Extrusion Seam Research Articles

Effect of subgrade on leakage through a defective geomembrane seam below saturated tailings

Experiments are conducted to quantify leakage through saturated tailings (with 30% fines) underlain by a geomembrane with either a 100-mm-length knife cut slit defect or a 110-mm-length defective extrusion seam. Various subgrades, a poorly graded gravel (GP) with or without nonwoven geotextile (450 or 1420 g/m2) above, a well-graded gravel (GW), and a poorly graded sand (SP) are evaluated. Test results show that leakage through the slit defect and defective seam increase with the subgrade coarseness and subgrade unevenness. The inferred upper and lower bounds opening width of a slit based on the measured leakage increase with the overburden pressure and are categorized for each subgrade. Indentations in the overlapped defective extrusion seam area arise from both the entrapped materials inside the overlap and the materials underlying/overlying the geomembrane, incrementally inducing a greater interface transmissivity with the increasing stress. Overlain by tailings at total overburden pressure of 510 kPa and water head of 35m, leakage through the slit defect is 1.1L/day for SP, 2.2L/day for GW, 2.6–3.3L/day for both GP and uneven GW; leakage drops to 0.8L/day with a geotextile layer directly above the GP; leakage through the defective extrusion seam is 0.4L/day for SP and 0.8L/day for GW.

Strain localization at longitudinal weld seams during plastic deformation of Al–Mg–Si–Mn–Cr extrusions: The role of microstructure

The current work was motivated by the increasing use of hollow aluminum extruded profiles for automotive applications and the need for a better understanding of the mechanical response of extrusion seam welds. Two Al–Mg–Si alloys were studied, one without Mn and one with 0.5 wt%Mn and 0.15 wt%Cr. A high temperature homogenization was applied, resulting in a high density of α-Al(Fe,Mn)Si dispersoids in the Mn containing alloy, and an essentially dispersoid free microstructure in the other. The alloys were extruded through a simple porthole die (with two ports) to produce a strip with a centerline weld seam. The Mn free extrudate had a recrystallized grain structure whereas the Mn and Cr containing material was unrecrystallised. There were significant spatial variations of microstructure between the weld seam and surrounding regions, in particular the crystallographic texture. Tensile tests were conducted with the loading direction perpendicular to the weld seam using digital image correlation (DIC) to characterize the local strain distribution. Strain localization and final fracture occurred at weld seam for the unrecrystallized material whereas these occurred away from the weld line in the recrystallized case. The role of local crystallographic texture was examined through polycrystal plasticity simulations using the visco-plastic self consistent code (VPSC). These simulations indicated that the weld seam region was mechanically stronger than the surrounding region for the recrystallized alloy and correspondingly weaker for the unrecrystallized case, thereby rationalizing the experimental results of strain localization and final fracture location.

A quantification of the short-term reliability of HDPE geomembrane seaming methods

This study provides a preliminary approximate quantification of the difference in seam reliability between fusion seams and extrusion seams of high-density polyethylene (HDPE) geomembranes based on leaks that exist at the end of installation. The two different seaming methods as well as seam testing methods are discussed. The reliability of the two seaming methods is compared using the number of leaks associated with extrusion seams versus fusion seams, which were found using electrical leak location surveys performed on a sampling of large geomembrane-lined facilities.

