Element Birth Research Articles

Minimization of wire-wound pressure vessel diameter based on distortion energy theory

This paper investigates the minimization of the diameter of wire-wound pressure vessels. The study is conducted in two stages. Firstly, the stresses arising from the wire winding of the vessel and the internal pressure application are extracted based on the distortion energy theory. It is assumed that the equivalent stress within the winding area in each layer, under the internal pressure condition, equals the allowable stress of the wire, and in the cylinder area, it does not exceed the allowable stress of the cylinder. The required number of layers and the wire tension during winding (two essential unknown parameters in the industrial winding process) are determined to satisfy these assumptions. In the second stage, the diameter optimization of the vessel is studied using the Distortion Energy (DE) theory. It is found that reducing the cylinder diameter results in a decrease in the vessel diameter. The occurrence of buckling or yielding in the cylinder is a limiting constraint for reducing the cylinder diameter. For validation, the results obtained from the derived equations are compared and confirmed against finite element results and the equations provided in the ASME code. Wire-winding simulation around the cylinder uses the element birth and death technique. The agreement between the derived equations and the code equations, as well as finite element results, is excellent. In the examined case study, using the DE theory leads to a 24 % reduction in wire consumption compared to the maximum shear stress (MSS) theory. In the optimization stage, the vessel weight is further reduced by 24 %. Compared to monobloc shells, the optimized wire-wound vessel weight based on the DE theory experiences a 77 % reduction.

Finite element analysis of self-tensioning and bursting of 210 L carbon fiber fully wound hydrogen storage cylinders

This paper focuses on a 210 L carbon fiber fully wound hydrogen storage cylinder. A 1/8 scale model is selected for analysis. Using the finite element software ANSYS APDL and secondary development language, an orthotropic material performance equation is formulated and applied to the composite material lay-up. Following DOT CFFC standards, the cylinder undergoes simulated loading and unloading analysis to determine the optimal self-tightening pressure. Subsequently, progressive failure theory and the Tsai-Wu failure criterion are employed to identify the failure modes of the composite material. Continual adjustments to the element stiffness are made during the loading process. Employing the element birth and death technique, failed elements are terminated and recorded, and based on increasing trends, the burst pressure of the cylinder can be predicted. The results closely align with experimental data, validating its applicability as the basis for burst prediction.

Optimizing SLM process parameters using FE analysis for distortion mitigation

The investigation aimed to determine the optimal value of process parameters to minimize distortion while reducing the overall printing time. To achieve this, different combinations of process parameters are selected, and 25 sets of FE experiments are prepared using an orthogonal matrix. The coupled thermomechanical analysis with the element birth technique is used to mimic the behavior of Selective Laser Melting (SLM). Initially, a mesh convergence study is performed to reduce computation time with the least sacrifice in results. To minimize the temperature gradient, simulations are performed at different levels of bed temperature ranging from 303 K to 843 K. The minimum distortion was observed for a higher bed temperature of 843 K, as at this temperature, the gradient in temperature is minimum, resulting in the least development of residual stresses. The interactive behavior between laser power and scanning speed is studied, revealing an approximately linear trend with respect to distortion while keeping all other parameters constant. Additionally, it was observed that laser power and layer thickness also exhibited a similar linear trend with respect to distortion. To identify the optimal process parameter value within the design space, the Multi-Island Genetic Algorithms (MIGA) technique is employed, leading to a remarkable minimum distortion of 0.45 mm for a specific set of input process parameters.

3D printing finite element analysis of continuous fiber reinforced composite materials considering printing pressure

Continuous fiber reinforced thermoplastic composite (CFRTC) 3D printing technology, as one of the most remarkable manufacturing techniques, has made significant advancements in various fields, including aerospace and automobile manufacturing. However, there is a dearth of research on simulating the printing process of CFRTC considering printing pressure. This article presents a finite element model that incorporates printing pressure and employs element birth and death technology to simulate the printing process. An in-situ pressure monitoring platform is built to provide real data for simulation. By comparing the simulation results with the experimental results, it is found that the errors of the finite element model simulation results with pressure under different printing parameters are predominantly less than 5 %. Furthermore, the impact of printing temperature and speed on the deformation of the 3D printed CFRTC is analyzed. The deformation of the printed sample is more sensitive to the printing temperature than the printing speed. This study can provide important theoretical guidance for engineering applications.

