Effects Of Notch Acuity Research Articles

Effect of notch acuity on the fracture behavior of AZ31 Mg alloy

In this work, the effect of notch acuity on fracture behavior of rolled AZ31 Mg alloy is investigated by conducting mode-I fracture experiments using four point bend specimens with different notch root radii. Digital Image Correlation (DIC) technique is employed to determine the angle of rotation of the specimen and the fracture toughness is obtained from moment versus rotation curves. It is found that the fracture toughness Jc increases linearly with notch root radius beyond a threshold value and is almost constant below this limit. This trend is rationalized from fractographic observations near the crack initiation region which show predominantly quasi-brittle features for fatigue pre-cracked specimen and dimples of increasing size in notched specimens with enhancement in notch root radius. Significant tensile twinning is noticed in the ligament for all specimens, especially near their far edge. This is found to impart substantial toughening even in the fatigue pre-cracked specimen which fails by a locally quasi-brittle mechanism. Finally, the strong increase in Jc with notch root radius beyond a threshold is interpreted using two ductile fracture initiation models.

Effect of notch acuity on the apparent fracture toughness

The fracture behaviour of a component or specimen that contains a sharp notch is governed essentially by the same theoretical relations known from cracks. The blunt notch root only causes an increase of the resistance against crack initiation, which depends on the fracture mechanism. In the present paper, the relation between fracture toughness and notch toughness is investigated by simple analytical models. The derived formulas were compared with experimental results obtained from fracture toughness tests on RPV-steel 24 NiCrMo 3-7 at various temperatures. 1T-CT- and 0.4T-SEB-specimens that contained a sharp notch with a root radius of 0.06mm introduced by spark erosion (EDM) instead of the standard fatigue crack were used. The predictions were found to agree well with the experimental data. The effect of the notch radius on fracture toughness is most pronounced in the brittle to ductile transition regime, where fracture toughness can be characterized by the master curve and the corresponding reference temperature T0 according to ASTM E1921. Accordingly, the effect of the notch radius can be quantified by a shift of T0. Since the shape of the transition curve depends on the notch radius, the procedure of ASTM E1921 to determine T0 is not applicable. An alternative is suggested. As limiting cases, ductile tearing and brittle fracture are also considered.

Notch acuity effects on the fracture toughness of freshwater ice : Wei, Y; DeFranco, S J; Dempsey, J P Proc 9th International Conference on Offshore Mechanics and Arctic Engineering, Houston, 18–23 February 1990V4, P253–257. Publ New York: ASME, 1990

Notch acuity effects on the fracture toughness of freshwater ice : Wei, Y; DeFranco, S J; Dempsey, J P Proc 9th International Conference on Offshore Mechanics and Arctic Engineering, Houston, 18–23 February 1990V4, P253–257. Publ New York: ASME, 1990

Notch-acuity effects on the fracture toughness of saline ice

Dynamic ocean-induced loading of ice has recently prompted interest in the fatigue strength of ice and, consequently, aspects of the fracture testing of ice need to be examined. One aspect in fracture testing, the effects of notch acuity on the apparent fracture toughness (KQ) of saline ice, was investigated in this study using four groups of single-edge notched-bend specimens with different crack-(or notch-) root radii, fabricated by four different methods; namely, drilling a small hole of two different radii at the crack tip, cutting a crack with a band saw and using a hand-held razor blade to scribe a sharp crack. For this study, tests were performed on saline ice using one crack length and orientation, constant thickness and constant temperature (−25°C). The mean values and the standard deviations of the apparent fracture toughness of the specimens with blunt notches were higher than those with sharp cracks. The results presented in a plot of fracture toughness versus where ρ is the crack-tip radius, provide a preliminary estimate of the required notch acuity for fracture-toughness testing of saline ice.

Crack-fabrication techniques and their effects on the fracture toughness and CTOD for fresh-water columnar ice

AbstractThe effects of notch acuity (crack-tip sharpness) on the fracture toughness of S2 ice were investigated using six groups of single-edge-notched-bend (SENB) specimens with different crack (or notch) root radii fabricated by six different methods. The mean value and standard deviations of the apparent fracture-toughness valuesKQof the specimens with blunt notches were significantly higher than those of the specimens with sharp cracks. The results presented in a plot of fracture toughness versus, wherepis the crack-tip radius, provide an estimate of the required notch acuity for fracture-toughness testing. The microstructural features in the immediate vicinity of the crack tip and the crack-tip geometry govern the magnitude of the apparent fracture toughness of the ice. The crack-tip-opening-displacement (CTOD) measured in this study indicates the existence of microplastic deformation in the vicinity of the crack tip at the initiation of unstable fracture.

