a complex process, where the stage of structural analysis is a priority. When there are a plenty of redundant links in mechanisms their load capacity and efficiency are reduced, increasing the requirements for the accuracy of manufacturing and assembly. It is desirable that mechanisms not requiring high torsional stiffness have no excessive connections; they should be self-aligning. With the advent of new multi-link spatial mechanisms, the task of creating mechanisms without redundant connections becomes more complicated. The structural analysis of the rhombic mechanism of the Stirling engine with a advanced connecting rod of the working group, carried out by the graph method.

Research advances in methods of cyclezation mechanism of sesquiterpenes

Terpenes are the largest group of natural products and contain the widest assortment of structural types. Terpene cyclization is also the most complex reaction found in nature. For a long time, terpenoids with diverse structures have attracted natural product chemists to explore their biosynthesis mechanism. Such a large number of terpene skeletons are catalyzed by enzymes called terpene synthase. Sesquiterpene synthase is a kind of terpene synthase, which can catalyze the cyclization of linear precursor farnesyl pyrophosphate(FPP) to sesquiterpene skeletons. Sesquiterpene synthase cyclize a single precursor FPP into many sesquiterpene skeletons. With the continuous discovery of sesquiterpene synthase, the cyclization mechanism of sesquiterpene synthase has been studied deeply. In recent years, with the development and improvement of isotope labeling of substrate FPP and structural analysis of sesquiterpene synthase, the structure and cyclization mechanism of sesquiterpene synthase have been studied more systematically and accurately. In this review, we reviewed the progress of the research methods on the mechanism of sesquiterpene cyclization by substrate isotope labeling and protein structure, as well as the summary and prospect of sesquiterpene synthase research.

Fracture mechanics analysis of two-dimensional cracked thin structures (from micro- to nano-scales) by an efficient boundary element analysis

In this paper, the boundary element method (BEM) based on the elasticity theory is developed for fracture analysis of cracked thin structures with the relative thickness-to-length ratio in the micro- or nano-scales. A special crack-tip element technique is employed for the direct and accurate calculation of stress intensity factors (SIFs). The nearly singular integrals, which are crucial in applying the BEM for thin-structural problems, are calculated accurately by using a nonlinear coordinate transformation method. The present BEM procedure requires no remeshing procedure regardless of the thickness of thin structure. Promising SIFs results with only a small number of boundary elements can be achieved with the relative thickness of the thin film is as small as 10−9, which is sufficient for modeling most of the thin bodies as used in, for example, smart materials and micro/nano-electro-mechanical systems.

Comparative Stress Evaluation between Bilayer, Monolithic and Cutback All-Ceramic Crown Designs: 3D Finite Element Study

Different all-ceramic crown designs are available to perform indirect restoration; however, the mechanical response of each model should still be elucidated. The study aims to evaluate the stress distribution in three different zirconia crown designs using finite element analysis. Different three-dimensional molar crowns were simulated: conventional bilayer zirconia covered with porcelain, a monolithic full-contour zirconia crown, and the cutback modified zirconia crown with porcelain veneered buccal face. The models were imported to the computer-aided engineering (CAE) software. Tetrahedral elements were used to form the mesh and the mechanical properties were assumed as isotropic, linear and homogeneous materials. The contacts were considered ideal. For the static structural mechanical analysis, 100 N occlusal load was applied and the bone tissue was fixed. Maximum principal stress showed that the stress pattern was different for the three crown designs, and the traditional bilayer model showed higher stress magnitude comparing to the other models. However, grayscale stress maps showed homogeneous stress distribution for all models. The all-ceramic crown designs affect the stress distribution, and the cutback porcelain-veneered zirconia crown can be a viable alternative to adequate function and esthetic when the monolithic zirconia crown cannot be indicated.

Geotechnical modelling of the climate change impact on world heritage properties in Alexandria, Egypt

Alexandria is one of the Mediterranean UNESCO World Heritage sites at risk from coastal flooding and erosion due to sea-level rise. The city’s position on the Mediterranean coast means it is especially vulnerable to rising sea levels. Alexandria is one of UNESCO sites in Egypt at risk from flooding. All the archaeological sites in the northern coast of Egypt are also said to be at risk from coastal erosion. The flood risk in Alexandria is expected to reach a tipping point by 2050. This research presents the numerical analysis of geotechnical and structural damage mechanism of Catacombs of Kom El-Shoqafa and El-Shatbi Necropolis; the sites have the lowest topography in Alexandria induced by the sea level rise and heavy rain due to the Climate Change, based on Finite Element PLAXIS Code. The purpose of the study was to investigate the behavior fully-saturated soft rock/ hard soil subjected to ground water intrusions. The main objective of this study is to very accurately record and analyze geotechnical problems and induced structural failure mechanisms that have been observed and accounted for in field, experimental and Numerical studies. The land area is also vulnerable to coastal flooding. It is widely expected that the numerical analysis of such geotechnical problems will contribute to the preservation of cultural heritage. The present research presents an attempt and experimental study to design a PLAXIS 2D FE model to simulate hard soil/hard rock problems, distortion and stress analysis of the complex structure of the catacombs. Plastic modeling or Mohr—Coulomb model was used in advanced soils during various stages of numerical analysis. Results are recorded and discussed regarding stress and volumetric behavior of soil/rocks. Groundwater infiltration into pores or fissures of rock and soil has a great influence on the engineering mechanical properties of rocks and soils.

Isogeometric analysis with the Reissner-Mindlin shell for hull structural mechanical analysis

Isogeometric Analysis (IGA) is an important emerging numerical method that is being studied in various field. IGA is proposed to seamlessly connect the Computer-Aided Engineering (CAE) and the Computer-Aided Design (CAD) systems, so that the costly mesh generating stage in traditional Finite Element Method (FEM) can be skipped to improve the efficiency of design and analysis. In this paper, an IGA approach is introduced to the hull structural mechanical analysis. A Reissner-Mindlin shell element is constructed in the IGA framework, and the expression of the element stiffness matrix and load vector are derived in detail. Using the proposed method, a typical hull block structure is analyzed under both bending and torsion load. The maximum relative error of the displacement results is 1.6% compared to the reference results obtained from ANSYS 17.0, and the correctness of the proposed method is verified. It also proves that the proposed method can be used in engineering practice, and can be used to realize the integration of design and analysis.