Regs for windshield:
9.5.C Windshield
9.5.C.1 All solar cars must have a windshield that is securely mounted to the solar car.
9.5.C.2 The windshield must be made of shatter-resistant material; the material must have a Notched Izod Impact Strength of at least 30 kJ/m2 (ISO 180/1A) or 320 J/m (ASTM D256).
9.5.C.3 The windshield must be free of excessive distortion.
9.5.C.4 The windshield should not be tinted to the extent that the driver cannot be clearly observed from outside the solar car.
9.5.C.5 The solar car driver must be able to discern traffic light colors through the windshield
9.5.D Rain Clearing
9.5.D.1 Solar cars must have a method to clear the windshield from any falling rain such that the vision requirements of Reg. 9.5.B can be met.
9.5.D.2 The clearing method must be operable at all times and must be in use when it becomes necessary to use the windshield wipers on the team’s support vehicles.
9.5.D.3 Hydrophobic coatings (such as Rain-X) are acceptable.
Additional Requirement:
Should be thermoformable (we will be getting this done externally since we simply cannot do it in house with our machine)
Potential Choices:
There are two plastics that are commonly used for custom thermoforming windshields, polycarbonate and acrylic.
Polycarbonate:
Impact resistant
Some grades are even used in military vehicles (bullet resistant)
More resistant/durable to chips and cracks
Offers sufficient visual clarity
Easy to thermoform
Look at this pdf for more specific specs. Note that from regs we need a Notched Izod Impact Strength of at least 30 kJ/m2 (ISO 180/1A) or 320 J/m (ASTM D256). Looking at the chart for general purpose polycarbonate for the ASTM D256, the value is of 12-16 ft-lb/in. 320J/m converted to ft-lb/in is 5.99. Clearly polycarbonate meets the requirements based on this sheet (I will confirm this more).
Acrylic:
Exceptional visual clarity
Decent strength, but not the greatest
Can break/crack during installation
From this pdf, acrylic just does not meet the regs (looking more into this). I was looking into MSXVII choices for windshield and acrylic was one of them and is commonly used for custom windshields, but at the same time 2018 regs did not have the requirement of a Notched Izod Impact Strength of at least 30 kJ/m2 (ISO 180/1A) or 320 J/m (ASTM D256).
Final Thoughts:
Based on the research thus far it seems that polycarbonate is the right direction to head in. The exact thickness still needs to be determined.
Next Steps:
P&A Plastics Inc - Hamilton (MSXVII mentioned them)
Located in Hamilton so it’s closeby
They make custom windshields for boats and motorcycles
Will call/email them to learn more about their requirements/rates/ability
2. Polymershapes - London