Bullet resistance & civilian vehicles, is thispossible?Evolution of the windshield:Auto glass has changed dramatically ove...
Over time aerodynamics and auto styling changed this and glass took on variousshapes and sizes.In 1921, German inventor Ed...
In modern times auto glass is still a challenge in order to take a off the marketcivilian piece of auto glass and retro fi...
Side glass in automobilesSide glass in cars, SUV’s, pick-ups, Vans, etc,… for the vast majority pose little or noproblem a...
Summary:Small arms fire, projectiles traveling less than 1000 feet per second can besuccessfully resisted on auto-glass. A...
How Can I Determine If Glass Is Tempered?Tempered glass, or safety glass, is formed by sealing two pieces of glass togethe...
Tempered safety glass is a single pieceof glass that gets tempered using aprocess that heats, and then quicklycools, the g...
It is this compressive stress that gives the toughened glass increased strength. Thisis because any surface flaws tend to ...
DisadvantagesToughened glass must be cut to size or pressed to shape before toughening andcannot be re-worked once toughen...
not normally visible, can become visible under certain light conditions especially polarized sky conditions. This is an in...
Properties & specification1. Density (approximate) :               2.42-2.52 g/cubic cm2. Tensile Strength :              ...
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Peter Fabian ACE : Evolution of windshield

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Peter fabian ACE with the evolution of Windshield

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Peter Fabian ACE : Evolution of windshield

  1. 1. Bullet resistance & civilian vehicles, is thispossible?Evolution of the windshield:Auto glass has changed dramatically over the years. When first introduced early1905, windshields were flat. So too were the side and rear windows. The glassconstruction was sufficient to block the wind and rain. No further thought was give tothe auto glass until a series of lawsuits led up to the development of strongerwindshields. The most notable example of this is the Pane vs. Ford case of 1917 thatdecided against Pane in that he was only injured through impaired driving. Theywere replaced with windshields made of toughened glass and were fitted in theframe using a rubber or neoprene seal. The hardened glass shattered into manymostly harmless fragments when the windshield broke.These windshields, however, could shatter from a simple stone chip. In 1919, TheFord Motor Company solved the problem of flying debris by using the new Frenchtechnology of glass laminating. Windshields made using this process were two layersof glass with a cellulose inner layer. This inner layer held the glass together when itfractured. Between 1919 and 1929, Ford ordered the use of laminated glass on all ofhis vehicles.Modern, glued-in windshields contribute to the vehicles rigidity, but the main forcefor innovation has historically been the need to prevent injury from sharp glassfragments. Almost all nations now require windshields to stay in one piece even ifbroken, except if pierced by a strong force. Properly installed automobile windshieldsare also essential to safety; along with the roof of the car, they provide protection tothe vehicles occupants in the case of a roll-over accident.
  2. 2. Over time aerodynamics and auto styling changed this and glass took on variousshapes and sizes.In 1921, German inventor EdmundRumpler created the Rumpler-Tropfenauto, which translates into"tear-drop car." Based on the mostaerodynamic shape in nature, theteardrop, it had a Cd of just .27, butits unique looks never caught on withthe public. The German designchanged not only the body but too theglass. On the American side, one of the biggest leaps ahead in aerodynamic design came in the 1930s with the Chrysler Airflow. Inspired by birds in flight, the Airflow was one of the first cars designed with aerodynamics in mind however major changes began in the mid forties and fifties with pickup and cars having an X-Y curve introduced. Looking at this example you can see that the windshield has an ‘X’ (flat) straight line in the vertical and the ‘Y’ axis has a severe curve wrapping around the sides providing a stylistic aerodynamics. All of these construction present unique issues should the requirement be to retro fit a product onto it that would resist bullets of any speed or threat. 2
  3. 3. In modern times auto glass is still a challenge in order to take a off the marketcivilian piece of auto glass and retro fit a product that will adhere sufficiently enoughto resist projectiles. Auto glass has changed once again beginning in the 1980’s withwindshields that adopted a third axis, the ‘C’ curve. As illustrated below, auto glasshas three curvatures, the X,Y,Z.In order to apply or retro fit a soft plastic bullet resistant material without creatingany serious visible distortion a low level small arms fire solution exists whereby whenapplying the ASLX vertical seems (butt joints) are incorporated in order to track thesurface of the glass without interruption on the horizontal plane. As thick P.E.T.cannot be heat shrunk satisfactorily, the only other method to adhering would be tocustom tailor the ASLX Security Laminate to fit the specimen allowing room forthermodynamic reactions to the air conditioning and heating system in the vehicle,along with exterior weather and temperate changes. 3
