Transition modelling of surface flaws to through cracks

2020 ◽  
Vol 43 (7) ◽  
pp. 1353-1367
Author(s):  
Morris Satin ◽  
W. Steven Johnson ◽  
Richard W. Neu ◽  
Balkrishna Annigeri ◽  
Brett Ziegler ◽  
...  
Keyword(s):  
Surface Flaws ◽  
Transition Modelling

Sem Examinations of Glass Knives

1970 ◽  
Vol 28 ◽  
pp. 282-283
Author(s):  
J. Temple Black
Keyword(s):  
Plastic Deformation ◽  
Tensile Loading ◽  
Resultant Force ◽  
Stress Concentrations ◽  
Edge Chipping ◽  
Surface Flaws ◽  
Edge Defects ◽  
Microscopic Surface

There are two types of edge defects common to glass knives as typically prepared for microtomy purposes: 1) striations and 2) edge chipping. The former is a function of the free breaking process while edge chipping results from usage or bumping of the edge. Because glass has no well defined planes in its structure, it should be highly resistant to plastic deformation of any sort, including tensile loading. In practice, prevention of microscopic surface flaws is impossible. The surface flaws produce stress concentrations so that tensile strengths in glass are typically 10-20 kpsi and vary only slightly with composition. If glass can be kept in compression, wherein failure is literally unknown (1), it will remain intact for long periods of time. Forces acting on the tool in microtomy produce a resultant force that acts to keep the edge in compression.

Glass Knife Geometry as Seen by the SEM

1971 ◽  
Vol 29 ◽  
pp. 454-455
Author(s):  
J. Temple Black
Keyword(s):  
Low Cost ◽  
Amorphous Material ◽  
Stress Concentrations ◽  
Basic Tool ◽  
Tool Materials ◽  
Optical Inspection ◽  
Surface Flaws ◽  
Slip Planes ◽  
Glass Knife ◽  
Diamond Knife

In ultramicrotomy, the two basic tool materials are glass and diamond. Glass because of its low cost and ease of manufacture of the knife itself is still widely used despite the superiority of diamond knives in many applications. Both kinds of knives produce plastic deformation in the microtomed section due to the nature of the cutting process and microscopic chips in the edge of the knife. Because glass has no well defined slip planes in its structure (it's an amorphous material), it is very strong and essentially never fails in compression. However, surface flaws produce stress concentrations which reduce the strength of glass to 10,000 to 20,000 psi from its theoretical or flaw free values of 1 to 2 million psi. While the microchips in the edge of the glass or diamond knife are generally too small to be observed in the SEM, the second common type of defect can be identified. This is the striations (also termed the check marks or feathers) which are always present over the entire edge of a glass knife regardless of whether or not they are visable under optical inspection. These steps in the cutting edge can be observed in the SEM by proper preparation of carefully broken knives and orientation of the knife, with respect to the scanning beam.

Controlled Surface Flaws in Hot-Pressed SiC

1976 ◽  
Vol 59 (1-2) ◽  
pp. 34-37 ◽  
Author(s):  
J. J. PETROVIC ◽  
L. A. JACOBSON
Keyword(s):  
Surface Flaws

Effect of Flaw Dimensions on Ductile Fracture Behavior of Non-Aligned Multiple Flaws in a Plate

2011 ◽  
Author(s):  
Katsumasa Miyazaki ◽  
Kunio Hasegawa ◽  
Koichi Saito
Keyword(s):  
Ductile Fracture ◽  
Flat Plate ◽  
Fracture Behavior ◽  
Maximum Load ◽  
Surface Flaws ◽  
Fracture Tests ◽  
The Difference ◽  
Almost All ◽  
Maximum Minimum

The fitness-for-service codes require the characterization of non-aligned multiple flaws for flaw evaluation, which is performed using a flaw proximity rule. Worldwide, almost all such codes provide their own proximity rule, often with unclear technical bases of the application of proximity rule to ductile or fully plastic fracture. In particular, the effect of flaw dimensions of multiple surface flaws on fully plastic fracture of non-aligned multiple flaws had not been clear. To clarify the effect of the difference of part through-wall and through-wall flaws on the behavior of fully plastic fracture, the fracture tests of flat plate specimens with non-aligned multiple part through-wall flaws were conducted. When the flaw depth a was shallow with 0.4 in ratio of a to thickness t, the maximum load Pmax occurred at penetration of multiple flaws and the effect of vertical distance of non-aligned multiple flaws H on Pmax was not so significant. However, when flaw depth was deep with 0.8 in a/t, Pmax occurred after penetration of flaws and the effect of H on Pmax could be seen clearly. It was judged that the through-wall flaw tests were appropriate for discussion of the effect of H on Pmax and the alignment rule of multiple flaws. In addition, in order to clarify the appropriate length parameter to estimate Pmax of test specimens with dissimilar non-aligned through-wall multiple flaws, the fracture tests of plate specimens were also conducted. The effect of different flaw length on Pmax was discussed with maximum, minimum and averages of dissimilar non-aligned multiple flaw lengths. Experimental results showed that the maximum length lmax would be an appropriate length parameter to estimate Pmax, when the non-aligned multiple through-wall flaws were dissimilar.

