Fracture Toughness Klc

Table 19.6 Mechanical properties (elastic modulus ( ), shear modulus (G), Poisson s ratio (v), hardness Hz), and fracture toughness Klc) of composites sintered by SPS...

The characteristic or fracture conveyed by Gic is sometimes expressed in two other ways. The first is the fracture toughness, Klc, which is related to Gic by the equation... 

It is clear that structure-sensitive dynamic properties [low-cycle fatigue (LCF) and fracture toughness (Klc)] notably increase for the alloy with the nondendritic structure. One more proof of the advantage of the nondendritic structure are the results on mechanical properties measured in three directions of forgings from a 1933 grade alloy obtained from large-scale ingots of 845 mm in diameter (Table 16). 

Relevant mechanical properties at this temperature, such as Youngs modulus, E, yield strengdi, (jy, and fracture toughness, Klc, were determined for the individual constituent materials and are listed in Table I. Glass-transition tempera-... 

Cracks propagate laterally when the stress intensity factor, Kt, exceeds the fracture toughness, Klc, of the scale. In a nonuniform stress field, also the stress intensity factor varies spatially according to formula (9). The position of the crack tip in a nonuniform stress field is determined by the equation Kx = /. .The last equation together with formula (9) permits, in principle, to derive the fracture toughness from the position of the crack tip provided the tensile stress is known as a function of the position (cf. Fig. 11). (In an accurate description, formula (9) has to be replaced by a corresponding relation /q(cr) which takes into account the interaction of parallel cracks.)... 

ASTM E399, Standard Test Method for Linear-Elastic Plane-Strain Fracture Toughness Klc of Metallic Materials(1983)... 

Alloy and con tion(a) Room- temperature yield strength Speci- men design Orienta- Fracture toughness, KlC ... 

Secondly, Irwin 6) found that the stress field around a sharp crack in a linear elastic material could be uniquely defined by a parameter named the stress-intensity factor, K and stated that fracture occurs when the value of K, exceeds some critical value, K C. Thus, K, is a stress field parameter independent of the material whereas Klc, often referred to as the fracture toughness, is a measure of a material property. Again the subscript I is used to denote the tensile-opening mode. 

Fracture toughness for siloxane-modified as well as ATBN- and CTBN-modified resins was monitored through KIC, plane-strain fracture toughness 44). The Klc values of at least five three-point bend (3PB) specimens of each material were calculated according to Eq. (1)... 

Our interest in PDMS as an epoxy modifier lies partly in its low Tg relative to the ATBN and CTBN modifiers. Up to this time, however, improvements in K,c through copolymerization of dimethyl siloxane with TFP and DP siloxane require raising the Tg of the siloxane modifier above that of PDMS, as shown by Table 1. It is hoped that increased understanding and control of the synthesis and morphologies of siloxane-modified epoxies will make it possible to retain the low Tg of the modifier while raising the fracture toughness of the resin. The true value of this objective could eventually be shown by measurement of Klc at temperatures below ambient. 

The effect of whisker-matrix interfaces on mechanical properties becomes clear when the same Al203-SiC materials are hot-pressed at different temperatures. While maintaining similar density, similar sizes of alumina grains, and identical whisker volumes, these composites have different fracture toughnesses as shown in Fig. 19. The differences in Klc values between A1203 with ACMC SC-9 SiC and A1203 with Tateho SCW... 

As the critical stress intensity factor (=fracture toughness) is Klc = ] IE y the fracture stress becomes... 

Conds condenser Klc plane strain fracture toughness... 

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