Sheet Thickening Research Articles

Failure analysis of 3D woven spacer sandwich composites with woven cross-links and face sheet thickening under compressive and flexural loading

The effect of face sheet thickening on the mechanical properties of sandwich structures reinforced with 3 D woven spacer fabrics having woven cross-links has been presented in this work. Spacer fabrics forming cells of rectangular (RECT), trapezoidal (TPZ) and triangular (TR) shapes were used as reinforcement of sandwich structures with non-thickened face sheets. While for thickened face sheet structures, additional layers of 2 D fabric were integrally woven with the top and bottom face sheets of spacer fabrics, having almost similar cell geometrical parameters as that of the former structures, in a single step of weaving. Composites manufactured from these structures were characterized for their out-of-plane compressive and flexural properties. The specific compressive load was observed to be lower for thickened face sheet structures. The flexural load was higher for thickened face sheet structures; but the specific bending load decreased for the same. Flexural stress was also found to decrease with thickening of the face sheets. The results obtained could be helpful in designing sandwich composites connected woven fabric cross-links with enhanced mechanical properties.

A flexible sheet-bulk forming demonstrator

Sheet-bulk forming (SBF) processes based on a combination of deep drawing and upsetting are being increasingly used to produce new sheet metal parts with significant changes in wall thickness to accommodate three-dimensional functional features such as solid bosses, teeth and ribs. The utilisation of sheet-bulk forming processes introduces additional complexity in the design, setup and costs of tooling due to the inherent high forces and complex material flow that easily lead to underfilling and failure in critical die regions. This paper is concerned with these issues and is focused on the development of a sheet-bulk forming demonstrator capable of replicating material flow and failure in sheet thickening, local sheet thickening and sheet injection operating conditions. The demonstrator combines sheet bending and upsetting operations with a flexible design concept based on the utilisation of active modular tool parts to allow different materials, geometries and tool concepts to be tested under laboratory conditions and rapidly transferred to industrial SBF tools.

Local sheet thickening by in-plane swaging

This paper presents a new sheet-bulk forming process to locally pile-up material in thin sheets for subsequent forming or joining operations. An analytical solution is proposed for explaining the influence of the major process parameters, estimating the thickening of the pile-up material and determining the normal and thrust forces applied by the tools. The approach is built upon the slip-line field theory under plane strain assumptions and results are compared against finite element predictions and experimental results using Aluminium EN AW-1050A (EN 573-3) sheets with 3mm thickness. The last part of the paper introduces a modified tool geometry that is able to control the pile-up material for subsequent mechanical fastening operations.

Influence of initial texture on cold deep drawability of Mg–3Al–1Zn alloy sheets

Mg–3Al–1Zn magnesium alloy sheets rolled at 350°C, 450°C and 525°C, which exhibit approximately the same grain size but a significant decrease in basal texture intensity with increasing rolling temperature, were used for investigating the influence of initial texture on deep drawing behaviour at room temperature. The sheets rolled at 350°C and 450°C fracture at drawing ratios of 1.5 and 1.7, respectively, while the sheet rolled at 525°C can be successfully drawn at a large drawing ratio of 1.8. The fracture site changes from the shoulder of drawn cup to the edge of the flange with the weakening of initial basal texture. At the flange, the basal texture dramatically changes to the TD-texture with basal planes perpendicular to the sheet plane accompanied with sheet thickening. Both tensile twinning and basal slip contribute to this texture change due to compressive stress along the circumferential direction. In the case of weak initial texture, relatively restricted tensile twinning and more activated basal slip delay the development of the TD-texture, which is favoured for maintaining deformation capability at the flange and in turn enhances deep drawability. The deformation behaviour is discussed in terms of the change in Schmid factor for basal slip during deep drawing.

A Brief Study on Modeling and Finite Element Analysis of Car Rear Sub-Frame Based on Intelligent Materials

This paper uses a rear sub-frame as the mother model and uses Reverse engineering technology to measure the rear sub-frame point cloud through ATOS non-contact scanners. Then, the point cloud‘s data processing is completed in Imageware. Finally, the point cloud is imported into UG NX4.0 software, after a series of surface cutting, chamfer suturing and sheet thickening; the sub-frame’s three-dimensional model is established. Besides, we complete the static finite element analysis and modal analysis of the sub-frame’s three-dimensional model through the ANSYS software. The results of analysis support theoretical basis for the structural improvement of sub-frame.

