Numerical and Analytical Modelling of Elastic-Plastic Fracture Mechanics Parameters

2007 ◽  
Vol 555 ◽  
pp. 565-570 ◽  
Author(s):  
Lj. Milović ◽  
Aleksandar Sedmak ◽  
Stojan Sedmak ◽  
S. Putić ◽  
Misa Zrilić
Keyword(s):  
Fracture Mechanics ◽  
Mixed Mode ◽  
Structural Integrity ◽  
Plastic Region ◽  
Crack Tip ◽  
Mixed Mode Fracture ◽  
Service Reliability ◽  
Integrity Assessment ◽  
Elastic Plastic ◽  
Edge Notch

Structural integrity and service reliability depend on the fracture resistance of a material. Cracks in the material are the locations of stress concentration, and elastic-plastic deformation can occur causing the development of mixed-mode type of fracture ahead the crack tip. Crack behavior in the elastic-plastic region is analyzed applying numerical and analytical simulation based on fracture mechanics parameters, characterizing the response of the material at the crack tip. Numerical and analytical results are compared with the corresponding experimental results obtained in previously performed fracture mechanics tests with standard single-edge notch bending – SEN(B) specimens. The comparison shows an acceptable level of agreement, enabling application of the proposed numerical model of crack growth in the mixed-mode fracture analysis for structural integrity assessment.

scholarly journals Analysis of Inclined Cracks in Thin-Walled Circular Tube under Mixed-Mode I + II Fracture

Proceedings ◽  
2018 ◽  
Vol 2 (8) ◽  
pp. 517 ◽  
Author(s):  
Boy Raymond Mabuza
Keyword(s):  
Fracture Mechanics ◽  
Mixed Mode ◽  
Crack Tip ◽  
Theoretical Models ◽  
Mode I ◽  
Mixed Mode Fracture ◽  
Shear Stresses ◽  
Inclined Crack ◽  
Mode Fracture ◽  
Thin Walled

This paper provides a study on mixed-mode fracture mechanics in thin-walled tube which is subjected to tension, shear and torsion loading. This type of loading causes an inclined crack to develop and generate a mixture of normal and shear stresses ahead of a crack tip. The stress state ahead of a crack tip is frequently based on mixed-mode type of interactions which designate the amplitude of the crack tip stresses. The analytical expressions for the stress intensity factors for mixed-mode I + II approach are presented. The Paris law for mixed-modes I + II has been discussed. Mixed-mode fracture mechanics is used with theoretical models to predict the path of crack growth when an inclined crack is subjected to a combination of mode I and mode II deformations. The torque at which crack propagation can be expected has been determined. The numerical calculations have been carried out by using MATLAB code. The results are good and could be useful for companies working with thin-walled circular tubes.

Crack Tip Constraint Under Biaxial Loading in Elastic-Plastic Materials

2010 ◽  
Author(s):  
Z. X. Wang ◽  
Jian-ye Huang ◽  
Y. J. Chao ◽  
P. S. Lam
Keyword(s):  
Driving Force ◽  
Enhancement Factor ◽  
Structural Integrity ◽  
Biaxial Loading ◽  
Crack Tip ◽  
Element Analysis ◽  
Crack Driving Force ◽  
Integrity Assessment ◽  
Elastic Plastic ◽  
Crack Tip Constraint

Crack tip constraint is known to affect the fracture resistance of materials. The effect of biaxial loading on a center crack in an X100 steel plate has been investigated. The crack driving force and the constraint parameter are estimated based on the two-parameter J-A2 theory in elastic-plastic fracture mechanics with the aid of finite element analysis. The center-cracked plate is subject to various degrees of biaxiality (defined as the ratio of the transverse stress parallel to the crack and the opening stress normal to the crack). Using the constraint parameter (A2) in uniaxial loading condition as a reference value, a Constraint Enhancement Factor is introduced to facilitate the investigation of crack tip constraint under biaxial loading. The analysis carried out in this paper has established a relationship between the Constraint Enhancement Factor and the biaxiality. With the J-A2 fracture model, the critical applied load and the critical crack driving force can be expressed as functions of biaxial loading ratio. The methodology and analysis results can be used in structural integrity assessment of a pressure vessel or piping which contains a crack under biaxial loading.

