Fracture Toughness of Freshwater Ice—Part II: Analysis and Micrography

1996 ◽  
Vol 118 (2) ◽  
pp. 141-147 ◽  
Author(s):  
L. J. Weber ◽  
W. A. Nixon
Keyword(s):  
Fracture Toughness ◽  
Fracture Surface ◽  
Experimental Technique ◽  
Loading Rate ◽  
Process Zone ◽  
Crack Tip ◽  
Simple Method ◽  
Dislocation Activity ◽  
Freshwater Ice

Experiments have been performed to determine the effect of loading rate and temperature on the fracture toughness of freshwater ice. A first paper (Weber and Nixon, 1996) presents the experimental technique and results, while this paper focuses on discussion of the crack tip process zone and fracture surface micrography. A simple method to estimate the size of the process zone will be presented. Also, fracture surface micrography will be used to interpret the results of the temperature experiments by considering evidence of dislocation activity in preferentially oriented grains.

Fracture Toughness of Freshwater Ice—Part I: Experimental Technique and Results

1996 ◽  
Vol 118 (2) ◽  
pp. 135-140 ◽  
Author(s):  
L. J. Weber ◽  
W. A. Nixon
Keyword(s):  
Fracture Toughness ◽  
Experimental Technique ◽  
Test Temperature ◽  
Significant Variation ◽  
Loading Rate ◽  
Companion Paper ◽  
Fractographic Analysis ◽  
Linear Elastic ◽  
Freshwater Ice ◽  
Crack Tip Plasticity

Experiments have been performed to determine the effect of loading rate and temperature on the fracture toughness of both granular and S2 columnar freshwater ice. Loading rate was varied from 0.04 to 40.0 kPam s-1, and over this range the fracture toughness was observed to decrease from 201 to 109 kPam. Examination of load—CMOD curves indicate that at a loading rate of 40 kPam s-1, the crack tip plasticity was sufficiently limited that the specimen behavior can be considered linear elastic, thus providing a valid Kq measurement. When test temperature was varied from −5 to −45°C for the S2 columnar ice, no significant variation in toughness was observed. In contrast, for granular ice, a higher toughness (144 kPam) was observed in the −5 to −20°C range than for the S2 columnar ice. However, the toughness of the granular ice at−45°C is not significantly different from that of the S2 columnar ice. A companion paper (Weber and Nixon, 1996) analyzes the results in greater detail comparing them with previous work, and presents a detailed fractographic analysis of the failure surfaces.

Fracture Behaviour of Two-Phase γ-Titanium Aluminides

1994 ◽  
Vol 364 ◽  
Author(s):  
Fritz Appel ◽  
Uwe Lorenz ◽  
Tao Zhang ◽  
Richard Wagner
Keyword(s):  
Fracture Toughness ◽  
Crack Propagation ◽  
Titanium Aluminides ◽  
Process Zone ◽  
Crack Tip ◽  
Lamellar Microstructure ◽  
High Fracture Toughness ◽  
High Fracture ◽  
Two Phase ◽  
Lamellar Interfaces

AbstractTitanium aluminides with a lamellar microstructure consisting of the intermetallic phases ֱ2 (Ti3Al) and γ(TiAl) suffer from brittleness at ambient temperatures but exhibit at the same time a relatively high fracture toughness. This discrepancy indicates particular processes stabilizing crack propagation in the lamellar microstructure. In this context, the toughening mechanisms were investigated in (α2 + γ) TiAl alloys which contained different volume fractions of lamellar colonies. The fracture toughness for crack propagation parallel or across the lamellar interfaces was estimated by using chevron-notched bending bars. Electron microscope studies were performed to characterize the related processes of crack tip plasticity. Special emphasis was paid to the crystallography of crack propagation and to the interaction of crack tips with lamellar interfaces. Accordingly, the lamellar morphology derives some of its toughness from interface-related processes which stabilize crack propagation by deflecting the crack tip and providing the necessary dislocation sources for crack tip shielding in the process zone ahead of the crack tip.

