I don’t think so.

http://www.abc.net.au/news/2015-04-14/police-investigate-alleged-children-remains-ballarat-orphanage/6392688

I’d be close to laying London to a brick that they find squat.

sibeen said:

http://www.abc.net.au/news/2015-04-14/police-investigate-alleged-children-remains-ballarat-orphanage/6392688

I’d be close to laying London to a brick that they find squat.

Ooops.

interesting question

http://en.wikipedia.org/wiki/Toughened_glass

Toughened or tempered glass is a type of safety glass processed by controlled thermal or chemical treatments to increase its strength compared with normal glass. Tempering puts the outer surfaces into compression and the inner surfaces into tension. Such stresses cause the glass, when broken, to crumble into small granular chunks instead of splintering into jagged shards as plate glass (aka: annealed glass) creates. The granular chunks are less likely to cause injury.

As a result of its safety and strength, toughened glass is used in a variety of demanding applications, including passenger vehicle windows, shower doors, architectural glass doors and tables, refrigerator trays, as a component of bulletproof glass, for diving masks, and various types of plates and cookware.

sibeen said:

sibeen said:

http://www.abc.net.au/news/2015-04-14/police-investigate-alleged-children-remains-ballarat-orphanage/6392688

I’d be close to laying London to a brick that they find squat.

Ooops.

Did you know this has very little to do with stored energy in toughened glass?

Who hosts this forum now btw?

Okay, I haven’t posted for a while, so I stuffed up…

Last night about half an hour after going to bed I was scared s**tless by a loud explosion and rumble in my house (and the wife woke up in a mad panic). Upon investigation I found that our semi-frameless shower screen had spontaneously exploded all over the bathroom. Apparently this can happen due to very small amounts of nickle sulphide inclusions. However the strange thing was that the elevnty billion small cubes of glass continued to snap, crackle and pop for another few hours. There was no obvious movement of the glass shrapnel, just the noise. I know that the process for toughening glass means that some energy is stored, but I was suprised at how long it could continue to make noise.

Stealth said:

That was an idea I first started playing with when I was about 16. High purity glass, with a decent refractive index change at the edges; light entering at the right angle is totally internally reflected. The light bounces around inside the prism until the prism is broken, then can be used for whatever is needed (my original design was for high intensity light causing burns when used for hand grenades.)

http://en.wikipedia.org/wiki/Spontaneous_glass_breakage

Nickel sulfide inclusions (“stones”) can be present in the glass. The most common cause of these inclusions is the use of stainless-steel machinery in the glassmaking and handling process. Small shavings of stainless steel containing nickel change structure over time and grow, creating internal stresses in the glass. When these stresses exceed the strength of the glass, breakage results. This type of breakage is almost always found in tempered glass and is indicated by a distinctive “figure eight” pattern, with each “loop” of the figure eight approx. 30mm in diameter.

Alternatively, small pieces of refractory brick can be eroded by the molten glass from the internal walls of the furnace during processing and become embedded in the finished glass. These are also known as “stones”, and can also break the glass when the glass is heated, as they create thermal anomalies.

http://failures.wikispaces.com/Glass+Breakage+-+Nickel+Sulfide+Inclusions?responseToken=08e51f5888b2586386c17890d9406144

Inherent in the glass production process are microscopic imperfections in the glass, known as inclusions. Most of these are completely harmless, but nickel sulfide (NiS) inclusions have been shown to cause disastrous failure of tempered glass. When annealed (aka float) glass is heated in the tempering process, so are any NiS inclusions present in the glass. However, when the glass is rapidly cooled to achieve the properties of tempered glass, the NiS remains in a high-temperature form. Over several years, the NiS will return to its low-temperature state, and in the process will increase in volume. This can cause cracking and additional tensile stresses which, in tempered glass, have lead to spectacular failures with no visible cause. This phenomenon has also been referred to as “glass cancer” and “spontaneous glass failure”.

