Controllability Over Wall Thickness of Tubular Structures and Encapsulation During Co-Axial Extrusion of a Thermal-Crosslinking Hydrogel

2020 ◽  
Vol 142 (8) ◽  
Author(s):  
Ilhan Yu ◽  
Samantha Grindrod ◽  
Roland Chen
Keyword(s):  
Flow Velocity ◽  
Wall Thickness ◽  
Dynamic Viscosity ◽  
Element Model ◽  
Extrusion Process ◽  
Tubular Structures ◽  
Needle Size ◽  
Thermal Crosslinking ◽  
Outer Needle ◽  
Phosphate Buffered Saline

Abstract Tubular structures of the hydrogel are used in a variety of applications such as delivering nutrient supplies for 3D cell culturing. The wall thickness of the tube determines the delivery rate. In this study, we used the coaxial extrusion process to fabricate tubular structures with varying wall thicknesses using a thermal-crosslinking hydrogel, gellan gum (GG). The objectives of this study are to investigate the thermal extrusion process of GG to form tubular structures, the range of achievable wall thickness, and a possibility to form tubular structures with closed ends to encapsulate fluid or drug inside the tube. The wall thickness is controlled by changing the relative flow velocity of the inner needle (phosphate-buffered saline, PBS) to the outer needle, while keeping the velocity of outer needles (GG) constant. Two pairs of coaxial needles were used which are 18-12 gauge (G) and 20-12G. The controllable wall thickness ranges from 0.618 mm (100% relative velocity) to 0.499 mm (250%) for 18-12G and from 0.77 mm (80%) to 0.69 (200%) for 20-12G. Encapsulation is possible in a smaller range of flow velocities in both needle combinations. A finite element model was developed to estimate the temperature distribution and the wall thickness. The model is found to be accurate. The dynamic viscosity of GG determines the pressure equilibrium and the range of achievable wall thickness. Changing the inner needle size or the flow velocity both affect the heat exchange and thus the temperature-dependent dynamic viscosity.

Fabrication of Gellan Gum Tubular Structure Using Coaxial Needles: A Study on Wall Thickness and Encapsulation

2018 ◽  
Author(s):  
Ilhan Yu ◽  
Roland Chen ◽  
Samantha Grindrod
Keyword(s):  
Wall Thickness ◽  
Rate Ratio ◽  
Gellan Gum ◽  
Flow Rate Ratio ◽  
Tubular Structures ◽  
Extrusion Speed ◽  
Extrusion Rate ◽  
Coaxial Needle ◽  
Thermal Crosslinking ◽  
Phosphate Buffered Saline

Tubular structures of hydrogel are used in a variety of applications such as 3D cell culturing for delivery of nutrient supplies. The wall thickness of the tube determines the speed of diffusion or delivery rate. In this study, we aimed to fabricate tubular structures with varying of wall thicknesses using a thermal-crosslinking hydrogel, gellan gum, with the coaxial needle approach. The wall thickness is controlled by changing the flow rate ratio between the inner (phosphate-buffered saline) and outer needles (gellan gum). A simulation model was developed to estimate the proper extrusion speed to allow the gellan gum to be extruded around its glass transition temperature. While keeping the extrusion rate of gellan gum fixed, different PBS extrusion rates were tested to investigate the printability to form continuous tubular structures, range of printable wall thickness, and possibility to form tubes with closed ends to encapsulate fluid or drug inside the tube. The ranges of printable wall thickness with two pairs of coaxial needle were identified. It was found that at about 200% of the baseline PBS extrusion speed, a maximum of 20% difference in wall thickness can be achieved, while a close end can still be formed.