Modeling of the Extrusion Seam Welding Based on the Void Evolution

Modeling of the Extrusion Seam Welding Based on the Void Evolution

Deformations in Idealized 2D Extrusion Welding

Metal flow inside the container and in the metal behind a butt-ended die bridge in idealized aluminum extrusion welding has been investigated by FEA and experiment with respect to the deformation of the material flowing around the bridge and into the layers close the extrusion seam weld. Along the mid-axis of the extrusion process the effective strain subjected to the extrusion material can be determined in three different ways. One way is to determine the strains from grid pattern experiments that reveal the real deformations. When it comes to FEA there are two options; the strains can be determined from the initial and final positions of a number of material points distributed along the mid-axis of the material, where after traditional theoretical strain-equations can be used to calculate the effective strain distribution along the axis. Another possibility is to use the post-processor of the software to calculate the strain distribution. In this work the effective strain distribution along the mid-axis of the billet inside the container volume were determined by all these three methods. The effective strain in the thin layer of the squeeze zone ahead of the dead zone in front of the die bridge determined from the experiments was found to be much larger than the strains elsewhere along this axis. The same was the case when effective strain was determined by FEA from the computed position of the points, but this strain value was predicted approximately 10% lower than the corresponding value from the experiments in the layer with the heaviest strains. However, when this effective strain distribution was calculated by the post-processor of the software the high-strain layer in the squeeze zone was not revealed at all, instead the effective strains were predicted rather even over the whole length of the mid-axis. Corresponding effective strain distributions were determined along the mid-axis of the extrusion material in the weld chamber also, and after outflow of this material into the extrusion seam weld of the resulting profile where no experimental information is available. When this effective strain distribution was computed by FEA, based on initial and final position of points, very different strain values were obtained as compared to when same strains were collected directly from the post-processor. It is believed that the first results, i.e., the effective strains computed from the points are quite accurate, while those values calculated by the post-processor are less reliable.

Preparation and Etching Methods for a Light-Optical Microscopy Analysis of Extrusion Seams and Microstructural Contrasting for Aluminum Alloys EN AW-6063 and EN AW-6082

Abstract To begin with, a visualization of the seam location as well as of the microstructure of the entire profile cross-section is necessary in order to evaluate the stability of extrusion processes and the resulting relationships between process, microstructure, and properties of extrusion profiles characterized by an extrusion seam. The investigations aim at determining appropriate preparation and etching methods for a light-optical microscope analysis of the longitudinal as well as the transversal extrusion seam in the alloys EN AW-6063 and EN AW-6082 and – in the best case – a simultaneous microstructural contrasting. For this purpose, different chemical etching techniques have been applied. A reliable uncovering of the seam was possible for both alloys using a HF solution. Etching with Weck's reagent after NaOH pre-etching turned out to be a promising method for microstructural contrasting of the EN AW-6063 alloy. The transversal extrusion seam could not be rendered visible by means of conventional etching methods. In this context, extrusion of both alloys (EN AW-6082 and EN AW-6063) applying the billet-to-billet extrusion method in line with visioplastic analyses allowed for an indirect representation of the extrusion seam.

Analysis of Gas Pocket Formation during Extrusion of Al Hollow Profiles and Establishing an Extrusion Seam Weld Limit Diagram

In extrusion of aluminium alloys, using porthole dies, the billet metal is split into separate metal streams during flow into the ports. After that, the streams join by seam pressure welding in the weld chamber of the die and finally flow through the die exit emerging as the desired extrusion. Because of re-joining of the metal streams the extrusion will contain as many extrusion seam welds as there are bridges in the die. Dependent on the die design the metal will flow in such a way that a gas pocket may form behind the die bridge and remain stable here throughout the course of the extrusion process. If, at this stage of the process, the feed of metal into the region behind the bridge is increased the space behind the bridge may fill up completely and the gas pocket will disappear. In this work we have investigated how finite element modeling can be used (for a simple idealized case of 2-D extrusion welding) to understand the extrusion seam welding process, and to characterize what extrusion conditions will provide stable gas pocket formation behind a bridge, and when the pocket will disappear. The geometry of the welding chamber and the die opening was varied in a number of simulations to study this phenomenon using the FEM-code Deform 2D®. Based on these simulations we have been able to propose an “extrusion seam weld limit diagram (ESWLD)”. The ESWLD shows when extrusion will occur with a gas pocket present behind the bridge and when there is transfer to a state where the pocket disappears and the die fills up completely with metal. By curve-fitting the results can be presented by a mathematical model, i.e. by an equation allowing the reduction in extrusion at the point of transfer from a state of presence of the pocket to a state of complete die filling, to be computed from the dimensions of the porthole and the weld chamber, for a given billet size and a given bridge geometry. The model also shows which geometrical extrusion parameters of the die will favor complete filling of the space behind a die bridge instead of gas pocket formation there.

