Maximum Stress Area Research Articles

A METHOD OF SIMULATING SEAT LOAD FOR NUMERICAL ANALYSIS OF WOOD CHAIR STRUCTURE

This study aimed to investigate the characteristic values of the human-seat interface in a normal sitting posture, and to numerically mode the load on the chair seat for the structural design of chairs. The stress distributions and the characteristic values of seat were measured under normal sitting posture by using a human body pressure distribution measurement system considering the effects of gender and body mass index (BMI). The stress distribution on the seat was then numerically modeled using three modeling methods. The observed results and the numerical analysisresults were compared. The results showed that an inverted U-shaped pressure distribution was observed in normal sitting posture. The stress was concentrated on the ischial tuberosity with a maximum value of 0.066 MPa. The ratio of the load on the seat to the gravity of the human body weight was about 65.3%. The numerical model established using the body pressure mapping method was superior to those of the uniform load method and the standard loading pad method in terms of stress distribution, maximum stress, and contact area.

The Change of Sealing Property in the Aging Process of NBR Sealing Equipment Based on Finite Element Analysis

Sealing rings are the core components of flange sealing structures and play a crucial role in the storage and operation of gas generators. The aging and deformation of seals affect the safe operation of the device. This paper aims to investigate the effect of rubber aging on the sealing performance of the components, which is realized by nonlinear finite element analysis. Firstly, an accelerated degradation test method was used to obtain the compression permanent deformation and stress–strain curve of rubber during the aging process. A two-dimensional finite element model of the sealing structure was constructed and the Yeoh model was utilized to describe the mechanical response of rubber. During the simulation, the contact area was modified based on the compression permanent deformation, and the Yeoh model was updated based on the stress–strain curve changes obtained by the test. The impact of key parameters such as material property changes, rubber physical section deformation, and fluid pressure on sealing performance during the seal ring aging process was systematically studied. The numerical results indicate that due to the aging deformation of rubber seals, there is a significant decrease in contact stress and contact width, as well as a shift in maximum equivalent stress area. Taking into account these findings, this study proposes a new design concept for sealing structures. This provides a relatively simple research method for studying flange sealing structure performance.

ELGO electric motorcycle: Design and analysis of trail-type electric motorcycle frame using finite element analysis

The frame is an important part of the motorcycle as it carries the load of the passenger. Therefore, it is necessary to design a frame that can withstand the load and is lightweight. A lighter motorcycle will reduce the power required to ride it. This research aims to redesign the frame of a trail-type ELGO electric motorbike by considering a reduction in frame weight. The research was carried out using finite element analysis. The data from the analysis were checked based on the maximum stress not exceeding the yield strength of the DIN 1.0030 material and the safety factor greater than 1. The results showed that the newly designed frame has a lighter weight, with a maximum stress less than the yield strength of the DIN 1.0030 material and a safety factor value greater than 1. The simulation results also indicate the potential for further research by showing the maximum and minimum stress areas on the frame.

Finite element analysis of the effect of tibial osteotomy on the stress of polyethylene liner in total knee arthroplasty.

To explore the effects of tibial osteotomy varus angle combined with posterior tibial slope (PTS) on the stress of polyethylene liner in total knee arthroplasty (TKA) by building finite element model (FEM). Established the FEM of standard TKA with tibial osteotomy varus angle 0° to 9° were established and divided into 10 groups. Next, each group was created 10 FEMs with 0° to 9° PTS separately. Calculated the stress on polyethylene liner in each group in Abaqus. Finally, the relevancy between tibial osteotomy angle and polyethylene liner stress was statistically analyzed using multiple regression analysis. As the varus angle increased, the area of maximum stress gradually shifted medially on the polyethylene liner. As the PTS increases, the percentage of surface contact forces on the medial and lateral compartmental of the polyethylene liner gradually converge to the same. When the varus angle is between 0° and 3°, the maximum stress of the medial compartmental surfaces of polyethylene liner rises smoothly with the increase of the PTS. When the varus angle is between 4° and 9°, as the increase of the PTS, the maximum stress of polyethylene liner rises first and then falls, forming a trough at PTS 5° and then rises again. Compared to the PTS, the varus angle has a large effect on the maximum stress of the polyethylene liner (p < .001). When the varus angle is 0° to 3°, PTS 0° is recommended, which will result in a more equalized stress distribution of the polyethylene liner in TKA.