Research on Design Method of Polygonal Roll Pass for Stretch Reduced Seamless Tubes

2010 ◽  
Vol 654-656 ◽  
pp. 1614-1617 ◽  
Author(s):  
Sheng Zhi Li ◽  
Hai Yan Bao ◽  
Zhi Chao Zhang ◽  
Yang Hua Li ◽  
Gong Ming Long
Keyword(s):  
Wall Thickness ◽  
Design Method ◽  
Element Model ◽  
Rolling Process ◽  
Contact Length ◽  
Transverse Wall ◽  
Roll Pass ◽  
Steel Tubes ◽  
Pass System ◽  
Lateral Curvature

the aid of commercially available software MSC.SuperForm, a 3-D finite element model has been established to simulate the rolling process of steel tubes on the stretch reducing mill (SRM) with group centralized differential drive in certain factories. A special effort was made to analyze the fluctuation of transverse wall thickness uniformity. It was found that the wall thickness of each stand was accumulated in the original pass 50°~60° along the circumferential direction, which caused the formation of the inner hexagon defects and worsen. In view of this, this paper proposes a modified roll pass design method which uses the interactive technology of CAD graph curve and MATLAB equation. By means of decreasing the lateral curvature of roll pass contour curve to enlarge the contact length between the tube and groove, also the rolling process using the new pass system were simulated and analyzed. The results indicate that the design of such polygonal roll pass can be effective in improving the inner hexagon defects.

Under Pressure Operations on Dense Phase CO2 Pipelines: Issues for the Operator

2014 ◽  
Author(s):  
Julian Barnett ◽  
Richard Wilkinson ◽  
Alan Kirkham ◽  
Keith Armstrong
Keyword(s):  
Natural Gas ◽  
Flow Velocity ◽  
Wall Thickness ◽  
Gaseous Phase ◽  
Operating Conditions ◽  
Cooling Time ◽  
Phase Behaviour ◽  
Pipeline System ◽  
Dense Phase ◽  
Pressure Welding

National Grid, in the United Kingdom (UK), has extensive experience in the management and execution of under pressure operations on its natural gas pipelines. These under pressure operations include welding, ‘hot tap’ and ‘stopple’ operations, and the installation of sleeve repairs. National Grid Carbon is pursuing plans to develop a pipeline network in the Humber and North Yorkshire areas of the UK to transport dense phase Carbon Dioxide (CO2) from major industrial emitters in the area to saline aquifers off the Yorkshire coast. One of the issues that needed to be resolved is the requirement to modify and/or repair dense phase CO2 pipeline system. Existing under pressure experience and procedures for natural gas systems have been proven to be applicable for gaseous phase CO2 pipelines; however, dense phase CO2 pipeline systems require further consideration due to their higher pressures and different phase behaviour. Consequently, there is a need to develop procedures and define requirements for dense phase CO2 pipelines. This development required an experimental programme of under pressure welding trials using a flow loop to simulate real dense phase CO2 pipeline operating conditions. This paper describes the experiments which involved: • Heat decay trials which demonstrated that the practical limitation for under pressure welding on dense phase CO2 systems will be maintaining a sufficient level of heat to achieve the cooling time from 250 °C to 150 °C (T250–150) above the generally accepted 40 second limit. • A successful welding qualification trial with a welded full encirclement split sleeve arrangement. The work found that for the same pipe wall thickness, flow velocity and pressure, dense phase CO2 has the fastest cooling time when compared with gaseous phase CO2 and natural gas. The major practical conclusion of the study is that for dense phase CO2 pipelines with a wall thickness of 19.0 mm or above, safe and practical under pressure welding is possible in accordance with the existing National Grid specification (i.e. T/SP/P/9) up to a flow velocity of around 0.9 m/s. The paper also outlines the work conducted into the use of the Manual Phased Array (MPA) inspection technique on under pressure welding applications. Finally, the paper identifies and considers the additional development work needed to ensure that a comprehensive suite of under pressure operations and procedures are available for the pipeline operator.

scholarly journals Effect of Process Parameters and Definition of Favorable Conditions in Multi-Material Extrusion of Bimetallic AZ31B–Ti6Al4V Billets

2020 ◽  
Vol 10 (22) ◽  
pp. 8048
Author(s):  
Daniel Fernández ◽  
Alvaro Rodríguez-Prieto ◽  
Ana María Camacho
Keyword(s):  
Influencing Factor ◽  
Element Model ◽  
Extrusion Process ◽  
Extrusion Force ◽  
Core Diameter ◽  
The Core ◽  
Ram Speed ◽  
Definition Of ◽  
Favorable Conditions ◽  
Influential Parameters

