Ovalization Of Cross-section Research Articles

Erpetosuchus, a crocodile-like basal archosaur from the Late Triassic of Elgin, Scotland

Erpetosuchus, a small archosaurian reptile from the Late Triassic of Scotland and North America, hasoften been implicated in the ancestry of crocodilians. A restudy of the type specimen, using new high-fidelity casts, as well as examination of new, hitherto undescribed material, allows a detailed description and restoration of Erpetosuchus granti from the Lossiemouth Sandstone Formation (late Carnian, Late Triassic). This small reptile is known only from the front end of its body; a complete skull, cervical vertebral column, anterior dorsals and ribs, shoulder girdle, and forelimb. The skull shows a number of unusual features: a reducedrow of only 4–5 teeth on the anterior part of the maxilla, a large antorbital fenestra set in a deep fossa whose margins aremarked by distinct sharply angled ridges, a jugal that is divided into a lateral and a ventral portion by a sharp ridge, a deeplyrecessed tympanic area, the angular and surangular marked by a strong ridge running back from the ventral margin of the mandibular fenestra, and teeth oval in cross-section and lacking anterior and posterior carinae and marginal serrations. The remains suggest that Erpetosuchus wasa light, cursorial animal that may have fed on insects. A cladistic analysis of crurotarsan archosaurs indicates that Erpetosuchus isthe closest sister group of Crocodylomorpha among known basal archosaurs. It shares with them a deep recess in the cheek region framed bythe quadrate and quadratojugal which slope forward side-by-side at an angle of 45° above horizontal, and reach the uppermargin of the lower temporal fenestra. In Erpetosuchus the recess is entirely lateral, while in crocodylomorphs, the recesspenetrates medially as well, since the quadrate/quadratojugal bar meets the side wall of the braincase.

나선형 증기 발생기 튜브의 정밀성형을 위한 스프링백 제어 연구

The spring back taking place after the coiling process of steam generator tube leads to the dimensional inaccuracy. In order to reduce the spring back, tension force was applied to the one end of the tube during forming. In this work, parametric study using FEM was performed to find the appropriate magnitude of tension force. The force that induces minimum spring back was found by simultaneously taking account if spring back amount, cross-sectional ovality, and thickness of the tube wall after deformation. In addition, stress relieving by heat treatment was also simulated as an alternative to the former method. The latter was found to be more effective under the given constraints.

Viscoplastic collapse of titanium alloy tubes under cyclic bending

This paper presents the experimetal result on the viscoplastic response and collapse of the titanium alloy tubes subjected to cyclic bending. Based on the capacity of the bending machine, three different curvature-rates were used to highlight the viscoplastic behavior of the titanium alloy tubes. The Curvature-controlled experiments were conducted by the curvature-ovalization measurement apparatus which was designed by Pan et al. (1998). It can be observed from experimental data that the higher the applied curvature-rate, the greater is the degree of hardening of titanium alloy tube. However, the higher the applied curvature-rate, the greater is the degree of ovalization of tube cross-section. Furthermore, due to the greater degree of the ovalization of tube cross-section for higher curvature-rates under cyclic bending, the number of cycles to produce buckling is correspondingly reduced. Finally, the theoretical formulation, proposed by Pan and Her (1998), was modified so that it can be used for simulating the relationship between the controlled curvature and the number of cycles to produce buckling for titanium alloy tubes under cyclic bending with different curvature-rates. The theoretical simulation was compared with the experimental test data. Good agreement between the experimental and theoretical results has been achieved.

Laser Bending of Tubes: Mechanism, Analysis, and Prediction

Laser bending of tubes is a process in which laser-induced thermal distortion is used to bend tubes without hard tooling or external forces. Mechanisms of the process are examined to better understand the deformation characteristics such as wall thickness variation, cross-section ovalization, bending radius, and asymmetry. Factors important to these characteristics are experimentally and numerically investigated. Temporal and spatial distributions of temperature and stress/strain obtained from experimentally validated simulation models are also used to better understand additional phenomena accompanying the process, and to help devise ways to improve the process such as reducing asymmetry. A closed-form expression for the bending angle is proposed.

An experimental study on creep deformation of thin-walled tubes under pure bending

The creep deformation of pure bending (hold constant moment for a period of time) tests were conducted in this paper. Thin-walled tubes of 304 stainless steel were used in this investigation. The curvature-ovalization measurement apparatus, designed by Pan et al. (1998), was used for conducting the present experiments. It has been found that as soon as the creep deformation is started, the magnitudes of the tube curvature and ovalization of tube cross-section quickly increase. The magnitudes of the creep curvature and ovalization of tube cross-section increase fast with a higher hold moment than that with a lower one. Owing to the continuously increasing curvature during the creep deformation, the tube specimen buckles eventually.