Design, fabrication and experimental analysis of piezoresistive bidirectional acoustic sensor

PurposeIdentification of the direction of the sound source is very important for human–machine interfacing in the applications such as target detection on military applications and wildlife conservation. Considering its vast applications, this study aims to design, simulate, fabricate and test a bidirectional acoustic sensor having two cantilever structures coated with piezoresistive material for sensing has been designed, simulated, fabricated and tested.Design/methodology/approachThe structure is a piezoresistive acoustic pressure sensor, which consists of two Kapton diaphragms with four piezoresistors arranged in Wheatstone bridge arrangement. The applied acoustic pressure causes diaphragm deflection and stress in diaphragm hinge, which is sensed by the piezoresistors positioned on the diaphragm. The piezoresistive material such as carbon or graphene is deposited at maximum stress area. Furthermore, the Wheatstone bridge arrangement has been formed to sense the change in resistance resulting into imbalanced bridge and two cantilever structures add directional properties to the acoustic sensor. The structure is designed, fabricated and tested and the dimensions of the structure are chosen to enable ease of fabrication without clean room facilities. This structure is tested with static and dynamic calibration for variation in resistance leading to bridge output voltage variation and directional properties.FindingsThis paper provides the experimental results that indicate sensor output variation in terms of a Wheatstone bridge output voltage from 0.45 V to 1.618 V for a variation in pressure from 0.59 mbar to 100 mbar. The device is also tested for directionality using vibration source and was found to respond as per the design.Research limitations/implicationsThe fabricated devices could not be tested for practical acoustic sources due to lack of facilities. They have been tested for a vibration source in place of acoustic source.Practical implicationsThe piezoresistive bidirectional sensor can be used for detection of direction of the sound source.Social implicationsIn defense applications, it is important to detect the direction of the acoustic signal. This sensor is suited for such applications.Originality/valueThe present paper discusses a novel yet simple design of a cantilever beam-based bidirectional acoustic pressure sensor. This sensor fabrication does not require sophisticated cleanroom for fabrication and characterization facility for testing. The fabricated device has good repeatability and is able to detect the direction of the acoustic source in external environment.

Comparison of finite element analysis results with strain gauge measurements of a front axle housing

Abstract. The strength of the front axle of tractors used on rough terrain is crucial in countries in which agriculture is widespread. Rough agricultural fields, rugged village roads, and ground irregularities cause unexpected reaction forces on the axles. Thus, it is important to analyze the front axle of a tractor with respect to stress, which eventually leads to cracks and premature failure. In this study, ANSYS 13.0 finite element analysis (FEA) software (ANSYS, 2010) was used to predict the strength of a design under loading conditions. ANSYS 13.0 allows products to be tested in a virtual environment and helps to prevent problems that may arise later and accordingly improve them. This study aims to investigate the stresses that occur on the housing of the front axle of a tractor. The reaction forces acting on the front axle housing can cause cracks near the middle of the housing. The study applies a static load of 30 000 N to both hubs at the end of the front axle housing and uses the FEA method to predict and evaluate the maximum stress areas on the housing. Strain gauges are bonded to these locations to measure the real-life stresses on the axle housing in these areas. The results of the FEA and strain gauge measurements were compared, and a correlation was found with 98 % accuracy.

Occlusal Loading Effect on Stress Distribution of Endodontically Treated Teeth: Finite Element Analysis Study.

