Discussion of “Mechanics of Confined Thin-Walled Cylinders Subjected to External Pressure,” (Vasilikis, D., and Karamanos, S., 2014, Appl. Mech. Rev., 66(1), p. 010801)

2013 ◽  
Vol 66 (1) ◽  
Author(s):  
Arnold M. Gresnigt
Keyword(s):  
Mechanical Properties ◽  
Residual Stresses ◽  
Experimental Test ◽  
Mechanical Response ◽  
External Pressure ◽  
Strain History ◽  
Test Results ◽  
Fabrication Method ◽  
Collapse Pressure ◽  
Thin Walled

The collapse pressure of confined cylinders depends on many factors. In addition to the thorough investigations of Vasilikis and Karamanos, more factors can be candidates for further investigation, such as the effect of variations in the material mechanical properties of the liner pipe in compression and the effect of residual stresses. The mechanical response of the materials in compression depends on the type of steel and the stress-strain history, which depends on the fabrication method of the cylinder. This is illustrated with theoretical and experimental results on pipes under external pressure, as used in offshore applications. There is a need for more experimental test results for validation. More applications of confined cylinders are mentioned that are worth investigation.

Response of Cold Sprayed Ti6Al4V Coatings to Solid Particle Erosion and Micro-Scratch Wear Processes

2018 ◽  
Vol 941 ◽  
pp. 1680-1685 ◽  
Author(s):  
Miguel Ángel Garrido ◽  
Paloma Sirvent ◽  
Daniel Elvira ◽  
Álvaro Rico ◽  
Claudio J. Múnez ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Residual Stresses ◽  
Solid Particle ◽  
Cold Spray ◽  
Mechanical Response ◽  
Operating Time ◽  
Wear Behaviour ◽  
Solid Particle Erosion ◽  
Particle Erosion ◽  
Spray Technique

Ti6Al4V alloy is widely used for aeronautical components due to a special combination of high mechanical properties, low density and good corrosion resistance at high temperature. These components are usually damaged by particles impacts during their operating time. When the reliability of these components is compromised, they are replaced with the consequent cost of material and time. Spraying coatings on the damaged surface could reveal as an alternative process to repair these components, increasing their operating life. Traditionally, thermal spray processes are used to repair the aeronautical components. However, the coatings produced by these processes are characterized by high residual stresses, porosity and oxidation. The cold spray technique is revealed as a promising spraying alternative due to the characteristic low temperature of the process. Consequently, residual stresses, oxidation, crack formation, phase transformations and microstructural changes are minimized. In this work, a cold spray technique was used to generate Ti6Al4V coatings onto a bulk of the same material. Three different spraying conditions were studied: Ti6Al4V coatings sprayed at 800oC; Ti6Al4V coatings sprayed at 1100oC; and Ti6Al4V coatings sprayed at 1100oC with a subsequent heat treatment: The wear resistance of these coatings was investigated by solid particle erosion and micro-scratch tests. The wear behaviour was determined under several wear tests conditions. Additionally, instrumented indentation tests were carried out on the coatings to determine their mechanical response. The wear mechanisms of the coatings were identified and compared to their microstructure and mechanical properties.

A Simple Procedure for the Prediction of the Collapse Pressure of Pipelines With Narrow and Long Corrosion Defects: Uncertainty and Sensibility Analysis

2018 ◽  
Author(s):  
Nara Oliveira ◽  
Theodoro Netto
Keyword(s):  
Simple Procedure ◽  
Experimental Tests ◽  
External Pressure ◽  
Experimental Program ◽  
Small Scale ◽  
Test Results ◽  
Collapse Pressure ◽  
Operational Conditions ◽  
Sensibility Analysis ◽  
Corrosion Defects

The collapse pressure of pipelines containing corrosion defects is usually predicted by deterministic methods, either numerically or through empirical formulations. The severity of each individual corrosion defect can be determined by comparing the differential pressure during operation with the estimated collapse pressure. A simple deterministic procedure for estimating the collapse pressure of pipes with narrow and long defects has been recently proposed by Netto (2010). This formulation was based on a combined small-scale experimental program and nonlinear numerical analyses accounting for different materials and defect geometries. However, loads and resistance parameters have uncertainties which define the basic reliability problem. These uncertainties are mailyrelated to the geometric and material parameters of the pipe and the operational conditions. This paper presents additional experimental tests on corroded pipes under external pressure. The collapse pressure calculated using the equation proposed by Netto (2010) is compared with this new set of experiments and also with test results available in open literature. These results are used to estimate the equation uncertainty. Finally, a sensitivity analysis is performed to identify how geometric parameters of the defects influence the reduction of collapse pressure.