Fatigue of Bridge Steel Wire: A Corrosion Pit Evolution Model under the Effects of Wind and Vehicles

To investigate the damage evolution behavior of corroded steel wires under the influence of alternating loads, a damage evolution model for steel wires based on the theory of continuous damage mechanics was established. The damage evolution process at corrosion pits was simulated by using the element birth and death technique in ANSYS 2020R2. Then, a certain cable-stayed bridge was chosen as the research subject, the stress–time data of the sling were computed using a traffic–bridge–wind simulation analysis model, and the influence of corrosion pit distribution on the mechanical properties and fatigue life of wires under an alternating load was discussed. The results show that, in comparison to single-pitted steel wires, double-pits distributed circumferentially across the cross-section of the steel wires lead to more severe stress concentration, accelerating the damage evolution process and significantly reducing the fatigue life of the steel wires. Conversely, the stress concentration caused by double pits distributed along the longitudinal direction of steel wire is similar to that caused by single pits, and it will be even weaker than that caused by single pits with the change in the relative distance of the double pits. Based on the calculation results of the damage evolution model of steel wire, it was found that the corrosion pit crack nucleation life of steel wire under alternating load accounts for nearly 80% of the fatigue life of steel wire, and different corrosion pit distribution modes will significantly affect the fatigue life of steel wire.

Research on Effect Factors of Mechanical Response of Polyethylene Gas Pipeline in Karst Area Based on Element Birth and Death Technique

Abstract Buried gas pipelines in karst area are inevitably affected by the geotechnical activities, which is difficult to resist the permanent ground displacement caused by soil dislocation and surface damage. In this paper, abaqus finite element software has been used to establish a pipe-soil nonlinear coupling model based on element birth and death technique. The influence rules of various sensitive factors on the stress response of gas pipelines are studied. The work presented in this paper can provide a reference for the design and safety of polyethylene gas pipeline crossing the karst area.

Associations of prenatal and childhood Pb exposure with allostatic load in adolescence: Findings from the ELEMENT cohort study

The biological pathways which link lead (Pb) and long-term outcomes are unclear, though rodent models and a few human studies suggest Pb may alter the body's stress response systems, which over time, can elicit dysregulated stress responses with cumulative impacts. This study examined associations between prenatal and early childhood Pb exposure and adolescent allostatic load, an index of an individual's body burden of stress in multiple biological systems, and further examined sex-based associations. Among 391 (51% male) participants in the ELEMENT birth cohort, we related trimester-specific maternal blood Pb, 1-month postpartum maternal tibia and patella Pb, and child blood Pb at 12–24 months to an allostatic load index in adolescence comprised of biomarkers of cardiovascular, metabolic, neuroendocrine, and immune function. The results were overall mixed, with prenatal exposure, particularly maternal bone Pb, being positively associated with allostatic load, and early childhood Pb showing mixed results for males and females. In adjusted Poisson regression models, 1 mcg/g increase in tibia Pb was associated with a 1% change in expected allostatic load (IRR = 1.01; 95%CI 0.99, 1.02). We found a significant Pb × sex interaction (IRR = 1.05; 95%CI 1.01, 1.10); where males saw an increasing percent change in allostatic load as 12 month Pb levels increased compared to females who saw a decreasing allostatic load. Further examination of allostatic load will facilitate the determination of potential mechanistic pathways between developmental toxicant exposures and later-in-life cardiometabolic outcomes.

Calcium supplementation and body mass index modify associations between prenatal phthalate exposure and perinatal bone ultrasound measures among pregnant women

Phthalates have endocrine activity that may interfere with bone health, particularly during pregnancy and the early postpartum period, when bone resorption increases. We evaluated associations between prenatal phthalate exposure and perinatal bone health among 289 mothers in the ELEMENT birth cohort in Mexico City who were randomized upon recruitment to receive 1,200 mg daily calcium supplementation or placebo throughout pregnancy. Spot urine samples at up to three timepoints during pregnancy were assayed for 9 phthalate metabolites. Bone integrity was assessed by quantitative ultrasound speed of sound (SOS) measurements of the phalange and distal radius at 3, 6, and 8 months of pregnancy and 1, 3, 7, and 12 months postpartum. Geometric means of specific gravity-corrected phthalate concentrations were used as overall measures of prenatal exposure. Linear mixed effect models estimated associations between phthalate exposure and repeated perinatal bone SOS measures, adjusting for age, pre-pregnancy body mass index (BMI), education, parity, calcium supplementation, and month of pregnancy/postpartum. Effect modification by calcium supplementation and BMI were assessed in sensitivity analyses. An interquartile range increase in MEP and MiBP increased pregnancy phalange z-scores (β: 0.11; 95%CI: 0.003, 0.31 and β: 0.15; 95%CI: 0.00,0.42, respectively). Higher concentrations of several phthalate metabolites resulted in lower SOS measures among women who received calcium supplements (compared to placebo group) but higher SOS measures among women with a BMI≥25 (compared to BMI<25). These results suggest that phthalate exposure may interfere with bone remodeling during pregnancy, and that consideration of effect modifiers is paramount to fully understand the effects of environmental exposures on bone health.

