Structural stress and modal analysis of escalator truss

Finite element analysis model is the discretion and simplification of actual structure. Due to some uncertain factors in the process of modeling, such as element type, material properties, geometric shape, the uncertainty of boundary conditions and so on, the finite element analysis model tends to have certain error, which will affect the accuracy of the analysis results. Therefore, model updating and validation are needed to improve the accuracy and reliability of the model. Model updating method based on the first-order optimization was employed to update finite element models referring to experimental modal parameters in the paper. Taking an aero-engine simulation casing as the research object, modal test was carried out to obtain experimental modes. Then the finite element software was used to calculate the corresponding modal parameters. The calculated modal parameters were compared with the experimental ones. As the calculated results obtained by the finite element method may be not so accurate, the test modal data was utilized to update the finite element model, and the modal parameters were selected as references for optimization. With the correction of elastic moduli in each part of the finite element model, modal parameters of the updated finite element model were obtained, and modes of the revised model were in good agreement with the experimental modal parameters. The modal frequency differences between the calculated and experimental results were significantly reduced and the modal shapes of them were identical. The results demonstrated that model updating method based on the correction of elastic modulus is feasible and suitable for the accurate finite element modeling of large and complex structures in engineering.

IntroductionGeometrical designs of nickel-titanium (NiTi) rotary instruments have a considerable influence on their mechanical performance, and thereby have the tendency to fracture.AimTo evaluate the effect of cross-sectional geometry, pitch, taper, and off-center cross-section on the stress distribution in NiTi instruments under bending and torsion conditions using finite element analysis (FEA).Materials and methodsEleven theoretical three-dimensional finite element (FE) models of rotary instruments were constructed and divided according to the geometric design tested into; group 1 (cross-section geometry): four FE models with four different cross-section designs (triangle, convex triangular, parallelogram, and rectangle). Group 2 (pitch): three FE models with different pitches (5, 10, and 15 threads). Group 3 (taper): two FEA models with two different tapers (0.04 and 0.06). Group 4 (centering): two FEA models (off-centered and centered cross section). The behavior of the instrument under bending and torsional conditions was analyzed mathematically in SolidWorks software package.ResultsThe pattern of stress distribution was varied by altering cross-sectional geometry, pitch, taper, and off-center cross section.ConclusionNo single geometrical design could be beneficial for all stress conditions. To decrease the stress accumulation during bending of rotary files in curved root canals, the rotary NiTi instruments should be designed with rectangle cross-section configuration, low pitch, reduced taper, and with centered cross section. This design improved the flexibility of rotary NiTi instruments. However, to improve the torsional resistance during root canal preparation of narrow canals, the file should be designed with parallelogram cross-sectional configuration, low pitch, increased taper, and eccentric cross-section design.

A nonlinear 3-D finite element analysis (FEA) model was developed to predict the behavior of eccentrically loaded concrete encased steel (CES) columns subjected to ISO-834 standard fire including heating and cooling phases. The finite element model has been validated against published tests conducted at elevated temperatures. Comparisons between the predicted results and the test results show that this model can accurately predict the behavior of CES columns under fire. The FEA model was then used to investigate the typical temperature-time curve and mid-height lateral deformation-time curve of eccentric compression CES columns in a complete loading history including initial loading, heating and cooling. It is shown that the temperature delay is obvious at the inner layers of concrete. The fire resistance of a CES column should be checked for the full process of fire exposure until temperatures everywhere in the column start to decrease. The lateral deformation of the column still gradually increases during the cooling phase and the column may fail during that phase. There is a large residual deformation after the fire exposure. Furthermore, the variables that influence the behavior of the CES columns under fire were investigated in parametric studies. It is found that the main parameters which influence the lateral deformation-time curve of the column during the full process of fire exposure are load ratio, slenderness ratio, duration time, depth to width ratio and steel ratio, and the main parameters which influence the residual deformation ratio of the column after fire are load ratio, duration time, cross-sectional depth and steel ratio.

Finite element simulation analysis was carried out on the seismic performance of the joint test specimens of built-in section steel assembled concrete shear wall. A finite element analysis model is established, and referring to specifications and existing research results, the definition of constitutive relation properties of concrete, section steel, steel bar and other materials is emphatically elaborated, in which the damage model is introduced to simulate the damage characteristics of concrete materials under low-cycle repeated action. After obtaining the cloud diagram and hysteretic curve of strain, stress, deformation and structural damage of the finite element test results, the differences between the finite element analysis and the experimental study are compared, it is found that the structural damage is obvious and the pinch effect of hysteretic curve reflects the characteristics of flexural-shear failure. Comparing the results of finite element analysis with the experimental results, the finite element analysis model can simulate the test conditions well, and basically embody the process of stress, strain, displacement, damage and failure characteristics of the specimens.