Mismatch Effect on Fracture Driving Force in Mismatched Girth Welded Pipes

2011 ◽  
Author(s):  
Gustavo M. Castelluccio ◽  
S. Cravero ◽  
R. Bravo ◽  
H. Ernst
Keyword(s):  
Fracture Mechanics ◽  
Structural Integrity ◽  
Crack Tip ◽  
J Integral ◽  
Inhomogeneous Materials ◽  
Crack Location ◽  
Unstable Failure ◽  
Edge Notch ◽  
Material Fracture ◽  
Crack Tip Constraint

Elasto-Plastic Fracture Mechanics (EPFM) is a useful tool for analyzing the structural integrity of components. However, EPFM has originally been developed for homogeneous materials and there are some concerns when it is applied to inhomogeneous materials. In the case of welds, the material fracture toughness and the applied fracture mechanics parameter on the structural member (J-integral, CTOD) should be adequately estimated. Furthermore, the mechanic mismatch influences on the local constraint may increase the risk of unstable failure. Hence, to study the effects of weld mismatch and crack locations on fracture behavior, single edge notch under tension (SE(T)) specimens and girth welded pipes under bending containing circumferential cracks were studied by means of finite elements simulations. Different weld widths and locations of cracks over the weld are considered. A study of the opening stresses ahead the crack tip developed in mismatched SE(T) specimens and cracked pipes allows the determination of the most critical combination of weld width and crack location in terms of applied J-integral and crack tip constraint level.

A new method for repairing aircraft structures containing aluminum alloy 2024-T3 using a combination of composite patch and bolt clamping

2018 ◽  
Vol 52 (30) ◽  
pp. 4203-4218 ◽  
Author(s):  
HN Maleki ◽  
TN Chakherlou
Keyword(s):  
Tensile Strength ◽  
Hybrid Method ◽  
Mixed Mode ◽  
Structural Integrity ◽  
Pure Shear ◽  
Shear Mode ◽  
Mixed Mode Fracture ◽  
Aircraft Structures ◽  
Repair Method ◽  
Composite Patch

Aircraft repair is gaining importance for extending the service life of aging aircraft and also for improving its structural integrity. In this paper, a new repair method of aircraft structures is presented, and the performance of this method in mixed mode fracture has been evaluated and compared with other two repair methods by conducting experimental and numerical investigations. To do so, four batches of specimens were prepared and each of them subjected to five level of mixed mode loading using a modified version of Arcan fixture. Further, finite element simulations were utilized to find stress intensity factors to explain the experimental test results. The experimental results indicate that the hybrid repair method is the most effective method in terms of increasing fracture load and it was observed a significant increase in the tensile strength of the repaired parts by all three methods compared to the simple cracked samples. Repaired samples with the hybrid method, composite patch and bolt clamping exhibited up to 49%, 44%, and 24% increase in tensile strength under pure tensile mode respectively. However, in pure shear mode, the fracture strength increased to 28%, 18%, and 9% by the hybrid method, bolt clamping and composite patch respectively.

Reactor Pressure Vessel Integrity Assessment: French Simplified Analysis Method Applied to Underclad Postulated Defect in Nozzle

2016 ◽  
Author(s):  
Adolfo Arrieta-Ruiz ◽  
Eric Meister ◽  
Stéphane Vidard
Keyword(s):  
Fracture Mechanics ◽  
Fracture Risk ◽  
Pressure Vessel ◽  
Reactor Pressure Vessel ◽  
Core Area ◽  
Integrity Assessment ◽  
Elastic Plastic ◽  
The Core ◽  
Simplified Method ◽  
Reactor Pressure

