Comparison of Ellipsoidal and Equivalent Torispherical Heads Under Internal Pressure: Buckling, Plastic Collapse and Design Rules

2020 ◽  
Vol 143 (2) ◽  
Author(s):  
Jinyang Zheng ◽  
Yehong Yu ◽  
Yehong Chen ◽  
Keming Li ◽  
Zekun Zhang ◽  
...  
Keyword(s):  
Failure Modes ◽  
Good Prediction ◽  
Plastic Collapse ◽  
Design Equation ◽  
Fe Method ◽  
Shape Deviation ◽  
Design Rules ◽  
Collapse Pressure ◽  
Current Design ◽  
The Difference

Abstract Ellipsoidal and torispherical heads, whose geometric shapes are close, are usually used as end closures of internally pressurized vessels. In pressure vessel codes, for example, ASME BPVC Section VIII and EN13445-3, ellipsoidal heads are designed as torispherical heads using geometric equivalency approaches. However, the difference between ellipsoidal and equivalent torispherical heads has not been studied in detail. In this paper, we first investigate shape deviation between the two types of heads. Then we compare elastic–plastic behaviors between ellipsoidal and equivalent torispherical heads as well as their failure modes, i.e., buckling and plastic collapse (bursting). It is found that ellipsoidal heads have more buckling resistance than equivalent torispherical heads, indicating that the current design rules for buckling of ellipsoidal heads based on the geometric equivalency approaches result in uneconomical design. In addition, experimental and numerical results show that such heads experience geometric strengthening. The finite element (FE) method considering the effect of geometric strengthening provides a good prediction of plastic collapse pressure. However, the current design equation for bursting does not consider the effect of geometric strengthening, also leading to uneconomical design. Therefore, in order to avoid uneconomical design, we recommend that (1) with respect to buckling of ellipsoidal heads, a new design equation be proposed rather than implementing the geometric equivalency approaches, and (2) the current design equation for bursting be deleted, and a new design equation, considering the effect of geometric strengthening, be proposed for bursting of ellipsoidal and torispherical heads.

Comparison of Ellipsoidal and Equivalent Torispherical Heads Under Internal Pressure: Buckling, Plastic Collapse and Design Rules

2019 ◽  
Author(s):  
Jinyang Zheng ◽  
Keming Li ◽  
Yehong Yu ◽  
Zekun Zhang ◽  
Wenzhu Peng ◽  
...  
Keyword(s):  
Internal Pressure ◽  
Failure Modes ◽  
Bursting Pressure ◽  
Good Prediction ◽  
Plastic Collapse ◽  
Design Equation ◽  
Fe Method ◽  
Shape Deviation ◽  
Design Rules ◽  
Current Design

Abstract Ellipsoidal and torispherical heads, whose geometric shapes are close, are usually used as end closures of internally pressurized vessels. In pressure vessel codes, for example, ASME BPVC Section VIII, ellipsoidal heads are designed as torispherical heads using geometric equivalency approaches. However, the difference between ellipsoidal and equivalent torispherical heads has not been studied in detail. In this paper, we first investigate the shape deviation between the two types of heads. Then we compare the elastic-plastic behaviors between ellipsoidal and equivalent torispherical heads as well as their failure modes, i.e., buckling and plastic collapse. It is found that ellipsoidal heads have more buckling resistance than equivalent torispherical heads, indicating that the current design rules for buckling failure based on the geometric equivalency approaches result in uneconomical design. Nevertheless, the shape deviation has little effect on plastic collapse pressures of ellipsoidal and equivalent torispherical heads, showing that the geometric equivalency approaches are applicable for such heads that fail by plastic collapse (bursting). In addition, the experimental and numerical results show that such heads experience geometric strengthening. The FE method considering the effect of geometric strengthening provides a good prediction about plastic collapse (bursting) pressure. However, the current design equation for bursting does not consider the effect of geometric strengthening, also leading to uneconomical design. Therefore, in order to avoid uneconomical design, we recommend that (1) with respect to the buckling of ellipsoidal heads, a new design equation be proposed rather than implementing the geometric equivalency approaches, and (2) the current design equation for bursting be deleted, and a new design equation, considering the effect of geometric strengthening, be proposed for the bursting of ellipsoidal and torispherical heads subjected to internal pressure.

