KIC Determination Research Articles

The equivalent energy method for KIC determination

The equivalent energy concept of using areas under the load-displacement record of a fracture test to any point on the linear portion of the curve and to the point of maximum load has been found to result in fracture toughness values that overestimated those determined according to the ASTM standard. The discrepancy was minimised if the 5% secant load point was used instead.

The effects of high intensity exercise on muscle and plasma levels of alpha-ketoisocaproic acid.

Alpha-ketoisocaproic acid (KIC) is the product of the transamination of the indispensable amino acid leucine, which is the first step in the complete degradation of leucine. To determine the effects of intense exercise on muscle and blood levels of KIC, 7 male volunteers performed cycle exercise to exhaustion. After pedaling at an intensity of 90 W for 3 min, the load was increased by 60 W every 3 min until volitional fatigue. Muscle biopsies were obtained prior to and immediately after exercise and rapidly frozen for later determination of KIC. During exercise, blood lactate levels increased as expected, while plasma KIC levels did not change. Following exercise, plasma KIC levels rose significantly with peak values occurring 15 min after exercise and did not return to pre-exercise values until 60 min after exercise. In contrast, muscle KIC levels increased during exercise from a pre-exercise mean of 49.4 +/- 4.1 mumol X kg-1 wet wt to 78.1 +/- 6.5 mumol X kg-1 after exercise, an average increase of 48% (P less than 0.05). These data indicate that during intense exercise, leucine transamination in muscle may continue at a faster rate than the decarboxylation of KIC. In addition, plasma levels of KIC did not reflect the intracellular accumulation of KIC during exercise, suggesting a delay in the diffusion of KIC from muscle.

Method of determination of KIc of ductile materials on a cylindrical specimen with a circular groove for surfacing

Method of determination of KIc of ductile materials on a cylindrical specimen with a circular groove for surfacing

Use of COD in KIC determination

It has been theoretically postulated that the crack opening displacement (COD) technique is applicable in characterising fracture of material in the generally yielded as well as linear elastic regimes. Hence, it is possible to determine the plane strain fracture toughness, K IC , of a material using the COD method if the onset of crack propagation and the location of the centre of rotation can be evaluated. In the present investigation, COD values at crack initiation, δ i , for Rochling Moulrex A steel were obtained with 3-point bend specimens at six different tempering temperatures using the multiple specimens load-unload extrapolation technique. It is found that by using the BS 5762:1979 analysis, K IC values were grossly over-estimated. The use of a constant rotational factor is observed to be inadequate. Under small scale yielding conditions, the centre of rotation is postulated from the present results to be located at approximately the end of the stretched zone. This supposition was applied to estimate the K IC values of standard compact tension specimens made from Rochling Moulrex A, Assab 25X and Comsteel En25 steels. Where the material was linear elastic, the estimation was good with discrepancy of less than 7%. Overestimation was seen at high tempering temperatures due to the increasing amount of plasticity in the material that shifted the location of the centre of rotation from the end of the stretched zone to a position closer to that suggested in the British Standard.

R-similarity criterion of plastic deformation instability and its use for KIC determination for steels

The paper reports an investigation of the application of the similarity theory, strain energy density concept and fracture mechanics to the fracture toughness ( K IC) determination. The method K IC determination is described using R-similarity criterion of plastic deformation instability. It allows to determine the true K IC value for ductile steels using specimens not satisfying linear fracture mechanics requirements.

Temperature dependence for the crack resistance of steel 15KhSND and some features of its fracture. Communication 1

1. The temperature dependence of crack-resistance parameters for low-alloy steel 15KhSND has been determined in the operating temperature range (+20 to −80°C) by a procedure making it possible to use relatively thin specimens. 2. The reliability of results obtained was confirmed by data for indirect determination of KIc by a method using fracture surface zone characteristics (combination of ductile and brittle zones) observed in specimens of the test steel close to the transitional temperature (0 to +20°C).

THE INFLUENCE OF POROSITY AND CARBON CONTENT ON THE FRACTURE TOUGHNESS OF SOME SINTERED STEELS

Fracture toughness (KIC) and mechanical properties at room temperature (RT) and at 200 K were evaluated for a range of sintered steels. In a series of quenched and tempered samples prepared from a lowalloy, atomized powder (Höganäs ATST-A) with 0·45 wt.-%C and density varying between 6·7 and 7·8 g/cm3 (powder forged), the KIC varied between 28 and 80 MN/m3/2 at RT and between 34 and 58 MN/m3/2 at 200 K. There was a correlation between the KIC and the yield strength of the porous materials, due to the fact that fracture of the specimen is effected by plastic instability on a micro scale. Adding carbon (0–0·84%C) and copper (2%) to a sponge-iron powder and sintering to a final density of 6·8 g/cm3 gave a material with a fracture toughness of ∼34 MN/m3/2 when the C content was >0·6%. At lower C contents the toughness was considerably increased, but it was not possible to obtain a valid. KIC determination. In this investigation a new type of fracture-toughness specimen was used, the RCT specimen, diameter 75 mm and thickness 29 mm; by using this type as opposed to the ordinary CT variant, specimens ∼50% larger could be used.

Influence of specimen geometry on the results of determination of KIc

Influence of specimen geometry on the results of determination of KIc