Inelastic Response and Stability of Titanium Alloy Tubes under Cyclic Bending.

The response and stability of titanium alloy tubes subjected to cyclic bending are presented in this paper. The curvature-ovalization measurement apparatus, designed by Pan et al., is used for conducting the present curvature-controlled experiments. It is observed from the moment-curvature curve that the titanium alloy tube is cyclically harden and becomes steady after a few cycles for symmetric curvature-controlled bending. However, from the ovalization-curvature curve, the ovalization of the tube cross-section increases in a ratchetting manner with the number of cycles. Owing to the progressive accumulation of the ovalization of the tube cross-section during the cyclic bending, the titanium alloy tubes buckle eventually. Theoretical formulation, proposed by Kyriakides and Shaw, is used for investigating the relationship between the magnitude of the controlled curvature range and the number of cycles to produce buckling. Good agreement between the experimental and theoretical results is achieved. Furthermore, experimental data of the titanium alloy tubes from present study are compared with the experimental results of 6061-T6 aluminum and 1018 steel tubes tested by Kyriakides and Shaw. It is shown that for similar outer diameter/wall thickness ratio, the stronger metal tube exhibits a shorter number of cycles to produce buckling.

An enhanced pipe elbow element?application in plastic limit analysis of pipe structures

In this paper, we present a new pipe elbow element based on a previous simplified model proposed by Bathe and Almeida [1, 2] and modified by Militello and Huespe [3]. It is really a beam-type element but it describes the ovalization, warping, radial expansion and non-symmetric deformation of cross-section of curved pipe with Fourier series. Therefore, it could model precisely enough a real pipe elbow structure but remains simple. The extensive loading cases are effectively implemented by the proposed numerical techniques and displacement model. The developed element is used in this paper in plastic limit analysis of pipe elbow structures. This is realized by means of a direct mathematical programming technique. Various elastic and plastic limit state analyses of straight pipes and elbow structures are presented, which illustrates the efficiency of the element and the numerical method. Copyright © 1999 John Wiley & Sons, Ltd.

Viscoplastic analysis of thin-walled tubes under cyclic bending

In this paper, different curvature-rates are controlled to highlight the characteristic of viscoplastic response in cyclic bending tests. The curvature-ovalization apparatus, which was designed by Pan et al. (1998), is used for conducting the curvature-controlled experiments on thin-walled tubular specimens for AISI 304 stainless steel under cyclic bending. The results reveals that the faster the curvature-rate implies, the fast degree of hardening of the metal tube. However, the ovalization of the tube cross-section increases when the curvature-rate increases.

Viscoplastic Collapse of Thin-Walled Tubes Under Cyclic Bending

This paper presents the experimental result on the response and stability of thin-walled tubes subjected to cyclic bending with different curvature-rates. The curvature-ovalization measurement apparatus, designed by Pan et al. (1998), was used for conducting the present curvature-controlled experiments on thin-walled tubular specimens of 304 stainless steel. It is observed that the higher the applied curvature-rate, the greater is the degree of hardening of metal tube. However, the ovalization of tube cross-section increases when the applied curvature-rate increases. Furthermore, due to the higher degree of the ovalization of tube cross-section for higher curvature-rates under cyclic bending, the number of cycles to produce buckling is correspondingly reduced.

Non-linear dynamic analysis of cantilever whipping pipes

This paper presents the results of numerical dynamic analyses of a number of pipe whip problems based on non-linear shell theory using the DYNA3D (version 6.0) finite element code. The calculations are mainly concerned with the transient deformation of the pipes during the whipping process. The main purpose of the study is to check the efficacy of a recently published theoretical elastic-plastic, hardening-softening (e-p-h-s) model for pipe whip developed by Reid et al. [1, 2]. This model is based upon beam theory but allows for the effects of ovalization of the pipe cross-section on the moment-curvature constitutive behaviour of the pipe. It is shown that the results using DYNA3D are in good agreement with both experimental data and the e-p-h-s model predictions and confirms the accuracy of the latter. While the DYNA3D study is not exhaustive, the localized shell bending deformation of whipping pipes in which ‘kinks’ are formed is reproduced with reasonable accuracy and it has permitted the effect of the strain-rate sensitivity of the yield stress of the pipe material to be examined in a preliminary manner.