Evaluate the influence of occlusal loading on the stress distribution of endodontically treated teeth after root canal preparation with different file's sizes and tapers by means of finite element analysis. Seven three-dimensional models of a single-rooted, single-canal lower second premolar were established, one healthy control and six endodontically treated and restored models. The shape of root canal preparations followed file configurations 30/.05, 30/.09, 35/.04, 35/.06, 40/.04, and 40/.06. Von- Mises equivalent stresses were calculated by applying 30 N, 90 N and 270 N loads to the buccal cusp tip, each one at 90º, 45º and 20º angles from the occlusal plane simulating occlusion, dental interference and laterality, respectively. 45º loading was more prone to formation of higher stress values. The simulation of occlusion and laterality resulted in maximum stress areas located at the inner side of the root curvature, while under occlusal interference they were on the lingual surface over the tooth's long axis. The angulation of occlusal loading and magnitude were determinants for stress distribution on dental structure. Both variations of size and taper were not determinants for the increase in the maximum stress areas.

Experimental and numerical simulation study on coupling tripping of partial trapezoidal threaded casing head and casing coupling

Casing connection is a common connection method in oil and gas reservoir production, and the tripping of casing will seriously hinder the production process. To study the casing tripping process and the minimum tensile load required for casing tripping under different loosening buckle states, three kinds of casing tripping tensile tests were carried out. The thread morphology of the casing head and casing coupling was analyzed by local cutting at the end of the experiment, and the thread failure area was analyzed by scanning electron microscope, and then other loosening states were studied and analyzed using numerical simulation. The research results show that as the number of loosening buckles increases, the minimum tensile load required for the casing head and casing coupling to trip decreases. The observation of the thread shape shows that the thread part of the casing head was seriously damaged. Scanning electron microscopy results show that the fracture mode at the thread of the casing head is ductile fracture. Numerical simulation results show that the maximum stress area during the tripping process is at the contact position between the thread heads. Based on the experimental and numerical simulation results, the relationship between the number of casing loosening and the minimum tensile load required for casing tripping is obtained. The research results can be used as the experimental and theoretical basis for the investigation of casing tripping accidents and can also provide experimental reference for the design of the next-generation of casing.

Flux jump and mechanical response in inhomogeneous high-temperature superconductor under the pulsed-field magnetization

The high-temperature bulk superconductors with high critical current density are brittle, and can be damaged by large Lorentz forces and thermal stress during magnetization. Several studies have reported the failure of bulk superconductors during flux jumps. In this study, we analyzed the magnetization characteristics and mechanical response of the HTS bulk with inhomogeneous current density along the c-axis. The numerical simulation was consistent with the experimental results presented in the reference. Moreover, a flux jump occurred near the area of the pre-arrangement flux during the second pulsed field magnetization. The maximum temperature is lower than the critical temperature during the flux jump. In the mechanical analysis, the flux jump led to an abrupt change in the maximum stress of the bulk, and the maximum radial stress was significantly higher than the maximum hoop stress during the flux jump. The maximum radial stress increased with decreasing ambient temperature during the flux jump, and the maximum stress area was always near the seeded plane. Subsequently, the magnetization characteristics and mechanical response were studied for different locations of the seeded surface, two concentric superconducting bulks, and non-uniform fields.

Simulation of the Mechanical Behavior of the Degradation L4-L5 Lumbar Spine

Degenerative changes in the lumbar spine significantly reduce the quality of life of people. To fully understand the biomechanics of the affected spine, it is crucial to consider the biomechanical alterations caused by degeneration of the intervertebral disc (IVD). Therefore this study is aimed at the development of a discrete element model of the mechanical behavior of the L4-L5 spinal motion segment, which covers all the degeneration grades from healthy IVD to its severe degeneration, and numerical study of the influence of the IVD degeneration on stress state and biomechanics of the spine. To analyze the effects of IVD degeneration on spine biomechanics we simulated physiological loading conditions using compressive forces. The results of modeling showed that at the initial stages of degenerative changes, an increase in the amplitude and area of maximum compressive stresses in the disc is observed. At the late stages of disc degradation, a decrease in the value of intradiscal pressure and a shift in the maximum compressive stresses in the dorsal direction are observed. Such an influence of the degradation of the geometric and mechanical parameters of the tissues of the disc leads to the effect of bulging, which in turn will lead to the formation of an intervertebral hernia.

