A Nondestructive Differential-Pressure Test for Thin Shells

1953 ◽  
Vol 20 (1) ◽  
pp. 48-52
Author(s):  
J. C. New
Keyword(s):  
Thin Shell ◽  
Salient Feature ◽  
External Pressure ◽  
Differential Pressure ◽  
Thin Shells ◽  
Pressure Test ◽  
Shell Design ◽  
Mechanical Factors ◽  
The Difference ◽  
Internal Volume

Abstract The differential-pressure test is an original, nondestructive, experimental technique for determining incipient buckling pressures of thin shells subjected to external pressure. Extensions of the basic test permit study of many buckling parameters as well as other mechanical factors in thin-shell design and evaluation. The salient feature of the technique is the filling of the internal volume of the shell with a compressible fluid, such as water, to control the magnitude and rate of shell deformation. The incipient buckling pressure is detected by noting the point at which the difference in internal and external pressure becomes constant. Experimental verification of the technique and its nondestructive aspect is presented. Applications and limitations of the test are discussed.

scholarly journals The thickness functions of the shells of revolution subjected to axisymmetrical loads

2005 ◽  
Vol 27 (2) ◽  
pp. 66-73
Author(s):  
Ngo Huong Nhu ◽  
Pham Hong Nga
Keyword(s):  
Differential Equations ◽  
Thin Shell ◽  
Numerical Solutions ◽  
External Pressure ◽  
Shells Of Revolution ◽  
Varying Thickness ◽  
Shell Design ◽  
Mathematical Difficulties ◽  
Thickness Function

The inverse problems for determining the meridian shape or varying thickness function of momentless shells of revolution under given loads were concerned in many works [2, 3, 4]. However, for the complexity of loads or configuration of a shell these problems haven' t bee.n solved perfectly because of its mathematical difficulties. In this paper, the problem for determining the thickness function of shells of revolution such as a parabola, sphere arc! under axisymmetrical loads is considered. The general integro-differential equations for determination of the meridian form and shell thickness are obtained. A solution of differential equations by semi-analytical and numerical methods for the thickness is presented. The numerical solutions are given for the parabola under external pressure, the sphere immerged in the fluid and the sphere arc. Obtained results may be used in the thin shell design.

On One Imperfection Estimation Method for Thin Shell Buckling in the Design Code RCC-MR

2019 ◽  
Vol 5 (4) ◽  
Author(s):  
Ashok Kumar ◽  
Anindya Chatterjee
Keyword(s):  
Thin Shell ◽  
Estimation Method ◽  
External Pressure ◽  
Alternative Methods ◽  
Design Code ◽  
Linear Elastic ◽  
The Third ◽  
Quantification Method ◽  
Shell Buckling ◽  
Shell Design

The thin shell design code RCC-MR is used for sodium-cooled fast breeder reactor components operating at high temperatures. Thin shells from such applications can be designed using linear elastic buckling analysis, following procedures given in RCC-MR. For human safety, such procedures can and should be examined by the broader scientific community. Among such procedures, RCC-MR provides three alternative methods to quantify an imperfection value; and that value is used in subsequent calculations to determine safe loads. Of these methods, the third seems potentially nonconservative for some situations. Here, we examine that third method using detailed numerical examples. These examples, found by trial and error, are the main contribution of this paper. The first example is a nonuniform cylindrical shell closed with a spherical endcap under external pressure. The second is a cylinder with an ellipsoidal head under internal pressure. The third is an L-shaped pipe with an end load. In all three cases, the new computed imperfection quantity is found to be surprisingly small compared to the actual value used for computations (e.g., 25 times smaller), and in two cases, the result is insensitive to the actual imperfection. We explain how the three examples “trick” the imperfection quantification method in three different ways. We suggest that this imperfection quantification method in RCC-MR should be re-examined. The primary value of our paper lies not in new mechanics, but in identifying unexpected ways in which a particular step in shell design using RCC-MR could be potentially nonconservative.