Metal flow in idealised a-symmetric 2D extrusion welding

It is common in aluminium extrusion industry to use extrusion dies that have portholes to produce hollow profiles. When the hollow profiles are to be produced with such a shape that different sections vary in thickness then usually dies with portholes of different sizes are used. A study has been performed in order to analyze metal flow in cases where two neighbouring porthole channels at each side of a die bridge are of different size. The study shows that there is of course more feed through the larger porthole, and that this effect has a significant influence on the deformations and metal flow in the region behind the bridge where the two metal streams meet and are joined together into an extrusion seam.

Simulation of the Co-Extrusion of Hybrid Mg/Al Profiles

Extrusion of composite materials can offer big advantages. In this work the manufacturing of a hybrid metal profile in a single production step was investigated. A porthole die was used, thus producing profiles with extrusion seams. Along the seams a material mix up was visible. The extrusion process was simulated with the Finite Element Method to investigate the material flow in die and welding chamber in order to understand the cause for the defects at the seams.

Effect of specimen orientation and extrusion welds on the fatigue life of an AA6063 alloy

The effect of specimen orientation and extrusion seam welds on the fatigue life of specimens milled from a hollow AA6063 aluminum alloy extrusion profile have been characterized in the form of S–N curves. The fatigue behavior of the fully recrystallized AA6063 alloy reported here is compared to previously reported results on a partially recrystallized AA6082 extruded aluminum alloy [Nanninga N, White C, Furu T, Anderson O, Dickson R. Effect of orientation and extrusion welds on the fatigue life of an Al–Mg–Si–Mn alloy. Int J Fatigue 2008; 30(9): 1569–78]. Specimen orientation with respect to the extrusion direction has a large effect on fatigue life, and is attributed to the orientation of extrusion die lines. Transverse specimens exhibit only a fraction of the high cycle fatigue life exhibited by longitudinal specimens. The presence of seam and/or charge welds, oriented both longitudinal and transverse to the loading direction, may also reduce the fatigue life. However, the effects of these welds are not as significant as the effects of orientation alone, and appear to be related to increased surface roughness at the welds. Variations in fatigue life are explained by surface roughness and variations in microstructure. Grain boundary separation was the primary mechanism of fatigue crack initiation in this study. Results from Auger energy spectroscopy and transmission electron microscope analyses suggest that localized strain in precipitate free zones may assist in this behavior.

Use of the Cone Expansion Test to Assess the Potential for Longitudinal Seam Failure in Extruded AZ31 and AM30 Mg Alloy Tubes

Magnesium generally has limited ductility which, in the case of extruded tubes, may be further reduced at the extrusion seams. These are locations where the material flow separates and rejoins during extrusion and are unavoidable when a hollow profile product is continuously extruded. When this type of magnesium tube is stressed along the circumferential direction, as in hydroforming, tube ruptures consistently occur along the extrusion seams. The aim of this project was to investigate the propensity to fail at these locations by means of cone expansion tests. These were performed to failure on batches of both magnesium AZ31 and AM30 tubes, at several temperatures and compression rates. In this paper, the role that microstructural changes at the seams such as those associated with precipitate dispersions, local texture changes, grain size changes and entrained material, play in failure is discussed. The sources of these irregularities in the extrusion process are discussed and some means of removing or mitigating them are presented. The most important cause of fracture is shown to be the voids present at the interface between the slowly and rapidly flowing streams of the material within the die. The effects of the extrusion parameters on the extent of such void formation are considered.

