Technical Basis for Characterization of Multiple Closely Separated Flaws Located in Different Planes

2017 ◽  
Author(s):  
Sébastien Blasset ◽  
Tomas Nicak ◽  
Elisabeth Keim ◽  
Ralf Tiete ◽  
Florian Obermeier
Keyword(s):  
Plastic Material ◽  
Material Behavior ◽  
Specific Work ◽  
3D Numerical Modeling ◽  
Elastic Plastic ◽  
Linear Elastic ◽  
Current Interaction ◽  
Elastic Plastic Material ◽  
Technical Basis ◽  
Non Destructive

Non-destructive inspection records have to be characterized before evaluation of acceptance if they are evaluated as material or fabrication flaws. When multiple flaws are detected by volumetric examination, the question of interacting flaws arises if they are close to each other: can the conventional approach based on individual flaw be applied? Alternative flaw characterization requirements may be applied in lieu of using current codes by considering recent fracture mechanics research. In order to relax the conservatism of current interaction criteria, specific work was performed to describe interaction rules for flaws located in different planes. The proximity criteria are valid for linear elastic or limited elastic plastic material behavior : this is generally the case in large components. This paper presents the technical basis including validation of the proximity criteria based on a specific component with several flaws and considering 3D numerical modeling using elastic-plastic material behavior in order to check if the plastic material behavior affects the selected proximity criteria. The component is submitted to uniform (pressure) and non-uniform loading (like thermal shock).

Fatigue Evaluation in Mixing Zones: Comparison of Different Criteria of Fatigue

2008 ◽  
Author(s):  
J. M. Stephan ◽  
C. Gourdin ◽  
J. Angles ◽  
S. Quilici ◽  
L. Jeanfaivre
Keyword(s):  
Fatigue Damage ◽  
Thermal Stresses ◽  
Plastic Material ◽  
Material Behavior ◽  
Damage Evaluation ◽  
Elastic Plastic ◽  
Different Types ◽  
Elastic Plastic Material ◽  
Fatigue Evaluation

The distribution of unsteady temperatures in the wall of the 6" FATHER mixing tee mock-up is calculated for a loading configuration: The results seem realistic even if they are not still very accurate (see paper PVP2005-71592 [11]). On this basis, thermal stresses are evaluated for elastic and elastic-plastic material behavior. Then, different types of fatigue criteria are used to evaluate the fatigue damage. The paper develops a brief description of the criteria, the corresponding fatigue damage evaluation and attempts to explain the differences.

Stress and Buckling of Internally Pressurized, Elastic-Plastic Torispherical Vessel Heads—Comparisons of Test and Theory

1977 ◽  
Vol 99 (1) ◽  
pp. 39-53 ◽  
Author(s):  
D. Bushnell ◽  
G. D. Galletly
Keyword(s):  
Mild Steel ◽  
Large Deflection ◽  
Plastic Material ◽  
Material Behavior ◽  
Nonlinear Material ◽  
Test Results ◽  
Elastic Plastic ◽  
State Of Stress ◽  
Elastic Plastic Material ◽  
Good Agreement

Several aluminum and mild steel torispherical heads were tested by Galletly and by Kirk and Gill and subsequently analyzed by Bushnell with use of the BOSOR5 computer program. The thinnest specimens buckled at pressures for which part of the toroidal knuckle was stressed well beyond the yield point. The analysis includes large deflection effects, nonlinear material behavior, and meridional variation of the thickness. The calculated strains in the thicker specimens agree reasonably well with the test results, but the calculated prebuckling strains in the thinnest specimens are generally greater than the values measured in the torodial knuckle after the onset of plastic flow. Reasonably good agreement between test and theory is obtained for the buckling pressures of aluminum specimens, but the calculated buckling pressures for mild steel specimens are much lower than the observed values, a discrepancy that is attributed to circumferentially varying thickness and possible inability of the analytical model of the elastic-plastic material to predict accurately the state of stress in the toroidal knuckle where loading is nonproportional once yielding has occurred.