Surfaces, Interfaces, and Changing Shapes in Multilayered Films

MRS Bulletin ◽  
1999 ◽  
Vol 24 (2) ◽  
pp. 39-43 ◽  
Author(s):  
Daniel Josell ◽  
Frans Spaepen
Keyword(s):  
Free Energy ◽  
Excess Free Energy ◽  
External Pressure ◽  
Electronic Density ◽  
Spherical Drop ◽  
Crystal Anisotropy ◽  
Fundamental Quantity ◽  
The Difference ◽  
Image Position ◽  
Work Done

It is generally recognized that the capillary forces associated with internal and external interfaces affect both the shapes of liquid-vapor surfaces and wetting of a solid by a liquid. It is less commonly understood that the same phenomenology often applies equally well to solid-solid or solid-vapor interfaces.The fundamental quantity governing capillary phenomena is the excess free energy associated with a unit area of interface. The microscopic origin of this excess free energy is often intuitively simple to understand: the atoms at a free surface have “missing bonds”; a grain boundary contains “holes” and hence does not have the optimal electronic density; an incoherent interface contains dislocations that cost strain energy; and the ordering of a liquid near a solid-liquid interface causes a lowering of the entropy and hence an increase in the free energy. In what follows we shall show how this fundamental quantity determines the shape of increasingly complex bodies: spheres, wires, thin films, and multilayers composed of liquids or solids. Crystal anisotropy is not considered here; all interfaces and surfaces are assumed isotropic.Consideration of the equilibrium of a spherical drop of radius R with surface free energy γ shows that pressure inside the droplet is higher than outside. The difference is given by the well-known Laplace equation:This result can be obtained by equating work done against internal and external pressure during an infinitesimal change of radius with the work of creating a new surface.

scholarly journals Effects of Casting Conditions for Reduced Pressure Test on Melt Quality of Al-Si Alloy

Metals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 1422
Author(s):  
Ho Sung Jang ◽  
Ho Jung Kang ◽  
Jin Young Park ◽  
Yoon Suk Choi ◽  
Sunmi Shin
Keyword(s):  
Sampling Method ◽  
Hydrogen Diffusion ◽  
Heating Temperature ◽  
Reduced Pressure ◽  
Hydrogen Diffusion Coefficient ◽  
Atmospheric Exposure ◽  
Pressure Test ◽  
The Difference ◽  
The One

The present study investigated the effect of the casting conditions for the reduced pressure test (RPT) on the melt quality of Al-Si alloy. The casting conditions considered in RPT were the atmospheric exposure during melting, sampling method, and mold pre-heating temperature. Density Index (DI) was measured to quantify the melt quality of the Al-Si alloy casted with the different casting conditions for the RPT. The sample with blocking atmospheric exposure during melting was 5.6% lower in DI than the one without blocking. DI showed a 1.9% gap between scooping-out and pouring sampling methods. Increasing mold pre-heating temperature from 100 °C to 250 °C increased the DI of the alloy from 8.5% to 18.7%. On the other hand, when the mold pre-heating temperature was 350 °C, the DI of the alloy dropped sharply to 0.9%. The melt quality of the alloys was analyzed by measuring the pores and microstructure and simulating the solidification of the samples. It was presumed that the oxides and inclusions in the molten alloys caused the difference in DI according to the atmospheric exposure and the sampling method. The difference in DI according to the mold pre-heating temperature could be understood by calculating the solidification starting time and hydrogen diffusion coefficient during the solidification of the alloys in RPT.

scholarly journals Optimum Design of Structural Parameters for Thin-walled Metal Container

2019 ◽  
Vol 288 ◽  
pp. 01007
Author(s):  
Liao Hongbo ◽  
Yang Dan ◽  
Yin Fenglong ◽  
Liang Xiaodong ◽  
Li Erkang ◽  
...  
Keyword(s):  
Structural Parameters ◽  
Optimization Method ◽  
External Pressure ◽  
Test System ◽  
Manufacturing Cost ◽  
Thin Wall ◽  
Pressure Test ◽  
Critical Instability ◽  
Thin Walled ◽  
Better Than