This paper investigates the extrusion process to manufacture bimetallic cylinders combining a magnesium alloy core (AZ31B) and a titanium alloy sleeve (Ti6Al4V) of interest in aeronautical applications. A robust finite element model has been developed to determine the most influential parameters and to study the effect of them on the extrusion force and damage induced by means of Design of Experiments (DOE) and Taguchi method. The results show that the most influential parameters in the extrusion forces are the friction between sleeve and container/die and the height of the cylinder; and the less influential ones are the process temperature and ram speed. Moreover, minimum values of forces along with low damage can be reached by favorable interface contact conditions, minimizing the friction at the core-container/die interface, as the main influencing factor; followed by the geometrical dimensions of the billet, being the billet height more important when paying attention to the minimum forces, and being the core diameter when considering the minimum damage as the most important criterion. The results can potentially be used to improve the efficiency of this kind of extrusion process and the quality of the extruded part that, along with the use of lightweight materials, can contribute to sustainable production approaches.

scholarly journals Numerical Analysis and Strength Evaluation of an Exposed River Crossing Pipeline with Casing Under Flood Load

2018 ◽  
Author(s):  
Xiaoben Liu ◽  
Hong Zhang ◽  
Mengying Xia ◽  
Yanfei Chen ◽  
Kai Wu ◽  
...  
Keyword(s):  
Finite Element ◽  
Flow Velocity ◽  
Yield Criterion ◽  
Element Model ◽  
Failure Criteria ◽  
General Purpose ◽  
Von Mises Stress ◽  
Critical Flow Velocity ◽  
Pipe Segment ◽  
Von Mises

Pipelines in service always experience complicated loadings induced by operational and environmental conditions. Flood is one of the common natural hazard threats for buried steel pipelines. One exposed river crossing X70 gas pipeline induced by flood erosion was used as a prototype for this study. A mechanical model was established considering the field loading conditions. Morison equations were adopted to calculate distributional hydrodynamic loads on spanning pipe caused by flood flow. Nonlinear soil constraint on pipe was considered using discrete nonlinear soil springs. An explicit solution of bending stiffness for pipe segment with casing was derived and applied to the numerical model. The von Mises yield criterion was used as failure criteria of the X70 pipe. Stress behavior of the pipe were analyzed by a rigorous finite element model established by the general-purpose Finite-Element package ABAQUS, with 3D pipe elements and pipe-soil interaction elements simulating pipe and soil constraints on pipe, respectively. Results show that, the pipe is safe at present, as the maximum von Mises stress in pipe with the field parameters is 185.57 MPa. The critical flow velocity of the pipe is 5.8 m/s with the present spanning length. The critical spanning length of the pipe is 467 m with the present flow velocity. The failure pipe sections locate at the connection point of the bare pipe and the pipe with casing or the supporting point of the bare pipe on riverbed.

scholarly journals On the Adequacy of Shell Models for Predicting Stresses and Strains in Thick-Walled Tubes Subjected to Detonation Loading

2013 ◽  
Author(s):  
Neal P. Bitter ◽  
Joseph E. Shepherd
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Shell Model ◽  
Wall Thickness ◽  
Axial Strain ◽  
Nonlinear Behavior ◽  
Element Model ◽  
Shell Models ◽  
Axial Curvature ◽  
Detonation Loading

This paper analyzes the adequacy of shell models for predicting stresses and strains in thick-walled tubes subjected to detonation loads. Of particular interest are the large axial strains which are produced at the inner and outer surfaces of the tube due to bending along the tube axis. First, comparisons between simple shell theory and a static finite element model are used to show that the axial strain varies proportionally with wall thickness and inversely with the square of the axial wavelength. For small wavelengths, this comparison demonstrates nonlinear behavior and a breakdown of the shell model. Second, a dynamic finite element model is used to evaluate the performance of transient shell equations. This comparison is used to quantify the error of the shell model with increasing wall thickness and show that shell models can be inaccurate near the load front where the axial curvature is high. Finally, the results of these analyses are used to show that the large axial strains which are sometimes observed in experiments cannot be attributed to through-wall bending and appear to be caused instead by non-ideal conditions present in the experiments.

