Lih-Jier Young

A boundary element application for mixed modeloading idealized sawtooth fracture surface

Abstract In this paper, a 2-D elastic-plastic BEM formulation predicting the reduced mode IIand the enhanced mode I stress intensity factors are presented. The dilatant boundary conditions (DBC) are assumed to be idealized uniform sawtooth crack surfaces and an effective Coulombsliding law. Three types of crack face boundary conditions, i.e. (1) BEM sawtooth model-elasticcenter crack tip; (2) BEM sawtooth model-plastic center crack tip; and (3) BEM sawtoothmodel-edge crack with asperity wear are presented. The model is developed to attempt todescribe experimentally observed non-monotonic, non-linear dependence of shear crack behavioron applied shear stress, superimposed tensile stress, and crack length. The asperity sliding isgoverned by Coulombs law of friction applied on the inclined asperity surface which hascoefficient of friction μ. The traction and displacement Greens functions which derive fromNaviers equations are obtained as well as the governing boundary integral equations for an infiniteelastic medium. Accuracy test is performed by comparison stress intensity factors of the BEMmodel with analytical solutions of the elastic center crack tip. The numerical results show thepotential application of the BEM model to investigate the effect of mixed mode loading problemswith various boundary conditions and physical interactions.

Lifetime evaluation of cracked shaft sleeve of reactor coolant pump under thermal striping

Thermal striping of a shaft sleeve of a reactor coolant pump at a nuclear power plant is caused by incomplete mixing of the low temperature cooling water flow from water seals and high temperature cooling water flow from the reactor. Temperature fluctuation results in a significant thermal fatigue damage and therefore, a network of longitudinal cracks is found on the outer surface of sleeve. After conservative computation and evaluation by considering thermal and mechanical stresses and fracture mechanics, it was found that the crack on the surface of sleeve will become deeper according to high frequency fatigue model if the depth of the crack is larger than 10% of sleeve wall thickness. Although the sleeve will not break dramatically before one crack through the wall of sleeve they may combine with one another and cause damage to the sleeve. Therefore, in this paper the life time of the sleeve is assumed to be the time needed for one crack to propagate through the wall of the sleeve. The life assessment for the sleeve, subject to surface temperature fluctuation, is presented.

A further investigation of mixed mode loading center crack problem

In this paper, a BEM model which describes the reduced mode II and enhanced mode I stress intensity factors of the center crack problem caused by fracture surface roughness is reenforced. The dilatant boundary conditions (DBC) are assumed to be idealized uniform sawtooth crack surface and effective Coulomb sliding law. Three types of crack boundary conditions are investigated and well defined: (1) open crack, (2) DBC crack with elastic tip, (3) DBC crack with plastic tip. In plastic case, the 2D Newtons method is described in the iteration process of getting the length of plastic zone. The method of obtaining the effective mode I and II stress intensity factors of the center crack problem and the boundary conditions of each different case as well are carefully and well described. The resulting crack opening displacement, crack sliding displacement and the stress distributions along the interface show the fracture surface interference of a rough DBC crack. The numerical results show the potential application of the BEM model to the effects of mixed mode loading center crack problem with various boundary non-linearities due to rough contact and plasticity.

Plastic hinges development and crack stability analysis in a circular ring

Abstract The primary purpose of this work is to demonstrate that the location of a crack can strongly affect the sequence of plastic hinge development which in turn affects crack stability of a structure. A specific example of an elastic–plastic ring loaded with diametrically opposite concentrated loads is employed to investigate these effects. The method used is based on elastic superposition to obtain the elastic–plastic behavior and to evaluate the crack stability with plastic hinges present.

A detailed study of rough edge crack with worn asperities

Abstract A boundary element model which describes the reduced mode II and enhanced mode I stress intensity factors of rough edge crack problem with worn asperities is enforced in this paper. The dilatant boundary conditions (DBC) are assumed to be idealized uniform sawtooth crack surface and effective Coulomb sliding law. The boundary conditions of the closed worn edge crack are well described. The resulting COD, CSD and the stress distributions along the interface show the interference of a rough DBC edge crack surface.

Numerical Application in Weight Reduction of Lateral Plate of Rescue Robot

In general, weight reduction will always lower the strength of the specimen. The primary purpose of this paper is weight reduction of lateral plate of rescue robot without causing the strength of it by using the Boundary Element Method (BEM). The dynamical loading conditions are performed before and after weight reduction. The numerical results of the stress distribution and the plastic deformation along the center line (interface) of the lateral plate show that the endure limits of the plate before and after weight reduction are almost the same and therefore, will not lower the strength of the plate.

A fracture mechanics analysis of the PWR nuclear power plant reactor pressure vessel beltline weld

Abstract In this paper, a generic pressured water reactor (PWR) power plant reactor vessel is analyzed. The primary purpose of this work is to assure structural integrity of the irradiated reactor pressure vessel (RPV) beltline weld under normal operating conditions at the end-of-life, as specified by the requirements of 10CFR50, App.G. It is found that suitable margins of safety are maintained at the end-of-life (32 effective full power years or 1.25×10 23 n/m 2 inner wall fluence).