Numerical Stress Analysis Research Articles

Strength and stiffness of 3D-printed connectors compared with the wooden mortise and tenon joints for chairs

ABSTRACT In this study, 3D-printed connectors to replace the typical L-shaped joints in the construction of a chair were developed, tested and numerically analysed. Different connectors were designed and manufactured with a fused deposition modelling (FDM) 3D printer using acrylonitrile butadiene styrene (ABS) with the aim to find a simple shaped connector which could be used to build chairs and withstand standard chair loading requirements. The strength and stiffness of the joints were tested and compared with traditional beech mortise-and-tenon joints. Numerical stress and strain analyses were performed with the finite element method for an orthotropic linear-elastic model. The experimental results showed that joints with 3D-printed connectors achieved lower strength than the traditional wooden mortise-and-tenon joints with similar dimensions. The results indicate that the effect of reinforcement of the connector were not recognised due to the small thickness and inadequate geometric position and arrangement of the reinforcement ABS material. The chair assembled with 3D-printed connectors could withstand the loads for seating, but failed the backrest test according to standard EN 1728:2002. The connectors need to be optimised and reinforced to withstand standard loads.

Research on Insurance Method for Energetic Materials on Information Self-Destruction Chips.

Detonation waves released by energetic materials provide an important means of physical self-destruction (Psd) for information storage chips (ISCs) in the information insurance field and offer advantages that include a rapid response and low driving energy. The high electrical sensitivity of energetic materials means that they are easily triggered by leakage currents and electrostatic forces. Therefore, a Psd module based on a graphene-based insurance actuator heterogeneously integrated with energetic materials is proposed. First, the force–balance relation between the electrostatic van der Waals force and the elastic recovery force of the insurance actuator’s graphene electrode is established to realize physical isolation and an electrical interconnection between the energetic materials and the peripheral electrical systems. Second, a numerical analysis of the detonation wave stress of the energetic materials in the air domain is performed, and the copper azide dosage required to achieve reliable ISC Psd is obtained. Third, the insurance actuator is prepared via graphene thin film processing and copper azide is prepared via an in situ reaction. The experimental results show that the energetic materials proposed can release physical isolation within 14 μs and can achieve ISC Psd under the application of a voltage signal (4.4–4.65 V). Copper azide (0.45–0.52 mg) can achieve physical damage over an ISC area (23.37–35.84 mm2) within an assembly gap (0.05–0.25 mm) between copper azide and ISC. The proposed method has high applicability for information insurance.

Numerical simulation and analysis of the thermal stresses of a planar solid oxide electrolysis cell

ABSTRACT Hydrogen production using solid oxide electrolysis cells (SOECs) is a highly efficient and low-carbon pathway to generate high purity hydrogen. However, high working temperatures may result in high thermal stress due to a mismatch in the coefficient of thermal expansion (CTE) between components with a nonuniform temperature distribution. Serious stress concentration may lead to structural failure of the SOEC stack. Hence, this work investigated the thermal stress of SOECs through a three-dimensional planar SOEC unit model. A stress analysis method was proposed via a multi-physics coupling model of SOECs using Comsol Multiphysics software. The impacts of voltage, flow direction, water mole fraction, and operating pressure on the thermal stress were evaluated. Numerical results show that the highest maximum principal stress is located in the electrolyte in the SOEC unit. Raising the water mole fraction and the CTE of the electrolyte could reduce the thermal stress if the voltage is below the thermoneutral voltage.

Numerical Analysis of Residual Stresses in Additively Manufactured Materials

A finite element modeling approach was used to study the transient temperature field and mechanical response during LPBF processing of Ti6Al4V powder. The using of the Newton-Raphson method in structural analysis is described in detail. Significant effect of process parameters on residual stress and microstructure was found.

Total Knee Replacement with an Uncemented Porous Tantalum Tibia Component: A Failure Analysis.

