Macroscopic Fracture Surface Research Articles

Relation between fracture surface area of a flexural strength specimen and fracture toughness for WC-10mass%Co cemented carbide and Si 3N 4 ceramics

The relation between flexural strength (σ m ) and number of fragments ( N f ) of a broken test piece was first investigated for WC-10mass%Co cemented carbide with a higher fracture toughness ( K IC ) than Si 3N 4-base ceramics that had been studied in our previous report. Then the relation between σ m and total macroscopic fracture surface area ( S mf ), and also the relation between K IC and the dependence of S mf on σ m were investigated for both specimens. It was found that N f of the cemented carbide also tended to become larger for higher σ m in a similar manner to the ceramics, and a strong positive correlation was observed between σ m and S mf for each specimen. σ m under a given N f or S mf was higher for the cemented carbide with higher K IC , compared with the ceramics. An equation of σ m = ΦK IC S mf 1/2 (Φ is a shape factor) was theoretically derived. The experimental results supported this equation; a good linear correlation was observed between σ m and S mf 1/2 for each specimen, and the ratio of the slopes of two σ m —S mf 1/2 regression lines for both specimens was in good accordance with the ratio of K IC measured by the SEPB method.

Development of Expert System for Fractography of Environmentally Assisted Cracking.

An expert system, which diagnoses the causes of failure of environmentally assisted cracking (EAC), based upon fractography has been developed. The system uses the OPS83 programming language expressing rules in a manner of production rules and is composed of three independent subsystems, which respectively deal with EACs of high-strength or high-tensile strength steel, aluminum alloy, and stainless steel in dry and humidified air, water, and aqueous solutions containing Cl, Br or I ions. The concerned EAC issues cover stress corrosion cracking (SCC), hydrogen embrittlement, cyclic SCC, dynamic SCC and corrosion fatigue as well as fatigue and overloaded fracture. The knowledge base covers the rules relating to not only environments, materials, and loading conditions, but also macroscopic and microscopic fracture surface morphology. In order to deal with vague expressions of fracture surface morphology, Fuzzy theory is used in the system, and the description of rules about vague fracture surface appearance is thereby possible. Applying the developed expert system to case histories, accurate diagnoses were made. We discussed the related diagnosis results and usefulness of the developed system

The effect of the loading rate on the fracture toughness of Poly(methyl methacrylate), Polyacetal, Polyetheretherketone and modified PVC

The mode-l-plane-strain fracture toughness at initiation of various engineering plastics was determined for test speeds between 10−4ms−1 and 1.0 ms−1, using a high-speed, servohydraulic testing apparatus. At high rates of testing, the transient acceleration of the specimen was reduced by the use of a damping technique aimed at overcoming dynamic effects. The results obtained are correlated with fractographic analysis performed by scanning electron microscopy (SEM) and by digital image analysis of macroscopic fracture surfaces. The results show that for some materials the high values of K lc measured at low testing rates are associated with deformation detectable by either method. The extent of such deformation tends to be reduced as the testing velocity is increased and the fracture toughness drops.

Effect of test temperature on fracture toughness of columnar grained ice.

The effects of test temperature on fracture toughness KC and on the fracture surface of columnar grained ice specimens were investigated at -5, -10, -30°C and -50°C. Sharply edge-notched specimens with section sizes of 25×50mm and 200×50mm were used. Three-point bending tests were conducted under the wide range of loaing rate K^.I covering from 0.8 up to 3500 kPa√(m)/s. The pop-in crack propagation was also investigated at -10°C using 25×50mm specimens under K^.I≒0.8 kPa√(m)/s. The KC value and its scatter obtained under K^.I≥30 KPa√(m)/s were substantially unaffected by test temperature and K^.I. In K^.I<30 kPa√(m)/s, the effect of test temperature on the KC value was observed. The macroscopic fracture surface was affected by test temperature and K^.I. Two types of pop-in cracks which extended along the grain boundary or the plane of cleavage were observed.

Microstructural influences on fatigue crack propagation in Ti-10V-2Fe-3Al

Tensile properties and Fatigue Crack Propagation (FCP) rates have been measured in laboratory air for a wide variety of different Ti-10-2-3 microstructures, all having nominal yield strengths of 1240 MPa. These microstructural variations included both recrystallized and unrecrystallized conditions, as well as varying amounts of primary α, both α- and Ω-aged conditions, and also several hot forming histories. With one exception, microstructure was found to have very little or no influence on FCP. Not only was the rate of FCP unaffected, but moreover, the macroscopic fracture surface roughness was largely unaltered. The one exception was a notable one: the Ω-aged condition. Strengthening through the precipitation of Ω instead of α was found to retard FCP significantly; no significant change in macroscopic fracture surface roughness was found, however. The retardation was attributed to changes in slip character and reversibility.

Macroscopic fracture surface energy of unidirectional metal matrix composites: experiment and theory

A method of measuring the macroscopic frature surface energyγ F is studied and its verification is made compared with the theoretical prediction. Metal matrix composites used in the experiment are unidirectional graphite fibre-reinforced 6061 aluminium. A good agreement between the experimental and theoretical results is obtained.

Fractographic Analysis of Fatigue Failures

Abstract Although fractography is usually applied to basic research, it can also be used in studies of machine components which have failed in service or in testing. This paper discusses fractographic methods which can be used to obtain information about the stress state, environmental factors, initiating cause, and crack growth characteristics of fatigue failures. The macroscopic and microscopic fracture surface features of fatigue failures are illustrated with photomacrographs and scanning electron microscope (SEM) fractographs, and the use of SEM fractography in crack growth studies is described.