Aluminium Extrusion Weld Formation and Metal Flow Analysis in Hollow Profile Extrusions of Different Section Thickness

2011 ◽  
Vol 491 ◽  
pp. 105-112 ◽  
Author(s):  
Yawar Abbas Khan ◽  
Henry Sigvart Valberg
Keyword(s):  
Wall Thickness ◽  
Perfect Match ◽  
Metal Flow ◽  
Extrusion Process ◽  
Experimental Results ◽  
Fe Model ◽  
Grid Pattern ◽  
Element Analysis ◽  
Weld Formation ◽  
Flow Through

Hollow and semi-hollow profiles are commonly produced by extrusion using porthole dies. The main characteristics of such dies are the presence of a mandrel (core) to shape the inner contour of hollow profile and bridges or legs to carry the mandrel. The bridges split the billet material into multiple metal streams that flow through the porthole channels and meet in the welding chamber behind the bridge where they are joined by pressure welding. When hollow profiles with different wall thickness are made the size of two adjacent portholes may be different. The material then flows through the two portholes with different flow velocity so that there is more feed through the bigger porthole into the weld chamber behind the bridge. Experiments have been performed and are reported here in which a grid pattern technique was used to characterize the metal flow through a 2D-die with porthole channels of unequal size. The design of the laboratory die has been modified in relation to the symmetric case to get different sizes of the two portholes. Since the metal flow through such a die is asymmetric the grid pattern technique was also modified to characterize the experimental flow. The results of an experimental metal flow study performed for a short billet was presented in a previous article [1]. Corresponding experiments performed with longer billets are now reported; so that two stages of the extrusion process is analysed here. The grid pattern technique has successfully mapped the non-symmetric material flow as in industrial extrusion when using different wall thickness over the section. The lateral movement of metal during extrusion is obtained from one set of experiments; the vertical movement from the other set. Finite element analysis of the extrusion process has been performed using Deform 3D. The encountering of the two metal streams behind the die bridge and the deformation characteristics within the welding chamber has been studied this way. Extrusion weld formation and deformations around the die bridge are considered here with the help of experimental results and simulation models. The nature of the metal flow achieved from the FE-model is compared with the experimental results. As regards the short billet some results are presented in [1], however improvement to the previous model gives a more perfect match. The model also provides information about the boundary conditions in real extrusion.

Finite Element Modeling of the Dynamic Response of a Steel Pipe During Water Hammer

2012 ◽  
Author(s):  
Juan C. Suárez ◽  
Paz Pinilla ◽  
Javier Alonso
Keyword(s):  
Finite Element ◽  
Wall Thickness ◽  
Pipe Wall ◽  
Element Model ◽  
Water Hammer ◽  
Steel Pipe ◽  
Dynamic Stresses ◽  
Rate Dependent ◽  
Simple Step ◽  
Von Mises

Water hammer imposes a steep rise in pipe pressure due to the rapid closure of a valve or a pump shutdown. Transversal strain waves propagate along the pipe wall at sonic velocities, and dynamic stresses are developed in the material, which can interact with discontinuities and contribute to an unexpected failure. Pressure increase has been modeled as a simple step front in a finite element model of a short section of a steel pipe. Boundary conditions have been considered to closely resemble the conditions of longer pipe behavior. The shock traveling along the length of the fluid-filled pipe causes a vibration response in the pipe wall. Dynamic strains and stresses follow the water hammer event with a certain delay, as is shown from the results of the FEA. Response of the material is strain rate dependent and dynamic peak stresses are substantially larger than the expected from the static pressure loads. Damping of the waves, neither by the material of the pipe nor by the interaction fluid-pipe, has not been considered in this simple model. Hoop, axial, radial, and Von Mises equivalent stresses have been evaluated both for the overshooting and the following phase of decompression of a pipe without discontinuities. However, dynamic stresses can be enhanced in the presence of discontinuities such as laminations, thickness losses in the pipe wall due to corrosion, changes in the wall thickness in neighboring pipe sections, dents, etc. These dynamic effects are able to explain how certain discontinuities that were reported as passing an Engineering Critical Assessment can eventually cause failure to the integrity of the structure. Deflections in the pipe wall can be altered by the welded transition from a pipe with a certain thickness to another with a smaller thickness, and wavelength changes of one order of magnitude can be expected. This can result in different approaches towards the risk assessment for discontinuities in the proximity of changes in wall thickness.

