8 ms·

Your windshield is safety glass, so consideration must be given for the need to dissipate energy when a human head collides with it. https://en.wikipedia.org/w

by gohrt 11y ago

Your windshield is safety glass, so consideration must be given for the need to dissipate energy when a human head collides with it. https://en.wikipedia.org/wiki/Windshield#Safety https://en.wikipedia.org/wiki/Windshield#Safety Trivia: A famous lawsuit about the safety of windshield glass was the _Pane_ vs. Ford case in 1917

Johnny555 11y ago
I don't think that safely fracturing when struck by a human is the safety function referred to in the linked article - once a person hits the windshield, the primary safety mechanisms (seatbelts, airbags, and structural integrity of the car) have already failed, so whatever happens at the windshield will make little difference. What the article says is that the safety role of a windshield (besides not breaking into dangerous shards of glass) is in being strong enough to maintain the structural integrity of the passenger compartment: Modern, glued-in windshields contribute to the vehicle's rigidity, but the main force for innovation has historically been the need to prevent injury from sharp glass fragments. Almost all nations now require windshields to stay in one piece even if broken, except if pierced by a strong force. Properly installed automobile windshields are also essential to safety; along with the roof of the car, they provide protection to the vehicle's occupants in the case of a roll-over accident. Today’s windshields are a safety device just like seat belts and airbags. The installation of the auto glass is done with an automotive grade urethane designed specifically for automobiles. The adhesive creates a molecular bond between the glass and the vehicle. If the adhesive bond fails at any point on the glass it can reduce the effectiveness of the air bag and substantially compromise the structural integrity of the roof.
- knowtheory 11y ago
  Yes, but your analysis discounts vehicles striking pedestrians and cyclists.
  - Johnny555 11y ago
    Well, no my analysis points out that the main safety purpose of windshield glass is to protect the structural integrity of the occupant cage -- it can't both protect against outside impact and penetration while also being a soft cushion for peoples heads to impact.
    - Someone 11y ago
      A window could give way in either direction without being penetrated, for example by stretching out and permanently deforming. Risk for people inside is that it would give too much way, so that that pole hits your head.
      - Johnny555 11y ago
        If it's flexible it's not going to support the roof in a rollover -- the windshield is a structural part of the occupant cage.
        Someone 11y ago
        "Permanently deforming" and "flexible" are different things. The crumple zone of a car isn't flexible, but does deform. But yes, this probably would either limit what you can do there or necessitate design changes (just like it would glass with some new properties)
- rtpg 11y ago
  > once a person hits the windshield, the primary safety mechanisms (seatbelts, airbags, and structural integrity of the car) have already failed, so whatever happens at the windshield will make little difference. There used to be an issue where people's head would go through a window but the glass wouldn't entirely shatter, so the rest of the body wouldn't go through. A deadly broken window collar Source: took the same tech class 2 years in a row, and watched some documentary on car safety _4 times_ each year. Yay for American middle school
- Natsu 11y ago
  Windshields are laminated safety glass, which it sounds like you might be confusing with tempered safety glass. There's a huge difference in how those break. Laminated glass remains in one solid mass held together by the plastic sheet in the middle, while tempered glass explodes into tiny pieces that are sharp but not overly harmful. Ordinary annealed glass breaks into long, dagger-like pieces that are dangerously sharp, which is why it's tempered or laminated into safety glass. So the windshield is meant not to break apart, because it's laminated rather than tempered. The polymer lining between the lites of glass prevents it from scattering and causes it to be quite impact resistant. [1] Conversely, you'd really hate to have tempered glass as your windshield, if it broke the entire thing would just pop into tiny pieces that would get into your eyes. If a rock hit hard enough to break a hypothetical tempered windshield, the parts that didn't pop would be filled with cracks and impossible to see through due to being white from being filled with tiny cracks, though you could just bat them out of the way as any parts were partially intact would simply crumble when moved. The side windows are tempered, incidentally. If you've ever broken a side window, you know what I mean about the whole thing just exploding. [2] If you manage to pop it, the entire window will just fall apart easily, which might be good if you had to leave from the window of a car. It can cause small cuts and scratches and such, but it's not terribly dangerous unless it gets in your eyes, even if, say, a sheet of 3mm, 33 1/4 x 73 1/4 inch glass breaks while you're holding it. [3] It's no fun, but when you compare it to the fact that annealed glass accidents have been fatal, it's not so bad. [4] Yes, I used to work for a glass factory, so when I say that I've seen hundreds of tons of broken glass, the word 'tons' should be understood in the literal, 2,000 lbs sense of the word. [1] Source: Determined empirically by beating on damaged pieces of it with a shovel, when said pieces wouldn't fit into the dumpster. Or you can read this, whatever: http://sem-proceedings.com/10f/sem.org-IMPLAST-2010-SEM-Fall-s004p01-Blast-Impact-Resistance-Laminated-Glass-Structures.pdf http://sem-proceedings.com/10f/sem.org-IMPLAST-2010-SEM-Fall... [2] See also: https://www.youtube.com/watch?v=xPwaq_6aXbo https://www.youtube.com/watch?v=xPwaq_6aXbo This normally happens only if hit from the corner or an edge, but it can happen just randomly. We usually saw this in winter, but only a few times a year, meaning there was at most about a 1 in 10,000 chance of spontaneous breakage in my experience and probably significantly less based on the average daily volume numbers I remember. When there's something containing the edge of tempered, it sometimes just takes on a white, broken look due to all the cracks, but crumbles to the touch. It tends to just disintegrate like in the video most of the time, though. [3] Source: Direct, personal experience on multiple occasions for that very size and many others. This is an every-day kind of thing and causes no injury to someone with proper safety gear. [4] Source: I'm directly aware of at least one such accident where someone was found dead after having their neck cut when attempting to dispose of a cracked sheet. I also provided first aid to someone who could've lost a hand to injury.