Children’s Revision of Textual Flaws

1997 ◽  
Vol 20 (4) ◽  
pp. 667-680 ◽  
Author(s):  
Catherine Ann Cameron ◽  
Gail Edmunds ◽  
Barbara Wigmore ◽  
Anne Kathryn Hunt ◽  
M. J. Linton
Keyword(s):  
Reading Difficulty ◽  
Fifth Grade ◽  
Second Grade ◽  
Writing Quality ◽  
Text Revision ◽  
Fifth Grade Students ◽  
Comprehension Skills ◽  
Surface Flaws ◽  
Text Reading ◽  
Reading Comprehension Skills

Two studies are reported here that investigated elementary school children’s text revision. In the first experiment, both semantic and surface flaws were inserted in texts that varied in reading difficulty. Second-grade through fifth-grade students revised these experimenter-generated passages, presented as examples of submissions to a class newspaper. Differences in text reading difficulty did not affect revision effectiveness, nor were the semantic flaws especially difficult to detect and revise. An age effect showed growth in the revision of both semantic and surface errors from grades 2 to 4 with 2nd-graders revising one-third of the inserted errors, and 4th- and 5th-graders revising three-quarters of them. Revision and cloze reading comprehension skills were correlated. A second study compared students’ revision of their own as well as another’s text flaws. Fifth-graders wrote a narrative for a classroom anthology, and they revised both their own and inserted flaws. Their writing was evaluated holistically. Rates of both semantic and surface revision were somewhat lower for their own as opposed to another’s text errors, but revision rates were nevertheless relatively high, and they correlated with writing quality; that is, children who wrote high-quality texts also revised more errors, especially experimenter-inserted flaws. These data confirm that children respond positively to writing challenges in the area of revision, a skill in process of development, which is amenable to inspection and appears ripe for facilitation.

Luminescence of different surface flaws in high purity silica glass under UV excitation

2011 ◽  
Author(s):  
J. Fournier ◽  
J. Néauport ◽  
P. Grua ◽  
V. Jubera ◽  
E. Fargin ◽  
...  
Keyword(s):  
High Purity ◽  
Silica Glass ◽  
Surface Flaws ◽  
Uv Excitation

Experimental Determination of Side Boundary Effects on Stress Intensity Factors in Surface Flaws

1975 ◽  
Vol 97 (1) ◽  
pp. 45-51 ◽  
Author(s):  
M. Jolles ◽  
J. J. McGowan ◽  
C. W. Smith
Keyword(s):  
Stress Intensity ◽  
Crack Length ◽  
Taylor Series ◽  
Stress Intensity Factors ◽  
Taylor Series Expansion ◽  
Correction Method ◽  
Intensity Factors ◽  
Surface Flaws ◽  
Plate Width

A technique consisting of stress-freezing photoelasticity coupled with a Taylor Series Expansion of the maximum local in-plane shearing stress known as the Taylor Series Correction Method (TSCM) is applied to the determination of stress intensity factors (SIF’s) in flat bottomed surface flaws of flaw depth/length ratios of approximately 0.033. Flaw depth/thickness ratios of approximately 0.20 and 0.40 were studied as were plate width/crack length ratios of approximately 2.33 and 1.25, the former of which corresponded to a nearly infinite width. Agreement to well within 10 percent was found with the Rice-Levy and Newman theories using a depth-modified secant correction and equivalent flaw depth/length ratios. The Shah-Kobayashi Theory, when compared on the same basis, was lower than the experimental results. Using a modified net section stress correction suggested by Shah, agreement with the Shah-Kobayashi Theory was greatly improved but agreement with the other theories was poorer. On the basis of the experiments alone, it was found that the SIF was intensified by about 10 percent by decreasing the plate width/crack length from 2.33 to 1.25.

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