Thermomechanical behavior of mechanical attachments in solar power tower receivers under preheating conditions: A numerical study

Thermal deflection of receiver tubes in solar power tower plants is typically reduced by means of mechanical attachments, each one consisting of a clip and a guide through which a rod connected to a reradiating wall can freely slide. As a side effect, these mechanical attachments act as heat sinks, promoting a local temperature reduction in the tube during the receiver preheating, thus increasing the risk of crystallization of the molten salt during the subsequent filling of the receiver. Additionally, the mechanical attachments and the tube are subjected to thermal stresses during the preheating of the system, remarking the importance of considering both thermal and mechanical effects during the design of these elements. This study uses three-dimensional thermomechanical simulations to characterize the behavior of both the mechanical attachment and the tube during the preheating of a solar power tower receiver. The results revealed that the areas of maximum stress occur in the tube, clip, and guide sequentially as the preheating process progresses. The maximum stresses are located in the connections of the clip with both the tube and the guide. An extensive parametric sweep on the dimensions of the mechanical attachment revealed a trade-off between the minimum temperature and the maximum stress of the tube. Based on this analysis, an optimal solution for the dimensions of the clip and guide in terms of their height is proposed. The systematic study here presented can serve as a basis for the design of improved mechanical attachments able to ensure an adequate minimum temperature of the tube during the preheating while keeping the stress of the system within acceptable limits.

Assessment of the Orthodontic External Resorption in Periodontal Breakdown-A Finite Elements Analysis (Part I).

This Finite Elements Analysis (FEA) assessed the accuracy of Tresca failure criteria (maximum shear stress) for the study of external root resorption. Additionally, the tooth absorption-dissipation ability was assessed. Overall, 81 models of the second mandibular premolar, out of a total of 324 simulations, were involved. Five orthodontic movements (intrusion, extrusion, rotation, translation, and tipping) were simulated under 0.6 N and 1.2 N in a horizontal progressive periodontal breakdown simulation of 0-8 mm. In all simulations, Tresca criteria accurately displayed the localized areas of maximum stress prone to external resorption risks, seeming to be adequate for the study of the resorptive process. The localized areas were better displayed in the radicular dentine-cementum component than in the entire tooth structure. The rotation and translation seem prone to a higher risk of external root resorption after 4 mm of loss. The resorptive risks seem to increase along with the progression of periodontal breakdown if the same amount of applied force is guarded. The localized resorption-prone areas follow the progression of bone loss. The two light forces displayed similar extensions of maximum stress areas. The stress displayed in the coronal dentine decreases along with the progression of bone loss. The absorption-dissipation ability of the tooth is about 87.99-97.99% of the stress.

Embedded Pt-PVDF sensor without compromising mechanical properties of GFRP for on-line sensing

A wide variety of embedded sensors are currently used for structural health monitoring of glass fiber reinforced polymer (GFRP) composites. However, some studies showed the sensor embedding scarified the mechanical performance; several studies showed less influence on static performance but not embedded in the maximum stress area. In this work, we designed an embedded sensor without scarifying static and fatigue mechanical performances of the composites based on the flexible piezoelectric film-polyvinylidene fluoride (PVDF). Moreover, the sensor in-situ monitored the damage and fatigue evolution successfully until the specimens failed. The PVDF sensor in this work provides a reliable alternative for GFRP in structural health monitoring.

ВПЛИВ МАТЕРІАЛУ СМУГИ ТА СХЕМИ УКЛАДАННЯ ШАРІВ КОМПОЗИЦІЙНОГО МАТЕРІАЛУ НА КОЕФІЦІЄНТ КОНЦЕНТРАЦІЇ НАПРУЖЕНЬ У СМУЗІ З ОТВОРОМ ПРИ ЇЇ РОЗТЯГУВАННІ