A numerical simulation approach for the residual prestress of composite barrel with non-round section of railgun with tension winding

In order to obtain the distributions of residual prestress of the filament wound composite barrel with non-round section for railgun caused by the winding tension, a new numerical approach is provided. Based on the idea of considering the fiber bundles as the main load-bearing material for each winding layer, the loading of the initial winding tension in the winding process can be simulated through loading the initial tensile stress of the fiber bundles in fiber direction of the winding layers’ elements. Firstly, combing with the element birth and death technology, a three dimension finite element model for a hybrid filament wound cylinder with metal liner is established to simulate its residual prestress caused by winding tension. Its results are compared with the ones obtained by the theoretical model, which verifies that this numerical simulation method is reliable to some extent. Then, this numerical simulation method is adopted to analyze the residual prestresses of the filament wound composite barrels with non-round section for railgun, which are under three different winding tension control modes respectively. The results can provide some references to the initial design of the filament wound composite barrel with non-round section for railgun.

Numerical simulation of the 3D propeller repair process by laser cladding of SUS316L on SUS304

The laser cladding (LC) process is widely used for repair and surface modification; however, it generates not only high residual stress, which can negatively impact fatigue life, but also large distortions. Therefore, this study aimed to predict and minimize the residual stress and distortion of the LC process. Three numerical analyses were conducted using different finite element models to simulate the 3D propeller repair process; 3D finite element models involving conductive, convective, contact, and radiative heat transfer and requiring an element birth and death technique for expressing the additive process of LC were developed and validated experimentally. The numerical simulation results for the temperature history, distortion, and residual stress were consistent with the experimental results. Furthermore, a mismatch in the thermal contraction due to high thermal gradients and the gap in the coefficient of thermal expansion between the substrate and LC coating primarily contributed to the generation of residual stress. In addition, the effects of preheating, fixing, scanning patterns, and cooling conditions on reducing residual stress and distortion were investigated. First, preheating reduced the distortion and residual tensile stress of the LC coating owing to a decrease in the thermal gradients. Second, fixing both ends suppressed deformation without generating significantly high tensile stresses in the LC coating. Finally, optimizing the scanning pattern and allowing a cooling time between the deposition tracks to lower the interpass temperature reduced the distortion and residual stress in the entire substrate. Thus, numerical simulation can help in the prediction and minimization of the residual stress and distortions during the LC process.

Failure time of reinforced concrete column under blast load

To explore the damage and the failure time of the reinforced concrete column in an adjacent physical field of explosion, a comprehensive finite element model of TNT-air-column in the software LS-DYNA is set up in consideration of the advanced numerical simulation technologies (i.e., element birth and death technology, large deformation technology, contact technology, etc) and the strain rate effects of the concrete and steel materials. First of all, an explosion test is conducted on two scale models of the reinforced concrete column, and the finite element model is validated by comparing the numerical simulation results with the experimental data. The failure process, failure mode, and failure criterion of the reinforced concrete column under blast load are further investigated. Thereafter, a series of parameter studies are conducted to investigate the damage and the failure time of the reinforced concrete column. Finally, a new method is proposed to estimate the failure time of the reinforced concrete column and the corresponding basic steps are given in this study. Through the researches and analyses of the typical cases, the results show that the failure modes change from punching failure to compression-flexure failure via compression-shear failure with the increase in the scaled distance. The medium damage and the high damage occur mostly on the reinforced concrete column in an adjacent physical field of explosion. The damage index of the reinforced concrete column varies significantly with the compressive strength of concrete, column height, column depth, longitudinal reinforcement ratio, transverse reinforcement ratio, and axial compression ratio, especially the column depth and the axial compression ratio; however it has little relation with the column width. The failure time of the reinforced concrete column is up to tens of milliseconds or even more than one hundred milliseconds. The calculation formulas used in the proposed method are based on previous research and simulation results. The proposed method is rigorous and thorough and the predicted results are highly accurate and effective. Besides, this method can provide a good prediction of the failure time of the reinforced concrete columns with different axial compression ratios.