Elastic-Plastic Analysis of Stresses and Initiation of Cracks in a Ceramic Coating Under Indentation by an Elastic Sphere

1998 ◽  
Vol 120 (3) ◽  
pp. 463-469 ◽  
Author(s):  
K. Hayashi ◽  
F. Yuan
Keyword(s):  
Ceramic Coating ◽  
Plastic Material ◽  
Circumferential Stress ◽  
Material Behavior ◽  
Elastic Sphere ◽  
The Finite Element Method ◽  
Elastic Plastic ◽  
Formation Of Cracks ◽  
Elastic Plastic Material ◽  
Radial Cracks

The elastic-plastic contact problem of a ceramic coating on a half-space indented by an elastic sphere is solved by the use of the finite element method under a variety of conditions. An elastic-plastic material behavior with isotropic strain hardening was employed. Results for stresses, during loading and after unloading, on the surface and along the axis of symmetry are presented and formation of cracks is discussed in detail, emphasizing the influence of the thickness of coating. It is shown that the circumferential stress on the surface of the coating is highly tensile so that radial cracks are induced for a sharp indenter. But, for a blunt indenter, the radial stress is tensile and is always larger than the circumferential stress, leading to the formation of circumferential cracks. It is also shown that, in the case of a sharp indenter, radial cracks can be induced during unloading.

Elastic–Plastic Multi-Asperity Contact Analysis of Cylinder-on-Flat Configuration

2007 ◽  
Vol 129 (2) ◽  
pp. 292-304 ◽  
Author(s):  
V. Sabelkin ◽  
S. Mall
Keyword(s):  
Rough Surface ◽  
Contact Area ◽  
Plastic Material ◽  
Material Behavior ◽  
Contact Load ◽  
Graphical Form ◽  
Complex Nature ◽  
Asperity Contact ◽  
Elastic Plastic ◽  
Elastic Plastic Material

The contact interaction between a rough cylindrical body (i.e., with asperities) and a deformable smooth flat was investigated using the finite-element analysis. Analysis included both elastic–plastic deformation and friction. Further, the effects of several parameters of rough surface on the evolution of the contact area with increasing contact load were investigated. These were radius, number, constraint, and placement of asperities. Contact area of rough surface is smaller than its counterpart of smooth surface, and this decrease depends on number, radius, constraint, and placement of asperities. The elastic material behavior results in considerably smaller contact area than that from elastic–plastic material behavior. The evolution of contact area with increasing contact load is of the complex nature with elastic–plastic material deformation since the yielded region widens and/or deepens with increasing load depending on number, radius, and constraint of asperities. The effect of constraint on the asperity depends upon its nature (i.e., from either sides or one side) and radius of the asperity. The effects of these several parameters on the contact area versus applied load relationships are expressed in the graphical form as well as in terms of equations wherever possible.

On the Effect of Scattering of Bolt Forces on Gasket Stress

2006 ◽  
Author(s):  
Manfred Schaaf ◽  
Friedrich Schoeckle ◽  
Jaroslav Bartonicek
Keyword(s):  
Plastic Material ◽  
Analytical Calculation ◽  
Large Degree ◽  
Outer Diameter ◽  
Elastic Plastic ◽  
Linear Elastic ◽  
Non Linear ◽  
Realistic Description ◽  
Lift Off ◽  
Elastic Plastic Material

To guarantee integrity and tightness of bolted flanged connections a set of gasket characteristics (for tightness e.g. QMIN(L), QSMIN(L), tightness class L) has to be known. These characteristics are determined in simplified standardized tests with uniform gasket stress levels, in which the effect of the scattering of the bolt force is neglected. In this paper, results of Finite Element studies with real flange models are presented in which the local distribution of the gasket stress was determined in dependence of the scatter of the bolt forces. In the calculations, different models of the material characteristics are evaluated. A linear elastic approach, a nonlinear elastic approach and a non-linear elastic-plastic approach of the gasket behaviour is analysed. The results of the FEM studies demonstrated that elastic-plastic material laws are necessary for a realistic description of the material behaviour. The calculations in which the elastic-plastic gasket behaviour is considered give a nearly uniform gasket stress distribution along the gasket circumference despite a large scatter in the bolt force. This means that a non-uniform load transmission into the BFC is “damped” through the flange rings to a large degree and the gasket is compressed almost uniformly along the circumference. In radial direction an increase of the gasket stress from the inner to the outer diameter can be observed. Depending on the material law used, a lift-off of the flange ring from the gasket at the inner diameter (caused by the flange rotation) is obtained (linear elastic approach). Using a non-linear elastic or elastic-plastic approach for the gasket material the gasket stays in contact with the flange surfaces over the entire width of the gasket. These experiences can only partly be considered in analytical calculation codes such as EN 1591-1 (1). This is one reason why there are often discussions about the tightening factors of different mounting procedures and therefore difficulties in stress and tightness analysis can occur.

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