This paper presents a predictive shimming methodology based on finite element analysis modeling (FEM) and laser scanning metrology. The aim of the predictive shimming methodology is to provide the geometry of the necessary shims for an assembly beforehand, so the shims can be manufactured in advance and placed on the exact location reducing ergonomic harmful conditions for plant personnel, improving accuracy, reducing the components assembly time and lowering manufacturing cost. The case study for the predictive shimming method is an aircraft torque box assembly (TBA). The interface of interest is the mating surface of the skin and the rib shear ties. A FEM model of the skin was developed to calculate the skin deformation under prescribed displacements at the shimming locations. The FEM model was successfully verified and validated. Using the FEM deformation data, the geometry of the shims needed for an assembly can be calculated. Laser scanning metrology is used to get a point cloud of the assembly, fine-tuning the shims geometry.

In various applications it is important to determine dynamically equivalent spatial finite element (FE) model of complex structures. For instance, obtaining the FE model of an existing aerospace structure is a major requirement for reliable aeroelastic analysis. In such applications a reliable FE model may not be always available, and when this is so a dynamically equivalent FE model derived from modal test will be very useful. This paper presents a noble method to determine spatial FE model of a structure by using experimentally measured modal data along with the connectivity information of measurement points. The method is based on the mass and stiffness orthogonality equations written using experimentally determined mode shapes and natural frequencies. These equations are solved for geometric and material properties constituting global spatial mass and stiffness matrices of an initial FE model. Starting from this initial FE model, mass and stiffness orthogonality equations are updated iteratively employing experimentally obtained natural frequencies and corresponding eigenvectors from the FE model. Iterations are continued until eigensolution of the updated FE model closely correlates with experimentally measured modal data. A simulated case study on GARTEUR scaled aircraft model is presented in order to demonstrate the applicability of the method.

The system of shear wall as an additive in retrofitting of soft storey structure has been investigated in previous and present research to improve the strength of structures due to seismic load. The aim of this research is to conduct comparative study on Equivalent Static Analysis (ESA), Response Spectrum Analysis (RSA) and Time History Analysis (THA) of structure between reference sample and shear wall systems was performed in order to determine the strength and stiffness of soft storey structure. The locations and shapes of shear wall system were used as retrofitting method. The retrofitting of soft storey structure was done for fives (5) models consist of one (1) model without shear wall as reference sample and the other four (4) models of different location and shape of shear wall systems. The models were tested by using SAP200 computer software to performed strength of structure. The models had been checking by value of lateral displacement and base shear resistance. Based on the collected data, the additional of shear wall was found to increase the strength and stiffness of soft storey structure. The swastika shape of shear wall and provide at centre experienced the maximum base shear resistance in all X, Y and Z direction and the least displacement compared to other model. Through this study had shown the improvement of strength of soft storey structure by applying shear wall system as an additive strength and stiffness of structure due earthquake event.

To establish a 3D finite element model of normal knee joint involved its meniscus, which can be used to simulate the anatomical morphology and characteristics of human knee joint, to verify the validity of the model by preliminary FEA mechanical analysis, and explain partially biomechanical mechanisms of meniscus. CT and MRI data were harvested by scanning the knee joint of a healthy male volunteer, and then these data were imported into Mimics 10.01 software and Geomagic Studio software to constructed the 3D models of tissue structures of knee joint. These models were combined to constructed the 3D model of intact knee joint and meshed in ANSA software. Therefore the finite element model of intact knee joint was established. Finally, after the definitionof its material behavior, boundary conditions and loading. The finite element model of knee joint was analyzed and verified using ANSYS software. Meanwhile The biomechanical properties of meniscus were analyzed. The complete knee finite element model composed of bone, meniscus, articular cartilage, and major ligaments was established. It could effectively simulate the anatomical morphology and characteristics of knee joint and its meniscus. The contact area of medial meniscus was 771.05 mm2, while the contact area of lateral meniscus was 634.31 mm2, and the ratio was 1.216. The stress distribution was uniform, but the stress of the medial meniscus was higher than that of the lateral meniscus, and the peak stress located in the posterior horn of the medial meniscus and the anterior horn of the lateral meniscus, respectively, and the peak stress value was 4.11 MPa. The maximum displacement of the meniscus was located in body, and the displacement of the medial meniscus was more remarkable than that of the lateral meniscus, and the maximum displacement value is 0.33 mm. The obtained finite element analysis results corresponded to that reported in the literature, which mean the model's reliability. The established finite element model of knee joint are proved to be have validity, and is a useful model for finite element analysis of meniscus tear and menisectomy. The results of finite element analysis can explain partially biomechanical mechanisms of meniscus which can provide theoretical guidance for clinical treatment of meniscus injury.

Securing the structural safety of blades has become crucial, owing to the increasing size and weight of blades resulting from the recent development of large wind turbines. Composites are primarily used for blade manufacturing because of their high specific strength and specific stiffness. However, in composite blades, joints may experience fractures from the loads generated during wind turbine operation, leading to deformation caused by changes in structural stiffness. In this study, 7132 debonding damage data, classified by damage type, position, and size, were selected to predict debonding damage based on natural frequency. The change in the natural frequency caused by debonding damage was acquired through finite element (FE) modeling and modal analysis. Synchronization between the FE analysis model and manufactured blades was achieved through modal testing and data analysis. Finally, the relationship between debonding damage and the change in natural frequency was examined using artificial neural network techniques.