On the Interaction to Thermal Cycle Curve and Numerous Theories of Failure Criteria for Weld-Induced Residual Stresses in AISI304 Steel using Element Birth and Death Technique

On the Interaction to Thermal Cycle Curve and Numerous Theories of Failure Criteria for Weld-Induced Residual Stresses in AISI304 Steel using Element Birth and Death Technique

A Particle Finite Element Method for Additive Manufacturing Simulations

Abstract In this work, the particle finite element method (PFEM) is extended to simulate additive manufacturing processes in a variety of different complicated geometries. A three-dimensional α-shape approach is used to carry out the material addition procedure. It overcomes the limitation of merely employing the traditional element birth and death technique and reduces the degrees-of-freedom compared to this technique. Furthermore, numerical examples are used to evaluate and demonstrate the applicability of the PFEM method for additive manufacturing within the framework of a weakly coupled thermoelasticity formulation. During additive manufacturing operations, deflections, stresses, and temperature are computed using a user-defined implementation in FEniCS.

Study of the Key Mechanical Properties of Welded Hollow Spherical Joints after Uniform Corrosion

The welded hollow spherical joint is the most common form of the spatial grid structure, but the corrosion treatment at the joint is difficult. There are many corrosion problems of the welded hollow spherical joint in the actual structure, which brings hidden problems to structural safety. To study the effects of uniform corrosion on the key mechanical properties of welded hollow spherical joints, the joint refinement FEM in one typical size is built considering the effect of uniform corrosion through the method of the element birth and death, and the tensile, compressive, and bending performance of the FEM has been analyzed. Based on the analysis results, the relation curves between the three bearing capacities of the welded hollow spherical joint and the uniform corrosion degree are given. The results show that the influence of early corrosion on the joint tensile and compressive performance is not obvious. After corrosion to a certain extent, the loss of tensile and compressive capacity has a significant linear relationship with the degree of corrosion, and the loss of bending capacity has a significant quadratic curve relationship with the degree of corrosion from the initial stage. This study can provide a theoretical reference for a better understanding of the mechanical properties of welded hollow spherical joints in one typical size after corrosion to evaluate structural safety.

Implementation of damped bipedal inverted pendulum model of pedestrian into FE environment for prediction of vertical structural vibration

Motivated by the limited availability of tools for vibration serviceability assessment of civil engineering structures under pedestrian excitation in finite element (FE) environment, this study proposes a strategy for transferring a damped bipedal inverted pendulum (DBIP) model for a pedestrian from the analytical to the numerical domain. The strategy is implemented in FE-software ANSYS to addresses the key challenge of pedestrian alternating between the left and right stance leg. This is achieved by using COMBIN14 element in conjunction with employing element birth and death techniques to model temporary nature of the foot-structure contact. The implementation in FE environment has been verified against the analytical results of the DBIP model. The proposed method successfully transfers the pedestrian load modelling approach from biomechanics to FE modelling environment typical of civil engineering projects enabling efficient vibration serviceability assessment.

Numerical Study on Welding Residual Stress Distribution of Corrugated Steel Webs

Residual stresses are an inevitable result of the welded fabrication process of corrugated steel webs (CSWs), resulting in structures with high and unpredictable stress fields, causing unexpected failures. The residual stress field is affected by structural parameters and the welding path of CSWs. This study proposes the welding process simulation method for CSWs with element birth and death technology. The optimization design method of heat source parameters is proposed. The feasibility of the simulation method is verified by comparing the numerical results with the experimental results of relevant literature. As a part of the study, a comparison of residual stress fields upon cooling welded CSWs with bending angles of 30, 45, and 60 degrees is presented. Thereafter, the effect of two types of single-sided welding paths and double-sided welding construction processes on residual stress distribution is discussed. Generally, the study results have shown that the equivalent residual stress near the weld reaches the maximum 344 MPa, which is very close to the Q345 steel yield strength. The size of the bending angle has no major effect on the residual stress distribution pattern, but it influences the residual stress value at the bending position. The residual stress at the bending position increases with the bending angle of CSWs. Different welding paths significantly impact the residual stress of the weld toe, and selecting a reasonable welding path can effectively reduce the residual stress value by 20 to 40 MPa.