At present, there is a tendency to increase percentage of the use of composite materials in the structures of modern aerospace technology. Experience in the operation of critical structures of aerospace engineering made of polymer composite materials has shown that their application instead of structures made of metal alloys provides a reduction in the mass of the structure by up to 30–50%, an increase in the service life by 2–5 times, a decrease in the labor intensity of manufacturing by 20–40% and material consumption - up to 50 %. Application of composite materials in the construction of aircrafts requires the development and application of methods for analysis their static and fatigue strength. The influence of the plate material and composite material plies stack-up sequence on the distribution of normal stresses and the stress concentration factor in the plate with a hole at B/d=6 under uniaxial tension has been studied. It has been shown by calculation that in the case of the orientation of the plies in the same direction with an angle q=0°, the maximum normal stress sх is 1.5 times greater than the corresponding stress value in a plate with a hole made of D16T aluminum alloy. Application of the plies stack-up sequence q [45°/-45°] enables to reduce the level of maximum stresses sх to the level of stresses in the plate with a hole made of D16T alloy. In this case, the area of maximum stresses is shifted from the vertical diametral point along the arc of the hole by an angle of 22.5°. For a woven composite, the level of maximum normal stresses sх is lower than the corresponding stress level for a fiber composite. When using plies stack-up sequence q [45°/-45°], the level of maximum normal stresses sх is lower than the level of the corresponding stresses in the plate with a hole made of D16T alloy. It has been found that, in contrast to the D16T alloy plate, in a plate with a hole at B/d=6, the stress concentration factor could be less or greater than 3, which is explained by the influence of plies stack-up sequence on the stress concentration factor. For a woven composite, when using plies stack-up sequence q [45°/-45°], we obtained the value of the stress concentration coefficient equal to 2.28.

Quantitative estimation of contribution of pore size and the distance between nearest neighbour pores on high cycle fatigue (HCF) crack initiation in Ti-6Al-4V MIM-sintered materials

The fatigue damages due to pores of MIM-sintered Ti64 were investigated using the synchrotron X-ray CT imaging. The effect of pores on the fatigue strength limits was analysed independently from that of grain size by introducing the fatigue limit ratio RF. The pores near to the maximum-stress area were identified by elastic FEM. The maximum stress intensity factor KI-max at the edge of the identified pores showed a negative correlation with RF. Moreover, the initial cleavage in the crack was influenced by the mutual interference of both stress fields by the proximity of the identified pore and its adjacent pores.

Mechanical effects of sagittal variations on Pauwels type III femoral neck fractures treated with Femoral Neck System(FNS)

BackgroundThe spatial position of internal fixation play a role in determining the stability of internal fixations, both in clinical practice and research. Researchers have examined the stability of FNS (Femoral neck system) in the presence of coronal plane changes. In our knowledge, due to the biomechanical limitations of the specimens, there are no mechanical studies on the sagittal variation of FNS. This study aimed to investigate the biomechanical behavior of sagittal variations on Pauwels type III femoral neck fractures treated with FNS through finite element analysis.MethodsFinite element models including Pauwels type III femoral neck fracture and FNS were reconstructed. Five fracture models(superior, central, inferior, anterior, posterior) were created in accordance with the bolt location in the sagittal plane within the femoral head. Equivalent stress, shear stress, and total deformation of each model under the same physiological load were recorded.ResultsAccording to the results, the central model exhibited the slightest stress and displacement, with the exception of the superior model. The internal fixation stress of the superior model was smaller than that of the central model. However, the maximum interfragmentary stress, total deformation and shear resistance area of the superior model was larger than that of the central model.ConclusionsCentral position of FNS in the sagittal plane allowed axial compression while reducing shear stress of internal fixation and interfragmentary equivalent stress. Off-axis fixation of the femoral neck increased the strain area and total displacement of the bone, raising the risk of fixation failure. Therefore, the central placement of FNS may be a better surgical target in the treatment of femoral neck fractures.