In order to further increase the volume, reduce the weight and manufacturing cost, the key structural parameters of thin-walled metal packing container are optimized. The instability conditions under circumferential external pressure and axial load are analyzed, a mathematical model with the constraint of critical instability strength, the maximum volume and minimum mass as the objective is constructed. Multi-objective optimization method with nonlinear constraints is used to solve the key structural parameters, such as wall thickness, diameter and height, and the optimization result is calculated by fgoalattain() function in the Matlab optimization toolbox. The instability pressure test system is constructed, the instability pressure of the optimized thin-wall metal packing container is tested. The results show that the unstable pressure is higher than 120kPa, which are better than the design index.

On the Dynamic Stability of Fluid-Conveying Pipes

1973 ◽  
Vol 40 (1) ◽  
pp. 48-52 ◽  
Author(s):  
D. S. Weaver ◽  
T. E. Unny
Keyword(s):  
Potential Theory ◽  
Dynamic Stability ◽  
Thin Shell ◽  
Critical Flow ◽  
Thin Shells ◽  
Classical Potential ◽  
Classical Potential Theory ◽  
Limiting Case ◽  
Beam Mode ◽  
Fluid Conveying Pipes

This paper presents a general analysis of the dynamic stability of a finite-length, fluid-conveying pipe. The Flu¨gge-Kempner equation is used in conjunction with classical potential theory so that circumferential modes as well as the usual beam modes may be considered. The cylinders are found to become unstable statically at first but flutter is predicted for higher velocities. The critical flow velocities for short, thin shells are associated with a number of circumferential waves. This number reduces for thicker and longer shells until the instability is in a beam mode. When the limiting case of a long thin shell is taken, it is found to agree with previous results obtained using a simpler beam approach.

Effects of Molecularly Thin Liquid Lubricant Film Materials on Slider Hysteresis Instability in Hard Disk Drives

2007 ◽  
Author(s):  
Norio Tagawa ◽  
Daisuke Tanaka ◽  
Atsunobu Mori
Keyword(s):  
Hard Disk Drives ◽  
Disk Surface ◽  
Intermolecular Forces ◽  
Experimental Results ◽  
Disk Drives ◽  
Friction Forces ◽  
Liquid Lubricant ◽  
Pressure Test ◽  
Lower Mobility ◽  
The Difference

In this study, the difference in the touchdown and takeoff pressures was monitored by using three types of lubricant materials, namely, Zdol2000, Ztetraol2000 and A20H2000 by using the pump down pressure test. The results indicated that the touchdown pressures depended on the lubricant materials; it was greatest for Ztetraol2000 and smallest for A20H2000. The takeoff pressure was greater for a lubricant with lower mobility. Considering these experimental results, it was suggested that the variation in the touchdown pressure is due to a variation in the intermolecular forces, taking into account the lubricant pickup by a slider. Further, it was suggested that the variation in the takeoff pressure is caused by a variation in the friction forces between the slider and disk surface.

scholarly journals Ischaemic wound complications in above-knee amputations in relation to the skin perfusion pressure

1980 ◽  
Vol 4 (2) ◽  
pp. 81-86 ◽  
Author(s):  
P. Holstein
Keyword(s):  
Complication Rate ◽  
Perfusion Pressure ◽  
Wound Complication ◽  
External Pressure ◽  
Wound Complications ◽  
Local Skin ◽  
Skin Perfusion ◽  
Skin Perfusion Pressure ◽  
The Difference

Healing of the stumps in 59 above-knee amputations was correlated with the local skin perfusion pressure (SPP) measured pre-operatively as the external pressure required to stop isotope washout using 131I-- or 125I--anti-pyrine mixed with histamine. Out of the 11 cases with an SPP below 30 mmHg no fewer than 9 (82 per cent) suffered wound complications. Out of the 48 cases with an SPP above 30 mmHg severe wound complications occurred in only 4 cases (8 per cent). The difference in wound complication rate is highly significant (P<0.01). It is concluded that the SPP can be used to predict ischaemic wound complications in above-knee amputations as has previously been shown to be the case in below-knee amputations.

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