Plasma sheet thickness during a bursty bulk flow reversal

On 17 March 2008 around 0912 UT the five THEMIS spacecraft P1–P5 were in the plasma sheet between 2200 and 2300 h magnetic local time (MLT), covering radial distances between 15 Earth radii (Re) (P1) and 9 Re (P5). All the spacecraft consecutively observed a bursty bulk flow (BBF) that traveled earthward, slowed down from 400 km/s to 50 km/s between P1 and P5, and then turned in the opposite direction. The most tailward‐located spacecraft, P1 and P2, detected thinning and then thickening of the plasma sheet around the time of the flow direction change. Meanwhile, the other three THEMIS spacecraft, which were located in a more dipolar region, observed plasma sheet thickening and then thinning. Observations indicated that the thinning/thickening was stronger around the BBF funnel. Further, during the interaction of the earthward‐flowing BBF plasma with the Earth's dipolar field lines, the BBF was deflected by about 70° at a scale of about 5 Re. The radial pressure gradient was substantially increased when the BBF reached the shortest radial distance to the Earth and substantially decreased after the tailward plasma flow. We conclude that the tailward pressure pulse produced by the enhanced radial pressure gradients after the earthward BBF stopped could be responsible for the observed tailward plasma flows.

Offsetting operations on non-manifold topological models

This paper describes non-manifold offsetting operations that add or remove a uniform thickness from a given non-manifold topological model. The mathematical definitions and properties of the non-manifold offsetting operations are investigated first, and then an offset algorithm based on the definitions is proposed and implemented using the non-manifold Euler operators proposed in this paper. In this algorithm, the offset elements of minimal size for the vertices, edges and faces of a given non-manifold model are generated first. Then, they are united into a single body using the non-manifold Boolean operations. In order to reduce computation time and numerical errors, the intersections between the offset elements are calculated considering the origins of the topological entities during union. Finally, all topological entities that are within the offset distance are detected and removed in turn. In addition to the original offset algorithm based on mathematical definitions, some variant offset algorithms, called sheet thickening and solid shelling, are proposed and implemented for more practical and efficient solid modeling of thin-walled plastic or sheet metal parts. In virtue of the proposed non-manifold offset operation and its variations, different offsetting operations for wireframes, sheets and solids can be integrated into one and applied to a wide range of applications with a great potential usefulness.

Tissue Structure and Ventricular Wall Mechanics

Considering that the left ventricle is a thick-walled body that maintains its volume while reducing intracavitary volume by two thirds, it should come as no surprise that the ventricular wall thickens during systole and that there is a transmural gradient in wall thickening. Wall thickening on the inner wall may exceed values of 40% measured by a variety of techniques. These values far exceed the 8% diameter increase estimated by simple conservation of volume in an individual myocyte shortening by 15%. Physiologists have long understood that changes in the macrostructure of the wall (cellular rearrangement) must account for the difference between wall thickening and estimates of cell thickening.1 Reorientation of laminae or sheets of muscle cells has been proposed to account for this change in macrostructure.2,3 The dichotomy between wall thickening and estimated change in myocyte diameter has been elegantly framed by Cheng et al4 in this issue of Circulation , which shows nearly identical transmural fiber shortening at 2 ventricular sites, with very different wall thickening in the ovine ventricle. Similar data have been shown for other species.5,6 However, the data presented by Cheng et al4 provide strong evidence that the cellular rearrangements are different at the 2 sites. Cheng et al4 used a method developed by Costa et al5 in which regional histological measurements of muscle fiber and sheet orientations were used to resolve 3-dimensional transmural strain distributions obtained from implanted arrays of radiopaque markers into components. These components were defined by local axes that are parallel to the fibers, transverse to the fibers in the sheet plane, and transverse to the sheets. Wall thickening then can be resolved into components of sheet motion. Costa et al5 and Takayama et al6 reported that the interlaminar shear-strain term (Esn) and …

Septal-lateral annnular cinching perturbs basal left ventricular transmural strains☆