The use of piezoceramic materials for structural sensing and actuation is a fairly well developed practice that has found use in a wide variety of applications. However, just as advanced composites offer numerous benefits over traditional engineering materials for structural design, actuators that utilize the active properties of piezoelectric fibers can improve upon many of the limitations encountered when using monolithic piezoceramic devices. Several new piezoelectric fiber composites have been developed; however, almost all studies have implemented these devices such that they are surface‐bonded patches used for sensing or actuation. This paper will introduce a novel active piezoelectric structural fiber that can be laid up in a composite material to perform sensing and actuation, in addition to providing load bearing functionality. The sensing and actuation aspects of this multifunctional material will allow composites to be designed with numerous embedded functions, including structural health monitoring, power generation, vibration sensing and control, damping, and shape control through anisotropic actuation. This effort has developed a set of manufacturing techniques to fabricate the multifunctional fiber using a SiC fiber core and a BaTiO3 piezoelectric shell. The electromechanical coupling of the fiber is characterized using an atomic force microscope for various aspect ratios and is compared to predictions made using finite element modeling in ABAQUS. The results show good agreement between the finite element analysis model and indicate that the fibers could have coupling values as high as 68% of the active constituent used.

Mobile steel building is a prefabricated building built in a factory, with advantages on moving conveniently, simple structure and scalability. There are still not enough relevant standards and requirements to conduct the design and construction of this kind of buildings. In order to precede to theoretical study on integral structures of mobile steel buildings a method which used to set up finite element analysis model about this kind of structure was proposed. This method is based on finite element analysis software, ANSYS. Using this method a two-story structure model with one box unit in each story was analyzed. Lateral deformations under design load of the integral structure were solved out by these finite element models and were compared with the former experimental results, and the results were discussed.

Experimental results for photothermal lens measurements are compared to finite elemental analysis models for commercial colored glass filters. Finite elemental analysis software is used to model the photothermal effect by simulating the coupling of heat both within the sample and out to the surroundings. Modeling shows that heat transfer between the glass surface and the air coupling fluid has a significant effect on the predicted time-dependent photothermal lens signals. For comparison with experimental signals, a simple equation based on the finite element analysis result is proposed for accounting for the variance of experimental data where this type of heat coupling situation occurs. The colored glass filters are found to have positive thermo-optical coefficients. The net positive dn/dT of CdSxSe(1-x) doped glass filters is considered to be the consequence of counteracting factors: optical nonlinearity, stress-induced birefringence, and the structural network of glass. Finite element analysis modeling results are also used to correlate experimental measurements of different sample geometries. In particular, the glass samples are compared to ethanol solutions of iron (II) dicylopentadiene in a sample cuvette even though heat transfer is different for these two samples.

Evaluation of bone excision effects on a human skull model-II: Finite element analysis.

Space trusses usually have a significant number of elements. As a result, it is inevitable that some elements have imperfections. In this study, the authors proposed a mixed finite element method for nonlinear geometrical analysis of space trusses. The post-buckling behavior of space trusses with length imperfections was predicted using a code list written in the programming software. The numerical results indicate that when the length imperfection approaches zero, the results converge to those obtained in studies on standard trusses. A second approach based on the displacement model is also proposed, in which the Lagrange multiplier method is used to deal with the member length imperfection. The results show that the two approaches proposed by the authors are effective, in which the mix formulation based on the finite element model is superior to that based on the displacement model. These results verify the accuracy of the method. Based on the proposed method, the effects of imperfections in the element layers on the truss were studied. The results show that the imperfections in the top two element layers have the maximum influence on the limit load value, whereas the remaining layers have a negligible influence. The combination of the imperfect lengths of these two layers of elements can produce results in which the limit load value is much larger than in the case of a perfect system. Based on the obtained results, it is possible to provide a solution for improving the overall stability of truss structures by creating reasonable imperfections.

The purpose of this paper is to explore the vibration characteristic of asphalt pavement with various structures for harvesting mechanical energy via finite element analysis (FEA) and analytic model. Part of energies in asphalt pavement caused by mechanical vibration can be harvested by piezoelectric transducers. In order to get more energy from pavement, the sensitivity of structure parameters such as thickness, modulus, mass and stiffness are analyzed by using semi-rigid asphalt pavement as an example. Finite element model and analytic model are established in the analysis, which are calibrated by field measurement and laboratory test. The results show that the vibration frequency of typical semi-rigid asphalt pavement is between 10 Hz and 20 Hz, which is far lower than frequency of typical piezoelectric transducers. The fundamental frequency of asphalt pavement decreases with increasing thickness and mass of surface, base and subbase. However, the fundamental frequency is increase with the modulus and stiffness of subgrade, the increment is about 23 Hz/10 MPa and 0.7 Hz/10⁶ (N/m).