Calculation of gear mesh stiffness and loaded tooth contact analysis based on ease-off surface topology

Based on the theory of rack-gear common-tangential conjugate generating, the constructing of ease-off surface has been done by means of the topology modification of polynomial surface. By analyzing topological structure characteristics of ease-off surface, the meshing characteristics such as the contact area, the contact line, and transmission error are determined. By using the geometric analysis of ease-off surface and the potential energy method, the calculation methods of gear tooth stiffness and loaded transmission error are given, and a series of results for the tooth meshing stiffness, loaded transmission error, and load distribution map under varied loads are obtained. In order to solve the stress problem of tooth surface edge contact, the calculation method of quasi-Hertz contact is proposed by subdividing finite contact elements. Taking the second-order parabolic topological modification as an example, the time-varying history characteristics of tooth surface meshing are analyzed. The simulation results of the maximum contact stress and contact area are in good agreement with those calculated by MASTA software. Based on the integration of the geometric analysis of ease-off surface, the tooth stiffness calculation of potential energy method and the quasi-Hertz contact, it provides a convenient method for loaded tooth contact analysis.

Development of a Computational Model of the Mechanical Behavior of the L4-L5 Lumbar Spine: Application to Disc Degeneration.

Degenerative changes in the lumbar spine significantly reduce the quality of life of people. In order to fully understand the biomechanics of the affected spine, it is crucial to consider the biomechanical alterations caused by degeneration of the intervertebral disc (IVD). Therefore, this study is aimed at the development of a discrete element model of the mechanical behavior of the L4–L5 spinal motion segment, which covers all the degeneration grades from healthy IVD to its severe degeneration, and numerical study of the influence of the IVD degeneration on stress state and biomechanics of the spine. In order to analyze the effects of IVD degeneration on spine biomechanics, we simulated physiological loading conditions using compressive forces. The results of modeling showed that at the initial stages of degenerative changes, an increase in the amplitude and area of maximum compressive stresses in the disc is observed. At the late stages of disc degradation, a decrease in the value of intradiscal pressure and a shift in the maximum compressive stresses in the dorsal direction is observed. Such an influence of the degradation of the geometric and mechanical parameters of the tissues of the disc leads to the effect of bulging, which in turn leads to the formation of an intervertebral hernia.

Research on Lateral Bearing Behavior of Spliced Helical Piles with the SPH Method

The length of a spliced pile is 2 m assembled from an original spiral pile using a connector. The whole pile is the structure of the upper straight pipe and the lower spiral. The pile–soil model is established with FEM-SPH by LS-DYNA to simulate and analyze the characteristics of the spliced piles. When the helical pile is subjected to a horizontal load, the pile rotates around the point of rotation, and the contact force position of the soil in the model is as expected. During the process of pile driving, the soil forms an inverted cone stress-area, and the maximum particle stress area near the pile tip and the ground surface is 400 Kpa, which is highly concentrated. When loaded laterally, the area of the interaction stress of the soil particles is divided into three regions: the stress effect region; the transition region; and the critical region. Then, 7° is defined as the ultimate horizontal bearing-capacity of the spliced pile, and the numerical simulation of the horizontal bearing-capacity fundamentally matches the test results. The simulation model realizes the transition from the pile installation to the lateral loading, predicts the ultimate horizontal bearing-capacity, and analyzes the stress distribution of the soil particles and the time-development of the soil displacement.

New Tribological Aspects in the Micro-Areas of the Symmetric Rolling-Sliding Contact

The study of wear that occurs during operation in the wheel–rail assembly is a difficult process to analyze. The phenomena that accompany the wear process are extremely complex and involve many factors, which vary greatly over different periods of time and at different times of wheel–rail contact. Estimating the behavior of the system and its wear in operation is difficult to obtain. However, for common engineering applications, for which the determining factors, such as road profile, load, skid, speed and weather conditions, are known, useful results can be obtained by laboratory tests or by numerical simulation. The article aims to model the complex phenomena that take place in the rail wheel system, taking into account the impact that most essential operational factors have. For this, the Finite Element Method (FEM) is used, thus, trying to explain the wear mechanisms of the wheel–rail system. The obtained results are verified in the laboratory. The main observation in the paper refers to the fact that in the areas of maximum stress and deformation, cracks appear at the micro scale. FEM proved to be a method that can predict the appearance of these microcracks, the experimental results validating the numerical experiments. The research offers results that can prove to be of great importance in practice, for the analysis and improvement of railway safety.