Septal-lateral annular cinching ('SLAC') corrects both acute and chronic ischemic mitral regurgitation in animal experiments, which has led to the development of therapeutic surgical and interventional strategies incorporating this concept (e.g., Edwards GeoForm ring, Myocor Coapsys, Ample Medical PS3). Changes in left ventricular (LV) transmural cardiac and fiber-sheet strains after SLAC, however, remain unknown. Eight normal sheep hearts had two triads of transmural radiopaque bead columns inserted adjacent to (anterobasal) and remote from (midlateral equatorial) the mitral annulus. Under acute, open chest conditions, 4D bead coordinates were obtained using videofluoroscopy before and after SLAC. Transmural systolic strains were calculated from bead displacements relative to local circumferential, longitudinal, and radial cardiac axes. Transmural cardiac strains were transformed into fiber-sheet coordinates (X(f), X(s), X(n)) oriented along the fiber (f), sheet (s), and sheet-normal (n) axes using fiber (alpha) and sheet (beta) angle measurements. SLAC markedly reduced (approximately 60%) septal-lateral annular diameter at both end-diastole (ED) (2.5+/-0.3 to 1.0+/-0.3 cm, p=0.001) and end-systole (ES) (2.4+/-0.4 to 1.0+/-0.3 cm, p=0.001). In the LV wall remote from the mitral annulus, transmural systolic strains did not change. In the anterobasal region adjacent to the mitral annulus, ED wall thickness increased (p=0.01) and systolic wall thickening was less in the epicardial (0.28+/-0.12 vs 0.20+/-0.06, p=0.05) and midwall (0.36+/-0.24 vs 0.19+/-0.11, p=0.04) LV layers. This impaired wall thickening was due to decreased systolic sheet thickening (0.20+/-0.8 to 0.12+/-0.07, p=0.01) and sheet shear (-0.15+/-0.07 to -0.11+/-0.04, p=0.02) in the epicardium and sheet extension (0.21+/-0.11 to 0.10+/-0.04, p=0.03) in the midwall. Transmural systolic and remodeling strains in the lateral midwall (remote from the annulus) were unaffected. Although SLAC is an alluring concept to correct ischemic mitral regurgitation, these data suggest that extreme SLAC adversely effects systolic wall thickening adjacent to the mitral annulus by inhibiting systolic sheet thickening, sheet shear, and sheet extension. Such alterations in LV strains could result in unanticipated deleterious remodeling and warrant further investigation.

Effects of Undersized Mitral Annuloplasty on Regional Transmural Left Ventricular Wall Strains and Wall Thickening Mechanisms

Undersized mitral annuloplasty, widely used for ischemic and functional mitral regurgitation (MR), has been proposed as an "annular solution to a ventricular problem." Beyond relief of MR, it is thought to improve global left ventricular (LV) shape, hence potentially reducing myocardial stress and promoting beneficial reverse LV remodeling. We previously observed that undersized annuloplasty inhibited systolic wall thickening at the LV base near the mitral annulus. In this study, we measured the effects of undersized annuloplasty on regional transmural LV wall fiber and sheet strains and wall thickening mechanisms. Nine sheep had transmural radiopaque beadsets surgically inserted into anterobasal and lateral equatorial LV regions, with additional markers silhouetting the LV and mitral annulus. 4-Dimensional marker dynamics were studied with biplane videofluoroscopy before and after tightening an adjustable Paneth-type mitral annuloplasty suture. Transmural circumferential, longitudinal, and radial systolic and remodeling strains in the subepicardium (20% depth), midwall (50%), and subendocardium (80%) in both regions were computed. Fiber and sheet angles from quantitative regional histology allowed transformation of these strains into local fiber (f), sheet (s), and sheet-normal (n) coordinates. Further analysis calculated the transmural contributions of sheet extension (E(ssc)), sheet thickening (E(nnc)), and sheet shear (E(snc)) to systolic wall thickening (E(33)). In the anterobasal region, undersized annuloplasty reduced systolic wall thickening (E33) by &50% at all transmural depths by inhibiting: (1) subendocardial systolic fiber shortening (-0.10+/-0.05 versus -0.04+/-0.05; P<0.05); (2) subepicardial (0.16+/-0.15 versus 0.09+/-0.08; P<0.05) and subendocardial (0.45+/-0.40 versus 0.19+/-0.18; P<0.05) systolic sheet thickening; (3) midwall sheet extension (0.22+/-0.12 versus 0.11+/-0.06; P<0.05); and (4) transmural sheet shear (subepicardium, -0.14+/-0.07 versus -0.08+/-0.07; midwall, 0.21+/-0.12 versus 0.10+/-0.11; subendocardium, -0.19+/-0.23 versus -0.11+/-0.16; P<0.05). In the remote lateral equatorial region, fiber-sheet strains and E33 were unchanged. In this acute animal study, undersized annuloplasty inhibited systolic wall thickening in the anterobasal region by reducing subendocardial systolic fiber shortening and laminar sheet wall thickening, but had no effects in a more distant LV region. This suggests that undersized mitral annuloplasty may have potentially deleterious effects on local myocardial mechanics.