  4. 4. Side glass in automobilesSide glass in cars, SUV’s, pick-ups, Vans, etc,… for the vast majority pose little or noproblem as they are either flat or are limited to the X-Y curvatures. The depth of the curvature at times will pose a problem for the installer, however as of 2010, we have not encountered any reason to install ACE’s ASLX security laminates imposing a horizontal seam or butt joint.When installing the ASLX on side glassthe glass must be removed. Installingthe security laminate as if it was awindow tint would be dangerous. Theauto-glass goes deep into the door,and if you were to install in a ‘line ofsight’ fashion you would have it thatonce the window is hit from the firstprojectile that window would fold rightat the edge of the door where theglass and door meet, leaving theoccupant at risk.In addition by installing the securitylaminate to the whole surface of theglass, you have added an additionsecurity feature that protects the lowerabdomen, and thighs of the occupants.Removing the glass from a door is arelatively easy task, it a matter ofremoving the panel and 2 screws thathold the window into the windingmechanism referred to as the‘regulator’. 4
  5. 5. Summary:Small arms fire, projectiles traveling less than 1000 feet per second can besuccessfully resisted on auto-glass. As each make and model of car differs so toodoes the style, thickness and quality of tempering differ.It is ACE’s recommendation that before anyone proceeds to retro-fit a vehicle withACE’s ASLX that a pre-test (given the threat risk) and verify if in fact that thisproduct meets with your criteria and tolerance.It was by doing this that the Federal Police in Mexico went a head using ACE, and soto the Military Police in Guatemala protecting their officers out on patrol, and morerecently the Indian Military protecting their soldiers from close range high poweredweapons. Amour Vehicles, US and Canadian APC’s in Afghanistan/Iraq are usingACE’s ASLX ensuring their people are safe and secure. Glass/ UL Threat Stopped Security Laminates P.E.T. Protection Level (example) Thickness inch I 9 mm .25 PASS II .357 Magnum .40 PASS III 44 Magnum .43 PASS IV 30 Calibre N/A V 30 Calibre N/A VIII 7.62 mm N/A IMPORTANT: When it comes to defending yourself, using traditional bullet proof glass that was not an option, however, the smart design of the ASLX allows security forces from within the vehicle the ability to shoot first, or return fire. All the while what was once a window of vulnerability not becomes your shield of defence! 5
  6. 6. How Can I Determine If Glass Is Tempered?Tempered glass, or safety glass, is formed by sealing two pieces of glass togetherwith a clear resin. Instead of shattering into shards upon breakage like normal glass,tempered glass is designed to hold together under light breakage conditions orshatter into very small pieces during severe breakage conditions. Due to thesequalities, tempered safety glass is used in such products as automobile windows,shower doors, microwaves and stained glass windows.You can try polarized sunglasses. If you look at the piece of glass whilewearing them, you might see various rainbow patterns in the glass, obscuringyour view. This is why polarized lenses are not recommended for driving; theside windows on cars are tempered 6
  7. 7. Tempered safety glass is a single pieceof glass that gets tempered using aprocess that heats, and then quicklycools, the glass to harden it. Thetempering process increases thestrength of the glass to five to 10times that of untempered glass.Tempered safety glass breaksdifferently than regular clear glass.When tempered safety glass is struckit does not break into sharp jaggedpieces of shrapnel-like glass as normalwindow panes or mirrors do. Instead,it breaks into little pebble-like pieces,without sharp edges. It is used in theside and rear windows of automobiles. When certain high grade ballistics laminates or Ceramic laminates are applied to glass, a rainbow effect occurs in lower quality of tempered glass or tempered glass that has not reached its full heat treatment when being processed. The greater contraction of the inner layer during manufacturing induces compressive stresses in the surface of the glass balanced by tensile stresses in the body of the glass.For glass to be considered toughened, this compressive stress on the surface of theglass should be a minimum of 69 MPa.For it to be considered safety glass, the surface compressive stress should exceed100 MPa. The greater the surface stress, the smaller the glass particles will be whenbroken. 7
  8. 8. It is this compressive stress that gives the toughened glass increased strength. Thisis because any surface flaws tend to be pressed closed by the retained compressiveforces, while the core layer remains relatively free of the defects which could cause acrack to begin. However, the toughened glass surface is not as hard as annealedplate glass and is therefore somewhat more susceptible to scratching. To preventthis, toughened glass manufacturers may apply various coatings and/or laminates tothe surface of the glass.Toughened glass is made from annealed plate glass via a thermal tempering process.The glass is placed onto a roller table, taking it through a furnace that heats it aboveits annealing point of about 720 °C. The glass is then rapidly cooled with forced airdrafts while the inner portion remains free to flow for a short time.An alternative chemical process involves forcing a surface layer of glass at least0.1mm thick into compression by ion exchange of the sodium ions in the glasssurface with the 30% larger potassium ions, by immersion of the glass into a bath ofmolten potassium nitrate. Chemical toughening results in increased toughnesscompared with thermal toughening, and can be applied to glass objects of complexshape.AdvantagesThe term toughened glass is generally used to describe fully tempered glass but issometimes used to describe heat strengthened glass as both types undergo athermal toughening process.There are two main types of heat treated glass, heat strengthened and fullytempered. Heat strengthened glass is twice as strong as annealed glass while fullytempered glass is typically four to six times the strength of annealed glass andwithstands heating in microwave ovens. The difference is the residual stress in theedge and glass surface. Fully tempered glass in the Canada and the US is generallyrated above 65 MPa (9427 psi) in pressure-resistance while Heat Strengthened glassis between 40 and 55 megapascals (5801 and 7977 psi respectively).It is important to note that the tempering process does not change the stiffness ofthe glass. Annealed glass deflects the same amount as tempered glass under thesame load, all else being equal. But Tempered glass will take a larger load, andtherefore deflect further at break. 8