scholarly journals Investigation on the Mechanical Properties of Fiber Reinforced Recycled Concrete

2016 ◽  
Vol 2 (1) ◽  
pp. 13-22 ◽  
Author(s):  
Hasan Jalilifar ◽  
Fatholla Sajedi ◽  
Sadegh Kazemi
Keyword(s):  
Mechanical Properties ◽  
Flexural Strength ◽  
Experimental Test ◽  
Fiber Volume Fraction ◽  
Volume Fraction ◽  
Fiber Content ◽  
Recycled Concrete ◽  
Test Results ◽  
Fiber Volume ◽  
Flexural Toughness

The flexural strength of conventional concrete material is known to be enhanced by incorporating a moderate volume-fraction of randomly distributed fibers. However, there is limited information on describing the influence of fiber volume-fraction on the compressive and flexural strength of recycled coarse aggregate concrete (RCA-C) material. This paper reports on experimental test results of the RCA-C material replaced with 0, 30, 50 and 100% recycled aggregate and 0, 0.5, 1 and 1.5% steel fiber volume fraction. Three-point flexural tests of notched prism specimens were completed. The mechanical properties in compression were characterized using cube specimens. Significant improvement in compressive and flexural strength of RCA-C was found as fiber content increased from 0 to 1.5%. The experimental test results of RCA-C were further evaluated to investigate the influence of fiber content on flexural toughness. According to test results, the addition of steel fibers to RCA-C material appreciably increased the flexural toughness.

Mechanics of Confined Thin-Walled Cylinders Subjected to External Pressure

2013 ◽  
Vol 66 (1) ◽  
Author(s):  
Daniel Vasilikis ◽  
Spyros A. Karamanos
Keyword(s):  
Mechanical Response ◽  
Surrounding Medium ◽  
External Pressure ◽  
Numerical Results ◽  
Maximum Pressure ◽  
Imperfection Sensitivity ◽  
Nonlinear Finite Elements ◽  
Good Comparison ◽  
Practical Engineering ◽  
Thin Walled

Motivated by practical engineering applications, the present paper examines the mechanical response of thin-walled cylinders surrounded by a rigid or deformable medium, subjected to uniform external pressure. Emphasis is given to structural stability in terms of buckling, postbuckling, and imperfection sensitivity. The present investigation is computational and employs a two-dimensional model, where the cylinder and the surrounding medium are simulated with nonlinear finite elements. The behavior of cylinders made of elastic material is examined first, and a successful comparison of the numerical results is conducted with available closed-form analytical solutions for rigidly confined cylinders. Subsequently, the response of confined thin-walled steel cylinders is examined. The numerical results show an unstable postbuckling response beyond the point of maximum pressure and indicate severe imperfection sensitivity on the value of the maximum pressure. A good comparison with limited available test data is also shown. Furthermore, the effects of the deformability of the surrounding medium are examined. In particular, soil embedment conditions are examined, with direct reference to the case of buried thin-walled steel pipelines. Finally, based on the numerical results, a comparison is attempted between the present buckling problem and the problem of “shrink buckling.” The differences between those two problems of confined cylinder buckling are pinpointed, emphasizing the issue of imperfection sensitivity.

Residual Stresses and Accuracy of Pipe Preparations by Manufacture Zirconium Tubes for the Nuclear Industry

2006 ◽  
Vol 524-525 ◽  
pp. 703-708 ◽  
Author(s):  
G. Kolmogorov ◽  
E. Kuznetsova ◽  
V. Filippov
Keyword(s):  
Mechanical Properties ◽  
Residual Stresses ◽  
Zirconium Alloys ◽  
Deformation Energy ◽  
Nuclear Industry ◽  
Technological Parameters ◽  
Actual Problem ◽  
Production Technologies ◽  
Thin Walled ◽  
Fuel Elements

The production technologies development of thermonuclear reactors is a actual problem of today. The work researches zirconium goods used in the atomic industry – thin-walled tubes for the fuel elements shells, thin-walled tubes for the channels of watery and boiling reactors, rods for lock – plugs of fuel elements; mechanical properties of zirconium and zirconium alloys, production methods and technologies as well. The power approach is used in the work. The potential energy of the elastic deformation is regarded as a part of the plastic deformation energy and a portion of the energy used for residual stresses formation. Using these methods the distributions of residual stresses are determined by the volume of a product depending on the main technological parameters of a process and mechanical properties of the material. The results have shown that hoop stresses take maximum values. The activity of residual stresses can lead to the elastic deformations and to the departure from the rated dimensions of a product, subsequently, that is inadmissible for the precision parts. These methods are used to determine the influence of residual stresses on mechanical properties, precision and operating strength of tube products made of different zirconium alloys.