Porous tantalum has been extensively used in orthopaedic surgery, including uncemented total knee arthroplasty (TKA). Favourable results were reported with earlier monobloc tibial components and the design evolved to modular implants. We aimed to analyse possible causes for extensive medial tibia bone loss, resulting in modular porous tantalum tibia baseplate fracture after primary TKA. Retrieved tissue samples were scanned with 3 MeV focused proton beam for Proton-Induced X-ray Emission (micro-PIXE) elemental analysis. Fractographic and microstructural analysis were performed by stereomicroscopy. A full 3D finite-element model was made for numerical analysis of stress–strain conditions of the tibial baseplate. Histological examination of tissue underneath the broken part of the tibial baseplate revealed dark-stained metal debris, which was confirmed by micro-PIXE to consist of tantalum and titanium. Fractographic analysis and tensile testing showed that the failure of the tibial baseplate fulfilled the criteria of a typical fatigue fracture. Microstructural analysis of the contact surface revealed signs of bone ingrowth in 22.5% of the surface only and was even less pronounced in the medial half of the tibial baseplate. Further studies are needed to confirm the responsibility of metal debris for an increased bone absorption leading to catastrophic tibial tray failure.

Local tailored design of deep water composite risers subjected to burst, collapse and tension loads

There is an increasing demand for more sustainable and adaptable technologies in the offshore industry. Thus, composite structures are more frequently used in the industry. Secondly, the shift in offshore exploration from shallow to deep waters has necessitated advancements on more lightweight composite structures to minimise platform loads, ease fluid transport, and service, using conduit pipes like composite production risers (CPR). The properties of composites are harnessed to improve riser weight and strength performance as Composite risers. In this research, the local tailored design of deep water composite risers was subjected to burst, collapse, tension and combined loads. Three design methodologies are considered-conventional, local, and tailored designs for different configurations. The structure is made up of configurations having 17 layers, 18 layers, 19 layers, 20 layers and 21 layers. The numerical technique for the CPR model with 3 m section considered five loadings. The model was developed utilising ANSYS ACP to conduct the numerical stress analysis with parametric studies. From the design, it is recommended to consider liners like PA12 and include environmental loads from global design. This study presents the CPR behaviour. Since CPR structures are response-sensitive and fatigue-sensitive, the global dynamic analysis of full-length composite riser is recommended.

Effect of malaligned knee prosthesis on stress and fatigue life of tibial tray

Among various health care demands for ageing population, the total knee arthroplasty (TKA) is currently one of the major health care expenses. TKA is a process to replace the surfaces of femur and tibia with the knee prosthesis, i.e., femoral component, tibial tray, and spacer. During service, the metal tibial tray is under cyclic bending; thus, the fatigue failure is possible. The cyclic bending and fatigue failure of tibial tray can be enhanced by the malalignment of knee prosthesis due to the change of bodily structure in ageing population. To investigate the influence of malaligned knee prosthesis on fatigue life, the numerical stress analysis and in-vitro fatigue test of tibial tray based on ASTM F1800 were performed. For tibial trays with malalignments, the location of the maximum stress range was near the junction between stem and tray, which corresponded to the location of fractures observed previously in clinical application.

Development of a method for numerical analysis of contact stresses in roller bearings

Development of a method for numerical analysis of contact stresses in roller bearings

Experimental and numerical stress and strain analysis of the boiler reversing chamber tube plate

Boilers are one of the most used units for both heat generation plants and industry systems. Their operation is subjected to different working loads and maintenance requirements. Exploitation experience points out critical boiler zones where failures and break downs typically occur. This paper analyzes critical zones in hot water fire-tube boiler. Experimental procedure was performed on the model of this type of boilers and its critical element. The tube plate of hot water boiler was identified as the most critical one. Experimental analysis and numerical model verification were performed using Aramis system based on 3-D digital image correlation method. Numerical analysis was done in ANSYS software package and verification of results was done based on measurements obtained by strain gauges and local measurements performed by the Aramis system. Stress-strain analysis indicates the critical zones of boiler tube plate. The character of change parameters such as strain and stress occurring in the critical zones can be verified both by experimental and numerical data. The paper presents a novel approach in experimental and numerical analyses that can be conducted in similar units and used for existing unit optimization, as well as for new product testing on different loads and provide opportunity for further development and improvement for practical industrial application.