  9. 9. DisadvantagesToughened glass must be cut to size or pressed to shape before toughening andcannot be re-worked once toughened. Polishing the edges or drilling holes in theglass is carried out before the toughening process starts. Because of the balancedstresses in the glass, damage to the glass will eventually result in the glassshattering into thumbnail-sized pieces.The glass is most susceptible to breakage due to damage to the edge of the glasswhere the tensile stress is the greatest, but shattering can also occur in the event ofa hard impact in the middle of the glass pane or if the impact is concentrated (forexample, striking the glass with a point). Using toughened glass can pose a securityrisk in some situations because of the tendency of the glass to shatter completelyupon hard impact rather than leaving shards in the window frame.The surface of tempered glass does exhibit surface waves caused by contact with therollers. This waviness is a significant problem when applying solar control or ceramicfilms to tempered glass. Key Quality Areas 1. Optical Distortion – Heat-strengthened glass that is manufactured in a horizontal tempering furnace may contain slight surface waves caused by contact with the rollers. This waviness or roller distortion can be detected when viewing reflected images from a distance. Orientation of the glass in the furnace is critical in order to minimize the appearance of the roll wave distortion. It is recommended that the roller wave be oriented parallel to the horizontal glass dimension. 2. Flatness – Heat-strengthened glass products are not as flat as flat as annealed glass due to processes used in manufacturing . For heat–treated glass products, the deviation for flatness is a function of thickness. Width, length and other factors. Usually, increasing thickness yields flatter products. 3. Strain Pattern - For heat-strengthened, a strain pattern or iridescence, which is 9
  10. 10. not normally visible, can become visible under certain light conditions especially polarized sky conditions. This is an inherent characteristics of heat –processed glass and should not be mistaken as discoloration or non uniform tint or color. Strain pattern is a result of air quenching (cooling) of the glass and is not considered a defect. 4. Bow & Warp- Since heat-strengthened are reheated to their softening points and rapidly cooled, a certain amount of wrap and bow is associated with each glass piece due to the resulting stress. Although warp and bow is not generally a significant factor to the design professional , it may appear as distorted reflected images under certain viewing conditions. For instances, it will be more noticeable in reflective glass. And, it is an inherent characteristics of heat-treated glass and is not considered a defect. 7. Scratches – Inspect glass from a distance of 10 ft.(3 m). Scratches up to 3” (76mm) are allowed. Scratches from 3” to 5” (76 mm to 127 mm) are only allowed within 3” (76 mm) from the edge of the glass. Concentrated scratches or abraded areas are not allowed. 8. Fragmentation:- Heat Strengthened glass breaks in similar fashion as an annealed glass breaks so it is not possible to gauge the quality of Heat Strengthened glass by doing a fragmentation test. 9. Spontaneous Breakage:- Heat Treated glass on rare occasion shatters for no apparent reason. The main reason for this are the presence of a microscopic inclusion known as Nickel Sulfide (NiS). NiS in annealed float glass do not pose an treat to the glass because during annealing the NiS gets sufficient time to loose its energy and reach its stable condition. Once the raw glass containing NiS is tempered the NiS stone gains energy and become unstable. So when it is installed at site it get impetus with temperature difference and various pressure to release its energy and break. Many research is done to eliminate the NiS stone from the float tank but till this time it is impossible to remove it from the raw material. Spontaneous breakage don’t depend upon the quality of tempering, if there is a presence of NiS in tempered glass then there is a possibility of breakage.Typically the NiS induced breakagewill be in the first 2-3 years and thenthe rate drastically reduce. Researchreveals that 1 to 2 % of temperedglass panes break due to NiSinclusions. NiS induced fracturereduces by the factor of 20 for heatstrengthen glass as the cooling ratesis slower allowing NiS particles toreturn back to their stable state. 10
  11. 11. Properties & specification1. Density (approximate) : 2.42-2.52 g/cubic cm2. Tensile Strength : 120 to 200 N/sq .mm3. Compressive Strength : 1000 N/sq.mm4. Modulus of Elasticity : 70Gpa-5. Coefficient of linear expansion : 9 x 10-^6 m/Mk6. U Value : 5.7 W/sq .m.K for 6mm thick clear.7. SF for 6 mm clear 81 %8 Shading coefficient of 6 mm clear .939 Selectivity 110 Visible light transmission of 6 mm clear 87 % 11

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