Annealing Effects on Toughened Intra-Type Nanocomposites

2006 ◽  
Vol 45 ◽  
pp. 1632-1639 ◽  
Author(s):  
Hideo Awaji ◽  
Seong Min Choi
Keyword(s):  
Fracture Toughness ◽  
Elevated Temperatures ◽  
Volume Fraction ◽  
Process Zone ◽  
Nitrate Solution ◽  
Crack Tip ◽  
Hydrogen Atmosphere ◽  
Second Phase ◽  
High Porosity ◽  
The Matrix

Intra-type nanocomposites, in which nanosized second-phase particles are embedded within matrix grains, generate dislocations around the dispersed nanoparticles. The intra-type nanostructure induces a thermal expansion mismatch between the matrix and the dispersed particles, which will yield nanoscale stress distribution around the particles and generate lattice defects, such as dislocations. The dislocations of ceramics can be generated at elevated temperatures, become sessile dislocations at room temperature, and serve as nanocrack nuclei in highly stresses fields, e.g. at a main crack tip. The frontal process zone size ahead of a crack tip is expanded due to creation of nanocracks and hence the fracture toughness is improved. Annealing after sintered nanocomposites is important in controlling the dislocation activities. Appropriate annealing will disperse dislocations into the matrix grains. However, dislocations are sensitive to temperature, and higher temperature or longer annealing time result in dislocation disappearance and cause the reduction of the strength and fracture toughness of nanocomposites. In this study, commercially available γ-alumina agglomerated powder with high porosity was used to create the intra-type nanostructure. Nickel nitrate solution was infiltrated into nanopores of the γ-alumina agglomerates in vacuum. The alumina/nickel composite powder following reduction in hydrogen atmosphere was sintered using a pulse electric current sintering method. The volume fraction of nickel was about 3 vol %. After appropriate annealing, the highest fracture toughness was obtained to be 7.6 MPam1/2, which is two times higher than that of monolithic alumina.

The Texture Effect on the Dynamic Fracture Properties of Magnesium Alloy AZ31B

2016 ◽  
Vol 715 ◽  
pp. 74-79
Author(s):  
Xia Yu ◽  
Yu Long Li ◽  
Tao Li
Keyword(s):  
Fracture Toughness ◽  
Grain Size ◽  
Fracture Surface ◽  
Dynamic Fracture ◽  
Texture Evolution ◽  
Crack Tip ◽  
Image Correlation ◽  
Coarse Grain ◽  
Alloy Plate ◽  
Fine Grain

In this work, Mode I dynamic fracture experiments are conducted on pre-cracked three point bending specimens by using modified split-Hopkinson pressure bar. Two sets of specimens with different initial textures are considered here: one set of the specimens are machined from a hot rolled AZ31B Mg alloy plate with a bigger grain size. The others are treated by four pass of equal channel angular pressing (ECAP) after they are cut from the initial material. They are with the finer grain size. Digital image correlation (DIC) technique is used to determine the strain contours around the crack tip and electron back scatter diffraction (EBSD) is employed to analyze the texture evolution after tests. It is found that the dynamic fracture toughness of finer grain specimen is higher than that of coarse grain specimen. The fracture toughness of both sets of specimens is enhanced by increasing the loading rates. Texture analysis shows the formation of tensile twinning in the ligament ahead of the crack tip in the coarse grain specimen but no sign in fine grain specimen. The brittle features e. g. cleavage planes and twinning lamellas are observed on the fracture surface of coarse grain specimen by scanning electron microscope (SEM). However, the relative ductile features such as micro-voids surrounding by tear ridges present on the fracture surface of fine grain specimen.