Plastic Collapse and the Controlling Failure Pressures of Thin 2:1 Ellipsoidal Shells Subjected to Internal Pressure

1979 ◽  
Vol 101 (1) ◽  
pp. 64-72 ◽  
Author(s):  
G. D. Galletly ◽  
R. W. Aylward
Keyword(s):  
Internal Pressure ◽  
Strain Hardening ◽  
Failure Modes ◽  
Companion Paper ◽  
Plastic Collapse ◽  
Collapse Pressure

In the first part of the paper, plastic collapse pressures of thin 2:1 ellipsoidal shells are determined. The effects of E, σyp and strain hardening, S, on the collapse pressure are presented and discussed. The second part of the paper is concerned with the controlling failure pressures of internally pressurized 2:1 ellipsoidal shells. This involves the consideration of both plastic collapse pressures and asymmetric buckling pressures (the latter were obtained from a companion paper). Curves of the controlling failure pressures versus D/t are given for several values of σyp and S. Both aluminum and steel shells are considered. Dimensionless buckling and collapse pressures are also tabulated and some very simple formulas for both failure modes are suggested which should be useful to designers.

Cold-formed steel battened built-up columns: Experimental behaviour and verification of different design rules developed

2021 ◽  
pp. 136943322110480
Author(s):  
A.R. Dar ◽  
S. Vijayanand ◽  
M. Anbarasu ◽  
M. Adil Dar
Keyword(s):  
Failure Modes ◽  
Numerical Models ◽  
Experimental Studies ◽  
Design Standards ◽  
Uniform Compression ◽  
Design Rules ◽  
The North ◽  
Current Design ◽  
Cold Formed Steel ◽  
In The Beginning

Some of the past studies on cold-formed steel (CFS) battened built-up columns have resulted in the development of new design rules for predicting their axial strengths. However, the main drawbacks of such studies are that they are purely numerical and the numerical models developed for such parametric studies were validated using the test results on similar built-up column configurations, but not the exact ones. Therefore, experimental studies on CFS battened columns comprising of lipped channels are needed for verifying the accuracy of the proposed design rules for CFS battened columns. This paper reports an experimental study performed on CFS built-up battened columns under axial compression. Adequately spaced identical lipped channels in the back-to-back arrangement were used as chords and were connected by batten plates laterally with self-driving screws to form the built-up members. The dimensions of chords were fixed as per the geometric limits given out in the North American Specifications (NAS) for the design of CFS structural members. The sectional compactness of the chords and the overall slenderness of the built-up columns were varied by altering the thickness of the channels and height of the built-up columns, respectively. A total of 20 built-up sections were tested under uniform compression to investigate the behavioural changes in the built-up columns due to these variations. The behaviour assessment was made in terms of peak strengths, load–displacement response and failure modes of the test specimens. The current design standards on CFS structures were used to determine the design strengths and were compared against the test strengths for assessing their adequacy. Furthermore, as discussed in the beginning, the test strengths were used to verify the accuracy of the different relevant proposed design rules in the literature.

Design Equations for Preventing Buckling in Fabricated Torispherical Shells Subjected to Internal Pressure

1986 ◽  
Vol 200 (2) ◽  
pp. 127-139 ◽  
Author(s):  
G D Galletly
Keyword(s):  
Internal Pressure ◽  
Failure Mode ◽  
Failure Modes ◽  
Experimental Results ◽  
Design Equation ◽  
Test Results ◽  
Theoretical Predictions ◽  
The Subject ◽  
The Difference ◽  
Empirical Constants

Design rules to prevent buckling in thin fabricated torispherical shells subjected to internal pressure are not yet available in either the American or the British pressure vessel Codes. They are the subject of the present paper and some possible design equations are suggested. The equations were obtained from the buckling equations for perfect torispheres after considering all known experimental results on fabricated models. The empirical constants in the proposed design equations depend on the type of head construction used, i.e. whether crown and segment or pressed and spun. For both types of head the equations give a factor of safety of at least 1.5. The design equation proposed for the crown and segment heads was also checked on several large vessels which had failed in service. The safety factors found for these cases were all greater than 1.7, which means that the vessels would not have buckled if the design equation had been available at the time. The other failure mode of these torispherical heads, i.e. large axisymmetric deformations leading to through-thickness yielding, is also discussed briefly. Curves are given which show that, for 300 < D/t < 500, buckling controls the failure mode in some cases and axisymmetric yielding in others. Neither the American nor the British codes recognize that buckling can occur in this D/t range but the theoretical predictions have been confirmed by experiments. However, the amount of test data is limited and more work is needed on the topic. It is also shown in the paper that, for torispherical shells with D/t ratios in the range 300 < D/t < 500, the axisymmetric limit pressures, pDS, are lower than both the internal buckling pressures and the large deflection axisymmetric yielding pressures. From this, one would expect the failure modes to be axisymmetric in this D/t range. However, as some non-symmetric buckling failures have occurred, the limit analysis predictions for the failure mode are thus not always correct. One feature of the experimental results on stainless steel torispherical shells which are reviewed in the paper is the relatively poor buckling performance of the heads tested by Kemper in comparison with similar heads tested by Stanley and Campbell. As the values of the empirical constants in the design equations are controlled by the lowest test results, the higher bucking pressures obtained by Stanley/Campbell cannot be utilized unless an adequate explanation for the difference in the two sets of results is forthcoming.