Notch-acuity effects on the fracture toughness of saline ice

Dynamic ocean-induced loading of ice has recently prompted interest in the fatigue strength of ice and, consequently, aspects of the fracture testing of ice need to be examined. One aspect in fracture testing, the effects of notch acuity on the apparent fracture toughness (KQ) of saline ice, was investigated in this study using four groups of single-edge notched-bend specimens with different crack-(or notch-) root radii, fabricated by four different methods; namely, drilling a small hole of two different radii at the crack tip, cutting a crack with a band saw and using a hand-held razor blade to scribe a sharp crack. For this study, tests were performed on saline ice using one crack length and orientation, constant thickness and constant temperature (−25°C). The mean values and the standard deviations of the apparent fracture toughness of the specimens with blunt notches were higher than those with sharp cracks. The results presented in a plot of fracture toughness versuswhere ρ is the crack-tip radius, provide a preliminary estimate of the required notch acuity for fracture-toughness testing of saline ice.

Effect of Notch Acuity on Critical COD

Effect of Notch Acuity on Critical COD

Effect of Notch Acuity on Critical COD with COD Bend Test Specimens

The conventional COD bend tests are frequently used for the purpose of obtaining a critical COD (δc). But it is well known that δc shows various values depending on notch acuities. Accordingly, COD bend test specimens have usually a fatigue notch. However the industrial material tests are desired to be simple. In this sense, it is desirable that COD bend test specimens have only machined notch.In this paper, the transformation equations of a mouth COD (Vtotal) for a machined notch to δc for a fatigue notch are proposed by considering the machined notch root displacement. These transformation equations are expressed as follows :δ= O.45 (W-a) /0.45W+0.55a+Z [(Vtotal-Ve) -V'] … (Vtotal-Ve≥2V')O.45 (W-a) /0.45W+0.55a+Z [(Vtotal-Ve) 2/4V'] … (Vtotal-Ve<2V')Ve= 0.8d0.3 … (Vtotal≥4V'){0.8d0.3-0.74d0.45 (1-Vtotal/4V')} Vtotal… (Vtotal<4V')whereV'=γσYW (1-v2) /E : limit elastic clip gauge COD defined by Wells, W : specimen width, a : crack depth, Z : distance from free surface to positions setting a clip gauge, d : initial notch root width (d≤0.4mm)The above proposed equations are obtained from results of F. E. M. analysis, and it was confirmed that the relation between δ by the above equations and the plastic zone size is not different in the case of various notch acuities of the specimens. These equations are engineeringly satisfactory in the range of d≤0.4 mm for various materials.

Microstructure and toughness of structural steels

AbstractThe effects of notch acuity, inclusion content, and strength level on the toughness of a variety of ductile steels have been investigated infully plastic single edge notched bend testpieces. Results for specimens containing fatigue precracks and sharp notches indicate that accurate predictions of a material's resistance to the initiation of fibrous fracture ahead of afatigue crack may be inferred from tests on notched testpieces andfrom a knowledge of the microstructure of the material; an experimental procedure has been proposed whereby this may be achieved for quality control and material evaluation purposes. The spacing of optically visible inclusions is found essentially to define both the unit of ductile crack extension and, for low-strength steels, the limiting lateral dimensions of the high-strain field ahead of the crack tip. As a consequence, the notch-tip ductility isfound to be invariant with the changes in notch acuity for sharp stress concentrators. The effect of increasing the purity...

The effect of notch acuity on fracture toughness testing

The effect of notch acuity on the fracture behaviour of a low alloy bainitic steel has been investigated. A simple model has been developed which relates the apparent fracture toughness at a given notch root radius, K A (ϱ), to the plane strain fracture toughness K 1C. It is shown that the apparent fracture toughness is not proportional to the square root of the notch root radius but is in good agreement with the expression given here.

Consistency of Critical COD and a Proposed Method of ρ+c Determination

The three-point bending COD test with clip gauge technique is a promising method of determining the toughness of structural steels in terms of the modern concept of fracture mechanics. The consistency of the critical COD value has been demonstrated by many investigators. The present authors supplement here some information in this aspect of problem, viz, the effect of notch acuity, the thickness insensitivity, comparison between small sized bending test and deeply notched wide plate tension test, and so on.A simple method of converting the critical COD to the value of ρ+c is experimentally established. It is supported by the fact that the critical COD divided by the yield strength is proportional to the fifth power of the absolute temperature. As an example of practical application, the welded-and-notched wide plate tension test is successfully analysed by the ρ+c concept. The ρ+c value used in the analysis is one converted from the critical COD value measured by simple testing.