Fracture, and ductility

The intermetallic alloy NiAl is discussed as a potential base alloy for high temperature structural materials. Its use is currently limited by low room temperature ductility and fracture toughness. Consequently, substantial research efforts have been directed towards understanding its mechanical behaviour [1, 2] so that detailed experimental [3, 4, 5] and theoretical [6, 7, 8] analyses of the deformation of NiAl are available today. 

Intermetallic alloys (compounds) are becoming of increasing interest as materials which possess significantly enhanced high temperature capabilities compared to many conventional metallic alloys. However, they suffer intrinsic problems associated with low-temperature ductility and fracture toughness. Two types of... 

The manifestation of hydrogen embrittlement in structural metals is enhanced susceptibility to fracture. Hydrogen reduces typical measures of fracture resistance such as tensile strength, ductility, and fracture toughness, accelerates fatigue crack propagation, and introduces additional material failure modes... 

The conservative strategy is to place an intermediate casing string seated at the boundary between ductile and fractured shales, having drilled the ductile shale with oil-based drilling fluid, then converting to a water-based fluid to drill out of the... 

In [ 1991 Par] the cast iron containing small contents of Cu and Mo was studied aiming to improve mechanical properties. Phase transformations during heat treatment and flieir influence on strengfli, ductility and fracture toughness were established. 

Very recently, in our group, enhanced self-reinforced PP composites based on commercial PP fabrics were obtained by the film stacking method followed by compression molding introducing different contents of micron-sized quartz particles in the matrix films (unpublished results). Simultaneous improvements of composite tensile strength, ductility and fracture toughness were observed from the addition of quartz to the polymer matrix (Table 14.1). Enhanced degree of consohdation was obtained for the composites with quartz as evidenced from the improved mechanical properties and by SEM observations. This was also confirmed by acoustic emission analysis in situ in tensile tests. 

Mechanical properties of the in-core components change as a result of the fast neutron flux damage. The strength increases and ductility and fracture toughness decrease to shelf levels that are acceptable for service. Recent developments in pressure tube technology have made the pressure tubes more resistant to decreases in fracture toughness caused by irradiation. 

As for all a-p alloys, excessive aluminum, oxygen, and nitrogen can reduce ductility and fracture toughness. Excessive beta stabilizers (for example, molybdenum or vanadium) affect the stability... 

Note Property variations for different microstructiual conditions as reported in C.H. Ward et al., crostructure, Ihnsile Ductility, and Fracture Toughness of Ti-25Al-10Nb-3V-lMo, Seventh World Conference on Titanium, to be published... 

A review of the literature shows that the details of the fracture process and the attempts to improve ductility vary from system to system, and that there are many individual reports on ductility and fracture in specific compounds. To bring all of this information together in a comprehensive way, we have organized this chapter as follows. We will first summarize the research that has been done on compounds with either the Llj (cP4) structure or the B2 (cP2) structure. These are emphasized because, as far as fracture and ductility are concerned, they have been investigated the most... 

In addition to the research on LI2 and B2 compounds described above, ductility and fracture mode have been reported on compounds with other crystal structures. We have chosen not to discuss these alloys in depth because the research on them has not been as broad and because most of the important features of brittle fracture in these compounds have already been described by considering the other systems. Table 7 summarizes these studies. (Note that in the table a crystal structure that is given in parentheses is the structure of the base compound but alloying additions have caused a change in the structure to the one that is listed first.) The main point to note is that, just as with the LI2 and B2 compounds, these compounds tend to be brittle at room temperature and the fracture is either cleavage or intergranular. Attempts to alloy these compounds have in some cases produced significant... 

Table 7. Ductility and fracture mode data for various intermetallic compounds...

The practical use of the cheaper types of building materials such as glass, gypsum, ceramics, calcium silicate, cement, and concrete is limited because of the notch sensitivity and brittleness of these materials. When loaded in tension the ultimate straining capacity of such materials is only some 100-200 U-strain (1 p-strain = 10 °) and the ductility and fracture energy is negligible in comparison with most other materials. 

It is worth noting that, except for the Young s modulus, the strength, ductility, and fracture toughness of the nanocomposite between the good exfoliation and moderate exfoliation are similar. 

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