Numerical study of the effect of rock anisotropy on stresses around an opening located in the fractured rock mass

The fractured rock mass is a discontinuous, heterogeneous, anisotropic medium in nature, including single, multiple or a network of joints with regular or irregular patterns located between the intact rocks. Anisotropy, as an inherent feature of rock mass, is a factor that causes the mechanical properties of rock to be various in different directions, so it is very important and necessary to be considered in the design of rock engineering structures. This study aims to investigate the effect of rock anisotropy on induced stresses around an opening like a borehole located in the fractured rock mass. For this purpose, the combination of discrete fracture network (DFN) method to construct a geometric model of rock mass, with distinct element method (DEM) to the numerical analysis of stress, was used. All coupled DEM-DFN models were developed based on the field data of the rock and joint system of the Sellafield site in the UK. The discrete fracture network models with different degrees of anisotropy, including a circular opening with two different cross-section areas placed at the center of model, were used for stress analysis. In each type of model, by applying different boundary conditions, the magnitude of induced stresses at selected points around opening is calculated, and then the obtained results are compared with the Kirsch method as a popular closed-form solution. The numerical results of this study showed that the presence of irregular joints with different orientations in the model caused anisotropy in the magnitude of induced stresses obtained around the opening. This is an important issue that the Kirsch method is not able to consider in the calculations. • Fractured rock mass is a discontinuous, heterogeneous and anisotropic medium including network of joints with the stochastic pattern located between intact rocks. • Anisotropy is a factor that causes the mechanical properties of rock to be various in different directions. • Coupled DEM-DFN models are developed to numerical analysis of stress around a borehole. • Presence of irregular joints with different orientations caused anisotropy in the amount of induced stresses around the borehole.

The Analytical and Numerical Stress Analysis of Various Domes for Composite Pressure Vessels

The paper describes analytical and numerical solutions for five selected domes (a spherical shell, a geodesicisotensoid shell, a shell with zero transversal strain, a shell with zero transversal stress, and a shell with identical strain) for composite pressure vessels manufactured by means of filament (helical) winding. The stresses and strains in the domes were evaluated analytically from known equations with the use of MATLAB script for numerical evaluation and via finite element analysis (FEA) with Abaqus software and results were compared with each other. Two failure criteria, interactive and non-interactive, were chosen for the evaluation of critical areas of the shells. Moreover, the best dome shape for a given material and polar hole/equator ratio was selected for various types of failure, i.e., a loss of tightness/leakage or the failure of the fibers.

The risk of rupture and abdominal aortic aneurysm morphology: A computational study.

Prediction of rupture and optimal timing for abdominal aortic aneurysm (AAA) surgical intervention remain wanting even after decades of clinical, histological, and numerical research. Although studies estimating rupture from AAA geometrical features from CT imaging showed some promising results, they are still not being used in practice. Patient-specific numerical stress analysis introduced too many assumptions about wall structure for the related rupture potential index (RPI) to be considered reliable. Growth and remodeling (G&R) numerical models eliminate some of these assumptions and thus might have the most potential to calculate mural stresses and RPI and increase our understanding of rupture. To recognize numerical models as trustworthy, it is necessary to validate the computed results with results derived from imaging. Elastin degradation function is one of the main factors that determine idealized aneurysm sac shape. Using a hundred different combinations of variables defining AAA geometry or influences AAA stability (elastin degradation function parameters, collagen mechanics, and initial healthy aortic diameters), we investigated the relationship between AAA morphology and RPI and compared numerical results with clinical findings. Good agreement of numerical results with clinical expectations from the literature gives us confidence in the validity of the numerical model. We show that aneurysm morphology significantly influences the stability of aneurysms. Additionally, we propose new parameters, geometrical rupture potential index (GRPI) and normalized aneurysm length (NAL), that might predict rupture of aneurysms without thrombus better than currently used criteria (i.e., maximum diameter and growth rate). These parameters can be computed quickly, without the tedious processing of CT images.