Structural characterization of the fullerene nanotubes prepared by the liquid–liquid interfacial precipitation method

2005 ◽  
Vol 20 (3) ◽  
pp. 688-695 ◽  
Author(s):  
Kun'ichi Miyazawa ◽  
Jun-ichi Minato ◽  
Tetsuro Yoshii ◽  
Masahisa Fujino ◽  
Tadatomo Suga
Keyword(s):  
Linear Relationship ◽  
Wall Thickness ◽  
Structural Characterization ◽  
Tube Wall ◽  
Precipitation Method ◽  
Outer Diameter ◽  
Tubular Structures ◽  
Growth Axis ◽  
Inner Diameter

Fine tubular fibers composed of C60 and C70 fullerene molecules were successfully fabricated by the liquid–liquid interfacial precipitation method. The walls of the tubular fibers were crystalline, and the fullerene molecules were densely packed along the growth axis of tube wall. The tubular structures are called “fullerene nanotubes.” The inner diameter and the outer diameter of C70 tubes showed a linear relationship, suggesting a constant wall thickness of the tubes. The tubular structures composed of C70 molecules could be formed when their diameter was larger than about 240 nm. The fullerene tubes were successfully fabricated by using a C60-C70 soot as well. The formation of fullerene nanotubes can be understood by assuming a mechanism of core dissolution of the solvated fullerene nanowhiskers.

scholarly journals Risk of Proximal Femoral Nail Antirotation Implant Failure Upon Different Lateral Femoral Wall Thickness in Intertrochanteric Fracture :A Finite Element Analysis.

2020 ◽  
Author(s):  
Liqin Zheng ◽  
Duo Wai-Chi Wong ◽  
Xinming Chen ◽  
Yuanzhuang Chen ◽  
Pengfei Li
Keyword(s):  
Wall Thickness ◽  
Intertrochanteric Fracture ◽  
Element Model ◽  
Implant Failure ◽  
Von Mises Stress ◽  
Element Analysis ◽  
Fracture Models ◽  
The Stability ◽  
Von Mises ◽  
Stability Type

Abstract PurposePFNA has been commonly used to treat intertrochanteric fractures, despite the risk of implant failure. The integrity of the femur could influence the risk of implant failure. This study aims to evaluate the influence of lateral femoral wall thickness on potential implant failure using a computational modeling approach. MethodsFinite element model of the hip was reconstructed from the Computed Tomography of a female patient. Five intertrochanteric fracture models at different lateral femoral wall thickness (T1 = 27.6 mm, T2 = 25.4 mm, T3 = 23.4 mm, T4 = 21.4 mm, and T5 = 19.3 mm) were created and fixed with PFNA. A critical loading condition was simulated that mimicked a high loading scenario during walking. The implant failure condition, stress and displacement of the PFNA implant and fracture femur were predicted for analysis. ResultsImplant failure of PNFA occurred at the sides of the proximal nail canal especially for the thinner wall models (T4 and T5).The maximum von Mises stress of the nail for T4 changed abruptly to 298.1 MPa. However, thinner wall decreased the displacement of the PFNA implant. There was approximately opponent trend of stress and displacement on proximal and distal fragments with decreasing thickness possibly due to the adaptation after failure.ConclusionA thinner wall increased the risk of PFNA implant failure. Our prediction showed that complete failure occurred when the thickness was 21.4 mm which was close to the value suggested to determine the stability type.

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