Quantitative Fractography Research Articles

Studies of tensile failure in oriented polymeric fibers by quantitative fractography

AbstractFor some fibers, such as the nylon monofilaments studied here, quantitative information may be obtained from scanning electron micrographs of fracture surfaces. On these surfaces the segment of the cross section that supports the load at the instant of rupture is seen distinctly, and its area can be measured. Normalizing breaking load by this area provides a breaking stress characteristic of the final supporting segment. “Ultimate” breaking stresses calculated in this way indicate (i) For notched filaments, the ultimate breaking stress is almost constant with notch depth and also with strain rate. (ii) For un‐notched filaments, there is an increase of breaking load with strain rate, due in part to the extent of the slow cleavage that precedes failure; however, the ultimate breaking stress increases as rate of strain decreases. These two findings are incompatible with mechanisms of failure based on growth of microcracks by heat‐ and stress‐activated chain breakage. A possible explanation involves rearrangement of microfibrils within the fiber which alters their strength distribution. (iii) The apparent strength reduction on wetting nylon filaments in water is due to a faster rate of growth of the slow‐cleavage area; the ultimate breaking stress is unchanged, except at high rates of strain.

Quantitative fractography of WC-Co cermets by Auger spectroscopy

A general procedure has been developed to determine the area fraction occupied by the binder on the fracture surfaces of cemented carbides. The area fraction of binder on the fracture surface was obtained from the relative peak-to-peak height ratios of elements in the binder and the carbide content was measured by Auger spectroscopy on the fracture surface and an adjacent polished section and the volume fraction of binder present in the cermet. This procedure was employed to determine the area fraction of binder on the fracture surfaces of WC-Co cermets with different binder contents and carbide grain sizes. The average binder mean free path and the area fraction of binder together yield the amount of plastically deformed binder per unit area of fracture surface. The volume of deformed binder and its in situ yield strength were combined to obtain a term proportional to the amount of plastic work done per unit area of fracture surface. It is shown that the correlation between this plastic work term and the fracture toughness of the cermets is good, while correlation with binder mean free path alone is poor.

A Quantitative Fractography in Impact and Fatigue Tests of Pearlitic Spheroidal Graphite Cast Iron

A Quantitative Fractography in Impact and Fatigue Tests of Pearlitic Spheroidal Graphite Cast Iron

A thinning transform for digital images

Given an elongated object in a digital image, a thinning transform is described to simultaneously calculate the coordinates of its medial line elements and a value for these elements equal to the width of the object at the element's coordinates. The transform is being used in the area of quantitative fractography in photo-micrographs of rock samples.

Experimental evaluation of crack resistance of structural steels using quantitative fractography

Experimental evaluation of crack resistance of structural steels using quantitative fractography

Quantitative fractography

Quantitative fractography

Seminar on Quantitative Fractography

Seminar on Quantitative Fractography

Utilisation de la métallographie quantitative et de la stéréologie à l'etude des matériaux composites. II. Application à l'etude de la rupture d'eprouvettes de flexion en WC-Co.

Having shown that it was possible to extend stereological and quantitative metallographic methods to quantitative fractography, these methods were used to study the various types of fracture on notched and unnotched plates in WC-Co. This investigation, made by electron microscopy on fracture areas and by optical microscopy on external fibers, indicates that the fracture, principally intergranular, is predominantly in the cobalt phase. This fracture is initiated on the largest carbide crystals and particularly when they are submitted to very dissymmetrical tensiles stresses (external fibers). It was also shown by the stereological methods that the microstructural parameter L 2( Co) D( WC) is directly linked to the rupture stress and to the deviation from the statistical fracture in the cobalt phase. This allows to put in evidence that the stereological methods can explain, in some cases, the fracture mechanism of materials.

Quantitative electron fractography of the brittle failure of iron in 15G2AFDps steel

Quantitative electron fractography of the brittle failure of iron in 15G2AFDps steel

Utilisation de la métallographie quantitative et de la stéréologie à l'etude des matériaux composites—I. Etude critique des méthodes. Application à la fractographie quantitative

To measure the parameters which characterise the morphology of materials, it is necessary to use quantitative metallography and stereology. It seemed natural to extend these methods to quantitative fractography. Firstly, it was shown that transmission and scanning electron microscopes are equivalent apparatus for the observation of fracture path. Then a critical investigation of stereological methods proved that corrective methods established for spherical particles can be used for non-spherical particles and, with modifications, for fracture path investigation. The critical study of the surface ratios of fracture occupied by each phase was investigated as a function of the conditions of observation for various microstructural parameters.

Influence of inclusion content on fatigue crack

Fatigue crack growth rates were measured at room temperature in dry air for three 7075-T6 aluminum alloys with different inclusion content. Volume fractions of inclusions were determined for each alloy by the point count method with two different automated systems. Plots of the fatigue crack growth rate (da/dN) vs the stress-intensity-factor range (ΔK) show a well defined change of slope at the transition between plane strain and plane stress fracture. This transition is associated with a marked increase in the amount of fracture by void growth around inclusions. The volume fraction and mean spacing of voids within the cyclic plastic zone have been determined as a function of ΔK by quantitative fractography. Fracture by voids is important when the mean spacing of such voids is approximately equal to the width of the cyclic plastic zone in the plane of the crack. It is concluded that the inclusion content increases the fatigue-crack growth rates only within the plane stress range, that is for values of the stress-intensity-factor range ΔK \s> 20 kpsi√in.