Geometrical Shielding Produced by Intergranular Crack-Tip Branching in Fe–V–P Alloy

2011 ◽  
Vol 465 ◽  
pp. 574-577
Author(s):  
Jana Horníková ◽  
Pavel Šandera ◽  
Libor Pantělejev ◽  
Jaroslav Pokluda
Keyword(s):  
Fracture Toughness ◽  
Fracture Surface ◽  
Intergranular Fracture ◽  
Triple Point ◽  
Intergranular Crack ◽  
Crack Tip ◽  
Crack Tip Shielding

The geometrical shielding produced by intergranular crack-tip branching in the fracture toughness tests of the Fe–V–P alloy is quantitatively assessed particularly with respect to the contribution of crack splitting. This process was evaluated by an identification of secondary intergranular cracks visualized on metalographical samples perpendicular to the fracture surface. The analysis of mixed trans/intergranular fracture revealed no special influence of triple-point branching (splitting) on the total crack tip shielding in cases of such highly spatially tortuous crack fronts. Thus, the previously reported results taking only the effect of crack tip kinking and meandering into account were proved to be correct.

scholarly journals A Simple Method for Estimating the Effect of Loading Rate on Fracture Toughness

1994 ◽  
Vol 1994 (176) ◽  
pp. 491-500
Author(s):  
Koji Gotoh ◽  
Hiroaki Hirasawa ◽  
Masahiro Toyosada
Keyword(s):  
Fracture Toughness ◽  
Loading Rate ◽  
Simple Method

Finite Element Analysis of Rubber Particles Size Distribution on Fracture Toughness of Rubber-Modified Polymer

2004 ◽  
Vol 261-263 ◽  
pp. 711-716 ◽  
Author(s):  
Husaini ◽  
Kikuo Kishimoto ◽  
Mitsuo Notomi
Keyword(s):  
Fracture Toughness ◽  
Cell Model ◽  
Numerical Study ◽  
Process Zone ◽  
Outer Region ◽  
Crack Tip ◽  
Small Scale ◽  
Homogeneous Material ◽  
Modified Polymer ◽  
Rubber Particles

A numerical study on the effects of the distribution of rubber particles size on the fracture toughness of rubber-modified polymer alloys was computed. FEM analyses were conducted on the deformation field near the crack tip under mode I for small scale yielding condition. Near the crack tip is modelled as composite of matrix materials and rubber particles. On the other hand, outer region is modelled as homogeneous material whose constitutive equation has been obtained by analysing unit cell model of matrix and rubber particle. Perfect bonding or partial debonding of the interface is assumed in the computation. Matrix and rubber particles are treated as Mises and Mooney-Rivlin materials, respectively. It is shown that energy flux into fracture process zone; Ĵ -integral is smaller for bimodal type than monomodal one. This behavior largely occurred on the partial debonding case. These results imply that the screening effects occurred in the bimodal type larger than monomodal one.

Adhesion of polymer–inorganic interfaces by nanoindentation

2001 ◽  
Vol 16 (12) ◽  
pp. 3378-3388 ◽  
Author(s):  
Min Li ◽  
C. Barry Carter ◽  
Marc A. Hillmyer ◽  
William W. Gerberich
Keyword(s):  
Fracture Toughness ◽  
Atomic Force Microscopy ◽  
Fracture Surface ◽  
Surface Characterization ◽  
Process Zone ◽  
Crack Arrest ◽  
Force Microscopy ◽  
Atomic Force ◽  
Glass Interface ◽  
Good Agreement

Nanoindentation combined with atomic force microscopy was applied to measure the fracture toughness of polystyrene/glass interfaces. Film delamination occurs when the inelastic penetration depth approximately equals or exceeds the film thickness. The delamination size was accurately measured using atomic force microscopy. Using multilayer indentation and annular-plate analyses, the interfacial fracture toughness was then assessed. The values obtained from the two analyses are in good agreement with the fracture toughness of the interface being approximately 350 mJ/m2. By appropriate fracture surface characterization, it was shown that fracture occurs along the polystyrene/glass interface. Crack arrest marks were observed, and their possible cause discussed. On the basis of the morphology of the fracture surface, the fracture toughness was also evaluated using a process zone analysis. The result agrees well with those obtained from the other two analyses.

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