Transmural sheet strains in the lateral wall of the ovine left ventricle

In an attempt to provide a better understanding of our finding that regions with contracting left ventricular myofibers need not develop a significant transmural systolic wall thickening gradient, the analytic approach of Costa et al. was applied to the four-dimensional dynamic data obtained 1 and 8 wk after surgical implantation of transmural radiopaque beads in the lateral equatorial left ventricular wall in seven ovine hearts. Quantitative histology of tissue blocks demonstrated that fiber angles varied linearly across the wall in this region from -37 degrees in the subepicardium to +18 degrees in the subendocardium. Sheet angles exhibited a pleated-sheet behavior, alternating sign from subepicardium to subendocardium. From end diastole (reference configuration) to end systole (deformed configuration), fiber strain was uniformly negative, sheet extension and sheet thickening were uniformly positive, and sheet-normal shear contributed to wall thickening at all wall depths. Subepicardial radial wall thickening increased significantly from week 1 to week 8, with significant increases in the contributions from subepicardial sheet extension and sheet-normal shear. At 1 and 8 wk, the contribution of sheet-normal shear to wall thickening was substantial at all transmural depths; the contribution of sheet extension to wall thickening was greatest in the subepicardium and least in the subendocardium, and the contribution of sheet thickening to wall thickening was greatest in the subendocardium and least in the subepicardium. A mechanistic model is proposed that provides a working hypothesis that a selective decrease in subepicardial intercellular matrix stiffness is responsible for elimination of the transmural wall thickening gradient 1-8 wk after marker implantation surgery.

The poleward leap of the auroral electrojet as seen in auroral images

This paper discusses a recently published series of 12 successive images of the northern auroral oval obtained by the University of Iowa's auroral imager on DE 1 during a substorm on November 8, 1981. The images showed a sudden (within &lt;12 min) thickening and poleward expansion of the midnight sector of the oval that occurred at the “maximum epoch” of the substorm, i.e., as auroral zone bays reached their peaks and began to subside about 90 min after the expansive phase onset. We propose that this was the auroral manifestation of the poleward leap of the auroral electrojet that has been reported on many occasions to coincide with thickening of the plasma sheet in the outer magnetotail (beyond ∼15 RE) late in a substorm. The plasma sheet thickening is thought to be associated with a tailward retreat of the substorm magnetic neutral line. We note evidence that the neutral line's tailward retreat influences auroral currents and particle precipitation even at low auroral latitudes. Modifications of the present auroral substorm model are suggested.

Multiple‐satellite studies of magnetospheric substorms: Plasma sheet recovery and the poleward leap of auroral zone activity

Particle observations from pairs of satellites (Ogo 5 and Vela 4A and 5A) during 28 plasma sheet thickening events are examined. These data indicate that thickening of the nighttime plasma sheet during substorms occurs in two main stages, one early stage of single or multiple expansions of the near‐earth (geocentric distances r ≲15 RE) plasma sheet at the onset of substorm expansions (Pi 2 bursts) on the ground and another later stage of plasma sheet recovery that starts near the time of maximum auroral zone bay activity and is characterized by a large‐scale thickening toward higher latitudes that occurs over a broad azimuthal scale and from ionospheric heights to beyond the Vela orbit (r ∼18 RE). A detailed analysis of two‐satellite observations during eight plasma sheet recoveries is presented, showing events that occurred within 5 min in widely separated locations at small (&lt;4 RE) distances from the tail's midplane and events that occurred concurrently in the Vela orbit and at high latitudes in the near‐earth region. Some events were accompanied by clear signatures of a poleward leap (to &gt;71° magnetic latitude) of electron precipitation and the westward electrojet that probably corresponded to an expansion poleward of the ionospheric projection of the recovering plasma sheet. The eight plasma sheet recoveries occurred 10–30 min after a Pi 2 burst on the ground, and mid‐latitude magnetograms showed no indications of a near‐coincident formation of a substorm current wedge in the local time sector of the spacecraft; this indicates that the plasma sheet recoveries and the poleward leaps were not caused directly by a late high‐latitude substorm expansion. Instead, these phenomena seem to represent a transition phase between a substorm expansion sequence and a substorm recovery.

Surface area and pore structure of compressed low-porosity cement pastes

Low-porosity portland cement pastes were prepared by pre-hydration compression at 5, 10, 30 and 70 atmospheres, followed by hydration in liquid water at 25°C for about two years. The thickness of the produced tobermorite sheets was found to depend on the pressure used in the pre-hydration compression. It seems that at the highest compression there is not enough room for complete hydration nor for sheet thickening. The simultaneous changes in the degree of hydration, the pore structure, and the specific surface area of the main hydration product due to pre-hydration compression, could affect the compressive strength measured for the various pastes, and an interpretation is given.