scholarly journals Fatigue Resistance and Failure Behavior of Penetration and Non-Penetration Laser Welded Lap Joints

2021 ◽  
Vol 34 (1) ◽  
Author(s):  
Xiangzhong Guo ◽  
Wei Liu ◽  
Xiqing Li ◽  
Haowen Shi ◽  
Zhikun Song
Keyword(s):  
Fatigue Resistance ◽  
Failure Modes ◽  
Plate Thickness ◽  
High Stress ◽  
Lap Joints ◽  
Failure Behavior ◽  
Passenger Cars ◽  
Plate Fracture ◽  
The Difference ◽  
Railway Passenger

AbstractPenetration and non-penetration lap laser welding is the joining method for assembling side facade panels of railway passenger cars, while their fatigue performances and the difference between them are not completely understood. In this study, the fatigue resistance and failure behavior of penetration 1.5+0.8-P and non-penetration 0.8+1.5-N laser welded lap joints prepared with 0.8 mm and 1.5 mm cold-rolled 301L plates were investigated. The weld beads showed a solidification microstructure of primary ferrite with good thermal cracking resistance, and their hardness was lower than that of the plates. The 1.5+0.8-P joint exhibited better fatigue resistance to low stress amplitudes, whereas the 0.8+1.5-N joint showed greater resistance to high stress amplitudes. The failure modes of 0.8+1.5-N and 1.5+0.8-P joints were 1.5 mm and 0.8 mm lower lap plate fracture, respectively, and the primary cracks were initiated at welding fusion lines on the lap surface. There were long plastic ribs on the penetration plate fracture, but not on the non-penetration plate fracture. The fatigue resistance stresses in the crack initiation area of the penetration and non-penetration plates calculated based on the mean fatigue limits are 408 MPa and 326 MPa, respectively, which can be used as reference stress for the fatigue design of the laser welded structures. The main reason for the difference in fatigue performance between the two laser welded joints was that the asymmetrical heating in the non-penetration plate thickness resulted in higher residual stress near the welding fusion line.

Experimental Investigation into Driver Behavior along Curved and Parallel Diverging Terminals of Exit Interchange Ramps

2021 ◽  
pp. 036119812199742
Author(s):  
Alberto Portera ◽  
Marco Bassani
Keyword(s):  
Design Stage ◽  
Lane Change ◽  
Age And Gender ◽  
Traffic Conditions ◽  
Current Design ◽  
The Difference ◽  
Safety Countermeasures ◽  
And Gender ◽  
Set Up ◽  
Curve Radius

Current design manuals provide guidance on how to design exit ramps to facilitate driving operations and minimize the incidence of crashes. They also suggest that interchanges should be built along straight roadway sections. These criteria may prove ineffective in situations where there is no alternative to terminals being located along curved motorway segments. The paper investigates driving behavior along parallel deceleration curved terminals, with attention paid to the difference in impact between terminals having a curvature which is the same sign as the motorway segment (i.e., continue design), and those having an opposite curvature (i.e., reverse design). A driving simulation study was set up to collect longitudinal and transversal driver behavioral data in response to experimental factor variations. Forty-eight drivers were stratified on the basis of age and gender, and asked to drive along three randomly assigned circuits with off-ramps obtained by combining experimental factors such as motorway mainline curve radius (2 values), terminal length (3), curve direction (2), and traffic conditions (2). The motorway radius was found to be significant for drivers’ preferred speed when approaching the terminal. Terminal length and traffic volume do not have a significant impact on either longitudinal or transversal driver outputs. However, the effect of curve direction was found to be significant, notably for reverse terminals which do not compel drivers to select appropriate speeds and lane change positions. This terminal type can give rise to critical driving situations that should be considered at the design stage to facilitate the adoption of appropriate safety countermeasures.