The relationship between extrusion die line roughness and high cycle fatigue life of an AA6082 alloy

The effect of surface finish on the fatigue life of hollow extruded AA6082 was studied by comparing results from specimens with as-extruded surfaces to results from specimens with polished surfaces. Extrusion die lines are the main contributor to surface roughening, and since die lines are parallel to the extrusion direction, distinct variations exist between fatigue lives of as-extruded specimens taken longitudinal and transverse to the extrusion direction [Nanninga N, White C, Furu T, Anderson O, Dickson R. Effect of orientation and extrusion welds on the fatigue life of an Al–Mg–Si–Mn alloy. Int J Fatigue 2008;30(9):1569–78]. Polishing specimen surfaces eliminated much of the variation between specimen orientations. Fatigue lives of polished specimens containing extrusion seam welds transverse to the loading direction were also studied. The seam weld did not appear to significantly affect the fatigue life. Die lines were modeled as notches and finite element analysis (FEA) was used to estimate a linear-elastic stress concentration factor for approximating fatigue run-out values for specimens with as-extruded surfaces loaded transverse to the die lines. The predicted run-out stress values based on the FEA match well with those obtained experimentally.

Longitudinal Seam Failure in Extruded AZ31 Alloy

Research is currently being conducted on the feasibility of hydroforming extruded magnesium tubes to integrate multiple parts into a single hydroformed section. Among other applications, such sections would reduce the weight of both cars and planes, particularly when used in the vehicle frame. This would lead to either reduced fuel costs, or the ability to carry an increased payload. Magnesium generally has limited ductility, which in the case of the current extruded tubes is even further reduced at the extrusion seams. These are locations where the material flow separates and rejoins during extrusion and are unavoidable when a hollow profile die is used. When the tubes were stressed in a circumferential direction, tube ruptures consistently occurred along the extrusion seams of the tubes. This led to the current project, an inquiry into the exact cause of failure at these locations. The creation of irregularities at the seams, such as precipitate dispersions, local texture changes, grain size changes and entrained material, is discussed. These irregularities are considered together with their roles in producing the failures. The results are summarized and the most fruitful directions for future work are outlined.

Production of long rods by sequential extrusion of wood powders

Wood-based materials are environment-friendly resources as they eventually decompose into carbon dioxide and water after disposal. However, there are a number of productivity and workability related problems: it takes many years for a tree to grow to a useable size, and wood materials are more difficult to process than metal and plastic materials. To overcome these problems, sequential extrusion of cryptomeria powders mixed with Japanese cypress was performed in an attempt to make long wooden rods. In sequential extrusion, the powder replenishment and short-stroke extrusion steps are alternated until the desired rods are obtained. In this process, a strong extrusion seams were required between the new powder batch and the extruded portion of the rod. A steel container with a device for controlling replenishment temperature was used to increase the bonding strength of extruded rods. The results showed that there exist an optimal replenishment pressure and temperature, and that, under these optimal conditions, long rods with the strength of natural wood can be obtained. Finally, it is found that the presence of back-pressure is key in producing sound, high-strength rods.

Analysis of Strain Concentration Next to Geomembrane Seams

Polyethylene geomembranes which are subjected to excessive tensile strains often fail next to seams. The analysis presented in this paper shows that strain concentration due to geomembrane bending in the vicinity of seams may play a significant role in geomembrane failures which occur next to seams. This is one of the many practical conclusions of this paper, which presents a theoretical analysis of strain concentration in geomembranes that result from the presence of seams. It is shown that maximum strain concentration occurs next to the seams when geomembranes are subjected to tensile strain, regardless of the causes of the tensile strain, such as: applied forces, geomembrane thermal contraction, and geomembrane irreversible shrinkage. Calculations performed for typical seams show that the strain in the geomembrane next to a seam can be more than twice as large as the average tensile strain in the geomembrane. A geomembrane embrittled by low temperature, or for other reasons, may not be able to withstand such strain. A parametric study presented in this paper indicates the influence of seam type and geometry on the magnitude of strain. A comparison of the seams typically used for polyethylene geomembranes indicates that fusion seams tend to cause less strain concentrations than extrusion seams.