Structural integrity of the Reactor Pressure Vessel (RPV) is one of the main concerns regarding safety and lifetime of Nuclear Power Plants (NPP) since this component is considered as not reasonably replaceable. Fast fracture risk is the main potential damage considered in the integrity assessment of RPV. In France, deterministic integrity assessment for RPV vis-à-vis the brittle fracture risk is based on the crack initiation stage. As regards the core area in particular, the stability of an under-clad postulated flaw is currently evaluated under a Pressurized Thermal Shock (PTS) through a dedicated fracture mechanics simplified method called “beta method”. However, flaw stability analyses are also carried-out in several other areas of the RPV. Thence-forward performing uniform simplified inservice analyses of flaw stability is a major concern for EDF. In this context, 3D finite element elastic-plastic calculations with flaw modelling in the nozzle have been carried out recently and the corresponding results have been compared to those provided by the beta method, codified in the French RSE-M code for under-clad defects in the core area, in the most severe events. The purpose of this work is to validate the employment of the core area fracture mechanics simplified method as a conservative approach for the under-clad postulated flaw stability assessment in the complex geometry of the nozzle. This paper presents both simplified and 3D modelling flaw stability evaluation methods and the corresponding results obtained by running a PTS event. It shows that the employment of the “beta method” provides conservative results in comparison to those produced by elastic-plastic calculations for the cases here studied.

Structural Integrity Research for Reactor Pressure Vessel Under In-Vessel Retention of a Core Melt

2016 ◽  
Author(s):  
Yongjian Gao ◽  
Yinbiao He ◽  
Ming Cao ◽  
Yuebing Li ◽  
Shiyi Bao ◽  
...  
Keyword(s):  
Pressure Vessel ◽  
Material Properties ◽  
Power Plants ◽  
Structural Integrity ◽  
Plastic Material ◽  
Plastic Region ◽  
Reactor Pressure Vessel ◽  
Elastic Plastic ◽  
Elastic Plastic Material ◽  
Reactor Pressure

In-Vessel Retention (IVR) is one of the most important severe accident mitigation strategies of the third generation passive Nuclear Power Plants (NPP). It is intended to demonstrate that in the case of a core melt, the structural integrity of the Reactor Pressure Vessel (RPV) is assured such that there is no leakage of radioactive debris from the RPV. This paper studied the IVR issue using Finite Element Analyses (FEA). Firstly, the tension and creep testing for the SA-508 Gr.3 Cl.1 material in the temperature range of 25°C to 1000°C were performed. Secondly, a FEA model of the RPV lower head was built. Based on the assumption of ideally elastic-plastic material properties derived from the tension testing data, limit analyses were performed under both the thermal and the thermal plus pressure loading conditions where the load bearing capacity was investigated by tracking the propagation of plastic region as a function of pressure increment. Finally, the ideal elastic-plastic material properties incorporating the creep effect are developed from the 100hr isochronous stress-strain curves, limit analyses are carried out as the second step above. The allowable pressures at 0 hr and 100 hr are obtained. This research provides an alternative approach for the structural integrity evaluation for RPV under IVR condition.

Elastic-Plastic Fracture Mechanics Analysis of Cast Stainless Steel Pipes (Influence of Axial Load on Z-Factor of Pipes With Circumferential Crack Under Bending Load)

2013 ◽  
Author(s):  
Masayuki Kamaya ◽  
Kiminobu Hojo
Keyword(s):  
Stainless Steel ◽  
Axial Load ◽  
Power Plants ◽  
Structural Integrity ◽  
Term Operation ◽  
Steel Pipes ◽  
Integrity Assessment ◽  
Plastic Failure ◽  
Elastic Plastic ◽  
Bending Load

Since the ductility of cast austenitic stainless steel pipes decreases due to thermal aging embrittlement after long term operation, not only plastic collapse failure but also unstable ductile crack propagation (elastic-plastic failure) should be taken into account for the structural integrity assessment of cracked pipes. In the ASME Section XI, the load multiplier (Z-factor) is used to derive the elastic-plastic failure of the cracked components. The Z-factor of cracked pipes under bending load has been obtained without considering the axial load. In this study, the influence of the axial load on Z-factor was quantified through elastic-plastic failure analyses under various conditions. It was concluded that the axial load increased the Z-factor; however, the magnitude of the increase was not significant, particularly for the main coolant pipes of PWR nuclear power plants.

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