Effects of Reeling on Pipe Structural Performance—Part I: Experiments

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Stelios Kyriakides
Keyword(s):  
Mechanical Properties ◽  
Local Buckling ◽  
External Pressure ◽  
Structural Performance ◽  
Plastic Range ◽  
Cross Sectional ◽  
Collapse Pressure ◽  
Bending Strain ◽  
Testing Facility ◽  
Different Levels

The winding and unwinding of a pipeline in the reeling installation process involve repeated excursions into the plastic range of the material, which induce ovality, elongation, and changes to the mechanical properties. The reeling/unreeling process involves some back tension required to safeguard the pipe from local buckling. This study examines the effects of winding/unwinding a pipe on a reel at different values of tension on the induced ovality and elongation and the resulting degradation in collapse pressure. In Part I, a model testing facility is used to simulate the reeling/unreeling process in the presence of tension. The combination of reel and tube diameters used induces a bending strain of 1.89%. A set of experiments involving three reeling/unreeling cycles at different levels of tension is performed on tubes with diameter-to-thickness ratios (D/t) of 20 and 15.5 in which the progressive changes in cross-sectional geometry and elongation are recorded. Both ovalization and elongation are shown to increase significantly as the back tension increases. A second set of experiments on the same two tube D/ts is performed in which following a reeling/unreeling cycle at a chosen level of tension, the tubes are collapsed under external pressure. The collapse pressure is shown to decrease significantly with tension, which is primarily caused by the reeling/unreeling-induced ovality. Part II presents models for simulating reeling and the induced structural degradation. The experimental results in Part I are used to evaluate the performance of the models.

scholarly journals Design and predicting performance of carbon nanotube reinforced cementitious materials : mechanical properties and dipersion characteristics.

2020 ◽  
Author(s):  
Mahyar Ramezani
Keyword(s):  
Mechanical Properties ◽  
Elastic Modulus ◽  
Aspect Ratio ◽  
Flexural Strength ◽  
Experimental Test ◽  
Cementitious Materials ◽  
Matrix Composition ◽  
Cement Matrix ◽  
Test Results ◽  
Cement Ratio

Recently, Carbon Nanotubes (CNTs) are drawing considerable attention of researchers for reinforcing cementitious materials due to their excellent mechanical properties and high aspect ratio (length-to-diameter ratio). However, CNTs might not disperse well within the cement matrix, resulting in little improvement or even degradation of concrete properties. The uncertainty in producing the consistent results in different studies might be attributed to multiple interactions between the experimental variables affecting the nanotube dispersion and the final properties of CNT-cement nanocomposites. Therefore, this research mainly focused on proposing equations that can reliably capture these interactions in order to correlate CNT dispersion with the mechanical properties. The main experimental variables studied included CNT concentration, aspect ratio, ultrasonication energy, ultrasonication amplitude, surfactant-to-CNTs ratio, water-to-cement ratio, sand-to-cement ratio, and hydration age of specimen. The study reported in this research was conducted in two parts: experimental program and modeling. In the experimental part of this research, a total of 63 different mix proportions were used to evaluate the flowability, mechanical properties, and durability characteristics of cement pastes and mortars containing CNTs. Using experimental test results reported in this study and the literature, three critical relations were proposed to consider the CNT dispersion, cement matrix composition, and hydration age of cement. The proposed critical relations were then added to available theoretical models in the literature. The flexural strength and elastic modulus of CNT-cement nanocomposites were predicted through a state-of-the-art probabilistic model using a Bayesian methodology. Finally, the developed probabilistic models were used to identify the optimum ranges of the experimental variables to maximize the mechanical properties. This was done through computing the conditional probability of not meeting the specified design requirement. The experimental results indicated that addition of CNTs could significantly improve different properties of cementitious materials, if the optimum range of each variable was used. Also, to achieve the desired mechanical properties, various combinations of the experimental variables might be used. The proposed prediction models were shown to capture the interactions between the experimental variables for predicting the mechanical properties within ±15% and ±18% of the experimental test results for flexural strength and elastic modulus, respectively. Based on the findings of this research, contour plots were developed to provide practical guidelines for future engineers to design CNT-cement nanocomposites.

scholarly journals Investigation of the frequency of free vibrations for pipelines with different physical and mechanical properties of the material