Aluminothermic welding modeling of heavy haul rails using the element birth and death technique

The aluminothermic welding process (ATW) of rail tracks is the most used in the field due to its low cost, execution time, and light equipment. In recent years, some experimental and numerical models have been developed to study ATW. The accuracy of the models is still being demonstrated. In this work, a new three-dimensional thermoelastoplastic numerical model of the ATW process is proposed. This model uses the Element Birth and Death (EBD) technique with Ansys® software to accurately simulate filling the pouring region with filler metal. The thermal and mechanical phenomena of all stages of a conventional rail track welding process were considered, as well as the effects of the material’s phase transformations during the process. First, the validation was carried out with experimental and numerical data from studies available in the literature for UIC60 rails. Then, the validated model was applied in the simulation of welding a TR68-type rail and an unprecedented analysis of the residual stresses resulting from this type of rail was performed. The ATW process could then be simulated using significantly fewer elements than the numerical models available in the literature and proved to be applicable for the study of the ATW process of railway tracks.

Development of correlation between temperature, liquid life span, molten pool, and porosity during Wire Arc Additive Manufacturing: A finite element approach

In recent times additive manufacturing (AM) has emerged as a crucial manufacturing process for custom-made metal workpieces. Wire Arc Additive Manufacturing (WAAM) is a rising technology that can cut back material usage and manufacturing time due to its higher deposition rate. This research aims to develop an efficient 3D thermal model to simulate the WAAM process and correlate the temperature with deposition quality. A moving heat source based on Goldac’s double ellipsoidal model was designed using the DFLUX subroutine. The element birth technique has been used to activate the various layers. The developed model is validated with experimentally observed temperature, and a good correlation is obtained. The effect of power and scan speed on the WAAM process has been studied to develop a relationship between maximum temperature, liquid lifetime, and porosity. An X-ray was done to check the porosity of the additively manufactured specimen. At higher power and lower scan speed, the liquid lifetime was observed to be increased along with the increase in depth of the molten pool leading to the formation of porosity. In other cases, at lower power and higher scan speed, the liquid lifetime was observed to be decreased along with the decrease in depth of the molten pool. The higher scan speeds resulted in higher cooling rates, which caused a lack of fusion between the layers of the product. In this case, a ball-shaped melt deposit was observed due to a lower deposition rate due to lower power. • A thermal model is developed to simulate WAAM and is validated with the experimentally observed temperature. • The element birth technique has been used to activate the various layers during the process. • A correlation between maximum temperature, liquid lifetime, and porosity is established. • Temperature contour and liquid lifespan can predict the formation of porosity during the process.

Numerical Simulation and Experimental Measurement of Residual Stresses in a Thick-Walled Buried-Arc Welded Pipe Structure

In this study, a numerical simulation of a single pass welding of two thick-walled pipes with the buried-arc method was performed in order to determine the residual stresses caused by welding. The numerical simulation procedure in the thermal analysis was performed by the element birth and death method while the structural analysis was performed simultaneously, without the application of the element birth and death technique in order to reduce the duration of the numerical simulation. The simulation results were validated by experimental residual stress measurements on the outside surfaces of the welded model using the X-ray diffraction technique. A good agreement between the results of the numerical simulation and experimental measurements was confirmed.

Effect of Welding Sequence and Constraint on the Residual Stress and Deformation of Thick Welded Butt Joint Made of Q345qD Steel

In this paper, the residual stress and deformation of 32 mm thick welded butt joints made of Q345qD steel using gas metal arc welding (GMAW) are studied by using the thermoelastic‐plastic finite element analysis (FEA). Element birth and death technique is used to simulate the deposition of the welding consumables, and the volume heat source in double‐ellipsoidal distribution is used. An in‐house python code is developed to enable the volume heat source movement. After the finite element model was verified against the experimental results, the effects of five welding sequences and two types of boundary constraint conditions on the residual stress and deformation of the thick welded butt joints were investigated. Results of the experimental measurement and the numerical simulation are in good agreement. The transverse residual stress and the vertical deformation can be significantly reduced by increasing the alternating times of the welding beads in two halves of the weld. The transverse residual stress and the vertical deformation can be reduced by 21.4% and 87.4%, respectively. In addition, the residual stress and deformation of the thick welded butt joints are significantly affected by the applied constraints. Increasing the constraint significantly increases the overall level of the transverse residual stress but can decrease the maximum longitudinal residual stress by 51.8% and the vertical deformation by 65.9%.