Why does glass fracture

When ever a sphere of a material hits the floor, the size of the area of contact in the collision is nonzero because it's not perfectly rigid. The maximum stress is at the area of contact and is approximately the mass of the sphere times the collisional acceleration divided by the square of the size of the area of contact. A sphere made of a brittle material will form a crack when the maximum stress exceeds a certain value approximately equal to the strength of the material.

We want to determine the speed a sphere must hit the diamond floor at in order to form a crack as a function of sheer modulus, strength, and density. From the square cube law, the speed is independent of the size of the sphere for a given density, sheer modulus and strength.

According to my answer at Why are so many forces explainable using inverse squares when space is three dimensional?

I think the theoretical strength of a smooth sphere of a given stable material actually approximately varies as the reciprocal of the log of how many times larger than an atom it is so the fraction of its theoretical strength lost from doubling its size also varies as the reciprocal of the log of how many times larger than an atom it is. According to the Wikipedia article Fracture mechanics , when a brittle material has cracks, it has a lower strength.

The speed a sphere must hit the diamond floor at in order to crack is a function of its observed strength, density, and shear modulus and not its theoretical strength. Although the question of whether a crack will start in the first place follows the square cube law, the question of how far in will propagate when it does start doesn't.

According to the square cube law, the size of the area of contact divided by the size of the sphere is independent of size of the sphere for a given shear modulus and strength.

When you multiply the density, strength, and sheer modulus all by the same amount, the speed and what fraction of the size of the sphere the size of the area of contact is don't change either.

Finally, when you multiply the strength by the same amount as the sheer modulus while leaving density and size constant, the speed multiplies by the square root of the amount you multiplied the sheer modulus by and the fraction of the size of the sphere that's the size of the area of contact doesn't change.

For a sphere of a given size, density, and speed it must go in order to form a crack, the stress varies as the collisional acceleration divided by square of the size of the area of contact but the collisional acceleration varies as the minus second power of the size of the area of contact so the stress varies as the minus fourth power of the size of the area of contact.

The sheer modulus is the stress divided by the strain but the strain varies as the size of the area of contact so the sheer modulus varies as the minus fifth power of the size of the area of contact. You can also multiply the sheer modulus by r by first dividing the strength by r then multiplying the sheer modulus and strength by r.

The density can be multiplied by r by first multiplying the density, sheer modulus, and strength by r then dividing the sheer modulus and strength by r. Finally, the speed is independent of the size of the sphere for a given strength, sheer modulus, and density. I don't know what power of strength, shear modulus, and density the speed required to create a crack that propagates all the way through breaking the sphere into more than one piece varies as.

I once read that the theoretical strength of glass is 31 GPa, almost as high as its shear modulus and that a tensile strength of 14 GPa was observed in wires of it drawn out from the molten state in a vacuum but can't find that web page anymore.

That's why glass appears to break instantly when the tension becomes too high. The deeper it gets scratched, the less tension is needed to make it fracture. It's the observed strength of the sphere from its surface cracks, not its theoretical strength that's used to predict whether those cracks will further propagate into cracks large enough to be visible.

Even with the cracks, glass is still stronger than plastic. It also has a similar density to plastic. Send me a picture- a detailed picture to support you. Suddenly a full glass has broke …. He only have minor injured as he touch the shatter surface when he trying to check what is happening. Can you advice what is this cause?

Ihave a cupboard door which spontaneously shattered after 4years. All the screws were protected by mushroom shaped plastic covering apart from the one in line with the centre of the radial cracks. Could this be the reason after 4 yrs. It does not stand in direct sunlight and room temperature constant.

I had a double pane window crack on the inside only, however, it looked like it was from the impact of something that would have had to have been from the outside. Is this possible? We ordered triple glass unit with heat strengthened inner lite instead of tempered. Is there any solution for this? I have a 2mm chip in the inside of my hurricane impact door. You cannot feel it from the inside or the outside as it is in between the glass. The vender says it is too small to worry about. I feel as if it is compromising the integrity of the door and is still under warranty and should be replaced.

Hi Kristin, If the glass in question is tempered glass, then the chip was in the glass before it was tempered. In which case your supplier is correct in his assessment.

If howvere, the glass is plain float laminated and is chipped, then there is a slight inherent weakness at the point of the chip, which could lead to cracking in the future if the glass is stressed.

Ourshower door exploded at about am this morning. We were sound asleep and no one wad in the bathroom,thank goodbess. Excellent article ; Very informative, concise and to the point. Bernard Heeney, Jones Engineering group, Ireland.

We have a terrace aluminium sliding door. We went back to our apt. We have a good idea as to how glass was broken, but we have been told that by resting carton on glass, this causes thermal breakages. Please help. I also have photos of breakage in case anyone wants to see. Hi, Yes this is possible.

Because it causes glass to heat and cool at different areas, leads to occur thermal stresses. In solar module manufacturing, sudden breakage of glass inside laminator which point of propagation is at edge could it be because of inclusion or stone? Pls give me some suggestions. My window has spontaneously shattered on a hot night. Should the manufacturer pay? They say No As it is over 3 years warranty. I have one incident on my handed over project. Laminated balustrade slope glass has broken and hanged outside.

There was no impact mark on glass. Even how come both internal glass has broken. Any faced similar situation and can guide.

Good day Michael L. I am impressed by reading your article, I found it a very informative post about Spontaneous Glass Breakage: Why it happens and what to do about it. This post is very useful for everyone. Your article is great I loved it and i will love to read more from you, dear. I need to remove some damaged wood for replacement.

Will cut using a small circular saw and an oscillating saw. I like how you have explained the problem and the solution too. I have seen similar information at one place, you can also see on Grandglass. You would get to know about the spontaneous glass breakage and why it happens and what to do about it. I enjoyed reading this article. It makes the work straight and easy for us. I like the way they have researched and presented it in front of us. We have experienced similar issue and seek an international consultancy firm to get engaged for a project in the Middle East Please let us know if anyone interested and have the capacity.

Good morning, I have this problem this morning I just the sound only to wake up and find my glass table all shuttled into small pieces, without any crack or anybody to temper with it, what could cause this, am really shocked and afraid.

I had a horroble incident happened with 12mm stardard glass full size placed on my garrage roof suddenly get broken 2 days after i put a PARANET directly on top of it. I have a picture window toughened double glaze. One night last week I went to draw the bedroom curtains and the whole of the inside panel of glass had shattered but not fallen. In architectural uses, the risk of unexpected shattering has caused the building industries to reevaluate how the public is exposed to tempered glass.

The most danger is caused by tempered glass overhead or in public areas. Many high-rise buildings use tempered glass, and greater scrutiny has been placed on safety measures to prevent pieces of glass from falling after breakage. The addition of safety window film has been recommended, and some building codes have been changed to require laminated or heat-soaked tempered glass in areas of risk.

Bradt, R. Karlsson, S. Konrad, K. Wilson, W. Nugent, and F. Jester ed. ISBN Napier and Blakely. Rupert, Michael L. ISSN Swain M. Tempered glass. Museum of Fine Arts, Boston. Back to List of Lexicon Terms. Log in. Navigation Main Page. Community portal. Current events. Recent changes. Random page. Specialty Groups Architecture.