In this study, we investigated the drawbacks of previous studies regarding the evaluation of fracture toughness from spherical indentation tests (SITs). This was achieved by an examination of the material damage mechanism during indentation tests, uniaxial tensile tests, and Mode I/II fracture tests. A new approach based on the energy release rate was proposed in this study to evaluate the fracture toughness of ductile metals. Scanning electron microscope (SEM) observations revealed that the mechanism for material damage during an indentation test was different with the material damage in uniaxial tensile tests and Mode I fracture tests, but similar to that in Mode II fracture tests. Thus, the energy release rate during SITs should be correlated with J IIC . Compared with previous studies, this new proposed method was more consistent with the actual damage mechanism and did not rely on the specific critical damage values. Experiments on SA508, SA533, 15CrMoR, and S30408 revealed that the maximum error from this energy release rate-based approach was no more than 13% when compared with their conventional counterparts (compact tension tests), and thus can meet the precision requirement of engineering applications.

In this work, a numerical analysis based on the linear hardening model and ball indentation test was proposed to determine the properties of materials such as austenitic stainless steels that obey linear hardening behavior. Experiments on 304 and 321 austenitic stainless steel showed that the numerical method provides yield and tensile strength values with a maximum error of less than 5% and the hardening behavior identical with uniaxial tensile tests, while the average error for yield strength was more than 30% with the empirical method. The reasons why the empirical method produces larger errors for non-power law materials were analyzed in detail. The elastic modulus calculation method was also re-investigated, and the model based on re-loading showed much bigger equivalent contact diameters and provided more accurate elastic modulus values in a simple way.

The authors researched the effects of specimen size on the very high cycle fatigue properties of FV520B-I through ultrasonic fatigue testing. The test results showed that the very high cycle fatigue mechanism was not changed and the fatigue properties declined as the specimen size increased. The S - N curve moved downward and the fatigue life decreased under the same stress level maybe due to the heat effects of large specimens in tests. The fatigue strength and the fatigue life were predicted by relevant models. The prediction of fatigue strength was close to test result, and the prediction of fatigue life was less effective compared with the previous prediction of small size specimen test results.

20 steel thick-wall high-pressure pipes are widely used in chemical industry in China, but brittle fracture accidents of them happen frequently in recent years. The strain aging steel pipes in this research were artificially made in the laboratory and naturally occurred in fabrication or service. The microstructure of strain aging in samples taken from the unused pipes and the accident pipes caused directly or mainly by strain aging were observed with optical microscopy, scanning electron microscopy, and transmission electron microscopy. The results show that: (1)uniform ferrite and pearlite with uniform lamellar structure can be achieved with normalizing; lamellar pearlite fractures and distorts while a large number of dislocation cells, micro-holes or cracks appear in material after strain aging; and broken distorted pearlite changes to uniform spherical structure after stress relieving; (2) both the samples taken from unused and accident pipes which strain aging artificially in the laboratory and naturally in fabrication or service have the same characteristics as following: the basic changes of microstructure after strain aging cannot be observed with optical microscopy, but can be observed with scanning electron microscopy and transmission electron microscopy.

A destructive explosion of a multilayered urea reactor on Mar. 21, 2005 in Shandong Province, China resulted in huge losses. About 10 urea reactors were scrapped in inspection and assessment after the explosion for the reason of layers severely cracking. Three scrapped urea reactors including the explosive reactor were anatomized layer by layer and 12 cracking reactors, and others were investigated for further study. Cracking morphology was observed in detail. Taking account of application conditions, the layer cracking can be divided into four categories: 1) severe cracking from the outmost layer inward, 2) severe cracking from the innermost layer outward, 3) randomly cracking from the outmost layer inward, or the innermost layer outward, or the middle layer, and 4) slight cracking. The reason for the layer cracking is SCC which is proved by means of visual observing the characteristics of the reactor cracking, metallographic experimenting on the samples taken from the cracking regions in the reactor and analyzing the corrosion products in the clearances between layers, the clearances of the cracks, and spills from air vent. The authors analyzed factors which caused different cracking categories from material, stress and media, gave advice on the leak detection of urea reactors: either the quality and flow of the leak detection steam should be strictly controlled, or better leak detection method should be used.