A Redescription of Cylicocyclus triramosus (Nematoda: Strongyloidea): A Parasite of the Zebra, Equus burchelli antiquorum

Cylicocyclus triramosus, a rare species of Cyathostominae from the southern African Burchell's zebra (Equus burchelli antiquorum) is redescribed, and a neotype is proposed. The external leaf-crown of the species consists of 30 elements and the internal leaf-crown numerous small and clear elements. The buccal capsule is cylindrical, oval in cross section, and approximately 3 times as wide as deep. The thin walls of the buccal capsule taper anteriorly from a large ringlike, hoop-shaped thickening around the posterior margin. The dorsal gutter is nipple-shaped. The mouth collar is notched dorsally and ventrally. The dorsal ray of the copulatory bursa is slightly elongate and distinctly set off from the lateral lobes. The branches of the dorsal ray have auxiliary branches. Appendages of the genital cone consist of 2 separated, large, semilunar plates with finger-shaped processes on the margins. The vulva-to-anus distance is greater than the tail length. The species is most similar to Cylicocyclus radiatus. Cylicocyclus triramosus differs from all similar species in the presence of dorsal and ventral notches in its mouth collar. In addition, C. triramosus also has a distinctive form of male genital cone appendage. Cylicocyclus radiatus differs further from C. triramosus in lacking a dorsal gutter and having a more elongate dorsal ray and a female tail nearly equal in length to the vulva-to-anus distance.

Bending Instability of Composite Tubes

In this paper, a set of simple formulations is derived to predict the instability critical loads of orthotropic composite tubes under pure bending. The formulations are based on the assumption that the instability of an orthotropic composite tube under pure bending is due to the ovalization of its cross section. For the static instability case, the ovalization increases steadily as the curvature increases, which results in a reduction in the bending rigidity of the tube. The interaction of longitudinal bending and cross-section ovalization causes the tube to have a limit load instability. For the dynamic instability case, the instability of the tube is due to the interaction of two vibrations, one is the longitudinal bending of the tube as a beam, the other is the circumfer­ ential bending of the tube as a thin-walled shell.

Dynamic elastic instability of long circular cylindrical shells under pure bending

The present paper studies the responses and instabilities of long circular cylindrical shells subjected to dynamic pure bending. The dynamic instability characteristics of the shells subjected to a sudden step bending load of infinite duration are explored. Analysis is performed using nonlinear finite element numerical methods. Critical dynamic moments are determined through the use of Budiansky and Routh's stability criterion. Numerical predictions for the dynamic instability are compared with those static results given earlier by Brazier. The effects of shell geometry on the dynamic stability of the shells are shown. It is found that the dominating factor to affect the shell stability is the ovalization of the shell cross-section in the centre of the shell.

Thermal buckling and progressive ovalization of pipes: experiences at the TTS sodium test facility and their analysis

Two remarkable thermally induced deformation mechanisms of pipes which may have serious effects on structural integrity, thermal buckling and progressive ovalization, were observed on the horizontal piping of the sodium test facility, called TTS, with which cyclic thermal transient tests of structures had been conducted. The thermal buckling, which was caused by thermal stratification, occurred at a circumferentially welded region of the pipe where a noticeable geometrical imperfection existed. The buckling was analyzed comprehensively for this pipe, using both the finite element method and a simplified method based on Gellin's analysis results. The predictions were reasonable and gave confidence in accounting for the sodium leakage encountered at the TTS. It was also demonstrated by the finite element analyses that the progressive ovalization of the pipe cross-section from a circular to a downward triangular shape can be caused by cyclic thermal stratification under the existence of cover gas in the pipe.

Elastoplastic dynamic instability of long circular cylindrical shells under pure bending

This paper presents a numerical study which is concerned with the prediction of the response and instabilities in long circular cylindrical shells under dynamic pure bending. Of particular interest is the response of such shells, bent into the plastic range of the material, and the various instability characteristics of the shells under dynamic bending (sudden step load). It was found that the major deformation characteristic of the shells is essentially similar to that observed in the static bending when the applied moment is much smaller than the critical dynamic moment. However, when the applied moment is close to the critical dynamic moment, the ovalization of the shell cross-section was found to be localized over a length of several shell diameters in the central region, even though the response of the shell curvature was shown to be still stable in this case. When the applied moment reaches the critical dynamic moment, the response of the shell curvature was shown significantly increasing with time and the shell buckled catastrophically. For thicker shells, it was found that the development of localized ovalization of the shell cross-section is the major factor that causes shell dynamic instability. For thinner shells, however, besides the localized ovalization, the bifurcation induced by short wavelength ripples on the compressed side of the shell was also observed in the initial buckling patterns. After the bifurcation, the initial buckling pattern was replaced by the final postbuckling mode characterized by a localized sharp cupping in the centre of the shell.