2020 ◽  
Vol 7 (1) ◽  
Author(s):  
Andrey Dmitriev
Keyword(s):  
Mechanical Properties ◽  
Large Diameter ◽  
Physical And Mechanical Properties ◽  
External Pressure ◽  
Pipe Length ◽  
Shell Form ◽  
Underground Pipelines ◽  
Elastic Resistance ◽  
Ground Conditions ◽  
Thin Walled

This paper raises the question of a new approach to the dynamic calculation of thin-walled underground pipelines of large diameter, which is based on the application of the Vlasov-Novozhilov half-time theory of medium-bend shells, which ignores the M1 moments that bend the cylindrical shell in the longitudinal direction, since they are much smaller than the M2 moments that bend it in the transverse direction. The resolving equation for this approach is a homogeneous 4th-order differential equation that uses two boundary conditions at each end to solve it. The resulting equation takes into account the parameter of the longitudinal force, the value of the internal pressure, the coefficient of elastic resistance of the soil, the parameter of thinness, as well as the attached mass of the soil. Based on the data obtained from the derived formulas, the frequency characteristics of thin-walled underground pipelines of large diameter with different physical and mechanical properties are determined depending on the length of the element, as well as ground conditions. It is established that the minimum frequencies for the shell form of vibrations in various ground conditions are realized only for steel pipes, and for polyethylene and fiberglass pipes, depending on the coefficient of elastic resistance of the soil, they can be realized both in the rod and shell form. At the same time, using a dynamic stability criterion, derived expressions to determine the critical external pressure, taking into account the pipe length and the number of half waves in the cross section in which there is a constructive denial of the pipeline. Based on this expression, a formula for determining the critical depth of laying for thin-walled pipelines is obtained.

Optimization of UOE Pipe Manufacturing Process for Improved Collapse Performance Under External Pressure

2006 ◽  
Author(s):  
Stelios Kyriakides ◽  
Mark D. Herynk ◽  
Heedo Yun
Keyword(s):  
Mechanical Properties ◽  
Parametric Study ◽  
Large Diameter ◽  
External Pressure ◽  
Material Degradation ◽  
Forming Process ◽  
Cold Forming ◽  
Collapse Pressure ◽  
Large Diameter Pipes ◽  
Pipe Manufacturing

Large-diameter pipes used in offshore applications are commonly manufactured by cold-forming plates through the UOE process. Collapse experiments have demonstrated that these steps, especially the final expansion, degrade the mechanical properties of the pipe and result in a reduction in its collapse pressure, upwards of 30%. In this study, the UOE forming process has been modeled numerically so that the effects of press parameters of each forming step on the final geometry and mechanical properties of the pipe can be established. The final step involves simulation of pipe collapse under external pressure. An extensive parametric study of the problem has been conducted, through which ways of optimizing the process for improved collapse performance have been established. For example, it was found that optimum collapse pressure requires a tradeoff between pipe shape (ovality) and material degradation. Generally, increase in the O-strain and decrease in the expansion strain improve the collapse pressure. Substituting the expansion by compression can not only alleviate the UOE collapse pressure degradation but can result in a significant increase in collapse performance.

Elastoplastic Collapse of Tubes Under External Pressure

1970 ◽  
Vol 92 (4) ◽  
pp. 735-742 ◽  
Author(s):  
O. Heise ◽  
E. P. Esztergar
Keyword(s):  
Safety Factor ◽  
External Pressure ◽  
Code Design ◽  
Test Results ◽  
Plastic Range ◽  
Safety Factors ◽  
Characteristic Ratio ◽  
Collapse Pressure ◽  
Asme Code ◽  
Current Design

The specific objective of this paper is to develop external pressure design safety factors that are consistent with theory, test results, and service experience for application in pressure vessel codes. The standard methods of collapse pressure predictions for the buckling of tubes in the elastic and the plastic ranges are briefly reviewed. Test results on tubes made of various materials were collected from the literature and are compared with the corresponding predictions. For thin tubes which buckle in the elastic range, the correlation between the theory and experimentally measured collapse pressure is shown to be poor, justifying the large safety factors used in current design practice. For intermediate and thick tubes which buckle in the plastic range, it is demonstrated that the correlation of test results and theory improves significantly with decreasing radius-to-thickness ratio of the tubes. The range of improved correlation is identified by a material dependent “characteristic ratio” of tube radius and wall thickness. Based on the experimental evidence, a variable safety factor is proposed for inclusion in the ASME Code design charts. A simple formula for the conversion of the present plastic range allowable pressure into the new increased allowable pressure is presented. The consequences of the variable safety factor are discussed with respect to the resulting actual margin of safety, the economic advantages, and the requirements for the development of design rules for the creep range.

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