The main risk this poses to the building industry comes from in-service failure of window panels containing tempered glass with NiS inclusions. When these windows break, they shatter into thousands of pieces which can fall from panes and cause injury to inhabitants of the building or pedestrians around it. The pieces can also cause damage to building finishes in addition to the cost of replacing the window, which can often be extremely costly. This article seeks to explain the history of NiS, how NiS is introduced into glass, how NiS effects tempered glass specifically, what measures are being taken to prevent NiS from ever entering glass, and finally how NiS can be detected in completed, installed glass. It concludes with several mini case studies indicating the typical magnitude and severity of NiS failure on a building.

Brief History of Nickel Sulfide Inclusions
The first acknowledgement of NiS as a problem was made by PPG Industries (a major US glass manufacturer) in the 1940’s. However, it was not until 1961 that any official documentation was published on the subject, when E.R. Ballantyne published a paper entitled “Fracture of toughened glass wall cladding” (Jacob 2001). M.V. Swain is also considered an authority on the subject for the research he published on the chemical composition of NiS in the Journal of Material Science in 1981. However, the first record that could be found by this author of a company publically acknowledging the problem was not given until 1990, by Luxguard S.A. (Bowler-Reed 2002). Since that time, the industry as a whole has made great strides in understanding and resolving the problem of nickel sulfide inclusions. As of yet, however, they have not succeeded in eliminating the concern entirely.

high rise have been having this problem , glass cracking and falling to the street

Was it another forum member who had this problem a few years back?

purple or misscarol?

I don’t know how they toughen the large sheets for shower screens, but we used to have a little furnace in the workshop for toughening glass spectacle lenses. They not infrequently went bang when they came out of the furnace and under the fan jets to cool.

https://books.google.com.au/books?id=dv2g8aOIhhsC&pg=PA466&lpg=PA466&dq=heat+toughening+spectacle+lenses&source=bl&ots=bFJupbuVWq&sig=vSgmIEHAB9WMDeW0_0W-qt15WUU&hl=en&sa=X&ei=1HstVZHaK4bNmwWn6oCIAw&ved=0CCEQ6AEwAg#v=onepage&q=heat%20toughening%20spectacle%20lenses&f=false

Probably over 20 years ago now we stopped doing that at all, just use plastic lenses and more recently polycarbonate lenses. Although for optical qualities, polycarb is shit to look through.

Interesting.

I don’t know what sibeen was on about though :)

transition said:

interesting question

http://en.wikipedia.org/wiki/Toughened_glass

Toughened or tempered glass is a type of safety glass processed by controlled thermal or chemical treatments to increase its strength compared with normal glass. Tempering puts the outer surfaces into compression and the inner surfaces into tension. Such stresses cause the glass, when broken, to crumble into small granular chunks instead of splintering into jagged shards as plate glass (aka: annealed glass) creates. The granular chunks are less likely to cause injury.

As a result of its safety and strength, toughened glass is used in a variety of demanding applications, including passenger vehicle windows, shower doors, architectural glass doors and tables, refrigerator trays, as a component of bulletproof glass, for diving masks, and various types of plates and cookware.

In engineering we’re well aware of “residual stresses” in all sorts of materials, such as concrete, steel, other metals, and glass. The usual idea is to avoid residual stresses as much as possible, because it usually leads to accelerated failure. Toughened glass is an exception. Because glass is brittle, it’s much weaker in tension than in compression, and also because it’s brittle, failure occurs by the growth of cracks that usually start on the surface. Putting the surface in compression suppresses crack growth and so suppresses failure. The breakage into small safe pieces that can’t cause deadly cuts is a bonus.

The closest analogy I can think of right now is prestressed concrete. The (outer) concrete is put in compression using tension in the (inner) steel.

I wonder if the same technique a toughened glass could be applied to ceramics such as porcelain – make the monolithic material stronger and safer by putting the outer layer in compression. I note from the web that prestressed ceramic is sometimes used in military armour.

There is another application I can think of. Annealing reduces prestress in metals. The opposite is quenching, which with some steels creates a martensite, which is “a highly strained body-centered tetragonal form of ferrite that is supersaturated with carbon”. But that’s not quite like toughened glass.

Just a note on Nickel sulphide inclusions.
If you find a guy dead on a battlefeild with a small hole in his head , you dont start looking for a bullet sized meteor , you look for a guy with a gun.

The shrinking of Nickel sulphide inclusions and other “Seeds” are just that , possible , but there are many other more likely reasons.

Brett