Tolga Asa_030070177_Week11

1. Liquid Metal Embrittlement (material degradation)


No old def.


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New def.



Liquid Metal Embrittlement, or LME, is caused by a combination of two
factors. These are 1.) The presence of a specific liquid (molten) metal in
contact with the affected component or structure, and 2.) An applied or
residual tensile stress acting on the affected component or structure while
in contact with the liquid metal. When these two conditions occur, the liquid
metal is absorbed in the components’ grain boundaries in a manner similar
to the capillary action of a paper towel absorbing water. A liquid-metal filled
crack is produced as the boundary between grains absorbs the molten
metal and breaks the bond between adjacent grains. The liquid metal cools
and solidifies leaving, in the case of our sign bridge, cracks in a steel
component filled with much weaker zinc. The absorption of the liquid
metal occurs at an extremely rapid rate. LME crack rate velocities of 4.0
inches in one hundredth of a second have been recorded.


(Metallurgical Associates (2004) , Metallurgical Minutes,, p. 3)


2. Intergranular Fracture & Transgranular Fracture (fracture mechanics)


No old def.


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New Def.

Types of Brittle Fracture

The first type of fracture is transgranular. In transgranular fracture, the fracture travels through the grain of the material. The fracture changes direction from grain to grain due to the different lattice orientation of atoms in each grain. In other words, when the crack reaches a new grain, it may have to find a new path or plane of atoms to travel on because it is easier to change direction for the crack than it is to rip through. Cracks choose the path of least resistance. You can tell when a crack has changed in direction through the material, because you get a slightly bumpy crack surface.
The second type of fracture is intergranular fracture. Intergranular fracture is the crack traveling along the grain boundaries, and not through the actual grains. Intergranular fracture usually occurs when the phase in the grain boundary is weak and brittle ( i.e. Cementite in Iron's grain boundaries). Think of a metal as one big 3-D puzzle. Transgranular fracture cuts through the puzzle pieces, and intergranular fracture travels along the puzzle pieces pre-cut edges.

(Ballard J.,  Virginia Tech Materials Science and Engineering , Brittle Fracture)


3. Advanced Ceramics (material)


no old def.


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There are two major families of advanced ceramics:oxides (e.g., alumina, beryllia and zirconate) and non-oxides (such as carbidesand nitrides). The common thread among oxides is the presence of oxygen inconjunction with the base mineral element, such as in zirconia and oxygen toform zirconium. Non-oxides utilize an element other than oxygen in theirmanufacture. For example, carbides (such as boron carbide, silicon carbide,titanium carbide and tungsten carbide) have a carbon constituent, while nitrides(e.g., aluminum nitride, boron nitride and silicon nitride) utilize nitrogen. In 2009,alumina (i.e., aluminum oxide) was the leading type of advanced ceramic,followed by titanate, ferrite and other ceramic types. Alumina use benefits fromthe material’s relatively low cost and favorable performance characteristics, suchas resistance to high temperatures, corrosion and abrasion; thermal conductivity;and electrical insulation. Titanate ceramics are manufactured from thecombination of a variety of ceramic powders, all of which contain titanium. Thereare two types of ferrite ceramics -- hard ferrites (which are permanentlymagnetized) and soft ferrites (which are temporarily magnetic).

(Freedonia, Advenced Ceramics, p. 8)

Constantly growing demand for advanced materials in the 20th century resulted in the development of new classes of ceramic materials that do not originate in clays. Suchmaterials, known as “advanced ceramics”, are manufactured either from pure metaloxides by ceramic forming techniques, or from other precursors using sol-gel processing, atomic layer deposition,or gas-phase synthesis. It wouldn’t be an exaggeration to say that advanced ceramics play a crucial role in most areas of modern science and technology. Their applications comprise electronic materials and devices, nanomaterials, coatings, structuralmaterials and composites.Alternative energy is an area where advanced ceramics have proven to be particularly valuable. For example, high-temperature superconducting ceramic materials demonstrate great potential for reducing energy losses in electrical systems and devices, thus increasing their energy efficiency. Thermoelectric ceramics are capable of clean energy generationby transforming waste heat into electricity. Highly porous complex oxide systems find useas media for safe storage of energy rich gases such as hydrogen. Ceramics are also usedas substrates for light emitting diodes, electrodes and electrolytes for solid oxide fuel cells(SOFC), highly efficient insulators etc.

(Aldrich Chemistry, Material Matters: Advanced Ceramics Material and Application, p. 1)

4. Energy Release Rate (fracture mechanics)

Old def.

When a flaw in an infinite plate is approximated by a line crack, the so-called flaw energy, i.e. the part of the stored energy attributed to the presence of the flaw, can be calculated exactly. The derivatie of the flaw energy with respect to the crack length is the so-called energy-release rate, a quantity of singular importance in the theory of fracture mechanics.

When a flaw is approximated by a cavity other than a line crack or when a line crack does not extend co-linearly, the energy release rate can-not be obtained by differentiating the flaw energy, even if the latter can be obtained exactly.

(Asymptotic methods and singular perturbations, Yazar: Robert E. O'Malley,American Mathematical Society,Society for Industrial and Applied , Page 153)

New def., better

11.2.1 Griffith Criterion

In 1920, Griffith first published his development of the strain energy release rate to describe the sudden fracture of glass. The concept of the strain energy release rate is that there is a characteristic energy per unit crack area required to initiate a crack extension. Alan Gent describes it most succinctly this way: "Griffith suggested that a flaw would propagate in a stressed material only when, by doing so, it brought about a reduction in elastic stored energy U more than sufficient to meet the free energy requirements of the newly formed fracture surfaces". The criterion governs the onset of sudden crack growth, not its size.

( Judson T. Bauma,Fatigue, Stress, and Strain of Rubber Components: Guide for Design Engineers, p. 143)


5. High-speed Automated Assembly (assembly automation)

No old def.

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11. Design for automated production.

 Automated production involves less flexibility than manual production. The product must be designed in a way that can be more handled with automation.  

There are two automation approaches:  1) flexible robotic assembly and  2) high speed 

automated assembly.  

Considerations with flexible robotic assembly are: 

design parts to utilize standard gripper and avoid gripper / tool change, 

use self- locating parts,  

use simple parts presentation devices,  

and avoid the need to secure or clamp parts.  

Considerations with high speed automated assembly are:  

use a minimum of parts or standard parts for minimum of feeding bowls, etc.,  

use closed parts (no projections, holes or slots) to avoid tangling,  

consider the potential for multi-axis assembly to speed the assembly cycle time, 

and use pre-oriented parts.

(Manner K., Detailed Design for Assembly Guidelines, p.5)