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The structural integrity of nuclear steam supply systems in the U.S.A. was assured by designs that adhered to the ASME Boiler and Pressure Vessel Code and many other regulatory standards. The requirements of these codes and standards are based on linear elastic fracture mechanics (LEFM) concepts. In much or all of the working temperature regime of nuclear systems, power and chemical plants, as well aircraft propulsion, the material is being stressed above the transition temperature, where the fracture response is ductile and the material capable of considerable plastic deformation.

Local approach to fracture has been developed for complete understanding of fracture mechanism [ 1 , 2 ], including the material degradation process. This approach combines theoretical, experimental and numerical solutions, enabling less conservative assessment of crack significance and residual stress.

Fretting fatigue occurs at the contact interface of mechanical joints which are designed to be at rest but that nevertheless experience some sort of relative movement due to vibration. This work aims to develop a crack initiation threshold condition for fretting fatigue. The methodology considers the use of Taylor’s stress point method [ 1 ] associated with multiaxial models, which divide the stress space in safe and damage zones [ 2 ]–[ 4 ].

This papers reviews the use of the Theory of Critical Distances (TCD) to predict high-cycle fatigue strength of real components when the complexity of their geometry causes stress concentration phenomena.

Weld bead geometry cannot, by its nature, be precisely defined. Parameters such as bead shape and toe radius vary from joint to joint even in well-controlled manufacturing operations (Taylor et al., [ 1 ]). In the notch stress intensity approach to the fatigue assessment of welded joints, the weld toe is modelled as a sharp V-notch and local stress distributions in plane configurations are given on the basis of the relevant mode I and mode II notch stress intensity factors (NSIFs). These factors quantify the magnitude of asymptotic stress distribution obeying Williams’ solution [ 2 ]. When the constancy of the weld toe angle is assured and the angle is large enough to make mode II contribution non-singular, the mode I NSIF can directly be used to describe the fatigue strength of fillet welded joints having different geometries (Lazzarin and Tovo [ 3 ], Lazzarin and Livieri [ 4 ]). As an example, Fig.1 summarised fatigue strength data related to fillet welded joints, with an angle at the weld toe equal to 135 degrees. In those welded joints, all fatigue failures originated at the weld toe.

Defects such as flaws and cracks may form in elastomeric materials due to the manufacturing, handling or ageing. To ensure the integrity and reliability for such structural components, fracture toughness should be ascertained so that the onset of the crack growth can be determined based on the fracture resistance of the material. The energy release rate is a measure of the fracture toughness, and commonly used as a criterion to determine the maximum operating loads for a given pre-existing defect.

Functionally graded materials (FGMs) are multiphase composites that have spatial variations in the composition and microstructure. These variations are intentionally introduced in order to take advantage of different thermomechanical properties of the constituent materials. The fracture mechanics theory and analysis of functionally graded materials is based on the assumption of continuous variations in the related thermomechanical properties (see for example Yildirim et al. [ 1 ] and Kim and Paulino [ 2 ]). Fracture mechanics problems that occur in FGMs are generally observed to be either due to mode I edge cracks that are perpendicular to the free boundaries or due to the embedded cracks that are parallel to the material surface. These observations could be attributed to the fact that some of the processing methods used to create graded layers induce an oriented microstructure. For example, as shown by Sampath et al. [ 3 ], FGMs that are processed by the plasma spray technique have a lamellar structure which has weak fracture planes parallel to the boundary. Embedded cracks that can initiate at the weak cleavage planes are inherently under mixed-mode mechanical or thermal loading. One of the approaches to examine fracture mechanics problems in this type of structures is to model the functionally graded medium as orthotropic with principal directions of orthotropy parallel and perpendicular to the free surface (Ozturk and Erdogan [ 4 ]).

A scheme for elastic-plastic finite element analysis (FEA) has been proposed for the study of stable crack growth (SCG) from initiation to instability in both mode I and mixed mode (I and II). In the analysis the condition for crack extension at every stage of the SCG is considered to be CTOA/CTOD reaching a critical value (Newman [ 1 ], Maiti and Mahanty [ 2 ], Maiti and Mourad [ 3 ]). The scheme permits predictions of load variation with load line displacement (LLD), crack tip current plastic zone and crack edge profile.

The fatigue threshold of materials with small defects or sharp notches is not controlled by the nucleation of fatigue cracks, but by its propagation. After nucleation, the fatigue crack first decelerates and then stops when the applied stress amplitude is below the fatigue threshold. Tanaka et al have shown that the development of crack closure with crack extension is primarily responsible for crack deceleration and stoppage. They have proposed the R -curve method for predicting the fatigue thresholds of notched components and have shown a good agreement with the experimental results for uniaxial loading cases. In this paper, this method is applied to the fatigue thresholds under combined loading.

A quasi-static penetration model of ballistic penetration of thick section composites is proposed. Quasi-static punch shear tests (QS-PST) and ballistic punch shear tests (B-PST) are conducted to identify five different phases of ballistic penetration, i.e., i) impact-contact, ii) hydrostatic compression, iii) compression-shear, iv) tension-shear, and v) structural vibration. It is well known that the energy absorption in QS-PST is much lower than the B-PST e.g., Mines et al [ 1 ]; and the physics of ballistic penetration is difficult to model with quasi-static models. In order to bridge the gap between QS-PST and B-PST energy absorption, conservation of momentum and energy principles is used to predict the rest kinetic energy of the projectile-laminate system in case of a partial penetrating projectile. Combining the QS-Penetration model and the analytical rest kinetic energy model, a good prediction of ballistic energy absorption is obtained. FIGURE 1. Quasi-Static Punch Shear Test: Load-Deflection and Damage.