by gohrt 11y ago

Johnny555 11y ago

I don't think that safely fracturing when struck by a human is the safety function referred to in the linked article - once a person hits the windshield, the primary safety mechanisms (seatbelts, airbags, and structural integrity of the car) have already failed, so whatever happens at the windshield will make little difference. What the article says is that the safety role of a windshield (besides not breaking into dangerous shards of glass) is in being strong enough to maintain the structural integrity of the passenger compartment: Modern, glued-in windshields contribute to the vehicle's rigidity, but the main force for innovation has historically been the need to prevent injury from sharp glass fragments. Almost all nations now require windshields to stay in one piece even if broken, except if pierced by a strong force. Properly installed automobile windshields are also essential to safety; along with the roof of the car, they provide protection to the vehicle's occupants in the case of a roll-over accident. Today’s windshields are a safety device just like seat belts and airbags. The installation of the auto glass is done with an automotive grade urethane designed specifically for automobiles. The adhesive creates a molecular bond between the glass and the vehicle. If the adhesive bond fails at any point on the glass it can reduce the effectiveness of the air bag and substantially compromise the structural integrity of the roof.

knowtheory 11y ago
Yes, but your analysis discounts vehicles striking pedestrians and cyclists.
- Johnny555 11y ago
  Well, no my analysis points out that the main safety purpose of windshield glass is to protect the structural integrity of the occupant cage -- it can't both protect against outside impact and penetration while also being a soft cushion for peoples heads to impact.
  - Someone 11y ago
    A window could give way in either direction without being penetrated, for example by stretching out and permanently deforming. Risk for people inside is that it would give too much way, so that that pole hits your head.
    - Johnny555 11y ago
      If it's flexible it's not going to support the roof in a rollover -- the windshield is a structural part of the occupant cage.
      - Someone 11y ago
        "Permanently deforming" and "flexible" are different things. The crumple zone of a car isn't flexible, but does deform. But yes, this probably would either limit what you can do there or necessitate design changes (just like it would glass with some new properties)
rtpg 11y ago
> once a person hits the windshield, the primary safety mechanisms (seatbelts, airbags, and structural integrity of the car) have already failed, so whatever happens at the windshield will make little difference. There used to be an issue where people's head would go through a window but the glass wouldn't entirely shatter, so the rest of the body wouldn't go through. A deadly broken window collar Source: took the same tech class 2 years in a row, and watched some documentary on car safety _4 times_ each year. Yay for American middle school
Natsu 11y ago
Windshields are laminated safety glass, which it sounds like you might be confusing with tempered safety glass. There's a huge difference in how those break. Laminated glass remains in one solid mass held together by the plastic sheet in the middle, while tempered glass explodes into tiny pieces that are sharp but not overly harmful. Ordinary annealed glass breaks into long, dagger-like pieces that are dangerously sharp, which is why it's tempered or laminated into safety glass. So the windshield is meant not to break apart, because it's laminated rather than tempered. The polymer lining between the lites of glass prevents it from scattering and causes it to be quite impact resistant. [1] Conversely, you'd really hate to have tempered glass as your windshield, if it broke the entire thing would just pop into tiny pieces that would get into your eyes. If a rock hit hard enough to break a hypothetical tempered windshield, the parts that didn't pop would be filled with cracks and impossible to see through due to being white from being filled with tiny cracks, though you could just bat them out of the way as any parts were partially intact would simply crumble when moved. The side windows are tempered, incidentally. If you've ever broken a side window, you know what I mean about the whole thing just exploding. [2] If you manage to pop it, the entire window will just fall apart easily, which might be good if you had to leave from the window of a car. It can cause small cuts and scratches and such, but it's not terribly dangerous unless it gets in your eyes, even if, say, a sheet of 3mm, 33 1/4 x 73 1/4 inch glass breaks while you're holding it. [3] It's no fun, but when you compare it to the fact that annealed glass accidents have been fatal, it's not so bad. [4] Yes, I used to work for a glass factory, so when I say that I've seen hundreds of tons of broken glass, the word 'tons' should be understood in the literal, 2,000 lbs sense of the word. [1] Source: Determined empirically by beating on damaged pieces of it with a shovel, when said pieces wouldn't fit into the dumpster. Or you can read this, whatever: http://sem-proceedings.com/10f/sem.org-IMPLAST-2010-SEM-Fall-s004p01-Blast-Impact-Resistance-Laminated-Glass-Structures.pdf http://sem-proceedings.com/10f/sem.org-IMPLAST-2010-SEM-Fall... [2] See also: https://www.youtube.com/watch?v=xPwaq_6aXbo https://www.youtube.com/watch?v=xPwaq_6aXbo This normally happens only if hit from the corner or an edge, but it can happen just randomly. We usually saw this in winter, but only a few times a year, meaning there was at most about a 1 in 10,000 chance of spontaneous breakage in my experience and probably significantly less based on the average daily volume numbers I remember. When there's something containing the edge of tempered, it sometimes just takes on a white, broken look due to all the cracks, but crumbles to the touch. It tends to just disintegrate like in the video most of the time, though. [3] Source: Direct, personal experience on multiple occasions for that very size and many others. This is an every-day kind of thing and causes no injury to someone with proper safety gear. [4] Source: I'm directly aware of at least one such accident where someone was found dead after having their neck cut when attempting to dispose of a cracked sheet. I also provided first aid to someone who could've lost a hand to injury.