The critical influence of some “tiny” geometrical details on the stress field in a Brazilian Disc with a central notch of finite width and length

The role of some geometrical characteristics of the notches ma­chined in circular discs, in order to determine the mode-I fracture tough­ness of brittle materials, is discussed. The study is implemented both analyti­cally and numerically. For the analytic study advantage is taken of a recently intro­duced solution for the stress- and displacement-fields developed in a finite disc with a central notch of finite width and length and rounded corners. The vari­ation of the stresses along strategic loci and the deformation of the peri­me­ter of the notch obtained analytically are used for the calibration/validation of a flexible nu­mer­ical model, which is then used for a parametric investiga­tion of the role of geometrical features of the notched disc (thickness of the disc, length and width of the notch, radius of the rounded corners of the notch). It is con­cluded that the role of the width of the notch is of critical im­port­ance. Both the ana­lytic and the numerical studies indicate definitely that ignoring the ac­curate geo­metric shape of the notch leads to erroneous results concerning the actual stress field around the crown of the notch. Therefore, it is possible that misleading values of the fracture toughness of the material of the disc may be obtained.

Numerical Study on Buckling Resistance of Uniaxially Compressed Laminates Containing V-Shaped Edge Notch

The purpose of this study is to investigate the impact of a V-shaped cutout on the buckling strength of E-glass epoxy composite laminates. In aircraft components, cutouts are more often used for inspection, ventilation, access to critical areas, fitting a particular component, and increasing the strength to weight ratio of the structure. In this paper, symmetric and antisymmetric laminates of E-Glass/Epoxy unidirectional are used and the effect of notch parameters such as notch radius(r), depth of the notch(h), and notch angle(α) is observed under monoaxial compression. Effects of end conditions and plate aspect ratio(l/b) are analyzed. It is observed that the notch radius does not have a considerable effect on buckling strength but the notch angle after 90⁰ shows a good dip in buckling loads as compared to 30⁰,45⁰, and 60⁰. Depth of notch and end conditions creates a considerable loss in buckling strength. As the h/b ratio is increased, the drop in buckling strength becomes significant. Clamped -pinned end condition of the plate gives a lower value of load multiplier as compared to clamped -clamped. As we increase the l/b ratio of the plate, buckling of the plate becomes easier. The position of the notch (a) also affects buckling strength which is maximum for a/l=0.25 and minimum for a/l=0.5.

On notch fracture mechanics

Different stress distributions for an elastic behavior are presented as analytical expressions for an ideal crack, a sharp notch and a blunt notch. The elastic plastic distribution at a blunt notch tip is analyzed. The concept of the notch stress intensity factor is deduced from the definition of the effective stress and the effective distance. The impacts of the notch radius and constraint on the critical notch stress intensity factor are presented. The paper ends with the presentation of the crack driving force Jρ for a notch in the elastic case and the impact of the notch radius on the notch fracture toughness Jρ,c. The notch fracture toughness Jρ,c is a measure of the fracture resistance which increases linearly with the notch radius due to the plastic work in the notch plastic zone. If this notch plastic zone does not invade totally the ligament, the notch fracture toughness Jρ,c is constant. This occurs when the notch radius is less than a critical one and there is no need to use the cracked specimen to measure a lower bound of the fracture resistance.

Quantification of the Material Ductility Effect on Notch Fracture Toughness Using Numerical Damage Analysis Method

In this study, the finite element (FE) damage analysis based on the multi-axial fracture strain model was applied to investigate the effect of the material ductility on fracture resistance of notched defect. (The fracture toughness is used only for a cracked specimen and the fracture resistance is used for notched specimens throughout the paper.) To obtain the material property with different ductility, the tensile and fracture toughness tests of the cold-worked SUS316 were used. The damage model was determined from comparing the experimental data with simulated FE analysis results. Then the FE analysis was applied to calculate the fracture resistance according to the notch radius in each material. It shows that the slope of initiation resistance according to the notch radius was related to the material ductility. To quantify this effect of ductility, the relationship between notch fracture resistance and material tensile properties was confirmed.

Fatigue Crack Growth from Notches: A Numerical Analysis

A numerical approach based on plastic crack tip opening displacement (CTOD) was followed to study fatigue crack growth (FCG) from notches. The identification of fundamental mechanisms was made considering notched and unnotched models, with and without contact of crack flanks. Different parameters were studied, namely, notch radius, crack length, stress state, and material. The notch increases the plastic CTOD, and therefore fatigue crack growth rate, da/dN, as expected. The reduction of notch radius increases da/dN but reduces the notch affected zone. Ahead of the notch affected zone, da/dN increases linearly with crack growth, with a rate that increases linearly with the plastic CTOD. The crack closure phenomenon has a dramatic effect under plane stress conditions but a limited effect on plane strain conditions. In the former case, the contact of crack flanks reduces substantially the effect of notch radius and the size of the notch affected zone. These trends are associated with the increase of crack closure level with notch radius. The material does not affect the global trends, but the reduction of yield stress increases the level of plastic deformation and therefore da/dN. The effect of material, and also of stress state, is mainly associated with crack closure.