Design Rules and Failure Modes of DMFC Stack Development

2019 ◽  
Vol 26 (1) ◽  
pp. 287-294 ◽  
Author(s):  
Youngseung Na ◽  
Seong Kee Yoon ◽  
Jungkurn Park ◽  
Jun Won Suh ◽  
Inseob Song ◽  
...  
Keyword(s):  
Failure Modes ◽  
Design Rules

Experimental-Numerical Characterization of Ordinary Concrete at the Meso-Scale

2021 ◽  
Author(s):  
GIANLUCA MAZZUCCO ◽  
Beatrice Pomaro ◽  
Giovanna Xotta ◽  
Enrico Garbin ◽  
Valentina Salomoni ◽  
...  
Keyword(s):  
Yield Criterion ◽  
Plain Concrete ◽  
Point Of View ◽  
Good Prediction ◽  
Deformation Capacity ◽  
Compression Tests ◽  
Fe Method ◽  
Stress States ◽  
Meso Scale

Modeling the post-peak behaviour of brittle materials like concrete is still a challenge from the point of view of computational mechanics, due to the strong nonlinearities arising in the material behaviour during softening and the complexity of the yield criterion that may describe their deformation capacity in generic triaxial stress states. A numerical model for plain concrete in compression is formulated within the framework of the coupled elasto-plastic-damage theory. The aim is to simulate via the Finite Element (FE) method the stress-strain behaviour of concrete at the meso-scale, where local confinement effects generally characterize the cement paste under the action of the surrounding aggregates. The mechanical characterization of the components are accomplished through a specific experimental campaign. With the subsequent validation study, it is shown that a few calibration parameters give a good prediction of load strength and deformation capacity coming from real uniaxial compression tests.

Tubular Nitinol Knit Meshes for External Reinforcement of Saphenous Vein Grafts: A Numerical Design Study

2008 ◽  
Author(s):  
Thomas Franz ◽  
Helena van der Merwe ◽  
Peter Zilla ◽  
Deon Bezuidenhout ◽  
B. Daya Reddy
Keyword(s):  
Mechanical Properties ◽  
Saphenous Vein ◽  
Vein Graft ◽  
Fe Method ◽  
Luminal Diameter ◽  
Vein Grafts ◽  
Saphenous Vein Grafts ◽  
Vascular Bypass ◽  
External Reinforcement ◽  
The Difference

The difference in mechanical properties between grafts and host arteries is a complicating factor for vascular bypass surgery and can cause patho-physiological problems after implantation [1–7]. Diffuse and focal intimal hyperplasia, one of the key factors of vein graft failure, has been attributed to over-distension and diametric irregularities of the veins when exposed to the arterial circulation [8]. The external reinforcement of saphenous vein grafts with open-mesh knitted Nitinol structures is suggested to prevent over-distension, smooth the luminal diameter, and address the mismatch in mechanical properties of vein graft and host vessel. The objectives of this work were: 1) development of Finite Element (FE) models of knitted Nitinol structures to assess mechanical behaviour and structural properties, e.g. vascular compliance, and 2) proof of feasibility of the FE method developed for structural design optimisation of the Nitinol mesh.

scholarly journals Numerical Parametric Study of Paravalvular Leak Following a Transcatheter Aortic Valve Deployment Into a Patient-Specific Aortic Root

2018 ◽  
Vol 140 (10) ◽  
Author(s):  
Wenbin Mao ◽  
Qian Wang ◽  
Susheel Kodali ◽  
Wei Sun
Keyword(s):  
Aortic Valve ◽  
Computational Model ◽  
Aortic Root ◽  
Paravalvular Leak ◽  
Patient Specific ◽  
Fe Method ◽  
Transcatheter Aortic Valve ◽  
Operative Planning ◽  
The Difference ◽  
The Impact

Paravalvular leak (PVL) is a relatively frequent complication after transcatheter aortic valve replacement (TAVR) with increased mortality. Currently, there is no effective method to pre-operatively predict and prevent PVL. In this study, we developed a computational model to predict the severity of PVL after TAVR. Nonlinear finite element (FE) method was used to simulate a self-expandable CoreValve deployment into a patient-specific aortic root, specified with human material properties of aortic tissues. Subsequently, computational fluid dynamics (CFD) simulations were performed using the post-TAVR geometries from the FE simulation, and a parametric investigation of the impact of the transcatheter aortic valve (TAV) skirt shape, TAV orientation, and deployment height on PVL was conducted. The predicted PVL was in good agreement with the echocardiography data. Due to the scallop shape of CoreValve skirt, the difference of PVL due to TAV orientation can be as large as 40%. Although the stent thickness is small compared to the aortic annulus size, we found that inappropriate modeling of it can lead to an underestimation of PVL up to 10 ml/beat. Moreover, the deployment height could significantly alter the extent and the distribution of regurgitant jets, which results in a change of leaking volume up to 70%. Further investigation in a large cohort of patients is warranted to verify the accuracy of our model. This study demonstrated that a rigorously developed patient-specific computational model can provide useful insights into underlying mechanisms causing PVL and potentially assist in pre-operative planning for TAVR to minimize PVL.

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