Failure analysis of ductile iron crankshaft in compact pickup truck diesel engine

The crankshaft is one of the structural components of the engine that converts the linear motion of the piston into rotational motion. In this study, the failure analysis of spheroidal graphite cast iron (SGCI) crankshafts of compact pickup truck diesel engine was investigated that premature failure occurred in the web-crankpin fillet zone of all four crankpins. A series of experiments including chemical composition, mechanical properties, hardness, and tensile tests were performed. Optical microscope (OM) and scanning electron microscopes (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS) were used to investigate the microstructure, defects, fracture surface, and failure cause. To estimate the crankshaft stress field under cyclic bending combined with steady torsion, a nonlinear three-dimensional stress analysis model was used. Fractography showed that the failure is a type of transient low cycle fatigue and includes three zones of crack initiation, fatigue crack propagation, and fast final fracture. Also, hardness and microstructure results revealed that there is no hardened surface layer on both the crankpin and the main journal (>600 HV0.1 proposed standard). In addition, the microstructural characteristics showed that the material nodularity used in the failed crankshafts is within the acceptable minimum range (>80% nodularity). Besides, numerical stress analysis showed that the highest stress is in the web-crankpin fillet zone, which is in good agreement with the experimental field measurements. Finally, recommendations have been provided to ensure long fatigue life and prevent premature failure.

Numerical stress analysis of tubular joints

The finite element analysis (FEA) presented in this paper pertains to the stress analysis of both the welded tubular T and X joints and is aimed to assess both the importance of the presence of the weld geometry and the suitability of shell and solid elements with regards to the FEA of welded tubular joints and, additionally, to confirm or dispute a correlation between the standards AWS D1.1 and DNVGL-RP-C203 with regards to the minimum size of the weld geometry. Using symmetry, three unit-load cases are investigated: axial loading, in-plane and out-of-plane bending. The results indicate that the FE models acknowledging the presence of the weld geometry and using solid elements are more suitable for the FEA of welded tubular joints and, moreover, the stress concentration factor (SCF) obtained at the chord “crown” location from the FE models subjected to the axial load case either approach, as in the case of the welded tubular T joint, or surpass, as in the case of the welded tubular X joint, the value estimated from the parametric equations as given in DNVGL-RP-C203.

A Study on a New Method for Flexoelectric Coefficient Estimation of the Flexoelectric Unimorph Sensing Element

In a flexoelectric sensing element using bending mode, estimation of the flexoelectric coefficient was investigated using 3-D stress/strain analysis and experiments. The proposed method uses the results (deformation and strain) from the finite element analysis (FEA). The estimated flexoelectric coefficients were compared with those obtained via the conventional method (Euler’s beam theory) under the assumption of the quasi 1-D stress field. The results show that the RMS value and standard deviation of the estimated flexoelectric coefficient for the 3-D stress field case of the sensing element are 31.51 µC/m and 0.24%, respectively. In addition, we found that the flexoelectric coefficient obtained from the results of the 3-D stress analysis is 1.8% smaller than that of the quasi-1-D stress analysis. Therefore, in order to obtain a more reliable flexoelectric coefficient in the sensing element, the results of the 3-D numerical stress analysis should be used for accurate estimation of the flexoelectric coefficient.

Optimal Localization of Smart Aggregate Sensor for Concrete Damage Monitoring in PSC Anchorage Zone.

This study investigates the feasibility of smart aggregate (SA) sensors and their optimal locations for impedance-based damage monitoring in prestressed concrete (PSC) anchorage zones. Firstly, numerical stress analyses are performed on the PSC anchorage zone to determine the location of potential damage that is induced by prestressing forces. Secondly, a simplified impedance model is briefly described for the SA sensor in the anchorage. Thirdly, numerical impedance analyses are performed to explore the sensitivities of a few SA sensors in the anchorage zone under the variation of prestressing forces and under the occurrence of artificial damage events. Finally, a real-scale PSC anchorage zone is experimentally examined to evaluate the optimal localization of the SA sensor for concrete damage detection. Impedance responses measured under a series of prestressing forces are statistically quantified to estimate the performance of damage monitoring via the SA sensor in the PSC anchorage.