Hardening-softening behaviour of tubular cantilever beams

In the large plastic deformation of a tubular cantilever beam loaded by a force at its tip, the strain hardening of the material tends to increase the load-carrying capacity, while local buckling and cross-sectional ovalization (flattening) occurring in the neighbourhood of the root tends to reduce the moment-carrying capacity and results in structural softening. Experiments were carried out for seamless mild steel tubular cantilevers of radius thickness ratio ranging from 9 to 20 to explore the development of local buckling and flattening and to examine its influence on the global load-carrying capacity of the beam. A simple theoretical model is proposed to predict the global hardening-softening behaviour of tubular cantilever beams in terms of the material properties and geometric parameters of the tube.

Bifurcation and localization instabilities in cylindrical shells under bending—I. Experiments

This two-part series of papers is concerned with the response and various instabilities which govern the behavior of circular cylindrical shells under pure bending. Part I describes the experimental part of the study and Part II presents the numerical simulation of the various phenomena observed experimentally. Experiments were conducted on long aluminum 6061-T6 shells with II different diameter-to-thickness ratios ranging from 60.5 to 19.5. For such geometries, the structural response and inherent instabilities are strongly influenced by the plastic characteristics of the material.Thinner shells were found to develop short wavelength periodic ripples on the compressed side of the shell. The shells buckled locally and collapsed soon after the appearance of the ripples. Thicker shells were found to exhibit a limit load instability as a direct consequence of the ovalization of the shell cross-section caused by bending. Following the limit load, the ovalization was found to localize, leading to the eventual collapse of the shells. For shells with intermediate D/t values, short wavelength ripples developed at the same time as localization of ovalization was recorded. The shells buckled locally and catastrophically following the development of a limit load.

An experimental investigation of the degradation and buckling of circular tubes under cyclic bending and external pressure

Cyclic bending of tubes into the plastic range of the material leads to a progressive accumulation of ovalization of the tube cross-section. Persistent cycling leads to local catastrophic buckling of the tube. This paper presents an experimental study of the problem. The main objective of the study was to establish the effect of the cyclic bending history and of the external presdure on the rate of accumulation of ovalization and on the onset of instability. The cyclic loading histories examined include curvature symmetric bending, bending about a mean value of curvature and moment-controlled bending about a mean value of moment. The rate at which ovalization accumulates in curvature-controlled cyclic bending was found not to be significantly affected by a mean curvature in the cycles. Moment-controlled bending about a mean moment leads to ratcheting in curvature as well as in ovalization. External pressure accelerates the accumulation of ovalization and leads to buckling in fewer cycles than in the corresponding pure bending cases. This was found to be true for all bending histories considered. Significant similarities were observed between the response and onset of instability in the monotonic bending case and all cyclic bending cases. For a group of aluminum tubes instability was found to occur when the ovalization of the cross-section reached a critical value. This critical value was found to be relatively independent of the bending history followed.

Analysis of pipe bends using pipe elbow element

The formulation of a simple and effective pipe elbow element for the analysis of pipe bends is presented. The element is enhanced to capture the general shell behaviour of elbows. The formulation is based on the curved beam theory incorporating shear as well as cross-section ovalization effects. The ovalization of the cross-section varies cubically along the element length. The formulation has been implemented in the computer program ELBOW and sample results are presented. The validity of the formulation is substantiated by comparison with other numerical and experimental results available in the literature.

Physical Properties, Sensory Receptors and Tactile Reflexes of the Antenna of the Australian Freshwater Crayfish Cherax Destructor

ABSTRACT The antennal flagellum of the crayfish Cherax destructor is very flexible, tapered and is almost as long as the body in mature animals. It consists of a series of short segments, oval in cross-section, that take the form of flattened rings at the base and slender tubes at the tip. There are no muscles in the flagellum. The flagellum’s mechanical resistance to being bent is not the same in all directions. It is most easily bent dorsally and least easily bent medially, when held stretched out horizontally in front of the animal. The resistance to bending is 10 times less than that of Astacus. The individual segments of the flagellum form curved articulating surfaces that may assist in reducing torsional movement of the flagellum when it is bent and, together with the tapered form, provide the flagellum with unique mechanical properties. Four main types of hairs are found on the flagellum. They are distributed in a specific manner, and total about 7000 hairs on the flagellum of a mature animal. Cross-sections through the sensory nerve reveal only about 2000 axons. Methylene blue applied to fresh preparations stains dendrites to all smooth hairs but never to procumbent feathered hairs. Physiological recordings from the sensory axons of the flagellar nerve allowed the characterization of the sensory hair response to displacement. Recordings were also made from slowly adapting receptors, sensitive to bending the flagellum in particular directions, but not related to mechanoreceptive hairs. Intracellular recordings from identified extensor and flexor motoneurones revealed the ordered projection of the inputs from the receptor hairs, and also provided a model that correlates specific receptor inputs with particular antennal reflexes, and links the unique mechanical properties of the flagellum with the detection of the distance of near objects.