Fatigue Performance Of Friction Stir Butt Welds In A6000 Series Aluminum Alloy

Friction stir welding is a novel solid state joining process for making low cost, energy efficient butt welds in aluminum alloy extrusions. The plate edges are clamped against a backing plate and the material is plastically deformed and stirred by a rotating tool moving along the joint line. The resulting weld bead is flush with the surface and exhibits little distortion. The material in the weld and heat affected zone (HAZ) has a fine-grained microstructure and a high tensile strength compared with welds produced by conventional arc welding methods. The present investigation was undertaken to determine the fatigue properties of friction stir welds in 5 mm thick plates in an AA6082 alloy. Extruded plates in the T4 condition were used in the test program. S-N tests in pulsating tension at R = 0.5 were performed on specimens with the weld transverse to the stress direction. Reference tests were made on the base material. Crack growth data were obtained for material in the weld metal, in the HAZ and base material. S-N tests were also made on conventional MIG butt welds from the same batch material to enable a comparison of the two welding methods. The results indicate that the fatigue strength of transverse friction stir welds is approximately 50 percent higher than the fatigue strength of MIG butt welds. The crack growth rates obtained for the weld material were lower than in the base material, probably due to a more fine grained microstructure in the weld region. INTRODUCTION The friction stir welding process has recently been developed as a cost effective alternative to conventional metal inert gas (MIG) and tungsten inert gas (TIG) Transactions on Engineering Sciences vol 8, © 1995 WIT Press, www.witpress.com, ISSN 1743-3533 226 Surface Treatment Effects II welding in aluminum alloys [1]. A major advantage of friction stir welding is that it is a solid state process involving a much lower heat input than that required in conventional arc welding methods. The weld itself and its adjacent narrow heat affected zone both have a very fine-grained microstructure with high mechanical strength. The high tensile strength of the weld material and the favorable geometry would also indicate that friction stir welds could have high levels of fatigue strength. A testing program was implemented to determine the fatigue properties of transverse butt welds of two alloys in the AA6000 series. The data presented in this paper are results from introductory tests on specimens fabricated from extruded plates in AA6082 material in the T4 temper condition. THE FRICTION STIR WELDING PROCESS In friction stir welding the plates to be joined are clamped on a backing plate to prevent movement A cylindrical shouldered tool with a specially profiled pin is rotated at a high speed, see Fig. la. The pin is slowly brought into contact with the joint line, and the material is heated by friction and plasticised in an annular volume around the pin. As the pin is lowered into the plates, soft material is extruded at the surface. Upon further lowering of the pin and movement along the joint line the shoulder face contacts the plate surface and the plasticised material is compressed against the face of the shoulder. The soft material is mashed by the leading face of the pin profile and transported to the trailing face of the pin where it consolidates and cools to form a solid-phase weld. The generation of a friction stir weld has many similarities with extrusion seam welds that form when material is joined in the weld chamber of an extrusion die [2]. The material flow, however, is somewhat different due to the more extensive mechanical mixing of the material from the two plates in the friction stir process. The properties of the weld are closely related to the tool technology. The tool bit shape and material determines the heating, plastic flow and forging pattern. Development of the friction stir welding process has up to now been concentrated mainly on butt and lap joints, however, introductory tests have shown that friction stir welding is suitable for a wide range of joint configurations [4], as shown in Fig. 2. EXPERIMENTAL PROGRAM The specimens were fabricated from AA6082 alloy plate material, in the T4 (as-extruded) condition. The plate thickness was 5 mm. The mechanical properties are listed in Table 1. Transactions on Engineering Sciences vol 8, © 1995 WIT Press, www.witpress.com, ISSN 1743-3533 Surface Treatment Effects II 227 Table 1. Mechanical properties of the AA6082 alloy in T4 temper.