Numerical Analysis of Additional Stresses in Railway Track Elements Due to Subgrade Settlement Using FEM Simulation

The prediction of additional stresses in ballasted track due to subgrade deformation is the main objective of the present paper. In this context, a 2D finite element model of ballasted railway track was built using the ANSYS Workbench program. Based on this model, an investigation of stresses and deformation values of track elements was conducted in three cases with different contact types. It was found that the case introducing the status of a new track, which has frictional contacts between sleepers and ballast with bonded contacts between other elements, has lower stresses in most of the track elements. Moreover, this case was applied for studying the effect of the settlement on track elements. It was found that stresses increased with increasing the settlement value. The average percentages of increased stresses are 4.18%, 5.85%, and 7.21% in railhead, tie plate, and sleeper, respectively, due to a 1 mm increase in the settlement. Finally, a second-degree polynomial equation was derived to predict the additional stresses in each element due to track settlement. It is expected that this study would help to decrease the maintenance costs and extend the service life of the track elements by predicting the additional stresses in them.

Study on a novel backlash-adjustable worm drive via the involute helical beveloid gear meshing with dual-lead involute cylindrical worm

This paper focuses on a novel backlash-adjustable worm drive, and it is composed of a dual-lead involute cylindrical (DIC) worm and an involute helical beveloid (IHB) gear. It is characterized by the low error sensitivity, easy to manufacture and with the backlash-adjustable. The design criteria for the novel worm drive are presented based on a variable-lead and variable-thickness media rack. Then the mathematical model and meshing performance analysis model are deduced and established, and the theory of backlash-adjustable is proposed. The tooth contact analysis (TCA) is conducted by the numerical calculation and stress analysis. Moreover, the experimental gearbox is manufactured, and the contact tests and transmission accuracy tests are completed. These results indicate that the novel worm drive can effectively adjust backlash without affecting the transmission accuracy. This theoretical research provides the theoretical support for further analysis and application of the novel backlash-adjustable worm drive.

The role of numerical analysis in the study of the behaviour of hard-rock pillars

Rock pillars can be defined as the in-situ rock between two or more underground openings. However, one aspect that is seldom considered in analysis of hard rock pillars, and indirectly in synthetic rock mass models to determine rock mass strength, is the actual stress level and stress path imposed on the pillar due to the excavation sequence and the location of the pillars within the mine lay out. In this paper we propose to use numerical stress analysis to determine how stresses vary across the excavated pillars in a typical room-and-pillar mine lay out, and thus generate a spatially variable determination of pillar stability. Because of the computational difficulty associated with hybrid modelling of realistic discrete fracture networks, synthetic rock mass modelling is commonly carried out using a 2D approach. By comparing 3D and 2D results for selected cross-sections across, we believe the results of the analysis will provide the opportunity to better constrain the stability implications of a 2D approach to pillar design and synthetic rock mass modelling.

Numerical simulation and thermal stress analysis of direct internal reforming SOFCs

ABSTRACT Hydrocarbon fuels such as CH4 can be converted into H2 and CO by direct internal reforming (DIR) processes within the anode of solid oxide fuel cells (SOFCs). DIR-SOFCs can reduce system complexity and capital cost due to the elimination of external reformers. However, the strong endothermic reforming reactions at the cell entrance may result in large thermal stress, leading to premature failure. In this study, a numerical simulation study was carried out to analyze the effect of operating conditions and cell structures on temperature, composition and thermal stress distributions in DIR-SOFCs. A two-dimensional axisymmetric model was developed by considering the coupling effects of the chemical/electrochemical reactions; transport processes of mass, charge, or heat; and thermal mechanical stress. The failure probability of the cell was estimated by stress distributions. Simulation results show that the increase of the steam-to-carbon ratio and operating voltage leads to higher thermal stresses and higher failure probability. The introduction of a metal supportive layer may release the thermal stress problem at severe DIR-SOFC operation conditions, which leads to a flatter temperature distribution and smaller failure probability compared to anode-supported SOFCs.