Stress Intensity Factors In Fracture Mechanics Research Articles

Diverter damper force analysis and stress intensity factors for its double fillet welds by boundary element method

Mechanisms usually transmit power by welded links into a shaft. Should this weld be partial, like fillet welds, there will be an area of stress concentration that could behave like a crack due to sharp corners. These can lead to structural failures due to fatigue. Consequently, to properly design, inspect and maintain these mechanisms it is necessary to use fracture mechanics stress intensity factors. The crack mesh simplicity required by the boundary element method allows easy modeling even for complex geometry. This technique will be used to obtain such parameters for a double fillet weld found in a diverter damper mechanism responsible for controlling hot gas flow to heat recovery steam generator in power plants. But the solutions presented can be used for similar geometrical configurations, specially to shaft link mechanisms. Empirical equations were also obtained to further ease fracture mechanics and fatigue analysis for this kind of geometry.

Fatigue crack growth in bending: Successful correlation of mean stress (stress ratio) effects using the change in net‐section strain energy

AbstractA physically based correlation of mean stress (or stress ratio) effects, during fatigue crack growth in bending, is demonstrated using the concept of the change in net‐section cyclic strain energy. This study extends the net‐section approach, which was successfully demonstrated previously for middle‐cracked tension specimens, here to bending. A straightforward analytical derivation of the change in net‐section cyclic strain energy is shown using the mechanics of beam bending. Using experimental data, it is shown that the change in net‐section cyclic strain energy successfully correlates the effect of mean stress on fatigue crack growth rates for a steel, an aluminium alloy, a titanium alloy, and a WC‐Co cermet. It is also shown that the net‐section‐based stress intensity factor, morphed from the change in net‐section strain energy, agrees excellently with the fracture mechanics‐based stress intensity factor. This is to show that the proposed net‐section‐centric fracture mechanics approach for fatigue is physical and that the origin of fracture mechanics stress intensity factor appears to be actually rooted in the change in the net‐section strain energy. Hence, the net‐section‐centric approach appears to be superior to the crack‐centric conventional fracture mechanics approach, and a physical treatment of the fatigue crack growth behaviour appears to be possible.

Considerations on the fatigue assessment methods of floating-structure details

The assessment of the finite element analysis results on stiffened plating structures is not straightforward because of the stress singularities that are inherent in the overall geometry. Some guidance is available but it is generally founded on limited comparisons with experiments rather than on an overall analysis of the problem, and the guidance is almost certainly not generally applicable. Fracture mechanics finite element methods are very useful but generally provide little understanding of the behaviour and a very limited basis for checking the quality of the results. This paper reports some work carried out recently to try to provide an understanding of the nature of the singularities in these details and some simple ‘rules of thumb’. This provides a direct calculation method for fracture mechanics stress intensity factors and stress concentration factors for fatigue analysis based on the S–N approach (where S is the stress and N is the number of cycles to failure). By providing a better understanding of the nature of the stress fields, it also provides a good foundation for a finite element analysis of these details. This paper concentrates on the analysis of a simple planar right-angled cruciform corner with no bending, overlapping plates or weld reinforcement geometry. Also the effects of the mean stress and the residual stress are ignored. Some initial insights into the stress field are studied when the detail is not planar; this gives some further understanding of the behaviour of real structure details.

Symmetric-Galerkin Boundary Element Analysis of the Quantized Fracture Mechanics Stress Intensity Factors in Nanoscale Fracture

Symmetric-Galerkin Boundary Element Analysis of the Quantized Fracture Mechanics Stress Intensity Factors in Nanoscale Fracture

Microstructure-based fatigue modeling of cast A356-T6 alloy

High cycle fatigue (HCF) life in cast Al–Mg–Si alloys is particularly sensitive to the combination of microstructural inclusions and stress concentrations. Inclusions can range from large-scale shrinkage porosity with a tortuous surface profile to entrapped oxides introduced during the pour. When shrinkage porosity is controlled, the relevant microstructural initiation sites are often the larger Si particles within eutectic regions. In this paper, a HCF model is introduced which recognizes multiple inclusion severity scales for crack formation. The model addresses the role of constrained microplasticity around debonded particles or shrinkage pores in forming and growing microstructurally small fatigue cracks and is based on the cyclic crack tip displacement rather than linear elastic fracture mechanics stress intensity factor. Conditions for transitioning to long crack fatigue crack growth behavior are introduced. The model is applied to a cast A356-T6 Al alloy over a range of inclusion severities.

Various processes for in situ formation of aluminium-aluminium nitride : Y.Takeda et al. (Sumitomo Electric Industries, Koyakita, Japan.)

The rates of low-cycle fatigue crack propagation in 1 Cr-1 Mo-0·25 V low alloy steel were determined under several types of loading at 1000 F. It was found that crack growth rates correlate well with the nominal crack tip stress. This method was also applied with good results to some published data where the fracture mechanics stress intensity factor had given only limited correlation. Several questions are thus raised regarding the relative importance of crack tip stress and crack length during crack growth in actual components.

Developments in sintered stainless steel

The rates of low-cycle fatigue crack propagation in 1 Cr-1 Mo-0·25 V low alloy steel were determined under several types of loading at 1000 F. It was found that crack growth rates correlate well with the nominal crack tip stress. This method was also applied with good results to some published data where the fracture mechanics stress intensity factor had given only limited correlation. Several questions are thus raised regarding the relative importance of crack tip stress and crack length during crack growth in actual components.

Initial fatigue crack growth behaviour in a notched component: V. Assessment of initial defect in respect to fatigue life of a notched component: Horikawa, K. and Cho, S.-M. Trans. JWRI 1988 17, (2), 433–440

The rates of low-cycle fatigue crack propagation in 1 Cr-1 Mo-0·25 V low alloy steel were determined under several types of loading at 1000 F. It was found that crack growth rates correlate well with the nominal crack tip stress. This method was also applied with good results to some published data where the fracture mechanics stress intensity factor had given only limited correlation. Several questions are thus raised regarding the relative importance of crack tip stress and crack length during crack growth in actual components.

High-temperature crack growth in low-cycle fatigue

The rates of low-cycle fatigue crack propagation in 1 Cr-1 Mo-0·25 V low alloy steel were determined under several types of loading at 1000 F. It was found that crack growth rates correlate well with the nominal crack tip stress. This method was also applied with good results to some published data where the fracture mechanics stress intensity factor had given only limited correlation. Several questions are thus raised regarding the relative importance of crack tip stress and crack length during crack growth in actual components.